Comparison study on mechanical properties single step and three step artificial aging on duralium

NASA Astrophysics Data System (ADS)

Tsamroh, Dewi Izzatus; Puspitasari, Poppy; Andoko, Sasongko, M. Ilman N.; Yazirin, Cepi

2017-09-01

Duralium is kind of non-ferro alloy that used widely in industrial. That caused its properties such as mild, high ductility, and resistance from corrosion. This study aimed to know mechanical properties of duralium on single step and three step articial aging process. Mechanical properties that discussed in this study focused on toughness value, tensile strength, and microstructure of duralium. Toughness value of single step artificial aging was 0.082 joule/mm2, and toughness value of three step artificial aging was 0,0721 joule/mm2. Duralium tensile strength of single step artificial aging was 32.36 kgf/mm^2, and duralium tensile strength of three step artificial aging was 32,70 kgf/mm^2. Based on microstructure photo of duralium of single step artificial aging showed that precipitate (θ) was not spreading evenly indicated by black spot which increasing the toughness of material. While microstructure photo of duralium that treated by three step artificial aging showed that it had more precipitate (θ) spread evenly compared with duralium that treated by single step artificial aging.

Effect of wear on the burst strength of l-80 steel casing

NASA Astrophysics Data System (ADS)

Irawan, S.; Bharadwaj, A. M.; Temesgen, B.; Karuppanan, S.; Abdullah, M. Z. B.

2015-12-01

Casing wear has recently become one of the areas of research interest in the oil and gas industry especially in extended reach well drilling. The burst strength of a worn out casing is one of the significantly affected mechanical properties and is yet an area where less research is done The most commonly used equations to calculate the resulting burst strength after wear are Barlow, the initial yield burst, the full yield burst and the rupture burst equations. The objective of this study was to estimate casing burst strength after wear through Finite Element Analysis (FEA). It included calculation and comparison of the different theoretical bursts pressures with the simulation results along with effect of different wear shapes on L-80 casing material. The von Misses stress was used in the estimation of the burst pressure. The result obtained shows that the casing burst strength decreases as the wear percentage increases. Moreover, the burst strength value of the casing obtained from the FEA has a higher value compared to the theoretical burst strength values. Casing with crescent shaped wear give the highest burst strength value when simulated under nonlinear analysis.

Evaluation of Mechanical Properties of Plywood Treated with a new Wood Preservative (CEB) Chemical

NASA Astrophysics Data System (ADS)

Kalawate, Aparna; Shahoo, Shadhu Charan; Khatua, Pijus Kanti; Das, Himadri Sekhar

2017-04-01

The objective of this study was to explore the physical and mechanical properties of the plywood made with phenolic glue and rubber wood as core veneer with CEB as a wood preservative. The studied properties were glue shear strength in dry, wet mycological, modulus of elasticity, modulus of rupture and tensile strength in parallel to grain direction as per IS:1734 part-4, 11 and 9 (1983) respectively. Results of the above mentioned tests were compared with the prescribed values given in IS 710-2010 and results revealed that samples conformed the prescribed values.

Increased Antibiotic Release from a Bone Cement Containing Bacterial Cellulose

PubMed Central

Nakai, Takahisa; Enomoto, Koichi; Uchio, Yuji; Yoshino, Katsumi

2010-01-01

Background Major disadvantages of antibiotic bone cements include limited drug release and reduced strength resulting from the addition of high doses of antibiotics. Bacterial cellulose, a three-dimensional hydrophilic mesh, may retain antibiotics and release them gradually. We hypothesized that the addition of cellulose to antibiotic bone cement would improve mechanical strength and antibiotic release. Questions/purposes We therefore examined the mechanical strength and antibiotic release of cellulose antibiotic cement. Methods A high dose of antibiotics (5 g per 40 g cement powder) was incorporated into bacterial cellulose and then mixed with bone cement. We compared the compression strength, fracture toughness, fatigue life, and elution kinetics of this formulation with those of plain cement and a traditional antibiotic cement. Results The average values for compression strength, fracture toughness, and fatigue life of the cellulose antibiotic cement were 97%, 97%, and 78% of the values obtained for plain cement, respectively. The corresponding values for the traditional antibiotic cement were 79%, 82%, and 17%, respectively. The cumulative elution over 35 days was 129% greater from the cellulose antibiotic cement than from the traditional antibiotic cement. Conclusions With a high dose of antibiotics, incorporating cellulose into the bone cement prevented compression and fracture fragility, improved fatigue life, and increased antibiotic elution. Clinical Relevance Antibiotic cements containing cellulose may have applications in clinical situations that require high levels of antibiotic release and preservation of the mechanical properties of the cement. PMID:20945120

A mechanism for value-sensitive decision-making.

PubMed

Pais, Darren; Hogan, Patrick M; Schlegel, Thomas; Franks, Nigel R; Leonard, Naomi E; Marshall, James A R

2013-01-01

We present a dynamical systems analysis of a decision-making mechanism inspired by collective choice in house-hunting honeybee swarms, revealing the crucial role of cross-inhibitory 'stop-signalling' in improving the decision-making capabilities. We show that strength of cross-inhibition is a decision-parameter influencing how decisions depend both on the difference in value and on the mean value of the alternatives; this is in contrast to many previous mechanistic models of decision-making, which are typically sensitive to decision accuracy rather than the value of the option chosen. The strength of cross-inhibition determines when deadlock over similarly valued alternatives is maintained or broken, as a function of the mean value; thus, changes in cross-inhibition strength allow adaptive time-dependent decision-making strategies. Cross-inhibition also tunes the minimum difference between alternatives required for reliable discrimination, in a manner similar to Weber's law of just-noticeable difference. Finally, cross-inhibition tunes the speed-accuracy trade-off realised when differences in the values of the alternatives are sufficiently large to matter. We propose that the model, and the significant role of the values of the alternatives, may describe other decision-making systems, including intracellular regulatory circuits, and simple neural circuits, and may provide guidance in the design of decision-making algorithms for artificial systems, particularly those functioning without centralised control.

Mechanism of strength degradation for hot corrosion of alpha-SiC

NASA Technical Reports Server (NTRS)

Smialek, J. L.; Jacobson, N. S.

1984-01-01

Sintered alpha SiC was corroded by thin films of Na2SO4 and Na2CO3 molten salts at 1000%. This hot corrosion attack reduced room temperature strengths by as much as 50%. Strength degradation was porportional to the degree and uniformity of corrosion pitting attack as controlled by the chemistry of the molten salt. Extensive fractography identified corrosion pits as the most prevalent source of failure. A fracture mechanics treatment of the strength/pit depth relationship produced an average K sub IC equal to 2.6 MPa sub m 1/2, which is consistent with published values.

Mechanism of strength degradation for hot corrosion of alpha-SiC

NASA Technical Reports Server (NTRS)

Smialek, James L.; Jacobson, Nathan S.

1986-01-01

Sintered alpha SiC was corroded by thin films of Na2SO4 and Na2CO3 molten salts at 1000 percent. This hot corrosion attack reduced room temperature strengths by as much as 50 percent. Strength degradation was proportional to the degree and uniformity of corrosion pitting attack as controlled by the chemistry of the molten salt. Extensive fractography identified corrosion pits as the most prevalent source of failure. A fracture mechanics treatment of the strength/pit depth relationship produced an average K sub IC equal to 2.6 MPa sub m 1/2, which is cnsistent ith published values.

Investigation into the effect of some additives on the mechanical strength, quality and thermal conductivity of clay bricks

NASA Astrophysics Data System (ADS)

Zaid, Adnan I. O.; Qandil, A.; Qattous, M. A. A.

2016-08-01

It was repeatedly reported that the clay bricks industry in Jordan is facing both weak mechanical strength and poor quality which caused marketing problems where it is expected to serve the increasing demand of housing in the country especially after the political crises in the neighboring countries Iraq and Syria. It is therefore anticipated that improvement of the mechanical strength and quality of the produced clay evaluation of the brick industry in Jordan is worth investigating. In this paper, theoretical and experimental investigation obtained from field visits to the factories producing clay bricks were carried out. Furthermore, the effect of using some additives from locally available materials namely: Battn El-Ghoul Clay, Suweileh sand and Olive extracts on the mechanical strength, thermal conductivity and surface quality of the produced bricks is investigated and discussed. The experimental results indicated that thermal conductivity, color and durability were all enhanced and the ultimate compressive strength was reduced but remained higher than the acceptable value for brickwork.

Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, High-Cycle and Low-Cycle Mechanical Fatigue, Creep and Thermal Fatigue Effects

NASA Technical Reports Server (NTRS)

Bast, Callie C.; Boyce, Lola

1995-01-01

The development of methodology for a probabilistic material strength degradation is described. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing predictions of high-cycle mechanical fatigue and high temperature effects with experiments are presented. Results from this limited verification study strongly supported that material degradation can be represented by randomized multifactor interaction models.

Homogeneity of Mechanical Properties of Underwater Friction Stir Welded 2219-T6 Aluminum Alloy

NASA Astrophysics Data System (ADS)

Liu, H. J.; Zhang, H. J.; Yu, L.

2011-11-01

Underwater friction stir welding (FSW) has been demonstrated to be available for the improvement in tensile strength of normal FSW joints. In order to illuminate the intrinsic reason for strength improvement through underwater FSW, a 2219 aluminum alloy was underwater friction stir welded and the homogeneity of mechanical properties of the joint was investigated by dividing the joint into three layers. The results indicate that the tensile strength of the three layers of the joint is all improved by underwater FSW, furthermore, the middle and lower layers have larger extent of strength improvement than the upper layer, leading to an increase in the homogeneity of mechanical properties of the joint. The minimum hardness value of each layer, especially the middle and lower layers, is improved under the integral water cooling effect, which is the intrinsic reason for the strength improvement of underwater joint.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Samavatian, Majid, E-mail: m.samavatian@srbiau.ac.ir; Halvaee, Ayoub; Amadeh, Ahmad Ali

Joining mechanism of Ti/Al dissimilar alloys was studied during liquid state diffusion bonding process using Cu/Sn/Cu interlayer at 510 °C under vacuum of 7.5 × 10{sup −5} Torr for various bonding times. The microstructure and compositional changes in the joint zone were analyzed by scanning electron microscopy equipped with energy dispersive spectroscopy and X-ray diffraction. Microhardness and shear strength tests were also applied to study the mechanical properties of the joints. It was found that with an increase in bonding time, the elements of interlayer diffused into the parent metals and formed various intermetallic compounds at the interface. Diffusion processmore » led to the isothermal solidification and the bonding evolution in the joint zone. The results from mechanical tests showed that microhardness and shear strength values have a straight relation with bonding time so that the maximum shear strength of joint was obtained for a bond made with 60 min bonding time. - Highlights: • Liquid state diffusion bonding of Al2024 to Ti–6Al–4V was performed successfully. • Diffusion of the elements caused the formation of various intermetallics at the interface. • Microhardness and shear strength values have a straight relation with bonding time. • The maximum shear strength reached to 36 MPa in 60 min bonding time.« less

Effect of protein and glycerol concentration on the mechanical, optical, and water vapor barrier properties of canola protein isolate-based edible films.

PubMed

Chang, Chang; Nickerson, Michael T

2015-01-01

Biodegradable edible films prepared using proteins are both economically and environmentally important to the food packaging industry relative to traditional petroleum-derived synthetic materials. In the present study, the mechanical and water vapor barrier properties of casted canola protein isolate edible films were investigated as a function of protein (5.0% and 7.5%) and glycerol (30%, 35%, 40%, 45%, and 50%) content. Specifically, tensile strength and elongation, elastic modulus, puncture strength and deformation, opacity, and water vapor permeability were measured. Results indicated that tensile strength, puncture strength, and elastic modulus decreased, while tensile elongation and puncture deformation values increased as glycerol concentration increased for both 5.0% and 7.5% canola protein isolate films. Furthermore, tensile strength, puncture strength, and elastic modulus values were found to increase at higher protein concentrations within the canola protein isolate films, whereas puncture deformation values decreased. Tensile elongation was found to be similar for both canola protein isolate protein levels. Canola protein isolate films became more transparent with increasing of glycerol concentration and decreasing of canola protein isolate concentration. Water vapor permeability value was also found to increase with increasing glycerol and protein contents. Overall, results indicated that canola protein isolate films were less brittle, more malleable and transparent, and had greater water vapor permeability at higher glycerol levels. However, as protein level increased, canola protein isolate films were more brittle, less malleable and more opaque, and also had increased water vapor permeability. © The Author(s) 2013 Reprints and permissions: sagepub.co.uk/journalsPermissions.nav.

Strength and fracture mechanism of iron reinforced tricalcium phosphate cermet fabricated by spark plasma sintering.

PubMed

Tkachenko, Serhii; Horynová, Miroslava; Casas-Luna, Mariano; Diaz-de-la-Torre, Sebastian; Dvořák, Karel; Celko, Ladislav; Kaiser, Jozef; Montufar, Edgar B

2018-05-01

The present work studies the microstructure and mechanical performance of tricalcium phosphate (TCP) based cermet toughened by iron particles. A novelty arises by the employment of spark plasma sintering for fabrication of the cermet. Results showed partial transformation of initial alpha TCP matrix to beta phase and the absence of oxidation of iron particles, as well as a lack of chemical reaction between TCP and iron components during sintering. The values of compressive and tensile strength of TCP/Fe cermet were 3.2 and 2.5 times, respectively, greater than those of monolithic TCP. Fracture analysis revealed the simultaneous action of crack-bridging and crack-deflection microstructural toughening mechanisms under compression. In contrast, under tension the reinforcing mechanism was only crack-bridging, being the reason for smaller increment of strength. Elastic properties of the cermet better matched values reported for human cortical bone. Thereby the new TCP/Fe cermet has potential for eventual use as a material for bone fractures fixation under load-bearing conditions. Copyright © 2018 Elsevier Ltd. All rights reserved.

Characteristics of ADC12/nano Al2O3composites with Addition of Ti Produced By Stir Casting Method

NASA Astrophysics Data System (ADS)

Zulfia, A.; Krisiphala; Ferdian, D.; Utomo, B. W.; Dhaneswara, D.

2018-03-01

The mechanical properties and microstructure of ADC12/nano Al2O3 matrix composites have been studied in this work. The composites were produced by stir casting method. ADC 12 as matrix composites was combined by Mg and Ti. The addition of Ti was varied from 0.02 to 0.08 wt-% as grain refinement wetting to improve mechanical properties such as tensile strength, hardness and wear resistance, while Mg addition was to promote wetting between ADC 12 and nano Al2O3. The optimum tensile strength was found at 0.04 wt-% addition of Ti with value of 132.5 MPa, further adding more Ti cause a poisoning mechanism that will hindered the grain refining process and reduce the tensile strength. The hardness and wear resistance of composites would also increase because of the refinement process. and the added Magnesium in the material that will form Mg2Si primary phases who have a high hardness value.

Influence of water immersion on the mechanical properties of fiber posts.

PubMed

Komada, Wataru; Inagaki, Tasuku; Ueda, Yoji; Omori, Satoshi; Hosaka, Keiichi; Tagami, Junji; Miura, Hiroyuki

2017-01-01

The purpose of this study was to evaluate the influence of water immersion on the mechanical properties of three kinds of glass fiber posts and the fracture resistance of structures using resin composites with glass fiber posts. Each post was divided into three groups; a control group and two water immersion groups (30 and 90 days). Flexural strength was determined by three-point bending test. Each structure was divided into two groups; a control group and a water immersion group for 30 days. The fracture strength of structures was determined by a static loading test. In the flexural strength, two kinds of post in water immersion groups showed lower values than control groups. In the fracture strength, two kinds of structures in water immersion group showed lower values than control groups. The prefabricated glass fiber posts and structures using resin composites with glass fiber posts were affected by water immersion. Copyright © 2016 Japan Prosthodontic Society. Published by Elsevier Ltd. All rights reserved.

Controlled and in situ target strengths of the jumbo squid Dosidicus gigas and identification of potential acoustic scattering sources.

PubMed

Benoit-Bird, Kelly J; Gilly, William F; Au, Whitlow W L; Mate, Bruce

2008-03-01

This study presents the first target strength measurements of Dosidicus gigas, a large squid that is a key predator, a significant prey, and the target of an important fishery. Target strength of live, tethered squid was related to mantle length with values standardized to the length squared of -62.0, -67.4, -67.9, and -67.6 dB at 38, 70, 120, and 200 kHz, respectively. There were relatively small differences in target strength between dorsal and anterior aspects and none between live and freshly dead squid. Potential scattering mechanisms in squid have been long debated. Here, the reproductive organs had little effect on squid target strength. These data support the hypothesis that the pen may be an important source of squid acoustic scattering. The beak, eyes, and arms, probably via the sucker rings, also play a role in acoustic scattering though their effects were small and frequency specific. An unexpected source of scattering was the cranium of the squid which provided a target strength nearly as high as that of the entire squid though the mechanism remains unclear. Our in situ measurements of the target strength of free-swimming squid support the use of the values presented here in D. gigas assessment studies.

Elongated Tetrakaidecahedron Micromechanics Model for Space Shuttle External Tank Foams

NASA Technical Reports Server (NTRS)

Sullivan, Roy M.; Ghosn, Louis J.; Lerch, Bradley A.; Baker, Eric H.

2009-01-01

The results of microstructural characterization studies and physical and mechanical testing of BX-265 and NCFI24-124 foams are reported. A micromechanics model developed previously by the authors is reviewed, and the resulting equations for the elastic constants, the relative density, and the strength of the foam in the principal material directions are presented. The micromechanics model is also used to derive equations to predict the effect of vacuum on the tensile strength and the strains induced by exposure to vacuum. Using a combination of microstructural dimensions and physical and mechanical measurements as input, the equations for the elastic constants and the relative density are applied and the remaining microstructural dimensions are predicted. The predicted microstructural dimensions are in close agreement with the average measured values for both BX-265 and NCFI24-124. With the microstructural dimensions, the model predicts the ratio of the strengths in the principal material directions for both foams. The model is also used to predict the Poisson s ratios, the vacuum-induced strains, and the effect of vacuum on the tensile strengths. However, the comparison of these predicted values with the measured values is not as favorable.

The relationship between compressive strength and flexural strength of pavement geopolymer grouting material

NASA Astrophysics Data System (ADS)

Zhang, L.; Han, X. X.; Ge, J.; Wang, C. H.

2018-01-01

To determine the relationship between compressive strength and flexural strength of pavement geopolymer grouting material, 20 groups of geopolymer grouting materials were prepared, the compressive strength and flexural strength were determined by mechanical properties test. On the basis of excluding the abnormal values through boxplot, the results show that, the compressive strength test results were normal, but there were two mild outliers in 7days flexural strength test. The compressive strength and flexural strength were linearly fitted by SPSS, six regression models were obtained by linear fitting of compressive strength and flexural strength. The linear relationship between compressive strength and flexural strength can be better expressed by the cubic curve model, and the correlation coefficient was 0.842.

Mechanical Properties of Elastomeric Impression Materials: An In Vitro Comparison

PubMed Central

De Angelis, Francesco; Caputi, Sergio; D'Amario, Maurizio; D'Arcangelo, Camillo

2015-01-01

Purpose. Although new elastomeric impression materials have been introduced into the market, there are still insufficient data about their mechanical features. The tensile properties of 17 hydrophilic impression materials with different consistencies were compared. Materials and Methods. 12 vinylpolysiloxane, 2 polyether, and 3 hybrid vinylpolyether silicone-based impression materials were tested. For each material, 10 dumbbell-shaped specimens were fabricated (n = 10), according to the ISO 37:2005 specifications, and loaded in tension until failure. Mean values for tensile strength, yield strength, strain at break, and strain at yield point were calculated. Data were statistically analyzed using one-way ANOVA and Tukey's tests (α = 0.05). Results. Vinylpolysiloxanes consistently showed higher tensile strength values than polyethers. Heavy-body materials showed higher tensile strength than the light bodies from the same manufacturer. Among the light bodies, the highest yield strength was achieved by the hybrid vinylpolyether silicone (2.70 MPa). Polyethers showed the lowest tensile (1.44 MPa) and yield (0.94 MPa) strengths, regardless of the viscosity. Conclusion. The choice of an impression material should be based on the specific physical behavior of the elastomer. The light-body vinylpolyether silicone showed high tensile strength, yield strength, and adequate strain at yield/brake; those features might help to reduce tearing phenomena in the thin interproximal and crevicular areas. PMID:26693227

Mechanical properties of {beta}-SiC pressureless sintered with Al{sub 2}O{sub 3} additions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mulla, M.A.; Krstic, V.D.

1994-01-01

Mechanical properties of pressureless sintered SiC with Al{sub 2}O{sub 3}addition were measured. The increase in fracture toughness and strength is attributed to the presence of a liquid phase which results in the formation of platelets of an {alpha}-SiC. The highest values for flexural strength and toughness were measured on samples with {approximately}10%Al{sub 2}O{sub 3} addition. Pull out, crack bridging and crack deflection are identified as the major strengthening and toughening mechanisms.

Continuous depth profile of mechanical properties in the Nankai accretionary prism based on drilling performance parameters

NASA Astrophysics Data System (ADS)

Hamada, Y.; Kitamura, M.; Yamada, Y.; Sanada, Y.; Moe, K.; Hirose, T.

2016-12-01

In-situ rock properties in/around seismogenic zone in an accretionary prism are key parameters to understand the development mechanisms of an accretionary prism, spatio-temporal variation of stress state, and so on. For the purpose of acquiring continuous-depth-profile of in-situ formation strength in an accretionary prism, here we propose the new method to evaluate the in-situ rock strength using drilling performance property. Drilling parameters are inevitably obtained by any drilling operation even in the non-coring intervals or at challenging environment where core recovery may be poor. The relationship between the rock properties and drilling parameters has been proposed by previous researches [e.g. Teale 1964]. We introduced the relationship theory of Teale [1964], and developed a converting method to estimate in-situ rock strength without depending on uncertain parameters such as weight on bit (WOB). Specifically, we first calculated equivalent specific toughness (EST) which represents gradient of the relationship between Torque energy and volume of penetration at arbitrary interval (in this study, five meters). Then the EST values were converted into strength using the drilling parameters-rock strengths correlation obtained by Karasawa et al. [2002]. This method was applied to eight drilling holes in the Site C0002 of IODP NanTroSEIZE in order to evaluate in-situ rock strength in shallow to deep accretionary prism. In the shallower part (0 - 300 mbsf), the calculated strength shows sharp increase up to 20 MPa. Then the strength has approximate constant value to 1500 mbsf without significant change even at unconformity around 1000 mbsf (boundary between forearc basin and accretionary prism). Below that depth, value of the strength gradually increases with depth up to 60 MPa at 3000 mbsf with variation between 10 and 80 MPa. Because the calculated strength is across approximately the same lithology, the increase trend can responds to the rock strength. This strength-depth curve correspond reasonably well with the strength data of core and cutting samples collected from hole C0002N and C0002P [Kitamura et al., 2016 AGU]. These results show the validity of the method evaluating in-situ strength from the drilling parameters.

Study of the effect of surface treatment of kenaf fibre on mechanical properties of kenaf filled unsaturated polyester composite

NASA Astrophysics Data System (ADS)

Salem, I. A. S.; Rozyanty, A. R.; Betar, B. O.; Adam, T.; Mohammed, M.; Mohammed, A. M.

2017-10-01

In this research, unsaturated polyester/kenaf fiber (UP/KF) composites was prepared by using hand lay-up process. The effect of surface treatment of kenaf fiber on mechanical properties of kenaf filled unsaturated polyester composites were studied. Different concentrationsof stearic acid (SA) were applied, i.e. 0, 0.4, and 0.8 wt%. Tensile strength of untreated UP/KF composites was found to be higher for 40 wt% loading of kenaf fiber. The highest tensile strength value was obtained after treatment with 0.4 wt% concentration of stearic acid at 56 MPa and tensile modulus was at 2409 MPa. From the flexural strength result obtained, it is clearly seen that 40 wt% loading of kenaf fiber and treatment with 0.4 wt% concentration of stearic acid give the highest value at 72 MPa and flexural modulus at 3929 MPa.

Method of preparing copper-dendritic composite alloys for mechanical reduction

DOEpatents

Verhoeven, John D.; Gibson, Edwin D.; Schmidt, Frederick A.; Spitzig, William A.

1988-01-01

Copper-dendritic composite alloys are prepared for mechanical reduction to increase tensile strength by dispersing molten droplets of the composite alloy into an inert gas; solidifying the droplets in the form of minute spheres or platelets; and compacting a mass of the spheres or platelets into an integrated body. The spheres preferably have diameters of from 50 to 2000 .mu.m, and the platelets thicknesses of 100 to 2000 .mu.m. The resulting spheres or platelets will contain ultra-fine dendrites which produce higher strengths on mechanical reduction of the bodies formed therefrom, or comparable strengths at lower reduction values. The method is applicable to alloys of copper with vanadium, niobium, tantalum, chromium, molybdenum, tungsten, iron and cobalt.

Method of preparing copper-dendritic composite alloys for mechanical reduction

DOEpatents

Verhoeven, J.D.; Gibson, E.D.; Schmidt, F.A.; Spitzig, W.A.

1988-09-13

Copper-dendritic composite alloys are prepared for mechanical reduction to increase tensile strength by dispersing molten droplets of the composite alloy into an inert gas; solidifying the droplets in the form of minute spheres or platelets; and compacting a mass of the spheres or platelets into an integrated body. The spheres preferably have diameters of from 50 to 2,000 [mu]m, and the platelets thicknesses of 100 to 2,000 [mu]m. The resulting spheres or platelets will contain ultra-fine dendrites which produce higher strengths on mechanical reduction of the bodies formed therefrom, or comparable strengths at lower reduction values. The method is applicable to alloys of copper with vanadium, niobium, tantalum, chromium, molybdenum, tungsten, iron and cobalt. 3 figs.

Effect of heavy metals and water content on the strength of magnesium phosphate cements.

PubMed

Buj, Irene; Torras, Josep; Casellas, Daniel; Rovira, Miquel; de Pablo, Joan

2009-10-15

In this paper the mechanical properties of magnesium potassium phosphate cements used for the Stabilization/Solidification (S/S) of galvanic wastes were investigated. Surrogate wastes (metal nitrate dissolutions) were employed containing Cd, Cr(III), Cu, Ni, Pb or Zn at a concentration of 25 g dm(-3) and different water-to-solid (W/S) ratios (0.3, 0.4, 0.5 and 0.6 dm(3)kg(-1)) have been employed. Cements were prepared by mixing hard burned magnesia of about 70% purity with potassium dihydrogen phosphate. Compressive strength and tensile strength of specimens were determined. In addition the volume of permeable voids was measured. It was found that when comparing pastes that the volume of permeable voids increases and mechanical strength decreases with the increase of water-to-solid ratio (W/S). Nevertheless pastes with the same material proportions containing different metals show different mechanical strength values. The hydration products were analyzed by XRD. With the increase of water content not previously reported hydration compound was detected: bobierrite.

Ultrafast-laser dicing of thin silicon wafers: strategies to improve front- and backside breaking strength

NASA Astrophysics Data System (ADS)

Domke, Matthias; Egle, Bernadette; Stroj, Sandra; Bodea, Marius; Schwarz, Elisabeth; Fasching, Gernot

2017-12-01

Thin 50-µm silicon wafers are used to improve heat dissipation of chips with high power densities. However, mechanical dicing methods cause chipping at the edges of the separated dies that reduce the mechanical stability. Thermal load changes may then lead to sudden chip failure. Recent investigations showed that the mechanical stability of the cut chips could be increased using ultrashort-pulsed lasers, but only at the laser entrance (front) side and not at the exit (back) side. The goal of this study was to find strategies to improve both front- and backside breaking strength of chips that were cut out of an 8″ wafer with power metallization using an ultrafast laser. In a first experiment, chips were cut by scanning the laser beam in single lines across the wafer using varying fluencies and scan speeds. Three-point bending tests of the cut chips were performed to measure front and backside breaking strengths. The results showed that the breaking strength of both sides increased with decreasing accumulated fluence per scan. Maximum breaking strengths of about 1100 MPa were achieved at the front side, but only below 600 MPa were measured for the backside. A second experiment was carried out to optimize the backside breaking strength. Here, parallel line scans to increase the distance between separated dies and step cuts to minimize the effect of decreasing fluence during scribing were performed. Bending tests revealed that breaking strengths of about 1100 MPa could be achieved also on the backside using the step cut. A reason for the superior performance could be found by calculating the fluence absorbed by the sidewalls. The calculations suggested that an optimal fluence level to minimize thermal side effects and periodic surface structures was achieved due to the step cut. Remarkably, the best breaking strengths values achieved in this study were even higher than the values obtained on state of the art ns-laser and mechanical dicing machines. This is the first study to the knowledge of the authors, which demonstrates that ultrafast-laser dicing improves the mechanical stability of thin silicon chips.

Tectonic stresses in the lithosphere: constraints provided by the experimental deformation of rocks.

USGS Publications Warehouse

Kirby, S.H.

1980-01-01

The strengths of rocks clearly place an upper limit on the stress that can be sustained by the upper half of the lithosphere. Laboratory data on rock rheology are generally lacking at intermediate temperatures and pressures on the important rock types expected in the lithosphere, so a definitive accounting of the strength distribution with depth in the upper lithosphere is presently unattainable. Analogies are drawn between the fragmentary strength data on slicates at intermediate temperature and the more extensive experimental data on marble and limestone, and several tentative conclusions are drawn: First, brittle processes, such as faulting and cataclasis, are expected to control rock strength at low pressures and temperatures. The strengths associated with these brittle mechanisms increase rapidly with increasing effective pressure and are relatively insensitive to temperature and strain rate. Second, the transitions between brittle and ductile processes occur at critical values of the least principal stress sigma3. I suggest that the concept of the deformation mechanism map of Ashby (1972) be extended to brittle-ductile transitions by normalizing the applied differential stress sigma by sigma3, i.e., the transitions occur at critical values of sigma/sigma3. -from Author

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sivakumar Babu, G.L., E-mail: gls@civil.iisc.ernet.in; Lakshmikanthan, P., E-mail: lakshmikanthancp@gmail.com; Santhosh, L.G., E-mail: lgsanthu2006@gmail.com

Highlights: • Shear strength properties of mechanically biologically treated municipal solid waste. • Effect of unit weight and particle size on the shear strength of waste. • Effect of particle size on the strength properties. • Stiffness ratio and the strength ratio of MSW. - Abstract: Strength and stiffness properties of municipal solid waste (MSW) are important in landfill design. This paper presents the results of comprehensive testing of shear strength properties of mechanically biologically treated municipal solid waste (MBT-MSW) in laboratory. Changes in shear strength of MSW as a function of unit weight and particle size were investigated bymore » performing laboratory studies on the MSW collected from Mavallipura landfill site in Bangalore. Direct shear tests, small scale and large scale consolidated undrained and drained triaxial tests were conducted on reconstituted compost reject MSW samples. The triaxial test results showed that the MSW samples exhibited a strain-hardening behaviour and the strength of MSW increased with increase in unit weight. Consolidated drained tests showed that the mobilized shear strength of the MSW increased by 40% for a unit weight increase from 7.3 kN/m{sup 3} to 10.3 kN/m{sup 3} at 20% strain levels. The mobilized cohesion and friction angle ranged from 5 to 9 kPa and 8° to 33° corresponding to a strain level of 20%. The consolidated undrained tests exhibited reduced friction angle values compared to the consolidated drained tests. The friction angle increased with increase in the unit weight from 8° to 55° in the consolidated undrained tests. Minor variations were found in the cohesion values. Relationships for strength and stiffness of MSW in terms of strength and stiffness ratios are developed and discussed. The stiffness ratio and the strength ratio of MSW were found to be 10 and 0.43.« less

Microstructure, mechanical properties, in vitro degradation and cytotoxicity evaluations of Mg-1.5Y-1.2Zn-0.44Zr alloys for biodegradable metallic implants.

PubMed

Fan, Jun; Qiu, Xin; Niu, Xiaodong; Tian, Zheng; Sun, Wei; Liu, Xiaojuan; Li, Yangde; Li, Weirong; Meng, Jian

2013-05-01

Mg-1.5Y-1.2Zn-0.44Zr alloys were newly developed as degradable metallic biomaterials. A comprehensive investigation of the microstructure, mechanical properties, in vitro degradation assessments and in vitro cytotoxicity evaluations of the as-cast state, as-heat treated state and as-extruded state alloys was done. The microstructure observations show that the Mg-1.5Y-1.2Zn-0.44Zr alloys are mainly composed of the matrix α-Mg phases and the Mg12ZnY secondary phases (LPS structure). The hot extrusion method significantly refined the grains and eliminated the defects of both as-cast and heat treated alloys and thereby contributed to the better mechanical properties and biodegradation resistance. The values of tensile strength and tensile yield strength of the alloy in the as-extruded condition are about 236 and 178 MPa respectively, with an excellent elongation of 28%. Meanwhile, the value of compressive strength is about 471 MPa and the value of bending strength is about 501 MPa. The superior bending strength further demonstrates the excellent ductility of the hot extruded alloys. The results of immersion tests and electrochemical measurements in the SBF indicate that a protective film precipitated on the alloy's surface with the extension of degradation. The protective film contains Mg(OH)2 and hydroxyapatite (HA) which can reinforce osteoblast activity and promote good biocompatibility. No significant cytotoxicity towards L-929 cells was detected and the immersion extracts of alloy samples could enhance the cell proliferation with time in the cytotoxicity evaluations, implying that the Mg-1.5Y-1.2Zn-0.44Zr alloys have the potential to be used for biomedical applications. Copyright © 2013 Elsevier B.V. All rights reserved.

The Effects of Carbon Nanotubes on the Mechanical and Wear Properties of AZ31 Alloy

PubMed Central

Zhou, Mingyang; Qu, Xiaoni; Ren, Lingbao; Fan, Lingling; Zhang, Yuwenxi; Guo, Yangyang; Quan, Gaofeng; Liu, Bin; Sun, Hao

2017-01-01

Carbon nanotube (CNT)-reinforced AZ31 matrix nanocomposites were successfully fabricated using a powder metallurgy method followed by hot extrusion. The influence of CNTs on microstructures, mechanical properties, and wear properties were systematically investigated by optical microscope (OM), scanning electron microscope (SEM), X-ray diffraction (XRD), hardness test, tensile test, and wear test. The results revealed that the nanocomposites showed a slightly smaller grain size compared with the matrix and uniform distribution that CNTs could achieve at proper content. As a result, the addition of CNTs could weaken basal plane texture. However, the yield strength and ultimate tensile strength of the composites were enhanced as the amount of CNTs increased up to 2.0 wt. %, reaching maximum values of 241 MPa (+28.2%) and 297 MPa (+6.1%), respectively. The load transfer mechanism, Orowan mechanism, and thermal mismatch mechanism played important roles in the enhancement of the yield strength, and several classical models were employed to predict the theoretical values. The effect of CNT content on the friction coefficient and weight loss of the nanocomposites was also studied. The relationships between the amount of CNTs, the friction coefficient, and weight loss could be described by the exponential decay model and the Boltzmann model, respectively. PMID:29207543

Atomistic modeling of mechanical properties of polycrystalline graphene.

PubMed

Mortazavi, Bohayra; Cuniberti, Gianaurelio

2014-05-30

We performed molecular dynamics (MD) simulations to investigate the mechanical properties of polycrystalline graphene. By constructing molecular models of ultra-fine-grained graphene structures, we studied the effect of different grain sizes of 1-10 nm on the mechanical response of graphene. We found that the elastic modulus and tensile strength of polycrystalline graphene decrease with decreasing grain size. The calculated mechanical proprieties for pristine and polycrystalline graphene sheets are found to be in agreement with experimental results in the literature. Our MD results suggest that the ultra-fine-grained graphene structures can show ultrahigh tensile strength and elastic modulus values that are very close to those of pristine graphene sheets.

Effect of C content on the mechanical properties of solution treated as-cast ASTM F-75 alloys.

PubMed

Herrera, M; Espinoza, A; Méndez, J; Castro, M; López, J; Rendón, J

2005-07-01

The mechanical properties of solution treated ASTM F-75 alloys with various carbon contents have been studied. Alloys cast under the same conditions were subjected to solution treatment for several periods and then their tensile properties were evaluated. In the as-cast conditions, the alloys exhibited higher strength values with increasing carbon content whereas their ductility was not significantly affected. For the solution treated alloys, the variation of the strength was characterized by a progressive increase for short treatment times until a maximum value was achieved, which was followed by a diminution in this property for longer treatment times. This behavior was more accentuated for the case of the alloys with medium carbon contents, which also exhibited the highest values of strength. Furthermore, the alloy's ductility was enhanced progressively with increasing solution treatment time. This improvement in ductility was significantly higher for the medium carbon alloys compared with the rest of the studied alloys. Thus, high and low carbon contents in solution treated ASTM F-75 alloys did not produced sufficiently high tensile properties.

Effect of prolonged isothermal heat treatment on the mechanical behavior of advanced NANOBAIN steel

NASA Astrophysics Data System (ADS)

Avishan, Behzad

2017-09-01

The microstructural evolution and consequent changes in strength and ductility of advanced NANOBAIN steel during prolonged isothermal heat-treatment stages were investigated. The microstructure and mechanical properties of nanostructured bainite were not expected to be influenced by extending the heat-treatment time beyond the optimum value because of the autotempering phenomenon and high tempering resistance. However, experimental results indicated that the microstructure was thermodynamically unstable and that prolonged austempering resulted in carbon depletion from high-carbon retained austenite and carbide precipitations. Therefore, austenite became thermally less stable and partially transformed into martensite during cooling to room temperature. Prolonged austempering did not lead to the typical tempering sequence of bainite, and the sizes of the microstructural constituents were independent of the extended heat-treatment times. This independence, in turn, resulted in almost constant ultimate tensile strength values. However, microstructural variations enhanced the yield strength and the hardness of the material at extended isothermal heat-treatment stages. Finally, although microstructural changes decreased the total elongation and impact toughness, considerable combinations of mechanical properties could still be achieved.

Effect of metallurgical structure and properties on adhesion and friction behavior of cobalt alloys

NASA Technical Reports Server (NTRS)

Keller, D. V., Jr.; Shatynski, S.; Vedamanikam, P. M.

1972-01-01

The metallurgical structure and some of the mechanical properties of two cobalt alloys, cobalt-50% iron and cobalt-25% molybdenum-10% chromium, were determined under various heat treated conditions. The mechanical properties of the bcc disordered Co-50Fe alloy, which was found to be very brittle, indicated an exceedingly low fracture strength, low hardness, and very weak grain boundary strength. Ordering by suitable heat treatment only produced a more brittle material with a lower fracture strength and a slightly higher hardness value. Work hardening was found to produce a finer grain structure and a greater grain boundary strength. Tensile properties were examined. It was found that the Co-25Mo-10Cr alloy was difficult to place in the alpha Co solid solution condition, which limited the ability to use precipitation as a hardening reaction. Over two hundred adhesion cycles from zero contact load, to maximum load, to fracture were conducted between couples for each of the above alloys in an ultrahigh vacuum system which would permit the sample surfaces to be cleaned of all contaminant layers. In the Co-50Fe case, the calculated fracture stress from the adhesion tests showed values in the range of 80 to 150 k.s.i., which is about ten times greater than the values from tension tests.

Porcelain surface conditioning protocols and shear bond strength of orthodontic brackets.

PubMed

Lestrade, Ashley M; Ballard, Richard W; Xu, Xiaoming; Yu, Qingzhao; Kee, Edwin L; Armbruster, Paul C

2016-05-01

The objective of the present study was to determine which of six bonding protocols yielded a clinically acceptable shear bond strength (SBS) of metal orthodontic brackets to CAD/CAM lithium disilicate porcelain restorations. A secondary aim was to determine which bonding protocol produced the least surface damage at debond. Sixty lithium disilicate samples were fabricated to replicate the facial surface of a mandibular first molar using a CEREC CAD/CAM machine. The samples were split into six test groups, each of which received different mechanical/chemical pretreatment protocols to roughen the porcelain surface prior to bonding a molar orthodontic attachment. Shear bond strength testing was conducted using an Instron machine. The mean, maximum, minimal, and standard deviation SBS values for each sample group including an enamel control were calculated. A t-test was used to evaluate the statistical significance between the groups. No significant differences were found in SBS values, with the exception of surface roughening with a green stone prior to HFA and silane treatment. This protocol yielded slightly higher bond strength which was statistically significant. Chemical treatment alone with HFA/silane yielded SBS values within an acceptable clinical range to withstand forces applied by orthodontic treatment and potentially eliminates the need to mechanically roughen the ceramic surface.

Burst strength of tubing and casing based on twin shear unified strength theory.

PubMed

Lin, Yuanhua; Deng, Kuanhai; Sun, Yongxing; Zeng, Dezhi; Liu, Wanying; Kong, Xiangwei; Singh, Ambrish

2014-01-01

The internal pressure strength of tubing and casing often cannot satisfy the design requirements in high pressure, high temperature and high H2S gas wells. Also, the practical safety coefficient of some wells is lower than the design standard according to the current API 5C3 standard, which brings some perplexity to the design. The ISO 10400: 2007 provides the model which can calculate the burst strength of tubing and casing better than API 5C3 standard, but the calculation accuracy is not desirable because about 50 percent predictive values are remarkably higher than real burst values. So, for the sake of improving strength design of tubing and casing, this paper deduces the plastic limit pressure of tubing and casing under internal pressure by applying the twin shear unified strength theory. According to the research of the influence rule of yield-to-tensile strength ratio and mechanical properties on the burst strength of tubing and casing, the more precise calculation model of tubing-casing's burst strength has been established with material hardening and intermediate principal stress. Numerical and experimental comparisons show that the new burst strength model is much closer to the real burst values than that of other models. The research results provide an important reference to optimize the tubing and casing design of deep and ultra-deep wells.

Burst Strength of Tubing and Casing Based on Twin Shear Unified Strength Theory

PubMed Central

Lin, Yuanhua; Deng, Kuanhai; Sun, Yongxing; Zeng, Dezhi; Liu, Wanying; Kong, Xiangwei; Singh, Ambrish

2014-01-01

The internal pressure strength of tubing and casing often cannot satisfy the design requirements in high pressure, high temperature and high H2S gas wells. Also, the practical safety coefficient of some wells is lower than the design standard according to the current API 5C3 standard, which brings some perplexity to the design. The ISO 10400: 2007 provides the model which can calculate the burst strength of tubing and casing better than API 5C3 standard, but the calculation accuracy is not desirable because about 50 percent predictive values are remarkably higher than real burst values. So, for the sake of improving strength design of tubing and casing, this paper deduces the plastic limit pressure of tubing and casing under internal pressure by applying the twin shear unified strength theory. According to the research of the influence rule of yield-to-tensile strength ratio and mechanical properties on the burst strength of tubing and casing, the more precise calculation model of tubing-casing's burst strength has been established with material hardening and intermediate principal stress. Numerical and experimental comparisons show that the new burst strength model is much closer to the real burst values than that of other models. The research results provide an important reference to optimize the tubing and casing design of deep and ultra-deep wells. PMID:25397886

Evaluating the fracture toughness and flexural strength of pressable dental ceramics: an in vitro study.

PubMed

Gurram, Ravi; Krishna, C H Vamsi; Reddy, K Mahendranadh; Reddy, G V K Mohan; Shastry, Y Mahadev

2014-12-01

The study was undertaken to evaluate the biaxial flexural strength, biaxial flexural strength after etching with 9 % HF acid and fracture toughness of three commonly used pressable all ceramic core materials. Ninety glass ceramic specimens were fabricated from three commercially available leucite based core ceramic material (1) Esthetic Empress, (2) Cergo, and (3) Performance Plus. Thirty discs of each material were divided into three groups of 10 discs each. Biaxial flexural strength (30 discs,) Biaxial flexural strength for samples treated with 9 % HF acid (30 discs) and fracture toughness (30 discs) were evaluated. Core material Performance Plus had the lowest biaxial strength of 124.89 MPa, Cergo had strength of 152.22 MPa and the highest value of 163.95 was reported for Esthetic Empress. For samples treated 9 % HF, Performance Plus had the lowest biaxial strength of 98.37 MPa, Cergo had strength of 117.42 MPa and the highest value of 143.74 was reported for Esthetic Empress. Core material Performance Plus had the lowest fracture toughness of 1.063 MPa, Cergo had strength of 1.112 MPa and the highest value of 1.225 was reported for Esthetic Empress. The results shows that Esthetic Empress had better mechanical properties compared to Cergo had Performance Plus in relation to the parameters tested.

Specimen geometry effects on graphite/PMR-15 composites during thermo-oxidative aging

NASA Technical Reports Server (NTRS)

Bowles, K. J.; Meyers, A.

1986-01-01

Studies were conducted to establish the effects of specimen geometry on the thermo-oxidative stability and the mechanical properties retention of unidirectional Celion 12000 graphite fiber reinforced PMR-15 polyimide composites. Weight loss, flexural strength and interlaminar shear strength are measured at isothermal aging times as long as 1639 hr at a temperature of 316 C for three different specimen geometries. It is found that the three different types of specimen surfaces exhibit different values of weight loss/unit area. The mechanical properties retention is also found to be dependent on geometry for these composites. The interlaminar shear strength decreases significantly over the complete range of aging times. The flexural strength retention starts showing geometric dependency after about 1000 hr of aging at 316C. Weight loss fluxes, associated with the three different types of exposed surfaces, are calculated and used to develop an empirical mathematical model for predicting the weight loss behavior of unidirectional composites of arbitrary geometries. Data are presented comparing experimentally determined weight loss with weight loss values predicted using the empirical model.

Specimen geometry effects on graphite/PMR-15 composites during thermo-oxidative aging

NASA Technical Reports Server (NTRS)

Bowles, K. J.; Meyers, A.

1986-01-01

Studies were conducted to establish the effects of specimen geometry on the thermo-oxidative stability and the mechanical properties retention of unidirectional Celion 12000 graphite fiber reinforced PMR-15 polyimide composites. Weight loss, flexural strength and interlaminar shear strength are measured at isothermal aging times as long as 1639 hr at a temperature of 316 C for three different specimen geometries. It is found that the three different types of specimen surfaces exhibit different values of weight loss/unit area. The mechanical properties retention is also found to be dependent on geometry for these composites. The interlaminar shear strength decreases significantly over the complete range of aging times. The flexural strength retention starts showing geometric dependency after about 1000 hr of aging at 316 C. Weight loss fluxes, associated with the three different types of exposed surfaces, are calculated and used to develop an empirical mathematical model for predicting the weight loss behavior of unidirectional composites of arbitrary geometries. Data are presented comparing experimentally determined weight loss with weight loss values predicted using the empirical model.

Effect of coating mild steel with CNTs on its mechanical properties and corrosion behaviour in acidic medium

NASA Astrophysics Data System (ADS)

Abdulmalik Abdulrahaman, Mahmud; Kamaldeeen Abubakre, Oladiran; Ambali Abdulkareem, Saka; Oladejo Tijani, Jimoh; Aliyu, Ahmed; Afolabi, Ayo Samuel

2017-03-01

The study investigated the mechanical properties and corrosion behaviour of mild steel coated with carbon nanotubes at different coating conditions. Multi-walled carbon nanotubes (MWCNTs) were synthesized via the conventional chemical vapour deposition reaction using bimetallic Fe-Ni catalyst supported on kaolin, with acetylene gas as a carbon source. The HRSEM/HRTEM analysis of the purified carbon materials revealed significant reduction in the diameters of the purified MWCNT bundles from 50 nm to 2 nm and was attributed to the ultrasonication assisted dispersion with surfactant (gum arabic) employed in purification process. The network of the dispersed MWCNTs was coated onto the surfaces of mild steel samples, and as the coating temperature and holding time increased, the coating thickness reduced. The mechanical properties (tensile strength, yield strength, hardness value) of the coated steel samples increased with increase in coating temperature and holding time. Comparing the different coating conditions, coated mild steels at the temperature of 950 °C for 90 min holding time exhibited high hardness, yield strength and tensile strength values compared to others. The corrosion current and corrosion rate of the coated mild steel samples decreased with increase in holding time and coating temperature. The lowest corrosion rate was observed on sample coated at 950 °C for 90 min.

Evaluation of Flexural Strength of Polymethyl Methacrylate modified with Silver Colloidal Nanoparticles subjected to Two Different Curing Cycles: An in vitro Study.

PubMed

Munikamaiah, Ranganath L; Jain, Saket K; Pal, Kapil S; Gaikwad, Ajay

2018-03-01

Silver colloidal nanoparticles have been incorporated into acrylic resins to induce antimicrobial properties. However, as additives, they can influence the mechanical properties of the final product. Mechanical properties are also dependent on different curing cycles. The aim of this study was to evaluate flexural strength of a denture base resin incorporated with different concentrations of silver colloidal nanoparticles subjected to two different curing cycles. Lucitone 199 denture base resin was used into which silver colloidal nanoparticles were incorporated at 0.5 and 5% by polymer mass. Specimens devoid of nanoparticles were used as controls. A total of 60 specimens were fabricated and divided into two groups. Each group was divided into three subgroups consisting of 10 specimens each. The specimens were fabricated according to American Dental Association (ADA) specification No. 12 and tested for flexural strength using universal testing machine. Silver colloidal nanoparticle incorporation at 0.5% concentration increased the mean flexural strength in both curing cycles by 7.5 and 4.4%, respectively, when compared with the control group. The study suggested that the mean flexural strength value of 0.5% silver colloidal nanoparticles in denture base resin was above the value of the control group both in short and long curing cycles, which makes it clinically suitable as a denture base material. However, at 5% concentration, the statistically significant amount of decrease in flexural strength compared with the value of control group both in short and long curing cycles gives it a questionable prognosis. The specimens incorporated with the antimicrobial agent 0.5% silver colloidal nanoparticles and processed by long curing cycles showed significant increase in its flexural strength compared with the control group, which makes it clinically suitable as a denture base material.

Parameter optimization of fusion splicing of photonic crystal fibers and conventional fibers to increase strength

NASA Astrophysics Data System (ADS)

Zhang, Chunxi; Zhang, Zuchen; Song, Jingming; Wu, Chunxiao; Song, Ningfang

2015-03-01

A splicing parameter optimization method to increase the tensile strength of splicing joint between photonic crystal fiber (PCF) and conventional fiber is demonstrated. Based on the splicing recipes provided by splicer or fiber manufacturers, the optimal values of some major splicing parameters are obtained in sequence, and a conspicuous improvement in the mechanical strength of splicing joints between PCFs and conventional fibers is validated through experiments.

Probabilistic material degradation model for aerospace materials subjected to high temperature, mechanical and thermal fatigue, and creep

NASA Technical Reports Server (NTRS)

Boyce, L.

1992-01-01

A probabilistic general material strength degradation model has been developed for structural components of aerospace propulsion systems subjected to diverse random effects. The model has been implemented in two FORTRAN programs, PROMISS (Probabilistic Material Strength Simulator) and PROMISC (Probabilistic Material Strength Calibrator). PROMISS calculates the random lifetime strength of an aerospace propulsion component due to as many as eighteen diverse random effects. Results are presented in the form of probability density functions and cumulative distribution functions of lifetime strength. PROMISC calibrates the model by calculating the values of empirical material constants.

Effect of cobalt doping on the mechanical properties of ZnO nanowires

DOE Office of Scientific and Technical Information (OSTI.GOV)

Vahtrus, Mikk; Šutka, Andris

In this work, we investigate the influence of doping on the mechanical properties of ZnO nanowires (NWs) by comparing the mechanical properties of pure and Co-doped ZnO NWs grown in similar conditions and having the same crystallographic orientation [0001]. The mechanical characterization included three-point bending tests made with atomic force microscopy and cantilever beam bending tests performed inside scanning electron microscopy. It was found that the Young's modulus of ZnO NWs containing 5% of Co was approximately a third lower than that of the pure ZnO NWs. Bending strength values were comparable for both materials and in both cases weremore » close to theoretical strength indicating high quality of NWs. Dependence of mechanical properties on NW diameter was found for both doped and undoped ZnO NWs. - Highlights: •Effect of Co doping on the mechanical properties of ZnO nanowires is studied. •Co substitutes Zn atoms in ZnO crystal lattice. •Co addition affects crystal lattice parameters. •Co addition results in significantly decreased Young's modulus of ZnO. •Bending strength for doped and undoped wires is close to the theoretical strength.« less

Carbon fiber composites for cryogenic filament-wound vessels

NASA Technical Reports Server (NTRS)

Larsen, J. V.; Simon, R. A.

1972-01-01

Advanced unidirectional and bidirectional carbon fiber/epoxy resin composites were evaluated for physical and mechanical properties over a cryogenic to room temperature range for potential application to cryogenic vessels. The results showed that Courtaulds HTS carbon fiber was the superior fiber in terms of cryogenic strength properties in epoxy composites. Of the resin systems tested in ring composites, CTBN/ERLB 4617 exhibited the highest composite strengths at cryogenic temperatures, but very low interlaminar shear strengths at room temperature. Tests of unidirectional and bidirectional composite bars showed that the Epon 828/Empol 1040 resin was better at all test temperatures. Neither fatigue cycling nor thermal shock had a significant effect on composite strengths or moduli. Thermal expansion measurements gave negative values in the fiber direction and positive values in the transverse direction of the composites.

Effect of chemical disinfectant on the transverse strength of heat-polymerized acrylic resins subjected to mechanical and chemical polishing: an in vitro study.

PubMed

Sharan, Smitha; Kavitha, H R; Konde, Harish; Kalahasti, Deepthi

2012-05-01

To evaluate the effect of chemical disinfectant on the transverse strength of heat-polymerized acrylic resins subjected to mechanical and chemical polishing. A total of 256 rectangular specimens (65 * 10 * 3 mm) 128 per resin (Lucitone-199 and Acralyn-H) were fabricated. One side of each specimen was not polished and the other was either mechanically (n = 96) or chemically (n = 96) polished and immersed for 10, 30 and 60 minutes in 2% alkaline glutaraldehyde. Mechanically polished (n = 32) and chemically polished (n = 32) control specimens were immersed only in distilled water. The transverse strength (N/mm(2)) was tested for failure in a universal testing machine, at a crosshead speed of 5 mm/min. Data were statistically analyzed using 2-way ANOVA and Student t-test. chemical polishing resulted in significantly lower transverse strength values than mechanical polishing. Lucitone- 199 resin demonstrated the highest overall transverse strength for the materials tested. Heat-polymerized acrylic resins either mechanically or chemically polished, did not demonstrate significant changes in transverse strength during immersion in the disinfecting solution tested, regardless of time of immersion. Lucitone-199 resin demonstrated the highest overall transverse strength for the materials tested and significantly stronger than Acralyn-H with either type of polishing following immersion in 2% alkaline glutaraldehyde. There is a concern that immersion in chemical solutions often used for cleansing and disinfection of prostheses may undermine the strength and structure of denture base resins. In this study it was observed that, the transverse strength of samples of Lucitone-199 was higher than that of the samples of Acralyn-H. The chances of fracture of the denture made of Lucitone-199 are less than that of dentures made of Acralyn-H. The chemically polished dentures may be more prone to fracture than mechanically polished dentures.

Design and Fabrication of 3D printed Scaffolds with a Mechanical Strength Comparable to Cortical Bone to Repair Large Bone Defects

PubMed Central

Roohani-Esfahani, Seyed-Iman; Newman, Peter; Zreiqat, Hala

2016-01-01

A challenge in regenerating large bone defects under load is to create scaffolds with large and interconnected pores while providing a compressive strength comparable to cortical bone (100–150 MPa). Here we design a novel hexagonal architecture for a glass-ceramic scaffold to fabricate an anisotropic, highly porous three dimensional scaffolds with a compressive strength of 110 MPa. Scaffolds with hexagonal design demonstrated a high fatigue resistance (1,000,000 cycles at 1–10 MPa compressive cyclic load), failure reliability and flexural strength (30 MPa) compared with those for conventional architecture. The obtained strength is 150 times greater than values reported for polymeric and composite scaffolds and 5 times greater than reported values for ceramic and glass scaffolds at similar porosity. These scaffolds open avenues for treatment of load bearing bone defects in orthopaedic, dental and maxillofacial applications. PMID:26782020

Design and Fabrication of 3D printed Scaffolds with a Mechanical Strength Comparable to Cortical Bone to Repair Large Bone Defects

NASA Astrophysics Data System (ADS)

Roohani-Esfahani, Seyed-Iman; Newman, Peter; Zreiqat, Hala

2016-01-01

A challenge in regenerating large bone defects under load is to create scaffolds with large and interconnected pores while providing a compressive strength comparable to cortical bone (100-150 MPa). Here we design a novel hexagonal architecture for a glass-ceramic scaffold to fabricate an anisotropic, highly porous three dimensional scaffolds with a compressive strength of 110 MPa. Scaffolds with hexagonal design demonstrated a high fatigue resistance (1,000,000 cycles at 1-10 MPa compressive cyclic load), failure reliability and flexural strength (30 MPa) compared with those for conventional architecture. The obtained strength is 150 times greater than values reported for polymeric and composite scaffolds and 5 times greater than reported values for ceramic and glass scaffolds at similar porosity. These scaffolds open avenues for treatment of load bearing bone defects in orthopaedic, dental and maxillofacial applications.

Production and mechanical properties of Al-SiC metal matrix composites

NASA Astrophysics Data System (ADS)

Karvanis, K.; Fasnakis, D.; Maropoulos, A.; Papanikolaou, S.

2016-11-01

The usage of Al-SiC Metal Matrix Composites is constantly increasing in the last years due to their unique properties such as light weight, high strength, high specific modulus, high fatigue strength, high hardness and low density. Al-SiC composites of various carbide compositions were produced using a centrifugal casting machine. The mechanical properties, tensile and compression strength, hardness and drop-weight impact strength were studied in order to determine the optimum carbide % in the metal matrix composites. Scanning electron microscopy was used to study the microstructure-property correlation. It was observed that the tensile and the compressive strength of the composites increased as the proportion of silicon carbide became higher in the composites. Also with increasing proportion of silicon carbide in the composite, the material became harder and appeared to have smaller values for total displacement and total energy during impact testing.

On improving the fracture toughness of a NiAl-based alloy by mechanical alloying

NASA Technical Reports Server (NTRS)

Kostrubanic, J.; Koss, D. A.; Locci, I. E.; Nathal, M.

1991-01-01

Mechanical alloying (MA) has been used to process the NiAl-based alloy Ni-35Al-20Fe, such that a fine-grain (about 2 microns) microstructure is obtained through the addition of 2 vol pct Y2O3 particles. When compared to a conventionally processed, coarse-grained (about 28 microns) Ni-35-20 alloy without the Y2O3 particles, the MA alloy exhibits two to three times higher fracture toughness values, despite a 50-percent increase in yield strength. Room-temperature K(O) values as high as 34 MPa sq rt m are observed, accompanied by a yield strength in excess of 1100 MPa. Fractography confirms a change in fracture characteristics of the fine-grained MA alloy.

Synthesis and properties of a novel bio-based polymer from modified soybean oil

NASA Astrophysics Data System (ADS)

Li, Y. T.; Yang, L. T.; Zhang, H.; Tang, Z. J.

2017-02-01

Maleated acrylated epoxidized soybean oil (MAESO) was prepared by acrylated epoxidized soybean oil (AESO) and maleic anhydride. AESO were obtained by the reaction of epoxidized soybean oil (ESO) with acrylic acid as the ring-opening reagent. The polymer was prepared by MAESO react with styrene. The structures of the products were studied by Fourier transformation infrared spectrometer (FT-IR), and were consistent with the theoretical structures. Swelling experiment indicated that the crosslinking degree increased with increasing epoxy value of ESO. Thermal properties was tested by thermo-gravimetric analysis (TG) and differential scanning calorimetry analysis (DSC), indicating that glass transition temperature (Tg) of the polymer increased with increasing epoxy value of ESO, and thermal stability of polymer have a good correlation with the crosslinking degree. Mechanical properties analysis presented that tensile strength and impact strength affected by epoxy value of ESO. With the increase of epoxy value, the tensile strength increase, while the impact strength decrease. The property of the polymer ranged from elastomer to plastic character depended on the functionality of the ESO.

Mechanical properties of acacia and eucalyptus wood chars

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, M.; Verma, B.B.; Gupta, R.C.

1999-10-01

In the present investigation the effects of carbonization conditions (temperature and heating rate) on the mechanical properties (such as crushing and impact strengths and shatter index) of acacia and eucalyptus wood chars have been determined. The crushing and impact strengths of both the acacia and eucalyptus wood chars (made by slow carbonization) decreased with increase of preparation temperature up to 600 C, followed by an increase thereafter. These wood chars showed a continuous increase in shatter index values with carbonization temperature. In contrast to slow carbonization (heating rate 4 C min{sup {minus}1}), rapid carbonization (heating rate 30 C min{sup {minus}1})more » yielded chars of lower crushing strengths. Slowly carbonized eucalyptus wood gave chars of superior crushing and impact strengths than those produced from acacia wood under the same carbonization conditions. The crushing and impact strengths of these wood chars, in general, have shown an increase with increase in their apparent density. The crushing strength of cubic-shaped wood char decreased with increase in size.« less

Effect of Cooling Rate on the Microstructure and Mechanical Properties of C-Mn-Al-Si-Nb Hot-Rolled TRIP Steels

NASA Astrophysics Data System (ADS)

Fu, B.; Y Lu, M.; Y Yang, W.; Li, L. F.; Y Zhao, Z.

2017-12-01

A novel thermomechanical process to manufacture hot-rolled TRIP steels has been proposed based on dynamic transformation of undercooled austenite (DTUA). The cooling rate between DTUA and isothermal bainitic treatment in the novel process is important. In the present study, effect of this cooling rate on the final microstructures and mechanical properties of a C-Mn-Al-Si-Nb TRIP steel was investigated. The results showed that the volume fractions of acicular ferrite and retained austenite were increased with the increment of cooling rate. As a consequence, higher yield strength and larger total elongation were obtained for the investigated steel with higher cooling rate. In addition, a value of 30.24 GPa% for the product of tensile strength and total elongation was acquired when the cooling rate was 25 K/s. This value has met the standard of the “Third Generation” of advanced high strength sheet steels.

Investigation of a Macromechanical Approach to Analyzing Triaxially-Braided Polymer Composites

NASA Technical Reports Server (NTRS)

Goldberg, Robert K.; Blinzler, Brina J.; Binienda, Wieslaw K.

2010-01-01

A macro level finite element-based model has been developed to simulate the mechanical and impact response of triaxially-braided polymer matrix composites. In the analytical model, the triaxial braid architecture is simulated by using four parallel shell elements, each of which is modeled as a laminated composite. The commercial transient dynamic finite element code LS-DYNA is used to conduct the simulations, and a continuum damage mechanics model internal to LS-DYNA is used as the material constitutive model. The material stiffness and strength values required for the constitutive model are determined based on coupon level tests on the braided composite. Simulations of quasi-static coupon tests of a representative braided composite are conducted. Varying the strength values that are input to the material model is found to have a significant influence on the effective material response predicted by the finite element analysis, sometimes in ways that at first glance appear non-intuitive. A parametric study involving the input strength parameters provides guidance on how the analysis model can be improved.

Crack Arrest Toughness of Two High Strength Steels (AISI 4140 and AISI 4340)

NASA Astrophysics Data System (ADS)

Ripling, E. J.; Mulherin, J. H.; Crosley, P. B.

1982-04-01

The crack initiation toughness ( K c ) and crack arrest toughness ( K a ) of AISI 4140 and AISI 4340 steel were measured over a range of yield strengths from 965 to 1240 MPa, and a range of test temperatures from -53 to +74°C. Emphasis was placed on K a testing since these values are thought to represent the minimum toughness of the steel as a function of loading rate. At the same yield strengths and test temperatures, K a for the AISI 4340 was about twice as high as it was for the AISI 4140. In addition, the K a values showed a more pronounced transition temperature than the K c values, when the data were plotted as a function of test temperature. The transition appeared to be associated with a change in fracture mechanism from cleavage to dimpled rupture as the test temperature was increased. The occurrence of a “pop-in” behavior at supertransition temperatures has not been found in lower strength steels, and its evaluation in these high strength steels was possible only because they are not especially tough at their supertransition temperatures. There is an upper toughness limit at which pop-in will not occur, and this was found for the AISI 4340 steel when it was tempered to its lowest yield strength (965 MPa). All the crack arrest data were identified as plane strain values, while only about one-half of the initiation values could be classified this way.

Mechanical properties of chemically modified Sansevieria trifasciata/natural rubber/high density polyethylene (STF/NR/HDPE) composites: Effect of silane coupling agent

NASA Astrophysics Data System (ADS)

Zakaria, Nurzam Ezdiani; Baharum, Azizah; Ahmad, Ishak

2018-04-01

The main objective of this research is to study the effects of chemical modification on the mechanical properties of treated Sansevieria trifasciata fiber/natural rubber/high density polyethylene (TSTF/NR/HDPE) composites. Processing of STF/NR/HDPE composites was done by using an internal mixer. The processing parameters used were 135°C for temperature and a mixing rotor speed of 55 rpm for 15 minutes. Filler loading was varied from 10% to 40% of STF and the fiber size used was 125 µm. The composite blends obtained then were pressed with a hot press machine to get test samples of 1 mm and 3 mm of thickness. Samples were evaluated via tensile tests, Izod impact test and scanning electron microscopy (SEM). Results showed that tensile strength and strain value decreased while tensile modulus increased when filler loading increased. Impact strength increased when filler loading increased and began to decrease after 10% of filler amount for treated composites. For untreated composites, impact strength began to decrease after 20% of filler loading. Chemical modification by using silane coupling agent has improved certain mechanical properties of the composites such as tensile strength, strain value and tensile modulus. Adding more amount of filler will also increase the viscosity and the stiffness of the materials.

Microstructure and Mechanical Properties of Reaction-Formed Silicon Carbide (RFSC) Ceramics

NASA Technical Reports Server (NTRS)

Singh, M.; Behrendt, D. R.

1994-01-01

The microstructure and mechanical properties of reaction-formed silicon carbide (RFSC) ceramics fabricated by silicon infiltration of porous carbon preforms are discussed. The morphological characterization of the carbon preforms indicates a very narrow pore size distribution. Measurements of the preform density by physical methods and by mercury porosimetry agree very well and indicate that virtually all of the porosity in the preforms is open to infiltrating liquids. The average room temperature flexural strength of the RFSC material with approximately 8 at.% free silicon is 369 +/- 28 MPa (53.5 +/- 4 ksi). The Weibull strength distribution data give a characteristic strength value of 381 MPa (55 ksi) and a Weibull modulus of 14.3. The residual silicon content is lower and the strengths are superior to those of most commercially available reaction-bonded silicon carbide materials.

Shear strength characteristics of mechanically biologically treated municipal solid waste (MBT-MSW) from Bangalore.

PubMed

Sivakumar Babu, G L; Lakshmikanthan, P; Santhosh, L G

2015-05-01

Strength and stiffness properties of municipal solid waste (MSW) are important in landfill design. This paper presents the results of comprehensive testing of shear strength properties of mechanically biologically treated municipal solid waste (MBT-MSW) in laboratory. Changes in shear strength of MSW as a function of unit weight and particle size were investigated by performing laboratory studies on the MSW collected from Mavallipura landfill site in Bangalore. Direct shear tests, small scale and large scale consolidated undrained and drained triaxial tests were conducted on reconstituted compost reject MSW samples. The triaxial test results showed that the MSW samples exhibited a strain-hardening behaviour and the strength of MSW increased with increase in unit weight. Consolidated drained tests showed that the mobilized shear strength of the MSW increased by 40% for a unit weight increase from 7.3kN/m(3) to 10.3kN/m(3) at 20% strain levels. The mobilized cohesion and friction angle ranged from 5 to 9kPa and 8° to 33° corresponding to a strain level of 20%. The consolidated undrained tests exhibited reduced friction angle values compared to the consolidated drained tests. The friction angle increased with increase in the unit weight from 8° to 55° in the consolidated undrained tests. Minor variations were found in the cohesion values. Relationships for strength and stiffness of MSW in terms of strength and stiffness ratios are developed and discussed. The stiffness ratio and the strength ratio of MSW were found to be 10 and 0.43. Copyright © 2015 Elsevier Ltd. All rights reserved.

Designing durable icephobic surfaces

PubMed Central

Golovin, Kevin; Kobaku, Sai P. R.; Lee, Duck Hyun; DiLoreto, Edward T.; Mabry, Joseph M.; Tuteja, Anish

2016-01-01

Ice accretion has a negative impact on critical infrastructure, as well as a range of commercial and residential activities. Icephobic surfaces are defined by an ice adhesion strength τice < 100 kPa. However, the passive removal of ice requires much lower values of τice, such as on airplane wings or power lines (τice < 20 kPa). Such low τice values are scarcely reported, and robust coatings that maintain these low values have not been reported previously. We show that, irrespective of material chemistry, by tailoring the cross-link density of different elastomeric coatings and by enabling interfacial slippage, it is possible to systematically design coatings with extremely low ice adhesion (τice < 0.2 kPa). These newfound mechanisms allow for the rational design of icephobic coatings with virtually any desired ice adhesion strength. By using these mechanisms, we fabricate extremely durable coatings that maintain τice < 10 kPa after severe mechanical abrasion, acid/base exposure, 100 icing/deicing cycles, thermal cycling, accelerated corrosion, and exposure to Michigan wintery conditions over several months. PMID:26998520

The flexural properties of endodontic post materials.

PubMed

Stewardson, Dominic A; Shortall, Adrian C; Marquis, Peter M; Lumley, Philip J

2010-08-01

To measure the flexural strengths and moduli of endodontic post materials and to assess the effect on the calculated flexural properties of varying the diameter/length (D/L) ratio of three-point bend test samples. Three-point bend testing of samples of 2mm diameter metal and fiber-reinforced composite (FRC) rods was carried out and the mechanical properties calculated at support widths of 16 mm, 32 mm and 64 mm. Weibull analysis was performed on the strength data. The flexural strengths of all the FRC post materials exceeded the yield strengths of the gold and stainless steel samples; the flexural strengths of two FRC materials were comparable with the yield strength of titanium. Stainless steel recorded the highest flexural modulus while the titanium and the two carbon fiber materials exhibited similar values just exceeding that of gold. The remaining glass fiber materials were of lower modulus within the range of 41-57 GPa. Weibull modulus values for the FRC materials ranged from 16.77 to 30.09. Decreasing the L/D ratio produced a marked decrease in flexural modulus for all materials. The flexural strengths of FRC endodontic post materials as new generally exceed the yield strengths of metals from which endodontic posts are made. The high Weibull modulus values suggest good clinical reliability of FRC posts. The flexural modulus values of the tested posts were from 2-6 times (FRC) to 4-10 times (metal) that of dentin. Valid measurement of flexural properties of endodontic post materials requires that test samples have appropriate L/D ratios. Copyright 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Modeling of Compressive Strength for Self-Consolidating High-Strength Concrete Incorporating Palm Oil Fuel Ash

PubMed Central

Safiuddin, Md.; Raman, Sudharshan N.; Abdus Salam, Md.; Jumaat, Mohd. Zamin

2016-01-01

Modeling is a very useful method for the performance prediction of concrete. Most of the models available in literature are related to the compressive strength because it is a major mechanical property used in concrete design. Many attempts were taken to develop suitable mathematical models for the prediction of compressive strength of different concretes, but not for self-consolidating high-strength concrete (SCHSC) containing palm oil fuel ash (POFA). The present study has used artificial neural networks (ANN) to predict the compressive strength of SCHSC incorporating POFA. The ANN model has been developed and validated in this research using the mix proportioning and experimental strength data of 20 different SCHSC mixes. Seventy percent (70%) of the data were used to carry out the training of the ANN model. The remaining 30% of the data were used for testing the model. The training of the ANN model was stopped when the root mean square error (RMSE) and the percentage of good patterns was 0.001 and ≈100%, respectively. The predicted compressive strength values obtained from the trained ANN model were much closer to the experimental values of compressive strength. The coefficient of determination (R2) for the relationship between the predicted and experimental compressive strengths was 0.9486, which shows the higher degree of accuracy of the network pattern. Furthermore, the predicted compressive strength was found very close to the experimental compressive strength during the testing process of the ANN model. The absolute and percentage relative errors in the testing process were significantly low with a mean value of 1.74 MPa and 3.13%, respectively, which indicated that the compressive strength of SCHSC including POFA can be efficiently predicted by the ANN. PMID:28773520

Modeling of Compressive Strength for Self-Consolidating High-Strength Concrete Incorporating Palm Oil Fuel Ash.

PubMed

Safiuddin, Md; Raman, Sudharshan N; Abdus Salam, Md; Jumaat, Mohd Zamin

2016-05-20

Modeling is a very useful method for the performance prediction of concrete. Most of the models available in literature are related to the compressive strength because it is a major mechanical property used in concrete design. Many attempts were taken to develop suitable mathematical models for the prediction of compressive strength of different concretes, but not for self-consolidating high-strength concrete (SCHSC) containing palm oil fuel ash (POFA). The present study has used artificial neural networks (ANN) to predict the compressive strength of SCHSC incorporating POFA. The ANN model has been developed and validated in this research using the mix proportioning and experimental strength data of 20 different SCHSC mixes. Seventy percent (70%) of the data were used to carry out the training of the ANN model. The remaining 30% of the data were used for testing the model. The training of the ANN model was stopped when the root mean square error (RMSE) and the percentage of good patterns was 0.001 and ≈100%, respectively. The predicted compressive strength values obtained from the trained ANN model were much closer to the experimental values of compressive strength. The coefficient of determination ( R ²) for the relationship between the predicted and experimental compressive strengths was 0.9486, which shows the higher degree of accuracy of the network pattern. Furthermore, the predicted compressive strength was found very close to the experimental compressive strength during the testing process of the ANN model. The absolute and percentage relative errors in the testing process were significantly low with a mean value of 1.74 MPa and 3.13%, respectively, which indicated that the compressive strength of SCHSC including POFA can be efficiently predicted by the ANN.

Mechanical behavior of glass and Blackglas{reg_sign} ceramic matrix composite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stawovy, R.H.; Kampe, S.L.; Curtin, W.A.

Room temperature tensile tests are reported on two low-cost ceramic matrix composite materials, comprised of matrices of Blackglas{reg_sign} and a proprietary glass composition each reinforced with Nicalon{reg_sign} SiC-based fibers. The measured mechanical behaviors, supplemented by post-fracture analysis of fiber pullout and fiber fracture mirrors, are compared in detail to the performance predicted theoretically. This allows for an assessment of the roles of the matrix, fiber strength, residual stresses, fiber geometry, and the fiber/matrix interfacial properties in determining mechanical response. The Blackglas{reg_sign} matrix cracks extensively during processing, and so the mechanical response is controlled by the deformation and fracture of themore » fiber bundle. The interfacial sliding resistance, {tau}, is determined to be {approx} 17 MPa and the in-situ (post-processed) fiber characteristic strength, {sigma}{sub c} is found to be {approx} 2.0 GPa, both similar to values reported in the literature for Nicalon{reg_sign}/CAS-glass systems. For the glass matrix, the unidirectional and cross-ply materials show marked differences in mechanical behavior. In the cross-ply composites, {tau} {approx} 14 MPa and {sigma}{sub c} {approx} 2.9 GPa; in the unidirectional variants, these values were 1.7 MPa and 1.6 GPa, respectively. With these data and other derived micromechanical parameters, the stress-strain and failure point of these materials was predicted using existing models, and excellent agreement with the experiments was obtained. These materials thus perform as expected given the in-situ fiber and interface properties. Notably, the cross-ply glass matrix composites exhibit high fiber strength retention and hence show tensile strengths that are better than other Nicalon{reg_sign}-based materials tested to date.« less

Mechanical torque measurement predicts load to implant cut-out: a biomechanical study investigating DHS anchorage in femoral heads.

PubMed

Suhm, Norbert; Hengg, Clemens; Schwyn, Ronald; Windolf, Markus; Quarz, Volker; Hänni, Markus

2007-08-01

Bone strength plays an important role in implant anchorage. Bone mineral density (BMD) is used as surrogate parameter to quantify bone strength and to predict implant anchorage. BMD can be measured by means of quantitative computer tomography (QCT) or dual energy X-ray absorptiometry (DXA). These noninvasive methods for BMD measurement are not available pre- or intra-operatively. Instead, the surgeon could determine bone strength by direct mechanical measurement. We have evaluated mechanical torque measurement for (A) its capability to quantify local bone strength and (B) its predictive value towards load at implant cut-out. Our experimental study was performed using sixteen paired human cadaver proximal femurs. BMD was determined for all specimens by QCT. The torque to breakaway of the cancellous bone structure (peak torque) was measured by means of a mechanical probe at the exact position of subsequent DHS placement. The fixation strength of the DHS achieved was assessed by cyclic loading in a stepwise protocol beginning with 1,500 N increasing 500 N every 5,000 cycles until 4,000 N. A highly significant correlation of peak torque with BMD (QCT) was found (r = 0.902, r (2) = 0.814, P < 0.001). Peak torque correlated highly significant with the load at implant cut-out (r = 0.795, P < 0.001). All specimens with a measured peak torque below 6.79 Nm failed at the first load level of 1,500 N. The specimens with a peak torque above 8.63 Nm survived until the last load level of 4,000 N. Mechanical peak torque measurement is able to quantify bone strength. In an experimental setup, peak torque identifies those specimens that are likely to fail at low load. In clinical routine, implant migration and cut-out depend on several parameters, which are difficult to control, such as fracture type, fracture reduction achieved, and implant position. The predictive value of peak torque towards cut-out in a clinical set-up therefore has to be carefully validated.

Mechanical Behavior of Brittle Rock-Like Specimens with Pre-existing Fissures Under Uniaxial Loading: Experimental Studies and Particle Mechanics Approach

NASA Astrophysics Data System (ADS)

Cao, Ri-hong; Cao, Ping; Lin, Hang; Pu, Cheng-zhi; Ou, Ke

2016-03-01

Joints and fissures with similar orientation or characteristics are common in natural rocks; the inclination and density of the fissures affect the mechanical properties and failure mechanism of the rock mass. However, the strength, crack coalescence pattern, and failure mode of rock specimens containing multi-fissures have not been studied comprehensively. In this paper, combining similar material testing and discrete element numerical method (PFC2D), the peak strength and failure characteristics of rock-like materials with multi-fissures are explored. Rock-like specimens were made of cement and sand and pre-existing fissures created by inserting steel shims into cement mortar paste and removing them during curing. The peak strength of multi-fissure specimens depends on the fissure angle α (which is measured counterclockwise from horizontal) and fissure number ( N f). Under uniaxial compressional loading, the peak strength increased with increasing α. The material strength was lowest for α = 25°, and highest for α = 90°. The influence of N f on the peak strength depended on α. For α = 25° and 45°, N f had a strong effect on the peak strength, while for higher α values, especially for the 90° sample, there were no obvious changes in peak strength with different N f. Under uniaxial compression, the coalescence modes between the fissures can be classified into three categories: S-mode, T-mode, and M-mode. Moreover, the failure mode can be classified into four categories: mixed failure, shear failure, stepped path failure, and intact failure. The failure mode of the specimen depends on α and N f. The peak strength and failure modes in the numerically simulated and experimental results are in good agreement.

Transcriptional response according to strength of calorie restriction in Saccharomyces cerevisiae.

PubMed

Lee, Yae-Lim; Lee, Cheol-Koo

2008-09-30

To characterize gene expression that is dependent on the strength of calorie restriction (CR), we obtained transcriptome at different levels of glucose, which is a major energy and carbon source for budding yeast. To faithfully mimic mammalian CR in yeast culture, we reconstituted and grew seeding yeast cells in fresh 2% YPD media before inoculating into 2%, 1%, 0.5% and 0.25% YPD media to reflect different CR strengths. We collected and characterized 160 genes that responded to CR strength based on the rigorous statistical analyses of multiple test corrected ANOVA (adjusted p0.7). Based on the individual gene studies and the GO Term Finder analysis of 160 genes, we found that CR dose-dependently and gradually increased mitochondrial function at the transcriptional level. Therefore, we suggest these 160 genes are markers that respond to CR strength and that might be useful in elucidating CR mechanisms, especially how stronger CR extends life span more.

Methods for the practical determination of the mechanical strength of tablets--from empiricism to science.

PubMed

Podczeck, Fridrun

2012-10-15

This review aims to awake an interest in the determination of the tensile strength of tablets of various shapes using a variety of direct and indirect test methods. The United States Pharmacopoeia monograph 1217 (USP35/NF30, 2011) has provided a very good approach to the experimental determination of and standards for the mechanical strength of tablets. Building on this monograph, it is hoped that the detailed account of the various methods provided in this review will encourage industrial and academic scientists involved in the development and manufacture of tablet formulations to take a step forward and determine the tensile strength of tablets, even if these are not simply flat disc-shaped or rectangular. To date there are a considerable number of valid test configurations and stress equations available, catering for many of the various shapes of tablets on the market. The determination of the tensile strength of tablets should hence replace the sole determination of a breaking force, because tensile strength values are more comparable and suggestions for minimum and/or maximum values are available. The review also identifies the gaps that require urgent filling. There is also a need for further analysis using, for example, Finite Element Method, to provide correct stress solutions for tablets of differing shapes, but this also requires practical experiments to find the best loading conditions, and theoretical stress solutions should be verified with practical experiments. Copyright © 2012 Elsevier B.V. All rights reserved.

(Finite) statistical size effects on compressive strength.

PubMed

Weiss, Jérôme; Girard, Lucas; Gimbert, Florent; Amitrano, David; Vandembroucq, Damien

2014-04-29

The larger structures are, the lower their mechanical strength. Already discussed by Leonardo da Vinci and Edmé Mariotte several centuries ago, size effects on strength remain of crucial importance in modern engineering for the elaboration of safety regulations in structural design or the extrapolation of laboratory results to geophysical field scales. Under tensile loading, statistical size effects are traditionally modeled with a weakest-link approach. One of its prominent results is a prediction of vanishing strength at large scales that can be quantified in the framework of extreme value statistics. Despite a frequent use outside its range of validity, this approach remains the dominant tool in the field of statistical size effects. Here we focus on compressive failure, which concerns a wide range of geophysical and geotechnical situations. We show on historical and recent experimental data that weakest-link predictions are not obeyed. In particular, the mechanical strength saturates at a nonzero value toward large scales. Accounting explicitly for the elastic interactions between defects during the damage process, we build a formal analogy of compressive failure with the depinning transition of an elastic manifold. This critical transition interpretation naturally entails finite-size scaling laws for the mean strength and its associated variability. Theoretical predictions are in remarkable agreement with measurements reported for various materials such as rocks, ice, coal, or concrete. This formalism, which can also be extended to the flowing instability of granular media under multiaxial compression, has important practical consequences for future design rules.

High Density Polyethylene Composites Reinforced with Hybrid Inorganic Fillers: Morphology, Mechanical and Thermal Expansion Performance

PubMed Central

Huang, Runzhou; Xu, Xinwu; Lee, Sunyoung; Zhang, Yang; Kim, Birm-June; Wu, Qinglin

2013-01-01

The effect of individual and combined talc and glass fibers (GFs) on mechanical and thermal expansion performance of the filled high density polyethylene (HDPE) composites was studied. Several published models were adapted to fit the measured tensile modulus and strength of various composite systems. It was shown that the use of silane-modified GFs had a much larger effect in improving mechanical properties and in reducing linear coefficient of thermal expansion (LCTE) values of filled composites, compared with the use of un-modified talc particles due to enhanced bonding to the matrix, larger aspect ratio, and fiber alignment for GFs. Mechanical properties and LCTE values of composites with combined talc and GF fillers varied with talc and GF ratio at a given total filler loading level. The use of a larger portion of GFs in the mix can lead to better composite performance, while the use of talc can help lower the composite costs and increase its recyclability. The use of 30 wt % combined filler seems necessary to control LCTE values of filled HDPE in the data value range generally reported for commercial wood plastic composites. Tensile modulus for talc-filled composite can be predicted with rule of mixture, while a PPA-based model can be used to predict the modulus and strength of GF-filled composites. PMID:28788322

Effects of cationic xylan from annual plants on the mechanical properties of paper.

PubMed

Deutschle, Alexander L; Römhild, Katrin; Meister, Frank; Janzon, Ron; Riegert, Christiane; Saake, Bodo

2014-02-15

Xylan from oat spelt and wheat was used as an additive to enhance the dry strength of paper. The absorption of xylan by the cellulose fibers was increased by cationization to different degrees of substitution. Paper hand sheets with different doses of xylan and industrial cationic starch were produced, and the mechanical properties were determined. Absorption measurements of cationic oat spelt xylan on pulp fibers explained the differing influences of low and high cationized xylan addition on paper strength. The addition of cationic oat spelt xylan with a degree of substitution of 0.1 at a 4% dose provided the largest improvement in the tensile-index (67%), burst-index (105%) and tear-index (77%). Compared to cationic starch, cationic oat spelt xylan additives led to similar paper strength values, excepting the tear strength. The structural differences and protein impurities made the wheat xylan unsuitable as a strength additive for paper pulp. Copyright © 2013 Elsevier Ltd. All rights reserved.

Effect of ball milling on structures and properties of dispersed-type dental amalgam.

PubMed

Chern Lin, Jiin-Huey; Chen, Fred Ying-Yi; Chiang, Hui-Ju; Ju, Chien-Ping

2011-04-01

The purpose of the present study was to investigate the effect of ball milling on the initial mercury vapor release rate and mechanical properties such as compressive strength, diametral tensile strength and creep value, of the dispersed-type dental amalgam, and comparison was made with respect to two commercial amalgam alloys. Ball milling was employed to modify the configuration of the originally spherical-shaped Ag-Cu-Pd dispersant alloy particles. Improvement in mechanical properties while maintaining a low early-stage mercury vapor release rate of the amalgam is attempted. The experimental results show that the amalgam (AmB10) which was made from Ag-Cu-Pd dispersant alloy particles that were ball-milled for 10 min and heat-treated at 300 °C for 2 days exhibited a low initial mercury vapor release rate of 69 pg/mm(2)/s, which was comparable with that of commercial amalgam alloy Tytin (68 pg/mm(2)/s), and was lower than that of Dispersalloy (73 pg/mm(2)/s). As for mechanical properties, amalgam AmB10 exhibited the highest 1h compressive strength (228 MPa), which was higher than that of commercial amalgam alloy Dispersalloy by 72%; while its 24h diametral tensile strength was also the highest (177 MPa), and was higher than that of Dispersalloy by 55%. Furthermore, the creep value of the amalgams made from Ag-Cu-Pd alloy particles with 10 min ball-milling and heat treatment at 300 °C for 2 days was measured to be 0.12%, which was about 20% that of Dispersalloy. It is found that ball milling of the dispersant Ag-Cu-Pd alloy particles for 10 min was able to modify the configuration of the alloy particles into irregular-shapes. Subsequently, heat treatment at 300 °C significantly lowered the initial mercury vapor release rate, increased its 1h compressive strength and 1h diametral tensile strength, and lowered its creep value. Copyright © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Interlaboratory study for nickel alloy 625 made by laser powder bed fusion to quantify mechanical property variability.

PubMed

Brown, Christopher U; Jacob, Gregor; Stoudt, Mark; Moylan, Shawn; Slotwinski, John; Donmez, Alkan

2016-08-01

Six different organizations participated in this interlaboratory study to quantify the variability in the tensile properties of Inconel 625 specimens manufactured using laser-powder-bed-fusion additive manufacturing machines. The tensile specimens were heat treated and tensile tests conducted until failure. The properties measured were yield strength, ultimate tensile strength, elastic modulus, and elongation. Statistical analysis revealed that between-participant variability for yield strength, ultimate tensile strength, and elastic modulus values were significantly higher (up to 4 times) than typical within-participant variations. Only between-participant and within-participant variability were both similar for elongation. A scanning electron microscope was used to examine one tensile specimen for fractography. The fracture surface does not have many secondary cracks or other features that would reduce the mechanical properties. In fact, the features largely consist of microvoid coalescence and are entirely consistent with ductile failure.

Interlaboratory study for nickel alloy 625 made by laser powder bed fusion to quantify mechanical property variability

PubMed Central

Brown, Christopher U.; Jacob, Gregor; Stoudt, Mark; Moylan, Shawn; Slotwinski, John; Donmez, Alkan

2017-01-01

Six different organizations participated in this interlaboratory study to quantify the variability in the tensile properties of Inconel 625 specimens manufactured using laser-powder-bed-fusion additive manufacturing machines. The tensile specimens were heat treated and tensile tests conducted until failure. The properties measured were yield strength, ultimate tensile strength, elastic modulus, and elongation. Statistical analysis revealed that between-participant variability for yield strength, ultimate tensile strength, and elastic modulus values were significantly higher (up to 4 times) than typical within-participant variations. Only between-participant and within-participant variability were both similar for elongation. A scanning electron microscope was used to examine one tensile specimen for fractography. The fracture surface does not have many secondary cracks or other features that would reduce the mechanical properties. In fact, the features largely consist of microvoid coalescence and are entirely consistent with ductile failure. PMID:28243032

Tailored Welding Technique for High Strength Al-Cu Alloy for Higher Mechanical Properties

NASA Astrophysics Data System (ADS)

Biradar, N. S.; Raman, R.

AA2014 aluminum alloy, with 4.5% Cu as major alloying element, offers highest strength and hardness values in T6 temper and finds extensive use in aircraft primary structures. However, this alloy is difficult to weld by fusion welding because the dendritic structure formed can affect weld properties seriously. Among the welding processes, AC-TIG technique is largely used for welding. As welded yield strength was in the range of 190-195 MPa, using conventional TIG technique. Welding metallurgy of AA2014 was critically reviewed and factors responsible for lower properties were identified. Square-wave AC TIG with Transverse mechanical arc oscillation (TMAO) was postulated to improve the weld strength. A systematic experimentation using 4 mm thick plates produced YS in the range of 230-240 MPa, has been achieved. Through characterization including optical and SEM/EDX was conducted to validate the metallurgical phenomena attributable to improvement in weld properties.

Interlaboratory Study for Nickel Alloy 625 Made by Laser Powder Bed Fusion to Quantify Mechanical Property Variability

NASA Astrophysics Data System (ADS)

Brown, Christopher U.; Jacob, Gregor; Stoudt, Mark; Moylan, Shawn; Slotwinski, John; Donmez, Alkan

2016-08-01

Six different organizations participated in this interlaboratory study to quantify the variability in the tensile properties of Inconel 625 specimens manufactured using laser powder bed fusion-additive manufacturing machines. The tensile specimens were heat treated and tensile tests were conducted until failure. The properties measured were yield strength, ultimate tensile strength, elastic modulus, and elongation. Statistical analysis revealed that between-participant variability for yield strength, ultimate tensile strength, and elastic modulus values were significantly higher (up to four times) than typical within-participant variations. Only between-participant and within-participant variability were both similar for elongation. A scanning electron microscope was used to examine one tensile specimen for fractography. The fracture surface does not have many secondary cracks or other features that would reduce the mechanical properties. In fact, the features largely consist of microvoid coalescence and are entirely consistent with ductile failure.

The development of fluorides for high power laser optics

NASA Astrophysics Data System (ADS)

Ready, J. F.; Vora, H.

1980-07-01

The laser assisted thermonuclear fusion program has need for improved optical materials with high transmission in the ultraviolet, and with low values of nonlinear index of refraction. Lithium fluoride possesses a combination of optical properties which are of use. Single crystalline LiF is limited by low mechanical strength. The technique of press forging to increase the mechanical strength is investigated. LiF single crystals were press forged over the temperature range 300 - 600 deg C to produce fine grained polycrystalline material. Optical homogenity at 633, stress birefringence, scattering at 633, residual absorption over the spectral range 339 - 3800 nm, and laser damage thresholds for 1 ns, 1064 nm and 700 ps, 266 nm laser pulses are evaluated. Single crystals can be press forged without seriously degrading their optical properties. Yield strength in compression, proportional limit and fracture strength in 3 and 4 point bending, fracture energy, and threshold for microyield are discussed.

Three-dimensional high-entropy alloy-polymer composite nanolattices that overcome the strength-recoverability trade-off.

PubMed

Zhang, Xuan; Yao, Jiahao; Liu, Bin; Yan, Jun; Lu, Lei; Li, Yi; Gao, Huajian; Li, Xiaoyan

2018-06-14

Mechanical metamaterials with three-dimensional micro- and nano-architectures exhibit unique mechanical properties, such as high specific modulus, specific strength and energy absorption. However, a conflict exists between strength and recoverability in nearly all the mechanical metamaterials reported recently, in particular the architected micro-/nanolattices, which restricts the applications of these materials in energy storage/absorption and mechanical actuation. Here, we demonstrated the fabrication of three-dimensional architected composite nanolattices that overcome the strength-recoverability trade-off. The nanolattices under study are made up of a high entropy alloy coated (14.2-126.1 nm in thickness) polymer strut (approximately 260 nm in the characteristic size) fabricated via two-photon lithography and magnetron sputtering deposition. In situ uniaxial compression inside a scanning electron microscope showed that these composite nanolattices exhibit a high specific strength of 0.027 MPa/kg m3, an ultra-high energy absorption per unit volume of 4.0 MJ/m3, and nearly complete recovery after compression under strains exceeding 50%, thus overcoming the traditional strength-recoverability trade-off. During multiple compression cycles, the composite nanolattices exhibit a high energy loss coefficient (converged value after multiple cycles) of 0.5-0.6 at a compressive strain beyond 50%, surpassing the coefficients of all the micro-/nanolattices fabricated recently. Our experiments also revealed that for a given unit cell size, the composite nanolattices coated with a high entropy alloy with thickness in the range of 14-50 nm have the optimal specific modulus, specific strength and energy absorption per unit volume, which is related to a transition of the dominant deformation mechanism from local buckling to brittle fracture of the struts.

Size effects on elasticity, yielding, and fracture of silver nanowires: In situ experiments

NASA Astrophysics Data System (ADS)

Zhu, Yong; Qin, Qingquan; Xu, Feng; Fan, Fengru; Ding, Yong; Zhang, Tim; Wiley, Benjamin J.; Wang, Zhong Lin

2012-01-01

This paper reports the quantitative measurement of a full spectrum of mechanical properties of fivefold twinned silver (Ag) nanowires (NWs), including Young's modulus, yield strength, and ultimate tensile strength. In-situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a scanning electron microscope (SEM). Young's modulus, yield strength, and ultimate tensile strength all increased as the NW diameter decreased. The maximum yield strength in our tests was found to be 2.64 GPa, which is about 50 times the bulk value and close to the theoretical value of Ag in the 110 orientation. The size effect in the yield strength is mainly due to the stiffening size effect in the Young's modulus. Yield strain scales reasonably well with the NW surface area, which reveals that yielding of Ag NWs is due to dislocation nucleation from surface sources. Pronounced strain hardening was observed for most NWs in our study. The strain hardening, which has not previously been reported for NWs, is mainly attributed to the presence of internal twin boundaries.

Reinforcement of SBR/waste rubber powder vulcanizate with in situ generated zinc dimethacrylate

NASA Astrophysics Data System (ADS)

Wang, X. P.; Cheng, B. K.; Zhang, X.; Jia, D. M.

2016-07-01

Methyl acrylic acid/zinc oxide (MAA/ZnO) was introduced to modify styrene- butadiene rubber/waste rubber powder (SBR/WRP) composites by blending. The enhanced mechanical properties and processing ability were presumably originated from improved compatibility and interfacial interaction between WRP and the SBR matrix by the in situ polymerization of zinc dimethacrylate (ZDMA). A refined interface of the modified SBR/WRP composite was observed by scanning electron microscopy. The formation of ZDMA significantly increased the ionic bond content in the vulcanizate, resulting in exceptional mechanical performance. The comprehensive mechanical properties including tensile strength, tear strength and dynamic heat-building performance reached optimum values with 16 phr MAA.

Effects of sandblasting and silica coating on the bond strength of rebonded mechanically retentive ceramic brackets.

PubMed

Toroglu, M Serdar; Yaylali, Sirin

2008-08-01

The aim of this study was to determine the bond strength of rebonded mechanically retentive ceramic brackets after treatment with 2 abrasive techniques. In addition to a group of new brackets, 3 groups were treated according to the following conditions of debonded ceramic bracket bases: sandblasting, sandblasting + silane, and silica coating + silane (15 in each group). Treated ceramic brackets were rebonded on premolars. The samples were stored in distilled deionized water for 24 hours at 37 degrees C in an incubator and then thermocycled for 1000 times between 5 degrees C and 55 degrees C. Shear force was applied to the enamel-adhesive interface until debonding. The highest bond strength values were in the silica coating + silane and the new bracket groups (12.7 and 12.0 MPa, respectively), followed by the sandblasting + silane group (10.5 MPa). The sandblasting group had a significantly lower bond strength value (4.5 MPa). No enamel fracture was noted in any sample tested. In the new bracket and the sandblasting + silane groups, 20% of the samples had adhesive remnant index scores of 2, and 80% had scores of 3. In the sandblasting group, all specimens debonded at the bracket-adhesive interface. The silica coating + silane group showed mixed failures. Sandblasting + silane and silica coating + silane applications on debonded ceramic bracket base can produce bond strengths comparable with new brackets.

Stress and strain analysis from dynamic loads of mechanical hand using finite element method

NASA Astrophysics Data System (ADS)

Hasanuddin, Iskandar; Husaini; Syahril Anwar, M.; Yudha, B. Z. Sandy; Akhyar, Hasan

2018-05-01

This research discusses the distribution of stress and strain due to the dynamic loads of mechanical hand. The stress and strain that occur on mechanical hand are the main concern for comparing the value of finite element analysis (FEA) and calculating for its material properties. The stress and strain analysis are done with a loading condition. The given loading condition is dynamic. The loading input condition in the simulation of using hydraulic hand dynamometer is from the grip strength measurement of ten samples. The form of the given loading to the mechanical hand is the increment value with a maximum of 708 N/m2 within 1 minute. The amount of maximum stress (von Mises) simulation is 1.731 x 105 Pa, and the amount of maximum strain is 7.441 x 10-7. The amount of maximum reaction force is 5.864 x 10-2 N, while the amount of maximum displacement that occurs on the distal part is 1.223 x 10 m. Based on the analysis, the maximum stress and strain were found both to occur at the extension part. The result of this study has shown that the stress and strain still occur far below from the yield strength and the shear strength from the material AISI 1010. It can be concluded that the mechanical hand is durable for the given loading and can hold an object with a minimum diameter of 45 mm.

Probabilistic Material Strength Degradation Model for Inconel 718 Components Subjected to High Temperature, Mechanical Fatigue, Creep and Thermal Fatigue Effects

NASA Technical Reports Server (NTRS)

Bast, Callie Corinne Scheidt

1994-01-01

This thesis presents the on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes four effects that typically reduce lifetime strength: high temperature, mechanical fatigue, creep, and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for four variables, namely, high temperature, mechanical fatigue, creep, and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using the current version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of mechanical fatigue, creep, and thermal fatigue was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

Effect of Carbon on Microstructure and Mechanical Properties of Low C-1.6 pct Mn-0.1 pct Cr-0.3 pct Mo-0.0005 pct B Dual-Phase Steels

NASA Astrophysics Data System (ADS)

Jeong, W. C.

2014-11-01

Effect of carbon on the microstructure and mechanical properties of 0.011 and 0.032 pct carbon dual-phase steels was investigated. r m value was increased to 1.52 at around 400 MPa tensile strength level through the optimal design in the steel chemistry and proper control of phase transformation during continuous galvanizing cycle. The isolated martensite particles are expected to increase the strength but are expected not to be desirable for the deep drawability.

A tale of two mechanisms. Strain-softening versus strain-hardening in single crystals under small stressed volumes

DOE PAGES

Bei, Hongbin; Xia, Yuzhi; Barabash, Rozaliya; ...

2015-08-10

Pre-straining defect-free single crystals will introduce heterogeneous dislocation nucleation sources that reduce the measured strength from the theoretical value, while pre-straining bulk samples will lead to strain hardening. Their competition is investigated by nanoindentation pop-in tests on variously pre-strained Mo single crystals with several indenter radii (~micrometer). Pre-straining primarily shifts deformation mechanism from homogeneous dislocation nucleation to a stochastic behavior, while strain hardening plays a secondary role, as summarized in a master plot of pop-in strength versus normalized indenter radius.

Value-added mechanical pulps for light weight, high opacity paper

Treesearch

Marguerite Sykes; John Klungness; Freya Tan; Said M. Abubakr

1998-01-01

Brightness, strength, economy, and paper machine runnability are common concerns of pacemakers who use virgin or recycled fiber furnishes. Fiber loadining, a process that precipitates calcium carbonate partially inside the fiber lumen, is a cost-effective technology that could substantially upgrade mechanical pulp furnishes. This study demonstrates the optical and...

Influence of Tension-Compression Asymmetry on the Mechanical Behavior of AZ31B Magnesium Alloy Sheets in Bending

NASA Astrophysics Data System (ADS)

Zhou, Ping; Beeh, Elmar; Friedrich, Horst E.

2016-03-01

Magnesium alloys are promising materials for lightweight design in the automotive industry due to their high strength-to-mass ratio. This study aims to study the influence of tension-compression asymmetry on the radius of curvature and energy absorption capacity of AZ31B-O magnesium alloy sheets in bending. The mechanical properties were characterized using tension, compression, and three-point bending tests. The material exhibits significant tension-compression asymmetry in terms of strength and strain hardening rate due to extension twinning in compression. The compressive yield strength is much lower than the tensile yield strength, while the strain hardening rate is much higher in compression. Furthermore, the tension-compression asymmetry in terms of r value (Lankford value) was also observed. The r value in tension is much higher than that in compression. The bending results indicate that the AZ31B-O sheet can outperform steel and aluminum sheets in terms of specific energy absorption in bending mainly due to its low density. In addition, the AZ31B-O sheet was deformed with a larger radius of curvature than the steel and aluminum sheets, which brings a benefit to energy absorption capacity. Finally, finite element simulation for three-point bending was performed using LS-DYNA and the results confirmed that the larger radius of curvature of a magnesium specimen is mainly attributed to the high strain hardening rate in compression.

Direct ink writing of highly porous and strong glass scaffolds for load-bearing bone defects repair and regeneration.

PubMed

Fu, Qiang; Saiz, Eduardo; Tomsia, Antoni P

2011-10-01

The quest for synthetic materials to repair load-bearing bone lost because of trauma, cancer, or congenital bone defects requires the development of porous, high-performance scaffolds with exceptional mechanical strength. However, the low mechanical strength of porous bioactive ceramic and glass scaffolds, compared with that of human cortical bone, has limited their use for these applications. In the present work bioactive 6P53B glass scaffolds with superior mechanical strength were fabricated using a direct ink writing technique. The rheological properties of Pluronic® F-127 (referred to hereafter simply as F-127) hydrogel-based inks were optimized for the printing of features as fine as 30 μm and of three-dimensional scaffolds. The mechanical strength and in vitro degradation of the scaffolds were assessed in a simulated body fluid (SBF). The sintered glass scaffolds showed a compressive strength (136 ± 22 MPa) comparable with that of human cortical bone (100-150 MPa), while the porosity (60%) was in the range of that of trabecular bone (50-90%). The strength is ~100-times that of polymer scaffolds and 4-5-times that of ceramic and glass scaffolds with comparable porosities. Despite the strength decrease resulting from weight loss during immersion in SBF, the value (77 MPa) is still far above that of trabecular bone after 3 weeks. The ability to create both porous and strong structures opens a new avenue for fabricating scaffolds for load-bearing bone defect repair and regeneration. Published by Elsevier Ltd.

Direct Ink Writing of Highly Porous and Strong Glass Scaffolds for Load-bearing Bone Defects Repair and Regeneration

PubMed Central

Fu, Qiang; Saiz, Eduardo; Tomsia, Antoni P.

2011-01-01

The quest for synthetic materials to repair load-bearing bone lost because of trauma, cancer, or congenital bone defects requires development of porous and high-performance scaffolds with exceptional mechanical strength. However, the low mechanical strength of porous bioactive ceramic and glass scaffolds, compared with that of human cortical bone, has limited their use for these applications. In the present work, bioactive 6P53B glass scaffolds with superior mechanical strength were fabricated using a direct ink writing technique. The rheological properties of Pluronic® F-127 (referred to hereafter simply as F-127) hydrogel-based inkswere optimized for the printing of features as fine as 30 μm and of the three-dimensional scaffolds. The mechanical strength and in vitro degradation of the scaffolds were assessed in a simulated body fluid (SBF). The sintered glass scaffolds show a compressive strength (136 ± 22 MPa) comparable to that of human cortical bone (100-150 MPa), while the porosity (60%) is in the range of that of trabecular bone (50-90%).The strength is ~100 times that of polymer scaffolds and 4–5 times that of ceramic and glass scaffolds with comparable porosities. Despite the strength decrease resulting from weight loss during immersion in an SBF, the value (77 MPa) is still far above that of trabecular bone after three weeks. The ability to create both porous and strong structures opens a new avenue for fabricating scaffolds for load-bearing bone defect repair and regeneration. PMID:21745606

Effect of ZnO nanoparticles to mechanical properties of thixoformed Mg-Al-Zn alloy

NASA Astrophysics Data System (ADS)

Kusharjanto; Soepriyanto, Syoni; Ardian Korda, Akhmad; Adi Dwiwanto, Supono

2018-03-01

Magnesium alloys are lightweight metallic materials with low mechanical properties. Therefore, in order to meet the requirements in various industrial sector applications such as automotive, aerospace and electronic frame, improvement strength and ductility is required. The purpose of this research is to investigate the effect of adding ZnO nanoparticles to changes in microstructure, hardness, mechanical properties regarding with yield and ultimate strength. In this research, the molten Mg-Al-Zn alloy is added ZnO nanoparticles with a various range of 0, 1; 3 and 5 wt% and then cooling in the room temperature. Futhermore, Mg-Al-Zn-ZnO is heated at a temperature of 530 °C (in the semi-solid temperature range 470 °C–595 °C or 53% solid fraction) and then thixoforming process is performed. The characterization results of the thixoforming product show that, the microstructure is globular in shape with maximum hardness value of 107.14 VHN, the yield strength of 214.87 MPa, and the ultimate tensile strength of 311.25 MPa in 5 wt% ZnO nanoparticles.

Novel high-strength biocomposites based on microfibrillated cellulose having nano-order-unit web-like network structure

NASA Astrophysics Data System (ADS)

Nakagaito, A. N.; Yano, H.

2005-01-01

A completely new kind of high-strength composite was manufactured using microfibrillated cellulose (MFC) derived from kraft pulp. Because of the unique structure of nano-order-scale interconnected fibrils and microfibrils greatly expanded in the surface area that characterizes MFC, it was possible to produce composites that exploit the extremely high strength of microfibrils. The Young’s modulus (E) and bending strength (σb) of composites using phenolic resin as binder achieved values up to 19 GPa and 370 MPa, respectively, with a density of 1.45 g/cm2, exhibiting outstanding mechanical properties for a plant-fiber-based composite.

Stress corrosion cracking susceptibility of 18 Ni maraging steel

NASA Technical Reports Server (NTRS)

Humphries, T. S.; Nelson, E. E.

1974-01-01

The stress corrosion cracking (SCC) resistance of 18Ni maraging steel (grades 200, 250, 300, and 350) was determined in 3.5 percent salt (NaCl) solution, synthetic sea water, high humidity, and outside MSFC atmosphere. All grades of the maraging steel were found to be susceptible to SCC in varying degrees according to their strengths, with the lowest strength steel (grade 200) being the least susceptible and the highest strength steel (grade 350), the most susceptible to SCC. The SCC resistance of 250 grade maraging steel was also evaluated in salt and salt-chromate solutions using fracture mechanics techniques. The threshold value, K sub SCC, was found to be approximately 44 MN/sq m square root m, (40 ksi square root in.) or 40 percent of the K sub Q value.

ZERODUR: deterministic approach for strength design

NASA Astrophysics Data System (ADS)

Hartmann, Peter

2012-12-01

There is an increasing request for zero expansion glass ceramic ZERODUR substrates being capable of enduring higher operational static loads or accelerations. The integrity of structures such as optical or mechanical elements for satellites surviving rocket launches, filigree lightweight mirrors, wobbling mirrors, and reticle and wafer stages in microlithography must be guaranteed with low failure probability. Their design requires statistically relevant strength data. The traditional approach using the statistical two-parameter Weibull distribution suffered from two problems. The data sets were too small to obtain distribution parameters with sufficient accuracy and also too small to decide on the validity of the model. This holds especially for the low failure probability levels that are required for reliable applications. Extrapolation to 0.1% failure probability and below led to design strengths so low that higher load applications seemed to be not feasible. New data have been collected with numbers per set large enough to enable tests on the applicability of the three-parameter Weibull distribution. This distribution revealed to provide much better fitting of the data. Moreover it delivers a lower threshold value, which means a minimum value for breakage stress, allowing of removing statistical uncertainty by introducing a deterministic method to calculate design strength. Considerations taken from the theory of fracture mechanics as have been proven to be reliable with proof test qualifications of delicate structures made from brittle materials enable including fatigue due to stress corrosion in a straight forward way. With the formulae derived, either lifetime can be calculated from given stress or allowable stress from minimum required lifetime. The data, distributions, and design strength calculations for several practically relevant surface conditions of ZERODUR are given. The values obtained are significantly higher than those resulting from the two-parameter Weibull distribution approach and no longer subject to statistical uncertainty.

A Comparison of Degradable Synthetic Polymer Fibers for Anterior Cruciate Ligament Reconstruction

PubMed Central

Tovar, Nick; Bourke, Sharon; Jaffe, Michael; Murthy, N. Sanjeeva; Kohn, Joachim; Gatt, Charles; Dunn, Michael G.

2009-01-01

We compared mechanical properties, degradation rates, and cellular compatibilities of two synthetic polymer fibers potentially useful as ACL reconstruction scaffolds: poly(desaminotyrosyl-tyrosine dodecyl dodecanedioate)(12,10), p(DTD DD) and poly(L-lactic acid), PLLA. The yield stress of ethylene oxide (ETO) sterilized wet fibers was 150 ± 22 MPa and 87 ± 12 MPa for p(DTD DD) and PLLA, respectively, with moduli of 1.7 ± 0.1 MPa and 4.4 ± 0.43 MPa. Strength and molecular weight retention were determined after incubation under physiological conditions at varying times. After 64 weeks strength decreased to 20 and 37% of the initial sterile fiber values and MW decreased to 41% and 36% of the initial values for p(DTD DD) and PLLA, respectively. ETO sterilization had no significant effect on mechanical properties. Differences in mechanical behavior may be due to the semicrystalline nature of PLLA and the small degree of crystallinity induced by mesogenic ordering in p(DTD DD) suggested by DSC analysis. Fibroblast growth was similar on 50-fiber scaffolds of both polymers through 16 days in vitro. These data suggest that p(DTD DD) fibers, with higher strength, lower stiffness, favorable degradation rate and cellular compatibility, may be a superior alternative to PLLA fibers for development of ACL reconstruction scaffolds. PMID:19623532

Comparative Analysis of the Mechanical Properties between the Fiber-Reinforced Composite and Zirconium Posts.

PubMed

Jurukovska-Shotarovska, Vesna; Kapusevska, Biljana

2015-01-01

To make a comparative analysis of the mechanical properties between FRC and zirconium posts Methods: The patients with FRC and zirconium posts were divided in two groups with three subgroups, each of them composed of 10 samples. Subgroup I with 1.2 mm; Subgroup II with 1.35 mm and Subgroup III with 1.5 mm post diameter. The fracture force, bending and tensile strength of each group were measured with Shimadzu Universal Testing Machine. The fracture force for the first group measured in the first, second and third subgroup was 34.80900N; 67.15390N; 46.53100N and for the second group, first, second and third subgroup was 34.80900N; 46.53100N; 67.15390N correspondingly. The bending strength for the first group measured in the first, second and third subgroup was 401.4420N; 444.6425N; 333.6828N and for the second group, first, second and third subgroup was 307.9352N; 289.1030N; 304.1649N correspondingly. The tensile strength for the first group measured in the first, second and third subgroup was 5.442267N; 4.350545N; 2.943465N and for the second group, first, second and third subgroup was 4.224141N; 3.751466N; 3.168756N correspondingly. The longest diameter of the posts significantly increases the resistance to fracture in relation to the two smaller diameters. The larger diameter, the higher values of the bending strength, as well as the lowest values of the tensile strength of the material contribute to improved mechanical properties of the fiber and zirconium posts.

Mechanical properties in crumple-formed paper derived materials subjected to compression.

PubMed

Hanaor, D A H; Flores Johnson, E A; Wang, S; Quach, S; Dela-Torre, K N; Gan, Y; Shen, L

2017-06-01

The crumpling of precursor materials to form dense three dimensional geometries offers an attractive route towards the utilisation of minor-value waste materials. Crumple-forming results in a mesostructured system in which mechanical properties of the material are governed by complex cross-scale deformation mechanisms. Here we investigate the physical and mechanical properties of dense compacted structures fabricated by the confined uniaxial compression of a cellulose tissue to yield crumpled mesostructuring. A total of 25 specimens of various densities were tested under compression. Crumple formed specimens exhibited densities in the range 0.8-1.3 g cm -3 , and showed high strength to weight characteristics, achieving ultimate compressive strength values of up to 200 MPa under both quasi-static and high strain rate loading conditions and deformation energy that compares well to engineering materials of similar density. The materials fabricated in this work and their mechanical attributes demonstrate the potential of crumple-forming approaches in the fabrication of novel energy-absorbing materials from low-cost precursors such as recycled paper. Stiffness and toughness of the materials exhibit density dependence suggesting this forming technique further allows controllable impact energy dissipation rates in dynamic applications.

Novel Translucent and Strong Submicron Alumina Ceramics for Dental Restorations.

PubMed

Zhao, M; Sun, Y; Zhang, J; Zhang, Y

2018-03-01

An ideal ceramic restorative material should possess excellent aesthetic and mechanical properties. We hypothesize that the high translucency and strength of polycrystalline ceramics can be achieved through microstructural tailoring. The aim of this study is to demonstrate the superior optical and mechanical properties of a new class of submicron grain-sized alumina ceramics relative to the current state-of-the-art dental ceramic materials. The translucency, the in-line transmission ( T IT ) in particular, of these submicron alumina ceramics has been examined with the Rayleigh-Gans-Debye light-scattering model. The theoretical predictions related very well with the measured T IT values. The translucency parameter ( TP) and contrast ratio ( CR) of the newly developed aluminas were measured with a reflectance spectrophotometer on a black-and-white background. For comparison, the T IT , TP, and CR values for a variety of dental ceramics, mostly measured in-house but also cited from the literature, were included. The flexural strength of the aluminas was determined with the 4-point bending test. Our findings have shown that for polycrystalline alumina ceramics, an average grain size <1 µm coupled with a porosity level <0.7% could yield translucency values ( T IT , TP, CR) similar to those of the commercial high-translucency porcelains. These values are far superior to the high-translucency lithium disilicate glass-ceramic and zirconias, including the most translucent cubic-containing zirconias. The strength of these submicron grain-sized aluminas was significantly higher than that of the cubic-containing zirconia (e.g., Zpex Smile) and lithia-based glass-ceramics (e.g., IPS e.max CAD HT). A coarse-grained alumina could also reach a translucency level comparable to that of dental porcelain. However, the relatively low strength of this material has limited its clinical indications to structurally less demanding applications, such as orthodontic brackets. With a combined high strength and translucency, the newly developed submicron grain-sized alumina may be considered a suitable material for dental restorations.

Fatigue Behavior of Crystalline-Reinforced Glass-Ceramics.

PubMed

Vicari, Carolina Barbosa; Magalhães, Bárbara de Oliveira; Griggs, Jason Alan; Borba, Márcia

2018-01-03

To evaluate the fatigue behavior of two crystalline-reinforced ceramics: leucite-reinforced (VL) and lithium disilicate-based (VD) glass-ceramics. Bar-shaped specimens (16 × 4 × 1.2 mm) were produced for each ceramic using prefabricated CAD/CAM blocks. For each group, 30 specimens were subjected to a three-point flexural strength test in a universal testing machine. For VL and VD, 36 and 41 specimens were subjected to a cyclic fatigue test, respectively. The cyclic fatigue test was performed with a pneumatic mechanical cycling machine (1 Hz; 37°C distilled water). Specimens were tested at two stress levels for each preset lifetime (10 3 and 10 4 cycles for VL; 10 4 and 10 5 cycles for VD) following the boundary technique. Fractography was performed with a scanning electron microscope. Data were analyzed with Weibull analysis. There were significant differences among groups for characteristic strength (σ 0 ) and Weibull modulus (m), as the confidence intervals did not overlap. The VD group presented the highest values of σ 0 , but the lowest Weibull modulus. Both groups showed a reduction of approximately 60% of the initial flexural strength (σ f ) after cycling for 10 4 cycles. For VD tested in fatigue, there was no degradation of σ f when the number of cycles was increased from 10 4 to 10 5 . The VL group showed an 18% decrease in σ f when the number of cycles increased from 10 3 to 10 4 . Flexural strength values estimated for a 5% probability of failure were 36 MPa for VL and 55 MPa for VD, after 10 4 cycles. Both glass-ceramics showed similar strength degradation (60%) after a lifetime of 10 4 cycles, despite their distinct mechanical properties. Mechanical cycling in humid conditions proved to be an important factor for the degradation of the mechanical properties of crystalline-reinforced glass-ceramics. © 2018 by the American College of Prosthodontists.

Importance of Tensile Strength on the Shear Behavior of Discontinuities

NASA Astrophysics Data System (ADS)

Ghazvinian, A. H.; Azinfar, M. J.; Geranmayeh Vaneghi, R.

2012-05-01

In this study, the shear behavior of discontinuities possessing two different rock wall types with distinct separate compressive strengths was investigated. The designed profiles consisted of regular artificial joints molded by five types of plaster mortars, each representing a distinct uniaxial compressive strength. The compressive strengths of plaster specimens ranged from 5.9 to 19.5 MPa. These specimens were molded considering a regular triangular asperity profile and were designed so as to achieve joint walls with different strength material combinations. The results showed that the shear behavior of discontinuities possessing different joint wall compressive strengths (DDJCS) tested under constant normal load (CNL) conditions is the same as those possessing identical joint wall strengths, but the shear strength of DDJCS is governed by minor joint wall compressive strength. In addition, it was measured that the predicted values obtained by Barton's empirical criterion are greater than the experimental results. The finding indicates that there is a correlation between the joint roughness coefficient (JRC), normal stress, and mechanical strength. It was observed that the mode of failure of asperities is either pure tensile, pure shear, or a combination of both. Therefore, Barton's strength criterion, which considers the compressive strength of joint walls, was modified by substituting the compressive strength with the tensile strength. The validity of the modified criterion was examined by the comparison of the predicted shear values with the laboratory shear test results reported by Grasselli (Ph.D. thesis n.2404, Civil Engineering Department, EPFL, Lausanne, Switzerland, 2001). These comparisons infer that the modified criterion can predict the shear strength of joints more precisely.

Coupled crystal orientation-size effects on the strength of nano crystals

PubMed Central

Yuan, Rui; Beyerlein, Irene J.; Zhou, Caizhi

2016-01-01

We study the combined effects of grain size and texture on the strength of nanocrystalline copper (Cu) and nickel (Ni) using a crystal-plasticity based mechanics model. Within the model, slip occurs in discrete slip events exclusively by individual dislocations emitted statistically from the grain boundaries. We show that a Hall-Petch relationship emerges in both initially texture and non-textured materials and our values are in agreement with experimental measurements from numerous studies. We find that the Hall-Petch slope increases with texture strength, indicating that preferred orientations intensify the enhancements in strength that accompany grain size reductions. These findings reveal that texture is too influential to be neglected when analyzing and engineering grain size effects for increasing nanomaterial strength. PMID:27185364

Multiscale mechanics of graphene oxide and graphene based composite films

NASA Astrophysics Data System (ADS)

Cao, Changhong

The mechanical behavior of graphene oxide is length scale dependent: orders of magnitude different between the bulk forms and monolayer counterparts. Understanding the underlying mechanisms plays a significant role in their versatile application. A systematic multiscale mechanical study from monolayer to multilayer, including the interactions between layers of GO, can provide fundamental support for material engineering. In this thesis, an experimental coupled with simulation approach was used to study the multiscale mechanics of graphene oxide (GO) and the methods developed for GO study are proved to be applicable also to mechanical study of graphene based composites. GO is a layered nanomaterial comprised of hierarchical units whose characteristic dimension lies between monolayer GO (0.7 nm - 1.2 nm) and bulk GO papers (≥ 1 mum). Mechanical behaviors of monolayer GO and GO nanosheets (10 nm- 100 nm) were comprehensively studied this work. Monolayer GO was measured to have an average strength of 24.7 GPa,, orders of magnitude higher than previously reported values for GO paper and approximately 50% of the 2D intrinsic strength of pristine graphene. The huge discrepancy between the strength of monolayer GO and that of bulk GO paper motivated the study of GO at the intermediate length scale (GO nanosheets). Experimental results showed that GO nanosheets possess high strength in the gigapascal range. Molecular Dynamic simulations showed that the transition in the failure behavior from interplanar fracture to intraplanar fracture was responsible for the huge strength discrepancy between nanometer scale GO and bulk GO papers. Additionally, the interfacial shear strength between GO layers was found to be a key contributing factor to the distinct mechanical behavior among hierarchical units of GO. The understanding of the multiscale mechanics of GO is transferrable in heterogeneous layered nanomaterials, such as graphene-metal oxide based anode materials in Li-ion batteries. The novel methods developed in this work to study GO multilayered structures were also applied to study the mechanics of graphene-TiO 2 composites. It was found that a critical thickness range of TiO2 deposition on graphene is required for the observed stiffness enhancement effect of graphene to influence the mechanical behavior of the composite.

Static penetration resistance of soils

NASA Technical Reports Server (NTRS)

Durgunoglu, H. T.; Mitchell, J. K.

1973-01-01

Model test results were used to define the failure mechanism associated with the static penetration resistance of cohesionless and low-cohesion soils. Knowledge of this mechanism has permitted the development of a new analytical method for calculating the ultimate penetration resistance which explicitly accounts for penetrometer base apex angle and roughness, soil friction angle, and the ratio of penetration depth to base width. Curves relating the bearing capacity factors to the soil friction angle are presented for failure in general shear. Strength parameters and penetrometer interaction properties of a fine sand were determined and used as the basis for prediction of the penetration resistance encountered by wedge, cone, and flat-ended penetrometers of different surface roughness using the proposed analytical method. Because of the close agreement between predicted values and values measured in laboratory tests, it appears possible to deduce in-situ soil strength parameters and their variation with depth from the results of static penetration tests.

Carbon fiber reinforced root canal posts. Mechanical and cytotoxic properties.

PubMed

Torbjörner, A; Karlsson, S; Syverud, M; Hensten-Pettersen, A

1996-01-01

The aim of this study was to compare the mechanical properties of a prefabricated root canal post made of carbon fiber reinforced composites (CFRC) with metal posts and to assess the cytotoxic effects elicited. Flexural modulus and ultimate flexural strength was determined by 3 point loading after CRFC posts had been stored either dry or in water. The bending test was carried out with and without preceding thermocycling of the CFRC posts. The cytotoxicity was evaluated by an agar overlay method after dry and wet storage. The values of flexural modulus and ultimate flexural strength were for dry stored CFRC post 82 +/- 6 GPa and 1154 +/- 65 MPa respectively. The flexural values decreased significantly after water storage and after thermocycling. No cytotoxic effects were observed adjacent to any CFRC post. Although fiber reinforced composites may have the potential to replace metals in many clinical situations, additional research is needed to ensure a satisfying life-span.

Synthesis and Characterization of Reactive Powder Concrete for its Application on Thermal Insulation Panels

NASA Astrophysics Data System (ADS)

Chozas, V.; Larraza, Í.; Vera-Agullo, J.; Williams-Portal, N.; Mueller, U.; Da Silva, N.; Flansbjer, M.

2015-11-01

This paper describes the synthesis and characterization of a set of textile reinforced reactive powder concrete (RPC) mixes that have been prepared in the framework of the SESBE project which aims to develop facade panels for the building envelope. In order to reduce the environmental impact, high concentration of type I and II mineral additions were added to the mixtures (up to 40% of cement replacement). The mechanical properties of the materials were analysed showing high values of compression strength thus indicating no disadvantages in the compression mechanical performance (∼140 MPa) and modulus of elasticity. In order to enable the use of these materials in building applications, textile reinforcement was introduced by incorporating layers of carbon fibre grids into the RPC matrix. The flexural performance of these samples was analysed showing high strength values and suitability for their further utilization.

Microstructural and mechanical properties on friction welding of dissimilar metals used in motor vehicles

NASA Astrophysics Data System (ADS)

Jesudoss Hynes, N. Rajesh; Shenbaga Velu, P.

2018-02-01

In the last two decades, major car manufacturing companies are exploring the possibilities of joining magnesium with aluminium, via friction welding technique for many crucial automotive applications. Our primary objective, is to carry out an experimental investigation in order to study the behaviour of dissimilar joints. The microscopic structure at the welded joint interface was analysed using an optical microscopy and scanning electron microscope. It was found that, by increasing the value of friction time, the value of the tensile strength increases and the result of tensile strength is found to be 120 MPa at a friction time of 10 s. Micro hardness was found to be higher at the interface of the weldment due to the development of a brittle intermetallic compound. Micro structural studies using SEM reveals, distinct zones such as an unaffected parent metal zone, the heat affected zone, a thermo-mechanically affected zone and a fully deformed plasticised zone.

Influence of Using Clinical Microscope as Auxiliary to Perform Mechanical Cleaning of Post Space: A Bond Strength Analysis.

PubMed

Ferreira, Ricardo; Prado, Maíra; de Jesus Soares, Adriana; Zaia, Alexandre Augusto; de Souza-Filho, Francisco José

2015-08-01

The aim of the present study was to evaluate the influence of using a clinical microscope while performing mechanical cleaning of post space walls on the bond strength of a fiberglass post to dentin. Forty-five bovine roots were used. After preparation, roots were filled using gutta-percha and Pulp Canal Sealer (SybronEndo, Orange, CA). Subsequently, for post space preparation, the roots were divided into 3 groups: control (only heat condenser + specific bur of the post system); cleaning without a microscope, mechanical cleaning (after the procedure described in the control group, round burs were used to improve cleaning); and cleaning with a microscope, mechanical cleaning performed with round burs visualized under a clinical microscope. Then, fiberglass posts were cemented. The roots were prepared and evaluated by the push-out test. Data were analyzed using Kruskal-Wallis and Student-Newman-Keuls tests (P < .05). The failure pattern was classified as follows: adhesive between the cement and dentin, adhesive dentin/cement/post, mixed cohesive within dentin, mixed cohesive post, and mixed cohesive post/dentin. The bond strength values (mean ± standard deviation) were control (cervical 1.17 ± 1.1, middle 0.40 ± 0.3, apical 0.52 ± 0.3, and total 0.95 ± 1.9), cleaning without a microscope (cervical 1.66 ± 2.3, middle 0.65 ± 1.1, apical 0.79 ± 1.2, and total1.04 ± 1.7), and cleaning with a microscope (cervical 3.26 ± 2.8, middle 1.97 ± 3.5, apical 1.85 ± 4.1, and total 2.37 ± 3.5). In the cleaning with a microscope group, the bond strength values were significantly higher than those in the other groups. In all groups, the main failure pattern was adhesive between cement and dentin. The use of a clinical microscope while performing mechanical cleaning during post space preparation improved the bond strength of a fiberglass post to dentin. Copyright © 2015 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Method, apparatus and system to compensate for drift by physically unclonable function circuitry

DOEpatents

Hamlet, Jason

2016-11-22

Techniques and mechanisms to detect and compensate for drift by a physically uncloneable function (PUF) circuit. In an embodiment, first state information is registered as reference information to be made available for subsequent evaluation of whether drift by PUF circuitry has occurred. The first state information is associated with a first error correction strength. The first state information is generated based on a first PUF value output by the PUF circuitry. In another embodiment, second state information is determined based on a second PUF value that is output by the PUF circuitry. An evaluation of whether drift has occurred is performed based on the first state information and the second state information, the evaluation including determining whether a threshold error correction strength is exceeded concurrent with a magnitude of error being less than the first error correction strength.

Integrating micro CT indices, CT imaging and computational modelling to assess the mechanical performance of fluoride treated bone.

PubMed

Sreenivasan, D; Watson, M; Callon, K; Dray, M; Das, R; Grey, A; Cornish, J; Fernandez, J

2013-12-01

In this study we evaluate the influence of low-dose fluoride treatment on 23 patient biopsies. Computational finite element (FE) models of each biopsy were subjected to a range of loads including compression, shear and torsion. The modelling framework was validated against three 3D printed models with known material properties subjected to compression till failure using an Instron machine. The primary outcomes from this study were that mechanical strength was not significantly correlated to low-dose (<10 mg/day) of fluoride levels (one-way ANOVA, P-values of 0.78, 0.69 and 0.62 for compression, shear and torsion, respectively). However, when bulk bone material properties were derived from DXA bone mineral density (BMD) from each patient's proximal femur a non-significant linear decline in mechanical strength with increase in fluoride was predicted. When the same material property was used for all bones (to evaluate bone architecture influence) then mechanical strength showed a characteristic concave upwards trend, consistent with the variation of micro CT derived percentage bone volume (BV/TV). The secondary outcomes from this study were that in compression, BV/TV was observed to be a strong surrogate measure for mechanical strength (R(2) = 0.83), while bone surface density (R(2)=0.6), trabecular thickness (R(2) = 0.5) and intersection surface (R(2) = 0.6) also explained the variation of mechanical strength well. However, trabecular separation and trabecular number were mildly correlated with mechanical strength (R(2) of 0.31 and 0.35, respectively). Compression was the loading mode most strongly correlated to micro CT indices. Material properties adapted from the proximal femur reduced the CT index correlations by up to 58% indicating that bulk density from a near proximity is a poor representation of specific localised density. Substituting the 3D micro CT indices with 2D histomorphometric data decreased correlations by at least 33% indicating that structural identification on a plane is not representative of the full 3D architecture necessary for a complete bone strength analysis. The presented computational framework may be used to assess the roles that bone architecture and loading modes play in bone quality, and which micro CT indices are good surrogate measures for mechanical strength. Copyright © 2013 IPEM. Published by Elsevier Ltd. All rights reserved.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamiya, Junichiro, E-mail: kamiya.junichiro@jaea.go.jp; Hikichi, Yusuke; Kinsho, Michikazu

For the vacuum systems of high-intensity beam accelerators, low radioactivation materials with good vacuum characteristics and high mechanical strength are required. The titanium alloy Ti-6Al-4V was investigated as a potential low activation vacuum material with high mechanical strength for the fabrication of vacuum components, particularly the flanges of beam pipes, in the J-PARC 3 GeV synchrotron. The dose rate of Ti-6Al-4V when irradiated by a 400 MeV proton was observed to decrease more rapidly than that of stainless steel. Furthermore, the generated radioactive isotopes were nuclides with relatively short half-lives. The outgassing rate per unit area of Ti-6Al-4V was approximately 10{sup −8 }Pamore » m{sup 3}/s m{sup 2} after pumping for 100 h, which is the same as the typical value for stainless steel. Additionally, the hydrogen concentration in bulk Ti-6Al-4V was reduced to approximately 1 ppm by vacuum firing at 700 °C for 9 h; the mechanical strength was not reduced by this process. These results indicate that Ti-6Al-4V is a good candidate for use as a low activation vacuum material with high mechanical strength.« less

Mechanical Properties of Calcium Fluoride-Based Composite Materials

PubMed Central

Kleczewska, Joanna; Pryliński, Mariusz; Podlewska, Magdalena; Sokołowski, Jerzy; Łapińska, Barbara

2016-01-01

Aim of the study was to evaluate mechanical properties of light-curing composite materials modified with the addition of calcium fluoride. The study used one experimental light-curing composite material (ECM) and one commercially available flowable light-curing composite material (FA) that were modified with 0.5–5.0 wt% anhydrous calcium fluoride. Morphology of the samples and uniformity of CaF2 distribution were analyzed using Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). Mechanical properties were tested after 24-hour storage of specimens in dry or wet conditions. Stored dry ECM enriched with 0.5–1.0 wt% CaF2 showed higher tensile strength values, while water storage of all modified ECM specimens decreased their tensile strength. The highest Vickers hardness tested after dry storage was observed for 2.5 wt% CaF2 content in ECM. The addition of 2.0–5.0 wt% CaF2 to FA caused significant decrease in tensile strength after dry storage and overall tensile strength decrease of modified FA specimens after water storage. The content of 2.0 wt% CaF2 in FA resulted in the highest Vickers hardness tested after wet storage. Commercially available composite material (FA), unmodified with fluoride addition, demonstrated overall significantly higher mechanical properties. PMID:28004001

Repair Bond Strength of Aged Resin Composite after Different Surface and Bonding Treatments

PubMed Central

Wendler, Michael; Belli, Renan; Panzer, Reinhard; Skibbe, Daniel; Petschelt, Anselm; Lohbauer, Ulrich

2016-01-01

The aim of this study was to compare the effect of different mechanical surface treatments and chemical bonding protocols on the tensile bond strength (TBS) of aged composite. Bar specimens were produced using a nanohybrid resin composite and aged in distilled water for 30 days. Different surface treatments (diamond bur, phosphoric acid, silane, and sandblasting with Al2O3 or CoJet Sand), as well as bonding protocols (Primer/Adhesive) were used prior to application of the repair composite. TBS of the specimens was measured and the results were analyzed using analysis of variance (ANOVA) and the Student–Newman–Keuls test (α = 0.05). Mechanically treated surfaces were characterized under SEM and by profilometry. The effect of water aging on the degree of conversion was measured by means of FTIR-ATR spectroscopy. An important increase in the degree of conversion was observed after aging. No significant differences in TBS were observed among the mechanical surface treatments, despite variations in surface roughness profiles. Phosphoric acid etching significantly improved repair bond strength values. The cohesive TBS of the material was only reached using resin bonding agents. Application of an intermediate bonding system plays a key role in achieving reliable repair bond strengths, whereas the kind of mechanical surface treatment appears to play a secondary role. PMID:28773669

Electronic properties and mechanical strength of β-phosphorene nano-ribbons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swaroop, Ram; Bhatia, Pradeep; Kumar, Ashok, E-mail: ashok@cup.ac.in

We have performed first principles calculations to find out the effect of mechanical strain on the electronic properties of zig-zag edged nano ribbons of β-phosphorene. It is found that electronic band-gap get opened-up to 2.61 eV by passivation of the edges of ribbons. Similarly, the mechanical strength is found to be increase from 1.75 GPa to 2.65 GPa on going from unpassivated nano ribbons to passivated ones along with the 2% increase in ultimate tensile strain. The band-gap value of passivated ribbon gets decreased to 0.43 eV on applying strain up to which the ribbon does not break. These tunable properties ofmore » β-phospherene with passivation with H-atom and applying mechanical strain offer its use in tunable nano electronics.« less

Chitosan fibers with improved biological and mechanical properties for tissue engineering applications.

PubMed

Albanna, Mohammad Z; Bou-Akl, Therese H; Blowytsky, Oksana; Walters, Henry L; Matthew, Howard W T

2013-04-01

The low mechanical properties of hydrogel materials such as chitosan hinder their broad utility for tissue engineering applications. Previous research efforts improved the mechanical properties of chitosan fiber through chemical and physical modifications; however, unfavorable toxicity effects on cells were reported. In this paper, we report the preparation of chitosan fibers with improved mechanical and biocompatibility properties. The structure-property relationships of extruded chitosan fibers were explored by varying acetic acid (AA) concentration, ammonia concentration, annealing temperature and degree of heparin crosslinking. Results showed that optimizing AA concentration to 2vol% improved fiber strength and stiffness by 2-fold. Extruding chitosan solution into 25wt% of ammonia solution reduced fiber diameters and improved fiber strength by 2-fold and stiffness by 3-fold, due to an increase in crystallinity as confirmed by XRD. Fiber annealing further reduced fiber diameter and improved fiber strength and stiffness as temperature increased. Chitosan fibers crosslinked with heparin had increased diameter but lower strength and stiffness properties and higher breaking strain values. When individual parameters were combined, further improvement in fiber mechanical properties was achieved. All mechanically improved fibers and heparin crosslinked fibers promoted valvular interstitial cells (VIC) attachment and growth over 10 day cultures. Our results demonstrate the ability to substantially improve the mechanical properties of chitosan fibers without adversely affecting their biological properties. The investigated treatments offer numerous advantages over previous physical/chemical modifications and thus are expected to expand the utility of chitosan fibers with tunable mechanical properties in various tissue engineering applications. Copyright © 2012 Elsevier Ltd. All rights reserved.

Surrogate Modeling of High-Fidelity Fracture Simulations for Real-Time Residual Strength Predictions

NASA Technical Reports Server (NTRS)

Spear, Ashley D.; Priest, Amanda R.; Veilleux, Michael G.; Ingraffea, Anthony R.; Hochhalter, Jacob D.

2011-01-01

A surrogate model methodology is described for predicting in real time the residual strength of flight structures with discrete-source damage. Starting with design of experiment, an artificial neural network is developed that takes as input discrete-source damage parameters and outputs a prediction of the structural residual strength. Target residual strength values used to train the artificial neural network are derived from 3D finite element-based fracture simulations. A residual strength test of a metallic, integrally-stiffened panel is simulated to show that crack growth and residual strength are determined more accurately in discrete-source damage cases by using an elastic-plastic fracture framework rather than a linear-elastic fracture mechanics-based method. Improving accuracy of the residual strength training data would, in turn, improve accuracy of the surrogate model. When combined, the surrogate model methodology and high-fidelity fracture simulation framework provide useful tools for adaptive flight technology.

The effect of thermal exposure on the mechanical properties of aluminum-graphite composites

NASA Technical Reports Server (NTRS)

Khan, I. H.

1975-01-01

The mechanical properties of aluminum-graphite composites were measured at room temperature in the as-received condition, after elevated temperature exposure and after thermal cycling. The composites were fabricated by solid-state diffusion bonding of liquid-phase Al-infiltrated Thornel 50 fibers. The results showed that the maximum longitudinal tensile strength of the as-received material was 80,000 psi, which corresponds well with the rule of mixture value. The composite strength was observed to vary widely, depending on the extent of wetting of the fibers by the aluminum. The strength of the composites in the transverse direction was generally very low, due to poor interfacial bonding. Aluminum carbide (Al4C3) formed at the surface of the fibers at temperatures greater than 500 C. Development of the carbide was shown to be diffusion-controlled and was dependent on the time and temperature used. It was shown that the tensile strength was virtually unaffected by heat-treatment up to 500 C; beyond that temperature a drastic degradation of tensile strength occurred. Thermal cycling of the composites below 500 C resulted in an observable degradation of the composite strength.

Boron nitride nanotubes enhance properties of chitosan-based scaffolds.

PubMed

Emanet, Melis; Kazanç, Emine; Çobandede, Zehra; Çulha, Mustafa

2016-10-20

With their low toxicity, high mechanical strength and chemical stability, boron nitride nanotubes (BNNTs) are good candidates to enhance the properties of polymers, composites and scaffolds. Chitosan-based scaffolds are exhaustively investigated in tissue engineering because of their biocompatibility and antimicrobial activity. However, their spontaneous degradation prevents their use in a range of tissue engineering applications. In this study, hydroxylated BNNTs (BNNT-OH) were included into a chitosan scaffold and tested for their mechanical strength, swelling behavior and biodegradability. The results show that inclusion of BNNTs-OH into the chitosan scaffold increases the mechanical strength and pore size at values optimal for high cellular proliferation and adhesion. The chitosan/BNNT-OH scaffold was also found to be non-toxic to Human Dermal Fibroblast (HDF) cells due to its slow degradation rate. HDF cell proliferation and adhesion were increased as compared to the chitosan-only scaffold as observed by scanning electron microscopy (SEM) and fluorescent microscopy images. Copyright © 2016 Elsevier Ltd. All rights reserved.

The Effects of Shielded Metal Arc Welding (Smaw) Welding On The Mechanical Characteristics With Heating Treatment inn S45c Steel

NASA Astrophysics Data System (ADS)

Munawar; Abbas, Hammada; Yusran Aminy, Ahmad

2018-02-01

Steel material has been used mainly for making tooling, automotive components, other household needs, power generators to frame buildings and bridges. This study aimed (1) to analyze the mechanical Characteristics of S45C steel with and without heating treatments, and (2) to analyze the temperature of heating treatment which could result in the maximal strength of S45C steel after the welding process. The research was conducted in the laboratory of mechanical engineering study program, Departement of mechanical Engineering, Christian university of indonesia paulus, makassar. The method used materials, instruments, and the dimensions determination of specimen based on the proposed testing standard, Next, was to determine the mechanical caracteristics of the S45C steel wich had been welded and heated.The tensile specimens, the hardness specimen, the impact specimen, and microstructures of which,each of the 3 specimens was the specimens was the specimen without treatment, the spesimen with the welding wthout heating and the specimen of 150°C, 250° C, 300° C. The research results indicated that the treatment process of 150°C, 250°C and 300°C produced the changes of mechanic charateristics with the tensile strength of 42 kgf/mm2 when the temperature had reached 300°C, but at the temperature 300°C, the its toughness would decrease to Hi = 0.836 j/m2 and its hardness would increase to 40.83 at the temperature of 300°C. The value of the maximum strengs was reached at the heating temperature of 300°C for the tensile strength and the hardness, while at the temperature of 300°C its impact value would decrease.

Calcaneal bone mineral density and mechanical strength of the metatarsals.

PubMed

Lidtke, R H; Patel, D; Muehleman, C

2000-10-01

The primary aim of this study was to determine the predictive value of the bone mineral density of the calcaneus for fracture of the metatarsals. The authors report a strong positive correlation between the bone mineral density of the calcaneus and the four-point bending strength of each of the five metatarsals (r2 = 0.76, 0.64, 0.70, 0.68, and 0.78 for metatarsals 1 through 5, respectively). In addition, the relative strengths of the metatarsals and the correlation with their in vivo loads during gait as previously reported in the literature are discussed.

The influence of total suction on the brittle failure characteristics of clay shales

NASA Astrophysics Data System (ADS)

Amann, F.; Linda, W.; Zimmer, S.; Thoeny, R.

2013-12-01

Clay shale testing is challenging and the results obtained from standard laboratory tests may not always reflect the strength of the clay shale in-situ. This is to a certain extend associated with the sensitivity of these rock types to desaturation processes during drilling, sample storage, and sample preparation. In this study the relationship between total suction, uniaxial compressive strength and Brazilian tensile (BTS) strength of cylindrical samples of Opalinus Clay was established in a systematic manner. Unconfined uniaxial compression and BTS tests were performed utilizing a servo-controlled testing procedure. Total suctions in the specimens was generated in air tight desiccators using supersaturated saline solutions which establish a relative humidity ranging from 20% to 99%. For unconfined compressive strength tests loading of the specimens occurred parallel to bedding. For BTS tests loading was either oriented normal or perpendicular to bedding. Both, the crack initiation and volumetric strain reversal threshold values were determined using volumetric and radial stress-strain methods. The results of BTS tests show that the tensile strength normal and perpendicular to bedding increases by a factor of approximately 3 when total suction is increased from 0 to 90 MPa (i.e. saturation decreases from 1.0 to 0.7) . Beyond 90 MPa total suction no further increase in tensile strength was observed, most probably due to shrinkage cracks which alter the tensile strength of the clay shale. Results obtained from UCS tests suggest that higher total suctions result in higher UCS values. Between total suctions of 0 to 90 MPa, the strength increase is almost linear (i.e. the UCS increases by a factor of 1.5 MPa). Beyond 90 MPa total suction no further strength increase was observed. A similar trend can be observed for crack initiation and crack damage values. In the same range of total suction the crack initiation stress increases by a factor of 5 (from 2 MPa to 10 MPa), and the crack damage stress increases by a factor of 2 (from 6 to 12 MPa). In addition to UCS tests, the water retention curve of intact and disturbed specimens was established. Here, results indicate that the drying path remains nearly unaffected by mechanical damage. However, the wetting path is considerably affected by mechanical damage.

Mechanical properties of hybrid SiC/CNT filled toughened epoxy nanocomposite

NASA Astrophysics Data System (ADS)

Ratim, S.; Ahmad, S.; Bonnia, N. N.; Yahaya, Sabrina M.

2018-01-01

Mechanical properties of epoxy nanocomposites filled single filler have been extensively studied by various researchers. However, there are not much discovery on the behavior of hybrid nanocomposite. In this study, single and hybrid nanocomposites of toughened epoxy filled CNT/SiC nanoparticles were investigated. The hybrid nanocomposites samples were prepared by combining CNT and SiC nanoparticles in toughened epoxy matrix via mechanical stirring method assisted with ultrasonic cavitations. Epoxy resin and liquid epoxidized natural rubber (LENR) mixture were first blend prior to the addition of nanofillers. Then, the curing process of the nanocomposite samples were conducted by compression molding technique at 130°C for 2 hours. The purpose of this study is to investigate the hybridization effect of CNT and SiC nanoparticles on mechanical properties toughened epoxy matrix. The total loading of single and hybrid nanofillers were fixed to 4% volume are 0, 4C, 4S, 3S1C, 2S2C, and 1S3C. Mechanical properties of hybrid composites show that the highest value of tensile strength achieved by 3S1C sample at about 7% increment and falls between their single composite values. Meanwhile, the stiffness of the same sample is significantly increased at about 31% of the matrix. On the other hand, a highest flexural property is obtained by 1S3C sample at about 20% increment dominated by CNT content. However, the impact strength shows reduction trend with the addition of SiC and CNT into the matrix. The hybridization of SiC and CNT show highest value in sample 1S3C at about 3.37 kJ/m2 of impact energy absorbed. FESEM micrograph have confirmed that better distributions and interaction observed between SiC nanoparticles and matrix compared to CNT, which contributed to higher tensile strength and modulus.

3D-printing zirconia implants; a dream or a reality? An in-vitro study evaluating the dimensional accuracy, surface topography and mechanical properties of printed zirconia implant and discs.

PubMed

Osman, Reham B; van der Veen, Albert J; Huiberts, Dennis; Wismeijer, Daniel; Alharbi, Nawal

2017-11-01

The aim of this study was to evaluate the dimensional accuracy, surface topography of a custom designed, 3D-printed zirconia dental implant and the mechanical properties of printed zirconia discs. A custom designed implant was 3D-printed in zirconia using digital light processing technique (DLP). The dimensional accuracy was assessed using the digital-subtraction technique. The mechanical properties were evaluated using biaxial flexure strength test. Three different build angles were adopted to print the specimens for the mechanical test; 0°(Vertical), 45° (Oblique) and 90°(Horizontal) angles. The surface topography, crystallographic phase structure and surface roughness were evaluated using scanning electron microscopy analysis (SEM), X-ray diffractometer and confocal microscopy respectively. The printed implant was dimensionally accurate with a root mean square (RMSE) value of 0.1mm. The Weibull analysis revealed a statistically significant higher characteristic strength (1006.6MPa) of 0° printed specimens compared to the other two groups and no significant difference between 45° (892.2MPa) and 90° (866.7MPa) build angles. SEM analysis revealed cracks, micro-porosities and interconnected pores ranging in size from 196nm to 3.3µm. The mean Ra (arithmetic mean roughness) value of 1.59µm (±0.41) and Rq (root mean squared roughness) value of 1.94µm (±0.47) was found. A crystallographic phase of primarily tetragonal zirconia typical of sintered Yttria tetragonal stabilized zirconia (Y-TZP) was detected. DLP prove to be efficient for printing customized zirconia dental implants with sufficient dimensional accuracy. The mechanical properties showed flexure strength close to those of conventionally produced ceramics. Optimization of the 3D-printing process parameters is still needed to improve the microstructure of the printed objects. Copyright © 2017 Elsevier Ltd. All rights reserved.

Experimental Study on Basic Mechanical Properties of BFRP Bars

NASA Astrophysics Data System (ADS)

Fan, Xiaochun; Xu, Ting; Zhou, Zhengrong; Zhou, Xun

2017-10-01

Basalt Fiber Reinforced Polymer (BFRP) bars have the advantages of corrosion resistance, high strength, light weight, good dielectric properties, and they are new type of green reinforced alternative material. In order to determine the mechanical properties of BFRP bars, the tensile strength of basalt fiber bars was necessary to be studied. The diameters of the basalt fiber bars were compared by means of uniaxial tensile test in this article. Then the stress-strain curve can be drawn out. The results show that the stress - strain curve of BFRP bars present straight line relation, and there is no sign before failure; there is no yield platform on the stress-strain curve of BFRP bars, which are typical brittle material;the tensile strength of BFRP bars is about 3 times higher than that of ordinary steel bars. and the elastic modulus is about 1/5 of that of ordinary steel; the ultimate tensile strength of BFRP bars varies little with the increase of diameter, but there exist some differences in modulus values.

Effect of strain rate and notch geometry on tensile properties and fracture mechanism of creep strength enhanced ferritic P91 steel

NASA Astrophysics Data System (ADS)

Pandey, Chandan; Mahapatra, M. M.; Kumar, Pradeep; Saini, N.

2018-01-01

Creep strength enhanced ferritic (CSEF) P91 steel were subjected to room temperature tensile test for quasi-static (less than 10-1/s) strain rate by using the Instron Vertical Tensile Testing Machine. Effect of different type of notch geometry, notch depth and angle on mechanical properties were also considered for different strain rate. In quasi-static rates, the P91 steel showed a positive strain rate sensitivity. On the basis of tensile data, fracture toughness of P91 steel was also calculated numerically. For 1 mm notch depth (constant strain rate), notch strength and fracture toughness were found to be increased with increase in notch angle from 45° to 60° while the maximum value attained in U-type notch. Notch angle and notch depth has found a minute effect on P91 steel strength and fracture toughness. The fracture surface morphology was studied by field emission scanning electron microscopy (FESEM).

Physical and mechanical properties of LDPE incorporated with different starch sources

NASA Astrophysics Data System (ADS)

Kormin, Shaharuddin; Kormin, Faridah; Dalour Hossen Beg, Mohammad; Bijarimi Mat Piah, Mohd

2017-08-01

In this study it was investigated the incorporation of different starches, such as sago starch, corn starch, potato starch, tapioca starch and wheat starch, in low-density polyethylene matrix (LDPE) to enhanced mechanical properties and to obtain partially biodegradable product with the aim to reduce the plastics wastes in the environment. For comparison, virgin LDPE, LDPE with different sources of starch blends were prepared and characterized under the same conditions. The starches were mixed to the LDPE using a twin screw extruder to guarantee the homogeneity of the formulations. The compound were shaping processed by injection moulding. The characterization of those compounds was done by physical (density, MFI), mechanical (Universal tensile machine). The addition of starch to LDPE reduced the MFI values, the tensile strength, elongation at break and impact strength, whereas the elastic modulus, flexural modulus and flexural strength increased. LDPE/SS show the good mechanical behavior compared to other formulation. The physical and mechanical properties were evident when 5 and 30 wt% were added. Water uptake increased with increased starch content and immersion time. The time taken for the composites to equilibrate was about one month even when they were immersed completely in water.

INFLUENCE OF HEMA CONTENT ON THE MECHANICAL AND BONDING PROPERTIES OF EXPERIMENTAL HEMA-ADDED GLASS IONOMER CEMENTS

PubMed Central

Lim, Ho-Nam; Kim, Seong-Hwan; Yu, Bin; Lee, Yong-Keun

2009-01-01

The purpose of this study was to determine the influence of incrementally added uncured HEMA in experimental HEMA-added glass ionomer cement (HAGICs) on the mechanical and shear bond strength (SBS) of these materials. Increasing contents of uncured HEMA (10-50 wt.%) were added to a commercial glass ionomer cement liquid (Fuji II, GC, Japan), and the compressive and diametral tensile strengths of the resulting HAGICs were measured. The SBS to non-precious alloy, precious alloy, enamel and dentin was also determined after these surfaces were subjected to either airborne-particle abrasion (Aa) or SiC abrasive paper grinding (Sp). Both strength properties of the HAGICs first increased and then decreased as the HEMA content increased, with a maximum value obtained when the HEMA content was 20% for the compressive strength and 40% for the tensile strength. The SBS was influenced by the HEMA content, the surface treatment, and the type of bonding surface (p<0.05). These results suggest that addition of an appropriate amount of HEMA to glass ionomer cement would increase diametral tensile strength as well as bond strength to alloys and teeth. These results also confirm that the optimal HEMA content ranged from 20 to 40% within the limitations of this experimental condition. PMID:19668995

Electro-mechanical characterization of structural supercapacitors

NASA Astrophysics Data System (ADS)

Gallagher, T.; LaMaster, D.; Ciocanel, C.; Browder, C.

2012-04-01

The paper presents electrical and mechanical properties of structural supercapacitors and discusses limitations associated with the approach taken for the electrical properties evaluation. The structural supercapacitors characterized in this work had the electrodes made of carbon fiber weave, separator made of several cellulose based products, and the solid electrolyte made as PEGDGE based polymer blend. The reported electrical properties include capacitance and leakage resistance; the former was measured using cyclic voltammetry. Mechanical properties have been evaluated thorough tensile and three point bending tests performed on structural supercapacitor coupons. The results indicate that the separator material plays an important role on the electrical as well as mechanical properties of the structural capacitor, and that Celgard 3501 used as separator leads to most benefits for both mechanical and electrical properties. Specific capacitance and leakage resistance as high as 1.4kF/m3 and 380kΩ, respectively, were achieved. Two types of solid polymer electrolytes were used in fabrication, with one leading to higher and more consistent leakage resistance values at the expense of a slight decrease in specific capacitance when compared to the other SPE formulation. The ultimate tensile strength and modulus of elasticity of the developed power storage composite were evaluated at 466MPa and 18.9MPa, respectively. These values are 58% and 69% of the tensile strength and modulus of elasticity values measured for a single layer composite material made with the same type of carbon fiber and with a West System 105 epoxy instead of solid polymer electrolyte.

Remedial processing of oil shale fly ash (OSFA) and its value-added conversion into glass-ceramics.

PubMed

Zhang, Zhikun; Zhang, Lei; Li, Aimin

2015-12-01

Recently, various solid wastes such as sewage sludge, coal fly ash and slag have been recycled into various products such as sintered bricks, ceramics and cement concrete. Application of these recycling approaches is much better and greener than conventional landfills since it can solve the problems of storage of industrial wastes and reduce exploration of natural resources for construction materials to protect the environment. Therefore, in this study, an attempt was made to recycle oil shale fly ash (OSFA), a by-product obtained from the extracting of shale oil in the oil shale industry, into a value-added glass-ceramic material via melting and sintering method. The influence of basicity (CaO/SiO2 ratio) by adding calcium oxide on the performance of glass-ceramics was studied in terms of phase transformation, mechanical properties, chemical resistances and heavy metals leaching tests. Crystallization kinetics results showed that the increase of basicity reduced the activation energies of crystallization but did not change the crystallization mechanism. When increasing the basicity from 0.2 to 0.5, the densification of sintering body was enhanced due to the promotion of viscous flow of glass powders, and therefore the compression strength and bending strength of glass-ceramics were increased. Heavy metals leaching results indicated that the produced OSFA-based glass-ceramics could be taken as non-hazardous materials. The maximum mechanical properties of compression strength of 186 ± 3 MPa, bending strength of 78 ± 6 MPa, good chemical resistances and low heavy metals leaching concentrations showed that it could be used as a substitute material for construction applications. The proposed approach will be one of the potential sustainable solutions in reducing the storage of oil shale fly ash as well as converting it into a value-added product. Copyright © 2015 Elsevier Ltd. All rights reserved.

The effect of aqueous media on the mechanical properties of fluorapatite-mullite glass-ceramics.

PubMed

Mollazadeh, S; Ajalli, Siamak; Kashi, Tahereh S Jafarzadeh; Yekta, Bijan Eftekhai; Javadpour, Jafar; Jafari, S; Youssefi, Abbas; Fazel, Akbar

2015-11-01

To verify the effects of alternating thermal changes in aqueous media and chemical composition on mechanical properties of apatite-mullite glass-ceramics and to investigate concentration of ions eluted from glass-ceramics in aqueous media. The glass compositions were from SiO2Al2O3P2O5CaOTiO2BaOZrO2CaF2 system. Glass-ceramics were prepared by heat-treating at 1100°C for 3h samples alternately immersed in water at 5 and 60°C. The 3-point bending strength (n=10) were determined using 3×4×25mm/bar and a universal testing machine, at a cross-head speed of 0.1mm/min. Vickers micro hardness were evaluated by applying a total of 15-20 indentations under a 100g load for 30s. Concentrations of ions eluted from glass-ceramics immersed in 60±5°C double distilled water were determined by ion chromatography. The toxicity of glass-ceramics was assessed by seeding the osteosarcoma cells (MG63) on powder for different days and their cell proliferation assessment was investigated by MTT assay. The data were analyzed using one way analysis of variance and the means were compared by Tukey's test (5% significance level). The highest flexural strength and hardness values after thermal changes belonged to TiO2 and ZrO2 containing glass-ceramics which contained lower amount of released ions. BaO containing glass-ceramic and sample with extra amount of silica showed the highest amount of reduction in their mechanical strength values. These additives enhanced the concentration of eluted ions in aqueous media. MTT results showed that glass-ceramics were almost equivalent concerning their in-vitro biological behavior. Thermal changes and chemical compositions had significant effects on flexural strength and Vickers micro-hardness values. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Composite material making from empty fruit bunches of palm oil (EFB) and Ijuk (Arengapinnata) using plastic bottle waste as adhesives

NASA Astrophysics Data System (ADS)

Rihayat, T.; Salim, S.; Audina, N.; Khan, N. S. P.; Zaimahwati; Sami, M.; Yunus, M.; Salisah, Z.; Alam, P. N.; Saifuddin; Yusuf, I.

2018-03-01

Reviewed from the current technological required a new methods to capable offering a high profit value without overriding the quality. The development of composite technology is now beginning to shift from traditional composite materials based petroleum to natural fibers composite. In the present study, aim to made specimens using natural fibers in form of EFB as a composite reinforcedment with Polyethylene Terephtalate (PET) derived from Plastic bottles waste as matrix with mixed composition parameters and time-tolerance in the mixing process to build a biocomposite material. The characterization of mechanical properties includes tensile test (ASTM D638-01) and bending test (ASTM D790-02) followed by thermal analysis using Thermogravimetric Analysis (TGA), and morphological analysis using scanning electron microscope (SEM). The analysis effect of EFB, Ijuk and PET mixtures on the composite matrix is very influential with mechanical properties characterization, including tensile test and bending strength. The results demonstrated that from the sample named : 50 : 25: 25, hybrid composites showed improved properties such as tensile strength of 167 MPa while the 90:05:05 based composites exhibited tensile strength values of 30 MPa, respectively. In term the flexural test the best result of composition on the properties with 10 minutes duration time its load value 7,5 Mpa for 80:10:10.

Effect of boron waste on the properties of mortar and concrete.

PubMed

Topçu, Iker Bekir; Boga, Ahmet Raif

2010-07-01

Utilization of by-products or waste materials in concrete production are important subjects for sustainable development and industrial ecology concepts. The usages as mineral admixtures or fine aggregates improve the durability properties of concrete and thus increase the economic and environmental advantages for the concrete industry. The effect of clay waste (CW) containing boron on the mechanical properties of concrete was investigated. CW was added in different proportions as cement additive in concrete. The effect of CW on workability and strength of concrete were analysed by fresh and hardened concrete tests. The results obtained were compared with control concrete properties and Turkish standard values. The results showed that the addition of CW had a small effect upon the workability of the concrete but an important effect on the reduction of its strength. It was observed that strength values were quite near to that of control concrete when not more than 10% CW was used in place of cement. In addition to concrete specimens, replacing cement with CW produced mortar specimens, which were investigated for their strength and durability properties. The tests of SO( 4) (2-) and Cl(-) effect as well as freeze-thaw behaviour related to the durability of mortar were performed. Consequently, it can be said that some improvements were obtained in durability properties even if mechanical properties had decreased with increasing CW content.

The effect of woven and non-woven fiber structure on mechanical properties polyester composite reinforced kenaf

NASA Astrophysics Data System (ADS)

Ratim, S.; Bonnia, N. N.; Surip, S. N.

2012-07-01

The effects of woven and non-woven kenaf fiber on mechanical properties of polyester composites were studied at different types of perform structures. Composite polyester reinforced kenaf fiber has been prepared via hand lay-up process by varying fiber forms into plain weave, twill and mats structure. The reinforcing efficiency of different fiber structure was compared with control of unreinforced polyester sample. It was found that the strength and stiffness of the composites are largely affected by fiber structure. A maximum value for tensile strength of composite was obtained for twill weave pattern of fiber structure while no significant different for plain weave and mat structure. The elastic modulus of composite has shown some improvement on plain and twill weave pattern. Meanwhile, lower value of modulus elasticity achieved by mats structure composite as well as control sample. The modulus of rupture and impact resistance were also analyzed. The improvement of modulus of rupture value can be seen on plain and twill weave pattern. However impact resistance doesn't show significant improvement in all types of structure except for mat fiber. The mechanical properties of kenaf fiber reinforced polyester composite found to be increased with woven and non-woven fiber structures in composite.

Physical and mechanical properties of spinach for whole-surface online imaging inspection

NASA Astrophysics Data System (ADS)

Tang, Xiuying; Mo, Chang Y.; Chan, Diane E.; Peng, Yankun; Qin, Jianwei; Yang, Chun-Chieh; Kim, Moon S.; Chao, Kuanglin

2011-06-01

The physical and mechanical properties of baby spinach were investigated, including density, Young's modulus, fracture strength, and friction coefficient. The average apparent density of baby spinach leaves was 0.5666 g/mm3. The tensile tests were performed using parallel, perpendicular, and diagonal directions with respect to the midrib of each leaf. The test results showed that the mechanical properties of spinach are anisotropic. For the parallel, diagonal, and perpendicular test directions, the average values for the Young's modulus values were found to be 2.137MPa, 1.0841 MPa, and 0.3914 MPa, respectively, and the average fracture strength values were 0.2429 MPa, 0.1396 MPa, and 0.1113 MPa, respectively. The static and kinetic friction coefficient between the baby spinach and conveyor belt were researched, whose test results showed that the average coefficients of kinetic and maximum static friction between the adaxial (front side) spinach leaf surface and conveyor belt were 1.2737 and 1.3635, respectively, and between the abaxial (back side) spinach leaf surface and conveyor belt were 1.1780 and 1.2451 respectively. These works provide the basis for future development of a whole-surface online imaging inspection system that can be used by the commercial vegetable processing industry to reduce food safety risks.

Quantification of bone strength by intraoperative torque measurement: a technical note.

PubMed

Suhm, Norbert; Haenni, Markus; Schwyn, Ronald; Hirschmann, Michael; Müller, Andreas Marc

2008-06-01

Bone strength describes the resistance of bone against mechanical failure. Bone strength depends on both the amount of bone and the bone's quality, and the bone strength may be looked upon as a relevant parameter to judge an osteosynthesis' stability. Information about bone strength was barely available intraoperatively in the past. The previous work of our group reported on development and laboratory evaluation of mechanical torque measurement as a method for the intraoperative quantification of bone strength. With the clinical series presented here we intend to verify that the im gesamten Text DensiProbe instrumentation for intraoperative torque measurement and the related measurement method are eligible for intraoperative use based on the following criteria: application of the method may not create complications, the measurement can be performed by the surgeon himself and may only cause a limited increase in the procedure time. From December 2006 until May 2007 ten patients with a pertrochanteric femoral fracture or a lateral femoral neck fracture eligible for stabilization with DHS were included in the study after having received informed consent. Any medication and comorbidity that might have influenced bone quality or bone mineral density (BMD) in these patients was documented. Bone strength was intraoperatively measured with DensiProbe. Complications that were obviously related with torque measurement were documented as well as any deviation from the suggested procedure; 6 and 12 weeks postoperative follow-up included clinical and radiological examination. The time required for torque measurement, the overall operating time and the number of persons present in the operating room were protocolled. BMD values of the contralateral femoral neck were postoperatively assessed by dual energy X-ray absorptiometry (DEXA) and compared to intraoperative peak torque values measured by DensiProbe. No major complication was observed during intraoperative application of DensiProbe by trained surgeons. The unintended extraction of the guide wire together with the torque measurement probe was reported only once and is looked upon as a minor complication. Fracture healing was uneventful in all patients. The mean time for torque measurement was 2.35 +/- 0.9 min accounting for 2.2 +/- 1.1% of total surgery time. The presence of an additional person was not required to perform torque measurement but to protocol the data. There was a tendency towards correlation between BMD values of the femoral neck and intraoperative peak torque values. The data presented clearly indicate that the DensiProbe instrumentation and measurement principle are eligible for routine intraoperative use by trained surgeons. Interpretation of possible correlations between BMD values measured by means of DEXA and the Peak Torque values assessed by DensiProbe has to be considered very carefully, because BMD and Peak Torque analyse bone at a different scale. Only within the framework of a multicenter study it will be possible to include a sufficient number of patients for calculation of the methods' predictive value towards implant failure and to verify acceptance of the method by the surgeons.

Surrogate Modeling of High-Fidelity Fracture Simulations for Real-Time Residual Strength Predictions

NASA Technical Reports Server (NTRS)

Spear, Ashley D.; Priest, Amanda R.; Veilleux, Michael G.; Ingraffea, Anthony R.; Hochhalter, Jacob D.

2011-01-01

A surrogate model methodology is described for predicting, during flight, the residual strength of aircraft structures that sustain discrete-source damage. Starting with design of experiment, an artificial neural network is developed that takes as input discrete-source damage parameters and outputs a prediction of the structural residual strength. Target residual strength values used to train the artificial neural network are derived from 3D finite element-based fracture simulations. Two ductile fracture simulations are presented to show that crack growth and residual strength are determined more accurately in discrete-source damage cases by using an elastic-plastic fracture framework rather than a linear-elastic fracture mechanics-based method. Improving accuracy of the residual strength training data does, in turn, improve accuracy of the surrogate model. When combined, the surrogate model methodology and high fidelity fracture simulation framework provide useful tools for adaptive flight technology.

Through thickness mechanical properties of chemical vapor infiltration and nano-infiltration and transient eutectic-phase processed SiC/SiC composites

DOE PAGES

Shih, Chunghao Phillip; Katoh, Yutai; Ozawa, Kazumi; ...

2014-04-08

The through thickness (interlaminar) shear strength and trans-thickness tensile strength of three different nuclear-grade SiC/SiC composites were evaluated at room temperature by the double-notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans-thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. Furthermore, the 2D woven composite had a higher trans-thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull-out and fiber failure.

Through thickness mechanical properties of chemical vapor infiltration and nano-infiltration and transient eutectic-phase processed SiC/SiC composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shih, Chunghao Phillip; Katoh, Yutai; Ozawa, Kazumi

The through thickness (interlaminar) shear strength and trans-thickness tensile strength of three different nuclear-grade SiC/SiC composites were evaluated at room temperature by the double-notched shear and diametral compression tests, respectively. With increasing densification of the interlaminar matrix region, a transition in failure locations from interlayer to intrafiber bundle was observed, along with significant increases in the value of the interlaminar shear strength. Under trans-thickness tensile loading, cracks were found to propagate easily in the unidirectional composite. Furthermore, the 2D woven composite had a higher trans-thickness tensile strength (38 MPa) because the failure mode involved debonding, fiber pull-out and fiber failure.

Industrial Test of High Strength Steel Plates Free Boron Q890D Used for Engineering Machinery

NASA Astrophysics Data System (ADS)

Dong, Ruifeng; Liu, Zetian; Gao, Jun

The chemistry composition, process parameters and the test results of Q890D free boron high strength steel plate used for engineering machinery was studied. The 16 40 mm thickness steel plates with good mechanical properties that was yield strength of 930 970 MPa, tensile strength of 978 1017 MPa, elongation of 13.5 15%, the average impact energy value of more than 100 J were developed by improving steel purity, adopting the reasonable controlled rolling and cooling process, using reasonable off-line quenching and tempering process. The test plates have good crack resistance in 60 °C preheat temperature condition because of that there are no any cracks in the surfaces, cross-section and roots of welding joints.

Effect of Controlled Rolling and Cooling On Microstructure and Mechanical Properties of 30crmnti Wire Rod

NASA Astrophysics Data System (ADS)

Ruan, Shipeng; Dong, Qing; Zhang, Lei; Wang, Lijun

2017-09-01

The effect of controlled rolling and cooling on microstructure and mechanical properties of alloy structure steel 30CrMnTi wire rod with diameter 6.5mm was studied. The results show that the lower finish rolling temperature resulted in a decrease in tensile strength but an increase in elongation and reduction of area. When the finish rolling temperature decreases from 950°C to 850°C, the tensile strength value decreases from 750MPa to 660MPa, and the elongation increases from 21% to 30%, the reduction of area increases from 64% to 71%. The grain size also refines from 20μm to 9.9μm when the finish rolling temperature decreases from 950°C to 850°C. The decrease of tensile strength is due to the change of microstructure which evolved from more bainite to ferrite and pearlite.

Microstructure of directionally solidified Ti-Fe eutectic alloy with low interstitial and high mechanical strength

NASA Astrophysics Data System (ADS)

Contieri, R. J.; Lopes, E. S. N.; Taquire de La Cruz, M.; Costa, A. M.; Afonso, C. R. M.; Caram, R.

2011-10-01

The performance of Ti alloys can be considerably enhanced by combining Ti and other elements, causing an eutectic transformation and thereby producing composites in situ from the liquid phase. This paper reports on the processing and characterization of a directionally solidified Ti-Fe eutectic alloy. Directional solidification at different growth rates was carried out in a setup that employs a water-cooled copper crucible combined with a voltaic electric arc moving through the sample. The results obtained show that a regular fiber-like eutectic structure was produced and the interphase spacing was found to be a function of the growth rate. Mechanical properties were measured using compression, microindentation and nanoindentation tests to determine the Vickers hardness, compressive strength and elastic modulus. Directionally solidified eutectic samples presented high values of compressive strength in the range of 1844-3000 MPa and ductility between 21.6 and 25.2%.

Microstructure and mechanical properties of rapidly solidified B2-type Zr–Co alloys containing a second phase of Zr2Co

NASA Astrophysics Data System (ADS)

Li, Peiyou

2018-04-01

Microstructure and mechanical properties of B2-type Zr–Co alloys containing a second phase (Zr2Co) were investigated. Results show that the as-cast Zr52Co48, Zr54Co46, and Zr56Co44 alloys are composed of a eutectic structure of B2 and Zr2Co phases. Relative amounts of Zr2Co phases increase with an increase in Zr content. Zr54Co46 exhibits high yield strength, high Vickers hardness, good ductility, and high toughness values, and thus, Zr54Co46 can be considered to be a novel engineering material. The increase in strength and decrease in plastic strain of the alloys are mainly attributed to the increase in high strength of the brittle Zr2Co phase and to grain refining of the B2 matrix phase.

Mechanical Degradation of Graphite/PVDF Composite Electrodes: A Model-Experimental Study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Kenji; Higa, Kenneth; Mair, Sunil

2015-12-11

Mechanical failure modes of a graphite/polyvinylidene difluoride (PVDF) composite electrode for lithium-ion batteries were investigated by combining realistic stress-stain tests and mathematical model predictions. Samples of PVDF mixed with conductive additive were prepared in a similar way to graphite electrodes and tested while submerged in electrolyte solution. Young's modulus and tensile strength values of wet samples were found to be approximately one-fifth and one-half of those measured for dry samples. Simulations of graphite particles surrounded by binder layers given the measured material property values suggest that the particles are unlikely to experience mechanical damage during cycling, but that the fatemore » of the surrounding composite of PVDF and conductive additive depends completely upon the conditions under which its mechanical properties were obtained. Simulations using realistic property values produced results that were consistent with earlier experimental observations.« less

Highway pavement performance test for colored thin anti-skidding layers

NASA Astrophysics Data System (ADS)

Gao, Wei; Cui, Wei; Xu, Ming

2018-03-01

Based on the actual service condition of highway pavement colored thin anti-skidding layers, with materials of color quartz sand and two-component acrylic resin as basis, we designed such tests as the bond strength, shearing strength, tear strength, fatigue performance and aggregate polished value, and included the freeze-thaw cycle and de-icing salt and other factors in the experiment, connecting with the climate characteristics of circumpolar latitude and low altitude in Heilongjiang province. Through the pavement performance test, it is confirmed that the colored thin anti-skidding layers can adapt to cold and humid climate conditions, and its physical mechanical properties are good.

Optimal estimation of the optomechanical coupling strength

NASA Astrophysics Data System (ADS)

Bernád, József Zsolt; Sanavio, Claudio; Xuereb, André

2018-06-01

We apply the formalism of quantum estimation theory to obtain information about the value of the nonlinear optomechanical coupling strength. In particular, we discuss the minimum mean-square error estimator and a quantum Cramér-Rao-type inequality for the estimation of the coupling strength. Our estimation strategy reveals some cases where quantum statistical inference is inconclusive and merely results in the reinforcement of prior expectations. We show that these situations also involve the highest expected information losses. We demonstrate that interaction times on the order of one time period of mechanical oscillations are the most suitable for our estimation scenario, and compare situations involving different photon and phonon excitations.

Experimental study on joining of AA6063 and AISI 1040 steel

NASA Astrophysics Data System (ADS)

Hynes, N. Rajesh Jesudoss; Raja, S.

2018-05-01

Feasibility of joining of dissimilar metals with different physical, chemical and thermal properties such as AA6063 alloy and AISI 1040 steel is worthwhile study, since it has tremendous applications in all most of all engineering domains. The mechanism of bonding is studied using scanning electron microscopy. Impact strength of AA2024/AISI joints, axial shortening distance, micro hardness distribution and joint strength are determined. Micro hardness profile shows increased hardness value at the joint interface, due to grain refinement.

The effects of heat treatment on some technological properties of Scots pine (Pinus sylvestris L.) wood.

PubMed

Korkut, Süleyman; Akgül, Mehmet; Dündar, Turker

2008-04-01

Heat treatment is often applied to wood species to improve their dimensional stability. This study examined the effect of heat treatment on certain mechanical properties of Scots pine (Pinus sylvestris L.), which has industrially high usage potential and large plantations in Turkey. Wood specimens obtained from Bolu, Turkey, were subjected to heat treatment under atmospheric pressure at varying temperatures (120, 150 and 180 degrees C) for varying durations (2, 6 and 10h). The test results of heat-treated Scots pine and control samples showed that technological properties including compression strength, bending strength, modulus of elasticity in bending, janka-hardness, impact bending strength and tension strength perpendicular to grain suffered with heat treatment, and increase in temperature and duration further diminished technological strength values of the wood specimens.

Interlaminar shear properties of graphite fiber, high-performance resin composites

NASA Technical Reports Server (NTRS)

Needles, H. L.; Kourtides, D. A.; Fish, R. H.; Varma, D. S.

1983-01-01

Short beam testing was used to determine the shear properties of laminates consisting of T-300 and Celion 3000 and 6000 graphite fibers, in epoxy, hot melt and solvent bismaleimide, polyimide and polystyrylpyridine (PSP). Epoxy, composites showed the highest interlaminar shear strength, with values for all other resins being substantially lower. The dependence of interlaminar shear properties on the fiber-resin interfacial bond and on resin wetting characteristics and mechanical properties is investigated, and it is determined that the lower shear strength of the tested composites, by comparison with epoxy resin matrix composites, is due to their correspondingly lower interfacial bond strengths. An investigation of the effect of the wettability of carbon fiber tow on shear strength shows wetting variations among resins that are too small to account for the large shear strength property differences observed.

Effect of Nano-CuO on Engineering and Microstructure Properties of Fibre-Reinforced Mortars Incorporating Metakaolin: Experimental and Numerical Studies

PubMed Central

Ghanei, Amir; Jafari, Faezeh; Mehrinejad Khotbehsara, Mojdeh; Mohseni, Ehsan; Cui, Hongzhi

2017-01-01

In this study, the effects of nano-CuO (NC) on engineering properties of fibre-reinforced mortars incorporating metakaolin (MK) were investigated. The effects of polypropylene fibre (PP) were also examined. A total of twenty-six mixtures were prepared. The experimental results were compared with numerical results obtained by adaptive neuro-fuzzy inference system (ANFIS) and Primal Estimated sub-GrAdient Solver for SVM (Pegasos) algorithm. Scanning Electron Microscope (SEM) was also employed to investigate the microstructure of the cement matrix. The mechanical test results showed that both compressive and flexural strengths of cement mortars decreased with the increase of MK content, however the strength values increased significantly with increasing NC content in the mixture. The water absorption of samples decreased remarkably with increasing NC particles in the mixture. When PP fibres were added, the strengths of cement mortars were further enhanced accompanied with lower water absorption values. The addition of 2 wt % and 3 wt % nanoparticles in cement mortar led to a positive contribution to strength and resistance to water absorption. Mixture of PP-MK10NC3 indicated the best results for both compressive and flexural strengths at 28 and 90 days. SEM images illustrated that the morphology of cement matrix became more porous with increasing MK content, but the porosity reduced with the inclusion of NC. In addition, it is evident from the SEM images that more cement hydration products adhered onto the surface of fibres, which would improve the fibre–matrix interface. The numerical results obtained by ANFIS and Pegasos were close to the experimental results. The value of R2 obtained for each data set (validate, test and train) was higher than 0.90 and the values of mean absolute percentage error (MAPE) and the relative root mean squared error (PRMSE) were near zero. The ANFIS and Pegasos models can be used to predict the mechanical properties and water absorptions of fibre-reinforced mortars with MK and NC. PMID:29065559

Strengthening Mechanisms in Nanostructured Al/SiCp Composite Manufactured by Accumulative Press Bonding

NASA Astrophysics Data System (ADS)

Amirkhanlou, Sajjad; Rahimian, Mehdi; Ketabchi, Mostafa; Parvin, Nader; Yaghinali, Parisa; Carreño, Fernando

2016-10-01

The strengthening mechanisms in nanostructured Al/SiCp composite deformed to high strain by a novel severe plastic deformation process, accumulative press bonding (APB), were investigated. The composite exhibited yield strength of 148 MPa which was 5 and 1.5 times higher than that of raw aluminum (29 MPa) and aluminum-APB (95 MPa) alloys, respectively. A remarkable increase was also observed in the ultimate tensile strength of Al/SiCp-APB composite, 222 MPa, which was 2.5 and 1.2 times greater than the obtained values for raw aluminum (88 MPa) and aluminum-APB (180 MPa) alloys, respectively. Analytical models well described the contribution of various strengthening mechanisms. The contributions of grain boundary, strain hardening, thermal mismatch, Orowan, elastic mismatch, and load-bearing strengthening mechanisms to the overall strength of the Al/SiCp microcomposite were 64.9, 49, 6.8, 2.4, 5.4, and 1.5 MPa, respectively. Whereas Orowan strengthening mechanism was considered as the most dominating strengthening mechanism in Al/SiCp nanocomposites, it was negligible for strengthening the microcomposite. Al/SiCp nanocomposite showed good agreement with quadratic summation model; however, experimental results exhibited good accordance with arithmetic and compounding summation models in the microcomposite. While average grain size of the composite reached 380 nm, it was less than 100 nm in the vicinity of SiC particles as a result of particle-stimulated nucleation mechanism.

An interlaminar tension strength specimen

NASA Technical Reports Server (NTRS)

Jackson, Wade C.; Martin, Roderick H.

1992-01-01

This paper describes a technique to determine interlaminar tension strength, sigma(sub 3c) of a fiber reinforced composite material using a curved beam. The specimen was a unidirectional curved beam, bent 90 degrees, with straight arms. Attached to each arm was a hinged loading mechanism which was held by the grips of a tensile testing machine. Geometry effects of the specimen, including the effects of loading arm length, inner radius, thickness, and width, were studied. The data sets fell into two categories: low strength corresponding to a macroscopic flaw related failure and high strength corresponding to a microscopic flaw related failure. From the data available, the loading arm length had no effect on sigma(sub 3c). The inner radius was not expected to have a significant effect on sigma(sub 3c), but this conclusion could not be confirmed because of differences in laminate quality for each curve geometry. The thicker specimens had the lowest value of sigma(sub 3c) because of poor laminate quality. Width was found to affect the value of sigma(sub 3c) only slightly. The wider specimens generally had a slightly lower strength since more material was under high stress, and hence, had a larger probability of containing a significant flaw.

Modal energy analysis for mechanical systems excited by spatially correlated loads

NASA Astrophysics Data System (ADS)

Zhang, Peng; Fei, Qingguo; Li, Yanbin; Wu, Shaoqing; Chen, Qiang

2018-10-01

MODal ENergy Analysis (MODENA) is an energy-based method, which is proposed to deal with vibroacoustic problems. The performance of MODENA on the energy analysis of a mechanical system under spatially correlated excitation is investigated. A plate/cavity coupling system excited by a pressure field is studied in a numerical example, in which four kinds of pressure fields are involved, which include the purely random pressure field, the perfectly correlated pressure field, the incident diffuse field, and the turbulent boundary layer pressure fluctuation. The total energies of subsystems differ to reference solution only in the case of purely random pressure field and only for the non-excited subsystem (the cavity). A deeper analysis on the scale of modal energy is further conducted via another numerical example, in which two structural modes excited by correlated forces are coupled with one acoustic mode. A dimensionless correlation strength factor is proposed to determine the correlation strength between modal forces. Results show that the error on modal energy increases with the increment of the correlation strength factor. A criterion is proposed to establish a link between the error and the correlation strength factor. According to the criterion, the error is negligible when the correlation strength is weak, in this situation the correlation strength factor is less than a critical value.

Damage formation, fatigue behavior and strength properties of ZrO{sub 2}-based ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kozulin, A. A., E-mail: kozulyn@ftf.tsu.ru; Kulkov, S. S.; Narikovich, A. S.

It is suggested that a non-destructive testing technique using a three-dimensional X-ray tomography be applied to detecting internal structural defects and monitoring damage formation in a ceramic composite structure subjected to a bending load. Three-point bending tests are used to investigate the fatigue behavior and mechanical and physical properties of medical-grade ZrO{sub 2}-based ceramics. The bending strength and flexural modulus are derived under static conditions at a loading rate of 2 mm/min. The fatigue strength and fatigue limit under dynamic loading are investigated at a frequency of 10 Hz in three stress ranges: 0.91–0.98, 0.8–0.83, and 0.73–0.77 MPa of themore » static bending strength. The average values of the bending strength and flexural modulus of sintered specimens are 43 MPa and 22 GPa, respectively. The mechanical properties of the ceramics are found to be similar to those of bone tissues. The testing results lead us to conclude that the fatigue limit obtained from 10{sup 5} stress cycles is in the range 33–34 MPa, i.e. it accounts for about 75% of the static bending strength for the test material.« less

In-vitro investigations of a pH- and ionic-strength-responsive polyelectrolytic hydrogel using a piezoresistive microsensor

PubMed Central

Schulz, Volker; Guenther, Margarita; Gerlach, Gerald; Magda, Jules J.; Tathireddy, Prashant; Rieth, Loren; Solzbacher, Florian

2010-01-01

Environmental responsive or smart hydrogels show a volume phase transition due to changes of external stimuli such as pH or ionic strength of an ambient solution. Thus, they are able to convert reversibly chemical energy into mechanical energy and therefore they are suitable as sensitive material for integration in biochemical microsensors and MEMS devices. In this work, micro-fabricated silicon pressure sensor chips with integrated piezoresistors were used as transducers for the conversion of mechanical work into an appropriate electrical output signal due to the deflection of a thin silicon bending plate. Within this work two different sensor designs have been studied. The biocompatible poly(hydroxypropyl methacrylate-N,N-dimethylaminoethyl methacrylate-tetra-ethyleneglycol dimethacrylate) (HPMA-DMA-TEGDMA) was used as an environmental sensitive element in piezoresistive biochemical sensors. This polyelectrolytic hydrogel shows a very sharp volume phase transition at pH values below about 7.4 which is in the range of the physiological pH. The sensor's characteristic response was measured in-vitro for changes in pH of PBS buffer solution at fixed ionic strength. The experimental data was applied to the Hill equation and the sensor sensitivity as a function of pH was calculated out of it. The time-dependent sensor response was measured for small changes in pH, whereas different time constants have been observed. The same sensor principal was used for sensing of ionic strength. The time-dependent electrical sensor signal of both sensors was measured for variations in ionic strength at fixed pH value using PBS buffer solution. Both sensor types showed an asymmetric swelling behavior between the swelling and the deswelling cycle as well as different time constants, which was attributed to the different nature of mechanical hydrogel-confinement inside the sensor. PMID:21152365

Investigation of Hydraulic Binding Characteristics of Lime Based Mortars Used in Historical Masonry Structures

NASA Astrophysics Data System (ADS)

Binal, Adil

2017-10-01

In the historic masonry structures, hard and large rock fragments were used as the construction materials. The hydraulic binder material prepared to keep this used material in its entirety is a different material than the cement used today. Khorasan mortar made by using aggregate and lime exhibits a more flexible structure than the concrete. This feature allows the historic building to be more durable. There is also a significant industrial value because of the use of Khorasan mortar in the restoration of historic masonry structures. Therefore, the calculation of the ideal mixture of Khorasan mortar and the determination of its mechanical and physical properties are of great importance regarding preserving historic buildings. In this study, the mixtures of different lime and brick fractions were prepared. It was determined that Khorasan mortar shows the highest compressive strength in mixtures with water/lime ratio of 0.55 and lime/aggregate ratio of 0.66. By keeping the mixing ratio constant, it was observed that the strengths of the samples kept in the humidity chamber for different curing times increased day by day. The early strength values of samples with the high lime/aggregate ratio (l/a: 0.83) were higher than those with the low lime/aggregate ratio (l/a: 0.5). For the samples with low lime/aggregate ratio, there was an increase in the strength values depending on the curing period. As the cure duration increases, a chemical reaction takes place between the lime and the brick fracture, and as a result of this reaction, the strength values are increased.

The determination of resistance of marble to thermal and moisture cycles: relevance and limits of the recent European natural stone standard

NASA Astrophysics Data System (ADS)

Bellopede, Rossana; Castelletto, Eleonora; Marini, Paola; Zichella, Lorena

2015-04-01

The recent European standard EN 16306:2013 specifies laboratory methodology on the determination of the resistance to thermal and moisture cycling of marble for cladding of building façades. In particular measurements of bowing and flexural strength should be performed before and at the end of the ageing cycles. Bowing is measured on specimens of dimension 30*100*400mm exposed to moisture from beneath and heating (gradually till 80°C) on the upper face. The flexural strength should be measured both on reference and on exposed specimens in order to assess the variation of mechanical properties. Additional non-destructive tests are foreseen but are not compulsory for the standard. Moreover, the Annex A of the EN 16306, contains a guidance of the limit values that could be useful for the building planner for façade panels dimensioning. Different varieties of marble (two from Italy, one from Greece and three from Portugal) have been tested by means of this laboratory ageing test. Non-destructive tests such as the measurements of Ultrasonic Pulse Velocity (UPV), porosity, and water absorption have been executed together with the conventional flexural strength test. Image analysis on thin sections soaked with methylene blue have been analysed to further investigate the correlation between porosity and tendency to bowing. Base on the results obtained, some consideration on the decrease of mechanical resistance and the bowing in relation to the variety of marble tested and the limit values indicated the Annex A of EN 16306 can be drawn. Besides, from the data analysed a deepened discussion has been made. It is known that bowing and rapid strength loss occur in some varieties of marble when used as exterior cladding but further considerations can be made: bowing and flexural strength are correlate and in which way? Often the bowing is related to the decrease of flexural strength but it happens that there is a decrease in the mechanical resistance of the stone also without the bowing phenomenon. Non-destructive tests are surely useful to evaluate deterioration of mechanical properties but attention should be paid to the analysis of results, correlating the information coming from UPV measures with that from porosity evaluation.

Curaua and eucalyptus nanofibers films by continuous casting: Mechanical and thermal properties.

PubMed

Claro, Pedro Ivo Cunha; Corrêa, Ana Carolina; de Campos, Adriana; Rodrigues, Vanessa Bolzan; Luchesi, Bruno Ribeiro; Silva, Luiz Eduardo; Mattoso, Luiz Henrique Capparelli; Marconcini, José Manoel

2018-02-01

A wide variety of new green materials such as curaua leaf fibers (CLFs) has potential applications in nanotechnology. This study aims to investigate the thermomechanical properties and morphological structure of cellulose nanocrystals (CNCs) and cellulose nanofibrils (CNFs) films obtained by continuous casting. The CNCs were obtained by acid hydrolysis and CNFs by mechanical shearing from bleached CLFs and eucalyptus pulp. The morphology after continuous casting resulted in oriented nanofibers, and as a consequence there was mechanical anisotropy. CNCs films showed the greatest values of tensile strength (36±4MPa) and the more effective fibrillation provided better mechanical strength of eucalyptus CNFs films than curaua CNFs films. Sulfur groups and mechanical shear degradation affected the stability of CNCs and CNFs films, respectively. Thus, the type of nanostructure, the way they interact to each other, the cellulose source and the process interfere significantly on the properties of the films. Copyright © 2017 Elsevier Ltd. All rights reserved.

Probabilistic material strength degradation model for Inconel 718 components subjected to high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue effects

NASA Technical Reports Server (NTRS)

Bast, Callie C.; Boyce, Lola

1995-01-01

This report presents the results of both the fifth and sixth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA). The research included on-going development of methodology for a probabilistic material strength degradation model. The probabilistic model, in the form of a postulated randomized multifactor equation, provides for quantification of uncertainty in the lifetime material strength of aerospace propulsion system components subjected to a number of diverse random effects. This model is embodied in the computer program entitled PROMISS, which can include up to eighteen different effects. Presently, the model includes five effects that typically reduce lifetime strength: high temperature, high-cycle mechanical fatigue, low-cycle mechanical fatigue, creep and thermal fatigue. Statistical analysis was conducted on experimental Inconel 718 data obtained from the open literature. This analysis provided regression parameters for use as the model's empirical material constants, thus calibrating the model specifically for Inconel 718. Model calibration was carried out for five variables, namely, high temperature, high-cycle and low-cycle mechanical fatigue, creep and thermal fatigue. Methodology to estimate standard deviations of these material constants for input into the probabilistic material strength model was developed. Using an updated version of PROMISS, entitled PROMISS93, a sensitivity study for the combined effects of high-cycle mechanical fatigue, creep and thermal fatigue was performed. Then using the current version of PROMISS, entitled PROMISS94, a second sensitivity study including the effect of low-cycle mechanical fatigue, as well as, the three previous effects was performed. Results, in the form of cumulative distribution functions, illustrated the sensitivity of lifetime strength to any current value of an effect. In addition, verification studies comparing a combination of high-cycle mechanical fatigue and high temperature effects by model to the combination by experiment were conducted. Thus, for Inconel 718, the basic model assumption of independence between effects was evaluated. Results from this limited verification study strongly supported this assumption.

Modeling of abnormal mechanical properties of nickel-based single crystal superalloy by three-dimensional discrete dislocation dynamics

NASA Astrophysics Data System (ADS)

Yang, Hui; Li, Zhenhuan; Huang, Minsheng

2014-12-01

Unlike common single crystals, the nickel-based single crystal superalloy shows surprisingly anomalous flow strength (i.e. with the increase of temperature, the yield strength first increases to a peak value and then decreases) and tension-compression (TC) asymmetry. A comprehensive three-dimensional discrete dislocation dynamics (3D-DDD) procedure was developed to model these abnormal mechanical properties. For this purpose, a series of complicated dynamic evolution details of Kear-Wilsdorf (KW) locks, which are closely related to the flow strength anomaly and TC asymmetry, were incorporated into this 3D-DDD framework. Moreover, the activation of the cubic slip system, which is the origin of the decrease in yield strength with increasing temperature at relatively high temperatures, was especially taken into account by introducing a competition criterion between the unlocking of the KW locks and the activation of the cubic slip system. To test our framework, a series of 3D-DDD simulations were performed on a representative volume cell model with a cuboidal Ni3Al precipitate phase embedded in a nickel matrix. Results show that the present 3D-DDD procedure can successfully capture the dynamic evolution of KW locks, the flow strength anomaly and TC asymmetry. Then, the underlying dislocation mechanisms leading to these abnormal mechanical responses were investigated and discussed in detail. Finally, a cyclic deformation of the nickel-based single crystal superalloy was modeled by using the present DDD model, with a special focus on the influence of KW locks on the Bauschinger effect and cyclic softening.

Laboratory mechanical parameters of composite resins and their relation to fractures and wear in clinical trials-A systematic review.

PubMed

Heintze, Siegward D; Ilie, Nicoleta; Hickel, Reinhard; Reis, Alessandra; Loguercio, Alessandro; Rousson, Valentin

2017-03-01

To evaluate a range of mechanical parameters of composite resins and compare the data to the frequency of fractures and wear in clinical studies. Based on a search of PubMed and SCOPUS, clinical studies on posterior composite restorations were investigated with regard to bias by two independent reviewers using Cochrane Collaboration's tool for assessing risk of bias in randomized trials. The target variables were chipping and/or fracture, loss of anatomical form (wear) and a combination of both (summary clinical index). These outcomes were modelled by time and material in a linear mixed effect model including random study and experiment effects. The laboratory data from one test institute were used: flexural strength, flexural modulus, compressive strength, and fracture toughness (all after 24-h storage in distilled water). For some materials flexural strength data after aging in water/saliva/ethanol were available. Besides calculating correlations between clinical and laboratory outcomes, we explored whether a model including a laboratory predictor dichotomized at a cut-off value better predicted a clinical outcome than a linear model. A total of 74 clinical experiments from 45 studies were included involving 31 materials for which laboratory data were also available. A weak positive correlation between fracture toughness and clinical fractures was found (Spearman rho=0.34, p=0.11) in addition to a moderate and statistically significant correlation between flexural strength and clinical wear (Spearman rho=0.46, p=0.01). When excluding those studies with "high" risk of bias (n=18), the correlations were generally weaker with no statistically significant correlation. For aging in ethanol, a very strong correlation was found between flexural strength decrease and clinical index, but this finding was based on only 7 materials (Spearman rho=0.96, p=0.0001). Prediction was not consistently improved with cutoff values. Correlations between clinical and laboratory outcomes were moderately positive with few significant results, fracture toughness being correlated with clinical fractures and flexural strength with clinical wear. Whether artificial aging enhances the prognostic value needs further investigations. Copyright © 2016 The Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Effect of gamma radiation on the physico-chemical properties of alginate-based films and beads

NASA Astrophysics Data System (ADS)

Huq, Tanzina; Khan, Avik; Dussault, Dominic; Salmieri, Stephane; Khan, Ruhul A.; Lacroix, Monique

2012-08-01

Alginate solution (3%, w/v) was prepared using deionized water from its powder. Then the solution was exposed to gamma radiation (0.1-25 kGy). The alginate films were prepared by solution casting. It was found that gamma radiation has strong effect on alginate solution. At low doses, mechanical strength of the alginate films improved but after 5 kGy dose, the strength started to decrease. The mechanism of alginate radiolysis in aqueous solution is discussed. Film formation was not possible from alginate solution at doses >5 kGy. The mechanical properties such as puncture strength (PS), puncture deformation (PD), viscoelasticity (Y) coefficient of the un-irradiated films were investigated. The values of PS, PD and Y coefficient of the films were 333 N/mm, 3.20 mm and 27%, respectively. Alginate beads were prepared from 3% alginate solution (w/v) by ionotropic gelation method in 5% CaCl2 solution. The rate of gel swelling improved in irradiated alginate-based beads at low doses (up to 0.5 kGy).

Reinforcement of thermoplastic chitosan hydrogel using chitin whiskers optimized with response surface methodology.

PubMed

Sun, Guohui; Zhang, Xin; Bao, Zixian; Lang, Xuqian; Zhou, Zhongzheng; Li, Yang; Feng, Chao; Chen, Xiguang

2018-06-01

To strengthen the mechanical strength of thermo-sensitive hydroxybutyl chitosan (HBC) hydrogel, chitin whiskers were used as sticker to fabricate reinforced HBC (HBCW) hydrogel by using response surface methodology. Unlike the intrinsic network of HBC hydrogel, HBCW hydrogel showed a laminar shape with firm structure. The preparation condition was optimized by three-factor-three-level Box-Behnken design. The maximum mechanical strength (1011.11 Pa) was achieved at 50 °C, when the concentrations of HBC and chitin whiskers were 5.1 wt% and 2.0 wt%, respectively. The effects of temperature, pH value and NaCl concentration on mechanical strength of HBCW hydrogels were investigated via the oscillatory stress sweeps. The results showed that HBCW hydrogel could reach the maximum stiffness (∼1126 Pa) at 37 °C pH 12.0. Low pH and high salty ions could decrease the stability of hydrogel, while chitin whiskers could increase the stress tolerance and related ruptured strain of HBCW hydrogels. Copyright © 2018. Published by Elsevier Ltd.

Mechanical properties of titanium-hydroxyapatite (Ti-HA) composite coating on stainless steel prepared by thermal spraying

NASA Astrophysics Data System (ADS)

Rosmamuhamadani, R.; Azhar, N. H.; Talari, M. K.; Yahaya, Sabrina M.; Sulaiman, S.; Ismail, M. I. S.

2017-09-01

Addition of hydroxyapatite (HA) can enhance the bioactivity of the common metallic implant due to its similarity with natural bones and teeth. In this investigation, high velocity oxy-fuel (HVOFT) technique was used to deposit titanium-hydroxyapatite (Ti-HA) composite on stainless steel substrate plate with different percentage of HA for biomedical applications. The aim of this research is to investigate the mechanical properties of Ti-HA coating such as hardness, adhesion strength and wear behaviour. The hardness and strength was determined by using SHIMADZU-microhardness Vickers tester and PosiTest AT portable adhesion tester respectively. The wear test was performed by using pin-on-disk equipment and field emission scanning electron microscope (FESEM) used to determine the extent of surface damage. From the results obtained, mechanical properties such as hardness and adhesion strength of titanium (Ti) coating decreased with the increased of HA contents. Meanwhile, the coefficient of friction of Ti-10% HA coating shows the highest value compare to others as three-body abrasion had occurred during the test.

Effect of heat treatment on mechanical properties of age-hardenable gold alloy at intraoral temperature.

PubMed

Watanabe, I; Watanabe, E; Cai, Z; Okabe, T; Atsuta, M

2001-09-01

The aim of this study was to investigate the effect of various heat treatments on the mechanical properties of gold alloys capable of age-hardening at intraoral temperature. Dumbbell-shaped patterns (ISO 6871) were cast with three gold alloys (Sofard; NC Type-IV; Aurum Cast, NihombashiTokuriki Co.). The Sofard alloy is age-hardenable at intraoral temperature. The castings underwent various heat treatments [as-cast (AC); solution treatment (ST); high-temperature aging (HA); intraoral aging (IA)]. After these heat treatments, ultimate tensile strength (UTS), 0.2% offset yield strength (YS), and elongation (EL) were measured at a strain rate of 1.7x10(-4)/s. Fracture surfaces of the specimens after tensile testing were observed using SEM. Vickers hardness was also measured after heat treating. After IA, the hardness values of the Sofard alloy increased and reached values similar to the hardness of the Sofard specimens aged at high temperature (HA). The hardness values of the NC Type-IV and Aurum Cast specimens slightly increased after IA, but did not reach the values of the specimens after HA. All the Sofard, NC Type-IV and Aurum Cast specimens showed significantly (P<0.05) greater hardness values after HA, compared with the values after any other heat treatments (AC, ST and IA). The UTS and YS of the specimens indicated a tendency similar to the results obtained for hardness. The Sofard specimens with ST showed the greatest elongation compared to the corresponding NC Type-IV and Aurum Cast specimens. However, the elongation of the Sofard specimens was abruptly reduced after intraoral aging. Intraoral aging significantly improved the mechanical properties and hardness of the Sofard alloy.

Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites: Influence of Interface Modification

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Eldridge, Jeffrey I.

1998-01-01

Unidirectional celsian matrix composites having 42-45 vol % of uncoated or BN-SIC coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 +/- 35 MPa and 0.27 +/- 0.01%, respectively, with ultimate strength as high as 960 MPa. The elastic Young modulus of the uncoated and coated fiber-reinforced composites were 184 +/- 4 GPa and 165 +/- 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of composite with uncoated fibers is due to degradation of the fiber strength from mechanical damage during processing. Because both the coated- and uncoated-fiber-reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SIC dual layer is primarily the protection of fibers from mechanical damage during processing.

Influence of airborne-particle abrasion on mechanical properties and bond strength of carbon/epoxy and glass/bis-GMA fiber-reinforced resin posts.

PubMed

Soares, Carlos Jose; Santana, Fernanda Ribeiro; Pereira, Janaina Carla; Araujo, Tatiana Santos; Menezes, Murilo Souza

2008-06-01

Controversy exists concerning the use of fiber-reinforced posts to improve bond strength to resin cement because some precementation treatments can compromise the mechanical properties of the posts. The purpose of this study was to analyze the influence of airborne-particle abrasion on the mechanical properties and microtensile bond strength (MTBS) of carbon/epoxy and glass/bis-GMA fiber-reinforced resin posts. Flexural strength (delta(f)), flexural modulus (E(f)), and stiffness (S) were assessed using a 3-point bending test for glass fiber-reinforced and carbon fiber-reinforced resin posts submitted to airborne-particle abrasion (AB) with 50-microm Al(2)O(3), and for posts without any surface treatment (controls) (n=10). Forty glass fiber (GF) and 40 carbon fiber (CF) posts were submitted to 1 of 4 surface treatments (n=10) prior to MTBS testing: silane (S); silane and adhesive (SA); airborne-particle abrasion with 50-microm Al(2)O(3) and silane (ABS); airborne-particle abrasion, silane, and adhesive (ABSA). Two composite resin restorations (Filtek Z250) with rounded depressions in the lateral face were bilaterally fixed to the post with resin cement (RelyX ARC). Next, the specimen was sectioned with a precision saw running perpendicular to the bonded surface to obtain 10 bonded beam specimens with a cross-sectional area of 1 mm(2). Each beam specimen was tested in a mechanical testing machine (EMIC 2,000 DL), under stress, at a crosshead speed of 0.5 mm/min until failure. Data were analyzed by 2-way ANOVA followed by Tukey HSD test (alpha=.05). Failure patterns of tested specimens were analyzed using scanning electron microscopy (SEM). The 3-point bending test demonstrated significant differences among groups only for the post type factor for flexural strength, flexural modulus, and stiffness. The carbon fiber posts exhibited significantly higher mean flexural strength (P=.001), flexural modulus (P=.003), and stiffness (P=.001) values when compared with glass fiber posts, irrespective of surface treatment. An alteration in the superficial structure of the posts could be observed by SEM after airborne-particle abrasion. MTBS testing showed no significant effect for the surface treatment type; however, significant effects for post system factor and for interaction between the 2 factors were observed. For the carbon fiber post, the ABSA surface treatment resulted in values significantly lower than the S surface treatment. SEM analysis of MTBS-tested specimens demonstrated adhesive and cohesive failures. Airborne-particle abrasion did not influence the mechanical properties of the post; however, it produced undesirable surface changes, which could reduce the bond strength to resin cement. For the surface treatments studied, if silane is applied, the adhesive system and airborne-particle abrasion are not necessary.

Formulation effects on the mechanical and release properties of metronidazole suppositories.

PubMed

Adegboye, T A; Itiola, O A

2003-09-01

A study of the effects of Tween 20 and Tween 80 non-ionic surfactants, and witepsol H15 and polyethylene glycol (PEG) 2850 bases, on the mechanical and release properties of metronidazole suppositories was made. Mechanical strength was assessed by breaking strength values F. The values of F increased with increase in concentration of surfactant. The values of F for formulations containing Tween 20 were higher than those obtained for formulations containing Tween 80. Witepsol bases gave higher values of F than corresponding PEG bases. Release characteristics were assessed by the time for 80% drug release (t80), values of dissolution rate constants, k1 and k2 and the time of intersection, t1. The values of t80 decreased while those of k1 and k2 increased with increase in surfactant concentration. The values of t80 were lower, while those of k1 and k2 were higher, for formulations containing Tween 20 than for those formulations containing Tween 80. Witepsol bases gave lower t80 values and higher k1 and k2 values than their corresponding PEG bases. The concentration of surfactant, C, had the largest individual effect on the mechanical and release parameters while the nature of surfactant, S, had the lowest. The ranking for the individual effects of the variables on F and k1 was C > N > S, on t80 and k2 was C > N approximately = S, was on t1 was C = N = S. The interactions between S and C were largest for F, t80 and k2, and lowest for k1 and t1. The ranking of the interaction effects of the variables on F and k2 was S-C > N-C > N-S, on t80 was S-C > N-S approximately = N-C, on k1 was N-C > N-S > S-C, and on t1 was N-S = N-C > S-C. The results suggest that the individual and interaction effects of formulation variables would provide useful guides in optimizing metronidazole suppository formulations.

Non-woven PET fabric reinforced and enhanced the performance of ultrafiltration membranes composed of PVDF blended with PVDF-g-PEGMA for industrial applications

NASA Astrophysics Data System (ADS)

Wang, Shuai; Li, Tong; Chen, Chen; Chen, Sheng; Liu, Baicang; Crittenden, John

2018-03-01

Ultrafiltration (UF) membranes composed of poly(vinylidene fluoride) (PVDF) blended with poly(vinylidene fluoride)-graft-poly(ethylene glycol) methyl ether methacrylate (PVDF-g-PEGMA) can present high flux and excellent foulant removal efficiencies under suitable preparation conditions. However, these PVDF/PVDF-g-PEGMA blended membranes cannot be applied industrially because of the insufficient mechanical strength (strength-to-break value of 8.4 ± 0.6 MPa). We incorporated two types of non-woven polyethylene terephthalate (PET) fabrics (thin hydrophobic and thick hydrophilic fabrics) as support layers to improve the mechanical properties of the blended membranes. The thin and thick PET fabrics were able to significantly improve the tensile strength to 23.3 ± 3.7 MPa and 30.1 ± 1.4 MPa, respectively. The PET fabrics had a limited impact on the separation-related membrane performance such as hydrophilicity, foulant rejection, whereas the mechanical strength and pure water flux was improved several folds. The enhanced flux was attributed to the higher surface porosity and wider finger-like voids in the cross-section. The thin PET fabric with larger porosity was able to maintain a consistent toughness simultaneously; thus it is recommended as a support material for this blended membrane.

Modification of conventional glass-ionomer cements with N-vinylpyrrolidone containing polyacids, nano-hydroxy and fluoroapatite to improve mechanical properties.

PubMed

Moshaverinia, Alireza; Ansari, Sahar; Movasaghi, Zanyar; Billington, Richard W; Darr, Jawwad A; Rehman, Ihtesham U

2008-10-01

The objective of this study was to enhance the mechanical strength of glass-ionomer cements, while preserving their unique clinical properties. Copolymers incorporating several different segments including N-vinylpyrrolidone (NVP) in different molar ratios were synthesized. The synthesized polymers were copolymers of acrylic acid and NVP with side chains containing itaconic acid. In addition, nano-hydroxyapatite and fluoroapatite were synthesized using an ethanol-based sol-gel technique. The synthesized polymers were used in glass-ionomer cement formulations (Fuji II commercial GIC) and the synthesized nanoceramic particles (nano-hydroxy or fluoroapatite) were also incorporated into commercial glass-ionomer powder, respectively. The synthesized materials were characterized using FTIR and Raman spectroscopy and scanning electron microscopy. Compressive, diametral tensile and biaxial flexural strengths of the modified glass-ionomer cements were evaluated. After 24h setting, the NVP modified glass-ionomer cements exhibited higher compressive strength (163-167 MPa), higher diametral tensile strength (DTS) (13-17 MPa) and much higher biaxial flexural strength (23-26 MPa) in comparison to Fuji II GIC (160 MPa in CS, 12MPa in DTS and 15 MPa in biaxial flexural strength). The nano-hydroxyapatite/fluoroapatite added cements also exhibited higher CS (177-179 MPa), higher DTS (19-20 MPa) and much higher biaxial flexural strength (28-30 MPa) as compared to the control group. The highest values for CS, DTS and BFS were found for NVP-nanoceramic powder modified cements (184 MPa for CS, 22 MPa for DTS and 33 MPa for BFS) which were statistically higher than control group. It was concluded that, both NVP modified and nano-HA/FA added glass-ionomer cements are promising restorative dental materials with improved mechanical properties.

Effects of Fiber Content on Mechanical Properties of CVD SiC Fiber-Reinforced Strontium Aluminosilicate Glass-Ceramic Composites

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

1996-01-01

Unidirectional CVD SiC(f)(SCS-6) fiber-reinforced strontium aluminosilicate (SAS) glass-ceramic matrix composites containing various volume fractions, approximately 16 to 40 volume %, of fibers were fabricated by hot pressing at 1400 C for 2 h under 27.6 MPa. Monoclinic celsian, SrAl2Si2O8, was the only crystalline phase formed, with complete absence of the undesired hexacelsian phase, in the matrix. Room temperature mechanical properties were measured in 3-point flexure. The matrix microcracking stress and the ultimate strength increased with increase in fiber volume fraction, reached maximum values for V(sub f) approximately equal to 0.35, and degraded at higher fiber loadings. This degradation in mechanical properties is related to the change in failure mode, from tensile at lower V(sub f) to interlaminar shear at higher fiber contents. The extent of fiber loading did not have noticeable effect on either fiber-matrix debonding stress, or frictional sliding stress at the interface. The applicability of micromechanical models in predicting the mechanical properties of the composites was also examined. The currently available theoretical models do not appear to be useful in predicting the values of the first matrix cracking stress, and the ultimate strength of the SCS-6/SAS composites.

Bioinspired design and assembly of layered double hydroxide/poly(vinyl alcohol) film with high mechanical performance.

PubMed

Shu, Yingqi; Yin, Penggang; Liang, Benliang; Wang, Hao; Guo, Lin

2014-09-10

Inspired by the hierarchical structure and excellent mechanical performance of nacre, LDH nanosheets with an appropriate aspect ratio to withstand significant loads and at the same time allow for rupture under the pull-out mode were synthesized as artificial building blocks for the fabrication of nacre-like films. Multilayered PVA/LDH films with a high tensile strength and ductility were prepared for the first time by bottom-up layer-by-layer assembly of pretreated LDH nanosheets and spin-coating of PVA. The weight fraction of inorganic LDH platelets in the hybrid PVA/LDH films (wp) was controlled by changing the concentration of PVA solution applied in the spin-coating process. The resulting films revealed that the PVA/LDH hybrid films were piled close together to form a well-defined stratified structure resembling the brick-and-mortar structure of natural nacre. In the hybrid films, the content of inorganic LDH platelets was comparable to the value in nacre, up to 96.9 wt %. It could be clearly seen that the mechanical performance of the as-prepared PVA/LDH films was greatly improved by increasing the rigid building-block LDHs. The tensile strength of the 2 wt % PVA/LDH hybrid film reached a value of 169.36 MPa, thus exceeding the strength of natural nacre and reaching 4 times that of a pure PVA film. Meanwhile, its elastic modulus was comparable to that of lamellar bone.

Improving the mechanical properties of nano-hydroxyapatite

NASA Astrophysics Data System (ADS)

Khanal, Suraj Prasad

Hydroxyapatite (HAp) is an ideal bioactive material that is used in orthopedics. Chemical composition and crystal structure properties of HAp are similar to the natural bone hence it promotes bone growth. However, its mechanical properties of synthetic HAp are not sufficient for major load-bearing bone replacement. The potential of improving the mechanical properties of synthetic hydroxyapatite (HAp) by incorporating carboxyl functionalized single walled carbon nanotubes (CfSWCNT) and polymerized epsilon-caprolactam (nylon) is studied. The fracture toughness, tensile strength, Young's modulus, stiffness and fracture energy were studied for a series of HAp samples with CfSWCNT concentrations varying from 0 to 1.5 wt. % without, and with nylon addition. X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM) and Differential Scanning Calorimetry (DSC) were used to characterize the samples. The fracture toughness and tensile test was performed under the standard protocol of ASTM D5045 and ASTM D638-02a respectively. Reproducible maximum values of (3.60 +/- 0.3) MPa.m1/2 for fracture toughness and 65.38 MPa for tensile strength were measured for samples containing 1 wt. % CfSWCNT and nylon. The Young's modulus, stiffness and fracture energy of the samples are 10.65 GPa, 1482.12 N/mm, and 644 J/m2 respectively. These values are comparable to those of the cortical bone. Further increase of the CfSWCNT content results to a decreased fracture toughness and tensile strength and formation of a secondary phase.

Coating hydroxiapatite on stainless steel 316 L by using sago starch as binder with dip-coating method

NASA Astrophysics Data System (ADS)

Fadli, A.; Akbar, F.; Prabowo, A.; Hidayah, P. H.

2018-04-01

Hydroxyapatite (HA) is a mineral form of naturally occurring apatite calcium with Ca10(PO4)6(OH)2 formula. One of the major innovations in the field of bone reconstruction is to apply HA as a surface coating on a mechanically strong implant metal and to improve the stability of bone implants thereby increasing the lifetime of the metal implants. Pure hydroxyapatite has poor mechanical properties so it is necessary to add sago starch as a binder to combine the strength and hardness of metal surfaces with bioactive properties of hydroxyapatite by Dip Coating method. Stainless steel 316L is the most commonly used alloy as an implant for bones and teeth due to its excellent corrosion and oxidation resistance and is easily formed. In this study, hydroxyapatite coatings used fixed variables as hydroxyapatite mass (10 grams), aquades mass (20 grams), dipping time (20 seconds), and calcination conditions (800°C, 1 hour). The variables are sago starch mass (1, 1.25, 1.5 gram) and stirring time (16, 20, 24 hours). The shear strength value is higher in the addition of 1.25, 10, 20, and again in the binder ratio of 1.5; 10; 20. The addition of stirring time causes a decrease in shear strength. The highest shear strength value obtained was 3.07 MPa. The layer attached to the substrate is a hydroxyapatite with a composition of 99.4% as evidenced by the results of XRD analysis.

A sampling study on rock properties affecting drilling rate index (DRI)

NASA Astrophysics Data System (ADS)

Yenice, Hayati; Özdoğan, Mehmet V.; Özfırat, M. Kemal

2018-05-01

Drilling rate index (DRI) developed in Norway is a very useful index in determining the drillability of rocks and even in performance prediction of hard rock TBMs and it requires special laboratory test equipment. Drillability is one of the most important subjects in rock excavation. However, determining drillability index from physical and mechanical properties of rocks is very important for practicing engineers such as underground excavation, drilling operations in open pit mining, underground mining and natural stone production. That is why many researchers have studied concerned with drillability to find the correlations between drilling rate index (DRI) and penetration rate, influence of geological properties on drillability prediction in tunneling, correlations between rock properties and drillability. In this study, the relationships between drilling rate index (DRI) and some physico-mechanical properties (Density, Shore hardness, uniaxial compressive strength (UCS, σc), Indirect tensile strength (ITS, σt)) of three different rock groups including magmatic, sedimentary and metamorphic were evaluated using both simple and multiple regression analysis. This study reveals the effects of rock properties on DRI according to different types of rocks. In simple regression, quite high correlations were found between DRI and uniaxial compressive strength (UCS) and also between DRI and indirect tensile strength (ITS) values. Multiple regression analyses revealed even higher correlations when compared to simple regression. Especially, UCS, ITS, Shore hardness (SH) and the interactions between them were found to be very effective on DRI values.

The effect of ultrasonics on the strength properties of carbon steel processed by cold plastic deformation

NASA Technical Reports Server (NTRS)

Atanasiu, N.; Dragan, O.; Atanasiu, Z.

1974-01-01

A study was made of the influence of ultrasounds on the mechanical properties of OLT 35 carbon steel tubes cold-drawn on a plug ultrasonically activated by longitudinal waves. Experimental results indicate that: 1. The reduction in the values of the flow limit and tensile strength is proportional to the increase in acoustic energy introduced into the material subjected to deformation. 2. The diminution in influence of ultrasounds on tensile strength and flow rate that is due to an increased degree of deformation is explained by a reduction in specific density of the acoustic energy at the focus of deformation. 3. The relations calculated on the basis of the variation in the flow limit and tensile strength as a function of acoustic energy intensity was verified experimentally.

High Temperature Tensile Properties of Unidirectional Hi-Nicalon/Celsian Composites In Air

NASA Technical Reports Server (NTRS)

Gyekenyesi, John Z.; Bansal, Narottam P.

2000-01-01

High temperature tensile properties of unidirectional BN/SiC-coated Hi-Nicalon SiC fiber reinforced celsian matrix composites have been measured from room temperature to 1200 C (2190 F) in air. Young's modulus, the first matrix cracking stress, and the ultimate strength decreased from room temperature to 1200 C (2190 F). The applicability of various micromechanical models, in predicting room temperature values of various mechanical properties for this CMC, has also been investigated. The simple rule of mixtures produced an accurate estimate of the primary composite modulus. The first matrix cracking stress estimated from ACK theory was in good agreement with the experimental value. The modified fiber bundle failure theory of Evans gave a good estimate of the ultimate strength.

Effect of kenaf short fiber loading on mechanical properties of biocomposites

NASA Astrophysics Data System (ADS)

Andilolo, J.; Nikmatin, S.; Nugroho, N.; Alatas, H.; Wismogroho, A. S.

2017-05-01

The research of biocomposite product with kenaf (Hibiscus cannabinus) short fiber as a filler and Acrylonitrile Butadiene Styrene (ABS) as the matrix had been done to understand the mechanical properties of this material. Kenaf short fiber was obtained from mechanical sieving after doing the mechanical milling. TAPPI method has been done to determine the chemical properties. In order to form a granular biocomposite a single screw extruder was performed with a variation of particle loading 10 and 15%. The original of acrylonitrile butadiene styrene (ABS) has been used as matrix. The fabrication of speciment had been done by molding injection process. Mechanical properties test was done by ASTM standarization. The results showed the density of the fibers of 1.008 g/cm3 with a fiber length of 897.07 µm and a diameter of 66.38 µm. Tensile strength of kenaf short fiber loading 10 and 15% was 23.522 ± 8.36 MPa and 20.739 ± 6.79 MPa, respectively. The tensile properties showed a decreasing trend as the fiber loading was increased. The values of impact strength were 68.657 ± 4.89 kJ m-2 and 82.090 ± 5.56 kJ m-2, respectively and the hardness values were 96.60 ± 6.03 HR and 105.20 ± 13.17 HR, respectively. Kenaf fiber can be a good reinforcement candidate for high performance polymer bio-composites.

Influences of the steam sterilization on the properties of calcium phosphate porous bioceramics.

PubMed

Li, Xiangfeng; Guo, Bo; Xiao, Yumei; Yuan, Tun; Fan, Yujiang; Zhang, Xingdong

2016-01-01

The influences of steam sterilization on the physicochemical properties of calcium phosphate (Ca-P) porous bioceramics, including β-tricalcium phosphate (β-TCP), biphasic calcium phosphate (BCP) and hydroxyapatite (HA) are investigated. After being steam sterilized in an autoclave (121 °C for 40 min), the porous bioceramics are dried and characterized. The steam sterilization has no obvious effects on the phase composition, thermal stability, pH value and dissolubility of β-TCP porous bioceramic, but changes its morphology and mechanical strength. Meanwhile, the steam sterilization leads to the significant changes of the morphology, phase composition, pH value and dissolubility of BCP porous bioceramic. The increase of dissolubility and mechanical strength, the decrease of pH value of the immersed solution and partial oriented growth of crystals are also observed in HA porous bioceramic after steam sterilization. These results indicate that the steam sterilization can result in different influences on the physicochemical properties of β-TCP, BCP and HA porous bioceramics, thus the application of the steam sterilization on the three kinds of Ca-P porous bioceramics should be considered carefully based on the above changed properties.

Variations in Compressive Strength of Geopolymer due to the CaO Added Fly Ash

NASA Astrophysics Data System (ADS)

Zhao, Yuqing; Koumoto, Tatsuya; Kondo, Fumiyoshi

Recently, geopolymer has been a noteworthy material which can be used as a replacement for portland cement. The mechanical characteristics and consistency of the geopolymer are strongly affected by its chemical components of fly ash. The variations in compressive strength of geopolymer due to the CaO added fly ash were investigated in this paper. The compressive strengths of geopolymer were increased with an increase in the curing period, and the characteristics changed from the one of plastic soil material to brittle material such as concrete, regardless of CaO content. Also, the results of compressive strength and modulus of deformation showed their maximum value in the case of 8-10% CaO content. From this result, the maximum characteristics of the strengths were assumed to be exerted in case which the water draining process of geopolymer was balanced with the water absorbing process of additional CaO.

Studies for understanding effects of additions on the strength of cement concrete

NASA Astrophysics Data System (ADS)

Bucur, R. D.; Barbuta, M.; Konvalina, P.; Serbanoiu, A. A.; Bernas, J.

2017-09-01

The paper analyzes the effects of different types of additions introduced in concrete mix on the compressive strength. The current studies show that additions contribute to improve some characteristics of concrete and to reduce the cement dosage, so it can obtain concretes which are cheaper and friendlier with environment. In the experimental mixes were introduced: crushed natural aggregates, slag aggregates, silica fume, fly ash, chopped tire, polystyrene granule, glass fibers and metallic fibers. The experimental values of compressive strengths were compared for two concrete grades (C20/25 and C25/30). The study shown that near the well-known possibilities of improving mechanical strengths of cement concrete by increasing cement dosage and strength, by using crushed aggregates and by reducing the water/cement ratio, there are other methods in which less cement is used by replacing it with different wastes or by adding fiber.

Critical desertification transition in semi-arid ecosystems: The role of local facilitation and colonization rate

NASA Astrophysics Data System (ADS)

Corrado, Raffaele; Cherubini, Anna Maria; Pennetta, Cecilia

2015-05-01

In this work we study the effect of two different ecological mechanisms on the desertification transition in arid or semi-arid ecosystems, modeled by a stochastic cellular automaton. Namely we consider the role of the facilitation mechanism, i.e. the local positive effects of plants on their neighborhood and of colonization factors, such as seed production, survival and germination probabilities. Within the model, the strength of these two mechanisms is determined by the parameters f and b, respectively controlling the rates of the recovery and colonization processes. In particular we focus on the full desertification transition occurring at increasing value of the mortality rate m and we discuss how the values of f and b affect the critical mortality mc , the critical exponents β and γσ‧, determining the power-law scaling of the average vegetation density and of the root-mean-square deviation of the density fluctuations, and the character of the transition: continuous or abrupt. We show that mc strongly depends on both f and b, a dependence which accounts for the higher resilience of the ecosystems to external stresses as a consequence of an increased effectiveness of positive feedback effects. On the other hand, concerning the value of the exponents and the character of the transition, our results point out that both these features are unaffected by changes in the strength of the local facilitation. Viceversa, we show that an increase of the colonization factor b significantly modifies the values of the exponents and the order of the transition, changing a continuous transition into an abrupt one. We explain these results in terms of the different range of the interactions characterizing facilitation and colonization mechanisms.

Role of segregation and precipitates on interfacial strengthening mechanisms in metal matrix composites when subjected to thermo-mechanical processing

NASA Astrophysics Data System (ADS)

Myriounis, Dimitrios

Metal Matrix ceramic-reinforced composites are rapidly becoming strong candidates as structural materials for many high temperatures and aerospace applications. Metal matrix composites combine the ductile properties of the matrix with a brittle phase of the reinforcement, leading to high stiffness and strength with a reduction in structural weight. The main objective of using a metal matrix composite system is to increase service temperature or improve specific mechanical properties of structural components by replacing existing superalloys.The satisfactory performance of metal matrix composites depends critically on their integrity, the heart of which is the quality of the matrix-reinforcement interface. The nature of the interface depends on the processing of the metal matrix composite component. At the micro-level the development of local stress concentration gradients around the ceramic reinforcement, as the metal matrix attempts to deform during processing, can be very different to the nominal conditions and play a crucial role in important microstructural events such as segregation and precipitation at the matrix-reinforcement interface. These events dominate the cohesive strength and subsequent mechanical properties of the interface.At present the relationship between the strength properties of metal matrix composites and the details of the thermo-mechanical forming processes is not well understood.The purpose of the study is to investigate several strengthening mechanisms and the effect of thermo-mechanical processing of SiCp reinforced A359 aluminium alloy composites on the particle-matrix interface and the overall mechanical properties of the material. From experiments performed on composite materials subjected to various thermo-mechanical conditions and by observation using SEM microanalysis and mechanical testing, data were obtained, summarised and mathematically/statistically analysed upon their significance.The Al/SiCp composites studied, processed in specific thermo-mechanical conditions in order to attain higher values of interfacial fracture strength, due to precipitation hardening and segregation mechanisms, also exhibited enhanced bulk mechanical and fracture resistant properties.An analytical model to predict the interfacial fracture strength in the presence of material segregation was also developed during this research effort. Its validity was determined based on the data gathered from the experiments.The tailoring of the properties due to the microstructural modification of the composites was examined in relation to the experimental measurements obtained, which define the macroscopical behaviour of the material.

High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

PubMed Central

Nguyen, Daniel; Chang, Kwang; Hedayatollahnajafi, Saba; Staninec, Michal; Chan, Kenneth; Lee, Robert; Fried, Daniel

2011-01-01

CO2 lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO2 laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO2 lasers with minimal peripheral thermal and mechanical damage and without excessive heat accumulation. PMID:21806256

High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage

NASA Astrophysics Data System (ADS)

Nguyen, Daniel; Chang, Kwang; Hedayatollahnajafi, Saba; Staninec, Michal; Chan, Kenneth; Lee, Robert; Fried, Daniel

2011-07-01

CO2 lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO2 laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO2 lasers with minimal peripheral thermal and mechanical damage and without excessive heat accumulation.

High-speed scanning ablation of dental hard tissues with a λ = 9.3 μm CO2 laser: adhesion, mechanical strength, heat accumulation, and peripheral thermal damage.

PubMed

Nguyen, Daniel; Chang, Kwang; Hedayatollahnajafi, Saba; Staninec, Michal; Chan, Kenneth; Lee, Robert; Fried, Daniel

2011-07-01

CO(2) lasers can be operated at high laser pulse repetition rates for the rapid and precise removal of dental decay. Excessive heat accumulation and peripheral thermal damage is a concern when using high pulse repetition rates. Peripheral thermal damage can adversely impact the mechanical strength of the irradiated tissue, particularly for dentin, and reduce the adhesion characteristics of the modified surfaces. The interpulpal temperature rise was recorded using microthermocouples situated at the roof of the pulp chamber on teeth that were occlusally ablated using a rapidly-scanned CO(2) laser operating at 9.3 μm with a pulse duration of 10 to 15 μs and repetition rate of 300 Hz over a 2 min time course. The adhesion strength of laser treated enamel and dentin surfaces was measured for various laser scanning parameters with and without post-ablation acid etching using the single-plane shear test. The mechanical strength of laser-ablated dentin surfaces were determined via the four-point bend test and compared to control samples prepared with 320 grit wet sand paper to simulate conventional preparations. Thermocouple measurements indicated that the temperature remained below ambient temperature if water-cooling was used. There was no discoloration of either dentin or enamel laser treated surfaces, the surfaces were uniformly ablated, and there were no cracks visible. Four-point bend tests yielded mean mechanical strengths of 18.2 N (s.d. = 4.6) for ablated dentin and 18.1 N (s.d. = 2.7) for control (p > 0.05). Shear tests yielded mean bond strengths approaching 30 MPa for both enamel and dentin under certain irradiation conditions. These values were slightly lower than nonirradiated acid-etched control samples. Additional studies are needed to determine if the slightly lower bond strength than the acid-etched control samples is clinically significant. These measurements demonstrate that enamel and dentin surfaces can be rapidly ablated by CO(2) lasers with minimal peripheral thermal and mechanical damage and without excessive heat accumulation.

Measure of microhardness, fracture toughness and flexural strength of N-vinylcaprolactam (NVC)-containing glass-ionomer dental cements.

PubMed

Moshaverinia, Alireza; Brantley, William A; Chee, Winston W L; Rohpour, Nima; Ansari, Sahar; Zheng, Fengyuan; Heshmati, Reza H; Darr, Jawwad A; Schricker, Scott R; Rehman, Ihtesham U

2010-12-01

To investigate the effects of N-vinylcaprolactam (NVC)-containing terpolymers on the fracture toughness, microhardness, and flexural strength of conventional glass-ionomer cements (GIC). The terpolymer of acrylic acid (AA)-itaconic acid (IA)-N-vinylcaprolactam (NVC) with 8:1:1 (AA:IA:NVC) molar ratio was synthesized by free radical polymerization and characterized using (1)H NMR and FTIR. Experimental GIC samples were made from a 50% solution of the synthesized terpolymer with Fuji IX powder in a 3.6:1 P/L ratio. Specimens were mixed and fabricated at room temperature. Plane strain fracture toughness (K(Ic)) was measured in accordance with ASTM Standard 399-05. Vickers hardness was determined using a microhardness tester. Flexural strength was measured using samples with dimensions of 2 mm×2 mm×20 mm. For all mechanical property tests, specimens were first conditioned in distilled water at 37°C for 1 day or 1 week. Fracture toughness and flexural strength tests were conducted on a screw-driven universal testing machine using a crosshead speed of 0.5mm/min. Values of mechanical properties for the experimental GIC were compared with the control group (Fuji IX GIC), using one-way ANOVA and the Tukey multiple range test at α=0.05. The NVC-modified GIC exhibited significantly higher fracture toughness compared to the commercially available Fuji IX GIC, along with higher mean values of flexural strength and Vickers hardness, which were not significantly different. It was concluded that NVC-containing polymers are capable of enhancing clinically relevant properties for GICs. This new modified glass-ionomer is a promising restorative dental material. Copyright © 2010 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Determination of Strength Exercise Intensities Based on the Load-Power-Velocity Relationship

PubMed Central

Jandačka, Daniel; Beremlijski, Petr

2011-01-01

The velocity of movement and applied load affect the production of mechanical power output and subsequently the extent of the adaptation stimulus in strength exercises. We do not know of any known function describing the relationship of power and velocity and load in the bench press exercise. The objective of the study is to find a function modeling of the relationship of relative velocity, relative load and mechanical power output for the bench press exercise and to determine the intensity zones of the exercise for specifically focused strength training of soccer players. Fifteen highly trained soccer players at the start of a competition period were studied. The subjects of study performed bench presses with the load of 0, 10, 30, 50, 70 and 90% of the predetermined one repetition maximum with maximum possible speed of movement. The mean measured power and velocity for each load (kg) were used to develop a multiple linear regression function which describes the quadratic relationship between the ratio of power (W) to maximum power (W) and the ratios of the load (kg) to one repetition maximum (kg) and the velocity (m•s−1) to maximal velocity (m•s−1). The quadratic function of two variables that modeled the searched relationship explained 74% of measured values in the acceleration phase and 75% of measured values from the entire extent of the positive power movement in the lift. The optimal load for reaching maximum power output suitable for the dynamics effort strength training was 40% of one repetition maximum, while the optimal mean velocity would be 75% of maximal velocity. Moreover, four zones: maximum power, maximum velocity, velocity-power and strength-power were determined on the basis of the regression function. PMID:23486484

Determination of strength exercise intensities based on the load-power-velocity relationship.

PubMed

Jandačka, Daniel; Beremlijski, Petr

2011-06-01

The velocity of movement and applied load affect the production of mechanical power output and subsequently the extent of the adaptation stimulus in strength exercises. We do not know of any known function describing the relationship of power and velocity and load in the bench press exercise. The objective of the study is to find a function modeling of the relationship of relative velocity, relative load and mechanical power output for the bench press exercise and to determine the intensity zones of the exercise for specifically focused strength training of soccer players. Fifteen highly trained soccer players at the start of a competition period were studied. The subjects of study performed bench presses with the load of 0, 10, 30, 50, 70 and 90% of the predetermined one repetition maximum with maximum possible speed of movement. The mean measured power and velocity for each load (kg) were used to develop a multiple linear regression function which describes the quadratic relationship between the ratio of power (W) to maximum power (W) and the ratios of the load (kg) to one repetition maximum (kg) and the velocity (m•s(-1)) to maximal velocity (m•s(-1)). The quadratic function of two variables that modeled the searched relationship explained 74% of measured values in the acceleration phase and 75% of measured values from the entire extent of the positive power movement in the lift. The optimal load for reaching maximum power output suitable for the dynamics effort strength training was 40% of one repetition maximum, while the optimal mean velocity would be 75% of maximal velocity. Moreover, four zones: maximum power, maximum velocity, velocity-power and strength-power were determined on the basis of the regression function.

Matrix density effects on the mechanical properties of SiC/RBSN composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Kiser, James D.

1990-01-01

The room temperature mechanical properties were measured for SiC fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27 to 138 MPa, the average pore size of the nitrided composites decreased from 0.04 to 0.02 microns and the composite density increased from 2.07 to 2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus were approx. 15 and 50 percent higher, respectively, and ultimate tensile strength values were approx. 40 percent lower than those for unHIPed SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIPed composites appears to be related to a degradation in fiber strength at the HIP temperature. However, the density effect on matrix fracture strength was much less than would be expected based on typical monolithic Si3N4 behavior, suggesting that composite theory is indeed operating. Possible practical implications of these observations are discussed.

Matrix density effects on the mechanical properties of SiC fiber-reinforced silicon nitride matrix properties

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.; Kiser, Lames D.

1990-01-01

The room temperature mechanical properties were measured for SiC fiber reinforced reaction-bonded silicon nitride composites (SiC/RBSN) of different densities. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers (Textron SCS-6) in a reaction-bonded Si3N4 matrix. The composite density was varied by changing the consolidation pressure during RBSN processing and by hot isostatically pressing the SiC/RBSN composites. Results indicate that as the consolidation pressure was increased from 27 to 138 MPa, the average pore size of the nitrided composites decreased from 0.04 to 0.02 microns and the composite density increased from 2.07 to 2.45 gm/cc. Nonetheless, these improvements resulted in only small increases in the first matrix cracking stress, primary elastic modulus, and ultimate tensile strength values of the composites. In contrast, HIP consolidation of SiC/RBSN resulted in a fully dense material whose first matrix cracking stress and elastic modulus were approx. 15 and 50 percent higher, respectively, and ultimate tensile strength values were approx. 40 percent lower than those for unHIPed SiC/RBSN composites. The modulus behavior for all specimens can be explained by simple rule-of-mixture theory. Also, the loss in ultimate strength for the HIPed composites appears to be related to a degradation in fiber strength at the HIP temperature. However, the density effect on matrix fracture strength was much less than would be expected based on typical monolithic Si3N4 behavior, suggesting that composite theory is indeed operating. Possible practical implications of these observations are discussed.

Ultrasound transmission measurements for tensile strength evaluation of tablets.

PubMed

Simonaho, Simo-Pekka; Takala, T Aleksi; Kuosmanen, Marko; Ketolainen, Jarkko

2011-05-16

Ultrasound transmission measurements were performed to evaluate the tensile strength of tablets. Tablets consisting of one ingredient were compressed from dibasic calcium phosphate dehydrate, two grades of microcrystalline cellulose and two grades of lactose monohydrate powders. From each powder, tablets with five different tensile strengths were directly compressed. Ultrasound transmission measurements were conducted on every tablet at frequencies of 2.25 MHz, 5 MHz and 10 MHz and the speed of sound was calculated from the acquired waveforms. The tensile strength of the tablets was determined using a diametrical mechanical testing machine and compared to the calculated speed of sound values. It was found that the speed of sound increased with the tensile strength for the tested excipients. There was a good correlation between the speed of sound and tensile strength. Moreover, based on the statistical tests, the groups with different tensile strengths can be differentiated from each other by measuring the speed of sound. Thus, the ultrasound transmission measurement technique is a potentially useful method for non-destructive and fast evaluation of the tensile strength of tablets. Copyright © 2011 Elsevier B.V. All rights reserved.

The use of index tests to determine the mechanical properties of crushed aggregates from Precambrian basement complex rocks, Ado-Ekiti, SW Nigeria

NASA Astrophysics Data System (ADS)

Afolagboye, Lekan Olatayo; Talabi, Abel Ojo; Oyelami, Charles Adebayo

2017-05-01

This study assessed the possibility of using index tests to determine the mechanical properties of crushed aggregates. The aggregates used in this study were derived from major Precambrian basement rocks in Ado-Ekiti, Nigeria. Regression analyses were performed to determine the empirical relations that mechanical properties of the aggregates may have with the point load strength (IS(50)), Schmidt rebound hammer value (SHR) and unconfined compressive strength (UCS) of the rocks. For all the data, strong correlation coefficients were found between IS(50), SHR, UCS, and mechanical properties of the aggregates. The regression analysis conducted on the different rocks separately showed that correlations coefficients obtained between the IS(50), SHR, UCS and mechanical properties of the aggregates were stronger than those of the grouped rocks. The T-test and F-test showed that the derived models were valid. This study has shown that the mechanical properties of the aggregates can be estimated from IS(50), SHR and USC but the influence of rock type on the relationships should be taken into consideration.

Flexural strength and failure modes of layered ceramic structures.

PubMed

Borba, Márcia; de Araújo, Maico D; de Lima, Erick; Yoshimura, Humberto N; Cesar, Paulo F; Griggs, Jason A; Della Bona, Alvaro

2011-12-01

To evaluate the effect of the specimen design on the flexural strength (σ(f)) and failure mode of ceramic structures, testing the hypothesis that the ceramic material under tension controls the mechanical performance of the structure. Three ceramics used as framework materials for fixed partial dentures (YZ--Vita In-Ceram YZ; IZ--Vita In-Ceram Zirconia; AL--Vita In-Ceram AL) and two veneering porcelains (VM7 and VM9) were studied. Bar-shaped specimens were produced in three different designs (n=10): monolithic, two layers (porcelain-framework) and three layers (TRI) (porcelain-framework-porcelain). Specimens were tested for three-point flexural strength at 1MPa/s in 37°C artificial saliva. For bi-layered design, the specimens were tested in both conditions: with porcelain (PT) or framework ceramic (FT) layer under tension. Fracture surfaces were analyzed using stereomicroscope and scanning electron microscopy (SEM). Young's modulus (E) and Poisson's ratio (ν) were determined using ultrasonic pulse-echo method. Results were statistically analyzed by Kruskal-Wallis and Student-Newman-Keuls tests. Except for VM7 and VM9, significant differences were observed for E values among the materials. YZ showed the highest ν value followed by IZ and AL. YZ presented the highest σ(f). There was no statistical difference in the σ(f) value between IZ and IZ-FT and between AL and AL-FT. σ(f) values for YZ-PT, IZ-PT, IZ-TRI, AL-PT, AL-TRI were similar to the results obtained for VM7 and VM9. Two types of fracture mode were identified: total and partial failure. The mechanical performance of the specimens was determined by the material under tension during testing, confirming the study hypothesis. Copyright © 2011 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Functional gradients in the pericarp of the green coconut inspire asymmetric fibre-composites with improved impact strength, and preserved flexural and tensile properties.

PubMed

Graupner, Nina; Labonte, David; Humburg, Heide; Buzkan, Tayfun; Dörgens, Anna; Kelterer, Wiebke; Müssig, Jörg

2017-02-28

Here we investigate the mechanical properties and structural design of the pericarp of the green coconut (Cocos nucifera L.). The pericarp showed excellent impact characteristics, and mechanical tests of its individual components revealed gradients in stiffness, strength and elongation at break from the outer to the inner layer of the pericarp. In order to understand more about the potential effect of such gradients on 'bulk' material properties, we designed simple, graded, cellulose fibre-reinforced polylactide (PLA) composites by stacking layers reinforced with fibres of different mechanical properties. Tensile properties of the graded composites were largely determined by the 'weakest' fibre, irrespective of the fibre distribution. However, a graded design led to pronounced asymmetric bending and impact properties. Bio-inspired, asymmetrically graded composites showed a flexural strength and modulus comparable to that of the strongest reference samples, but the elongation at maximum load was dependent on the specimen orientation. The impact strength of the graded composites showed a similar orientation-dependence, and peak values exceeded the impact strength of a non-graded reference composite containing identical fibre fractions by up to a factor of three. In combination, our results show that an asymmetric, systematic variation of fibre properties can successfully combine desirable properties of different fibre types, suggesting new routes for the development of high-performance composites, and improving our understanding of the structure-function relationship of the coconut pericarp.

Stiffness of reinforced concrete walls resisting in-place shear -- Tier 2: Aging and durability of concrete used in nuclear power plants. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monteiro, P.J.M.; Moehle, J.P.

1995-12-01

Reinforced concrete walls are commonly used in power-plant construction to resist earthquake effects. Determination of wall stiffness is of particular importance for establishing design forces on attached equipment. Available experimental data indicate differences between the measured and calculated stiffness of walls in cases where concrete mechanical properties are well defined. Additional data indicate that in-situ concrete mechanical properties may differ significantly from those specified in design. The work summarized in this report was undertaken to investigate the mechanical properties of concrete considering aging and deterioration. Existing data on mechanical properties of concrete are evaluated, and new tests are carried outmore » on concrete cylinders batched for nuclear power plants and stored under controlled conditions for up to twenty years. It is concluded that concretes batched for nuclear power plants commonly have 28-day strength that exceeds the design value by at least 1000 psi. Under curing conditions representative of those in the interior of thick concrete elements, strength gain with time can be estimated conservatively using the expression proposed by ACI Committee 209, with strengths at 25 years being approximately 1.3 times the 28-day strength. Young`s modulus can be estimated using the expression given by ACI Committee 318. Variabilities in mechanical properties are identified. A review of concrete durability identified the main causes and results of concrete deterioration that are relevant for the class of concretes and structures commonly used in nuclear power plants. Prospects for identifying the occurrence and predicting the extent of deterioration are discussed.« less

Strength of single-pole utility structures

Treesearch

Ronald W. Wolfe

2006-01-01

This section presents three basic methods for deriving and documenting Rn as an LTL value along with the coefficient of variation (COVR) for single-pole structures. These include the following: 1. An empirical analysis based primarily on tests of full-sized poles. 2. A theoretical analysis of mechanics-based models used in...

Mechanical properties of natural chitosan/hydroxyapatite/magnetite nanocomposites for tissue engineering applications.

PubMed

Heidari, Fatemeh; Razavi, Mehdi; E Bahrololoom, Mohammad; Bazargan-Lari, Reza; Vashaee, Daryoosh; Kotturi, Hari; Tayebi, Lobat

2016-08-01

Chitosan (CS), hydroxyapatite (HA), and magnetite (Fe3O4) have been broadly employed for bone treatment applications. Having a hybrid biomaterial composed of the aforementioned constituents not only accumulates the useful characteristics of each component, but also provides outstanding composite properties. In the present research, mechanical properties of pure CS, CS/HA, CS/HA/magnetite, and CS/magnetite were evaluated by the measurements of bending strength, elastic modulus, compressive strength and hardness values. Moreover, the morphology of the bending fracture surfaces were characterized using a scanning electron microscope (SEM) and an image analyzer. Studies were also conducted to examine the biological response of the human Mesenchymal Stem Cells (hMSCs) on different composites. We conclude that, although all of these composites possess in-vitro biocompatibility, adding hydroxyapatite and magnetite to the chitosan matrix can noticeably enhance the mechanical properties of the pure chitosan. Copyright © 2016 Elsevier B.V. All rights reserved.

Preparation and characterization of a novel willemite bioceramic.

PubMed

Zhang, Meili; Zhai, Wanyin; Chang, Jiang

2010-04-01

Willemite (Zn(2)SiO(4)) ceramics were prepared by sintering the willemite green compacts. The effects of sintering temperature on the linear shrinkage, porosity and mechanical strength of the ceramics were examined. With the sintering temperature increased, the linear shrinkage of the ceramics increased and the porosity decreased. When sintered at 1,300 degrees C, willemite ceramics showed mechanical properties of the same order of magnitude as values for human cortical bone, as measured by bending strength (91.2 +/- 4.2 MPa) and Young's modulus (37.5 +/- 1.5 GPa). In addition, the adhesion and proliferation of rabbit bone marrow stromal cells (BMSCs) on willemite ceramics was investigated. The results showed that the ceramics supported cell adhesion and stimulated the proliferation. All these findings suggest that willemite ceramics possess suitable mechanical properties and favorable biocompatibility and might be a promising biomaterial for bone implant applications.

Hardening Potential of an Al-Cu-Li Friction Stir Weld

NASA Astrophysics Data System (ADS)

Ivanov, Rosen; Boselli, Julien; Denzer, Diana; Larouche, Daniel; Gauvin, Raynald; Brochu, Mathieu

The evolution of the microstructure during friction stir welding of a third generation AA2199 Al-Li alloy has been described and related to the mechanical properties of welds. The coupling of electron microscopy and micro-hardness have helped generate an understanding of the relationship between grain structure, precipitate density and morphology behind the observed changes in mechanical properties during post weld artificial ageing. The ability of welds to recover hardness and strength during post weld heat treatment was linked to the limited formation of large scale precipitates which act as sinks for alloying elements. Welds obtained with high tool rotation speed (within parameters studied) showed ultimate tensile strength levels of about 93% of the base metal, an elongation of 6% at fracture, and hardness values ranging between 120-140 HV in the stir zone, thermo-mechanically affected zone, and heat affected zone upon post weld heat treatment.

Spheroidization of glass powders for glass ionomer cements.

PubMed

Gu, Y W; Yap, A U J; Cheang, P; Kumar, R

2004-08-01

Commercial angular glass powders were spheroidized using both the flame spraying and inductively coupled radio frequency plasma spraying techniques. Spherical powders with different particle size distributions were obtained after spheroidization. The effects of spherical glass powders on the mechanical properties of glass ionomer cements (GICs) were investigated. Results showed that the particle size distribution of the glass powders had a significant influence on the mechanical properties of GICs. Powders with a bimodal particle size distribution ensured a high packing density of glass ionomer cements, giving relatively high mechanical properties of GICs. GICs prepared by flame-spheroidized powders showed low strength values due to the loss of fine particles during flame spraying, leading to a low packing density and few metal ions reacting with polyacrylic acid to form cross-linking. GICs prepared by the nano-sized powders showed low strength because of the low bulk density of the nano-sized powders and hence low powder/liquid ratio of GICs.

Cutting thin glass by femtosecond laser ablation

NASA Astrophysics Data System (ADS)

Shin, Hyesung; Kim, Dongsik

2018-06-01

The femtosecond laser ablation process for cutting thin aluminoborosilicate glass sheets of thickness 100 μm was investigated with emphasis on effective cutting speed (Veff) and mechanical strength of diced samples. The process parameters including the laser fluence (F), overlap ratio (r) of the laser beam and polarization direction were varied at a fixed pulse repetition rate f = 1 kHz to find the optimal process condition that maximizes Veff and edge strength. A three-point bending test was performed to evaluate the front-side and back-side bending (edge) strength of the laser-cut samples. Veff was proportional to F unless r exceeded a critical value, at which excessive energy began to be delivered at the same spot. The front-side edge strength was bigger than the back-side strength because of the back-side damages such as chipping. Good edge strength, as high as ∼280 MPa (front-side) and ∼230 MPa (back-side), was obtained at F = 19 J/m2, r = 0.99, with laser polarization vertical to the cutting path.

Modelling dental implant extraction by pullout and torque procedures.

PubMed

Rittel, D; Dorogoy, A; Shemtov-Yona, K

2017-07-01

Dental implants extraction, achieved either by applying torque or pullout force, is used to estimate the bone-implant interfacial strength. A detailed description of the mechanical and physical aspects of the extraction process in the literature is still missing. This paper presents 3D nonlinear dynamic finite element simulations of a commercial implant extraction process from the mandible bone. Emphasis is put on the typical load-displacement and torque-angle relationships for various types of cortical and trabecular bone strengths. The simulations also study of the influence of the osseointegration level on those relationships. This is done by simulating implant extraction right after insertion when interfacial frictional contact exists between the implant and bone, and long after insertion, assuming that the implant is fully bonded to the bone. The model does not include a separate representation and model of the interfacial layer for which available data is limited. The obtained relationships show that the higher the strength of the trabecular bone the higher the peak extraction force, while for application of torque, it is the cortical bone which might dictate the peak torque value. Information on the relative strength contrast of the cortical and trabecular components, as well as the progressive nature of the damage evolution, can be revealed from the obtained relations. It is shown that full osseointegration might multiply the peak and average load values by a factor 3-12 although the calculated work of extraction varies only by a factor of 1.5. From a quantitative point of view, it is suggested that, as an alternative to reporting peak load or torque values, an average value derived from the extraction work be used to better characterize the bone-implant interfacial strength. Copyright © 2017 Elsevier Ltd. All rights reserved.

Interfacial Microstructure and Mechanical Strength of 93W/Ta Diffusion-Bonded Joints with Ni Interlayer

NASA Astrophysics Data System (ADS)

Luo, Guoqiang; Zhang, Jian; Li, Meijuan; Wei, Qinqin; Shen, Qiang; Zhang, Lianmeng

2013-02-01

93W alloy and Ta metal were successfully diffusion bonded using a Ni interlayer. Ni4W was found at the W-Ni interface, and Ni3Ta and Ni2Ta were formed at the Ni-Ta interface. The shear strength of the joints increases with increasing holding time, reaching a value of 202 MPa for a joint prepared using a 90-minute holding time at 1103 K (830 °C) and 20 MPa. The fracture of this joint occurred within the Ni/Ta interface.

Variations in Crustal Structure, Lithospheric Flexural Strength, and Isostatic Compensation Mechanisms of Mars

NASA Astrophysics Data System (ADS)

Ding, M.; Lin, J.; Zuber, M. T.

2014-12-01

We analyze gravity and topography of Mars to investigate the spatial variations in crustal thickness, lithospheric strength, and mechanisms of support of prominent topographic features on Mars. The latest gravity model JGMRO110c (released in 2012) from the Mars Reconnaissance Orbiter mission has a spatial block size resolution of ~97 km (corresponding to degree-110), enabling us to resolve crustal structures at higher spatial resolution than those determined from previous degree-80 and 85 gravity models [Zuber et al., 2000; McGovern et al., 2002, 2004; Neumann et al., 2004; Belleguic et al., 2005]. Using the latest gravity data, we first inverted for a new version of crustal thickness model of Mars assuming homogeneous crust and mantle densities of 2.9 and 3.5 g/cm3. We calculated "isostatic" topography for the Airy local isostatic compensation mechanism, and "non-isostatic" topography after removing the isostatic part. We find that about 92% of the Martian surface is in relatively isostatic state, indicating either relatively small lithospheric strength and/or small vertical loading. Relatively isostatic regions include the hemispheric dichotomy, Hellas and Argyre Planitia, Noachis and Arabia Terra, and Terra Cimmeria. In contrast, regions with significant amount of non-isostatic topography include the Olympus, Ascraeus, Arsia, Pavonis, Alba, and Elysium Mons, Isidis Planitia and Valles Marineris. Their relatively large "non-isostatc topography" implies relatively strong lithospheric strength and large vertical loading. Spectral analysis of the admittance and correlation relationship between gravity and topography were conducted for the non-isostatic regions using the localized spectra method [Wieczorek and Simons, 2005, 2007] and thin-shell lithospheric flexural approximation [Forsyth, 1985; McGovern et al., 2002, 2004]. The best-fitting models reveal significant variations in the effective lithospheric thickness with the greatest values for the Olympus Mon, Valles Marineris, and Isidis Planitia; reduced values for the Ascraeus, Arsis, and Pavonis Mons; and smallest values for the Alba and Elysium Mons. Our models also suggest that there could be significant sub-surface loading underneath the Olympus, Ascraeus, Arsia, and Pavonis Mons, and Isidis Planitia.

Mechanical performance of encapsulated restorative glass-ionomer cements for use with Atraumatic Restorative Treatment (ART).

PubMed

Molina, Gustavo Fabián; Cabral, Ricardo Juan; Mazzola, Ignacio; Lascano, Laura Brain; Frencken, Jo E

2013-01-01

The Atraumatic Restorative Treatment (ART) approach was suggested to be a suitable method to treat enamel and dentine carious lesions in patients with disabilities. The use of a restorative glass-ionomer with optimal mechanical properties is, therefore, very important. To test the null-hypotheses that no difference in diametral tensile, compressive and flexural strengths exists between: (1) The EQUIA system and (2) The Chemfil Rock (encapsulated glass-ionomers; test materials) and the Fuji 9 Gold Label and the Ketac Molar Easymix (hand-mixed conventional glass-ionomers; control materials); (3) The EQUIA system and Chemfil Rock. Specimens for testing flexural (n = 240) and diametral tensile (n=80) strengths were prepared according to standardized specifications; the compressive strength (n=80) was measured using a tooth-model of a class II ART restoration. ANOVA and Tukey B tests were used to test for significant differences between dependent and independent variables. The EQUIA system and Chemfil Rock had significantly higher mean scores for all the three strength variables than the Fuji 9 Gold Label and Ketac Molar Easymix (α=0.05). The EQUIA system had significant higher mean scores for diametral tensile and flexural strengths than the Chemfil Rock (α=0.05). The two encapsulated high-viscosity glass-ionomers had significantly higher test values for diametral tensile, flexural and compressive strengths than the commonly used hand-mixed high-viscosity glass-ionomers.

Super-strong materials for temperatures exceeding 2000 °C.

PubMed

Silvestroni, Laura; Kleebe, Hans-Joachim; Fahrenholtz, William G; Watts, Jeremy

2017-01-19

Ceramics based on group IV-V transition metal borides and carbides possess melting points above 3000 °C, are ablation resistant and are, therefore, candidates for the design of components of next generation space vehicles, rocket nozzle inserts, and nose cones or leading edges for hypersonic aerospace vehicles. As such, they will have to bear high thermo-mechanical loads, which makes strength at high temperature of great importance. While testing of these materials above 2000 °C is necessary to prove their capabilities at anticipated operating temperatures, literature reports are quite limited. Reported strength values for zirconium diboride (ZrB 2 ) ceramics can exceed 1 GPa at room temperature, but these values rapidly decrease, with all previously reported strengths being less than 340 MPa at 1500 °C or above. Here, we show how the strength of ZrB 2 ceramics can be increased to more than 800 MPa at temperatures in the range of 1500-2100 °C. These exceptional strengths are due to a core-shell microstructure, which leads to in-situ toughening and sub-grain refinement at elevated temperatures. Our findings promise to open a new avenue to designing materials that are super-strong at ultra-high temperatures.

Super-strong materials for temperatures exceeding 2000 °C

NASA Astrophysics Data System (ADS)

Silvestroni, Laura; Kleebe, Hans-Joachim; Fahrenholtz, William G.; Watts, Jeremy

2017-01-01

Ceramics based on group IV-V transition metal borides and carbides possess melting points above 3000 °C, are ablation resistant and are, therefore, candidates for the design of components of next generation space vehicles, rocket nozzle inserts, and nose cones or leading edges for hypersonic aerospace vehicles. As such, they will have to bear high thermo-mechanical loads, which makes strength at high temperature of great importance. While testing of these materials above 2000 °C is necessary to prove their capabilities at anticipated operating temperatures, literature reports are quite limited. Reported strength values for zirconium diboride (ZrB2) ceramics can exceed 1 GPa at room temperature, but these values rapidly decrease, with all previously reported strengths being less than 340 MPa at 1500 °C or above. Here, we show how the strength of ZrB2 ceramics can be increased to more than 800 MPa at temperatures in the range of 1500-2100 °C. These exceptional strengths are due to a core-shell microstructure, which leads to in-situ toughening and sub-grain refinement at elevated temperatures. Our findings promise to open a new avenue to designing materials that are super-strong at ultra-high temperatures.

Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling).

PubMed

Agrawal, Amit; Hashmi, Syed W; Rao, Yogesh; Garg, Akanksha

2015-07-01

Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly.

Evolution of cooperation through adaptive interaction in a spatial prisoner's dilemma game

NASA Astrophysics Data System (ADS)

Pan, Qiuhui; Liu, Xuesong; Bao, Honglin; Su, Yu; He, Mingfeng

2018-02-01

In this paper, we study the effect of adaptive interaction on the evolution of cooperation in a spatial prisoner's dilemma game. The connections of players are co-evolutionary with cooperation; whether adjacent players can play the prisoner's dilemma game is associated with the strategies they took in the preceding round. If a player defected in the preceding round, his neighbors will refuse to play the prisoner's dilemma game with him in accordance with a certain probability distribution. We use the disconnecting strength to represent this probability. We discuss the evolution of cooperation with different values of temptation to defect, sucker's payoff and disconnecting strength. The simulation results show that cooperation can be significantly enhanced through increasing the value of the disconnecting strength. In addition, the increase in disconnecting strength can improve the cooperators' ability to resist the increase in temptation and the decrease in reward. We study the parameter ranges for three different evolutionary results: cooperators extinction, defectors extinction, cooperator and defector co-existence. Meanwhile, we recruited volunteers and designed a human behavioral experiment to verify the theoretical simulation results. The punishment of disconnection has a positive effect on cooperation. A higher disconnecting strength will enhance cooperation more significantly. Our research findings reveal some significant insights into efficient mechanisms of the evolution of cooperation.

Super-strong materials for temperatures exceeding 2000 °C

PubMed Central

Silvestroni, Laura; Kleebe, Hans-Joachim; Fahrenholtz, William G.; Watts, Jeremy

2017-01-01

Ceramics based on group IV-V transition metal borides and carbides possess melting points above 3000 °C, are ablation resistant and are, therefore, candidates for the design of components of next generation space vehicles, rocket nozzle inserts, and nose cones or leading edges for hypersonic aerospace vehicles. As such, they will have to bear high thermo-mechanical loads, which makes strength at high temperature of great importance. While testing of these materials above 2000 °C is necessary to prove their capabilities at anticipated operating temperatures, literature reports are quite limited. Reported strength values for zirconium diboride (ZrB2) ceramics can exceed 1 GPa at room temperature, but these values rapidly decrease, with all previously reported strengths being less than 340 MPa at 1500 °C or above. Here, we show how the strength of ZrB2 ceramics can be increased to more than 800 MPa at temperatures in the range of 1500–2100 °C. These exceptional strengths are due to a core-shell microstructure, which leads to in-situ toughening and sub-grain refinement at elevated temperatures. Our findings promise to open a new avenue to designing materials that are super-strong at ultra-high temperatures. PMID:28102327

Mechanical characteristics of the new BONE-LOK bi-cortical internal fixation device.

PubMed

Cachia, Victor V; Shumway, Don; Culbert, Brad; Padget, Marty

2003-01-01

The purpose of this study was to evaluate the mechanical characteristics of a new and unique titanium compression anchor with BONE-LOK (Triage Medical, Inc, Irvine, CA) technology for compressive, bi-cortical internal fixation of bone. This device provides fixation through the use of a distal grasping anchor and an adjustable proximal collar that are joined by an axially movable pin and guide wire. The titanium compression anchor, in 2.0-, 2.7-, and 3.5-mm diameters, were compared with cortex screws (Synthes USA, Paoli, PA) of the same diameter and material for pullout strength in 20 lb/cu ft and 30 lb/cu ft solid rigid polyurethane foam; and for compression strength in 20 lb/cu ft foam. Retention strength of the collar was tested independently. The results showed significantly greater pullout strength of the 2.7-mm and 3.5-mm titanium compression anchor as compared with the 2.7-mm and 3.5-mm cortex screws in these test models. Pullout strength of the 2.0-mm titanium compression anchor was not statistically different in comparison with the 2.0-mm cortical screws. Compression strength of the titanium compression anchor was significantly greater than the cortical screws for all diameters tested. These differences represent a distinct advantage with the new device, which warrants further in vivo testing. Collar retention strength testing values were obtained for reference only and have no comparative significance.

Investigation on mechanical properties of welded material under different types of welding filler (shielded metal arc welding)

NASA Astrophysics Data System (ADS)

Tahir, Abdullah Mohd; Lair, Noor Ajian Mohd; Wei, Foo Jun

2018-05-01

The Shielded Metal Arc Welding (SMAW) is (or the Stick welding) defined as a welding process, which melts and joins metals with an arc between a welding filler (electrode rod) and the workpieces. The main objective was to study the mechanical properties of welded metal under different types of welding fillers and current for SMAW. This project utilized the Design of Experiment (DOE) by adopting the Full Factorial Design. The independent variables were the types of welding filler and welding current, whereas the other welding parameters were fixed at the optimum value. The levels for types of welding filler were by the models of welding filler (E6013, E7016 and E7018) used and the levels for welding current were 80A and 90A. The responses were the mechanical properties of welded material, which include tensile strength and hardness. The experiment was analyzed using the two way ANOVA. The results prove that there are significant effects of welding filler types and current levels on the tensile strength and hardness of the welded metal. At the same time, the ANOVA results and interaction plot indicate that there are significant interactions between the welding filler types and the welding current on both the hardness and tensile strength of the welded metals, which has never been reported before. This project found that when the amount of heat input with increase, the mechanical properties such as tensile strength and hardness decrease. The optimum tensile strength for welded metal is produced by the welding filler E7016 and the optimum of hardness of welded metal is produced by the welding filler E7018 at welding current of 80A.

Polyvinyl Alcohol Microspheres Reinforced Thermoplastic Starch Composites

PubMed Central

Zha, Dongdong; Li, Bengang; Yin, Peng; Li, Panxin

2018-01-01

We reported a new method to prepare polyvinyl alcohol (PVA)/thermoplastic starch (TPS) composites by using polyvinyl alcohol microspheres (PVAMS). The PVAMS/TPS composites were characterized using tensile test, scanning electron microscopy (SEM), dynamic mechanical thermal analysis (DMTA) and thermogravimetric analysis (TGA). The results exhibited that adding small amounts of PVAMSs can effectively improve the mechanical strength and toughness of the composites, especially for the 1 wt %PVAMS in TPS matrix, with a tensile strength of 3.5 MPa, an elongation at break at 71.73% and an impact strength of 33.4 kJ/m2. Furthermore, the SEM and shift in the tan δ peak (Tα and Tβ) at the maximum value of 69.87 and −36.52 °C indicates that the PVAMS decreased the mobility of the amorphous starch molecules due to the strong intermolecular hydrogen bonds between PVAMS and TPS. The peak temperature of maximum decomposition rate (Tp) of 1 wt % PVAMS/TPS composites increased about 5 °C compared with TPS in TGA curves. PMID:29690506

Effect of doping of KDP crystal with amino acid L-arginine on the strength properties and character of laser damage

NASA Astrophysics Data System (ADS)

Dolzhenkova, E. F.; Kostenyukova, E. I.; Bezkrovnaya, O. N.; Pritula, I. M.

2017-11-01

Studied were the strength characteristics of KDP crystals doped with L-arginine under a concentrated load and irradiation of the first harmonic YAG:Nd3+ laser. The crystals were obtained by means of the temperature reduction method on a point seed, the content of L-arginine in the aqueous solution being 0.3, 0.4, 1.0 and 1.4 wt%. The character of the dependence of KDP microhardness versus the concentration of amino acid in the crystal was investigated. The regularities of brittle damage of the doped KDP crystal at mechanical testing and laser irradiation were shown to be similar. As confirmed in the study, the planes of easy crack extension in the crystal are {2 2 1}, (1 0 0), and (0 0 1) planes, the cracks mainly propagate parallel to {2 2 1} planes. The mechanical and laser strength values of doped KDP crystals were evaluated.

Cellulose Nanofibers as a Modifier for Rheology, Curing and Mechanical Performance of Oil Well Cement.

PubMed

Sun, Xiuxuan; Wu, Qinglin; Lee, Sunyoung; Qing, Yan; Wu, Yiqiang

2016-08-16

The influence of nanocellulose on oil well cement (OWC) properties is not known in detail, despite recent advances in nanocellulose technology and its related composite materials. The effect of cellulose nanofibers (CNFs) on flow, hydration, morphology, and strength of OWC was investigated using a range of spectroscopic methods coupled with rheological modelling and strength analysis. The Vom-Berg model showed the best fitting result of the rheology data. The addition of CNFs increased the yield stress of OWC slurry and degree of hydration value of hydrated CNF-OWC composites. The flexural strength of hydrated OWC samples was increased by 20.7% at the CNF/OWC ratio of 0.04 wt%. Excessive addition of CNFs into OWC matrix had a detrimental effect on the mechanical properties of hydrated CNF-OWC composites. This phenomenon was attributed to the aggregation of CNFs as observed through coupled morphological and elemental analysis. This study demonstrates a sustainable reinforcing nano-material for use in cement-based formulations.

Cellulose Nanofibers as a Modifier for Rheology, Curing and Mechanical Performance of Oil Well Cement

NASA Astrophysics Data System (ADS)

Sun, Xiuxuan; Wu, Qinglin; Lee, Sunyoung; Qing, Yan; Wu, Yiqiang

2016-08-01

The influence of nanocellulose on oil well cement (OWC) properties is not known in detail, despite recent advances in nanocellulose technology and its related composite materials. The effect of cellulose nanofibers (CNFs) on flow, hydration, morphology, and strength of OWC was investigated using a range of spectroscopic methods coupled with rheological modelling and strength analysis. The Vom-Berg model showed the best fitting result of the rheology data. The addition of CNFs increased the yield stress of OWC slurry and degree of hydration value of hydrated CNF-OWC composites. The flexural strength of hydrated OWC samples was increased by 20.7% at the CNF/OWC ratio of 0.04 wt%. Excessive addition of CNFs into OWC matrix had a detrimental effect on the mechanical properties of hydrated CNF-OWC composites. This phenomenon was attributed to the aggregation of CNFs as observed through coupled morphological and elemental analysis. This study demonstrates a sustainable reinforcing nano-material for use in cement-based formulations.

Mechanical Properties of Recycled Concrete in Marine Environment

PubMed Central

Wang, Jianxiu; Huang, Tianrong; Liu, Xiaotian; Wu, Pengcheng; Guo, Zhiying

2013-01-01

Experimental work was carried out to develop information about mechanical properties of recycled concrete (RC) in marine environment. By using the seawater and dry-wet circulation to simulate the marine environment, specimens of RC were tested with different replacement percentages of 0%, 30%, and 60% after immersing in seawater for 4, 8, 12, and 16 months, respectively. Based on the analysis of the stress-strain curves (SSCs) and compressive strength, it is revealed that RC' peak value and elastic modulus decreased with the increase of replacement percentage and corroding time in marine environment. And the failure of recycled concrete was speeded up with more obvious cracks and larger angles of 65° to 85° in the surface when compared with normal concrete. Finally, the grey model (GM) with equal time intervals was constructed to investigate the law of compressive strength of recycled concrete in marine environment, and it is found that the GM is accurate and feasible for the prediction of RC compressive strength in marine environment. PMID:23766707

Cellulose Nanofibers as a Modifier for Rheology, Curing and Mechanical Performance of Oil Well Cement

PubMed Central

Sun, Xiuxuan; Wu, Qinglin; Lee, Sunyoung; Qing, Yan; Wu, Yiqiang

2016-01-01

The influence of nanocellulose on oil well cement (OWC) properties is not known in detail, despite recent advances in nanocellulose technology and its related composite materials. The effect of cellulose nanofibers (CNFs) on flow, hydration, morphology, and strength of OWC was investigated using a range of spectroscopic methods coupled with rheological modelling and strength analysis. The Vom-Berg model showed the best fitting result of the rheology data. The addition of CNFs increased the yield stress of OWC slurry and degree of hydration value of hydrated CNF-OWC composites. The flexural strength of hydrated OWC samples was increased by 20.7% at the CNF/OWC ratio of 0.04 wt%. Excessive addition of CNFs into OWC matrix had a detrimental effect on the mechanical properties of hydrated CNF-OWC composites. This phenomenon was attributed to the aggregation of CNFs as observed through coupled morphological and elemental analysis. This study demonstrates a sustainable reinforcing nano-material for use in cement-based formulations. PMID:27526784

Excellent mechanical properties and resistance to cavitation erosion for an ultra-low carbon CrMnN stainless steel through quenching and partitioning treatment

NASA Astrophysics Data System (ADS)

Zhou, Ze-an; Fu, Wan-tang; Zhu, Zhe; Li, Bin; Shi, Zhong-ping; Sun, Shu-hua

2018-05-01

The retained austenite content (RAC), the mechanical properties, and the resistance to cavitation erosion (CE) of the 00Cr13Mn8MoN steel after quenching and partitioning (Q&P) processing were investigated. The results show that the Q&P process affected the RAC, which reached the maximum value after partitioning at 400°C for 10 min. The tensile strength of the steel slightly decreased with increasing partitioning temperature and time. However, the elongation and product of strength and elongation first increased and then decreased. The sample partitioned at 400°C for 10 min exhibited the optimal property: a strength-ductility of 23.8 GPa·%. The resistance to CE for the 00Cr13Mn8MoN steel treated by the Q&P process was improved due to work hardening, spalling, and cavitation-induced martensitic transformation of the retained austenite.

Pullout bond strength of fiber posts luted to different depths and submitted to artificial aging.

PubMed

Macedo, V C; Souza, N A Y; Faria e Silva, A L; Cotes, C; da Silva, C; Martinelli, M; Kimpara, E T

2013-01-01

The extension of fiber post cementation often does not seem to influence the fracture resistance of restorations. This study evaluated the effects of cementation depths on the retention of fiber posts submitted to artificial aging. One hundred and sixty bovine incisors were selected to assess post retention. Following endodontic treatment, the canals were flared with diamonds burs. Postholes were prepared in lengths of 5 or 10 mm, after which fiber posts were relined with composite resin and luted with RelyX ARC or RelyX Unicem. The samples were then submitted to thermal and/or mechanical cycling before testing their pullout bond strengths. Absence of cycling was used as a control. The results of each cement were submitted to two-way and post hoc Tukey tests (α=0.05). Independent of the aging protocol, a depth of 10 mm showed higher pullout bond strength than did 5 mm, except for RelyX Unicem without cycling. For RelyX ARC, thermomechanical cycling resulted in lower values than in the absence of cycling. Mechanical cycling alone promoted the highest bond strength when the posts were luted with RelyX Unicem. The effect of artificial aging on the pullout bond strength is dependent on the type of material and the depth.

Effect of pressing temperature on the mechanical properties of waste styrofoam filled sawdust composite

NASA Astrophysics Data System (ADS)

Nasution, H.; Harahap, H.; Riani, R.; Pelawi, A. I.

2018-02-01

This study has investigated the effect of pressing temperature on mechanical properties of waste styrofoam composite filled with sawdust. The waste styrofoam as the matrix was mixed with sawdust as filler and maleic anhydride (6%wt) as a compatibilizer. The weight fraction ratio between matrix and filler 70:30 (wt) and wood fiber size of 100 mesh were conducted. The pressing temperatures were investigated using a hot press with temperatures varied viz. 120, 130, 150, and 170 °C. Surface modification was applied to sawdust to diminish its polarity so that it could be compatible with the non-polar waste styrofoam matrix. Composites were evaluated using Instron and impact tester machine to investigate the tensile strength and impact strength of the material, respectively. The result indicated that tensile strength has decreased with the increase of pressing temperature where the largest tensile strength is at 130 °C of 33 MPa. The same trend has occurred on impact strength, where the value has reached of 300 J/cm2 on pressing temperature of 130 °C. From scanning electron microscopy (SEM) analysis it is also confirmed that during impact test, the resistance of the composite which has been pressed at the temperature of 130 °C have given better morphology than the composite at 170 °C.

Impact of Wetting/Oven-Drying Cycles on the Mechanical and Physical Properties of Birch Plywood

NASA Astrophysics Data System (ADS)

Sooru, M.; Kasepuu, K.; Kask, R.; Lille, H.

2015-11-01

The objective of this study was to explore some physical and mechanical properties and the dimensional stability of birch (Betula sp.) nine-ply veneers glued with phenol-formaldehyde (PF) after 10 cycles of soaking/oven-drying. The properties to be determined were bending strength (BS), modulus of elasticity in bending (MOE), Janka hardness (JH) and thickness swelling (TS), which were tested according to the European Standards (EN). An analytical equation was used for approximation of the change in the physical and mechanical properties of the samples depending on the number of cycles. It was shown that the values of the studied properties were affected most by the first soaking and drying cycles after which BS and MOE decreased continuously while the values of JH and TS stabilized. After 10 cycles the final values of BS, MOE, JH and TS accounted for 75-81%, 95%, 82% and 98.5% of the initial values, respectively.

Usage of CT data in biomechanical research

NASA Astrophysics Data System (ADS)

Safonov, Roman A.; Golyadkina, Anastasiya A.; Kirillova, Irina V.; Kossovich, Leonid Y.

2017-02-01

Object of study: The investigation is focused on development of personalized medicine. The determination of mechanical properties of bone tissues based on in vivo data was considered. Methods: CT, MRI, natural experiments on versatile test machine Instron 5944, numerical experiments using Python programs. Results: The medical diagnostics methods, which allows determination of mechanical properties of bone tissues based on in vivo data. The series of experiments to define the values of mechanical parameters of bone tissues. For one and the same sample, computed tomography (CT), magnetic resonance imaging (MRI), ultrasonic investigations and mechanical experiments on single-column test machine Instron 5944 were carried out. The computer program for comparison of CT and MRI images was created. The grayscale values in the same points of the samples were determined on both CT and MRI images. The Haunsfield grayscale values were used to determine rigidity (Young module) and tensile strength of the samples. The obtained data was compared to natural experiments results for verification.

Repairability of CAD/CAM high-density PMMA- and composite-based polymers.

PubMed

Wiegand, Annette; Stucki, Lukas; Hoffmann, Robin; Attin, Thomas; Stawarczyk, Bogna

2015-11-01

The study aimed to analyse the shear bond strength of computer-aided design and computer-aided manufacturing (CAD/CAM) polymethyl methacrylate (PMMA)- and composite-based polymer materials repaired with a conventional methacrylate-based composite after different surface pretreatments. Each 48 specimens was prepared from six different CAD/CAM polymer materials (Ambarino high-class, artBloc Temp, CAD-Temp, Lava Ultimate, Telio CAD, Everest C-Temp) and a conventional dimethacrylate-based composite (Filtek Supreme XTE, control) and aged by thermal cycling (5000 cycles, 5-55 °C). The surfaces were left untreated or were pretreated by mechanical roughening, aluminium oxide air abrasion or silica coating/silanization (each subgroup n = 12). The surfaces were further conditioned with an etch&rinse adhesive (OptiBond FL) before the repair composite (Filtek Supreme XTE) was adhered to the surface. After further thermal cycling, shear bond strength was tested, and failure modes were assessed. Shear bond strength was statistically analysed by two- and one-way ANOVAs and Weibull statistics, failure mode by chi(2) test (p ≤ 0.05). Shear bond strength was highest for silica coating/silanization > aluminium oxide air abrasion = mechanical roughening > no surface pretreatment. Independently of the repair pretreatment, highest bond strength values were observed in the control group and for the composite-based Everest C-Temp and Ambarino high-class, while PMMA-based materials (artBloc Temp, CAD-Temp and Telio CAD) presented significantly lowest values. For all materials, repair without any surface pretreatment resulted in adhesive failures only, which mostly were reduced when surface pretreatment was performed. Repair of CAD/CAM high-density polymers requires surface pretreatment prior to adhesive and composite application. However, four out of six of the tested CAD/CAM materials did not achieve the repair bond strength of a conventional dimethacrylate-based composite. Repair of PMMA- and composite-based polymers can be achieved by surface pretreatment followed by application of an adhesive and a conventional methacrylate-based composite.

Effects of strain rate and temperature on the mechanical behavior of carbon black reinforced elastomers based on butyl rubber and high molecular weight polyethylene

NASA Astrophysics Data System (ADS)

Hussein, M.

2018-06-01

The influence of the mechanical property and morphology of different blend ratio of Butyl rubber (IIR)/high molecular weight polyethylene (PE) by temperature and strain rate are performed. Special attention has been considered to a ductile-brittle transition that is known to occur at around 60 °C. The idea is to explain the unexpected phenomenon of brittleness which directly related to all tensile mechanical properties such as the strength of blends, modulus of elasticity of filled and unfilled IIR-polyethylene blends. In particular, the initial Young's modulus, tensile strength and strain at failure exhibit similar dependency on strain rate and temperature. These quantities lowered and increased with an increment of temperature, whereas the increased with increasing of strain rate. Furthermore, the tensile strength and strain at failure decreases for all temperatures range with the increase of PE content in the blend, except Young's modulus in reverse. The strain rate sensitivity index parameter of the examined polymeric materials is consistent with the micro-mechanisms of deformation and the behavior was well described by an Eyring relationship leading to an activation volume of ∼1 nm3, except for the highest value of unfilled IIR ∼8.45 nm3.

Tensile Flow Behavior of Tungsten Heavy Alloys Produced by CIPing and Gelcasting Routes

NASA Astrophysics Data System (ADS)

Panchal, Ashutosh; Ravi Kiran, U.; Nandy, T. K.; Singh, A. K.

2018-04-01

Present work describes the flow behavior of tungsten heavy alloys with nominal compositions 90W-7Ni-3Fe, 93W-4.9Ni-2.1Fe, and 95W-3.5Ni-1.5Fe (wt pct) produced by CIPing and gelcasting routes. The overall microstructural features of gelcasting are finer than those of CIPing alloys. Both the grain size of W and corresponding contiguity values increase with increase in W content in the present alloys. The volume fraction of matrix phase decreases with increase in W content in both the alloys. The lattice parameter values of the matrix phase also increase with increase in W content. The yield strength (σ YS) continuously increases with increase in W content in both the alloys. The σ YS values of CIPing alloys are marginally higher than those of gelcasting at constant W. The ultimate tensile strength (σ UTS) and elongation values are maximum at intermediate W content. Present alloys exhibit two slopes in true stress-true plastic strain curves in low and high strain regimes and follow a characteristic Ludwigson relation. The two slopes are associated with two deformation mechanisms that are occurring during tensile deformation. The overall nature of differential curves of all the alloys is different and these curves contain three distinctive stages of work hardening (I, II, and III). This suggests varying deformation mechanisms during tensile testing due to different volume fractions of constituent phases. The slip is the predominant deformation mechanism of the present alloys during tensile testing.

Tensile Flow Behavior of Tungsten Heavy Alloys Produced by CIPing and Gelcasting Routes

NASA Astrophysics Data System (ADS)

Panchal, Ashutosh; Ravi Kiran, U.; Nandy, T. K.; Singh, A. K.

2018-06-01

Present work describes the flow behavior of tungsten heavy alloys with nominal compositions 90W-7Ni-3Fe, 93W-4.9Ni-2.1Fe, and 95W-3.5Ni-1.5Fe (wt pct) produced by CIPing and gelcasting routes. The overall microstructural features of gelcasting are finer than those of CIPing alloys. Both the grain size of W and corresponding contiguity values increase with increase in W content in the present alloys. The volume fraction of matrix phase decreases with increase in W content in both the alloys. The lattice parameter values of the matrix phase also increase with increase in W content. The yield strength ( σ YS) continuously increases with increase in W content in both the alloys. The σ YS values of CIPing alloys are marginally higher than those of gelcasting at constant W. The ultimate tensile strength ( σ UTS) and elongation values are maximum at intermediate W content. Present alloys exhibit two slopes in true stress-true plastic strain curves in low and high strain regimes and follow a characteristic Ludwigson relation. The two slopes are associated with two deformation mechanisms that are occurring during tensile deformation. The overall nature of differential curves of all the alloys is different and these curves contain three distinctive stages of work hardening (I, II, and III). This suggests varying deformation mechanisms during tensile testing due to different volume fractions of constituent phases. The slip is the predominant deformation mechanism of the present alloys during tensile testing.

Strength and reversibility of stereotypes for a rotary control with linear scales.

PubMed

Chan, Alan H S; Chan, W H

2008-02-01

Using real mechanical controls, this experiment studied strength and reversibility of direction-of-motion stereotypes and response times for a rotary control with horizontal and vertical scales. Thirty-eight engineering undergraduates (34 men and 4 women) ages 23 to 47 years (M=29.8, SD=7.7) took part in the experiment voluntarily. The effects of instruction of change of pointer position and control plane on movement compatibility were analyzed with precise quantitative measures of strength and a reversibility index of stereotype. Comparisons of the strength and reversibility values of these two configurations with those of rotary control-circular display, rotary control-digital counter, four-way lever-circular display, and four-way lever-digital counter were made. The results of this study provided significant implications for the industrial design of control panels for improved human performance.

Dynamic mechanical thermal analysis of composite resins with CQ and PPD as photo-initiators photoactivated by QTH and LED units.

PubMed

Brandt, William Cunha; Silva, Cristina Gomes; Frollini, Elisabete; Souza-Junior, Eduardo Jose Carvalho; Sinhoreti, Mário Alexandre Coelho

2013-08-01

The aim of this study was to evaluate the thermal and mechanical properties of the composite resins containing the photo-initiators camphorquinone (CQ) and/or phenyl-propanodione (PPD) when photoactivated with halogen lamp (XL2500/3M-ESPE), monowave (UltraBlueIS/DMC) and polywave (UltraLume5/Ultradent) LED units. A blend of BisGMA, UDMA, BisEMA and TEGDMA was prepared with the same wt% of photo-initiators CQ and/or PPD and 65wt% of silaneted filler particles. Compression strength (CS), diametral tensile strength (DTS) and diametral modulus (DM) were tested. Thermogravimetric analysis (TGA) was made and the lost residual monomer were verified. Dynamic mechanical thermal analysis (DMTA) was used for to analyze the glass transition temperature (Tg) and the storage modulus in 37°C. Degree of conversion (DC) was accomplished in the same samples of DMA using middle-infrared spectroscopy (mid-IR). CQ, CQ/PPD and PPD obtained the same results for all mechanical properties (CS, DTS and DM), lost residual monomer and storage modulus in 37°C, regardless LCU used. The results of Tg showed that the combination PPD-UltraLume5 produced the highest values. DC showed that the combination CQ-UltraLume5 resulted in the highest values and PPD-XL2500 in the lowest DC values. The study shows that PPD is not only effective photosensitizers, but also photocrosslinking agents for dental composite resins with a similar efficiency to CQ. Copyright © 2013 Elsevier Ltd. All rights reserved.

[Evolution in muscle strength in critical patients with invasive mechanical ventilation].

PubMed

Via Clavero, G; Sanjuán Naváis, M; Menéndez Albuixech, M; Corral Ansa, L; Martínez Estalella, G; Díaz-Prieto-Huidobro, A

2013-01-01

To assess the evolution of muscle strength in critically ill patients with mechanical ventilation (MV) from withdrawal of sedatives to hospital discharge. A cohort study was conducted in two intensive care units in the Hospital Universitari de Bellvitge from November 2011 to March 2012. Consecutive patients with MV > 72h. Dependent outcome: Muscle strength measured with the Medical Research Council (MRC) scale beginning on the first day the patient was able to answer 3 out of 5 simple orders (day 1), every week, at ICU discharge and at hospital discharge or at day 60 Independent outcomes: factors associated with muscle strength loss, ventilator-free days, ICU length of stay and hospital length of stay. The patients were distributed into two groups (MRC< 48, MRC ≥ 48) after the first measurement. Thirty-four patients were assessed. Independent outcomes associated with muscle strength weakness were: days with cardiovascular SOFA >2 (P<.001) and days with costicosteroids (P<.001). Initial MRC in MRC<48 group was 38 (27-43), and 52 (50-54) in MRC ≥ 48. The largest muscle strength gain was obtained the first week (31% versus 52%). A MRC < 48 value was associated with more MV days (P<.007) and a longer ICU stay. (P<.003). The greatest muscle strength gain after withdrawing of the sedatives was achieved in the first week. Muscle strength loss was associated with a cardiovascular SOFA > 2 and costicosteroids. Patients with a MRC < 48 required more days with MV and a longer ICU stay. Copyright © 2013 Elsevier España, S.L. y SEEIUC. All rights reserved.

Heat resistance study of basalt fiber material via mechanical tests

NASA Astrophysics Data System (ADS)

Gao, Y. Q.; Jia, C.; Meng, L.; Li, X. H.

2017-12-01

This paper focuses on the study of the relationship between the fracture strength of basalt rovings and temperature. Strong stretching performance of the rovings has been tested after the treatment at fixed temperatures but different heating time and then the fracture strength of the rovings exposed to the heating at different temperatures and cooled in different modes investigated. Finally, the fracture strength of the basalt material after the heat treatment was studied. The results showed that the room-temperature strength tends to decrease with an increase of the heat treatment time at 250 °C, but it has the local maximum after 2h heating. And the basalt rovings strength increased after the heat treatment up to 200 °C. It was 16.7 percent higher than the original strength. The strength depends not only on the temperature and duration of the heating, but also on the cooling mode. The value of the strength measured after cold water cooling was less by 6.3% compared with an ambient air cooling mode. The room-temperature breaking strength of the rovings heated at 200 °C and 100 °C for 2 hours each increased by about 14.6% with respect to unpretreated basalt rovings.

Some physical and mechanical properties of recycled polyurethane foam blends

NASA Astrophysics Data System (ADS)

Bledzki, A. K.; Zicans, J.; Merijs Meri, R.; Kardasz, D.

2008-09-01

Blends of secondary rigid polyurethane foams (RPUFs) with soft polyurethane foams (SPUFs) were investigated. The effect of SPUF content and its chemical nature on some physical and mechanical properties of the blends was evaluated. Owing to the stronger intermolecular interaction and higher values of cohesion energy, the blends of RPUFs with polyester SPUFs showed higher mechanical properties than those with polyether SPUFs. The density, hardness, ultimate strength, and the tensile, shear, and flexural moduli increased, while the impact toughness, ultimate elongation, and damping characteristics decreased with increasing RPUF content in the blends.

Porous titanium materials with entangled wire structure for load-bearing biomedical applications.

PubMed

He, Guo; Liu, Ping; Tan, Qingbiao

2012-01-01

A kind of porous metal-entangled titanium wire material has been investigated in terms of the pore structure (size and distribution), the strength, the elastic modulus, and the mechanical behavior under uniaxial tensile loading. Its functions and potentials for surgical application have been explained. In particular, its advantages over competitors (e.g., conventional porous titanium) have been reviewed. In the study, a group of entangled titanium wire materials with non-woven structure were fabricated by using 12-180 MPa forming pressure, which have porosity in a range of 48%-82%. The pores in the materials are irregular in shape, which have a nearly half-normal distribution in size range. The yield strength, ultimate tensile strength, and elastic modulus are 75 MPa, 108 MPa, and 1.05 GPa, respectively, when its porosity is 44.7%. The mechanical properties decrease significantly as the porosity increases. When the porosity is 57.9%, these values become 24 MPa, 47.5 MPa, and 0.33 GPa, respectively. The low elastic modulus is due to the structural flexibility of the entangled titanium wire materials. For practical reference, a group of detailed data of the porous structure and the mechanical properties are reported. This kind of material is very promising for implant applications because of their very good toughness, perfect flexibility, high strength, adequate elastic modulus, and low cost. Copyright © 2011 Elsevier Ltd. All rights reserved.

Preparation and mechanical properties of carbon fiber reinforced hydroxyapatite/polylactide biocomposites.

PubMed

Shen, Lie; Yang, Hui; Ying, Jia; Qiao, Fei; Peng, Mao

2009-11-01

A novel biocomposite of carbon fiber (CF) reinforced hydroxyapatite (HA)/polylactide (PLA) was prepared by hot pressing a prepreg which consisting of PLA, HA and CF. The prepreg was manufactured by solvent impregnation process. Polymer resin PLA dissolved with chloroform was mixed with HA. After reinforcement CF bundle was impregnated in the mixture, the solvent was dried completely and subsequently hot-pressed uniaxially under a pressure of 40 MPa at 170 degrees C for 20 min. A study was carried out to investigate change in mechanical properties of CF/HA/PLA composites before and after degradation in vitro. The composites have excellent mechanical properties. A peak showed in flexural strength, flexural modulus and shear strength aspects, reaching up 430 MPa, 22 GPa, 212 MPa, respectively, as the HA content increased. Degraded in vitro for 3 months, the flexural strength and flexural modulus of the CF/HA/PLA fell 13.2% and 5.4%, respectively, while the shear strength of the CF/HA/PLA composites remains at the 190 MPa level. The SEM photos showed that there were gaps between the PLA matrix and CF after degradation. Water uptake increased to 5%, but the mass loss rate was only 1.6%. The pH values of the PBS dropped less than 0.1. That's because the alkaline of HA neutralize the acid degrades from PLA, which can prevent the body from the acidity harm.

[Effect of two-step sintering method on properties of zirconia ceramic].

PubMed

Huang, Hui; Wei, Bin; Zhang, Fu-Qiang; Sun, Jing; Gao, Lian

2008-04-01

To study the influence of two-step sintering method on the sintering property, mechanical properties and microstructure of zirconia ceramic. The nano-size zirconia powder were compacted and divided into two groups, one group for one-step sintering method, another group for two-step sintering method. All samples sintered at different temperature. The relative density, three-bend strength, HV hardness, fracture toughness and microstructure of sintered block were investigated. Two-step sintering method influenced the sintering property and mechanical properties of zirconia ceramic. The maximal relative density was 98.49% at 900 degrees C/1,450 degrees C sintering temperature. There were significant difference of mechanical properties between one-step sintering and two-step sintering, the three-bend strength and fracture toughness declined, hardness increased at two-step sintering. The three-bend strength, HV hardness and fracture toughness reached to maximum value as 1,059.08 MPa +/- 75.24 MPa, 1,377.00 MPa +/- 16.37 MPa and 5.92 MPa x m1/2 +/- 0.37 MPa x m1/2 at 900 degrees C/1,450 degrees C sintering temperature respectively. Microscopy revealed the relationship between the porosity and shapes of grains was correlated to strength of the zirconia ceramics. Despite of the two-step sintering method influences the properties of zirconia, it also is a promising esthetic all-ceramic dental material.

A mechanics framework for a progressive failure methodology for laminated composites

NASA Technical Reports Server (NTRS)

Harris, Charles E.; Allen, David H.; Lo, David C.

1989-01-01

A laminate strength and life prediction methodology has been postulated for laminated composites which accounts for the progressive development of microstructural damage to structural failure. A damage dependent constitutive model predicts the stress redistribution in an average sense that accompanies damage development in laminates. Each mode of microstructural damage is represented by a second-order tensor valued internal state variable which is a strain like quantity. The mechanics framework together with the global-local strategy for predicting laminate strength and life is presented in the paper. The kinematic effects of damage are represented by effective engineering moduli in the global analysis and the results of the global analysis provide the boundary conditions for the local ply level stress analysis. Damage evolution laws are based on experimental results.

Experimental and constitutive modeling approaches for a study of biomechanical properties of human coronary arteries.

PubMed

Jankowska, Malgorzata A; Bartkowiak-Jowsa, Magdalena; Bedzinski, Romuald

2015-10-01

The study concerns the determination of mechanical properties of human coronary arterial walls with both experimental and constitutive modeling approaches. The research material was harvested from 18 patients (range 50-84 years). On the basis of hospital records and visual observation, each tissue sample was classified according to the stage (0, I, II, III) of atherosclerosis development (SAD). Then, strip samples considered as a membrane with the shape of rectangular parallelepiped were preconditioned and subjected to uniaxial tensile tests in longitudinal (n=27) and circumferential (n=4) direction. With experimental data obtained, the stress-strain characteristics were prepared. Furthermore, tensile strengths and related strains, stiffness coefficients and tangent modules of elasticity were computed. For a constitutive model of passive mechanical behavior of coronary arteries, values of material parameters were computed. The studies led to the following conclusions. Most importantly, the atherosclerotic changes affect all the mechanical properties of arterial walls. A progress of arteriosclerosis contributes to an increase of vascular stiffness. The highest values of the stiffness coefficients are obtained for the tissues in the advanced stage of the disease. We were also able to observe that gradual calcification, progression of atherosclerosis and degradation of collagen in the tissue caused a decrease of tensile strengths and related strains. Finally, a comparison made for the tissues with the advanced SAD showed that the tensile strengths and strains were much higher in the case of the samples with the circumferential orientation rather than those with the longitudinal one. Copyright © 2015 Elsevier Ltd. All rights reserved.

Preparation and mechanical properties of photo-crosslinked poly(trimethylene carbonate) and nano-hydroxyapatite composites.

PubMed

Geven, Mike A; Barbieri, Davide; Yuan, Huipin; de Bruijn, Joost D; Grijpma, Dirk W

2015-01-01

Composite materials of photo-crosslinked poly(trimethylene carbonate) and nanoscale hydroxyapatite were prepared and their mechanical characteristics for application as orbital floor implants were assessed. The composites were prepared by solvent casting poly(trimethylene carbonate) macromers with varying amounts of nano-hydroxyapatite and subsequent photo-crosslinking. The incorporation of the nano-hydroxyapatite into the composites was examined by thermogravimetric analysis, scanning electron microscopy and gel content measurements. The mechanical properties were investigated by tensile testing and trouser tearing experiments. Our results show that nano-hydroxyapatite particles can readily be incorporated into photo-crosslinked poly(trimethylene carbonate) networks. Compared to the networks without nano-hydroxyapatite, incorporation of 36.3 wt.% of the apatite resulted in an increase of the E modulus, yield strength and tensile strength from 2.2 MPa to 51 MPa, 0.5 to 1.4 N/mm2 and from 1.3 to 3.9 N/mm2, respectively. We found that composites containing 12.4 wt.% nano-hydroxyapatite had the highest values of strain at break, toughness and average tear propagation strength (376% , 777 N/mm2 and 3.1 N/mm2, respectively).

Mechanical properties of niobium radio-frequency cavities

DOE PAGES

Ciovati, Gianluigi; Dhakal, Pashupati; Matalevich, Joseph R.; ...

2015-07-02

Radio-frequency cavities made of bulk niobium are one of the components used in modern particle accelerators. The mechanical stability is an important aspect of cavity design, which typically relies on finite-element analysis simulations using material properties from tensile tests on sample. This contribution presents the results of strain and resonant frequency measurements as a function of a uniform pressure up to 722 kPa, applied to single-cell niobium cavities with different crystallographic structure, purity and treatments. In addition, burst tests of high-purity multi-cell cavities with different crystallographic structure have been conducted up to the tensile strength of the material. Finite-element analysismore » of the single-cell cavity geometry is in good agreement with the observed behavior in the elastic regime assuming a Young's modulus value of 88.5 GPa and a Poisson's ratio of 0.4, regardless of crystallographic structure, purity or treatment. However, the measured yield strength and tensile strength depend on crystallographic structure, material purity and treatment. In particular, the results from this study show that the mechanical properties of niobium cavities with large crystals are comparable to those of cavities made of fine-grain niobium.« less

Novel biochar-concrete composites: Manufacturing, characterization and evaluation of the mechanical properties.

PubMed

Akhtar, Ali; Sarmah, Ajit K

2018-03-01

In this study, biochar, a carbonaceous solid material produced from three different waste sources (poultry litter, rice husk and pulp and paper mill sludge) was utilized to replace cement content up to 1% of total volume and the effect of individual biochar mixed with cement on the mechanical properties of concrete was investigated through different characterization techniques. A total of 168 samples were prepared for mechanical testing of biochar added concrete composites. The results showed that pulp and paper mill sludge biochar at 0.1% replacement of total volume resulted in compressive strength close to the control specimen than the rest of the biochar added composites. However, rice husk biochar at 0.1% slightly improved the splitting tensile strength with pulp and papermill sludge biochar produced comparable values. Biochar significantly improved the flexural strength of concrete in which poultry litter and rice husk biochar at 0.1% produced optimum results with 20% increment than control specimens. Based on the findings, we conclude that biochar has the potential to improve the concrete properties while replacing the cement in minor fractions in conventional concrete applications. Copyright © 2017 Elsevier B.V. All rights reserved.

Preparation of acetylated nanofibrillated cellulose from corn stalk microcrystalline cellulose and its reinforcing effect on starch films.

PubMed

Cheng, Li; Zhang, Dongli; Gu, Zhengbiao; Li, Zhaofeng; Hong, Yan; Li, Caiming

2018-05-01

Acetylated nanofibrillated cellulose (ANFC) with different degrees of substitution (DS) was prepared from corn-stalk microcrystalline cellulose (MCC) using chemical-mechanical combined processes. The physicochemical properties of nanofibrillated cellulose (NFC) and ANFC were investigated together with the influence of added nanoparticles on the mechanical properties of starch films. The acetylation reaction was monitored by Fourier transform infrared (FT-IR) and titration. Particle size and morphological of NFC and ANFC were studied by atomic force microscope (AFM). The results suggested that NFC had nano-order-unit web-like network with mean diameter of ~24 nm. The thermostability of all samples was found to decrease as the modification extent rose, and mechanical disposal revealed no significant influence on the DS and crystalline structure of cellulose. The ANFC with the DS value of 0.35 demonstrated the best enhancement effect on starch films, with increased tension strength (TS) by 201%. The tensile tests confirmed that the web-like network structure of NFC was more conducive to strength, and proper chemical modification could improve the uniform dispersion of nano-fillers in starch to result in higher strength performances. Copyright © 2018 Elsevier B.V. All rights reserved.

Effects of Interface Modification on Mechanical Behavior of Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Eldridge, Jeffrey I.

1997-01-01

Unidirectional celsian matrix composites having approx. 42 volume percent of uncoated or BN/SiC-coated Hi-Nicalon fibers were tested in three-point bend at room temperature. The uncoated fiber-reinforced composites showed catastrophic failure with strength of 210 +/- 35 MPa and a flat fracture surface. In contrast, composites reinforced with BN/SiC-coated fibers exhibited graceful failure with extensive fiber pullout. Values of first matrix cracking stress and strain were 435 +/- 35 MPa and 0.27 +/- 0.01 %, respectively, with ultimate strength as high as 960 MPa. The elastic Young's modulus of the uncoated and BN/SiC-coated fiber-reinforced composites were measured as 184 q 4 GPa and 165 +/- 5 GPa, respectively. Fiber push-through tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interface. The low strength of the uncoated fiber-reinforced composite is probably due to degradation of the fibers from mechanical surface damage during processing. Because both the coated and uncoated fiber reinforced composites exhibited weak interfaces, the beneficial effect of the BN-SiC dual layer is primarily the protection of fibers from mechanical damage during processing.

Influence of Fluidized Bed Quenching on the Mechanical Properties and Quality Index of T6 Tempered B319.2-Type Aluminum Alloys

NASA Astrophysics Data System (ADS)

Ragab, Kh. A.; Samuel, A. M.; Al-Ahmari, A. M. A.; Samuel, F. H.; Doty, H. W.

2013-11-01

The current study aimed to investigate the effect of fluidized sand bed (FB) quenching on the mechanical performance of B319.2 aluminum cast alloys. Traditional water and conventional hot air (CF) quenching media were used to establish a relevant comparison with FB quenching. Quality charts were generated using two models of quality indices to support the selection of material conditions on the basis of the proposed quality indices. The use of an FB for the direct quenching-aging treatment of B319.2 casting alloys yields greater UTS and YS values compared to conventional furnace quenched alloys. The strength values of T6 tempered B319 alloys are greater when quenched in water compared with those quenched in an FB or CF. For the same aging conditions (170°C/4h), the fluidized bed quenched-aged 319 alloys show nearly the same or better strength values than those quenched in water and then aged in a CF or an FB. Based on the quality charts developed for alloys subjected to different quenching media, higher quality index values are obtained by conventional furnace quenched-aged T6-tempered B319 alloys. The modification factor has the most significant effect on the quality results of the alloys investigated, for all heat treatment cycles, as compared to other metallurgical parameters. The results of alloys subjected to multi-temperature aging cycles reveal that the optimum strength properties of B319.2 alloys, however, is obtained by applying multi-temperature aging cycles such as, for example, 240 °C/2 h followed by 170 °C/8 h, rather than T6 aging treatments. The regression models indicate that the mean quality values of B319 alloys are highly quench sensitive due to the formation of a larger percent of clusters in Al-Si-Cu-Mg alloys. These clusters act as heterogeneous nucleation sites for precipitation and enhance the aging process.

Mechanical properties of resin cements with different activation modes.

PubMed

Braga, R R; Cesar, P F; Gonzaga, C C

2002-03-01

Dual-cured cements have been studied in terms of the hardness or degree of conversion achieved with different curing modes. However, little emphasis is given to the influence of the curing method on other mechanical properties. This study investigated the flexural strength, flexural modulus and hardness of four proprietary resin cements. Materials tested were: Enforce and Variolink II (light-, self- and dual-cured), RelyX ARC (self- and dual-cured) and C & B (self-cured). Specimens were fractured using a three-point bending test. Pre-failure loads corresponding to specific displacements of the cross-head were used for flexural modulus calculation. Knoop hardness (KHN) was measured on fragments obtained after the flexural test. Tests were performed after 24 h storage at 37 degrees C. RelyX ARC dual-cured showed higher flexural strength than the other groups. RelyX ARC and Variolink II depended upon photo-activation to achieve higher hardness values. Enforce showed similar hardness for dual- and self-curing modes. No correlation was found between flexural strength and hardness, indicating that other factors besides the degree of cure (e.g. filler content and monomer type) affect the flexural strength of composites. No statistical difference was detected in the flexural modulus among the different groups.

The influence of flame hardening process to aluminum 7075 series on the mechanical strength and micro structure

NASA Astrophysics Data System (ADS)

Koin, Sudibtia Titio; Triyono, Teguh; Surojo, Eko

2018-02-01

The 7075 series alloys are heat treatable wrought aluminum alloys based on the Al-Zn-Mg(-Cu) system. They are widely used in high-performance structural aerospace and transportation applications. Apart from compositional, casting and thermo-mechanical processing effects, the balance of properties is also significantly influenced by the way in which the materials are heat-treated. This paper describes the effect of flame hardening process to aluminum 7075 series on the increasing hardness, tensile strength, and evolution of microstructure. A test specimen had made by machining process and flame heating. Temperature of solution heat treatment is varied on 350 °C, 400 °C, 450 °C and 500 °C. After that process a test specimen would be quenched at nitrate-nitrite liquid during 45 minutes and artificial aging at 120°C until two days. The testing specimen consist of hardness and tensile strength according to ASTM. The result showed that specimen had precipitation on microstructure lead to an increase in aluminum properties. On the temperature 450°C solution heat treatment, the aluminum properties reached the highest value, namely, hardness of 129 HVN and tensile strength 570 MPa.

Converting non-metallic printed circuit boards waste into a value added product.

PubMed

Muniyandi, Shantha Kumari; Sohaili, Johan; Hassan, Azman; Mohamad, Siti Suhaila

2013-01-01

The aim of this study was to investigate the feasibility of using nonmetallic printed circuit board (PCB) waste as filler in recycled HDPE (rHDPE) in production of rHDPE/PCB composites. Maleic anhydride modified linear low-density polyethylene (MAPE) was used as compatibilizer. In particular, the effects of nonmetallic PCB and MAPE on mechanical properties of the composites were assessed through tensile, flexural and impact testing. Scanning electron microscope (SEM) was used to study the dispersion of nonmetallic PCB and MAPE in the matrix. Nonmetallic PCB was blended with rHDPE from 0-30 wt% and prepared by counter-rotating twin screw extruder followed by molding into test samples via hot press for analysis. A good balance between stiffness, strength and toughness was achieved for the system containing 30 wt% PCB. Thus, this system was chosen in order to investigate the effect of the compatibilizer on the mechanical properties of the composites. The results indicate that MAPE as a compatiblizer can effectively promote the interfacial adhesion between nonmetallic PCB and rHDPE. The addition of 6 phr MAPE increased the flexural strength, tensile strength and impact strength by 71%, 98% and 44% respectively compared to the uncompatibilized composites.

Converting non-metallic printed circuit boards waste into a value added product

PubMed Central

2013-01-01

The aim of this study was to investigate the feasibility of using nonmetallic printed circuit board (PCB) waste as filler in recycled HDPE (rHDPE) in production of rHDPE/PCB composites. Maleic anhydride modified linear low-density polyethylene (MAPE) was used as compatibilizer. In particular, the effects of nonmetallic PCB and MAPE on mechanical properties of the composites were assessed through tensile, flexural and impact testing. Scanning electron microscope (SEM) was used to study the dispersion of nonmetallic PCB and MAPE in the matrix. Nonmetallic PCB was blended with rHDPE from 0–30 wt% and prepared by counter-rotating twin screw extruder followed by molding into test samples via hot press for analysis. A good balance between stiffness, strength and toughness was achieved for the system containing 30 wt% PCB. Thus, this system was chosen in order to investigate the effect of the compatibilizer on the mechanical properties of the composites. The results indicate that MAPE as a compatiblizer can effectively promote the interfacial adhesion between nonmetallic PCB and rHDPE. The addition of 6 phr MAPE increased the flexural strength, tensile strength and impact strength by 71%, 98% and 44% respectively compared to the uncompatibilized composites. PMID:24764542

Mechanical Properties of Fe-Ni Meteorites

NASA Astrophysics Data System (ADS)

Roberta, Mulford; El Dasher, B.

2010-10-01

Iron-nickel meteorites exhibit a unique lamellar microstructure, Widmanstatten patterns, consisting of small regions with steep-iron-nickel composition gradients.1,2 The microstructure arises as a result of extremely slow cooling in a planetary core or other large mass. Mechanical properties of these structures have been investigated using microindentation, x-ray fluorescence, and EBSD. Observation of local mechanical properties in these highly structured materials supplements bulk measurements, which can exhibit large variation in dynamic properties, even within a single sample. 3 Accurate mechanical properties for meteorites may enable better modeling of planetary cores, the likely origin of these objects. Appropriate values for strength are important in impact and crater modeling and in understanding the consequences of observed impacts on planetary crusts. Previous studies of the mechanical properties of a typical iron-nickel meteorite, a Diablo Canyon specimen, indicated that the strength of the composite was higher by almost an order of magnitude than values obtained from laboratory-prepared specimens.4 This was ascribed to the extreme work-hardening evident in the EBSD measurements. This particular specimen exhibited only residual Widmanstatten structures, and may have been heated and deformed during its traverse of the atmosphere. Additional specimens from the Canyon Diablo fall (type IAB, coarse octahedrite) and examples from the Muonionalusta meteorite and Gibeon fall ( both IVA, fine octahedrite), have been examined to establish a range of error on the previously measured yield, to determine the extent to which deformation upon re-entry contributes to yield, and to establish the degree to which the strength varies as a function of microstructure. 1. A. Christiansen, et.al., Physica Scripta, 29 94-96 (1984.) 2. Goldstein and Ogilvie, Geochim Cosmochim Acta, 29 893-925 (1965.) 3. M. D. Furnish, M.B. Boslough, G.T. Gray II, and J.L. Remo, Int. J. Impact Eng, 17 341-352 (1995.) 4. J.J. Petrovic, J. Mater. Sci., 36 1579-1583 (2001.)

Investigations on structural, optical, electrical, mechanical and third-order nonlinear behaviour of 3-aminopyridinium 2,4-dinitrophenolate single crystal

NASA Astrophysics Data System (ADS)

Mohanbabu, B.; Bharathikannan, R.; Siva, G.

2017-10-01

The single crystals of 3-aminopyridinium 2,4-dinitrophenolate (APDP) have been synthesized and grown by slow evaporation technique at room temperature. The crystal system was identified and lattice dimensions were measured from the single-crystal X-ray diffraction (SXRD) analysis. UV-visible absorption and transmittance spectra have been recorded in the region between 250 and 1100 nm. The different vibrational modes of the molecule were studied by Fourier transform infrared (FTIR) spectroscopic analysis. The decreasing tendency of dielectric constant with increasing frequency was analysed in dielectric study. The polarizability value calculated using Penn analysis well agrees with the value calculated using Clausius-Mossotti equation. The photoconductivity and photoluminescence behaviour were also studied on grown APDP crystal. The mechanical strength of the crystal has been studied using a Vickers' microhardness test. The stiffness constant and yield strength of the crystal were also calculated from the microhardness test. The third-order nonlinear optical parameters such as refractive index, absorption coefficient and third-order susceptibility were estimated by Z-scan studies.

Attenuation of dopamine-modulated prefrontal value signals underlies probabilistic reward learning deficits in old age

PubMed Central

Axelsson, Jan; Riklund, Katrine; Nyberg, Lars; Dayan, Peter; Bäckman, Lars

2017-01-01

Probabilistic reward learning is characterised by individual differences that become acute in aging. This may be due to age-related dopamine (DA) decline affecting neural processing in striatum, prefrontal cortex, or both. We examined this by administering a probabilistic reward learning task to younger and older adults, and combining computational modelling of behaviour, fMRI and PET measurements of DA D1 availability. We found that anticipatory value signals in ventromedial prefrontal cortex (vmPFC) were attenuated in older adults. The strength of this signal predicted performance beyond age and was modulated by D1 availability in nucleus accumbens. These results uncover that a value-anticipation mechanism in vmPFC declines in aging, and that this mechanism is associated with DA D1 receptor availability. PMID:28870286

Reference Values of Grip Strength, Prevalence of Low Grip Strength, and Factors Affecting Grip Strength Values in Chinese Adults.

PubMed

Yu, Ruby; Ong, Sherlin; Cheung, Osbert; Leung, Jason; Woo, Jean

2017-06-01

The objectives of this study were to update the reference values of grip strength, to estimate the prevalence of low grip strength, and to examine the impact of different aspects of measurement protocol on grip strength values in Chinese adults. A cross-sectional survey of Chinese men (n = 714) and women (n = 4014) aged 18-102 years was undertaken in different community settings in Hong Kong. Grip strength was measured with a digital dynamometer (TKK 5401 Grip-D; Takei, Niigata, Japan). Low grip strength was defined as grip strength 2 standard deviations or more below the mean for young adults. The effects of measurement protocol on grip strength values were examined in a subsample of 45 men and women with repeated measures of grip strength taken with a hydraulic dynamometer (Baseline; Fabrication Enterprises Inc, Irvington, NY), using pair t-tests, intraclass correlation coefficient, and Bland and Altman plots. Grip strength was greater among men than among women (P < .001) and the rate of decline differed between sexes (P < .001). The prevalence of low grip strength also increased with age, reaching a rate of 16.5% in men and 20.6% in women aged 65+. Although the TKK digital dynamometer gave higher grip strength values than the Baseline hydraulic dynamometer (P < .001), the degree of agreement between the 2 dynamometers was satisfactory. Higher grip strength values were also observed when the measurement was performed with the elbow extended in a standing position, compared with that with the elbow flexed at 90° in a sitting position, using the same dynamometer (P < .05). This study updated the reference values of grip strength and estimated the prevalence of low grip strength among Chinese adults spanning a wide age range. These findings might be useful for risk estimation and evaluation of interventions. However, grip strength measurements should be interpreted with caution, as grip strength values can be affected by type of dynamometer used, assessment posture, and elbow position. Copyright © 2017 AMDA – The Society for Post-Acute and Long-Term Care Medicine. Published by Elsevier Inc. All rights reserved.

The effect of porosity and microcracking on the thermomechanical properties of cordierite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shyam, A.; Bruno, G.; Watkins, T. R.

2015-08-28

The effect of porosity and microcracking on the mechanical properties (strength, fracture toughness, Young’s modulus, and fracture energy) and thermal expansion of diesel particulate filter (DPF) grade cordierite materials has been investigated. A method to deconvolute the effect of porosity and microcracking on Young’s modulus is proposed. In addition, the microcrack density and the pore morphology factor are calculated by applying a micromechanical differential scheme. The values of the investigated mechanical properties are shown to decrease with an increase in porosity, but the thermal expansion values are insensitive to porosity. The variation in mechanical properties as a function of porositymore » leads to distinct porosity dependence of thermal shock resistance for crack initiation and crack propagation for DPF grade synthetic cordierite.« less

The Role of Glottal Surface Adhesion on Vocal Folds Biomechanics

PubMed Central

Bhattacharya, Pinaki; Siegmund, Thomas

2014-01-01

The airway surface liquid (ASL) is a very thin mucus layer and covers the vocal fold (VF) surface. Adhesion mediated by the ASL occurs during phonation as the VFs separate after collision. Such adhesion is hypothesized to determine voice quality and health. However, biomechanical insights into the adhesive processes during VF oscillation are lacking. Here, a computational study is reported on self-sustained VF vibration involving contact and adhesion. The VF structural model and the glottal airflow are considered fully three-dimensional. The mechanical behavior of the ASL is described through a constitutive traction–separation law where mucosal cohesive strength, cohesive energy and rupture length enter. Cohesive energy values considered are bound below by the cohesive energy of water at standard temperature and pressure. Cohesive strength values considered are bound above by prior reported data on the adhesive strength of mucosal surface of rat small intestine. This model introduces a mechanical length scale into the analysis. The sensitivity of various aspects of VF dynamics such as flow-declination rate, VF separation under adhesive condition and formation of multiple local fluid bridges is determined in relation to specific ASL adhesive properties. It is found that for the ASL considered here, the characteristics of the VF separation process are of debond type. Instabilities lead to the breakup of the bond area into several smaller bond patches. Such finding is consistent with in-vivo observations. PMID:25034504

Micro-mechanics of hydro-mechanical coupled processes during hydraulic fracturing in sandstone

NASA Astrophysics Data System (ADS)

Caulk, R.; Tomac, I.

2017-12-01

This contribution presents micro-mechanical study of hydraulic fracture initiation and propagation in sandstone. The Discrete Element Method (DEM) Yade software is used as a tool to model fully coupled hydro-mechanical behavior of the saturated sandstone under pressures typical for deep geo-reservoirs. Heterogeneity of sandstone strength tensile and shear parameters are introduced using statistical representation of cathodoluminiscence (CL) sandstone rock images. Weibull distribution of statistical parameter values was determined as a best match of the CL scans of sandstone grains and cement between grains. Results of hydraulic fracturing stimulation from the well bore indicate significant difference between models with the bond strengths informed from CL scans and uniform homogeneous representation of sandstone parameters. Micro-mechanical insight reveals formed hydraulic fracture typical for mode I or tensile cracking in both cases. However, the shear micro-cracks are abundant in the CL informed model while they are absent in the standard model with uniform strength distribution. Most of the mode II cracks, or shear micro-cracks, are not part of the main hydraulic fracture and occur in the near-tip and near-fracture areas. The position and occurrence of the shear micro-cracks is characterized as secondary effect which dissipates the hydraulic fracturing energy. Additionally, the shear micro-crack locations qualitatively resemble acoustic emission cloud of shear cracks frequently observed in hydraulic fracturing, and sometimes interpreted as re-activation of existing fractures. Clearly, our model does not contain pre-existing cracks and has continuous nature prior to fracturing. This observation is novel and interesting and is quantified in the paper. The shear particle contact forces field reveals significant relaxation compared to the model with uniform strength distribution.

The effect of pore size and porosity on mechanical properties and biological response of porous titanium scaffolds.

PubMed

Torres-Sanchez, C; Al Mushref, F R A; Norrito, M; Yendall, K; Liu, Y; Conway, P P

2017-08-01

The effect of pore size and porosity on elastic modulus, strength, cell attachment and cell proliferation was studied for Ti porous scaffolds manufactured via powder metallurgy and sintering. Porous scaffolds were prepared in two ranges of porosities so that their mechanical properties could mimic those of cortical and trabecular bone respectively. Space-holder engineered pore size distributions were carefully determined to study the impact that small changes in pore size may have on mechanical and biological behaviour. The Young's moduli and compressive strengths were correlated with the relative porosity. Linear, power and exponential regressions were studied to confirm the predictability in the characterisation of the manufactured scaffolds and therefore establish them as a design tool for customisation of devices to suit patients' needs. The correlations were stronger for the linear and the power law regressions and poor for the exponential regressions. The optimal pore microarchitecture (i.e. pore size and porosity) for scaffolds to be used in bone grafting for cortical bone was set to <212μm with volumetric porosity values of 27-37%, and for trabecular tissues to 300-500μm with volumetric porosity values of 54-58%. The pore size range 212-300μm with volumetric porosity values of 38-56% was reported as the least favourable to cell proliferation in the longitudinal study of 12days of incubation. Copyright © 2017 Elsevier B.V. All rights reserved.

Composite materials for space applications

NASA Technical Reports Server (NTRS)

Rawal, Suraj P.; Misra, Mohan S.; Wendt, Robert G.

1990-01-01

The objectives of the program were to: generate mechanical, thermal, and physical property test data for as-fabricated advanced materials; design and fabricate an accelerated thermal cycling chamber; and determine the effect of thermal cycling on thermomechanical properties and dimensional stability of composites. In the current program, extensive mechanical and thermophysical property tests of various organic matrix, metal matrix, glass matrix, and carbon-carbon composites were conducted, and a reliable database was constructed for spacecraft material selection. Material property results for the majority of the as-fabricated composites were consistent with the predicted values, providing a measure of consolidation integrity attained during fabrication. To determine the effect of thermal cycling on mechanical properties, microcracking, and thermal expansion behavior, approximately 500 composite specimens were exposed to 10,000 cycles between -150 and +150 F. These specimens were placed in a large (18 cu ft work space) thermal cycling chamber that was specially designed and fabricated to simulate one year low earth orbital (LEO) thermal cycling in 20 days. With this rate of thermal cycling, this is the largest thermal cycling unit in the country. Material property measurements of the thermal cycled organic matrix composite laminate specimens exhibited less than 24 percent decrease in strength, whereas, the remaining materials exhibited less than 8 percent decrease in strength. The thermal expansion response of each of the thermal cycled specimens revealed significant reduction in hysteresis and residual strain, and the average CTE values were close to the predicted values.

Evaluation of five CAD/CAM materials by microstructural characterization and mechanical tests: a comparative in vitro study.

PubMed

Sonmez, Nesrin; Gultekin, Pinar; Turp, Volkan; Akgungor, Gokhan; Sen, Deniz; Mijiritsky, Eitan

2018-01-08

Polymer infiltrated ceramics and nano-ceramic resins are the new restorative materials which have been developed in order to enhance the adverse properties of glass-matrix ceramics and resin composites. The aim of the present in vitro study was to evaluate the characteristics of various CAD/CAM materials through mechanical, microstructural, and SEM analysis. Five test groups (n = 22) were formed by using the indicated CAD/CAM blocks: VITA Enamic (VITA Zahnfabrik), Lava Ultimate (3 M ESPE), IPS e.max CAD (Ivoclar Vivadent), IPS Empress CAD (Ivoclar Vivadent), and VITA Mark II (VITA Zahnfabrik). Two specimens from each test group were used for XRD and EDS analysis. Remaining samples were divided into two subgroups (n = 10). One subgroup specimens were thermocycled (5 °C to 55 °C, 30s, 10,000 cycles) whereas the other were not. All of the specimens were evaluated in terms of flexural strength, Vickers hardness, and fracture toughness. Results were statistically analyzed using two-way ANOVA, one-way ANOVA, Tukey's HSD, and Student's t tests (α = .05). Fractured specimens were evaluated using SEM. The highest Vickers microhardness value was found for VITA Mark II (p < .001), however flexural strength and fracture toughness results were lowest conversely (p < .05). IPS e.max CAD was found to have the highest flexural strength (p < .001). Fracture toughness of IPS e.max CAD was also higher than other tested block materials (p < .001). Lava Ultimate and VITA Enamic's mechanical properties were affected negatively from thermocycling (p < .05). Microhardness, flexural strength, and fracture toughness values of Lava Ultimate and VITA Enamic were found to be similar to VITA Mark II and IPS Empress CAD groups. It should be realised that simulated aging process seem to affect ceramic-polymer composite materials more significantly than glass ceramics.

A castor oil-containing dental luting agent: effects of cyclic loading and storage time on flexural strength

PubMed Central

DERCELI, Juliana dos Reis; FAIS, Laiza Maria Grassi; PINELLI, Lígia Antunes Pereira

2014-01-01

Favorable results in the use of castor oil polyurethane (COP) as pulp capping, membrane material, sealer, mouthwash and in bone repair, associated with the fact that Ricinus communis is not derived from petroleum and it is abundant in Brazil, encourage researches in the development of luting agents. Objectives This study compared the flexural strength (FS) of a castor oil-containing dental luting agent with a weight percentage of 10% (wt%) of calcium carbonate (COP10) with RelyX ARC (RX) after mechanical cycling (MC) and distilled water storage. Material and Methods Sixty-four specimens (25x2x2 mm) were fabricated and divided into two groups, COP10 and RX (control). Each group was divided into 4 subgroups (n=8) according to the storage time, 24 hours (24 h) or 60 days (60 d), and the performance (MC+FS) or not (only FS) of the mechanical cycling test. The FS (10 kN; 0.5 mm/min) and MC tests (10,000 cycles, 5 Hz, 0.5 mm/min) were carried out using an MTS-810 machine. The data were analyzed using ANOVA (α=0.05). Results The obtained FS (MPa) values were: COP10 24h- 19.04±2.41; COP10 60d- 17.92±3.54; RX 24h- 75.19±3.43; RX 60d- 88.77±6.89. All the RX specimens submitted to MC fractured, while the values for COP10 after MC were as follows: COP10 24h- 17.90±1.87 and COP10 60d- 18.60±1.60. Conclusions A castor oil-containing dental luting agent with a weight percentage of 10% (wt%) of calcium carbonate is resistant to mechanical cycling without decreases in flexural strength. However, mean COP10 showed only about 25% of the RelyX ARC mean flexural strength. PMID:25591018

[Effect of three kinds of rare earth oxides on chromaticity and mechanical properties of zirconia ceramic].

PubMed

Huang, Hui; Zhang, Fu-qiang; Sun, Jing; Gao, Lian

2006-06-01

To evaluate the colouration of zirconia ceramic by adding three kinds of rare earth oxides. The influence of the pigments concentration on the mechanical properties and the microstructure was also analyzed. Added different concentrations of CeO(2), Er(2)O(3) and Pr(6)O(11) in tetragonal zirconia poly crystals stabilized with 3 mol% yttria (3Y-T2P) powder, compacted at 200 MPa using cold isostatic pressure, and sintered to 1 400 degrees C. The heating rate was 150 degrees C/h and the dwelling time was 2 hours. The chromaticity of sintered bodies was measured with chroma meter. The relative density, hardness, flexure strength and fracture toughness were investigated as well. The phase stability of the colorized and pure zirconia was evaluated by X-ray diffraction (XRD) using an automated diffractometer. The microstructures of the specimens were evaluated by scanning electron microscope (SEM). Several kinds of color achieved by the different pigments praseodym oxide, cerium oxide and erbium oxide were presented in the CIELab system. The a* value increased with the added amount of Er(2)O(3), while b* value rose with the increasing amount of CeO(2) and Pr(6)O(11). However, three pigments failed to decrease L* value and the sintered body appeared too bright. Adding three pigments influenced flexure strength of zirconia ceramic significantly, but had little influence on the hardness and fracture toughness. Microscopy revealed the relationship between the porosity and shapes of grains was correlated to strength of the diphase ceramics. No additional phase could be detected by XRD, except t-ZrO(2) in all colorized samples after sintering at 1 400 degrees C for 120 min. Zirconia ceramic can be colorized by CeO(2), Er(2)O(3), and Pr(6)O(11). Pigments even in a small amount influence the mechanical properties of the colorized zirconia material, which necessitates further investigation.

Confined compressive strength analysis can improve PDC bit selection. [Polycrystalline Diamond Compact

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fabain, R.T.

1994-05-16

A rock strength analysis program, through intensive log analysis, can quantify rock hardness in terms of confined compressive strength to identify intervals suited for drilling with polycrystalline diamond compact (PDC) bits. Additionally, knowing the confined compressive strength helps determine the optimum PDC bit for the intervals. Computing rock strength as confined compressive strength can more accurately characterize a rock's actual hardness downhole than other methods. the information can be used to improve bit selections and to help adjust drilling parameters to reduce drilling costs. Empirical data compiled from numerous field strength analyses have provided a guide to selecting PDC drillmore » bits. A computer analysis program has been developed to aid in PDC bit selection. The program more accurately defines rock hardness in terms of confined strength, which approximates the in situ rock hardness downhole. Unconfined compressive strength is rock hardness at atmospheric pressure. The program uses sonic and gamma ray logs as well as numerous input data from mud logs. Within the range of lithologies for which the program is valid, rock hardness can be determine with improved accuracy. The program's output is typically graphed in a log format displaying raw data traces from well logs, computer-interpreted lithology, the calculated values of confined compressive strength, and various optional rock mechanic outputs.« less

The modelling influence of water content to mechanical parameter of soil in analysis of slope stability

NASA Astrophysics Data System (ADS)

Gusman, M.; Nazki, A.; Putra, R. R.

2018-04-01

One of the parameters in slope stability analysis is the shear strength of the soil. Changes in soil shear strength characteristics lead to a decrease in safety factors on the slopes. This study aims to see the effect of increased moisture content on soil mechanical parameters. The case study study was conducted on the slopes of Sitinjau Lauik Kota Padang. The research method was done by laboratory analysis and simple liniear regression analysis and multiple. Based on the test soil results show that the increase in soil water content causes a decrease in cohesion values and internal shear angle. The relationship of moisture content to cohesion is described in equation Y = 55.713-0,6X with R2 = 0.842. While the relationship of water content to shear angle in soil is described in the equation Y = 38.878-0.258X with R2 = 0.915. From several simulations of soil water level improvement, calculation of safety factor (SF) of slope. The calculation results show that the increase of groundwater content is very significant affect the safety factor (SF) slope. SF slope values are in safe condition when moisture content is 50% and when it reaches maximum water content 73.74% slope safety factor value potentially for landslide.

Characterization of new biodegradable edible film made from basil seed (Ocimum basilicum L.) gum.

PubMed

Khazaei, Naimeh; Esmaiili, Mohsen; Djomeh, Zahra Emam; Ghasemlou, Mehran; Jouki, Mohammad

2014-02-15

It is well known that the market for edible films is experiencing remarkable growth and expected to continue. This study investigated the using of basil seed gum (BSG) as a new film-forming material under the influence of addition of glycerol (GLY) as plasticizer. Edible films based on BSG and three different concentrations of GLY (25%, 35%, and 50% w/w BSG) were developed, and their water vapor permeability (WVP), as well as physical, thermal and mechanical properties were measured. The addition of glycerol significantly increased water vapor permeability and solubility of the film (p<0.05). As expected, the increase in GLY concentration from 25% to 50% (w/w) increased the extensibility, but decreased tensile strength. This suggests weaker mechanical strength and higher mobility of polymer chains by plasticizing effect of GLY. The color measurement values showed that increasing the glycerol concentration in polymer matrix caused the b and L values increased while ΔE value decreased. The electron scanning micrograph showed plasticized films as smooth, and uniform which lacked pores or cracks compared with those were not plasticized. This study revealed that the BSG had a good potential to be used in producing edible films for various food applications. Copyright © 2013 Elsevier Ltd. All rights reserved.

Structure, texture, and mechanical properties of an MA2-1hp magnesium alloy after two-stage equal-channel angular pressing and intermediate annealing

NASA Astrophysics Data System (ADS)

Serebryany, V. N.; Perezhogin, V. Yu.; Raab, G. I.; Kopylov, V. I.; Tabachkova, N. Yu.; Sirotinkin, V. P.; Dobatkin, S. V.

2015-01-01

The effect of two-stage equal-channel angular pressing (ECAP) on the microstructure, the texture, and the mechanical properties of an MA2-1hp magnesium alloy is analyzed. ECAP leads to the formation of a submicrocrystalline structure with an average grain size of 640 nm, which includes Mg17Al12 phase particles with an average grain size of 240 nm and a volume fracture of 5.5%. A scattered tilted basal texture forms after ECAP, and its experimental pole figures are used for calculating orientation distribution functions and determining the volume fractions of the main orientations and the Schmid factors for different deformation systems. An increased activation of basal slip is found after both the first and the second stages of ECAP. As a result of two-stage ECAP, the strength properties of the alloy that correspond to the minimum acceptable values achieved by direct compression are obtained. Ductility is 44 and 18% after the first stage of ECAP plus subsequent annealing and after the second stage, respectively, which is almost four and two times higher than the initial value. The resulting strength mechanical properties of the alloy after the first and the second ECAP stages are analyzed using the Hall-Petch relation.

An investigation of the effect of migratory type corrosion inhibitor on mechanical properties of zeolite-based novel geopolymers

NASA Astrophysics Data System (ADS)

Auqui, Nestor Ulloa; Baykara, Haci; Rigail, Andres; Cornejo, Mauricio H.; Villalba, Jose Luis

2017-10-01

The effects of migratory type corrosion inhibitor and curing time on the thermal stability and mechanical properties of Ecuadorian natural zeolite-based geopolymers were evaluated. Geopolymer samples were prepared by alkali activation of the natural zeolite by 8 M NaOH solution and calcium hydroxide Ca(OH)2 1-3 wt%, with an activator/binder ratio of 0.6. The geopolymer samples cured for 24 h at 40 °C and then for 6 days more at room temperature showed the compressive strength values in a range of 3-5,5 MPa. Mineralogical analysis of natural zeolite obtained by XRD is as follows: Mordenite (∼67%), quartz (∼27%) and amorphous (∼6%). SEM-EDS micrographs analysis of geopolymers revealed the presence of Na and Ca which proves the incorporation of the activators, NaOH and Ca(OH)2. The compressive strength values obtained indicate that the use of alkali activation of natural zeolites is an effective method for the synthesis of geopolymers. The mechanical properties of geopolymers were slightly but not adversely affected by the addition of the migratory corrosion inhibitor, MCI-2005 NS. These results will be used in future research on geopolymer concrete with embedded reinforcing steel.

Influence of lactose addition to gentamicin-loaded acrylic bone cement on the kinetics of release of the antibiotic and the cement properties.

PubMed

Frutos, Gloria; Pastor, José Ygnacio; Martínez, Noelia; Virto, María Rosa; Torrado, Susana

2010-03-01

The purpose of this study was to characterize a poly(methyl methacrylate) bone cement that was loaded with the antibiotic gentamicin sulphate (GS) and lactose, which served to modulate the release of GS from cement specimens. The release of GS when the cement specimens were immersed in phosphate-buffered saline at 37 degrees Celsius was determined spectrophotometrically. The microstructure, porosity, density, tensile properties and flexural properties of the cements were determined before and after release of GS. A kinetics model of the release of GS from the cement that involved a coupled mechanism based on dissolution/diffusion processes and an initial burst effect was proposed. Dissolution assay results showed that drug elution was controlled by a diffusion mechanism which can be modulated by lactose addition. Density values and mechanical properties (tensile strength, flexural strength, elastic modulus and fracture toughness) were reduced by the increased porosity resulting from lactose addition, but maintained acceptable values for the structural functions of bone cement. The present results suggest that lactose-modified, gentamicin-loaded acrylic bone cements are potential candidates for use in various orthopaedic and dental applications. Copyright 2009 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Synthesis and mechanical behavior of β-tricalcium phosphate/titania composites addressed to regeneration of long bone segments.

PubMed

Sprio, Simone; Guicciardi, Stefano; Dapporto, Massimiliano; Melandri, Cesare; Tampieri, Anna

2013-01-01

Bioactive tricalcium phosphate/titania ceramic composites were synthesized by pressureless air sintering of mixed hydroxyapatite and titania (TiO2) powders. The sintering process was optimized to achieve dense ceramic bodies consisting in a bioactive/bioresorbable matrix (β-tricalcium phosphate) reinforced with defined amounts of sub-micron sized titania particles. Extensive chemico-physical and mechanical characterization was carried out on the resulting composites, which displayed values of flexural strength, fracture toughness and elastic modulus in the range or above the typical ranges of values manifested by human cortical bone. It was shown that titania particles provided a toughening effect to the calcium-phosphate matrix and a reinforcement in fracture strength, in comparison with sintered hydroxyapatite bodies characterized by similar relative density. The characteristics of the resulting composites, i.e. bioactivity/bioresorbability and ability of manifesting biomimetic mechanical behavior, are features that can promote processes of bone regeneration in load-bearing sites. Hence, in the perspective of developing porous bone scaffolds with high bioactivity and improved biomechanical behavior, TCP/TiO2 composites with controlled composition can be considered as very promising biomaterials for application in a field of orthopedics where no acceptable clinical solutions still exist. Copyright © 2012 Elsevier Ltd. All rights reserved.

Image analysis software as a strategy to improve the radiographic determination of fracture healing.

PubMed

Duryea, Jeffrey; Evans, Christopher; Glatt, Vaida

2018-05-28

To develop and validate an unbiased, accurate, convenient and inexpensive means of determining when an osseous defect has healed and recovered sufficient strength to allow weight-bearing. A novel image processing software algorithm was created to analyze the radiographic images and produce a metric designed to reflect the bone strength. We used a rat femoral segmental defect model that provides a range of healing responses from complete union to non-union. Femora were examined by X-ray, micro-computed tomography (µCT) and mechanical testing. Accurate simulated radiographic images at different incident X-ray beam angles were produced from the µCT data files. The software-generated metric (SC) showed high levels of correlation with both the mechanical strength (τMech) and the polar moment of inertia (pMOI), with the mechanical testing data having the highest association. The optimization analysis yielded optimal oblique angles θB of 125° for τMech and 50° for pMOI. The Pearson's R values for the optimized model were 0.71 and 0.64 for τMech and pMOI, respectively. Further validation using true radiographs also demonstrated that the metric was accurate, and that the simulations were realistic. The preliminary findings suggest a very promising methodology to assess bone fracture healing using conventional radiography. With radiographs acquired at appropriate incident angles, it proved possible to calculate accurately the degree of healing and the mechanical strength of the bone. Further research is necessary to refine this approach and determine whether it translates to the human clinical setting.

Steady-state mechanical squeezing and ground-state cooling of a Duffing anharmonic oscillator in an optomechanical cavity assisted by a nonlinear medium

NASA Astrophysics Data System (ADS)

Momeni, F.; Naderi, M. H.

2018-05-01

In this paper, we study theoretically a hybrid optomechanical system consisting of a degenerate optical parametric amplifier inside a driven optical cavity with a moving end mirror which is modeled as a stiffening Duffing-like anharmonic quantum mechanical oscillator. By providing analytical expressions for the critical values of the system parameters corresponding to the emergence of the multistability behavior in the steady-state response of the system, we show that the stiffening mechanical Duffing anharmonicity reduces the width of the multistability region while the optical parametric nonlinearity can be exploited to drive the system toward the multistability region. We also show that for appropriate values of the mechanical anharmonicity strength the steady-state mechanical squeezing and the ground-state cooling of the mechanical resonator can be achieved. Moreover, we find that the presence of the nonlinear gain medium can lead to the improvement of the mechanical anharmonicity-induced cooling of the mechanical motion, as well as to the mechanical squeezing beyond the standard quantum limit of 3 dB.

Super-strengthening and stabilizing with carbon nanotube harnessed high density nanotwins in metals by shock loading

PubMed Central

Lin, Dong; Saei, Mojib; Suslov, Sergey; Jin, Shengyu; Cheng, Gary J.

2015-01-01

CNTs reinforced metal composites has great potential due to their superior properties, such as light weight, high strength, low thermal expansion and high thermal conductivity. The current strengthening mechanisms of CNT/metal composite mainly rely on CNTs’ interaction with dislocations and CNT’s intrinsic high strength. Here we demonstrated that laser shock loading the CNT/metal composite results in high density nanotwins, stacking fault, dislocation around the CNT/metal interface. The composites exhibit enhanced strength with excellent stability. The results are interpreted by both molecular dynamics simulation and experiments. It is found the shock wave interaction with CNTs induces a stress field, much higher than the applied shock pressure, surrounding the CNT/metal interface. As a result, nanotwins were nucleated under a shock pressure much lower than the critical values to generate twins in metals. This hybrid unique nanostructure not only enhances the strength, but also stabilize the strength, as the nanotwin boundaries around the CNTs help pin the dislocation movement. PMID:26493533

Improved silicon carbide for advanced heat engines. II - Pressureless sintering and mechanical properties of injection molded silicon carbide

NASA Technical Reports Server (NTRS)

Whalen, Thomas J.; Baer, J. R.

1989-01-01

The influence on density and strength of pressureless sintering in vacuum and argon environments has been evaluated with injection molded SiC materials. Main effects and two factor interactions of sintering (cycle variables temperature, time, heating rate, and atmosphere) were assessed. An improved understanding of the influence of the processing flaws and sintering conditions has been obtained. Strength and density have improved from a baseline level of 299 MPa (43.3 Ksi) and 94 pct of theoretical density to values greater than 483 MPa (70 Ksi) and 97 pct.

Strain rate, temperature, and humidity on strength and moduli of a graphite/epoxy composite

NASA Technical Reports Server (NTRS)

Lifshitz, J. M.

1981-01-01

Results of an experimental study of the influence of strain rate, temperature and humidity on the mechanical behavior of a graphite/epoxy fiber composite are presented. Three principal strengths (longitudinal, transverse and shear) and four basic moduli (E1, E2, G12 and U12) of a unidirectional graphite/epoxy composite were followed as a function of strain rate, temperature and humidity. Each test was performed at a constant tensile strain rate in an environmental chamber providing simultaneous temperature and humidity control. Prior to testing, specimens were given a moisture preconditioning treatment at 60 C. Values for the matrix dominated moduli and strength were significantly influenced by both environmental and rate parameters, whereas the fiber dominated moduli were not. However, the longitudinal strength was significantly influenced by temperature and moisture content. A qualitative explanation for these observations is presented.

Interfacial Healing and Transport Phenomena Modeling ff Biopolymers

NASA Astrophysics Data System (ADS)

Lebron, Karla

This research focuses on the characterization of bioplastics joined using ultrasonic welding and modeling of temperature distributions and interfacial healing. Polylactic acid (PLA), which is typically derived from starch-rich crops such as corn, was studied. While the measurement of activation energy for interfacial healing at weld interfaces of PLA films has been reported, here, this information is used to predict the weld strength of rigid PLA samples welded by ultrasonics. A characterization of the mechanical properties was completed with a tensile test to determine the effects of amplitude, melt velocity and collapse distance on weld strength. From previous interfacial healing activation energy measurements based on an impulse welding method, it was also possible to predict weld strength. It was found that the most influential parameters were weld time, collapse distance and weld velocity. In general, the model predicted weld strength reasonably well with r2 values between 0.77 and 0.78.

Thermomechanical treatment of 2124 PM aluminum alloys with low and high dispersoid levels

NASA Technical Reports Server (NTRS)

Sarkar, B.; Lisagor, W. B.

1986-01-01

The effects of thermomechanical treatment (TMT) on the mechanical properties and metallurgical structure of 2124 powder metallurgy aluminum alloys prepared from rapidly solidified powders were investigated. The alloys were prepared by using a standard canning/vacuum degassing/hot consolidation/extrusion sequence. Two compositions, with manganese contents of 0.5 and 1.5 percent, were investigated to examine the effects of low and high dispersoid levels. The results indicate that significant improvements in strength can be accomplished through TMT for this PM alloy system with little loss in toughness. The increase in strength observed is attributed to the presence of much finer, more homogeneous S-prime precipitation than that observed without TMT. Rolling deformation at room temperature resulted in some tendency for nonuniform (planar) deformation and resulted in slightly lower notch strength values. The lower notch strengths observed in the higher manganese composition were attributed to the coarser, more dense dispersoids observed in this material.

Improving the toughness of ultrahigh strength steel

NASA Astrophysics Data System (ADS)

Sato, Koji

2002-01-01

The ideal structural steel combines high strength with high fracture toughness. This dissertation discusses the toughening mechanism of the Fe/Co/Ni/Cr/Mo/C steel, AerMet 100, which has the highest toughness/strength combination among all commercial ultrahigh strength steels. The possibility of improving the toughness of this steel was examined by considering several relevant factors. Chapter 1 reviews the mechanical properties of ultrahigh strength steels and the physical metallurgy of AerMet 100. It also describes the fracture mechanisms of steel, i.e. ductile microvoid coalescence, brittle transgranular cleavage, and intergranular separation. Chapter 2 examines the strength-toughness relationship for three heats of AerMet 100. A wide variation of toughness is obtained at the same strength level. The toughness varies despite the fact that all heat fracture in the ductile fracture mode. The difference originates from the inclusion content. Lower inclusion volume fraction and larger inclusion spacing gives rise to a greater void growth factor and subsequently a higher fracture toughness. The fracture toughness value, JIc, is proportional to the particle spacing of the large non-metallic inclusions. Chapter 3 examines the ductile-brittle transition of AerMet 100 and the effect of a higher austenitization temperature, using the Charpy V-notch test. The standard heat treatment condition of AerMet 100 shows a gradual ductile-brittle transition due to its fine effective grain size. Austenitization at higher temperature increases the prior austenite grain size and packet size, leading to a steeper transition at a higher temperature. Both transgranular cleavage and intergranular separation are observed in the brittle fracture mode. Chapter 4 examines the effect of inclusion content, prior austenite grain size, and the amount of austenite on the strength-toughness relationship. The highest toughness is achieved by low inclusion content, small prior austenite grain size, and a small content of stable austenite. The low inclusion content increases the strain at the fracture. The reduction in prior austenite grain size prevents the fast unstable crack propagation by cleavage. And the stable austenite decreases the strength of the intergranular separation at the prior austenite grain boundary, which provides the stress relief at the crack tip.

3D Rheological Modeling of NW Intraplate Europe, Deciphering Spatial Integrated strength patterns, Mechanical Strong Layering and EET

NASA Astrophysics Data System (ADS)

Beekman, F.; Hardebol, N.; Cloetingh, S.; Tesauro, M.

2006-12-01

Better understanding of 3D rheological heterogeneity of the European Lithosphere provide the key to tie the recorded intraplate deformation pattern to stress fields transmitted into plate interior from plate boundary forces. The first order strain patterns result from stresses transmitted through the European lithosphere that is marked by a patchwork of high strength variability from inherited structural and compositional heterogeneities and upper mantle thermal perturbations. As the lithospheric rheology depends primarily on its spatial structure, composition and thermal estate, the 3D strength model for the European lithosphere relies on a 3D compositional model that yields the compositional heterogeneities and an iteratively calculated thermal cube using Fouriers law for heat conduction. The accurate appraisal of spatial strength variability results from proper mapping and integration of the geophysical compositional and thermal input parameters. Therefore, much attention has been paid to a proper description of first order structural and tectonic features that facilitate compilation of the compositional and thermal input models. As such, the 3D strength model reflects the thermo-mechanical structure inherited from the Europeans polyphase deformation history. Major 3D spatial mechanical strength variability has been revealed. The East-European and Fennoscandian Craton to the NE exhibit high strength (30-50 1012 N/m) from low mantle temperatures and surface heatflow of 35-60 mW/m2 while central and western Europe reflect a polyphase Phanerozoic thermo- tectonic history. Here, regions with high rigidity are formed primarily by patches of thermally stabilized Variscan Massifs (e.g. Rhenish, Armorican, Bohemian, and Iberian Massif) with low heatflow and lithospheric thickness values (50-65 mW/m2; 110-150 km) yielding strengths of ~15-25 1012 N/m. In contrast, major axis of weakened lithosphere coincides with Cenozoic Rift System (e.g. Upper and Lower Rhine Grabens, Pannonian Basin and Massif Central) attributed to the presence of tomographically imaged plumes. This study has elucidated the memory of the present-days Europeans lithosphere induced by compositional and thermal heterogeneities. The resulting lateral strength variations has a clear signature of the pst lithospheres polyphase deformation and also entails active tectonics, tectonically induced topography and surface processes.

Mechanical performance of encapsulated restorative glass-ionomer cements for use with Atraumatic Restorative Treatment (ART)

PubMed Central

MOLINA, Gustavo Fabián; CABRAL, Ricardo Juan; MAZZOLA, Ignacio; BRAIN LASCANO, Laura; FRENCKEN, Jo. E.

2013-01-01

The Atraumatic Restorative Treatment (ART) approach was suggested to be a suitable method to treat enamel and dentine carious lesions in patients with disabilities. The use of a restorative glass-ionomer with optimal mechanical properties is, therefore, very important. Objective: To test the null-hypotheses that no difference in diametral tensile, compressive and flexural strengths exists between: (1) The EQUIA system and (2) The Chemfil Rock (encapsulated glass-ionomers; test materials) and the Fuji 9 Gold Label and the Ketac Molar Easymix (hand-mixed conventional glass-ionomers; control materials); (3) The EQUIA system and Chemfil Rock. Material and Methods: Specimens for testing flexural (n=240) and diametral tensile (n=80) strengths were prepared according to standardized specifications; the compressive strength (n=80) was measured using a tooth-model of a class II ART restoration. ANOVA and Tukey B tests were used to test for significant differences between dependent and independent variables. Results: The EQUIA system and Chemfil Rock had significantly higher mean scores for all the three strength variables than the Fuji 9 Gold Label and Ketac Molar Easymix (α=0.05). The EQUIA system had significant higher mean scores for diametral tensile and flexural strengths than the Chemfil Rock (α=0.05). Conclusion: The two encapsulated high-viscosity glass-ionomers had significantly higher test values for diametral tensile, flexural and compressive strengths than the commonly used hand-mixed high-viscosity glass-ionomers. PMID:23857657

Thermomechanical Characterization of SiC Fiber Tows and Implications for CMC

NASA Technical Reports Server (NTRS)

Yun, H. M.; DiCarlo, J. A.

1999-01-01

In order to better understand SiC fiber behavior within CMC microstructures, mechanical tests were performed on multifilament tows consisting of different types of as produced and pretreated fibers. Tensile strengths of tows and single fibers were measured at room temperature for nonstoichiometric Hi-Nicalon and ZMI fibers and for stoichiometric Hi-Nicalon-S, Tyranno SA. and Sylramic fibers. Based on simple bundle theory, measured strengths for as-produced and sized tows were in general agreement with the single fiber results. However, after sizing removal under inert conditions, tow strengths for the coarser grained stoichiometric fibers were typically lower than those predicted from individual fiber data. This effect is attributed to enhanced fiber-fiber mechanical interaction caused by sizing removal from the rough surfaces of these fibers. In support of this, tow strengths remained high for those fiber types with fine grains or excess surface carbon; and, when re-coated with a BN interphase coating, tow strengths for the coarser grained fibers returned to their as-produced values. When the tows were pretreated in air at intermediate temperatures, tow strengths decreased in a manner that could be correlated with the oxidation characteristics of each fiber type as measured by thermogravimetric analysis. The creep and rupture properties of Hi-Nicalon and Sylramic tows were also measured in air and argon from 1200 to 1400 C. Although displaying transient and environmental effects similar to single fibers, the tows crept faster at short times and slower at long times. This resulted in the tow rupture strengths at long time being much greater than the rupture strengths of single fibers. The CMC implications of the tow results are discussed, as well as the benefits and limitations of tow testing.

Evaluation of Surface Roughness and Tensile Strength of Base Metal Alloys Used for Crown and Bridge on Recasting (Recycling)

PubMed Central

Hashmi, Syed W.; Rao, Yogesh; Garg, Akanksha

2015-01-01

Background Dental casting alloys play a prominent role in the restoration of the partial dentition. Casting alloys have to survive long term in the mouth and also have the combination of structure, molecules, wear resistance and biologic compatibility. According to ADA system casting alloys were divided into three groups (wt%); high noble, Noble and predominantly base metal alloys. Aim To evaluate the mechanical properties such as tensile strength and surface roughness of the new and recast base metal (nickel-chromium) alloys. Materials and Methods Recasting of the base metal alloys derived from sprue and button, to make it reusable has been done. A total of 200 test specimens were fabricated using specially fabricated jig of metal and divided into two groups- 100 specimens of new alloy and 100 specimens of recast alloys, which were tested for tensile strength on universal testing machine and surface roughness on surface roughness tester. Results Tensile strength of new alloy showed no statistically significant difference (p-value>0.05) from recast alloy whereas new alloy had statistically significant surface roughness (Maximum and Average surface roughness) difference (p-value<0.01) as compared to recast alloy. Conclusion Within the limitations of the study it is concluded that the tensile strength will not be affected by recasting of nickel-chromium alloy whereas surface roughness increases markedly. PMID:26393194

Quasi-static and dynamic experimental studies on the tensile strength and failure pattern of concrete and mortar discs.

PubMed

Jin, Xiaochao; Hou, Cheng; Fan, Xueling; Lu, Chunsheng; Yang, Huawei; Shu, Xuefeng; Wang, Zhihua

2017-11-10

As concrete and mortar materials widely used in structural engineering may suffer dynamic loadings, studies on their mechanical properties under different strain rates are of great importance. In this paper, based on splitting tests of Brazilian discs, the tensile strength and failure pattern of concrete and mortar were investigated under quasi-static and dynamic loadings with a strain rate of 1-200 s -1 . It is shown that the quasi-static tensile strength of mortar is higher than that of concrete since coarse aggregates weaken the interface bonding strength of the latter. Numerical results confirmed that the plane stress hypothesis lead to a lower value tensile strength for the cylindrical specimens. With the increase of strain rates, dynamic tensile strengths of concrete and mortar significantly increase, and their failure patterns change form a single crack to multiple cracks and even fragment. Furthermore, a relationship between the dynamic increase factor and strain rate was established by using a linear fitting algorithm, which can be conveniently used to calculate the dynamic increase factor of concrete-like materials in engineering applications.

Changes of strength characteristics of pervious concrete due to variations in water to cement ratio

NASA Astrophysics Data System (ADS)

Kovac, M.; Sicakova, A.

2017-10-01

Pervious concrete is considered to be a sustainable pavement material due to high water permeability. The experiment presented in this paper was aimed at study the influence of water to cement ratio on both the compressive and splitting tensile strength of pervious concrete. Typically, less water content in concrete mixture leads to less porosity of cement paste and thus it provides desirable mechanical properties. In case of conventional dense concrete, the lower is the water to cement ratio, the higher or better is the strength, density and durability of concrete. This behaviour is not quite clear in case of pervious concrete because of low amount of cement paste present. Results of compressive and splitting tensile strength of pervious concrete are discussed in the paper while taking into account values measured after 2 and 28 days of hardening and variations in water to cement ratio. The results showed that changes of water to cement ratio from 0.25 to 0.35 caused only slight differences in strength characteristics, and this applied to both types of tested strength.

Physical Properties of Synthetic Resin Materials

NASA Technical Reports Server (NTRS)

Fishbein, Meyer

1939-01-01

A study was made to determine the physical properties of synthetic resins having paper, canvas, and linen reinforcements, and of laminated wood impregnated with a resin varnish. The results show that commercial resins have moduli of elasticity that are too low for structural considerations. Nevertheless, there do exist plastics that have favorable mechanical properties and, with further development, it should be possible to produce resin products that compare favorably with the light-metal alloys. The results obtained from tests on Compound 1840, resin-impregnated wood, show that this material can stand on its own merit by virtue of a compressive strength four times that of the natural wood. This increase in compressive strength was accomplished with an increase of density to a value slightly below three times the normal value and corrected one of the most serious defects of the natural product.

Precision measurement of the electromagnetic dipole strengths in Be11

NASA Astrophysics Data System (ADS)

Kwan, E.; Wu, C. Y.; Summers, N. C.; Hackman, G.; Drake, T. E.; Andreoiu, C.; Ashley, R.; Ball, G. C.; Bender, P. C.; Boston, A. J.; Boston, H. C.; Chester, A.; Close, A.; Cline, D.; Cross, D. S.; Dunlop, R.; Finlay, A.; Garnsworthy, A. B.; Hayes, A. B.; Laffoley, A. T.; Nano, T.; Navrátil, P.; Pearson, C. J.; Pore, J.; Quaglioni, S.; Svensson, C. E.; Starosta, K.; Thompson, I. J.; Voss, P.; Williams, S. J.; Wang, Z. M.

2014-05-01

The electromagnetic dipole strength in Be11 between the bound states has been measured using low-energy projectile Coulomb excitation at bombarding energies of 1.73 and 2.09 MeV/nucleon on a Pt196 target. An electric dipole transition probability B(E1;1/2-→1/2+)=0.102(2) e2fm was determined using the semi-classical code Gosia, and a value of 0.098(4) e2fm was determined using the Extended Continuum Discretized Coupled Channels method with the quantum mechanical code FRESCO. These extracted B(E1) values are consistent with the average value determined by a model-dependent analysis of intermediate energy Coulomb excitation measurements and are approximately 14% lower than that determined by a lifetime measurement. The much-improved precisions of 2% and 4% in the measured B(E1) values between the bound states deduced using Gosia and the Extended Continuum Discretized Coupled Channels method, respectively, compared to the previous accuracy of ˜10% will help in our understanding of and better improve the realistic inter-nucleon interactions.

Result of International Round Robin Test on Young's Modulus Measurement of 304L and 316L Steels at Cryogenic Temperatures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shibata, K.; Ogata, T.; Nyilas, A.

2006-03-31

Ogata et al. reported in 1996 results of international Round Robin tests on mechanical property measurement of several metals at cryogenic temperatures. Following the report, the standard deviation of Young's modulus of 316L steel is much larger than those of yield and tensile strengths, that is, 4.6 % of the mean value for Young's modulus, while 1.4 % and 1.6 % of the mean values for yield and for tensile strengths, respectively. Therefore, an international Round Robin test on Young's modulus of two austenitic stainless steels at cryogenic temperatures under the participation often institutes from four nations has been initiatedmore » within these two years. As a result, the ratios of standard deviation to the mean values are 4.2 % for 304L and 3.6 % for 316L. Such a drop in the standard deviation is attributable to the decrease in the number of institute owing to the application of single extensometer or direct strain gage technique.« less

The Influence of Processing on Strengthening Mechanisms in Pb-Free Solder Joints

NASA Astrophysics Data System (ADS)

Mutuku, Francis; Arfaei, Babak; Cotts, Eric J.

2017-04-01

The number, and the spacing, of Ag3Sn precipitates in Sn-Ag-Cu/Cu solder joints were related to separate processing parameters. The mechanical properties of an individual solder joint were directly related to the resulting distribution of different dispersoids in the joint. As the number of Ag3Sn precipitates increased, so did solder joint strength and shear fatigue lifetime. The room-temperature shear fatigue lifetime was inversely correlated with the separation between Ag3Sn precipitates. Bi and Sb solid solution strengthening was found to result in significantly larger values of shear strength and shear fatigue lifetime for one Pb-free solder. Room-temperature shear fatigue lifetime tests were identified as a relatively straightforward, yet sensitive means to gain insight into the reliability of Sn-Ag-Cu (SAC) solder joints.

Fracture mechanics in fiber reinforced composite materials, taking as examples B/A1 and CRFP

NASA Technical Reports Server (NTRS)

Peters, P. W. M.

1982-01-01

The validity of linear elastic fracture mechanics and other fracture criteria was investigated with laminates of boron fiber reinforced aluminum (R/A1) and of carbon fiber reinforced epoxide (CFRP). Cracks are assessed by fracture strength Kc or Kmax (critical or maximum value of the stress intensity factor). The Whitney and Nuismer point stress criterion and average stress criterion often show that Kmax of fiber composite materials increases with increasing crack length; however, for R/A1 and CFRP the curve showing fracture strength as a function of crack length is only applicable in a small domain. For R/A1, the reason is clearly the extension of the plastic zone (or the damage zone n the case of CFRP) which cannot be described with a stress intensity factor.

Effect of low dose and moderate dose gamma irradiation on the mechanical properties of bone and soft tissue allografts.

PubMed

Balsly, Colleen R; Cotter, Andrew T; Williams, Lisa A; Gaskins, Barton D; Moore, Mark A; Wolfinbarger, Lloyd

2008-12-01

The increased use of allograft tissue for musculoskeletal repair has brought more focus to the safety of allogenic tissue and the efficacy of various sterilization techniques. Gamma irradiation is an effective method for providing terminal sterilization to biological tissue, but it is also reported to have deleterious effects on tissue mechanics in a dose-dependent manner. At irradiation ranges up to 25 kGy, a clear relationship between mechanical strength and dose has yet to be established. The aim of this study was to investigate the mechanical properties of bone and soft tissue allografts, irradiated on dry ice at a low absorbed dose (18.3-21.8 kGy) and a moderate absorbed dose (24.0-28.5 kGy), using conventional compressive and tensile testing, respectively. Bone grafts consisted of Cloward dowels and iliac crest wedges, while soft tissue grafts consisted of patellar tendons, anterior tibialis tendons, semitendinosus tendons, and fascia lata. There were no statistical differences in mechanical strength or modulus of elasticity for any graft irradiated at a low absorbed dose, compared to control groups. Also, bone allografts and two soft tissue allografts (anterior tibialis and semitendinosus tendon) that were irradiated at a moderate dose demonstrated similar strength and modulus of elasticity values to control groups. The results of this study support the use of low dose and moderate dose gamma irradiation of bone grafts. For soft tissue grafts, the results support the use of low dose irradiation.

Influence of surface defects on the tensile strength of carbon fibers

NASA Astrophysics Data System (ADS)

Vautard, F.; Dentzer, J.; Nardin, M.; Schultz, J.; Defoort, B.

2014-12-01

The mechanical properties of carbon fibers, especially their tensile properties, are affected by internal and surface defects. In order to asses in what extent the generation of surface defects can result in a loss of the mechanical properties, non-surface treated carbon fibers were oxidized with three different surface treatment processes: electro-chemical oxidation, oxidation in nitric acid, and oxidation in oxygen plasma. Different surface topographies and surface chemistries were obtained, as well as different types and densities of surface defects. The density of surface defects was measured with both a physical approach (Raman spectroscopy) and a chemical approach (Active Surface Area). The tensile properties were evaluated by determining the Weibull modulus and the scale parameter of each reference, after measuring the tensile strength for four different gauge lengths. A relationship between the tensile properties and the nature and density of surface defects was noticed, as large defects largely control the value of the tensile strength. When optimized, some oxidation surface treatment processes can generate surface functional groups as well as an increase of the mechanical properties of the fibers, because of the removal of the contamination layer of pyrolytic carbon generated during the carbonization of the polyacrylonitrile precursor. Oxidation in oxygen plasma revealed to be a promising technology for alternative surface treatment processes, as high levels of functionalization were achieved and a slight improvement of the mechanical properties was obtained too.

Effect of thermal cycling on flexural properties of carbon-graphite fiber-reinforced polymers.

PubMed

Segerström, Susanna; Ruyter, I Eystein

2009-07-01

To determine flexural strength and modulus after water storage and thermal cycling of carbon-graphite fiber-reinforced (CGFR) polymers based on poly(methyl methacrylate) and a copolymer matrix, and to examine adhesion between fiber and matrix by scanning electron microscopy (SEM). Solvent cleaned carbon-graphite (CG) braided tubes of fibers were treated with a sizing resin. The resin mixture of the matrix was reinforced with 24, 36, 47 and 58wt% (20, 29, 38 and 47vol.%) CG-fibers. After heat polymerization the specimens were kept for 90 days in water and thereafter hydrothermally cycled (12,000 cycles, 5/55 degrees C). Mechanical properties were evaluated by three-point bend testing. After thermal cycling, the adhesion between fibers and matrix was evaluated by SEM. Hydrothermal cycling did not decrease flexural strength of the CGFR polymers with 24 and 36wt% fiber loadings; flexural strength values after thermocycling were 244.8 (+/-32.33)MPa for 24wt% and 441.3 (+/-68.96)MPa for 36wt%. Flexural strength values after thermal cycling were not further increased after increasing the fiber load to 47 (459.2 (+/-45.32)MPa) and 58wt% (310.4 (+/-52.79)MPa). SEM revealed good adhesion between fibers and matrix for all fiber loadings examined. The combination of the fiber treatment and resin matrix described resulted in good adhesion between CG-fibers and matrix. The flexural values for fiber loadings up to 36wt% appear promising for prosthodontic applications such as implant-retained prostheses.

Bulk flow strength of forsterite?enstatite composites as a function of forsterite content

NASA Astrophysics Data System (ADS)

Ji, Shaocheng; Wang, Zichao; Wirth, Richard

2001-11-01

Creep experiments have been conducted to investigate the effect of varying forsterite content ( VFo) on the bulk flow strength of dry forsterite-enstatite (Fo-En) aggregates in order to evaluate the applicability of existing theoretical models to two-phase rocks, as well as to understand the rheology of polyphase systems in general. The experiments were performed at temperatures of 1423-1593 K, stresses of 18-100 MPa, oxygen fugacities of 10 -14-10 -2.5 MPa and 0.1 MPa total pressure. The fine-grained (Fo: 10-17 μm; En: 14-31 μm) composites of various Fo volume fractions ( VFo=0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1) were synthesized by isostatically hot-pressing in a gas-medium apparatus at 1523 and 350 MPa. Our experiments show that flow strength contrasts between Fo and En are in the range of 3-8 at the given experimental conditions, with Fo as the stronger phase. The measured stress exponent ( n) and activation energy ( Q) values of the Fo-En composites fall between those of the end-members. The n values show a nearly linear increase from 1.3 to 2.0, while the Q values display a non-linear increase from 472 to 584 kJ/mol with En volume fraction from 0 to 1.0. There is no clear dependence of creep rates on oxygen fugacity for the Fo-En composites. The mechanical data and TEM microstructural observations suggest no change in deformation mechanism of each phase when in the composites, compared to when in a single-phase aggregate, the En deformed mainly by dislocation creep while the Fo deformed by dislocation-accommodated diffusion creep for our grain sizes and experimental conditions. Comparisons between the measured composite strengths and various theoretical models indicate that none of the existing theoretical models can give a precise predication over the entire VFo range from 0 to 1. However, the theoretical models based on weak-phase supported structures (WPS) yield a good prediction for the flow strengths of the composites with VFo<0.4, while those based on strong-phase supported structures (SPS) are better for the composites with VFo>0.6. No model gives a good prediction for the bulk strength of two-phase composites in the transitional regime ( VFo=0.4-0.6). Applications of the WPS- and SPS-based models in the transitional regime result in under- and over-estimations for the composite flow strength, respectively. Thus, the effect of rock microstructure should be taken into consideration in modeling the bulk flow strengths of the crust and upper mantle using laboratory-determined flow laws of single-phase aggregates.

Preparation of hybrid nano biocomposite κ-carrageenan/cellulose nanocrystal/nanoclay

NASA Astrophysics Data System (ADS)

Zakuwan, Siti Zarina; Ahmad, Ishak; Ramli, Nazaruddin

2013-11-01

Biodegradable composites film based on κ-carrageenan and nano particles as filler was prepared to study the mechanical strength of carrageenan composites. Solution casting technique was used to prepare_this biocomposite. Preparation of composite film and nano filler involve two stages, preparation of cellulose nanocrystals (CNC) from kenaf with alkali treatment, bleaching, and hydrolysis followed by the preparation of two types of nano composite. Tensile test was carried on the composite film based on κ-carrageenan with the variation percentage of CNC and nano clay to obtain the optimum CNC and nano clay loading. After that hybrid nano-biocomposite film based on κ-carrageenan with the variation percentage of CNC/nano clay (OMMT) according to optimum value of composite carrageenan/CNC and composite carrageenan/nano clay film was prepared. The effect of nano filler on the mechanical properties of carrageenan films was examined. κ-carrageenan biocomposite increased with the optimum at 4% CNC and nano clay composition. Additional improvement of tensile strength with hybridization of CNC and nanoclay indicated better mechanical properties.

Influence of Nano-HA Coated Bone Collagen to Acrylic (Polymethylmethacrylate) Bone Cement on Mechanical Properties and Bioactivity

PubMed Central

Li, Tao; Weng, Xisheng; Bian, Yanyan; Zhou, Lei; Cui, Fuzhai; Qiu, Zhiye

2015-01-01

Objective This research investigated the mechanical properties and bioactivity of polymethylmethacrylate (PMMA) bone cement after addition of the nano-hydroxyapatite(HA) coated bone collagen (mineralized collagen, MC). Materials & Methods The MC in different proportions were added to the PMMA bone cement to detect the compressive strength, compression modulus, coagulation properties and biosafety. The MC-PMMA was embedded into rabbits and co-cultured with MG 63 cells to exam bone tissue compatibility and gene expression of osteogenesis. Results 15.0%(wt) impregnated MC-PMMA significantly lowered compressive modulus while little affected compressive strength and solidification. MC-PMMA bone cement was biologically safe and indicated excellent bone tissue compatibility. The bone-cement interface crosslinking was significantly higher in MC-PMMA than control after 6 months implantation in the femur of rabbits. The genes of osteogenesis exhibited significantly higher expression level in MC-PMMA. Conclusions MC-PMMA presented perfect mechanical properties, good biosafety and excellent biocompatibility with bone tissues, which has profoundly clinical values. PMID:26039750

Influence of Nano-HA Coated Bone Collagen to Acrylic (Polymethylmethacrylate) Bone Cement on Mechanical Properties and Bioactivity.

PubMed

Li, Tao; Weng, Xisheng; Bian, Yanyan; Zhou, Lei; Cui, Fuzhai; Qiu, Zhiye

2015-01-01

This research investigated the mechanical properties and bioactivity of polymethylmethacrylate (PMMA) bone cement after addition of the nano-hydroxyapatite(HA) coated bone collagen (mineralized collagen, MC). The MC in different proportions were added to the PMMA bone cement to detect the compressive strength, compression modulus, coagulation properties and biosafety. The MC-PMMA was embedded into rabbits and co-cultured with MG 63 cells to exam bone tissue compatibility and gene expression of osteogenesis. 15.0%(wt) impregnated MC-PMMA significantly lowered compressive modulus while little affected compressive strength and solidification. MC-PMMA bone cement was biologically safe and indicated excellent bone tissue compatibility. The bone-cement interface crosslinking was significantly higher in MC-PMMA than control after 6 months implantation in the femur of rabbits. The genes of osteogenesis exhibited significantly higher expression level in MC-PMMA. MC-PMMA presented perfect mechanical properties, good biosafety and excellent biocompatibility with bone tissues, which has profoundly clinical values.

Effect of chemical treatment of Kevlar fibers on mechanical interfacial properties of composites.

PubMed

Park, Soo-Jin; Seo, Min-Kang; Ma, Tae-Jun; Lee, Douk-Rae

2002-08-01

In this work, the effects of chemical treatment on Kevlar 29 fibers have been studied in a composite system. The surface characteristics of Kevlar 29 fibers were characterized by pH, acid-base value, X-ray photoelectron spectroscopy (XPS), and FT-IR. The mechanical interfacial properties of the final composites were studied by interlaminar shear strength (ILSS), critical stress intensity factor (K(IC)), and specific fracture energy (G(IC)). Also, impact properties of the composites were investigated in the context of differentiating between initiation and propagation energies and ductile index (DI) along with maximum force and total energy. As a result, it was found that chemical treatment with phosphoric acid solution significantly affected the degree of adhesion at interfaces between fibers and resin matrix, resulting in improved mechanical interfacial strength in the composites. This was probably due to the presence of chemical polar groups on Kevlar surfaces, leading to an increment of interfacial binding force between fibers and matrix in a composite system.

Enhancement of the Mechanical Properties of Basalt Fiber-Wood-Plastic Composites via Maleic Anhydride Grafted High-Density Polyethylene (MAPE) Addition.

PubMed

Chen, Jinxiang; Wang, Yong; Gu, Chenglong; Liu, Jianxun; Liu, Yufu; Li, Min; Lu, Yun

2013-06-18

This study investigated the mechanisms, using microscopy and strength testing approaches, by which the addition of maleic anhydride grafted high-density polyethylene (MAPE) enhances the mechanical properties of basalt fiber-wood-plastic composites (BF-WPCs). The maximum values of the specific tensile and flexural strengths are achieved at a MAPE content of 5%-8%. The elongation increases rapidly at first and then continues slowly. The nearly complete integration of the wood fiber with the high-density polyethylene upon MAPE addition to WPC is examined, and two models of interfacial behavior are proposed. We examined the physical significance of both interfacial models and their ability to accurately describe the effects of MAPE addition. The mechanism of formation of the Model I interface and the integrated matrix is outlined based on the chemical reactions that may occur between the various components as a result of hydrogen bond formation or based on the principle of compatibility, resulting from similar polarity. The Model I fracture occurred on the outer surface of the interfacial layer, visually demonstrating the compatibilization effect of MAPE addition.

Mechanical and morphological properties of polypropylene/nano α-Al2O3 composites.

PubMed

Mirjalili, F; Chuah, L; Salahi, E

2014-01-01

A nanocomposite containing polypropylene (PP) and nano α-Al2O3 particles was prepared using a Haake internal mixer. Mechanical tests, such as tensile and flexural tests, showed that mechanical properties of the composite were enhanced by addition of nano α-Al2O3 particles and dispersant agent to the polymer. Tensile strength was approximately ∼ 16% higher than pure PP by increasing the nano α-Al2O3 loading from 1 to 4 wt% into the PP matrix. The results of flexural analysis indicated that the maximum values of flexural strength and flexural modulus for nanocomposite without dispersant were 50.5 and 1954 MPa and for nanocomposite with dispersant were 55.88 MPa and 2818 MPa, respectively. However, higher concentration of nano α-Al2O3 loading resulted in reduction of those mechanical properties that could be due to agglomeration of nano α-Al2O3 particles. Transmission and scanning electron microscopic observations of the nanocomposites also showed that fracture surface became rougher by increasing the content of filler loading from 1 to 4% wt.

An Analysis of Strengthening Mechanisms and Rate-Dependence in a High Strength Aluminum Alloy

NASA Astrophysics Data System (ADS)

Cao, B.; Shaeffer, M.; Cadel, D.; Ramesh, K. T.; Prasad, S.

2017-11-01

We examine the strengthening mechanisms within a high-strength aluminum alloy with the objective of providing guidelines for increased strength. First, we measure the mechanical behavior of the age-hardenable Al-Cu-Mg-Ag alloy known as Al 2139 in the T8 condition, and observe strengths of 500 MPa at quasistatic strain rates and average strengths of up to 600 MPa at high strain rates. Next, we explore the reasons for the high strength of this alloy by considering the contributions of various strengthening mechanisms to the total strength of the material. Finally, we develop an analytical approach to estimating the strengthening developed through the mechanism of dislocation cutting of closely spaced plate-like semi-coherent precipitates. Our results suggest that dislocation cutting of the Ω phase is the primary strengthening mechanism in this alloy.

Fibre-matrix bond strength studies of glass, ceramic, and metal matrix composites

NASA Technical Reports Server (NTRS)

Grande, D. H.; Mandell, J. F.; Hong, K. C. C.

1988-01-01

An indentation test technique for compressively loading the ends of individual fibers to produce debonding has been applied to metal, glass, and glass-ceramic matrix composites; bond strength values at debond initiation are calculated using a finite-element model. Results are correlated with composite longitudinal and interlaminar shear behavior for carbon and Nicalon fiber-reinforced glasses and glass-ceramics including the effects of matrix modifications, processing conditions, and high-temperature oxidation embrittlement. The data indicate that significant bonding to improve off-axis and shear properties can be tolerated before the longitudinal behavior becomes brittle. Residual stress and other mechanical bonding effects are important, but improved analyses and multiaxial interfacial failure criteria are needed to adequately interpret bond strength data in terms of composite performance.

Effect of Photoactivation Timing on the Mechanical Properties of Resin Cements and Bond Strength of Fiberglass Post to Root Dentin.

PubMed

Pereira, R D; Valdívia, A D C M; Bicalho, A A; Franco, S D; Tantbirojn, D; Versluis, A; Soares, C J

2015-01-01

This study tested the hypothesis that photoactivation timing and resin cement affect mechanical properties and bond strength of fiberglass posts to root dentin at different depths. Fiberglass posts (Exacto, Angelus) were luted with RelyX Unicem (3M ESPE), Panavia F 2.0 (Kuraray), or RelyX ARC (3M ESPE) using three photoactivation timings: light curing immediately, after three minutes, or after five minutes. Push-out bonding strength, PBS (n=10) was measured on each root region (coronal, middle, apical). The elastic modulus (E) and Vickers hardness (VHN) of the cement layer along the root canal were determined using dynamic indentation (n=5). A strain-gauge test was used to measure post-gel shrinkage of each cement (n=10). Residual shrinkage stress was assessed with finite element analysis. Data were analyzed with two-way analysis of variance in a split-plot arrangement and a Tukey test (α=0.05). Multiple linear regression analysis was used to determine the influence of study factors. The five-minute delay photoactivation timing significantly increased the PBS for all resin cements evaluated. The PBS decreased significantly from coronal to apical root canal regions. The mean values for E and VHN increased significantly with the delayed photoactivation for RelyX Unicem and decreased from coronal to apical root regions for all resin cements with the immediate-curing timing. The PBS of fiber posts to root dentin, E, and VHN values were affected by the root canal region, photoactivation timing, and resin cement type. Shrinkage stress values decreased gradually with delayed photoactivation for all the cements.

Radiological and material characterization of high volume fly ash concrete.

PubMed

Ignjatović, I; Sas, Z; Dragaš, J; Somlai, J; Kovács, T

2017-03-01

The main goal of research presented in this paper was the material and radiological characterization of high volume fly ash concrete (HVFAC) in terms of determination of natural radionuclide content and radon emanation and exhalation coefficients. All concrete samples were made with a fly ash content between 50% and 70% of the total amount of cementitious materials from one coal burning power plant in Serbia. Physical (fresh and hardened concrete density) and mechanical properties (compressive strength, splitting tensile strength and modulus of elasticity) of concrete were tested. The radionuclide content ( 226 Ra, 232 Th and 40 K) and radon massic exhalation of HVFAC samples were determined using gamma spectrometry. Determination of massic exhalation rates of HVFAC and its components using radon accumulation chamber techniques combined with a radon monitor was performed. The results show a beneficial effect of pozzolanic activity since the increase in fly ash content resulted in an increase in compressive strength of HVFAC by approximately 20% for the same mass of cement used in the mixtures. On the basis of the obtained radionuclide content of concrete components the I -indices of different HVFAC samples were calculated and compared with measured values (0.27-0.32), which were significantly below the recommended 1.0 index value. The prediction was relatively close to the measured values as the ratio between the calculated and measured I-index ranged between 0.89 and 1.14. Collected results of mechanical and radiological properties and performed calculations clearly prove that all 10 designed concretes with a certain type of fly ash are suitable for structural and non-structural applications both from a material and radiological point of view. Copyright © 2016 Elsevier Ltd. All rights reserved.

Fabrication and characterisation of phantom material made of Tannin-added Rhizophora spp. particleboards for photon and electron beams

NASA Astrophysics Data System (ADS)

Yusof, M. F. Mohd; Hamid, P. N. K. Abd; Tajuddin, A. A.; Hashim, R.; Bauk, S.; Isa, N. Mohd; Isa, M. J. Md

2017-05-01

Particleboards made of Rhizophora spp. with addition of tannin adhesive were fabricated at target density of 1.0 g/cm3. The physical and mechanical properties of the particleboards including internal bond strength (IB) and modulus of rupture (MOR) were measured based on Japanese Industrial Standards (JIS A-5908). The characterisation of the particleboards including the effective atomic number, CT number and relative electron density were determined and compared to water. The mass attenuation coefficient of the particleboards were measured and compared to the calculated value of water using photon cross-section database (XCOM). The results showed that the physical and mechanical properties of the particleboards complied with Type 13 and 18 of JIS A-5908. The values of effective atomic number, CT number and relative electron density were also close to the value of water. The value of mass attenuation coefficients of the particleboards showed good agreement with water (XCOM) at low and high energy photon indicated by the χ2 values.

Investigations of subcritical crack propagation of the Empress 2 all-ceramic system.

PubMed

Mitov, Gergo; Lohbauer, Ulrich; Rabbo, Mohammad Abed; Petschelt, Anselm; Pospiech, Peter

2008-02-01

The mechanical properties and slow crack propapagation of the all-porcelain system Empress 2 (Ivoclar Vivadent, Schaan, Liechtenstein) with its framework compound Empress 2 and the veneering compounds "Empress 2 and Eris were examined. For all materials, the fracture strength, Weibull parameter and elastic moduli were experimentally determined in a four-point-bending test. For the components of the Empress 2 system, the fracture toughness K(IC) was determined, and the crack propagation parameters n and A were determined in a dynamic fatigue method. Using these data, life data analysis was performed and lifetime diagrams were produced. The development of strength under static fatigue conditions was calculated for a period of 5 years. The newly developed veneering ceramic Eris showed a higher fracture strength (sigma(0)=66.1 MPa) at a failure probability of P(F)=63.2%, and crack growth parameters (n=12.9) compared to the veneering ceramic Empress 2 (sigma(0)=60.3 MPa). For Empress 2 veneer the crack propagation parameter n could only be estimated (n=9.5). This is reflected in the prognosis of long-term resistance presented in the SPT diagrams. For all materials investigated, the Weibull parameter m values (Empress 2 framework m=4.6; Empress 2 veneer m=7.9; Eris m=6.9) were much lower than the minimum demanded by the literature (m=15). The initial fracture strength value alone is not sufficient to characterize the mechanical resistance of ceramic materials, since their stressability is time-dependent. Knowledge about the crack propagation parameters n and A are of great importance when preclinically predicting the clinical suitability of dental ceramic materials. The use of SPT diagrams for lifetime calculation of ceramic materials is a valuable method for comparing different ceramics.

Changes in hydraulic conductivity, mechanical properties, and density reflecting the fall in strain along the lateral roots of two species of tropical trees.

PubMed

Christensen-Dalsgaard, Karen K; Ennos, Anthony R; Fournier, Meriem

2007-01-01

Roots have been described as having larger vessels and so greater hydraulic efficiency than the stem. Differences in the strength and stiffness of the tissue within the root system itself are thought to be an adaptation to the loading conditions experienced by the roots and to be related to differences in density. It is not known how potential mechanical adaptations may affect the hydraulic properties of the roots. The change in strength, stiffness, conductivity, density, sapwood area, and second moment of area distally along the lateral roots of two tropical tree species in which the strain is known to decrease rapidly was studied and the values were compared with those of the trunk. It was found that as the strain fell distally along the roots, so did the strength and stiffness of the tissue, whereas the conductivity increased exponentially. These changes appeared to be related to differences in density. In contrast to the distal-most roots, the tissue of the proximal roots had a lower conductivity and higher strength than that of the trunk. This suggests that mechanical requirements on the structure rather than the water potential gradient from roots to branches are responsible for the general pattern that roots have larger vessels than the stem. In spite of their increased transectional area, the buttressed proximal roots were subjected to higher levels of stress and had a lower total conductivity than the rest of the root system.

Compression fatigue behavior and failure mechanism of porous titanium for biomedical applications.

PubMed

Li, Fuping; Li, Jinshan; Huang, Tingting; Kou, Hongchao; Zhou, Lian

2017-01-01

Porous titanium and its alloys are believed to be one of the most attractive biomaterials for orthopedic implant applications. In the present work, porous pure titanium with 50-70% porosity and different pore size was fabricated by diffusion bonding. Compression fatigue behavior was systematically studied along the out-of-plane direction. It resulted that porous pure titanium has anisotropic pore structure and the microstructure is fine-grained equiaxed α phase with a few twins in some α grains. Porosity and pore size have some effect on the S-N curve but this effect is negligible when the fatigue strength is normalized by the yield stress. The relationship between normalized fatigue strength and fatigue life conforms to a power law. The compression fatigue behavior is characteristic of strain accumulation. Porous titanium experiences uniform deformation throughout the entire sample when fatigue cycle is lower than a critical value (N T ). When fatigue cycles exceed N T , strain accumulates rapidly and a single collapse band forms with a certain angle to the loading direction, leading to the sudden failure of testing sample. Both cyclic ratcheting and fatigue crack growth contribute to the fatigue failure mechanism, while the cyclic ratcheting is the dominant one. Porous titanium possesses higher normalized fatigue strength which is in the range of 0.5-0.55 at 10 6 cycles. The reasons for the higher normalized fatigue strength were analyzed based on the microstructure and fatigue failure mechanism. Copyright © 2016 Elsevier Ltd. All rights reserved.

Influence of PP-g-MA compatibilizer characteristics on mechanical properties of glass fiber reinforced polypropylene composites

NASA Astrophysics Data System (ADS)

Guan, Zhuo

Glass fiber (GF) reinforced polypropylene (PP) has become a common composite material used for various applications. Previous reports indicated that grafting ratio and molecular weight (MW) of znaleic anhydride grafted polypropylene (PP-g-MA) are the two most significant factors affecting the mechanical properties of PP/PP-g-MA/GF composites, but the combined effect of these two factors remains controversial. The study of the importance of MA grafting ratio and MW is continued in this work using PPIPP-g MA/GF composites containing various grades and concentrations of PP-g MA compatibilizer. First, MFR and FT1R analyses were performed to characterize the physical and chemical properties- of each PP-g-MA resin. Then, premixed PP and PP-g-MA blend were compounded with GF via twin screw extrusion, with the compounds injection molded into tensile, flexural and Izod impact specimens (all ASTM standard) for mechanical properties testing. Generally speaking, at a given GF content, higher compatibilizer concentrations led to higher tensile, flexural and notched Izod impact strength up to an optimum MA concentrations above which these properties tended to level off PP-g-MA resins with higher grafting ratio were more efficient compatibilizers as indicated by improved tensile, flexural and impact properties at lower PP-g-MA contents. In addition, MW was expected to affect properties as well, with too high and too 16w MW values leading to reduced reinforcement. While the optimum MW values for tensile and impact strength were still not clear based on present results, the estimated optimum weight average MW for maximum flexural strength was 90,000 +/- 1,400 g/mol.

Leaching behaviour and mechanical properties of copper flotation waste in stabilized/solidified products.

PubMed

Mesci, Başak; Coruh, Semra; Ergun, Osman Nuri

2009-02-01

This research describes the investigation of a cement-based solidification/stabilization process for the safe disposal of copper flotation waste and the effect on cement properties of the addition of copper flotation waste (CW) and clinoptilolite (C). In addition to the reference mixture, 17 different mixtures were prepared using different proportions of CW and C. Physical properties such as setting time, specific surface area and compressive strength were determined and compared to a reference mixture and Turkish standards (TS). Different mixtures with the copper flotation waste portion ranging from 2.5 to 12.5% by weight of the mixture were tested for copper leachability. The results show that as cement replacement materials especially clinoptilolite had clear effects on the mechanical properties. Substitution of 5% copper flotation waste for Portland cement gave a similar strength performance to the reference mixture. Higher copper flotation waste addition such as 12.5% replacement yielded lower strength values. As a result, copper flotation waste and clinoptilolite can be used as cementitious materials, and copper flotation waste also can be safely stabilized/solidified in a cement-based solidification/stabilization system.

Influence of triallyl cyanurate as co-agent on gamma irradiation cured high density polyethylene/reclaimed tire rubber blend

NASA Astrophysics Data System (ADS)

Mali, Manoj N.; Arakh, Amar A.; Dubey, K. A.; Mhaske, S. T.

2017-02-01

Utilization of waste from tire industry as reclaimed tire rubber (RTR) by formation of blends with high density polyethylene (HDPE) is great area to be focused. Enhancement of properties by the addition of triallyl cyanurate (TAC) as a co-agent with 1%, 3% and 5% to blend of HDPE 50 wt% and RTR 50 wt% in presence of gamma irradiation curing were investigated. Specifically, mechanical and thermal properties were studied as a function of amount of TAC and gamma irradiation dose in range of 50-200 kGy. The resultant blends were evaluated for the values of impact strength, gel content, thermal stability, tensile properties, rheological properties and morphological properties with increasing irradiation dosage and TAC loading. The mechanical properties tensile strength, hardness, impact strength of blend containing 3% of TAC were substantially increased with increasing irradiation dosage up to 150 KGy. Rheological analysis has shown increase in viscosity with increase in TAC loading up to 3% and 150 KGy irradiation dosages. 3% loading of TAC lead to better set of properties with150 KGy gamma irradiation dosage.

Impact and hardness optimisation of composite materials inspired by the babassu nut (Orbignya speciosa).

PubMed

Staufenberg, Gerrit; Graupner, Nina; Müssig, Jörg

2015-08-20

The babassu nut is the fruit of the babassu palm Orbignya speciosa. The combination of hardness and impact strength is difficult to acquire for artificial materials, making the babassu nut a promising source for biomimetic inspiration. Unnotched Charpy impact tests, Shore D hardness tests and scanning electron microscopy were used for mechanical and microscopical analysis of the pericarp. Four major principles were found for a biomimetic approach: a hard core ((1); endocarp) is embedded in a soft outer layer of high impact strength ((2); epicarp) and is reinforced with fibres of variable fineness (3), some of which are oriented radial to the core (4). Biomimetic fibre-reinforced composites were produced using abstracted mechanisms of the babassu nut based on regenerated cellulose fibres (lyocell, L) with two different fineness values as reinforcement embedded in a polylactide (PLA) core matrix and polypropylene (PP) based outer layers. The biomimetic fibre composite reaches a significantly higher impact strength that is 1.6 times higher than the reference sample produced from a PLA/PP/L-blend. At the same time the hardness is slightly increased compared to PP/L.

Influence of the field humiture environment on the mechanical properties of 316L stainless steel repaired with Fe314

NASA Astrophysics Data System (ADS)

Zhang, Lianzhong; Li, Dichen; Yan, Shenping; Xie, Ruidong; Qu, Hongliang

2018-04-01

The mechanical properties of 316L stainless steel repaired with Fe314 under different temperatures and humidities without inert gas protection were studied. Results indicated favorable compatibility between Fe314 and 316L stainless steel. The average yield strength, tensile strength, and sectional contraction percentage were higher in repaired samples than in 316L stainless steel, whereas the elongation rate was slightly lower. The different conditions of humiture environment on the repair sample exerted minimal influence on tensile and yield strengths. The Fe314 cladding layer was mainly composed of equiaxed grains and mixed with randomly oriented columnar crystal and tiny pores or impurities in the tissue. Results indicated that the hardness value of Fe314 cladding layer under different humiture environments ranged within 419-451.1 HV0.2. The field humiture environment also showed minimal impact on the average hardness of Fe314 cladding layers. Furthermore, 316L stainless steel can be repaired through laser cladding by using Fe314 powder without inert gas protection under different temperatures and humidity environments.

Investigation of specimen size effects by in-situ microcompression of equal channel angular pressed copper

DOE Office of Scientific and Technical Information (OSTI.GOV)

Howard, C.; Frazer, D.; Lupinacci, A.

Here, micropillar compression testing was implemented on Equal Channel Angular Pressed copper samples ranging from 200 nm to 10 µm in side length in order to measure the mechanical properties yield strength, first load drop during plastic deformation at which there was a subsequent stress decrease with increasing strain, work hardening, and strain hardening exponent. Several micropillars containing multiple grains were investigated in a 200 nm grain sample. The effective pillar diameter to grain size ratios, D/d, were measured to be between 1.9 and 27.2. Specimens having D/d ratios between 0.2 and 5 were investigated in a second sample thatmore » was annealed at 200 °C for 2 h with an average grain size of 1.3 µm. No yield strength or elastic modulus size effects were observed in specimens in the 200 nm grain size sample. However work hardening increases with a decrease in critical ratios and first stress drops occur at much lower stresses for specimens with D/d ratios less than 5. For comparison, bulk tensile testing of both samples was performed, and the yield strength values of all micropillar compression tests for the 200 nm grained sample are in good agreement with the yield strength values of the tensile tests.« less

Investigation of specimen size effects by in-situ microcompression of equal channel angular pressed copper

DOE PAGES

Howard, C.; Frazer, D.; Lupinacci, A.; ...

2015-09-30

Here, micropillar compression testing was implemented on Equal Channel Angular Pressed copper samples ranging from 200 nm to 10 µm in side length in order to measure the mechanical properties yield strength, first load drop during plastic deformation at which there was a subsequent stress decrease with increasing strain, work hardening, and strain hardening exponent. Several micropillars containing multiple grains were investigated in a 200 nm grain sample. The effective pillar diameter to grain size ratios, D/d, were measured to be between 1.9 and 27.2. Specimens having D/d ratios between 0.2 and 5 were investigated in a second sample thatmore » was annealed at 200 °C for 2 h with an average grain size of 1.3 µm. No yield strength or elastic modulus size effects were observed in specimens in the 200 nm grain size sample. However work hardening increases with a decrease in critical ratios and first stress drops occur at much lower stresses for specimens with D/d ratios less than 5. For comparison, bulk tensile testing of both samples was performed, and the yield strength values of all micropillar compression tests for the 200 nm grained sample are in good agreement with the yield strength values of the tensile tests.« less

Analysis of the microstructure and mechanical performance of composite resins after accelerated artificial aging.

PubMed

De Oliveira Daltoé, M; Lepri, C Penazzo; Wiezel, J Guilherme G; Tornavoi, D Cremonezzi; Agnelli, J A Marcondes; Reis, A Cândido Dos

2013-03-01

Researches that assess the behavior of dental materials are important for scientific and industrial development especially when they are tested under conditions that simulate the oral environment, so this work analyzed the compressive strength and microstructure of three composite resins subjected to accelerated artificial aging (AAA). Three composites resins of 3M (P90, P60 and Z100) were analyzed and were obtained 16 specimens for each type (N.=48). Half of each type were subjected to UV-C system AAA and then were analyzed the surfaces of three aged specimens and three not aged of each type through the scanning electron microscope (SEM). After, eight specimens of each resin, aged and not aged, were subjected to compression test. After statistical analysis of compressive strength values, it was found that there was difference between groups (α <0.05). The resin specimens aged P60 presented lower values of compressive strength statistically significant when compared to the not subject to the AAA. For the other composite resins, there was no difference, regardless of aging, a fact confirmed by SEM. The results showed that the AAA influenced the compressive strength of the resin aged P60; confirmed by surface analysis by SEM, which showed greater structural disarrangement on surface material.

Laser welded versus resistance spot welded bone implants: analysis of the thermal increase and strength.

PubMed

Fornaini, Carlo; Meleti, Marco; Bonanini, Mauro; Lagori, Giuseppe; Vescovi, Paolo; Merigo, Elisabetta; Nammour, Samir

2014-01-01

The first aim of this "ex vivo split mouth" study was to compare the thermal elevation during the welding process of titanium bars to titanium implants inserted in pig jaws by a thermal camera and two thermocouples. The second aim was to compare the strength of the joints by a traction test with a dynamometer. Six pigs' jaws were used and three implants were placed on each side of them for a total of 36 fixtures. Twelve bars were connected to the abutments (each bar on three implants) by using, on one side, laser welding and, on the other, resistance spot welding. Temperature variations were recorded by thermocouples and by thermal camera while the strength of the welded joint was analyzed by a traction test. For increasing temperature, means were 36.83 and 37.06, standard deviations 1.234 and 1.187, and P value 0.5763 (not significant). For traction test, means were 195.5 and 159.4, standard deviations 2.00 and 2.254, and P value 0.0001 (very significant). Laser welding was demonstrated to be able to connect titanium implant abutments without the risk of thermal increase into the bone and with good results in terms of mechanical strength.

Biomechanical and clinical factors related to stage I posterior tibial tendon dysfunction.

PubMed

Rabbito, Melissa; Pohl, Michael B; Humble, Neil; Ferber, Reed

2011-10-01

Case control. To investigate differences in arch height, ankle muscle strength, and biomechanical factors in individuals with stage I posterior tibial tendon dysfunction (PTTD) in comparison to healthy individuals. PTTD is a progressive condition, so early recognition and treatment are essential to help delay or reverse the progression. However, no previous studies have investigated stage I PTTD, and no single study has measured static anatomical structure, muscle strength, and gait mechanics in this population. Twelve individuals with stage I PTTD and 12 healthy, age- and gender-matched control subjects, who were engaged in running-related activities, participated in this study. Measurements of arch height index, maximum voluntary ankle invertor muscle strength, and 3-dimensional rearfoot and medial longitudinal arch kinematics during walking were obtained. The runners with PTTD demonstrated significantly lower seated arch height index (P = .02) and greater (P = .03) and prolonged (P = .05) peak rearfoot eversion angle during gait, compared to the healthy runners. No differences were found in standing arch height index values (P = .28), arch rigidity index (P = .06), ankle invertor strength (P = .49), or peak medial longitudinal arch values (P = .49) between groups. The increased foot pronation is hypothesized to place greater strain on the posterior tibialis muscle, which may partially explain the progressive nature of this condition.

Laser Welded versus Resistance Spot Welded Bone Implants: Analysis of the Thermal Increase and Strength

PubMed Central

Fornaini, Carlo; Meleti, Marco; Bonanini, Mauro; Lagori, Giuseppe; Vescovi, Paolo; Merigo, Elisabetta; Nammour, Samir

2014-01-01

Introduction. The first aim of this “ex vivo split mouth” study was to compare the thermal elevation during the welding process of titanium bars to titanium implants inserted in pig jaws by a thermal camera and two thermocouples. The second aim was to compare the strength of the joints by a traction test with a dynamometer. Materials and Methods. Six pigs' jaws were used and three implants were placed on each side of them for a total of 36 fixtures. Twelve bars were connected to the abutments (each bar on three implants) by using, on one side, laser welding and, on the other, resistance spot welding. Temperature variations were recorded by thermocouples and by thermal camera while the strength of the welded joint was analyzed by a traction test. Results. For increasing temperature, means were 36.83 and 37.06, standard deviations 1.234 and 1.187, and P value 0.5763 (not significant). For traction test, means were 195.5 and 159.4, standard deviations 2.00 and 2.254, and P value 0.0001 (very significant). Conclusion. Laser welding was demonstrated to be able to connect titanium implant abutments without the risk of thermal increase into the bone and with good results in terms of mechanical strength. PMID:25110731

Slope stability improvement using low intensity field electrosmosis

NASA Astrophysics Data System (ADS)

Armillotta, Pasquale

2014-05-01

The electrosmosis technique has been introduced in the past for slope stabilization. However, its application to real cases has been scarce due to several drawbacks mostly related to the high intensity electric field needed (1.0 V/cm or higher): the rapid degradation of the electrodes, the high system management cost, the heating and cracking of the soil and the reduction of its colloidal fraction. Thanks to the introduction of new materials, the technique is currently applied to decrease the consolidation time of saturated clay soils (forcing the elimination of water), consequently improving its mechanical strength. In clay soils, the volume variation is influenced by the presence of smectites. The clay compressibility decreases with the increasing of electrolytes concentration. Soil containing smectites that have interacted with calcium showed a reduction or the absence of swelling during hydration with distilled water and a positive increase of their shear strength. The different values of pH between the anode (acid) and the cathode (basic), induced by the electrosmosis create the conditions for the precipitation of CaCO3 near the cathode. The injection of solutions containing calcium in soils and their diffusion induced by the electrosmosis, lead to calcium precipitation and consequential increase of the shear strength. The material technological advances and the laboratory experiences described in this paper, demonstrate that the use low electric field (0.1 V/cm or lower) intensity electrosmosis (LEFE in acronym) can be effective for soil dewatering and shear strength increase while reducing its adverse effect. The LEFE can be used to: reduce the potential for swelling of active clay minerals through the introduction of ions and the precipitation of hardening substances; induce the "dewatering" in cohesive soils. Several Lab activities were carried out, using custom made electrosmosis equipment. These activities can be divided in two phases: Phase 1: Carbonates were mixed to a natural soil obtaining three groups of soil samples at different carbonates level; the geotechnical characterization of each group was carried out; Phase 2: LEFE was applied to induce the precipitation of CaCO3, the reduction of the swelling potential of clay minerals and the increment of the soil shear strength. The outcomes of Phase 1 indicated that: the values of specific gravity of the grains, plasticity index (PI) and Value of Blue (VB) decrease with the increase carbonate content; the shear strength increases with the carbonates content. From the second laboratory phase, we observed: an almost constant pH values within the sample; an increment of the carbonate content after LEFE treatment regardless of its duration; this increment is particularly significant after 60 days of treatment; a reduction of the swelling potential of soil; that the water content at the end of each treatment, regardless of its duration and intensity of the electric field, shows similar values; that the values of the soil shear strength (after 60 days of LEFE treatment) are always greater than those of the natural soil (average +7%). During the LEFE treatment, the pore fluid used is water taken from the local groundwater, with pH = 7.3 and hardness of 34.6 ° F. The CaCO3 content in treated samples increases with the duration of treatment. The application of LEFE appears to be effective in increasing the carbonate content and improve mechanical strenght of the soil; further development of the research will apply the LEFE to an ideal slope model and to a real case.

OsMYB103L, an R2R3-MYB transcription factor, influences leaf rolling and mechanical strength in rice (Oryza sativa L.).

PubMed

Yang, Chunhua; Li, Dayong; Liu, Xue; Ji, Chengjun; Hao, Lili; Zhao, Xianfeng; Li, Xiaobing; Chen, Caiyan; Cheng, Zhukuan; Zhu, Lihuang

2014-06-06

The shape of grass leaves possesses great value in both agronomy and developmental biology research. Leaf rolling is one of the important traits in rice (Oryza sativa L.) breeding. MYB transcription factors are one of the largest gene families and have important roles in plant development, metabolism and stress responses. However, little is known about their functions in rice. In this study, we report the functional characterization of a rice gene, OsMYB103L, which encodes an R2R3-MYB transcription factor. OsMYB103L was localized in the nucleus with transactivation activity. Overexpression of OsMYB103L in rice resulted in a rolled leaf phenotype. Further analyses showed that expression levels of several cellulose synthase genes (CESAs) were significantly increased, as was the cellulose content in OsMYB103L overexpressing lines. Knockdown of OsMYB103L by RNA interference led to a decreased level of cellulose content and reduced mechanical strength in leaves. Meanwhile, the expression levels of several CESA genes were decreased in these knockdown lines. These findings suggest that OsMYB103L may target CESA genes for regulation of cellulose synthesis and could potentially be engineered for desirable leaf shape and mechanical strength in rice.

New tools for nanotechnology and measurement of the mechanical properties of individual carbon nanotubes

NASA Astrophysics Data System (ADS)

Yu, Min-Feng

A new tool capable of three-dimensional manipulation and measurement of the mechanics of nanometer-sized materials inside a scanning electron microscopy is developed and demonstrated. The design and function of this home-built SEM nanomanipulator is explained. The first free-space manipulation of carbon nanotubes is presented. The tensile strength and the breaking mechanism of individual multi-walled carbon nanotubes (MWCNT) and single wall carbon nanotube (SWCNT) ropes are measured using the nanomanipulator, and from the data set the stress-strain relationship is determined. The results indicate that carbon nanotubes have remarkably high tensile strength values, about 50 GPa. The shear strength measurement of sliding nested shells in individual MWCNTs is also achieved for the first time. The experiment provides a new way to directly study the nano-scale interaction involved in the motion of a nanobearing. In a separate work, atomic force microscopy is used to study the lateral deformability of individual MWCNTs. The average force provided by the tapping tip in tapping mode AFM is investigated by both simulation and experiment. An imaging procedure for controlling the average tapping force is developed and is used to study the deformability of carbon nanotubes. The stability of different structures of carbon nanotube is also experimentally studied.

Influence of Annealing on Microstructure and Mechanical Properties of Refractory CoCrMoNbTi0.4 High-Entropy Alloy

NASA Astrophysics Data System (ADS)

Zhang, Mina; Zhou, Xianglin; Zhu, Wuzhi; Li, Jinghao

2018-04-01

A novel refractory CoCrMoNbTi0.4 high-entropy alloy (HEA) was prepared via vacuum arc melting. After annealing treatment at different temperatures, the microstructure evolution, phase stability, and mechanical properties of the alloy were investigated. The alloy was composed of two primary body-centered cubic structures (BCC1 and BCC2) and a small amount of (Co, Cr)2Nb-type Laves phase under different annealing conditions. The microhardness and compressive strength of the heat-treated alloy was significantly enhanced by the solid-solution strengthening of the BCC phase matrix and newborn Laves phase. Especially, the alloy annealed at 1473 K (1200 °C) achieved the maximum hardness and compressive strength values of 959 ± 2 HV0.5 and 1790 MPa, respectively, owing to the enhanced volume fraction of the dispersed Laves phase. In particular, the HEAs exhibited promising high-temperature mechanical performance, when heated to an elevated temperature of 1473 K (1200 °C), with a compressive fracture strength higher than 580 MPa without fracture at a strain of more than 20 pct. This study suggests that the present refractory HEAs have immense potential for engineering applications as a new class of high-temperature structural materials.

Experimental Study on Mechanical and Acoustic Emission Characteristics of Rock-Like Material Under Non-uniformly Distributed Loads

NASA Astrophysics Data System (ADS)

Wang, Xiao; Wen, Zhijie; Jiang, Yujing; Huang, Hao

2018-03-01

The mechanical and acoustic emission characteristics of rock-like materials under non-uniform loads were investigated by means of a self-developed mining-induced stress testing system and acoustic emission monitoring system. In the experiments, the specimens were divided into three regions and different initial vertical stresses and stress loading rates were used to simulate different mining conditions. The mechanical and acoustic emission characteristics between regions were compared, and the effects of different initial vertical stresses and different stress loading rates were analysed. The results showed that the mechanical properties and acoustic emission characteristics of rock-like materials can be notably localized. When the initial vertical stress and stress loading rate are fixed, the peak strength of region B is approximately two times that of region A, and the maximum acoustic emission hit value of region A is approximately 1-2 times that of region B. The effects of the initial vertical stress and stress loading rate on the peck strain, maximum hit value, and occurrence time of the maximum hit are similar in that when either of the former increase, the latter all decrease. However, peck strength will increase with the increase in loading rate and decrease with the increase in initial vertical stress. The acoustic emission hits can be used to analyse the damage in rock material, but the number of acoustic emission hits cannot be used alone to determine the degree of rock damage directly.

The effect of silver (Ag) addition to mechanical and electrical properties of copper alloy (Cu) casting product

NASA Astrophysics Data System (ADS)

Felicia, Dian M.; Rochiem, R.; Laia, Standley M.

2018-04-01

Copper have good mechanical properties and good electrical conductivities. Therefore, copper usually used as electrical components. Silver have better electrical conductivities than copper. Female contact resistor is one of the electrical component used in circuit breaker. This study aims to analyze the effect of silver addition to hardness, strength, and electric conductivity properties of copper alloy. This study uses variation of 0; 0.035; 0.07; 0.1 wt. % Ag (silver) addition to determine the effect on mechanical properties and electrical properties of copper alloy through sand casting process. Modelling of thermal analysis and structural analysis was calculated to find the best design for the sand casting experiments. The result of Cu-Ag alloy as cast will be characterized by OES test, metallography test, Brinell hardness test, tensile test, and LCR meter test. The result of this study showed that the addition of silver increase mechanical properties of Cu-Ag. The maximum hardness value of this alloy is 83.1 HRB which is Cu-0.01 Ag and the lowest is 52.26 HRB which is pure Cu. The maximum strength value is 153.2 MPa which is Cu-0.07 Ag and the lowest is 94.6 MPa which is pure Cu. Silver addition decrease electrical properties of this alloy. The highest electric conductivity is 438.98 S/m which is pure Cu and the lowest is 52.61 S.m which is Cu-0.1 Ag.

Acid-resistant calcium silicate-based composite implants with high-strength as load-bearing bone graft substitutes and fracture fixation devices.

PubMed

Wei, Chung-Kai; Ding, Shinn-Jyh

2016-09-01

To achieve the excellent mechanical properties of biodegradable materials used for cortical bone graft substitutes and fracture fixation devices remains a challenge. To this end, the biomimetic calcium silicate/gelatin/chitosan oligosaccharide composite implants were developed, with an aim of achieving high strength, controlled degradation, and superior osteogenic activity. The work focused on the effect of gelatin on mechanical properties of the composites under four different kinds of mechanical stresses including compression, tensile, bending, and impact. The evaluation of in vitro degradability and fatigue at two simulated body fluid (SBF) of pH 7.4 and 5.0 was also performed, in which the pH 5.0 condition simulated clinical conditions caused by bacterial induced local metabolic acidosis or tissue inflammation. In addition, human mesenchymal stem cells (hMSCs) were sued to examine osteogenic activity. Experimental results showed that the appropriate amount of gelatin positively contributed to failure enhancement in compressive and impact modes. The 10wt% gelatin-containing composite exhibits the maximum value of the compressive strength (166.1MPa), which is within the reported compressive strength for cortical bone. The stability of the bone implants was apparently affected by the in vitro fatigue, but not by the initial pH environments (7.4 or 5.0). The gelatin not only greatly enhanced the degradation of the composite when soaked in the dynamic SBF solution, but effectively promoted attachment, proliferation, differentiation, and formation of mineralization of hMSCs. The 10wt%-gelatin composite with high initial strength may be a potential implant candidate for cortical bone repair and fracture fixation applications. Copyright © 2016 Elsevier Ltd. All rights reserved.

Mechanical & morphological properties of attapulgite/NR composites: Effect of mixing time variation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Nor, Nor Aina Mohd, E-mail: ayena90@yahoo.com; Othman, Nadras, E-mail: srnadras@usm.my; Ismail, Hanafi, E-mail: ihanafi@usm.my

2015-07-22

The development of composite material based on attapulgite clay (ATP) as a filler and natural rubber (NR) matrices were prepared by combination of melt mixing and latex compounding methods. Sonication technique was chosen in this work to disperse the attapulgite suspension. 6 phr of attapulgite loading was fabricated using different time of mixing ranging from 30 minutes until 2 hours and sonication time was kept constant at 15 minutes. Then, co-coagulating HA latex with attapulgite clay suspension through latex compounding method produced the masterbatch. The masterbatch was compounded with natural rubber by melt mixing method. The mechanical and morphological characteristicsmore » were investigated in this work. From mechanical testing, M1 showed the highest value of tensile and tear strength. By comparing with M30 and M2, M1 shows high 300% tensile modulus and lower crosslink density. However, when the time of mixing was prolonged to 2 hours, the results for tensile strength, elongation at break and tear strength were decreased. This is due to flocculation of attapulgite particles. Sonication techniques also proved that the tensile strength and elongation at break of these three samples were higher compared to gum NR (NR) and attapulgite compounded with NR using a conventional method (in-situ 6). From field emission scanning electron microscope (FESEM) results, it revealed that M1 had good dispersion in the NR system. It is proved that the higher tensile strength was due to good dispersion of attapulgite clay in the NR matrix. It was also supported from crosslink density, which is lower than NR and in-situ 6 results. It showed that the penetration of toluene solvent into rubber compound was restricted. The optimum time, M1 give the best results, which can be compared to control the sample.« less

Preliminary study of the biomechanical behavior and physical characteristics of tantalum (Ta)-coated prostheses.

PubMed

Duan, Yonghong; Liu, Lie; Wang, Ling; Guo, Fei; Li, Haoping; Shi, Lei; Li, Mao; Yin, Dayu; Jiang, Chi; Zhu, Qingsheng

2012-03-01

Use of Ta biomaterials in medicine started in the middle of the last century. The good biocompatibility and chemical stability, and the unique physical characteristics of Ta metal have resulted in many possible developments of Ta biomaterials. In this study, histopathological observation, histomorphometric analysis, scanning electron microscope (SEM) observation, energy-dispersive X-ray spectroscopy (EDX) analysis, biomechanical testing, and examination of the coating's mechanical strength have been used to evaluate the value of clinical application of Ta-coated prostheses prepared by a plasma-spraying process. Histopathological observation has demonstrated that the periprosthetic new bone tissues tightly and stably adhere to the Ta coating after the implantation, with no signs of loosening. Early after implantation, there is no significant difference in periprosthetic bone volume and ultimate shear strength between Ta-coated and Ti-coated prostheses (P > 0.05). EDX analysis suggests that the ultimate shear stress does not damage Ta coating. Mechanical strength testing shows that the adhesive strength and Vicker's surface hardness (HV) of the Ta coating are significantly higher than those of the Ti coating (P < 0.01). Ta coating has good stability and bone biocompatibility; the extraordinary physical characteristics of Ta coating have great significance in maintaining prosthetic stability and surface porosity after implantation.

Spatial complexity reduces interaction strengths in the meta-food web of a river floodplain mosaic

USGS Publications Warehouse

Bellmore, James Ryan; Baxter, Colden Vance; Connolly, Patrick J.

2015-01-01

Theory states that both the spatial complexity of landscapes and the strength of interactions between consumers and their resources are important for maintaining biodiversity and the 'balance of nature.' Spatial complexity is hypothesized to promote biodiversity by reducing potential for competitive exclusion; whereas, models show weak trophic interactions can enhance stability and maintain biodiversity by dampening destabilizing oscillations associated with strong interactions. Here we show that spatial complexity can reduce the strength of consumer-resource interactions in natural food webs. By sequentially aggregating food webs of individual aquatic habitat patches across a floodplain mosaic, we found that increasing spatial complexity resulted in decreases in the strength of interactions between predators and prey, owing to a greater proportion of weak interactions and a reduced proportion of strong interactions in the meta-food web. The main mechanism behind this pattern was that some patches provided predation refugia for species which were often strongly preyed upon in other patches. If weak trophic interactions do indeed promote stability, then our findings may signal an additional mechanism by which complexity and stability are linked in nature. In turn, this may have implications for how the values of landscape complexity, and the costs of biophysical homogenization, are assessed.

Application of an Elongated Kelvin Model to Space Shuttle Foams

NASA Technical Reports Server (NTRS)

Sullivan, Roy M.; Ghosn, Louis J.; Lerch, Bradley A.

2009-01-01

The space shuttle foams are rigid closed-cell polyurethane foams. The two foams used most-extensively oil space shuttle external tank are BX-265 and NCFL4-124. Because of the foaming and rising process, the foam microstructures are elongated in the rise direction. As a result, these two foams exhibit a nonisotropic mechanical behavior. A detailed microstructural characterization of the two foams is presented. Key features of the foam cells are described and the average cell dimensions in the two foams are summarized. Experimental studies are also conducted to measure the room temperature mechanical response of the two foams in the two principal material directions (parallel to the rise and perpendicular to the rise). The measured elastic modulus, proportional limit stress, ultimate tensile strength, and Poisson's ratios are reported. The generalized elongated Kelvin foam model previously developed by the authors is reviewed and the equations which result from this model are summarized. Using the measured microstructural dimensions and the measured stiffness ratio, the foam tensile strength ratio and Poisson's ratios are predicted for both foams and are compared with the experimental data. The predicted tensile strength ratio is in close agreement with the measured strength ratio for both BX-265 and NCFI24-124. The comparison between the predicted Poisson's ratios and the measured values is not as favorable.

The effect of pre-straining and pre-ageing on a novel thermomechanical treatment for improving the mechanical properties of AA2139 aerospace aluminium alloys

NASA Astrophysics Data System (ADS)

Bakare, F.; Alsubhi, Y.; Ragkousis, A.; Ebomwonyi, O.; Damisa, J.; Okunzuwa, S.

2017-07-01

The novel thermomechanical treatment employed by Wang Z et al (2014 Mater. Sci. Eng. A 607 313-7) in enhancing the mechanical and microstructure properties of 6000 series aluminium alloys has been replicated for AA2139 aerospace aluminium alloys. The novel route which involves under-ageing, cold-rolling reductions and re-ageing at a fixed temperature has been carried out focusing on the effect of pre-straining and pre-ageing on the alloy properties. The influence of varying cold-rolling reductions and pre-ageing has been examined by tensile testing, hardness testing, differential scanning calorimetry, thermoelectric power measurements and scanning electron microscope (SEM). Further analyses were conducted with DSC and TEP measurements to check for precipitation sequence and solute retention respectively. On comparing the hardness and strength of the non pre-aged to the pre-aged samples, there is a remarkable increase in the hardness and strength of the aerospace alloy showing the huge influence of both pre-ageing and pre-straining stage of the novel thermomechanical treatment as observed in the 6000 series alloy, albeit at a higher rate. The treatments that exhibited the most promising mechanical properties (hardness, yield and ultimate tensile strength, elongation to failure) were found to be at a pre-ageing temperature of 175 °C for 1.5 h, 40% cold-rolling and re-ageing at 150 °C. The material was found to have yield strength of 590 MPa and 8.1% uniform elongation, which is well above the 5% acceptable value for structural applications and with strength levels adaptable for aerospace industries. The presence of higher volume fraction of well dispersed precipitates observed in the SEM further shows that intermediate cold-rolling reductions combines well with pre-ageing to give the best mechanical properties in this alloy.

Normative values of isometric elbow strength in healthy adults: a systematic review.

PubMed

Kotte, Shamala H P; Viveen, Jetske; Koenraadt, Koen L M; The, Bertram; Eygendaal, Denise

2018-07-01

Post-traumatic deformities such as biceps tendon rupture or (peri-)articular fractures of the elbow are often related to a decrease in muscle strength. Postoperative evaluation of these deformities requires normative values of elbow strength. The purpose of this systematic review was to determine these normative values of isometric elbow strength in healthy adults resulting from studies evaluating this strength (i.e. flexion, extension, pronation and supination strength). The databases of PubMed, EMBASE and Web of Sciences were searched and screened for studies involving the isometric elbow strength as measured in asymptomatic volunteers. The quality of the studies was assessed and studies of low quality were excluded. Nineteen studies met the inclusion criteria and were of sufficiently high quality to be included in the present review. In these studies, elbow strength was measured in a total of 1880 healthy volunteers. The experimental set-up and devices used to measure elbow strength varied between studies. Using some assumptions, a normative values table was assembled. Large standard deviations of normative values in combination with different measurement devices used, as well as the different measurement positions of the subjects, demonstrated that there is no consensus about measuring the isometric elbow strength and therefore the normative values have to be interpreted with caution.

Effect of organo clay on curing, mechanical and dielectric properties of NR/SBR blends

NASA Astrophysics Data System (ADS)

Ravikumar, K.; Joseph, Reji; Ravichandran, K.

2018-04-01

Natural rubber (NR) and styrene butadiene rubber (SBR) based elastomeric blends reinforced with organically modified Sodium bentonite clay were prepared by two roll mills. Vulcanization parameters such as minimum and maximum torque values scorch and cure times are measured by Oscillating Disc Rheometer. Mechanical properties such as Tensile strength, modulus at 100%, 200% and 300% elongation and elongation at break and Hardness were measured by Universal testing machine and Durometer Shore A hardness meter respectively. Dielectric properties such as dielectric constant (ε’), dissipation factor (tanδ) and volume resistivity (ρv) were measured at room temperature. The curing studies show that torque values are increasing in NR/SBR blends by increase NR content. The scorch and optimum cure time in NR/SBR blends reinforced organo modified clay was found through increase in the SBR content. This may be due to better processing safety of the NR/SBR blends reinforced with organo modified clay. Mechanical properties show that addition of SBR in blends, tensile strength, elongation modulus increases, but 100% modulus slightly increases and no change was observed in Hardness. Dielectric studies show that dielectric constant of NR and SBR rubbers are almost same, it may due to their non-polar nature. But addition of SBR in NR/SBR blend, dielectric constant gradually increases and maximum value observed at 50/50 ratio. But no considerable change was observed in dissipation factor. Frequency dependant resistivity shows that volume resistivity was not changed with respect to frequency up to 3.5 kHz and beyond that the frequency dependence resistivity was found.

Effect of in vitro aging on the flexural strength and probability to fracture of Y-TZP zirconia ceramics for all-ceramic restorations.

PubMed

Siarampi, Eleni; Kontonasaki, Eleana; Andrikopoulos, Konstantinos S; Kantiranis, Nikolaos; Voyiatzis, George A; Zorba, Triantafillia; Paraskevopoulos, Konstantinos M; Koidis, Petros

2014-12-01

Dental zirconia restorations should present long-term clinical survival and be in service within the oral environment for many years. However, low temperature degradation could affect their mechanical properties and survival. The aim of this study was to investigate the effect of in vitro aging on the flexural strength of yttrium-stabilized (Y-TZP) zirconia ceramics for ceramic restorations. One hundred twenty bar-shaped specimens were prepared from two ceramics (ZENO Zr (WI) and IPS e.max(®) ZirCAD (IV)), and loaded until fracture according to ISO 6872. The specimens from each ceramic (nx=60) were divided in three groups (control, aged for 5h, aged for 10h). One-way ANOVA was used to assess statistically significant differences among flexural strength values (P<0.05). The variability of the flexural strength values was analyzed using the two-parameter Weibull distribution function, which was applied for the estimation of Weibull modulus (m) and characteristic strength (σ0). The crystalline phase polymorphs of the materials (tetragonal, t, and monoclinic, m, zirconia) were investigated by X-ray diffraction (XRD) analysis, Raman spectroscopy and Fourier transform infrared (FTIR) spectroscopy. A slight increase of the flexural strength after 5h, and a decrease after 10h of aging, was recorded for both ceramics, however statistically significant was for the WI group (P<0.05). Both ceramics presented a t→m phase transformation, with the m-phase increasing from 4 to 5% at 5h to around 15% after 10h. The significant reduction of the flexural strength after 10h of in vitro aging, suggests high fracture probability for one of the zirconia ceramics tested. Copyright © 2014 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Characterization of Mechanical Properties of Nuclear Graphite Using Subsize Specimens and Reusing Tested Specimens

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ji Hyun, Yoon; Byun, Thak Sang; Strizak, Joe P

2011-01-01

The mechanical properties of NBG-18 nuclear grade graphite have been characterized using small specimen test techniques and statistical treatment on the test results. New fracture strength and toughness test techniques were developed to use subsize cylindrical specimens with glued heads and to reuse their broken halves. Three sets of subsize cylindrical specimens with the different diameters of 4 mm, 8 mm, and 12 mm were tested to obtain tensile fracture strength. The longer piece of the broken halves was cracked from side surfaces and tested under three-point bend loading to obtain fracture toughness. Both the strength and fracture toughness datamore » were analyzed using Weibull distribution models focusing on size effect. The mean fracture strength decreased from 22.9 MPa to 21.5 MPa as the diameter increased from 4 mm to 12 mm, and the mean strength of 15.9 mm diameter standard specimen, 20.9 MPa, was on the extended trend line. These fracture strength data indicate that in the given diameter range the size effect is not significant and much smaller than that predicted by the Weibull statistics-based model. Further, no noticeable size effect existed in the fracture toughness data, whose mean values were in a narrow range of 1.21 1.26 MPa. The Weibull moduli measured for fracture strength and fracture toughness datasets were around 10. It is therefore believed that the small or negligible size effect enables to use the subsize specimens and that the new fracture toughness test method to reuse the broken specimens to help minimize irradiation space and radioactive waste.« less

Mechanical Characteristics of Resin-Coated Papers and their Electrical Breakdown Characteristics in Composite Insulation Systems with Insulation Oil

NASA Astrophysics Data System (ADS)

Kurihara, Takashi; Takahashi, Toshihiro; Mizutani, Yoshinobu; Suzuki, Hiroshi; Okamoto, Tatsuki; Ogura, Nobuyuki; Iwamoto, Kazuyoshi; Kitagawa, Setsuo

Three types of resin-coated papers were investigated; kraft papers and heat-resistant kraft papers partially covered with epoxy resin, and a kraft paper covered with phenol resin; those were laminated to certain thickness. They were thermally degraded at 120°C for 240 to 1320 hours, and their mechanical characteristics such as tensile strength and average polymerization degree were measured. As a result, it was found that the tensile strength of the first and second resin-coated papers was larger than that of the pressboard, but the tensile strength of the third one was smaller. As the effect of the heating time, it was found that the tensile strength of the first resin-coated paper decreased down to that of pressboards after 500 hours of heating time while those of the second and third ones almost retained the initial values after 1320 hours of the heating time. Then, electrical breakdown characteristics of composite insulation systems with a resin-coated paper and insulation oil were investigated. In the system, an oil-filled gap was artificially introduced between a resin-coated paper and a plane electrode to induce partial discharges (PDs) at the same location. PDs occurred before breakdowns and it was found that their PD inception electric field strength was almost as high as that of the pressboard and the effect of the heating time was negligible. It was also found that the electrical breakdown field strength has similar characteristics to those of the PD inception field strength; negligible effects of the type of resin-coated papers and the heating time. Electrical breakdown occurred at the oil-filled gap and the edge of a high voltage electrode.

Effect of stacking fault energy on mechanism of plastic deformation in nanotwinned FCC metals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.

Starting from a semi-empirical potential designed for Cu, we have developed a series of potentials that provide essentially constant values of all significant (calculated) materials properties except for the intrinsic stacking fault energy, which varies over a range that encompasses the lowest and highest values observed in nature. In addition, these potentials were employed in molecular dynamics (MD) simulations to investigate how stacking fault energy affects the mechanical behavior of nanotwinned face-centered cubic (FCC) materials. The results indicate that properties such as yield strength and microstructural stability do not vary systematically with stacking fault energy, but rather fall into twomore » distinct regimes corresponding to 'low' and 'high' stacking fault energies.« less

Effect of stacking fault energy on mechanism of plastic deformation in nanotwinned FCC metals

DOE PAGES

Borovikov, Valery; Mendelev, Mikhail I.; King, Alexander H.; ...

2015-05-15

Starting from a semi-empirical potential designed for Cu, we have developed a series of potentials that provide essentially constant values of all significant (calculated) materials properties except for the intrinsic stacking fault energy, which varies over a range that encompasses the lowest and highest values observed in nature. In addition, these potentials were employed in molecular dynamics (MD) simulations to investigate how stacking fault energy affects the mechanical behavior of nanotwinned face-centered cubic (FCC) materials. The results indicate that properties such as yield strength and microstructural stability do not vary systematically with stacking fault energy, but rather fall into twomore » distinct regimes corresponding to 'low' and 'high' stacking fault energies.« less

Behaviour of Rotating Bose Einstein Condensates Under Shrinking

NASA Astrophysics Data System (ADS)

Zhai, Hui; Zhou, Qi

2005-01-01

When the repulsive interaction strength between atoms decreases, the size of a rotating Bose-Einstein condensate will consequently shrink. We find that the rotational frequency will increase during the shrinking of condensate, which is a quantum mechanical analogy to ballet dancing. Compared to a non-rotating condensate, the size of a rotating BEC will eventually be saturated at a finite value when the interaction strength is gradually reduced. We also calculate the vortex dynamics induced by the atomic current, and discuss the difference of vortex dynamics in this case and that observed in a recent experiment carried out by the JILA group [Phys. Rev. Lett. 90 (2003) 170405].

Influence of board density, mat construction, and chip type on performance of particleboard made from eastern redcedar

Treesearch

Zhiyong Cai; Qinglin Wu; Jong N. Lee; Salim Hiziroglu

2004-01-01

The purpose of this study was to investigate mechanical and physical performances of particleboard made from low-value eastern redcedar trees. The properties evaluated included bending strength and stiffness, swelling, surface hardness, and screw holding capacity as a function of processing variables (i.e., density, chip type, and board construction). Two types of...

Fracture toughness study on LIGA fabricated microstructures

NASA Astrophysics Data System (ADS)

Oropeza, Catherine; Lian, Kun; Wang, Wanjun

2003-01-01

One of the major difficulties faced by MEMS researchers today is the lack of data regarding properties of electroplated metals or alloys at micro-levels as those produced by the LIGA and the LIGA related process. These mechanical properties are not well known and they cannot be extrapolated from macro-scale data without experimental verification. This lack of technical information about physical properties at microscale has affected the consistency and reliability of batch-fabricated components and leads to very low rates of successful fabrication. Therefore, this material issue is of vital importance to the development of LIGA technology and to its industrial applications. The research work reported in this paper focuses on the development of a new capability based on design, fabrication, and testing of groups of UV-LIGA fabricated nickel microspecimens for the evaluation of fracture strength. The devised testing mechanism demonstrated compatibility with the fabricated samples and capability of performing the desired experimentation by generating resistance-to-fracture values of the nickel specimens. The average fracture strength value obtained, expressed with a 95% confidence interval, was 315 +/- 54 Mpa. Further data acquisition, especially involving tensile specimen testing, and material analysis is needed to fully understand the implications of the information obtained.

Tensile Properties and Fracture Characteristics of Nanostructured Copper and Cu-SiC Nanocomposite Produced by Mechanical Milling and Spark Plasma Sintering Process

NASA Astrophysics Data System (ADS)

Akbarpour, M. R.

2018-03-01

The presence of large grains within nanometric and ultrafine grain matrix is an effective method in order to enhance strength while keeping the high ductility of metals. For this purpose, in this research, spark plasma sintering (SPS) was used to consolidate milled Cu and Cu-SiC powders. In SPS process, local sparks with high temperature between particles take place and locally lead to intense grain growth, and therefore, this method has the ability to produce bimodal grain structures in copper and copper-based composites. Microstructural and mechanical studies showed ≈ 185 and ≈ 437 nm matrix grain sizes, high tensile yield strength values of ≈ 188.4 and ≈ 296.9 MPa, and fracture strain values of 15.1 and 6.7% for sintered Cu and Cu-4 vol.% SiC nanocomposite materials, respectively. The presence of nanoparticles promoted the occurrence of static recrystallization and decreased the fraction of coarse grains in microstructure. The high tensile properties of the produced materials are attributed to fine grain size, homogenous dispersion of nanoparticles and retarded grain boundary migration during sintering.

Prediction of mechanical and wear properties of 6026 aluminum alloy waste to be used in prosthetics limbs

NASA Astrophysics Data System (ADS)

Arbilei, Marwan N.

2018-05-01

This paper aimed to recycle high power electrical wires west in prosthetics limbs manufacturing. The effect of grain size on mechanical properties (Hardness and Tensile Strength), and wear resistance of commercial 6026 T9 Aluminum alloys that used in electrical industry have been modeled to be predicted. Six sets of samples were prepared with different annealing heat treatment parameters, (300,350 and 400)°C with (1 and 2) hours. Each treatment gained different grain sizes (23-71) μm and evenly HV (61-169) values. The grain size that produced from heat treatments was ranged from. Tensile properties regarding HV have been reviewed and all data haven collected to create a mathematical model showing the relation between Tensile strength and Hardness. The Sliding wear tests applied with (3 and 8) N with five periods (20-100) minutes. Multiple regression model prepared for predicting the values of weight loss for wear process. The model was tested and validated for the properties. The main purpose of this research is to provide an effective and accurate way to predict weight loose rate in wear process.

Investigation of Microstructure and Mechanical Properties of ECAP-Processed AM Series Magnesium Alloy

NASA Astrophysics Data System (ADS)

Gopi, K. R.; Nayaka, H. Shivananda; Sahu, Sandeep

2016-09-01

Magnesium alloy Mg-Al-Mn (AM70) was processed by equal channel angular pressing (ECAP) at 275 °C for up to 4 passes in order to produce ultrafine-grained microstructure and improve its mechanical properties. ECAP-processed samples were characterized for microstructural analysis using optical microscopy, scanning electron microscopy, and transmission electron microscopy. Microstructural analysis showed that, with an increase in the number of ECAP passes, grains refined and grain size reduced from an average of 45 to 1 µm. Electron backscatter diffraction analysis showed the transition from low angle grain boundaries to high angle grain boundaries in ECAP 4 pass sample as compared to as-cast sample. The strength and hardness values an showed increasing trend for the initial 2 passes of ECAP processing and then started decreasing with further increase in the number of ECAP passes, even though the grain size continued to decrease in all the successive ECAP passes. However, the strength and hardness values still remained quite high when compared to the initial condition. This behavior was found to be correlated with texture modification in the material as a result of ECAP processing.

Developmental biomechanics of neck musculature

PubMed Central

Lavallee, Amy V.; Ching, Randal P.; Nuckley, David J.

2012-01-01

Neck mechanics is central to head injury prevention since it is the musculoskeletal neck, which dictates the position and movement of the head. In the US, traumatic injury is the leading cause of death for children; however prevention is hampered by the lack of data concerning the mechanics of the immature head-and-neck. Thus, the objective of this study was to quantify neck muscle strength and endurance across the maturation spectrum and correlate these with head-and-neck anthropometry. A factorial study was performed on 91 human subjects measuring head-and-neck anthropometry and neck strength and endurance in three bending directions (flexion, extension, and lateral) as a function of age (6–23 years). Using a custom device, neck maximum voluntary contraction (MVC) force was measured in triplicate. Next, neck muscle endurance (sustained effort) was measured as the subjects’ ability to maintain 70% of peak force over 30 s. Linear regression of peak force and endurance as a function of age revealed each direction to significantly (p<0.0001) increase with age. The MVC force, averaged across all directions and normalized to the adult values, exhibits the following maturation curve: %MVC Force= −0.0879(age)2+6.018(age)+8.120. Neck muscle strength, similar between young males and females, becomes disparate in adolescence and adulthood with males exhibiting greater strength. Bending direction differences were also found with extension strength being the greatest regardless of age and sex. Furthermore, neck circumference appears predictive of neck strength and endurance in children. Together, these relationships may facilitate improved design of injury prevention interventions. PMID:23127787

Analysis of mechanical strength to fixing the femoral neck fracture in synthetic bone type Asnis

PubMed Central

Freitas, Anderson; Lula, Welder Fernandes; de Oliveira, Jonathan Sampaio; Maciel, Rafael Almeida; Souto, Diogo Ranier de Macedo; Godinho, Patrick Fernandes

2014-01-01

OBJECTIVE: To analyze the results of biomechanical assays of fixation of Pauwels type III femoral neck fracture in synthetic bone, using 7.5mm cannulated screws in inverted triangle formation, in relation to the control group. METHODS: Ten synthetic bones were used, from a domestic brand, divided into two groups: test and control. In the test group, a 70° tilt osteotomy of the femoral neck was fixated using three cannulated screws in inverted triangle formation. The resistance of this fixation and its rotational deviation were analyzed at 5mm displacement (phase 1) and 10mm displacement (phase 2). The control group was tested in its integrity until the fracture of the femoral neck occurred. The Mann-Whitney test was used for group analysis and comparison. RESULTS: The values in the test group in phase 1, in samples 1-5, showed a mean of 579N and SD =77N. Rotational deviations showed a mean of 3.33°, SD = 2.63°. In phase 2, the mean was 696N and SD =106N. The values of the maximum load in the control group had a mean of 1329N and SD=177N. CONCLUSION: The analysis of mechanical strength between the groups determined a statistically significant lower value in the test group. Level of Evidence III, Control Case. PMID:25246851

Interface morphology and mechanical properties of Al-Cu-Al laminated composites fabricated by explosive welding and subsequent rolling process

NASA Astrophysics Data System (ADS)

Hoseini-Athar, M. M.; Tolaminejad, B.

2016-07-01

Explosive welding is a well-known solid state method for joining similar and dissimilar materials. In the present study, tri-layered Al-Cu-Al laminated composites with different interface morphologies were fabricated by explosive welding and subsequent rolling. Effects of explosive ratio and rolling thickness reduction on the morphology of interface and mechanical properties were evaluated through optical/scanning electron microscopy, micro-hardness, tensile and tensile-shear tests. Results showed that by increasing the thickness reduction, bonding strength of specimens including straight and wavy interfaces increases. However, bonding strength of the specimens with melted layer interface decreases up to a threshold thickness reduction, then rapidly increases by raising the reduction. Hardness Values of welded specimens were higher than those of original material especially near the interface and a more uniform hardness profile was obtained after rolling process.

Fabrication of Al/Mg/Al Composites via Accumulative Roll Bonding and Their Mechanical Properties

PubMed Central

Nie, Jinfeng; Liu, Mingxing; Wang, Fang; Zhao, Yonghao; Li, Yusheng; Cao, Yang; Zhu, Yuntian

2016-01-01

Al(1060)/Mg(AZ31)/Al(1060) multilayered composite was successfully produced using an accumulative roll bonding (ARB) process for up to four cycles at an elevated temperature (400 °C). The microstructure evolution of the composites and the bonding characteristics at the interfaces between Al and Mg layers with increasing ARB cycles were characterized through optical microscopy, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). It was found that the grains of Al and Mg layers were significantly refined and Al3Mg2 and Al12 Mg17 intermetallic compound layers formed at the Al/Mg bonding interfaces. The strength increased gradually and the ultimate tensile strength (UTS) reached a maximum value of about 240 MPa at the third pass. Furthermore, the strengthening mechanism of the composite was analyzed based on the fracture morphologies. PMID:28774072

Application of bioethanol derived lignin for improving physico-mechanical properties of thermoset biocomposites.

PubMed

Bajwa, Dilpreet S; Wang, Xinnan; Sitz, Evan; Loll, Tyler; Bhattacharjee, Sujal

2016-08-01

Lignin is the most abundant of renewable polymers next to cellulose with a global annual production of 70million tons, largely produced from pulping and second generation biofuel industries. Low value of industrial lignin makes it an attractive biomaterial for wide range of applications. The study investigated the application of wheat straw and corn stover based lignin derived from ethanol production for use in thermoset biocomposites. The biocomposite matrix constituted a two component low viscosity Araldite(®)LY 8601/Aradur(®) 8602 epoxy resin system and the lignin content varied from 0 to 25% by weight fraction. The analysis of the physical and mechanical properties of the biocomposites show bioethanol derived lignin can improve selective properties such as impact strength, and thermal stability without compromising the modulus and strength attributes. Copyright © 2016 Elsevier B.V. All rights reserved.

Brillouin light scattering spectroscopy for tissue engineering application

NASA Astrophysics Data System (ADS)

Akilbekova, Dana; Yakupov, Talgat; Ogay, Vyacheslav; Umbayev, Bauyrzhan; Yakovlev, Vladislav V.; Utegulov, Zhandos N.

2018-02-01

Biomechanical properties of mammalian bones, such as strength, toughness and plasticity, are essential for understanding how microscopic scale mechanical features can link to macroscale bones' strength and fracture resistance. We employ Brillouin light scattering (BLS) micro-spectroscopy for local assessment of elastic properties of bones under compression and the efficacy of the tissue engineering approach based on heparin-conjugated fibrin (HCF) hydrogels, bone morphogenic proteins (BMPs) and osteogenic stem cells in the regeneration of the bone tissues. BLS is noninvasive and label-free imaging modality for probing mechanical properties of hard tissues that can give information on structure-function properties of normal and pathological tissues. Results showed that HCF gels containing combination of all factors had the best effect with complete defect regeneration at week 9 and that the bones with fully consolidated fractures have higher values of elastic moduli compared to the bones with defects.

Avalanche weak layer shear fracture parameters from the cohesive crack model

NASA Astrophysics Data System (ADS)

McClung, David

2014-05-01

Dry slab avalanches release by mode II shear fracture within thin weak layers under cohesive snow slabs. The important fracture parameters include: nominal shear strength, mode II fracture toughness and mode II fracture energy. Alpine snow is not an elastic material unless the rate of deformation is very high. For natural avalanche release, it would not be possible that the fracture parameters can be considered as from classical fracture mechanics from an elastic framework. The strong rate dependence of alpine snow implies that it is a quasi-brittle material (Bažant et al., 2003) with an important size effect on nominal shear strength. Further, the rate of deformation for release of an avalanche is unknown, so it is not possible to calculate the fracture parameters for avalanche release from any model which requires the effective elastic modulus. The cohesive crack model does not require the modulus to be known to estimate the fracture energy. In this paper, the cohesive crack model was used to calculate the mode II fracture energy as a function of a brittleness number and nominal shear strength values calculated from slab avalanche fracture line data (60 with natural triggers; 191 with a mix of triggers). The brittleness number models the ratio of the approximate peak value of shear strength to nominal shear strength. A high brittleness number (> 10) represents large size relative to fracture process zone (FPZ) size and the implications of LEFM (Linear Elastic Fracture Mechanics). A low brittleness number (e.g. 0.1) represents small sample size and primarily plastic response. An intermediate value (e.g. 5) implies non-linear fracture mechanics with intermediate relative size. The calculations also implied effective values for the modulus and the critical shear fracture toughness as functions of the brittleness number. The results showed that the effective mode II fracture energy may vary by two orders of magnitude for alpine snow with median values ranging from 0.08 N/m (non-linear) to 0.18 N/m (LEFM) for median slab density around 200 kg/m3. Schulson and Duval (2009) estimated the fracture energy of solid ice (mode I) to be about 0.22-1 N/m which yields rough theoretical limits of about 0.05- 0.2 N/m for density 200 kg/m3 when the ice volume fraction is accounted for. Mode I results from lab tests (Sigrist, 2006) gave 0.1 N/m (200 kg/m3). The median effective mode II shear fracture toughness was calculated between 0.31 to 0.35 kPa(m)1/2 for the avalanche data. All the fracture energy results are much lower than previously calculated from propagation saw tests (PST) results for a weak layer collapse model (1.3 N/m) (Schweizer et al., 2011). The differences are related to model assumptions and estimates of the effective slab modulus. The calculations in this paper apply to quasi-static deformation and mode II weak layer fracture whereas the weak layer collapse model is more appropriate for dynamic conditions which follow fracture initiation (McClung and Borstad, 2012). References: Bažant, Z.P. et al. (2003) Size effect law and fracture mechanics of the triggering of dry snow slab avalanches, J. Geophys. Res. 108(B2): 2119, doi:10.1029/2002JB))1884.2003. McClung, D.M. and C.P. Borstad (2012) Deformation and energy of dry snow slabs prior to fracture propagation, J. Glaciol. 58(209), 2012 doi:10.3189/2012JoG11J009. Schulson, E.M and P. Duval (2009) Creep and fracture of ice, Cambridge University Press, 401 pp. Schweizer, J. et al. (2011) Measurements of weak layer fracture energy, Cold Reg. Sci. and Tech. 69: 139-144. Sigrist, C. (2006) Measurement of fracture mechanical properties of snow and application to dry snow slab avalanche release, Ph.D thesis: 16736, ETH, Zuerich: 139 pp.

Strengthening Mechanisms in Microtruss Metals

NASA Astrophysics Data System (ADS)

Ng, Evelyn K.

Microtrusses are hybrid materials composed of a three-dimensional array of struts capable of efficiently transmitting an externally applied load. The strut connectivity of microtrusses enables them to behave in a stretch-dominated fashion, allowing higher specific strength and stiffness values to be reached than conventional metal foams. While much attention has been given to the optimization of microtruss architectures, little attention has been given to the strengthening mechanisms inside the materials that make up this architecture. This thesis examines strengthening mechanisms in aluminum alloy and copper alloy microtruss systems with and without a reinforcing structural coating. C11000 microtrusses were stretch-bend fabricated for the first time; varying internal truss angles were selected in order to study the accumulating effects of plastic deformation and it was found that the mechanical performance was significantly enhanced in the presence of work hardening with the peak strength increasing by a factor of three. The C11000 microtrusses could also be significantly reinforced with sleeves of electrodeposited nanocrystalline Ni-53wt%Fe. It was found that the strength increase from work hardening and electrodeposition were additive over the range of structures considered. The AA2024 system allowed the contribution of work hardening, precipitation hardening, and hard anodizing to be considered as interacting strengthening mechanisms. Because of the lower formability of AA2024 compared to C11000, several different perforation geometries in the starting sheet were considered in order to more effectively distribute the plastic strain during stretch-bend fabrication. A T8 condition was selected over a T6 condition because it was shown that the plastic deformation induced during the final step was sufficient to enhance precipitation kinetics allowing higher strengths to be reached, while at the same time eliminating one annealing treatment. When hard anodizing treatments were conducted on O-temper and T8 temper AA2024 truss cores, the strength increase was different for different architectures, but was nearly the same for the two parent material tempers. Finally, the question of how much microtruss strengthening can be obtained for a given amount of parent metal strengthening was addressed by examining the interaction of material and geometric parameters in a model system.

Ultra-high modulus organic fiber hybrid composites

NASA Technical Reports Server (NTRS)

Champion, A. R.

1981-01-01

An experimental organic fiber, designated Fiber D, was characterized, and its performance as a reinforcement for composites was investigated. The fiber has a modulus of 172 GPa, tensile strength of 3.14 GPa, and density of 1.46 gm/cu cm. Unidirectional Fiber D/epoxy laminates containing 60 percent fiber by volume were evaluated in flexure, shear, and compression, at room temperature and 121 C in both the as fabricated condition and after humidity aging for 14 days at 95 percent RH and 82 C. A modulus of 94.1 GPa, flexure strength of 700 MPa, shear strength of 54 MPa, and compressive strength of 232 MPa were observed at room temperature. The as-fabricated composites at elevated temperature and humidity aged material at room temperature had properties 1 to 20 percent below these values. Combined humidity aging plus evaluated temperature testing resulted in even lower mechanical properties. Hybrid composite laminates of Fiber D with Fiber FP alumina or Thornel 300 graphite fiber were also evaluated and significant increases in modulus, flexure, and compressive strengths were observed.

Perturbation theory for arbitrary coupling strength?

NASA Astrophysics Data System (ADS)

Mahapatra, Bimal P.; Pradhan, Noubihary

2018-03-01

We present a new formulation of perturbation theory for quantum systems, designated here as: “mean field perturbation theory” (MFPT), which is free from power-series-expansion in any physical parameter, including the coupling strength. Its application is thereby extended to deal with interactions of arbitrary strength and to compute system-properties having non-analytic dependence on the coupling, thus overcoming the primary limitations of the “standard formulation of perturbation theory” (SFPT). MFPT is defined by developing perturbation about a chosen input Hamiltonian, which is exactly solvable but which acquires the nonlinearity and the analytic structure (in the coupling strength) of the original interaction through a self-consistent, feedback mechanism. We demonstrate Borel-summability of MFPT for the case of the quartic- and sextic-anharmonic oscillators and the quartic double-well oscillator (QDWO) by obtaining uniformly accurate results for the ground state of the above systems for arbitrary physical values of the coupling strength. The results obtained for the QDWO may be of particular significance since “renormalon”-free, unambiguous results are achieved for its spectrum in contrast to the well-known failure of SFPT in this case.

Award-Winning CARES/Life Ceramics Durability Evaluation Software Is Making Advanced Technology Accessible

NASA Technical Reports Server (NTRS)

1997-01-01

Products made from advanced ceramics show great promise for revolutionizing aerospace and terrestrial propulsion and power generation. However, ceramic components are difficult to design because brittle materials in general have widely varying strength values. The CARES/Life software developed at the NASA Lewis Research Center eases this by providing a tool that uses probabilistic reliability analysis techniques to optimize the design and manufacture of brittle material components. CARES/Life is an integrated package that predicts the probability of a monolithic ceramic component's failure as a function of its time in service. It couples commercial finite element programs--which resolve a component's temperature and stress distribution - with reliability evaluation and fracture mechanics routines for modeling strength - limiting defects. These routines are based on calculations of the probabilistic nature of the brittle material's strength.

Effects of neutral sodium hydrogen phosphate on setting reaction and mechanical strength of hydroxyapatite putty.

PubMed

Ishikawa, K; Miyamoto, Y; Takechi, M; Ueyama, Y; Suzuki, K; Nagayama, M; Matsumura, T

1999-03-05

The setting reaction and mechanical strength in terms of diametral tensile strength (DTS) of hydroxyapatite (HAP) putty made of tetracalcium phosphate, dicalcium phosphate anhydrous, and neutral sodium hydrogen phosphate (Na1.8H1.2PO4) solution containing 8 wt % sodium alginate were evaluated as a function of the Na1.8H1.2PO4 concentration. In one condition, HAP putty was placed in an incubator kept at 37 degrees C and 100% relative humidity. In the other condition, immediately after mixing HAP putty was immersed in serum kept at 37 degrees C. Longer setting times and lower DTS values were observed when HAP putty was immersed in serum regardless of the Na1.8H1.2PO4 concentration. The setting times of the HAP putty in both conditions became shorter with an increase in the Na1. 8H1.2PO4 concentration, reaching approximately 7-13 min when the Na1. 8H1.2PO4 concentration was 0.6 mol/L or higher. The DTS value of HAP putty was relatively constant (10 MPa) regardless of the Na1.8H1. 2PO4 concentration (0.2-1.0 mol/L) when HAP putty was kept in an incubator. In contrast, when HAP putty was immersed in serum, the DTS value was dependent on the Na1.8H1.2PO4 concentration. It increased with the Na1.8H1.2PO4 concentration and reached approximately 5 MPa when the Na1.8H1.2PO4 concentration was 0.6 mol/L, after which it showed a relatively constant DTS value. We therefore would recommend a HAP putty that uses 0.6 mol/L Na1.8H1. 2PO4 since at that concentration the putty's setting time (approximately 10 min) is proper for clinical use and it shows good DTS value (approximately 5 MPa) even when it is immersed in serum immediately after mixing. Copyright 1999 John Wiley & Sons, Inc.

Mechanical properties of silorane-based and methacrylate-based composite resins after artificial aging.

PubMed

de Castro, Denise Tornavoi; Lepri, César Penazzo; Valente, Mariana Lima da Costa; dos Reis, Andréa Cândido

2016-01-01

The aim of this study was to compare the compressive strength of a silorane-based composite resin (Filtek P90) to that of conventional composite resins (Charisma, Filtek Z250, Fill Magic, and NT Premium) before and after accelerated artificial aging (AAA). For each composite resin, 16 cylindrical specimens were prepared and divided into 2 groups. One group underwent analysis of compressive strength in a universal testing machine 24 hours after preparation, and the other was subjected first to 192 hours of AAA and then the compressive strength test. Data were analyzed by analysis of variance, followed by the Tukey HSD post hoc test (α = 0.05). Some statistically significant differences in compressive strength were found among the commercial brands (P < 0.001). The conventional composite resin Fill Magic presented the best performance before (P < 0.05) and after AAA (P < 0.05). Values for compressive strength of the silorane-based composite were among the lowest obtained, both before and after aging. Comparison of each material before and after AAA revealed that the aging process did not influence the compressive strength of the tested resins (P = 0.785).

Temperature effects on the mechanical properties of annealed and HERF 304L stainless steel.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antoun, Bonnie R.

2004-11-01

The effect of temperature on the tensile properties of annealed 304L stainless steel and HERF 304L stainless steel forgings was determined by completing experiments over the moderate range of -40 F to 160 F. Temperature effects were more significant in the annealed material than the HERF material. The tensile yield strength of the annealed material at -40 F averaged twenty two percent above the room temperature value and at 160 F averaged thirteen percent below. The tensile yield strength for the three different geometry HERF forgings at -40 F and 160 F changed less than ten percent from room temperature.more » The ultimate tensile strength was more temperature dependent than the yield strength. The annealed material averaged thirty six percent above and fourteen percent below the room temperature ultimate strength at -40 F and 160 F, respectively. The HERF forgings exhibited similar, slightly lower changes in ultimate strength with temperature. For completeness and illustrative purposes, the stress-strain curves are included for each of the tensile experiments conducted. The results of this study prompted a continuation study to determine tensile property changes of welded 304L stainless steel material with temperature, documented separately.« less

Mechanical and bond strength properties of light-cured and chemically cured glass ionomer cements.

PubMed

McCarthy, M F; Hondrum, S O

1994-02-01

The purpose of this study was to evaluate the mechanical and bond strength properties of a commercially available light-cured glass ionomer cement and of a chemically cured glass ionomer cement. Sixty recently extracted human molars were randomly divided into six equal groups, and the bond strengths of the two cement types were evaluated at 1 hour, 24 hours, and 7 days. Stainless steel lingual buttons were bonded to prepared enamel surfaces, and the samples were placed in a water bath at 37 degrees C until testing. The shear bond strength of each sample was determined with a universal testing instrument. The mechanical strength properties of the two cements were then evaluated. The transverse flexural strength, compressive strength, rigidity, and diametral tensile strength were tested for each cement at 1 hour, 24 hours, and 7 days. The results of the mechanical property strength tests were then compared with the results of the bond strength tests.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of SiO2 nano-particles on tribological and mechanical properties of aluminum matrix composites by different dispersion methods

NASA Astrophysics Data System (ADS)

Azadi, Mahboobeh; Zolfaghari, Mehrdad; Rezanezhad, Saeid; Azadi, Mohammad

2018-05-01

This study has been presented with mechanical properties of aluminum matrix composites, reinforced by SiO2 nano-particles. The stir casting method was employed to produce various aluminum matrix composites. Different composites by varying the SiO2 nano-particle content (including 0.5 and 1 weight percents) and two dispersion methods (including ball-milling and pre-heating) were made. Then, the density, the hardness, the compression strength, the wear resistance and the microstructure of nano-composites have been studied in this research. Besides, the distribution of nano-particles in the aluminum matrix for all composites has been also evaluated by the field emission scanning electron microscopy (FESEM). Obtained results showed that the density, the elongation and the ultimate compressive strength of various nano-composites decreased by the presence of SiO2 nano-particles; however, the hardness, the wear resistance, the yield strength and the elastic modulus of composites increased by auditioning of nano-particles to the aluminum alloy. FESEM images indicated better wetting of the SiO2 reinforcement in the aluminum matrix, prepared by the pre-heating dispersion method, comparing to ball-milling. When SiO2 nano-particles were added to the aluminum alloy, the morphology of the Si phase and intermetallic phases changed, which enhanced mechanical properties. In addition, the wear mechanism plus the friction coefficient value were changed for various nano-composites with respect to the aluminum alloy.

The Mechanism of High Strength-Ductility Steel Produced by a Novel Quenching-Partitioning-Tempering Process and the Mechanical Stability of Retained Austenite at Elevated Temperatures

NASA Astrophysics Data System (ADS)

Zhou, S.; Zhang, K.; Wang, Y.; Gu, J. F.; Rong, Y. H.

2012-03-01

The designed steel of Fe-0.25C-1.5Mn-1.2Si-1.5Ni-0.05Nb (wt pct) treated by a novel quenching-partitioning-tempering (Q-P-T) process demonstrates an excellent product of strength and elongation (PSE) at deformed temperatures from 298 K to 573 K (25 °C to 300 °C) and shows a maximum value of PSE (over 27,000 MPa pct) at 473 K (200 °C). The results fitted by the exponent decay law indicate that the retained austenite fraction with strain at a deformed temperature of 473 K (200 °C) decreases slower than that at 298 K (25 °C); namely, the transformation induced plasticity (TRIP) effect occurs in a larger strain range at 473 K (200 °C) than at 298 K (25 °C), showing better mechanical stability. The work-hardening exponent curves of Q-P-T steel further indicate that the largest plateau before necking appears at the deformed temperature of 473 K (200 °C), showing the maximum TRIP effect, which is due to the mechanical stability of considerable retained austenite. The microstructural characterization reveals that the high strength of Q-P-T steels results from dislocation-type martensite laths and dispersively distributed fcc NbC or hcp ɛ-carbides in martensite matrix, while excellent ductility is attributed to the TRIP effect produced by considerable retained austenite.

Lithospheric flexural strength and effective elastic thicknesses of the Eastern Anatolia (Turkey) and surrounding region

NASA Astrophysics Data System (ADS)

Oruç, Bülent; Gomez-Ortiz, David; Petit, Carole

2017-12-01

The Lithospheric structure of Eastern Anatolia and the surrounding region, including the northern part of the Arabian platform is investigated via the analysis and modeling of Bouguer anomalies from the Earth Gravitational Model EGM08. The effective elastic thickness of the lithosphere (EET) that corresponds to the mechanical cores of the crust and lithospheric mantle is determined from the spectral coherence between Bouguer anomalies and surface elevation data. Its average value is 18.7 km. From the logarithmic amplitude spectra of Bouguer anomalies, average depths of the lithosphere-asthenosphere boundary (LAB), Moho, Conrad and basement in the study area are constrained at 84 km, 39 km, 16 km and 7 km, respectively. The geometries of the LAB and Moho are then estimated using the Parker-Oldenburg inversion algorithm. We also present a lithospheric strength map obtained from the spatial variations of EET determined by Yield Stress Envelopes (YSE). The EET varies in the range of 12-23 km, which is in good agreement with the average value obtained from spectral analysis. Low EET values are interpreted as resulting from thermal and flexural lithospheric weakening. According to the lithospheric strength of the Eastern Anatolian region, the rheology model consists of a strong but brittle upper crust, a weak and ductile lower crust, and a weak lower part of the lithosphere. On the other hand, lithosphere strength corresponds to weak and ductile lower crust, a strong upper crust and a strong uppermost lithospheric mantle for the northern part of the Arabian platform.

An Interlaminar Tensile Strength Specimen

NASA Technical Reports Server (NTRS)

Martin, Roderick H.; Jackson, Wade C.

1993-01-01

This paper describes a technique to determine interlaminar tensile strength, sigma(sub 3c), of a fiber reinforced composite material using a curved beam. The specimen was a unidirectional curved beam, bent 90 deg, with straight arms. Attached to each arm was a hinged loading mechanism that was held by the grips of a tension testing machine. Geometry effects of the specimen, including the effects of loading arm length, inner radius, thickness, and width, were studied. The data sets fell into two categories: low strength corresponding to a macroscopic flaw related failure and high strength corresponding to a microscopic flaw related failure. From the data available, the specimen width and loading arm length had little effect on sigma(sub 3c). The inner radius was not expected to have a significant effect on sigma(sub 3c), but this conclusion could not be confirmed because of differences in laminate quality for each curve geometry. The thicker specimens had the lowest value of sigma(sub 3c) because of poor laminate quality.

Failures in sand in reduced gravity environments

NASA Astrophysics Data System (ADS)

Marshall, Jason P.; Hurley, Ryan C.; Arthur, Dan; Vlahinic, Ivan; Senatore, Carmine; Iagnemma, Karl; Trease, Brian; Andrade, José E.

2018-04-01

The strength of granular materials, specifically sand is important for understanding physical phenomena on other celestial bodies. However, relatively few experiments have been conducted to determine the dependence of strength properties on gravity. In this work, we experimentally investigated relative values of strength (the peak friction angle, the residual friction angle, the angle of repose, and the peak dilatancy angle) in Earth, Martian, Lunar, and near-zero gravity. The various angles were captured in a classical passive Earth pressure experiment conducted on board a reduced gravity flight and analyzed using digital image correlation. The data showed essentially no dependence of the peak friction angle on gravity, a decrease in the residual friction angle between Martian and Lunar gravity, no dependence of the angle of repose on gravity, and an increase in the dilation angle between Martian and Lunar gravity. Additionally, multiple flow surfaces were seen in near-zero gravity. These results highlight the importance of understanding strength and deformation mechanisms of granular materials at different levels of gravity.

Effect of Composite Fabrication on the Strength of Single Crystal Al2O3 Fibers in Two Fe-Base Alloy Composites

NASA Technical Reports Server (NTRS)

Draper, Susan L.; Aiken, Beverly J. M.

1998-01-01

Continuous single-crystal Al2O3 fibers have been incorporated into a variety of metal and intermetallic matrices and the results have consistently indicated that the fiber strength had been reduced by 32 to 50% during processing. Two iron-based alloys, FeNiCoCrAl and FeAlVCMn, were chosen as matrices for Al2O3 fiber reinforced metal matrix composites (MMC) with the goal of maintaining Al2O3 fiber strength after composite processing. The feasibility of Al2O3/FeNiCoCrAl and Al2O3/FeAlVCMn composite systems for high temperature applications were assessed in terms of fiber-matrix chemical compatibility, interfacial bond strength, and composite tensile properties. The strength of etched-out fibers was significantly improved by choosing matrices containing less reactive elements. The ultimate tensile strength (UTS) values of the composites could generally be predicted with existing models using the strength of etched-out fibers. However, the UTS of the composites were less than desired due to a low fiber Weibull modulus. Acoustic emission analysis during tensile testing was a useful tool for determining the efficiency of the fibers in the composite and for determining the failure mechanism of the composites.

Mechanical properties and microstructures of glass-ionomer cements.

PubMed

Xie, D; Brantley, W A; Culbertson, B M; Wang, G

2000-03-01

The objective of this study was to determine the flexural strength (FS), compressive strength (CS), diametral tensile strength (DTS), Knoop hardness (KHN) and wear resistance of ten commercial glass-ionomer cements (GICs). The fracture surfaces of these cements were examined using scanning electron microscopic (SEM) techniques to ascertain relationships between the mechanical properties and microstructures of these cements. Specimens were fabricated according to the instructions from each manufacturer. The FS, CS, DTS, KHN and wear rate were measured after conditioning the specimens for 7 d in distilled water at 37 degrees C. One-way analysis of variance with the post hoc Tukey-Kramer multiple range test was used to determine which specimen groups were significantly different for each test. The fracture surface of one representative specimen of each GIC from the FS tests was examined using a scanning electron microscope. The resin-modified GICs (RM GICs) exhibited much higher FS and DTS, not generally higher CS, often lower Knoop hardness and generally lower wear resistance, compared to the conventional GICs (C GICs). Vitremer (3M) had the highest values of FS and DTS; Fuji II LC (GC International) and Ketac-Molar (ESPE) had the highest CS; Ketac-Fil (ESPE) had the highest KHN. Ketac-Bond (ESPE) had the lowest FS; alpha-Silver (DMG-Hamburg) had the lowest CS. Four GICs (alpha-Fil (DMG-Hamburg), alpha-Silver, Ketac-Bond and Fuji II) had the lowest values of DTS, which were not significantly different from each other; alpha-Silver and Ketac-Silver had the lowest values of KHN. The highest wear resistance was exhibited by alpha-Silver and Ketac-Fil; F2LC had the lowest wear resistance. The C GICs exhibited brittle behavior, whereas the RM GICs underwent substantial plastic deformation in compression. The more integrated the microstructure, the higher were the FS and DTS. Higher CS was correlated with smaller glass particles, and higher KHN was found where there was a combination of smaller glass particles and lower porosity. Larger glass particle sizes and a more integrated microstructure contributed to a higher wear resistance. The mechanical properties of GICs were closely related to their microstructures. Factors such as the integrity of the interface between the glass particles and the polymer matrix, the particle size, and the number and size of voids have important roles in determining the mechanical properties.

Effect of fiber addition on slow crack growth of a dental porcelain.

PubMed

de Araújo, Maico Dutra; Miranda, Ranulfo Benedito de Paula; Fredericci, Catia; Yoshimura, Humberto Naoyuki; Cesar, Paulo Francisco

2015-04-01

To evaluate the effect of the processing method (conventional sintering, S, and heat-pressing, HP) and addition of potassium titanate fibers, PTF, on the microstructure, mechanical properties (flexural strength, σf, and Weibull parameters, m and σ5%), slow crack growth parameters n (stress corrosion susceptibility coefficient), and optical properties (translucency parameter, TP, and opalescence index, OI) of a feldsphatic dental porcelain. Disks (n = 240, Ø12 × 1 mm) of porcelain (Vintage-Halo, Shofu) were produced using S and HP methods with and without addition of 10 wt% (conventional sintering) or 5 wt% (heat-pressing) of PTF. For the S method, porcelain was sintered in a conventional furnace. In the HP technique, refractory molds were produced by lost wax technique. The porcelain slurry was dry-pressed (3t/30s) to form a cylinder with 12 mm (diameter) and 20mm (height), which was heat-pressed for 5 min/3.5 bar into the mold. Specimens were tested for biaxial flexural strength in artificial saliva at 37°C. Weibull analysis was used to determine m and σ5%. Slow crack growth (SCG) parameters were determined by the dynamic fatigue test, and specimens were tested in biaxial flexure at five stress rates: 10(-2), 10(-1), 10(0), 10(1) and 10(2)MPa/s (n=10), immersed in artificial saliva at 37°C. Parameter n was calculated and statistically analyzed according to ASTM F394-78. Optical properties were determined in a spectrophotometer in the diffuse reflectance mode. The highest n value was obtained by the combination of heat-pressing with fiber addition (37.1) and this value was significantly higher than those obtained by both sintered groups (26.2 for control group and 27.7 for sintered with fiber). Although heat-pressing alone also resulted in higher n values compared to the sintered groups, there were no significant differences among them. Fiber addition had no effect on mechanical strength, but it resulted in decreased TP values and increased OI values for both processing methods. Heat-pressing alone was able to reduce the porosity level of the porcelain. Addition of PTF combined with heat-pressing can reduce strength degradation of a dental porcelain compared to sintered materials with or without fibers. Heat-pressing (HP) alone should be considered as a good alternative for clinical cases where high translucency is required. Copyright © 2014 Elsevier Ltd. All rights reserved.

The Effects of a Macromolecular Charring Agent with Gas Phase and Condense Phase Synergistic Flame Retardant Capability on the Properties of PP/IFR Composites

PubMed Central

Chen, Hongda; Wang, Jihui; Ding, Anxin; Han, Xia; Sun, Ziheng

2018-01-01

In order to improve the efficiency of intumescent flame retardants (IFRs), a novel macromolecular charring agent named poly(ethanediamine-1,3,5-triazine-p-4-amino-2,2,6,6-tetramethylpiperidine) (PETAT) with gas phase and condense phase synergistic flame-retardant capability was synthesized and subsequently dispersed into polypropylene (PP) in combination with ammonium polyphosphate (APP) via a melt blending method. The chemical structure of PETAT was investigated by Fourier transform infrared spectroscopy (FTIR), and 1H nuclear magnetic resonance (NMR) spectroscopy. Thermal properties of the PETAT and IFR systems were tested by thermogravimetric-derivative thermogravimetric analysis (TGA-DTG) and thermogravimetry–Fourier transform infrared spectroscopy (TG-FTIR). The mechanical properties, thermal stability, flame-retardant properties, water resistance, and structures of char residue in flame-retardant composites were characterized using tensile and flexural strength property tests, TGA, limiting oxygen index (LOI) values before and after soaking, underwritten laboratory-94 (UL-94) vertical burning test, cone calorimetric test (CCT), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDXS), and FTIR. The results indicated that PETAT was successfully synthesized, and when the ratio of APP to PETAT was 2:1 with 25 wt % loading, the novel IFR system could reduce the deterioration of tensile strength and enhance the flexural strength of composites. Meanwhile, the flame-retardant composite was able to pass the UL-94 V-0 rating with an LOI value of 30.3%, and the peak of heat release rate (PHRR), total heat release (THR), and material fire hazard values were considerably decreased compared with others. In addition, composites also exhibited excellent water resistance properties compared with traditional IFR composites. SEM-EDXS and FTIR analyses of the char residues, as well as TG-FTIR analyses of IFR were used to investigate the flame-retardant mechanism of the APP/PETAT IFR system. The results indicated that the efficient flame retardancy of PP/IFR composites could be attributed to the synergism of the free radical-quenching and char layer-protecting mechanisms in the gas phase and condense phase, respectively. PMID:29324716

The Effects of a Macromolecular Charring Agent with Gas Phase and Condense Phase Synergistic Flame Retardant Capability on the Properties of PP/IFR Composites.

PubMed

Chen, Hongda; Wang, Jihui; Ni, Aiqing; Ding, Anxin; Han, Xia; Sun, Ziheng

2018-01-11

In order to improve the efficiency of intumescent flame retardants (IFRs), a novel macromolecular charring agent named poly(ethanediamine-1,3,5-triazine-p-4-amino-2,2,6,6-tetramethylpiperidine) (PETAT) with gas phase and condense phase synergistic flame-retardant capability was synthesized and subsequently dispersed into polypropylene (PP) in combination with ammonium polyphosphate (APP) via a melt blending method. The chemical structure of PETAT was investigated by Fourier transform infrared spectroscopy (FTIR), and ¹H nuclear magnetic resonance (NMR) spectroscopy. Thermal properties of the PETAT and IFR systems were tested by thermogravimetric-derivative thermogravimetric analysis (TGA-DTG) and thermogravimetry-Fourier transform infrared spectroscopy (TG-FTIR). The mechanical properties, thermal stability, flame-retardant properties, water resistance, and structures of char residue in flame-retardant composites were characterized using tensile and flexural strength property tests, TGA, limiting oxygen index (LOI) values before and after soaking, underwritten laboratory-94 (UL-94) vertical burning test, cone calorimetric test (CCT), scanning electron microscopy with energy dispersive X-ray spectrometry (SEM-EDXS), and FTIR. The results indicated that PETAT was successfully synthesized, and when the ratio of APP to PETAT was 2:1 with 25 wt % loading, the novel IFR system could reduce the deterioration of tensile strength and enhance the flexural strength of composites. Meanwhile, the flame-retardant composite was able to pass the UL-94 V-0 rating with an LOI value of 30.3%, and the peak of heat release rate (PHRR), total heat release (THR), and material fire hazard values were considerably decreased compared with others. In addition, composites also exhibited excellent water resistance properties compared with traditional IFR composites. SEM-EDXS and FTIR analyses of the char residues, as well as TG-FTIR analyses of IFR were used to investigate the flame-retardant mechanism of the APP/PETAT IFR system. The results indicated that the efficient flame retardancy of PP/IFR composites could be attributed to the synergism of the free radical-quenching and char layer-protecting mechanisms in the gas phase and condense phase, respectively.

Investigation of the Self-Healing Behaviors of Microcapsules/Bitumen Composites by a Repetitive Direct Tension Test

PubMed Central

Su, Jun-Feng; Yang, Peng; Wang, Ying-Yuan; Han, Shan; Han, Ning-Xu; Li, Wei

2016-01-01

The aim of this work was to evaluate the self-healing behaviors of bitumen using microcapsules containing rejuvenator by a modified fracture healing–refracture method through a repetitive tension test. Microcapsules had mean size values of 10, 20 and 30 μm with a same core/shell ratio of 1/1. Various microcapsules/bitumen samples were fabricated with microcapsule contents of 1.0, 3.0 and 5.0 wt. %, respectively. Tension strength values of microcapsules/bitumen samples were measured by a reparative fracture-healing process under different temperatures. It was found that these samples had tensile strength values larger than the data of pure bitumen samples under the same conditions after the four tensile fracture-healing cycles. Fracture morphology investigation and mechanism analysis indicated that the self-healing process was a process consisting of microcapsules being broken, penetrated and diffused. Moreover, the crack healing of bitumen can be considered as a viscosity driven process. The self-healing ability partly repaired the damage of bitumen during service life by comparing the properties of virgin and rejuvenated bitumen. PMID:28773722

Enhancement of the Mechanical Properties of Basalt Fiber-Wood-Plastic Composites via Maleic Anhydride Grafted High-Density Polyethylene (MAPE) Addition

PubMed Central

Chen, Jinxiang; Wang, Yong; Gu, Chenglong; Liu, Jianxun; Liu, Yufu; Li, Min; Lu, Yun

2013-01-01

This study investigated the mechanisms, using microscopy and strength testing approaches, by which the addition of maleic anhydride grafted high-density polyethylene (MAPE) enhances the mechanical properties of basalt fiber-wood-plastic composites (BF-WPCs). The maximum values of the specific tensile and flexural strengths areachieved at a MAPE content of 5%–8%. The elongation increases rapidly at first and then continues slowly. The nearly complete integration of the wood fiber with the high-density polyethylene upon MAPE addition to WPC is examined, and two models of interfacial behavior are proposed. We examined the physical significance of both interfacial models and their ability to accurately describe the effects of MAPE addition. The mechanism of formation of the Model I interface and the integrated matrix is outlined based on the chemical reactions that may occur between the various components as a result of hydrogen bond formation or based on the principle of compatibility, resulting from similar polarity. The Model I fracture occurred on the outer surface of the interfacial layer, visually demonstrating the compatibilization effect of MAPE addition. PMID:28809285

Defining the Brittle Failure Envelopes of Individual Reaction Zones Observed in CO2-Exposed Wellbore Cement.

PubMed

Hangx, Suzanne J T; van der Linden, Arjan; Marcelis, Fons; Liteanu, Emilia

2016-01-19

To predict the behavior of the cement sheath after CO2 injection and the potential for leakage pathways, it is key to understand how the mechanical properties of the cement evolves with CO2 exposure time. We performed scratch-hardness tests on hardened samples of class G cement before and after CO2 exposure. The cement was exposed to CO2-rich fluid for one to six months at 65 °C and 8 MPa Ptotal. Detailed SEM-EDX analyses showed reaction zones similar to those previously reported in the literature: (1) an outer-reacted, porous silica-rich zone; (2) a dense, carbonated zone; and (3) a more porous, Ca-depleted inner zone. The quantitative mechanical data (brittle compressive strength and friction coefficient) obtained for each of the zones suggest that the heterogeneity of reacted cement leads to a wide range of brittle strength values in any of the reaction zones, with only a rough dependence on exposure time. However, the data can be used to guide numerical modeling efforts needed to assess the impact of reaction-induced mechanical failure of wellbore cement by coupling sensitivity analysis and mechanical predictions.

Mechanical and Morphological Properties of Polypropylene/Nano α-Al2O3 Composites

PubMed Central

Mirjalili, F.; Chuah, L.; Salahi, E.

2014-01-01

A nanocomposite containing polypropylene (PP) and nano α-Al2O3 particles was prepared using a Haake internal mixer. Mechanical tests, such as tensile and flexural tests, showed that mechanical properties of the composite were enhanced by addition of nano α-Al2O3 particles and dispersant agent to the polymer. Tensile strength was approximately ∼16% higher than pure PP by increasing the nano α-Al2O3 loading from 1 to 4 wt% into the PP matrix. The results of flexural analysis indicated that the maximum values of flexural strength and flexural modulus for nanocomposite without dispersant were 50.5 and 1954 MPa and for nanocomposite with dispersant were 55.88 MPa and 2818 MPa, respectively. However, higher concentration of nano α-Al2O3 loading resulted in reduction of those mechanical properties that could be due to agglomeration of nano α-Al2O3 particles. Transmission and scanning electron microscopic observations of the nanocomposites also showed that fracture surface became rougher by increasing the content of filler loading from 1 to 4% wt. PMID:24688421

Mechanical properties and mechanism of single crystal Cu pillar by in situ TEM compression and molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Lin, Kai-Peng; Fang, Te-Hua; Lin, Ying-Jhin

2018-02-01

In this study, we investigate the mechanical properties of single-crystal copper (Cu) nanopillars. Critical deformation variations of Cu-nanopillared structures are estimated using in situ transmission electron microscopy compression tests and molecular dynamics simulations. The Young’s moduli of Cu nanopillars with diameters of 2-6 nm were 90.20-124.47 GPa. The contact stiffnesses of the Cu nanopillars with diameters of 400 and 500 nm were 1.33 and 3.86 N m-1, respectively; the Poisson’s ratios for these nanopillars were 0.32 and 0.33. The yield strength of the nanopillars varied from 0.25 GPa at 500 nm to 0.42 GPa at 400 nm; the yield strength of single-crystal Cu nanopillars decreased with increasing diameter. The values of the indented hardness of the Cu block were 0.27 and 1.06 GPa, respectively. Through experimental work and molecular dynamics simulations, we demonstrate that Cu nanopillars exhibit internal stress transmission during compression. When compression reaches the maximum strain, it can be observed that Cu slips. Our results are useful for understanding the mechanical properties, contact, and local deformation of Cu nanopillars.

Clean Cast Steel Technology: Effect of Micro-porosity on Tensile and Charpy Properties of Four Cast Steels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Griffin, John, A.; Bates, Charles, E.

2005-09-19

The effect of these large shrink cavities on mechanical properties could be easily calculated using well established engineering formulas. Over the years, increases in computational and metallurgical resources have allowed the modeler to improve accuracy and increase the complexity of numerical predictors. An accurate prediction of micro-porosity, not observable using conventional radiographic techniques, and an engineering understanding of the effect on mechanical properties would give a designer confidence in using a more efficient casting design and a lower safety factor. This will give castings an additional design advantage. The goal of this project is to provide current and future modelers/designersmore » with a tensile and Charpy property dataset for validation of micro-porosity predictors. The response of ultimate strength, elongation, and reduction in area to micro-porosity was very similar in all four alloys. Ultimate strength was largely unaffected by tensile fracture surface porosity until values of about 25% were reached and decreased linearly with increasing values. Elongation and reduction in area decreased sharply after less than 5% fracture surface porosity. Niyama values of about 0.7 were produced sound material and acceptable tensile properties. Ultrasonic velocities of 0.233 in/usec and higher produced acceptable tensile properties. Metallographic examination revealed a ratio of 4-6 to 1 in fracture surface porosity to metallographic porosity. Charpy impact properties were largely unaffected by the microporosity concentrations examined in this study and did not correlate to either Niyama values, fracture surface porosity, or metallographic porosity.« less

Present-day heat flow model of Mars

PubMed Central

Parro, Laura M.; Jiménez-Díaz, Alberto; Mansilla, Federico; Ruiz, Javier

2017-01-01

Until the acquisition of in-situ measurements, the study of the present-day heat flow of Mars must rely on indirect methods, mainly based on the relation between the thermal state of the lithosphere and its mechanical strength, or on theoretical models of internal evolution. Here, we present a first-order global model for the present-day surface heat flow for Mars, based on the radiogenic heat production of the crust and mantle, on scaling of heat flow variations arising from crustal thickness and topography variations, and on the heat flow derived from the effective elastic thickness of the lithosphere beneath the North Polar Region. Our preferred model finds heat flows varying between 14 and 25 mW m−2, with an average value of 19 mW m−2. Similar results (although about ten percent higher) are obtained if we use heat flow based on the lithospheric strength of the South Polar Region. Moreover, expressing our results in terms of the Urey ratio (the ratio between total internal heat production and total heat loss through the surface), we estimate values close to 0.7–0.75, which indicates a moderate contribution of secular cooling to the heat flow of Mars (consistent with the low heat flow values deduced from lithosphere strength), unless heat-producing elements abundances for Mars are subchondritic. PMID:28367996

Prediction of mechanical properties of composites of HDPE/HA/EAA.

PubMed

Albano, C; Perera, R; Cataño, L; Karam, A; González, G

2011-04-01

In this investigation, the behavior of the mechanical properties of composites of high-density polyethylene/hydroxyapatite (HDPE/HA) with and without ethylene-acrylic acid copolymer (EAA) as possible compatibilizer, was studied. Different mathematical models were used to predict their Young's modulus, tensile strength and elongation at break. A comparison with the experimental results shows that the theoretical models of Guth and Kerner modified can be used to predict the Young's modulus. On the other hand, the values obtained by the Verbeek model do not show a good agreement with the experimental data, since different factors that influence the mechanical properties are considered in this model such as: aspect ratio of the reinforcement, interfacial adhesion, porosity and binder content. TEM analysis confirms the discrepancies obtained between the experimental Young's modulus values and those predicted by the Verbeek model. The values of "P", "a" and "σ(A)" suggest that an interaction among the carboxylic groups of the copolymer and the hydroxyl groups of hydroxyapatite might be present. In composites with 20 and 30 wt% of filler, this interaction does not improve the Young's modulus values, since the deviations of the Verbeek model are significant. Copyright © 2010 Elsevier Ltd. All rights reserved.

Strength and deformability of concrete beams reinforced by non-metallic fiber and composite rebar

NASA Astrophysics Data System (ADS)

Kudyakov, K. L.; Plevkov, V. S.; Nevskii, A. V.

2015-01-01

Production of durable and high-strength concrete structures with unique properties has always been crucial. Therefore special attention has been paid to non-metallic composite and fiber reinforcement. This article describes the experimental research of strength and deformability of concrete beams with dispersed and core fiber-based reinforcement. As composite reinforcement fiberglass reinforced plastic rods with diameters 6 mm and 10 mm are used. Carbon and basalt fibers are used as dispersed reinforcement. The developed experimental program includes designing and production of flexural structures with different parameters of dispersed fiber and composite rebar reinforcement. The preliminary testing of mechanical properties of these materials has shown their effectiveness. Structures underwent bending testing on a special bench by applying flexural static load up to complete destruction. During the tests vertical displacements were recorded, as well as value of actual load, slippage of rebars in concrete, crack formation. As a result of research were obtained structural failure and crack formation graphs, value of fracture load and maximum displacements of the beams at midspan. Analysis of experimental data showed the effectiveness of using dispersed reinforcement of concrete and the need for prestressing of fiberglass composite rebar.

[Physical activity/sports and bone mineral density].

PubMed

Inomoto, Takeaki

2008-09-01

This study observed the amount of exercise of Japanese schoolchildren as recorded by pedometer. Schools are necessary venues to increase children's mobility, but home environments are hotbeds for lack of exercise on weekends and during holidays and vacations. This research measured the L(2 - 4)BMD of 185 male and female primary schoolchildren using a DEXA method. Results showed significant partial correlations for measurements of boys' grip strength, boys' standing broad jump, and girls' grip strength, indicating the influence of mechanical stress. In a parallel study, L(2 - 4)BMD measurements for high school athletic club members (14 and 10 sports for boys and girls respectively) were taken, and it was found that the L(2 - 4)BMD (60 kg/weight) values were significantly higher than the control values for boys' boxing and weightlifting but significantly lower for boys' sumo. No significance was found in L(2 - 4)BMD (50 kg/weight) among the different girls' sports. From both studies, it was concluded that with approximately 2 hours of moderate play and exercise daily, the bone density of children rises with increase of overall muscle quantity, resulting in higher athletic ability and overall physical strength.

On cyclic yield strength in definition of limits for characterisation of fatigue and creep behaviour

NASA Astrophysics Data System (ADS)

Gorash, Yevgen; MacKenzie, Donald

2017-06-01

This study proposes cyclic yield strength as a potential characteristic of safe design for structures operating under fatigue and creep conditions. Cyclic yield strength is defined on a cyclic stress-strain curve, while monotonic yield strength is defined on a monotonic curve. Both values of strengths are identified using a two-step procedure of the experimental stress-strain curves fitting with application of Ramberg-Osgood and Chaboche material models. A typical S-N curve in stress-life approach for fatigue analysis has a distinctive minimum stress lower bound, the fatigue endurance limit. Comparison of cyclic strength and fatigue limit reveals that they are approximately equal. Thus, safe fatigue design is guaranteed in the purely elastic domain defined by the cyclic yielding. A typical long-term strength curve in time-to-failure approach for creep analysis has two inflections corresponding to the cyclic and monotonic strengths. These inflections separate three domains on the long-term strength curve, which are characterised by different creep fracture modes and creep deformation mechanisms. Therefore, safe creep design is guaranteed in the linear creep domain with brittle failure mode defined by the cyclic yielding. These assumptions are confirmed using three structural steels for normal and high-temperature applications. The advantage of using cyclic yield strength for characterisation of fatigue and creep strength is a relatively quick experimental identification. The total duration of cyclic tests for a cyclic stress-strain curve identification is much less than the typical durations of fatigue and creep rupture tests at the stress levels around the cyclic yield strength.

Length and temperature dependence of the mechanical properties of finite-size carbyne

NASA Astrophysics Data System (ADS)

Yang, Xueming; Huang, Yanhui; Cao, Bingyang; To, Albert C.

2017-09-01

Carbyne is an ideal one-dimensional conductor and the thinnest interconnection in an ultimate nano-device and it requires an understanding of the mechanical properties that affect device performance and reliability. Here, we report the mechanical properties of finite-size carbyne, obtained by a molecular dynamics simulation study based on the adaptive intermolecular reactive empirical bond order potential. To avoid confusion in assigning the effective cross-sectional area of carbyne, the value of the effective cross-sectional area of carbyne (4.148 Å2) was deduced via experiment and adopted in our study. Ends-constraints effects on the ultimate stress (maximum force) of the carbyne chains are investigated, revealing that the molecular dynamics simulation results agree very well with the experimental results. The ultimate strength, Young's Modulus and maximum strain of carbyne are rather sensitive to the temperature and all decrease with the temperature. Opposite tendencies of the length dependence of the overall ultimate strength and maximum strain of carbyne at room temperature and very low temperature have been found, and analyses show that this originates in the ends effect of carbyne.

Relationship between notch strengthening threshold and mechanical property for ductile cast iron

NASA Astrophysics Data System (ADS)

Ikeda, T.; Noda, N.-A.; Sano, Y.; Umetani, T.; Kai, N.

2018-06-01

In this study, dynamic tensile tests were conducted at the various strain rates and temperatures for traditional ductile cast iron. Then, the notch strength {σ }{{B}}{{noth}} and the static tensile strength at room temperature {σ }{{B,}\\quad {{RT}}}{{smooth}} were discussed in terms of the strain rate- temperature parameter R, which is known to be useful for evaluating the combined influence of strain rate and temperature. This study focuses on the notch strengthening threshold R ≧ R th where {σ }{{B}}{{noth}} is larger than {σ }{{B,}\\quad {{RT}}}{{smooth}} and therefore notched components can be used safely. In other words, if R ≧ R th, {σ }{{B,}\\quad {{RT}}}{{smooth}} can be used to evaluate notched components in mechanical design to prevent the instantaneous fracture. In this study, it was found that the R th value can be predicted from the static tensile property and Brinell hardness. Since the traditional ductile cast iron considered in this paper has a broad range of mechanical properties, the present approach and discussion can be applied to evaluate other materials under various temperature and strain rate.

Origin of anomalous inverse notch effect in bulk metallic glasses

NASA Astrophysics Data System (ADS)

Pan, J.; Zhou, H. F.; Wang, Z. T.; Li, Y.; Gao, H. J.

2015-11-01

Understanding notch-related failure is crucial for the design of reliable engineering structures. However, substantial controversies exist in the literature on the notch effect in bulk metallic glasses (BMGs), and the underlying physical mechanism responsible for the apparent confusion is still poorly understood. Here we investigate the physical origin of an inverse notch effect in a Zr-based metallic glass, where the tensile strength of the material is dramatically enhanced, rather than decreased (as expected from the stress concentration point of view), by introduction of a notch. Our experiments and molecular dynamics simulations show that the seemingly anomalous inverse notch effect is in fact caused by a transition in failure mechanism from shear banding at the notch tip to cavitation and void coalescence. Based on our theoretical analysis, the transition occurs as the stress triaxiality in the notched sample exceeds a material-dependent threshold value. Our results fill the gap in the current understanding of BMG strength and failure mechanism by resolving the conflicts on notch effects and may inspire re-interpretation of previous reports on BMG fracture toughness where pre-existing notches were routinely adopted.

Low-temperature mechanical properties of superconducting radio frequency cavity materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Byun, Thak Sang; Kim, Sang-Ho; Mammosser, John

2009-01-01

Low temperature mechanical behaviors have been investigated for the constituent materials of superconducting radio frequency cavities. Test materials consist of small grain Nb, single crystal Nb, large grain Nb (bicrystal), Ti45Nb-Nb weld joint (e-beam welded), and Ti-316L bimetal joint (explosion welded). The strength of all test metals displayed strong temperature dependence and the Ti-316L bimetal showed the highest strength and lowest ductility among the test materials. The fracture toughness of the small grain Nb metals decreased with decreasing test temperature and reached the lower shelf values (30 40 MPa m) at or above 173 K. The Ti45Nb base and Ti45Nb-Nbmore » weld metals showed much higher fracture toughness than the small grain Nb. An extrapolation and comparison with existing data showed that the fracture toughness of the small grain Nb metals at 4 K was expected to be similar to those at 173 K and 77 K. The results from optical photography at a low magnification and fractography by a scanning electron microscope were consistent with corresponding mechanical properties.« less

Fatigue of the Resin-Enamel Bonded Interface and the Mechanisms of Failure

PubMed Central

Yahyazadehfar, Mobin; Mutluay, Mustafa Murat; Majd, Hessam; Ryou, Heonjune; Arola, Dwayne

2013-01-01

The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under both static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominately by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding. PMID:23571321

Effect of slip-area scaling on the earthquake frequency-magnitude relationship

NASA Astrophysics Data System (ADS)

Senatorski, Piotr

2017-06-01

The earthquake frequency-magnitude relationship is considered in the maximum entropy principle (MEP) perspective. The MEP suggests sampling with constraints as a simple stochastic model of seismicity. The model is based on the von Neumann's acceptance-rejection method, with b-value as the parameter that breaks symmetry between small and large earthquakes. The Gutenberg-Richter law's b-value forms a link between earthquake statistics and physics. Dependence between b-value and the rupture area vs. slip scaling exponent is derived. The relationship enables us to explain observed ranges of b-values for different types of earthquakes. Specifically, different b-value ranges for tectonic and induced, hydraulic fracturing seismicity is explained in terms of their different triggering mechanisms: by the applied stress increase and fault strength reduction, respectively.

Lattice strain of osmium diboride under high pressure and nonhydrostatic stress

NASA Astrophysics Data System (ADS)

Kavner, Abby; Weinberger, Michelle B.; Shahar, Anat; Cumberland, Robert W.; Levine, Jonathan B.; Kaner, Richard B.; Tolbert, Sarah H.

2012-07-01

The lattice strain behavior of osmium diboride—a member of a group of third-row transition metal borides associated with hard/superhard behavior—has been studied using radial diffraction in a diamond anvil cell under high pressure and non-hydrostatic stress. We interpret the average values of the measured lattice strains as a lower-bound to the lattice-plane dependent yield strengths using existing estimates for the elastic constants of OsB2, with a yield strength of 11 GPa at 27.5 GPa of hydrostatic pressure. The measured differential lattice strains show significant plane-dependent anisotropy, with the (101) lattice plane showing the largest differential strain and the (001) lattice plane showing the least strain. At the highest pressure, the a-axis develops a larger compressive strain and supports a larger differential strain than either the b or c axes. This causes an increase in the c/a ratio and a decrease in the a/b ratio especially in the maximum stress direction. The large strength anisotropy of this material points to possible ways to modulate directional mechanical properties by taking advantage of the interplay between aggregate polycrystalline texture with directional mechanical properties.

Internal geometry effect of structured PLA materials manufactured by dropplet-based 3D printer on its mechanical properties

NASA Astrophysics Data System (ADS)

Wicaksono, Sigit T.; Ardhyananta, Hosta; Rasyida, Amaliya; Hidayat, Mas Irfan P.

2018-04-01

Rapid Prototyping (RP) technologies, the manufacturing technology with less time consuming including high precission and complicated structure of products, are now become high demanding technologies. Those technologies can be base on top-down or bottom-up approaches. One of the bottom-up approach of RP technology is 3D printing machine. In this research, we have succeed to apply the droplet-based 3D printer to make the structured PLA (Polylactic Acid) materials with different internal geometry structures. The internal geometry used are triangle and honeycomb structure with different size of each symmetry axis of 4.5 mm and 9 mm and the thickness varied of 1 mm and 2 mm as well. The mechanical properties of those structures including tensile and bending stregth are evaluated by using tensile and flexural test respectively. Test results show that the best performance obtained by measuring its tensile and flexural strength is the sampel with triangle geometry of 9 mm geometrical size and 2 mm of thickness. The tensile strength and flexural strength values of the specimens are 59.2996 MPa and 123 MPa respectively.

Completion of evaluation of manufacturing processes for B/Al composites containing 0.2mm diameter boron fibers

NASA Technical Reports Server (NTRS)

Moore, T. J.; Moorhead, P. E.

1980-01-01

Four fabricators produced a total of 54 B/1100 Al, B/6061 Al, and B/2024 Al panels for evaluation. The 8 ply unidirectional, 45 to 50 volume percent, panels were made using 0.20 mm diameter boron fibers which were obtained from a single supplier. Hot press consolidation was carried out in vacuum except for one set of dry woven tape panels which were hot pressed in air. A single testing contractor conducted nondestructive inspection, metallography, fractography and mechanical property tests. The mechanical property tests included 21 and 260 C tensile tests and 21 C shear tests. Panel quality, as measured by nondestructive evaluation, was generally good as were the 21 C tensile properties. The panels hot pressed in air delaminated in the shear tests. Shear strength values were lower in these panels. But tensile strengths were not affected by the delaminations because of the relation between the tensile loading direction and the delaminations. Composite tensile strength was found to be proportional to the volume percent boron and the aluminum matrix rather than to the tape used or fabrication technique. Suitability of these composites for 260 C service was confirmed by tensile tests.

Structure, mechanical and thermal behaviour of mixtures of polyester resin and dental ceramic waste

NASA Astrophysics Data System (ADS)

Peña Rodríguez, G.; Martínez Maldonado, L.; Dulce Moreno, H. J.

2016-02-01

The tensile strength and bending strength, structure and thermal behaviour of mixtures of polyester resin (P-2000) and powders (ASTM sieve 200, <75μm) of dental ceramic wastes (dentals impressions, alginate and gypsum) was reported. The samples consisted of mixtures with percentage weights of 50-50%, 60-40%, 70-30%, 80-20%, 90-10%, where the resin was the majority phase, the Mekc (4% wt) was used as catalyst. The structure was studied using SEM and XRD, the thermal behaviour using DSC, TGA and DMA, while the mechanical strength was tested using standards ASTM D790 and D638. Irregular morphology and presence of small agglomerations was observed, with particle sizes between 29.63 and 38.67μm, the presence of different phases of calcium sulphate was found, and that to the increasing the concentration of the powder, the materials becomes more crystalline, increasing its density. An average service temperature of 69.15±4.60°C was found. Vickers hardness values are reported in ranges from 18.65 to 27.96. Considering the elastic modules was established that the materials become more rigid by having more powder concentration.

Tensile behavior of porous scaffolds made from poly(para phenylene) - biomed 2013.

PubMed

Dirienzo, Amy L; Yakacki, Christopher M; Safranski, David L; Frick, Carl P

2013-01-01

The goal of this study was to fabricate and mechanically characterize a high-strength porous polymer scaffold for potential use as an orthopedic device. Poly(para-phenylene) (PPP) is an excellent candidate due to its exceptional strength and stiffness and relative inertness, but has never been explicitly investigated for use as a biomedical device. PPP has strength values 3 to 10 times higher and an elastic modulus nearly an order of magnitude higher than traditional polymers such as poly(methyl methacrylate) (PMMA), polycaprolactone (PCL), ultra-high molecular weight polyethylene (UHMWPE), and polyurethane (PU) and is significantly stronger and stiffer than polyetheretherketone (PEEK). By utilizing PPP we can overcome the mechanical limitations of traditional porous polymeric scaffolds since the outstanding stiffness of PPP allows for a highly porous structure appropriate for osteointegration that can match the stiffness of bone (100-250 MPa), while maintaining suitable mechanical properties for soft-tissue fixation. Porous samples were manufactured by powder sintering followed by particle leaching. The pore volume fraction was systematically varied from 50–80 vol% for a pore sizes from150-500 µm, as indicated by previous studies for optimal osteointegration. The tensile modulus of the porous samples was compared to the rule of mixtures, and closely matches foam theory up to 70 vol%. The experimental modulus for 70 vol% porous samples matches the stiffness of bone and contains pore sizes optimal for osteointegration.

The recycling of comminuted glass-fiber-reinforced resin from electronic waste.

PubMed

Duan, Huabo; Jia, Weifeng; Li, Jinhui

2010-05-01

The reuse of comminuted glass-fiber-reinforced resin with various granularities gathered from printed circuit manufacturing residues was investigated. As fillers, these residues were converted into polymeric composite board by an extrusion and injection process using polypropylene as a bonding agent. The mechanical properties of the reproduced composite board were examined by considering the effects of mass fraction and glass-fiber distribution. Interfacial-layer micrograph analysis of the composite material fracture surface was used to study the fiber reinforcement mechanism. Results showed that using comminuted glass-fiber-reinforced resin as a filler material greatly enhanced the performance properties of the composite board. Although the length and diameter of filler varied, these variations had no appreciable effect on the mechanical properties of the processed board. Maximum values of 48.30 MPa for flexural strength, 31.34 MPa for tensile strength, and 31.34 J/m for impact strength were achieved from a composite board containing mass fractions of 30, 10, and 20% glass-fiber-reinforced resin waste, respectively. It was found that the maximum amount of recyclate that could be added to a composite board was 30% of weight. Beyond these percentages, the materials blend became unmanageable and the mixture less amenable to impregnation with fiber. Presented studies indicated that comminuted glass-fiber-reinforced resin waste-filled polypropylene composites are promising candidates for structural applications where high stiffness and fracture resistance are required.

Numerical simulations of mechanical and ignition-deflagration responses for PBXs under low-to-medium-level velocity impact loading.

PubMed

Yang, Kun; Wu, Yanqing; Huang, Fenglei; Li, Ming

2017-09-05

An effective computational model is required to accurately predict the dynamic responses in accidental initiations of explosives. The present work uses a series of two-dimensional mechanical-chemical simulations performed via a hydrodynamic-code, DREXH-2D, to efficiently describe the mechanical and ignition-deflagration responses of cased cylindrical polymer-bonded explosives (PBXs) undergoing a low-to-medium-level impact (70-350m/s) in longitudinal direction. The ignition response was predicted based on an ignition criterion of effective plastic work. Slow burning and its growth to deflagration were described through a pressure-dependent reaction rate equation. The extreme value of effective plastic work was found to be useful to determine the ignition threshold velocity for PBXs. For low-level velocity impact, the incident stress wave reflection from lateral surfaces contributed to the formation of ignition regions. After the ignition, the deflagration was induced in the medium-level impact, and its violence was related to the shock strength. However, the low-strength stress wave only induced reaction at local regions, and sequent burning was no longer sensitive to the strength of incident wave. The predicted pressure and temperature results of PBXs were consistent with the medium-level impact tests performed by China Academy of Engineering Physics. Copyright © 2017 Elsevier B.V. All rights reserved.

Shear Strength of Stabilized Kaolin Soil Using Liquid Polymer

NASA Astrophysics Data System (ADS)

Azhar, A. T. S.; Fazlina, M. I. S.; Nizam, Z. M.; Fairus, Y. M.; Hakimi, M. N. A.; Riduan, Y.; Faizal, P.

2017-08-01

The purpose of this research is to investigate the suitability of polymer in soil stabilization by examining its strength to withstand compressive strength. Throughout this research study, manufactured polymer was used as a chemical liquid soil stabilizer. The liquid polymer was diluted using a proposed dilution factor of 1 : 3 (1 part polymer: 3 parts distilled water) to preserve the workability of the polymer in kaolin mixture. A mold with a diameter of 50 mm and a height of 100 mm was prepared. Kaolin soil was mixed with different percentages of polymer from 10%, 15%, 20%, 25%, 30% and 35% of the mass of the kaolin clay sample. Kaolin mixtures were tested after a curing period of 3 days, 7 days, 14 days and 28 days respectively. The physical properties were determined by conducting a moisture content test and Atterberg limit test which comprise of liquid limit, plastic limit and shrinkage limit. Meanwhile, the mechanical properties of the soil shear strength were identified through an unconfined compressive strength (UCS) test. Stabilized kaolin soil showed the highest compressive strength value when it was mixed with 35% of polymer compared to other percentages that marked an increment in strength which are 45.72% (3 days), 67.57% (7 days), 81.73% (14 days) and 77.84% (28 days). Hence, the most effective percentage of liquid polymer which should be used to increase the strength of kaolin soil is 35%.

New insights on poly(vinyl acetate)-based coated floating tablets: characterisation of hydration and CO2 generation by benchtop MRI and its relation to drug release and floating strength.

PubMed

Strübing, Sandra; Abboud, Tâmara; Contri, Renata Vidor; Metz, Hendrik; Mäder, Karsten

2008-06-01

The purpose of this study was to investigate the mechanism of floating and drug release behaviour of poly(vinyl acetate)-based floating tablets with membrane controlled drug delivery. Propranolol HCl containing tablets with Kollidon SR as an excipient for direct compression and different Kollicoat SR 30 D/Kollicoat IR coats varying from 10 to 20mg polymer/cm2 were investigated regarding drug release in 0.1N HCl. Furthermore, the onset of floating, the floating duration and the floating strength of the device were determined. In addition, benchtop MRI studies of selected samples were performed. Coated tablets with 10mg polymer/cm2 SR/IR, 8.5:1.5 coat exhibited the shortest lag times prior to drug release and floating onset, the fastest increase in and highest maximum values of floating strength. The drug release was delayed efficiently within a time interval of 24 h by showing linear drug release characteristics. Poly(vinyl acetate) proved to be an appropriate excipient to ensure safe and reliable drug release. Floating strength measurements offered the possibility to quantify the floating ability of the developed systems and thus to compare different formulations more efficiently. Benchtop MRI studies allowed a deeper insight into drug release and floating mechanisms noninvasively and continuously.

Design of High Voltage Electrical Breakdown Strength measuring system at 1.8K with a G-M cryocooler

NASA Astrophysics Data System (ADS)

Li, Jian; Huang, Rongjin; Li, Xu; Xu, Dong; Liu, Huiming; Li, Laifeng

2017-09-01

Impregnating resins as electrical insulation materials for use in ITER magnets and feeder system are required to be radiation stable, good mechanical performance and high voltage electrical breakdown strength. In present ITER project, the breakdown strength need over 30 kV/mm, for future DEMO reactor, it will be greater than this value. In order to develop good property insulation materials to satisfy the requirements of future fusion reactor, high voltage breakdown strength measurement system at low temperature is necessary. In this paper, we will introduce our work on the design of this system. This measuring system has two parts: one is an electrical supply system which provides the high voltage from a high voltage power between two electrodes; the other is a cooling system which consists of a G-M cryocooler, a superfluid chamber and a heat switch. The two stage G-M cryocooler pre-cool down the system to 4K, the superfluid helium pot is used for a container to depress the helium to superfluid helium which cool down the sample to 1.8K and a mechanical heat switch connect or disconnect the cryocooler and the pot. In order to provide the sufficient time for the test, the cooling system is designed to keep the sample at 1.8K for 300 seconds.

Suspended tungsten-based nanowires with enhanced mechanical properties grown by focused ion beam induced deposition

NASA Astrophysics Data System (ADS)

Córdoba, Rosa; Lorenzoni, Matteo; Pablo-Navarro, Javier; Magén, César; Pérez-Murano, Francesc; María De Teresa, José

2017-11-01

The implementation of three-dimensional (3D) nano-objects as building blocks for the next generation of electro-mechanical, memory and sensing nano-devices is at the forefront of technology. The direct writing of functional 3D nanostructures is made feasible by using a method based on focused ion beam induced deposition (FIBID). We use this technique to grow horizontally suspended tungsten nanowires and then study their nano-mechanical properties by three-point bending method with atomic force microscopy. These measurements reveal that these nanowires exhibit a yield strength up to 12 times higher than that of the bulk tungsten, and near the theoretical value of 0.1 times the Young’s modulus (E). We find a size dependence of E that is adequately described by a core-shell model, which has been confirmed by transmission electron microscopy and compositional analysis at the nanoscale. Additionally, we show that experimental resonance frequencies of suspended nanowires (in the MHz range) are in good agreement with theoretical values. These extraordinary mechanical properties are key to designing electro-mechanically robust nanodevices based on FIBID tungsten nanowires.

Consideration of the oxide particle-dislocation interaction in 9Cr-ODS steel

NASA Astrophysics Data System (ADS)

Ijiri, Yuta; Oono, N.; Ukai, S.; Yu, Hao; Ohtsuka, S.; Abe, Y.; Matsukawa, Y.

2017-05-01

The interaction between oxide particles and dislocations in a 9Cr-ODS ferritic steel is investigated by both static and in situ TEM observation under dynamic straining conditions and room temperature. The measured obstacle strength (?) of the oxide particles was no greater than 0.80 and the average was 0.63. The dislocation loops around some coarsened particles were also observed. The calculated obstacle strength by a stress formula of the Orowan interaction is nearly equaled to the average experimental value. Not only cross-slip system but also the Orowan interaction should be considered as the main interaction mechanism between oxide particles and dislocation in 9CrODS ferritic steel.

Physical, mechanical, and barrier properties of sodium alginate/gelatin emulsion based-films incorporated with canola oil

NASA Astrophysics Data System (ADS)

Syarifuddin, A.; Hasmiyani; Dirpan, A.; Mahendradatta, M.

2017-12-01

The development of mixed emulsion-based films formed by sodium alginate/gelatin incorporated with canola oil can offer particular properties such as water vapor barrier properties. The different ratios of sodium alginate/gelatin and sodium alginate/gelatin emulsion-based films incorporated with canola oil were developed and their effects on films’ physical, mechanical and barrier properties were assessed. Here we set out to examine whether canola oil addition and different ratio of sodium alginate/gelatin modified physical, mechanical, and barrier properties of films. To do so, the films were prepared by vary the ratio of sodium alginate/gelatin (2.5, 1, 0.5). Canola oil addition induced changes in moisture content, thickness, solubility, water vapor transmission rate (WVTR), percent elongation at break (p<0.05). In addition, it is apparent that varying ratio of sodium alginate to gelatin induced change the mechanical properties of films. The reduction of sodium alginate to gelatin decreased the tensile strength of both films. Improved values of WVTR, tensile strength and solubility at break were observed when the ratio of sodium alginate/gelatin emulsion film incorporated with canola oil was 2.5. Therefore, different ratio of sodium alginate/gelatin incorporated with canola oil can be used to tailor emulsion films with enhanced water vapor barrier and mechanical properties.

Mechanical properties and cytocompatibility of carbon fibre reinforced nano-hydroxyapatite/polyamide66 ternary biocomposite.

PubMed

Zhang, Xuesong; Zhang, Yonggang; Zhang, Xuelian; Wang, Yan; Wang, Jiaqi; Lu, Ming; Li, Hong

2015-02-01

Fibre-reinforced composites with good strength and ductility as bone repair biomaterials have been attracting increasing attention in biomedical applications. In the present study, a novel ternary composite was prepared using carbon fibre (CF) to reinforce a nano-hydroxyapatite/polyamide66 composite (HA/PA). The interface and mechanical strength of the ternary composite (CF/HA/PA) were characterised. In addition, to assess the cytocompatibility, the composite was co-cultured with MG-63 cells, and the cell morphology, MTT, and ALP were tested. The results indicated that CFs were uniformly distributed in the HA/PA matrix with random orientation and that the CFs bonded well to the HA/PA matrix. The reinforced ternary composite exhibited a compressive strength of 116-212 MPa, a bending strength of 89-138 MPa, a tensile strength of 109-181 MPa, with the breaking elongation ratio of 6.2-9.1%, and a tensile modulus of 2.9-5.8 GPa, with the values varying with increasing CF content from 5 to 20 (mass fraction). The MG-63 cells of normal phenotype were well extended and spread onto the ternary composite surface. In addition, its proliferation and differentiation on the composite surface were significantly increased with time, indicating that the incorporation of CFs into HA/PA had little negative effects on MG-63 cells. The incorporation of CFs into a HA/PA66 composite improved the strength and ductility and introduced no negative effects on the cytocompatibility. Hence, the CF/HA/PA ternary composite has potential to be used as a bone repair materials and in fixation devices. Copyright © 2014 Elsevier Ltd. All rights reserved.

Mechanical and Thermal Properties of Epoxy Composites Containing Zirconia-Impregnated Halloysite Nanotubes with Different Loadings.

PubMed

Kim, Suhyun; Kim, Moon Il; Shon, Minyoung; Seo, Bongkuk; Lim, Choongsun

2018-09-01

Epoxy resins are widely used in various industrial fields due to their low cost, good workability, heat resistance, and good mechanical strength. However, they suffer from brittleness, an issue that must be addressed for further applications. To solve this problem, additional fillers are needed to improve the mechanical and thermal properties of the resins; zirconia is one such filler. However, it has been reported that aggregation may occur in the epoxy composites as the amount of zirconia increases, preventing enhancement of the mechanical strength of the epoxy composites. Herein, to reduce the aggregation, zirconia was well dispersed on halloysite nanotubes (HNTs), which have high thermal and mechanical strength, by a conventional wet impregnation method. The HNTs were impregnated with zirconia at different loadings using zirconyl chloride octahydrate as a precursor. The mechanical and thermal strengths of the epoxy composites with these fillers were investigated. The zirconia-impregnated HNTs (Zr/HNT) were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and tunneling electron microscopy (TEM). The hardening conditions of the epoxy composites were analyzed by differential scanning calorimetry (DSC). The thermal strength of the epoxy composites was studied by thermomechanical analysis (TMA) and micro-calorimetry and the mechanical strength of the epoxy composites (flexural strength and tensile strength) was studied by using a universal testing machine (UTM). The mechanical and thermal strengths of the epoxy composites with Zr/HNT were improved compared to those of the epoxy composite with HNT, and also increased as the zirconia loading on HNT increased.

Shear bond strength of one-step self-etch adhesives: pH influence

PubMed Central

Poggio, Claudio; Beltrami, Riccardo; Scribante, Andrea; Colombo, Marco; Chiesa, Marco

2015-01-01

Background: The aim of this study was to compare the shear bond strength of four one-step self-etch adhesives with different pH values to enamel and dentin. Materials and Methods: In this in vitro study, 200 bovine permanent mandibular incisors were used. Four one-step self-etch adhesives with different pH values were tested both on enamel and on dentin: Adper™ Easy Bond Self-Etch Adhesive (pH = 0.8-1), Futurabond NR (pH=2), G-aenial Bond (pH = 1.5), Clearfil S3 Bond (pH = 2.7). After adhesive systems application, a nanohybrid composite resin was inserted into the bonded surface. The specimens were placed in a universal testing machine. The shear bond strength was performed at a cross-head speed of 1 mm/min until the sample rupture. The shear bond strength values (MPa) of the different groups were compared with analysis of variance after that Kolmogorov and Smirnov tests were applied to assess normality of distributions. P < 0.05 was considered as significant. Results: In enamel shear bond strength, the highest shear bond strength values were reported with Futurabond NR (P < 0.01); however, no significant differences were found with Clearfil S3 Bond. The others adhesive systems showed lower shear bond strength values with significant differences between them (P < 0.05). When comparing the dentin shear bond strength, the lowest shear bond strength values were reported with Clearfil S3 Bond (P < 0.05), while there were no significant differences among the other three products (P > 0.05). Conclusion: The pH values of adhesive systems did not influence significantly their shear bond strength to enamel or dentin. PMID:26005459

Maximal isometric muscle strength values obtained By hand-held dynamometry in children between 6 and 15 years of age.

PubMed

Escobar, Raul G; Munoz, Karin T; Dominguez, Angelica; Banados, Pamela; Bravo, Maria J

2017-01-01

In this study we aimed to determine the maximal isometric muscle strength of a healthy, normal-weight, pediatric population between 6 and 15 years of age using hand-held dynamometry to establish strength reference values. The secondary objective was determining the relationship between strength and anthropometric parameters. Four hundred normal-weight Chilean children, split into 10 age groups, separated by 1-year intervals, were evaluated. Each age group included between 35 and 55 children. The strength values increased with increasing age and weight, with a correlation of 0.83 for age and 0.82 for weight. The results were similar to those reported in previous studies regarding the relationships among strength, age, and anthropometric parameters, but the reported strength differed. These results provide normal strength parameters for healthy and normal-weight Chilean children between 6 and 15 years of age and highlight the relevance of ethnicity in defining reference values for muscle strength in a pediatric population. Muscle Nerve 55: 16-22, 2017. © 2016 Wiley Periodicals, Inc.

Physicochemical and mechanical properties of zirconium oxide and niobium oxide modified Portland cement-based experimental endodontic sealers.

PubMed

Viapiana, R; Flumignan, D L; Guerreiro-Tanomaru, J M; Camilleri, J; Tanomaru-Filho, M

2014-05-01

To evaluate the physicochemical and mechanical properties of Portland cement-based experimental sealers (ES) with different radiopacifying agents (zirconium oxide and niobium oxide micro- and nanoparticles) in comparison with the following conventional sealers: AH Plus, MTA Fillapex and Sealapex. The materials were tested for setting time, compressive strength, flow, film thickness, radiopacity, solubility, dimensional stability and formaldehyde release. Data were subjected to anova and Tukey tests (P < 0.05). MTA Fillapex had the shortest setting time and lowest compressive strength values (P < 0.05) compared with the other materials. The ES had flow values similar to the conventional materials, but higher film thickness (P < 0.05) and lower radiopacity (P < 0.05). Similarly to AH Plus, the ES were associated with dimensional expansion (P > 0.05) and lower solubility when compared with MTA Fillapex and Sealapex (P < 0.05). None of the endodontic sealers evaluated released formaldehyde after mixing. With the exception of radiopacity, the Portland cement-based experimental endodontic sealers presented physicochemical properties according to the specifications no 57 ANSI/ADA (ADA Professional Product Review, 2008) and ISO 6876 (Dentistry - Root Canal Sealing Materials, 2012, British Standards Institution, London, UK). The sealers had setting times and flow ability that was adequate for clinical use, satisfactory compressive strength and low solubility. Additional studies should be carried out with the purpose of decreasing the film thickness and to determine the ideal ratio of radiopacifying agents in Portland cement-based root canal sealers. © 2013 International Endodontic Journal. Published by John Wiley & Sons Ltd.

Development of high strength and high ductility nanostructured TWIP steel

NASA Astrophysics Data System (ADS)

Kou, Hong Ning

Strength and ductility are two exclusive mechanical properties of structural materials. One challenge for material research is to develop bulk nanostructured metals with simultaneous high strength and good ductility. To meet this objective, steels with twinning induced plasticity (TWIP) effect are selected for surface mechanical attrition treatment (SMAT) in this study. Tensile tests reveal extremely high yield strength and simultaneously sufficient ductility in these SMATed TWIP steel samples. With the duration increase of SMAT, both yield strength and tensile strength firstly monotonically increase to a maximum value of 2.25GPa with 18% total elongation. However, further increase of SMAT duration results in decreases of both strength and elongation. The excellent ductility of coarse-grained TWIP steels is attributed to the instantaneous generation of deformation twins in tension. Based on this, an interesting hierarchically tertiary twinning system is revealed by TEM/HRTEM in SMATed samples, composed of multi-scale twins respectively produced by annealing treatment, SMAT and tensile deformation. On one hand, boundaries of hierarchical twins with different orientations form three-dimensional networks that restrict each other and act as strong barriers to dislocation motion, leading to ultrahigh strength. On the other hand, stress concentration is relieved due to deformation transfer caused by twinning from grain to grain, resulting in large plasticity. Therefore, the hierarchical twinning structure is regarded as the most effective element that induces both extraordinary ultrahigh strength and good elongation in SMATed TWIP. The stable austenite also contributes to the preservation of good ductility. Martensite is only observed in SMATed TWIP by longest SMAT duration. Another route of fabricating nanostructured TWIP is performed by combining SMAT and thermomechanical treatment. The interval heat treatment between double SMAT benefits the total elongation to over 50%, with 980 MPa yield strength. Nanograins are observed at 60mum depth, different from their usual emergence on top surface. Martensitic phase transformation is discovered. Most nanostructured SMATed TWIP samples demonstrate typical ductile fractures with large quantities of dimples in different sizes, following the same trend of gradient grains. Long SMAT duration produces slight brittle crack with tearing ribs. Microvoids coalescence with manganese carbides leads to final rupture.

Statistical distribution of mechanical properties for three graphite-epoxy material systems

NASA Technical Reports Server (NTRS)

Reese, C.; Sorem, J., Jr.

1981-01-01

Graphite-epoxy composites are playing an increasing role as viable alternative materials in structural applications necessitating thorough investigation into the predictability and reproducibility of their material strength properties. This investigation was concerned with tension, compression, and short beam shear coupon testing of large samples from three different material suppliers to determine their statistical strength behavior. Statistical results indicate that a two Parameter Weibull distribution model provides better overall characterization of material behavior for the graphite-epoxy systems tested than does the standard Normal distribution model that is employed for most design work. While either a Weibull or Normal distribution model provides adequate predictions for average strength values, the Weibull model provides better characterization in the lower tail region where the predictions are of maximum design interest. The two sets of the same material were found to have essentially the same material properties, and indicate that repeatability can be achieved.

Alloy and structural optimization of a directionally solidified lamellar eutectic alloy

NASA Technical Reports Server (NTRS)

Sheffler, K. D.

1976-01-01

Mechanical property characterization tests of a directionally solidified Ni-20 percent Cb-2.5 percent Al-6 percent Cr cellular eutectic turbine blade alloy demonstrated excellent long time creep stability and indicated intermediate temperature transverse tensile ductility and shear strength to be somewhat low for turbine blade applications. Alloy and structural optimization significantly improves these off-axis properties with no loss of longitudinal creep strength or stability. The optimized alloy-structure combination is a carbon modified Ni-20.1 percent Cb-2.5 percent Al-6.0 percent Cr-0.06 percent C composition processed under conditions producing plane front solidification and a fully-lamellar microstructure. With current processing technology, this alloy exhibits a creep-rupture advantage of 39 C over the best available nickel base superalloy, directionally solidified MAR M200+ Hf. While improved by about 20 percent, shear strength of the optimized alloy remains well below typical superalloy values.

Effect of fatigue protocols on flexural strength of lithium disilicate bars with clamped-ends.

PubMed

de Pinho Barcellos, Aline Serrado; Marinho, Caroline Cotes; Miranda, Jean Soares; Amaral, Marina; Shiino, Marcos Yutaka; Kimpara, Estevão Tomomitsu

2018-05-01

The aim of this study was compare the effect of two in vitro ageing protocols to intraoral aging on the flexural strength of a lithium disilicate (LD) ceramic bars with clamped ends. After polishing and crystallization, the both ends of the bars were cemented to a metallic device and subjected to mechanical cycling, thermomechanical cycling, or intraoral ageing. Ten volunteers used an intraoral device - similar to an occlusal splint with a balanced contact condition on the occlusal surface of the ceramic bar - during 8 h night time / 30 days. Both in vitro and intraoral ageing decreased the flexural residual strength of LD, with the lowest values obtained after intraoral ageing. Thus, the in vitro ageing protocols tested in this study revealed to be less deleterious than intraoral ageing of LD. Copyright © 2018. Published by Elsevier Ltd.

Fracture Anisotropy and Toughness in the Mancos Shale: Implications for crack-growth geometry

NASA Astrophysics Data System (ADS)

Chandler, M. R.; Meredith, P. G.; Brantut, N.; Crawford, B. R.

2013-12-01

The hydraulic fracturing of gas-shales has drawn attention to the fundamental fracture properties of shales. Fracture propagation is dependent on a combination of the in-situ stress field, the fracturing fluid and pressure, and the mechanical properties of the shale. However, shales are strongly anisotropic, and there is a general paucity of available experimental data on the anisotropic mechanical properties of shales in the scientific literature. The mode-I stress intensity factor, KI, quantifies the concentration of stress at crack tips. The Fracture Toughness of a linear elastic material is then defined as the critical value of this stress intensity factor; KIc, beyond which rapid catastrophic crack growth occurs. However, shales display significant non-linearity, which produces hysteresis during experimental cyclic loading. This allows for the calculation of a ductility coefficient using the residual displacement after successive loading cycles. From this coefficient, a ductility corrected Fracture Toughness value, KIcc can be determined. In the Mancos Shale this ductility correction can be as large as 60%, giving a Divider orientation KIcc value of 0.8 MPa.m0.5. Tensile strength and mode-I Fracture Toughness have been experimentally determined for the Mancos Shale using the Brazil Disk and Short-Rod methodologies respectively. The three principal fracture orientations; Arrester, Divider and Short-Transverse were all analysed. A significant anisotropy is observed in the tensile strength, with the Arrester value being 1.5 times higher than the Short-Transverse value. Even larger anisotropy is observed in the Fracture Toughness, with KIcc in the Divider and Arrester orientations being around 1.8 times that in the Short-Transverse orientation. For both tensile strength and fracture toughness, the Short-Transverse orientation, where the fracture propagates in the bedding plane in a direction parallel to the bedding, is found to have significantly lower values than the other two orientations. This anisotropy and variability in fracture properties is seen to cause deviation of the fracture direction during experiments on Arrester and Short-Transverse oriented samples, and can be expected to influence the geometry of propagating fractures. A comparison between the anisotropic tensile strength of the material and the crack-tip stress field in a transversely isotropic material has been used to develop a crack-tip deflection criterion in terms of the elasticity theory of cracks. This criterion suggests that a small perturbation in the incident angle of a mode-I crack propagating perpendicular to the bedding is likely to lead to a substantial deflection towards bedding-parallel (Short-Transverse) propagation. Further experimental work is currently underway on anisotropic Fracture Toughness measurements at elevated pressures and temperatures, simulating conditions in Shale Gas reservoirs at depths up to around 4km.

Reinforced chitosan-based heart valve scaffold and utility of bone marrow-derived mesenchymal stem cells for cardiovascular tissue engineering

NASA Astrophysics Data System (ADS)

Albanna, Mohammad Zaki

Recent research has demonstrated a strong correlation between the differentiation profile of mesenchymal stem cells (MSCs) and scaffold stiffness. Chitosan is being widely studied for tissue engineering applications due to its biocompatibility and biodegradability. However, its use in load-bearing applications is limited due to moderate to low mechanical properties. In this study, we investigated the effectiveness of a fiber reinforcement method for enhancing the mechanical properties of chitosan scaffolds. Chitosan fibers were fabricated using a solution extrusion and neutralization method and incorporated into porous chitosan scaffolds. The effects of different fiber/scaffold mass ratios, fiber mechanical properties and fiber lengths on scaffold mechanical properties were studied. The results showed that incorporating fibers improved scaffold strength and stiffness in proportion to the fiber/scaffold mass ratio. A fiber-reinforced heart valve leaflet scaffold achieved strength values comparable to the radial values of human pulmonary and aortic valves. Additionally, the effects of shorter fibers (2 mm) were found to be up to 3-fold greater than longer fibers (10 mm). Despite this reduction in fiber mechanical properties caused by heparin crosslinking, the heparin-modified fibers still improved the mechanical properties of the reinforced scaffolds, but to a lesser extent than the unmodified fibers. The results demonstrate that chitosan fiber-reinforcement can be used to generate tissue-matching mechanical properties in porous chitosan scaffolds and that fiber length and mechanical properties are important parameters in defining the degree of mechanical improvement. We further studied various chemical and physical treatments to improve the mechanical properties of chitosan fibers. With combination of chemical and physical treatments, fiber stiffness improved 40fold compared to unmodified fibers. We also isolated ovine bone marrow-derived MSCs and evaluated their utility for cardiovascular tissue engineering applications. Moreover, we evaluated the effect of various glycosaminoglycans (GAGs) on MSCs morphology and proliferation. Lastly, we studied the effect of stiffness of mechanically improved chitosan fibers on MSCs viability, attachment and proliferation. Results showed that MSCs proliferation improved in proportion to fiber stiffness.

Failure mechanisms of fibrin-based surgical tissue adhesives

NASA Astrophysics Data System (ADS)

Sierra, David Hugh

A series of studies was performed to investigate the potential impact of heterogeneity in the matrix of multiple-component fibrin-based tissue adhesives upon their mechanical and biomechanical properties both in vivo and in vitro. Investigations into the failure mechanisms by stereological techniques demonstrated that heterogeneity could be measured quantitatively and that the variation in heterogeneity could be altered both by the means of component mixing and delivery and by the formulation of the sealant. Ex vivo tensile adhesive strength was found to be inversely proportional to the amount of heterogeneity. In contrast, in vivo tensile wound-closure strength was found to be relatively unaffected by the degree of heterogeneity, while in vivo parenchymal organ hemostasis in rabbits was found to be affected: greater heterogeneity appeared to correlate with an increase in hemostasis time and amount of sealant necessary to effect hemostasis. Tensile testing of the bulk sealant showed that mechanical parameters were proportional to fibrin concentration and that the physical characteristics of the failure supported a ductile mechanism. Strain hardening as a function of percentage of strain, and strain rate was observed for both concentrations, and syneresis was observed at low strain rates for the lower fibrin concentration. Blister testing demonstrated that burst pressure and failure energy were proportional to fibrin concentration and decreased with increasing flow rate. Higher fibrin concentration demonstrated predominately compact morphology debonds with cohesive failure loci, demonstrating shear or viscous failure in a viscoelastic rubbery adhesive. The lower fibrin concentration sealant exhibited predominately fractal morphology debonds with cohesive failure loci, supporting an elastoviscous material condition. The failure mechanism for these was hypothesized and shown to be flow-induced ductile fracture. Based on these findings, the failure mechanism was stochastic in nature because the mean failure energy and burst pressure values were not predictive of locus and morphology. Instead, flow rate and fibrin concentration showed the most predictive value, with the outcome best described as a probability distribution rather than a specific deterministic outcome.

Crack propagation from a filled flaw in rocks considering the infill influences

NASA Astrophysics Data System (ADS)

Chang, Xu; Deng, Yan; Li, Zhenhua; Wang, Shuren; Tang, C. A.

2018-05-01

This study presents a numerical and experimental study of the cracking behaviour of rock specimen containing a single filled flaw under compression. The primary aim is to investigate the influences of infill on crack patterns, load-displacement response and specimen strength. The numerical code RFPA2D (Rock Failure Process Analysis) featured by the capability of modeling heterogeneous materials is employed to develop the numerical model, which is further calibrated by physical tests. The results indicate that there exists a critical infill strength which controls crack patterns for a given flaw inclination angle. For case of infill strength lower than the critical value, the secondary or anti-cracks are disappeared by increasing the infill strength. If the infill strength is greater than the critical value, the filled flaw has little influence on the cracking path and the specimen fails by an inclined crack, as if there is no flaw. The load-displacement responses show specimen stiffness increases by increasing infill strength until the infill strength reaches its critical value. The specimen strength increases by increasing the infill strength and almost keeps constant as the infill strength exceeds its critical value.

Factors affecting the work productivity of Oraon agricultural laborers of Jalpaiguri district, West Bengal.

PubMed

Roy, Subrata K

2002-03-01

In developing countries like India, where the incidence of protein-calorie malnutrition is high and mechanization is at a minimum, human labor provides much of the power for physical activity. This study presents anthropometric measurements, somatotypes, food intakes, energy expenditures, and work outputs of Oraon agricultural laborers of the Jalpaiguri district, West Bengal, in an attempt to identify the factors that predict high work productivity. Specifically, this study investigates 1) the relationship between morphological variation (anthropometric measurements and somatotype) and work productivity, 2) the nature and extent of the relationship between nutritional status and work productivity, and 3) the best predictor variables of work output. Classification of groups on the basis of median values of work output show that in the aggregate, the high productive groups are significantly younger than low-productive groups in both sexes. Before age-adjustment, the high productive groups show higher mean values of a few body dimensions, though these differ by sex, and both males and females exhibit a normal range of blood pressure and pulse rate values. Mean values of grip strength and back strength are higher in high-output men and women. Mean values of both food intake and energy expenditure are also higher among men in high-output groups, with only food intake higher in high-output women. However, after eliminating the effects of age, the differences between low-productive groups and high-productive groups in most of the variables are not significant. Productivity predictors in males consist of age, food intake and chest girth (inhalation). Females, on the other hand, show age and grip strength (left) as work output predictors. Copyright 2002 Wiley-Liss, Inc.

Mechanical Retention and Waterproof Properties of Bacterial Cellulose-Reinforced Thermoplastic Starch Biocomposites Modified with Sodium Hexametaphosphate

PubMed Central

Wang, Da-wei; Xu, Ying-juan; Li, Xin; Huang, Chao-ming; Huang, Kuo-shien; Wang, Chuen-kai; Yeh, Jen-taut

2015-01-01

The waterproof and strength retention properties of bacterial cellulose (BC)-reinforced thermoplastic starch (TPS) resins were successfully improved by reacting with sodium hexametaphosphate (SHMP). After modification with SHMP, the tensile strength (σf) and impact strength (Is) values of initial and conditioned BC-reinforced TPS, modified with varying amounts of SHMP(TPS100BC0.02SHMPx), and their blends with poly(lactic acid)((TPS100BC0.02SHMPx)75PLA25) specimens improved significantly and reached a maximal value as SHMP content approached 10 parts per hundred parts of TPS resin (phr), while their moisture content and elongation at break (ɛf) was reduced to a minimal value as SHMP contents approached 10 phr. The σf, Is and ɛf retention values of a (TPS100BC0.02SHMP10)75PLA25 specimen conditioned for 56 days are 52%, 50% and 3 times its initial σf, Is and ɛf values, respectively, which are 32.5 times, 8.9 times and 40% of those of a corresponding conditioned TPS100BC0.02 specimen, respectively. As evidenced by FTIR analyses of TPS100BC0.02SHMPx specimens, hydroxyl groups of TPS100BC0.02 resins were successfully reacted with the phosphate groups of SHMP molecules. New melting endotherms and diffraction peaks of VH-type crystals were found on DSC thermograms and WAXD patterns of TPS or TPS100BC0.02 specimens conditioned for 7 days, while no new melting endotherm or diffraction peak was found for TPS100BC0.02SHMPx and/or (TPS100BC0.02SHMPx)75PLA25 specimens conditioned for less than 14 and 28 days, respectively.

An Evaluation of the Binding Strength of Okra Gum and the Drug Release Characteristics of Tablets Prepared from It.

PubMed

Hussain, Amjad; Qureshi, Farah; Abbas, Nasir; Arshad, Muhammad Sohail; Ali, Ejaz

2017-06-02

The aim of this study is to evaluate the adhesion ability of okra gum, which is gaining popularity as a tablet binder. For this purpose, gum was extracted from okra pods, and the binding strength of different concentrations (1%, 3%, and 5%) was determined quantitatively. Additionally, naproxen sodium tablets were prepared by using okra gum as a binder and were evaluated for their properties including hardness, friability, disintegration time, and dissolution rate. The binding strength values were compared with that of pre-gelatinized starch, a commonly used tablet binder. The results from universal testing machine indicate that the binding strengths of all dispersions of okra increase as the concentration increases from 1% to 5% and ranges from 2.5 to 4.5 N, which are almost twice a high as those of pre-gelatinized starch. The tablets prepared with okra gum have shown good mechanical strength with hardness values of 7-8.5 kg/cm² and a friability <1%, comparable to tablets prepared with starch. The disintegration time was longer (7.50 min with okra gum and 5.05 min with starch paste), and the drug release from these tablets was slower than the formulations with starch. The higher binding ability of okra gum probably linked with its chemical composition as it mainly contains galactose, rhamnose, and galacturonic acid. This study concludes that okra gum is a better binder than pre-gelatinized starch, it might be explored in future for introduction as a cost-effective binder in the pharmaceutical industry.

Effect of opacifiers and UV absorbers on pigmented maxillofacial silicone elastomer, part 2: mechanical properties after artificial aging.

PubMed

Nguyen, Caroline Tram; Chambers, Mark S; Powers, John M; Kiat-Amnuay, Sudarat

2013-06-01

There are reports of dissatisfaction with color instability and reduced lifetime of extraoral maxillofacial prostheses. Previous studies showed that UV mineral-based light-protecting agent (LP) improved color stability of MDX4-4210/Type A silicone elastomer. However, effects of this agent and opacifiers on mechanical properties of the elastomer are unknown. The purpose of this study was to evaluate the effect of 2 commonly used opacifiers and LP, a new opacifier, when combined with pigments on the mechanical properties of MDX4-4210/Type A silicone elastomer before and after artificial aging. Two commonly used opacifiers, titanium white dry pigment (TW) and silicone intrinsic white (SW) and LP were each combined with MDX4-4210/type A. Artists' oil pigment was then combined with the LP and TW groups, and silicone intrinsic pigments were combined with the SW group with 5 colors (no pigment=control, red, yellow, blue, or a combination of the 3 pigments). Ten dumbbell-shaped and 10 trouser-shaped specimens of each opacifier + pigment mixture, plus a control group with no opacifier and no pigment, were made for a total of 320 specimens. Half of the specimens (n=5) were aged in a chamber at 450 kJ/m(2). Specimens were tested for hardness (ASTM D2240), tensile strength (ASTM D412), tear strength (ASTM D624), and percentage elongation in a universal testing machine. A 3-way ANOVA and the Fisher PLSD test were performed (α=.05) for each mechanical property. After accelerated aging, values of Shore A hardness were the lowest for LP with all 5 pigments and the control, followed by SW and TW (P<.001). After accelerated aging, tear strength, tensile strength, and elongation decreased significantly (P<.001) for LP, whereas changes for SW and TW varied depending on the pigment. The mechanical properties of specimens with the light-protecting opacifier were adversely affected after being subjected to artificial aging. SW and TW preserved the mechanical properties of silicone in this study. Copyright © 2013 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Physical, mechanical, and flexural properties of 3 orthodontic wires: an in-vitro study.

PubMed

Juvvadi, Shubhaker Rao; Kailasam, Vignesh; Padmanabhan, Sridevi; Chitharanjan, Arun B

2010-11-01

Understanding the biologic requirements of orthodontic patients requires proper characterization studies of new archwire alloys. The aims of this study were to evaluate properties of wires made of 2 new materials and to compare their properties with those of stainless steel. The sample consisted of 30 straight lengths of 3 types of wires: stainless steel, titanium-molybdenum alloy, and beta-titanium alloy. Eight properties were evaluated: wire dimension, edge bevel, composition, surface characteristics, frictional characteristics, ultimate tensile strength (UTS), modulus of elasticity (E), yield strength (YS), and load deflection characteristics. A toolmaker's microscope was used to measure the edge bevel, and x-ray fluorescence was used for composition analysis. Surface profilometry and scanning electron microscopy were used for surface evaluation. A universal testing machine was used to evaluate frictional characteristics, tensile strength, and 3-point bending. Stainless steel was the smoothest wire; it had the lowest friction and spring-back values and high values for stiffness, E, YS, and UTS. The titanium-molybdenum alloy was the roughest wire; it had high friction and intermediate spring-back, stiffness, and UTS values. The beta-titanium alloy was intermediate for smoothness, friction, and UTS but had the highest spring-back. The beta-titanium alloy with increased UTS and YS had a low E value, suggesting that it would have greater resistance to fracture, thereby overcoming a major disadvantage of titanium-molybdenum alloy wires. The beta-titanium alloy wire would also deliver gentler forces. Copyright © 2010 American Association of Orthodontists. Published by Mosby, Inc. All rights reserved.

Mechanical properties and micro-morphology of fiber posts.

PubMed

Zicari, F; Coutinho, E; Scotti, R; Van Meerbeek, B; Naert, I

2013-04-01

To evaluate flexural properties of different fiber posts systems and to morphologically characterize their micro-structure. Six types of translucent fiber posts were selected: RelyX Post (3M ESPE), ParaPost Taper Lux (Colthéne-Whaledent), GC Fiber Post (GC), LuxaPost (DMG), FRC Postec Plus (Ivoclar-Vivadent), D.T. Light-Post (RTD). For each post system and size, ten specimens were subjected to a three-points bending test. Maximum fracture load, flexural strength and flexural modulus were determined using a universal loading device (5848 MicroTester(®), Instron). Besides, for each system, three intact posts of similar dimensions were processed for scanning electron microscopy to morphologically characterize the micro-structure. The following structural characteristics were analyzed: fibers/matrix ratio, density of fibers, diameter of fibers and distribution of fibers. Data were statistically analyzed with ANOVA. Type and diameter of posts were found to significantly affect the fracture load, flexural strength and flexural modulus (p<0.05). Regarding maximum fracture load, it was found to increase with post diameter, in each post system (p<0.001). Regarding flexural strength and flexural modulus, the highest values were recorded for posts with the smallest diameter (p<0.001). Finally, structural characteristics significantly varied among the post systems tested. However, any correlation has been found between flexural strength and structural characteristics. Flexural strength appeared not to be correlated to structural characteristics of fiber posts, but it may rather be affected by mechanical properties of the resin matrix and the interfacial adhesion between fibers and resin matrix. Copyright © 2013. Published by Elsevier Ltd.

Multiparameter structural optimization of single-walled carbon nanotube composites: toward record strength, stiffness, and toughness.

PubMed

Shim, Bong Sup; Zhu, Jian; Jan, Edward; Critchley, Kevin; Ho, Szushen; Podsiadlo, Paul; Sun, Kai; Kotov, Nicholas A

2009-07-28

Efficient coupling of mechanical properties of SWNTs with the matrix leading to the transfer of unique mechanical properties of SWNTs to the macroscopic composites is a tremendous challenge of today's materials science. The typical mechanical properties of known SWNT composites, such as strength, stiffness, and toughness, are assessed in an introductory survey where we focused on concrete numerical parameters characterizing mechanical properties. Obtaining ideal stress transfer will require fine optimization of nanotube-polymer interface. SWNT nanocomposites were made here by layer-by-layer (LBL) assembly with poly(vinyl alcohol) (PVA), and the first example of optimization in respect to key parameters determining the connectivity at the graphene-polymer interface, namely, degree of SWNT oxidation and cross-linking chemistry, was demonstrated. The resulting SWNT-PVA composites demonstrated tensile strength (σ(ult)) = 504.5 ± 67.3 MPa, stiffness (E) = 15.6 ± 3.8 GPa, and toughness (K) = 121.2 ± 19.2 J/g with maximum values recorded at σ(ult) = 600.1 MPa, E = 20.6 GPa, and K = 152.1 J/g. This represents the strongest and stiffest nonfibrous SWNT composites made to date outperforming other bulk composites by 2-10 times. Its high performance is attributed to both high nanotube content and efficient stress transfer. The resulting LBL composite is also one of the toughest in this category of materials and exceeding the toughness of Kevlar by 3-fold. Our observation suggests that the strengthening and toughening mechanism originates from the synergistic combination of high degree of SWNT exfoliation, efficient SWNT-PVA binding, crack surface roughening, and fairly efficient distribution of local stress over the SWNT network. The need for a multiscale approach in designing SWNT composites is advocated.

Multiscale structure and damage tolerance of coconut shells.

PubMed

Gludovatz, B; Walsh, F; Zimmermann, E A; Naleway, S E; Ritchie, R O; Kruzic, J J

2017-12-01

We investigated the endocarp of the fruit of Cocos nucifera (i.e., the inner coconut shell), examining the structure across multiple length scales through advanced characterization techniques and in situ testing of mechanical properties. Like many biological materials, the coconut shell possesses a hierarchical structure with distinct features at different length scales that depend on orientation and age. Aged coconut was found to have a significantly stronger (ultimate tensile strength, UTS = 48.5MPa), stiffer (Young's modulus, E = 1.92GPa), and tougher (fracture resistance (R-curve) peak of K J = 3.2MPa m 1/2 ) endocarp than the younger fruit for loading in the latitudinal orientation. While the mechanical properties of coconut shell were observed to improve with age, they also become more anisotropic: the young coconut shell had the same strength (17MPa) and modulus (0.64GPa) values and similar R-curves for both longitudinal and latitudinal loading configurations, whereas the old coconut had 82% higher strength for loading in the latitudinal orientation, and >50% higher crack growth toughness for cracking on the latitudinal plane. Structural aspects affecting the mechanical properties across multiple length scales with aging were identified as improved load transfer to the cellulose crystalline nanostructure (identified by synchrotron x-ray diffraction) and sclerification of the endocarp, the latter of which included closing of the cell lumens and lignification of the cell walls. The structural changes gave a denser and mechanically superior micro and nanostructure to the old coconut shell. Additionally, the development of anisotropy was attributed to the formation of an anisotropic open channel structure throughout the shell of the old coconut that affected both crack initiation during uniaxial tensile tests and the toughening mechanisms of crack trapping and deflection during crack propagation. Copyright © 2017 Elsevier Ltd. All rights reserved.

Measurements of near-ultimate strength for multiwalled carbon nanotubes and irradiation-induced crosslinking improvements.

PubMed

Peng, Bei; Locascio, Mark; Zapol, Peter; Li, Shuyou; Mielke, Steven L; Schatz, George C; Espinosa, Horacio D

2008-10-01

The excellent mechanical properties of carbon nanotubes are being exploited in a growing number of applications from ballistic armour to nanoelectronics. However, measurements of these properties have not achieved the values predicted by theory due to a combination of artifacts introduced during sample preparation and inadequate measurements. Here we report multiwalled carbon nanotubes with a mean fracture strength >100 GPa, which exceeds earlier observations by a factor of approximately three. These results are in excellent agreement with quantum-mechanical estimates for nanotubes containing only an occasional vacancy defect, and are approximately 80% of the values expected for defect-free tubes. This performance is made possible by omitting chemical treatments from the sample preparation process, thus avoiding the formation of defects. High-resolution imaging was used to directly determine the number of fractured shells and the chirality of the outer shell. Electron irradiation at 200 keV for 10, 100 and 1,800 s led to improvements in the maximum sustainable loads by factors of 2.4, 7.9 and 11.6 compared with non-irradiated samples of similar diameter. This effect is attributed to crosslinking between the shells. Computer simulations also illustrate the effects of various irradiation-induced crosslinking defects on load sharing between the shells.

Measurements of near-ultimate strength for multiwalled carbon nanotubes and irradiation-induced crosslinking improvements.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, B.; Locascio, M.; Zapol, P.

2008-01-01

The excellent mechanical properties of carbon nanotubes are being exploited in a growing number of applications from ballistic armour to nanoelectronics. However, measurements of these properties have not achieved the values predicted by theory due to a combination of artifacts introduced during sample preparation and inadequate measurements. Here we report multiwalled carbon nanotubes with a mean fracture strength >100 GPa, which exceeds earlier observations by a factor of approximately three. These results are in excellent agreement with quantum-mechanical estimates for nanotubes containing only an occasional vacancy defect, and are {approx}80% of the values expected for defect-free tubes. This performance ismore » made possible by omitting chemical treatments from the sample preparation process, thus avoiding the formation of defects. High-resolution imaging was used to directly determine the number of fractured shells and the chirality of the outer shell. Electron irradiation at 200 keV for 10, 100 and 1,800 s led to improvements in the maximum sustainable loads by factors of 2.4, 7.9 and 11.6 compared with non-irradiated samples of similar diameter. This effect is attributed to crosslinking between the shells. Computer simulations also illustrate the effects of various irradiation-induced crosslinking defects on load sharing between the shells.« less

Elastic properties of suspended black phosphorus nanosheets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wang, Jia-Ying; Li, Yang; Zhen, Liang

2016-01-04

The mechanical properties of black phosphorus (BP) nanosheets suspended over circular holes were measured by an atomic force microscope nanoindentation method. The continuum mechanic model was introduced to calculate the elastic modulus and pretension of BP nanosheets with thicknesses ranging from 14.3 to 34 nm. Elastic modulus of BP nanosheets declines with thickness, and the maximum value is 276 ± 32.4 GPa. Besides, the effective strain of BP ranges from 8 to 17% with a breaking strength of 25 GPa. Our results show that BP nanosheets serve as a promising candidate for flexible electronic applications.

Long term mechanical properties of alkali activated slag

NASA Astrophysics Data System (ADS)

Zhu, J.; Zheng, W. Z.; Xu, Z. Z.; Leng, Y. F.; Qin, C. Z.

2018-01-01

This article reports a study on the microstructural and long-term mechanical properties of the alkali activated slag up to 180 days, and cement paste is studied as the comparison. The mechanical properties including compressive strength, flexural strength, axis tensile strength and splitting tensile strength are analyzed. The results showed that the alkali activated slag had higher compressive and tensile strength, Slag is activated by potassium silicate (K2SiO3) and sodium hydroxide (NaOH) solutions for attaining silicate modulus of 1 using 12 potassium silicate and 5.35% sodium hydroxide. The volume dosage of water is 35% and 42%. The results indicate that alkali activated slag is a kind of rapid hardening and early strength cementitious material with excellent long-term mechanical properties. Single row of holes block compressive strength, single-hole block compressive strength and standard solid brick compressive strength basically meet engineering requirements. The microstructures of alkali activated slag are studied by X-ray diffraction (XRD). The hydration products of alkali-activated slag are assured as hydrated calcium silicate and hydrated calcium aluminate.

Effects of High-Temperature Annealing in Air on Hi-Nicalon Fiber-Reinforced Celsian Matrix Composites

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.

2008-01-01

BN/SiC-coated Hi-Nicalon fiber-reinforced celsian matrix composites (CMC) were annealed for 100 h in air at various temperatures to 1200 C, followed by flexural strength measurements at room temperature. Values of yield stress and strain, ultimate strength, and composite modulus remain almost unchanged for samples annealed up to 1100 C. A thin porous layer formed on the surface of the 1100 C annealed sample and its density decreased from 3.09 to 2.90 g/cu cm. The specimen annealed at 1200 C gained 0.43 wt%, was severely deformed, and was covered with a porous layer of thick shiny glaze which could be easily peeled off. Some gas bubbles were also present on the surface. This surface layer consisted of elongated crystals of monoclinic celsian and some amorphous phase(s). The fibers in this surface ply of the CMC had broken into small pieces. The fiber-matrix interface strength was characterized through fiber push-in technique. Values of debond stress, alpha(sub d), and frictional sliding stress, tau(sub f), for the as-fabricated CMC were 0.31+/-0.14 GPa and 10.4+/-3.1 MPa, respectively. These values compared with 0.53+/-0.47 GPa and 8.33+/-1.72 MPa for the fibers in the interior of the 1200 C annealed sample, indicating hardly any change in fiber-matrix interface strength. The effects of thermal aging on microstructure were investigated using scanning electron microscopy. Only the surface ply of the 1200 C annealed specimens had degraded from oxidation whereas the bulk interior part of the CMC was unaffected. A mechanism is proposed explaining the various steps involved during the degradation of the CMC on annealing in air at 1200 C.

Effect of ZrO2 on the sintering behavior, strength and high-frequency dielectric properties of electrical ceramic porcelain insulator

NASA Astrophysics Data System (ADS)

Singh Mehta, Niraj; Sahu, Praveen Kumar; Ershad, Md; Saxena, Vipul; Pyare, Ram; Ranjan Majhi, Manas

2018-01-01

In the present study, the effect of ZrO2 on the sintering, strength and dielectric behavior of electrical ceramic porcelain insulator with substituting alumina content by zirconia (in weight percentage from 0% to 30%) is investigated. The different composition of samples containing different zirconia (ZrO2) contents of 0, 10, 20, and 30 wt% are prepared using the uniaxial pressure technique applying 160 MPa pressure. Further, the prepared samples are also analyzed for sintering temperatures (1350 °C), and effects are observed on mechanical and electric properties of porcelain insulator. Different characterizations such as Dilatometer, x-ray diffraction, scanning electron microscopy and differential thermal analysis/thermo gravimetric analysis were used to evaluate the thermal, phase detection, micro structural and weight loss changes by increasing concentration of ZrO2 on base porcelain composition. At 1350 °C, for the composition having 20 wt% ZrO2 with 10 wt% alumina, the maximum density was observed 2.81 g cm-3 with a porosity of 2.23%. The highest tensile strength of 41 ± 3 MPa is observed for the same sample composition. The minimum value of thermal expansion coefficient is found to be in the range of 10-6 for the sample with 30 wt% ZrO2 content sintered at 1350 °C compared to other prepared samples. Similarly, the highest dielectric value (5.1-4.4) having dielectric loss (0.08-0.12) is achieved for the sample with 30 wt% ZrO2 content sintered at 1350 °C in the frequency range of 4-20 GHz at room temperature. According to the mechanical properties, the composition having 20 wt% ZrO2 on base ceramic porcelain composition has enormous potential to serve as a high strength refractory material. For dielectric properties, the composition having 30 wt% ZrO2 is more suitable for the electrical application.

Effects of incorporation of 2.5 and 5 wt% TiO2 nanotubes on fracture toughness, flexural strength, and microhardness of denture base poly methyl methacrylate (PMMA).

PubMed

Abdulrazzaq Naji, Sahar; Behroozibakhsh, Marjan; Jafarzadeh Kashi, Tahereh Sadat; Eslami, Hossein; Masaeli, Reza; Mahgoli, Hosseinali; Tahriri, Mohammadreza; Ghavvami Lahiji, Mehrsima; Rakhshan, Vahid

2018-04-01

The aim of this preliminary study was to investigate, for the first time, the effects of addition of titania nanotubes (n-TiO 2 ) to poly methyl methacrylate (PMMA) on mechanical properties of PMMA denture base. TiO 2 nanotubes were prepared using alkaline hydrothermal process. Obtained nanotubes were assessed using FESEM-EDX, XRD, and FT-IR. For 3 experiments of this study (fracture toughness, three-point bending flexural strength, and Vickers microhardness), 135 specimens were prepared according to ISO 20795-1:2013 (n of each experiment=45). For each experiment, PMMA was mixed with 0% (control), 2.5 wt%, and 5 wt% nanotubes. From each TiO 2 :PMMA ratio, 15 specimens were fabricated for each experiment. Effects of n-TiO 2 addition on 3 mechanical properties were assessed using Pearson, ANOVA, and Tukey tests. SEM images of n-TiO 2 exhibited the presence of elongated tubular structures. The XRD pattern of synthesized n-TiO 2 represented the anatase crystal phase of TiO 2 . Moderate to very strong significant positive correlations were observed between the concentration of n-TiO 2 and each of the 3 physicomechanical properties of PMMA (Pearson's P value ≤.001, correlation coefficient ranging between 0.5 and 0.9). Flexural strength and hardness values of specimens modified with both 2.5 and 5 wt% n-TiO 2 were significantly higher than those of control ( P ≤.001). Fracture toughness of samples reinforced with 5 wt% n-TiO 2 (but not those of 2.5% n-TiO 2 ) was higher than control ( P =.002). Titania nanotubes were successfully introduced for the first time as a means of enhancing the hardness, flexural strength, and fracture toughness of denture base PMMA.

Effects of Ceramic Density and Sintering Temperature on the Mechanical Properties of a Novel Polymer-Infiltrated Ceramic-Network Zirconia Dental Restorative (Filling) Material.

PubMed

Li, Weiyan; Sun, Jian

2018-05-10

BACKGROUND Polymer-infiltrated ceramic-network (PICN) dental material is a new and practical development in orthodontics. Sintering is the process of forming a stable solid mass from a powder by heating without melting. The aim of this study was to evaluate the effects of sintering temperature on the mechanical properties of a PICN zirconia dental material. MATERIAL AND METHODS A dense zirconia ceramic and four PICN zirconia dental materials, with varying porosities, were sintered at three different temperatures; 12 PICN zirconia dental materials based on these porous ceramics were prepared, as well as a pure polymer. After the specimen preparation, flexural strength and elastic modulus values were measured using the three-point bending test, and fracture toughness were determined by the single-edge notched beam (SENB) method. The Vickers hardness test method was used with an indentation strength (IS) test. Scanning electron microscopy (SEM) was used to examine the microstructure of the ceramic surface and the fracture surface. RESULTS Mechanical properties of the PICN dental materials, including flexural strength, elastic modulus, fracture toughness, and hardness, were more similar to the properties of natural teeth when compared with traditional dental ceramic materials, and were affected by the density and sintering temperature. SEM showed that the porous ceramic network became cohesive and that the length of cracks in the PICN dental material was reduced. CONCLUSIONS PICN zirconia dental materials were characterized by similar mechanical properties to natural dental tissues, but further studies are required continue to improve the similarities with natural human enamel and dentin.

Effects of Ceramic Density and Sintering Temperature on the Mechanical Properties of a Novel Polymer-Infiltrated Ceramic-Network Zirconia Dental Restorative (Filling) Material

PubMed Central

Li, Weiyan

2018-01-01

Background Polymer-infiltrated ceramic-network (PICN) dental material is a new and practical development in orthodontics. Sintering is the process of forming a stable solid mass from a powder by heating without melting. The aim of this study was to evaluate the effects of sintering temperature on the mechanical properties of a PICN zirconia dental material. Material/Methods A dense zirconia ceramic and four PICN zirconia dental materials, with varying porosities, were sintered at three different temperatures; 12 PICN zirconia dental materials based on these porous ceramics were prepared, as well as a pure polymer. After the specimen preparation, flexural strength and elastic modulus values were measured using the three-point bending test, and fracture toughness were determined by the single-edge notched beam (SENB) method. The Vickers hardness test method was used with an indentation strength (IS) test. Scanning electron microscopy (SEM) was used to examine the microstructure of the ceramic surface and the fracture surface. Results Mechanical properties of the PICN dental materials, including flexural strength, elastic modulus, fracture toughness, and hardness, were more similar to the properties of natural teeth when compared with traditional dental ceramic materials, and were affected by the density and sintering temperature. SEM showed that the porous ceramic network became cohesive and that the length of cracks in the PICN dental material was reduced. Conclusions PICN zirconia dental materials were characterized by similar mechanical properties to natural dental tissues, but further studies are required continue to improve the similarities with natural human enamel and dentin. PMID:29746449

Mechanical and interfacial characterization of laser welded Co-Cr alloy with different joint configurations

PubMed Central

Kokolis, John; Chakmakchi, Makdad; Theocharopoulos, Antonios; Prombonas, Anthony

2015-01-01

PURPOSE The mechanical and interfacial characterization of laser welded Co-Cr alloy with two different joint designs. MATERIALS AND METHODS Dumbbell cast specimens (n=30) were divided into 3 groups (R, I, K, n=10). Group R consisted of intact specimens, group I of specimens sectioned with a straight cut, and group K of specimens with a 45° bevel made at the one welding edge. The microstructure and the elemental distributions of alloy and welding regions were examined by an SEM/EDX analysis and then specimens were loaded in tension up to fracture. The tensile strength (TS) and elongation (ε) were determined and statistically compared among groups employing 1-way ANOVA, SNK multiple comparison test (α=.05) and Weibull analysis where Weibull modulus m and characteristic strength σο were identified. Fractured surfaces were imaged by a SEM. RESULTS SEM/EDX analysis showed that cast alloy consists of two phases with differences in mean atomic number contrast, while no mean atomic number was identified for welded regions. EDX analysis revealed an increased Cr and Mo content at the alloy-joint interface. All mechanical properties of group I (TS, ε, m and σο) were found inferior to R while group K showed intermediated values without significant differences to R and I, apart from elongation with group R. The fractured surfaces of all groups showed extensive dendritic pattern although with a finer structure in the case of welded groups. CONCLUSION The K shape joint configuration should be preferred over the I, as it demonstrates improved mechanical strength and survival probability. PMID:25722836

Estimation of internal friction angle of subduction zone in northeast of Japan by using seismic focal mechanisms

NASA Astrophysics Data System (ADS)

Miyakawa, A.; Sato, K.; Otsubo, M.

2017-12-01

Physical properties, such as friction angle of the material, is important to understand the interplate earthquake of a subduction zone. Coulomb wedge model (Davis et al., 1983, JGR) is successfully revealed the relationship between a geometry of an accretionary wedge in a subduction zone and the physical properties of the material composing the accretionary wedge (e.g. Dahlen, 1984, JGR). An internal friction angle of the wedge and the frictional strength of the plate boundary fault control the wedge angle according to the Coulomb wedge model. However, the internal friction angle of the wedge and the frictional strength of the plate boundary fault are hard to estimate. Many previous works assumed the internal friction angle of the wedge on the basis of the laboratory experiments. Then, the frictional strength of the plate boundary fault, which is usually most interested, were evaluated from the observed wedge angle and the assumed internal friction angle of the wedge. Consequently, we should be careful of the selection of the internal friction angle of the wedge, otherwise, the uncertain an inappropriate internal friction angle may mislead the frictional strength of the plate boundary fault. In this study, we employed the newly developed technique to evaluate the internal friction angle of the wedge from the earthquake focal mechanisms occurred in the wedge along Japan Trench, northeast Japan. We used 650 earthquake mechanisms determined by NIED, Japan for the stress and friction coefficient inversion. The stress and friction coefficient inversion method is modified to handle the earthquake focal mechanisms from a computerized method to estimate the friction coefficient from the orientation distribution of faults (Sato, 2016, JSG). Finally, we obtained 25 degrees of internal friction angle of the wedge from the inversion. This value of friction angle is lower than usually assumed internal friction angle (30 degrees) (Byerlee, 1978, PAGEOPH). This lower internal friction angle leads to lower frictional strength of plate boundary fault ( 0.35) according to the Coulomb wedge model. These constrained physical parameters can contribute to understanding the interplate earthquake at each subduction zones.

Cytocompatibility, mechanical and dissolution properties of high strength boron and iron oxide phosphate glass fibre reinforced bioresorbable composites.

PubMed

Sharmin, Nusrat; Hasan, Muhammad S; Parsons, Andrew J; Rudd, Chris D; Ahmed, Ifty

2016-06-01

In this study, Polylactic acid (PLA)/phosphate glass fibres (PGF) composites were prepared by compression moulding. Fibres produced from phosphate based glasses P2O5-CaO-MgO-Na2O (P45B0), P2O5-CaO-MgO-Na2O-B2O3 (P45B5), P2O5-CaO-MgO-Na2O-Fe2O3 (P45Fe3) and P2O5-CaO-MgO-Na2O-B2O3-Fe2O3 (P45B5Fe3) were used to reinforce the bioresorbable polymer PLA. Fibre mechanical properties and degradation rate were investigated, along with the mechanical properties, degradation and cytocompatibility of the composites. Retention of the mechanical properties of the composites was evaluated during degradation in PBS at 37°C for four weeks. The fibre volume fraction in the composite varied from 19 to 23%. The flexural strength values (ranging from 131 to 184MPa) and modulus values (ranging from 9.95 to 12.29GPa) obtained for the composites matched those of cortical bone. The highest flexural strength (184MPa) and modulus (12.29GPa) were observed for the P45B5Fe3 composite. After 28 days of immersion in PBS at 37°C, ~35% of the strength profile was maintained for P45B0 and P45B5 composites, while for P45Fe3 and P45B5Fe3 composites ~40% of the initial strength was maintained. However, the overall wet mass change of P45Fe3 and P45B5Fe3 remained significantly lower than that of the P45B0 and P45B5 composites. The pH profile also revealed that the P45B0 and P45B5 composites degraded quicker, correlating well with the degradation profile. From SEM analysis, it could be seen that after 28 days of degradation, the fibres in the fractured surface of P45B5Fe3 composites remain fairly intact as compared to the other formulations. The in vitro cell culture studies using MG63 cell lines revealed both P45Fe3 and P45B5Fe3 composites maintained and showed higher cell viability as compared to the P45B0 and P45B5 composites. This was attributed to the slower degradation rate of the fibres in P45Fe3 and P45B5Fe3 composites as compared with the fibres in P45B0 and P45B5 composites. Copyright © 2015 Elsevier Ltd. All rights reserved.

Simultaneous increase in strength and ductility by decreasing interface energy between Zn and Al phases in cast Al-Zn-Cu alloy.

PubMed

Han, Seung Zeon; Choi, Eun-Ae; Park, Hyun Woong; Lim, Sung Hwan; Lee, Jehyun; Ahn, Jee Hyuk; Hwang, Nong-Moon; Kim, Kwangho

2017-09-22

Cast-Al alloys that include a high amount of the second element in their matrix have comparatively high strength but low ductility because of the high volume fraction of strengthening phases or undesirable inclusions. Al-Zn alloys that have more than 30 wt% Zn have a tensile strength below 300 MPa, with elongation under 5% in the as-cast state. However, we found that after substitution of 2% Zn by Cu, the tensile strength of as-cast Al-Zn-Cu alloys was 25% higher and ductility was four times higher than for the corresponding Al-35% Zn alloy. Additionally, for the Al-43% Zn alloy with 2% Cu after 1 h solution treatment at 400 °C and water quenching, the tensile strength unexpectedly reached values close to 600 MPa. For the Al-33% Zn alloy with 2% Cu, the tensile strength was 500 MPa with 8% ductility. The unusual trends of the mechanical properties of Al-Zn alloys with Cu addition observed during processing from casting to the subsequent solution treatment were attributed to the precipitation of Zn in the Al matrix. The interface energy between the Zn particles and the Al matrix decreased when using a solution of Cu in Zn.

Impact tensile properties and strength development mechanism of glass for reinforcement fiber

NASA Astrophysics Data System (ADS)

Kim, T.; Oshima, K.; Kawada, H.

2013-07-01

In this study, impact tensile properties of E-glass were investigated by fiber bundle testing under a high strain rate. The impact tests were performed employing two types of experiments. One is the tension-type split Hopkinson pressure bar system, and the other is the universal high-speed tensile-testing machine. As the results, it was found that not only the tensile strength but also the fracture strain of E-glass fiber improved with the strain rate. The absorbed strain energy of this material significantly increased. It was also found that the degree of the strain rate dependency of E-glass fibers on the tensile strength was varied according to fiber diameter. As for the strain rate dependency of the glass fiber under tensile loading condition, change of the small crack-propagation behaviour was considered to clarify the development of the fiber strength. The tensile fiber strength was estimated by employing the numerical simulation based on the slow crack-growth model (SCG). Through the parametric study against the coefficient of the crack propagation rate, the numerical estimation value was obtained for the various testing conditions. It was concluded that the slow crack-growth behaviour in the glass fiber was an essential for the increase in the strength of this material.

Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep and thermal fatigue

NASA Technical Reports Server (NTRS)

Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

1992-01-01

This report presents the results of a fourth year effort of a research program, conducted for NASA-LeRC by the University of Texas at San Antonio (UTSA). The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subject to a number of effects or primitive variables. These primitive variables may include high temperature, fatigue or creep. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation has been randomized and is included in the computer program, PROMISS. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 has been analyzed using the developed methodology.

Computational simulation of probabilistic lifetime strength for aerospace materials subjected to high temperature, mechanical fatigue, creep, and thermal fatigue

NASA Technical Reports Server (NTRS)

Boyce, Lola; Bast, Callie C.; Trimble, Greg A.

1992-01-01

The results of a fourth year effort of a research program conducted for NASA-LeRC by The University of Texas at San Antonio (UTSA) are presented. The research included on-going development of methodology that provides probabilistic lifetime strength of aerospace materials via computational simulation. A probabilistic material strength degradation model, in the form of a randomized multifactor interaction equation, is postulated for strength degradation of structural components of aerospace propulsion systems subjected to a number of effects or primitive variables. These primitive variables may include high temperature, fatigue, or creep. In most cases, strength is reduced as a result of the action of a variable. This multifactor interaction strength degradation equation was randomized and is included in the computer program, PROMISC. Also included in the research is the development of methodology to calibrate the above-described constitutive equation using actual experimental materials data together with regression analysis of that data, thereby predicting values for the empirical material constants for each effect or primitive variable. This regression methodology is included in the computer program, PROMISC. Actual experimental materials data were obtained from industry and the open literature for materials typically for applications in aerospace propulsion system components. Material data for Inconel 718 was analyzed using the developed methodology.

Role of orthopyroxene in rheological weakening of the lithosphere via dynamic recrystallization

PubMed Central

Farla, Robert J. M.; Karato, Shun-ichiro; Cai, Zhengyu

2013-01-01

For plate tectonics to operate on a terrestrial planet, the surface layer (the lithosphere) must have a modest strength (Earth, ≤200 MPa), but a standard strength profile based on olivine far exceeds this threshold value. Consequently, it is essential to identify mechanisms that reduce the strength of the lithosphere on Earth. Here we report results of high-strain laboratory deformation experiments on a representative olivine–orthopyroxene composition that show the addition of orthopyroxene substantially reduces the strength in the ductile regime within a certain temperature window. The reduction in strength is associated with the formation of small orthopyroxene and olivine grains. Our samples show heterogeneous microstructures similar to those observed in natural peridotites in shear zones: fine-grained regions containing both orthopyroxene and olivine that form interconnected bands where a large fraction of strain is accommodated. A model is developed to apply these results to geological conditions. Such a model, combined with our experimental observations, suggests that orthopyroxene may play a key role in the plastic deformation of the lithosphere in a critical temperature range, leading to long-term weakening associated with strain localization in the lithosphere. PMID:24067645

Compressive and bonding strength of fly ash based geopolymer mortar

NASA Astrophysics Data System (ADS)

Zailani, Warid Wazien Ahmad; Abdullah, Mohd Mustafa Al Bakri; Zainol, Mohd Remy Rozainy Mohd Arif; Razak, Rafiza Abd.; Tahir, Muhammad Faheem Mohd

2017-09-01

Geopolymer which is produced by synthesizing aluminosilicate source materials with an alkaline activator solution promotes sustainable and excellent properties of binder. The purpose of this paper is to determine the optimum binder to sand ratio of geopolymer mortars based on mechanical properties. In order to optimize the formulation of geopolymer mortar, various binder to sand ratios (0.25, 0.33, 0.5, 1.0, 2.0, 3.0, and 4.0) are prepared. The investigation on the effect of sand inclusion to the compressive and bonding strength of geopolymer mortar is approached. The experimental results show that the bonding strength performance of geopolymer is also depends on the various binder to sand ratio, where the optimum ratio 0.5 gives a highest strength of 12.73 MPa followed by 12.35 MPa, which corresponds the ratio 1.0 for geopolymer, while the compared value of OPC bonding strength is given by 9.3 MPa. The morphological structure at the interface zone is determined by Scanning Electron Microscope (SEM) and the homogenous bonding between geopolymer and substrate can be observed. Fly ash based geopolymers reveal a new category of mortar which has high potential to be used in the field of concrete repair and rehabilitation.

Strength and Formability Improvement of Al-Cu-Mn Aluminum Alloy Complex Parts by Thermomechanical Treatment with Sheet Hydroforming

NASA Astrophysics Data System (ADS)

Chen, Yi-Zhe; Liu, Wei; Yuan, Shi-Jian

2015-05-01

Normally, the strength and formability of aluminum alloys can be increased largely by severe plastic deformation and heat treatment. However, many plastic deformation processes are more suitable for making raw material, not for formed parts. In this article, an experimental study of the thermomechanical treatment by using the sheet hydroforming process was developed to improve both mechanical strength and formability for aluminum alloys in forming complex parts. The limiting drawing ratio, thickness, and strain distribution of complex parts formed by sheet hydroforming were investigated to study the formability and sheet-deformation behavior. Based on the optimal formed parts, the tensile strength, microhardness, grain structure, and strengthening precipitates were analyzed to identify the strengthening effect of thermomechanical treatment. The results show that in the solution state, the limiting drawing ratio of cylindrical parts could be increased for 10.9% compared with traditional deep drawing process. The peak values of tensile stress and microhardness of formed parts are 18.0% and 12.5% higher than that in T6 state. This investigation shows that the thermomechanical treatment by sheet hydroforming is a potential method for the products manufacturing of aluminum alloy with high strength and good formability.

Differentiation of molecular chain entanglement structure through laser Raman spectrum measurement of High strength PET fibers under stress

NASA Astrophysics Data System (ADS)

Go, D.; Takarada, W.; Kikutani, T.

2017-10-01

The aim of this study was to investigate the mechanism for the improvement of mechanical properties of poly(ethylene terephthalate) (PET) fibers based on the concept of controlling the state of molecular entanglement. For this purpose, five different PET fibers were prepared through either the conventional melt spinning and drawing/annealing process or the high-speed melt spinning process. In both cases, the melt spinning process was designed so as to realize different Deborah number conditions. The prepared fibers were subjected to the laser Raman spectroscopy measurement and the characteristics of the scattering peak at around 1616 cm-1, which corresponds to the C-C/C=C stretching mode of the aromatic ring in the main chain, were investigated in detail. It was revealed that the fibers drawn and annealed after the melt spinning process of lower Deborah number showed higher tensile strength as well as lower value of full width at half maximum (FWHM) in the laser Raman spectrum. Narrow FWHM was considered to represent the homogeneous state of entanglement structure, which may lead to the higher strength and toughness of fibers because individual molecular chains tend to bare similar level of tensile stress when the fiber is stretched. In case of high-speed spun fibers prepared with a high Deborah number condition, the FWHM was narrow presumably because much lower tensile stress in comparison with the drawing/annealing process was applied when the fiber structure was developed, however the value increased significantly upon applying tensile load to the fibers during the laser Raman spectrum measurement. From these results, it was concluded that the Laser Raman spectroscopy could differentiate molecular chain entanglement structure of various fiber samples, in that low FWHM, which corresponds to either homogeneous state of molecular entanglement or lower level of mean residual stress, and small increase of FWTH upon applying tensile stress are considered to be the key factors for the improvement of the mechanical properties of PET fibers.

The effect of impurities elements on titanium alloy (Ti-6Al-4V) MIM sintered part properties

NASA Astrophysics Data System (ADS)

Ahmad, M. Azmirruddin; Jabir, M.; Johari, N.; Ibrahim, R.; Hamidi, N.

2017-12-01

The titanium alloys (Ti-6Al-4V) compact were fabricated by Metal Injection Molding (MIM). However, the real challenge of MIM processing for titanium alloy is its affinity to be contaminated by interstitial light elements such as oxygen and carbon which could degrade the mechanical properties of sintered titanium alloy such as its tensile strength and ductility. The sintering temperature effect on carbon and oxygen content that affects its physical and mechanical properties of the sintered titanium alloy was studied. The titanium MIM brown specimen was sintered at four different sintering temperatures which are 1100 °C, 1150 °C, 1200 °C and 1250 °C for 4 hours under furnace control atmosphere. The experimental result indicated that the specimen which has been made from 100% gas atomized powder have a relative density of 92.2 % - 97.6 %, the range of porosity percent around 2.38 %-3.84 %. Ultimate tensile strength of 873.11 MPa - 1007.19 MPa and ductility percent in range of 1.89 %-3.46 %. The titanium alloy MIM specimen which was sintered at 1150 °C contained 0.145 % of carbon and 0.143 % of oxygen possess the highest value of density and tensile strength, with value of 4.344 gcm-3 and 1007.2 MPa respectively. Meanwhile, the titanium alloy MIM specimen which was sintered at 1200 °C contains 0.130 % of carbon and 0.127 % of oxygen, has the highest percentage of ductility with 3.46 %. The carbon content level increased as the sintering temperature increased due to decomposition of high molecule weight of residue binder system which could not be eliminated during solvent extraction debinding process and sintered at low temperature. Contrarily, the oxygen content level indicates a decrease as the sintering temperature increased. Briefly, the sintering temperature could influence the physical and mechanical properties of titanium alloy MIM sintered specimen as it influences the oxygen and carbon content level in the alloys.

Rheological principles of development hetero-modulus and hetero-viscous complex materials with extreme dynamic strength

NASA Astrophysics Data System (ADS)

Gömze, L. A.; Gömze, L. N.

2017-02-01

Materials with different crystalline and morphological compositions have different chemical, physical, mechanical and rheological properties, including wear protection, melting temperature, module of elasticity and viscosity. Examining the material structures and behaviors of differentceramic bodies and CMCs under high speed collisions in several years the authors have understood the advantages of hetero-modulus and hetero-viscous complex material systems to absorb and dissipate the kinetic energy of objects during high speed collisions. Applying the rheo-mechanical principles the authors successfully developed a new family of hetero-modulus and hetero-viscous alumina matrix composite materials with extreme mechanical properties including dynamic strength. These new corundum-matrix composite materials reinforced with Si2ON 2, Si3N4 , SiAlON and AlN submicron and nanoparticles have excellent dynamic strength during collisions with high density metallic bodies with speeds about 1000 m/sec or more. At the same time in the alumina matrix composites can be observed a phase transformation of submicron and nanoparticles of alpha and beta silicone-nitride crystals into cubicc-Si3N4 diamond-like particles can be observed, when the high speed collision processes are taken place in vacuum or oxygen-free atmosphere. Using the rheological principles and the energy engorgement by fractures, heating and melting of components the authors successfully developed several new hetero-modulus, hetero-viscous and hetero-plastic complex materials. These materials generally are based on ceramic matrixes and components having different melting temperatures and modules of elasticity from low values like carbon and light metals (Mg, Al, Ti, Si) up to very high values like boride, nitride and carbide ceramics. Analytical methods applied in this research were scanning electron microscopy, X-ray diffractions and energy dispersive spectrometry. Digital image analysis was applied to microscopy results to enhance the results of transformations.

Laboratory strength of glass ionomer and zinc phosphate cements.

PubMed

Piwowarczyk, A; Ottl, P; Lauer, H C

2001-09-01

The present in vitro study examined 3 mechanical properties, namely compressive, flexural, and diametral tensile strength, of various commercially available cements and core materials as a function of time after mixing. The examined materials were 2 cermet cements (Ketac Silver [ESPE, Seefeld, Germany] and Chelon Silver [ESPE]), 1 metal-reinforced glass ionomer cement (Miracle Mix [GC Dental Industrial Corp, Tokyo, Japan]), 2 conventional glass ionomer cements (Ketac Bond [ESPE] and Ketac Cem [ESPE]), 1 standard cure zinc phosphate cement (Harvard Cement [Richter and Hoffmann, Berlin, Germany]), and 1 zinc phosphate cement with the addition of 30% silver amalgam alloy powder (Harvard Cement 70% with Dispersalloy 30% [Richter and Hoffmann/Johnson and Johnson, East Windsor, NJ]). Properties were measured using a universal testing machine at 15 minutes, 1 hour, and 24 hours after first mixing. Compressive strengths varied widely between the 3 times of measurement from 5.8 +/- 6.6 MPa for Ketac Cem to 144.3 +/- 10.2 MPa for Ketac Silver. Twenty-four hours after mixing, the Bonferroni test showed significant (p

Ultrasonic pulse velocity for the evaluation of physical and mechanical properties of a highly porous building limestone.

PubMed

Vasanelli, Emilia; Colangiuli, Donato; Calia, Angela; Sileo, Maria; Aiello, Maria Antonietta

2015-07-01

UPV as non-destructive technique can effectively contribute to the low invasive in situ analysis and diagnosis of masonry elements related to the conservation, rehabilitation and strengthening of the built heritage. The use of non-destructive and non-invasive techniques brings all the times many advantages in diagnostic activities on pre-existing buildings in terms of sustainability; moreover, it is a strong necessity with respect to the conservation constraints when dealing with the historical-architectural heritage. In this work laboratory experiments were carried out to investigate the effectiveness of ultrasonic pulse velocity (UPV) in evaluating physical and mechanical properties of Lecce stone, a soft and porous building limestone. UPV and selected physical-mechanical parameters such as density and uniaxial compressive strength (UCS) were determined. Factors such as anisotropy and water presence that induce variations on the ultrasonic velocity were also assessed. Correlations between the analysed parameters are presented and discussed. The presence of water greatly affected the values of the analysed parameters, leading to a decrease of UPV and to a strong reduction of the compressive strength. A discussion of the role of the water on these results is provided. Regression analysis showed a reliable linear correlation between UPV and compressive strength, which allows a reasonable estimation of the strength of Lecce stone by means of non-destructive testing methods such as the ultrasonic wave velocity. Low correlation between UPV and density was found, suggesting that other factors than density, related to the fabric and composition, also influence the response of the selected stone to the UPV. They have no influence on the UCS, that instead showed to be highly correlated with the packing density. Copyright © 2015 Elsevier B.V. All rights reserved.

Step-stress analysis for predicting dental ceramic reliability

PubMed Central

Borba, Márcia; Cesar, Paulo F.; Griggs, Jason A.; Bona, Álvaro Della

2013-01-01

Objective To test the hypothesis that step-stress analysis is effective to predict the reliability of an alumina-based dental ceramic (VITA In-Ceram AL blocks) subjected to a mechanical aging test. Methods Bar-shaped ceramic specimens were fabricated, polished to 1µm finish and divided into 3 groups (n=10): (1) step-stress accelerating test; (2) flexural strength- control; (3) flexural strength- mechanical aging. Specimens from group 1 were tested in an electromagnetic actuator (MTS Evolution) using a three-point flexure fixture (frequency: 2Hz; R=0.1) in 37°C water bath. Each specimen was subjected to an individual stress profile, and the number of cycles to failure was recorded. A cumulative damage model with an inverse power law lifetime-stress relation and Weibull lifetime distribution were used to fit the fatigue data. The data were used to predict the stress level and number of cycles for mechanical aging (group 3). Groups 2 and 3 were tested for three-point flexural strength (σ) in a universal testing machine with 1.0 s in 37°C water. Data were statistically analyzed using Mann-Whitney Rank Sum test. Results Step-stress data analysis showed that the profile most likely to weaken the specimens without causing fracture during aging (95% CI: 0–14% failures) was: 80 MPa stress amplitude and 105 cycles. The median σ values (MPa) for groups 2 (493±54) and 3 (423±103) were statistically different (p=0.009). Significance The aging profile determined by step-stress analysis was effective to reduce alumina ceramic strength as predicted by the reliability estimate, confirming the study hypothesis. PMID:23827018

Step-stress analysis for predicting dental ceramic reliability.

PubMed

Borba, Márcia; Cesar, Paulo F; Griggs, Jason A; Della Bona, Alvaro

2013-08-01

To test the hypothesis that step-stress analysis is effective to predict the reliability of an alumina-based dental ceramic (VITA In-Ceram AL blocks) subjected to a mechanical aging test. Bar-shaped ceramic specimens were fabricated, polished to 1μm finish and divided into 3 groups (n=10): (1) step-stress accelerating test; (2) flexural strength-control; (3) flexural strength-mechanical aging. Specimens from group 1 were tested in an electromagnetic actuator (MTS Evolution) using a three-point flexure fixture (frequency: 2Hz; R=0.1) in 37°C water bath. Each specimen was subjected to an individual stress profile, and the number of cycles to failure was recorded. A cumulative damage model with an inverse power law lifetime-stress relation and Weibull lifetime distribution were used to fit the fatigue data. The data were used to predict the stress level and number of cycles for mechanical aging (group 3). Groups 2 and 3 were tested for three-point flexural strength (σ) in a universal testing machine with 1.0MPa/s stress rate, in 37°C water. Data were statistically analyzed using Mann-Whitney Rank Sum test. Step-stress data analysis showed that the profile most likely to weaken the specimens without causing fracture during aging (95% CI: 0-14% failures) was: 80MPa stress amplitude and 10(5) cycles. The median σ values (MPa) for groups 2 (493±54) and 3 (423±103) were statistically different (p=0.009). The aging profile determined by step-stress analysis was effective to reduce alumina ceramic strength as predicted by the reliability estimate, confirming the study hypothesis. Copyright © 2013 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Influence of dentin pretreatment on bond strength of universal adhesives.

PubMed

Poggio, Claudio; Beltrami, Riccardo; Colombo, Marco; Chiesa, Marco; Scribante, Andrea

2017-01-01

Objective: The purpose of the present study was to compare bond strength of different universal adhesives under three different testing conditions: when no pretreatment was applied, after 37% phosphoric acid etching and after glycine application. Materials and methods: One hundred and fifty bovine permanent mandibular incisors were used as a substitute for human teeth. Five different universal adhesives were tested: Futurabond M+, Scotchbond Universal, Clearfil Universal Bond, G-Premio BOND, Peak Universal Bond. The adhesive systems were applied following each manufacturer's instructions. The teeth were randomly assigned to three different dentin surface pretreatments: no pretreatment agent (control), 37% phosphoric acid etching, glycine pretreatment. The specimens were placed in a universal testing machine in order to measure and compare bond strength values. Results: The Kruskal-Wallis analysis of variance and the Mann-Whitney test were applied to assess significant differences among the groups. Dentin pretreatments provided different bond strength values for the adhesives tested, while similar values were registered in groups without dentin pretreatment. Conclusions: In the present report, dentin surface pretreatment did not provide significant differences in shear bond strength values of almost all groups. Acid pretreatment lowered bond strength values of Futurabond and Peak Universal Adhesives, whereas glycine pretreatment increased bond strength values of G Praemio Bond adhesive system.

Influence of dentin pretreatment on bond strength of universal adhesives

PubMed Central

Poggio, Claudio; Beltrami, Riccardo; Colombo, Marco; Chiesa, Marco; Scribante, Andrea

2017-01-01

Abstract Objective: The purpose of the present study was to compare bond strength of different universal adhesives under three different testing conditions: when no pretreatment was applied, after 37% phosphoric acid etching and after glycine application. Materials and methods: One hundred and fifty bovine permanent mandibular incisors were used as a substitute for human teeth. Five different universal adhesives were tested: Futurabond M+, Scotchbond Universal, Clearfil Universal Bond, G-Premio BOND, Peak Universal Bond. The adhesive systems were applied following each manufacturer’s instructions. The teeth were randomly assigned to three different dentin surface pretreatments: no pretreatment agent (control), 37% phosphoric acid etching, glycine pretreatment. The specimens were placed in a universal testing machine in order to measure and compare bond strength values. Results: The Kruskal–Wallis analysis of variance and the Mann–Whitney test were applied to assess significant differences among the groups. Dentin pretreatments provided different bond strength values for the adhesives tested, while similar values were registered in groups without dentin pretreatment. Conclusions: In the present report, dentin surface pretreatment did not provide significant differences in shear bond strength values of almost all groups. Acid pretreatment lowered bond strength values of Futurabond and Peak Universal Adhesives, whereas glycine pretreatment increased bond strength values of G Praemio Bond adhesive system. PMID:28642929

Subsurface Evolution: Weathering and Mechanical Strength Reduction in Bedrock of Lower Gordon Gulch, Colorado Front Range

NASA Astrophysics Data System (ADS)

Kelly, P. J.; Anderson, S. P.; Anderson, R. S.; Blum, A.; Foster, M. A.; Langston, A. L.

2011-12-01

Weathering processes drive mobile regolith production at the surface of the earth. Chemical and physical weathering weakens rock by creating porosity, opening fractures, and transforming minerals. Increased porosity provides habitat for living organisms, which aid in further breakdown of the rock, leaving it more susceptible to displacement and transport. In this study, we test mechanical and chemical characteristics of weathered profiles to better understand weathering processes. We collect shallow bedrock cores from tors and isovolumetrically weathered bedrock in lower Gordon Gulch to characterize the mechanical strength, mineralogy, and bulk chemistry of samples to track changes in the subsurface as bedrock weathers to mobile regolith. Gordon Gulch is a small (2.7 km2), E-W trending catchment within the Boulder Creek Critical Zone Observatory underlain by Pre-Cambrian gneiss and granitic bedrock. The basin is typical of the "Rocky Mountain Surface" of the Front Range, characterized by low relief, a lack of glacial or fluvial incision, and deep weathering. Although the low-curvature, low-relief Rocky Mountain Surface would appear to indicate a landscape roughly in steady-state, shallow seismic surveys (Befus et al., 2011, Vadose Zone Journal) indicate depth to bedrock is highly variable. Block style release of saprolite into mobile regolith could explain this high variability and should be observable in geotechnical testing. Gordon Gulch also displays a systematic slope-aspect dependent control on weathering, with N-facing hillslopes exhibiting deeper weathering profiles than the S-facing hillslope. We believe comparisons of paired geotechnical-testing, XRD, and XRF analyses may explain this hillslope anisotropy. Rock quality designation (RQD) values, a commonly used indicator of rock mass quality (ASTM D6032), from both N- and S- facing aspects in Gordon Gulch indicate that granitic bedrock in both outcrop and saprolitic rock masses is poor to very poor. Brazilian tensile testing of outcrop core samples show relatively low tensile failure forces, and exhibit a roughly logarithmic increase in failure force, and hence tensile strength, with depth. For many of the granitic strength profiles, the point of greatest curvature is around 0.5 m depth. Tests reveal small-scale variation in the tensile strength, suggesting that the tight fracture-spacing bounding blocks of saprolite plays an important role in regolith production. The origin of the micro- and macro-fractures is unclear. Preliminary results do not correlate clear depth-trends in mineralogy or bulk chemistry with mechanical strength. The lack of a strong signature from chemical or mineralogical weathering suggests that mechanical processes, such as frost cracking or biotite hydration, may dominate.

Shear Bond Strength of Superficial, Intermediate and Deep Dentin In Vitro with Recent Generation Self-etching Primers and Single Nano Composite Resin.

PubMed

Singh, Kulshrest; Naik, Rajaram; Hegde, Srinidhi; Damda, Aftab

2015-01-01

This in vitro study is intended to compare the shear bond strength of recent self-etching primers to superficial, intermediate, and deep dentin levels. All teeth were sectioned at various levels and grouped randomly into two experimental groups and two control groups having three subgroups. The experimental groups consisted of two different dentin bonding system. The positive control group consisted of All Bond 2 and the negative control group was without the bonding agent. Finally, the specimens were subjected to shear bond strength study under Instron machine. The maximum shear bond strengths were noted at the time of fracture. The results were statistically analyzed. Comparing the shear bond strength values, All Bond 2 (Group III) demonstrated fairly higher bond strength values at different levels of dentin. Generally comparing All Bond 2 with the other two experimental groups revealed highly significant statistical results. In the present investigation with the fourth generation, higher mean shear bond strength values were recorded compared with the self-etching primers. When intermediate dentin shear bond strength was compared with deep dentin shear bond strength statistically significant results were found with Clearfil Liner Bond 2V, All Bond 2 and the negative control. There was a statistically significant difference in shear bond strength values both with self-etching primers and control groups (fourth generation bonding system and without bonding system) at superficial, intermediate, and deep dentin. There was a significant fall in bond strength values as one reaches deeper levels of dentin from superficial to intermediate to deep.

Evaluation of in vitro push-out bond strengths of different post-luting systems after artificial aging.

PubMed

Marigo, Luca; D' Arcangelo, Camillo; DE Angelis, Francesco; Cordaro, Massimo; Vadini, Mirco; Lajolo, Carlo

2017-02-01

The purpose of this study was to evaluate the push-out bond strengths of four commercially available adhesive luting systems (two self-adhesive and two etch-and-rinse systems) after mechanical aging. Forty single-rooted anterior teeth were divided into four groups according to the luting cement system used: Cement-One (Group 1); One-Q-adhesive Bond + Axia Core Dual (Group 2); SmartCem® 2 (Group 3); and XP Bond® + Core-X™ Flow (Group 4). Anatomical Post was cemented in groups 1 and 2, and D.T. Light-Post Illusion was cemented in groups 3 and 4. All samples were subjected to masticatory stress simulation consisting of 300,000 cycles applied with a computer-controlled chewing simulator. Push-out bond strength values (MPa) were calculated at cervical, middle, and apical each level, and the total bond strengths were calculated as the averages of the three levels. Statistical analysis was performed with data analysis software and significance was set at P<0.05. Statistically significant differences in total bond strength were detected between the cements (Group 4: 3.28 MPa, Group 1: 2.77 MPa, Group 2: 2.36 MPa, Group 3: 1.13 MPa; P<0.05). Specifically, Group 1 exhibited a lower bond strength in the apical zone, Group 3 exhibited a higher strength in this zone, and groups 2 and 4 exhibited more homogeneous bonding strengths across the different anatomical zones. After artificial aging, etch-and-rinse luting systems exhibited more homogeneous bond strengths; nevertheless, Cement-One exhibited a total bond strength second only to Core-X Flow.

High-tensile strength sticking induced by ArF excimer laser surface treatment of poly(tetrafluoroethylene)

NASA Astrophysics Data System (ADS)

Hopp, Bela; Revesz, K.; Bor, Zsolt

1998-07-01

A successful enhancement of sticking of PTFE is demonstrated using ArF excimer laser irradiation in the presence of novel photoreagents. The applied laser fluence was very low at the sample - photoreagent liquid interface compared to the energy density applied in earlier investigations. After the treatment the PTFE films were glued by epoxy resin. It was found that at low doses the tensile strength of the sticking increased rapidly with the UV pulse number and the reached a saturation value, which was 6.66 MPa for triethylamine, 5.56 MPa in the case of 1,2-diaminoethane and 4.64 MPa for triethylene-tetramine. These are around two hundred times higher than the value of the untreated surface. It was found that this procedure makes the metallization and painting of PTFE surface also possible. A photoinduced electron transfer mechanism was suggested to describe the photoreaction, which is responsible for the increase of adhesion features on PTFE surface.

Dynamic Yielding and Spall Behavior of Commercially Pure Grade 4 Titanium

NASA Astrophysics Data System (ADS)

Thadhani, Naresh; Whelchel, R. L.; Sanders, Tom; Mehkote, D. S.; Iyer, K. A.; Georgia Instiutute of Technology Collaboration; Johns Hopkins University, Applied Physics Labortaory Collaboration

2015-06-01

The dynamic yielding and fracture (spalling) of commercially pure (grade 4) titanium are investigated using symmetric plate impact experiments over a peak stress range of 5.6 GPa to 12.5 GPa, using the 80-mm single-stage gas-gun. VISAR rear free surface velocity profiles display both a Hugoniot elastic limit (HEL) and a velocity pullback, which are indicative of dynamic compressive yielding and tensile fracture (spalling), respectively. The HEL values appear to show a slight decrease with peak stress from 2.2 GPa to 2.0 GPa along with a corresponding increase in twinning observed in recovered impacted samples. The spall strength on the other hand increases with peak stress from a value of 3.3 GPa to 3.8 GPa and shows a good power law fit with the decompression strain rate. The differing responses in dynamic yield and fracture behavior suggest that void nucleation may be the dominant mechanism affecting the spall strength of grade 4 titanium.

Study of the Effects of High Temperatures on the Engineering Properties of Steel 42CrMo4

NASA Astrophysics Data System (ADS)

Brnic, Josip; Turkalj, Goran; Canadija, Marko; Lanc, Domagoj; Brcic, Marino

2015-02-01

The paper presents and analyzes the experimental results of the effect of elevated temperatures on the engineering properties of steel 42CrMo4. Experimental data relating to the mechanical properties of the material, the creep resistance as well as Charpy impact energy. Temperature dependence of the mentioned properties is also shown. Some of creep curves were simulated using rheological models and an analytical equation. Finally, an assessment of fracture toughness was made that was based on experimentally determined Charpy impact energy. Based on the obtained results it is visible that the tensile strength (617 MPa) and yield strength (415 MPa) have the highest value at the room temperature while at the temperature of 700 °C (973 K) these values significantly decrease. This steel can be considered resistant to creep at 400 °C (673 K), but at higher temperatures this steel can be subjected to low levels of stress in a shorter time.

Effect of sintering process and additives on the properties of cordierite based ceramics

NASA Astrophysics Data System (ADS)

Rundans, M.; Sperberga, I.; Sedmale, G.; Stinkulis, G.

2013-12-01

It is possible to obtain cordierite ceramics with high temperature synthesis using both synthetic and raw natural materials. This paper discusses the possibilities to obtain cordierite ceramics, replacing part of required oxides with raw materials from various Latvian deposits of dolomite and clay. The obtained raw cordierite powders were ground in two modes (3 and 12 hours) and fired at 1200 °C. Ceramic samples were characterized by hydrostatic weighting method; crystalline phase composition was studied by XRD. Obtained samples were evaluated by their mechanical (compressive) strength and linear coefficient of thermal expansion (CTE). Thermal shock resistance was tested using water quenching method and afterwards evaluated by using ultrasonic method to test changes in Young's modulus of elasticity. Results show that increase in grinding time causes samples to densify and promote formation of cordierite crystalline phase which corresponds to increase in total compressive strength and decrease of CTE values. CTE values of samples ground for 12 hours conform to that of obtained in other researches.

Effect of fiber content on tensile retention properties of Cellulose Microfiber Reinforced Polymer Composites for Automobile Application

NASA Astrophysics Data System (ADS)

Aseer, J. R.; Sankaranarayanasamy, K.

2017-12-01

Today, the utilization of biodegradable materials has been hogging much attention throughout the world. Due to the disposal issues of petroleum based products, there is a focus towards developing biocomposites with superior mechanical properties and degradation rate. In this research work, Hibiscus Sabdariffa (HS) fibers were used as the reinforcement for making biocomposites. The HS fibers were reinforced in the polyester resin by compression moulding method. Water absorption studies of the composite at room temperature are carried out as per ASTM D 570. Also, degradation behavior of HS/Polyester was done by soil burial method. The HS/polyester biocomposites containing 7.5 wt% of HS fiber has shown higher value of tensile strength. The tensile strength retention of the HS/Polyester composites are higher than the neat polyester composites. This value increases with increase of HS fiber loading in the composites. The results indicated that HS/polyester biocomposites can be used for making automobile components such as bumper guards etc.

Tremor activity inhibited by well-drained conditions above a megathrust

PubMed Central

Nakajima, Junichi; Hasegawa, Akira

2016-01-01

Tremor occurs on megathrusts under conditions of near-lithostatic pore-fluid pressures and extremely weakened shear strengths. Although metamorphic reactions in the slab liberate large amounts of fluids, the mechanism for enhancing pore-fluid pressures along the megathrust to near-lithostatic values remains poorly understood. Here we show anti-correlation between low-frequency earthquake (LFE) activity and properties that are markers of the degree of metamorphism above the megathrust, whereby LFEs occur beneath the unmetamorphosed overlying plate but are rare or limited below portions that are metamorphosed. The extent of metamorphism in the overlying plate is likely controlled by along-strike contrasts in permeability. Undrained conditions are required for pore-fluid pressures to be enhanced to near-lithostatic values and for shear strength to reduce sufficiently for LFE generation, whereas well-drained conditions reduce pore-fluid pressures at the megathrust and LFEs no longer occur at the somewhat strengthened megathrust. Our observations suggest that undrained conditions are a key factor for the genesis of LFEs. PMID:27991588

Geological and geomechanical properties of the carbonate rocks at the eastern Black Sea Region (NE Turkey)

NASA Astrophysics Data System (ADS)

Ersoy, Hakan; Yalçinalp, Bülent; Arslan, Mehmet; Babacan, Ali Erden; Çetiner, Gözde

2016-11-01

Turkey located in the Alpine-Himalayan Mountain Belt has 35% of the natural stone reserves of the world and has good quality marble, limestone, travertine and onyx reserves especially in the western regions of the country. The eastern Black Sea Region with a 1.4 million meters cubes reserve has a little role on the natural stone production in the country. For this reason, this paper deals with investigation on the potential of carbonate stone in the region and determination of the geological and geo-mechanical properties of these rocks in order to provide economic contribution to the national economy. While the study sites are selected among the all carbonate rock sites, the importance as well as the representative of the sites were carefully considered for the region. After representative samples were analyzed for major oxide and trace element compositions to find out petrochemical variations, the experimental program conducted on rock samples for determination of both physical and strength properties of the carbonate rocks. The results of the tests showed that there are significant variations in the geo-mechanical properties of the studied rock groups. The density values vary from 2.48 to 2.70 gr/cm3, water absorption by weight values range from 0.07 to 1.15% and the apparent porosity of the carbonate rocks are between 0.19 and 3.29%. However, the values of the UCS shows variation from 36 to 80 MPa. Tensile and bending strength values range from 3.2 to 7.5 MPa and 6.0-9.2 MPa respectively. Although the onyx samples have the lowest values of apparent porosity and water absorption by weight, these samples do not have the highest values of UCS values owing to occurrence of the micro-cracks. The UCS values of the rock samples were also found after cycling tests However, the limestone samples have less than 5% deterioration after freezing-thawing and wetting-drying tests, but travertine and onyx samples have more than 15% deterioration. Exception of the apparent porosity values of travertine samples, all geo-mechanical properties of the studied carbonate rocks were determined in the acceptance values given by Turkish Standards Institute (TSE) for using as a natural dimension stone. After these investigations, it is anticipated that in the near future the number of quarries and factories will increase and more types of natural stones will be discovered in the eastern Black Sea Region and thus this will provide economic contribution to the economy of the country.

Relationships among the structural topology, bond strength, and mechanical properties of single-walled aluminosilicate nanotubes.

PubMed

Liou, Kai-Hsin; Tsou, Nien-Ti; Kang, Dun-Yen

2015-10-21

Carbon nanotubes (CNTs) are regarded as small but strong due to their nanoscale microstructure and high mechanical strength (Young's modulus exceeds 1000 GPa). A longstanding question has been whether there exist other nanotube materials with mechanical properties as good as those of CNTs. In this study, we investigated the mechanical properties of single-walled aluminosilicate nanotubes (AlSiNTs) using a multiscale computational method and then conducted a comparison with single-walled carbon nanotubes (SWCNTs). By comparing the potential energy estimated from molecular and macroscopic material mechanics, we were able to model the chemical bonds as beam elements for the nanoscale continuum modeling. This method allowed for simulated mechanical tests (tensile, bending, and torsion) with minimum computational resources for deducing their Young's modulus and shear modulus. The proposed approach also enabled the creation of hypothetical nanotubes to elucidate the relative contributions of bond strength and nanotube structural topology to overall nanotube mechanical strength. Our results indicated that it is the structural topology rather than bond strength that dominates the mechanical properties of the nanotubes. Finally, we investigated the relationship between the structural topology and the mechanical properties by analyzing the von Mises stress distribution in the nanotubes. The proposed methodology proved effective in rationalizing differences in the mechanical properties of AlSiNTs and SWCNTs. Furthermore, this approach could be applied to the exploration of new high-strength nanotube materials.

Predicting fracture of mortar beams under three-point bending using non-extensive statistical modeling of electric emissions

NASA Astrophysics Data System (ADS)

Stergiopoulos, Ch.; Stavrakas, I.; Triantis, D.; Vallianatos, F.; Stonham, J.

2015-02-01

Weak electric signals termed as 'Pressure Stimulated Currents, PSC' are generated and detected while cement based materials are found under mechanical load, related to the creation of cracks and the consequent evolution of cracks' network in the bulk of the specimen. During the experiment a set of cement mortar beams of rectangular cross-section were subjected to Three-Point Bending (3PB). For each one of the specimens an abrupt mechanical load step was applied, increased from the low load level (Lo) to a high final value (Lh) , where Lh was different for each specimen and it was maintained constant for long time. The temporal behavior of the recorded PSC show that during the load increase a spike-like PSC emission was recorded and consequently a relaxation of the PSC, after reaching its final value, follows. The relaxation process of the PSC was studied using non-extensive statistical physics (NESP) based on Tsallis entropy equation. The behavior of the Tsallis q parameter was studied in relaxation PSCs in order to investigate its potential use as an index for monitoring the crack evolution process with a potential use in non-destructive laboratory testing of cement-based specimens of unknown internal damage level. The dependence of the q-parameter on the Lh (when Lh <0.8Lf), where Lf represents the 3PB strength of the specimen, shows an increase on the q value when the specimens are subjected to gradually higher bending loadings and reaches a maximum value close to 1.4 when the applied Lh becomes higher than 0.8Lf. While the applied Lh becomes higher than 0.9Lf the value of the q-parameter gradually decreases. This analysis of the experimental data manifests that the value of the entropic index q obtains a characteristic decrease while reaching the ultimate strength of the specimen, and thus could be used as a forerunner of the expected failure.

Liquid crystal polyester-carbon fiber composites

NASA Technical Reports Server (NTRS)

Chung, T. S.

1984-01-01

Liquid crystal polymers (LCP) have been developed as a thermoplastic matrix for high performance composites. A successful melt impregnation method has been developed which results in the production of continuous carbon fiber (CF) reinforced LCP prepreg tape. Subsequent layup and molding of prepreg into laminates has yielded composites of good quality. Tensile and flexural properties of LCP/CF composites are comparable to those of epoxy/CF composites. The LCP/CF composites have better impact resistance than the latter, although epoxy/CF composites possess superior compression and shear strength. The LCP/CF composites have good property retention until 200 F (67 % of room temperature value). Above 200 F, mechanical properties decrease significantly. Experimental results indicate that the poor compression and shear strength may be due to the poor interfacial adhesion between the matrix and carbon fiber as adequate toughness of the LCP matrix. Low mechanical property retention at high temperatures may be attributable to the low beta-transition temperature (around 80 C) of the LCP matrix material.

Kenaf-glass fiber reinforced unsaturated polyester hybrid composites: Tensile properties

NASA Astrophysics Data System (ADS)

Zhafer, S. F.; Rozyanty, A. R.; Shahnaz, S. B. S.; Musa, L.; Zuliahani, A.

2016-07-01

The use of natural fibers in composite is rising in recent years due their lightweight, non-abrasive, combustible, non-toxic, low cost and biodegradable properties. However, in comparison with synthetic fibers, the mechanical properties of natural fibers are lower. Therefore, the inclusion of synthetic fibers could improve the mechanical performance of natural fiber based composites. In this study, kenaf bast fiber and glass fiber at different weight percentage loading were used as reinforcement to produce hybrid composites. Unsaturated polyester (UP) resin was used as matrix and hand lay-up process was performed to apply the UP resin on the hybrid kenaf bast/glass fiber composite. Effect of different fiber loading on tensile strength, tensile modulus and elongation at break of the hybrid composite was studied. It has been found that the highest value of tensile strength and modulus was achieved at 10 wt.% kenaf/10 wt.% glass fiber loading. It was concluded that addition of glass fiber has improved the tensile properties of kenaf bast fiber based UP composites.

Development of oxidised and heat-moisture treated potato starch film.

PubMed

Zavareze, Elessandra da Rosa; Pinto, Vânia Zanella; Klein, Bruna; El Halal, Shanise Lisie Mello; Elias, Moacir Cardoso; Prentice-Hernández, Carlos; Dias, Alvaro Renato Guerra

2012-05-01

This study investigated the effects of sodium hypochlorite oxidation and a heat-moisture treatment of potato starch on the physicochemical, pasting and textural properties of potato starches in addition to the water vapour permeability (WVP) and mechanical properties of potato starch films produced from these starches. The carbonyl contents, carboxyl contents, swelling power, solubility, pasting properties and gel texture of the native, oxidised and heat-moisture treated (HMT) starches were evaluated. The films made of native, oxidised and HMT starches were characterised by thickness, water solubility, colour, opacity, mechanical properties and WVP. The oxidised and HMT starches had lower viscosity and swelling power compared to the native starch. The films produced from oxidised potato starch had decreased solubility, elongation and WVP values in addition to increased tensile strength compared to the native starch films. The HMT starch increased the tensile strength and WVP of the starch films compared to the native starch. Copyright © 2011 Elsevier Ltd. All rights reserved.

Effect of resin infiltration on the thermal and mechanical properties of nano-sized silica-based thermal insulation.

PubMed

Lee, Jae Chun; Kim, Yun-Il; Lee, Dong-Hun; Kim, Won-Jun; Park, Sung; Lee, Dong Bok

2011-08-01

Several kinds of nano-sized silica-based thermal insulation were prepared by dry processing of mixtures consisting of fumed silica, ceramic fiber, and a SiC opacifier. Infiltration of phenolic resin solution into the insulation, followed by hot-pressing, was attempted to improve the mechanical strength of the insulation. More than 22% resin content was necessary to increase the strength of the insulation by a factor of two or more. The structural integrity of the resin-infiltrated samples could be maintained, even after resin burn-out, presumably due to reinforcement from ceramic fibers. For all temperature ranges and similar sample bulk density values, the thermal conductivities of the samples after resin burn-out were consistently higher than those of the samples obtained from the dry process. Mercury intrusion curves indicated that the median size of the nanopores formed by primary silica aggregates in the samples after resin burn-out is consistently larger than that of the sample without resin infiltration.

Oxidation effects on the mechanical properties of SiC fiber-reinforced reaction-bonded silicon nitride matrix composites

NASA Technical Reports Server (NTRS)

Bhatt, Ramakrishna T.

1989-01-01

The room temperature mechanical properties of SiC fiber reinforced reaction bonded silicon nitride composites were measured after 100 hrs exposure at temperatures to 1400 C in nitrogen and oxygen environments. The composites consisted of approx. 30 vol percent uniaxially aligned 142 micron diameter SiC fibers in a reaction bonded Si3N4 matrix. The results indicate that composites heat treated in a nitrogen environment at temperatures to 1400 C showed deformation and fracture behavior equivalent to that of the as-fabricated composites. Also, the composites heat treated in an oxidizing environment beyond 400 C yielded significantly lower tensile strength values. Specifically in the temperature range from 600 to 1000 C, composites retained approx. 40 percent of their as-fabricated strength, and those heat treated in the temperatures from 1200 to 1400 C retained 70 percent. Nonetheless, for all oxygen heat treatment conditions, composite specimens displayed strain capability beyond the matrix fracture stress; a typical behavior of a tough composite.

Modeling and analysis of film composition on mechanical properties of maize starch based edible films.

PubMed

Prakash Maran, J; Sivakumar, V; Thirugnanasambandham, K; Kandasamy, S

2013-11-01

The present study investigates the influence of composition (content of maize starch (1-3 g), sorbitol (0.5-1.0 ml), agar (0.5-1.0 g) and tween-80 (0.1-0.5 ml)) on the mechanical properties (tensile strength, elongation, Young's modulus, puncture force and puncture deformation) of the maize starch based edible films using four factors with three level Box-Behnken design. The edible films were obtained by casting method. The results showed that, tween-80 increases the permeation of sorbitol in to the polymer matrix. Increasing concentration of sorbitol (hydrophilic nature and plasticizing effect of sorbitol) decreases the tensile strength, Young's modulus and puncture force of the films. The results were analyzed by Pareto analysis of variance (ANOVA) and second order polynomial models were obtained for all responses with high R(2) values (R(2)>0.95). 3D response surface plots were constructed to study the relationship between process variables and the responses. Copyright © 2013 Elsevier B.V. All rights reserved.

Comparison on mechanical properties of single layered and bilayered chitosan-gelatin coated porous hydroxyapatite scaffold prepared through freeze drying method

NASA Astrophysics Data System (ADS)

Effendi, M. D.; Gustiono, D.; Lukmana; Ayu, D.; Kurniawati, F.

2017-02-01

Biopolymer coated porous hydroxyapatite (HA) scaffolds were prepared for tissue engineering trough freeze drying method and impregnation. in this study, to mimic the mineral and organic component of natural bone, synthetic hydroxapatite (HA) scaffolds coated by polymer were prepared. Highly porous Hap scaffolds, fabricated by synthetic HA impregnation method on polyurethane foam, were coated with polymer coating solution, consisting of chitosan, Gelatin, and bilayered chitosan-gelatin prepared by aging and impregnating technique. For the purpose of comparison, The bare scaffolds without polymer coating layer were investigated. The Bare scaffolds were highly porous and interconnected with a pore size of around 150 µm-714 µm, has porosity at around 67,7% -85,7%, and has mechanical strength at around 0.06 Mpa - 0.071 Mpa, which is suitable for osteoblast cell Proliferation. Chitosan coated porous HA scaffold and gelatin coated porous HA scaffold had mechanical strength at around 0.81-0.85 Mpa, and 1.32-1.34 Mpa, respectively, with weight ratio of biopolymer and Hap was around 18%-22%. To compare these results, the coating on the bare scaffold with gelatin and chitosan had been conducted. Based on the result of FTIR, it could be concluded that coating procedure applied on porous hydroxy apatite (HA) coated by gelatin, chitosan coated HA scaffold, and bilayered Gelatin-chitosan coated porous HA scaffold, confirming that for allsampleshad no significant chemical effect on the coating structure. The compressive strength of bilayered Gelatin-chitosan coated HA scaffold had middle values between the rest, at around 1,06-1.2 Mpa for the samples at the same weight ratio of biopolymer: HA (around 18% - 22%). These results also confirming that coating by gelatin on porous hydroxyapatite was highest compresive strength and can be applied to improve mechanical properties of porous hydroxyapatite bare scaffold

Incorporation of polydimethylsiloxane with reduced graphene oxide and zinc oxide for tensile and electrical properties

NASA Astrophysics Data System (ADS)

Danial, N. S.; Ramli, Muhammad. M.; Halin, D. S. C.; Hong, H. C.; Isa, S. Salwa M.; Abdullah, M. M. A. B.; Anhar, N. A. M.; Talip, L. F. A.; Mazlan, N. S.

2017-09-01

Polydimethylsiloxane (PDMS) is an organosilicon polymer that is commonly used to incorporate with other fillers. PDMS in high viscous liquid form is mechanically stirred with reduced graphene oxide (rGO) and mixed with zinc oxide (ZnO) with specific ratio, thus rendering into two types of samples. The mechanical and electrical properties of both samples are characterized. The result shows that PDMS sample with 50 mg rGO has the highest tensile strength with the value of 9.1 MPa. For electrical properties, sample with the lowest resistance is PDMS with 50 mg rGO and ZnO with the value of l.67×l05 Ω. This experiment shows the significant role of conductive fillers like rGO and ZnO incorporated in polymeric material such as PDMS to improve its electrical properties.

Polarographic determination of lead hydroxide formation constants at low ionic strength

USGS Publications Warehouse

Lind, Carol J.

1978-01-01

Values of formation constants for lead hydroxide at 25 ??C were calculated from normal pulse polarographic measurements of 10-6 M lead in 0.01 M sodium perchlorate. The low concentrations simulate those found in many freshwaters, permitting direct application of the values when considering distributions of lead species. The precise evaluation of species distribution in waters at other ionic strengths requires activity coefficient corrections. As opposed to much of the previously published work done at high ionic strength, the values reported here were obtained at low ionic strength, permitting use of smaller and better defined activity coefficient corrections. These values were further confirmed by differential-pulse polarography and differential-pulse anodic stripping voltammetry data. The logs of the values for ??1??? ??2???, and ??3??? were calculated to be 6.59, 10.80, and 13.63, respectively. When corrected to zero ionic strength these values were calculated to be 6.77, 11.07, and 13.89, respectively.

Remnant Woven Bone and Calcified Cartilage in Mouse Bone: Differences between Ages/Sex and Effects on Bone Strength

PubMed Central

Ip, Victoria; Toth, Zacharie; Chibnall, John; McBride-Gagyi, Sarah

2016-01-01

Introduction Mouse models are used frequently to study effects of bone diseases and genetic determinates of bone strength. Murine bones have an intracortical band of woven bone that is not present in human bones. This band is not obvious under brightfield imaging and not typically analyzed. Due to the band’s morphology and location it has been theorized to be remnant bone from early in life. Furthermore, lamellar and woven bone are well known to have differing mechanical strengths. The purpose of this study was to determine (i) if the band is from early life and (ii) if the woven bone or calcified cartilage contained within the band affect whole bone strength. Woven Bone Origin Studies In twelve to fourteen week old mice, doxycycline was used to label bone formed prior to 3 weeks old. Doxycycline labeling and woven bone patterns on contralateral femora matched well and encompassed an almost identical cross-sectional area. Also, we highlight for the first time in mice the presence of calcified cartilage exclusively within the band. However, calcified cartilage could not be identified on high resolution cone-beam microCT scans when examined visually or by thresholding methods. Mechanical Strength Studies Subsequently, three-point bending was used to analyze the effects of woven bone and calcified cartilage on whole bone mechanics in a cohort of male and female six and 13 week old Balb/C mice. Three-point bending outcomes were correlated with structural and compositional measures using multivariate linear regression. Woven bone composed a higher percent of young bones than older bones. However, calcified cartilage in older bones was twice that of younger bones, which was similar when normalized by area. Area and/or tissue mineral density accounted for >75% of variation for most strength outcomes. Percent calcified cartilage added significant predictive power to maximal force and bending stress. Calcified cartilage and woven bone could have more influence in genetic models where calcified cartilage percent is double our highest value. PMID:27829059

Effects of Fiber/Matrix Interface and its Composition on Mechanical Properties of Hi-Nicalon/Celsian Composites

NASA Technical Reports Server (NTRS)

Bansal, Narottam P.; Eldridge, Jeffrey I.

1999-01-01

To evaluate the effects of fiber coatings on composite mechanical properties. unidirectional celsian matrix composites reinforced with uncoated Hi-Nicalon fibers and those precoated with a dual BN/SiC layer in two separate batches (batch 1 and batch 2) were tested in three-point flexure. The uncoated-fiber reinforced composites showed catastrophic failure with strength of 210+/-35 MPa and a flat fracture surface. In contrast, composites reinforced with coated fibers exhibited graceful failure with extensive fiber pullout and showed significantly higher ultimate strengths, 904 and 759 MPa for the batch 1 and 2 coatings. respectively. Fiber push-in tests and microscopic examination indicated no chemical reaction at the uncoated or coated fiber-matrix interfaces that might be responsible for fiber strength degradation. Instead, the low strength of composite with uncoated fibers was due to degradation of the fiber strength from mechanical damage during composite processing. Despite identical processing, the first matrix cracking stresses (Sigma(sub mc)) of the composites reinforced with fibers coated in batch 1 and batch 2 were quite different, 436 and 122 MPa, respectively. The large difference in Sigma(sub mc) of the coated-fiber composites was attributed to differences in fiber sliding stresses (Tau(sub friction)), 121.2+/-48.7 and 10.4+/-3.1 MPa, respectively. for the two composites as determined by the fiber push-in method. Such a large difference in Tau(sub friction). for the two composites was found to be due to the difference in the compositions of the interface coatings. Scanning Auger microprobe analysis revealed the presence of carbon layers between the fiber and BN. and also between the BN and SiC coatings in the composite showing lower Tau(sub friction). This resulted in lower Sigma(sub mc) in agreement with the ACK theory. The ultimate strengths of the two composites depended mainly on the fiber volume fraction and were not significantly effected by Tau(sub friction) values, as expected. The poor reproducibility of the fiber coating composition between the two batches was judged to be the primary source of the large differences in performance of the two composites.

Cholesteric pitch transitions induced by mechanical strain.

PubMed

Lelidis, I; Barbero, G; Alexe-Ionescu, A L

2013-02-01

We investigate thickness and surface anchoring strength influence on pitch transitions in a planar cholesteric liquid crystal layer. The cholesteric-nematic transition is also investigated. We assume planar boundary conditions, with strong anchoring strength at one interface and weak anchoring strength at the other. The surface anchoring energy we consider to describe the deviation of the surface twist angle from the easy axis induced by a bulk deformation is a parabolic potential or Rapini and Papoular periodic potential, respectively. We show that under strain, all pitch transitions take place at a critical thickness that is equal to the quarter of the natural cholesteric pitch. The latter result does not depend on the anchoring strength, the particular surface potential, or material properties. The twist angle on the limiting surface characterized by weak anchoring varies with strain either by slipping and or in a discontinuous manner according to the thickness of the sample. The position of the bifurcation point depends only on the ratio of the extrapolation length over the layer thickness, but its value is model dependent. Multistability and multiplicity of the transition are discussed.

Mechanical properties of polymer-infiltrated-ceramic (sodium aluminum silicate) composites for dental restoration.

PubMed

Cui, Bencang; Li, Jing; Wang, Huining; Lin, Yuanhua; Shen, Yang; Li, Ming; Deng, Xuliang; Nan, Cewen

2017-07-01

To fabricate indirect restorative composites for CAD/CAM applications and evaluate the mechanical properties. Polymer-infiltrated-ceramic composites were prepared through infiltrating polymer into partially sintered sodium aluminum silicate ceramic blocks and curing. The corresponding samples were fabricated according to standard ISO-4049 using for mechanical properties measurement. The flexural strength and fracture toughness were measured using a mechanical property testing machine. The Vickers hardness and elastic modulus were calculated from the results of nano-indentation. The microstructures were investigated using secondary electron detector. The density of the porous ceramic blocks was obtained through TG-DTA. The conversion degrees were calculated from the results of mid-infrared spectroscopy. The obtained polymer infiltrated composites have a maximum flexural strength value of 214±6.5MPa, Vickers hardness of 1.76-2.30GPa, elastic modulus of 22.63-27.31GPa, fracture toughness of 1.76-2.35MPam 1/2 and brittleness index of 0.75-1.32μm -1/2 . These results were compared with those of commercial CAD/CAM blocks. Our results suggest that these materials with good mechanical properties are comparable to two commercial CAD/CAM blocks. The sintering temperature could dramatically influence the mechanical properties. Restorative composites with superior mechanical properties were produced. These materials mimic the properties of natural dentin and could be a promising candidate for CAD/CAM applications. Copyright © 2017 Elsevier Ltd. All rights reserved.

Joint weak value for all order coupling using continuous variable and qubit probe

NASA Astrophysics Data System (ADS)

Kumari, Asmita; Pan, Alok Kumar; Panigrahi, Prasanta K.

2017-11-01

The notion of weak measurement in quantum mechanics has gained a significant and wide interest in realizing apparently counterintuitive quantum effects. In recent times, several theoretical and experimental works have been reported for demonstrating the joint weak value of two observables where the coupling strength is restricted to the second order. In this paper, we extend such a formulation by providing a complete treatment of joint weak measurement scenario for all-order-coupling for the observable satisfying A 2 = 𝕀 and A 2 = A, which allows us to reveal several hitherto unexplored features. By considering the probe state to be discrete as well as continuous variable, we demonstrate how the joint weak value can be inferred for any given strength of the coupling. A particularly interesting result we pointed out that even if the initial pointer state is uncorrelated, the single pointer displacement can provide the information about the joint weak value, if at least third order of the coupling is taken into account. As an application of our scheme, we provide an all-order-coupling treatment of the well-known Hardy paradox by considering the continuous as well as discrete meter states and show how the negative joint weak probabilities emerge in the quantum paradoxes at the weak coupling limit.

TEM in situ micropillar compression tests of ion irradiated oxide dispersion strengthened alloy

NASA Astrophysics Data System (ADS)

Yano, K. H.; Swenson, M. J.; Wu, Y.; Wharry, J. P.

2017-01-01

The growing role of charged particle irradiation in the evaluation of nuclear reactor candidate materials requires the development of novel methods to assess mechanical properties in near-surface irradiation damage layers just a few micrometers thick. In situ transmission electron microscopic (TEM) mechanical testing is one such promising method. In this work, microcompression pillars are fabricated from a Fe2+ ion irradiated bulk specimen of a model Fe-9%Cr oxide dispersion strengthened (ODS) alloy. Yield strengths measured directly from TEM in situ compression tests are within expected values, and are consistent with predictions based on the irradiated microstructure. Measured elastic modulus values, once adjusted for the amount of deformation and deflection in the base material, are also within the expected range. A pillar size effect is only observed in samples with minimum dimension ≤100 nm due to the low inter-obstacle spacing in the as received and irradiated material. TEM in situ micropillar compression tests hold great promise for quantitatively determining mechanical properties of shallow ion-irradiated layers.

Zinc oxide eugenol paste jeopardises the adhesive bonding to primary dentine.

PubMed

Pires, C W; Lenzi, T L; Soares, F Z M; Rocha, R O

2018-05-12

This was to evaluate the influence of root canal filling pastes on microshear bond strength (µSBS) of an adhesive system to primary dentine. Human (32) primary molars were randomly assigned into four experimental groups (n = 8): zinc oxide eugenol paste (ZOE); iodoform paste (Guedes-Pinto paste); calcium hydroxide paste thickened with zinc oxide; and no filling paste (control). Flat dentine surfaces were covered with a 1 mm-thick layer of the pastes for 15 min at 37 °C. The pastes were mechanically removed from dentine surfaces, followed by rinsing and drying. After adhesive application (Adper Single Bond 2, 3M ESPE), starch tubes were placed over pre-treated dentine and filled with composite resin (Z250, 3M ESPE). The µSBS test was performed after 24 h of water storage at 37 °C. The failure mode was evaluated using a stereomicroscope. The µSBS values (MPa) were analysed with one-way ANOVA and Tukey post-hoc tests (α = 0.05). The lowest µSBS values were achieved when ZOE was used. No difference was found among other filling pastes compared with control group. All specimens showed adhesive/mixed failures. Zinc oxide eugenol paste negatively influenced the bond strength of adhesive systems to primary dentine. Iodoform-based Guedes-Pinto paste and calcium hydroxide paste thickened with zinc oxide did not influence the microshear bond strength values.

Poly(2-hydroxyethyl methacrylate) biomimetic coating to improve osseointegration of a PMMA/HA/glass composite implant: in vivo mechanical and histomorphometric assessments.

PubMed

Giavaresi, G; Branda, F; Causa, F; Luciani, G; Fini, M; Nicoli Aldini, N; Rimondini, L; Ambrosio, L; Giardino, R

2004-08-01

Bone implants must simultaneously satisfy many requirements, even though the surface properties remain a crucial aspect in osseointegration success. Since a single material with a uniform structure cannot satisfy all of these requirements, composite materials specifically designed for orthopedic or dental implant application should be envisaged. Two poly(methylmethacrylate)/hydroxyapatite composites reinforced by E-glass fibres, uncoated (PMMA/HA/Glass) and poly(2-hydroxyethyl methacrylate) (PMMA/HA/Glass+pHEMA) coated by the biomimetic method, were mechanically (push-out test) and histomorphometrically (Affinity Index, AI) investigated in an in vivo rabbit model. Cylindrical implants (diameter 2 mm x 5 mm length) were inserted into rabbit femoral cortical (mid-diaphysis) and cancellous (distal epiphysis) bone, under general anesthesia. The highest values of push-out force and ultimate shear strength were observed for the PMMA/HA/Glass at 12 weeks, which significantly (p < 0.001) differed from those of PMMA/HA/Glass+pHEMA at the same experimental time and from those of PMMA/HA/Glass at 4 weeks. At both experimental times, significantly (p < 0.0005) lower values of AI were observed in the PMMA/HA/Glass+pHEMA versus PMMA/HA/Glass (distal femoral epiphysis: 4 weeks = 33%; 12 weeks = 19%; femoral diaphysis: 4 weeks = 15%; 12 weeks = 11%). The good mechanical and histomorphometric results obtained with PMMA/HA/Glass should be followed by further evaluation of bone remodeling processes and mechanical strength around loaded PMMA/HA/Glass implants at longer experimental times. Finally, the biomimetic method applied to pHEMA needs to be further investigated in order to improve the positive effect of SBF on pHEMA and to enhance the coating adhesion.

Mechanically-competent and cytocompatible polycaprolactone-borophosphosilicate hybrid biomaterials.

PubMed

Mondal, Dibakar; Dixon, S Jeffrey; Mequanint, Kibret; Rizkalla, Amin S

2017-11-01

Organic-inorganic class II hybrid materials have domain sizes at the molecular level and chemical bonding between the organic and inorganic phases. We have previously reported the synthesis of class II hybrid biomaterials from alkoxysilane-functionalized polycaprolactone (PCL) and borophosphosilicate (B 2 O 3 -P 2 O 5 -SiO 2 ) glass (BPSG) through a non-aqueous sol-gel process. In the present study, the mechanical properties and degradability of these PCL/BPSG hybrid biomaterials were studied and compared to those of their conventional composite counterparts. The compressive strength, modulus and toughness of the hybrid biomaterials were significantly greater compared to the conventional composites, likely due to the covalent bonding between the organic and inorganic phases. A hybrid biomaterial (50wt% PCL and 50wt% BPSG) exhibited compressive strength, modulus and toughness values of 32.2 ± 3.5MPa, 573 ± 85MPa and 1.54 ± 0.03MPa, respectively; whereas the values for composite of similar composition were 18.8 ± 1.6MPa, 275 ± 28MPa and 0.76 ± 0.03MPa, respectively. Degradation in phosphate-buffered saline was slower for hybrid biomaterials compared to their composite counterparts. Thus, these hybrid materials possess superior mechanical properties and more controlled degradation characteristics compared to their corresponding conventional composites. To assess in vitro cytocompatibility, MC3T3-E1 pre-osteoblastic cells were seeded onto the surfaces of hybrid biomaterials and polycaprolactone (control). Compared to polycaprolactone, cells on the hybrid material displayed enhanced spreading, focal adhesion formation, and cell number, consistent with excellent cytocompatibility. Thus, based on their mechanical properties, degradability and cytocompatibility, these novel biomaterials have potential for use as scaffolds in bone tissue engineering and related applications. Copyright © 2017. Published by Elsevier Ltd.

Study of the microstructure and mechanical properties of white clam shell.

PubMed

Liang, Yunhong; Zhao, Qian; Li, Xiujuan; Zhang, Zhihui; Ren, Luquan

2016-08-01

The microstructure and mechanical properties of white clam shell were investigated, respectively. It can be divided into horny layer, prismatic layer and nacreous layer. Crossed-lamellar structure was the microstructural characteristic. The extension direction of lamellae in prismatic layer was different from that in nacreous layer, which formed an angle on the interface between prismatic layer and nacreous layer. The phase component of three layers was CaCO3 with crystallization morphology of aragonite, which confirmed the crossed-lamellar structural characteristic. White calm shell exhibited perfect mechanical properties. The microhardness values of three layers were 273HV, 240HV and 300HV, respectively. The average values of flexure and compression strength were 110.2MPa and 80.1MPa, respectively. The macroscopical cracks crossed the lamellae and finally terminated within the length range of about 80μm. It was the microstructure characteristics, the angle on the interface between prismatic and nacreous layer and the hardness diversity among the different layers that enhanced mechanical properties of white calm shell. Copyright © 2016 Elsevier Ltd. All rights reserved.

Glass fiber effect on mechanical properties of Eco-SCC

NASA Astrophysics Data System (ADS)

Prasad M. L., V.; Loksesh, G.; Ramanjaneyulu, B.; Venkatesh, S.; Mousumi, K.

2017-07-01

Sustainable Construction encouraging the use of recycled materials and implies adoption of fewer natural resources in buildings and other infrastructure. In this paper Quarry Dust (QD) is used as partial replacement for River Sand (RS) to make Self Compacting Concrete (SCC) of grade M40. Glass fiber is used as strengthening material to the developed concrete. The present study mainly focused to develop Eco-SCC using QD. In this study it was found that, for developing Eco-SCC, what is the optimum dosage of replacement of QD in RS. Fresh properties of SCC are satisfying the EFNARC specifications and also target strength is achieved. Further it is concluded that, with the glass fiber addition there is an improvement in the split and flexural strength values.

Quantitative evaluation of the mechanical strength of titanium/composite bonding using laser-generated shock waves

NASA Astrophysics Data System (ADS)

Ducousso, M.; Bardy, S.; Rouchausse, Y.; Bergara, T.; Jenson, F.; Berthe, L.; Videau, L.; Cuvillier, N.

2018-03-01

Intense acoustic shock waves were applied to evaluate the mechanical strength of structural epoxy bonds between a TA6V4 titanium alloy and a 3D woven carbon/epoxy composite material. Two bond types with different mechanical strengths were obtained from two different adhesive reticulations, at 50% and 90% of conversion, resulting in longitudinal static strengths of 10 and 39 MPa and transverse strengths of 15 and 35 MPa, respectively. The GPa shock waves were generated using ns-scale intense laser pulses and reaction principles to a confined plasma expansion. Simulations taking into account the laser-matter interaction, plasma relaxation, and non-linear shock wave propagation were conducted to aid interpretation of the experiments. Good correlations were obtained between the experiments and the simulation and between different measurement methods of the mechanical strength (normalized tests vs laser-generated shock waves). Such results open the door toward certification of structural bonding.

The synthesis and characterization of hydrogel chitosan-alginate with the addition of plasticizer lauric acid for wound dressing application

NASA Astrophysics Data System (ADS)

Izak Rudyardjo, Djony; Wijayanto, Setiawan

2017-05-01

The writers conducted a study about the synthesis and characterization of hydrogel chitosan-alginate by addition plasticizer lauric acid for wound dressing application. The purpose was to find out the impact of lauric acid concentration variation on hydrogel chitosan-alginate to get the best mechanical and physical properties to be applied as wound dressing in accordance with existing standards. This study used commercially chitosan from extract of shells crab, commercially-available alginate from the extract of sargassum sp, and commercial lauric acid from palm starch. The addition of lauric acid was aimed to repair mechanical properties of hydrogel. The composition of chitosan-alginate is 4:1 (v/v), while the lauric acid concentration variations are 0%, 1%, 2%, 3%, 4%, and 5% w/v. The characterization of mechanical properties test (Tensile strength and Elongation at break) at hydrogel showed the hydrogel chitosan-alginate-lauric acid have the characteristic which meets the standard of mechanical properties for human skin. The best performance of hydrogel chitosan-alginate-lauric acid was obtained by increasing luric acid concentration by 4%, which has a thickness value of 125.46±0.63 µm, elongation 28.89±1.01 %, tensile strength (9.01±0.65) MPa, and ability to absorb liquids (601.45 ±1.24) %.

Anabolic and catabolic biomarkers as predictors of muscle strength decline: the InCHIANTI study.

PubMed

Stenholm, Sari; Maggio, Marcello; Lauretani, Fulvio; Bandinelli, Stefania; Ceda, Gian Paolo; Di Iorio, Angelo; Giallauria, Francesco; Guralnik, Jack M; Ferrucci, Luigi

2010-02-01

Poor muscle strength is a major public health concern in older persons, predisposing to functional limitations, increased fall risk, and higher mortality. Understanding risk factors for muscle strength decline may offer opportunities for prevention and treatment. One of the possible causes of muscle strength decline is imbalance between catabolic and anabolic signaling. This study aims to examine whether high levels of multiple catabolic and low levels of multiple anabolic biomarkers predict accelerated decline of muscle strength. In a representative sample of 716 men and women aged >or=65 years in the InCHIANTI study we measured C-reactive protein, interleukin-6 (IL-6), IL-1 receptor antagonist (IL-1RA), tumor necrosis factor-alpha receptor 1 as well as dehydroepiandrosterone sulfate (DHEA-S), insulin-like growth factor-1, and bioavailable testosterone. Biomarker values were divided into tertiles and the numbers of catabolic/anabolic biomarkers in the highest/lowest tertile were calculated. Hand-grip strength was measured at baseline and 3- and 6-year follow up. In adjusted linear mixed models, higher concentration of IL-6 (p = 0.02) and IL-1RA (p = 0.04) as well as lower levels of DHEA-S (p = 0.01) predicted muscle strength decline. After combining all inflammatory markers, the rate of decline in grip strength was progressively greater with the increasing number of dysregulated catabolic biomarkers (p = 0.01). No effect on accelerated muscle strength decline was seen according to number of dysregulated anabolic hormones. Having multiple elevated catabolic biomarkers is a better predictor of muscle strength decline than a single biomarker alone, suggesting that a catabolic dysregulation is at the core of the mechanism leading to muscle strength decline with aging.

Anabolic and Catabolic Biomarkers As Predictors of Muscle Strength Decline: The InCHIANTI Study

PubMed Central

Maggio, Marcello; Lauretani, Fulvio; Bandinelli, Stefania; Ceda, Gian Paolo; Di Iorio, Angelo; Giallauria, Francesco; Guralnik, Jack M.; Ferrucci, Luigi

2010-01-01

Abstract Background Poor muscle strength is a major public health concern in older persons, predisposing to functional limitations, increased fall risk, and higher mortality. Understanding risk factors for muscle strength decline may offer opportunities for prevention and treatment. One of the possible causes of muscle strength decline is imbalance between catabolic and anabolic signaling. This study aims to examine whether high levels of multiple catabolic and low levels of multiple anabolic biomarkers predict accelerated decline of muscle strength. Methods In a representative sample of 716 men and women aged ≥65 years in the InCHIANTI study we measured C-reactive protein, interleukin-6 (IL-6), IL-1 receptor antagonist (IL-1RA), tumor necrosis factor-α receptor 1 as well as dehydroepiandrosterone sulfate (DHEA-S), insulin-like growth factor-1, and bioavailable testosterone. Biomarker values were divided into tertiles and the numbers of catabolic/anabolic biomarkers in the highest/lowest tertile were calculated. Hand-grip strength was measured at baseline and 3- and 6-year follow up. Results In adjusted linear mixed models, higher concentration of IL-6 (p = 0.02) and IL-1RA (p = 0.04) as well as lower levels of DHEA-S (p = 0.01) predicted muscle strength decline. After combining all inflammatory markers, the rate of decline in grip strength was progressively greater with the increasing number of dysregulated catabolic biomarkers (p = 0.01). No effect on accelerated muscle strength decline was seen according to number of dysregulated anabolic hormones. Conclusions Having multiple elevated catabolic biomarkers is a better predictor of muscle strength decline than a single biomarker alone, suggesting that a catabolic dysregulation is at the core of the mechanism leading to muscle strength decline with aging. PMID:20230273

Microstructure and mechanical properties of composite resins subjected to accelerated artificial aging.

PubMed

dos Reis, Andréa Cândido; de Castro, Denise Tornavoi; Schiavon, Marco Antônio; da Silva, Leandro Jardel; Agnelli, José Augusto Marcondes

2013-01-01

The aim of this study was to investigate the influence of accelerated artificial aging (AAA) on the microstructure and mechanical properties of the Filtek Z250, Filtek Supreme, 4 Seasons, Herculite, P60, Tetric Ceram, Charisma and Filtek Z100. composite resins. The composites were characterized by Fourier-transform Infrared spectroscopy (FTIR) and thermal analyses (Differential Scanning Calorimetry - DSC and Thermogravimetry - TG). The microstructure of the materials was examined by scanning electron microscopy. Surface hardness and compressive strength data of the resins were recorded and the mean values were analyzed statistically by ANOVA and Tukey's test (α=0.05). The results showed significant differences among the commercial brands for surface hardness (F=86.74, p<0.0001) and compressive strength (F=40.31, p<0.0001), but AAA did not affect the properties (surface hardness: F=0.39, p=0.53; compressive strength: F=2.82, p=0.09) of any of the composite resins. FTIR, DSC and TG analyses showed that resin polymerization was complete, and there were no differences between the spectra and thermal curve profiles of the materials obtained before and after AAA. TG confirmed the absence of volatile compounds and evidenced good thermal stability up to 200 °C, and similar amounts of residues were found in all resins evaluated before and after AAA. The AAA treatment did not significantly affect resin surface. Therefore, regardless of the resin brand, AAA did not influence the microstructure or the mechanical properties.

Experimental validation of 3D printed material behaviors and their influence on the structural topology design

NASA Astrophysics Data System (ADS)

Yang, Kai Ke; Zhu, Ji Hong; Wang, Chuang; Jia, Dong Sheng; Song, Long Long; Zhang, Wei Hong

2018-05-01

The purpose of this paper is to investigate the structures achieved by topology optimization and their fabrications by 3D printing considering the particular features of material microstructures and macro mechanical performances. Combining Digital Image Correlation and Optical Microscope, this paper experimentally explored the anisotropies of stiffness and strength existing in the 3D printed polymer material using Stereolithography (SLA) and titanium material using Selective Laser Melting (SLM). The standard specimens and typical structures obtained by topology optimization were fabricated along different building directions. On the one hand, the experimental results of these SLA produced structures showed stable properties and obviously anisotropic rules in stiffness, ultimate strengths and places of fractures. Further structural designs were performed using topology optimization when the particular mechanical behaviors of SLA printed materials were considered, which resulted in better structural performances compared to the optimized designs using `ideal' isotropic material model. On the other hand, this paper tested the mechanical behaviors of SLM printed multiscale lattice structures which were fabricated using the same metal powder and the same machine. The structural stiffness values are generally similar while the strength behaviors show a difference, which are mainly due to the irregular surface quality of the tiny structural branches of the lattice. The above evidences clearly show that the consideration of the particular behaviors of 3D printed materials is therefore indispensable for structural design and optimization in order to improve the structural performance and strengthen their practical significance.

A molecular dynamics study of the role of molecular water on the structure and mechanics of amorphous geopolymer binders.

PubMed

Sadat, Mohammad Rafat; Bringuier, Stefan; Asaduzzaman, Abu; Muralidharan, Krishna; Zhang, Lianyang

2016-10-07

In this paper, molecular dynamics simulations are used to study the effect of molecular water and composition (Si/Al ratio) on the structure and mechanical properties of fully polymerized amorphous sodium aluminosilicate geopolymer binders. The X-ray pair distribution function for the simulated geopolymer binder phase showed good agreement with the experimentally determined structure in terms of bond lengths of the various atomic pairs. The elastic constants and ultimate tensile strength of the geopolymer binders were calculated as a function of water content and Si/Al ratio; while increasing the Si/Al ratio from one to three led to an increase in the respective values of the elastic stiffness and tensile strength, for a given Si/Al ratio, increasing the water content decreased the stiffness and strength of the binder phase. An atomic-scale analysis showed a direct correlation between water content and diffusion of alkali ions, resulting in the weakening of the AlO 4 tetrahedral structure due to the migration of charge balancing alkali ions away from the tetrahedra, ultimately leading to failure. In the presence of water molecules, the diffusion behavior of alkali cations was found to be particularly anomalous, showing dynamic heterogeneity. This paper, for the first time, proves the efficacy of atomistic simulations for understanding the effect of water in geopolymer binders and can thus serve as a useful design tool for optimizing composition of geopolymers with improved mechanical properties.