Tensile and compressive stress-strain behavior of heat treated boron-aluminum

NASA Technical Reports Server (NTRS)

Kennedy, J. M.; Tenney, D. R.; Herakovich, C. T.

1978-01-01

An experimental study was conducted to assess the effects of heat treatment and cyclic mechanical loading on the tensile and compressive stress-strain behavior of six boron-aluminum composites having different laminate orientations and being subjected to different heat treatments. The heat treatments were as-fabricated, T6, and T6N consisting of T6 treatment followed by cryogenic quench in liquid nitrogen prior to testing. All laminates were tested in monotonic and cyclic compression, while the tensile-test data are taken from the literature for comparison purposes. It is shown that the linear elastic range of the T6- and T6N-condition specimens is larger than that of the as-fabricated specimens, and that cyclic loading in tension or compression strain hardens the specimens and extends the linear elastic range. For laminates containing 0-deg plies, the stress-strain behavior upon unloading is found to be nonlinear, whereas the other laminates exhibit a linear behavior upon unloading. Specimens in the T6 and T6N conditions show higher strain hardening than the as-fabricated specimens.

Compressive Testing of Stitched Frame and Stringer Alternate Configurations

NASA Technical Reports Server (NTRS)

Leone, Frank A., Jr.; Jegley, Dawn C.

2016-01-01

A series of single-frame and single-stringer compression tests were conducted at NASA Langley Research Center on specimens harvested from a large panel built using the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. Different frame and stringer designs were used in fabrication of the PRSEUS panel. In this report, the details of the experimental testing of single-frame and single-stringer compression specimens are presented, as well as discussions on the performance of the various structural configurations included in the panel.

Effect of silica fume on compressive strength of oil-polluted concrete in different marine environments

NASA Astrophysics Data System (ADS)

Shahrabadi, Hamid; Sayareh, Sina; Sarkardeh, Hamed

2017-12-01

In the present research, effect of silica fume as an additive and oil polluted sands as aggregates on compressive strength of concrete were investigated experimentally. The amount of oil in the designed mixtures was assumed to be constant and equal to 2% of the sand weight. Silica fume accounting for 10%, 15% and 20% of the weight is added to the designed mixture. After preparation and curing, concrete specimens were placed into the three different conditions: fresh, brackish and saltwater environments (submerged in fresh water, alternation of exposed in air & submerged in sea water and submerged in sea water). The result of compressive strength tests shows that the compressive strength of the specimens consisting of silica fume increases significantly in comparison with the control specimens in all three environments. The compressive strength of the concrete with 15% silica fume content was about 30% to 50% higher than that of control specimens in all tested environments under the condition of using polluted aggregates in the designed mixture.

The Effect of Compressive Loading on the Fatigue Lifetime of Graphite/ Epoxy Laminates

DTIC Science & Technology

1979-10-01

Un-notched 11 3 Specimen Configuration, Notched 12 4 Location of Thickness and Width Measurements 14 5 Overall View of Composite Compression Test...Grips in Universal Testing Machine 24 8 Specimen Positioning Device 26 9 "Full-Fixity" Apparatus, Showing Auxiliary Platens 26 10 Specimen and Restraint...the accumu- lation of a statistically significant data base. * IA previous research study [11 showed that graphite/epoxy composites under constant

Previous concrete as one of the technology to overcome the puddle

NASA Astrophysics Data System (ADS)

Agung Putra Handana, M.; Karolina, Rahmi; Syahputra, Eko; Zulfikar

2018-03-01

Some construction waste has been utilized as a material in certain concrete compositions for engineering building materials. One is a concrete that has been removed after testing at a laboratory called recycle concrete. Disposed concrete, crushed and filtered with filter number 50; 37.5; 19; 9.5; and 4.75 mm are subsequently converted into rough aggregate materials in the manufacture of pervious concrete to be tested for compressive strength and infiltration velocity to water. Pervious concrete test specimens in the form of cylinders with dimensions (15 x 30) cm and plate-shaped with dimension (100 x 100 x 10) cm with the quality plan Fc ' = 15 MPa at age 28 days. The research methodology consisted of testing of wear, test object preparation, periodic maintenance, visual inspection, compressive strength testing, and infiltration rate of specimens against water (based on ASTM C1701). Treatment of specimens by spraying periodically before the test time. From the results of the Los Angeles wear test, it appears that recycled aggregate has an average wear rate of 20.88% (based on SNI 03-2417-1991) on the Los Angeles test) and the visual test on the specimen is appropriate (based on SNI 03 -0691-1996 on paving block) as the basis for testing the specimens. The largest compressive strength was found in pervious concrete with 9.5 mm graded aggregates of 5.89 MPa, while the smallest compressive strength of 50 mm gradation was 2.15 MPa and had a compressive strength of 28% of pervious concrete compressive strength on generally (based on SNI 03-6805-2002). The fastest infiltration speed occurs in 50 mm pervious gradient concrete at 4.52 inc / hr and is late in 9.5 mm grading of 2.068 inc / hr or an inflation rate inflation rate of 54.25% for gradation of 9.5 mm to 50 mm gradation, So that in accordance with the purpose of pervious concrete use, concrete that can drain water to the bottom layer

Compressive Behavior of Fiber-Reinforced Concrete with End-Hooked Steel Fibers.

PubMed

Lee, Seong-Cheol; Oh, Joung-Hwan; Cho, Jae-Yeol

2015-03-27

In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize the effect of specimen size on fiber distribution, 48 cylinder specimens 150 mm in diameter and 300 mm in height were prepared and then subjected to uniaxial compression. From the test results, it was shown that steel fiber-reinforced concrete (SFRC) specimens exhibited ductile behavior after reaching their compressive strength. It was also shown that the strain at the compressive strength generally increased along with an increase in the fiber volumetric ratio and fiber aspect ratio, while the elastic modulus decreased. With consideration for the effect of steel fibers, a model for the stress-strain relationship of SFRC under compression is proposed here. Simple formulae to predict the strain at the compressive strength and the elastic modulus of SFRC were developed as well. The proposed model and formulae will be useful for realistic predictions of the structural behavior of SFRC members or structures.

Tensile and compressive constitutive response of 316 stainless steel at elevated temperatures

NASA Technical Reports Server (NTRS)

Manson, S. S.; Muralidharan, U.; Halford, G. R.

1982-01-01

It is demonstrated that creep rate of 316 SS is lower by factors of 2 to 10 in compression than in tension if the microstructure is the same and tests are conducted at identical temperatures and equal but opposite stresses. Such behavior was observed for both monotonic creep and conditions involving cyclic creep. In the latter case creep rate in both tension and compression progressively increases from cycle to cycle, rendering questionable the possibility of expressing a time-stabilized constitutive relationship. The difference in creep rates in tension and compression is considerably reduced if the tension specimen is first subjected to cycles of tensile creep (reversed by compressive plasticity), while the compression specimen is first subjected to cycles of compressive creep (reversed by tensile plasticity). In both cases, the test temperature is the same and the stresses are equal and opposite. Such reduction is a reflection of differences in microstructure of the specimens resulting from different prior mechanical history.

Design and fabrication of composite wing panels containing a production splice

NASA Technical Reports Server (NTRS)

Reed, D. L.

1975-01-01

Bolted specimens representative of both upper and lower wing surface splices of a transport aircraft were designed and manufactured for static and random load tension and compression fatigue testing including ground-air-ground load reversals. The specimens were fabricated with graphite-epoxy composite material. Multiple tests were conducted at various load levels and the results were used as input to a statistical wearout model. The statically designed specimens performed very well under highly magnified fatigue loadings. Two large panels, one tension and compression, were fabricated for testing by NASA-LRC.

Biomechanics of the Proximal Radius Following Drilling of the Bicipital Tuberosity to Mimic Cortical Button Distal Biceps Repair Technique.

PubMed

Oak, Nikhil R; Lien, John R; Brunfeldt, Alexander; Lawton, Jeffrey N

2018-05-01

A fracture through the proximal radius is a theoretical concern after cortical button distal biceps fixation in an active patient. The permanent, nonossified cortical defect and medullary tunnel is at risk during a fall eliciting rotational and compressive forces. We hypothesized that during simulated torsion and compression, in comparison with unaltered specimens, the cortical button distal biceps repair model would have decreased torsional and compressive strength and would fracture in the vicinity of the bicipital tuberosity bone tunnel. Sixteen fourth-generation composite radius Sawbones models were used in this controlled laboratory study. A bone tunnel was created through the bicipital tuberosity to mimic the exact bone tunnel, 8 mm near cortex and 3.2 mm far cortex, made for the BicepsButton distal biceps tendon repair. The radius was then prepared and mounted on either a torsional or compression testing device and compared with undrilled control specimens. Compression tests resulted in average failure loads of 9015.2 N in controls versus 8253.25 N in drilled specimens ( P = .074). Torsional testing resulted in an average failure torque of 27.3 Nm in controls and 19.3 Nm in drilled specimens ( P = .024). Average fracture angle was 35.1° in controls versus 21.1° in drilled. Gross fracture patterns were similar in compression testing; however, in torsional testing all fractures occurred through the bone tunnel in the drilled group. There are weaknesses in the vicinity of the bone tunnel in the proximal radius during biomechanical stress testing which may not be clinically relevant in nature. In cortical button fixation, distal biceps repairs creates a permanent, nonossified cortical defect with tendon interposed in the bone tunnel, which can alter the biomechanical properties of the proximal radius during compressive and torsional loading.

Rolling contact fatigue strengths of shot-peened and crack-healed ceramics

NASA Astrophysics Data System (ADS)

Takahashi, K.; Oki, T.

2018-06-01

The effects of shot-peening (SP) and crack-healing on the rolling contact fatigue (RCF) strengths of Al2O3/SiC composite ceramics were investigated. Non-shot-peened, shot- peened, and shot-peened + crack-healed specimens were prepared. SP was performed using ZrO2 beads. The shot-peened + crack-healed specimen was crack-healed after SP. X-ray diffraction clearly showed that SP induced a compressive residual stress up to 300 MPa at the specimen surfaces. Furthermore, the shot-peened + crack-healed specimen retained a compressive residual stress of 200 MPa. The apparent surface fracture toughness of the shot- peened specimens increased owing to the positive effects of the compressive residual stress. RCF tests were performed using a thrust load-bearing test device. The RCF lives of the shot- peened specimens did not improve compared to that of the non-shot-peened specimen, because the numerous SP-introduced surface cracks could act as crack initiation sites during the RCF tests. However, the RCF life of the shot-peened + crack-healed specimen did improve compared to those of non-shot-peened and shot-peened specimens, implying that combining SP and crack-healing was an effective strategy for improving the RCF lives of Al2O3/SiC composite ceramics.

Effective Size Analysis of the Diametral Compression (Brazil) Test Specimen

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

Jadaan, Osama M.; Wereszczak, Andrew A

2009-04-01

This study considers the finite element analysis (FEA) simulation and Weibull effective size analysis for the diametral compression (DC) or Brazil specimen loaded with three different push-rod geometries. Those geometries are a flat push-rod, a push-rod whose radius of curvature is larger than that for the DC specimen, and a push-rod whose radius of curvature matches that of the DC specimen. Such established effective size analysis recognizes that the tensile strength of structural ceramics is typically one to two orders of magnitude less than its compressive strength. Therefore, because fracture is much more apt to result from a tensile stressmore » than a compressive one, this traditional analysis only considers the first principal tensile stress field in the mechanically loaded ceramic component for the effective size analysis. The effective areas and effective volumes were computed as function of Weibull modulus using the CARES/Life code. Particular attention was devoted to the effect of mesh sensitivity and localized stress concentration. The effect of specimen width on the stress state was also investigated. The effects of push-rod geometry, the use of steel versus WC push-rods, and considering a frictionless versus no-slip interface between push-rod and specimen on the maximum stresses, where those stresses are located, and the effective area and effective volume results are described. Of the three push-rod geometries, it is concluded that the push-rod (made from WC rather than steel) whose radius of curvature matches that of the DC specimen is the most apt to cause fracture initiation within the specimen's bulk rather than at the loading interface. Therefore, its geometry is the most likely to produce a valid diametral compression strength test. However, the DC specimen remains inefficient in terms of its area and volume efficiencies; namely, the tensile strength of only a few percent of the specimen's entire area or volume is sampled. Given the high probability that a valid (or invalid) test can be proven by ceramic fractographic practices suggests that this test method and specimen is questionable for use with relatively strong structural ceramics.« less

Compression of thick laminated composite beams with initial impact-like damage

NASA Technical Reports Server (NTRS)

Breivik, N. L.; Guerdal, Z.; Griffin, O. H., Jr.

1992-01-01

While the study of compression after impact of laminated composites has been under consideration for many years, the complexity of the damage initiated by low velocity impact has not lent itself to simple predictive models for compression strength. The damage modes due to non-penetrating, low velocity impact by large diameter objects can be simulated using quasi-static three-point bending. The resulting damage modes are less coupled and more easily characterized than actual impact damage modes. This study includes the compression testing of specimens with well documented initial damage states obtained from three-point bend testing. Compression strengths and failure modes were obtained for quasi-isotropic stacking sequences from 0.24 to 1.1 inches thick with both grouped and interspersed ply stacking. Initial damage prior to compression testing was divided into four classifications based on the type, extent, and location of the damage. These classifications are multiple through-thickness delaminations, isolated delamination, damage near the surface, and matrix cracks. Specimens from each classification were compared to specimens tested without initial damage in order to determine the effects of the initial damage on the final compression strength and failure modes. A finite element analysis was used to aid in the understanding and explanation of the experimental results.

Compressive Behavior of Fiber-Reinforced Concrete with End-Hooked Steel Fibers

PubMed Central

Lee, Seong-Cheol; Oh, Joung-Hwan; Cho, Jae-Yeol

2015-01-01

In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize the effect of specimen size on fiber distribution, 48 cylinder specimens 150 mm in diameter and 300 mm in height were prepared and then subjected to uniaxial compression. From the test results, it was shown that steel fiber-reinforced concrete (SFRC) specimens exhibited ductile behavior after reaching their compressive strength. It was also shown that the strain at the compressive strength generally increased along with an increase in the fiber volumetric ratio and fiber aspect ratio, while the elastic modulus decreased. With consideration for the effect of steel fibers, a model for the stress–strain relationship of SFRC under compression is proposed here. Simple formulae to predict the strain at the compressive strength and the elastic modulus of SFRC were developed as well. The proposed model and formulae will be useful for realistic predictions of the structural behavior of SFRC members or structures. PMID:28788011

The effect on the flexural strength, flexural modulus and compressive strength of fibre reinforced acrylic with that of plain unfilled acrylic resin - an in vitro study.

PubMed

Thomas, Tony C; K, Aswini Kumar; Mohamed, Shamaz; Krishnan, Vinod; Mathew, Anil; V, Manju

2015-03-01

The aim of this in vitro study was to compare the flexural strength, the flexural modulus and compressive strength of the acrylic polymer reinforced with glass, carbon, polyethylene and Kevlar fibres with that of plain unfilled resin. A total of 50 specimens were prepared and divided into 10 specimens each under 5 groups namely group 1- control group without any fibres, group 2 - carbon fibres, group 3- glass fibres, group 4 - polyethylene, group 5- Kevlar. Universal testing machine (Tinius olsen, USA) was used for the testing of these specimens. Out of each group, 5 specimens were randomly selected and testing was done for flexural strength using a three point deflection test and three point bending test for compressive strength and the modulus was plotted using a graphical method. Statistical analysis was done using statistical software. The respective mean values for samples in regard to their flexural strength for PMMA plain, PMMA+ glass fibre, PMMA+ carbon, PMMA+ polyethylene and PMMA+ Kevlar were 90.64, 100.79, 102.58, 94.13 and 96.43 respectively. Scheffes post hoc test clearly indicated that only mean flexural strength values of PMMA + Carbon, has the highest mean value. One-way ANOVA revealed a non-significant difference among the groups in regard to their compressive strength. The study concludes that carbon fibre reinforced samples has the greatest flexural strength and greatest flexural modulus, however the compressive strength remains unchanged.

An Experimental Study of Shear-Dominated Failure in the 2013 Sandia Fracture Challenge Specimen

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

Corona, Edmundo; Deibler, Lisa Anne; Reedlunn, Benjamin

2015-04-01

This report presents an experimental study motivated by results obtained during the 2013 Sandia Fracture Challenge. The challenge involved A286 steel, shear-dominated compression specimens whose load-deflection response contained a load maximum fol- lowed by significant displacement under decreasing load, ending with a catastrophic fracture. Blind numerical simulations deviated from the experiments well before the maximum load and did not predict the failure displacement. A series of new tests were conducted on specimens machined from the original A286 steel stock to learn more about the deformation and failure processes in the specimen and potentially improve future numerical simulations. The study consistedmore » of several uniaxial tension tests to explore anisotropy in the material, and a set of new tests on the compression speci- men. In some compression specimen tests, stereo digital image correlation (DIC) was used to measure the surface strain fields local to the region of interest. In others, the compression specimen was loaded to a given displacement prior to failure, unloaded, sectioned, and imaged under the microscope to determine when material damage first appeared and how it spread. The experiments brought the following observations to light. The tensile tests revealed that the plastic response of the material is anisotropic. DIC during the shear- dominated compression tests showed that all three in-plane surface strain components had maxima in the order of 50% at the maximum load. Sectioning of the specimens revealed no signs of material damage at the point where simulations deviated from the experiments. Cracks and other damage did start to form approximately when the max- imum load was reached, and they grew as the load decreased, eventually culminating in catastrophic failure of the specimens. In addition to the steel specimens, a similar study was carried out for aluminum 7075-T651 specimens. These specimens achieved much lower loads and displacements, and failure occurred very close to the maximum in the load-deflection response. No material damage was observed in these specimens, even when failure was imminent. In the future, we plan to use these experimental results to improve numerical simu- lations of the A286 steel experiments, and to improve plasticity and failure models for the Al 7075 stock. The ultimate goal of our efforts is to increase our confidence in the results of numerical simulations of elastic-plastic structural behavior and failure.« less

Analysis of the Mechanical Behavior and Surface Rugosity of Different Dental Die Materials.

PubMed

Niekawa, Ciro T; Kreve, Simone; A'vila, Gisseli Bertozzi; Godoy, Gilmar Gil; Eduardo Vieira da Silva, J R; Dias, Sergio Candido

2017-01-01

This work evaluated the mechanical and surface behavior of different die materials. The studied materials are polyurethane resin Exakto-Form (Bredent), Gypsum type IV, Fuji Rock EP (Gc), and Durone (Dentsply). Two metallic matrices molded in polyvinyl siloxane provided 30 cylindrical test specimens for the diametral compression test and 30 hemispherical test specimens for the surface rugosity test. The cylindrical test specimens were submitted to tests of diametral compression strength using a DL2000 universal assay machine, with a load cell of 2000 Kgf and constant speed of 1 mm/min connected to the software. Kruskal-Wallis and Dunn's nonparametric tests were used to analyze the results. The hemispheres were submitted to the surface rugosity assay using a SJ201-P rugosimeter with a sensitivity of 300 μm, speed of 0.5 mm/s, and cut-off of 0.8 mm, and the readings were taken on the convex surface of the test specimens and metallic matrix. Results were analyzed using with Fisher's least significant differences test (LSD) and Dunnett's test. Kruskal-Wallis test showed significant difference between die materials for diametral compression strength ( P = 0.002). Dunn's test showed significantly higher values for modified polyurethane resin (Exakto-Form). The gypsum type IV, which did not significantly differ regarding diametral compression strength, showed 34.0% (Durone) and 42.7% (Fuji Rock) lower values in comparison to Exakto-Form. Within the parameters adopted in this study, it is possible to conclude that Exakto-Form polyurethane resin showed higher resistance to compression and was closer to the metallic matrix rugosity, and, along with the gypsum type IV Durone, showed better reproducibility of details relative to the Fuji Rock.

Experimental study on mix proportion of fiber reinforced cementitious composites

NASA Astrophysics Data System (ADS)

Jia, Yi; Zhao, Renda; Liao, Ping; Li, Fuhai; Yuan, Yuan; Zhou, Shuang

2017-10-01

To study the mechanical property of fiber reinforced cementations composites influenced by the fiber length, quartz sand diameter, matrix of water cement ratio, volume fraction of fiber and magnesium acrylate solution. Several 40×40×160 mm standard test specimens, "8" specimens and long "8" specimens and 21 groups of fiber concrete specimens were fabricated. The flexural, compressive and uniaxial tensile strength were tested by using the bending resistance, compression resistance and electronic universal testing machine. The results show that flexural and compressive strength of fiber reinforced cementations composites increases along with the increase of quartz sand diameter, with the growth of the PVA fiber length increases; When the water-binder ratio is 0.25 and powder-binder ratio is 0.3, the PVA fiber content is 1.5% of the mass of cementations materials, there is a phenomenon of strain hardening; The addition of magnesium acrylate solution reduces the tensile strength of PVA fiber reinforced cementations composites, the tensile strength of the specimens in the curing age of 7d is decreased by about 21% and the specimens in curing age of 28d is decreased by more than 50%.

Behavior of reinforcement SCC beams under elevated temperatures

NASA Astrophysics Data System (ADS)

Fathi, Hamoon; Farhang, Kianoosh

2015-09-01

This experimental study focuses on the behavior of heated reinforced concrete beams. Four types of concrete mixtures were used for the tested self-compacting concrete beams. A total of 72 reinforced concrete beams and 72 standard cylindrical specimens were tested. The compressive strength under uniaxial loading at 23 °C ranged from 30 to 45 MPa. The specimens were exposed to different temperatures. The test parameters of interest were the compressive strength and the temperature of the specimens. The effect of changes in the parameters was examined so as to control the behavior of the tested concrete and that of the reinforced concrete beam. The results indicated that flexibility and compressive strength of the reinforced concrete beams decreased at higher temperatures. Furthermore, heating beyond 400 °C produced greater variations in the structural behavior of the materials in both the cylindrical samples and the reinforced concrete beams.

Redistribution of Welding Residual Stresses of Crack Tip Opening Displacement Specimen by Local Compression.

PubMed

Kim, Young-Gon; Song, Kuk-Hyun; Lee, Dong-Hoon; Joo, Sung-Min

2018-03-01

The demand of crack tip opening displacement (CTOD) test which evaluates fracture toughness of a cracked material is very important to ensure the stability of structure under severe service environment. The validity of the CTOD test result is judged using several criterions of the specification standards. One of them is the artificially generated fatigue pre-crack length inside the specimen. For acceptable CTOD test results, fatigue pre-crack must have a reasonable sharp crack front. The propagation of fatigue crack started from the tip of the machined notch, which might have propagated irregularly due to residual stress field. To overcome this problem, test codes suggest local compression method, reversed bending method and stepwise high-R ratio method to reduce the disparity of residual stress distribution inside the specimen. In this paper, the relation between the degree of local compression and distribution of welding residual stress has been analyzed by finite element analyses in order to determine the amount of effective local compression of the test piece. Analysis results show that initial welding residual stress is dramatically varied three-dimensionally while cutting, notch machining and local compressing due to the change of internal restraint force. From the simulation result, the authors find that there is an optimum amount of local compression to modify regularly for generating fatigue pre-crack propagation. In the case of 0.5% compressions of the model width is the most effective for uniforming residual stress distribution.

Developing the elastic modulus measurement of asphalt concrete using the compressive strength test

NASA Astrophysics Data System (ADS)

Setiawan, Arief; Suparma, Latif Budi; Mulyono, Agus Taufik

2017-11-01

Elastic modulus is a fundamental property of an asphalt mixture. An analytical method of the elastic modulus is needed to determine the thickness of flexible pavement. It has a role as one of the input values on a stress-strain analysis in the finite element method. The aim of this study was to develop the measurement of the elastic modulus by using compressive strength testing. This research used a set of specimen mold tool and Delta Dimensi software to record strain changes occurring in the proving ring of compression machine and the specimens. The elastic modulus of the five types of aggregate gradation and 2 types of asphalt were measured at optimum asphalt content. Asphalt Cement 60/70 and Elastomer Modified Asphalt (EMA) were used as a binder. Manufacturing success indicators of the specimens used void-in-the-mix (VIM) 3-5 % criteria. The success rate of the specimen manufacturing was more than 76%. Thus, the procedure and the compressive strength test equipment could be used for the measurement of the elastic modulus. The aggregate gradation and asphalt types significantly affected the elastic modulus of the asphalt concrete.

Long-term Isothermal Aging Effects on Weight Loss, Compression Properties, and Dimensions of T650-35 Fabric-reinforced PMR-15 Composites-data

NASA Technical Reports Server (NTRS)

Bowles, Kenneth J.; Tsuji, Luis; Kamvouris, John; Roberts, Gary D.

2003-01-01

A cooperative program was conducted with the General Electric Aircraft Engines plant in Evendale, Ohio, to study the effects of long-term isothermal aging at elevated temperatures on compression and thermal durability properties of T650 35 fabric-reinforced PMR 15 composites. This degradation study was conducted over an approximate time period of 3 1/2 yr. The aging temperatures were 204, 260, 288, 316, and 343 C. Specimens of different dimensions were evaluated. Specimens with ratios of the cut edge to total surface area of 0.03 to 0.89 were fabricated and aged. The aged and unaged specimens were tested in compression as specified in Test Method for Compressive Properties of Rigid Plastics (ASTM D695M). Thickness changes, degraded surface layer growth, weight loss, and failure modes were monitored and recorded. All property changes were thickness dependent.

The Effect on the Flexural Strength, Flexural Modulus and Compressive Strength of Fibre Reinforced Acrylic with That of Plain Unfilled Acrylic Resin – An in Vitro Study

PubMed Central

Thomas, Tony C; K, Aswini Kumar; Krishnan, Vinod; Mathew, Anil; V, Manju

2015-01-01

Aim: The aim of this in vitro study was to compare the flexural strength, the flexural modulus and compressive strength of the acrylic polymer reinforced with glass, carbon, polyethylene and Kevlar fibres with that of plain unfilled resin. Materials and Methods: A total of 50 specimens were prepared and divided into 10 specimens each under 5 groups namely group 1- control group without any fibres, group 2 – carbon fibres, group 3- glass fibres, group 4 – polyethylene, group 5- Kevlar. Universal testing machine (Tinius olsen, USA) was used for the testing of these specimens. Out of each group, 5 specimens were randomly selected and testing was done for flexural strength using a three point deflection test and three point bending test for compressive strength and the modulus was plotted using a graphical method. Statistical analysis was done using statistical software. Results: The respective mean values for samples in regard to their flexural strength for PMMA plain, PMMA+ glass fibre, PMMA+ carbon, PMMA+ polyethylene and PMMA+ Kevlar were 90.64, 100.79, 102.58, 94.13 and 96.43 respectively. Scheffes post hoc test clearly indicated that only mean flexural strength values of PMMA + Carbon, has the highest mean value. One-way ANOVA revealed a non-significant difference among the groups in regard to their compressive strength. Conclusion: The study concludes that carbon fibre reinforced samples has the greatest flexural strength and greatest flexural modulus, however the compressive strength remains unchanged. PMID:25954696

The Evaluation of Damage Effects on MgO Added Concrete with Slag Cement Exposed to Calcium Chloride Deicing Salt.

PubMed

Jang, Jae-Kyeong; Kim, Hong-Gi; Kim, Jun-Hyeong; Ryou, Jae-Suk

2018-05-14

Concrete systems exposed to deicers are damaged in physical and chemical ways. In mitigating the damage from CaCl₂ deicers, the usage of ground slag cement and MgO are investigated. Ordinary Portland cement (OPC) and slag cement are used in different proportions as the binding material, and MgO in doses of 0%, 5%, 7%, and 10% are added to the systems. After 28 days of water-curing, the specimens are immersed in 30% CaCl₂ solution by mass for 180 days. Compressive strength test, carbonation test, chloride penetration test, chloride content test, XRD analysis, and SEM-EDAX analysis are conducted to evaluate the damage effects of the deicing solution. Up to 28 days, plain specimens with increasing MgO show a decrease in compressive strength, an increase in carbonation resistance, and a decrease in chloride penetration resistance, whereas the S30- and S50- specimens show a slight increase in compressive strength, an increase in carbonation resistance, and a slight increase in chloride penetration resistance. After 180 days of immersion in deicing solution, specimens with MgO retain their compressive strength longer and show improved durability. Furthermore, the addition of MgO to concrete systems with slag cement induces the formation of magnesium silicate hydrate (M-S-H) phases.

Reactive Material Structures

DTIC Science & Technology

2014-03-31

dissimilar materials ( steel end fixtures and RMS). 2.6.4 Compression Tests To prevent the ends of the specimens from mushrooming during compression ...RMS cylinder. The compression test was modeled in ANSYS by applying a fixed displacement in the axial direction. The first ply to exceed the...four phases of loading: 1) a compressive acceleration during gun launch, 2) a tensile unloading on exit from the barrel , 3) a compressive decelera

Measurements of the stress supported by the crush zone in open hole composite laminates loaded in compression

NASA Technical Reports Server (NTRS)

Guynn, E. Gail; Bradley, Walter L.

1989-01-01

Measurements of the stress supported by the crush zone in open hole specimens loaded in compression were carried out on two composite laminates, AS4/PEEK and IM6/HST-7, containing circular holes of three different diameters. Compression tests were conducted in a specially designed high-axial-alignment material test system machine. Results indicated that the local stress supported in the crush zone is much less than the stress required to initiate the crush, providing the reason for the finding of Guynn et al. (1987) that the Dugdale model does not accurately predict the load-damage size relationship of open hole composite specimens loaded in compression.

The Pack Method for Compressive Tests of Thin Specimens of Materials Used in Thin-Wall Structures

NASA Technical Reports Server (NTRS)

Aitchison, C S; Tuckerman, L B

1939-01-01

The strength of modern lightweight thin-wall structures is generally limited by the strength of the compression members. An adequate design of these members requires a knowledge of the compressive stress-strain graph of the thin-wall material. The "pack" method was developed at the National Bureau of Standards with the support of the National Advisory Committee for Aeronautics to make possible a determination of compressive stress-strain graphs for such material. In the pack test an odd number of specimens are assembled into a relatively stable pack, like a "pack of cards." Additional lateral stability is obtained from lateral supports between the external sheet faces of the pack and outside reactions. The tests seems adequate for many problems in structural research.

Assessment of the Damage Tolerance of Postbuckled Hat-Stiffened Panels Using Single-Stringer Specimens

NASA Technical Reports Server (NTRS)

Bisagni, Chiara; Vescovini, Riccardo; Davila, Carlos G.

2010-01-01

A procedure is proposed for the assessment of the damage tolerance and collapse of stiffened composite panels using a single-stringer compression specimen. The dimensions of the specimen are determined such that the specimen s nonlinear response and collapse are representative of an equivalent multi-stringer panel in compression. Experimental tests are conducted on specimens with and without an embedded delamination. A shell-based finite element model with intralaminar and interlaminar damage capabilities is developed to predict the postbuckling response as well as the damage evolution from initiation to collapse.

Compressive Loading and Modeling of Stitched Composite Stiffeners

NASA Technical Reports Server (NTRS)

Leone, Frank A., Jr.; Jegley, Dawn C.; Linton, Kim A.

2016-01-01

A series of single-frame and single-stringer compression tests were conducted at NASA Langley Research Center on specimens harvested from a large panel built using the Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS) concept. Different frame and stringer designs were used in fabrication of the PRSEUS panel. In this paper, the details of the experimental testing of single-frame and single-stringer compression specimens are presented, as well as discussions on the performance of the various structural configurations included in the panel. Nonlinear finite element models were developed to further understand the failure processes observed during the experimental campaign.

High-strain rate tensile characterization of graphite platelet reinforced vinyl ester based nanocomposites using split-Hopkinson pressure bar

NASA Astrophysics Data System (ADS)

Pramanik, Brahmananda

The dynamic response of exfoliated graphite nanoplatelet (xGnP) reinforced and carboxyl terminated butadiene nitrile (CTBN) toughened vinyl ester based nanocomposites are characterized under both dynamic tensile and compressive loading. Dynamic direct tensile tests are performed applying the reverse impact Split Hopkinson Pressure Bar (SHPB) technique. The specimen geometry for tensile test is parametrically optimized by Finite Element Analysis (FEA) using ANSYS Mechanical APDLRTM. Uniform stress distribution within the specimen gage length has been verified using high-speed digital photography. The on-specimen strain gage installation is substituted by a non-contact Laser Occlusion Expansion Gage (LOEG) technique for infinitesimal dynamic tensile strain measurements. Due to very low transmitted pulse signal, an alternative approach based on incident pulse is applied for obtaining the stress-time history. Indirect tensile tests are also performed combining the conventional SHPB technique with Brazilian disk test method for evaluating cylindrical disk specimens. The cylindrical disk specimen is held snugly in between two concave end fixtures attached to the incident and transmission bars. Indirect tensile stress is estimated from the SHPB pulses, and diametrical transverse tensile strain is measured using LOEG. Failure diagnosis using high-speed digital photography validates the viability of utilizing this indirect test method for characterizing the tensile properties of the candidate vinyl ester based nanocomposite system. Also, quasi-static indirect tensile response agrees with previous investigations conducted using the traditional dog-bone specimen in quasi-static direct tensile tests. Investigation of both quasi-static and dynamic indirect tensile test responses show the strain rate effect on the tensile strength and energy absorbing capacity of the candidate materials. Finally, the conventional compressive SHPB tests are performed. It is observed that both strength and energy absorbing capacity of these candidate material systems are distinctively less under dynamic tension than under compressive loading. Nano-reinforcement appears to marginally improve these properties for pure vinyl ester under dynamic tension, although it is found to be detrimental under dynamic compression.

Electromechanical Apparatus Measures Residual Stress

NASA Technical Reports Server (NTRS)

Chern, Engmin J.; Flom, Yury

1993-01-01

Nondestructive test exploits relationship between stress and eddy-current-probe resistance. Yields data on residual stress or strain in metal tension/compression specimen (stress or strain remaining in specimen when no stress applied from without). Apparatus is assembly of commercial equipment: tension-or-compression testing machine, eddy-current probe, impedance gain-and-phase analyzer measuring impedance of probe coil, and desktop computer, which controls other equipment and processes data received from impedance gain-and-phase analyzer.

Evaluation of Ceramic Honeycomb Core Compression Behavior at Room Temperature

NASA Technical Reports Server (NTRS)

Bird, Richard K.; Lapointe, Thomas S.

2013-01-01

Room temperature flatwise compression tests were conducted on two varieties of ceramic honeycomb core specimens that have potential for high-temperature structural applications. One set of specimens was fabricated using strips of a commercially-available thin-gage "ceramic paper" sheet molded into a hexagonal core configuration. The other set was fabricated by machining honeycomb core directly from a commercially available rigid insulation tile material. This paper summarizes the results from these tests.

Compression failure mechanisms of single-ply, unidirectional, carbon-fiber composites

NASA Technical Reports Server (NTRS)

Ha, Jong-Bae; Nairn, John A.

1992-01-01

A single-ply composite compression test was used to study compression failure mechanisms as a function of fiber type, matrix type, and interfacial strength. Composites made with low- and intermediate-modulus fibers (Hercules AS4 and IM7) in either an epoxy (Hercules 3501-6) or a thermoplastic (ULTEM and LARC-TPI) matrix failed by kink banding and out-of-plane slip. The failures proceeded by rapid and catastrophic damage propagation across the specimen width. Composites made with high-modulus fibers (Hercules HMS4/3501-6) had a much lower compression strength. Their failures were characterized by kink banding and longitudinal splitting. The damage propagated slowly across the specimen width. Composites made with fibers treated to give low interfacial strength had low compression strength. These composites typically failed near the specimen ends and had long kink bands.

Testing compression strength of wood logs by drilling resistance

NASA Astrophysics Data System (ADS)

Kalny, Gerda; Rados, Kristijan; Rauch, Hans Peter

2017-04-01

Soil bioengineering is a construction technique using biological components for hydraulic and civil engineering solutions, based on the application of living plants and other auxiliary materials including among others log wood. Considering the reliability of the construction it is important to know about the durability and the degradation process of the wooden logs to estimate and retain the integral performance of a soil bioengineering system. An important performance indicator is the compression strength, but this parameter is not easy to examine by non-destructive methods. The Rinntech Resistograph is an instrument to measure the drilling resistance by a 3 mm wide needle in a wooden log. It is a quasi-non-destructive method as the remaining hole has no weakening effects to the wood. This is an easy procedure but result in values, hard to interpret. To assign drilling resistance values to specific compression strengths, wooden specimens were tested in an experiment and analysed with the Resistograph. Afterwards compression tests were done at the same specimens. This should allow an easier interpretation of drilling resistance curves in future. For detailed analyses specimens were investigated by means of branch inclusions, cracks and distances between annual rings. Wood specimens are tested perpendicular to the grain. First results show a correlation between drilling resistance and compression strength by using the mean drilling resistance, average width of the annual rings and the mean range of the minima and maxima values as factors for the drilling resistance. The extended limit of proportionality, the offset yield strength and the maximum strength were taken as parameters for compression strength. Further investigations at a second point in time strengthen these results.

A Damage Tolerance Comparison of Composite Hat-Stiffened and Honeycomb Sandwich Structure for Launch Vehicle Interstage Applications

NASA Technical Reports Server (NTRS)

Nettles, A. T.

2011-01-01

In this study, a direct comparison of the compression-after-impact (CAI) strength of impact-damaged, hat-stiffened and honeycomb sandwich structure for launch vehicle use was made. The specimens used consisted of small substructure designed to carry a line load of approx..3,000 lb/in. Damage was inflicted upon the specimens via drop weight impact. Infrared thermography was used to examine the extent of planar damage in the specimens. The specimens were prepared for compression testing to obtain residual compression strength versus damage severity curves. Results show that when weight of the structure is factored in, both types of structure had about the same CAI strength for a given damage level. The main difference was that the hat-stiffened specimens exhibited a multiphase failure whereas the honeycomb sandwich structure failed catastrophically.

Evaluation of superplastic forming and co-diffusion bonding of Ti-6Al-4V titanium alloy expanded sandwich structures

NASA Technical Reports Server (NTRS)

Arvin, G. H.; Israeli, L.; Stolpestad, J. H.; Stacher, G. W.

1981-01-01

The application of the superplastic forming/diffusion bonding (SPF/DB) process to supersonic cruise research is investigated. The capability of an SPF/DB titanium structure to meet the structural requirements of the inner wing area of the NASA arrow-wing advanced supersonic transport design is evaluated. Selection of structural concepts and their optimization for minimum weight, SPF/DB process optimization, fabrication of representative specimens, and specimen testing and evaluation are described. The structural area used includes both upper and lower wing panels, where the upper wing panel is used for static compression strength evaluation and the lower panel, in tension, is used for fracture mechanics evaluations. The individual test specimens, cut from six large panels, consist of 39 static specimens, 10 fracture mechanics specimens, and one each full size panel for compression stability and fracture mechanics testing. Tests are performed at temperatures of -54 C (-65 F), room temperature, and 260 C (500 F).

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.

The Evaluation of Damage Effects on MgO Added Concrete with Slag Cement Exposed to Calcium Chloride Deicing Salt

PubMed Central

Jang, Jae-Kyeong; Kim, Hong-Gi; Kim, Jun-Hyeong

2018-01-01

Concrete systems exposed to deicers are damaged in physical and chemical ways. In mitigating the damage from CaCl2 deicers, the usage of ground slag cement and MgO are investigated. Ordinary Portland cement (OPC) and slag cement are used in different proportions as the binding material, and MgO in doses of 0%, 5%, 7%, and 10% are added to the systems. After 28 days of water-curing, the specimens are immersed in 30% CaCl2 solution by mass for 180 days. Compressive strength test, carbonation test, chloride penetration test, chloride content test, XRD analysis, and SEM-EDAX analysis are conducted to evaluate the damage effects of the deicing solution. Up to 28 days, plain specimens with increasing MgO show a decrease in compressive strength, an increase in carbonation resistance, and a decrease in chloride penetration resistance, whereas the S30- and S50- specimens show a slight increase in compressive strength, an increase in carbonation resistance, and a slight increase in chloride penetration resistance. After 180 days of immersion in deicing solution, specimens with MgO retain their compressive strength longer and show improved durability. Furthermore, the addition of MgO to concrete systems with slag cement induces the formation of magnesium silicate hydrate (M-S-H) phases. PMID:29758008

Numerical simulation of a relaxation test designed to fit a quasi-linear viscoelastic model for temporomandibular joint discs.

PubMed

Commisso, Maria S; Martínez-Reina, Javier; Mayo, Juana; Domínguez, Jaime

2013-02-01

The main objectives of this work are: (a) to introduce an algorithm for adjusting the quasi-linear viscoelastic model to fit a material using a stress relaxation test and (b) to validate a protocol for performing such tests in temporomandibular joint discs. This algorithm is intended for fitting the Prony series coefficients and the hyperelastic constants of the quasi-linear viscoelastic model by considering that the relaxation test is performed with an initial ramp loading at a certain rate. This algorithm was validated before being applied to achieve the second objective. Generally, the complete three-dimensional formulation of the quasi-linear viscoelastic model is very complex. Therefore, it is necessary to design an experimental test to ensure a simple stress state, such as uniaxial compression to facilitate obtaining the viscoelastic properties. This work provides some recommendations about the experimental setup, which are important to follow, as an inadequate setup could produce a stress state far from uniaxial, thus, distorting the material constants determined from the experiment. The test considered is a stress relaxation test using unconfined compression performed in cylindrical specimens extracted from temporomandibular joint discs. To validate the experimental protocol, the test was numerically simulated using finite-element modelling. The disc was arbitrarily assigned a set of quasi-linear viscoelastic constants (c1) in the finite-element model. Another set of constants (c2) was obtained by fitting the results of the simulated test with the proposed algorithm. The deviation of constants c2 from constants c1 measures how far the stresses are from the uniaxial state. The effects of the following features of the experimental setup on this deviation have been analysed: (a) the friction coefficient between the compression plates and the specimen (which should be as low as possible); (b) the portion of the specimen glued to the compression plates (smaller areas glued are better); and (c) the variation in the thickness of the specimen. The specimen's faces should be parallel to ensure a uniaxial stress state. However, this is not possible in real specimens, and a criterion must be defined to accept the specimen in terms of the specimen's thickness variation and the deviation of the fitted constants arising from such a variation.

Compressive strength of marine material mixed concrete

NASA Astrophysics Data System (ADS)

Adnan; Parung, H.; Tjaronge, M. W.; Djamaluddin, R.

2017-11-01

Many cement factories have been incorporated fly ash with clinker cement to produce blended cement. PCC is a type of blended cement incorporated fly ash that produced in Indonesia cement factories. To promote the sustainable development in the remote islands this present paper attempted to study the suitability of sea water, marine sand that available abundantly surround the remote island with Portland Composite Cement (PCC) and crushed river stone to produce concrete. Slump test was conducted to evaluate the workability of fresh concrete and also compressive strength with stress-strain relationship was carried out to evaluate the hardened concrete that cured with two curing condition (e.g. sea water curing, and tap water-wet burlap curing). Test result indicated that fresh concrete had proper workability and all hardened specimens appeared a good compaction result. Compressive strength of specimens cured which sea water was higher than the specimens which cured by tap water-wet burlap where stress-strain behavior of specimens made with sea water, marine sand, and PCC had similar behavior with specimens which made with PCC and tap water.

A low cost method of testing compression-after-impact strength of composite laminates

NASA Technical Reports Server (NTRS)

Nettles, Alan T.

1991-01-01

A method was devised to test the compression strength of composite laminate specimens that are much thinner and wider than other tests require. The specimen can be up to 7.62 cm (3 in) wide and as thin as 1.02 mm (.04 in). The best features of the Illinois Institute of Technology Research Institute (IITRI) fixture are combined with an antibuckling jig developed and used at the University of Dayton Research Institute to obtain a method of compression testing thin, wide test coupons on any 20 kip (or larger) loading frame. Up to 83 pct. less composite material is needed for the test coupons compared to the most commonly used compression-after-impact (CAI) tests, which calls for 48 ply thick (approx. 6.12 mm) test coupons. Another advantage of the new method is that composite coupons of the exact lay-up and thickness of production parts can be tested for CAI strength, thus yielding more meaningful results. This new method was used to compression test 8 and 16 ply laminates of T300/934 carbon/epoxy. These results were compared to those obtained using ASTM standard D 3410-87 (Celanese compression test). CAI testing was performed on IM6/3501-6, IM7/SP500 and IM7/F3900. The new test method and associated fixture work well and is a valuable asset to MSFC's damage tolerance program.

The fracture characteristic of three collinear cracks under true triaxial compression.

PubMed

Liu, Jianjun; Zhu, Zheming; Wang, Bo

2014-01-01

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses.

The Fracture Characteristic of Three Collinear Cracks under True Triaxial Compression

PubMed Central

Liu, Jianjun; Zhu, Zheming; Wang, Bo

2014-01-01

The mechanical behavior of multicracks under compression has become a very important project in the field of fracture mechanics and rock mechanics. In this paper, experimental and numerical studies on the fracture property of three collinear cracks under compression were implemented. The specimens were a square concrete plate, and the cracks were made by a very thin film. The tests were conducted by using true triaxial loading device. In the numerical study, the Abaqus code was employed. The effect of crack orientation and the confining stress on cracked specimen compressive strength were investigated. The results show that the critical stresses of cracked specimens change with crack inclination angles, and, as the angle is 45°, the critical stress is the lowest; the critical stresses increase with the confining stresses. PMID:24790569

Effect of Impact Compression on the Age-Hardening of Rapidly Solidified Al-Zn-Mg Base Alloys

NASA Astrophysics Data System (ADS)

Horikawa, Keitaro; Kobayashi, Hidetoshi

Effect of impact compression on the age-hardening behavior and the mechanical properties of Mesoalite aluminum alloy was examined by means of the high-velocity plane collision between a projectile and Mesoalite by using a single powder gun. By imposing the impact compression to the Meso10 and Meso20 alloys in the state of quenching after the solution heat treatment, the following age-hardening at 110 °C was highly increased, comparing with the Mesoalite without the impact compression. XRD results revealed that high plastic strain was introduced on the specimen inside after the impact compression. Compression test results also clarified that both Meso10 and Meso20 alloy specimens imposed the impact compressive stresses more than 5 GPa after the peak-aging at 110°C showed higher yield stresses, comparing with the alloys without the impact compression. It was also shown that the Meso10 and Meso20 specimens after the solution heat treatment, followed by the high-velocity impact compression (12 GPa) and the peak-aging treatment indicated the highest compressive yield stresses such as 994 GPa in Meso10 and 1091 GPa in Meso20.

Effect of Impact Damage and Open Hole on Compressive Strength of Hybrid Composite Laminates

NASA Technical Reports Server (NTRS)

Hiel, Clement; Brinson, H. F.

1993-01-01

Impact damage tolerance is a frequently listed design requirement for composites hardware. The effect of impact damage and open hole size on laminate compressive strength was studied on sandwich beam specimens which combine CFRP-GFRP hybrid skins and a syntactic foam core. Three test specimen configurations have been investigated for this study. The first two were sandwich beams which were loaded in pure bending (by four point flexure). One series had a skin damaged by impact, and the second series had a circular hole machined through one of the skins. The reduction of compressive strength with increasing damage (hole) size was compared. Additionally a third series of uniaxially loaded open hole compression coupons were tested to generate baseline data for comparison with both series of sandwich beams.

Loading Mode and Environment Effects on Surface Profile Characteristics of Martensite Plates in Cu-Based SMAs

NASA Astrophysics Data System (ADS)

Suru, Marius-Gabriel; Paraschiv, Adrian-Liviu; Lohan, Nicoleta Monica; Pricop, Bogdan; Ozkal, Burak; Bujoreanu, Leandru-Gheorghe

2014-07-01

The present work reports the influence of the loading mode provided during training under constant stress, in bending, applied to lamellar specimens of Cu-Zn-Al shape memory alloys (SMAs). During training, the specimens were bent by a load fastened at their free end, while being martensitic at room temperature and they lifted the load by one-way effect (1WE), during heating up to austenitic field. On cooling to martensite field, the lower concave surface of bent specimens was compressed, and during heating it was elongated, being subjected to a series of tension-compression cycles, during heating-cooling, respectively. Conversely, the upper convex surface of bent specimens was elongated during cooling and compressed during heating, being subjected to compression-tension cycles. Furthermore, 2WE-trained actuators were tested by means of a hydraulic installation where, this time heating-cooling cycles were performed in oil conditions. Considering that the lower concave surface of the specimens was kept in compressed state, while the upper convex surface was kept in elongated state, the study reveals the influence of the two loading modes and environments on the width of martensite plates of the specimens trained under various numbers of cycles. In this purpose, Cu-Zn-Al specimens, trained under 100-300-500 cycles, were prepared and analyzed by atomic force microscopy (AFM) as well as optical and scanning electron microscopy (OM and SEM, respectively). The analysis also included AFM micrographs corroborated with statistical evaluations in order to reveal the effects of loading mode (tension or compression) in different environmental conditions of the specimens, on the surface profile characteristics of martensite plates, revealed by electropolishing.

Improving the properties of geopolymer containing oil-contaminated clay, metakaolin, and blast furnace slag by applying nano-SiO2.

PubMed

Luo, Huan-Lin; Lin, Deng-Fong; Chen, Shih-Chieh

2017-07-01

In this study, geopolymer specimens based on calcined oil-contaminated clays (OCCs), metakaolin replacements of OCCs, and blast furnace slag were manufactured by the addition of nano-SiO 2 to improve their properties. The effects of adding 0, 1, 2, or 3% nano-SiO 2 on the properties and microstructures of the geopolymer specimens were determined using compressive strength tests, flow tests, setting time tests, scanning electron microscopy (SEM), and silicon nuclear magnetic resonance spectroscopy (Si-NMR). The results showed that the setting time and flowability of the geopolymer specimens decreased and the compressive strength increased as the amount of nano-SiO 2 increased. These results were supported by the SEM and Si-NMR assays. This study suggests that the addition of nano-SiO 2 was beneficial and improved the properties of the geopolymer specimens containing calcined OCC.

Compression, bend, and tension studies on forged Al67Ti25Cr8 and Al66Ti25Mn(g) L1(2) compounds

NASA Technical Reports Server (NTRS)

Kumar, K. S.; Brown, S. A.; Whittenberger, J. D.

1991-01-01

Cast, homogenized, and isothermally forged aluminum-rich L1(2) compounds Al67Ti25Cr8 and Al66Ti25Mn(g) were tested in compression as a function of temperature and as a function of strain rate at elevated temperatures (1000 K and 1100 K). Three-point bend specimens were tested as a function of temperature in the range 300 K to 873 K. Strain gages glued on the tensile side of the ambient and 473 K specimens enabled direct strain measurements. A number of 'buttonhead' tensile specimens were electro-discharge machined, fine polished, and tested between ambient and 1073 K for yield strength and ductility as a function of temperature. Scanning electron microscope (SEM) examination of fracture surfaces from both the bend and tensile specimens revealed a gradual transition from transgranular cleavage to intergranular failure with increasing temperature.

Moment measurements in dynamic and quasi-static spine segment testing using eccentric compression are susceptible to artifacts based on loading configuration.

PubMed

Van Toen, Carolyn; Carter, Jarrod W; Oxland, Thomas R; Cripton, Peter A

2014-12-01

The tolerance of the spine to bending moments, used for evaluation of injury prevention devices, is often determined through eccentric axial compression experiments using segments of the cadaver spine. Preliminary experiments in our laboratory demonstrated that eccentric axial compression resulted in "unexpected" (artifact) moments. The aim of this study was to evaluate the static and dynamic effects of test configuration on bending moments during eccentric axial compression typical in cadaver spine segment testing. Specific objectives were to create dynamic equilibrium equations for the loads measured inferior to the specimen, experimentally verify these equations, and compare moment responses from various test configurations using synthetic (rubber) and human cadaver specimens. The equilibrium equations were verified by performing quasi-static (5 mm/s) and dynamic experiments (0.4 m/s) on a rubber specimen and comparing calculated shear forces and bending moments to those measured using a six-axis load cell. Moment responses were compared for hinge joint, linear slider and hinge joint, and roller joint configurations tested at quasi-static and dynamic rates. Calculated shear force and bending moment curves had similar shapes to those measured. Calculated values in the first local minima differed from those measured by 3% and 15%, respectively, in the dynamic test, and these occurred within 1.5 ms of those measured. In the rubber specimen experiments, for the hinge joint (translation constrained), quasi-static and dynamic posterior eccentric compression resulted in flexion (unexpected) moments. For the slider and hinge joints and the roller joints (translation unconstrained), extension ("expected") moments were measured quasi-statically and initial flexion (unexpected) moments were measured dynamically. In the cadaver experiments with roller joints, anterior and posterior eccentricities resulted in extension moments, which were unexpected and expected, for those configurations, respectively. The unexpected moments were due to the inertia of the superior mounting structures. This study has shown that eccentric axial compression produces unexpected moments due to translation constraints at all loading rates and due to the inertia of the superior mounting structures in dynamic experiments. It may be incorrect to assume that bending moments are equal to the product of compression force and eccentricity, particularly where the test configuration involves translational constraints and where the experiments are dynamic. In order to reduce inertial moment artifacts, the mass, and moment of inertia of any loading jig structures that rotate with the specimen should be minimized. Also, the distance between these structures and the load cell should be reduced.

Gamma Radiation Aging Study of a Dow Corning SE 1700 Porous Structure Made by Direct Ink Writing

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

Small, Ward; Alviso, Cindy T.; Metz, Tom R.

Dow Corning SE 1700 (reinforced polydimethylsiloxane) porous structures were made by direct ink writing (DIW). The specimens (~50% porosity) were subjected to a compressive strain of ~25% while exposed to a gamma radiation dose of 1, 5, or 10 Mrad under vacuum. Compression set and load retention of the aged specimens were measured after a ~24 h relaxation period. Compression set (relative to deflection) increased with radiation dose: 11, 35, and 51% after 1, 5, and 10 Mrad, respectively. Load retention was 96-97% for the doses tested. The SE 1700 compared favorably to M9763 cellular silicone tested under the samemore » conditions.« less

Impact compressive and bending behaviour of rocks accompanied by electromagnetic phenomena.

PubMed

Kobayashi, Hidetoshi; Horikawa, Keitaro; Ogawa, Kinya; Watanabe, Keiko

2014-08-28

It is well known that electromagnetic phenomena are often observed preceding earthquakes. However, the mechanism by which these electromagnetic waves are generated during the fracture and deformation of rocks has not been fully identified. Therefore, in order to examine the relationship between the electromagnetic phenomena and the mechanical properties of rocks, uniaxial compression and three-point bending tests for two kinds of rocks with different quartz content, granite and gabbro, have been carried out at quasi-static and dynamic rates. Especially, in the bending tests, pre-cracked specimens of granite were also tested. Using a split Hopkinson pressure bar and a ferrite-core antenna in close proximity to the specimens, both the stress-strain (load-displacement) curve and simultaneous electromagnetic wave magnitude were measured. It was found that the dynamic compressive and bending strengths and the stress increase slope of both rocks were higher than those observed in static tests; therefore, there is a strain-rate dependence in their strength and stress increase rate. It was found from the tests using the pre-cracked bending specimens that the intensity of electromagnetic waves measured during crack extension increased almost proportionally to the increase of the maximum stress intensity factor of specimens. This tendency was observed in both the dynamic and quasi-static three-point bending tests for granite. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Hypothesis to Explain the Size Effect Observed in APO-BMI Compression Tests

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

Schembri, Philip Edward; Siranosian, Antranik Antonio; Kingston, Lance Allen

2015-01-07

In 2013 compression tests were performed on cylindrical specimens of carbon-microballoon-APOBMI syntactic foam machined to different lengths (0.25, 0.5, and 2.8 inches1) (Kingston, 2013). In 2014 similar tests were performed on glass-microballoon-APO-BMI of different lengths (~0.15”, ~0.32”, and ~0.57”). In all these tests it was observed that, when strains were calculated from the platen displacement (corrected for machine compliance), the apparent Young’s modulus of the material decreased with specimen size, as shown in Table 1. The reason for this size effect was speculated to be a layer of damage on or near the top and bottom machined surfaces of themore » specimens (Kingston, Schembri, & Siranosian, 2014). This report examines that hypothesis in further detail.« less

Mechanical behavior of Kenaf/Epoxy corrugated sandwich structures

NASA Astrophysics Data System (ADS)

Bakhori, S.; Hassan, M. Z.; Daud, Y.; Sarip, S.; Rahman, N.; Ismail, Z.; Aziz, S. A.

2015-12-01

This study presents the response of kenaf/epoxy corrugated sandwich structure during quasi-static test. Force-displacements curves have been deducted to determine the deformation pattern and collapse behavior of the structure. Kenaf/epoxy sandwich structures skins fabricated by using hand layup technique and the corrugated core were moulded by using steel mould. Different thicknesses of corrugated core web with two sizes of kenaf fibers were used. The corrugated core is then bonded with the skins by using poly-epoxy resin and has been cut into different number of cells. The specimens then tested under tensile and compression at different constant speeds until the specimens fully crushed. Tensile tests data showed the structure can be considered brittle when it breaking point strain, ε less than 0.025. In compression test, the specimens fail due to dominated by stress concentration that initiated by prior cracks. Also, the specimens with more number of cells and thicker core web have higher strength and the ability to absorb higher energy.

The shear fracture toughness, KIIc, of graphite

DOE PAGES

Burchell, Timothy D.; Erdman, III, Donald L.

2015-11-05

In this study, the critical shear stress intensity factor, KIIc, here-in referred to as the shear fracture toughness, KIIc (MPa m), of two grades of graphite are reported. The range of specimen volumes was selected to elucidate any specimen size effect, but smaller volume specimen tests were largely unsuccessful, shear failure did not occur between the notches as expected. This was probably due to the specimen geometry causing the shear fracture stress to exceed the compressive failure stress. In subsequent testing the specimen geometry was altered to reduce the compressive footprint and the notches (slits) made deeper to reduce themore » specimen's ligament length. Additionally, we added the collection of Acoustic Emission (AE) during testing to assist with the identification of the shear fracture load. The means of KIIc from large specimens for PCEA and NBG-18 are 2.26 MPa m with an SD of 0.37 MPa m and 2.20 MPa m with an SD of 0.53 MPa m, respectively. The value of KIIc for both graphite grades was similar, although the scatter was large. In this work we found the ratio of KIIc/ KIc ≈ 1.6. .« less

Effects of Range of Stress and of Special Notches on Fatigue Properties of Aluminum Alloys Suitable for Airplane Propellers

NASA Technical Reports Server (NTRS)

Dolan, Thomas J

1942-01-01

Laboratory tests were made to obtain information on the load-resisting properties of X76S-T aluminum alloy when subjected to static, impact, and repeated loads. Results are presented from static-load test of unnotched specimens in tension and in torsion and of notched specimens in tension. Charpy impact values obtained from bend tests on notched specimens and tension impact values for both notched and unnotched specimens tested at several different temperatures are included. The endurance limits obtained from repeated bending fatigue tests made on three different types of testing machine are given for unnotched polished specimens, and the endurance limits of notched specimens subjected to six different ranges of bending stress are also reported. The results indicated that: (a) polished rectangular specimens had an endurance limit about 30 percent less than that obtained for round specimens; (b) a comparison of endurance limits obtained from tests on three different types of machine indicated that there was no apparent effect of speed of testing on the endurance limit for the range of speeds used (1,750 to 13,000 rpm). (c) the fatigue strength (endurance limit) of the X76S-T alloy was greatly decreased by the presence of a notch in the specimens; (d) no complete fractures of the entire specimens occurred in notched fatigue specimens when subjected to stress cycles for which the mean stress at the notch during the cycle was a compressive stress; for this test condition a microscopic cracking occurred near the root of the notch and was used as a criterion of failure of the specimen. (e) as the mean stress at the notch was decreased from a tensile (+) stress to a compressive (-) stress, it was found that the alternating stress that could be superimposed on the mean stress in the cycle without causing failure of the specimens was increased.

Influence of Water Content on Mechanical Properties of Rock in Both Saturation and Drying Processes

NASA Astrophysics Data System (ADS)

Zhou, Zilong; Cai, Xin; Cao, Wenzhuo; Li, Xibing; Xiong, Cheng

2016-08-01

Water content has a pronounced influence on the properties of rock materials, which is responsible for many rock engineering hazards, such as landslides and karst collapse. Meanwhile, water injection is also used for the prevention of some engineering disasters like rock-bursts. To comprehensively investigate the effect of water content on mechanical properties of rocks, laboratory tests were carried out on sandstone specimens with different water contents in both saturation and drying processes. The Nuclear Magnetic Resonance technique was applied to study the water distribution in specimens with variation of water contents. The servo-controlled rock mechanics testing machine and Split Hopkinson Pressure Bar technique were used to conduct both compressive and tensile tests on sandstone specimens with different water contents. From the laboratory tests, reductions of the compressive and tensile strength of sandstone under static and dynamic states in different saturation processes were observed. In the drying process, all of the saturated specimens could basically regain their mechanical properties and recover its strength as in the dry state. However, for partially saturated specimens in the saturation and drying processes, the tensile strength of specimens with the same water content was different, which could be related to different water distributions in specimens.

Response of Honeycomb Core Sandwich Panel with Minimum Gage GFRP Face-Sheets to Compression Loading After Impact

NASA Technical Reports Server (NTRS)

McQuigg, Thomas D.; Kapania, Rakesh K.; Scotti, Stephen J.; Walker, Sandra P.

2011-01-01

A compression after impact study has been conducted to determine the residual strength of three sandwich panel constructions with two types of thin glass fiber reinforced polymer face-sheets and two hexagonal honeycomb Nomex core densities. Impact testing is conducted to first determine the characteristics of damage resulting from various impact energy levels. Two modes of failure are found during compression after impact tests with the density of the core precipitating the failure mode present for a given specimen. A finite element analysis is presented for prediction of the residual compressive strength of the impacted specimens. The analysis includes progressive damage modeling in the face-sheets. Preliminary analysis results were similar to the experimental results; however, a higher fidelity core material model is expected to improve the correlation.

The Effect of Temperature on Compressive and Tensile Strengths of Commonly Used Luting Cements: An In Vitro Study

PubMed Central

Patil, Suneel G; Sajjan, MC Suresh; Patil, Rekha

2015-01-01

Background: The luting cements must withstand masticatory and parafunctional stresses in the warm and wet oral environment. Mouth temperature and the temperature of the ingested foods may induce thermal variation and plastic deformation within the cements and might affect the strength properties. The objectives of this study were to evaluate the effect of temperature on the compressive and diametral tensile strengths of two polycarboxylate, a conventional glass ionomer and a resin modified glass ionomer luting cements and, to compare the compressive strength and the diametral tensile strength of the selected luting cements at varying temperatures. Materials and Methods: In this study, standardized specimens were prepared. The temperature of the specimens was regulated prior to testing them using a universal testing machine at a crosshead speed of 1 mm/min. Six specimens each were tested at 23°C, 37°C and 50°C for both the compressive and diametral tensile strengths, for all the luting cements. Results: All the luting cements showed a marginal reduction in their compressive and diametral tensile strengths at raised temperatures. Fuji Plus was strongest in compression, followed by Fuji I > Poly F > Liv Carbo. Fuji Plus had the highest diametral tensile strength values, followed by Poly F = Fuji I = Liv Carbo, at all temperatures. Conclusion: An increase in the temperature caused no significant reduction in the compressive and diametral tensile strengths of the cements evaluated. The compressive strength of the luting cements differed significantly from one another at all temperatures. The diametral tensile strength of resin modified glass ionomers differed considerably from the other cements, whereas there was no significant difference between the other cements, at all the temperatures. PMID:25859100

The effect of temperature on compressive and tensile strengths of commonly used luting cements: an in vitro study.

PubMed

Patil, Suneel G; Sajjan, Mc Suresh; Patil, Rekha

2015-02-01

The luting cements must withstand masticatory and parafunctional stresses in the warm and wet oral environment. Mouth temperature and the temperature of the ingested foods may induce thermal variation and plastic deformation within the cements and might affect the strength properties. The objectives of this study were to evaluate the effect of temperature on the compressive and diametral tensile strengths of two polycarboxylate, a conventional glass ionomer and a resin modified glass ionomer luting cements and, to compare the compressive strength and the diametral tensile strength of the selected luting cements at varying temperatures. In this study, standardized specimens were prepared. The temperature of the specimens was regulated prior to testing them using a universal testing machine at a crosshead speed of 1 mm/min. Six specimens each were tested at 23°C, 37°C and 50°C for both the compressive and diametral tensile strengths, for all the luting cements. All the luting cements showed a marginal reduction in their compressive and diametral tensile strengths at raised temperatures. Fuji Plus was strongest in compression, followed by Fuji I > Poly F > Liv Carbo. Fuji Plus had the highest diametral tensile strength values, followed by Poly F = Fuji I = Liv Carbo, at all temperatures. An increase in the temperature caused no significant reduction in the compressive and diametral tensile strengths of the cements evaluated. The compressive strength of the luting cements differed significantly from one another at all temperatures. The diametral tensile strength of resin modified glass ionomers differed considerably from the other cements, whereas there was no significant difference between the other cements, at all the temperatures.

Experimental Evaluation of Fatigue Damage Progression in Postbuckled Single Stringer Composite Specimens

NASA Technical Reports Server (NTRS)

Bisagni, Chiara; Davila, Carlos G.; Rose, Cheryl A.; Zalameda, Joseph N.

2014-01-01

The durability and damage tolerance of postbuckled composite structures are not yet completely understood, and remain difficult to predict due to the nonlinearity of the geometric response and its interaction with local damage modes. A research effort was conducted to investigate experimentally the quasi-static and fatigue damage progression in a single-stringer compression (SSC) specimen. Three specimens were manufactured with a hat-stiffener, and an initial defect was introduced with a Teflon film embedded between one flange of the stringer and the skin. One of the specimens was tested under quasi-static compressive loading, while the remaining two specimens were tested by cycling in postbuckling. The tests were performed at the NASA Langley Research Center under controlled conditions and with instrumentation that allows a precise evaluation of the postbuckling response and of the damage modes. Three-dimensional digital image correlation VIC-3D systems were used to provide full field displacements and strains on the skin and the stringer. Passive thermal monitoring was conducted during the fatigue tests using an infrared camera that showed the location of the delamination front while the specimen was being cycled. The live information from the thermography was used to stop the fatigue tests at critical stages of the damage evolution to allow detailed ultrasonic scans.

The effect of shredding and test apparatus size on compressibility and strength parameters of degraded municipal solid waste.

PubMed

Hossain, M S; Gabr, M A; Asce, F

2009-09-01

In many situations, MSW components are processed and shredded before use in laboratory experiments using conventional soil testing apparatus. However, shredding MSW material may affect the target property to be measured. The objective of this study is to contribute to the understanding of the effect of shredding of MSW on the measured compressibility and strength properties. It is hypothesized that measured properties can be correlated to an R-value, the ratio of waste particle size to apparatus size. Results from oedometer tests, conducted on 63.5 mm, 100 mm, 200 mm diameter apparatus, indicated the dependency of the compressibility parameters on R-value. The compressibility parameters are similar for the same R-value even though the apparatus size varies. The results using same apparatus size with variable R-values indicated that shredding of MSW mainly affects initial compression. Creep and biological strain rate of the tested MSW are not significantly affected by R-value. The shear strength is affected by shredding as the light-weight reinforcing materials are shredded into smaller pieces during specimen preparation. For example, the measured friction angles are 32 degrees and 27 degrees for maximum particle sizes of 50 mm and 25 mm, respectively. The larger MSW components in the specimen provide better reinforcing contribution. This conclusion is however dependent on comparing specimen at the same level of degradation since shear strength is also a function of extent of degradation.

Strength and deformation behaviors of veined marble specimens after vacuum heat treatment under conventional triaxial compression

NASA Astrophysics Data System (ADS)

Su, Haijian; Jing, Hongwen; Yin, Qian; Yu, Liyuan; Wang, Yingchao; Wu, Xingjie

2017-10-01

The mechanical behaviors of rocks affected by high temperature and stress are generally believed to be significant for the stability of certain projects involving rocks, such as nuclear waste storage and geothermal resource exploitation. In this paper, veined marble specimens were treated to high temperature treatment and then used in conventional triaxial compression tests to investigate the effect of temperature, confining pressure, and vein angle on strength and deformation behaviors. The results show that the strength and deformation parameters of the veined marble specimens changed with the temperature, presenting a critical temperature of 600 °C. The triaxial compression strength of a horizontal vein (β = 90°) is obviously larger than that of a vertical vein (β = 0°). The triaxial compression strength, elasticity modulus, and secant modulus have an approximately linear relation to the confining pressure. Finally, Mohr-Coulomb and Hoek-Brown criteria were respectively used to analyze the effect of confining pressure on triaxial compression strength.

Compression failure of composite laminates

NASA Technical Reports Server (NTRS)

Pipes, R. B.

1983-01-01

This presentation attempts to characterize the compressive behavior of Hercules AS-1/3501-6 graphite-epoxy composite. The effect of varying specimen geometry on test results is examined. The transition region is determined between buckling and compressive failure. Failure modes are defined and analytical models to describe these modes are presented.

Mechanical Degradation of Porous NiTi Alloys Under Static and Cyclic Loading

NASA Astrophysics Data System (ADS)

Hosseini, Seyyed Alireza

2017-12-01

Pore characteristics and morphology have significant effect on mechanical behavior of porous NiTi specimens. In this research, porous NiTi with different pore sizes, shapes and morphology were produced by powder metallurgy methods using space-holder materials. The effect of the pore characteristics on the mechanical properties was investigated by static and cyclic compression tests at body temperature. The results show that specimens with low porosity and isolated pores exhibit more mechanical strength and recoverable strain. The specimen with 36% porosity produced without space holder could preserve its properties up to 10% strain and its strain recovery was complete after cyclic compression tests. On the other hand, the specimens produced by a urea space holder with more than 60% interconnected porosity show rapid degradation of their scaffolds. The highly porous specimens degraded even below 5% strain due to crack formation and propagation in the thin pore walls. For highly porous specimens produced by a NaCl space holder, the pores are partially interconnected with a cubic shape; nevertheless, their mechanical behavior is close to low-porosity specimens.

Dynamic fracture of sintered Nd-Fe-B magnet under uniaxial compression

NASA Astrophysics Data System (ADS)

Wang, Huanran; Wan, Yin; Chen, Danian; Lei, Guohua; Ren, Chunying

2018-06-01

The dynamic fracture of the Nd-Fe-B magnets under uniaxial compression is investigated using a split Hopkinson pressure bar (SHPB). The surface deformation and fracture processes of the Nd-Fe-B specimens are recorded adopting a high-speed photography (HSP) with digital image correlation (DIC). The load and work applied to the specimens in the SHPB tests are determined with the strain signals of the transmitted and reflected waves. The surface strain distributions of the Nd-Fe-B specimen during the SHPB testing are revealed with DIC. It is shown by the HSP with DIC that when the load is near the maximum, the cracks at some positions on the surface of the expanding Nd-Fe-B specimen are formed and ran along certain directions. The work applied to the specimen per unit volume which corresponds to the maximal load is used to characterize the impact stability of the Nd-Fe-B specimen. The localized fracture strains at some positions on the surface of the expanding specimens at some characteristic times are determined with DIC, which are the projections of the strains onto the DIC plane.

Effects of partial interlaminar bonding on impact resistance and loaded-hole behavior of graphite/epoxy quasi-isotropic laminates

NASA Technical Reports Server (NTRS)

Illg, W.

1986-01-01

A partial-bonding interlaminar toughening concept was evaluated for resistance to impact and for behavior of a loaded hole. Perforated Mylar sheets were interleaved between all 24 plies of a graphite/epoxy quasi-isotropic lay-up. Specimens were impacted by aluminum spheres while under tensile or compressive loads. Impact-failure thresholds and residual strengths were obtained. Loaded-hole specimens were tested in three configurations that were critical in bearing, shear, or tension. Partial bonding reduced the tensile and compressive strengths of undamaged specimens by about one-third. For impact, partial bonding did not change the threshold for impact failure under tensile preload. However, under compressive preload, partial bonding caused serious degradation of impact resistance. Partial bonding reduced the maximum load-carrying capacity of all three types of loaded-hole specimens. Overall, partial bonding degraded both impact resistance and bearing strength of holes.

Tensile testing grips ensure uniform loading of bimetal tubing specimens

NASA Technical Reports Server (NTRS)

Driscol, S. D.; Hunt, V.

1968-01-01

Tensile testing grip uniformly distributes stresses to the internal and external tube of bimetal tubing specimens. The grip is comprised of a slotted external tube grip, a slotted internal tube grip, a machine bolt and nut, an internal grip expansion cone, and an external grip compression nut.

Fatigue degradation in compressively loaded composite laminates. [graphite-epoxy composites

NASA Technical Reports Server (NTRS)

Ramkumar, R. L.

1981-01-01

The effect of imbedded delaminations on the compression fatigue behavior of quasi-isotropic, T300/5208, graphite/epoxy laminates was investigated. Teflon imbedments were introduced during panel layup to create delaminations. Static and constant amplitude (R=10, omega = 10 Hz) fatigue tests were conducted. S-N data and half life residual strength data were obtained. During static compression loading, the maximum deflection of the buckled delaminated region was recorded. Under compression fatigue, growth of the imbedded delamination was identified as the predominant failure mode in most of the test cases. Specimens that exhibited others failures had a single low stiffness ply above the Teflon imbedment. Delamination growth during fatigue was monitored using DIB enhanced radiography. In specimens with buried delaminations, the dye penetrant (DIB) was introduced into the delaminated region through a minute laser drilled hole, using a hypodermic needle. A low kV, microfocus, X-ray unit was mounted near the test equipment to efficiently record the cyclic growth of buried delaminations on Polaroid film.

Strengthening silicon carbide by quenching

NASA Technical Reports Server (NTRS)

Gruver, R. M.; Platts, D. R.; Kirchner, H. P.

1974-01-01

Quenching was used to form compressive surface layers in hot-pressed silicon carbide. The presence of the compressive stresses was verified by slotted rod tests. The slotted rod tip deflection was retained at temperatures to at least 1380 C, showing that the stresses are not relieved immediately at elevated temperatures. The flexural strength and impact resistance of specimens quenched from moderate temperatures (2000 C) were increased. Frequently, specimens quenched from higher temperatures were weakened by thermal shock damage.

An ultrasonic measurement for in vitro depth-dependent equilibrium strains of articular cartilage in compression

NASA Astrophysics Data System (ADS)

Zheng, Y. P.; Mak, A. F. T.; Lau, K. P.; Qin, L.

2002-09-01

The equilibrium depth-dependent biomechanical properties of articular cartilage were measured using an ultrasound-compression method. Ten cylindrical bovine patella cartilage-bone specimens were tested in compression followed by a period of force-relaxation. A 50 MHz focused ultrasound beam was transmitted into the cartilage specimen through a remaining bone layer and a small hole at the centre of a specimen platform. The ultrasound echoes reflected or scattered within the articular cartilage were collected using the same transducer. The displacements of the tissues at different depths of the articular cartilage were derived from the ultrasound echo signals recorded during the compression and the subsequent force-relaxation. For two steps of 0.1 mm compression, the average strain at the superficial 0.2 mm thick layer (0.35 +/- 0.09) was significantly (p < 0.05) larger than that at the subsequent 0.2 mm thick layer (0.05 +/- 0.07) and that at deeper layers (0.01 +/- 0.02). It was demonstrated that the compressive biomechanical properties of cartilage were highly depth-dependent. The results suggested that the ultrasound-compression method could be a useful tool for the study of the depth-dependent biomechanical properties of articular cartilage.

Dynamic loads on human and animal surrogates at different test locations in compressed-gas-driven shock tubes

NASA Astrophysics Data System (ADS)

Alay, E.; Skotak, M.; Misistia, A.; Chandra, N.

2018-01-01

Dynamic loads on specimens in live-fire conditions as well as at different locations within and outside compressed-gas-driven shock tubes are determined by both static and total blast overpressure-time pressure pulses. The biomechanical loading on the specimen is determined by surface pressures that combine the effects of static, dynamic, and reflected pressures and specimen geometry. Surface pressure is both space and time dependent; it varies as a function of size, shape, and external contour of the specimens. In this work, we used two sets of specimens: (1) anthropometric dummy head and (2) a surrogate rodent headform instrumented with pressure sensors and subjected them to blast waves in the interior and at the exit of the shock tube. We demonstrate in this work that while inside the shock tube the biomechanical loading as determined by various pressure measures closely aligns with live-fire data and shock wave theory, significant deviations are found when tests are performed outside.

Column strength of tubes elastically restrained against rotation at the ends

NASA Technical Reports Server (NTRS)

Osgood, William R

1938-01-01

Report presents the results of a study made of the effects of known end restraint on commercially available round and streamline tubing of chromium-molybdenum steel, duralumin, stainless steel, and heat-treated chromium-molybdenum steel; and a more accurate method than any previously available, but still a practical method, was developed for designing compression members in riveted or welded structures, particularly aircraft. Two hundred specimens were tested as short, medium-length, and long columns with freely supported ends or elastically restrained ends. Tensile and compressive tests were made on each piece of original tubing from which column specimens were cut.

Fabrication and testing of prestressed composite rotor blade spar specimens

NASA Technical Reports Server (NTRS)

Gleich, D.

1974-01-01

Prestressed composite spar specimens were fabricated and evaluated by crack propagation and ballistic penetration tests. The crack propagation tests on flawed specimens showed that the prestressed composite spar construction significantly suppresses crack growth. Damage from three high velocity 30 caliber projectile hits was confined to three small holes in the ballistic test specimen. No fragmentation or crack propagation was observed indicating good ballistic damage resistance. Rotor attachment approaches and improved structural performance configurations were identified. Design theory was verified by tests. The prestressed composite spar configuration consisted of a compressively prestressed high strength ARDEFORM 301 stainless steel liner overwrapped with pretensioned S-994 fiberglass.

Compressive Strength of Notched Poly(Phenylene Sulfide) Aerospace Composite: Influence of Fatigue and Environment

NASA Astrophysics Data System (ADS)

Niitsu, G. T.; Lopes, C. M. A.

2013-08-01

The purpose of this work is to evaluate the influences of fatigue and environmental conditions (-55 °C, 23 °C, and 82 °C/Wet) on the ultimate compression strength of notched carbon-fiber-reinforced poly(phenylene sulfide) composites by performing open-hole compression (OHC) tests. Analysis of the fatigue effect showed that at temperatures of -55 and 23 °C, the ultimate OHC strengths were higher for fatigued than for not-fatigued specimens; this could be attributed to fiber splitting and delamination during fatigue cycling, which reduces the stress concentration at the hole edge, thus increasing the composite strength. This effect of increasing strength for fatigued specimens was not observed under the 82 °C/Wet conditions, since the test temperature near the matrix glass transition temperature ( T g) together with moisture content resulted in matrix softening, suggesting a reduction in fiber splitting during cycling; similar OHC strengths were verified for fatigued and not-fatigued specimens tested at 82 °C/Wet. Analysis of the temperature effect showed that the ultimate OHC strengths decreased with increasing temperature. A high temperature together with moisture content (82 °C/Wet condition) reduced the composite compressive strengths, since a temperature close to the matrix T g resulted in matrix softening, which reduced the lateral support provided by the resin to the 0° fibers, leading to fiber instability failure at reduced applied loads. On the other hand, a low temperature (-55 °C) improved the compressive strength because of possible fiber-matrix interfacial strengthening, increasing the fiber contribution to compressive strength.

Test Methods for Composites: A Status Report. Volume 2. Compression Test Methods

DTIC Science & Technology

1993-06-01

glass and Kevlar fibers in a phenolic matrix) were relatively thick (24 plies), and more importantly, failed at very low compressive strength levels...ICH LAMINATE SPECIMEN TEST METHOD ........................................ 29 2.4 RECOMMENDATIONS...Thickness in the Middle of the Gage Section, for Four Laminate Thicknesses [711 ................... 143 52. Axial Stress Distributions in an AS4/3502 Carbon

Fracture Property of Y-Shaped Cracks of Brittle Materials under Compression

PubMed Central

Zhang, Xiaoyan; Zhu, Zheming; Liu, Hongjie

2014-01-01

In order to investigate the properties of Y-shaped cracks of brittle materials under compression, compression tests by using square cement mortar specimens with Y-shaped crack were conducted. A true triaxial loading device was applied in the tests, and the major principle stresses or the critical stresses were measured. The results show that as the branch angle θ between the branch crack and the stem crack is 75°, the cracked specimen has the lowest strength. In order to explain the test results, numerical models of Y-shaped cracks by using ABAQUS code were established, and the J-integral method was applied in calculating crack tip stress intensity factor (SIF). The results show that when the branch angle θ increases, the SIF K I of the branch crack increases from negative to positive and the absolute value K II of the branch crack first increases, and as θ is 50°, it is the maximum, and then it decreases. Finally, in order to further investigate the stress distribution around Y-shaped cracks, photoelastic tests were conducted, and the test results generally agree with the compressive test results. PMID:25013846

Testing of Action of Direct Flame on Concrete

PubMed Central

Valek, Jaroslav; Novosad, Petr

2015-01-01

The paper states results of experimental exposition of concrete test specimens to direct flame. Concrete test specimens made from various mixtures differing in the type of aggregate, binder, dispersed reinforcement, and technological procedure were subjected to thermal load. Physicomechanical and other properties of all test specimens were tested before exposition to open flame: density, compressive strength, flexural strength, moisture content, and surface appearance. The specimens were visually observed during exposition to open flame and changes were recorded. Exposed surface was photographically documented before thermal load and at 10-minute intervals. Development of temperature of the specimens was documented with a thermocamera. After exposition to thermal load and cooling down, concrete specimens were visually observed, network of cracks was photographically documented, and maximal depth of spalled area was measured. PMID:25830162

Mechanical Behavior of Recycled Aggregate Concrete-Filled Steel Tubular Columns before and after Fire.

PubMed

Liu, Wenchao; Cao, Wanlin; Zhang, Jianwei; Wang, Ruwei; Ren, Lele

2017-03-09

Recycled aggregate concrete (RAC) is an environmentally friendly building material. This paper investigates the mechanical behavior of recycled aggregate concrete filled steel tube (RACFST) columns exposed to fire. Two groups of 12 columns were designed and tested, under axial compression, before and after fire, to evaluate the degradation of bearing capacity due to fire exposure. Six specimens were subjected to axial compression tests at room temperature and the other six specimens were subjected to axial compression tests after a fire exposure. The main parameters of the specimens include the wall thickness of the steel tube (steel content) and the type of concrete materials. Several parameters as obtained from the experimental results were compared and analyzed, including the load-bearing capacity, deformation capacity, and failure characteristics of the specimens. Meanwhile, rate of loss of bearing capacity of specimens exposed to fire were calculated based on the standards EC4 and CECS28:90. The results show that concrete material has a large influence on the rate of loss of bearing capacity in the case of a relatively lower steel ratio. While steel content has little effect on the rate of loss of bearing capacity of concrete-filled steel tube (CFST) columns after fire, it has a relatively large influence on the loss rate of bearing capacity of the RACFST columns. The loss of bearing capacity of the specimens from the experiment is more serious than that from the calculation. As the calculated values are less conservative, particular attention should be given to the application of recycled aggregate concrete in actual structures.

Mechanical Behavior of Recycled Aggregate Concrete-Filled Steel Tubular Columns before and after Fire

PubMed Central

Liu, Wenchao; Cao, Wanlin; Zhang, Jianwei; Wang, Ruwei; Ren, Lele

2017-01-01

Recycled aggregate concrete (RAC) is an environmentally friendly building material. This paper investigates the mechanical behavior of recycled aggregate concrete filled steel tube (RACFST) columns exposed to fire. Two groups of 12 columns were designed and tested, under axial compression, before and after fire, to evaluate the degradation of bearing capacity due to fire exposure. Six specimens were subjected to axial compression tests at room temperature and the other six specimens were subjected to axial compression tests after a fire exposure. The main parameters of the specimens include the wall thickness of the steel tube (steel content) and the type of concrete materials. Several parameters as obtained from the experimental results were compared and analyzed, including the load-bearing capacity, deformation capacity, and failure characteristics of the specimens. Meanwhile, rate of loss of bearing capacity of specimens exposed to fire were calculated based on the standards EC4 and CECS28:90. The results show that concrete material has a large influence on the rate of loss of bearing capacity in the case of a relatively lower steel ratio. While steel content has little effect on the rate of loss of bearing capacity of concrete-filled steel tube (CFST) columns after fire, it has a relatively large influence on the loss rate of bearing capacity of the RACFST columns. The loss of bearing capacity of the specimens from the experiment is more serious than that from the calculation. As the calculated values are less conservative, particular attention should be given to the application of recycled aggregate concrete in actual structures. PMID:28772634

Repeatability and Reproducibility of Compression Strength Measurements Conducted According to ASTM E9

NASA Technical Reports Server (NTRS)

Luecke, William E.; Ma, Li; Graham, Stephen M.; Adler, Matthew A.

2010-01-01

Ten commercial laboratories participated in an interlaboratory study to establish the repeatability and reproducibility of compression strength tests conducted according to ASTM International Standard Test Method E9. The test employed a cylindrical aluminum AA2024-T351 test specimen. Participants measured elastic modulus and 0.2 % offset yield strength, YS(0.2 % offset), using an extensometer attached to the specimen. The repeatability and reproducibility of the yield strength measurement, expressed as coefficient of variations were cv(sub r)= 0.011 and cv(sub R)= 0.020 The reproducibility of the test across the laboratories was among the best that has been reported for uniaxial tests. The reported data indicated that using diametrically opposed extensometers, instead of a single extensometer doubled the precision of the test method. Laboratories that did not lubricate the ends of the specimen measured yield stresses and elastic moduli that were smaller than those measured in laboratories that lubricated the specimen ends. A finite element analysis of the test specimen deformation for frictionless and perfect friction could not explain the discrepancy, however. The modulus measured from stress-strain data were reanalyzed using a technique that finds the optimal fit range, and applies several quality checks to the data. The error in modulus measurements from stress-strain curves generally increased as the fit range decreased to less than 40 % of the stress range.

Methodology for Mechanical Property Testing on Fuel Cladding Using an Expanded Plug Wedge Test

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

Wang, Jy-An John; Jiang, Hao

To determine the tensile properties of irradiated fuel cladding in a hot cell, a simple test was developed at ORNL and is described fully in US Patent Application 20060070455, Expanded plug method for developing circumferential mechanical properties of tubular materials. This method is designed for testing fuel rod cladding ductility in a hot cell utilizing an expandable plug to stretch a small ring of irradiated cladding material. The specimen strain is determined using the measured diametrical expansion of the ring. This method removes many complexities associated with specimen preparation and testing. The advantages are the simplicity of measuring the testmore » component assembly in the hot cell and the direct measurement of specimen strain. It was also found that cladding strength could be determined from the test results. The basic approach of this test method is to apply an axial compressive load to a cylindrical plug of polyurethane (or other materials) fitted inside a short ring of the test material to achieve radial expansion of the specimen. The diameter increase of the specimen is used to calculate the circumferential strain accrued during the test. The other two basic measurements are total applied load and amount of plug compression (extension). A simple procedure is used to convert the load circumferential strain data from the ring tests into material pseudo-stress-strain curves. However, several deficiencies exist in this expanded-plug loading ring test, which will impact accuracy of test results and introduce potential shear failure of the specimen due to inherited large axial compressive stress from the expansion plug test. First of all, the highly non-uniform stress and strain distribution resulted in the gage section of the clad. To ensure reliable testing and test repeatability, the potential for highly non-uniform stress distribution or displacement/strain deformation has to be eliminated at the gage section of the specimen. Second, significant compressive stresses were induced by clad bending deformation due to a clad bulging effect (or the barreling effect). The barreling effect caused very large localized shear stress in the clad and left testing material at a high risk of shear failure. The above combined effects will result in highly non-conservative predictions both in strength and ductility of the tested clad, and the associated mechanical properties as well. To overcome/mitigate the mentioned deficiencies associated with the current expansion plug test, systematic studies have been conducted. Through detailed parameter investigation on specific geometry designs, careful filtering of material for the expansion plug, as well as adding newly designed parts to the testing system, a method to reconcile the potential non-conservatism embedded in the expansion plug test system has been discovered. A modified expansion plug testing protocol has been developed based on the method. In order to closely resemble thin-wall theory, a general procedure was also developed to determine the hoop stress in the tested ring specimen. A scaling factor called -factor is defined to correlate the ring load P into hoop stress . , = . The generated stress-strain curve agrees very well with tensile test data in both the elastic and plastic regions.« less

Study of the influence of hole quality on composite materials

NASA Technical Reports Server (NTRS)

Pengra, J. J.

1980-01-01

The influence of hole quality on the structural behavior of composite materials was investigated. From an industry survey it was determined that the most frequent imperfections encountered during hole fabrication are chipout, delamination, and oversize conditions. These hole flaw types were generated in critical areas of static, compression, and fatigue specimens fabricated from T300/5208 graphite/epoxy system. The specimens were tested in static and cyclic pin bearing modes in addition to compression loading. Results of these tests are presented and discussed. The hole chipout defect reduced the static and cyclic endurance characteristics. Oversize holes also lowered the cyclic pin bearing endurance, but had no influence of the static pin bearing characteristics. Delamination had no insignificant influence on the static tension and cyclic pin bearing characteristics. Compression tests demonstrated a deleterious effect for chipout of delamination defects. Hole quality requirements proposed are discussed.

The increase of compressive strength of natural polymer modified concrete with Moringa oleifera

NASA Astrophysics Data System (ADS)

Susilorini, Rr. M. I. Retno; Santosa, Budi; Rejeki, V. G. Sri; Riangsari, M. F. Devita; Hananta, Yan's. Dianaga

2017-03-01

Polymer modified concrete is one of some concrete technology innovations to meet the need of strong and durable concrete. Previous research found that Moringa oleifera can be applied as natural polymer modifiers into mortars. Natural polymer modified mortar using Moringa oleifera is proven to increase their compressive strength significantly. In this resesearch, Moringa oleifera seeds have been grinded and added into concrete mix for natural polymer modified concrete, based on the optimum composition of previous research. The research investigated the increase of compressive strength of polymer modified concrete with Moringa oleifera as natural polymer modifiers. There were 3 compositions of natural polymer modified concrete with Moringa oleifera referred to previous research optimum compositions. Several cylinder of 10 cm x 20 cm specimens were produced and tested for compressive strength at age 7, 14, and, 28 days. The research meets conclusions: (1) Natural polymer modified concrete with Moringa oleifera, with and without skin, has higher compressive strength compared to natural polymer modified mortar with Moringa oleifera and also control specimens; (2) Natural polymer modified concrete with Moringa oleifera without skin is achieved by specimens contains Moringa oleifera that is 0.2% of cement weight; and (3) The compressive strength increase of natural polymer modified concrete with Moringa oleifera without skin is about 168.11-221.29% compared to control specimens

The Fire Resistance Performance of Recycled Aggregate Concrete Columns with Different Concrete Compressive Strengths

PubMed Central

Dong, Hongying; Cao, Wanlin; Bian, Jianhui; Zhang, Jianwei

2014-01-01

In order to ascertain the fire resistance performance of recycled aggregate concrete (RAC) components with different concrete compressive strengths, four full-scaled concrete columns were designed and tested under high temperature. Two of the four specimens were constructed by normal concrete with compressive strength ratings of C20 and C30, respectively, while the others were made from recycled coarse aggregate (RCA) concrete of C30 and C40, respectively. Identical constant axial forces were applied to specimens while being subjected to simulated building fire conditions in a laboratory furnace. Several parameters from the experimental results were comparatively analyzed, including the temperature change, vertical displacement, lateral deflection, fire endurance, and failure characteristics of specimens. The temperature field of specimens was simulated with ABAQUS Software (ABAQUS Inc., Provindence, RI, USA) and the results agreed quite well with those from the experiments. Results show that the rate of heat transfer from the surface to the interior of the column increases with the increase of the concrete’s compressive strength for both RAC columns and normal concrete columns. Under the same initial axial force ratio, for columns with the same cross section, those with lower concrete compressive strengths demonstrate better fire resistance performance. The fire resistance performance of RAC columns is better than that of normal concrete columns, with the same concrete compressive strength. PMID:28788279

The Fire Resistance Performance of Recycled Aggregate Concrete Columns with Different Concrete Compressive Strengths.

PubMed

Dong, Hongying; Cao, Wanlin; Bian, Jianhui; Zhang, Jianwei

2014-12-08

In order to ascertain the fire resistance performance of recycled aggregate concrete (RAC) components with different concrete compressive strengths, four full-scaled concrete columns were designed and tested under high temperature. Two of the four specimens were constructed by normal concrete with compressive strength ratings of C20 and C30, respectively, while the others were made from recycled coarse aggregate (RCA) concrete of C30 and C40, respectively. Identical constant axial forces were applied to specimens while being subjected to simulated building fire conditions in a laboratory furnace. Several parameters from the experimental results were comparatively analyzed, including the temperature change, vertical displacement, lateral deflection, fire endurance, and failure characteristics of specimens. The temperature field of specimens was simulated with ABAQUS Software (ABAQUS Inc., Provindence, RI, USA) and the results agreed quite well with those from the experiments. Results show that the rate of heat transfer from the surface to the interior of the column increases with the increase of the concrete's compressive strength for both RAC columns and normal concrete columns. Under the same initial axial force ratio, for columns with the same cross section, those with lower concrete compressive strengths demonstrate better fire resistance performance. The fire resistance performance of RAC columns is better than that of normal concrete columns, with the same concrete compressive strength.

Reinforced cementitous composite with in situ shrinking microfibers

NASA Astrophysics Data System (ADS)

Kim, Eric S.; Lee, Jason K.; Lee, Patrick C.; Huston, Dryver R.; Tan, Ting; Al-Ghamdi, Saleh

2017-03-01

This paper describes an innovative fiber reinforcement technology for cementitious composite structures that employs in situ shrinking microfibers to provide supplemental strength-enhancing compressive stresses. Reinforced concrete is one of the most commonly used structural materials in construction industry, primarily due to its cost, durability, ability to be easily fabricated into a variety of shapes on site, and locally abundant raw material availability almost everywhere. Unlike incumbent passive reinforcing microfiber technology, in situ shrinking microfibers that respond to an in situ stimulus such as heat, pH, or moisture variations can induce pre-compression to matrix and create additional resistance from external loads, creating stronger composite structures. In this paper, heat-activated-shrinking (HAS) microfibers made from polyolefin, and pH-activated-shrinking (pHAS) microfibers made from chitosan powder were used to study effects of shrinking microfiber reinforcing in concrete. Shrinking ratios and tensile strengths of both microfibers were measured. Cementitious specimens with active shrinking microfibers, passive non shrinking fibers, as well as control samples were made. Mechanical properties of the samples were compared with compression and three-point bending tests. The optimum microfiber weight percentages for HAS microfibers were 0.5 wt% in compression tests, and 1.0 wt% in three-point bending tests. For pHAS microfibers, the optimum weight percentages were 0.5 wt% in three-point bending tests. Compared to heat passive microfibers specimens, 45% increase in the maximum compression strengths, and 124% increase in the maximum bending strengths were achieved at the optimum weight percentages of HAS microfibers. In addition, with 0.5 wt% of pHAS microfibers, 145% increase in the maximum bending strengths of three-point bending tests resulted compared to pH passive microfibers specimens.

The Lateral Stability of Equal-flanged Aluminum-alloy I-beams Subjected to Pure Bending

NASA Technical Reports Server (NTRS)

Dumont, C; Hill, H N

1940-01-01

Equal-flange beams of a special extruded I-section of 27ST aluminum alloy were tested in pure bending. Complete end fixity was not attained. Loading was continued until a definite maximum value had been reached. Tensile tests were made on specimens cut from the flanges and the web of each beam. Compressive stress-strain characteristics were determined by pack compression tests on specimens cut from the flanges. Values computed from an equation previously suggested by one of the authors for the critical stress at which such beams become unstable were found to be in good agreement with values computed from experimentally determined critically bending moments.

Effects of fiber, matrix, and interphase on carbon fiber composite compression strength

NASA Technical Reports Server (NTRS)

Nairn, John A.; Harper, Sheila I.; Bascom, Willard D.

1994-01-01

The major goal of this project was to obtain basic information on compression failure properties of carbon fiber composites. To do this, we investigated fiber effects, matrix effects, and fiber/matrix interface effects. Using each of nine fiber types, we prepared embedded single-fiber specimens, single-ply specimens, and full laminates. From the single-fiber specimens, in addition to the standard fragmentation test analysis, we were able to use the low crack density data to provide information about the distribution of fiber flaws. The single-ply specimens provided evidence of a correlation between the size of kink band zones and the quality of the interface. Results of the laminate compression experiments mostly agreed with the results from single-ply experiments, although the ultimate compression strengths of laminates were higher. Generally, these experiments showed a strong effect of interfacial properties. Matrix effects were examined using laminates subjected to precracking under mixed-mode loading conditions. A large effect of precracking conditions on the mode 1 toughness of the laminates was found. In order to control the properties of the fiber/matrix interface, we prepared composites of carbon fiber and polycarbonate and subjected these to annealing. The changes in interfacial properties directly correlated with changes in compression strength.

High Pressure Compression-Molding of α-Cellulose and Effects of Operating Conditions.

PubMed

Pintiaux, Thibaud; Viet, David; Vandenbossche, Virginie; Rigal, Luc; Rouilly, Antoine

2013-05-30

Commercial α-cellulose was compression-molded to produce 1A dog-bone specimens under various operating conditions without any additive. The resulting agromaterials exhibited a smooth, plastic-like surface, and constituted a suitable target as replacement for plastic materials. Tensile and three-points bending tests were conducted according to ISO standards related to the evaluation of plastic materials. The specimens had strengths comparable to classical petroleum-based thermoplastics. They also exhibited high moduli, which is characteristic of brittle materials. A higher temperature and higher pressure rate produced specimens with higher mechanical properties while low moisture content produced weaker specimens. Generally, the strong specimen had higher specific gravity and lower moisture content. However, some parameters did not follow the general trend e.g., thinner specimen showed much higher Young's Modulus, although their specific gravity and moisture content remained similar to control, revealing a marked skin-effect which was confirmed by SEM observations.

High Pressure Compression-Molding of α-Cellulose and Effects of Operating Conditions

PubMed Central

Pintiaux, Thibaud; Viet, David; Vandenbossche, Virginie; Rigal, Luc; Rouilly, Antoine

2013-01-01

Commercial α-cellulose was compression-molded to produce 1A dog-bone specimens under various operating conditions without any additive. The resulting agromaterials exhibited a smooth, plastic-like surface, and constituted a suitable target as replacement for plastic materials. Tensile and three-points bending tests were conducted according to ISO standards related to the evaluation of plastic materials. The specimens had strengths comparable to classical petroleum-based thermoplastics. They also exhibited high moduli, which is characteristic of brittle materials. A higher temperature and higher pressure rate produced specimens with higher mechanical properties while low moisture content produced weaker specimens. Generally, the strong specimen had higher specific gravity and lower moisture content. However, some parameters did not follow the general trend e.g., thinner specimen showed much higher Young’s Modulus, although their specific gravity and moisture content remained similar to control, revealing a marked skin-effect which was confirmed by SEM observations. PMID:28809271

Concepts for improving the damage tolerance of composite compression panels

NASA Technical Reports Server (NTRS)

Rhodes, M. D.; Williams, J. G.

1981-01-01

The results of an experimental evaluation of graphite-epoxy composite compression panel impact damage tolerance and damage propagation arrest concepts are reported. The tests were conducted on flat plate specimens and blade-stiffened structural panels such as those used in commercial aircraft wings, and the residual strength of damaged specimens and their sensitivity to damage while subjected to in-plane compression loading were determined. Results suggest that matrix materials that fail by delamination have the lowest damage tolerance, and it is concluded that alternative matrix materials with transverse reinforcement to suppress the delamination failure mode and yield the higher-strain value transverse shear crippling mode should be developed.

PRELIMINARY RESULTS OF THE AGC-4 IRRADIATION IN THE ADVANCED TEST REACTOR AND DESIGN OF AGC-5 (HTR16-18469)

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

Davenport, Michael; Petti, D. A.

The United States Department of Energy’s Advanced Reactor Technologies (ART) Program will irradiate up to six nuclear graphite creep experiments in the Advanced Test Reactor (ATR) located at the Idaho National Laboratory (INL). The graphite experiments are being irradiated over an approximate eight year period to support development of a graphite irradiation performance data base on the new nuclear grade graphites now available for use in high temperature gas reactors. The goals of the irradiation experiments are to obtain irradiation performance data, including irradiation creep, at different temperatures and loading conditions to support design of the Very High Temperature Gasmore » Reactor (VHTR), as well as other future gas reactors. The experiments each consist of a single capsule that contain six stacks of graphite specimens, with half of the graphite specimens in each stack under a compressive load, while the other half of the specimens are not be subjected to a compressive load during irradiation. The six stacks have differing compressive loads applied to the top half of diametrically opposite pairs of specimen stacks. A seventh specimen stack in the center of the capsule does not have a compressive load. The specimens are being irradiated in an inert sweep gas atmosphere with on-line temperature and compressive load monitoring and control. There are also samples taken of the sweep gas effluent to measure any oxidation or off-gassing of the specimens that may occur during initial start-up of the experiment. The first experiment, AGC-1, started its irradiation in September 2009, and the irradiation was completed in January 2011. The second experiment, AGC-2, started its irradiation in April 2011 and completed its irradiation in May 2012. The third experiment, AGC-3, started its irradiation in late November 2012 and completed in the April of 2014. AGC-4 is currently being irradiated in the ATR. This paper will briefly discuss the preliminary irradiation results of the AGC-4 experiment, as well as the design of AGC-5.« less

The dynamic properties behavior of high strength concrete under different strain rate

NASA Astrophysics Data System (ADS)

Abdullah, Hasballah; Husin, Saiful; Umar, Hamdani; Rizal, Samsul

2005-04-01

This paper present a number experimental data and numerical technique used in the dynamic behavior of high strength concrete. A testing device is presented for the experimental study of dynamic behavior material under high strain rates. The specimen is loaded by means of a high carbon steel Hopkinson pressure bar (40 mm diameter, 3000 mm long input bar and 1500 mm long out put bar) allowing for the testing of specimen diameter is large enough in relation to the size of aggregates. The other method also proposed for measuring tensile strength, the measurement method based on the superposition and concentration of tensile stress wave reflected both from the free-free ends of striking bar and the specimen bar. The compression Hopkinson bar test, the impact tensile test of high strength concrete bars are performed, together with compression static strength test. In addition, the relation between break position under finite element simulation and impact tensile strength are examined. The three-dimensional simulation of the specimen under transient loading are presented and comparisons between the experimental and numerical simulation on strain rate effects of constitutive law use in experimental are study.

In Situ Elevated Temperature Testing of Fly Ash Based Geopolymer Composites.

PubMed

Vickers, Les; Pan, Zhu; Tao, Zhong; van Riessen, Arie

2016-06-03

In situ elevated temperature investigations using fly ash based geopolymers filled with alumina aggregate were undertaken. Compressive strength and short term creep tests were carried out to determine the onset temperature of viscous flow. Fire testing using the standard cellulose curve was performed. Applying a load to the specimen as the temperature increased reduced the temperature at which viscous flow occurred (compared to test methods with no applied stress). Compressive strength increased at the elevated temperature and is attributed to viscous flow and sintering forming a more compact microstructure. The addition of alumina aggregate and reduction of water content reduced the thermal conductivity. This led to the earlier onset and shorter dehydration plateau duration times. However, crack formation was reduced and is attributed to smaller thermal gradients across the fire test specimen.

Effects of Strain Rate on Compressive Properties in Bimodal 7075 Al-SiCp Composite

NASA Astrophysics Data System (ADS)

Lee, Hyungsoo; Choi, Jin Hyeok; Jo, Min Chul; Jo, Ilguk; Lee, Sang-Kwan; Lee, Sunghak

2018-07-01

A 7075 Al alloy matrix composite reinforced with SiC particulates (SiCps) whose sizes were 10 and 30 μm, i.e., a bimodal Al-SiCp composite, was made by a liquid pressing process, and its quasi-static and dynamic compressive properties were evaluated by using a universal testing machine and a split Hopkinson pressure bar, respectively. Mg-Si-, Al-Fe-, and Cu-rich intermetallic compounds existed inside the Al matrix, but might not deteriorate compressive properties because of their low volume fraction (about 2.6%) which was much lower than that of SiCp. The dynamic compressive strength was higher than the quasi-static strength, and was higher in the specimen tested at 2800 s-1 than in the specimen tested at 1400 s-1 according to the strain-rate hardening. For explaining the strain data, the blocking extent of crack propagation by the Al matrix was quantitatively examined. The melting of Al matrix occurred by adiabatic heating was favorable for the improvement in compressive strain because it favorably worked for activating the shear band formation and for blocking the crack propagation, thereby leading to the excellent compressive strain (10.9-11.6%) as well as maximum compressive strength (1057-1147 MPa). Thus, the present bimodal 7075 Al-SiCp composite provides a promise for new applications to high-performance armor plates.

Effects of Strain Rate on Compressive Properties in Bimodal 7075 Al-SiCp Composite

NASA Astrophysics Data System (ADS)

Lee, Hyungsoo; Choi, Jin Hyeok; Jo, Min Chul; Jo, Ilguk; Lee, Sang-Kwan; Lee, Sunghak

2018-03-01

A 7075 Al alloy matrix composite reinforced with SiC particulates (SiCps) whose sizes were 10 and 30 μm, i.e., a bimodal Al-SiCp composite, was made by a liquid pressing process, and its quasi-static and dynamic compressive properties were evaluated by using a universal testing machine and a split Hopkinson pressure bar, respectively. Mg-Si-, Al-Fe-, and Cu-rich intermetallic compounds existed inside the Al matrix, but might not deteriorate compressive properties because of their low volume fraction (about 2.6%) which was much lower than that of SiCp. The dynamic compressive strength was higher than the quasi-static strength, and was higher in the specimen tested at 2800 s-1 than in the specimen tested at 1400 s-1 according to the strain-rate hardening. For explaining the strain data, the blocking extent of crack propagation by the Al matrix was quantitatively examined. The melting of Al matrix occurred by adiabatic heating was favorable for the improvement in compressive strain because it favorably worked for activating the shear band formation and for blocking the crack propagation, thereby leading to the excellent compressive strain (10.9-11.6%) as well as maximum compressive strength (1057-1147 MPa). Thus, the present bimodal 7075 Al-SiCp composite provides a promise for new applications to high-performance armor plates.

Shear compression testing of glass-fibre steel specimens after 4K reactor irradiation: Present status and facility upgrade

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

Gerstenberg, H.; Kraehling, E.; Katheder, H.

1997-06-01

The shear strengths of various fibre reinforced resins being promising candidate insulators for superconducting coils to be used tinder a strong radiation load, e.g. in future fusion reactors were investigated prior and subsequent to reactor in-core irradiation at liquid helium temperature. A large number of sandwich-like (steel-bonded insulation-steel) specimens representing a widespread variety of materials and preparation techniques was exposed to irradiation doses of up to 5 x 10{sup 7} Gy in form of fast neutrons and {gamma}-radiation. In a systematic study several experimental parameters including irradiation dose, postirradiation storage temperature and measuring temperature were varied before the determination ofmore » the ultimate shear strength. The results obtained from the different tested materials are compared. In addition an upgrade of the in-situ test rig installed at the Munich research reactor is presented, which allows combined shear/compression loading of low temperature irradiated specimens and provides a doubling of the testing rate.« less

Contribution of collagen fibers to the compressive stiffness of cartilaginous tissues.

PubMed

Römgens, Anne M; van Donkelaar, Corrinus C; Ito, Keita

2013-11-01

Cartilaginous tissues such as the intervertebral disk are predominantly loaded under compression. Yet, they contain abundant collagen fibers, which are generally assumed to contribute to tensile loading only. Fiber tension is thought to originate from swelling of the proteoglycan-rich nucleus. However, in aged or degenerate disk, proteoglycans are depleted, whereas collagen content changes little. The question then rises to which extend the collagen may contribute to the compressive stiffness of the tissue. We hypothesized that this contribution is significant at high strain magnitudes and that the effect depends on fiber orientation. In addition, we aimed to determine the compression of the matrix. Bovine inner and outer annulus fibrosus specimens were subjected to incremental confined compression tests up to 60 % strain in radial and circumferential direction. The compressive aggregate modulus was determined per 10 % strain increment. The biochemical composition of the compressed specimens and uncompressed adjacent tissue was determined to compute solid matrix compression. The stiffness of all specimens increased nonlinearly with strain. The collagen-rich outer annulus was significantly stiffer than the inner annulus above 20 % compressive strain. Orientation influenced the modulus in the collagen-rich outer annulus. Finally, it was shown that the solid matrix was significantly compressed above 30 % strain. Therefore, we concluded that collagen fibers significantly contribute to the compressive stiffness of the intervertebral disk at high strains. This is valuable for understanding the compressive behavior of collagen-reinforced tissues in general, and may be particularly relevant for aging or degenerate disks, which become more fibrous and less hydrated.

An experimental study on fracture mechanical behavior of rock-like materials containing two unparallel fissures under uniaxial compression

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Tian, Wen-Ling; Zeng, Wei; Yu, Li-Yuan

2016-06-01

Strength and deformability characteristics of rock with pre-existing fissures are governed by cracking behavior. To further research the effects of pre-existing fissures on the mechanical properties and crack coalescence process, a series of uniaxial compression tests were carried out for rock-like material with two unparallel fissures. In the present study, cement, quartz sand, and water were used to fabricate a kind of brittle rock-like material cylindrical model specimen. The mechanical properties of rock-like material specimen used in this research were all in good agreement with the brittle rock materials. Two unparallel fissures (a horizontal fissure and an inclined fissure) were created by inserting steel during molding the model specimen. Then all the pre-fissured rock-like specimens were tested under uniaxial compression by a rock mechanics servo-controlled testing system. The peak strength and Young's modulus of pre-fissured specimen all first decreased and then increased when the fissure angle increased from 0° to 75°. In order to investigate the crack initiation, propagation and coalescence process, photographic monitoring was adopted to capture images during the entire deformation process. Moreover, acoustic emission (AE) monitoring technique was also used to obtain the AE evolution characteristic of pre-fissured specimen. The relationship between axial stress, AE events, and the crack coalescence process was set up: when a new crack was initiated or a crack coalescence occurred, the corresponding axial stress dropped in the axial stress-time curve and a big AE event could be observed simultaneously. Finally, the mechanism of crack propagation under microscopic observation was discussed. These experimental results are expected to increase the understanding of the strength failure behavior and the cracking mechanism of rock containing unparallel fissures.

Collaborative analysis of wheat endosperm compressive material properties

USDA-ARS?s Scientific Manuscript database

The objective measurement of cereal endosperm texture, for wheat (Triticum L.) in particular, is relevant to the milling, processing and utilization of grain. The objective of this study was to evaluate the inter-laboratory results of compression failure testing of wheat endosperm specimens of defi...

Experimental investigation of graphite/polyimide sandwich panels in edgewise compression

NASA Technical Reports Server (NTRS)

Camarda, C. J.

1980-01-01

The local and general buckling behavior of graphite/polyimide sandwich panels simply supported along all four edges and loaded in uniaxial edgewise compression was investigated. Material properties of adhesive and facings were determined from flatwise tension and sandwich beam flexure tests. Tensile and compressive material properties of the facings were determined at 116, R.T., and 589 K (-250, R.T., and 600 F) using the sandwich beam flexure test method. Results indicate that Gr/PI is a usable structural material for short term use at temperatures as high as 589 K (600 F). Buckling specimens were 30.5 X 33.0 cm (12 x 13 in.), had quasi-isotropic symmetric facings and a glass/polyimide honeycomb core. Core thicknesses varied and three panels of each thickness were tested in edgewise compression at room temperature to investigate failure modes and corresponding buckling formulas. Specimens 0.635 cm (0.25 in.) thick failed by overall buckling at loads close to the analytically predicted buckling load; all other panels failed by face wrinkling. Results of the winkling tests indicate that several buckling formulas were unconservative and therefore not suitable for design purposes; recommended wrinkling equations are presented.

Hydromechanics in dentine: role of dentinal tubules and hydrostatic pressure on mechanical stress-strain distribution.

PubMed

Kishen, A; Vedantam, S

2007-10-01

This investigation is to understand the role of free water in the dentinal tubules on the mechanical integrity of bulk dentine. Three different experiments were conducted in this study. In experiment 1, three-dimensional models of dentine with gradient elastic modulus, homogenous elastic modulus, and with and without hydrostatic pressure were simulated using the finite element method. Static compressive loads of 15, 50 and 100 N were applied and the distribution of the principal stresses, von Mises stresses, and strains in loading direction were determined. In experiment 2, experimental compression testing of fully hydrated and partially dehydrated dentine (21 degrees C for 72 h) was conducted using a Universal testing machine. In experiment 3, Fourier transform infrared spectroscopic analysis of hydrated and partially dehydrated dentine was carried out. The finite element analysis revealed that the dentine model with simulated hydrostatic pressure displayed residual tensile stresses and strains in the inner region adjacent to the root canal. When external compressive loads were applied to the model, the residual stresses and strains counteracted the applied loads. Similarly the hydrated specimens subjected to experimental compression loads showed greater toughness when compared to the partially dehydrated specimens. The stress at fracture was significantly higher in partially dehydrated specimens (p=0.014), while the strain at fracture was significantly higher in hydrated dentine specimens (p=0.037). These experiments highlighted the distinct role of free water in the dentinal tubules and hydrostatic pressure on the stress-strain distribution within the bulk dentine.

An in vitro study to compare the transverse strength of thermopressed and conventional compression-molded polymethylmethacrylate polymers.

PubMed

Raut, Anjana; Rao, Polsani Laxman; Vikas, B V J; Ravindranath, T; Paradkar, Archana; Malakondaiah, G

2013-01-01

Acrylic resins have been in the center stage of Prosthodontics for more than half a century. The flexural fatigue failure of denture base materials is the primary mode of clinical failure. Hence there is a need for superior physical and mechanical properties. This in vitro study compared the transverse strength of specimens of thermopressed injection-molded and conventional compression-molded polymethylmethacrylate polymers and examined the morphology and microstructure of fractured acrylic specimens. The following denture base resins were examined: Brecrystal (Thermopressed injection-molded, modified polymethylmethacrylate) and Pyrax (compression molded, control group). Specimens of each material were tested according to the American Society for Testing and Materials standard D790-03 for flexural strength testing of reinforced plastics and subsequently examined under SEM. The data was analyzed with Student unpaired t test. Flexural strength of Brecrystal (82.08 ± 1.27 MPa) was significantly higher than Pyrax (72.76 ± 0.97 MPa). The tested denture base materials fulfilled the requirements regarding flexural strength (>65 MPa). The scanning electron microscopy image of Brecrystal revealed a ductile fracture with crazing. The fracture pattern of control group specimens exhibited poorly defined crystallographic planes with a high degree of disorganization. Flexural strength of Brecrystal was significantly higher than the control group. Brecrystal showed a higher mean transverse strength value of 82.08 ± 1.27 MPa and a more homogenous pattern at microscopic level. Based on flexural strength properties and handling characteristics, Brecrystal may prove to be an useful alternative to conventional denture base resins.

Designing a Uniaxial Tension/Compression Test for Springback Analysis in High-Strength Steel Sheets

PubMed Central

Stoudt, M. R.; Levine, L. E.; Ma, L.

2016-01-01

We describe an innovative design for an in-plane measurement technique that subjects thin sheet metal specimens to bidirectional loading. The goal of this measurement is to provide the critical performance data necessary to validate complex predictions of the work hardening behavior during reversed uniaxial deformation. In this approach, all of the principal forces applied to the specimen are continually measured in real-time throughout the test. This includes the lateral forces that are required to prevent out of plane displacements in the specimen that promote buckling. This additional information will, in turn, improve the accuracy of the compensation for the friction generated between the anti-bucking guides and the specimen during compression. The results from an initial series of experiments not only demonstrate that our approach is feasible, but that it generates data with the accuracy necessary to quantify the directionally-dependent changes in the yield behavior that occur when the strain path is reversed (i.e., the Bauschinger Effect). PMID:28133391

Analysis for delamination initiation in postbuckled dropped-ply laminates

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Johnson, Eric R.

1992-01-01

The compression strength of dropped-ply, graphite-epoxy laminated plates for the delamination mode of failure is studied by analysis and corroborated with experiments. The nonlinear response of the test specimens is modeled by a geometrically nonlinear finite element analysis. The methodology for predicting delamination is based on a quadratic interlaminar stress criterion evaluated at a characteristic distance from the ply drop-off. The compression strength of specimens exhibiting a linear response is greater than the compression strength of specimens with the same layup exhibiting a geometrically nonlinear response. The analyses for both linear and nonlinear response show that severe interlaminar stress gradients occur in the interfaces at the drop-off because of the thickness/stiffness discontinuity. However, these interlaminar stress distributions are altered in the geometrically nonlinear response such that, with increasing load, their growth at the center of the laminate is retarded while their growth near the unloaded supported edge is increased.

Compression of Composite Materials: A Review,

DTIC Science & Technology

1987-11-01

epoxy tension face, . and a plexiglass core under the specimen gage-section. A Kevlar /glass phenolic hybrid composite system was evaluated in the...epoxy [0116 specimens, S2/SP-250 7 glass/epoxy [0/±45/9012s specimens, Kevlar 285 weave/Cycom 4143 Aramid/epoxy specimens, unidirectional FP alumina...bundles tested erc- E-glass, T300 graphite, T700 graphite, P75 graphite, Kevlar 49, and FP alumina. " -1. They observed that bundle failure

In Situ Elevated Temperature Testing of Fly Ash Based Geopolymer Composites

PubMed Central

Vickers, Les; Pan, Zhu; Tao, Zhong; van Riessen, Arie

2016-01-01

In situ elevated temperature investigations using fly ash based geopolymers filled with alumina aggregate were undertaken. Compressive strength and short term creep tests were carried out to determine the onset temperature of viscous flow. Fire testing using the standard cellulose curve was performed. Applying a load to the specimen as the temperature increased reduced the temperature at which viscous flow occurred (compared to test methods with no applied stress). Compressive strength increased at the elevated temperature and is attributed to viscous flow and sintering forming a more compact microstructure. The addition of alumina aggregate and reduction of water content reduced the thermal conductivity. This led to the earlier onset and shorter dehydration plateau duration times. However, crack formation was reduced and is attributed to smaller thermal gradients across the fire test specimen. PMID:28773568

Design, fabrication and test of graphite/polyimide composite joints and attachments for advanced aerospace vehicles

NASA Technical Reports Server (NTRS)

1980-01-01

Principal program activities dealt with the literature survey, design of joint concepts, assessment of GR/PI material quality, fabrication of test panels and specimens, and small specimen testing. Bonded and bolted designs are presented for each of the four major attachment types. Quality control data are presented for prepreg Lots 2W4651 and 3W2020. Preliminary design allowables test results for tension tests and compression tests of laminates are also presented.

Non-destructive testing techniques for the forensic engineering investigation of reinforced concrete buildings.

PubMed

Hobbs, Brian; Tchoketch Kebir, Mohamed

2007-04-11

This study describes in detail the results of a laboratory investigation where the compressive strength of 150mm side-length cubes was evaluated. Non-destructive testing (NDT) was carried out using ultrasonic pulse velocity (UPV) and impact rebound hammer (IRH) techniques to establish a correlation with the compressive strengths of compression tests. To adapt the Schmidt hammer apparatus and the ultrasonic pulse velocity tester to the type of concrete used in Algeria, concrete mix proportions that are recommended by the Algerian code were chosen. The resulting correlation curve for each test is obtained by changing the level of compaction, water/cement ratio and concrete age of specimens. Unlike other works, the research highlights the significant effect of formwork material on surface hardness of concrete where two different mould materials for specimens were used (plastic and wood). A combined method for the above two tests, reveals an improvement in the strength estimation of concrete. The latter shows more improvement by including the concrete density. The resulting calibration curves for strength estimation were compared with others from previous published literature.

Effect of compression load and temperature on thermomechanical tests for gutta-percha and Resilon®.

PubMed

Tanomaru-Filho, M; Silveira, G F; Reis, J M S N; Bonetti-Filho, I; Guerreiro-Tanomaru, J M

2011-11-01

To analyse a method used to evaluate the thermomechanical properties of gutta-percha and Resilon(®) at different temperatures and compression loads. Two hundred and seventy specimens measuring 10 mm in diameter and 1.5 mm in height were made from the following materials: conventional gutta-percha (GCO), thermoplastic gutta-percha (GTP) and Resilon(®) cones (RE). After 24 h, the specimens were placed in water at 50 °C, 60 °C or 70 °C for 60 s. After that, specimens were placed between two glass slabs, and loads weighing 1.0, 3.0 or 5.0 kg were applied. Images of the specimens were digitized before and after the test and analysed using imaging software to determine their initial and final areas. The thermomechanical property of each material was determined by the difference between the initial and final areas of the specimens. Data were subjected to anova and SNK tests at 5% significance. To verify a possible correlation between the results of the materials, linear regression coefficients (r) were calculated. Data showed higher flow area values for RE under all compression loads at 70 °C and under the 5.0 kg load at 60 °C (P < 0.05). Regarding gutta-percha, GTP showed higher flow under loads weighing 3.0 and 5.0 kg, at 60 and 70 °C (P < 0.05). GCO presented higher flow at 70 °C with a load of 5.0 kg. Regression analyses showed a poor linear correlation amongst the results of the materials under the different experimental conditions. Gutta-percha and Resilon(®) cones require different compression loads and temperatures for evaluation of their thermomechanical properties. For all materials, the greatest flow occurred at 70 °C under a load of 5.0 kg; therefore, these parameters may be adopted when evaluating endodontic filling materials. © 2011 International Endodontic Journal.

Characterization of commercial rigid polyurethane foams used as bone analogs for implant testing.

PubMed

Calvert, Kayla L; Trumble, Kevin P; Webster, Thomas J; Kirkpatrick, Lynn A

2010-05-01

Mechanical properties and microstructure characterization of a series of graded commercial rigid polyurethane foams commonly used to mimic trabecular bone in testing orthopaedic devices is reported. Compressive testing conducted according to ASTM standard F1839-08, which requires large specimens (50.8 mm x 50.8 mm x 25.4 mm blocks) gave elastic modulus and compressive strength values ranging from 115 to 794 MPa and 4.7 to 24.7 MPa, respectively, for foams having densities of 0.240-0.641 g/cm(3). All these results were within the requirements of the specification for the corresponding grades. Compression testing using smaller specimens (7.5 mm diameter x 15 mm) typical of testing bone, gave results in good agreement with those obtained in the standard tests. Microstructural measurements showed the average pore size ranged from 125 to 234 microm for densities ranging from 0.641 to 0.159 g/cm(3), respectively. The relative modulus as a function of relative density of the foams fit well to the model of Gibson and Ashby. Cyclic testing revealed hysteresis in the lower density foams with a loading modulus statistically equivalent to that measured in monotonic testing. Shore DO durometry (hardness) measurements show good correlations to elastic modulus and compressive strength. The results suggest additional parameters to consider for the evaluation of polyurethane foams for bone analog applications.

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

Song, Bo; Nelson, Kevin; Lipinski, Ronald J.

Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-temperature high-strain-rate performance are needed for understanding high-speed impacts in severe elevated-temperature environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain-rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. Current high-temperature Kolsky compression bar techniques are not capable of obtaining satisfactory high-temperature high-strain-rate stress-strain response of thin iridium specimens investigated in this study. We analyzedmore » the difficulties encountered in high-temperature Kolsky compression bar testing of thin iridium alloy specimens. Appropriate modifications were made to the current high-temperature Kolsky compression bar technique to obtain reliable compressive stress-strain response of an iridium alloy at high strain rates (300 – 10000 s -1) and temperatures (750°C and 1030°C). Uncertainties in such high-temperature high-strain-rate experiments on thin iridium specimens were also analyzed. The compressive stress-strain response of the iridium alloy showed significant sensitivity to strain rate and temperature.« less

Compressive strength performance of OPS lightweight aggregate concrete containing coal bottom ash as partial fine aggregate replacement

NASA Astrophysics Data System (ADS)

Muthusamy, K.; Mohamad Hafizuddin, R.; Mat Yahaya, F.; Sulaiman, M. A.; Syed Mohsin, S. M.; Tukimat, N. N.; Omar, R.; Chin, S. C.

2018-04-01

Concerns regarding the negative impact towards environment due to the increasing use of natural sand in construction industry and dumping of industrial solid wastes namely coal bottom ash (CBA) and oil palm shell (OPS) has resulted in the development of environmental friendly lightweight concrete. The present study investigates the effect of coal bottom ash as partial fine aggregate replacement towards workability and compressive strength of oil palm shell lightweight aggregate concrete (OPS LWAC). The fresh and mechanical properties of this concrete containing various percentage of coal bottom ash as partial fine aggregate replacement were investigated. The result was compared to OPS LWAC with 100 % sand as a control specimen. The concrete workability investigated by conducting slump test. All specimens were cast in form of cubes and water cured until the testing age. The compressive strength test was carried out at 7 and 28 days. The finding shows that integration of coal bottom ash at suitable proportion enhances the strength of oil palm shell lightweight aggregate concrete.

Substantial vertebral body osteophytes protect against severe vertebral fractures in compression

PubMed Central

Aubin, Carl-Éric; Chaumoître, Kathia; Mac-Thiong, Jean-Marc; Ménard, Anne-Laure; Petit, Yvan; Garo, Anaïs; Arnoux, Pierre-Jean

2017-01-01

Recent findings suggest that vertebral osteophytes increase the resistance of the spine to compression. However, the role of vertebral osteophytes on the biomechanical response of the spine under fast dynamic compression, up to failure, is unclear. Seventeen human spine specimens composed of three vertebrae (from T5-T7 to T11-L1) and their surrounding soft tissues were harvested from nine cadavers, aged 77 to 92 years. Specimens were imaged using quantitative computer tomography (QCT) for medical observation, classification of the intervertebral disc degeneration (Thomson grade) and measurement of the vertebral trabecular density (VTD), height and cross-sectional area. Specimens were divided into two groups (with (n = 9) or without (n = 8) substantial vertebral body osteophytes) and compressed axially at a dynamic displacement rate of 1 m/s, up to failure. Normalized force-displacement curves, videos and QCT images allowed characterizing failure parameters (force, displacement and energy at failure) and fracture patterns. Results were analyzed using chi-squared tests for sampling distributions and linear regression for correlations between VTD and failure parameters. Specimens with substantial vertebral body osteophytes present higher stiffness (2.7 times on average) and force at failure (1.8 times on average) than other segments. The presence of osteophytes significantly influences the location, pattern and type of fracture. VTD was a good predictor of the dynamic force and energy at failure for specimens without substantial osteophytes. This study also showed that vertebral body osteophytes provide a protective mechanism to the underlying vertebra against severe compression fractures. PMID:29065144

The Effects of Compressive Preloads on the Compression-After-Impact Strength of Carbon/Epoxy

NASA Technical Reports Server (NTRS)

Nettles, Alan T.

1994-01-01

A fixture to apply compressive loads to composite specimens during an impact event was used to assess the effect of prestresses on the compression-after-impact (CAI) strength of 16 ply quasi-isotropic carbon/epoxy test coupons. Advanced design of experiments techniques were used to evaluate a range of prestresses and impact energies on two material systems, T300/934 and IM7/8551-7. An instrumented drop tower supplied impact energies between 1 and 9 Joules for the T300/934 material and between 4 and 16 Joules for the IM7/8551-7 material. The prestress values varied between a low of 5.7 Wa and a high of 287 NDa. Results showed some change in CAI strength that could be attributed to the prestresses on the specimens.

The effects of compressive preloads on the compression-after-impact strength of carbon/epoxy

NASA Technical Reports Server (NTRS)

Nettles, A. T.; Lance, D. G.

1992-01-01

A preloading device was used to examine the effects of compressive prestress on the compression-after-impact (CAI) strength of 16-ply, quasi-isotropic carbon epoxy test coupons. T300/934 material was evaluated at preloads from 200 to 4000 lb at impact energies from 1 to 9 joules. IM7/8551-7 material was evaluated at preloads from 4000 to 10,000 lb at impact energies from 4 to 16 joules. Advanced design of experiments methodology was used to design and evaluate the test matrices. The results showed that no statistically significant change in CAI strength could be contributed to the amount of compressive preload applied to the specimen.

Experimental investigation of time dependent behavior of welded Topopah Spring Tuff

NASA Astrophysics Data System (ADS)

Ma, Lumin

Four types of laboratory tests have been performed. Specimens were attained from four lithophysal zones of the welded Topopah Spring Tuff unit at Yucca Mountain, Nevada: upper lithophysal, middle nonlithophysal, lower lithophysal and lower nonlithophysal zones. Two types of tests are conducted to study time-dependent behavior: constant strain rate and creep tests. Sixty-five specimens from the middle nonlithophysal zone were tested at six strain rates: 10-2, 10-4, 10-5, 10-6, 10-7, and 10-8 s-1. Test durations range from 2 seconds to 7 days. Fourteen specimens from middle nonlithophysal, lower lithophysal and lower nonlithophysal zones are creep tested by incremental stepwise loading. All the tests are conducted under uniaxial compression at room temperature and humidity. Specimens exhibit extremely brittle fracture and fail by axial splitting, and show very little dilatancy if any. It is assumed that microfracturing dominates the inelastic deformation and failure of the tuff. Nonlinear regression is applied to the results of the constant strain rate tests to estimate the relations between peak strength, peak axial strain, secant modulus and strain rate. All three these parameters decrease with a decrease of strain rate and follow power functions: sigmapeak = 271.37 3˙0.0212 0.0212, epsilonpeak = 0.006 3˙0.0083 , ES = 41985.4 3˙0.015 . Secant modulus is introduced mainly as a tool to analyze strain rate dependent axial strain. Two threshold stresses define creep behavior. Below about 50% of peak strength, a specimen does not creep. Above about 94% of peak strength, a specimen creeps at an accelerating rate. Between the two threshold stresses, a power law relates strain rate and stress. One hundred fifty-eight Brazilian (Indirect tensile splitting) tests have been performed at six different constant strain rates. Nineteen lithophysal specimens were tested in uniaxial compression to study their fracture pattern. These specimens have a far less brittle failure mode. They slowly crumble, collapse, and maintain considerable relative strength beyond the peak. Due to the presence of multiple relatively large lithophysal cavities, they are far weaker and softer than the nonlithophysal specimens.

Morphological and mechanical characterization of composite bone cement containing polymethylmethacrylate matrix functionalized with trimethoxysilyl and bioactive glass.

PubMed

Puska, Mervi; Moritz, Niko; Aho, Allan J; Vallittu, Pekka K

2016-06-01

Medical polymers of biostable nature (e.g. polymethylmetacrylate, PMMA) are widely used in various clinical applications. In this study, novel PMMA-based composite bone cement was prepared. Bioactive glass (BAG) particulate filler (30wt%) was added to enhance potentially the integration of bone to the cement. The polymer matrix was functionalized with trimethoxysilyl to achieve an interfacial bond between the matrix and the fillers of BAG. The amount of trimethoxysilyl in the monomer system varied from 0 to 75wt%. The effects of dry and wet (simulated body fluid, SBF at +37°C for 5 weeks) conditions were investigated. In total, 20 groups of specimens were prepared. The specimens were subjected to a destructive mechanical test in compression. Scanning electron microscopy (SEM) and micro-computed tomography (micro-CT) were used to study the surface and the three-dimensional morphology of the specimens. The results of the study indicated that the addition of trimethoxysilyl groups led to the formation of a hybrid polymer matrix which, in lower amounts (<10wt% of total weight), did not significantly affect the compression properties. However, when the specimens stored in dry and wet conditions were compared, the water sorption increased the compression strength (~5-10MPa per test group). At the same time, the water sorption also caused an evident porous structure formation for the specimens containing BAG and siloxane formation in the hybrid polymer matrix. Copyright © 2015 Elsevier Ltd. All rights reserved.

Apparatus for Testing Flat Specimens of Thermal Insulation

NASA Technical Reports Server (NTRS)

Fesmire, James E.; Augustynowicz, Stanislaw D.

2005-01-01

An apparatus has been developed to implement an improved method of testing flat-plate specimens of thermal-insulation materials for cryogenic application. The method includes testing under realistic use conditions that could include vacuum and mechanical loading at a pressure up to 70 psi (=0.48 MPa). The apparatus can accommodate a rigid or flexible specimen having thickness up to 1.25 in. (=3.2 cm) and diameters between 6 and 10 in. (about 15.2 and 25.4 cm, respectively). Typical test conditions include boundary temperatures between 77 K and 373 K and vacuum/interstitial gas filling at a pressure between 10(exp -6) torr (=1.3 x 10(exp -4) Pa) and 760 torr (atmospheric pressure =0.1 MPa). The interstitial gas could be N2, He, CO2, or any other suitable gas to which the insulation is expected to be exposed in use. Relative to prior apparatuses and testing methods, this apparatus and the testing method that it implements offer advantages of relative simplicity and ease of use. The basic principle of operation of the apparatus is that of boil-off calorimetry, using liquid nitrogen or any other suitable liquid that boils at a desired temperature below ambient temperature. Comparative rates of flow of heat through the thicknesses of the specimens (heat-leak rates) and apparent-thermal-conductivity values are obtained from tests of specimens. Absolute values of heat-leak rates and apparent thermal conductivities are computed from a combination of (1) the aforementioned comparative values and (2) calibration factors obtained by testing reference specimens of materials that have known thermal-insulation properties. The apparatus includes a full complement of temperature sensors, a vacuum pump and chamber, a monitoring and control system, and tools and fixtures that enable rapid and reliable installation and removal of specimens. A specimen is installed at the bottom of the vacuum chamber, and a cold-mass assembly that includes a tank is lowered into position above and around the specimen (see figure). A spring-based compensating fixture helps to ensure adequate thermal contact with possibly irregular specimen surfaces. For a high-compression test, the springs can be replaced with spacers. A flat circular load cell at the bottom of the chamber measures the compressive load on the specimen. Once the desired compressive-load, temperature, and vacuum/gas-filling conditions are established, testing begins. During a test, all measurements are recorded by use of a portable data-acquisition system and a computer. The total heat-leak rate is measured and calculated as the boil-off flow rate multiplied by the latent heat of vaporization. The parasitic heat leak (to the side of the specimen and to the top and side of the cold-mass tank) is reduced to a small fraction of the total heat leak by use of a combination of multilayer-insulation (MLI) shield rings, reflective film, a fiberglass/epoxy centering ring, and a bulk fill of aerogel beads. This combination eliminates the need for a cryogenic guard chamber used in a typical prior apparatus to reduce the parasitic heat leak.

Strain rate sensitivity of autoclaved aerated concrete from quasi-static regime to shock loading

NASA Astrophysics Data System (ADS)

Mespoulet, Jérôme; Plassard, Fabien; Hereil, Pierre Louis

2015-09-01

The quasi-static mechanical behavior of autoclaved aerated concrete is well-known and can be expressed as a function of its density. There are however not much studies dealing with its dynamic behavior and its damping ability when subjected to a mechanical shock or a blast. This study presents experimental results obtained at the Shock Physics Laboratory of THIOT INGENIERIE company. The test specimens are made of YTONG(TM ) cellular concrete with porosity in the range of 75 to 80%. Experimental tests cover a large strain rate amplitude (higher than 104 s-1) for specimens up to 250 mm. They were carried out with a small compression press and with two facilities dedicated to dynamic material characterization: JUPITER dynamic large press (2 MN, 3 ms rising time) and TITAN multi-caliber single-stage gas gun. Results in un-confined conditions show an increase of the compressive strength when strain rate increases (45% increase at 5.102 s-1) but dynamic tests induce damage early in the experiment. This competition between dynamic strength raise and specimen fracture makes the complete compaction curve determination not to be done in unconfined dynamic condition. A 25% increase of the compressive strength has been observed between unconfined and confined condition in Q.S. regime.

Damage mechanisms in bithermal and thermomechanical fatigue of Haynes 188

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; Halford, Gary R.

1992-01-01

Post failure fractographic and metallographic studies were conducted on Haynes 188 specimens fatigued under bithermal and thermomechanical loading conditions between 316 and 760 C. Bithermal fatigue specimens examined included those tested under high strain rate in-phase and out-phase, tensile creep in-phase, and compressive creep out-of-phase loading conditions. Specimens tested under in-phase and out-of-phase thermomechanical fatigue were also examined. The nature of failure mode (transgrandular versus intergranular), the topography of the fracture surface, and the roles of oxidation and metallurgical changes were studied for each type of bithermal and thermomechanical test.

Ply-level failure analysis of a graphite/epoxy laminate under bearing-bypass loading

NASA Technical Reports Server (NTRS)

Naik, R. A.; Crews, J. H., Jr.

1988-01-01

A combined experimental and analytical study was conducted to investigate and predict the failure modes of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Tests were conducted in a test machine that allowed the bearing-bypass load ratio to be controlled while a single-fastener coupon was loaded to failure in either tension or compression. Onset and ultimate failure modes and strengths were determined for each test case. The damage-onset modes were studied in detail by sectioning and micrographing the damaged specimens. A two-dimensional, finite-element analysis was conducted to determine lamina strains around the bolt hole. Damage onset consisted of matrix cracks, delamination, and fiber failures. Stiffness loss appeared to be caused by fiber failures rather than by matrix cracking and delamination. An unusual offset-compression mode was observed for compressive bearing-bypass laoding in which the specimen failed across its width along a line offset from the hole. The computed lamina strains in the fiber direction were used in a combined analytical and experimental approach to predict bearing-bypass diagrams for damage onset from a few simple tests.

Ply-level failure analysis of a graphite/epoxy laminate under bearing-bypass loading

NASA Technical Reports Server (NTRS)

Naik, R. A.; Crews, J. H., Jr.

1990-01-01

A combined experimental and analytical study was conducted to investigate and predict the failure modes of a graphite/epoxy laminate subjected to combined bearing and bypass loading. Tests were conducted in a test machine that allowed the bearing-bypass load ratio to be controlled while a single-fastener coupon was loaded to failure in either tension or compression. Onset and ultimate failure modes and strengths were determined for each test case. The damage-onset modes were studied in detail by sectioning and micrographing the damaged specimens. A two-dimensional, finite-element analysis was conducted to determine lamina strains around the bolt hole. Damage onset consisted of matrix cracks, delamination, and fiber failures. Stiffness loss appeared to be caused by fiber failures rather than by matrix cracking and delamination. An unusual offset-compression mode was observed for compressive bearing-bypass loading in which the specimen failed across its width along a line offset from the hole. The computed lamina strains in the fiber direction were used in a combined analytical and experimental approach to predict bearing-bypass diagrams for damage onset from a few simple tests.

Evaluation of the Behavior of Technova Corporation Rod-Stiffened Stitched Compression Specimens

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

2013-01-01

Under Space Act Agreement 1347 between NASA and Technova Corporation, Technova designed and fabricated two carbon-epoxy crippling specimens and NASA loaded them to failure in axial compression. Each specimen contained a pultruded rod stiffener which was held to the specimen skin with through-the-thickness stitches. One of these specimens was designed to be nominally the same as pultruded rod stitched specimens fabricated by Boeing under previous programs. In the other specimen, the rod was prestressed in a Technova manufacturing process to increase its ability to carrying compressive loading. Experimental results demonstrated that the specimen without prestressing carried approximately the same load as the similar Boeing specimens and that the specimen with prestressing carried significantly more load than the specimen without prestressing.

Compression After Impact Testing of Sandwich Structures Using the Four Point Bend Test

NASA Technical Reports Server (NTRS)

Nettles, Alan T.; Gregory, Elizabeth; Jackson, Justin; Kenworthy, Devon

2008-01-01

For many composite laminated structures, the design is driven by data obtained from Compression after Impact (CAI) testing. There currently is no standard for CAI testing of sandwich structures although there is one for solid laminates of a certain thickness and lay-up configuration. Most sandwich CAI testing has followed the basic technique of this standard where the loaded ends are precision machined and placed between two platens and compressed until failure. If little or no damage is present during the compression tests, the loaded ends may need to be potted to prevent end brooming. By putting a sandwich beam in a four point bend configuration, the region between the inner supports is put under a compressive load and a sandwich laminate with damage can be tested in this manner without the need for precision machining. Also, specimens with no damage can be taken to failure so direct comparisons between damaged and undamaged strength can be made. Data is presented that demonstrates the four point bend CAI test and is compared with end loaded compression tests of the same sandwich structure.

The compressive mechanical properties of diabetic and non-diabetic plantar soft tissue.

PubMed

Pai, Shruti; Ledoux, William R

2010-06-18

Diabetic subjects are at an increased risk of developing plantar ulcers. Knowledge of the physiologic compressive properties of the plantar soft tissue is critical to understanding the possible mechanisms of ulcer formation and improving treatment options. The purpose of this study was to determine the compressive mechanical properties of the plantar soft tissue in both diabetic and non-diabetic specimens from six relevant locations beneath the foot, namely the hallux (big toe), first, third, and fifth metatarsal heads, lateral midfoot, and calcaneus (heel). Cylindrical specimens (1.905 cm diameter) from these locations were excised and separated from the skin and bone from 4 diabetic and 4 non-diabetic age-matched, elderly, fresh-frozen cadaveric feet. Specimens were then subjected to biomechanically realistic strains of approximately 50% in compression using triangle wave tests conducted at five frequencies ranging from 1 to 10 Hz to determine tissue modulus, energy loss, and strain rate dependence. Diabetic vs. non-diabetic results across all specimens, locations, and testing frequencies demonstrated altered mechanical properties with significantly increased modulus (1146.7 vs. 593.0 kPa) but no change in energy loss (68.5 vs. 67.9%). All tissue demonstrated strain rate dependence and tissue beneath the calcaneus was found to have decreased modulus and energy loss compared to other areas. The results of this study could be used to generate material properties for all areas of the plantar soft tissue in diabetic or non-diabetic feet, with implications for foot computational modeling efforts and potentially for pressure alleviating footwear that could reduce plantar ulcer incidence. Published by Elsevier Ltd.

The compressive mechanical properties of diabetic and non-diabetic plantar soft tissue

PubMed Central

Pai, Shruti; Ledoux, William R.

2010-01-01

Diabetic subjects are at an increased risk of developing plantar ulcers. Knowledge of the physiologic compressive properties of the plantar soft tissue is critical to understanding possible mechanisms of ulcer formation and improving treatment options. The purpose of this study was to determine the compressive mechanical properties of the plantar soft tissue in both diabetic and non-diabetic specimens from six relevant locations beneath the foot, namely the hallux (big toe), first, third, and fifth metatarsal heads, lateral midfoot, and calcaneus (heel). Cylindrical specimens (1.905cm diameter) from these locations were excised and separated from the skin and bone from 4 diabetic and 4 non-diabetic age-matched, elderly, fresh-frozen cadaveric feet. Specimens were then subjected to biomechanically realistic strains of ∼50% in compression using triangle wave tests conducted at five frequencies ranging from 1 to 10 Hz to determine tissue modulus, energy loss, and strain rate dependence. Diabetic vs. non-diabetic results across all specimens, locations, and testing frequencies demonstrated altered mechanical properties with significantly increased modulus (1146.7 vs. 593.0kPa) but no change in energy loss (68.5 vs. 67.9%). All tissue demonstrated strain rate dependence and tissue beneath the calcaneus was found to have decreased modulus and energy loss compared to other areas. The results of this study could be used to generate material properties for all areas of the plantar soft tissue in diabetic or non-diabetic feet, with implications for foot computational modeling efforts and potentially for pressure alleviating footwear that could reduce plantar ulcer incidence. PMID:20207359

Analysis and testing of axial compression in imperfect slender truss struts

NASA Technical Reports Server (NTRS)

Lake, Mark S.; Georgiadis, Nicholas

1990-01-01

The axial compression of imperfect slender struts for large space structures is addressed. The load-shortening behavior of struts with initially imperfect shapes and eccentric compressive end loading is analyzed using linear beam-column theory and results are compared with geometrically nonlinear solutions to determine the applicability of linear analysis. A set of developmental aluminum clad graphite/epoxy struts sized for application to the Space Station Freedom truss are measured to determine their initial imperfection magnitude, load eccentricity, and cross sectional area and moment of inertia. Load-shortening curves are determined from axial compression tests of these specimens and are correlated with theoretical curves generated using linear analysis.

Biomechanical performance of rigid compared to dynamic anterior cervical plating: analysis of adjacent upper and lower level compressive forces.

PubMed

Connor, David E; Shamieh, Khader Samer; Ogden, Alan L; Mukherjee, Debi P; Sin, Anthony; Nanda, Anil

2012-12-01

Dynamic anterior cervical plating is well established as a means of enhancing graft loading and subsequent arthrodesis. Current concerns center on the degree of adjacent-level stress induced by these systems. The aim of this study was to evaluate and compare the load transferred to adjacent levels for single-level anterior cervical discectomy and fusion utilizing rigid compared to dynamic anterior plating systems. Nine cadaveric adult human cervical spine specimens were subjected to range-of-motion testing prior to and following C5-C6 anterior cervical discectomy and fusion procedures. Interbody grafting was performed with human fibula tissue. Nondestructive biomechanical testing included flexion/extension and lateral bending loading modes. A constant displacement of 5mm was applied in each direction and the applied load was measured in newtons (N). Specimens were tested in the following order: intact, following discectomy, after rigid plating, then after dynamic plating. Adjacent level (C4-C5 [L(S)] and C6-C7 [L(I)]) compressive forces were measured using low profile load cells inserted into each disc space. The measured load values for plating systems were then normalized using values measured for the intact specimens. Mean loads transferred to L(S) and L(I) during forced flexion in specimens with rigid plating were 23.47 N and 8.76 N, respectively; while the corresponding values in specimens with dynamic plating were 18.55 N and 1.03 N, respectively. Dynamic plating yielded no significant change at L(I) and a 21.0% decrease in load at L(S) when compared with rigid plating, although the difference was not significant. The observed trend suggests that dynamic plating may diminish superior adjacent level compressive stresses. Copyright © 2012 Elsevier Ltd. All rights reserved.

Neoprene pads for capping concrete cylinders.

DOT National Transportation Integrated Search

1979-01-01

The possibility of using neoprene pads as an alternate to sulfur mortar for capping concrete specimens subjected to compression tests was investigated. In preliminary tests to determine the feasibility of the investigation, two batches of concrete we...

Thermomechanical Testing and Microstructural Development of Class L Steel Wheel Alloy

DOT National Transportation Integrated Search

1994-03-01

Macrostructure, microstructure, and quantitative metallographic analysis is conducted on Association of American Railroads Class L wheel steel specimens tested in a Gleeble 1500 under combined mechanical compression and resistance heating to temperat...

Investigation of tension-compression fatigue behavior of a cross-ply metal matrix composite at room and elevated temperatures. Master's thesis

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

Boyum, E.A.

1993-12-01

This research, the first load-controlled tension-compression fatigue testing to be performed on a MMC, extends the existing knowledge of MMC fatigue damage mechanisms to include the tension compression loading condition. To accomplish this, a (0/90)2, SCS-6/Ti-15-3 laminate was subjected to tension-tension fatigue at room temperature, and tension-compression fatigue at both room temperature and 427 deg C. Stress and strain data was taken to evaluate the macro-mechanic behavior of the material. Microscopy and fractography were performed to characterize the damage on a micro-mechanic level. On a maximum applied stress basis, the room temperature tension-tension specimens had longer fatigue lives than themore » room temperature tension-compression specimens. The room and high temperature tension-compression fatigue lives were nearly identical in the fiber-dominated high stress region of the SN curve. However, the increased ductility and diffused plasticity of the titanium matrix at 427 deg C delayed the onset and severity of matrix cracking, and thus increased the elevated temperature fatigue lives in the matrix dominated region of the SN curve. In all cases, matrix damage initiated at reaction zone cracks which nucleated both matrix plasticity and matrix cracking. Metal matrix composite, Elevated temperature, Fatigue testing, Compression, Fully-reversed, Titanium, Silicon carbide.« less

Experimental Study of the Impact Damage on AN Al2O3-COATED Glass Under Stress

NASA Astrophysics Data System (ADS)

Suh, Chang-Min; Kim, Sung-Ho; Suh, Duck-Young

The impact damage of an Al2O3-coated soda-lime glass under tensile and compressive stress conditions was investigated by an impact test using a steel ball (2mm dia.). The size of the glass specimens was 40×40×5(mm). In order to change the porosity percent of each specimen, the target distance was set at 120mm and 70mm. Also, the effect of the thickness of the coating layer was shown by two amounts (100 μm and 50 μm). The velocity of the steel balls was set between 30 and 60m/s. After the impact test, the crack patterns and lengths were measured using a stereo-microscope. The tensile and compressive specimens were prepared by inflation and deflation of air pressure within a pressure vessel. It was confirmed that the crack length of the glass under tensile stress was longer than that of glass under compressive stress. Also, the optimum conditions were a target distance of 70mm and 100 μm of a coating thickness, thus resulting in a minimization of porosity percent and area.

Testing Ceramics for Diesel Engines

NASA Technical Reports Server (NTRS)

Schneider, H. W.

1985-01-01

Adaptation of diesel engine allows prestressed ceramic materials evaluated under realistic pressure, temperature, and stress without introducing extraneous stress. Ceramic specimen part of prechamber of research engine. Specimen held in place by clamp, introduces required axial compressive stress. Specimen -- cylindrical shell -- surrounded by chamber vented or pressurized to introduce requisite radial stress in ceramic. Pressure chamber also serves as safety shield in case speimen disintegrates. Materials under consideration as cylinder liners for diesel engines.

Formation of Gaps at the Specimen-Bar Interfaces in Numerical Simulations of Compression Hopkinson Bar Tests on Soft, Nearly Incompressible Materials

DTIC Science & Technology

2010-09-01

history of the axial stress at the S-TB interface is qualitatively and quantitatively similar, with the times delayed by about 1 s (see figure 12). In...average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed...the specimen and sufficiently short rise times to the final strain rate, small gaps formed at both the specimen-incident bar and the specimen

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

Evaluation of suitable porosity for sintered porous {beta}-tricalcium phosphate as a bone substitute

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

Park, Jin-Hong; Bae, Ji-Yong; Shim, Jaebum

2012-09-15

Structural and mechanical characterization is performed for sintered porous beta tricalcium phosphate ({beta}-TCP) to determine the appropriate porosity for use as a bone substitute. Four different types of porous {beta}-TCP specimen with different porosities are fabricated through a sintering process. For structural characterization, scanning electron microscopy and a Microfocus X-ray computed tomography system are used to investigate the pore openings on the specimen's surface, pore size, pore distribution, and pore interconnections. Compression tests of the specimens are performed, and mechanical properties such as the elastic modulus and compressive strength are obtained. Also, the geometric shape and volume of the {beta}-TCPmore » around the contact region of two pores, which need to be initially resolved after implantation in order to increase the size of the pore openings, are evaluated through simple calculations. The results show that porous {beta}-TCP with 42.1% porosity may be a suitable bone substitute candidate in terms of sustaining external loads, and inducing and cultivating bone cells. - Highlights: Black-Right-Pointing-Pointer Structural and mechanical characterization was performed for sintered porous {beta}-TCP specimens. Black-Right-Pointing-Pointer For structural characterization, SEM and Microfocus X-ray CT system were used. Black-Right-Pointing-Pointer For mechanical characterization, compression tests were performed. Black-Right-Pointing-Pointer Porous {beta}-TCP with 42.1% porosity may be a suitable bone substitute.« less

Interface bonding of shotcrete reinforced brick masonry assemblages, volume 1

NASA Astrophysics Data System (ADS)

Robinson, D. W.; Kahn, L. F.

1982-09-01

Nine 9 sq ft. shotcrete reinforced brick masonry assemblages and one 9 sq ft brick masonry control specimen were tested under a single reversed cycle diagonal compression load similar to the ASTM E519-74 testing procedures. The interface surface conditions, between the brick and shotcrete were varied. The surfaces of the single sythe of old brick were either dry, wet, or epoxy coated before application of the 3-inch reinforced shotcrete layer. Ultimate load capacities of the specimens were similar, however, specimens with epoxy-enhanced interfaces were the most ductile; the dry brick specimens showed interface bond failure immediately after the ultimate inplane load was attained.

On the mechanical characteristics of a self-setting calcium phosphate cement.

PubMed

Bimis, A; Canal, L P; Karalekas, D; Botsis, J

2017-04-01

To perform a mechanical characterization of a self-setting calcium phosphate cement in function of the immersion time in Ringer solution. Specimens of self-setting calcium phosphate cement were prepared from pure α-TCP powder. The residual strains developed during hardening stage were monitored using an embedded fiber Bragg grating sensor. Additionally, the evolution of the elastic modulus was obtained for the same time period by conducting low-load indentation tests. Micro-computed tomography as well as microscope-assisted inspections were employed to evaluate the porosity in the specimens. Moreover, diametral compression tests were conducted in wet and dried specimens to characterize the material strength. The volume of the estimated porosity and absorbed fluid mass, during the first few minutes of the material's exposure in a wet environment, coincide. The immersion in Ringer solution lead to a noticeable increase in the moduli values. The critical value of stresses obtained from the diametral compression tests were combined with the data from uniaxial compression tests, to suggest a Mohr-Coulomb failure criterion. This study presents different techniques to characterize a self-setting calcium phosphate cement and provides experimental data on porosity, mechanical properties and failure. The investigated material possessed an open porosity at its dried state with negligible residual strains and its Young's modulus, obtained from micro-indentation tests, increased with hardening time. The failure loci may be described by a Mohr-Coulomb criterion, characteristic of soil and rock materials. Copyright © 2017 Elsevier Ltd. All rights reserved.

A study on the dynamic behavior of the Meuse/Haute-Marne argillite

NASA Astrophysics Data System (ADS)

Cai, M.; Kaiser, P. K.; Suorineni, F.; Su, K.

Excavation of underground tunnels can be conducted by tunnel boring machines (TBM) or drill-and-blast. TBMs cause minimum damage to excavation walls. Blasting effects on excavation walls depend on the care with which the blasting is executed. For blast-induced damage in excavation walls, two issues have to be addressed: rate of loss of confinement (rate of excavation) and dynamic loading from wave propagation that causes both intended and unintended damage. To address these two aspects, laboratory dynamic tests were conducted for the determination of the dynamic properties of the Meuse/Haute-Marne argillite. In the present study, 17 tensile (Brazilian) and 15 compression split Hopkinson pressure bar (SHPB) tests were conducted. The test revealed that the dynamic strengths of the argillite are strain rate dependent. The average dynamic increase factors (ratio of dynamic strength to static strength) for tensile and compressive strength are about 3.3 and 2.4, respectively. A high-speed video camera was used to visualize the initiation of failure and subsequent deformation of the specimens. The direct compression specimens were found to deform and fail uniformly around the circumference of the specimen, by a spalling process. The SHPB Brazilian tests indicated that failure occurred in tension along the line of load application. Radial fractures were also observed. The test results can be used for the development of a dynamic constitutive model for the argillite for the prediction of damage in underground excavation utilizing the drill-and blast method.

Graphs of Soil Mechanics Tests in Orbit

NASA Technical Reports Server (NTRS)

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Comparison of mechanical compressive properties of commercial and autologous fibrin glues for tissue engineering applications.

PubMed

Cravens, Matthew G; Behn, Anthony W; Dragoo, Jason L

2017-11-01

Fibrin glues are widely used in orthopedic surgery as adhesives and hemostatic agents. We evaluated the compressive properties of selected fibrin glues in order to identify which are appropriate for tissue regeneration applications subject to compression. Uniaxial unconfined compression tests were performed on fibrin gels prepared from commercial and autologous products: (1) Evicel (Ethicon), (2) Tisseel (Baxter), (3) Angel (Arthrex), and (4) ProPlaz (Biorich). Cyclic loads were applied from 0 to 30% strain for 100cycles at 0.5Hz. Following cyclic testing, specimens were subjected to ramp displacement of 1% strain per second to 80% strain. Throughout cyclic loading, Evicel and Tisseel deformed (shortened) less than Angel at all but one time point, and deformed less than ProPlaz at cycles 10 and 20. The dynamic moduli, peak stress, and strain energy were significantly greater in Tisseel than all other groups. Evicel displayed significantly greater dynamic moduli, peak stress, and strain energy than Angel and ProPlaz. Following cyclic testing, Tisseel and Evicel were significantly less deformed than Angel. No specimens exhibited gross failure during ramp loading to 80% strain. Ramp loading trends mirrored those of cyclic loading. The tested commercial glues were significantly more resistant to compression than the autologous products. The compressive properties of Tisseel were approximately twice those of Evicel. All preparations displayed moduli multiple orders of magnitude less than that of native articular cartilage. We conclude that in knee surgeries requiring fibrin glue to undergo compression of daily activity, commercial products are preferable to autologous preparations from platelet-poor plasma, though both will deform significantly. Copyright © 2017 Elsevier Ltd. All rights reserved.

Creep of a Silicon Nitride Under Various Specimen/Loading Configurations

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Powers, Lynn M.; Holland, Frederic A.; Gyekenyesi, John P.; Holland, F. A. (Technical Monitor)

2000-01-01

Extensive creep testing of a hot-pressed silicon nitride (NC132) was performed at 1300 C in air using five different specimen/loading configurations, including pure tension, pure compression, four-point uniaxial flexure, ball-on-ring biaxial flexure, and ring-on-ring biaxial flexure. Nominal creep strain and its rate for a given nominal applied stress were greatest in tension, least in compression, and intermediate in uniaxial and biaxial flexure. Except for the case of compressive loading, nominal creep strain generally decreased with time, resulting in less-defined steady-state condition. Of the four different creep formulations - power-law, hyperbolic sine, step, redistribution models - the conventional power-law model still provides the most convenient and reasonable means to estimate simple, quantitative creep parameters of the material. Predictions of creep deformation for the case of multiaxial stress state (biaxial flexure) were made based on pure tension and compression creep data by using the design code CARES/Creep.

Determination of friction coefficient in unconfined compression of brain tissue.

PubMed

Rashid, Badar; Destrade, Michel; Gilchrist, Michael D

2012-10-01

Unconfined compression tests are more convenient to perform on cylindrical samples of brain tissue than tensile tests in order to estimate mechanical properties of the brain tissue because they allow homogeneous deformations. The reliability of these tests depends significantly on the amount of friction generated at the specimen/platen interface. Thus, there is a crucial need to find an approximate value of the friction coefficient in order to predict a possible overestimation of stresses during unconfined compression tests. In this study, a combined experimental-computational approach was adopted to estimate the dynamic friction coefficient μ of porcine brain matter against metal platens in compressive tests. Cylindrical samples of porcine brain tissue were tested up to 30% strain at variable strain rates, both under bonded and lubricated conditions in the same controlled environment. It was established that μ was equal to 0.09±0.03, 0.18±0.04, 0.18±0.04 and 0.20±0.02 at strain rates of 1, 30, 60 and 90/s, respectively. Additional tests were also performed to analyze brain tissue under lubricated and bonded conditions, with and without initial contact of the top platen with the brain tissue, with different specimen aspect ratios and with different lubricants (Phosphate Buffer Saline (PBS), Polytetrafluoroethylene (PTFE) and Silicone). The test conditions (lubricant used, biological tissue, loading velocity) adopted in this study were similar to the studies conducted by other research groups. This study will help to understand the amount of friction generated during unconfined compression of brain tissue for strain rates of up to 90/s. Copyright © 2012 Elsevier Ltd. All rights reserved.

Acoustic emission from trabecular bone during mechanical testing: the effect of osteoporosis and osteoarthritis.

PubMed

Leichter, I; Bivas, A; Margulies, J Y; Roman, I; Simkin, A

1990-01-01

This study examines the relation between the nature of acoustic emission signals emitted from cancellous bone under compression and the mechanical properties of the tissue. The examined bone specimens were taken from 12 normal, 31 osteoporotic and six osteoarthritic femoral heads. The mechanical behaviour of the osteoporotic bone specimens was found to be significantly different from that of the normal specimens both in the pre-yield and post-yield ranges. In the osteoarthritic bones only the elastic behaviour was significantly different. The rates of acoustic events before yield and beyond it were found to be significantly higher both in the osteoporotic and osteoarthritic bone specimens. The average peak amplitude of the signals was also significantly higher in the diseased bones. Stepwise regression analysis showed that a combination of the acoustic emission parameters could significantly predict some mechanical properties of the bone. The energy absorbed during compression and the ultimate compressive stress of the specimens could be estimated from the rate of pre-yield acoustic events, the average amplitude of the signals and the rate of post-yield events. However, the explanation power of the acoustic emission parameters was only moderate. The nature of acoustic emission signals was thus demonstrated to be a potential tool for assessing bone quality.

Column strength of magnesium alloy AM-57S

NASA Technical Reports Server (NTRS)

Holt, M

1942-01-01

Tests were made to determine the column strength of extruded magnesium alloy AM-57S. Column specimens were tested with round ends and with flat ends. It was found that the compressive properties should be used in computations for column strengths rather than the tensile properties because the compressive yield strength was approximately one-half the tensile yield strength. A formula for the column strength of magnesium alloy AM-57S is given.

Apparatus for pre-stress-straining rod-type specimens in tension for in-situ passive fracture testing

DOEpatents

Wang, John Jy-an [Oak Ridge, TN; Liu, Ken C [Oak Ridge, TN; Feng, Zhili [Knoxville, TN

2013-07-31

A stress-strain testing apparatus imposes a stress-strain on a specimen while disposed in a controlled environment. Each end of the specimen is fastened to an end cap and a strain gage is attached to the specimen. An adjusting mechanism and a compression element are disposed between the end caps forming a frame for applying forces to the end caps and thereby stress-straining the specimen. The adjusting mechanism may be extended or retracted to increase or decrease the imposed stress-strain on the specimen, and the stress-strain is measured by the strain gage on the specimen while the apparatus is exposed to an environment such as high pressure hydrogen. Strain gages may be placed on the frame to measure stress-strains in the frame that may be caused by the environment.

Mechanical properties and polymerization shrinkage of composite resins light-cured using two different lasers.

PubMed

Kim, Tae-Wan; Lee, Jang-Hoon; Jeong, Seung-Hwa; Ko, Ching-Chang; Kim, Hyung-Il; Kwon, Yong Hoon

2015-04-01

The purpose of the present study was to investigate the usefulness of 457 and 473 nm lasers for the curing of composite resins during the restoration of damaged tooth cavity. Monochromaticity and coherence are attractive features of laser compared with most other light sources. Better polymerization of composite resins can be expected. Eight composite resins were light cured using these two lasers and a light-emitting diode (LED) light-curing unit (LCU). To evaluate the degrees of polymerization achieved, polymerization shrinkage and flexural and compressive properties were measured and compared. Polymerization shrinkage values by 457 and 473 nm laser, and LED ranged from 10.9 to 26.8, from 13.2 to 26.1, and from 11.5 to 26.3 μm, respectively. The values by 457 nm laser was significantly different from those by 473 and LED LCU (p<0.05). However, there was no statistical difference between values by 473 and LED LCU. Before immersion in distilled water, flexural strength (FS) and compressive modulus (CM) of the specimens were inconsistently influenced by LCUs. On the other hand, flexural modulus (FM) and compressive strength (CS) were not significantly different for the three LCUs (p>0.05). For the tested LCUs, no specific LCU could consistently achieve highest strength and modulus from the specimens tested. Two lasers (457 and 473 nm) can polymerize composite resins to the level that LED LCU can achieve despite inconsistent trends of polymerization shrinkage and flexural and compressive properties of the tested specimens.

Shape memory characteristics and mechanical properties of powder metallurgy processed Ti50Ni40Cu10 alloy.

PubMed

Kim, Yeon-Wook

2014-10-01

Ti-Ni-Cu alloy powders were prepared by gas atomization and porous bulk specimens were fabricated by spark plasma sintering (SPS). The microstructure of as-solidified powders exhibited a cellular structure and they contained a high density of nano-sized porosities which were located in the intercellular regions. XRD analysis showed that one-step martensitic transformation of B2-B19 occurred in all alloy powders and SPS specimens. When the martensitic transformation start temperature (M(s)) and austenite transformation finish temperature (A(f)) were determined in order to analyze the dependence of powder size on transformation temperatures, the M(s) increased slightly from -17.5 degrees C to - 14.6 degrees C as increasing the powder size ranging from between 25 and 50 μm to ranging between 100 and 150 μm. However, the M(s) and A(f) of the as-atomized powders is much smaller than those of SPS specimens and the M(s) of porous specimen was about 10.9 degrees C. Loading-unloading compressive tests were carried out to investigate the mechanical properties of porous Ti-Ni-Cu specimen. The specimen was compressed to the strain of 6% at a temperature higher than A,. After unloading, the residual strain was 2.1%. After the compressed specimen was heated to 60 degrees C and held for 30 minutes and then cooled to room temperature, the changes in the length of the specimens were measured. Then it was found that the recovered strain ascribed to shape memory effect was 1.5%.

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. III - Tension-compression anisotropy

NASA Technical Reports Server (NTRS)

Miner, R. V.; Gabb, T. P.; Gayda, J.; Hemker, K. J.

1986-01-01

Single crystal superalloy specimens with various crystallographic directions along their axes were tested in compression at room temperature, 650, 760, 870, and 980 deg C. These results are compared with the tensile behavior studied previously. The alloy, Rene N4, was developed.

Experimental Study on Cementitious Composites Embedded with Organic Microcapsules

PubMed Central

Wang, Xianfeng; Xing, Feng; Zhang, Ming; Han, Ningxu; Qian, Zhiwei

2013-01-01

The recovery behavior for strength and impermeability of cementitious composites embedded with organic microcapsules was investigated in this study. Mortar specimens were formed by mixing the organic microcapsules and a catalyst with cement and sand. The mechanical behaviors of flexural and compression strength were tested. The results showed that strength could increase by up to nine percent with the addition of a small amount of microcapsules and then decrease with an increasing amount of microcapsules. An orthogonal test for investigating the strength recovery rate was designed and implemented for bending and compression using the factors of water/cement ratio, amount of microcapsules, and preloading rate. It is shown that the amount of microcapsules plays a key role in the strength recovery rate. Chloride ion permeability tests were also carried out to investigate the recovery rate and healing effect. The initial damage was obtained by subjecting the specimens to compression. Both the recovery rate and the healing effect were nearly proportional to the amount of microcapsules. The obtained cementitious composites can be seen as self-healing owing to their recovery behavior for both strength and permeability. PMID:28788318

Evolution of saturated hydraulic conductivity with compression and degradation for municipal solid waste.

PubMed

Ke, Han; Hu, Jie; Xu, Xiao Bing; Wang, Wen Fang; Chen, Yun Min; Zhan, Liang Tong

2017-07-01

Municipal solid waste (MSW) specimens were created from synthetic fresh MSW degraded in a laboratory scale enhanced degradation reactor. The degree of degradation and saturated hydraulic conductivity k s were measured to study the effects of compression and degradation on k s of MSW. The degree of degradation was characterized through the ratio of cellulose content to lignin content (i.e., C/L) and the loss ratio of volatile solid (i.e., DOD). k s of MSW specimens with different degrees of degradation was measured through triaxial permeameter tests under different confining pressures. It was found that, when the degradation time increased from 0month to 18months, k s decreased less than 1 order of magnitude for specimens with the same porosity (i.e., n=0.63 or 0.69). However, for specimens with the same degradation time, the decrease of k s could reach 2 orders of magnitude with n decreasing from 0.8 to 0.6. It indicates that compression has much greater influence on the reduction of k s than that of degradation. Based on the Kozeny-Carman model and first-order kinetics, a prediction model related to n and C/L (or DOD) of MSW was proposed to analyze the evolution of k s with compression and biodegradation. The methods to determine the values of model parameters were also proposed. Copyright © 2017 Elsevier Ltd. All rights reserved.

The use of glass powder in making batako

NASA Astrophysics Data System (ADS)

Nursyamsi, N.; Indrawan, I.

2018-02-01

Along with the increase in construction materials, innovation is needed to lessen the use of them, and one of them is by using cement [1]. In this research, it is reduced by glass powder; the reason for using it as the substitution of cement is that some chemical elements in cement are similar to those in glass powder such as SiO2, A12o3, Fe2O3, and CaO. The glass powder used was the one who passed sieve no. 100 and was hampered in sieve no. 200. It passed sieve no. 200 with its composition of 0%, 10%, 15%, 20%, 25%, and 30% from the volume of the use of cement. The specimen would treat within 28 days before the testing of compressive strength, water absorption, and tensile strength [2]. The variation which produced optimum result would mix with the foaming agent as the material for reducing the weight of the specimen. After that, the test of compressive strength, water absorption, and tensile strength on the installment of batako walls were done. The data analyzed by using SNI 02-0349-1989[3] reference about concrete brick for wall installment. The variation of 20% of glass powder passing sieve no. 200 gave optimum result. A specimen of the variation on glass powder of 20% which passed sieve no. 200 and the foaming agent was higher than the compressive strength of the specimen which used glass powder substitution of 0% of passing sieve no. 200 and foaming agent. The compressive strength of batako walls which used the batako construction with glass powder substitution of 20% of passing sieve no. 200 and the foaming agent was also higher than the compressive strength of the assaying object which used glass powder substitution of 0% of passing sieve no. 200 and foaming agent.

Influence of Structure and Composition on Dynamic Viscoelastic Property of Cartilaginous Tissue: Criteria for Classification between Hyaline Cartilage and Fibrocartilage Based on Mechanical Function

NASA Astrophysics Data System (ADS)

Miyata, Shogo; Tateishi, Tetsuya; Furukawa, Katsuko; Ushida, Takashi

Recently, many types of methodologies have been developed to regenerate articular cartilage. It is important to assess whether the reconstructed cartilaginous tissue has the appropriate mechanical functions to qualify as hyaline (articular) cartilage. In some cases, the reconstructed tissue may become fibrocartilage and not hyaline cartilage. In this study, we determined the dynamic viscoelastic properties of these two types of cartilage by using compression and shear tests, respectively. Hyaline cartilage specimens were harvested from the articular surface of bovine knee joints and fibrocartilage specimens were harvested from the meniscus tissue of the same. The results of this study revealed that the compressive energy dissipation of hyaline cartilage showed a strong dependence on testing frequency at low frequencies, while that of fibrocartilage did not. Therefore, the compressive energy dissipation that is indicated by the loss tangent could become the criterion for the in vitro assessment of the mechanical function of regenerated cartilage.

Silicon Nitride Creep Under Various Specimen-Loading Configurations

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Holland, Frederic A.

2000-01-01

Extensive creep testing of a hot-pressed silicon nitride (NC 132) was performed at 1300 C in air using five different specimen-loading configurations: (1) pure tension, (2) pure compression, (3) four-point uniaxial flexure, (4) ball-on-ring biaxial flexure, and (5) ring-on-ring biaxial flexure. This paper reports experimental results as well as test techniques developed in this work. Nominal creep strain and its rate for a given nominal applied stress were greatest in tension, least in compression, and intermediate in uniaxial and biaxial flexure. Except for the case of compression loading, nominal creep strain generally decreased with time, resulting in a less-defined steady-state condition. Of the four creep formulations-power-law, hyperbolic sine, step, and redistribution--the conventional power-law formulation still provides the most convenient and reasonable estimation of the creep parameters of the NC 132 material. The data base to be obtained will be used to validate the NASA Glenn-developed design code CARES/Creep (ceramics analysis and reliability evaluation of structures and creep).

Microgravity

NASA Image and Video Library

1998-01-01

On STS-89, three Mechanics of Granular Materials (MGM) test cells were subjected to five cycles of compression and relief (left) and three were subjected to shorter displacement cycles that simulate motion during an earthquake (right). In the compression/relief tests, the sand particles rearranged themselves and slightly re-expanded the column during relief. In the short displacement tests, the specimen's resistance to compression decreases, even though the displacement remains the same. The specimens were cycled up to 100 times or until the resistive force was less than 1% that of the previous cycle. Sand and soil grains have faces that can cause friction as they roll and slide against each other, or even cause sticking and form small voids between grains. This complex behavior can cause soil to behave like a liquid under certain conditions such as earthquakes or when powders are handled in industrial processes. Mechanics of Granular Materials (MGM) experiments aboard the Space Shuttle use the microgravity of space to simulate this behavior under conditons that carnot be achieved in laboratory tests on Earth. MGM is shedding light on the behavior of fine-grain materials under low effective stresses. Applications include earthquake engineering, granular flow technologies (such as powder feed systems for pharmaceuticals and fertilizers), and terrestrial and planetary geology. Nine MGM specimens have flown on two Space Shuttle flights. Another three are scheduled to fly on STS-107. The principal investigator is Stein Sture of the University of Colorado at Boulder. Credit: NASA/Marshall Space Flight Center (MSFC)

Impact damage and residual strength analysis of composite panels with bonded stiffeners. [for primary aircraft structures

NASA Technical Reports Server (NTRS)

Madan, Ram C.; Shuart, Mark J.

1990-01-01

Blade-stiffened, compression-loaded cover panels were designed, manufactured, analyzed, and tested. All panels were fabricated from IM6/1808I interleafed graphite-epoxy. An orthotropic blade stiffener and an orthotropic skin were selected to satisfy the design requirements for an advanced aircraft configuration. All specimens were impact damaged prior to testing. Experimental results were obtained for three- and five-stiffener panels. Analytical results described interlaminar forces caused by impact and predicted specimen residual strength. The analytical results compared reasonably with the experimental results for residual strength of the specimens.

Experimental study of the seismic performance of L-shaped columns with 500 MPa steel bars.

PubMed

Wang, Tiecheng; Liu, Xiao; Zhao, Hailong

2014-01-01

Based on tests on six L-shaped RC columns with 500 MPa steel bars, the effect of axial compression ratios and stirrup spacing on failure mode, bearing capacity, displacement, and curvature ductility of the specimens is investigated. Test results show that specimens with lower axial load and large stirrup characteristic value (larger than about 0.35) are better at ductility and seismic performance, while specimens under high axial load or with a small stirrup characteristic value (less than about 0.35) are poorer at ductility; L-shaped columns with 500 MPa steel bars show better bearing capacity and ductility in comparison with specimens with HRB400 steel bars.

Mechanical Properties of Aerogels

NASA Technical Reports Server (NTRS)

Parmenter, Kelly E.; Milstein, Frederick

1995-01-01

Aerogels are extremely low density solids that are characterized by a high porosity and pore sizes on the order of nanometers. Their low thermal conductivity and sometimes transparent appearance make them desirable for applications such as insulation in cryogenic vessels and between double paned glass in solar architecture. An understanding of the mechanical properties of aerogels is necessary before aerogels can be used in load bearing applications. In the present study, the mechanical behavior of various types of fiber-reinforced silica aerogels was investigated with hardness, compression, tension and shear tests. Particular attention was paid to the effects of processing parameters, testing conditions, storage environment, and age on the aerogels' mechanical response. The results indicate that the addition of fibers to the aerogel matrix generally resulted in softer, weaker materials with smaller elastic moduli. Furthermore, the testing environment significantly affected compression results. Tests in ethanol show an appreciable amount of scatter, and are not consistent with results for tests in air. In fact, the compression specimens appeared to crack and begin to dissolve upon exposure to the ethanol solution. This is consistent with the inherent hydrophobic nature of these aerogels. In addition, the aging process affected the aerogels' mechanical behavior by increasing their compressive strength and elastic moduli while decreasing their strain at fracture. However, desiccation of the specimens did not appreciably affect the mechanical properties, even though it reduced the aerogel density by removing trapped moisture. Finally, tension and shear test results indicate that the shear strength of the aerogels exceeds the tensile strength. This is consistent with the response of brittle materials. Future work should concentrate on mechanical testing at cryogenic temperatures, and should involve more extensive tensile tests. Moreover, before the mechanical response of reinforced aerogels can be fully understood, more tests of unreinforced aerogels are necessary. Unreinforced aerogels are of particular use because their birefringent nature allows for visual determination of stress fields during mechanical testing. The success of any future tests depends on the availability of a large supply of quality specimens with well-documented preparation and storage histories.

Compression Testing of Textile Composite Materials

NASA Technical Reports Server (NTRS)

Masters, John E.

1996-01-01

The applicability of existing test methods, which were developed primarily for laminates made of unidirectional prepreg tape, to textile composites is an area of concern. The issue is whether the values measured for the 2-D and 3-D braided, woven, stitched, and knit materials are accurate representations of the true material response. This report provides a review of efforts to establish a compression test method for textile reinforced composite materials. Experimental data have been gathered from several sources and evaluated to assess the effectiveness of a variety of test methods. The effectiveness of the individual test methods to measure the material's modulus and strength is determined. Data are presented for 2-D triaxial braided, 3-D woven, and stitched graphite/epoxy material. However, the determination of a recommended test method and specimen dimensions is based, primarily, on experimental results obtained by the Boeing Defense and Space Group for 2-D triaxially braided materials. They evaluated seven test methods: NASA Short Block, Modified IITRI, Boeing Open Hole Compression, Zabora Compression, Boeing Compression after Impact, NASA ST-4, and a Sandwich Column Test.

Mechanical Testing of IN718 Lattice Block Structures

NASA Technical Reports Server (NTRS)

Krause, David L.; Whittenberger, John D.; Kantzos, Pete T.; Hebsur, Mohan G.

2002-01-01

Lattice block construction produces a flat, structurally rigid panel composed of thin ligaments of material arranged in a three-dimensional triangulated truss-like structure. Low-cost methods of producing cast metallic lattice block panels are now available that greatly expand opportunities for using this unique material system in today's high-performance structures. Additional advances are being made in NASA's Ultra Efficient Engine Technology (UEET) program to extend the lattice block concept to superalloy materials. Advantages offered by this combination include high strength, light weight, high stiffness, and elevated temperature capabilities. Recently under UEET, the nickel-based superalloy Inconel 718 (IN718) was investment cast into lattice block panels with great success. To evaluate casting quality and lattice block architecture merit, individual ligaments, and structural subelement specimens were extracted from the panels. Tensile tests, structural compression, and bending strength tests were performed on these specimens. Fatigue testing was also completed for several bend test specimens. This paper first presents metallurgical and optical microscopy analysis of the castings. This is followed by mechanical test results for the tensile ligament tests and the subelement compression and bending strength tests, as well as for the fatigue tests that were performed. These tests generally showed comparable properties to base IN718 with the same heat treatment, and they underscored the benefits offered by lattice block materials. These benefits might be extended with improved architecture such as face sheets.

Results of Mechanical Testing for Pyroceram(tm) Glass-Ceramic

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Gyekenyesi, John P.

2003-01-01

Mechanical testing for Pyroceram (trademark) 9606 glass-ceramic fabricated by Corning was conducted to determine mechanical properties of the material including slow crack growth.Valid testing was not achieved in tension, compression, and shear testing due to inappropriate test specimen configurations provided and primarily due to the existence of fortified layer( in tension).

Effect of grain orientation on aluminum relocation at incipient melt conditions

DOE PAGES

Yilmaz, Nadir; Vigil, Francisco M.; Vigil, Miquela S.; ...

2015-09-01

Aluminum is commonly used for structural applications in the aerospace industry because of its high strength in relation to its weight. It is necessary to understand the mechanical response of aluminum structures at elevated temperatures such as those experienced in a fire. Additionally, aluminum alloys exhibit many complicated behaviors that require further research and understanding, such as aluminum combustion, oxide skin formation and creep behavior. This paper discusses the effect of grain orientation on aluminum deformation subjected to heating at incipient melt conditions. Experiments were conducted by applying a vertical compressive force to aluminum alloy 7075 block test specimens. Furthermore,more » compression testing was done on test specimens with the applied load on the long transverse and short transverse orientations. Our results showed that the grain orientation significantly influences aluminum’s strength and mode of failure.« less

Impact Deformation of Thin-Walled Circular Tube Filled with Aluminum Foam in Lateral Compression

NASA Astrophysics Data System (ADS)

Kobayashi, Hidetoshi; Horikawa, Keitaro; Ogawa, Kinya; Hori, Masahiro

In this study, the impact deformation of thin-walled circular tubes filled with aluminum foam in lateral compression was investigated using a special load cell for long time measurement and a high-speed video camera to check the displacement of specimens. It was found that the absorbed energy up to the deformation of 60% of the specimen diameter obtained from impact tests is greater than that obtained in static tests, because of strain rate dependency of aluminum foam. The loaddisplacement curve of circular tubes with aluminum foam just inserted was consistent with the sum of the curves individually obtained. In both dynamic and static tests, however, the load of the tube with the foam inserted and glued by adhesive resin became larger than the sum of the individual loads, because of the interaction between circular tubes and aluminum foam cores.

Seismic performance of recycled concrete-filled square steel tube columns

NASA Astrophysics Data System (ADS)

Chen, Zongping; Jing, Chenggui; Xu, Jinjun; Zhang, Xianggang

2017-01-01

An experimental study on the seismic performance of recycled concrete-filled square steel tube (RCFST) columns is carried out. Six specimens were designed and tested under constant axial compression and cyclic lateral loading. Two parameters, replacement percentage of recycled coarse aggregate (RCA) and axial compression level, were considered in the test. Based on the experimental data, the hysteretic loops, skeleton curves, ductility, energy dissipation capacity and stiffness degradation of RCFST columns were analyzed. The test results indicate that the failure modes of RCFST columns are the local buckling of the steel tube at the bottom of the columns, and the hysteretic loops are full and their shapes are similar to normal CFST columns. Furthermore, the ductility coefficient of all specimens are close to 3.0, and the equivalent viscous damping coefficient corresponding to the ultimate lateral load ranges from 0.323 to 0.360, which demonstrates that RCFST columns exhibit remarkable seismic performance.

Compression failure of angle-ply laminates

NASA Technical Reports Server (NTRS)

Peel, L. D.; Hyer, M. W.; Shuart, M. J.

1992-01-01

Test results from the compression loading of (+ or - Theta/ - or + Theta)(sub 6s) angle-ply IM7-8551-7a specimens, 0 less than or = Theta less than or = 90 degs, are presented. The observed failure strengths and modes are discussed, and typical stress-strain relations shown. Using classical lamination theory and the maximum stress criterion, an attempt is made to predict failure stress as a function of Theta. This attempt results in poor correlation with test results and thus a more advanced model is used. The model, which is based on a geometrically nonlinear theory, and which was taken from previous work, includes the influence of observed layer waviness. The waviness is described by the wave length and the wave amplitude. The theory is briefly described and results from the theory are correlated with test results. It is shown that by using levels of waviness observed in the specimens, the correlation between predictions and observations is good.

Perspectives of SiC-Based Ceramic Composites and Their Applications to Fusion Reactors 5.Development of Evaluation and Application Techniques of SiC⁄SiC Composites for Fusion Reactors

NASA Astrophysics Data System (ADS)

Hinoki, Tatsuya

Evaluation techniques and mechanical properties of silicon carbide composites (SiC⁄SiC composites) reinforced with highly crystalline fibers are reviewed for fusion applications. The SiC⁄SiC composites used were fabricated by means of the CVI method. The evaluation includes in-plane tensile strength by in-plane tensile test, transthickness tensile strength by transthickness tensile test and diametral compression test and shear strength by compression test using double-notched specimen. All tests were successfully conducted using small specimens for neutron irradiation experiment. As application technique, the novel tungsten(W) coating technique on SiC is reviewed. The W powder melted by high power lamp in a few seconds and formed coating on SiC. No thick reaction layers of WC and W5Si3, which are formed by the other coating methods, were formed by this method.

Technical Operations Support III (TOPS III). Delivery Order 0081: Novel Pitch Materials for High Thermal Conductivity Carbon Fibers, Foams and Composites - Phase 3

DTIC Science & Technology

2011-06-01

mm Diameter Barrel and (c) a 12-Hole Spinneret with 150 Micrometer Diameter Holes...6  3. A Schematic of a Mounted Specimen for Compressive Testing Using a High-Speed Camera for Capturing...Tension-Recoil Compressive ..................................................................... 8  4. SEM Images of Oxidized 0 wt% ARHP Mesophase Pitch

Extrusion-mixing compared with hand-mixing of polyether impression materials?

PubMed

McMahon, Caroline; Kinsella, Daniel; Fleming, Garry J P

2010-12-01

The hypotheses tested were two-fold (a) whether altering the base:catalyst ratio influences working time, elastic recovery and strain in compression properties of a hand-mixed polyether impression material and (b) whether an extrusion-mixed polyether impression material would have a significant advantage over a hand-mixed polyether impression material mixed to the optimum base:catalyst ratio. The polyether was hand-mixed at the optimum (manufacturers recommended) base:catalyst ratios (7:1) and further groups were made by increasing or decreasing the catalyst length by 25%. Additionally specimens were also made from an extrusion-mixed polyether impression material and compared with the optimum hand-mixed base:catalyst ratio. A penetrometer assembly was used to measure the working time (n=5). Five cylindrical specimens for each hand-mixed and extrusion mixed group investigated were employed for elastic recovery and strain in compression testing. Hand-mixing polyether impression materials with 25% more catalyst than that recommended significantly decreased the working time while hand-mixing with 25% less catalyst than that recommended significantly increased the strain in compression. The extrusion-mixed polyether impression material provided similar working time, elastic recovery and strain in compression to the hand-mixed polyether mixed at the optimum base:catalyst ratio.

The effect of condensation pressure on selected physical properties of mineral trioxide aggregate.

PubMed

Nekoofar, M H; Adusei, G; Sheykhrezae, M S; Hayes, S J; Bryant, S T; Dummer, P M H

2007-06-01

To examine the effect of condensation pressure on surface hardness, microstructure and compressive strength of mineral trioxide aggregate (MTA). White ProRoot MTA (Dentsply Tulsa Dental, Johnson City, TN, USA) was mixed and packed into cylindrical polycarbonate tubes. Six groups each of 10 specimens were subjected to pressures of 0.06, 0.44, 1.68, 3.22, 4.46 and 8.88 MPa respectively. The surface hardness of each specimen was measured using Vickers microhardness. Cylindrical specimens of 4 mm in diameter and 6 mm in height were prepared in polycarbonate cylindrical moulds for testing the compressive strength. Five groups of 10 specimens were prepared using pressures of 0.06, 0.44, 1.68, 3.22 or 4.46 MPa. Data were subjected to one-way anova. The microstructure was analysed using a scanning electron microscope (SEM) after sectioning specimens with a scalpel. A trend was observed for higher condensation pressures to produce lower surface hardness values. A condensation pressure of 8.88 MPa produced specimens with significantly lower values in terms of surface hardness than other groups (P<0.001). A condensation pressure of 1.68 MPa conferred the maximum compressive strength; however, it was not statistically different. Higher condensation pressures resulted in fewer voids and microchannels when analysed with SEM. In specimens prepared with lower condensation pressures distinctive crystalline structures were observed. They tended to appear around microchannels. Condensation pressure may affect the strength and hardness of MTA. Use of controlled condensation pressure in sample preparation for future studies is suggested.

Biomechanical Comparison of Locking Compression Plate versus Positive Profile Pins and Polymethylmethacrylate for Stabilization of the Canine Lumbar Vertebrae.

PubMed

Sturges, Beverly K; Kapatkin, Amy S; Garcia, Tanya C; Anwer, Cona; Fukuda, Shimpei; Hitchens, Peta L; Wisner, Tristan; Hayashi, Kei; Stover, Susan M

2016-04-01

To compare the stiffness, angular deformation, and mode of failure of lumbar vertebral column constructs stabilized with bilateral pins and polymethylmethacrylate (Pin-PMMA) or with a unilateral (left) locking compression plate (LCP) with monocortical screws. Ex vivo biomechanical, non-randomized. Cadaveric canine thoracolumbar specimens (n=16). Thoracolumbar (T13-L3) vertebral specimens had the L1-L2 vertebral motion unit stabilized with either Pin-PMMA or LCP. Stiffness in flexion, extension, and right and left lateral bending after nondestructive testing were compared between intact (pretreated) specimens and Pin-PMMA, and LCP constructs. The Pin-PMMA and LCP constructs were then tested to failure in flexion and left lateral bending. Both the Pin-PMMA and LCP constructs had reduced range of motion at the stabilized L1-L2 vertebral motion unit compared to intact specimens. The Pin-PMMA constructs had less range of motion for the flexion elastic zone than LCP constructs. The Pin-PMMA constructs were stiffer than intact specimens in flexion, extension, and lateral bending, and stiffer than LCP constructs in flexion and left lateral bending. The Pin-PMMA constructs had less angular deformation at construct yield and lower residual deformation at L1-L2 than LCP constructs after destructive testing to failure in flexion. The Pin-PMMA constructs were stiffer, stronger, and had less deformation at yield than LCP constructs after destructive testing to failure in lateral bending. Most constructs failed distant to the implant and fixation site. Pin-PMMA constructs had greater lumbar vertebral stiffness and reduced ROM than LCP constructs; however, both Pin-PMMA and LCP constructs were stronger than intact specimens. © Copyright 2016 by The American College of Veterinary Surgeons.

Random lattice structures. Modelling, manufacture and FEA of their mechanical response

NASA Astrophysics Data System (ADS)

Maliaris, G.; Sarafis, I. T.; Lazaridis, T.; Varoutoglou, A.; Tsakataras, G.

2016-11-01

The implementation of lightweight structures in various applications, especially in Aerospace/ Automotive industries and Orthopaedics, has become a necessity due to their exceptional mechanical properties with respect to reduced weight. In this work we present a Voronoi tessellation based algorithm, which has been developed for modelling stochastic lattice structures. With the proposed algorithm, is possible to generate CAD geometry with controllable structural parameters, such as porosity, cell number and strut thickness. The digital structures were transformed into physical objects through the combination of 3D printing technics and investment casting. This process was applied to check the mechanical behaviour of generated digital models. Until now, the only way to materialize such structures into physical objects, was feasible through 3D printing methods such as Selective Laser Sintering/ Melting (SLS/ SLM). Investment casting possesses numerous advantages against SLS or SLA, with the major one being the material variety. On the other hand, several trials are required in order to calibrate the process parameters to have successful castings, which is the major drawback of investment casting. The manufactured specimens were subjected to compression tests, where their mechanical response was registered in the form of compressive load - displacement curves. Also, a finite element model was developed, using the specimens’ CAD data and compression test parameters. The FE assisted calculation of specimen plastic deformation is identical with the one of the physical object, which validates the conclusions drawn from the simulation results. As it was observed, strut contact is initiated when specimen deformation is approximately 5mm. Although FE calculated compressive force follows the same trend for the first 3mm of compression, then diverges because of the elasto-plastic FE model type definition and the occurred remeshing steps.

Changes in compressive strength on ageing in glass polyalkenoate (glass-ionomer) cements prepared from acrylic/maleic acid copolymers.

PubMed

Nicholson, J W; Abiden, F

1997-01-01

Previous studies have shown that glass-ionomers made from acrylic/maleic copolymers stored in water reach a maximum strength at about 1 week, and after 4 months have become significantly weaker. This finding, which contrasts with the behaviour of glass-ionomers based on poly(acrylic acid), was originally attributed to hydrolytic instability. This interpretation has been tested in the current work. Specimens of glass-ionomer prepared from acrylic/maleic acid copolymer have been stored for up to 4 months in different media, namely deionized water, dry air and vegetable oil, then tested for compressive strength. Specimens were in the form of cylinders of dimensions 6 mm high x 4 mm diameter, and storage temperature was 37 degrees C. Data were analysed using two-way analysis of variance (ANOVA) and in all three media specimens became weaker at 4 months than they had been at 1 week (P < 0.05). However, for the specimens stored in dry air and in water, the 1-week values were not the maximum. The fact that there was a loss of strength under all conditions led to the conclusion that it is not, after all, due to hydrolysis.

Cyclic Inelastic Deformation and Fatigue Resistance of a Rail Steel : Experimental Results and Mathematical Models

DOT National Transportation Integrated Search

1981-10-01

Experimental results developed from tests of uniaxial, smooth specimens obtained from the head of an unused section of rail have been reported. Testing encompassed a broad range of conditions - monotonic tension, monotonic compression, and fully reve...

Failure of Castlegate Sandstone under True Triaxial Loading

NASA Astrophysics Data System (ADS)

Ingraham, M. D.; Issen, K. A.; Holcomb, D. J.

2011-12-01

Understanding the stress conditions that cause deformation bands to form can provide insight into the geologic processes in a given location. In particular, understanding the relationship of the intermediate principal stress with respect to maximum and minimum compression when bands form, could provide useful information about the intermediate principal stress in field settings. Therefore, a series of tests were performed to investigate the effect of the intermediate principal stress on the mechanical response and failure of Castlegate sandstone under true triaxial states of stress. Constant mean stress tests were run at five different stress states ranging from: 1) intermediate principal stress equal to minimum compression to 2) intermediate principal stress equal to maximum compression. Failure occurred either through deformation band formation or apparent bulk compaction. Specimens that formed a deformation band experienced a stress drop at band formation. For a given level of intermediate principal stress, the peak stress increases with increasing mean stress. Additionally, as intermediate principal stress increases, the peak stress decreases for a given mean stress. Acoustic emissions (AE) recorded during testing were used to locate failure events in three-dimensional space within the sample. This allowed for more detailed investigation of the formation and propagation of the band(s) within the specimen. In specimens that appear to have undergone bulk compaction, AE events were randomly distributed throughout the sample. For specimens with bands, the band angles were measured as the angle between the maximum principal stress direction and the normal to the band that formed. Band angles tend to increase with increasing intermediate principal stress, and decrease with increasing mean stress. Results from the AE data shows that the band angle evolves during testing and the band that is expressed on the surface of the specimen at the conclusion of testing is not always the band that initially formed. AE results also show that low angle bands tend to be more diffuse than higher angle bands. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000.

Failure Mechanisms of Brittle Rocks under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Liu, Taoying; Cao, Ping

2017-09-01

The behaviour of a rock mass is determined not only by the properties of the rock matrix, but mostly by the presence and properties of discontinuities or fractures within the mass. The compression test on rock-like specimens with two prefabricated transfixion fissures, made by pulling out the embedded metal inserts in the pre-cured period was carried out on the servo control uniaxial loading tester. The influence of the geometry of pre-existing cracks on the cracking processes was analysed with reference to the experimental observation of crack initiation and propagation from pre-existing flaws. Based on the rock fracture mechanics and the stress-strain curves, the evolution failure mechanism of the fissure body was also analyzed on the basis of exploring the law of the compression-shear crack initiation, wing crack growth and rock bridge connection. Meanwhile, damage fracture mechanical models of a compression-shear rock mass are established when the rock bridge axial transfixion failure, tension-shear combined failure, or wing crack shear connection failure occurs on the specimen under axial compression. This research was of significance in studying the failure mechanism of fractured rock mass.

A biomechanical evaluation of a cannulated compressive screw for use in fractures of the scaphoid.

PubMed

Rankin, G; Kuschner, S H; Orlando, C; McKellop, H; Brien, W W; Sherman, R

1991-11-01

The compressive force generated by a 3.5 mm ASIF cannulated cancellous screw with a 5 mm head was compared with that generated by a standard 3.5 mm ASIF screw (6 mm head), a 2.7 mm ASIF screw (5 mm head), and a Herbert screw. The screws were evaluated in the laboratory with the use of a custom-designed load washer (transducer) to the maximum compressive force generated by each screw until failure, either by thread stripping or by head migration into the specimen. Testing was done on paired cadaver scaphoids. To minimize the variability that occurs with human bone, and because of the cost and difficulty of obtaining human tissue specimens, a study was also done on polyurethane foam simulated bones. The 3.5 cannulated screw generated greater compressive forces than the Herbert screw but less compression than the 2.7 mm and 3.5 mm ASIF cortical screws. The 3.5 mm cannulated screw offers more rigid internal fixation for scaphoid fractures than the Herbert screw and gives the added advantage of placement over a guide wire.

Investigation of compression behavior of PE/EVA foam injection molded parts

NASA Astrophysics Data System (ADS)

Spina, Roberto

2017-10-01

The main objective of the presented work is to evaluate the compression behavior of a polymeric foam blend by using a robust framework for the testing sequence of foaming injection molded parts, with the aim of establishing a standard testing cycle for the evaluation of new matrix material. The research purpose is to assess parameters influencing compression behavior and give useful suggestions for the implementation of a finite element analysis. The polymeric blend consisted of a mixture of low density polyethylenes (LDPEs), a high-density polyethylene (HDPE), an ethylene-vinyl acetate (EVA) and an azodicarbonamide (ADC). The thermal, rheological and compression properties of the blend are fully described, as well as the injection molding process for two specimen types.

Combined meso-scale modeling and experimental investigation of the effect of mechanical damage on the transport properties of cementitious composites

NASA Astrophysics Data System (ADS)

Raghavan, Balaji; Niknezhad, Davood; Bernard, Fabrice; Kamali-Bernard, Siham

2016-09-01

The transport properties of cementitious composites such as concrete are important indicators of their durability, and are known to be heavily influenced by mechanical loading. In the current work, we use meso-scale hygro-mechanical modeling with a morphological 3D two phase mortar-aggregate model, in conjunction with experimentally obtained properties, to investigate the coupling between mechanical loading and damage and the permeability of the composite. The increase in permeability of a cylindrical test specimen at 28% aggregate fraction during a uniaxial displacement-controlled compression test at 85% of the peak load was measured using a gas permeameter. The mortar's mechanical behavior is assumed to follow the well-known compression damaged plasticity (CDP) model with isotropic damage, at varying thresholds, and obtained from different envelope curves. The damaged intrinsic permeability of the mortar evolves according to a logarithmic matching law with progressive loading. We fit the matching law parameters to the experimental result for the test specimen by inverse identification using our meso-scale model. We then subject a series of virtual composite specimens to quasi-static uniaxial compressive loading with varying boundary conditions to obtain the simulated damage and strain evolutions, and use the damage data and the previously identified parameters to determine the evolution of the macroscopic permeability tensor for the specimens, using a network model. We conduct a full parameter study by varying aggregate volume fraction, granulometric distribution, loading/boundary conditions and "matching law" parameters, as well as for different strain-damage thresholds and uniaxial loading envelope curves. Based on this study, we propose Avrami equation-based upper and lower bounds for the evolution of the damaged permeability of the composite.

The Effects of Specimen Geometry on the Plastic Deformation of AA 2219-T8 Aluminum Alloy Under Dynamic Impact Loading

NASA Astrophysics Data System (ADS)

Owolabi, G. M.; Bolling, D. T.; Odeshi, A. G.; Whitworth, H. A.; Yilmaz, N.; Zeytinci, A.

2017-12-01

The effects of specimen geometry on shear strain localization in AA 2219-T8 aluminum alloy under dynamic impact loading were investigated. The alloy was machined into cylindrical, cuboidal and conical (frustum) test specimens. Both deformed and transformed adiabatic shear bands developed in the alloy during the impact loading. The critical strain rate for formation of the deformed band was determined to be 2500 s-1 irrespective of the specimen geometry. The critical strain rate required for formation of transformed band is higher than 3000 s-1 depending on the specimen geometry. The critical strain rate for formation of transformed bands is lowest (3000 s-1) in the Ø5 mm × 5 mm cylindrical specimens and highest (> 6000 s-1) in the conical specimens. The cylindrical specimens showed the greatest tendency to form transformed bands, whereas the conical specimen showed the least tendency. The shape of the shear bands on the impacted plane was also observed to be dependent on the specimen geometry. Whereas the shear bands on the compression plane of the conical specimens formed elongated cycles, two elliptical shaped shear bands facing each other were observed on the cylindrical specimens. Two parallel shear bands were observed on the compression planes of the cuboidal specimens. The dynamic stress-strain curves vary slightly with the specimen geometry. The cuboidal specimens exhibit higher tendency for strain hardening and higher maximum flow stress than the other specimens. The microstructure evolution leading to the formation of transformed bands is also discussed in this paper.

Comparison between Different Methods for Biomechanical Assessment of Ex Vivo Fracture Callus Stiffness in Small Animal Bone Healing Studies

PubMed Central

Steiner, Malte; Volkheimer, David; Meyers, Nicholaus; Wehner, Tim; Wilke, Hans-Joachim; Claes, Lutz; Ignatius, Anita

2015-01-01

For ex vivo measurements of fracture callus stiffness in small animals, different test methods, such as torsion or bending tests, are established. Each method provides advantages and disadvantages, and it is still debated which of those is most sensitive to experimental conditions (i.e. specimen alignment, directional dependency, asymmetric behavior). The aim of this study was to experimentally compare six different testing methods regarding their robustness against experimental errors. Therefore, standardized specimens were created by selective laser sintering (SLS), mimicking size, directional behavior, and embedding variations of respective rat long bone specimens. For the latter, five different geometries were created which show shifted or tilted specimen alignments. The mechanical tests included three-point bending, four-point bending, cantilever bending, axial compression, constrained torsion, and unconstrained torsion. All three different bending tests showed the same principal behavior. They were highly dependent on the rotational direction of the maximum fracture callus expansion relative to the loading direction (creating experimental errors of more than 60%), however small angular deviations (<15°) were negligible. Differences in the experimental results between the bending tests originate in their respective location of maximal bending moment induction. Compared to four-point bending, three-point bending is easier to apply on small rat and mouse bones under realistic testing conditions and yields robust measurements, provided low variation of the callus shape among the tested specimens. Axial compressive testing was highly sensitive to embedding variations, and therefore cannot be recommended. Although it is experimentally difficult to realize, unconstrained torsion testing was found to be the most robust method, since it was independent of both rotational alignment and embedding uncertainties. Constrained torsional testing showed small errors (up to 16.8%, compared to corresponding alignment under unconstrained torsion) due to a parallel offset between the specimens’ axis of gravity and the torsional axis of rotation. PMID:25781027

Formability and macroscopic shearing of a titanium alloy Ti-6Al-4V under channel die compression

NASA Astrophysics Data System (ADS)

Francillette, Henri; Garand, Christian

2017-10-01

The mechanical behavior of Ti-6Al-4V is analyzed using channel die compression tests at room temperature. Specimens were cut out from a starting sheet in order to consider samples with specific initial crystallographic textures. Three types of specimens are considered in the study using an angle θ defined with the initial directions LD0, TD0 and ND0 of the starting sheet. The following values of θ are considered : 0°, 45° and 90°. Plastic deformations up to 20% are considered. Several experimental techniques are used, namely optical microscopy, SEM and Xray diffraction for texture evolution. The true stress-strain curves are plotted and the shape change of the specimens is analyzed. A macroscopic shearing is observed for one the three types of initial textures considered, notably θ = 45°. To complete the study, the Taylor model is applied in order to compare the activation of the mechanisms of the α phase in the different specimens.

Experimental Study of the Seismic Performance of L-Shaped Columns with 500 MPa Steel Bars

PubMed Central

Wang, Tiecheng; Liu, Xiao; Zhao, Hailong

2014-01-01

Based on tests on six L-shaped RC columns with 500 MPa steel bars, the effect of axial compression ratios and stirrup spacing on failure mode, bearing capacity, displacement, and curvature ductility of the specimens is investigated. Test results show that specimens with lower axial load and large stirrup characteristic value (larger than about 0.35) are better at ductility and seismic performance, while specimens under high axial load or with a small stirrup characteristic value (less than about 0.35) are poorer at ductility; L-shaped columns with 500 MPa steel bars show better bearing capacity and ductility in comparison with specimens with HRB400 steel bars. PMID:24967420

Physical properties of concrete made with Apollo 16 lunar soil sample

NASA Technical Reports Server (NTRS)

Lin, T. D.; Love, H.; Stark, D.

1992-01-01

This paper describes the first phase of the long-term investigation for the construction of concrete lunar bases. In this phase, petrographic and scanning electron microscope examinations showed that the morphology and elemental composition of the lunar soil made it suitable for use as a fine aggregate for concrete. Based on this finding, calcium aluminate cement and distilled water were mixed with the lunar soil to fabricate test specimens. The test specimens consisted of a 1-in cube, a 1/2-in cube, and three 0.12 x 0.58 x 3.15-in beam specimens. Tests were performed on these specimens to determine compressive strength, modulus of rupture, modulus of elasticity, and thermal coefficient of expansion. Based on examination of the material and test results, it is concluded that lunar soil can be used as a fine aggregate for concrete.

The direct-stress fatigue strength of 17S-T aluminum alloy throughout the range from 1/2 to 500,000,000 cycles of stress

NASA Technical Reports Server (NTRS)

Hartmann, E C; Stickley, G W

1942-01-01

Fatigue-test were conducted on six specimens made from 3/4-inch-diameter 17S-T rolled-and-drawn rod for the purpose of obtaining additional data on the fatigue life of the material at stresses up to the static strength. The specimens were tested in direct tension using a stress range from zero to a maximum in tension. A static testing machine was used to apply repeated loads in the case of the first three specimens; the other three specimens were tested in a direct tension-compression fatigue machine. The direct-stress fatigue curve obtained for the material indicates that, in the range of stresses above about two-thirds the tensile strength, the fatigue strength is higher than might be expected by simply extrapolating the ordinary curve of stress plotted against the number of cycles determined at lower stresses.

Materials research for high-speed civil transport and generic hypersonics: Composites durability

NASA Technical Reports Server (NTRS)

Allen-Lilly, Heather; Cregger, Eric; Hoffman, Daniel; Mccool, Jim

1995-01-01

This report covers a portion of an ongoing investigation of the durability of composites for the High Speed Civil Transport (HSCT) program. Candidate HSCT composites need to possess the high-temperature capability required for supersonic flight. This program was designed to initiate the design, analysis, fabrication, and testing of equipment intended for use in validating the long-term durability of materials for the HSCT. This equipment includes thermally actuated compression and tension fixtures, hydraulic-actuated reversible load fixtures, and thermal chambers. This equipment can be used for the durability evaluation of both composite and adhesive materials. Thermally actuated fixtures are recommended for fatigue cycling when long-term thermomechanical fatigue (TMF) data are required on coupon-sized tension or compression specimens. Long term durability testing plans for polymer matrix composite specimens are included.

Compressive evaluation of homogeneous and graded epoxy-glass particulate composites.

PubMed

Seaglar, J; Rousseau, C-E

2015-04-01

The propagation of stress waves in epoxy-glass particulate composites and graded materials was studied experimentally. Materials tested in this study consisted of an epoxy matrix with various concentrations of spherical glass particles having a mean diameter of 42μm. Plate impact experiments were performed using a gas gun. Embedded within the specimens were manganin stress gauges used to record propagating compressive longitudinal stress waves through the material. High strain rate experiments using a Split Hopkinson Pressure Bar (SHPB) apparatus were also performed to evaluate the dynamic strength of the specimens, while quasi-static compression tests were undertaken to characterize their quasi-static behavior. Ultrasonic wave speed measurements were carried-out in order to obtain additional material properties and characterize the gradation in functionally graded materials (FGM). It was found that low volume fractions of particles are detrimental to the performance of the material under impact loading, while concentrations in the range of about 30 to 45% by volume exhibit characteristics of higher degrees of scattering. This suggests that materials in this latter range would be more effective in the thwarting of destructive shock waves than the homogeneous matrix material. Impact testing of FGM specimens suggests that impact loading on the stiff (high volume fraction) face results in much higher levels of scattering. Therefore, such materials would be effective for use in light weight armor or as shielding materials due to their effective attenuation of mechanical impulses. Copyright © 2015 Elsevier B.V. All rights reserved.

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.

Altered disc pressure profile after an osteoporotic vertebral fracture is a risk factor for adjacent vertebral body fracture

PubMed Central

Tzermiadianos, Michael N.; Renner, Susan M.; Phillips, Frank M.; Hadjipavlou, Alexander G.; Zindrick, Michael R.; Havey, Robert M.; Voronov, Michael

2008-01-01

This study investigated the effect of endplate deformity after an osteoporotic vertebral fracture in increasing the risk for adjacent vertebral fractures. Eight human lower thoracic or thoracolumbar specimens, each consisting of five vertebrae were used. To selectively fracture one of the endplates of the middle VB of each specimen a void was created under the target endplate and the specimen was flexed and compressed until failure. The fractured vertebra was subjected to spinal extension under 150 N preload that restored the anterior wall height and vertebral kyphosis, while the fractured endplate remained significantly depressed. The VB was filled with cement to stabilize the fracture, after complete evacuation of its trabecular content to ensure similar cement distribution under both the endplates. Specimens were tested in flexion-extension under 400 N preload while pressure in the discs and strain at the anterior wall of the adjacent vertebrae were recorded. Disc pressure in the intact specimens increased during flexion by 26 ± 14%. After cementation, disc pressure increased during flexion by 15 ± 11% in the discs with un-fractured endplates, while decreased by 19 ± 26.7% in the discs with the fractured endplates. During flexion, the compressive strain at the anterior wall of the vertebra next to the fractured endplate increased by 94 ± 23% compared to intact status (p < 0.05), while it did not significantly change at the vertebra next to the un-fractured endplate (18.2 ± 7.1%, p > 0.05). Subsequent flexion with compression to failure resulted in adjacent fracture close to the fractured endplate in six specimens and in a non-adjacent fracture in one specimen, while one specimen had no adjacent fractures. Depression of the fractured endplate alters the pressure profile of the damaged disc resulting in increased compressive loading of the anterior wall of adjacent vertebra that predisposes it to wedge fracture. This data suggests that correction of endplate deformity may play a role in reducing the risk of adjacent fractures. PMID:18795344

Three-Dimensional Numerical Simulation on Triaxial Failure Mechanical Behavior of Rock-Like Specimen Containing Two Unparallel Fissures

NASA Astrophysics Data System (ADS)

Huang, Yan-Hua; Yang, Sheng-Qi; Zhao, Jian

2016-12-01

A three-dimensional particle flow code (PFC3D) was used for a systematic numerical simulation of the strength failure and cracking behavior of rock-like material specimens containing two unparallel fissures under conventional triaxial compression. The micro-parameters of the parallel bond model were first calibrated using the laboratory results of intact specimens and then validated from the experimental results of pre-fissured specimens under triaxial compression. Numerically simulated stress-strain curves, strength and deformation parameters and macro-failure modes of pre-fissured specimens were all in good agreement with the experimental results. The relationship between stress and the micro-crack numbers was summarized. Crack initiation, propagation and coalescence process of pre-fissured specimens were analyzed in detail. Finally, horizontal and vertical cross sections of numerical specimens were derived from PFC3D. A detailed analysis to reveal the internal damage behavior of rock under triaxial compression was carried out. The experimental and simulated results are expected to improve the understanding of the strength failure and cracking behavior of fractured rock under triaxial compression.

Insights into the effects of tensile and compressive loadings on human femur bone.

PubMed

Havaldar, Raviraj; Pilli, S C; Putti, B B

2014-01-01

Fragile fractures are most likely manifestations of fatigue damage that develop under repetitive loading conditions. Numerous microcracks disperse throughout the bone with the tensile and compressive loads. In this study, tensile and compressive load tests are performed on specimens of both the genders within 19 to 83 years of age and the failure strength is estimated. Fifty five human femur cortical samples are tested. They are divided into various age groups ranging from 19-83 years. Mechanical tests are performed on an Instron 3366 universal testing machine, according to American Society for Testing and Materials International (ASTM) standards. The results show that stress induced in the bone tissue depends on age and gender. It is observed that both tensile and compression strengths reduces as age advances. Compressive strength is more than tensile strength in both the genders. The compression and tensile strength of human femur cortical bone is estimated for both male and female subjecting in the age group of 19-83 years. The fracture toughness increases till 35 years in male and 30 years in female and reduces there after. Mechanical properties of bone are age and gender dependent.

Improving Non-Destructive Concrete Strength Tests Using Support Vector Machines

PubMed Central

Shih, Yi-Fan; Wang, Yu-Ren; Lin, Kuo-Liang; Chen, Chin-Wen

2015-01-01

Non-destructive testing (NDT) methods are important alternatives when destructive tests are not feasible to examine the in situ concrete properties without damaging the structure. The rebound hammer test and the ultrasonic pulse velocity test are two popular NDT methods to examine the properties of concrete. The rebound of the hammer depends on the hardness of the test specimen and ultrasonic pulse travelling speed is related to density, uniformity, and homogeneity of the specimen. Both of these two methods have been adopted to estimate the concrete compressive strength. Statistical analysis has been implemented to establish the relationship between hammer rebound values/ultrasonic pulse velocities and concrete compressive strength. However, the estimated results can be unreliable. As a result, this research proposes an Artificial Intelligence model using support vector machines (SVMs) for the estimation. Data from 95 cylinder concrete samples are collected to develop and validate the model. The results show that combined NDT methods (also known as SonReb method) yield better estimations than single NDT methods. The results also show that the SVMs model is more accurate than the statistical regression model. PMID:28793627

Fatigue Life Estimation under Cumulative Cyclic Loading Conditions

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh; McGaw, Michael A; Halford, Gary R.

1999-01-01

The cumulative fatigue behavior of a cobalt-base superalloy, Haynes 188 was investigated at 760 C in air. Initially strain-controlled tests were conducted on solid cylindrical gauge section specimens of Haynes 188 under fully-reversed, tensile and compressive mean strain-controlled fatigue tests. Fatigue data from these tests were used to establish the baseline fatigue behavior of the alloy with 1) a total strain range type fatigue life relation and 2) the Smith-Wastson-Topper (SWT) parameter. Subsequently, two load-level multi-block fatigue tests were conducted on similar specimens of Haynes 188 at the same temperature. Fatigue lives of the multi-block tests were estimated with 1) the Linear Damage Rule (LDR) and 2) the nonlinear Damage Curve Approach (DCA) both with and without the consideration of mean stresses generated during the cumulative fatigue tests. Fatigue life predictions by the nonlinear DCA were much closer to the experimentally observed lives than those obtained by the LDR. In the presence of mean stresses, the SWT parameter estimated the fatigue lives more accurately under tensile conditions than under compressive conditions.

The fatigue growth of internal delaminations under compressive loading of cross-ply composite plates

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

Pelegri, A.A.; Kardomateas, G.A.; Malik, B.U.

1997-12-31

This study focuses on the mode dependence of delamination growth under cyclic compressive loads in cross-ply composite plates. The model proposed makes use of an initial postbuckling solution derived from a perturbation procedure. A mode-dependent crack growth criterion is introduced. Expressions describing the fatigue crack growth are derived in terms of the distribution of the mode adjusted energy release rate. The resulting crack growth laws are numerically integrated to produce delamination growth versus number of cycles diagrams. The model does not impose any restrictive assumptions on the relative thickness of the delaminated and the base plates, although transverse shear stressmore » effects are not considered. Experimental results are presented for cross-ply graphite/epoxy specimens, and the results are compared with experimental results for unidirectional specimens. The test data are obtained for different delamination locations and for different values of applied compressive strain.« less

Effect of unground oil palm ash as mixing ingredient towards properties of concrete

NASA Astrophysics Data System (ADS)

Sulaiman, M. A.; Muthusamy, K.; Mat Aris, S.; Rasid, M. H. Mohd; Paramasivam, R.; Othman, R.

2018-04-01

Malaysia being one of the world largest palm oil producers generates palm oil fuel ash (POFA), a by-product in increasing quantity. This material which usually disposed as solid waste causes pollution to the environment. Success in converting this waste material into benefitting product would reduce amount of waste disposed and contributes towards cleaner environment. This research explores the potential of unground oil palm ash being used as partial sand replacement in normal concrete production. Experimental work has been conducted to determine the workability, compressive strength and flexural strength of concrete when unground oil palm ash is added as partial sand replacement. A total of five mixes containing various percentage of oil palm ash, which are 0%, 5%, 10%, 15% and 20% have been prepared. All specimens were water cured until the testing date. The slump test, compressive strength test and flexural strength test was conducted. The findings show that mix produced using 10% of palm oil fuel ash exhibit higher compressive strength and flexural strength as compared to control specimen. Utilization of unground oil palm ash as partial sand replacement would be able to reduce dependency of construction industry on natural sand supply and also as one of the solution to reuse palm oil industry waste.

Development of a stress-mode sensitive viscoelastic constitutive relationship for asphalt concrete: experimental and numerical modeling

NASA Astrophysics Data System (ADS)

Karimi, Mohammad M.; Tabatabaee, Nader; Jahanbakhsh, H.; Jahangiri, Behnam

2017-08-01

Asphalt binder is responsible for the thermo-viscoelastic mechanical behavior of asphalt concrete. Upon application of pure compressive stress to an asphalt concrete specimen, the stress is transferred by mechanisms such as aggregate interlock and the adhesion/cohesion properties of asphalt mastic. In the pure tensile stress mode, aggregate interlock plays a limited role in stress transfer, and the mastic phase plays the dominant role through its adhesive/cohesive and viscoelastic properties. Under actual combined loading patterns, any coordinate direction may experience different stress modes; therefore, the mechanical behavior is not the same in the different directions and the asphalt specimen behaves as an anisotropic material. The present study developed an anisotropic nonlinear viscoelastic constitutive relationship that is sensitive to the tension/compression stress mode by extending Schapery's nonlinear viscoelastic model. The proposed constitutive relationship was implemented in Abaqus using a user material (UMAT) subroutine in an implicit scheme. Uniaxial compression and indirect tension (IDT) testing were used to characterize the viscoelastic properties of the bituminous materials and to calibrate and validate the proposed constitutive relationship. Compressive and tensile creep compliances were calculated using uniaxial compression, as well as IDT test results, for different creep-recovery loading patterns at intermediate temperature. The results showed that both tensile creep compliance and its rate were greater than those of compression. The calculated deflections based on these IDT test simulations were compared with experimental measurements and were deemed acceptable. This suggests that the proposed viscoelastic constitutive relationship correctly demonstrates the viscoelastic response and is more accurate for analysis of asphalt concrete in the laboratory or in situ.

Experimental Study on the Growth, Coalescence and Wrapping Behaviors of 3D Cross-Embedded Flaws Under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Zhou, Xiao-Ping; Zhang, Jian-Zhi; Wong, Louis Ngai Yuen

2018-05-01

The crack initiation, growth, wrapping and coalescence of two 3D pre-existing cross-embedded flaws in PMMA specimens under uniaxial compression are investigated. The stress-strain curves of PMMA specimens with 3D cross-embedded flaws are obtained. The tested PMMA specimens exhibit dominant elastic deformation and eventual brittle failure. The experimental results show that four modes of crack initiation and five modes of crack coalescence are observed. The initiations of oblique secondary crack and anti-wing crack in 3D cracking behaviors are first reported as well as the coalescence of anti-wing cracks. Moreover, two types of crack wrapping are found. Substantial wrapping of petal cracks, which includes open and closed modes of wrapping, appears to be the major difference between 2D and 3D cracking behaviors of pre-existing flaws, which are also first reported. Petal crack wraps symmetrically from either the propagated wing cracks or the coalesced wing cracks. Besides, only limited growth of petal cracks is observed, and ultimate failure of specimens is induced by the further growth of the propagated wing crack. The fracture mechanism of the tested PMMA specimens is finally revealed. In addition, the initiation stress and the peak stress versus the geometry of two 3D pre-existing cross-embedded flaws are also investigated in detail.

Effects of maximum aggregate size on UPV of brick aggregate concrete.

PubMed

Mohammed, Tarek Uddin; Mahmood, Aziz Hasan

2016-07-01

Investigation was carried out to study the effects of maximum aggregate size (MAS) (12.5mm, 19.0mm, 25.0mm, 37.5mm, and 50.0mm) on ultrasonic pulse velocity (UPV) of concrete. For investigation, first class bricks were collected and broken to make coarse aggregate. The aggregates were tested for specific gravity, absorption capacity, unit weight, and abrasion resistance. Cylindrical concrete specimens were made with different sand to aggregate volume ratio (s/a) (0.40 and 0.45), W/C ratio (0.45, 0.50, and 0.55), and cement content (375kg/m(3) and 400kg/m(3)). The specimens were tested for compressive strength and Young's modulus. UPV through wet specimen was measured using Portable Ultrasonic Non-destructive Digital Indicating Tester (PUNDIT). Results indicate that the pulse velocity through concrete increases with an increase in MAS. Relationships between UPV and compressive strength; and UPV and Young's modulus of concrete are proposed for different maximum sizes of brick aggregate. Copyright © 2016 Elsevier B.V. All rights reserved.

Estimation of Crack Initiation and Propagation Thresholds of Confined Brittle Coal Specimens Based on Energy Dissipation Theory

NASA Astrophysics Data System (ADS)

Ning, Jianguo; Wang, Jun; Jiang, Jinquan; Hu, Shanchao; Jiang, Lishuai; Liu, Xuesheng

2018-01-01

A new energy-dissipation method to identify crack initiation and propagation thresholds is introduced. Conventional and cyclic loading-unloading triaxial compression tests and acoustic emission experiments were performed for coal specimens from a 980-m deep mine with different confining pressures of 10, 15, 20, 25, 30, and 35 MPa. Stress-strain relations, acoustic emission patterns, and energy evolution characteristics obtained during the triaxial compression tests were analyzed. The majority of the input energy stored in the coal specimens took the form of elastic strain energy. After the elastic-deformation stage, part of the input energy was consumed by stable crack propagation. However, with an increase in stress levels, unstable crack propagation commenced, and the energy dissipation and coal damage were accelerated. The variation in the pre-peak energy-dissipation ratio was consistent with the coal damage. This new method demonstrates that the crack initiation threshold was proportional to the peak stress ( σ p) for ratios that ranged from 0.4351 to 0.4753 σ p, and the crack damage threshold ranged from 0.8087 to 0.8677 σ p.

Enhancing Ultimate Compressive Strength of Notch Embedded Steel Cylinders Using Overwrap CFRP Patch

NASA Astrophysics Data System (ADS)

Kabir, Mohammad Z.; Nazari, Alireza

2012-06-01

In this study, the application of Fiber Reinforced Polymer (FRP) patch for strengthening of the damaged area in thin walled steel cylinders under compression loading was investigated. In this direction, some experimental tests were carried out on the selected notch induced specimens with unique diameter-to-thickness ratio (D/t). The obtained results were compared to the intact cylinder in order to find out the reduction effect of notch on the buckling load of cylinders. Following that, the notched specimens were treated using externally FRP by wrapping around the notched area and the stability strength of the retrofitted specimens was measured experimentally. The investigation was also carried out in numerical analysis using FEM in order to develop the proposed technique for determination of optimum FRP configurations and also better understanding of the experimental observations considering the nonlinear behavior and failure modes for composite member.

Experimental studies of graphite-epoxy and boron-epoxy angle ply laminates in compression

NASA Technical Reports Server (NTRS)

Weller, T.

1977-01-01

A test program aimed at studying the nonlinear/inelastic response under axial compression across a wide range of angle ply was graphite-epoxy and boron-epoxy laminates was presented and described. The strength allowables corresponding to the various laminate configurations were defined and the failure mechanisms which dictate their mode of failure were detected. The program involved two types of specimens for each laminate configuration: compression sandwich coupons and compression tubes. The test results indicate that the coupons perform better than the tubes displaying considerably high stress-strain allowables and mechanical properties relative to the tubes. Also, it is observed that depending on their dimensions the coupons are susceptible to very pronounced edge effects. This sensitivity results in assigning to the laminate conservative mechanical properties rather than the actual ones.

The Effect of Hole Quality on the Fatigue Life of 2024-T3 Aluminum Alloy Sheet

NASA Technical Reports Server (NTRS)

Everett, Richard A., Jr.

2004-01-01

This paper presents the results of a study whose main objective was to determine which type of fabrication process would least affect the fatigue life of an open-hole structural detail. Since the open-hole detail is often the fundamental building block for determining the stress concentration of built-up structural parts, it is important to understand any factor that can affect the fatigue life of an open hole. A test program of constant-amplitude fatigue tests was conducted on five different sets of test specimens each made using a different hole fabrication process. Three of the sets used different mechanical drilling procedures while a fourth and fifth set were mechanically drilled and then chemically polished. Two sets of specimens were also tested under spectrum loading to aid in understanding the effects of residual compressive stresses on fatigue life. Three conclusions were made from this study. One, the residual compressive stresses caused by the hole-drilling process increased the fatigue life by two to three times over specimens that were chemically polished after the holes were drilled. Second, the chemical polishing process does not appear to adversely affect the fatigue life. Third, the chemical polishing process will produce a stress-state adjacent to the hole that has insignificant machining residual stresses.

Evaluation of the Transient Liquid Phase (TLP) Bonding Process for Ti3Al-Based Honeycomb Core Sandwich Structure

NASA Technical Reports Server (NTRS)

Bird, R. Keith; Hoffman, Eric K.

1998-01-01

The suitability of using transient liquid phase (TLP) bonding to fabricate honeycomb core sandwich panels with Ti-14Al-21Nb (wt%) titanium aluminide (T3Al) face sheets for high-temperature hypersonic vehicle applications was evaluated. Three titanium alloy honeycomb cores and one Ti3Al alloy honeycomb core were investigated. Edgewise compression (EWC) and flatwise tension (FWT) tests on honeycomb core sandwich specimens and tensile tests of the face sheet material were conducted at temperatures ranging from room temperature to 1500 F. EWC tests indicated that the honeycomb cores and diffusion bonded joints were able to stabilize the face sheets up to and beyond the face sheet compressive yield strength for all temperatures investigated. The specimens with the T3Al honeycomb core produced the highest FWT strengths at temperatures above 1000 F. Tensile tests indicated that TLP processing conditions resulted in decreases in ductility of the Ti-14Al-21Nb face sheets. Microstructural examination showed that the side of the face sheets to which the filler metals had been applied was transformed from equiaxed alpha2 grains to coarse plates of alpha2 with intergranular Beta. Fractographic examination of the tensile specimens showed that this transformed region was dominated by brittle fracture.

Influence of High Temperature Treatment on Mechanical Behavior of a Coarse-grained Marble

NASA Astrophysics Data System (ADS)

Rong, G.; Peng, J.; Jiang, M.

2017-12-01

High temperature has a significant influence on the physical and mechanical behavior of rocks. With increasing geotechnical engineering structures concerning with high temperature problems such as boreholes for oil or gas production, underground caverns for storage of radioactive waste, and deep wells for injection of carbon dioxides, etc., it is important to study the influence of temperature on the physical and mechanical properties of rocks. This paper experimentally investigates the triaxial compressive properties of a coarse-grained marble after exposure to different high temperatures. The rock specimens were first heated to a predetermined temperature (200, 400, and 600 oC) and then cooled down to room temperature. Triaxial compression tests on these heat-treated specimens subjected to different confining pressures (i.e., 0, 5, 10, 15, 20, 25, 30, 35, and 40 MPa) were then conducted. Triaxial compression tests on rock specimens with no heat treatment were also conducted for comparison. The results show that the high temperature treatment has a significant influence on the microstructure, porosity, P-wave velocity, stress-strain relation, strength and deformation parameters, and failure mode of the tested rock. As the treatment temperature gradually increases, the porosity slightly increases and the P-wave velocity dramatically decreases. Microscopic observation on thin sections reveals that many micro-cracks will be generated inside the rock specimen after high temperature treatment. The rock strength and Young's modulus show a decreasing trend with increase of the treatment temperature. The ductility of the rock is generally enhanced as the treatment temperature increases. In general, the high temperature treatment weakens the performance of the tested rock. Finally, a degradation parameter is defined and a strength degradation model is proposed to characterize the strength behavior of heat-treated rocks. The results in this study provide useful data for evaluation of rock properties in high temperature condition.

Energy monitoring and analysis during deformation of bedded-sandstone: use of acoustic emission.

PubMed

Wasantha, P L P; Ranjith, P G; Shao, S S

2014-01-01

This paper investigates the mechanical behaviour and energy releasing characteristics of bedded-sandstone with bedding layers in different orientations, under uniaxial compression. Cylindrical sandstone specimens (54 mm diameter and 108 mm height) with bedding layers inclined at angles of 10°, 20°, 35°, 55°, and 83° to the minor principal stress direction, were produced to perform a series of Uniaxial Compressive Strength (UCS) tests. One of the two identical sample sets was fully-saturated with water before testing and the other set was tested under dry conditions. An acoustic emission system was employed in all the testing to monitor the acoustic energy release during the whole deformation process of specimens. From the test results, the critical joint orientation was observed as 55° for both dry and saturated samples and the peak-strength losses due to water were 15.56%, 20.06%, 13.5%, 13.2%, and 13.52% for the bedding orientations 10°, 20°, 35°, 55°, and 83°, respectively. The failure mechanisms for the specimens with bedding layers in 10°, 20° orientations showed splitting type failure, while the specimens with bedding layers in 55°, 83° orientations were failed by sliding along a weaker bedding layer. The failure mechanism for the specimens with bedding layers in 35° orientation showed a mixed failure mode of both splitting and sliding types. Analysis of the acoustic energy, captured from the acoustic emission detection system, revealed that the acoustic energy release is considerably higher in dry specimens than that of the saturated specimens at any bedding orientation. In addition, higher energy release was observed for specimens with bedding layers oriented in shallow angles (which were undergoing splitting type failures), whereas specimens with steeply oriented bedding layers (which were undergoing sliding type failures) showed a comparatively less energy release under both dry and saturated conditions. Moreover, a considerable amount of energy dissipation before the ultimate failure was observed for specimens with bedding layers oriented in shallow angles under both dry and saturated conditions. These results confirm that when rock having bedding layers inclined in shallow angles the failures could be more violent and devastative than the failures of rock with steeply oriented bedding layers. Copyright © 2013 Elsevier B.V. All rights reserved.

Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy Rene N4. 3: Tension-compression anisotropy

NASA Technical Reports Server (NTRS)

Miner, R. V.; Gaab, T. P.; Gayda, J.; Hemker, K. J.

1985-01-01

Single crystal superalloy specimens with various crystallographic directions along their axes were tested in compression at room temperature, 650, 760, 870, and 980 deg C. These results are compared with the tensile behavior studied previously. The alloy, Rene N4, was developed for gas turbine engine blades and has the nominal composition 3.7 Al, 4.2 Ti, 4 Ta, 0.5 Nb, 6 W, 1.5 Mo 9 Cr. 7.5 Co, balance Ni, in weight percent. Slip trace analysis showed that primary cube slip occurred even at room temperature for the 111 specimens. With increasing test temperature more orientations exhibited primary cube slip, until at 870 deg C only the 100 and 011 specimens exhibited normal octahedral slip. The yield strength for octahedral slip was numerically analysed using a model proposed by Lall, Chin, and Pope to explain deviations from Schmid's Law in the yielding behavior of a single phase Gamma prime alloy, Ni3(Al, Nb). The Schmid's Law deviations in Rene N4 were found to be largely due to a tension-compression anisotropy. A second effect, which increases trength for orientations away from 001, was found to be small in Rene N4. Analysis of recently published data on the single crystal superalloy PWA 1480 yielded the same result.

Joining strength performances of metal skin and CFRP core laminate structures realized by compression-curing process, with supporting experiments

NASA Astrophysics Data System (ADS)

Quagliato, Luca; Jang, Changsoon; Kim, Naksoo

2018-05-01

In the recent years, the trend of lightening vehicles and structures of every kind has become an ever-growing issue, both for university and industrial researchers. As demonstrated in previous authors' works, laminate structures made of metal skin (MS) and carbon fiber reinforced polymer (CFRP) core show high specific bending strength properties while granting considerable weight reduction but, so far, no investigations have been carried out on the hole sensitivity and joinability of these hybrid structures. In the present research work, the hole size sensitivity of MS-CFRP structure has been studied by means of uniaxial tensile test on 160mm (length), 25mm (width), 2.0mm (average thickness) specimens bored with Ø06mm, Ø9mm, and Ø12mm holes. The specimen thickness is composed of two metal skins of 0.4mm thickness each, 8×0.2mm CFRP stacked layers and two thin epoxy-based adhesive layers. The specimens have been manufactured by means of a compression-curing process in which the different materials are stacked and, thanks to die pressure and temperature, the curing process is completed in a relatively short time (15˜20 minutes). The specimens have been tested by means of simple tension test showing that, for the MS-CFRP material, the smaller the hole the smaller the maximum bearable load. Moreover, specimens with the same hole sizes have been bolted together with class 12 resistance bolts and tested by means of tensile test, allowing to determine the maximum transferable load between the two MS-CFRP plates. Aiming to prove the improvement in the specific transferable load, experiments on only-steel specimens with the same weight of the MS-CFRP ones and joined with the same method and bolts have been carried out, allowing to conclude that, for the 9mm hole bolted plates, the proposed material has a specific maximum transferable 27% higher than that of the steel composing their skins.

Orthotropic elasto-plastic behavior of AS4/APC-2 thermoplastic composite in compression

NASA Technical Reports Server (NTRS)

Sun, C. T.; Rui, Y.

1989-01-01

Uniaxial compression tests were performed on off-axis coupon specimens of unidirectional AS4/APC-2 thermoplastic composite at various temperatures. The elasto-plastic and strength properties of AS4/APC-2 composite were characterized with respect to temperature variation by using a one-parameter orthotropic plasticity model and a one-parameter failure criterion. Experimental results show that the orthotropic plastic behavior can be characterized quite well using the plasticity model, and the matrix-dominant compressive strengths can be predicted very accurately by the one-parameter failure criterion.

Effect of palm oil fuel ash on compressive strength of palm oil boiler stone lightweight aggregate concrete

NASA Astrophysics Data System (ADS)

Muthusamy, K.; Zamri, N. A.; Kusbiantoro, A.; Lim, N. H. A. S.; Ariffin, M. A. Mohd

2018-04-01

Both palm oil fuel ash (POFA) and palm oil boiler stone (POBS) are by-products which has been continuously generated by local palm oil mill in large amount. Both by products is usually disposed as profitless waste and considered as nuisance to environment. The present research investigates the workability and compressive strength performance of lightweight aggregate concrete (LWAC) made of palm oil boiler stone (POBS) known as palm oil boiler stone lightweight aggregate concrete (POBS LWAC) containing various content of palm oil fuel ash. The control specimen that is POBS LWAC of grade 60 were produced using 100% OPC. Then, another 4 mixes were prepared by varying the POFA percentage from 10%, 20%, 30% and 40% by weight of cement. Fresh mixes were subjected to slump test to determine its workability before casted in form of cubes. Then, all specimens were subjected to water curing up to 28 days and then tested for its compressive strength. It was found out that utilizing of optimum amount of POFA in POBS LWAC would improve the workability and compressive strength of the concrete. However, inclusion of POFA more than optimum amount is not recommended as it will increase the water demand leading to lower workability and strength reduction.

Experimental Investigation on the Fatigue Mechanical Properties of Intermittently Jointed Rock Models Under Cyclic Uniaxial Compression with Different Loading Parameters

NASA Astrophysics Data System (ADS)

Liu, Yi; Dai, Feng; Dong, Lu; Xu, Nuwen; Feng, Peng

2018-01-01

Intermittently jointed rocks, widely existing in many mining and civil engineering structures, are quite susceptible to cyclic loading. Understanding the fatigue mechanism of jointed rocks is vital to the rational design and the long-term stability analysis of rock structures. In this study, the fatigue mechanical properties of synthetic jointed rock models under different cyclic conditions are systematically investigated in the laboratory, including four loading frequencies, four maximum stresses, and four amplitudes. Our experimental results reveal the influence of the three cyclic loading parameters on the mechanical properties of jointed rock models, regarding the fatigue deformation characteristics, the fatigue energy and damage evolution, and the fatigue failure and progressive failure behavior. Under lower loading frequency or higher maximum stress and amplitude, the jointed specimen is characterized by higher fatigue deformation moduli and higher dissipated hysteresis energy, resulting in higher cumulative damage and lower fatigue life. However, the fatigue failure modes of jointed specimens are independent of cyclic loading parameters; all tested jointed specimens exhibit a prominent tensile splitting failure mode. Three different crack coalescence patterns are classified between two adjacent joints. Furthermore, different from the progressive failure under static monotonic loading, the jointed rock specimens under cyclic compression fail more abruptly without evident preceding signs. The tensile cracks on the front surface of jointed specimens always initiate from the joint tips and then propagate at a certain angle with the joints toward the direction of maximum compression.

Characterization of Dilatant Shear Bands in Castlegate Sandstone Using Micro-Computed Tomography

NASA Astrophysics Data System (ADS)

Rosenthal, R. E.; Issen, K. A.; Richards, M. C.; Ingraham, M. D.

2016-12-01

Deformation bands in granular rock are thin tabular zones of localized shear and/or volumetric strain, which affect permeability and can impact fluid flow, extraction and storage. The present work characterizes dilatant shear bands formed in Castlegate sandstone (a high porosity reservoir analog) during true triaxial laboratory testing (Ingraham et al., 2013a) at low mean stresses. X-ray micro-computed tomography (micro-CT) scans produced 3-dimensional voxel files containing density information of tested specimens. Micro-CT data were thresholded to extract the least dense voxels, corresponding to pore space and localized dilation. Plane fits were determined by a custom algorithm that calculated the angle between the band normal and maximum compression direction. For tests at the same mean stress, the band angle is lower when intermediate principal stress approaches minimum compression and higher when it approaches maximum compression. Micro-CT band angles were compared to angles from the specimen jackets (Ingraham et al., 2013a), and band angles from plane fits through located acoustic emissions (AE) events (Ingraham et al. 2013b). For non-axisymmetric stress states (three unique principal stresses), one primary dilatant shear band formed in each specimen. Occasionally, secondary bands traversing part of the specimen were also identified. The principal band angles from the micro-CT scans were on average within 3 degrees of the jacket angles and within 9 degrees of AE angles. For axisymmetric stress states (intermediate principal stress equal to maximum or minimum compression) micro-CT results reveal multiple conjugate and/or parallel bands. Each jacket angle correlated to a micro-CT angle within 4 degrees. Micro-CT results also reveal that, regardless of stress state, each band is comprised of a network of interconnected pore space pathways meandering between grain clusters, as opposed to an opening fracture/joint. Ingraham MD, KA Issen, DJ Holcomb, 2013a, J. Geophys. Res. Solid Earth, Vol. 118, pp. 536-552, doi:10.1002/jgrb.50084. Ingraham MD, KA Issen, DJ Holcomb, 2013b, Acta Geotech., Vol. 8, Iss. 6, pp. 645-663, DOI: 10.1007/s11440-013-0275-y.

Carbon Nanofiber Cement Sensors to Detect Strain and Damage of Concrete Specimens Under Compression

PubMed Central

Baeza, F. Javier; Garcés, Pedro

2017-01-01

Cement composites with nano-additions have been vastly studied for their functional applications, such as strain and damage sensing. The capacity of a carbon nanofiber (CNF) cement paste has already been tested. However, this study is focused on the use of CNF cement composites as sensors in regular concrete samples. Different measuring techniques and humidity conditions of CNF samples were tested to optimize the strain and damage sensing of this material. In the strain sensing tests (for compressive stresses up to 10 MPa), the response depends on the maximum stress applied. The material was more sensitive at higher loads. Furthermore, the actual load time history did not influence the electrical response, and similar curves were obtained for different test configurations. On the other hand, damage sensing tests proved the capability of CNF cement composites to measure the strain level of concrete samples, even for loads close to the material’s strength. Some problems were detected in the strain transmission between sensor and concrete specimens, which will require specific calibration of each sensor one attached to the structure. PMID:29186797

Carbon Nanofiber Cement Sensors to Detect Strain and Damage of Concrete Specimens Under Compression.

PubMed

Galao, Oscar; Baeza, F Javier; Zornoza, Emilio; Garcés, Pedro

2017-11-24

Cement composites with nano-additions have been vastly studied for their functional applications, such as strain and damage sensing. The capacity of a carbon nanofiber (CNF) cement paste has already been tested. However, this study is focused on the use of CNF cement composites as sensors in regular concrete samples. Different measuring techniques and humidity conditions of CNF samples were tested to optimize the strain and damage sensing of this material. In the strain sensing tests (for compressive stresses up to 10 MPa), the response depends on the maximum stress applied. The material was more sensitive at higher loads. Furthermore, the actual load time history did not influence the electrical response, and similar curves were obtained for different test configurations. On the other hand, damage sensing tests proved the capability of CNF cement composites to measure the strain level of concrete samples, even for loads close to the material's strength. Some problems were detected in the strain transmission between sensor and concrete specimens, which will require specific calibration of each sensor one attached to the structure.

Advantages of Residual Stresses in Dynamically Riveted Joints.

DTIC Science & Technology

1978-02-01

strain distribution around a rivet hole, and describes an experimental method for measuring the radial velocity of an expanding rivet. The advantages of... benefits of compressive residual stresses in riveted joints, fatigue specimens made of 2024-T81 aluminum were used. The specimens were tested at constant...concentration of in-service tensile stresses near the hole surfaze. Substan;Aal and significant benefits in design life and structural weight can be

End Restraints for Impact-Energy-Absorbing Tube Specimens

NASA Technical Reports Server (NTRS)

Farley, G. L.; Modlin, J. T.

1985-01-01

Inexpensive device developed that eliminates tipping problem without affecting crushing process. Device consists of soft sponge-rubber insert approximately 0.5 inches (1.3 centimeters) thick, cut to same diameter as internal diameter of tube specimen. Metal washer, slightly smaller than internal diameter of tube, placed on top of rubber insert. Screw passed through washer and rubber insert and threaded into base of test machine. As screw tightened against washer, rubber insert compressed and expands radially. Radial expansion applies pressure against internal wall of tube specimen, which provides sufficient support to tube to prevent tipping.

A study on the crushing behavior of basalt fiber reinforced composite structures

NASA Astrophysics Data System (ADS)

Pandian, A.; Veerasimman, A. P.; Vairavan, M.; Francisco, C.; Sultan, M. T. H.

2016-10-01

The crushing behavior and energy absorption capacity of basalt fiber reinforced hollow square structure composites are studied under axial compression. Using the hand layup technique, basalt fiber reinforced composites were fabricated using general purpose (GP) polyester resin with the help of wooden square shaped mould of varying height (100 mm, 150 mm and 200 mm). For comparison, similar specimens of glass fiber reinforced polymer composites were also fabricated and tested. Axial compression load is applied over the top end of the specimen with cross head speed as 2 mm/min using Universal Testing Machine (UTM). From the experimental results, the load-deformation characteristics of both glass fiber and basalt fiber composites were investigated. Crashworthiness and mode of collapse for the composites were determined from load-deformation curve, and they were then compared to each other in terms of their crushing behaviors.

Mechanical properties of new dental pulp-capping materials.

PubMed

Nielsen, Matthew J; Casey, Jeffery A; VanderWeele, Richard A; Vandewalle, Kraig S

2016-01-01

The mechanical properties of pulp-capping materials may affect their resistance to fracture during placement of a final restorative material or while supporting an overlying restoration over time. The purpose of this study was to compare the compressive strength, flexural strength, and flexural modulus of 2 new pulp-capping materials (TheraCal LC and Biodentine), mineral trioxide aggregate (MTA), and calcium hydroxide over time. Specimens were created in molds and tested to failure in a universal testing machine after 15 minutes, 3 hours, and 24 hours. The MTA specimens did not set at 15 minutes. At all time periods, TheraCal LC had the greatest compressive and flexural strengths. After 3 and 24 hours, Biodentine had the greatest flexural modulus. TheraCal LC had greater early strength to potentially resist fracture during immediate placement of a final restorative material. Biodentine had greater stiffness after 3 hours to potentially provide better support of an overlying restoration under function over time.

Microstructure and mechanical properties of selective laser melted Ti6Al4V alloy

NASA Astrophysics Data System (ADS)

Losertová, M.; Kubeš, V.

2017-11-01

The present work was focused on the properties of porous Ti6Al4V specimens processed by selective laser melting (SLM) and tested in tension and compression before and after heat treatment. The SLM samples were annealed at 955 °C, water quenched and aged at 600 °C with following air cooling. The values of the mechanical tests showed that the samples exhibited high mechanical properties. The anisotropy of tensile and compressive strength was observed, which was related to the occurrence of voids. The plastic properties of specimens were improved by means of the heat treatment that led to the transformation of martensitic to lamellar structure composed of α + β phases. The microstructure of SLM samples were evaluated before and after the heat treatment. The brittle nature of failures of non-heat treated samples can be explained by synergy of martensite presence, microcracks and residual stresses produced by SLM.

Notched Strength Allowables and Inplane Shear Strength of AS4/VRM-34 Textile Laminates

NASA Technical Reports Server (NTRS)

Grenoble, Ray W.; Johnston, William M.

2013-01-01

Notched and unnotched strength allowables were developed for a textile composite to provide input data to analytical structural models based on the Pultruded Rod Stiffened Efficient Unitized Structure (PRSEUS) concept. Filled-hole tensile strength, filled-hole compressive strength, and inplane shear strength along stitch lines have been measured. The material system evaluated in this study is based on warp-knitted preforms of AS4 carbon fibers and VRM-34 epoxy resin, which have been processed via resin infusion and oven curing. All specimens were tested in as-fabricated (dry) condition. Filled-hole strengths were evaluated with and without through-thickness stitching. The effects of scaling on filled-hole tensile strength were evaluated by testing specimens in two widths, but with identical width / hole-diameter ratios. Inplane shear specimens were stitched in two configurations, and two specimen thicknesses were tested for each stitch configuration.

Production of ultrafine grained aluminum by cyclic severe plastic deformation at ambient temperature

NASA Astrophysics Data System (ADS)

Bereczki, P.; Szombathelyi, V.; Krallics, G.

2014-08-01

In the present study the possibilities of grain refinement was investigated by applying large-scale of cyclic plastic deformation to aluminum at ambient temperature. The specimens are processed by multiaxial forging, which is one of the severe plastic deformation techniques. The aim of the experiments with the aluminum alloy 6082M was the determination of the equivalent stress and strain by multiaxial forging and the investigation of evolution of mechanical properties in relation with the accumulated deformation in the specimen. The mechanical properties of raw material was determined by plane strain compression test as well as by hardness measurements. The forming experiments were carried out on Gleeble 3800 physical simulator with MaxStrain System. The mechanical properties of the forged specimens were investigated by micro hardness measurements and tensile tests. A mechanical model, based on the principle of virtual velocities was developed to calculate the flow curves using the measured dimensional changes of the specimen and the measured force. With respect to the evolution of these curves, the cyclic growth of the flow stress can be observed at every characteristic points of the calculated flow curves. In accordance with this tendency, the evolution of the hardness along the middle cross section of the deformed volume has also a nonmonotonous characteristic and the magnitudes of these values are much smaller than by the specimen after plane strain compression test. This difference between the flow stresses respect to the monotonic and non-monotonic deformation can be also observed. The formed microstructure, after a 10-passes multiaxial forging process, consists of mainly equiaxial grains in the submicron grain scale.

Strain-controlled fatigue of acrylic bone cement.

PubMed

Carter, D R; Gates, E I; Harris, W H

1982-09-01

Monotonic tensile tests and tension-compression fatigue tests were conducted of wet acrylic bone cement specimens at 37 degrees C. All testing was conducted in strain control at a strain rate of 0.02/s. Weibull analysis of the tensile tests indicated that monotonic fracture was governed more strongly by strain than stress. The number of cycles to fatigue failure was also more strongly controlled by strain amplitude than stress amplitude. Specimen porosity distribution played a major role in determining the tensile and fatigue strengths. The degree of data scatter suggests that Weibull analysis of fatigue data may be useful in developing design criteria for the surgical use of bone cement.

Palm Oil Fuel Ash (POFA) and Eggshell Powder (ESP) as Partial Replacement for Cement in Concrete

NASA Astrophysics Data System (ADS)

Ezdiani Mohamad, Mazizah; Mahmood, Ali A.; Min, Alicia Yik Yee; Nur Nadhira A., R.

2018-03-01

This study is an attempt to partially replace Ordinary Portland cement (OPC) in concrete with palm oil fuel ash (POFA) and eggshell powder (ESP). The mix proportions of POFA and ESP were varied at 10% of cement replacement and compared with OPC concrete as control specimen. The fineness of POFA is characterized by passing through 300 μm sieve and ESP by passing through 75 μm sieve. Compressive strength testing was conducted on concrete specimens to determine the optimum mix proportion of POFA and ESP. Generally the compressive strength of OPC concrete is higher compared to POFA-ESP concrete. Based on the results of POFA-ESP concrete overall, it shows that the optimum mix proportion of concrete is 6%POFA:4% ESP achieved compressive strength of 38.60 N/mm2 at 28 days. The compressive strength of OPC concrete for the same period was 42.37 N/mm2. Higher water demand in concrete is needed due to low fineness of POFA that contributing to low compressive strength of POFA-ESP concrete. However, the compressive strength and workability of the POFA-ESP concrete were within the ranges typically encountered in regular concrete mixtures indicating the viability of this replacement procedure for structural and non-structural applications.

Investigation of Dynamic Crack Coalescence Using a Gypsum-Like 3D Printing Material

NASA Astrophysics Data System (ADS)

Jiang, Chao; Zhao, Gao-Feng; Zhu, Jianbo; Zhao, Yi-Xin; Shen, Luming

2016-10-01

Dynamic crack coalescence attracts great attention in rock mechanics. However, specimen preparation in experimental study is a time-consuming and difficult procedure. In this work, a gypsum-like material by powder bed and inkjet 3D printing technique was applied to produce specimens with preset cracks for split Hopkinson pressure bar (SHPB) test. From micro X-ray CT test, it was found that the 3D printing technique could successfully prepare specimens that contain preset cracks with width of 0.2 mm. Basic mechanical properties of the 3D printing material, i.e., the elastic modulus, the Poisson's ratio, the density, the compressive strength, the indirect tensile strength, and the fracture toughness, were obtained and reported. Unlike 3D printed specimens using polylactic acid, these gypsum-like specimens can produce failure patterns much closer to those observed in classical rock mechanical tests. Finally, the dynamic crack coalescence of the 3D printed specimens with preset cracks were captured using a high-speed camera during SHPB tests. Failure patterns of these 3D printed specimens are similar to the specimens made by Portland cement concrete. Our results indicate that sample preparation by 3D printing is highly competitive due to its quickness in prototyping, precision and flexibility on the geometry, and high material homogeneity.

Material Property Characterization of AS4/VRM-34 Textile Laminates

NASA Technical Reports Server (NTRS)

Grenoble, Ray W.; Johnston, William M

2013-01-01

Several material properties (modulus, strengths, and fracture toughness) of a textile composite have been evaluated to provide input data to analytical models of Pultruded Rod Stiffened Efficient Unitized Structure (PRSEUS). The material system is based on warp-knitted preforms of AS4 carbon fibers and VRM-34 epoxy resin, which have been processed via resin infusion and oven curing. Tensile, compressive, shear, and fracture toughness properties have been measured at ambient and elevated temperatures. All specimens were tested in as-fabricated (dry) condition. Specimens were tested with and without through-thickness stitching.

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).

29 CFR Appendix A to Subpart Q of... - References to subpart Q of Part 1926

Code of Federal Regulations, 2010 CFR

2010-07-01

... (ASTM C39-86). • Standard Test Method for Making and Curing Concrete Test Specimens in the Field (ASTM C31-85). • Standard Test Method for Penetration Resistance of Hardened Concrete (ASTM C803-82... (ASTM C873-85). • Standard Method for Developing Early Age Compressive Test Values and Projecting Later...

Initial Mechanical Testing of Superalloy Lattice Block Structures Conducted

NASA Technical Reports Server (NTRS)

Krause, David L.; Whittenberger, J. Daniel

2002-01-01

The first mechanical tests of superalloy lattice block structures produced promising results for this exciting new lightweight material system. The testing was performed in-house at NASA Glenn Research Center's Structural Benchmark Test Facility, where small subelement-sized compression and beam specimens were loaded to observe elastic and plastic behavior, component strength levels, and fatigue resistance for hundreds of thousands of load cycles. Current lattice block construction produces a flat panel composed of thin ligaments arranged in a three-dimensional triangulated trusslike structure. Investment casting of lattice block panels has been developed and greatly expands opportunities for using this unique architecture in today's high-performance structures. In addition, advances made in NASA's Ultra-Efficient Engine Technology Program have extended the lattice block concept to superalloy materials. After a series of casting iterations, the nickel-based superalloy Inconel 718 (IN 718, Inco Alloys International, Inc., Huntington, WV) was successfully cast into lattice block panels; this combination offers light weight combined with high strength, high stiffness, and elevated-temperature durability. For tests to evaluate casting quality and configuration merit, small structural compression and bend test specimens were machined from the 5- by 12- by 0.5-in. panels. Linear elastic finite element analyses were completed for several specimen layouts to predict material stresses and deflections under proposed test conditions. The structural specimens were then subjected to room-temperature static and cyclic loads in Glenn's Life Prediction Branch's material test machine. Surprisingly, the test results exceeded analytical predictions: plastic strains greater than 5 percent were obtained, and fatigue lives did not depreciate relative to the base material. These assets were due to the formation of plastic hinges and the redundancies inherent in lattice block construction, which were not considered in the simplified computer models. The fatigue testing proved the value of redundancies since specimen strength was maintained even after the fracture of one or two ligaments. This ongoing test program is planned to continue through high-temperature testing. Also scheduled for testing are IN 718 lattice block panels with integral face sheets, as well as specimens cast from a higher temperature alloy. The initial testing suggests the value of this technology for large panels under low and moderate pressure loadings and for high-risk, damage-tolerant structures. Potential aeropropulsion uses for lattice blocks include turbine-engine actuated panels, exhaust nozzle flaps, and side panel structures.

Freeing Space for NASA: Incorporating a Lossless Compression Algorithm into NASA's FOSS System

NASA Technical Reports Server (NTRS)

Fiechtner, Kaitlyn; Parker, Allen

2011-01-01

NASA's Fiber Optic Strain Sensing (FOSS) system can gather and store up to 1,536,000 bytes (1.46 megabytes) per second. Since the FOSS system typically acquires hours - or even days - of data, the system can gather hundreds of gigabytes of data for a given test event. To store such large quantities of data more effectively, NASA is modifying a Lempel-Ziv-Oberhumer (LZO) lossless data compression program to compress data as it is being acquired in real time. After proving that the algorithm is capable of compressing the data from the FOSS system, the LZO program will be modified and incorporated into the FOSS system. Implementing an LZO compression algorithm will instantly free up memory space without compromising any data obtained. With the availability of memory space, the FOSS system can be used more efficiently on test specimens, such as Unmanned Aerial Vehicles (UAVs) that can be in flight for days. By integrating the compression algorithm, the FOSS system can continue gathering data, even on longer flights.

Dynamic Response and Failure Mechanism of Brittle Rocks Under Combined Compression-Shear Loading Experiments

NASA Astrophysics Data System (ADS)

Xu, Yuan; Dai, Feng

2018-03-01

A novel method is developed for characterizing the mechanical response and failure mechanism of brittle rocks under dynamic compression-shear loading: an inclined cylinder specimen using a modified split Hopkinson pressure bar (SHPB) system. With the specimen axis inclining to the loading direction of SHPB, a shear component can be introduced into the specimen. Both static and dynamic experiments are conducted on sandstone specimens. Given carefully pulse shaping, the dynamic equilibrium of the inclined specimens can be satisfied, and thus the quasi-static data reduction is employed. The normal and shear stress-strain relationships of specimens are subsequently established. The progressive failure process of the specimen illustrated via high-speed photographs manifests a mixed failure mode accommodating both the shear-dominated failure and the localized tensile damage. The elastic and shear moduli exhibit certain loading-path dependence under quasi-static loading but loading-path insensitivity under high loading rates. Loading rate dependence is evidently demonstrated through the failure characteristics involving fragmentation, compression and shear strength and failure surfaces based on Drucker-Prager criterion. Our proposed method is convenient and reliable to study the dynamic response and failure mechanism of rocks under combined compression-shear loading.

Structural Influence on the Mechanical Response of Adolescent Gottingen Porcine Cranial Bone

DTIC Science & Technology

2016-10-01

specimens were then loaded in quasi -static compression to measure their mechanical response. The surface strain distribution on the specimen face was...13 Fig. 10 Apparent stress-strain responses of a sample of specimens loaded in quasi -static compression...modulus-BVF experimental results shown in Fig. 15 ..................................................................................19 Fig. 17 The

Effects of age and loading rate on equine cortical bone failure.

PubMed

Kulin, Robb M; Jiang, Fengchun; Vecchio, Kenneth S

2011-01-01

Although clinical bone fractures occur predominantly under impact loading (as occurs during sporting accidents, falls, high-speed impacts or other catastrophic events), experimentally validated studies on the dynamic fracture behavior of bone, at the loading rates associated with such events, remain limited. In this study, a series of tests were performed on femoral specimens obtained post-mortem from equine donors ranging in age from 6 months to 28 years. Fracture toughness and compressive tests were performed under both quasi-static and dynamic loading conditions in order to determine the effects of loading rate and age on the mechanical behavior of the cortical bone. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack initiation between dynamic and quasi-static experiments. Compressive properties were measured on bone loaded parallel and transverse to the osteonal growth direction. Fracture propagation was then analyzed using scanning electron and scanning confocal microscopy to observe the effects of microstructural toughening mechanisms at different strain rates. Specimens from each horse were also analyzed for dry, wet and mineral densities, as well as weight percent mineral, in order to investigate possible influences of composition on mechanical behavior. Results indicate that bone has a higher compressive strength, but lower fracture toughness when tested dynamically as compared to quasi-static experiments. Fracture toughness also tends to decrease with age when measured quasi-statically, but shows little change with age under dynamic loading conditions, where brittle "cleavage-like" fracture behavior dominates. Copyright © 2010 Elsevier Ltd. All rights reserved.

Constitutive Soil Properties for Mason Sand and Kennedy Space Center

NASA Technical Reports Server (NTRS)

Thomas, Michael A.; Chitty, Daniel E.

2011-01-01

Accurate soil models are required for numerical simulations of land landings for the Orion Crew Exploration Vehicle (CEV). This report provides constitutive material models for two soil conditions at Kennedy Space Center (KSC) and four conditions of Mason Sand. The Mason Sand is the test sand for LaRC s drop tests and swing tests of the Orion. The soil models are based on mechanical and compressive behavior observed during geotechnical laboratory testing of remolded soil samples. The test specimens were reconstituted to measured in situ density and moisture content. Tests included: triaxial compression, hydrostatic compression, and uniaxial strain. A fit to the triaxial test results defines the strength envelope. Hydrostatic and uniaxial tests define the compressibility. The constitutive properties are presented in the format of LSDYNA Material Model 5: Soil and Foam. However, the laboratory test data provided can be used to construct other material models. The soil models are intended to be specific to the soil conditions they were tested at. The two KSC models represent two conditions at KSC: low density dry sand and high density in-situ moisture sand. The Mason Sand model was tested at four conditions which encompass measured conditions at LaRC s drop test site.

Thermal Aging Study of a Dow Corning SE 1700 Porous Structure Made by Direct Ink Writing: 1-Year Results and Long-Term Predictions

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

Small, Ward; Pearson, Mark A.; Maiti, Amitesh

Dow Corning SE 1700 (reinforced polydimethylsiloxane) porous structures were made by direct ink writing (DIW). The specimens (~50% porosity) were subjected to various compressive strains (15, 30, 45%) and temperatures (room temperature, 35, 50, 70°C) in a nitrogen atmosphere (active purge) for 1 year. Compression set and load retention of the aged specimens were measured periodically during the study. Compression set increased with strain and temperature. After 1 year, specimens aged at room temperature, 35, and 50°C showed ~10% compression set (relative to the applied compressive deflection), while those aged at 70°C showed 20-40%. Due to the increasing compression set,more » load retention decreased with temperature, ranging from ~90% at room temperature to ~60-80% at 70°C. Long-term compression set and load retention at room temperature were predicted by applying time-temperature superposition (TTS). The predictions show compression set relative to the compressive deflection will be ~10-15% with ~70-90% load retention after 50 years at 15-45% strain, suggesting the material will continue to be mechanically functional. Comparison of the results to previously acquired data for cellular (M97*, M9760, M9763) and RTV (S5370) silicone foams suggests that the SE 1700 DIW porous specimens are on par with, or outperform, the legacy foams.« less

Hydrostatic Stress Effects in Metal Plasticity

NASA Technical Reports Server (NTRS)

Wilson, Christopher D.

1999-01-01

Since the 1940s, the theory of plasticity has assumed that hydrostatic stress does not affect the yield or postyield behavior of metals. This assumption is based on the early work of Bridgman. Bridgman found that hydrostatic pressure (compressive stress) does not affect yield behavior until a substantial amount of pressure (greater than 100 ksi) is present. The objective of this study was to determine the effect of hydrostatic tension on yield behavior. Two different specimen geometries were examined: an equal-arm bend specimen and a double edge notch specimen. The presence of a notch is sufficient to develop high enough hydrostatic tensile stresses to affect yield. The von Mises yield function, which does not have a hydrostatic component, and the Drucker-Prager yield function, which includes a hydrostatic component, were used in finite element analyses of the two specimen geometries. The analyses were compared to test data from IN 100 specimens. For both geometries, the analyses using the Drucker-Prager yield function more closely simulated the test data. The von Mises yield function lead to 5-10% overprediction of the force-displacement or force-strain response of the test specimens.

Effect of Applied Stress on the Mechanical Properties of a Zr-Cu-Ag-Al Bulk Metallic Glass with Two Different Structure States

PubMed Central

Chen, Heng; Zhang, Taihua; Ma, Yi

2017-01-01

In order to investigate the effect of applied stress on mechanical properties in metallic glasses, nanoindentation tests were conducted on elastically bent Zr-Cu-Ag-Al metallic glasses with two different structure states. From spherical P-h curves, elastic modulus was found to be independent on applied stress. Hardness decreased by ~8% and ~14% with the application of 1.5% tensile strain for as-cast and 650 K annealed specimens, while it was slightly increased at the compressive side. Yield stress could be obtained from the contact pressure at first pop-in position with a conversion coefficient. The experimental result showed a symmetrical effect of applied stress on strengthening and a reduction of the contact pressure at compressive and tensile sides. It was observed that the applied stress plays a negligible effect on creep deformation in as-cast specimen. While for the annealed specimen, creep deformation was facilitated by applied tensile stress and suppressed by applied compressive stress. Strain rate sensitivities (SRS) were calculated from steady-state creep, which were constant for as-cast specimen and strongly correlated with applied stress for the annealed one. The more pronounced effect of applied stress in the 650 K annealed metallic glass could be qualitatively explained through the variation of the shear transformation zone (STZ) size. PMID:28773065

Monitoring fatigue damage in carbon fiber composites using an acoustic impact technique

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

Haque, A.; Raju, P.K.

1998-06-01

The acoustic impact technique (AIT) of nondestructive testing (NDT) has been used to identify the damage that results from the compressive and tension-compression cycle loading around a circular notch of quasiisotropic carbon-fiber composites. This method involves applying a low velocity impact to the test specimen and evaluating the resulting localized acoustic response. Results indicate that AIT can be applied for identification of both compressive and fatigue damage in composite laminates. The gross area of compressive and fatigue damage is detected through an increase in the pulse width, and a decrease in the amplitude, of the force-time signal. The response obtainedmore » in AIT is sensitive to the frequency of the impactor and the amplitude of the impact force and requires careful monitoring of these values to achieve repeatability of results.« less

Roughness and compressive strength of FDM 3D printed specimens affected by acetone vapour treatment

NASA Astrophysics Data System (ADS)

Beniak, Juraj; Križan, Peter; Šooš, Ľubomír; Matúš, Miloš

2018-01-01

Rapid Prototyping technologies are the fastest growing technologies in the manufacturing of components and parts. There are many techniques which can be used with different materials and different purposes of produced part. Gradually, Rapid Prototyping systems have grown into Additive Manufacturing, because technology expansion brings faster production, improved manufactured components, and expanded palette of used materials. So now this techniques are also used for regular production of special parts, where is usual change of part design, where is necessary to produce variety of different designs and shapes. The following article deals with Fused Deposition Modelling (FDM) technology, the core of which is the manufacture models and components from thermoplastic polymers by deposition single fibres of semi-molten plastic material layer by layer. The article focuses on the results of research for testing of manufactured specimens by FDM technology. Components are modified by acetone vapour for surface smoothing. The purpose is to point out how the additional specimen treatment influence the strength properties. Presented paper shows realized experiments and measurements of compressive force on specimens and surface roughness which are influenced by acetone vapour treatment.

Hardness and compression resistance of natural rubber and synthetic rubber mixtures

NASA Astrophysics Data System (ADS)

Arguello, J. M.; Santos, A.

2016-02-01

This project aims to mechanically characterize through compression resistance and shore hardness tests, the mixture of hevea brasiliensis natural rubber with butadiene synthetic rubber (BR), styrene-butadiene rubber (SBR) and ethylene-propylene-diene monomer rubber (EPDM). For each of the studied mixtures were performed 10 tests, each of which increased by 10% the content of synthetic rubber in the mixture; each test consisted of carrying out five tests of compression resistance and five tests of shore hardness. The specimens were vulcanized on a temperature of 160°C, during an approximate time of 15 minutes, and the equipment used in the performance of the mechanical tests were a Shimadzu universal machine and a digital durometer. The results show that the A shore hardness increases directly proportional, with a linear trend, with the content of synthetic BR, SBR or EPDM rubber present in the mixture, being the EPDM the most influential. With respect to the compression resistance is observed that the content of BR or SBR increase this property directly proportional through a linear trend; while the EPDM content also increases but with a polynomial trend.

Effect of waste banner as fiber on mechanical properties of concrete

NASA Astrophysics Data System (ADS)

Rahmawati, Anis; Saputro, Ida Nugroho

2017-06-01

Banner is broadly used as advertisement media and event backdrop that is usually only used at one moment, resulting to a lot of waste banners. Banner made from nylon fiber is covered by polyvinyl. Nylon is well known as a material with high tensile strength. This research was done as a preliminary investigation on the opportunity of using the waste banner as fiber material of concrete by evaluating its mechanical properties, namely compressive and flexural strength. Research conducted by making cylinder shape specimens of 15 mm in diameter and 300 mm in height for the compressive strength test. While the specimen shape for flexural strength test was a rectangular prism with dimension of 150 mm in height, 150 mm in width, and 600 mm in length. Fiber generated from waste banner was added in concrete mixtures with percentage of 0.00%, 0.20%, 0.40%, 0.60%, 0.80%, and 1.00% by weight of concrete. The concrete strength was tested at 28 days after standard moisture and temperature curing. Experimental results indicated that the addition of 0.20% of waste banner obtained the highest compressive strength that was 21.967 Mpa, while 0.40% of waste banner obtained the highest flexural strength of 4.663 Mpa.

Corrosion and Fatigue Behavior of High-Strength Steel Treated with a Zn-Alloy Thermo-diffusion Coating

NASA Astrophysics Data System (ADS)

Mulligan, C. P.; Vigilante, G. N.; Cannon, J. J.

2017-11-01

High and low cycle fatigue tests were conducted on high-strength steel using four-point bending. The materials tested were ASTM A723 steel in the as-machined condition, grit-blasted condition, MIL-DTL-16232 heavy manganese phosphate-coated condition, and ASTM A1059 Zn-alloy thermo-diffusion coated (Zn-TDC). The ASTM A723 steel base material exhibits a yield strength of 1000 MPa. The effects of the surface treatments versus uncoated steel were examined. The fatigue life of the Zn-TDC specimens was generally reduced on as-coated specimens versus uncoated or phosphate-coated specimens. Several mechanisms are examined including the role of compressive residual stress relief with the Zn-TDC process as well as fatigue crack initiation from the hardened Zn-Fe alloy surface layer produced in the gas-metal reaction. Additionally, the effects of corrosion pitting on the fatigue life of coated specimens are explored as the Zn-TDC specimens exhibit significantly improved corrosion resistance over phosphate-coated and oiled specimens.

Crashworthy Troop Seat Testing Program

DTIC Science & Technology

1977-11-01

19 ’rest 4 . . . . . . . . . .. . 29 | Detail Design’Finalization. .... 29 Vertical Wire - Bending Energy Attenuator 32 Toggle Latch...Strut Wire - Bending Attenuator Force Deflection. . . . ................... 28 15 Notched Wire and Pin Anchorage Test Specimen . 30 16 Quick-Disconnect...and Hold-Down Cable ......... 31 17 Failed Hold-Down Cable ...... . . . . 31 18 Wire - Bending Tension/Compression Energy Attenuator

Controls on radon emission from granite as evidenced by compression testing to failure

NASA Astrophysics Data System (ADS)

Koike, Katsuaki; Yoshinaga, Tohru; Suetsugu, Kenta; Kashiwaya, Koki; Asaue, Hisafumi

2015-10-01

A set of uniaxial compression tests of granite specimens taken from five localities across Japan was conducted to identify the factors controlling the quantity of radon (Rn) emission (sum of 222Rn and 220Rn) during compression and failure. An α-scintillation detector and a gas flow unit were installed with a testing machine to enable continuous measurement of Rn emissions. Common to all specimens, Rn emissions remained at or slightly declined from the background level after the start of loading; this is similar to the natural phenomenon of decline in groundwater-dissolved Rn before an earthquake. Closure of original microcracks is the most likely cause of the initial Rn decline. Then, Rn emissions begin to increase at 46-57 per cent stress level to the uniaxial compressive strength, and continue to increase even after the failure of specimen. This commencement stress level is close to the general stress level at outbreak of acoustic emissions caused by the development and connection of microcracks. The Rn increase after failure is similar to a phenomenon observed in aftershocks, which may originate from the enhancement of Rn emanations from grains due to the large increase in total surface area and stress release. In addition to the initial radioelement content in rock, the failure pattern (conjugate shear versus longitudinal tensile type), compressive strength, and grain size are possible control factors of the maximum quantity of Rn emissions induced by failure. This maximum may also be affected by the development velocity of the emanation area, which is related to the Rn emanation fraction, associated with the fragmentation. In addition to the magnitude of an earthquake and its hypocentre distance to Rn detectors, the magnitude of increase in Rn concentration in soil gas and groundwater before, during, and after an earthquake in crystalline rocks depends on the intrinsic radioelement content, the mineral texture, and the mechanical properties of rocks. Rock fracturing and failure do not necessarily induce increase in Rn emission due to these rock properties, which can be used to understand the sensitivity of Rn concentration in soil gas or groundwater in connection with an earthquake.

Damage development under compression-compression fatigue loading in a stitched uniwoven graphite/epoxy composite material

NASA Technical Reports Server (NTRS)

Vandermey, Nancy E.; Morris, Don H.; Masters, John E.

1991-01-01

Damage initiation and growth under compression-compression fatigue loading were investigated for a stitched uniweave material system with an underlying AS4/3501-6 quasi-isotropic layup. Performance of unnotched specimens having stitch rows at either 0 degree or 90 degrees to the loading direction was compared. Special attention was given to the effects of stitching related manufacturing defects. Damage evaluation techniques included edge replication, stiffness monitoring, x-ray radiography, residual compressive strength, and laminate sectioning. It was found that the manufacturing defect of inclined stitches had the greatest adverse effect on material performance. Zero degree and 90 degree specimen performances were generally the same. While the stitches were the source of damage initiation, they also slowed damage propagation both along the length and across the width and affected through-the-thickness damage growth. A pinched layer zone formed by the stitches particularly affected damage initiation and growth. The compressive failure mode was transverse shear for all specimens, both in static compression and fatigue cycling effects.

Thermal Performance of Precast Concrete Sandwich Panel (PCSP) Design for Sustainable Built Environment

NASA Astrophysics Data System (ADS)

Ern, Peniel Ang Soon; Ling, Lim Mei; Kasim, Narimah; Hamid, Zuhairi Abd; Masrom, Md Asrul Nasid Bin

2017-10-01

Malaysia’s awareness of performance criteria in construction industry towards a sustainable built environment with the use of precast concrete sandwich panel (PCSP) system is applied in the building’s wall to study the structural behaviour. However, very limited studies are conducted on the thermal insulation of exterior and interior panels in PCSP design. In hot countries such as Malaysia, proper designs of panel are important to obtain better thermal insulation for building. This study is based on thermal performance of precast concrete sandwich panel design for sustainable built environment in Malaysia. In this research, three full specimens, which are control specimen (C), foamed concrete (FC) panels and concrete panels with added palm oil fuel ash (FC+ POFA), where FC and FC+POFA sandwiched with gypsum board (G) were produced to investigate their thermal performance. Temperature difference of exterior and interior surface of specimen was used as indicators of thermal-insulating performance of PCSP design. Heat transfer test by halogen lamp was carried out on three specimens where the exterior surface of specimens was exposed to the halogen lamp. The temperature reading of exterior and interior surface for three specimens were recorded with the help of thermocouple. Other factors also studied the workability, compressive strength and axial compressive strength of the specimens. This study has shown that FC + POFA specimen has the strength nearer to normal specimen (C + FC specimen). Meanwhile, the heat transfer results show that the FC+POFA has better thermal insulation performance compared to C and FC specimens with the highest temperature difference, 3.4°C compared to other specimens. The results from this research are useful to be implemented in construction due to its benefits such as reduction of energy consumption in air-conditioning, reduction of construction periods and eco-friendly materials.

Effect of moisture on the fatigue behavior of graphite/epoxy composite laminates

NASA Technical Reports Server (NTRS)

Ramani, S. V.; Nelson, H. G.

1979-01-01

The form of the moisture distribution in the specimen (gradient and flat profile) was considered to establish the influence of accelerated moisture conditioning on fatigue behavior. For the gradient specimens having an average moisture content of 1.4 percent, fatigue life was reduced by a factor of 8 at all stress levels investigated. Corresponding reduction in fatigue life for the flat moisture profile specimens at the same average moisture content was comparatively smaller, being about a factor of 5 from the value in dry specimens. X-ray radiographic analysis of damage accumulation in compression-compression fatigue revealed interlaminar cracking to be the dominant mode of failure responsible for the observed enhanced cyclic degradation of moisture-conditioned specimens. This finding was corroborated by the observed systematic reduction in interlaminar shear strength as a function of moisture content, which, in turn, increased the propensity for delamination under cyclic compressive loads. Residual strength measurements on cycled specimens indicated significant strength reductions at long lives, particularly in moisture conditioned specimens.

Overload and Underload Effects on the Fatigue Crack Growth Behavior of the 2024-T3 Aluminum Alloy

NASA Technical Reports Server (NTRS)

Dawicke, David S.

1997-01-01

Fatigue crack growth tests were conducted on 0.09 inch thick, 3.0 inch wide middle-crack tension specimens cut from sheets of 2024-T3 aluminum alloy. The tests were conducted using a load sequence that consisted of a single block of 2,500 cycles of constant amplitude loading followed by an overload/underload combination. The largest fatigue crack growth life occurred for the tests with the overload stress equal to 2 times the constant amplitude stress and the underload stress equal to the constant amplitude minimum stress. For the tests with compressive underloads, the fatigue crack growth life decreased with increasing compressive underload stress.

Fabrication and evaluation of cold/formed/weldbrazed beta-titanium skin-stiffened compression panels

NASA Technical Reports Server (NTRS)

Royster, D. M.; Bales, T. T.; Davis, R. C.; Wiant, H. R.

1983-01-01

The room temperature and elevated temperature buckling behavior of cold formed beta titanium hat shaped stiffeners joined by weld brazing to alpha-beta titanium skins was determined. A preliminary set of single stiffener compression panels were used to develop a data base for material and panel properties. These panels were tested at room temperature and 316 C (600 F). A final set of multistiffener compression panels were fabricated for room temperature tests by the process developed in making the single stiffener panels. The overall geometrical dimensions for the multistiffener panels were determined by the structural sizing computer code PASCO. The data presented from the panel tests include load shortening curves, local buckling strengths, and failure loads. Experimental buckling loads are compared with the buckling loads predicted by the PASCO code. Material property data obtained from tests of ASTM standard dogbone specimens are also presented.

Role of age and injury mechanism on cervical spine injury tolerance from head contact loading.

PubMed

Yoganandan, Narayan; Chirvi, Sajal; Voo, Liming; Pintar, Frank A; Banerjee, Anjishnu

2018-02-17

The objective of this study was to determine the influence of age and injury mechanism on cervical spine tolerance to injury from head contact loading using survival analysis. This study analyzed data from previously conducted experiments using post mortem human subjects (PMHS). Group A tests used the upright intact head-cervical column experimental model. The inferior end of the specimen was fixed, the head was balanced by a mechanical system, and natural lordosis was removed. Specimens were placed on a testing device via a load cell. The piston applied loading at the vertex region. Spinal injuries were identified using medical images. Group B tests used the inverted head-cervical column experimental model. In one study, head-T1 specimens were fixed distally, and C7-T1 joints were oriented anteriorly, preserving lordosis. Torso mass of 16 kg was added to the specimen. In another inverted head-cervical column study, occiput-T2 columns were obtained, an artificial head was attached, T1-T2 was fixed, C4-C5 disc was maintained horizontal in the lordosis posture, and C7-T1 was unconstrained. The specimens were attached to the drop test carriage carrying a torso mass of 15 kg. A load cell at the inferior end measured neck loads in both studies. Axial neck force and age were used as the primary response variable and covariate to derive injury probability curves using survival analysis. Group A tests showed that age is a significant (P < .05) and negative covariate; that is, increasing age resulted in decreasing force for the same risk. Injuries were mainly vertebral body fractures and concentrated at one level, mid-to-lower cervical spine, and were attributed to compression-related mechanisms. However, age was not a significant covariate for the combined data from group B tests. Both group B tests produced many soft tissue injuries, at all levels, from C1 to T1. The injury mechanism was attributed to mainly extension. Multiple and noncontiguous injuries occurred. Injury probability curves, ±95% confidence intervals, and normalized confidence interval sizes representing the quality of the mean curve are given for different data sets. For compression-related injuries, specimen age should be used as a covariate or individual specimen data may be prescaled to derive risk curves. For distraction- or extension-related injuries, however, specimen age need not be used as a covariate in the statistical analysis. The findings from these tests and survival analysis indicate that the age factor modulates human cervical spine tolerance to impact injury.

Effect of simulated sampling disturbance on creep behaviour of rock salt

NASA Astrophysics Data System (ADS)

Guessous, Z.; Gill, D. E.; Ladanyi, B.

1987-10-01

This article presents the results of an experimental study of creep behaviour of a rock salt under uniaxial compression as a function of prestrain, simulating sampling disturbance. The prestrain was produced by radial compressive loading of the specimens prior to creep testing. The tests were conducted on an artifical salt to avoid excessive scattering of the results. The results obtained from several series of single-stage creep tests show that, at short-term, the creep response of salt is strongly affected by the preloading history of samples. The nature of this effect depends upon the intensity of radial compressive preloading, and its magnitude is a function of the creep stress level. The effect, however, decreases with increasing plastic deformation, indicating that large creep strains may eventually lead to a complete loss of preloading memory.

Development and Evaluation of Stitched Sandwich Panels

NASA Technical Reports Server (NTRS)

Stanley, Larry E.; Adams, Daniel O.; Reeder, James R. (Technical Monitor)

2001-01-01

This study explored the feasibility and potential benefits provided by the addition of through-the-thickness reinforcement to sandwich structures. Through-the-thickness stitching is proposed to increase the interlaminar strength and damage tolerance of composite sandwich structures. A low-cost, out-of-autoclave processing method was developed to produce composite sandwich panels with carbon fiber face sheets, a closed-cell foam core, and through-the-thickness Kevlar stitching. The sandwich panels were stitched in a dry preform state, vacuum bagged, and infiltrated using Vacuum Assisted Resin Transfer Molding (VARTM) processing. For comparison purposes, unstitched sandwich panels were produced using the same materials and manufacturing methodology. Test panels were produced initially at the University of Utah and later at NASA Langley Research Center. Four types of mechanical tests were performed: flexural testing, flatwise tensile testing, core shear testing, and edgewise compression testing. Drop-weight impact testing followed by specimen sectioning was performed to characterize the damage resistance of stitched sandwich panels. Compression after impact (CAI) testing was performed to evaluate the damage tolerance of the sandwich panels. Results show significant increases in the flexural stiffness and strength, out-of-plane tensile strength, core shear strength, edgewise compression strength, and compression-after-impact strength of stitched sandwich structures.

Improvement in engineering properties of soft-soil using cement and lime additives: A case study of southern Vietnam

NASA Astrophysics Data System (ADS)

To-Anh Phan, Vu; Ngoc-Anh Pham, Kha

2018-04-01

This paper presents the experimental results of using two additives to improve natural soft soil properties in southern Vietnam (i.g., cement and cement-lime mixture). The specimens were prepared by compacting method. Firstly, the natural soil was mixed with cement or cement-lime to determine the optimum water contents of various additive contents. Then, optimum water content was used to produce samples to test some engineering properties such as unconfined compressive strength, splitting tensile strength, and Young’s modulus. The specimens were tested by various curing duration of 7, 14, and 28 days. Results indicated that using cement additive is suitable for improvement of soft soil in the local area and cement-soil stabilization can be replaced as the subbase layer of the flexible pavement according to current Vietnamese standard. In addition, a higher cement content has a greater compressive strength as well as tensile strength. Besides, the Young’ modulus has significantly increased with a long-term curing age and more cement content. No evidences of increasing in strength and modulus are found with the cement-lime-soil stabilization. Finally, the best-fit power function is established by the relationships between unconfined compressive strength and splitting tensile strength as well unconfined compressive strength and Young’s Modulus, with the coefficient of determination, R2>0.999.

Assessing Impact Direction in 3-point Bending of Human Femora: Incomplete Butterfly Fractures and Fracture Surfaces,.

PubMed

Isa, Mariyam I; Fenton, Todd W; Deland, Trevor; Haut, Roger C

2018-01-01

Current literature associates bending failure with butterfly fracture, in which fracture initiates transversely at the tensile surface of a bent bone and branches as it propagates toward the impact surface. The orientation of the resulting wedge fragment is often considered diagnostic of impact direction. However, experimental studies indicate bending does not always produce complete butterfly fractures or produces wedge fragments variably in tension or compression, precluding their use in interpreting directionality. This study reports results of experimental 3-point bending tests on thirteen unembalmed human femora. Complete fracture patterns varied following bending failure, but incomplete fractures and fracture surface characteristics were observed in all impacted specimens. A flat, billowy fracture surface was observed in tension, while jagged, angular peaks were observed in compression. Impact direction was accurately reconstructed using incomplete tension wedge butterfly fractures and tension and compression fracture surface criteria in all thirteen specimens. © 2017 American Academy of Forensic Sciences.

Fracture resistance of five pin-retained core build-up materials on teeth with and without extracoronal preparation.

PubMed

Burke, F J; Shaglouf, A G; Combe, E C; Wilson, N H

2000-01-01

Core build-ups should provide satisfactory strength and resistance to fracture both before and after crown preparation. This paper examines the resistance to fracture of core build-ups in different materials and the fracture resistance of core build-ups when these have been reduced for full crown preparation. Standardized core build-ups were made on groups of extracted molar teeth of similar size, with 10 teeth per group. Three resin-composite (prisma APH: Dentsply, Weybridge, UK; Ti-Core, Essential Dental Systems, NJ, US and Coradent, Vivadent, Liechtenstein), one cermet (Ketac-Silver, ESPE GmbH, Seefeld, Germany) and one amalgam material (Duralloy, Degussa Ltd, Cheshire, UK). These specimens were subjected to compressive force on a universal testing machine and the force at fracture noted. Standardized full crown preparations were made on a further five groups of core build-up specimens using the same materials as above. These prepared specimens were subjected to compressive force on a universal testing machine and the force to fracture noted. The results indicated that amalgam core build-ups demonstrated higher fracture resistance than the other materials examined. There was a general decrease in the fracture strength of the specimens following crown preparation, with the teeth restored with the amalgam core build-ups showing a greater percentage reduction in fracture strength than the other materials tested. Prepared core build-ups in a hybrid composite material provided the highest fracture resistance. The cermet material used provided the lowest resistance to fracture in both the core build-up and crown preparation specimens. In terms of fracture resistance, no advantage was apparent in using the two composite materials designated as being specifically appropriate for core build-ups.

Dynamic High-temperature Testing of an Iridium Alloy in Compression at High-strain Rates: Dynamic High-temperature Testing

DOE PAGES

Song, B.; Nelson, K.; Lipinski, R.; ...

2014-08-21

Iridium alloys have superior strength and ductility at elevated temperatures, making them useful as structural materials for certain high-temperature applications. However, experimental data on their high-strain -rate performance are needed for understanding high-speed impacts in severe environments. Kolsky bars (also called split Hopkinson bars) have been extensively employed for high-strain -rate characterization of materials at room temperature, but it has been challenging to adapt them for the measurement of dynamic properties at high temperatures. In our study, we analyzed the difficulties encountered in high-temperature Kolsky bar testing of thin iridium alloy specimens in compression. We made appropriate modifications using themore » current high-temperature Kolsky bar technique in order to obtain reliable compressive stress–strain response of an iridium alloy at high-strain rates (300–10 000 s -1) and temperatures (750 and 1030°C). The compressive stress–strain response of the iridium alloy showed significant sensitivity to both strain rate and temperature.« less

Mechanical properties of 2D and 3D braided textile composites

NASA Technical Reports Server (NTRS)

Norman, Timothy L.

1991-01-01

The purpose of this research was to determine the mechanical properties of 2D and 3D braided textile composite materials. Specifically, those designed for tension or shear loading were tested under static loading to failure to investigate the effects of braiding. The overall goal of the work was to provide a structural designer with an idea of how textile composites perform under typical loading conditions. From test results for unnotched tension, it was determined that the 2D is stronger, stiffer, and has higher elongation to failure than the 3D. It was also found that the polyetherether ketone (PEEK) resin system was stronger, stiffer, and had higher elongation at failure than the resin transfer molding (RTM) epoxy. Open hole tension tests showed that PEEK resin is more notch sensitive than RTM epoxy. Of greater significance, it was found that the 3D is less notch sensitive than the 2D. Unnotched compression tests indicated, as did the tension tests, that the 2D is stronger, stiffer, and has higher elongation at failure than the RTM epoxy. The most encouraging results were from compression after impact. The 3D braided composite showed a compression after impact failure stress equal to 92 percent of the unimpacted specimen. The 2D braided composite failed at about 67 percent of the unimpacted specimen. Higher damage tolerance is observed in textiles over conventional composite materials. This is observed in the results, especially in the 3D braided materials.

Experimental determination of the yield stress curve of the scotch pine wood materials

NASA Astrophysics Data System (ADS)

Günay, Ezgi; Aygün, Cevdet; Kaya, Şükrü Tayfun

2013-12-01

Yield stress curve is determined for the pine wood specimens by conducting a series of tests. In this work, pinewood is modeled as a composite material with transversely isotropic fibers. Annual rings (wood grain) of the wood specimens are taken as the major fiber directions with which the strain gauge directions are aligned. For this purpose, three types of tests are arranged. These are tensile, compression and torsion loading tests. All of the tests are categorized with respect to fiber orientations and their corresponding loading conditions. Each test within these categories is conducted separately. Tensile and compression tests are conducted in accordance with standards of Turkish Standards Institution (TSE) whereas torsion tests are conducted in accordance with Standards Australia. Specimens are machined from woods of Scotch pine which is widely used in boat building industries and in other structural engineering applications. It is determined that this species behaves more flexibly than the others. Strain gauges are installed on the specimen surfaces in such a way that loading measurements are performed along directions either parallel or perpendicular to the fiber directions. During the test and analysis phase of yield stress curve, orientation of strain gauge directions with respect to fiber directions are taken into account. The diagrams of the normal stress vs. normal strain or the shear stress vs. shear strain are plotted for each test. In each plot, the yield stress is determined by selecting the point on the diagram, the tangent of which is having a slope of 5% less than the slope of the elastic portion of the diagram. The geometric locus of these selected points constitutes a single yield stress curve on σ1-σ2 principal plane. The resulting yield stress curve is plotted as an approximate ellipse which resembles Tsai-Hill failure criterion. The results attained in this work, compare well with the results which are readily available in the literature.

Fracture toughness of SiC/Al metal matrix composite

NASA Technical Reports Server (NTRS)

Flom, Yury; Parker, B. H.; Chu, H. P.

1989-01-01

An experimental study was conducted to evaluate fracture toughness of SiC/Al metal matrix composite (MMC). The material was a 12.7 mm thick extrusion of 6061-T6 aluminum alloy with 40 v/o SiC particulates. Specimen configuration and test procedure conformed to ASTM E399 Standard for compact specimens. It was found that special procedures were necessary to obtain fatigue cracks of controlled lengths in the preparation of precracked specimens for the MMC material. Fatigue loading with both minimum and maximum loads in compression was used to start the precrack. The initial precracking would stop by self-arrest. Afterwards, the precrack could be safely extended to the desired length by additional cyclic tensile loading. Test results met practically all the E399 criteria for the calculation of plane strain fracture toughness of the material. A valid K sub IC value of the SiC/Al composite was established as K sub IC = 8.9 MPa square root of m. The threshold stress intensity under which crack would cease to grow in the material was estimated as delta K sub th = 2MPa square root of m for R = 0.09 using the fatigue precracking data. Fractographic examinations show that failure occurred by the micromechanism involved with plastic deformation although the specimens broke by brittle fracture. The effect of precracking by cyclic loading in compression on fracture toughness is included in the discussion.

Steady-state temperature determination on the base of hysteresis loop energy for CuZn37 brass

NASA Astrophysics Data System (ADS)

Lipski, Adam; Skibicki, Dariusz; Pejkowski, Łukasz

2017-03-01

This paper presents the verification of the relationship between the temperature and the hysteresis loop energy for the CuZn37 brass under multiaxial fatigue loading. Fatigue tests were performed on the hollow specimens subjected to fully reversed tension-compression, torsion, proportional loading, 90° out-of-phase non-proportional loading and two another non-proportional loadings with frequency differences. All test were strain-controlled. Calculations of a plastic strain energy were based on midlife strain hysteresis loops data. The calculated specimen temperatures were compared with temperatures observed by thermographic camera.

Compressive residual strength of graphite/epoxy laminates after impact

NASA Technical Reports Server (NTRS)

Guy, Teresa A.; Lagace, Paul A.

1992-01-01

The issue of damage tolerance after impact, in terms of the compressive residual strength, was experimentally examined in graphite/epoxy laminates using Hercules AS4/3501-6 in a (+ or - 45/0)(sub 2S) configuration. Three different impactor masses were used at various velocities and the resultant damage measured via a number of nondestructive and destructive techniques. Specimens were then tested to failure under uniaxial compression. The results clearly show that a minimum compressive residual strength exists which is below the open hole strength for a hole of the same diameter as the impactor. Increases in velocity beyond the point of minimum strength cause a difference in the damage produced and cause a resultant increase in the compressive residual strength which asymptotes to the open hole strength value. Furthermore, the results show that this minimum compressive residual strength value is independent of the impactor mass used and is only dependent upon the damage present in the impacted specimen which is the same for the three impactor mass cases. A full 3-D representation of the damage is obtained through the various techniques. Only this 3-D representation can properly characterize the damage state that causes the resultant residual strength. Assessment of the state-of-the-art in predictive analysis capabilities shows a need to further develop techniques based on the 3-D damage state that exists. In addition, the need for damage 'metrics' is clearly indicated.

Creep of salt from the ERDA-9 borehole and the WIPP (Waste Isolation Pilot Plant) workings

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

Senseny, P.E.

1990-01-01

Six triaxial compression creep tests were performed to measure the creep deformation of salt from the ERDA-9 borehole and salt from the underground workings at the Waste Isolation Pilot Plant (WIPP). Even though the test matrix is quite limited, important results were obtained that added to existing data from previous test matrices. The WIPP salt was annealed to reduce the hardening that occurred as the openings deformed after mining. Five tests were performed at a temperature of 25{degree}C, a confining pressure of 15 MPa, and stress differences of either 10.0 or 15.0 MPa. The sixth test was performed at amore » temperature of 22{degree}C, a confining pressure of 20.7 MPa, and a stress difference of 11.7 MPa. Test duration ranged from approximately 160 to 335 days. Deformation of these six specimens is compared with that obtained previously under identical test conditions for specimens from other horizons of the ERDA-9 borehole and from unannealed specimens from the WIPP workings. Results suggest that the magnitude of the transient deformation depends on the horizon from which the specimen was taken and whether or not the specimen hardened in situ as the mined openings deformed. 9 refs., 7 figs., 3 tabs.« less

Strength development of pervious concrete containing engineered biomass aggregate

NASA Astrophysics Data System (ADS)

Sharif, A. A. M.; Shahidan, S.; Koh, H. B.; Kandash, A.; Zuki, S. S. Mohd

2017-11-01

Pervious concrete with high porosity has good permeability and low mechanical strengths are commonly used in controlling storm water management. It is different from normal concrete. It is only containing single size of coarse aggregate and has lower density compared with normal concrete. This study was focused on the effect of Engineered Biomass Aggregate (EBA) on the compressive strength, void ratio and water permeability of pervious concrete. EBA was prepared by coating the biomass aggregate with epoxy resin. EBA was used to replace natural coarse aggregate ranging from 0% to 25%. 150 mm cube specimens were prepared and used to study the compressive strength, void ratio and water permeability. Compressive strength was tested at 7, 14 and 28 days. Meanwhile, void ratio and permeability tests were carried out on 28 days. The experimental results showed that pervious concrete containing EBA gained lower compressive strength. The compressive strength was reduced gradually by increasing the percentage of EBA. Overall, Pervious concrete containing EBA achieved higher void ratio and permeability.

Concepts for improving the damage tolerance of composite compression panels. [aircraft structures

NASA Technical Reports Server (NTRS)

Rhodes, M. D.; Williams, J. G.

1984-01-01

The residual strength of specimens with damage and the sensitivity to damage while subjected to an applied inplane compression load were determined for flatplate specimens and blade-stiffened panels. The results suggest that matrix materials that fail by delamination have the lowest damage tolerance capability. Alternate matrix materials or laminates which are transversely reinforced suppress the delamination mode of failure and change the failure mode to transverse shear crippling which occurs at a higher strain value. Several damage-tolerant blade-stiffened panel design concepts are evaluated. Structural efficiency studies conducted show only small mass penalties may result from incorporating these damage-tolerant features in panel design. The implication of test results on the design of aircraft structures was examined with respect to FAR requirements.

Shear transfer in concrete reinforced with carbon fibers

NASA Astrophysics Data System (ADS)

El-Mokadem, Khaled Mounir

2001-10-01

Scope and method of study. The research started with preliminary tests and studies on the behavior and effect of carbon fibers in different water solutions and mortar/concrete mixes. The research work investigated the use of CF in the production of concrete pipes and prestressed concrete double-tee sections. The research then focused on studying the effect of using carbon fibers on the direct shear transfer of sand-lightweight reinforced concrete push-off specimens. Findings and conclusions. In general, adding carbon fibers to concrete improved its tensile characteristics but decreased its compressive strength. The decrease in compressive strength was due to the decrease in concrete density as fibers act as three-dimensional mesh that entrapped air. The decrease in compressive strength was also due to the increase in the total surface area of non-cementitious material in the concrete. Sand-lightweight reinforced concrete push-off specimens with carbon fibers had lower shear carrying capacity than those without carbon fibers for the same cement content in the concrete. Current building codes and specifications estimate the shear strength of concrete as a ratio of the compressive strength. If applying the same principals then the ratio of shear strength to compressive strength for concrete reinforced with carbon fibers is higher than that for concrete without carbon fibers.

Effect of angle-ply orientation on compression strength of composite laminates

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

DeTeresa, S J; Hoppel, C P

1999-03-01

An experimental program was initiated to investigate the effect of angle-ply orientations on the compressive strength (X{sub 1C}) of 0{degree} plies in fiber reinforced composite laminates. Graphite fiber-reinforced epoxy test coupons with the generic architecture [0{sub 2}/{+-}{theta}] (where {theta} varied between 0{degree} and 90{degree}) and for the quasi-isotropic architecture were evaluated. The effective compressive strength of the 0{degree} plies varied considerably. The results were related to the Poisson's ratios of the laminates with high Poisson's ratios leading to high transverse tensile strains in the test coupons and lower than expected strengths. Specimens with the [O{sub 2}/{+-}30] architecture had both themore » highest Poisson's ratio and the lowest calculated ply-level compression strength for the 0{degree} plies. This work has implications in the selection of composite failure criterion for compression performance, design of test coupons for acceptance testing, and the selection of laminate architectures for optimum combinations of compressive and shear behavior. Two commonly used composite failure criteria, the maximum stress and the Tsai-Wu, predict significantly different laminate strengths depending on the Poisson's ratio of the laminate. This implies that the biaxial stress state in the laminate needs to be carefully considered before backing out unidirectional properties.« less

Strain distribution in the lumbar vertebrae under different loading configurations.

PubMed

Cristofolini, Luca; Brandolini, Nicola; Danesi, Valentina; Juszczyk, Mateusz M; Erani, Paolo; Viceconti, Marco

2013-10-01

The stress/strain distribution in the human vertebrae has seldom been measured, and only for a limited number of loading scenarios, at few locations on the bone surface. This in vitro study aimed at measuring how strain varies on the surface of the lumbar vertebral body and how such strain pattern depends on the loading conditions. Eight cadaveric specimens were instrumented with eight triaxial strain gauges each to measure the magnitude and direction of principal strains in the vertebral body. Each vertebra was tested in a three adjacent vertebrae segment fashion. The loading configurations included a compressive force aligned with the vertebral body but also tilted (15°) in each direction in the frontal and sagittal planes, a traction force, and torsion (both directions). Each loading configuration was tested six times on each specimen. The strain magnitude varied significantly between strain measurement locations. The strain distribution varied significantly when different loading conditions were applied (compression vs. torsion vs. traction). The strain distribution when the compressive force was tilted by 15° was also significantly different from the axial compression. Strains were minimal when the compressive force was applied coaxial with the vertebral body, compared with all other loading configurations. Also, strain was significantly more uniform for the axial compression, compared with all other loading configurations. Principal strains were aligned within 19° to the axis of the vertebral body for axial-compression and axial-traction. Conversely, when the applied force was tilted by 15°, the direction of principal strain varied by a much larger angle (15° to 28°). This is the first time, to our knowledge, that the strain distribution in the vertebral body is measured for such a variety of loading configurations and a large number of strain sensors. The present findings suggest that the structure of the vertebral body is optimized to sustain compressive forces, whereas even a small tilt angle makes the vertebral structure work under suboptimal conditions. Copyright © 2013 Elsevier Inc. All rights reserved.

Constitutive Soil Properties for Cuddeback Lake, California and Carson Sink, Nevada

NASA Technical Reports Server (NTRS)

Thomas, Michael A.; Chitty, Daniel E.; Gildea, Martin L.; T'Kindt, Casey M.

2008-01-01

Accurate soil models are required for numerical simulations of land landings for the Orion Crew Exploration Vehicle. This report provides constitutive material modeling properties for four soil models from two dry lakebeds in the western United States. The four soil models are based on mechanical and compressive behavior observed during geotechnical laboratory testing of remolded soil samples from the lakebeds. The test specimens were reconstituted to measured in situ density and moisture content. Tests included: triaxial compression, hydrostatic compression, and uniaxial strain. A fit to the triaxial test results defines the strength envelope. Hydrostatic and uniaxial tests define the compressibility. The constitutive properties are presented in the format of LS-DYNA Material Model 5: Soil and Foam. However, the laboratory test data provided can be used to construct other material models. The four soil models are intended to be specific only to the two lakebeds discussed in the report. The Cuddeback A and B models represent the softest and hardest soils at Cuddeback Lake. The Carson Sink Wet and Dry models represent different seasonal conditions. It is possible to approximate other clay soils with these models, but the results would be unverified without geotechnical tests to confirm similar soil behavior.

The effect of lateral eccentricity on failure loads, kinematics, and canal occlusions of the cervical spine in axial loading.

PubMed

Van Toen, C; Melnyk, A D; Street, J; Oxland, T R; Cripton, P A

2014-03-21

Current neck injury criteria do not include limits for lateral bending combined with axial compression and this has been observed as a clinically relevant mechanism, particularly for rollover motor vehicle crashes. The primary objectives of this study were to evaluate the effects of lateral eccentricity (the perpendicular distance from the axial force to the centre of the spine) on peak loads, kinematics, and spinal canal occlusions of subaxial cervical spine specimens tested in dynamic axial compression (0.5 m/s). Twelve 3-vertebra human cadaver cervical spine specimens were tested in two groups: low and high eccentricity with initial eccentricities of 1 and 150% of the lateral diameter of the vertebral body. Six-axis loads inferior to the specimen, kinematics of the superior-most vertebra, and spinal canal occlusions were measured. High speed video was collected and acoustic emission (AE) sensors were used to define the time of injury. The effects of eccentricity on peak loads, kinematics, and canal occlusions were evaluated using unpaired Student t-tests. The high eccentricity group had lower peak axial forces (1544 ± 629 vs. 4296 ± 1693 N), inferior displacements (0.2 ± 1.0 vs. 6.6 ± 2.0 mm), and canal occlusions (27 ± 5 vs. 53 ± 15%) and higher peak ipsilateral bending moments (53 ± 17 vs. 3 ± 18 Nm), ipsilateral bending rotations (22 ± 3 vs. 1 ± 2°), and ipsilateral displacements (4.5 ± 1.4 vs. -1.0 ± 1.3 mm, p<0.05 for all comparisons). These results provide new insights to develop prevention, recognition, and treatment strategies for compressive cervical spine injuries with lateral eccentricities. © 2013 Published by Elsevier Ltd.

Numerical investigation of the mechanical properties of the additive manufactured bone scaffolds fabricated by FDM: The effect of layer penetration and post-heating.

PubMed

Naghieh, S; Karamooz Ravari, M R; Badrossamay, M; Foroozmehr, E; Kadkhodaei, M

2016-06-01

In recent years, thanks to additive manufacturing technology, researchers have gone towards the optimization of bone scaffolds for the bone reconstruction. Bone scaffolds should have appropriate biological as well as mechanical properties in order to play a decisive role in bone healing. Since the fabrication of scaffolds is time consuming and expensive, numerical methods are often utilized to simulate their mechanical properties in order to find a nearly optimum one. Finite element analysis is one of the most common numerical methods that is used in this regard. In this paper, a parametric finite element model is developed to assess the effects of layers penetration׳s effect on inter-layer adhesion, which is reflected on the mechanical properties of bone scaffolds. To be able to validate this model, some compression test specimens as well as bone scaffolds are fabricated with biocompatible and biodegradable poly lactic acid using fused deposition modeling. All these specimens are tested in compression and their elastic modulus is obtained. Using the material parameters of the compression test specimens, the finite element analysis of the bone scaffold is performed. The obtained elastic modulus is compared with experiment indicating a good agreement. Accordingly, the proposed finite element model is able to predict the mechanical behavior of fabricated bone scaffolds accurately. In addition, the effect of post-heating of bone scaffolds on their elastic modulus is investigated. The results demonstrate that the numerically predicted elastic modulus of scaffold is closer to experimental outcomes in comparison with as-built samples. Copyright © 2016 Elsevier Ltd. All rights reserved.

Permeability and compression characteristics of municipal solid waste samples

NASA Astrophysics Data System (ADS)

Durmusoglu, Ertan; Sanchez, Itza M.; Corapcioglu, M. Yavuz

2006-08-01

Four series of laboratory tests were conducted to evaluate the permeability and compression characteristics of municipal solid waste (MSW) samples. While the two series of tests were conducted using a conventional small-scale consolidometer, the two others were conducted in a large-scale consolidometer specially constructed for this study. In each consolidometer, the MSW samples were tested at two different moisture contents, i.e., original moisture content and field capacity. A scale effect between the two consolidometers with different sizes was investigated. The tests were carried out on samples reconsolidated to pressures of 123, 246, and 369 kPa. Time settlement data gathered from each load increment were employed to plot strain versus log-time graphs. The data acquired from the compression tests were used to back calculate primary and secondary compression indices. The consolidometers were later adapted for permeability experiments. The values of indices and the coefficient of compressibility for the MSW samples tested were within a relatively narrow range despite the size of the consolidometer and the different moisture contents of the specimens tested. The values of the coefficient of permeability were within a band of two orders of magnitude (10-6-10-4 m/s). The data presented in this paper agreed very well with the data reported by previous researchers. It was concluded that the scale effect in the compression behavior was significant. However, there was usually no linear relationship between the results obtained in the tests.

The effect of sludge water treatment plant residuals on the properties of compressed brick

NASA Astrophysics Data System (ADS)

Shamsudin, Shamrul-Mar; Shahidan, S.; Azmi, M. A. M.; Ghaffar, S. A.; Ghani, M. B. Abdul; Saiful Bahari, N. A. A.; Zuki, S. S. M.

2017-11-01

The focus of this study is on the production of compressed bricks which contains sludge water treatment plant (SWTP) residuals obtained from SAJ. The main objective of this study is to utilise and incorporate discarded material (SWTP) in the form of residual solution to produce compressed bricks. This serves as one of the recycling efforts to conserve the environment. This study determined the optimum mix based on a mix ratio of 1:2:4 (cement: sand: soil) in the production of compressed bricks where 5 different mixes were investigated i. e. 0%, 5%, 10%, 20%, and 30% of water treatment plant residue solution. The production of the compressed bricks is in accordance with the Malaysian Standard MS 7.6: 1972 and British Standard BS 3921: 1985 - Compressive Strength & Water Absorption. After being moulded and air dried, the cured bricks were subjected to compression tests and water absorption tests. Based on the tests conducted, it was found that 20% of water treatment plant residue solution which is equivalent to 50% of soil content replacement with a mix composition of [10: cement] [20: sand] [20: soil] [20: water treatment plant residue solution] is the optimum mix. It was also observed that the bricks containing SWTP residuals were lighter in weight compared to the control specimens

Numerical calibration of the stable poisson loaded specimen

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Calomino, Anthony M.; Brewer, Dave N.

1992-01-01

An analytical calibration of the Stable Poisson Loaded (SPL) specimen is presented. The specimen configuration is similar to the ASTM E-561 compact-tension specimen with displacement controlled wedge loading used for R-Curve determination. The crack mouth opening displacements (CMOD's) are produced by the diametral expansion of an axially compressed cylindrical pin located in the wake of a machined notch. Due to the unusual loading configuration, a three-dimensional finite element analysis was performed with gap elements simulating the contact between the pin and specimen. In this report, stress intensity factors, CMOD's, and crack displacement profiles are reported for different crack lengths and different contacting conditions. It was concluded that the computed stress intensity factor decreases sharply with increasing crack length, thus making the SPL specimen configuration attractive for fracture testing of brittle, high modulus materials.

Analytical stress intensity solution for the Stable Poisson Loaded specimen

NASA Technical Reports Server (NTRS)

Ghosn, Louis J.; Calomino, Anthony M.; Brewer, David N.

1993-01-01

An analytical calibration of the Stable Poisson Loaded (SPL) specimen is presented. The specimen configuration is similar to the ASTM E-561 compact-tension specimen with displacement controlled wedge loading used for R-curve determination. The crack mouth opening displacements (CMODs) are produced by the diametral expansion of an axially compressed cylindrical pin located in the wake of a machined notch. Due to the unusual loading configuration, a three-dimensional finite element analysis was performed with gap elements simulating the contact between the pin and specimen. In this report, stress intensity factors, CMODs, and crack displacement profiles, are reported for different crack lengths and different contacting conditions. It was concluded that the computed stress intensity factor decreases sharply with increasing crack length thus making the SPL specimen configuration attractive for fracture testing of brittle, high modulus materials.

Double-Lap Shear Test For Honeycomb Core

NASA Technical Reports Server (NTRS)

Nettles, Alan T.; Hodge, Andrew J.

1992-01-01

Double-lap test measures shear strength of panel made of honeycomb core with 8-ply carbon-fiber/epoxy face sheets. Developed to overcome three principal disadvantages of prior standard single-lap shear test: specimen had to be more than 17 in. long; metal face sheets had to be used; and test introduced torque, with consequent bending and peeling of face sheets and spurious tensile or compressive loading of honeycomb.

A Biomechanical Analysis of 2 Constructs for Metacarpal Spiral Fracture Fixation in a Cadaver Model: 2 Large Screws Versus 3 Small Screws.

PubMed

Eu-Jin Cheah, Andre; Behn, Anthony W; Comer, Garet; Yao, Jeffrey

2017-12-01

Surgeons confronted with a long spiral metacarpal fracture may choose to fix it solely with lagged screws. A biomechanical analysis of a metacarpal spiral fracture model was performed to determine whether 3 1.5-mm screws or 2 2.0-mm screws provided more stability during bending and torsional loading. Second and third metacarpals were harvested from 12 matched pairs of fresh-frozen cadaveric hands and spiral fractures were created. One specimen from each matched pair was fixed with 2 2.0-mm lagged screws whereas the other was fixed with 3 1.5-mm lagged screws. Nine pairs underwent combined cyclic cantilever bending and axial compressive loading followed by loading to failure. Nine additional pairs were subjected to cyclic external rotation while under a constant axial compressive load and were subsequently externally rotated to failure under a constant axial compressive load. Paired t tests were used to compare cyclic creep, stiffness, displacement, rotation, and peak load levels. Average failure torque for all specimens was 7.2 ± 1.7 Nm. In cyclic torsional testing, the group with 2 screws exhibited significantly less rotational creep than the one with 3 screws. A single specimen in the group with 2 screws failed before cyclic bending tests were completed. No other significant differences were found between test groups during torsional or bending tests. Both constructs were biomechanically similar except that the construct with 2 screws displayed significantly less loosening during torsional cyclic loading, although the difference was small and may not be clinically meaningful. Because we found no obvious biomechanical advantage to using 3 1.5-mm lagged screws to fix long spiral metacarpal fractures, the time efficiency and decreased implant costs of using 2-2.0 mm lagged screws may be preferred. Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Experimental and numerical study of the failure process and energy mechanisms of rock-like materials containing cross un-persistent joints under uniaxial compression.

PubMed

Cao, Rihong; Cao, Ping; Lin, Hang; Fan, Xiang

2017-01-01

Joints and fissures in natural rocks have a significant influence on the stability of the rock mass, and it is often necessary to evaluate strength failure and crack evolution behavior. In this paper, based on experimental tests and numerical simulation (PFC2D), the macro-mechanical behavior and energy mechanism of jointed rock-like specimens with cross non-persistent joints under uniaxial loading were investigated. The focus was to study the effect of joint dip angle α and intersection angle γ on the characteristic stress, the coalescence modes and the energy release of jointed rock-like specimens. For specimens with γ = 30° and 45°, the UCS (uniaxial compression strength), CIS (crack initiation stress) and CDiS (critical dilatancy stress) increase as α increases from 0° to 75°. When γ = 60° and 75°, the UCS, CIS and CDiS increase as α increases from 0° to 60° and decrease when α is over 60°. Both the inclination angle α and intersection angle γ have great influence on the failure pattern of pre-cracked specimens. With different α and γ, specimens exhibit 4 kinds of failure patterns. Both the experimental and numerical results show that the energy of a specimen has similar trends with characteristic stress as α increases.

Modeling rock specimens through 3D printing: Tentative experiments and prospects

NASA Astrophysics Data System (ADS)

Jiang, Quan; Feng, Xiating; Song, Lvbo; Gong, Yahua; Zheng, Hong; Cui, Jie

2016-02-01

Current developments in 3D printing (3DP) technology provide the opportunity to produce rock-like specimens and geotechnical models through additive manufacturing, that is, from a file viewed with a computer to a real object. This study investigated the serviceability of 3DP products as substitutes for rock specimens and rock-type materials in experimental analysis of deformation and failure in the laboratory. These experiments were performed on two types of materials as follows: (1) compressive experiments on printed sand-powder specimens in different shapes and structures, including intact cylinders, cylinders with small holes, and cuboids with pre-existing cracks, and (2) compressive and shearing experiments on printed polylactic acid cylinders and molded shearing blocks. These tentative tests for 3DP technology have exposed its advantages in producing complicated specimens with special external forms and internal structures, the mechanical similarity of its product to rock-type material in terms of deformation and failure, and its precision in mapping shapes from the original body to the trial sample (such as a natural rock joint). These experiments and analyses also successfully demonstrate the potential and prospects of 3DP technology to assist in the deformation and failure analysis of rock-type materials, as well as in the simulation of similar material modeling experiments.

Comparison of the compressive strengths for stitched and toughened composite systems

NASA Technical Reports Server (NTRS)

Reeder, James R.

1994-01-01

The compression strength of a stitched and a toughened matrix graphite/epoxy composite was determined and compared to a baseline unstitched untoughened composite. Two different layups with a variety of test lengths were tested under both ambient and hot/wet conditions. No significant difference in strength was seen for the different materials when the gage lengths of the specimens were long enough to lead to a buckling failure. For shorter specimens, a 30 percent reduction in strength from the baseline was seen due to stitching for both a 48-ply quasi-isotropic and a (0/45/0/-45/90/-45/0/45/0)s laminate. Analysis of the results suggested that the decrease in strength was due to increased fiber misalignment due to the stitches. An observed increasing strength with decreasing gage length, which was seen for all materials, was explained with a size effect model. The model assumed a random distribution of flaws (misaligned fibers). The toughened materials showed a small increase in strength over the baseline material for both laminates presumably due to the compensating effects of a more compliant matrix and straighter fibers in the toughened material. The hot/wet strength of the stitched and baseline material fell 30 percent below their ambient strengths for shorter, nonbuckling specimen, while the strength of the toughened matrix material only fell 20 percent. Video images of the failing specimen were recorded and showed local failures prior to global collapse of the specimen. These images support the theory of a random distribution of flaws controlling composite failure. Failed specimen appearance, however, seems to be a misleading indication of the cause of failure.

Evaluation of Giga-cycle Fatigue Properties of Austenitic Stainless Steels Using Ultrasonic Fatigue Test

NASA Astrophysics Data System (ADS)

Takahashi, Kyouhei; Ogawa, Takeshi

Ultrasonic fatigue tests have been performed in austenitic stainless steel, SUS316NG, in order to investigate giga-cycle fatigue strength of pre-strained materials, i.e. 5, 10 and 20% tensile pre-strains and -20% compressive pre-strain. The pre-strains were applied before specimen machining. The austenitic stainless steels are known to exhibit remarkable self-heating during the fatigue experiment. Therefore, heat radiation method was established by setting fatigue specimens in a low temperature chamber at about -100°C. The self-heating was controlled by intermittent loading condition, which enabled us to maintain the test section of the specimens at about room temperature. The results revealed that the fatigue strength increased with increasing pre-strain levels. Fish-eye fracture was observed for -20% pre-strained specimen fractured at 4.11×107 cycles, while the other specimens exhibited ordinary fatigue fracture surface originated from stage I facet on the specimen surface. The increase in fatigue limit was predicted by Vickers hardness, HV, which depended on the size of indented region. The prediction was successful using HV values obtained by the size of the indented region similar to those of the stage I facets.

Development of procedures for calculating stiffness and damping properties of elastomers. Part 3: The effects of temperature, dissipation level and geometry

NASA Technical Reports Server (NTRS)

Smalley, A. J.; Tessarzik, J. M.

1975-01-01

Effects of temperature, dissipation level and geometry on the dynamic behavior of elastomer elements were investigated. Force displacement relationships in elastomer elements and the effects of frequency, geometry and temperature upon these relationships are reviewed. Based on this review, methods of reducing stiffness and damping data for shear and compression test elements to material properties (storage and loss moduli) and empirical geometric factors are developed and tested using previously generated experimental data. A prediction method which accounts for large amplitudes of deformation is developed on the assumption that their effect is to increase temperature through the elastomers, thereby modifying the local material properties. Various simple methods of predicting the radial stiffness of ring cartridge elements are developed and compared. Material properties were determined from the shear specimen tests as a function of frequency and temperature. Using these material properties, numerical predictions of stiffness and damping for cartridge and compression specimens were made and compared with corresponding measurements at different temperatures, with encouraging results.

Response of resin transfer molded (RTM) composites under reversed cyclic loading

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

Mahfuz, H.; Haque, A.; Yu, D.

1996-01-01

Compressive behavior and the tension-compression fatigue response of resin transfer molded IM7 PW/PR 500 composite laminate with a circular notch have been studied. Fatigue damage characteristics have been investigated through the changes in the laminate strength and stiffness by gradually incrementing the fatigue cycles at a preselected load level. Progressive damage in the surface of the laminate during fatigue has been investigated using cellulose replicas. Failure mechanisms during static and cyclic tests have been identified and presented in detail. Extensive debonding of filaments and complete fiber bundle fracture accompanied by delamination were found to be responsible for fatigue failures, whilemore » fiber buckling, partial fiber fracture and delamination were characterized as the failure modes during static tests. Weibull analysis of the static, cyclic and residual tests have been performed and described in detail. Fractured as well as untested specimens were C-scanned, and the progressive damage growth during fatigue is presented. Optical Microscopy (OM) and Scanning Electron Microscopy (SEM) for the fractured specimen were also performed and the analysis of the failure behavior is presented.« less

In situ micro-compression testing of He2+ ion irradiated titanium aluminide

NASA Astrophysics Data System (ADS)

Wei, Tao; Xu, Alan; Zhu, Hanliang; Ionescu, Mihail; Bhattacharyya, Dhriti

2017-10-01

A titanium aluminide (TiAl) alloy 45XD has been irradiated by a He ion beam with an energy of 5 MeV on a tandem accelerator at the Australian Nuclear Science and Technology Organization (ANSTO). The total fluence of He ions was 5 × 1017 ion cm-2. A 17 μm uniform damage region from the material surface with a helium concentration of about 5000 appm was achieved by using an energy degrading wheel in front of the TiAl target. The micro-size test specimens from the damage layer were fabricated using a focused ion beam & scanning electron microscope (FIB-SEM) system. The in situ SEM micromechanical compressive testing was carried out inside an SEM and the results indicated irradiation embrittlement in the helium affected region. Electron back scatter diffraction (EBSD) analysis has been applied to reveal the orientation of the lamellae in the TiAl specimens, and used to understand the deformation processes in the sample. The irradiation damage of gallium ion beam from FIB on the surface of TiAl sample was also investigated.

Methodology to predict delayed failure due to slow crack growth in ceramic tubular components using data from simple specimens

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

Jadaan, O.M.; Tressler, R.E.

1993-04-01

The methodology to predict the lifetime of sintered [alpha]-silicon carbide (SASC) tubes subjected to slow crack growth (SCG) conditions involved the experimental determination of the SCG parameters of that material and the scaling analysis to project the stress rupture data from small specimens to large components. Dynamic fatigue testing, taking into account the effect of threshold stress intensity factor, of O-ring and compressed C-ring specimens was used to obtain the SCG parameters. These SCG parameters were in excellent agreement with those published in the literature and extracted from stress rupture tests of tensile and bend specimens. Two methods were usedmore » to predict the lifetimes of internally heated and pressurized SASC tubes. The first is a fracture mechanics approach that is well known in the literature. The second method used a scaling analysis in which the stress rupture distribution (lifetime) of any specimen configuration can be predicted from stress rupture data of another.« less

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.

Tension-Compression Fatigue of a Nextel™720/alumina Composite at 1200 °C in Air and in Steam

NASA Astrophysics Data System (ADS)

Lanser, R. L.; Ruggles-Wrenn, M. B.

2016-08-01

Tension-compression fatigue behavior of an oxide-oxide ceramic-matrix composite was investigated at 1200 °C in air and in steam. The composite is comprised of an alumina matrix reinforced with Nextel™720 alumina-mullite fibers woven in an eight harness satin weave (8HSW). The composite has no interface between the fiber and matrix, and relies on the porous matrix for flaw tolerance. Tension-compression fatigue behavior was studied for cyclical stresses ranging from 60 to 120 MPa at a frequency of 1.0 Hz. The R ratio (minimum stress to maximum stress) was -1.0. Fatigue run-out was defined as 105 cycles and was achieved at 80 MPa in air and at 70 MPa in steam. Steam reduced cyclic lives by an order of magnitude. Specimens that achieved fatigue run-out were subjected to tensile tests to failure to characterize the retained tensile properties. Specimens subjected to prior cyclic loading in air retained 100 % of their tensile strength. The steam environment severely degraded tensile properties. Tension-compression cyclic loading was considerably more damaging than tension-tension cyclic loading. Composite microstructure, as well as damage and failure mechanisms were investigated.

Strength and fracture energy of foamed concrete incorporating rice husk ash and polypropylene mega-mesh 55

NASA Astrophysics Data System (ADS)

Jaini, Z. M.; Rum, R. H. M.; Boon, K. H.

2017-10-01

This paper presents the utilization of rice husk ash (RHA) as sand replacement and polypropylene mega-mesh 55 (PMM) as fiber reinforcement in foamed concrete. High pozzolanic reaction and the ability to become filler make RHA as a strategic material to enhance the strength and durability of foamed concrete. Furthermore, the presence of PMM optimizes the toughness of foamed concrete in resisting shrinkage and cracking. In this experimental study, cube and cylinder specimens were prepared for the compression and splitting-tensile tests. Meanwhile, notched beam specimens were cast for the three-point bending test. It was found that 40% RHA and 9kg/m3 PMM contribute to the highest strength and fracture energy. The compressive, tensile and flexural strengths are 32MPa, 2.88MPa and 6.68MPa respectively, while the fracture energy achieves 42.19N/m. The results indicate high potential of RHA and PMM in enhancing the mechanical properties of foamed concrete.

Effect of molding conditions on fracture mechanisms and stiffness of a composite of grid structure

NASA Astrophysics Data System (ADS)

Nikolaev, V. P.; Pichugin, V. S.; Korobeinikov, A. G.

1999-01-01

Methods of determining a complex of stiffness and deformability characteristics of a composite with rhomb-type grid structure were elaborated. Rhomb-type specimens were used for testing the ribs of the structure in tension, compression, and bending and the nodal points in shear in the plane of the ribs. The effect of additional tensioning of the ribs preceding the curing of the binder was investigated (ten tensioning levels ranging from 8 to 70 N/bundle with a linear density of 390 tex were applied). In testing epoxy-carbon specimens (UKN-5000+EHD-MK) in compression and tension, the failure mode changed depending on the tensioning level, i.e., the presence or absence of delamination and the appearance of "dry" fibers were detected. Dependences of the mechanical properties on tensioning were of a markedly pronounced extreme nature. The methods elaborated allow us to investigate the effect of other molding parameters, as well as the conditions and nature of loading, on the mechanical characteristics of composites.

Physeal growth arrest by excessive compression: histological, biochemical, and micro-CT observations in rabbits.

PubMed

Yoo, Won Joon; Cheon, Jung-Eun; Lee, Hye Ran; Cho, Tae-Joon; Choi, In Ho

2011-12-01

Compressive force across the growth plate may cause retardation and even arrest of physeal growth. The purpose of this study was to investigate histologic changes, metabolic changes in terms of glycosaminoglycan (GAG) concentration, and contrast-enhanced micro-computed tomography (CEMCT) findings of physeal cartilage in a rabbit model of physeal damage caused by excessive compression. Compressive forces were applied via external fixators for two weeks to the growth plates of distal femurs and proximal tibiae of right hind-legs in 8-week-old rabbits. Left hind-legs remained intact and were used as controls. Forty-four bone specimens containing growth plates of distal femurs or proximal tibiae were harvested one week (n = 12) and four weeks (n = 32) after surgery, and examined for histologic findings (H&E staining) and GAGs quantification in physeal cartilage. After incubation in an ionic contrast material for 48 hours, specimens were scanned by CEMCT, and the pixel values of physeal cartilage were measured. CEMCT showed a thin, highly attenuated line parallel to the growth plate in compressed specimens harvested at four weeks after surgery, which was found to be transversely connected trabecular bone. In these specimens, GAG content in physeal cartilage was significantly lower, and CEMCT pixel values of physeal cartilage were significantly higher than in the specimens from the contralateral control side. Excessive compressive force applied to growth plates produces altered histologic features and metabolic function in terms of decreased GAG content in physeal cartilage, changes that can be demonstrated by CEMCT.

Effect of low-speed impact damage and damage location on behavior of composite panels

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.

1992-01-01

The effect of low speed impact damage on the compression and tension strength of thin and moderately thick composite specimens was investigated. Impact speed ranged from 50 to 550 ft./sec., with corresponding impact energies from 0.25 to 30.7 ft. x lb. Impact locations were near the center of the specimen or near a lateral unloaded edge. In this study, thin specimens with only 90 degree and + or - 45 degree plies that were impacted away from the unloaded edge suffered less reduction in load carrying capability because of impact damage than of the same specimens impacted near the unloaded edge. Failure loads of thicker compression loaded specimens with a similar stacking sequence were independent of impact location. Failure loads of thin tension loaded specimens with 0 degree plies was independent of impact location, whereas failure loads of thicker compression loaded specimens with 0 degree plies were dependent upon impact location. A finite element analysis indicated that high axial strains occurred near the unloaded edges of the postbuckled panels. Thus, impacts near the unloaded edge would significantly affect the behavior of the postbuckled panel.

Ten-year ground exposure of composite materials used on the Bell Model 206L helicopter flight service program

NASA Technical Reports Server (NTRS)

Baker, Donald J.

1994-01-01

Residual strength results are presented for four composite material systems that have been exposed for up to 10 years to the environment at five different locations on the North American continent. The exposure locations are near where the Bell Model 206L helicopters, which participated in a flight service program sponsored by NASA Langley Research Center and the U.S. Army, were flying in daily commercial service. The composite material systems are (1) Kevlar-49 fabric/F-185 epoxy; (2) Kevlar-49 fabric/LRF-277 epoxy; (3) Kevlar-49 fabric/CE-306 epoxy; and (4) T-300 graphite/E-788 epoxy. Six replicates of each material were removed and tested after 1, 3, 5, 7, and 10 years of exposure. The average baseline strength was determined from testing six as-fabricated specimens. More than 1700 specimens have been tested. All specimens that were tested to determine their strength were painted with a polyurethane paint. Each set of specimens also included an unpainted panel for observing the weathering effects on the composite materials. A statistically based procedure has been used to determine the strength value above which at least 90 percent of the population is expected to fall with a 95-percent confidence level. The computed compression strengths are 80 to 90 percent of the baseline (no-exposure) strengths. The resulting compression strengths are approximately 8 percent below the population mean strengths. The computed short-beam-shear strengths are 83 to 92 percent of the baseline (no-exposure) strengths. The computed tension strength of all materials is 93 to 97 percent of the baseline (no-exposure) strengths.

Thermoplastic composites for veneering posterior teeth-a feasibility study.

PubMed

Gegauff, Anthony G; Garcia, Jose L; Koelling, Kurt W; Seghi, Robert R

2002-09-01

This pilot study was conducted to explore selected commercially-available thermoplastic composites that potentially had physical properties superior to currently available dental systems for restoring esthetic posterior crowns. Polyurethane, polycarbonate, and poly(ethylene/tetrafluoroethylene) (ETFE) composites and unfilled polyurethane specimens were injection molded to produce shapes adaptive to five standardized mechanical tests. The mechanical testing included abrasive wear rate, yield strength, apparent fracture toughness (strength ratio), flexural strength, and compressive strength. Compared to commercially available dental composites, abrasion wear rates were lower for all materials tested, yield strength was greater for the filled polycarbonates and filled polyurethane resins, fracture toughness testing was invalid (strength ratios were calculated for comparison of the pilot test materials), flexural strength was roughly similar except for the filled ETFE which was significantly greater, and compressive strength was lower. Commercially available thermoplastic resin composites, such as polyurethane, demonstrate the potential for development of an artificial crown material which exceeds the mechanical properties of currently available esthetic systems, if compressive strength can be improved.

Compressive and shear properties of commercially available polyurethane foams.

PubMed

Thompson, Mark S; McCarthy, Ian D; Lidgren, Lars; Ryd, Leif

2003-10-01

The shear properties of rigid polyurethane (PU-R) foams, routinely used to simulate cancellous bone, are not well characterized. The present assessment of the shear and compressive properties of four grades of Sawbones "Rigid cellular" PU-R foam tested 20 mm gauge diameter dumb-bell specimens in torsion and under axial loading. Shear moduli ranged from 13.3 to 99.7 MPa, shear strengths from 0.7 MPa to 4.2 MPa. Compressive yield strains varied little with density while shear yield strains had peak values with "200 kgm-3" grade. PU-R foams may be used to simulate the elastic but not failure properties of cancellous bone.

The failure of brittle materials under overall compression: Effects of loading rate and defect distribution

NASA Astrophysics Data System (ADS)

Paliwal, Bhasker

The constitutive behaviors and failure processes of brittle materials under far-field compressive loading are studied in this work. Several approaches are used: experiments to study the compressive failure behavior of ceramics, design of experimental techniques by means of finite element simulations, and the development of micro-mechanical damage models to analyze and predict mechanical response of brittle materials under far-field compression. Experiments have been conducted on various ceramics, (primarily on a transparent polycrystalline ceramic, aluminum oxynitride or AlON) under loading rates ranging from quasi-static (˜ 5X10-6) to dynamic (˜ 200 MPa/mus), using a servo-controlled hydraulic test machine and a modified compression Kolsky bar (MKB) technique respectively. High-speed photography has also been used with exposure times as low as 20 ns to observe the dynamic activation, growth and coalescence of cracks and resulting damage zones in the specimen. The photographs were correlated in time with measurements of the stresses in the specimen. Further, by means of 3D finite element simulations, an experimental technique has been developed to impose a controlled, homogeneous, planar confinement in the specimen. The technique can be used in conjunction with a high-speed camera to study the in situ dynamic failure behavior of materials under confinement. AlON specimens are used for the study. The statically pre-compressed specimen is subjected to axial dynamic compressive loading using the MKB. Results suggest that confinement not only increases the load carrying capacity, it also results in a non-linear stress evolution in the material. High-speed photographs also suggest an inelastic deformation mechanism in AlON under confinement which evolves more slowly than the typical brittle-cracking type of damage in the unconfined case. Next, an interacting micro-crack damage model is developed that explicitly accounts for the interaction among the micro-cracks in brittle materials. The model incorporates pre-existing defect distributions and a crack growth law. The damage is defined as a scalar parameter which is a function of the micro-crack density, the evolution of which is a function of the existing defect distribution and the crack growth dynamics. A specific case of a uniaxial compressive loading under constant strain-rate has been studied to predict the effects of the strain-rate, defect distribution and the crack growth dynamics on the constitutive response and failure behavior of brittle materials. Finally, the effects of crack growth dynamics on the strain-rate sensitivity of brittle materials are studied with the help of the micro-mechanical damage model. The results are compared with the experimentally observed damage evolution and the rate-sensitive behavior of the compressive strength of several engineering ceramics. The dynamic failure of armor-grade hot-pressed boron carbide (B 4C) under loading rates of ˜ 5X10-6 to 200 MPa/mus is also discussed.

Development of high-temperature Kolsky compression bar techniques for recrystallization investigation

NASA Astrophysics Data System (ADS)

Song, B.; Antoun, B. R.; Boston, M.

2012-05-01

We modified the design originally developed by Kuokkala's group to develop an automated high-temperature Kolsky compression bar for characterizing high-rate properties of 304L stainless steel at elevated temperatures. Additional features have been implemented to this high-temperature Kolsky compression bar for recrystallization investigation. The new features ensure a single loading on the specimen and precise time and temperature control for quenching to the specimen after dynamic loading. Dynamic compressive stress-strain curves of 304L stainless steel were obtained at 21, 204, 427, 649, and 871 °C (or 70, 400, 800, 1200, and 1600 °F) at the same constant strain rate of 332 s-1. The specimen subjected to specific time and temperature control for quenching after a single dynamic loading was preserved for investigating microstructure recrystallization.

Development of a thermally-assisted piercing (TAP) process for introducing holes into thermoplastic composites

NASA Astrophysics Data System (ADS)

Brown, Nicholas W. A.

Composite parts can be manufactured to near-net shape with minimum wastage of material; however, there is almost always a need for further machining. The most common post-manufacture machining operations for composite materials are to create holes for assembly. This thesis presents and discusses a thermally-assisted piercing process that can be used as a technique for introducing holes into thermoplastic composites. The thermally-assisted piercing process heats up, and locally melts, thermoplastic composites to allow material to be displaced around a hole, rather than cutting them out from the structure. This investigation was concerned with how the variation of piercing process parameters (such as the size of the heated area, the temperature of the laminate prior to piercing and the geometry of the piercing spike) changed the material microstructure within carbon fibre/Polyetheretherketone (PEEK) laminates. The variation of process parameters was found to significantly affect the formation of resin rich regions, voids and the fibre volume fraction in the material surrounding the hole. Mechanical testing (using open-hole tension, open-hole compression, plain-pin bearing and bolted bearing tests) showed that the microstructural features created during piercing were having significant influence over the resulting mechanical performance of specimens. By optimising the process parameters strength improvements of up to 11% and 21% were found for pierced specimens when compared with drilled specimens for open-hole tension and compression loading, respectively. For plain-pin and bolted bearing tests, maximum strengths of 77% and 85%, respectively, were achieved when compared with drilled holes. Improvements in first failure force (by 10%) and the stress at 4% hole elongation (by 18%), however, were measured for the bolted bearing tests when compared to drilled specimens. The overall performance of pierced specimens in an industrially relevant application ultimately depends on the properties required for that specific scenario. The results within this thesis show that the piercing technique could be used as a direct replacement to drilling depending on this application.

On the Crack Bifurcation and Fanning of Crack Growth Data

NASA Technical Reports Server (NTRS)

Forman, Royce G.; Zanganeh, Mohammad

2015-01-01

Crack growth data obtained from ASTM load shedding method for different R values show some fanning especially for aluminum alloys. It is believed by the authors and it has been shown before that the observed fanning is due to the crack bifurcation occurs in the near threshold region which is a function of intrinsic properties of the alloy. Therefore, validity of the ASTM load shedding test procedure and results is confirmed. However, this position has been argued by some experimentalists who believe the fanning is an artifact of the test procedure and thus the obtained results are invalid. It has been shown that using a special test procedure such as using compressively pre-cracked specimens will eliminate the fanning effect. Since not using the fanned data fit can result in a significantly lower calculated cyclic life, design of a component, particularly for rotorcraft and propeller systems will considerably be impacted and therefore this study is of paramount importance. In this effort both test procedures i.e. ASTM load shedding and the proposed compressive pre-cracking have been used to study the fatigue crack growth behavior of compact tension specimens made of aluminum alloy 2524-T3. Fatigue crack growth paths have been closely observed using SEM machines to investigate the effects of compression pre-cracking on the crack bifurcation behavior. The results of this study will shed a light on resolving the existing argument by better understanding of near threshold fatigue crack growth behavior.

Fatigue Crack Topography.

DTIC Science & Technology

1984-01-01

nominal cycle frequency of 15 Hz. Buckling of the specimens during compression loading was prevented by felt-lined aluminium alloy antibuckling guides...evaluating ciack initiation time and crack propagation, prgram I was used for performing the major fatigue test with the aircraft structure. In...direction of the notch to prevent scratches in the through-the-thickness direction. Prior to testing, the notch surfaces were lightly etched to reveal

Summer research fellowship program

NASA Technical Reports Server (NTRS)

Darden, G. C. (Compiler)

1979-01-01

Significant accomplishments reported include uniaxial compression tests of high strength graphite-epoxy laminates. The results show that Young's modulus and fracture stress depend upon the specimen's dimensions. Also presented are: an investigation of robot vision; estimation of spectral signatures of algae from the airborne lidar oceanographic probing equipment; impact tests on polymeric compounds; calibration of quartz crystal microbalance; and a profile of naturally occurring hydrocarbons.

Influence of residual welding stresses, overload and specimen preparation on fatigue crack growth under axial compression

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

Greasley, A.

1995-02-01

Double edge notched axial compression specimens taken from thick welded steel joints have been used to grow fatigue cracks under pulsating compressive loads at mean stresses up to 55% of that needed for general yielding. The redistribution of residual stresses during specimen preparation and during crack growth influences the nucleation, growth rate and extent of fatigue cracks. Crack growth rates which are comparable to the equivalent tensile situation have been observed in as-welded, welded plus overloaded and stress relieved plus overloaded joints. Multiple nucleation and curved crack profiles have been observed in all cases. 5 refs.

An Experimental Study on the Edgewise Compressive Failure of Paper Honeycomb Sandwich Panels with Respect to Various Aspect Ratios

NASA Astrophysics Data System (ADS)

Samad, W. A.; Warsame, A. A.; Khan, A.

2018-04-01

The present work investigates the edgewise compression failure for honeycomb paperboards. Various panels are tested under a fixed loading rate with varying aspect ratios. The influence of the varying properties aspect ratio on yield strength is recorded. The experimental results indicate that the honeycomb paperboards are subject a decrease in yield strength with an increase in aspect ratio towards more slender bodies. Buckling was not observed in any of the tested specimens. All experiments are conducted under the general framework of ASTM C364/C364M -16 with a few noted changes.

Space environmental effects on graphite-epoxy compressive properties and epoxy tensile properties

NASA Technical Reports Server (NTRS)

Fox, Derek J.; Sykes, George F., Jr.; Herakovich, Carl T.

1987-01-01

This study characterizes the effects of electron radiation and temperature on a graphite-epoxy composite material. Compressive properties of the T300/934 material system were obtained at -250 F (-157 C), room temperature, and 250 F (121 C). Tensile specimens of the Fiberite 934 epoxy resin were fabricated and tested at room temperature and 250 F (121 C). Testing was conducted in the baseline (nonirradiated) and irradiated conditions. The radiation exposure was designed to simulate 30 year, worst-case exposure in geosynchronous Earth orbit. Mechanical properties tended to degrade at elevated temperature and improve at cryogenic temperature. Irradiation generally degraded properties at all temperatures.

Evaluation of Different Experience Levels of Orthopaedic Residents Effect on Polymethylmethacrylate (PMMA) Bone Cement Mechanical Properties.

PubMed

Struemph, Jonathon M; Chong, Alexander C M; Wooley, Paul H

2015-01-01

PMMA bone cement is a brittle material and the creation of defects that increase porosity during mixing or injecting is a significant factor in reducing its mechanical properties. The goal during residency training is to learn how to avoid creating increased porosity during mixing and injecting the material. The aim of this study was to evaluate and compare tensile and compression strength for PMMA cement mixed by intern orthopaedic residents (PGY-1) and senior orthopaedic residents (PGY-5). The hypothesis was that the mechanical properties of PMMA cement mixed by PGY-5 would be significantly better than PMMA cement mixed by PGY-1 residents. Four PGY-1 and four PGY-5 orthopaedic residents each prepared eight tensile specimens. The bone cement used was Simplex™ P bone cement (Stryker Howmedica Osteonics, Mahwah, NJ) under vacuum mixing in a cement-delivery system. Tensile testing of the specimens was performed in an MTS Bionix servohydraulic materials testing system with loading rate of 2.54 mm/min at room temperature. The mean and standard deviation of the ultimate tensile strength (UTS) for each orthopaedic resident group was calculated. The compression specimens were cylinders formed with a central core to mimic a prosthetic implant. Ten samples from each orthopaedic resident were tested using the same MTS system under identical conditions at room temperature. The specimens were loaded from -50 N to complete structural failure at the rate of 20 mm/min. The ultimate compressive strength (UCS) was then determined and the mean and standard deviation calculated for each group. The average UTS of the bone cement for the PGY-1 and PGY-5 residents was 37.5 ± 4.5 MPa and 39.2 ± 5.0 MPa, respectively, and there was no statistically significant difference between the two groups. For the tensile elastic modulus of the bone cement, the results for the PGY-1 and PGY-5 residents were 2.40 ± 0.09 GPa and 2.44 ± 0.08 GPa, respectively, and again there was no statistically significant difference. For the compression elastic modulus of the bone cement, the results for the PGY-1 and PGY-5 residents were 1.19 ± 0.13 GPa and 1.21 ± 0.18 GPa, respectively, with no statistically significant difference. However, the UCS of the bone cement for the PGY-1 and PGY-5 residents was 87.4 ± 5.8 MPa and 91.1 ± 4.5 MPa, respectively, and there was a statistically significant difference between the groups. The PMMA specimens prepared by both the PGY-1 and PGY-5 resident groups had similar characteristics during tensile and compression testing, and were similar to known standards. Although mixing and applying bone cement is an important skill for joint replacement surgery, our results indicate that no special training appears to be necessary for orthopaedic residents. Rather, a basic training video demonstrating manufacturer standard procedure is all that is necessary. The results of this study indicate the importance of experience in bone cement mixing and injecting on cement mechanical properties, but indicate that no special training appears to be necessary for orthopaedic residents.

Significance of Compression in Binucleation while Differentiating Reactive Cellular Changes Between Human Papillomavirus and Candida Infections

PubMed Central

Okodo, Mitsuaki; Okayama, Kaori; Fukui, Tadasi; Shiina, Natsuko; Caniz, Timothy; Yabusaki, Hiromi; Fujii, Masahiko

2017-01-01

Purpose: Binucleation is a reactive cellular change (RCC) in Pap smears due to Candida infection. However, the origin of these binucleated cells as RCCs remains unclear. The purpose of this study was to examine binucleation in patients negative for intraepithelial lesion or malignancy (NILM) and infected with Candida and those infected with high-risk human papillomavirus (hr-HPV) and to clarify the origin of the binucleated cells. Methods: A total of 115 endocervical swab specimens with a combined diagnosis of NILM, Candida infection, and RCCs were used for this study. Pap smears were used to identify binucleated cells and then separate them into two groups, compression-positive and compression-negative. In addition, hr-HPV was detected using polymerase chain reaction (PCR) with a specific primer on the DNA extracted from the remaining residual cytology specimens. To make the hr-HPV-infected binucleated cells visible, an in situ PCR assay was performed on the Pap smear. Result: Of the 115 specimens, 69.6% contained binucleated cells, 26 (32.5%) showed only the compressed form, 35 (43.8%) showed only the non-compressed form, and 19 showed both the compressed and non-compressed forms of binucleated cells. Also, 34 specimens (29.6%) were positive for hr-HPV. The sensitivity and specificity of compression-positive binucleated cells were 91.2% and 82.7% (p < 0.001), but they were not significant in the compression-negative group (p = 0.156). Also, 34 cases with hr-HPV contained 99 compression-positive and 24 compression-negative cells. The hr-HPV-positive cells accounted for 68 (68.7%) of the 99 compression-positive and 2 (8.3%) of the 24 compression-negative binucleated cells as determined by an in situ PCR assay for hr-HPV. The relationship between compression and hr-HPV was statistically significant (p < 0.001). Conclusion: Compression-positive binucleated cells may be present as a result of hr-HPV infection and not RCC, which is caused due to inflammation in NILM cases infected with Candida. PMID:28952287

Investigation of the Constitutive Model Used in Nonlinear, Incremental Structural Analyses.

DTIC Science & Technology

1998-06-01

package, ABAQUS , was chosen for performing NISA studies in part because user supplied subroutines could be used for constitutive relationships. After a...loading and the shrinkage and thermally induced strains determined from control specimens. The majority of creep tests are uniaxial compressive tests...Kennedy, and Perry (1970). Description of FE Model The tests were simulated using the finite element (FE) program ABAQUS and the aging viscoelastic

A statistical comparison of two carbon fiber/epoxy fabrication techniques

NASA Technical Reports Server (NTRS)

Hodge, A. J.

1991-01-01

A statistical comparison of the compression strengths of specimens that were fabricated by either a platen press or an autoclave were performed on IM6/3501-6 carbon/epoxy composites of 16-ply (0,+45,90,-45)(sub S2) lay-up configuration. The samples were cured with the same parameters and processing materials. It was found that the autoclaved panels were thicker than the platen press cured samples. Two hundred samples of each type of cure process were compression tested. The autoclaved samples had an average strength of 450 MPa (65.5 ksi), while the press cured samples had an average strength of 370 MPa (54.0 ksi). A Weibull analysis of the data showed that there is only a 30 pct. probability that the two types of cure systems yield specimens that can be considered from the same family.

Internal state variable plasticity-damage modeling of AISI 4140 steel including microstructure-property relations: temperature and strain rate effects

NASA Astrophysics Data System (ADS)

Nacif el Alaoui, Reda

Mechanical structure-property relations have been quantified for AISI 4140 steel. under different strain rates and temperatures. The structure-property relations were used. to calibrate a microstructure-based internal state variable plasticity-damage model for. monotonic tension, compression and torsion plasticity, as well as damage evolution. Strong stress state and temperature dependences were observed for the AISI 4140 steel. Tension tests on three different notched Bridgman specimens were undertaken to study. the damage-triaxiality dependence for model validation purposes. Fracture surface. analysis was performed using Scanning Electron Microscopy (SEM) to quantify the void. nucleation and void sizes in the different specimens. The stress-strain behavior exhibited. a fairly large applied stress state (tension, compression dependence, and torsion), a. moderate temperature dependence, and a relatively small strain rate dependence.

Constitutive Soil Properties for Unwashed Sand and Kennedy Space Center

NASA Technical Reports Server (NTRS)

Thomas, Michael A.; Chitty, Daniel E.; Gildea, Martin L.; T'Kindt, Casey M.

2008-01-01

Accurate soil models are required for numerical simulations of land landings for the Orion Crew Exploration Vehicle. This report provides constitutive material models for one soil, unwashed sand, from NASA Langley's gantry drop test facility and three soils from Kennedy Space Center (KSC). The four soil models are based on mechanical and compressive behavior observed during geotechnical laboratory testing of remolded soil samples. The test specimens were reconstituted to measured in situ density and moisture content. Tests included: triaxial compression, hydrostatic compression, and uniaxial strain. A fit to the triaxial test results defines the strength envelope. Hydrostatic and uniaxial tests define the compressibility. The constitutive properties are presented in the format of LS-DYNA Material Model 5: Soil and Foam. However, the laboratory test data provided can be used to construct other material models. The four soil models are intended to be specific to the soil conditions discussed in the report. The unwashed sand model represents clayey sand at high density. The KSC models represent three distinct coastal sand conditions: low density dry sand, high density in-situ moisture sand, and high density flooded sand. It is possible to approximate other sands with these models, but the results would be unverified without geotechnical tests to confirm similar soil behavior.

Evaluation of Light-Activated Provisional Resin Materials for Periodontal Soft Tissue Management

PubMed Central

Jun, Soo-Kyung; Lee, Hae-Hyoung

2016-01-01

The purpose of this study was to determine mechanical properties using a compressive test with cylinder specimen (h = 6 mm and ϕ = 4 mm) as well as cytotoxicity using elutes from disk specimen (ϕ = 10 mm and h = 2 mm) against human gingival fibroblasts and oral keratinocytes with light-activated provisional resin materials (Revotek LC and Luxatemp Solar) compared to chemically activated counterpart (Snap, Trim II, and Jet). Significantly increased compressive strength (210~280 MPa) was detected in light-activated products compared to chemically activated ones (20~65 MPa, P < 0.05) and similar compressive modulus was detected in both types (0.8~1.5 and 0.5~1.3 GPa). Simultaneously, the light-activated products showed less adverse effects on the periodontal soft tissue cells in any polymerization stage compared to the chemically activated products. Particularly, chemically activated products had significantly greater adverse effects during the “polymerizing” phase compared to those that were “already set” (P < 0.05), as shown in confocal microscopic images of live and dead cells. In conclusion, light-activated provisional resin materials have better mechanical properties as well as biocompatibility against two tested types of oral cells compared to the chemically activated counterpart, which are considered as more beneficial choice for periodontal soft tissue management. PMID:27672651

Evaluation of Light-Activated Provisional Resin Materials for Periodontal Soft Tissue Management.

PubMed

Jun, Soo-Kyung; Lee, Hae-Hyoung; Lee, Jung-Hwan

The purpose of this study was to determine mechanical properties using a compressive test with cylinder specimen ( h = 6 mm and ϕ = 4 mm) as well as cytotoxicity using elutes from disk specimen ( ϕ = 10 mm and h = 2 mm) against human gingival fibroblasts and oral keratinocytes with light-activated provisional resin materials (Revotek LC and Luxatemp Solar) compared to chemically activated counterpart (Snap, Trim II, and Jet). Significantly increased compressive strength (210~280 MPa) was detected in light-activated products compared to chemically activated ones (20~65 MPa, P < 0.05) and similar compressive modulus was detected in both types (0.8~1.5 and 0.5~1.3 GPa). Simultaneously, the light-activated products showed less adverse effects on the periodontal soft tissue cells in any polymerization stage compared to the chemically activated products. Particularly, chemically activated products had significantly greater adverse effects during the "polymerizing" phase compared to those that were "already set" ( P < 0.05), as shown in confocal microscopic images of live and dead cells. In conclusion, light-activated provisional resin materials have better mechanical properties as well as biocompatibility against two tested types of oral cells compared to the chemically activated counterpart, which are considered as more beneficial choice for periodontal soft tissue management.

Cyclic compression response of micropillars extracted from textured nanocrystalline NiTi thin-walled tubes

DOE PAGES

Ghassemi-Armaki, Hassan; Leff, Asher C.; Taheri, Mitra L.; ...

2017-06-22

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C ismore » compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less

Mechanical-physical experimental tests on lime mortars and bricks reinforced with hemp

NASA Astrophysics Data System (ADS)

Formisano, Antonio; Dessı, Enzo; Landolfo, Raffaele

2017-11-01

Hemp is an agricultural product used for various applications. In the Civil Engineering field, only a limited use of this natural material, called the "green pig" since exploitation of all its constituent parts is allowed, has been done. For this reason, in the paper an experimental activity on lime mortars and bricks reinforced with hemp components has been performed. Compression and bending tests have been carried out on specimens manufactured with hemp shives and fibres, respectively. The achieved results have shown that hemp products change the failure modes from brittle to ductile, leaving basically unaltered the strength capacity of reinforced specimens with respect to unreinforced ones.

Design, fabrication and test of graphite/polyimide composite joints and attachments for advanced aerospace vehicles

NASA Technical Reports Server (NTRS)

Skoumal, D. E.

1980-01-01

Bonded and bolted designs are presented for each of four major attachment types. Prepreg processing problems are discussed and quality control data are given for lots 2W4604, 2W4632 and 2W4643. Preliminary design allowables test results for tension tests and compression tests of laminates are included. The final small specimen test matrix is defined and the configuration of symmetric step-lap joint specimens are shown. Finite element modeling studies of a double lap joint were performed to evaluate the number of elements required through the adhesive thickness to assess effects of various joint parameters on stress distributions. Results of finite element analyses assessing the effect of an adhesive fillet on the stress distribution in a double lap joint are examined.

A comparison of the lattice discrete particle method to the finite-element method and the K&C material model for simulating the static and dynamic response of concrete.

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

Smith, Jovanca J.; Bishop, Joseph E.

2013-11-01

This report summarizes the work performed by the graduate student Jovanca Smith during a summer internship in the summer of 2012 with the aid of mentor Joe Bishop. The projects were a two-part endeavor that focused on the use of the numerical model called the Lattice Discrete Particle Model (LDPM). The LDPM is a discrete meso-scale model currently used at Northwestern University and the ERDC to model the heterogeneous quasi-brittle material, concrete. In the first part of the project, LDPM was compared to the Karagozian and Case Concrete Model (K&C) used in Presto, an explicit dynamics finite-element code, developed atmore » Sandia National Laboratories. In order to make this comparison, a series of quasi-static numerical experiments were performed, namely unconfined uniaxial compression tests on four varied cube specimen sizes, three-point bending notched experiments on three proportional specimen sizes, and six triaxial compression tests on a cylindrical specimen. The second part of this project focused on the application of LDPM to simulate projectile perforation on an ultra high performance concrete called CORTUF. This application illustrates the strengths of LDPM over traditional continuum models.« less

Creep and cracking of concrete hinges: insight from centric and eccentric compression experiments.

PubMed

Schlappal, Thomas; Schweigler, Michael; Gmainer, Susanne; Peyerl, Martin; Pichler, Bernhard

2017-01-01

Existing design guidelines for concrete hinges consider bending-induced tensile cracking, but the structural behavior is oversimplified to be time-independent. This is the motivation to study creep and bending-induced tensile cracking of initially monolithic concrete hinges systematically. Material tests on plain concrete specimens and structural tests on marginally reinforced concrete hinges are performed. The experiments characterize material and structural creep under centric compression as well as bending-induced tensile cracking and the interaction between creep and cracking of concrete hinges. As for the latter two aims, three nominally identical concrete hinges are subjected to short-term and to longer-term eccentric compression tests. Obtained material and structural creep functions referring to centric compression are found to be very similar. The structural creep activity under eccentric compression is significantly larger because of the interaction between creep and cracking, i.e. bending-induced cracks progressively open and propagate under sustained eccentric loading. As for concrete hinges in frame-like integral bridge construction, it is concluded (i) that realistic simulation of variable loads requires consideration of the here-studied time-dependent behavior and (ii) that permanent compressive normal forces shall be limited by 45% of the ultimate load carrying capacity, in order to avoid damage of concrete hinges under sustained loading.

Fabrication and investigation on field-dependent properties of natural rubber based magneto-rheological elastomer isolator

NASA Astrophysics Data System (ADS)

Ain Abd Wahab, Nurul; Amri Mazlan, Saiful; Ubaidillah; Kamaruddin, Shamsul; Intan Nik Ismail, Nik; Choi, Seung-Bok; Haziq Rostam Sharif, Amirul

2016-10-01

This study presents a laminated magnetorheological elastomer (MRE) isolator which applies to vibration control in practice. The proposed isolator is fabricated with multilayer MRE sheets associated with the natural rubber (NR) as a matrix, and steel plates. The fabricated MRE isolator is then magnetically analysed to achieve high magnetic field intensity which can produce high damping force required for effective vibration control. Subsequently, the NR-based MRE specimen is tested to identify the field-dependent rheological properties such as storage modulus with 60 weight percentage of carbonyl iron particles. It is shown from this test that the MR effect of MRE specimen is quantified to reach up to 120% at 0.8 T. Following the design stage, the electromagnetic simulation using the finite element method magnetic (FEMM) software is carried out for analysing the magnetic flux distribution in the laminated MRE isolator. The laminated MRE isolator is then examined to a series of compression for static and dynamic test under various applied currents using the dynamic fatigue machine and biaxial dynamic testing machine. It is shown that the static compression force is increased by 14.5% under strong magnetic field compared to its off-state. Meanwhile, the dynamic compression test results show that the force increase of the laminated MRE isolator is up to 16% and 7% for low and high frequency respectively. From the results presented in this work, it is demonstrated that the full-scale concept of the MRE isolator can be one of the potential candidates for vibration control applications by tunability of the dynamic stiffness.

In vitro assessment of retention and resistance failure loads of two preparation designs for maxillary anterior teeth.

PubMed

Bintivanou, Aimilia; Pissiotis, Argirios; Michalakis, Konstantinos

2017-04-01

Parallel labiolingual walls and the preservation of the cingulum in anterior tooth preparations have been advocated. However, their contribution to retention and resistance form has not been evaluated. The purpose of this in vitro study was to evaluate the retention and resistance failure loads of 2 preparation designs for maxillary anterior teeth. Forty metal restorations were fabricated and paired with 40 cobalt-chromium prepared tooth analogs. Twenty of the specimens had parallel buccolingual walls at the cervical part (group PBLW; the control group), whereas the remaining 20 had converging buccolingual walls (group CBLW; the experimental group). The restorations were cemented to the tooth analogs with a resin-modified glass ionomer luting agent. Ten specimens from each group were subjected to tensile loading with a universal testing machine; the rest were subjected to compression loading until failure. Descriptive statistics and the independent t test (α=.05) were used to determine the effect of failure loads in the tested groups. The independent t test revealed statistically significant differences between the tested groups in tensile loading (P<.001) and in compressive loading (P<.001). The PBLW group presented a higher tensile failure load than the CBLW. On the contrary, the PBLW group presented a smaller compression failure load than the CBLW. Parallelism of the buccolingual axial walls in anterior maxillary teeth increased the retention form but decreased the resistance form. Copyright © 2016 Editorial Council for the Journal of Prosthetic Dentistry. Published by Elsevier Inc. All rights reserved.

Comparison of the compressive strength of 3 different implant design systems.

PubMed

Pedroza, Jose E; Torrealba, Ysidora; Elias, Augusto; Psoter, Walter

2007-01-01

The aims of this study were twofold: to compare the static compressive strength at the implant-abutment interface of 3 design systems and to describe the implant abutment connection failure mode. A stainless steel holding device was designed to align the implants at 30 degrees with respect to the y-axis. Sixty-nine specimens were used, 23 for each system. A computer-controlled universal testing machine (MTS 810) applied static compression loading by a unidirectional vertical piston until failure. Specimens were evaluated macroscopically for longitudinal displacement, abutment looseness, and screw and implant fracture. Data were analyzed by analysis of variance (ANOVA). The mean compressive strength for the Unipost system was 392.5 psi (SD +/-40.9), for the Spline system 342.8 psi (SD+/-25.8), and for the Screw-Vent system 269.1 psi (SD+/-30.7). The Unipost implant-abutment connection demonstrated a statistically significant superior mechanical stability (P < or = .009) compared with the Spline implant system. The Spline implant system showed a statistically significant higher compressive strength than the Screw-Vent implant system (P < or =.009). Regarding failure mode, the Unipost system consistently broke at the same site, while the other systems failed at different points of the connection. The Unipost system demonstrated excellent fracture resistance to compressive forces; this resistance may be attributed primarily to the diameter of the abutment screw and the 2.5 mm counter bore, representing the same and a unique piece of the implant. The Unipost implant system demonstrated a statistically significant superior compressive strength value compared with the Spline and Screw-Vent systems, at a 30 degrees angulation.

Design, fabrication, and implementation of thermally driven outdoor testing devices for building joint sealants.

PubMed

White, C C; Tan, K T; O'Brien, E P; Hunston, D L; Chin, J W; Williams, R S

2011-02-01

The paper describes the development, implementation, and testing of two thermally driven outdoor exposure instruments. These devices are unique in their ability to impose field generated thermally induced strain on sealant specimens while monitoring their resulting load and displacement. The instruments combine a fixed wood and steel supporting frame with a moving polyvinyl chloride frame, and employ differences in the coefficients of thermal expansion between the supporting frame and moving frame to induce strain on the sealant specimens. Two different kinds of instruments have been fabricated, "winter/tension" and "winter/compression" designs. In the winter/tension design, the thermally induced dimensional change is directly transferred to the specimens; while in the winter/compression design, the samples are loaded in an opposite direction with the dimensional change. Both designs are instrumented to monitor load and displacement and are built so that the strain on the specimen does not exceed ±25% over the range of temperatures expected in Gaithersburg, MD. Additionally, a weather station is colocated with the device to record environmental conditions in 1 min intervals. This combination of weather information with mechanical property data enables a direct link between environmental conditions and the corresponding sealant response. The reliability and effectiveness of these instruments are demonstrated with a typical sealant material. The results show that the instruments work according to the design criteria and provide a meaningful quantitative platform to monitor the mechanical response of sealant exposed to outdoor weathering.

Earlywood and latewood elastic properties in loblolly pine

Treesearch

Steven Cramer; David Kretschmann; Roderic Lakes; Troy Schmidt

2005-01-01

The elastic properties of earlywood and latewood and their variability were measured in 388 specimens from six loblolly pine trees in a commercial plantation. Properties measured included longitudinal modulus of elasticity, shear modulus, specific gravity, microfibril angle and presence of compression wood. Novel testing procedures were developed to measure properties...

Out-of-pile creep behavior of uranium carbide

NASA Technical Reports Server (NTRS)

Wright, T. R.; Seltzer, M. S.

1974-01-01

Compression creep tests were investigated on various UC-based fuel materials having a variation in both density and composition. Specimens were prepared by casting and by hot pressing. Steady-state creep rates were measured under vacuum at 1400 to 1800 C in the stress range 500-4000 psi.

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.

Behavior of a centrally notched cross-ply and unidirectional ceramic matrix composite in tension-compression fatigue. Master's thesis

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

Weidenaar, W.A.

1992-12-01

Centrally notched (hole), cross-ply, ((0/90) sub 2) sub s, and unidirectional, (0) sub 8 laminates of Silicon Carbide fiber-reinforced Aluminosilicate glass, SiC/1723, were fatigue tested under tension-compression loading with a load ratio of -1. Damage accumulated continuously for both lay-ups, leading to eventual failure and a reduced fatigue life. Critical damage in the cross-ply consisted of longitudinal cracks in the 90 deg plies growing and combining with transverse cracks to effectively eliminate the 90 deg plies' load carrying capability and allowing the specimen to buckle. Critical damage in the unidirectional lay-up consisted of longitudinal cracks which initiated at the shearmore » stress concentration points on the hole periphery. Reversed cyclic loading caused continued crack growth at maximum stresses below the tension-tension fatigue limit. The cross-ply lay-up appeared insensitive to the hole, while critical damage in the unidirectional lay-up was dependent on the shear stress concentrations at the hole.... Ceramic matrix composite, Tension-compression fatigue, Notched specimen.« less

Dynamic Stabilization of Simple Fractures With Active Plates Delivers Stronger Healing Than Conventional Compression Plating

PubMed Central

Tsai, Stanley; Bliven, Emily K.; von Rechenberg, Brigitte; Kindt, Philipp; Augat, Peter; Henschel, Julia; Fitzpatrick, Daniel C.; Madey, Steven M.

2017-01-01

Objectives: Active plates dynamize a fracture by elastic suspension of screw holes within the plate. We hypothesized that dynamic stabilization with active plates delivers stronger healing relative to standard compression plating. Methods: Twelve sheep were randomized to receive either a standard compression plate (CP) or an active plate (ACTIVE) for stabilization of an anatomically reduced tibial osteotomy. In the CP group, absolute stabilization was pursued by interfragmentary compression with 6 cortical screws. In the ACTIVE group, dynamic stabilization after bony apposition was achieved with 6 elastically suspended locking screws. Fracture healing was analyzed weekly on radiographs. After sacrifice 9 weeks postsurgery, the torsional strength of healed tibiae and contralateral tibiae was measured. Finally, computed tomography was used to assess fracture patterns and healing modes. Results: Healing in both groups included periosteal callus formation. ACTIVE specimens had almost 6 times more callus area by week 9 (P < 0.001) than CP specimens. ACTIVE specimens recovered on average 64% of their native strength by week 9, and were over twice as strong as CP specimens, which recovered 24% of their native strength (P = 0.008). Microcomputed tomography demonstrated that compression plating induced a combination of primary bone healing and gap healing. Active plating consistently stimulated biological bone healing by periosteal callus formation. Conclusions: Compared with compression plating, dynamic stabilization of simple fractures with active plates delivers significantly stronger healing. PMID:27861456

Blast protection of infrastructure using advanced composites

NASA Astrophysics Data System (ADS)

Brodsky, Evan

This research was a systematic investigation detailing the energy absorption mechanisms of an E-glass web core composite sandwich panel subjected to an impulse loading applied orthogonal to the facesheet. Key roles of the fiberglass and polyisocyanurate foam material were identified, characterized, and analyzed. A quasi-static test fixture was used to compressively load a unit cell web core specimen machined from the sandwich panel. The web and foam both exhibited non-linear stress-strain responses during axial compressive loading. Through several analyses, the composite web situated in the web core had failed in axial compression. Optimization studies were performed on the sandwich panel unit cell in order to maximize the energy absorption capabilities of the web core. Ultimately, a sandwich panel was designed to optimize the energy dissipation subjected to through-the-thickness compressive loading.

Experimental and computational correlation of fracture parameters KIc, JIc, and GIc for unimodular and bimodular graphite components

NASA Astrophysics Data System (ADS)

Bhushan, Awani; Panda, S. K.

2018-05-01

The influence of bimodularity (different stress ∼ strain behaviour in tension and compression) on fracture behaviour of graphite specimens has been studied with fracture toughness (KIc), critical J-integral (JIc) and critical strain energy release rate (GIc) as the characterizing parameter. Bimodularity index (ratio of tensile Young's modulus to compression Young's modulus) of graphite specimens has been obtained from the normalized test data of tensile and compression experimentation. Single edge notch bend (SENB) testing of pre-cracked specimens from the same lot have been carried out as per ASTM standard D7779-11 to determine the peak load and critical fracture parameters KIc, GIc and JIc using digital image correlation technology of crack opening displacements. Weibull weakest link theory has been used to evaluate the mean peak load, Weibull modulus and goodness of fit employing two parameter least square method (LIN2), biased (MLE2-B) and unbiased (MLE2-U) maximum likelihood estimator. The stress dependent elasticity problem of three-dimensional crack progression behaviour for the bimodular graphite components has been solved as an iterative finite element procedure. The crack characterizing parameters critical stress intensity factor and critical strain energy release rate have been estimated with the help of Weibull distribution plot between peak loads versus cumulative probability of failure. Experimental and Computational fracture parameters have been compared qualitatively to describe the significance of bimodularity. The bimodular influence on fracture behaviour of SENB graphite has been reflected on the experimental evaluation of GIc values only, which has been found to be different from the calculated JIc values. Numerical evaluation of bimodular 3D J-integral value is found to be close to the GIc value whereas the unimodular 3D J-value is nearer to the JIc value. The significant difference between the unimodular JIc and bimodular GIc indicates that GIc should be considered as the standard fracture parameter for bimodular brittle specimens.

Mechanical and analytical screening of braided composites for transport fuselage applications

NASA Technical Reports Server (NTRS)

Fedro, Mark J.; Gunther, Christian; Ko, Frank K.

1991-01-01

The mechanics of materials progress in support of the goal of understanding the application of braided composites in a transport aircraft fuselage are summarized. Composites consisting of both 2-D and 3-D braid patterns are investigated. Both consolidation of commingled graphite/PEEK and resin transfer molding of graphite-epoxy braided composite processes are studied. Mechanical tests were used to examine unnotched tension, open hole tension, compression, compression after impact, in-plane shear, out-of-plane tension, bearing, and crippling. Analytical methods are also developed and applied to predict the stiffness and strengths of test specimens. A preliminary study using the test data and analytical results is performed to assess the applicability of braided composites to a commercial aircraft fuselage.

Effects of the addition of nanoparticulate calcium carbonate on setting time, dimensional change, compressive strength, solubility and pH of MTA.

PubMed

Bernardi, A; Bortoluzzi, E A; Felippe, W T; Felippe, M C S; Wan, W S; Teixeira, C S

2017-01-01

To evaluate nanoparticulate calcium carbonate (NPCC) using transmission electron microscopy and the effects of NPCC addition to MTA in regard to the setting time, dimensional change, compressive strength, solubility and pH. The experimental groups were G1 (MTA), G2 (MTA with 5% NPCC) and G3 (MTA with 10% NPCC). The tests followed ISO and ADA standards. The specimens in the dimensional change and compressive strength tests were measured immediately after setting, after 24 h and after 30 days. In the solubility test, rings filled with cement were weighed after setting and after 30 days. The pH was measured after 24 h and 30 days. The data were analysed with the ANOVA, Tukey's and Kruskal-Wallis tests (α = 5%). The setting time was reduced (P < 0.05) in samples from G2 and G3 compared to G1. After 24 h, the dimensional change was similar amongst the groups, and after 30 days, G2 was associated with less alteration than G1 and G3. There was a difference in the compressive strength (P < 0.001) after 24 h and 30 days (G1 > G2 > G3). The solubility test revealed a difference amongst the groups when the specimens were hydrated: G2 > G1 > G3 and dehydrated: G3 > G2 > G1. The pH of the groups was similar at 24 h with higher values in each group after 30 days (P < 0.05), and G2 and G3 had similar mean pH values but both were higher than G1. Nanoparticulate calcium carbonate had a cubic morphology with few impurities. The addition of nanoparticulate calcium carbonate to MTA accelerated the setting time, decreased compressive strength and, after 30 days, resulted in lower dimensional change (G2), higher solubility and a higher pH. © 2015 International Endodontic Journal. Published by John Wiley & Sons Ltd.

Energy Absorption in Chopped Carbon Fiber Compression Molded Composites

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

Starbuck, J.M.

2001-07-20

In passenger vehicles the ability to absorb energy due to impact and be survivable for the occupant is called the ''crashworthiness'' of the structure. To identify and quantify the energy absorbing mechanisms in candidate automotive composite materials, test methodologies were developed for conducting progressive crush tests on composite plate specimens. The test method development and experimental set-up focused on isolating the damage modes associated with the frond formation that occurs in dynamic testing of composite tubes. Quasi-static progressive crush tests were performed on composite plates manufactured from chopped carbon fiber with an epoxy resin system using compression molding techniques. Themore » carbon fiber was Toray T700 and the epoxy resin was YLA RS-35. The effect of various material and test parameters on energy absorption was evaluated by varying the following parameters during testing: fiber volume fraction, fiber length, fiber tow size, specimen width, profile radius, and profile constraint condition. It was demonstrated during testing that the use of a roller constraint directed the crushing process and the load deflection curves were similar to progressive crushing of tubes. Of all the parameters evaluated, the fiber length appeared to be the most critical material parameter, with shorter fibers having a higher specific energy absorption than longer fibers. The combination of material parameters that yielded the highest energy absorbing material was identified.« less

Fatigue resistance and microleakage of CAD/CAM ceramic and composite molar crowns.

PubMed

Kassem, Amr S; Atta, Osama; El-Mowafy, Omar

2012-01-01

The aim of this study was to determine effect of compressive cyclic loading on fatigue resistance and microleakage of monolithic CAD/CAM molar ceramic and composite crowns. Thirty-two extracted molars were prepared to receive CEREC crowns according to manufacturer's guidelines using a special paralleling device (Parallel-A-Prep). Sixteen feldspathic ceramic crowns (VITABLOCS Mark II) (VMII) and 16 resin-composite crowns (Paradigm-MZ100 blocks) (PMZ) were milled using a CEREC-3D machine. Eight crowns of each group were cemented to their respective teeth using self-etching resin cement (Panavia-F-2.0) (PAN), and eight were cemented using self-adhesive resin cement (RelyX-Unicem-Clicker) (RXU). Following storage for 1 week in water, specimens were subjected to uniaxial compressive cyclic loading in an Instron testing machine at 12 Hz for 1,000,000 cycles. Load was applied at the central fossa, and the cycle range was 60-600 N. Specimens were then subjected to microleakage testing. Data were statistically analyzed using factorial ANOVA and Post Hoc (Tukey HSD) tests. All composite crowns survived compressive cyclic loading without fracture, while three ceramic crowns from the subgroup cemented with RXU developed surface cracks at the center of occlusal surfaces, extending laterally. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other three subgroups (p < 0.05). After 1,000,000 cycles of compressive cyclic loading, PMZ composite molar crowns were more fatigue-resistant than VMII ceramic crowns. Cement type had a significant effect on fatigue resistance of the ceramic crowns but not the composite ones. Microleakage scores of ceramic crowns cemented with PAN were significantly lower than those of the other subgroups (p < 0.05). © 2011 by The American College of Prosthodontists.

Analytical and experimental investigation of fatigue in a sheet specimen with an interference-fit bolt

NASA Technical Reports Server (NTRS)

Crews, J. H., Jr.

1975-01-01

A fatigue analysis, based on finite-element calculations and fatigue tests, was conducted for an aluminum-alloy sheet specimen with a steel interference-fit bolt. The stress analysis of the region near the bolt hole showed that the beneficial effect of an interference-fit bolt can be interpreted as the combined result of two effects: (1) load transfer through the bolt and (2) the compressive interference stresses in the sheet. Results of the fatigue tests show that progressively higher interference levels produced longer fatigue lives. The tests also show that a high level of interference prevents fretting at the bolt-sheet interface and that interferences larger than this level produced little additional improvement in fatigue life.

Study of Experiment on Rock-like Material Consist of fly-ash, Cement and Mortar

NASA Astrophysics Data System (ADS)

Nan, Qin; Hongwei, Wang; Yongyan, Wang

2018-03-01

Study the uniaxial compression test of rock-like material consist of coal ash, cement and mortar by changing the sand cement ratio, replace of fine coal, grain diameter, water-binder ratio and height-diameter ratio. We get the law of four factors above to rock-like material’s uniaxial compression characteristics and the quantitative relation. The effect law can be sum up as below: sample’s uniaxial compressive strength and elasticity modulus tend to decrease with the increase of sand cement ratio, replace of fine coal and water-binder ratio, and it satisfies with power function relation. With high ratio increases gradually, the uniaxial compressive strength and elastic modulus is lower, and presents the inverse function curve; Specimen tensile strength decreases gradually with the increase of fly ash. By contrast, uniaxial compression failure phenomenon is consistent with the real rock common failure pattern.

DEM code-based modeling of energy accumulation and release in structurally heterogeneous rock masses

NASA Astrophysics Data System (ADS)

Lavrikov, S. V.; Revuzhenko, A. F.

2015-10-01

Based on discrete element method, the authors model loading of a physical specimen to describe its capacity to accumulate and release elastic energy. The specimen is modeled as a packing of particles with viscoelastic coupling and friction. The external elastic boundary of the packing is represented by particles connected by elastic springs. The latter means introduction of an additional special potential of interaction between the boundary particles, that exercises effect even when there is no direct contact between the particles. On the whole, the model specimen represents an element of a medium capable of accumulation of deformation energy in the form of internal stresses. The data of the numerical modeling of the physical specimen compression and the laboratory testing results show good qualitative consistency.

Tissue-engineered articular cartilage exhibits tension-compression nonlinearity reminiscent of the native cartilage.

PubMed

Kelly, Terri-Ann N; Roach, Brendan L; Weidner, Zachary D; Mackenzie-Smith, Charles R; O'Connell, Grace D; Lima, Eric G; Stoker, Aaron M; Cook, James L; Ateshian, Gerard A; Hung, Clark T

2013-07-26

The tensile modulus of articular cartilage is much larger than its compressive modulus. This tension-compression nonlinearity enhances interstitial fluid pressurization and decreases the frictional coefficient. The current set of studies examines the tensile and compressive properties of cylindrical chondrocyte-seeded agarose constructs over different developmental stages through a novel method that combines osmotic loading, video microscopy, and uniaxial unconfined compression testing. This method was previously used to examine tension-compression nonlinearity in native cartilage. Engineered cartilage, cultured under free-swelling (FS) or dynamically loaded (DL) conditions, was tested in unconfined compression in hypertonic and hypotonic salt solutions. The apparent equilibrium modulus decreased with increasing salt concentration, indicating that increasing the bath solution osmolarity shielded the fixed charges within the tissue, shifting the measured moduli along the tension-compression curve and revealing the intrinsic properties of the tissue. With this method, we were able to measure the tensile (401±83kPa for FS and 678±473kPa for DL) and compressive (161±33kPa for FS and 348±203kPa for DL) moduli of the same engineered cartilage specimens. These moduli are comparable to values obtained from traditional methods, validating this technique for measuring the tensile and compressive properties of hydrogel-based constructs. This study shows that engineered cartilage exhibits tension-compression nonlinearity reminiscent of the native tissue, and that dynamic deformational loading can yield significantly higher tensile properties. Copyright © 2013 Elsevier Ltd. All rights reserved.

Controlled crack growth specimen for brittle systems

NASA Technical Reports Server (NTRS)

Calomino, Anthony M.; Brewer, David N.

1990-01-01

A pure Mode 1 fracture specimen and test procedure has been developed which provides extended, stable, through-thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson's expansion of a compressively loaded cylindrical pin. Stable cracks were successfully grown in soda-lime glass and monolithic Al2O3 for lengths in excess of 20 mm without uncontrollable catastrophic failure.

Controlled crack growth specimen for brittle systems

NASA Technical Reports Server (NTRS)

Calomino, Anthony M.; Brewer, David N.

1992-01-01

A pure Mode 1 fracture specimen and test procedure has been developed which provides extended, stable, through-thickness crack growth in ceramics and other brittle, nonmetallic materials. Fixed displacement loading, applied at the crack mouth, promotes stable crack extension by reducing the stored elastic strain energy. Extremely fine control of applied displacements is achieved by utilizing the Poisson's expansion of a compressively loaded cylindrical pin. Stable cracks were successfully grown in soda-lime glass and monolithic Al2O3 for lengths in excess of 2O mm without uncontrollable catastrophic failure.

Local buckling and crippling of composite stiffener sections

NASA Technical Reports Server (NTRS)

Bonanni, David L.; Johnson, Eric R.; Starnes, James H., Jr.

1988-01-01

Local buckling, postbuckling, and crippling (failure) of channel, zee, and I- and J-section stiffeners made of AS4/3502 graphite-epoxy unidirectional tape are studied by experiment and analysis. Thirty-six stiffener specimens were tested statically to failure in axial compression as intermediate length columns. Web width is 1.25 inches for all specimens, and the flange width-to-thickness ratio ranges from 7 to 28 for the specimens tested. The radius of the stiffener corners is either 0.125 or 0.250 inches. A sixteen-ply orthotropic layup, an eight-ply quasi-isotropic layup, and a sixteen-ply quasi-isotropic layup are examined. Geometrically nonlinear analyses of five specimens were performed with the STAGS finite element code. Analytical results are compared to experimental data. Inplane stresses from STAGS are used to conduct a plane stress failure analysis of these specimens. Also, the development of interlaminar stress equations from equilibrium for classical laminated plate theory is presented. An algorithm to compute high order displacement derivatives required by these equations based on the Discrete Fourier Transform (DFT) is discussed.

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

Corona, Edmundo

The Kolsky compression bar, or split Hopkinson pressure bar (SHPB), is an ex- perimental apparatus used to obtain the stress-strain response of material specimens at strain rates in the order of 10 2 to 10 4 1/s. Its operation and associated data re- duction are based on principles of one-dimensional wave propagation in rods. Second order effects such as indentation of the bars by the specimen and wave dispersion in the bars, however, can significantly affect aspects of the measured material response. Finite element models of the experimental apparatus were used here to demonstrate these two effects. A proceduremore » proposed by Safa and Gary (2010) to account for bar indentation was also evaluated and shown to improve the estimation of the strain in the bars significantly. The use of pulse shapers was also shown to alleviate the effects of wave dispersion. Combining the two can lead to more reliable results in Kolsky compression bar testing.« less

Manipulator having thermally conductive rotary joint for transferring heat from a test specimen

DOEpatents

Haney, Steven J.; Stulen, Richard H.; Toly, Norman F.

1985-01-01

A manipulator for rotatably moving a test specimen in an ultra-high vacuum chamber includes a translational unit movable in three mutually perpendicular directions. A manipulator frame is rigidly secured to the translational unit for rotatably supporting a rotary shaft. A first copper disc is rigidly secured to an end of the rotary shaft for rotary movement within the vacuum chamber. A second copper disc is supported upon the first disc. The second disc receives a cryogenic cold head and does not rotate with the first disc. A sapphire plate is interposed between the first and second discs to prevent galling of the copper material while maintaining high thermal conductivity between the first and second discs. A spring is disposed on the shaft to urge the second disc toward the first disc and compressingly engage the interposed sapphire plate. A specimen mount is secured to the first disc for rotation within the vacuum chamber. The specimen maintains high thermal conductivity with the second disc receiving the cryogenic transfer line.

Shear transfer capacity of reinforced concrete exposed to fire

NASA Astrophysics Data System (ADS)

Ahmad, Subhan; Bhargava, Pradeep; Chourasia, Ajay

2018-04-01

Shear transfer capacity of reinforced concrete elements is a function of concrete compressive strength and reinforcement yield strength. Exposure of concrete and steel to elevated temperature reduces their mechanical properties resulting in reduced shear transfer capacity of RC elements. The objective of present study is to find the effect of elevated temperature on shear transfer capacity of reinforced concrete. For this purpose pushoff specimens were casted using normal strength concrete. After curing, specimens were heated to 250°C and 500°C in an electric furnace. Cooled specimens were tested for shear transfer capacity in a universal testing machine. It was found that shear transfer capacity and stiffness (slope of load-slip curve) were reduced when the specimens were heated to 250°C and 500°C. Load level for the initiation of crack slip was found to be decreased as the temperature was increased. A simple analytical approach is also proposed to predict the shear transfer capacity of reinforced concrete after elevated temperature.

Experiments, constitutive modeling and FE simulations of the impact behavior of Molybdenum

NASA Astrophysics Data System (ADS)

Kleiser, Geremy; Revil-Baudard, Benoit

For polycrystalline high-purity molybdenum the feasibility of a Taylor test is questionable because the very large tensile stresses generated at impact would result in disintegration of the specimen. We report an experimental investigation and new model to account simultaneously for the experimentally observed anisotropy, tension-compression asymmetry and strain-rate sensitivity of this material. To ensure high-fidelity predictions, a fully-implicit algorithm was used for implementing the new model in the FE code ABAQUS. Based on model predictions, the impact velocity range was established for which specimens may be recovered. Taylor impact tests in this range (140-165 m/s) were successfully conducted for different specimen taken along the rolling direction (RD), the transverse direction and 45o to the RD. Comparison between the measured profiles of impact specimens and FE model predictions show excellent agreement. Furthermore, simulations were performed to gain understanding of the dynamic event: time evolution of the pressure, the extent of plastic deformation, distribution of plastic strain rates, and transition to quasi-stable deformation occurs.

Calcium leaching behavior of cementitious materials in hydrochloric acid solution.

PubMed

Yang, Huashan; Che, Yujun; Leng, Faguang

2018-06-11

The calcium leaching behavior of cement paste and silica fume modified calcium hydroxide paste, exposed to hydrochloric acid solution, is reported in this paper. The kinetic of degradation was assessed by the changes of pH of hydrochloric acid solution with time. The changes of compressive strength of specimens in hydrochloric acid with time were tested. Hydration products of leached specimens were also analyzed by X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric (TG), and atomic force microscope (AFM). Tests results show that there is a dynamic equilibrium in the supply and consumption of calcium hydroxide in hydrochloric acid solution, which govern the stability of hydration products such as calcium silicate hydrate (C-S-H). The decrease of compressive strength indicates that C-S-H are decomposed due to the lower concentration of calcium hydroxide in the pore solution than the equilibrium concentration of the hydration products. Furthermore, the hydration of unhydrated clinker delayed the decomposition of C-S-H in hydrochloric acid solution due to the increase of calcium hydroxide in pore solution of cementitious materials.

Properties of Controlled Low Strength Material with Circulating Fluidized Bed Combustion Ash and Recycled Aggregates

PubMed Central

Weng, Tsai-Lung; Cheng, An; Chao, Sao-Jeng; Hsu, Hui-Mi

2018-01-01

This study aims to investigate the effect of adding circulating fluidized bed combustion (CFBC) ash, desulfurization slag, air-cooled blast-furnace slag and coal bottom ash to the controlled low-strength material (CLSM). Test methods include slump flow test, ball drop test, water soluble chloride ion content measurement, compressive strength and length change measurement. The results show that (1) the use of CFBC hydration ash with desulfurization slag of slump flow is the best, and the use of CFBC hydration ash with coal bottom ash and slump flow is the worst; (2) CFBC hydration ash with desulfurization slag and chloride ion content is the highest; (3) 24 h ball drop test (diameter ≤ 76 mm), and test results are 70 mm to 76 mm; (4) CFBC hydration ash with desulfurization slag and compression strength is the highest, with the coal bottom ash being the lowest; increase of CFBC hydration ash can reduce compressive strength; and (5) the water-quenched blast furnace slag and CFBC hydration ash would expand, which results in length changes of CLSM specimens. PMID:29724055

Determination of Compressive Properties of Fibre Composites in the In-plane Direction According to ISO 14126. Part 1: A Round Robin Test

NASA Astrophysics Data System (ADS)

Schneider, Konrad

2007-01-01

Over the years different tests are established to characterise the compressive properties of composites in the in-plane direction. The international standard ISO 14126 (2000) (Fibre-reinforced plastic composites — determination of compressive properties in the in-plane direction, ISO 14126: 1999 (E), Faserverstärkte Kunststoffe, Bestimmung der Druckeigenschaften in der Laminatebene, DIN EN ISO 14126: 2000-12) tries to standardise these tests. The described wide range of arrangements enables to continue with the present practice to a large extent. But the standard doesn’t say anything about the precision of the method. Four labs performed a round robin test to check the precision and reproducibility of the Celanese-type arrangement for different composite materials, structures and dimensions. The test procedure is critically discussed and some proposals for the applicability of the method are derived. Mainly the advantages of optical monitoring the overall as well as the local strain of the specimen are demonstrated for the characterisation the failure process. By this method some of the reasons of unsatisfying reproducibility can be cleared up.

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.

Materials and processes laboratory composite materials characterization task, part 1. Damage tolerance

NASA Technical Reports Server (NTRS)

Nettles, A. T.; Tucker, D. S.; Patterson, W. J.; Franklin, S. W.; Gordon, G. H.; Hart, L.; Hodge, A. J.; Lance, D. G.; Russel, S. S.

1991-01-01

A test run was performed on IM6/3501-6 carbon-epoxy in which the material was processed, machined into specimens, and tested for damage tolerance capabilities. Nondestructive test data played a major role in this element of composite characterization. A time chart was produced showing the time the composite material spent within each Branch or Division in order to identify those areas which produce a long turnaround time. Instrumented drop weight testing was performed on the specimens with nondestructive evaluation being performed before and after the impacts. Destructive testing in the form of cross-sectional photomicrography and compression-after-impact testing were used. Results show that the processing and machining steps needed to be performed more rapidly if data on composite material is to be collected within a reasonable timeframe. The results of the damage tolerance testing showed that IM6/3501-6 is a brittle material that is very susceptible to impact damage.

ASTM D395 Short-Term Compression Set of Solid (Non-Porous) Siloxanes: SE 1700, Sylgard 184, and "New" M9787

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

Small, Ward; Pearson, Mark A.; Jensen, Wayne A.

2015-09-13

Compression set of solid (non-porous) Dow Corning SE 1700, Sylgard 184, and “new” M9787 siloxane elastomers was measured according to ASTM D395 Method B. Specimens of SE 1700 were made using (1) the manufacturer’s suggested cure of 150°C for 30 min and (2) an extended cure of 60°C for 6 h and 150°C for 1 h followed by a post-cure under nitrogen purge at 125°C for 12 h. Four specimens of each material were aged at 25-27% compressive strain at 70°C under nitrogen purge for 70 h. Final thickness of each specimen was measured after a 30-min cooling/relaxation period, andmore » compression set relative to deflection was calculated. The average compression set relative to deflection was 6.0% for SE 1700 made using the extended cure and post-cure, 11.3% for SE 1700 made using the manufacturer’s suggested cure, 12.1% for Sylgard 184, and 1.9% for M9787. The extended cure and post-cure reduced the amount of compression set in SE 1700.« less

A Kolsky tension bar technique using a hollow incident tube

NASA Astrophysics Data System (ADS)

Guzman, O.; Frew, D. J.; Chen, W.

2011-04-01

Load control of the incident pulse profiles in compression Kolsky bar experiments has been widely used to subject the specimen to optimal testing conditions. Tension Kolsky bars have been used to determine dynamic material behavior since the 1960s with limited capability to shape the loading pulses due to the pulse-generating mechanisms. We developed a modified Kolsky tension bar where a hollow incident tube is used to carry the incident stress waves. The incident tube also acts as a gas gun barrel that houses the striker for impact. The main advantage of this new design is that the striker impacts on an impact cap of the incident tube. Compression pulse shapers can be attached to the impact cap, thus fully utilizing the predictive compression pulse-shaping capability in tension experiments. Using this new testing technique, the dynamic tensile material behavior for Al 6061-T6511 and TRIP 800 (transformation-induced plasticity) steel has been obtained.

Characterization of Shear Properties for APO/MBI Syntactic Foam

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

Reser, Patrick M.; Lewis, Matthew W.; Clark, Jarod

Triaxial compression testing is a means for mechanical characterization of a material. A unique feature of the triaxial compression test is the application of two different magnitudes of compressive pressures on the material simultaneously. The material behavior under these different compressive pressures can be monitored over time. Several important characteristics of the material, such as stress yield values and the shear failure envelope may then be determined. Also mechanical properties such as Poisson’s ratio, Young’s modulus and bulk modulus can be determined from the triaxial compression test. The triaxial compression test was employed in this investigation to characterize the shearmore » behavior, shear failure envelope, and mechanical properties of a syntactic foam. Los Alamos National Laboratory (LANL) supplied a total of 36 samples of APO-BMI syntactic foam to the University of New Mexico, Department of Civil Engineering for testing between December 2003 and May 2004. Each sample had a diameter of 1.395±0.005 in. (3.543±0.013cm.) and a length of 2.796±0.004 in. (7.102±0.010 cm.). The samples had an average density of 0.295 g/cm3. Additional information about the material tested in this investigation can be found in the “Specimen Description” section contained in Chapter 1. The nomenclatures used in this study is presented in Chapter 1. In addition to designing and implementing triaxial compression tests capable of up to 2,000 psi. confining pressure (minor principal stress) and roughly 13,000 psi. in axial pressure (major principal stress), a pure tension test was designed and conducted on the foam material. The purpose of this pure tension test was to obtain maximum tensile stress values to enhance the characterization of the shear envelope in the stress space. The sampling procedure and specimen preparation for a standard test can be found in the American Society for Testing Materials (ASTM) D 5379/ D 5379 – 93. The above tests mentioned and their procedures are discussed in Chapter 2. Chapter 2 contains the types of tests performed and the apparatus used for testing the material. Chapter 2 also has a brief explanation of the equipment and the procedures used for conducting the tests. In Chapter 3, the material characteristics and mechanical properties obtained from the tests are described; composite plots of deviatoric vs. mean stress and deviatoric stress vs. longitudinal strain are also included. The plots of deviatoric stress vs. mean stress clearly identify the shear envelope for the material. Chapter 4 summarizes the vital information obtained from the tests and the conclusions made. All the necessary plots and the data generated during the testing have been included in the Appendix. The information in the appendix includes plots of: Strain vs. Time, Stress vs. Time, Stress vs. Strain, Mean Stress vs. Volumetric Strain, Lateral Strain vs. Longitudinal Strain, and q vs. p. Bulk modulus, Poisson’s ratio, and Young’s modulus are displayed in the appropriate plots in each appendix.« less

Statistical Analysis of Compressive and Flexural Test Results on the Sustainable Adobe Reinforced with Steel Wire Mesh

NASA Astrophysics Data System (ADS)

Jokhio, Gul A.; Syed Mohsin, Sharifah M.; Gul, Yasmeen

2018-04-01

It has been established that Adobe provides, in addition to being sustainable and economic, a better indoor air quality without spending extensive amounts of energy as opposed to the modern synthetic materials. The material, however, suffers from weak structural behaviour when subjected to adverse loading conditions. A wide range of mechanical properties has been reported in literature owing to lack of research and standardization. The present paper presents the statistical analysis of the results that were obtained through compressive and flexural tests on Adobe samples. Adobe specimens with and without wire mesh reinforcement were tested and the results were reported. The statistical analysis of these results presents an interesting read. It has been found that the compressive strength of adobe increases by about 43% after adding a single layer of wire mesh reinforcement. This increase is statistically significant. The flexural response of Adobe has also shown improvement with the addition of wire mesh reinforcement, however, the statistical significance of the same cannot be established.

Test methods for textile composites

NASA Technical Reports Server (NTRS)

Minguet, Pierre J.; Fedro, Mark J.; Gunther, Christian K.

1994-01-01

Various test methods commonly used for measuring properties of tape laminate composites were evaluated to determine their suitability for the testing of textile composites. Three different types of textile composites were utilized in this investigation: two-dimensional (2-D) triaxial braids, stitched uniweave fabric, and three-dimensional (3-D) interlock woven fabric. Four 2-D braid architectures, five stitched laminates, and six 3-D woven architectures were tested. All preforms used AS4 fibers and were resin-transfer-molded with Shell RSL-1895 epoxy resin. Ten categories of material properties were investigated: tension, open-hole tension, compression, open-hole compression, in-plane shear, filled-hole tension, bolt bearing, interlaminar tension, interlaminar shear, and interlaminar fracture toughness. Different test methods and specimen sizes were considered for each category of test. Strength and stiffness properties obtained with each of these methods are documented in this report for all the material systems mentioned above.

Fatigue failure of dentin-composite disks subjected to cyclic diametral compression

PubMed Central

Li, Yuping; Carrera, Carola; Chen, Ruoqiong; Li, Jianying; Chen, Yungchung; Lenton, Patricia; Rudney, Joel. D.; Jones, Robert S.; Aparicio, Conrado; Fok, Alex

2015-01-01

Objective Our aim was to establish the relationship between cyclic loading and fatigue life of the dentin-composite interface using the newly developed disk in diametral compression tests. The results were then used to estimate the fatigue life of restored teeth under occlusal loading. Methods Disk specimens (5mm dia. × 2mm thick) were prepared using bovine incisors and restored with either a methacrylate-based composite Z100™ with Adper Single Bond Plus (Z100) or silorane-based composite Filtek ™ LS with LS System adhesive (LS). The dentin-composite disks were tested under cyclic diametral compression to determine the number of cycles to failure (Nf) at three load levels (n = 3 per group). Finite element analysis (FEA) was used to calculate the interfacial stresses (σ) within the specimen, to establish the σ vs. Nf curves, and those within a restored tooth under normal chewing forces (15N maximum). These were then used to estimate the lifetime of the restored tooth for the two restorative systems. Results The disks restored with LS had a higher fatigue resistance than those restored with Z100. The maximum interfacial stress in the restored tooth determined by FEA was ∼0.5MPa. Based on the estimate of 300,000 cycles of chewing per year, the predicted lifetime under occlusal loading for teeth restored with LS and Z100 was 33 and 10 years, respectively. Significance The disk in cyclic diametral compression has been used successfully to provide fatigue data which allows the lifetime of composite-restored teeth under occlusal loading to be predicted using numerical simulation. PMID:25958269

Impact testing of textile composite materials

NASA Technical Reports Server (NTRS)

Portanova, Marc

1995-01-01

The objectives of this report were to evaluate the impact damage resistance and damage tolerance of a variety of textile composite materials. Static indentation and impact tests were performed on the stitched and unstitched uniweave composites constructed from AS4/3501-6 Carbon/Epoxy with a fiberglass yarn woven in to hold the fibers together while being stitched. Compression and tension were measured after the tests to determine the damage resistance, residual strength and the damage tolerance of the specimens.

A Finite Element Analysis for Predicting the Residual Compressive Strength of Impact-Damaged Sandwich Panels

NASA Technical Reports Server (NTRS)

Ratcliffe, James G.; Jackson, Wade C.

2008-01-01

A simple analysis method has been developed for predicting the residual compressive strength of impact-damaged sandwich panels. The method is tailored for honeycomb core-based sandwich specimens that exhibit an indentation growth failure mode under axial compressive loading, which is driven largely by the crushing behavior of the core material. The analysis method is in the form of a finite element model, where the impact-damaged facesheet is represented using shell elements and the core material is represented using spring elements, aligned in the thickness direction of the core. The nonlinear crush response of the core material used in the analysis is based on data from flatwise compression tests. A comparison with a previous analysis method and some experimental data shows good agreement with results from this new approach.

A Finite Element Analysis for Predicting the Residual Compression Strength of Impact-Damaged Sandwich Panels

NASA Technical Reports Server (NTRS)

Ratcliffe, James G.; Jackson, Wade C.

2008-01-01

A simple analysis method has been developed for predicting the residual compression strength of impact-damaged sandwich panels. The method is tailored for honeycomb core-based sandwich specimens that exhibit an indentation growth failure mode under axial compression loading, which is driven largely by the crushing behavior of the core material. The analysis method is in the form of a finite element model, where the impact-damaged facesheet is represented using shell elements and the core material is represented using spring elements, aligned in the thickness direction of the core. The nonlinear crush response of the core material used in the analysis is based on data from flatwise compression tests. A comparison with a previous analysis method and some experimental data shows good agreement with results from this new approach.

Laboratory study of the characteristics of fault breccias in Busan area in Korea

NASA Astrophysics Data System (ADS)

Woo, I.; Um, J.

2012-12-01

The physical and mechanical characteristics of fault breccias from near the Mt. Kumjung were estimated from laboratory tests on fractured fault breccias. Mt. Kumjung is surrounded by Yangsan Fault and Dongrae Fault which are major faults traversing the southeast part of Korea in the direction of NE-SW. The undisturbed samples were obtained from boreholes drilled in this region. The microscopic analysis on the thin sections of fault breccias showed the microstructure and the porosity of breccias. The fault breccias are composed of mainly fine quartz grains, and of angular quartz grains and weathered microcline grains. This microstructure of fault breccias might be formed by the catalasis during brittle deformation processes of the fault. 20 to 40% porosity of fault breccias could play an important role in the passage of groundwater and then in the development of fault gouge in the core part of fault. The mechanical characteristics were estimated by means of uniaxial compressive strength tests on the undisturbed breccias samples. Since fault breccias are not cohesive enough to use it directly as a test specimen, the epoxy resin was utilized to fix the outer surface of core samples. The thin plastic wrap had been enveloped before the epoxy resin was applied in order that the epoxy resin could not penetrate into the core specimens. The thickness of epoxy resin was less than 1mm not to disturb the results of uniaxial compressive strength of core samples. The measured uniaxial compressive strengths are 10 to 15MPa for the only physically fractured breccias and 8 to 10 MPa for the core specimens with hydrothermally altered surface. These results can be compared with the Hoek and Brown failure criteria : 7 to 10MPa for GSI value 40 to 50 for fault breccias with fresh surface. The overall measured strength of fault breccias is less than the strength obtained empirically by Hoek and Brown failure criteria.; ;

The Effect of Grain Size on the Strain Hardening Behavior for Extruded ZK61 Magnesium Alloy

NASA Astrophysics Data System (ADS)

Zhang, Lixin; Zhang, Wencong; Chen, Wenzhen; Duan, Junpeng; Wang, Wenke; Wang, Erde

2017-12-01

The effects of grain size on the tensile and compressive strain hardening behaviors for extruded ZK61 alloys have been investigated by uniaxial tensile and compressive tests along the extrusion directions. Cylindrical tension and compression specimens of extruded ZK61 alloys with various sized grain were fabricated by annealing treatments. Tensile and compressive tests at ambient temperature were conducted at a strain rate of 0.5 × 10-3 s-1. The results indicate that both tensile strain hardening and compressive strain hardening of ZK61 alloys with different grain sizes have an athermal regime of dislocation accumulation in early deformation. The threshold stress value caused dynamic recovery is predominantly related to grain size in tensile strain hardening, but the threshold stress values for different grain sizes are almost identical in compressive strain hardening. There are obvious transition points on the tensile strain hardening curves which indicate the occurrence of dynamic recrystallization (DRX). The tensile strain hardening rate of the coarse-grained alloy obviously decreases faster than that of fine-grained alloys before DRX and the tensile strain hardening curves of different grain sizes basically tend to parallel after DRX. The compressive strain hardening rate of the fine-grained alloy obviously increases faster than that of coarse-grained alloy for twin-induced strain hardening, but compressive strain hardening curves also tend to parallel after twinning is exhausted.

Effects of compression on human skin optical properties

NASA Astrophysics Data System (ADS)

Chan, Eric K.; Sorg, Brian S.; Protsenko, Dmitry E.; O'Neil, Michael P.; Motamedi, Massoud; Welch, Ashley J.

1997-08-01

Tissue optical properties are necessary parameters for prescribing light dosimetry in photomedicine. In many diagnostic or therapeutic applications where optical fiber probes are used, pressure is often applied to the tissue to reduce index mismatch and increase light transmittance. In this study, we have measured in vitro optical properties as a function of pressure with a visible-IR spectrophotometer. A spectral range of 400 - 1800 nm with a spectral resolution of 5 nm was used for all measurements. Skin specimens of two Hispanic donors and three caucasian donors were obtained from the tissue bank. Each specimen, sandwiched between microscope slides, was compressed by a spring-loaded apparatus. Then diffuse reflectance and transmittance of each sample were measured at no load and at approximately 0.1 and 1 kgf/cm2. Under compression, tissue thicknesses were reduced up to 78%. Generally, reflectance decreased while the overall transmittance increased under compression. The absorption and reduced scattering coefficients were calculated using the inverse adding doubling method. Compared with the no-load controls, there was an increase in the absorption and scattering coefficients among most of the compressed specimens.

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

Ghassemi-Armaki, Hassan; Leff, Asher C.; Taheri, Mitra L.

Compression-compression cyclic deformation of nanocrystalline NiTi tubes intended for medical stents and with an outer diameter of 1 mm and wall thickness of 70 μm was studied using micropillars produced by FIB with the loading axis orthogonal to the tube axis. These micropillars were cycled in a displacement-controlled mode using a nanoindenter equipped with a flat punch to strain levels of 4, 6 and 8% in each cycle and specimens were subjected to several hundred cycles. Furthermore, the cyclic response of two NiTi tubes, one with Af of 17 °C and the other with an Af of -5 °C ismore » compared. The texture of the tube with the Af of -5 °C was measured at the microscopic level using transmission electron microscopy and at the macroscopic level by X-ray diffraction and good agreement was noted. Characteristics such as i) a reduction in the forward transformation stress, ii) increase in maximum stress for a given displacement amplitude, and iii) a reduction in the hysteresis loop area, all with increasing number of cycles, observed typically during cyclic deformation of conventional macroscopic specimens, were captured in the micropillar cyclic tests. Our observations lead to the conclusion that micropillar compression testing in a cyclic mode can enable characterizing the orientation-dependent response in such small dimension components that see complex loading in service, and additionally provide an opportunity for calibrating constitutive equations in micromechanical models.« less

Promoting the use of crumb rubber concrete in developing countries.

PubMed

Batayneh, Malek K; Marie, Iqbal; Asi, Ibrahim

2008-11-01

The use of accumulated waste materials in third world countries is still in its early phases. It will take courage for contractors and others in the construction industry to recycle selected types of waste materials in the concrete mixes. This paper addresses the recycling of rubber tires accumulated every year in Jordan to be used in concrete mixes. The main objectives of this research were to provide more scientific evidence to support the use of legislation or incentive-based schemes to promote the reuse of accumulated waste tires. This research focused on using crumb tires as a replacement for a percentage of the local fine aggregates used in the concrete mixes in Jordan. Different concrete specimens were prepared and tested in terms of uniaxial compression and splitting tension. The main variable in the mixture was the volumetric percentage of crumb tires used in the mix. The test results showed that even though the compressive strength is reduced when using the crumb tires, it can meet the strength requirements of light weight concrete. In addition, test results and observations indicated that the addition of crumb rubber to the mix has a limited effect toward reducing the workability of the mixtures. The mechanical test results demonstrated that the tested specimens of the crumb rubber concrete remained relatively intact after failure compared to the conventional concrete specimens. It is also concluded that modified concrete would contribute to the disposal of the non-decaying scrap tires, since the amount being accumulated in third world countries is creating a challenge for proper disposal. Thus, obliging authorities to invest in facilitating the use of waste tires in concrete, a fundamental material to the booming construction industry in theses countries, serves two purposes.

Behavior of an MBT waste in monotonic triaxial shear tests

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

Bhandari, Athma Ram, E-mail: athma.bhandari@beg.utexas.edu; Powrie, William, E-mail: w.powrie@soton.ac.uk

2013-04-15

Highlights: ► We studied the stress–strain–strength characteristics of an MBT waste. ► Rate of mobilization of strength with strain depends on initial density. ► Image analysis technique was used to determine whole-specimen displacement fields. ► Initial mode of deformation of a loose specimen is one-dimensional compression. ► Reinforcing elements enhance the resistance to lateral and volumetric deformation. - Abstract: Legislation in some parts of the world now requires municipal solid waste (MSW) to be processed prior to landfilling to reduce its biodegradability and hence its polluting potential through leachate and fugitive emission of greenhouse gases. This pre-processing may be achievedmore » through what is generically termed mechanical–biological-treatment (MBT). One of the major concerns relating to MBT wastes is that the strength of the material may be less than for raw MSW, owing to the removal of sheet, stick and string-like reinforcing elements during processing. Also, the gradual increase in mobilized strength over strains of 30% or so commonly associated with unprocessed municipal solid waste may not occur with treated wastes. This paper describes a series of triaxial tests carried out to investigate the stress–strain–strength characteristics of an MBT waste, using a novel digital image analysis technique for the determination of detailed displacement fields over the whole specimen. New insights gained into the mechanical behavior of MBT waste include the effect of density on the stress–strain response, the initial 1-D compression of lightly consolidated specimens, and the likely reinforcing effect of small sheet like particles remaining in the waste.« less

Damage-Tolerance Characteristics of Composite Fuselage Sandwich Structures with Thick Facesheets

NASA Technical Reports Server (NTRS)

McGowan, David M.; Ambur, Damodar R.

1997-01-01

Damage tolerance characteristics and results from experimental and analytical studies of a composite fuselage keel sandwich structure subjected to low-speed impact damage and discrete-source damage are presented. The test specimens are constructed from graphite-epoxy skins borided to a honeycomb core, and they are representative of a highly loaded fuselage keel structure. Results of compression-after-impact (CAI) and notch-length sensitivity studies of 5-in.-wide by 10-in.long specimens are presented. A correlation between low-speed-impact dent depth, the associated damage area, and residual strength for different impact-energy levels is described; and a comparison of the strength for undamaged and damaged specimens with different notch-length-to-specimen-width ratios is presented. Surface strains in the facesheets of the undamaged specimens as well as surface strains that illustrate the load redistribution around the notch sites in the notched specimens are presented and compared with results from finite element analyses. Reductions in strength of as much as 53.1 percent for the impacted specimens and 64.7 percent for the notched specimens are observed.

Permeability of Concrete with Recycled Concrete Aggregate and Pozzolanic Materials under Stress

PubMed Central

Wang, Hailong; Sun, Xiaoyan; Wang, Junjie; Monteiro, Paulo J.M.

2016-01-01

The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the permeability of RAC is much lower than that of the reference concrete due to the on-going hydration and the pozzolanic reaction provided by the PHS and GGBS additives in the RAC mixture. The permeability of chloride under flexural load is much more sensitive than that under compressive load due to the differences in porosity and cracking pattern. At low compressive stress levels, the permeability of chloride decreased by the closing of pores and microcracks within RAC specimens. However, in a relatively short time the chloride diffusion coefficient and the chloride content increased rapidly with the increase of compressive stress when it exceeded a threshold stress level of approximate 35% of the ultimate compressive strength. Under flexural stress, the chloride transport capability increased with the increase of stress level and time. At high compressive and flexural stress levels, creep had a significant effect on the permeability of chloride in the RAC specimens due to the damage from the nucleation and propagation of microcracks over time. It is apparent that mortar cracking has more of a significant effect on the chloride transport in concrete than cracking in the interfacial transition zone (ITZ). PMID:28773376

Permeability of Concrete with Recycled Concrete Aggregate and Pozzolanic Materials under Stress.

PubMed

Wang, Hailong; Sun, Xiaoyan; Wang, Junjie; Monteiro, Paulo J M

2016-03-30

The research reported herein studied the permeability of concrete containing recycled-concrete aggregate (RA), superfine phosphorous slag (PHS), and ground granulated blast-furnace slag (GGBS) with and without stress. Test results showed that the chloride diffusion coefficient of RA concrete (RAC) without external loads decreased with time, and the permeability of RAC is much lower than that of the reference concrete due to the on-going hydration and the pozzolanic reaction provided by the PHS and GGBS additives in the RAC mixture. The permeability of chloride under flexural load is much more sensitive than that under compressive load due to the differences in porosity and cracking pattern. At low compressive stress levels, the permeability of chloride decreased by the closing of pores and microcracks within RAC specimens. However, in a relatively short time the chloride diffusion coefficient and the chloride content increased rapidly with the increase of compressive stress when it exceeded a threshold stress level of approximate 35% of the ultimate compressive strength. Under flexural stress, the chloride transport capability increased with the increase of stress level and time. At high compressive and flexural stress levels, creep had a significant effect on the permeability of chloride in the RAC specimens due to the damage from the nucleation and propagation of microcracks over time. It is apparent that mortar cracking has more of a significant effect on the chloride transport in concrete than cracking in the interfacial transition zone (ITZ).

Estimation of static parameters based on dynamical and physical properties in limestone rocks

NASA Astrophysics Data System (ADS)

Ghafoori, Mohammad; Rastegarnia, Ahmad; Lashkaripour, Gholam Reza

2018-01-01

Due to the importance of uniaxial compressive strength (UCS), static Young's modulus (ES) and shear wave velocity, it is always worth to predict these parameters from empirical relations that suggested for other formations with same lithology. This paper studies the physical, mechanical and dynamical properties of limestone rocks using the results of laboratory tests which carried out on 60 the Jahrum and the Asmari formations core specimens. The core specimens were obtained from the Bazoft dam site, hydroelectric supply and double-curvature arch dam in Iran. The Dynamic Young's modulus (Ed) and dynamic Poisson ratio were calculated using the existing relations. Some empirical relations were presented to estimate uniaxial compressive strength, as well as static Young's modulus and shear wave velocity (Vs). Results showed the static parameters such as uniaxial compressive strength and static Young's modulus represented low correlation with water absorption. It is also found that the uniaxial compressive strength and static Young's modulus had high correlation with compressional wave velocity and dynamic Young's modulus, respectively. Dynamic Young's modulus was 5 times larger than static Young's modulus. Further, the dynamic Poisson ratio was 1.3 times larger than static Poisson ratio. The relationship between shear wave velocity (Vs) and compressional wave velocity (Vp) was power and positive with high correlation coefficient. Prediction of uniaxial compressive strength based on Vp was better than that based on Vs . Generally, both UCS and static Young's modulus (ES) had good correlation with Ed.

Performance of "Waterless Concrete"

NASA Technical Reports Server (NTRS)

Toutanji, H. A.; Grugel, R. N.

2009-01-01

Waterless concrete consists of molten elementary sulfur and aggregate. The aggregates in a lunar environment will be lunar rocks and soil. Sulfur is present on the Moon in Troilite soil (FeS) and, by oxidation of the soil, iron and sulfur can be produced. Sulfur concrete specimens were cycled between liquid nitrogen (approx.]91 C) and room temperature (^21 C) to simulate exposure to a lunar environment. Cycled and control specimens were subsequently tested in compression at room temperatures (^21 C) and ^-101 C. Test results showed that due to temperature cycling, the compressive strength of cycled specimens was 20% of those non-cycled. This reduction in strength can be attributed to the large differences in thermal coefficients of expansion of the materials constituting the concrete which promoted cracking. Similar sulfur concrete mixtures were strengthened with short and long glass fibres. The lunar regolith simulant was melted in a 25 cc Pt- Rh crucible in a Sybron Thermoline high temperature MoSi2 furnace at melting temperatures of 1450 to 1600 C for times of 30 min to i hour. Glass fibres and small rods were pulled from the melt. The glass fibres were used to reinforce sulfur concrete plated to improve the flexural strength of the sulfur concrete. Beams strengthened with glass fibres showed to exhibit an increase in the flexural strength by as much as 45%.

Physical and Chemical Character of Fly Ash of Coal Fired Power Plant in Java

NASA Astrophysics Data System (ADS)

Triwulan; Priadana, K. A.; Ekaputri, J. J.; Bayuaji, R.

2017-11-01

Quality of fly ash is varying widely in the field, it depends on the combustion process and the quality of the basic ingredients, namely coal. It will affect the physical and mechanical properties of the concrete mixtures used. This study used 12 samples of fly ash. The physical and chemical properties and finesse modulus were analyzed. The fly ash was mixed with OPC (Ordinary Portland Cement) with the proportion of 20% fly ash and 80% OPC. The specimens were form with mortar dimension of 5cm x 5 cm. The test was affected by the correlation of fly ash fineness modulus to compressive strength, correlation density of fly ash to compressive strength, and correlation of carbon content to the compressive strength.

Confinement of NORMAL- AND HIGH-STRENGTH CONCRETE by Shape Memory Alloy (SMA) Spirals

NASA Astrophysics Data System (ADS)

Gholampour, A.; Ozbakkaloglu, T.

2018-01-01

This paper presents the results of an experimental study on the axial compressive behaviour of normal- and high-strength concrete (NSC and HSC) confined by shape memory alloy (SMA) spirals. A spiral pitch space of 36 and 20 mm was used for SMA confinement of NSC and HSC columns, respectively. The confining pressure was applied on the concrete cylinders by SMA spirals that were prestrained at 0, 5.5, and 9.5%. The compression test results on the SMA-confined specimens indicate that the prestrain level of SMA significantly affects the axial compressive behaviour of both NSC and HSC. An increase in the level of prestrain leads to an increase in the peak axial stress and corresponding strain of SMA-confined concrete.

Temperature Effects on the Impact Behavior of Fiberglass and Fiberglass/Kevlar Sandwich Composites

NASA Astrophysics Data System (ADS)

Halvorsen, Aaron; Salehi-Khojn, Amin; Mahinfalah, Mohammad; Nakhaei-Jazar, Reza

2006-11-01

Impact tests were performed on sandwich composites with Fiberglass and Fiberglass/Kevlar face sheets subjected to varied temperatures. A number of specimens were tested at -50 to 120 °C temperature range and at 20, 30, and 45 J low velocity energy levels. Impact properties of the sandwich composites that were evaluated include maximum normal and shear stresses, maximum energy absorption, non-dimensional parameters (AEMP, PI, and RD), and compression after impact strength. Composite specimens tested have a urethane foam filled honeycomb center sandwiched between a variation of four layered Fiberglass and Kevlar/Fiberglass face sheets in a thermoset polymer epoxy matrix. Results showed that the impact performance of these sandwich composites changed over the range of temperature considered and with the addition of a Kevlar layer.

Buckling test of a 3-meter-diameter corrugated graphite-epoxy ring-stiffened cylinder

NASA Technical Reports Server (NTRS)

Davis, R. C.

1982-01-01

A three m diameter by three m long corrugated cylindrical shell with external stiffening rings was tested to failure by buckling. The corrugation geometry for the graphite epoxy composite cylinder wall was optimized to withstand a compressive load producing an ultimate load intensity of 157.6 kN/m without buckling. The test method used to produce the design load intensity was to mount the specimen as a cantilevered cylinder and apply a pure bending moment to the end. A load introduction problem with the specimen was solved by using the BOSOR 4 shell of revolution computer code to analyze the shell and attached loading fixtures. The cylinder test loading achieved was 101 percent of design ultimate, and the resulting mass per unit of shell wall area was 1.96 kg/sq m.

A new application of Fe-28Mn-6Si-5Cr (mass%) shape memory alloy, for self-adjustable axial preloading of ball bearings

NASA Astrophysics Data System (ADS)

Paleu, V.; Gurău, G.; Comăneci, R. I.; Sampath, V.; Gurău, C.; Bujoreanu, L. G.

2018-07-01

A new application of Fe-Mn-Si based shape memory alloys (SMAs) was developed under the form of truncated cone-shaped module, for self-adaptive axial preload control in angular contact bearings. The modules were processed by high-speed high-pressure torsion (HS-HPT), from circular crowns cut from axially drilled ingots of Fe-28Mn-6Si-9Cr (mass%) SMA. The specimens were mechanically tested in the hot rolled state, prior to HS-HPT processing, demonstrating free-recovery shape memory effect (SME) and high values for ultimate tensile stress and strain as well as low cycle fatigue life. The HS-HPT modules were subjected to static loading–unloading compression, without/with lubrication at specimen-tool interface, both individually and in different coupling modes. Dry compression cycles revealed reproducible stress plateaus both during loading and unloading stages, being associated with hardness gradient, along cone generator, caused by HS-HPT processing. Constrained recovery tests, performed using compressed modules, emphasized the continuous generation of stress during heating, by one way SME, at a rate of ∼9.3 kPa/%. Dynamic compression tests demonstrated the capability of modules to develop closed stress–strain loops after 50 000 cycles, without visible signs of fatigue. HS-HPT caused the fragmentation of crystalline grains, while compression cycles enabled the formation of ε hexagonal close-packed stress-induced martensite (ε), which is characterized by a high density of stacking faults. Using an experimental setup, specifically designed and manufactured for this purpose, both feasibility and functionality tests were performed using HS-HPT modules. The feasibility tests proved the existence of a general tendency of both axial force and friction torque to increase in time, favoured by the increase of initial preloading force and the augmentation of rotation speed. Functionality tests, performed on two pairs of HS-HPT modules fastened in base-to-base coupling mode, demonstrated the capacity of modules to accommodate high preloads while maintaining both axial force and friction torque at constant values in time. These preliminary results suggest that, for the time being, the modules can operate only as single use applications, more effective during the running-in period. This bevahior recommends HS-HPT modules as a new application of Fe-Mn-Si SMAs, with the potential to be used for the development of new temperature-responsive compression displacement systems.

Optimization of Elastically Tailored Tow-Placed Plates with Holes

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.; Tatting, Brian F.; Guerdal, Zafer

2003-01-01

Elastic stiffness tailoring of laminated composite panels by allowing the fibers to curve within the plane of the laminate is a design concept that has been demonstrated to be both beneficial and practical. The objective of the present paper is to demonstrate the effectiveness of stiffness tailoring through the use of curvilinear fibers to reduce stress concentrations around the hole and improve the load carrying capability of panels. Preliminary panel designs that are to be manufactured and tested were determined through design studies for flat plates without holes under axial compression using an optimization program. These candidate designs were then analyzed with finite element models that accurately reflect the test conditions and geometries in order to decide upon the final designs for manufacture and testing. An advanced tow-placement machine is used to manufacture the test panels with varying fiber orientation angles. A total of six large panels measuring three feet by six feet, each of which is used to produce four specimens with or without holes, are fabricated. The panels were machined into specimens with holes and tested at NASA Langley Research Center. Buckling response and failure of panels without holes and with two different hole dimensions are presented. Buckling and failure loads of tow-steered specimens are significantly greater than the buckling and failure loads of traditional straight-fiber specimens.

The Influence of Addition of Plastiment-VZ to Concrete Characteristics in Riau Province

NASA Astrophysics Data System (ADS)

Wahyuni Megasari, Shanti; Winayati

2017-12-01

Riau Province has an area of 8,702,000 ha consisting of 7,121.344,00 ha of forest and 3,867,000 ha in the form of peatlands. Peat structures are soft and have pores that make it easy to hold water. Peat water has a high color intensity, low pH, high organic content and has an acidic properties So it does not qualify as a mixture of concrete. To meet the needs of water in the concrete mix then water should be obtained from another place but it will require a greater cost and time. To resolve the issue, the advancement of concrete technology has resulted in admixture that can help in maintaining the quality of concrete. Plastiment-VZ is a plasticizer material that can increase workability of concrete without adding water. However, for the use in the field, the selection of admixture must be adjusted to the planned concrete situation and condition. Excessive use of admixture will also result in uneconomical concrete. The design of the job mix using the Department of Environment (DOE) method with compressive strength concrete plan fc ' = 25 MPa. The percentage of Plastiment-VZ addition is 0%, 0,05%; 0,10%; 0,15% and 0,20% to the weight of cement. The reduction of the amount of water in this study is 10% of the total amount of water. Specimens in each variation were made using cylinder mold with 15 cm in diameter and 30 cm high. After specimens are created and maintained, testing of compressive strength concrete held in 28 days. The test results show that the trend of average compressive strength has increased along with the addition of Plastiment-VZ percentage. The equation resulting from the average compressive strength is y = -362,7x2 + 133,3x + 28,10 with value R2 = 0,969. The highest average compressive strength value was obtained in the addition of 0,20% Plastiment-VZ at 40,76 MPa. Statistical testing with Analysis of Variance - ANOVA states that there is a very real interaction or treatment between the compressive strength of the concrete with the addition of Plastiment-VZ. So it can be concluded that the reduction of the amount of water with the addition of Plastiment-VZ has an effect on the increasing of concrete compressive strength characteristics.

The effect of veneering and heat treatment on the flexural strength of Empress 2 ceramics.

PubMed

Cattell, M J; Palumbo, R P; Knowles, J C; Clarke, R L; Samarawickrama, D Y D

2002-05-01

The aims of the study were to test and compare the biaxial flexural strength and reliability of Empress 2 ceramics after heat treatment and the addition of the veneering material and to characterise their microstructures. Forty disc specimens (2 x 14 mm) and forty disc specimens (1 x 14 mm) were produced by heat pressing in the EP 500 press furnace. Group 1 (2 x 14 mm Empress 2 core) was as heat pressed and group 2 (2 x 14 mm Empress 2 core) was subjected to the recommended firing cycles. Groups 3 and 4 (1 x 14 mm Empress 2 core) were veneered with the dentine material and heat-treated as per group 2. Groups 1, 2 and 3 were lapped to 800 grit silicon carbide paper on the compressive surface only and group 4 on both the compressive and tensile test surfaces. Twenty disc specimens per group were tested using the biaxial flexure test at a crosshead speed of 0.15 mm/min. Specimens were characterised using X-ray diffraction (XRD) and secondary electron imaging (SEM). Mean biaxial flexural strengths (MPa+/-SD) were group 1: 265.5+/-25.7; group 2: 251.3+/-30.2; group 3: 258.6+/-21.4 and group 4: 308.6+/-37.7. There was no statistical difference between groups 1, 2 and 3 (p>0.05), but differences for group 4 (p<0.05). XRD and SEM revealed lithium disilicate and lithium orthophosphate in the Empress 2 core material and an amorphous glass and some evidence of a crystalline phase in the dentine material. CONCLUSIONS; Veneering or heat treatment of Empress 2 ceramics did not significantly affect the mean biaxial flexural strength (p>0.05) or reliability. Surface modification of the Empress 2 core material increased the mean biaxial flexural strength (p<0.05).

Design and fabrication of Rene 41 advanced structural panels. [their performance under axial compression, shear, and bending loads

NASA Technical Reports Server (NTRS)

Greene, B. E.; Northrup, R. F.

1975-01-01

The efficiency was investigated of curved elements in the design of lightweight structural panels under combined loads of axial compression, inplane shear, and bending. The application is described of technology generated in the initial aluminum program to the design and fabrication of Rene 41 panels for subsequent performance tests at elevated temperature. Optimum designs for two panel configurations are presented. The designs are applicable to hypersonic airplane wing structure, and are designed specifically for testing at elevated temperature in the hypersonic wing test structure located at the NASA Flight Research Center. Fabrication methods developed to produce the Rene panels are described, and test results of smaller structural element specimens are presented to verify the design and fabrication methods used. Predicted strengths of the panels under several proposed elevated temperature test load conditions are presented.

Effects of Control Mode and R-Ratio on the Fatigue Behavior of a Metal Matrix Composite

NASA Technical Reports Server (NTRS)

2005-01-01

Composite Because of their high specific stiffness and strength at elevated temperatures, continuously reinforced metal matrix composites (MMC's) are under consideration for a future generation of aeropropulsion systems. Since components in aeropropulsion systems experience substantial cyclic thermal and mechanical loads, the fatigue behavior of MMC's is of great interest. Almost without exception, previous investigations of the fatigue behavior of MMC's have been conducted in a tension-tension, load-controlled mode. This has been due to the fact that available material is typically less than 2.5-mm thick and, therefore, unable to withstand high compressive loads without buckling. Since one possible use of MMC's is in aircraft skins, this type of testing mode may be appropriate. However, unlike aircraft skins, most engine components are thick. In addition, the transient thermal gradients experienced in an aircraft engine will impose tension-compression loading on engine components, requiring designers to understand how the MMC will behave under fully reversed loading conditions. The increased thickness of the MMC may also affect the fatigue life. Traditionally, low-cycle fatigue (LCF) tests on MMC's have been performed in load control. For monolithic alloys, low-cycle fatigue tests are more typically performed in strain control. Two reasons justify this choice: (1) the critical volume from which cracks initiate and grow is generally small and elastically constrained by the larger surrounding volume of material, and (2) load-controlled, low-cycle fatigue tests of monolithics invariably lead to unconstrained ratcheting and localized necking--an undesired material response because the failure mechanism is far more severe than, and unrelated to, the fatigue mechanism being studied. It is unknown if this is the proper approach to composite testing. However, there is a lack of strain-controlled data on which to base any decisions. Consequently, this study addresses the isothermal, LCF behavior of a [0]_32 MMC tested under strain- and load-controlled conditions for both zero-tension and tension-compression loading conditions. These tests were run at 427 C on thick specimens of SiC-reinforced Ti-15-3. For the fully-reversed tests, no difference was observed in the lives between the load- and strain-controlled tests. However, for the zero-tension tests, the strain-controlled tests had longer lives by a factor of 3 in comparison to the load-controlled tests. This was due to the fact that under strain-control the specimens cyclically softened, reducing the cracking potential. In contrast, the load-controlled tests ratcheted toward larger tensile strains leading to an eventual overload of the fibers. Fatigue tests revealed that specimens tested under fully-reversed conditions had lives approximately an order of magnitude longer than for those specimens tested under zero tension. When examined on a strain-range basis, the fully reversed specimens had similar, but still shorter lives than those of the unreinforced matrix material. However, the composite had a strain limitation at short lives because of the limited strain capacity of the brittle ceramic fiber. The composite also suffered at very high lives because of the lack of an apparent fatigue limit in comparison to the unreinforced matrix. The value of adding fibers to the matrix is apparent when the fatigue lives are plotted as a function of stress range. Here, the composite is far superior to the unreinforced matrix because of the additional load-carrying capacity of the fibers.

Evaluation of Braided Stiffener Concepts for Transport Aircraft Wing Structure Applications

NASA Technical Reports Server (NTRS)

Deaton, Jerry W.; Dexter, H. Benson (Editor); Markus, Alan; Rohwer, Kim

1995-01-01

Braided composite materials have potential for application in aircraft structures. Stiffeners, wing spars, floor beams, and fuselage frames are examples where braided composites could find application if cost effective processing and damage requirements are met. Braiding is an automated process for obtaining near-net shape preforms for fabrication of components for structural applications. Previous test results on braided composite materials obtained at NASA Langley indicate that damage tolerance requirements can be met for some applications. In addition, the braiding industry is taking steps to increase the material through-put to be more competitive with other preform fabrication processes. Data are presented on the compressive behavior of three braided stiffener preform fabric constructions as determined from individual stiffener crippling test and three stiffener wide panel tests. Stiffener and panel fabrication are described and compression data presented for specimens tested with and without impact damage. In addition, data are also presented on the compressive behavior of the stitched stiffener preform construction currently being used by McDonnell Douglas Aerospace in the NASA ACT wing development program.

Mechanical behaviour of fibre reinforced concrete using soft - drink can

NASA Astrophysics Data System (ADS)

Ilya, J.; Cheow Chea, C.

2017-11-01

This research was carried out to study the behaviour of concrete, specifically compressive and flexural strength, by incorporating recycled soft drink aluminium can as fibre reinforcement in the concrete. Another aim of the research is to determine the maximum proportion of fibres to be added in the concrete. By following standard mix design, Ordinary Portland Cement (OPC) concrete was made to have a target mean strength of 30 N/mm2 with not more than 30 mm of slump. Having the same workability, OPC concrete with 0%, 1% and 2% of soft drink can aluminium fibre was prepared based on weight of cement. The specimens were tested for compressive strength and flexural strength. Laboratory test results based on short term investigation reveals that the compressive strength and flexural strength of concrete containing fibre are higher than of normal OPC concrete. Among two volume fractions, concrete with 1% of soft drink can fibre have performed better result in compressive strength and flexural strength compared with 2% amount of soft drink can fibre. The optimum proportion of aluminium fibre to be added in the concrete as fibre reinforcement is 1% fibre content by weight of cement which gave all the positive response from all the tests conducted.

Analysis of Crushing Response of Composite Crashworthy Structures

NASA Astrophysics Data System (ADS)

David, Matthew; Johnson, Alastair F.; Voggenreiter, H.

2013-10-01

The paper describes quasi-static and dynamic tests to characterise the energy absorption properties of polymer composite crash energy absorbing segment elements under axial loads. Detailed computer tomography scans of failed specimens are used to identify local compression crush failure mechanisms at the crush front. The varied crushing morphology between the compression strain rates identified in this paper is observed to be due to the differences in the response modes and mechanical properties of the strain dependent epoxy matrix. The importance of understanding the role of strain rate effects in composite crash energy absorbing structures is highlighted in this paper.

Tensile and Laterally Confined Compression Properties of Various 3-Dimensional (3-D) Woven Composites

DTIC Science & Technology

2014-11-01

such as orthogonal (Z- fiber) weave, layer-to-layer, and angle interlock. Figure 1 provides an example of 2 different types of 3-D woven structures...o.~os~~~o. t Deflection (in) (c) 90° Orientation 18 6.4 LCC Test Specimen Failure Analysis LCC posttest failure analysis was conducted

Combining Digital Image Correlation and Acoustic Emission for Monitoring of the Strain Distribution until Yielding During Compression of Bovine Cancellous Bone

NASA Astrophysics Data System (ADS)

Tsirigotis, Athanasios; Deligianni, Despoina D.

2017-12-01

In this work, the surface heterogeneity in mechanical compressive strain of cancellous bone was investigated with digital image correlation (DIC). Moreover, the onset and progression of failure was studied by acoustic emission (AE). Cubic cancellous bone specimens, with side of 15 mm, were obtained from bovine femur and kept frozen at -20ºC until testing. Specimen strain was analyzed by measuring the change of distance between the platens (crosshead) and via an optical method, by following the strain evolution with a camera. Simultaneously, AE monitoring was performed. The experiments showed that compressive Young’s modulus determined by crosshead strain is underestimated at 23% in comparison to optically determined strain. However, surface strain fields defined by DIC displayed steep strain gradients, which can be attributed to cancellous bone porosity and inhomogeneity. The cumulative number of events for the total AE activity recorded from the sensors showed that the activity started at a mean load level of 36% of the maximum load and indicated the initiation of micro-cracking phenomena. Further experiments, determining 3D strain with μCT apart from surface strain, are necessary to clarify the issue of strain inhomogeneity in cancellous bone.

Material test machine for tension-compression tests at high temperature

DOEpatents

Cioletti, Olisse C.

1988-01-01

Apparatus providing a device for testing the properties of material specimens at high temperatures and pressures in controlled water chemistries includes, inter alia, an autoclave housing the specimen which is being tested. The specimen is connected to a pull rod which couples out of the autoclave to an external assembly which includes one or more transducers, a force balance chamber and a piston type actuator. The pull rod feeds through the force balance chamber and is compensated thereby for the pressure conditions existing within the autoclave and tending to eject the pull rod therefrom. The upper end of the push rod is connected to the actuator through elements containing a transducer comprising a linear variable differential transformer (LVDT). The housing and coil assembly of the LVDT is coupled to a tube which runs through a central bore of the pull rod into the autoclave where it is connected to one side of the specimen. The movable core of the LVDT is coupled to a stem which runs through the tube where it is then connected to the other side of the specimen through a coupling member. A transducer in the form of a load cell including one or more strain gages is located on a necked-down portion of the upper part of the pull rod intermediate the LVDT and force balance chamber.

Interaction Effects of Simultaneous Torsional and Compressional Cyclic Loading of Sand.

DTIC Science & Technology

1979-12-01

loading 3a AftrRACT (rwo si .v1W f9111 t "Ofslr -d IderufI ST *lack ""iha)ln experimental research program based on laboratory test studies and scaled...experimental research program based on laboratory test studies and scaled slope model tests was conducted with specimens of Monterey No. 0 sand. The principal...objective of the research was to study the effects of interactive coupling during combined compression (normal) and shear loading on the response of

Experimental and Numerical Analysis of Axially Compressed Circular Cylindrical Fiber-Reinforced Panels with Various Boundary Conditions.

DTIC Science & Technology

1981-10-01

Numerical predictions used in the compari- sons were obtained from the energy -based, finite-difference computer proqram CLAPP. Test specimens were clamped...edges V LONGITUDINAL STIFFENERS 45 I. Introduction 45 2. Stiffener Strain Energy 46 3. Stiffener Energy in Matrix Form 47 4. Displacement Continuity 49...that theoretical bifurcation loads predicted by the energy method represent upper bounds to the classical bifurcation loads associated with the test

Highly Porous NiTi with Isotropic Pore Morphology Fabricated by Self-Propagated High-Temperature Synthesis

NASA Astrophysics Data System (ADS)

Hosseini, S. A.; Alizadeh, M.; Ghasemi, A.; Meshkot, M. A.

2013-02-01

Highly porous NiTi with isotropic pore morphology has been successfully produced by self-propagating high-temperature synthesis of elemental Ni/Ti metallic powders. The effects of adding urea and NaCl as temporary pore fillers were investigated on pore morphology, microstructure, chemical composition, and the phase transformation temperatures of specimens. These parameters were studied by optical microscopy, scanning electron microscopy, x-ray diffraction, and differential scanning calorimetry (DSC). Highly porous specimens were obtained with up to 83% total porosity and pore sizes between 300 and 500 μm in diameter. Results show pore characteristics were improved from anisotropic to isotropic and pore morphology was changed from channel-like to irregular by adding pore filler powders. Furthermore, the highly porous specimens produced when using urea as a space holder, were of more uniform composition in comparison to NaCl. DSC results showed that a two-step martensitic phase transformation takes place during the cooling cycles and the austenite finish temperature ( A f) is close to human body temperature. Compression test results reveal that the compressive strength of highly porous NiTi is about 155 MPa and recoverable strain about 6% in superelasticity regime.

Normalization of Impact Energy by Laminate Thickness for Compression After Impact Testing

NASA Technical Reports Server (NTRS)

Nettles, A. T.; Hromisin, S. M.

2013-01-01

The amount of impact energy used to damage a composite laminate is a critical parameter when assessing residual strength properties. The compression after impact (CAI) strength of impacted laminates is dependent upon how thick the laminate is and this has traditionally been accounted for by normalizing (dividing) the impact energy by the laminate's thickness. However, when comparing CAI strength values for a given lay-up sequence and fiber/resin system, dividing the impact energy by the specimen thickness has been noted by the author to give higher CAI strength values for thicker laminates. A study was thus undertaken to assess the comparability of CAI strength data by normalizing the impact energy by the specimen thickness raised to a power to account for the higher strength of thicker laminates. One set of data from the literature and two generated in this study were analyzed by dividing the impact energy by the specimen thickness to the 1, 1.5, 2, and 2.5 powers. Results show that as laminate thickness and damage severity decreased, the value which the laminate thickness needs to be raised to in order to yield more comparable CAI data increases.

Evaluation of Repair Efficiency in Structures Made of Fibrous Polymer Composite Materials

NASA Astrophysics Data System (ADS)

Anoshkin, A. N.; Vil'deman, V. E.; Lobanov, D. S.; Chikhachev, A. I.

2014-07-01

Full-scale experimental investigations into the residual strength of structurally similar elements of acoustical panels after a local repair of defects, such as through breakdown, were conducted. Local repairs without using the vacuum technology were carried out. The technology of repair consists in removing and layer-bylayer replacing the damaged layers of material with repaired ones. For comparison, undamaged and repaired sandwich panel specimens were tested in tension and compression. The specimens were produced by serial technology from a VPS-33 fiberglass prepreg. Their deformation and fracture mechanisms are analyzed, and their loading diagrams are obtained.

Fatigue Life of Postbuckled Structures with Indentation Damage

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Bisagni, Chiara

2016-01-01

The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of the stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 37 millimeters to 56 millimeters were tested in fatigue and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

Investigation on Flexure Test of Composite Beam of Repair Materials and Substrate Concrete for Durable Repair

NASA Astrophysics Data System (ADS)

Pattnaik, Rashmi R.; Rangaraju, Prasada Rao

2014-12-01

An experimental study was conducted on composite beam of repair materials and substrate concrete to investigate the failures of concrete repair due to differences in strength of repair materials and substrate concrete. In this investigation the flexural strength, load-deflection curves and failure patterns of the composite beam specimens are studied for the durability of the concrete repair. Flexure test was conducted to simulate tensile stress in the concrete repair material. Compressive strength and split tensile strength of the repair materials and substrate concrete are investigated to aid in the analysis of the concrete repair. It was observed that the repair materials of higher compressive strength than the substrate concrete are causing an incompatible failure in the concrete repair.

The Effects of Shot and Laser Peening on Fatigue Life and Crack Growth in 2024 Aluminum Alloy and 4340 Steel

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.; Matthews, W. T.; Prabhakaran, R.; Newman, J. C., Jr.; Dubberly, M. J.

2001-01-01

Fatigue and crack growth tests have been conducted on 4340 steel and 2024-T3 aluminum alloy, respectively, to assess the effects of shot peening on fatigue life and the effects of shot and laser peening on crack growth. Two current programs involving fixed and rotary-wing aircraft will not be using shot peened structures. Since the shot peening compressive residual stress depth is usually less than the 0.05-inch initial damage tolerance crack size, it is believed by some that shot peening should have no beneficial effects toward retarding crack growth. In this study cracks were initiated from an electronic-discharged machining flaw which was cycled to produce a fatigue crack of approximately 0.05-inches in length and then the specimens were peened. Test results showed that after peening the crack growth rates were noticeably slower when the cracks were fairly short for both the shot and laser peened specimens resulting in a crack growth life that was a factor of 2 to 4 times greater than the results of the average unpeened test. Once the cracks reached a length of approximately 0.1-inches the growth rates were about the same for the peened and unpeened specimens. Fatigue tests on 4340 steel showed that the endurance limit of a test specimen with a 0.002-inch-deep machining-like scratch was reduced by approximately 40 percent. However, if the "scratched" specimen was shot peened after inserting the scratch, the fatigue life returned to almost 100 percent of the unflawed specimens original fatigue life.

Microstructure and mechanical properties of an ultrafine Ti–Si–Nb alloy

DOE PAGES

Cao, G. H.; Jian, G. Y.; Liu, N.; ...

2015-08-19

In this study, Nb-modified ultrafine Ti–Si eutectic alloy was made by cold crucible levitation melting, tested in compression at room temperature, and characterized by electron microscopy. Compression tests of (Ti 86.5Si 13.5) 97Nb 3 specimens measured an ultimate compressive strength of 1180 MPa and a compressive plastic strain of 12%, both of which are higher than in eutectic Ti 86.5Si 13.5 alloy. Electron microscopy showed that the Ti–Si–Nb alloy had a bimodal microstructure with micrometer-scale primary α-Ti dendrites distributed in an ultrafine eutectic (α-Ti + Ti 5Si 3) matrix. The enhanced ductility is attributed to the morphology of the phase constituents and to the larger lattice mismatches between α-Ti and Ti 5Si 3 phases caused by the Nb addition. The crystallographic orientation relationship of Ti 5Si 3 with α-Ti is (more » $$1\\bar{1}00$$)[$$\\overline{11}$$26]Ti 5Si 3∥($$01\\bar{1}1$$)[5$$\\overline{143}$$] α–Τi.« less

Impact resistance and interlaminar fracture toughness of through-the-thickness reinforced graphite/epoxy

NASA Technical Reports Server (NTRS)

Dexter, H. B.; Funk, J. G.

1986-01-01

Five through-the-thickness stitch configurations are analyzed to determine the effect of impact resistance and interlaminar fracture toughness on T3000/3501-6 graphite/epoxy. The test specimens were stitched with either polyester or Kevlar yarns and with various stitch parameters. Tension and compression mechanical, impact and compression-after-impact, and double cantilever beam tests were conducted. It is observed that the stitched laminates have tension and compression strengths 20-25 percent lower than the strengths of unstitched laminates, the tension strength of stitched laminates is reduced with increasing number of stitches, and the compression strength increases as the number of stitches are increased. The impact data reveal that the Kevlar stitched laminates have less damage than unstitched laminates; the most effective configuration for suppressing impact damage and improving interlaminar fracture toughness consists of Kevlar yarns 1/4 inch apart with eight stitches per inch. The mode 1 critical strain energy release rate for the 1/4 inch Kevlar eight stitch laminate was calculated as 30 times higher than that of the unstitched.

Comparison of physical and mechanical properties of river sand concrete with quarry dust concrete

NASA Astrophysics Data System (ADS)

Opara, Hyginus E.; Eziefula, Uchechi G.; Eziefula, Bennett I.

2018-03-01

This study compared the physical and mechanical properties of river sand concrete with quarry dust concrete. The constituent materials were batched by weight. The water-cement ratio and mix ratio selected for the experimental investigation were 0.55 and 1:2:4, respectively. The specimens were cured for 7, 14, 21 and 28 days. Slump, density and compressive strength tests were carried out. The results showed that river sand concrete had greater density and compressive strength than quarry dust concrete for all curing ages. At 28 days of curing, river sand concrete exceeded the target compressive strength by 36%, whereas quarry dust concrete was less than the target compressive strength by 12%. Both river sand concrete and quarry dust concrete for the selected water/cement ratio and mix ratio are suitable for non-structural applications and lightly-loaded members where high strength is not a prerequisite.

A Comparative Evaluation of Sorption, Solubility, and Compressive Strength of Three Different Glass Ionomer Cements in Artificial Saliva: An in vitro Study

PubMed Central

Bhatia, Hind P; Sood, Shveta; Sharma, Naresh

2017-01-01

Aim To evaluate and compare the sorption, solubility, and compressive strength of three different glass ionomer cements in artificial saliva - type IX glass ionomer cement, silver-reinforced glass ionomer cement, and zirconia-reinforced glass ionomer cement, so as to determine the material of choice for stress-bearing areas. Materials and methods A total of 90 cylindrical specimens (4 mm diameter and 6 mm height) were prepared for each material following the manufacturer’s instructions. After subjecting the specimens to thermocycling, 45 specimens were immersed in artificial saliva for 24 hours for compressive strength testing under a universal testing machine, and the other 45 were evaluated for sorption and solubility, by first weighing them by a precision weighing scale (W1), then immersing them in artificial saliva for 28 days and weighing them (W2), and finally dehydrating in an oven for 24 hours and weighing them (W3). Results Group III (zirconomer) shows the highest compressive strength followed by group II (Miracle Mix) and least compressive strength is seen in group I (glass ionomer cement type IX-Extra) with statistically significant differences between the groups. The sorption and solubility values in artificial saliva were highest for glass ionomer cement type IX - Extra-GC (group I) followed by zirconomer-Shofu (group III), and the least value was seen for Miracle Mix-GC (group II). Conclusion Zirconia-reinforced glass ionomer cement is a promising dental material and can be used as a restoration in stress-bearing areas due to its high strength and low solubility and sorption rate. It may be a substitute for silver-reinforced glass ionomer cement due to the added advantage of esthetics. Clinical significance This study provides vital information to pediatric dental surgeons on relatively new restorative materials as physical and mechanical properties of the new material are compared with conventional materials to determine the best suited material in terms of durability, strength and dimensional stability. This study will boost confidence among dental surgeons in terms of handling characteristics, cost effectiveness and success rate. This study will help clinically and scientifically; pediatric dental surgeons to use this material in stress-bearing areas in pediatric patients. How to cite this article Bhatia HP, Singh S, Sood S, Sharma N. A Comparative Evaluation of Sorption, Solubility, and Com-pressive Strength of Three Different Glass Ionomer Cements in Artificial Saliva: An in vitro Study. Int J Clin Pediatr Dent 2017;10(1):49-54. PMID:28377656

Correlation between compressive strength and ultrasonic pulse velocity of high strength concrete incorporating chopped basalt fibre

NASA Astrophysics Data System (ADS)

Shafiq, Nasir; Fadhilnuruddin, Muhd; Elshekh, Ali Elheber Ahmed; Fathi, Ahmed

2015-07-01

Ultrasonic pulse velocity (UPV), is considered as the most important test for non-destructive techniques that are used to evaluate the mechanical characteristics of high strength concrete (HSC). The relationship between the compressive strength of HSC containing chopped basalt fibre stands (CBSF) and UPV was investigated. The concrete specimens were prepared using a different ratio of CBSF as internal strengthening materials. The compressive strength measurements were conducted at the sample ages of 3, 7, 28, 56 and 90 days; whilst, the ultrasonic pulse velocity was measured at 28 days. The result of HSC's compressive strength with the chopped basalt fibre did not show any improvement; instead, it was decreased. The UPV of the chopped basalt fibre reinforced concrete has been found to be less than that of the control mix for each addition ratio of the basalt fibre. A relationship plot is gained between the cube compressive strength for HSC and UPV with various amounts of chopped basalt fibres.

Macro-mesoscopic Fracture and Strength Character of Pre-cracked Granite Under Stress Relaxation Condition

NASA Astrophysics Data System (ADS)

Liu, Junfeng; Yang, Haiqing; Xiao, Yang; Zhou, Xiaoping

2018-05-01

The fracture characters are important index to study the strength and deformation behavior of rock mass in rock engineering. In order to investigate the influencing mechanism of loading conditions on the strength and macro-mesoscopic fracture character of rock material, pre-cracked granite specimens are prepared to conduct a series of uniaxial compression experiments. For parts of the experiments, stress relaxation tests of different durations are also conducted during the uniaxial loading process. Furthermore, the stereomicroscope is adopted to observe the microstructure of the crack surfaces of the specimens. The experimental results indicate that the crack surfaces show several typical fracture characters in accordance with loading conditions. In detail, some cleavage fracture can be observed under conventional uniaxial compression and the fractured surface is relatively rough, whereas as stress relaxation tests are attached, relative slip trace appears between the crack faces and some shear fracture starts to come into being. Besides, the crack faces tend to become smoother and typical terrace structures can be observed in local areas. Combining the macroscopic failure pattern of the specimens, it can be deduced that the duration time for the stress relaxation test contributes to the improvement of the elastic-plastic strain range as well as the axial peak strength for the studied material. Moreover, the derived conclusion is also consistent with the experimental and analytical solution for the pre-peak stage of the rock material. The present work may provide some primary understanding about the strength character and fracture mechanism of hard rock under different engineering environments.

Biomechanical evaluation of a second generation headless compression screw for ankle arthrodesis in a cadaver model.

PubMed

Somberg, Andrew Max; Whiteside, William K; Nilssen, Erik; Murawski, Daniel; Liu, Wei

2016-03-01

Many types of screws, plates, and strut grafts have been utilized for ankle arthrodesis. Biomechanical testing has shown that these constructs can have variable stiffness. More recently, headless compression screws have emerged as an evolving method of achieving compression in various applications but there is limited literature regarding ankle arthrodesis. The aim of this study was to determine the biomechanical stability provided by a second generation fully threaded headless compression screw compared to a standard headed, partially threaded cancellous screw in a cadaveric ankle arthrodesis model. Twenty fresh frozen human cadaver specimens were subjected to simulated ankle arthrodesis with either three standard cancellous-bone screws (InFix 7.3mm) or with three headless compression screws (Acumed Acutrak 2 7.5mm). The specimens were subjected to cyclic loading and unloading at a rate of 1Hz, compression of 525 Newtons (N) and distraction of 20N for a total of 500 cycles using an electromechanical load frame (Instron). The amount of maximum distraction was recorded as well as the amount of motion that occurred through 1, 10, 50, 100, and 500 cycles. No significant difference (p=0.412) was seen in the amount of distraction that occurred across the fusion site for either screw. The average maximum distraction after 500 cycles was 201.9μm for the Acutrak 2 screw and 235.4μm for the InFix screw. No difference was seen throughout each cycle over time for the Acutrak 2 screw (p-value=0.988) or the InFix screw (p-value=0.991). Both the traditional InFix type screw and the second generation Acumed Acutrak headless compression screws provide adequate fixation during ankle arthrodesis under submaximal loads. There is no demonstrable difference between traditional cannulated partially threaded screws and headless compression screws studied in this model. Copyright © 2015 European Foot and Ankle Society. Published by Elsevier Ltd. All rights reserved.

Retention of cast crown copings cemented to implant abutments.

PubMed

Dudley, J E; Richards, L C; Abbott, J R

2008-12-01

The cementation of crowns to dental implant abutments is an accepted form of crown retention that requires consideration of the properties of available cements within the applied clinical context. Dental luting agents are exposed to a number of stressors that may reduce crown retention in vivo, not the least of which is occlusal loading. This study investigated the influence of compressive cyclic loading on the physical retention of cast crown copings cemented to implant abutments. Cast crown copings were cemented to Straumann synOcta titanium implant abutments with three different readily used and available cements. Specimens were placed in a humidifier, thermocycled and subjected to one of four quantities of compressive cyclic loading. The uniaxial tensile force required to remove the cast crown copings was then recorded. The mean retention values for crown copings cemented with Panavia-F cement were statistically significantly greater than both KetacCem and TempBond non-eugenol cements at each compressive cyclic loading quantity. KetacCem and TempBond non-eugenol cements produced relatively low mean retention values that were not statistically significantly different at each quantity of compressive cyclic loading. Compressive cyclic loading had a statistically significant effect on Panavia-F specimens alone, but increased loading quantities produced no further statistically significant difference in mean retention. Within the limitations of the current in vitro conditions employed in this study, the retention of cast crown copings cemented to Straumann synOcta implant abutments with a resin, glass ionomer and temporary cement was significantly affected by cement type but not compressive cyclic loading. Resin cement is the cement of choice for the definitive non-retrievable cementation of cast crown copings to Straumann synOcta implant abutments out of the three cements tested.

Fatigue resistance of unnotched and post impact(+/- 30 deg/0 deg) 3-D braided composites

NASA Technical Reports Server (NTRS)

Portanova, Marc A.

1994-01-01

The fatigue resistance of a multiaxial braided (3-D) graphite/expoxy composite in both unnotched and post impacted conditions has been evaluated. The material tested is a (+/- 30/0 deg) multiaxial braid constructed from AS4/12K tow graphite fibers and British Petroleum E905L epoxy resin. These materials were braided as dry preforms and the epoxy was added using a resin transfer molding process (RTM). The unnotched and post-impact specimens were tested in compression-compression fatigue at 10 Hz with a stress ratio of R=10. The unnotched tension-tension fatigue specimens were tested at S Hz with a stress ration of R=0.1. Damage initiation and growth was documented through the application of radiography and ultrasonic through transmission (C-scans). Visible inspection of surface and edge damage was also noted to describe the initiation and progression of damage in these materials. The mechanisms leading to damage initiation were established and failure modes were determined. Stiffness and strength degradation were measured as a function of applied cycles. These 3-D braided composite results were compared to strain levels currently used to design primary structure in commercial aircraft composite components made from prepreg tape and autoclave cured.

Experimental Observations of Localization Phenomena in Sands: Plane Strain Versus Triaxial Compression Conditions

NASA Technical Reports Server (NTRS)

Alshibli, Khalid A.; Batiste, Susan N.; Sture, Stein; Curreri, Peter A. (Technical Monitor)

2002-01-01

A comprehensive experimental investigation was conducted to investigate the effects of loading condition and confining pressure on strength properties and instability phenomena in sands. A uniform sub-rounded to rounded natural silica sand known as F-75 Ottawa sand was used in the investigation. The results of a series on Conventional Triaxial Compression (CTC) experiments tested under very low confining pressures (0.05 - 1.30) kPa tested in a Microgravity environment abroad the NASA Space Shuttle are presented in addition to the results similar specimens tested in terrestrial laboratory to investigate the effect of confining pressure on the constitutive behavior of sands. The behavior of the CTC experiments is compared with the results of Plane Strain (PS) experiments. Computed tomography and other digital imaging techniques were used to study the development and evolution of shear bands.

Principles and practices of irradiation creep experiment using pressurized mini-bellows

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

Byun, Thak Sang; Li, Meimei; Snead, Lance Lewis

2013-01-01

This article is to describe the key design principles and application practices of the newly developed in-reactor irradiation creep testing technology using pressurized mini-bellows. Miniature creep test frames were designed to fit into the high flux isotope reactor (HFIR) rabbit capsule whose internal diameter is slightly less than 10 mm. The most important consideration for this in-reactor creep testing technology was the ability of the small pressurized metallic bellows to survive irradiation at elevated temperatures while maintaining applied load to the specimen. Conceptual designs have been developed for inducing tension and compression stresses in specimens. Both the theoretical model andmore » the in-furnace test confirmed that a gas-pressurized bellows can produce high enough stress to induce irradiation creep in subsize specimens. Discussion focuses on the possible stress range in specimens induced by the miniature gas-pressurized bellows and the limitations imposed by the size and structure of thin-walled bellows. A brief introduction to the in-reactor creep experiment for graphite is provided to connect to the companion paper describing the application practices and irradiation creep data. An experimental and calculation procedure to obtain in-situ applied stress values from post irradiation in-furnace force measurements is also presented.« less

Manipulator having thermally conductive rotary joint for transferring heat from a test specimen

DOEpatents

Haney, S.J.; Stulen, R.H.; Toly, N.F.

1983-05-03

A manipulator for rotatably moving a test specimen in an ultra-high vacuum chamber includes a translational unit movable in three mutually perpendicular directions. A manipulator frame is rigidly secured to the translational unit for rotatably supporting a rotary shaft. A first copper disc is rigidly secured to an end of the rotary shaft for rotary movement within the vacuum chamber. A second copper disc is supported upon the first disc. The second disc receives a cryogenic cold head and does not rotate with the first disc. The second disc receives a cryogenic cold head and does not rotate with the first disc. A sapphire plate is interposed between the first and second discs to prevent galling of the copper material while maintaining high thermal conductivity between the first and second discs. A spring is disposed on the shaft to urge the second disc toward the first disc and compressingly engage the interposed sapphire plate. A specimen mount is secured to the first disc for rotation within the vacuum chamber. The specimen maintains high thermal conductivity with the second disc receiving the cryogenic transfer line.

Optimization of fly ash and bottom ash substitution against paving block manufacture according to SNI 03-0691-1996

NASA Astrophysics Data System (ADS)

Karolina, R.; Syahrizal; Bahri, N.

2018-02-01

The waste of coal burning has a very negative impact on the environment if the waste is not managed as well as possible. The remaining waste of coal combustion consists of fly ash and bottom ash. FA and BA can be developed into substitution materials in the process of making paving blocks. The purpose of this study was to determine the quality of paving block in accordance with SK SNI 03-0691-1996 with optimization in the use of FA and BA. This study uses a 351 paving block sample size of 20x10x6 cm. Paving blocks are divided by 4 categories, namely normal paving block, paving block with FA substitution, BA substitution and combination of FA-BA with each variation 0%, 25%, 50%, 75% and 100%. Each variation amounted to 27 samples. Paving block quality measurement is done through 4 tests: absorption, compressive strength, sodium sulphate resistance and Los Angeles tests. The result of the test shows the absorption of normal paving block is 3,229%, paving block with 25% FA is 3,889%, paving block with 50% BA is 5,560% and paving block with 25% FA-BA combination is 5,794%. Compressive strength in normal paving block is 25,50 MPa, paving block with 25% FA is 25,28 MPa, paving block with 25% BA is equal to 27,61 MPa and paving block with 25% FA-BA is 26, 00 MPa. In testing of sodium sulfate resistance, almost all test specimens are eligible except for paving block with 50% FA and 75% FA. In the test of wear resistance, no specimen is eligible according to SK SNI 03-0691-1996. The comparison of the strength of the test specimen can be seen in substitution with 25% BA which reaches maximum strength.

Producing Zirconium Diboride Components with Complex, Near-Net Shape Geometries by Aqueous Room-Temperature Injection Molding

NASA Technical Reports Server (NTRS)

Wiesner, Valerie L.; Youngblood, Jeffrey; Trice, Rodney

2014-01-01

Room-temperature injection molding is proposed as a novel, low-cost and more energy efficient manufacturing process capable of forming complex-shaped zirconium diboride (ZrB2) parts. This innovative processing method utilized aqueous suspensions with high powder loading and a minimal amount (5 vol.) of water-soluble polyvinylpyrrolidone (PVP), which was used as a viscosity modifier. Rheological characterization was performed to evaluate the room-temperature flow properties of ZrB2-PVP suspensions. ZrB2 specimens were fabricated with high green body strength and were machinable prior to binder removal despite their low polymer content. After binder burnout and pressureless sintering, the bulk density and microstructure of specimens were characterized using Archimedes technique and scanning electron microscopy. X-Ray Diffraction was used to determine the phase compositions present in sintered specimens. Ultimate strength of sintered specimens will be determined using ASTM C1323-10 compressive C-ring test.

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

NASA Technical Reports Server (NTRS)

Dunlap, Patrick H., Jr.

2014-01-01

NASA is developing advanced space-rated elastomeric seals to support future space exploration missions to low Earth orbit, the Moon, near Earth asteroids, and other destinations. This includes seals for a new docking system and vehicle hatches. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them, and seal adhesion forces must be low to allow the sealed interface to be separated when required (e.g., during undocking or hatch opening). NASA Glenn Research Center has developed a number of unique test fixtures to measure the leak rates and compression and adhesion loads of candidate seal designs under simulated thermal, vacuum, and engagement conditions. Tests can be performed on fullscale seals with diameters on the order of 50 in., subscale seals that are about 12 in. in diameter, and smaller specimens such as O-rings. Test conditions include temperatures ranging from -238 to 662degF (-150 to 350degC), operational pressure gradients, and seal-on-seal or seal-on-flange mating configurations. Nominal and off-nominal conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features and capabilities of each type of test apparatus and provides an overview of advanced seal development activities at NASA Glenn.

An Overview of Advanced Elastomeric Seal Development and Testing Capabilities at NASA Glenn Research Center

NASA Technical Reports Server (NTRS)

Dunlap, Patrick H.

2014-01-01

NASA is developing advanced space-rated elastomeric seals to support future space exploration missions to low Earth orbit, the Moon, near Earth asteroids, and other destinations. This includes seals for a new docking system and vehicle hatches. These seals must exhibit extremely low leak rates to ensure that astronauts have sufficient breathable air for extended missions. Seal compression loads must be below prescribed limits so as not to overload the mechanisms that compress them, and seal adhesion forces must be low to allow the sealed interface to be separated when required (e.g., during undocking or hatch opening). NASA Glenn Research Center has developed a number of unique test fixtures to measure the leak rates and compression and adhesion loads of candidate seal designs under simulated thermal, vacuum, and engagement conditions. Tests can be performed on full-scale seals with diameters on the order of 50 in., subscale seals that are about 12 in. in diameter, and smaller specimens such as O-rings. Test conditions include temperatures ranging from -238 to 662 F (-150 to 350 C), operational pressure gradients, and seal-on-seal or seal-on-flange mating configurations. Nominal and off-nominal conditions (e.g., incomplete seal compression) can also be simulated. This paper describes the main design features and capabilities of each type of test apparatus and provides an overview of advanced seal development activities at NASA Glenn.

Foamed concrete containing rice husk ash as sand replacement: an experimental study on compressive strength

NASA Astrophysics Data System (ADS)

Rum, R. H. M.; Jaini, Z. M.; Boon, K. H.; Khairaddin, S. A. A.; Rahman, N. A.

2017-11-01

This study presents the utilization of rice husk ash (RHA) as sand replacement in foamed concrete. The study focuses on the effect of RHA on the compressive strength of foamed concrete. RHA contains high pozzolanic material that reacts with cementitious to enhance the strength and durability of foamed concrete. RHA also acts as filler causing the foamed concrete to become denser while retaining its unique low density. A total 243 cube specimens was prepared for the compression test. Two sets of mix design were employed at water-cement (W/C) ratio of 0.55, 0.60 and cement-sand ratio of 0.50, 0.33. The results revealed that the presence of RHA as sand replacement resulted in an increase in the compressive strength of foamed concrete. Moreover, 30% to 40% RHA was the optimum content level, contributing to the compressive strength of 18.1 MPa to 22.4 MPa. The W/C ratio and superplasticiser dosage play small roles in improving workability. In contrast, density governs the compressive strength of foamed concrete.

The Influence of GI and GII on the Compression After Impact Strength of Carbon Fiber/Epoxy Laminates and Sandwich Structure

NASA Technical Reports Server (NTRS)

Nettles, A. T.; Scharber, L. L.

2017-01-01

This study measured the compression after impact strength of IM7 carbon fiber laminates made from epoxy resins with various mode I and mode II toughness values to observe the effects of these toughness values on the resistance to damage formation and subsequent residual compression strength-carrying capabilities. Both monolithic laminates and sandwich structure were evaluated. A total of seven different epoxy resin systems were used ranging in approximate GI values of 245-665 J/sq m and approximate GII values of 840-2275 J/sq m. The results for resistance to impact damage formation showed that there was a direct correlation between GII and the planar size of damage, as measured by thermography. Subsequent residual compression strength testing suggested that GI had no influence on the measured values and most of the difference in compression strength was directly related to the size of damage. Thus, delamination growth assumed as an opening type of failure mechanism does not appear to be responsible for loss of compression strength in the specimens examined in this study.

Tensile and pack compressive tests of some sheets of aluminum alloy, 1025 carbon steel, and chromium-nickel steel

NASA Technical Reports Server (NTRS)

Atchison, C S; Miller, James A

1942-01-01

Tensile and compressive stress-strain curves, stress-deviation curves, and secant modulus-stress curves are given for longitudinal and transverse specimens of 17S-T, 24S-T, and 24S-RT aluminum-alloy sheet in thicknesses from 0.032 to 0.081 inch, 1025 carbon steel sheet in thicknesses of 0.054 and 0.120 inch, and chromium-nickel steel sheet in thicknesses form 0.020 to 0.0275 inch. Significant differences were found between the tensile and the compressive stress-strain curves, and also the corresponding corollary curves; similarly, differences were found between the curves for the longitudinal and transverse directions. These differences are of particular importance in considering the compressive strength of aircraft structures made of thin sheet. They are explored further for the case of compression by giving tangent modulus-stress curves in longitudinal and transverse compression and dimensionless curves of the ratio of tangent modulus to Young's modulus and of the ratio of reduced modulus for a rectangular section to Young's modulus, both plotted against the ratio of stress to secant yield strength.

Compression failure mechanisms of uni-ply composite plates with a circular cutout

NASA Technical Reports Server (NTRS)

Khamseh, A. R.; Waas, A. M.

1992-01-01

The effect of circular-hole size on the failure mode of uniply graphite-epoxy composite plates is investigated experimentally and analytically for uniaxial compressive loading. The test specimens are sandwiched between polyetherimide plastic for nondestructive evaluations of the uniply failure mechanisms associated with a range of hole sizes. Finite-element modeling based on classical lamination theory is conducted for the corresponding materials and geometries to reproduce the experimental results analytically. The type of compressive failure is found to be a function of hole size, with fiber buckling/kinking at the hole being the dominant failure mechanism for hole diam/plate width ratios exceeding 0.062. The results of the finite-element analysis supported the experimental data for these failure mechanisms and for those corresponding to smaller hole sizes.

Experimental investigation of the strength and failure behavior of layered sandstone under uniaxial compression and Brazilian testing

NASA Astrophysics Data System (ADS)

Yin, Peng-Fei; Yang, Sheng-Qi

2018-05-01

As a typical inherently anisotropic rock, layered sandstones can differ from each other in several aspects, including grain size, type of material, type of cementation, and degree of compaction. An experimental study is essential to obtain and convictive evidence to characterize the mechanical behavior of such rock. In this paper, the mechanical behavior of a layered sandstone from Xuzhou, China, is investigated under uniaxial compression and Brazilian test conditions. The loading tests are conducted on 7 sets of bedding inclinations, which are defined as the angle between the bedding plane and horizontal direction. The uniaxial compression strength (UCS) and elastic modulus values show an undulatory variation when the bedding inclination increases. The overall trend of the UCS and elastic modulus values with bedding inclination is decreasing. The BTS value decreases with respect to the bedding inclination and the overall trend of it is approximating a linear variation. The 3D digital high-speed camera images reveal that the failure and fracture of a specimen are related to the surface deformation. Layered sandstone tested under uniaxial compression does not show a typical failure mode, although shear slip along the bedding plane occurs at high bedding inclinations. Strain gauge readings during the Brazilian tests indicate that the normal stress on the bedding plane transforms from compression to tension as the bedding inclination increases. The stress parallel to the bedding plane in a rock material transforms from tension to compression and agrees well with the fracture patterns; "central fractures" occur at bedding inclinations of 0°-75°, "layer activation" occurs at high bedding inclinations of 75°-90°, and a combination of the two occurs at 75°.

Biomechanical behavior of cavity configuration on micropush-out test: a finite-element-study.

PubMed

Cekic-Nagas, Isil; Shinya, Akikazu; Ergun, Gulfem; Vallittu, Pekka K; Lassila, Lippo V J

2011-01-01

The objective of this study was to simulate the micropush-out bond strength test from a biomechanical point of view. For this purpose, stress analysis using finite element (FE) method was performed. Three different occlusal cavity shapes were simulated in disc specimens (model A: 1.5 mm cervical, 2 mm occlusal diameter; model B: 1.5 mm cervical, 1.75 mm occlusal diameter; model C: 1.5 mm cervical, 1.5 mm occlusal diameter). Quarter sizes of 3D FE specimen models of 4.0 x 4.0 x 1.25 mm3 were constructed. In order to avoid quantitative differences in the stress value in the models, models were derived from a single mapping mesh pattern that generated 47.182 elements and 66.853 nodes. The materials that were used were resin composite (Filtek Z250, 3M ESPE), bonding agent (Adper Scotchbond Multi-Purpose, 3M ESPE) and dentin as an isotropic material. Loading conditions consisted of subjecting a press of 4 MPa to the top of the resin composite discs. The postprocessing files allowed the calculation of the maximum principal stress, minimum principal stress and displacement within the disc specimens and stresses at the bonding layer. FE model construction and analysis were performed on PC workstation (Precision Work Station 670, Dell Inc.) using FE analysis program (ANSYS 10 Sp, ANSYS Inc.). Compressive stress concentrations were observed equally in the bottom interface edge of dentin. Tensile stresses were observed on the top area of dentin and at the half of lower side of composite under the loading point in all of the FE models. The FE model revealed differences in displacement and stress between different cavity shaped disc specimens. As the slope of the cavity was increased, the maximum displacement, compressive and tensile stresses also increased.

Biomechanical Analysis of an Expandable Lumbar Interbody Spacer.

PubMed

Soriano-Baron, Hector; Newcomb, Anna G U S; Malhotra, Devika; Palma, Atilio E; Martinez-Del-Campo, Eduardo; Crawford, Neil R; Theodore, Nicholas; Kelly, Brian P; Kaibara, Taro

2018-06-01

Recently developed expandable interbody spacers are widely accepted in spinal surgery; however, the resulting biomechanical effects of their use have not yet been fully studied. We analyzed the biomechanical effects of an expandable polyetheretherketone interbody spacer inserted through a bilateral posterior approach with and without different modalities of posterior augmentation. Biomechanical nondestructive flexibility testing was performed in 7 human cadaveric lumbar (L2-L5) specimens followed by axial compressive loading. Each specimen was tested under 6 conditions: 1) intact, 2) bilateral L3-L4 cortical screw/rod (CSR) alone, 3) WaveD alone, 4) WaveD + CSR, 5) WaveD + bilateral L3-L4 pedicle screw/rod (PSR), and 6) WaveD + CSR/PSR, where CSR/PSR was a hybrid construct comprising bilateral cortical-level L3 and pedicle-level L4 screws interconnected by rods. The range of motion (ROM) with the interbody spacer alone decreased significantly compared with the intact condition during flexion-extension (P = 0.02) but not during lateral bending or axial rotation (P ≥ 0.19). The addition of CSR or PSR to the interbody spacer alone condition significantly decreased the ROM compared with the interbody spacer alone (P ≤ 0.002); and WaveD + CSR, WaveD + PSR, and WaveD + CSR/PSR (hybrid) (P ≥ 0.29) did not differ. The axial compressive stiffness (resistance to change in foraminal height during compressive loading) with the interbody spacer alone did not differ from the intact condition (P = 0.96), whereas WaveD + posterior instrumentation significantly increased compressive stiffness compared with the intact condition and the interbody spacer alone (P ≤ 0.001). The WaveD alone significantly reduced ROM during flexion-extension while maintaining the axial compressive stiffness. CSR, PSR, and CSR/PSR hybrid constructs were all effective in augmenting the expandable interbody spacer system and improving its stability. Copyright © 2018 Elsevier Inc. All rights reserved.

Treatability Study Report for In SITU Lead Immobilization Using Phosphate-Based Binders

DTIC Science & Technology

2008-05-01

include lead, zinc, copper, cadmium, nickel, uranium, barium, cesium, strontium, plutonium, thorium, and other lanthanide and actinide metals. There...Density Bulk density is the measure of the mass per unit volume of the whole soil specimen. American Society for Testing and Materials (ASTM) D 698...Where: m = mass of the soil (grams) V = Volume of sample (cm3) 4.2.2.1.3 Unconfined Compressive Strength (UCS) The UCS test was used to

Mechanical characterization of Al-2024 reinforced with fly ash and E-glass by stir casting method

NASA Astrophysics Data System (ADS)

Ramesh, B. T.; Swamy, R. P.; Vinayak, Koppad

2018-04-01

The properties of MMCs enhance their handling in automotive and various applications for the reason that of encouraging properties of high stiffness and high strength, low density, high electrical and thermal conductivity, corrosion resistance, improved wear resistance etc. Metal Matrix Composites are a vital family of materials designed at achieving an improved combination of properties. Our paper deals through to fabricate Hybrid Composite by heating Al 2024 in furnace at a temperature of around 4000 C. E-Glass fiber & Fly ash will be added to the molten metal with changing weight fractions and stirred strongly. Then the ensuing composition will poured into the mould to obtain hybrid composite casting. Aluminium alloy (2024) is the matrix metal used in the present investigation. Fly ash and e-glass are used as the reinforced materials to produce the composite by stir casting. Fly ash is selected because of it is less expensive and low density reinforcement available in great quantities as solid disposal from thermal power plants. The Test specimen is prepared as per ASTM standards size by machining operations to conduct Tensile, Compression, Hardness, and wear test. The test specimens are furnished for tensile, compression strength and wear as per ASTM standard E8, E9 and G99 respectively using Universal Testing Machine and pin on disk machine. It is seen that the fabricated MMC obtained has got enhanced mechanical strength.

Effects of bolt-hole contact on bearing-bypass damage-onset strength

NASA Technical Reports Server (NTRS)

Crews, John H., Jr.; Naik, Rajiv A.

1991-01-01

A combined experimental and analytical study was conducted to investigate the effects of bolt-hole contact on the bearing bypass strength of a graphite-epoxy laminate. Tests were conducted on specimens consisting of 16-ply quasi-isotropic T300/5208 laminates with a centrally located hole. Bearing loads were applied through a clearance-fit steel bolt. Damage onset strength and damage mode were determined for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each test case. A finite element procedure was used to calculate the bolt-hole stresses and bolt contact for each measured damage-onset strength. For the tension bearing-bypass cases tested, the bolt contact half-angle was approximately 60 degrees at damage onset. For compression, the contact angle was 20 degrees as the bypass load increased. A corresponding decrease in the bearing damage onset strength was attributed to the decrease in contact angle which made the bearing loads more severe. Hole boundary stresses were also computed by superimposing stresses for separate bearing and bypass loading. Stresses at the specimen net section were accurately approximated by the superposition procedure. However, the peak bearing stresses had large errors because the bolt contact angles were not represented correctly. For compression, peak bearing stress errors of nearly 50 percent were calculated.

Kinematic response of the spine during simulated aircraft ejections.

PubMed

Damon, Andrew M; Lessley, David J; Salzar, Robert S; Bass, Cameron R; Shen, Francis H; Paskoff, Glenn R; Shender, Barry S

2010-05-01

Military aviators are susceptible to spinal injuries during high-speed ejection scenarios. These injuries commonly arise as a result of strains induced by extreme flexion or compression of the spinal column. This study characterizes the vertebral motion of two postmortem human surrogates (PMHS) during a simulated catapult phase of ejection on a horizontal decelerator sled. During testing, the PMHS were restrained supinely to a mock ejection seat and subjected to a horizontal deceleration profile directed along the local z-axis. Two midsized males (175.3 cm, 77.1 kg; 185.4 cm, 72.6 kg) were tested. High-rate motion capture equipment was used to measure the three-dimensional displacement of the head, vertebrae, and pelvis during the ejection event. The two PMHS showed generally similar kinematic motion. Head injury criterion (HIC) results were well below injury threshold levels for both specimens. The specimens both showed compression of the spine, with a reduction in length of 23.9 mm and 45.7 mm. Post-test autopsies revealed fractures in the C5, T1, and L1 vertebrae. This paper provides an analysis of spinal motion during an aircraft ejection.The injuries observed in the test subjects were consistent with those seen in epidemiological studies. Future studies should examine the effects of gender, muscle tensing, out-of-position (of head from neutral position) occupants, and external forces (e.g., windblast) on spinal kinematics during aircraft ejection.

Comparative experimental study of dynamic compressive strength of mortar with glass and basalt fibres

NASA Astrophysics Data System (ADS)

Kruszka, Leopold; Moćko, Wojciech; Fenu, Luigi; Cadoni, Ezio

2015-09-01

Specimen reinforced with glass and basalt fibers were prepared using Standard Portland cement (CEM I, 52.5 R as prescribed by EN 197-1) and standard sand, in accordance with EN 196-1. From this cementitious mixture, a reference cement mortar without fibers was first prepared. Compressive strength, modulus of elasticity, and mod of fracture were determined for all specimens. Static and dynamic properties were investigated using Instron testing machine and split Hopkinson pressure bar, respectively. Content of the glass fibers in the mortar does not influence the fracture stress at static loading conditions in a clearly observed way. Moreover at dynamic range 5% content of the fiber results in a significant drop of fracture stress. Analysis of the basalt fibers influence on the fracture stress shows that optimal content of this reinforcement is equal to 3% for both static and dynamic loading conditions. Further increase of the fiber share gives the opposite effect, i.e. drop of the fracture stress.

Compressive strength, flexural strength and water absorption of concrete containing palm oil kernel shell

NASA Astrophysics Data System (ADS)

Noor, Nurazuwa Md; Xiang-ONG, Jun; Noh, Hamidun Mohd; Hamid, Noor Azlina Abdul; Kuzaiman, Salsabila; Ali, Adiwijaya

2017-11-01

Effect of inclusion of palm oil kernel shell (PKS) and palm oil fibre (POF) in concrete was investigated on the compressive strength and flexural strength. In addition, investigation of palm oil kernel shell on concrete water absorption was also conducted. Total of 48 concrete cubes and 24 concrete prisms with the size of 100mm × 100mm × 100mm and 100mm × 100mm × 500mm were prepared, respectively. Four (4) series of concrete mix consists of coarse aggregate was replaced by 0%, 25%, 50% and 75% palm kernel shell and each series were divided into two (2) main group. The first group is without POF, while the second group was mixed with the 5cm length of 0.25% of the POF volume fraction. All specimen were tested after 7 and 28 days of water curing for a compression test, and flexural test at 28 days of curing period. Water absorption test was conducted on concrete cube age 28 days. The results showed that the replacement of PKS achieves lower compressive and flexural strength in comparison with conventional concrete. However, the 25% replacement of PKS concrete showed acceptable compressive strength which within the range of requirement for structural concrete. Meanwhile, the POF which should act as matrix reinforcement showed no enhancement in flexural strength due to the balling effect in concrete. As expected, water absorption was increasing with the increasing of PKS in the concrete cause by the porous characteristics of PKS

Experimental observations and finite element analysis of the initiation of fiber microbuckling in notched composite laminates

NASA Technical Reports Server (NTRS)

Guynn, E. Gail; Bradley, Walter L.

1989-01-01

An understanding was developed of the factors that determine the semi-circular edge-notched compressive strength and the associated failure mode(s) were identified of thermoplastic composite laminates with multidirectional stacking sequences. The experimental observations and the detailed literature review suggest at least four factors that affected the determination of the strain levels at which fiber microbuckling initiates and thus, partially control the composite's compression strength. The dependent variables studied are the compressive strength of a reduced gage section compression specimen and the compression strength of a compression specimen with two semi-circular edge notches (no opposite free edges) centered along the gage section. In this research, specimens containing two semi-circular edge notches (no opposite free edges) were loaded in compression at a relatively slow rate to provide more stable development of fiber microbuckling damage. The results indicate that the local constraints (free surfaces, supporting ply orientation, and resin-rich regions) significantly affect the strain level for the initiation of in-plane fiber microbuckling. Preliminary results at an elevated temperature, 77 C, showed the shear stress yield strength of the resin was reduced and consequently, the resistance to fiber microbuckling was also reduced. The finite element analysis of the perfectly straight fiber problem indicates that the free surface effect causes a 10 percent reduction in the critical buckling strain. However, the experimentally measured reduction for fibers with an initial fiber curvature, was 35 percent.

Optimal Design and Damage Tolerance Verification of an Isogrid Structure for Helicopter Application

NASA Technical Reports Server (NTRS)

Baker, Donald J.; Fudge, Jack; Ambur, Damodar R.; Kassapoglou, Christos

2003-01-01

A composite isogrid panel design for application to a rotorcraft fuselage is presented. An optimum panel design for the lower fuselage of the rotorcraft that is subjected to combined in-plane compression and shear loads was generated using a design tool that utilizes a smeared-stiffener theory in conjunction with a genetic algorithm. A design feature was introduced along the edges of the panel that facilitates introduction of loads into the isogrid panel without producing undesirable local bending gradients. A low-cost manufacturing method for the isogrid panel that incorporates these design details is also presented. Axial compression tests were conducted on the undamaged and low-speed impact damaged panels to demonstrate the damage tolerance of this isogrid panel. A combined loading test fixture was designed and utilized that allowed simultaneous application of compression and shear loads to the test specimen. Results from finite element analyses are presented for the isogrid panel designs and these results are compared with experimental results. This study illustrates the isogrid concept to be a viable candidate for application to the helicopter lower fuselage structure.

Design and evaluation of a bolted joint for a discrete carbon-epoxy rod-reinforced hat section

NASA Technical Reports Server (NTRS)

Rousseau, Carl Q.; Baker, Donald J.

1996-01-01

The use of prefabricated pultruded carbon-epoxy rods has reduced the manufacturing complexity and costs of stiffened composite panels while increasing the damage tolerance of the panels. However, repairability of these highly efficient discrete stiffeners has been a concern. Design, analysis, and test results are presented in this paper for a bolted-joint repair for the pultruded rod concept that is capable of efficiently transferring axial loads in a hat-section stiffener on the upper skin segment of a heavily loaded aircraft wing component. A tension and a compression joint design were evaluated. The tension joint design achieved approximately 1.0% strain in the carbon-epoxy rod-reinforced hat-section and failed in a metal fitting at 166% of the design ultimate load. The compression joint design failed in the carbon-epoxy rod-reinforced hat-section test specimen area at approximately 0.7% strain and at 110% of the design ultimate load. This strain level of 0.7% in compression is similar to the failure strain observed in previously reported carbon-epoxy rod-reinforced hat-section column tests.

Insights Gained from Ultrasonic Testing of Piping Welds Subjected to the Mechanical Stress Improvement Process

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

Anderson, Michael T.; Cinson, Anthony D.; Crawford, Susan L.

2010-12-01

Pacific Northwest National Laboratory (PNNL) is assisting the United States Nuclear Regulatory Commission (NRC) in developing a position on the management of primary water stress corrosion cracking (PWSCC) in leak-before-break piping systems. Part of this involves determining whether inspections alone, or inspections plus mitigation, are needed. This work addresses the reliability of ultrasonic testing (UT) of cracks that have been mitigated by the mechanical stress improvement process (MSIP). The MSIP has been approved by the NRC (NUREG-0313) since 1986 and modifies residual stresses remaining after welding with compressive, or neutral, stresses near the inner diameter surface of the pipe. Thismore » compressive stress is thought to arrest existing cracks and inhibit new crack formation. To evaluate the effectiveness of the MSIP and the reliability of ultrasonic inspections, flaws were evaluated both before and after MSIP application. An initial investigation was based on data acquired from cracked areas in 325-mm-diameter piping at the Ignalina Nuclear Power Plant (INPP) in Lithuania. In a follow-on exercise, PNNL acquired and evaluated similar UT data from a dissimilar metal weld (DMW) specimen containing implanted thermal fatigue cracks. The DMW specimen is a carbon steel nozzle-to-safe end-to-stainless steel pipe section that simulates a pressurizer surge nozzle. The flaws were implanted in the nozzle-to-safe end Alloy 82/182 butter region. Results are presented on the effects of MSIP on specimen surfaces, and on UT flaw responses.« less

Ultra-Lightweight Nanocomposite Foams and Sandwich Structures for Space Structure Applications

NASA Technical Reports Server (NTRS)

Tan, Seng

2012-01-01

Microcellular nanocomposite foams and sandwich structures have been created to have excellent electrical conductivity and radiation-resistant properties using a new method that does not involve or release any toxicity. The nanocomposite structures have been scaled up in size to 12 X 12 in. (30 X 30 cm) for components fabrication. These sandwich materials were fabricated mainly from PE, CNF, and carbon fibers. Test results indicate that they have very good compression and compression-after-impact properties, excellent electrical conductivity, and superior space environment durability. Compression tests show that 1000 ESH (equivalent Sun hours) of UV exposure has no effect on the structural properties of the sandwich structures. The structures are considerably lighter than aluminum alloy (= 36 percent lighter), which translates to 36 percent weight savings of the electronic enclosure and its housing. The good mechanical properties of the materials may enable the electronic housing to be fabricated with a thinner structure that further reduces the weight. There was no difficulty in machining the sandwich specimens into electronic enclosure housing.

Methodology for Mechanical Property Testing of Fuel Cladding Using a Expanded Plug Wedge Test

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

Jiang, Hao; Wang, Jy-An John

2014-01-01

An expanded plug method was developed earlier for determining the tensile properties of irradiated fuel cladding. This method tests fuel rod cladding ductility by utilizing an expandable plug to radially stretch a small ring of irradiated cladding material. The circumferential or hoop strain is determined from the measured diametrical expansion of the ring. A developed procedure is used to convert the load circumferential strain data from the ring tests into material pseudo-stress-strain curves, from which material properties of the cladding can be extracted. However, several deficiencies existed in this expanded-plug test that can impact the accuracy of test results, suchmore » as that the large axial compressive stress resulted from the expansion plug test can potentially induce the shear failure mode of the tested specimen. Moreover, highly nonuniform stress and strain distribution in the deformed clad gage section and significant compressive stresses, induced by bending deformation due to clad bulging effect, will further result in highly nonconservative estimates of the mechanical properties for both strength and ductility of the tested clad. To overcome the aforementioned deficiencies associated with the current expansion plug test, systematic studies have been conducted. By optimizing the specific geometry designs, selecting the appropriate material for the expansion plug, and adding new components into the testing system, a modified expansion plug testing protocol has been developed. A general procedure was also developed to determine the hoop stress in the tested ring specimen. A scaling factor, -factor, was used to convert the ring load Fring into hoop stress , and is written as _ = F_ring/tl , where t is the clad thickness and l is the clad length. The generated stress-strain curve agrees well with the associated tensile test data in both elastic and plastic deformation regions.« less

Standard Test Methods for Textile Composites

NASA Technical Reports Server (NTRS)

Masters, John E.; Portanova, Marc A.

1996-01-01

Standard testing methods for composite laminates reinforced with continuous networks of braided, woven, or stitched fibers have been evaluated. The microstructure of these textile' composite materials differs significantly from that of tape laminates. Consequently, specimen dimensions and loading methods developed for tape type composites may not be applicable to textile composites. To this end, a series of evaluations were made comparing testing practices currently used in the composite industry. Information was gathered from a variety of sources and analyzed to establish a series of recommended test methods for textile composites. The current practices established for laminated composite materials by ASTM and the MIL-HDBK-17 Committee were considered. This document provides recommended test methods for determining both in-plane and out-of-plane properties. Specifically, test methods are suggested for: unnotched tension and compression; open and filled hole tension; open hole compression; bolt bearing; and interlaminar tension. A detailed description of the material architectures evaluated is also provided, as is a recommended instrumentation practice.

Specimen Holder for Analytical Electron Microscopes

NASA Technical Reports Server (NTRS)

Clanton, U. S.; Isaacs, A. M.; Mackinnon, I.

1985-01-01

Reduces spectral contamination by spurious X-ray. Specimen holder made of compressed carbon, securely retains standard electron microscope grid (disk) 3 mm in diameter and absorbs backscattered electrons that otherwise generate spurious X-rays. Since holder inexpensive, dedicated to single specimen when numerous samples examined.

The structural behavior of a graphite-polymide honeycomb sandwich panel with quasi-isotropic face sheets and an orthotropic core

NASA Technical Reports Server (NTRS)

Hyer, M. W.; Hagaman, J. A.

1979-01-01

The results of a series of tests of graphite-polyimide honeycomb sandwich panels are presented. The panels were 1.22 m long, 0.508 m wide, and approximately 13.3 m thick. The face sheets were a T-300/PMR-15 fabric in a quasi-isotropic layup and were 0.279 mm thick. The core was Hexcel HRH 327-3/16 - 4.0 glass reinforced polyimide honeycomb, 12.7 mm thick. Three panels were used in the test: one was cut into smaller pieces for testing as beam, compression, and shear specimens; a second panel was used for plate bending tests; the third panel was used for in-plane stability tests. Presented are the experimental results of four point bending tests, short block compression tests, core transverse shear modulus, three point bending tests, vibration tests, plate bending tests, and panel stability tests. The results of the first three tests are used to predict the results of some of the other tests. The predictions and experimental results are compared, and the agreement is quite good.

Etude comparative sur la propagation de l'endommagement apres impact des composites carbone/epoxy renforces par piquage au fil Kevlar et titane-nickel

NASA Astrophysics Data System (ADS)

Vachon, Pierre-Luc

Composite laminates have strong in-plane mechanical properties, but they are generally weaker through their thickness. This specificity makes the laminates prone to delamination, particularly under low-velocity impact loads. Consequently numerous research efforts have been dedicated to developing interlaminar reinforcing methods, such as transverse stitching. The present project proposes the use of the stitching technique combined with a special stitching thread made of superelastic TiNi alloy. This technology is intended to improve the delamination toughness in composite laminates loaded in bending. In the first part of this study a numerical model was developed for analyzing composite structures. The 3-D finite element model was built with the ANSYS commercial software using 20-node solid and 8-node shell elements. The progressive damage modeling technique was used, allowing the prediction of delamination propagation in a laminate submitted to various loading modes. The model was validated for a plate under quasi-static traction load, and it was then used to simulate three-point bending tests. Secondly, carbon/epoxy composite panels were fabricated, with each panel containing unstitched and stitched specimens. Two different materials were used for the stitching thread: superelastic TiNi wires and Kevlar threads as a reference. Some stitched specimens were cut in slices in order to make some observations of the internal stitch using an optical microscope. Standardized low-velocity impact tests and compression after impact tests were carried out on stitched and unstitched specimens (ASTM D7136 and D7137). The Kevlar reinforcements have shown great performance in reducing the delaminated zone after impact, as well as in improving the residual compression strength. The TiNi reinforcements provided encouraging results during the impact tests, though being less effective than the Kevlar threads. During the compression after impact tests, only a slight difference could be measured between the TiNi-stitched and the unstitched specimens. Then the bending performance of the specimens was quantified experimentally by calculating the energy required to create a unit volume of damaged material (Gv, J/mm3). This metric is similar to the Strain Energy Release Rate (SERR) commonly used in studies on delamination. According to the experimental results, the damage resistance in three-point bending was not improved by the Kevlar reinforcements, despite the reduced damaged zone after the impact test. Indeed, when the strain energy in bending is relativized to the induced damaged volume during propagation, it turns out that the TiNi reinforcements are more effective than the Kevlar's for improving the damage resistance. Finally, the numerical study on the behavior of both types of stitched reinforcements allowed identifying subtle differences between those. Indeed, both stitching threads (TiNi and Kevlar) promoted the interlaminar propagation of the delamination during simulation of the bending test, with this behavior being less pronounced for the TiNi-stitched plate. However the Kevlar threads seemed more effective for stopping this propagation in the zones between the stitches. Keywords: composite materials, stitching, numerical model, shape memory alloy, three-point bending, low-velocity impact, ultrasound imaging.

Residual-stress-induced grain growth of twinned grains and its effect on formability of magnesium alloy sheet at room temperature

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

Kim, Se-Jong; Kim, Daeyong, E-mail: daeyong@kims.re.kr; Lee, Keunho

2015-11-15

A magnesium alloy sheet was subjected to in-plane compression along with a vertical load to avoid buckling during compression. Pre-compressed specimens machined from the sheet were annealed at different temperatures and the changes in microstructure and texture were observed using electron back scattered diffraction (EBSD). Twinned grains preferentially grew during annealing at 300 °C, so that a strong texture with the < 0001 > direction parallel to the transverse direction developed. EBSD analysis confirmed that the friction caused by the vertical load induced inhomogeneous distribution of residual stress, which acted as an additional driving force for preferential grain growth ofmore » twinned grain during annealing. The annealed specimen showed excellent formability. - Highlights: • A magnesium alloy sheet subjected to in-plane compression under a vertical load • The vertical load induced inhomogeneous distribution of the residual stress. • The residual stress acted as an additional driving force for grain growth. • The annealed specimen with strong non-basal texture showed excellent formability.« less

Effect of crosslinking UHMWPE on its tensile and compressive creep performance.

PubMed

Lewis, G; Carroll, M

2001-01-01

The in vitro quasi-static tensile and compressive creep properties of three sets of GUR 1050 ultra-high-molecular-weight polyethylene (UHMWPE) specimens were obtained. These sets were: control (as-received stock); "low-gamma" (specimens were crosslinked using gamma radiation, with a minimum dose of 5 Mrad); and "high-gamma" (specimens were crosslinked using gamma radiation, with a minimum dose of 15 Mrad). The % crystallinity (%C) and crosslink density (rho(x)) of the specimens in the three sets were also obtained. It was found that, in both tension and compression, crosslinking resulted in a significant depreciation in the creep properties, relative to control. The trend in the creep results is explained in terms of the impact of crosslinking on the polymer's %C and rho(x). The present results are in contrast to literature reports that show that crosslinking enhances the wear resistance of the polymer. The implications of the present results, taken together with the aforementioned literature results, are fully discussed vis-a-vis the use of crosslinked UHMWPE for fabricating articular components for arthroplasties.

Corrosion-fatigue of laser-repaired commercially pure titanium and Ti-6Al-4V alloy under different test environments.

PubMed

Zavanelli, R A; Guilherme, A S; Pessanha-Henriques, G E; de Arruda Nóbilo, M Antônio; Mesquita, M F

2004-10-01

This study evaluated the corrosion-fatigue life of laser-repaired specimens fabricated from commercially pure titanium (CP Ti) and Ti-6Al-4V alloy, tested under different storage conditions. For each metal, 30 dumbbell rods with a central 2.3 mm diameter were prepared by lost-wax casting with the Rematitan System. Simulating the failure after service, corrosion-fatigue life in different media at room temperature (air, synthetic saliva and fluoride synthetic saliva) was determined at a testing frequency of 10 Hz for intact specimens and after laser repairing, using a square waveform with equal maximum tensile and compressive stress that was 30% lower than the 0.2% offset yield strength. For laser welding, the fractured specimens were rejoined using a jig to align the sections invested in type-IV dental stone. The adjacent areas of the gap was air-abraded with 100 microm aluminum oxide, laser welded and retested under the same conditions as the initial intact specimens. The number of cycles at failure was recorded, and the fracture surface was examined with a scanning electron microscope (SEM). The number of cycles for failure of the welded and intact specimens was compared by anova and the Tukey test at a 5% probability level. Within the limitations of this study, the number of cycles required for fracture decreased in wet environments and the laser repairing process adversely affected the life of both metals under the corrosion-fatigue conditions.

The effect of mechanical stress on electric resistance of nanographite-epoxy composites

NASA Astrophysics Data System (ADS)

Vovchenko, L.; Lazarenko, A.; Matzui, L.; Zhuravkov, A.

2012-03-01

The in-plane electric resistance Ra of composite materials (CMs) thermoexfoliated graphite(TEG)-epoxy resin(ED) under compression along compacting C-axis has been investigated by four-probe method. TEG content was 5-75 wt%. It was shown that specimens prepared by cold pressing are denser and reveal lower values of electric resistivity in comparison with specimens prepared by pouring. It was found that compression of the specimens leads to plastic deformation of specimens (εpl) and essential irreversible decrease of electric resistance during the first cycle of loading (up to 50 MPa), especially for the poured specimens with low density. Within the proposed model the contact resistance Rk between graphite particles in CM has been evaluated and it was shown that it increased with the decrease in TEG content in CM and depends on compacting method of CMs and the dispersity of graphite filler.

Experimental Study on the Seismic Performance of Recycled Concrete Brick Walls Embedded with Vertical Reinforcement.

PubMed

Cao, Wanlin; Zhang, Yongbo; Dong, Hongying; Zhou, Zhongyi; Qiao, Qiyun

2014-08-19

Recycled concrete brick (RCB) is manufactured by recycled aggregate processed from discarded concrete blocks arising from the demolishing of existing buildings. This paper presents research on the seismic performance of RCB masonry walls to assess the applicability of RCB for use in rural low-rise constructions. The seismic performance of a masonry wall is closely related to the vertical load applied to the wall. Thus, the compressive performance of RCB masonry was investigated firstly by constructing and testing eighteen RCB masonry compressive specimens with different mortar strengths. The load-bearing capacity, deformation and failure characteristic were analyzed, as well. Then, a quasi-static test was carried out to study the seismic behavior of RCB walls by eight RCB masonry walls subjected to an axial compressive load and a reversed cyclic lateral load. Based on the test results, equations for predicting the compressive strength of RCB masonry and the lateral ultimate strength of an RCB masonry wall were proposed. Experimental values were found to be in good agreement with the predicted values. Meanwhile, finite element analysis (FEA) and parametric analysis of the RCB walls were carried out using ABAQUS software. The elastic-plastic deformation characteristics and the lateral load-displacement relations were studied.

Experimental Study on the Seismic Performance of Recycled Concrete Brick Walls Embedded with Vertical Reinforcement

PubMed Central

Cao, Wanlin; Zhang, Yongbo; Dong, Hongying; Zhou, Zhongyi; Qiao, Qiyun

2014-01-01

Recycled concrete brick (RCB) is manufactured by recycled aggregate processed from discarded concrete blocks arising from the demolishing of existing buildings. This paper presents research on the seismic performance of RCB masonry walls to assess the applicability of RCB for use in rural low-rise constructions. The seismic performance of a masonry wall is closely related to the vertical load applied to the wall. Thus, the compressive performance of RCB masonry was investigated firstly by constructing and testing eighteen RCB masonry compressive specimens with different mortar strengths. The load-bearing capacity, deformation and failure characteristic were analyzed, as well. Then, a quasi-static test was carried out to study the seismic behavior of RCB walls by eight RCB masonry walls subjected to an axial compressive load and a reversed cyclic lateral load. Based on the test results, equations for predicting the compressive strength of RCB masonry and the lateral ultimate strength of an RCB masonry wall were proposed. Experimental values were found to be in good agreement with the predicted values. Meanwhile, finite element analysis (FEA) and parametric analysis of the RCB walls were carried out using ABAQUS software. The elastic-plastic deformation characteristics and the lateral load-displacement relations were studied. PMID:28788170

Evaluation of Early-Age Concrete Compressive Strength with Ultrasonic Sensors.

PubMed

Yoon, Hyejin; Kim, Young Jin; Kim, Hee Seok; Kang, Jun Won; Koh, Hyun-Moo

2017-08-07

Surface wave velocity measurement of concrete using ultrasonic sensors requires testing on only one side of a member. Thus, it is applicable to concrete cast inside a form and is often used to detect flaws and evaluate the compressive strength of hardened concrete. Predicting the in situ concrete strength at a very early stage inside the form helps with determining the appropriate form removal time and reducing construction time and costs. In this paper, the feasibility of using surface wave velocities to predict the strength of in situ concrete inside the form at a very early stage was evaluated. Ultrasonic sensors were used to measure a series of surface waves for concrete inside a form in the first 24 h after placement. A continuous wavelet transform was used to compute the travel time of the propagating surface waves. The cylindrical compressive strength and penetration resistance tests were also performed during the test period. Four mixtures and five curing temperatures were used for the specimens. The surface wave velocity was confirmed to be applicable to estimating the concrete strength at a very early age in wall-like elements. An empirical formula is proposed for evaluating the early-age compressive strength of concrete considering the 95% prediction intervals.

Evaluation of Early-Age Concrete Compressive Strength with Ultrasonic Sensors

PubMed Central

Yoon, Hyejin; Kim, Young Jin; Kim, Hee Seok; Kang, Jun Won; Koh, Hyun-Moo

2017-01-01

Surface wave velocity measurement of concrete using ultrasonic sensors requires testing on only one side of a member. Thus, it is applicable to concrete cast inside a form and is often used to detect flaws and evaluate the compressive strength of hardened concrete. Predicting the in situ concrete strength at a very early stage inside the form helps with determining the appropriate form removal time and reducing construction time and costs. In this paper, the feasibility of using surface wave velocities to predict the strength of in situ concrete inside the form at a very early stage was evaluated. Ultrasonic sensors were used to measure a series of surface waves for concrete inside a form in the first 24 h after placement. A continuous wavelet transform was used to compute the travel time of the propagating surface waves. The cylindrical compressive strength and penetration resistance tests were also performed during the test period. Four mixtures and five curing temperatures were used for the specimens. The surface wave velocity was confirmed to be applicable to estimating the concrete strength at a very early age in wall-like elements. An empirical formula is proposed for evaluating the early-age compressive strength of concrete considering the 95% prediction intervals. PMID:28783128

Influence of High-Current-Density Impulses on the Compression Behavior: Experiments with Iron and a Nickel-Based Alloy

NASA Astrophysics Data System (ADS)

Demler, E.; Gerstein, G.; Dalinger, A.; Epishin, A.; Rodman, D.; Nürnberger, F.

2017-01-01

Difficulties of processing of high strength and/or brittle materials by plastic deformation, e.g., by forging, require to develop new industrial technologies. In particular, the feasible deformation rates are limited for low-ductile metallic materials. For this reason, processes were investigated to improve the deformability in which electrical impulses are to be applied to lower the yield strength. However, owing to the impulse duration and low current densities, concomitant effects always occur, e.g., as a result of Joule heating. Current developments in power electronics allow now to transmit high currents as short pulses. By reducing the impulse duration and increasing the current density, the plasticity of metallic materials can be correspondingly increased. Using the examples of polycrystalline iron and a single-crystal, nickel-based alloy (PWA 1480), current advances in the development of methods for forming materials by means of high-current-density impulses are demonstrated. For this purpose, appropriate specimens were loaded in compression and, using novel testing equipment, subjected to a current strength of 10 kA with an impulse duration of 2 ms. For a pre-defined strain, the test results show a significant decrease in the compressive stress during the compression test and a significant change in the dislocation distribution following the current impulse treatment.

Loading simulation of lumbar spine vertebrae during a compression test using the finite elements method and trabecular bone strength properties, determined by means of nanoindentations.

PubMed

Bouzakis, K D; Mitsi, S; Michailidis, N; Mirisidis, I; Mesomeris, G; Maliaris, G; Korlos, A; Kapetanos, G; Antonarakos, P; Anagnostidis, K

2004-06-01

The mechanical strength properties of lumbar spine vertebrae are of great importance in a wide range of applications. Herein, through nanoindentations and appropriate evaluation of the corresponding results, trabecular bone struts stress-strain characteristics can be determined. In the frame of the present paper, an L2 fresh cadaveric vertebra, from which posterior elements were removed, was subjected to compression. With the aid of developed finite elements method based algorithms, the cortical shell and the cancellous core bulk elasticity moduli and stresses were determined, whereas the tested vertebra geometrical model used in these algorithms was considered as having a compound structure, consisting of the cancellous bone surrounded by the cortical shell. Moreover nanoindentations were conducted and an appropriate evaluation method of the obtained results was applied to extract stress-strain curves of individual lumbar spine vertebra trabecular bone struts. These data were used in the mathematical description of the vertebrae compression test. The vertebral cancellous bone structure was simulated by a beam elements network, possessing an equivalent porosity and different stiffnesses in vertical and horizontal direction. Thus, the measured course of the compression load versus the occurring specimen deformation was verified.

Postbuckling behavior of graphite-epoxy panels

NASA Technical Reports Server (NTRS)

Starnes, J. H., Jr.; Dickson, J. N.; Rouse, M.

1984-01-01

Structurally efficient fuselage panels are often designed to allow buckling to occur at applied loads below ultimate. Interest in applying graphite-epoxy materials to fuselage primary structure led to several studies of the post-buckling behavior of graphite-epoxy structural components. Studies of the postbuckling behavior of flat and curved, unstiffened and stiffened graphite-epoxy panels loaded in compression and shear were summarized. The response and failure characteristics of specimens studied experimentally were described, and analytical and experimental results were compared. The specimens tested in the studies described were fabricated from commercially available 0.005-inch-thick unidirectional graphite-fiber tapes preimpregnated with 350 F cure thermosetting epoxy resins.

Fatigue Life of Postbuckled Structures with Indentation Damages

NASA Technical Reports Server (NTRS)

Davila, Carlos G.; Bisagni, Chiara

2016-01-01

The fatigue life of composite stiffened panels with indentation damage was investigated experimentally using single stringer compression specimens. Indentation damage was induced on one of the two flanges of each stringer. The experiments were conducted using advanced instrumentation, including digital image correlation, passive thermography, and in-situ ultrasonic scanning. Specimens with initial indentation damage lengths of 32 millimeters to 56 millimeters were tested quasi-statically and in fatigue, and the effects of cyclic load amplitude and damage size were studied. A means of comparison of the damage propagation rates and collapse loads based on a stress intensity measure and the Paris law is proposed.

Probing Shells Against Buckling: A Nondestructive Technique for Laboratory Testing

NASA Astrophysics Data System (ADS)

Thompson, J. Michael T.; Hutchinson, John W.; Sieber, Jan

2017-12-01

This paper addresses testing of compressed structures, such as shells, that exhibit catastrophic buckling and notorious imperfection sensitivity. The central concept is the probing of a loaded structural specimen by a controlled lateral displacement to gain quantitative insight into its buckling behavior and to measure the energy barrier against buckling. This can provide design information about a structure’s stiffness and robustness against buckling in terms of energy and force landscapes. Developments in this area are relatively new but have proceeded rapidly with encouraging progress. Recent experimental tests on uniformly compressed spherical shells, and axially loaded cylinders, show excellent agreement with theoretical solutions. The probing technique could be a valuable experimental procedure for testing prototype structures, but before it can be used a range of potential problems must be examined and solved. The probing response is highly nonlinear and a variety of complications can occur. Here, we make a careful assessment of unexpected limit points and bifurcations, that could accompany probing, causing complications and possibly even collapse of a test specimen. First, a limit point in the probe displacement (associated with a cusp instability and fold) can result in dynamic buckling as probing progresses, as demonstrated in the buckling of a spherical shell under volume control. Second, various types of bifurcations which can occur on the probing path which result in the probing response becoming unstable are also discussed. To overcome these problems, we outline the extra controls over the entire structure that may be needed to stabilize the response.

Fracto-mechanoluminescent light emission of EuD4TEA-PDMS composites subjected to high strain-rate compressive loading

NASA Astrophysics Data System (ADS)

Ryu, Donghyeon; Castaño, Nicolas; Bhakta, Raj; Kimberley, Jamie

2017-08-01

The objective of this study is to understand light emission characteristics of fracto-mechanoluminescent (FML) europium tetrakis(dibenzoylmethide)-triethylammonium (EuD4TEA) crystals under high strain-rate compressive loading. As a sensing material that can play a pivotal role for the self-powered impact sensor technology, it is important to understand transformative light emission characteristics of the FML EuD4TEA crystals under high strain-rate compressive loading. First, EuD4TEA crystals were synthesized and embedded into polydimethylsiloxane (PDMS) elastomer to fabricate EuD4TEA-PDMS composite test specimens. Second, the prepared EuD4TEA-PDMS composites were tested using the modified Kolsky bar setup equipped with a high-speed camera. Third, FML light emission was captured to yield 12 bit grayscale video footage, which was processed to quantify the FML light emission. Finally, quantitative parameters were generated by taking into account pixel values and population of pixels of the 12 bit grayscale images to represent FML light intensity. The FML light intensity was correlated with high strain-rate compressive strain and strain rate to understand the FML light emission characteristics under high strain-rate compressive loading that can result from impact occurrences.

On the dynamic behavior of mineralized tissues

NASA Astrophysics Data System (ADS)

Kulin, Robb Michael

Mineralized tissues, such as bone and antler, are complex hierarchical materials that have adapted over millennia to optimize strength and fracture resistance for their in vivo applications. As a structural support, skeletal bone primarily acts as a rigid framework that is resistant to fracture, and able to repair damage and adapt to sustained loads during its lifetime. Antler is typically deciduous and subjected to large bending moments and violent impacts during its annual cycle. To date, extensive characterization of the quasi-static mechanical properties of these materials has been performed. However, very little has been done to characterize their dynamic properties, despite the fact that the majority of failures in these materials occur under impact loads. Here, an in depth analysis of the dynamic mechanical behavior of these two materials is presented, using equine bone obtained post-mortem from donors ranging in age from 6 months to 28 years, and antler from the North American Elk. Specimens were tested under compressive strain rates of 10-3, 100, and 103 sec-1 in order to investigate their strain rate dependent compressive response. Fracture toughness experiments were performed using a four-point bending geometry on single and double-notch specimens in order to measure fracture toughness, as well as observe differences in crack propagation between dynamic (˜2x105 MPa˙m1/2/s) and quasi-static (˜0.25 MPa˙m1/2/s) loading rates. After testing, specimens were analyzed using a combination of optical, electron and confocal microscopy. Results indicated that the mechanical response of these materials is highly dependent on loading rate. Decreasing quasi-static fracture toughness is observed with age in bone specimens, while dynamic specimens show no age trends, yet universally decreased fracture toughness compared to those tested quasi-statically. For the first time, rising R-curve behavior in bone was also shown to exist under both quasi-static and dynamic loading. Antler demonstrated itself to be extremely resistant to impact loading, often requiring multiple impacts to fracture a specimen. Microscopy observations of deformation and crack propagation mechanisms indicate that differences in mechanical behavior between bone and antler, and at varying strain rates, are the result of subtle differences in bulk composition and active microstructural toughening mechanisms.

Assessment of compressive failure process of cortical bone materials using damage-based model.

PubMed

Ng, Theng Pin; R Koloor, S S; Djuansjah, J R P; Abdul Kadir, M R

2017-02-01

The main failure factors of cortical bone are aging or osteoporosis, accident and high energy trauma or physiological activities. However, the mechanism of damage evolution coupled with yield criterion is considered as one of the unclear subjects in failure analysis of cortical bone materials. Therefore, this study attempts to assess the structural response and progressive failure process of cortical bone using a brittle damaged plasticity model. For this reason, several compressive tests are performed on cortical bone specimens made of bovine femur, in order to obtain the structural response and mechanical properties of the material. Complementary finite element (FE) model of the sample and test is prepared to simulate the elastic-to-damage behavior of the cortical bone using the brittle damaged plasticity model. The FE model is validated in a comparative method using the predicted and measured structural response as load-compressive displacement through simulation and experiment. FE results indicated that the compressive damage initiated and propagated at central region where maximum equivalent plastic strain is computed, which coincided with the degradation of structural compressive stiffness followed by a vast amount of strain energy dissipation. The parameter of compressive damage rate, which is a function dependent on damage parameter and the plastic strain is examined for different rates. Results show that considering a similar rate to the initial slope of the damage parameter in the experiment would give a better sense for prediction of compressive failure. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effect of Zirconium Oxide and Zinc Oxide Nanoparticles on Physicochemical Properties and Antibiofilm Activity of a Calcium Silicate-Based Material

PubMed Central

Guerreiro-Tanomaru, Juliane Maria; Trindade-Junior, Adinael; Cesar Costa, Bernardo; da Silva, Guilherme Ferreira; Drullis Cifali, Leonardo; Basso Bernardi, Maria Inês

2014-01-01

The aim of the present study was to evaluate the antibiofilm activity against Enterococcus faecalis, compressive strength. and radiopacity of Portland cement (PC) added to zirconium oxide (ZrO2), as radiopacifier, with or without nanoparticulated zinc oxide (ZnO). The following experimental materials were evaluated: PC, PC + ZrO2, PC + ZrO2 + ZnO (5%), and PC + ZrO2 + ZnO (10%). Antibiofilm activity was analyzed by using direct contact test (DCT) on Enterococcus faecalis biofilm, for 5 h or 15 h. The analysis was conducted by using the number of colony-forming units (CFU/mL). The compressive strength was performed in a mechanical testing machine. For the radiopacity tests, the specimens were radiographed together with an aluminium stepwedge. The results were submitted to ANOVA and Tukey tests, with level of significance at 5%. The results showed that all materials presented similar antibiofilm activity (P > 0.05). The addition of nanoparticulated ZnO decreased the compressive strength of PC. All materials presented higher radiopacity than pure PC. It can be concluded that the addition of ZrO2 and ZnO does not interfere with the antibiofilm activity and provides radiopacity to Portland cement. However, the presence of ZnO (5% or 10%) significantly decreased the compressive strength of the materials. PMID:25431798

Flexural testing on carbon fibre laminates taking into account their different behaviour under tension and compression

NASA Astrophysics Data System (ADS)

Serna Moreno, M. C.; Romero Gutierrez, A.; Martínez Vicente, J. L.

2016-07-01

An analytical model has been derived for describing the results of three-point-bending tests in materials with different behaviour under tension and compression. The shift of the neutral plane and the damage initiation mode and its location have been defined. The validity of the equations has been reviewed by testing carbon fibre-reinforced polymers (CFRP), typically employed in different weight-critical applications. Both unidirectional and cross-ply laminates have been studied. The initial failure mode produced depends directly on the beam span- thickness relation. Therefore, specimens with different thicknesses have been analysed for examining the damage initiation due to either the bending moment or the out-of-plane shear load. The experimental description of the damage initiation and evolution has been shown by means of optical microscopy. The good agreement between the analytical estimations and the experimental results shows the validity of the analytical model exposed.

Fabrication Of Carbon-Boron Reinforced Dry Polymer Matrix Composite Tape

NASA Technical Reports Server (NTRS)

Belvin, Harry L.; Cano, Roberto J.; Treasure, Monte; Shahood, Thomas W.

1999-01-01

Future generation aerospace vehicles will require specialized hybrid material forms for component structure fabrication. For this reason, high temperature composite prepregs in both dry and wet forms are being developed at NASA Langley Research Center (LaRC). In an attempt to improve compressive properties of carbon fiber reinforced composites, a hybrid carbon-boron tape was developed and used to fabricate composite laminates which were subsequently cut into flexural and compression specimens and tested. The hybrid material, given the designation HYCARB, was fabricated by modifying a previously developed process for the manufacture of dry polymer matrix composite (PMC) tape at LaRC. In this work, boron fibers were processed with IM7/LaRC(TradeMark)IAX poly(amide acid) solution-coated prepreg to form a dry hybrid tape for Automated Tow Placement (ATP). Boron fibers were encapsulated between two (2) layers of reduced volatile, low fiber areal weight poly(amide acid) solution-coated prepreg. The hybrid prepreg was then fully imidized and consolidated into a dry tape suitable for ATP. The fabrication of a hybrid boron material form for tow placement aids in the reduction of the overall manufacturing cost of boron reinforced composites, while realizing the improved compression strengths. Composite specimens were press-molded from the hybrid material and exhibited excellent mechanical properties.

A novel dentin bond strength measurement technique using a composite disk in diametral compression.

PubMed

Huang, Shih-Hao; Lin, Lian-Shan; Rudney, Joel; Jones, Rob; Aparicio, Conrado; Lin, Chun-Pin; Fok, Alex

2012-04-01

New methods are needed that can predict the clinical failure of dental restorations that primarily rely on dentin bonding. Existing methods have shortcomings, e.g. severe deviation in the actual stress distribution from theory and a large standard deviation in the measured bond strength. We introduce here a novel test specimen by examining an endodontic model for dentin bonding. Specifically, we evaluated the feasibility of using the modified Brazilian disk test to measure the post-dentin interfacial bond strength. Four groups of resin composite disks which contained a slice of dentin with or without an intracanal post in the center were tested under diametral compression until fracture. Advanced nondestructive examination and imaging techniques in the form of acoustic emission (AE) and digital image correlation (DIC) were used innovatively to capture the fracture process in real time. DIC showed strain concentration first appearing at one of the lateral sides of the post-dentin interface. The appearance of the interfacial strain concentration also coincided with the first AE signal detected. Utilizing both the experimental data and finite-element analysis, the bond/tensile strengths were calculated to be: 11.2 MPa (fiber posts), 12.9 MPa (metal posts), 8.9 MPa (direct resin fillings) and 82.6 MPa for dentin. We have thus established the feasibility of using the composite disk in diametral compression to measure the bond strength between intracanal posts and dentin. The new method has the advantages of simpler specimen preparation, no premature failure, more consistent failure mode and smaller variations in the calculated bond strength. Copyright © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Experimental Research Into the Effect Of External Actions and Polluting Environments on the Serviceablity of Fiber-Reinforced Polymer Composite Materials

NASA Astrophysics Data System (ADS)

Lobanov, D. S.; Vildeman, V. E.; Babin, A. D.; Grinev, M. A.

2015-03-01

The results of mechanical tests of fiberglass and CFRP specimens in transverse bending and interlaminar shear (the short-beam method) and of sandwich panels in tension and compression are presented. The effect of external polluting environments on the mechanical properties of fiber-reinforced polymer composite materials and structures is estimated. Stress-strain diagrams are constructed.

Damage Arresting Composites for Shaped Vehicles - Phase II Final Report

NASA Technical Reports Server (NTRS)

Velicki, Alex; Yovanof, Nicolette; Baraja, Jaime; Linton, Kim; Li, Victor; Hawley, Arthur; Thrash, Patrick; DeCoux, Steve; Pickell, Robert

2011-01-01

This report describes the development of a novel structural concept, Pultruded Rod Stitched Efficient Unitized Structure (PRSEUS), that addresses the demanding fuselage loading requirements for the Hybrid Wing or Blended Wing Body (BWB) airplane configuration. In addition to the analytical studies, a three specimen test program was also completed to assess the concept under axial tension loading, axial compression loading, and internal pressure loading.

Failure of flight feathers under uniaxial compression.

PubMed

Schelestow, Kristina; Troncoso, Omar P; Torres, Fernando G

2017-09-01

Flight feathers are light weight engineering structures. They have a central shaft divided in two parts: the calamus and the rachis. The rachis is a thinly walled conical shell filled with foam, while the calamus is a hollow tube-like structure. Due to the fact that bending loads are produced during birds' flight, the resistance to bending of feathers has been reported in different studies. However, the analysis of bent feathers has shown that compression could induce failure by buckling. Here, we have studied the compression of feathers in order to assess the failure mechanisms involved. Axial compression tests were carried out on the rachis and the calamus of dove and pelican feathers. The failure mechanisms and folding structures that resulted from the compression tests were observed from images obtained by scanning electron microscopy (SEM). The rachis and calamus fail due to structural instability. In the case of the calamus, this instability leads to a progressive folding process. In contrast, the rachis undergoes a typical Euler column-type buckling failure. The study of failed specimens showed that delamination buckling, cell collapse and cell densification are the primary failure mechanisms of the rachis structure. The role of the foam is also discussed with regard to the mechanical response of the samples and the energy dissipated during the compression tests. Critical stress values were calculated using delamination buckling models and were found to be in very good agreement with the experimental values measured. Failure analysis and mechanical testing have confirmed that flight feathers are complex thin walled structures with mechanical adaptations that allow them to fulfil their functions. Copyright © 2017 Elsevier B.V. All rights reserved.

Effect of Strength Enhancement of Soil Treated with Environment-Friendly Calcium Carbonate Powder

PubMed Central

Park, Kyungho; Jun, Sangju; Kim, Daehyeon

2014-01-01

This study aims to investigate the effects of the strength improvement of soft ground (sand) by producing calcium carbonate powder through microbial reactions. To analyze the cementation effect of calcium carbonate produced through microbial reaction for different weight ratios, four different types of specimens (untreated, calcium carbonate, cement, and calcium carbonate + cement) with different weight ratios (2%, 4%, 6%, and 8%) were produced and cured for a period of 3 days, 7 days, 14 days, 21 days, and 28 days to test them. The uniaxial compression strength of specimens was measured, and the components in the specimen depending on the curing period were analyzed by means of XRD analysis. The result revealed that higher weight ratios and longer curing period contributed to increased strength of calcium carbonate, cement, and calcium carbonate + cement specimens. The calcium carbonate and the calcium carbonate + cement specimens in the same condition showed the tendency of decreased strength approximately 3 times and two times in comparison with the 8% cement specimens cured for 28 days, but the tendency of increased strength was approximately 4 times and 6 times in comparison with the untreated specimen. PMID:24688401

Effect of strength enhancement of soil treated with environment-friendly calcium carbonate powder.

PubMed

Park, Kyungho; Jun, Sangju; Kim, Daehyeon

2014-01-01

This study aims to investigate the effects of the strength improvement of soft ground (sand) by producing calcium carbonate powder through microbial reactions. To analyze the cementation effect of calcium carbonate produced through microbial reaction for different weight ratios, four different types of specimens (untreated, calcium carbonate, cement, and calcium carbonate + cement) with different weight ratios (2%, 4%, 6%, and 8%) were produced and cured for a period of 3 days, 7 days, 14 days, 21 days, and 28 days to test them. The uniaxial compression strength of specimens was measured, and the components in the specimen depending on the curing period were analyzed by means of XRD analysis. The result revealed that higher weight ratios and longer curing period contributed to increased strength of calcium carbonate, cement, and calcium carbonate + cement specimens. The calcium carbonate and the calcium carbonate + cement specimens in the same condition showed the tendency of decreased strength approximately 3 times and two times in comparison with the 8% cement specimens cured for 28 days, but the tendency of increased strength was approximately 4 times and 6 times in comparison with the untreated specimen.

Damage assessment and residual compression strength of thick composite plates with through-the-thickness reinforcements

NASA Technical Reports Server (NTRS)

Smith, Barry T.

1990-01-01

Damage in composite materials was studied with through-the-thickness reinforcements. As a first step it was necessary to develop new ultrasonic imaging technology to better assess internal damage of the composite. A useful ultrasonic imaging technique was successfully developed to assess the internal damage of composite panels. The ultrasonic technique accurately determines the size of the internal damage. It was found that the ultrasonic imaging technique was better able to assess the damage in a composite panel with through-the-thickness reinforcements than by destructively sectioning the specimen and visual inspection under a microscope. Five composite compression-after-impact panels were tested. The compression-after-impact strength of the panels with the through-the-thickness reinforcements was almost twice that of the comparable panel without through-the-thickness reinforcement.

Mechanical Characterization of Mancos Shale

NASA Astrophysics Data System (ADS)

Broome, S.; Ingraham, M. D.; Dewers, T. A.

2015-12-01

A series of tests on Mancos shale have been undertaken to determine the failure surface and to characterize anisotropy. This work supports additional studies which are being performed on the same block of shale; fracture toughness, permeability, and chemical analysis. Mechanical tests are being conducted after specimens were conditioned for at least two weeks at 70% constant relative humidity conditions. Specimens are tested under drained conditions, with the constant relative humidity condition maintained on the downstream side of the specimen. The upstream is sealed. Anisotropy is determined through testing specimens that have been cored parallel and perpendicular to the bedding plane. Preliminary results show that when loaded parallel to bedding the shale is roughly 50% weaker. Test are run under constant mean stress conditions when possible (excepting indirect tension, unconfined compression, and hydrostatic). Tests are run in hydrostatic compaction to the desired mean stress, then differential stress is applied axially in displacement control to failure. The constant mean stress condition is maintained by decreasing the confining pressure by half of the increase in the axial stress. Results will be compared to typical failure criteria to investigate the effectiveness of capturing the behavior of the shale with traditional failure theory. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Nuclear Security Administration under contract DE-AC04-94AL85000. SAND2015-6107 A.

An examination of the damage tolerance enhancement of carbon/epoxy using an outer lamina of spectra (R)

NASA Technical Reports Server (NTRS)

Lance, D. G.; Nettles, A. T.

1991-01-01

Low velocity instrumented impact testing was utilized to examine the effects of an outer lamina of ultra-high molecular weight polyethylene (Spectra) on the damage tolerance of carbon epoxy composites. Four types of 16-ply quasi-isotropic panels (0, +45, 90, -45) were tested. Some panels contained no Spectra, while others had a lamina of Spectra bonded to the top (impacted side), bottom, or both sides of the composite plates. The specimens were impacted with energies up to 8.5 J. Force time plots and maximum force versus impact energy graphs were generated for comparison purposes. Specimens were also subjected to cross-sectional analysis and compression after impact tests. The results show that while the Spectra improved the maximum load that the panels could withstand before fiber breakage, the Spectra seemingly reduced the residual strength of the composites.

Benchmark cyclic plastic notch strain measurements

NASA Technical Reports Server (NTRS)

Sharpe, W. N., Jr.; Ward, M.

1983-01-01

Plastic strains at the roots of notched specimens of Inconel 718 subjected to tension-compression cycling at 650 C are reported. These strains were measured with a laser-based technique over a gage length of 0.1 mm and are intended to serve as 'benchmark' data for further development of experimental, analytical, and computational approaches. The specimens were 250 mm by 2.5 mm in the test section with double notches of 4.9 mm radius subjected to axial loading sufficient to cause yielding at the notch root on the tensile portion of the first cycle. The tests were run for 1000 cycles at 10 cpm or until cracks initiated at the notch root. The experimental techniques are described, and then representative data for the various load spectra are presented. All the data for each cycle of every test are available on floppy disks from NASA.

Thrombus Formation After Percutaneous Catheterization and Manual Compression of the Femoral Artery in Heparinized Sheep

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

Kim, Young Hwan; Pavcnik, Dusan, E-mail: pavcnikd@ohsu.edu; Kakizawa, Hideyaki

The purpose of this study was to evaluate the angiographic and histopathologic changes in the superficial femoral artery (SFA) in heparinized sheep shortly after catheterization with an 8-Fr sheath and manual compression hemostasis either with standard manual compression (SMC) or with the use of a procoagulant chitosan-based HemCon Bandage. The evaluation was done in 38 SFAs of 19 heparinized (100 mg/kg) sheep. After a 5-min catheterization with an 8-Fr sheath, a 5-min compression was applied. Follow-up angiograms to evaluate hemostasis were done immediately after release of compression and then at 2.5-min intervals until no extravasation was present. Compression was reappliedmore » between angiograms. Final angiograms were performed approximately 30 min after hemostasis and after 3 min of passive flexion and extension of sheep hind limbs. Sheep were then euthanized and SFA specimens with surrounding tissues excised for histopathologic evaluation. Both types of compression caused similar changes in the catheterized SFAs. Follow-up angiograms showed mild arterial narrowing in 14 SFAs and intraluminal clots in 9 SFAs. Histology revealed periarterial hematoma in all 38 specimens. Intraluminal thrombi consisting predominantly of platelets and fibrin were present in 32 SFAs. Their size varied from superficial elevations (8 arteries) to medium-sized, 1- to 2-mm, polypoid protrusions (15 arteries) to large polypoid clots, 3-4 mm long (9 arteries). In six SFAs, the arterial access sites were not included in the obtained specimens. In conclusion, hemostasis with manual compression is achieved in the acute phase by formation of a predominantly platelet-fibrin thrombus occluding the arterial wall access site and often extending significantly into the arterial lumen. The healing process of arterial access sites should be explored several days after catheterization.« less

Effect of CO2 concentration on strength development and carbonation of a MgO-based binder for treating fine sediment.

PubMed

Hwang, Kyung-Yup; Kim, Jin Young; Phan, Hoang Quang Huy; Ahn, Jun-Young; Kim, Tae Yoo; Hwang, Inseong

2018-05-28

We previously described a MgO-based binder for treating fine sediment and simultaneously store CO 2 . Here, we describe a study of the physical/mechanical characteristics and carbonation reactions of the MgO-based binder used to solidify/stabilize fine sediment in atmospheres containing different CO 2 concentrations. Carbonation of the sediment treated with the MgO-based binder at the atmospheric CO 2 concentration markedly improved the compressive strength of the product. The compressive strength was 4.78 MPa after 365 days of curing, 1.3 times higher than the compressive strength of sediment treated with portland cement. This improvement was caused by the formation of carbonation products, such as hydromagnesite, nesquehonite, and lansfordite, and the constant high pH (~ 12) of the specimen, which favored the growth of hydration products such as calcium silicate hydrates and portlandite. Very low compressive strengths were found when 50 and 100% CO 2 atmospheres were used because of excessive formation of carbonation products, which occupied 78% of the specimen depth. Abundant carbonation products increased the specimen volume and decreased the pH to 10.2, slowing the growth of hydration products. The absence of brucite in specimens produced in a 100% CO 2 atmosphere indicated that MgO carbonation is favored over hydration at high CO 2 concentrations.

Effect of Compressive Mode I on the Mixed Mode I/II Fatigue Crack Growth Rate of 42CrMo4

NASA Astrophysics Data System (ADS)

Heirani, Hasan; Farhangdoost, Khalil

2018-01-01

Subsurface cracks in mechanical contact loading components are subjected to mixed mode I/II, so it is necessary to evaluate the fatigue behavior of materials under mixed mode loading. For this purpose, fatigue crack propagation tests are performed with compact tension shear specimens for several stress intensity factor (SIF) ratios of mode I and mode II. The effect of compressive mode I loading on mixed mode I/II crack growth rate and fracture surface is investigated. Tests are carried out for the pure mode I, pure mode II, and two different mixed mode loading angles. On the basis of the experimental results, mixed mode crack growth rate parameters are proposed according to Tanaka and Richard with Paris' law. Results show neither Richard's nor Tanaka's equivalent SIFs are very useful because these SIFs depend strongly on the loading angle, but Richard's equivalent SIF formula is more suitable than Tanaka's formula. The compressive mode I causes the crack closure, and the friction force between the crack surfaces resists against the crack growth. In compressive loading with 45° angle, d a/d N increases as K eq decreases.

Intraspecific variation in adult Uvitellina iraquensis Dronen, Ali & Al-Amura, 2013 (Cyclocoelidae: Haematotrephinae) from two collection sites of white-tailed lapwing, Vanellus leucurus (Lichtenstein) (Charadriiformes: Charadriidae), in Iraq.

PubMed

Dronen, Norman O; Al-Kassar, Nothiala R; Ali, Atheer H; Abdulhameed, Mohanad F; Abdullah, Basim H; Al-Mayah, Sabeeh H

2017-03-09

A total of 19 white-tailed lapwing, Vanellus leucurus, were collected from Huwazah Marsh, north-eastern Basrah Province, Iraq from February to March and in October, 2011 (collection site #1) and 60 V. leucurus were collected from Al-Hammar Marshes, Thi-Qar Province, southern Iraq from July to November, 2012 (collection site #2), and examined for cyclocoelids. Nineteen Uvitellina iraquensis Dronen, Ali & Al-Amura, 2013 from site #1 and 17 specimens from site #2 were fixed with minimal compression for comparisons of morphological characteristics, measurements, morphometric percentages and morphometric ratios commonly used to distinguish species of cyclocoelids. An additional five adult specimens from site #1 were fixed without compression for comparisons. Specimens from site # 1 (n=24) represented only fully-developed, non-senescing adults, while those from site #2 (n=17) could be divided into fully-developed (non-senescing) adults (n=8); younger (smaller, less developed) adults (n=5) and senescing adults (n=4). The following characteristics were relatively consistent, and appeared to be valuable in identifying groups of similar species and distinguishing species in Uvitellina: the presence or absence of the oral sucker; the oral sucker/pharynx width ratio; the posterior extent of the cirrus sac relative to the intestinal bifurcation; the position of the genital pore relative to the pharynx; the position of the testes in the body; the length of the intertesticular space; the length of the posttesticular space; the lateral disposition of the uterine loops; the presence of a posteriorly-directed, tail-like extension off the posterior confluence of the vitelline fields; the posterior extent of the uterine loops relative to the gonads; and the size of fully-developed eggs. It may be beneficial to calculate the percentage that measurements represent relative to the body length to provide insight into the relationship of the size of a structure to increased size of the specimens (growth). Specimens fixed without compression appeared to be less uniform, less symmetrical, shorter, more distorted and the internal details were more difficult to see.

Fatigue pre-cracking and fracture toughness in polycrystalline tungsten and molybdenum

NASA Astrophysics Data System (ADS)

Taguchi, Katsuya; Nakadate, Kazuhito; Matsuo, Satoru; Tokunaga, Kazutoshi; Kurishita, Hiroaki

2018-01-01

Fatigue pre-cracking performance and fracture toughness in polycrystalline tungsten (W) and molybdenum (Mo) have been investigated in relation to grain boundary (GB) configuration with respect to the crack advance direction. Sub-sized, single edge notched bend (SENB) specimens with three different orientations, R-L (ASTM notation) for a forged Mo rod and L-S and T-S for a rolled W plate, were pre-cracked in two steps: fully uniaxial compression fatigue loading to provoke crack initiation and its stable growth from the notch root, and subsequent 3-point bend (3PB) fatigue loading to extend the crack. The latter step intends to minimize the influence of the residual tensile stresses generated during compression fatigue by moving the crack tip away from the plastic zone. It is shown that fatigue pre-cracking performance, especially pre-crack extension behavior, is significantly affected by the specimen orientation. The R-L orientation, giving the easiest cracking path, permitted crack extension completely beyond the plastic zone, while the L-S and T-S orientations with the thickness cracking direction of the rolled plate sustained the crack lengths around or possibly within the plastic zone size due to difficulty in crack advance through an aligned grain structure. Room temperature fracture toughness tests revealed that the 3PB fatigued specimens exhibited appreciably higher fracture toughness by about 30% for R-L, 40% for L-S and 60% for T-S than the specimens of each orientation pre-cracked by compression fatigue only. This indicates that 3PB fatigue provides the crack tip front out of the residual tensile stress zone by crack extension or leads to reduction in the residual stresses at the crack tip front. Strong dependence of fracture toughness on GB configuration was evident. The obtained fracture toughness values are compared with those in the literature and its strong GB configuration dependence is discussed in connection with the appearance of pop-in.

Comparative evaluation of the amount of the residual monomer in conventional and deep-frozen heat cure polymethylmethacrylate acrylic resin: An in vitro study.

PubMed

Jadhav, Sonali S; Mahajan, Neerja; Sethuraman, Rajesh

2018-01-01

Heat cure acrylic resin material with reduced monomer content is generally recommended for clinical usage as it leads to improved mechanical, physical, and biocompatibility properties. The purpose of the present study was to evaluate and compare the amount of the residual monomer in the conventional and three different groups of deep-frozen heat cure polymethylmethacrylate (PMMA) acrylic resin. Totally 40 Specimens of heat cure PMMA acrylic resin (DPI India) (10 conventional heat cure and 30 deep frozen) were made using two disc-shaped stainless steel molds and invested into type II dental stone using compression molding technique. Each group contained 10 specimens ( n = 10). Group 1: Control group of conventional polished PMMA specimen stored in water for 24 h at +37°C (10 specimens), Group 2: Deep frozen unpolished PMMA (10 specimens), Group 3: Deep frozen polished PMMA (10 specimens), and Group 4: Deep frozen polished PMMA specimen stored in water for 24 h at +37°C (10 specimens). Amount of the residual monomer content in all the specimens was measured using high-performance liquid chromatography. Data were analyzed using One-Way Analysis of Variance and multiple comparison Tukey's post hoc test (α = 0.05). Least residual monomer content was found in Group 4 (0.12 wt%) followed by Group 3 (0.19 wt%), Group 2 (0.23 wt%), and Group 1 (0.26 wt%). Statistically significant difference ( P < 0.05) was found in residual monomer content for all the four groups tested. Post hoc test for intergroup comparison also showed a significant difference between groups. The amount of the residual monomer was found to be least in deep-frozen polished PMMA specimen stored in water for 24 h at +37°C (Group 4). Thus, it can be concluded that deep freezing, polishing, and storing in water can reduce the residual monomer content.

Fossil Platygastroidea in the National Museum of Natural History, Smithsonian Institution

USDA-ARS?s Scientific Manuscript database

Platygastroid wasps preserved in Dominican amber and oil shale from the Kishenehn formation (Montana, USA) in the National Museum of Natural History are catalogued. Compression fossils in Kishenehn oil shale yield a specimen of Fidiobia, a specimen of Telenominae, and a specimen with a Scelio-type o...

[Contact characteristics research of acetabular weight-bearing area with different internal fixation methods after compression fracture of acetabular dome].

PubMed

Xu, Bowen; Zhang, Qingsong; An, Siqi; Pei, Baorui; Wu, Xiaobo

2017-08-01

To establish the model of compression fracture of acetabular dome, and to measure the contact characteristics of acetabular weight-bearing area of acetabulum after 3 kinds of internal fixation. Sixteen fresh adult half pelvis specimens were randomly divided into 4 groups, 4 specimens each group. Group D was the complete acetabulum (control group), and the remaining 3 groups were prepared acetabular dome compression fracture model. The fractures were fixed with reconstruction plate in group A, antegrade raft screws in group B, and retrograde raft screws in group C. The pressure sensitive films were attached to the femoral head, and the axial compression test was carried out on the inverted single leg standing position. The weight-bearing area, average stress, and peak stress were measured in each group. Under the loading of 500 N, the acetabular weight-bearing area was significantly higher in group D than in other 3 groups ( P <0.05), and the average stress and peak stress were significantly lower than in other 3 groups ( P <0.05). The acetabular weight-bearing area were significantly higher in group B and group C than in group A, and the average stress and peak stress were significantly lower than in group A ( P <0.05). There was no significant difference in the above indexes between group B and group C ( P >0.05). For the compression fracture of the acetabular dome, the contact characteristics of the weight-bearing area can not restore to the normal level, even if the anatomical reduction and rigid internal fixation were performed; compared with the reconstruction plate fixation, antegrade and retrograde raft screws fixations can increase the weight-bearing area, reduce the average stress and peak stress, and reduce the incidence of traumatic arthritis.

The Metacarpal Locked Intramedullary Nail: Comparative Biomechanical Evaluation of New Implant Design for Metacarpal Fractures.

PubMed

Boonyasirikool, Chinnakart; Tanakeatsakul, Sakkarin; Niempoog, Sunyarn

2015-04-01

The optimal fixation of metacarpal fracture should provide sufficient stability to permit early functionfor all types of fracture. However; it must preserve surrounding soft tissue during application and not require secondary removal due to its prominence. The prototype of metacarpal locked intramedullary nail (MCLN) was designed by our institute aiming to achieve those allfeatures. To biomechanically test our newly designed, locked metacarpal nail and compare with common current available fixation methods. Thirty chicken humeri were devided into 3 groups (n = 1 per group) according tofixation techniques: MCLN, 1.5 mm miniplate (Synthes), and Kirschner wire. After complete fixation, all specimens were osteotomized at mid-shaft creating transverse fractures. Five specimens from each group were tested by load of failure under axial compression, and another five under bending force. In axial compression model, the loads tofailure in MCLN group was greatest (460 ± 17 N), which was significant higher than the Kirschner wire group. The MCLN group also showed the highest load to failure in bending test (341 ± 10 N). This value reaches statistical significance when compared with plate and Kirschner wire groups. The MCLN construct provided higher stability than miniplate and Kirschner wire fixation both in axial and bending mode. Together with the minimally invasive and soft tissue-friendly design concept, this study suggests that MCLN is promising fixation option for metacarpal fracture.

Implementation of recycled cellulosic fibres into cement based composites and testing their influence on resulting properties

NASA Astrophysics Data System (ADS)

Hospodarova, V.; Stevulova, N.; Vaclavik, V.; Dvorsky, T.

2017-10-01

Nowadays, the application of raw materials from renewable sources such as wood, plants and waste paper to building materials preparing has gained a significant interest in this research area. The aim of this paper is to investigate the impact of the selected plasticizer on properties of fibres composites made of cellulosic fibres coming from recycled waste paper and cement. Investigations were performed on specimens with 0.5 wt. % of fibre addition without and with plasticizer. A comparative study did not show positive influence of plasticizer on the density and thermal conductivity of 28 days hardened composite. The specimens after 1, 3 and 7 days of hardening with plasticizer exhibited the highest impact on compressive strength in comparison to composite without plasticizer but 28 days hardened specimens reached the same value of strength characteristic (41 MPa).

Direct Shear Tests of Sandstone Under Constant Normal Tensile Stress Condition Using a Simple Auxiliary Device

NASA Astrophysics Data System (ADS)

Cen, Duofeng; Huang, Da

2017-06-01

Tension-shear failure is a typical failure mode in the rock masses in unloading zones induced by excavation or river incision, etc., such as in excavation-disturbed zone of deep underground caverns and superficial rocks of high steep slopes. However, almost all the current shear failure criteria for rock are usually derived on the basis of compression-shear failure. This paper proposes a simple device for use with a servo-controlled compression-shear testing machine to conduct the tension-shear tests of cuboid rock specimens, to test the direct shear behavior of sandstone under different constant normal tensile stress conditions ( σ = -1, -1.5, -2, -2.5 and -3 MPa) as well as the uniaxial tension behavior. Generally, the fracture surface roughness decreases and the proportion of comminution areas in fracture surface increases as the change of stress state from tension to tension-shear and to compression-shear. Stepped fracture is a primary fracture pattern in the tension-shear tests. The shear stiffness, shear deformation and normal deformation (except the normal deformation for σ = -1 MPa) decrease during shearing, while the total normal deformation containing the pre-shearing portion increases as the normal tensile stress level (| σ|) goes up. Shear strength is more sensitive to the normal tensile stress than to the normal compressive stress, and the power function failure criterion (or Mohr envelope form of Hoek-Brown criterion) is examined to be the optimal criterion for the tested sandstone in the full region of tested normal stress in this study.

Development and comparison of processing maps of Mg-3Sn-1Ca alloy from data obtained in tension versus compression

NASA Astrophysics Data System (ADS)

Rao, K. P.; Suresh, K.; Prasad, Y. V. R. K.; Hort, N.

2018-01-01

The hot workability of extruded Mg-3Sn-1Ca alloy has been evaluated by developing processing maps with flow stress data from compression and tensile tests with a view to find the effect of the applied state-of-stress. The processing maps developed at a strain of 0.2 are essentially similar irrespective of the mode of deformation - compression or tension, and exhibit three domains in the temperature ranges: (1) 350 - 425 °C, and (2) 450 - 550 °C and (3) 400 - 500 °C, the first two occurring at lower strain rates and the third occurring at higher strain rates. In all the three domains, dynamic recrystallization occurs and is caused by non-basal slip and controlled by lattice self-diffusion in the first and second domains and grain boundary self-diffusion in the third domain. The state-of-stress imposed on the specimen (compression or tension) does not have any significant effect on the processing maps.

Compressive Strength and Modulus of Elasticity of Concrete with Cubed Waste Tire Rubbers as Coarse Aggregates

NASA Astrophysics Data System (ADS)

Haryanto, Y.; Hermanto, N. I. S.; Pamudji, G.; Wardana, K. P.

2017-11-01

One feasible solution to overcome the issue of tire disposal waste is the use of waste tire rubber to replace aggregate in concrete. We have conducted an experimental investigation on the effect of rubber tire waste aggregate in cuboid form on the compressive strength and modulus of elasticity of concrete. The test was performed on 72 cylindrical specimens with the height of 300 mm and diameter of 150 mm. We found that the workability of concrete with waste tire rubber aggregate has increased. The concrete density with waste tire rubber aggregate was decreased, and so was the compressive strength. The decrease of compressive strength is up to 64.34%. If the content of waste tire rubber aggregate is more than 40%, then the resulting concrete cannot be categorized as structural concrete. The modulus of elasticity decreased to 59.77%. The theoretical equation developed to determine the modulus of elasticity of concrete with rubber tire waste aggregate has an accuracy of 84.27%.

Allowable compressive stress at prestress transfer.

DOT National Transportation Integrated Search

2008-12-01

In 2004, The Texas Department of Transportation initiated Project 5197 to investigate the feasibility of : increasing the allowable compressive stress limit at prestress transfer. Initially, the live load performance of 36 : specimens was evaluated b...

Effect of pre-straining on the evolution of material anisotropy in rolled magnesium alloy AZ31 sheet

NASA Astrophysics Data System (ADS)

Qiao, H.; Guo, X. Q.; Wu, P. D.

2013-12-01

The large strain Elastic Visco-Plastic Self-Consistent (EVPSC) model and the recently developed Twinning and De-Twinning (TDT) model are applied to study the mechanical behavior of rolled magnesium alloy AZ31 sheet. Three different specimen orientations with tilt angles of 0°, 45° and 90° between the rolling direction and longitudinal specimen axis are used to study the mechanical anisotropy under both uniaxial tension and compression. The effect of pre-strain in uniaxial compression along the rolling direction on subsequent uniaxial tension/compression along the three directions is also investigated. It is demonstrated that the twinning during pre-strain in compression and the detwinning in the subsequent deformation have a significant influence on the mechanical anisotropy. Numerical results are in good agreement with the experimental observations found in the literature.

Failure Behavior of Unidirectional Composites under Compression Loading: Effect of Fiber Waviness

PubMed Central

Yue, Chee Yoon

2017-01-01

The key objective of this work is to highlight the effect of manufacturing-induced fiber waviness defects on the compressive failure of glass fiber-reinforced unidirectional specimens. For this purpose, in-plane, through-thickness waviness defects (with different waviness severities) are induced during the manufacturing of the laminate. Numerical and experimental results show that the compressive strength of the composites decreases as the severity of the waviness defects increases. A reduction of up to 75% is noted with a wave severity of 0.075. Optical and scanning electron microscopy observations of the failed specimens reveal that kink-bands are created in the wavy regions and lead to failure. PMID:28783057

Fracture-induced mechanophore activation and solvent healing in poly(methyl methacrylate)

NASA Astrophysics Data System (ADS)

Celestine, Asha-Dee N.

Damage detection is a highly desirable functionality in engineering materials. The potential of using mechanophores, stress-sensitive molecules, as material stress sensors has been established through tensile, compressive and shear tests. Spiropyran (SP) has been the chosen mechanophore and this molecule undergoes a ring opening reaction (activation) upon the application of mechanical stress. This activation is accompanied by a change in color and fluorescence as the colorless SP is converted to the highly colored merocyanine (MC) form. One requirement for SP activation in bulk polymers is large scale plastic deformation. In order to induce this plastic deformation during fracture testing of SP-linked brittle polymers such as poly(methyl methacrylate) (PMMA), rubber nanoparticles can be incorporated into the matrix material. These nanoparticles facilitate the increased shear yielding necessary for SP activation during mechanical testing. Cross-linked SP-PMMA, containing 7.3 wt% rubber nanoparticles is synthesized via a free radical polymerization. Specimens of this material are fabricated for Single Edge Notch Tension (SENT) testing. The rubber toughened SP-PMMA specimens are first prestretched to approximately 35% axial strain to align the spiropyran molecules in the direction of applied force and thus increase the likelihood of fracture-induced activation. After prestretching the specimens are pre-notched and irradiated with 532 nm wavelength light to revert the colored merocyanine to the colorless spiropyran form. Specimens are then fracture tested to failure using the SENT test. The evolution of mechanophore activation is monitored via in situ fluorescence imaging and inspection of the specimens after testing. Activation of the SP is observed ahead of the crack tip and along the propagated crack. Also, the degree of activation is found to increase with crack growth and the size of the activation zone is linearly correlated to the size of the plastic zone ahead of the crack tip. Control specimens in which the mechanophore is absent or tethered in positions in which no mechanochemical activation is expected are also tested and exhibit no change in color or fluorescence intensity with crack propagation. The relationship between fracture-induced mechanophore activation in rubber toughened SP-PMMA and the strain and stress ahead of the propagating crack is also studied. SP activation is again detected and quantified by in situ fluorescence imaging. Digital Image Correlation (DIC) is used to measure the strain ahead of the crack tip. The corresponding stress is generated through the use of the Hutchinson-Rice-Rosengren (HRR) singularity field equations. Mechanophore activation ahead of the crack tip is shown to follow a power law distribution that is closely aligned with strain. The potential of SP as a damage sensor is explored further by incorporating the spiropyran into the core of rubber nanoparticles. SP-linked rubber nanoparticles are synthesized using a seeded emulsion polymerization process and incorporated into cross-linked PMMA at a concentration of 5 wt%. Cylindrical specimens are torsion tested and the activation of the SP within the nanoparticles is monitored via full field fluorescence imaging. SP activation within the core is shown to increase with shear strain. Autonomous damage repair in PMMA is also investigated. The first demonstration of fully autonomous self-healing in PMMA is achieved through the use of solvent microcapsules. Solvent microcapsules with a PMMA-anisole liquid core are prepared and embedded within a linear PMMA matrix. Specimens of the microcapsule-loaded material are then fabricated for Double Cleavage Drilled Compression (DCDC) fracture testing. The DCDC specimens, containing increasing concentrations of solvent microcapsules, are tested and then allowed to heal for a fixed period of time before a second DCDC test. The healing efficiency of each material system is evaluated based on the recovery of fracture toughness and is shown to be dependent on healing time and microcapsule concentration. (Abstract shortened by UMI.).

A Study for the Characteristic Changes Under the Repeated Thermal Exposure in the Process of Repairing Aircraft Sandwich Structures

NASA Astrophysics Data System (ADS)

Kim, Yun Hae; Han, Joong Won; Kim, Don Won; Choi, Byung Keun; Murakami, R.

Delamination can be observed in the sound areas during and/or after a couple times exposure to the elevated curing temperature due to the repeated repair condition. This study was conducted for checking the degree of degradation of properties of the cured parts and delamination between skin prepreg and honeycomb core. Specimens with glass honeycomb sandwich construction and glass/epoxy prepreg were prepared. The specimens were cured 1 to 5 times at 260°F in an autoclave and each additionally exposed 50, 100 and 150 hours in the 260°F oven. Each specimen was tested for tensile strength, compressive strength, flatwise tensile strength and interlaminar shear strength. To monitor the characteristics of the resin itself, the cured resin was tested using DMA and DSC. As a results, the decrease of Tg value were observed in the specific specimen which is exposed over 50 hrs at 260°F. This means the change or degradative of resin properties is also related to the decrease of flatwise tensile properties. Accordingly, minimal exposure on the curing temperature is recommended for parts in order to prevent the delation and maintain the better condition.

Investigation of Tensile Creep of a Normal Strength Overlay Concrete.

PubMed

Drexel, Martin; Theiner, Yvonne; Hofstetter, Günter

2018-06-12

The present contribution deals with the experimental investigation of the time-dependent behavior of a typical overlay concrete subjected to tensile stresses. The latter develop in concrete overlays, which are placed on existing concrete structures as a strengthening measure, due to the shrinkage of the young overlay concrete, which is restrained by the substrate concrete. Since the tensile stresses are reduced by creep, creep in tension is investigated on sealed and unsealed specimens, loaded at different concrete ages. The creep tests as well as the companion shrinkage tests are performed in a climatic chamber at constant temperature and constant relative humidity. Since shrinkage depends on the change of moisture content, the evolution of the mass water content is determined at the center of each specimen by means of an electrolytic resistivity-based system. Together with the experimental results for compressive creep from a previous study, a consistent set of time-dependent material data, determined for the same composition of the concrete mixture and on identical specimens, is now available. It consists of the hygral and mechanical properties, creep and shrinkage strains for both sealed and drying conditions, the respective compliance functions, and the mass water contents in sealed and unsealed, loaded and load-free specimens.

Mechanical response of unidirectional boron/aluminum under combined loading

NASA Technical Reports Server (NTRS)

Becker, Wolfgang; Pindera, Marek-Jerzy; Herakovich, Carl T.

1987-01-01

Three test methods were employed to characterize the response of unidirectional Boron/Aluminum metal matrix composite material under monotonic and cyclic loading conditions, namely, losipescu shear, off-axis tension and compression. The characterization of the elastic and plastic response includes the elastic material properties, yielding and subsequent hardening of the unidirectional composite under different stress ratios in the material principal coordinate system. Yield loci generated for different stress ratios are compared for the three different test methods, taking into account residual stresses and specimen geometry. Subsequently, the yield locus for in-plane shear is compared with the prediction of an analytical, micromechanical model. The influence of the scatter in the experimental data on the predicted yield surface is also analyzed. Lastly, the experimental material strengths in tension and compression are correlated with the maximum stress and the Tsai-Wu failure criterion.

Using a visual discrimination model for the detection of compression artifacts in virtual pathology images.

PubMed

Johnson, Jeffrey P; Krupinski, Elizabeth A; Yan, Michelle; Roehrig, Hans; Graham, Anna R; Weinstein, Ronald S

2011-02-01

A major issue in telepathology is the extremely large and growing size of digitized "virtual" slides, which can require several gigabytes of storage and cause significant delays in data transmission for remote image interpretation and interactive visualization by pathologists. Compression can reduce this massive amount of virtual slide data, but reversible (lossless) methods limit data reduction to less than 50%, while lossy compression can degrade image quality and diagnostic accuracy. "Visually lossless" compression offers the potential for using higher compression levels without noticeable artifacts, but requires a rate-control strategy that adapts to image content and loss visibility. We investigated the utility of a visual discrimination model (VDM) and other distortion metrics for predicting JPEG 2000 bit rates corresponding to visually lossless compression of virtual slides for breast biopsy specimens. Threshold bit rates were determined experimentally with human observers for a variety of tissue regions cropped from virtual slides. For test images compressed to their visually lossless thresholds, just-noticeable difference (JND) metrics computed by the VDM were nearly constant at the 95th percentile level or higher, and were significantly less variable than peak signal-to-noise ratio (PSNR) and structural similarity (SSIM) metrics. Our results suggest that VDM metrics could be used to guide the compression of virtual slides to achieve visually lossless compression while providing 5-12 times the data reduction of reversible methods.

Mechanical characterization of human brain tissue.

PubMed

Budday, S; Sommer, G; Birkl, C; Langkammer, C; Haybaeck, J; Kohnert, J; Bauer, M; Paulsen, F; Steinmann, P; Kuhl, E; Holzapfel, G A

2017-01-15

Mechanics are increasingly recognized to play an important role in modulating brain form and function. Computational simulations are a powerful tool to predict the mechanical behavior of the human brain in health and disease. The success of these simulations depends critically on the underlying constitutive model and on the reliable identification of its material parameters. Thus, there is an urgent need to thoroughly characterize the mechanical behavior of brain tissue and to identify mathematical models that capture the tissue response under arbitrary loading conditions. However, most constitutive models have only been calibrated for a single loading mode. Here, we perform a sequence of multiple loading modes on the same human brain specimen - simple shear in two orthogonal directions, compression, and tension - and characterize the loading-mode specific regional and directional behavior. We complement these three individual tests by combined multiaxial compression/tension-shear tests and discuss effects of conditioning and hysteresis. To explore to which extent the macrostructural response is a result of the underlying microstructural architecture, we supplement our biomechanical tests with diffusion tensor imaging and histology. We show that the heterogeneous microstructure leads to a regional but not directional dependence of the mechanical properties. Our experiments confirm that human brain tissue is nonlinear and viscoelastic, with a pronounced compression-tension asymmetry. Using our measurements, we compare the performance of five common constitutive models, neo-Hookean, Mooney-Rivlin, Demiray, Gent, and Ogden, and show that only the isotropic modified one-term Ogden model is capable of representing the hyperelastic behavior under combined shear, compression, and tension loadings: with a shear modulus of 0.4-1.4kPa and a negative nonlinearity parameter it captures the compression-tension asymmetry and the increase in shear stress under superimposed compression but not tension. Our results demonstrate that material parameters identified for a single loading mode fail to predict the response under arbitrary loading conditions. Our systematic characterization of human brain tissue will lead to more accurate computational simulations, which will allow us to determine criteria for injury, to develop smart protection systems, and to predict brain development and disease progression. There is a pressing need to characterize the mechanical behavior of human brain tissue under multiple loading conditions, and to identify constitutive models that are able to capture the tissue response under these conditions. We perform a sequence of experimental tests on the same brain specimen to characterize the regional and directional behavior, and we supplement our tests with DTI and histology to explore to which extent the macrostructural response is a result of the underlying microstructure. Results demonstrate that human brain tissue is nonlinear and viscoelastic, with a pronounced compression-tension asymmetry, and we show that the multiaxial data can best be captured by a modified version of the one-term Ogden model. Copyright © 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Experimental analysis and constitutive modelling of steel of A-IIIN strength class

NASA Astrophysics Data System (ADS)

Kruszka, Leopold; Janiszewski, Jacek

2015-09-01

Fundamentally important is the better understanding of behaviour of new building steels under impact loadings, including plastic deformations. Results of the experimental analysis in wide range of strain rates in compression at room temperature, as well as constitutive modelling for and B500SP structural steels of new A-IIIN Polish strength class, examined dynamically by split Hopkinson pressure bar technique at high strain rates, are presented in table and graphic forms. Dynamic mechanical characteristics of compressive strength for tested building structural steel are determined as well as dynamic mechanical properties of this material are compared with 18G2-b steel of A-II strength class, including effects of the shape of tested specimens, i.e. their slenderness. The paper focuses the attention on those experimental tests, their interpretation, and constitutive semi-empirical modelling of the behaviour of tested steels based on Johnson-Cook's model. Obtained results of analyses presented here are used for designing and numerical simulations of reinforced concrete protective structures.

Mechanical properties of polymer-modified porous concrete

NASA Astrophysics Data System (ADS)

Ariffin, N. F.; Jaafar, M. F. Md.; Shukor Lim, N. H. Abdul; Bhutta, M. A. R.; Hussin, M. W.

2018-04-01

In this research work, polymer-modified porous concretes (permeable concretes) using polymer latex and redispersible polymer powder with water-cement ratio of 30 %, polymer-cement ratios of 0 to 10 % and cement content of 300 kg/m3 are prepared. The porous concrete was tested for compressive strength, flexural strength, water permeability and void ratio. The cubes size of specimen is 100 mm ×100 mm × 100 mm and 150 mm × 150 mm × 150 mm while the beam size is 100 mm × 100 mm × 500 mm was prepared for particular tests. The tests results show that the addition of polymer as a binder to porous concrete gives an improvement on the strength properties and coefficient of water permeability of polymer-modified porous concrete. It is concluded from the test results that increase in compressive and flexural strengths and decrease in the coefficient of water permeability of the polymer-modified porous concrete are clearly observed with increasing of polymer-cement ratio.