Damage evaluation of fiber reinforced plastic-confined circular concrete-filled steel tubular columns under cyclic loading using the acoustic emission technique

NASA Astrophysics Data System (ADS)

Li, Dongsheng; Du, Fangzhu; Ou, Jinping

2017-03-01

Glass-fiber reinforced plastic (GFRP)-confined circular concrete-filled steel tubular (CCFT) columns comprise of concrete, steel, and GFRP and show complex failure mechanics under cyclic loading. This paper investigated the failure mechanism and damage evolution of GFRP-CCFT columns by performing uniaxial cyclic loading tests that were monitored using the acoustic emission (AE) technique. Characteristic AE parameters were obtained during the damage evolution of GFRP-CCFT columns. Based on the relationship between the loading curve and these parameters, the damage evolution of GFRP-CCFT columns was classified into three stages that represented different damage degrees. Damage evolution and failure mode were investigated by analyzing the b-value and the ratio of rise time to waveform amplitude and average frequency. The damage severity of GFRP-CCFT columns were quantitatively estimated according to the modified index of damage and NDIS-2421 damage assessment criteria corresponding to each loading step. The proposed method can explain the damage evolution and failure mechanism for GFRP-CCFT columns and provide critical warning information for composite structures.

Fatigue and creep to leak tests of proton exchange membranes using pressure-loaded blisters

NASA Astrophysics Data System (ADS)

Li, Yongqiang; Dillard, David A.; Case, Scott W.; Ellis, Michael W.; Lai, Yeh-Hung; Gittleman, Craig S.; Miller, Daniel P.

In this study, three commercially available proton exchange membranes (PEMs) are biaxially tested using pressure-loaded blisters to characterize their resistance to gas leakage under either static (creep) or cyclic fatigue loading. The pressurizing medium, air, is directly used for leak detection. These tests are believed to be more relevant to fuel cell applications than quasi-static uniaxial tensile-to-rupture tests because of the use of biaxial cyclic and sustained loading and the use of gas leakage as the failure criterion. They also have advantages over relative humidity cycling test, in which a bare PEM or catalyst coated membrane is clamped with gas diffusion media and flow field plates and subjected to cyclic changes in relative humidity, because of the flexibility in allowing controlled mechanical loading and accelerated testing. Nafion ® NRE-211 membranes are tested at three different temperatures and the time-temperature superposition principle is used to construct stress-lifetime master curve. Tested at 90 °C, 2%RH extruded Ion Power ® N111-IP membranes have a longer lifetime than Gore™-Select ® 57 and Nafion ® NRE-211 membranes.

Strength, Fracture Toughness, Fatigue, and Standardization Issues of Free-standing Thermal Barrier Coatings

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Zhu, Dong-Ming; Miller, Robert A.

2003-01-01

Strength, fracture toughness and fatigue behavior of free-standing thick thermal barrier coatings of plasma-sprayed ZrO2-8wt % Y2O3 were determined at ambient and elevated temperatures in an attempt to establish a database for design. Strength, in conjunction with deformation (stress-strain behavior), was evaluated in tension (uniaxial and trans-thickness), compression, and uniaxial and biaxial flexure; fracture toughness was determined in various load conditions including mode I, mode II, and mixed modes I and II; fatigue or slow crack growth behavior was estimated in cyclic tension and dynamic flexure loading. Effect of sintering was quantified through approaches using strength, fracture toughness, and modulus (constitutive relations) measurements. Standardization issues on test methodology also was presented with a special regard to material's unique constitutive relations.

Experimental Investigation on Deformation Failure Characteristics of Crystalline Marble Under Triaxial Cyclic Loading

NASA Astrophysics Data System (ADS)

Yang, Sheng-Qi; Tian, Wen-Ling; Ranjith, P. G.

2017-11-01

The deformation failure characteristics of marble subjected to triaxial cyclic loading are significant when evaluating the stability and safety of deep excavation damage zones. To date, however, there have been notably few triaxial experimental studies on marble under triaxial cyclic loading. Therefore, in this research, a series of triaxial cyclic tests was conducted to analyze the mechanical damage characteristics of a marble. The post-peak deformation of the marble changed gradually from strain softening to strain hardening as the confining pressure increased from 0 to 10 MPa. Under uniaxial compression, marble specimens showed brittle failure characteristics with a number axial splitting tensile cracks; in the range of σ 3 = 2.5-7.5 MPa, the marble specimens assumed single shear fracture characteristics with larger fracture angles of about 65°. However, at σ 3 = 10 MPa, the marble specimens showed no obvious shear fracture surfaces. The triaxial cyclic experimental results indicate that in the range of the tested confining pressures, the triaxial strengths of the marble specimens under cyclic loading were approximately equal to those under monotonic loading. With the increase in cycle number, the elastic strains of the marble specimens all increased at first and later decreased, achieving maximum values, but the plastic strains of the marble specimens increased nonlinearly. To evaluate quantitatively the damage extent of the marble under triaxial cyclic loading, a damage variable is defined according to the irreversible deformation for each cycle. The evolutions of the elastic modulus for the marble were characterized by four stages: material strengthening, material degradation, material failure and structure slippage. Based on the experimental results of the marble specimens under complex cyclic loading, the cohesion of the marble decreased linearly, but the internal friction angles did not depend on the damage extent. To describe the peak strength characteristics of the marble specimens under complex cyclic loadings with various deformation positions, a revised strength criterion for damaged rocks is offered.

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.

Ratcheting induced cyclic softening behaviour of 42CrMo4 steel

NASA Astrophysics Data System (ADS)

Kreethi, R.; Mondal, A. K.; Dutta, K.

2015-02-01

Ratcheting is an important field of fatigue deformation which happens under stress controlled cyclic loading of materials. The aim of this investigation is to study the uniaxial ratcheting behavior of 42CrMo4 steel in annealed condition, under various applied stresses. In view of this, stress controlled fatigue tests were carried out at room temperature up to 200 cycles using a servo-hydraulic universal testing machine. The results indicate that accumulation of ratcheting strain increases monotonically with increasing maximum applied stress however; the rate of strain accumulation attains a saturation plateau after few cycles. The investigated steel shows cyclic softening behaviour under the applied stress conditions. The nature of strain accumulation and cyclic softening has been discussed in terms of dislocation distribution and plastic damage incurred in the material.

A Three-Parameter Model for Predicting Fatigue Life of Ductile Metals Under Constant Amplitude Multiaxial Loading

NASA Astrophysics Data System (ADS)

Liu, Jia; Li, Jing; Zhang, Zhong-ping

2013-04-01

In this article, a fatigue damage parameter is proposed to assess the multiaxial fatigue lives of ductile metals based on the critical plane concept: Fatigue crack initiation is controlled by the maximum shear strain, and the other important effect in the fatigue damage process is the normal strain and stress. This fatigue damage parameter introduces a stress-correlated factor, which describes the degree of the non-proportional cyclic hardening. Besides, a three-parameter multiaxial fatigue criterion is used to correlate the fatigue lifetime of metallic materials with the proposed damage parameter. Under the uniaxial loading, this three-parameter model reduces to the recently developed Zhang's model for predicting the uniaxial fatigue crack initiation life. The accuracy and reliability of this three-parameter model are checked against the experimental data found in literature through testing six different ductile metals under various strain paths with zero/non-zero mean stress.

Brain tissue deforms similarly to filled elastomers and follows consolidation theory

NASA Astrophysics Data System (ADS)

Franceschini, G.; Bigoni, D.; Regitnig, P.; Holzapfel, G. A.

2006-12-01

Slow, large deformations of human brain tissue—accompanying cranial vault deformation induced by positional plagiocephaly, occurring during hydrocephalus, and in the convolutional development—has surprisingly received scarce mechanical investigation. Since the effects of these deformations may be important, we performed a systematic series of in vitro experiments on human brain tissue, revealing the following features. (i) Under uniaxial (quasi-static), cyclic loading, brain tissue exhibits a peculiar nonlinear mechanical behaviour, exhibiting hysteresis, Mullins effect and residual strain, qualitatively similar to that observed in filled elastomers. As a consequence, the loading and unloading uniaxial curves have been found to follow the Ogden nonlinear elastic theory of rubber (and its variants to include Mullins effect and permanent strain). (ii) Loaded up to failure, the "shape" of the stress/strain curve qualitatively changes, evidencing softening related to local failure. (iii) Uniaxial (quasi-static) strain experiments under controlled drainage conditions provide the first direct evidence that the tissue obeys consolidation theory involving fluid migration, with properties similar to fine soils, but having much smaller volumetric compressibility. (iv) Our experimental findings also support the existence of a viscous component of the solid phase deformation. Brain tissue should, therefore, be modelled as a porous, fluid-saturated, nonlinear solid with very small volumetric (drained) compressibility.

Mechanical Behavior and Microcrack Development in Nominally Dry Synthetic Salt-rock During Cyclic Loading

NASA Astrophysics Data System (ADS)

Ding, J.; Chester, F. M.; Chester, J. S.; Zhu, C.; Shen, X.; Arson, C. F.

2016-12-01

Synthetic salt-rock is produced through uniaxial consolidation of sieved granular salt (0.3-0.355 mm grain diam.) at 75-107 MPa pressure and 100-200 0 C for 15 min duration, to produce low porosity (3%-6%) aggregates. Based on microstructural observations, consolidation mechanisms are grain rearrangement, intragranular plastic flow, and minor microfracture and recrystallization. Following consolidation, the salt-rock is deformed by cyclic, triaxial loading at room temperature and 4 MPa confining pressure to investigate microfracture development, closure and healing effects on elastic properties and flow strength. Load cycles are performed within the elastic regime, up to yielding, and during steady ductile flow. The mechanical properties are determined using an internal load cell and strain gages bonded to the samples. Elastic properties vary systematically during deformation reflecting cracking and pore and grain shape changes. Between triaxial load cycles, samples are held at isostatic loads for durations up to one day to determine healing rates and strength recovery; a change in mechanical behavior is observed when significant healing is induced. The microstructures of all samples are characterized before and after cyclic loading using optical microscopy. The consolidation and cyclic triaxial tests, and optical microscopy investigations, are conducted in a controlled low-humidity environment to ensure nominally dry conditions. The microstructures of samples from different stages of cyclic triaxial deformation indicate that intracrystalline plasticity, accompanied by minor recovery by recrystallization, is dominant; but, grain-boundary crack opening also becomes significant. Grain-boundary microcracks have preferred orientations that are sub-parallel to the load axis. The stress-strain behavior correlates with microcrack fabrics and densities during cyclic loading. These experiments are used to both inform and test continuum damage mechanics models of salt-rock deformation in the semibrittle domain, as well as to help design and optimize salt-rock storage facilities.

Application of an Uncoupled Elastic-plastic-creep Constitutive Model to Metals at High Temperature

NASA Technical Reports Server (NTRS)

Haisler, W. E.

1983-01-01

A uniaxial, uncoupled constitutive model to predict the response of thermal and rate dependent elastic-plastic material behavior is presented. The model is based on an incremental classicial plasticity theory extended to account for thermal, creep, and transient temperature conditions. Revisions to he combined hardening rule of the theory allow for better representation of cyclic phenomenon including the high rate of strain hardening upon cyclic reyield and cyclic saturation. An alternative approach is taken to model the rate dependent inelastic deformation which utilizes hysteresis loops and stress relaxation test data at various temperatures. The model is evaluated and compared to experiments which involve various thermal and mechanical load histories on 5086 aluminum alloy, 304 stainless steel and Hastelloy-X.

Effects of mechanical strain on human mesenchymal stem cells and ligament fibroblasts in a textured poly(L-lactide) scaffold for ligament tissue engineering.

PubMed

Kreja, Ludwika; Liedert, Astrid; Schlenker, Heiter; Brenner, Rolf E; Fiedler, Jörg; Friemert, Benedikt; Dürselen, Lutz; Ignatius, Anita

2012-10-01

The purpose of this study was to prove the effect of cyclic uniaxial intermittent strain on the mRNA expression of ligament-specific marker genes in human mesenchymal stem cells (MSC) and anterior cruciate ligament-derived fibroblasts (ACL-fibroblasts) seeded onto a novel textured poly(L-lactide) scaffold (PLA scaffold). Cell-seeded scaffolds were mechanically stimulated by cyclic uniaxial stretching. The expression of ligament matrix gene markers: collagen types I and III, fibronectin, tenascin C and decorin, as well as the proteolytic enzymes matrix metalloproteinase MMP-1 and MMP-2 and their tissue specific inhibitors TIMP-1 and TIMP-2 was investigated by analysing the mRNA expression using reverse transcriptase polymerase chain reaction and related to the static control. In ACL-fibroblasts seeded on PLA, mechanical load induced up-regulation of collagen types I and III, fibronectin and tenascin C. No effect of mechanical stimulation on the expression of ligament marker genes was found in undifferentiated MSC seeded on PLA. The results indicated that the new textured PLA scaffold could transfer the mechanical load to the ACL-fibroblasts and improved their ligament phenotype. This scaffold might be suitable as a cell-carrying component of ACL prostheses.

Damage-based life prediction model for uniaxial low-cycle stress fatigue of super-elastic NiTi shape memory alloy microtubes

NASA Astrophysics Data System (ADS)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2015-08-01

Based on the experimental observations for the uniaxial low-cycle stress fatigue failure of super-elastic NiTi shape memory alloy microtubes (Song et al 2015 Smart Mater. Struct. 24 075004) and a new definition of damage variable corresponding to the variation of accumulated dissipation energy, a phenomenological damage model is proposed to describe the damage evolution of the NiTi microtubes during cyclic loading. Then, with a failure criterion of Dc = 1, the fatigue lives of the NiTi microtubes are predicted by the damage-based model, the predicted lives are in good agreement with the experimental ones, and all of the points are located within an error band of 1.5 times.

Modeling Geometry and Progressive Failure of Material Interfaces in Plain Weave Composites

NASA Technical Reports Server (NTRS)

Hsu, Su-Yuen; Cheng, Ron-Bin

2010-01-01

A procedure combining a geometrically nonlinear, explicit-dynamics contact analysis, computer aided design techniques, and elasticity-based mesh adjustment is proposed to efficiently generate realistic finite element models for meso-mechanical analysis of progressive failure in textile composites. In the procedure, the geometry of fiber tows is obtained by imposing a fictitious expansion on the tows. Meshes resulting from the procedure are conformal with the computed tow-tow and tow-matrix interfaces but are incongruent at the interfaces. The mesh interfaces are treated as cohesive contact surfaces not only to resolve the incongruence but also to simulate progressive failure. The method is employed to simulate debonding at the material interfaces in a ceramic-matrix plain weave composite with matrix porosity and in a polymeric matrix plain weave composite without matrix porosity, both subject to uniaxial cyclic loading. The numerical results indicate progression of the interfacial damage during every loading and reverse loading event in a constant strain amplitude cyclic process. However, the composites show different patterns of damage advancement.

Benchmark notch test for life prediction

NASA Technical Reports Server (NTRS)

Domas, P. A.; Sharpe, W. N.; Ward, M.; Yau, J. F.

1982-01-01

The laser Interferometric Strain Displacement Gage (ISDG) was used to measure local strains in notched Inconel 718 test bars subjected to six different load histories at 649 C (1200 F) and including effects of tensile and compressive hold periods. The measurements were compared to simplified Neuber notch analysis predictions of notch root stress and strain. The actual strains incurred at the root of a discontinuity in cyclically loaded test samples subjected to inelastic deformation at high temperature where creep deformations readily occur were determined. The steady state cyclic, stress-strain response at the root of the discontinuity was analyzed. Flat, double notched uniaxially loaded fatigue specimens manufactured from the nickel base, superalloy Inconel 718 were used. The ISDG was used to obtain cycle by cycle recordings of notch root strain during continuous and hold time cycling at 649 C. Comparisons to Neuber and finite element model analyses were made. The results obtained provide a benchmark data set in high technology design where notch fatigue life is the predominant component service life limitation.

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.

Cyclic tensile response of a pre-tensioned polyurethane

NASA Astrophysics Data System (ADS)

Nie, Yizhou; Liao, Hangjie; Chen, Weinong W.

2018-05-01

In the research reported in this paper, we subject a polyurethane to uniaxial tensile loading at a quasi-static strain rate, a high strain rate and a jumping strain rate where the specimen is under quasi-static pre-tension and is further subjected to a dynamic cyclic loading using a modified Kolsky tension bar. The results obtained at the quasi-static and high strain rate clearly show that the mechanical response of this material is significantly rate sensitive. The rate-jumping experimental results show that the response of the material behavior is consistent before jumping. After jumping the stress-strain response of the material does not jump to the corresponding high-rate curve. Rather it approaches the high-rate curve asymptotically. A non-linear hyper-viscoelastic (NLHV) model, after having been calibrated by monotonic quasi-static and high-rate experimental results, was found to be capable of describing the material tensile behavior under such rate jumping conditions.

A kinematic hardening constitutive model for the uniaxial cyclic stress-strain response of magnesium sheet alloys at room temperature

NASA Astrophysics Data System (ADS)

He, Zhitao; Chen, Wufan; Wang, Fenghua; Feng, Miaolin

2017-11-01

A kinematic hardening constitutive model is presented, in which a modified form of von Mises yield function is adopted, and the initial asymmetric tension and compression yield stresses of magnesium (Mg) alloys at room temperature (RT) are considered. The hardening behavior was classified into slip, twinning, and untwinning deformation modes, and these were described by two forms of back stress to capture the mechanical response of Mg sheet alloys under cyclic loading tests at RT. Experimental values were obtained for AZ31B-O and AZ31B sheet alloys under both tension-compression-tension (T-C-T) and compression-tension (C-T) loadings to calibrate the parameters of back stresses in the proposed model. The predicted parameters of back stresses in the twinning and untwinning modes were expressed as a cubic polynomial. The predicted curves based on these parameters showed good agreement with the tests.

The multiaxial fatigue response of cylindrical geometry under proportional loading subject to fluctuating tractions

NASA Astrophysics Data System (ADS)

Martinez, Rudy D.

A multiaxial fatigue model is proposed, as it would apply to cylindrical geometry in the form of industrial sized pressure vessels. The main focus of the multiaxial fatigue model will be based on using energy methods with the loading states confined to fluctuating tractions under proportional loading. The proposed fatigue model is an effort to support and enhance existing fatigue life predicting methods for pressure vessel design, beyond the ASME Boiler and Pressure Vessel codes, ASME Section VIII Division 2 and 3, which is currently used in industrial engineering practice for pressure vessel design. Both uniaxial and biaxial low alloy pearlittic-ferritic steel cylindrical cyclic test data are utilized to substantiate the proposed fatigue model. Approximate material hardening and softening aspects from applied load cycling states and the Bauschinger effect are accounted for by adjusting strain control generated hysteresis loops and the cyclic stress strain curve. The proposed fatigue energy model and the current ASME fatigue model are then compared with regards to the accuracy of predicting fatigue life cycle consistencies.

Advanced Joining of Aerospace Metallic Materials.

DTIC Science & Technology

1986-07-01

uniaxial tensile test with varying temperature and cyclic loading. This simple test problem excercises maray aspects of the phenomena. suOn- ,Ual Yield...6vidence Ia seconde configuration apparait plus n~ faste . 5.3. Ents-e-igne-men-t-s s-u r a dyna-mique de. bain-s de fu-sion A lusage il svest r~vle que la...scanning system for fast and exact alignment of the EB-qun is used. In a fixture the cleaned detail parts are positioned exactly and clamped for welding. At

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading

PubMed Central

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-01-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress–strain responses for each cycle, and the hysteresis stress–strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given. PMID:26937465

Fatigue data for polyether ether ketone (PEEK) under fully-reversed cyclic loading.

PubMed

Shrestha, Rakish; Simsiriwong, Jutima; Shamsaei, Nima

2016-03-01

In this article, the data obtained from the uniaxial fully-reversed fatigue experiments conducted on polyether ether ketone (PEEK), a semi-crystalline thermoplastic, are presented. The tests were performed in either strain-controlled or load-controlled mode under various levels of loading. The data are categorized into four subsets according to the type of tests, including (1) strain-controlled fatigue tests with adjusted frequency to obtain the nominal temperature rise of the specimen surface, (2) strain-controlled fatigue tests with various frequencies, (3) load-controlled fatigue tests without step loadings, and (4) load-controlled fatigue tests with step loadings. Accompanied data for each test include the fatigue life, the maximum (peak) and minimum (valley) stress-strain responses for each cycle, and the hysteresis stress-strain responses for each collected cycle in a logarithmic increment. A brief description of the experimental method is also given.

Observation on the transformation domains of super-elastic NiTi shape memory alloy and their evolutions during cyclic loading

NASA Astrophysics Data System (ADS)

Xie, Xi; Kan, Qianhua; Kang, Guozheng; Li, Jian; Qiu, Bo; Yu, Chao

2016-04-01

The strain field of a super-elastic NiTi shape memory alloy (SMA) and its variation during uniaxial cyclic tension-unloading were observed by a non-contact digital image correlation method, and then the transformation domains and their evolutions were indirectly investigated and discussed. It is seen that the super-elastic NiTi (SMA) exhibits a remarkable localized deformation and the transformation domains evolve periodically with the repeated cyclic tension-unloading within the first several cycles. However, the evolutions of transformation domains at the stage of stable cyclic transformation depend on applied peak stress: when the peak stress is low, no obvious transformation band is observed and the strain field is nearly uniform; when the peak stress is large enough, obvious transformation bands occur due to the residual martensite caused by the prevention of enriched dislocations to the reverse transformation from induced martensite to austenite. Temperature variations measured by an infrared thermal imaging method further verifies the formation and evolution of transformation domains.

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.

Some Recent Developments in the Endochronic Theory with Application to Cyclic Histories

NASA Technical Reports Server (NTRS)

Valanis, K. C.; Lee, C. F.

1983-01-01

Constitutive equations with only two easily determined material constants predict the stress (strain) response of normalized mild steel to a variety of general strain (stress) histories, without a need for special unloading-reloading rules. The equations are derived from the endochronic theory of plasticity of isotropic materials with an intrinsic time scale defined in the plastic strain space. Agreement between theoretical predictions and experiments are are excellent quantitatively in cases of various uniaxial constant amplitude histories, variable uniaxial strain amplitude histories and cyclic relaxation. The cyclic ratcheting phenomenon is predicted by the present theory.

Effects of Cyclic Loading on the Uniaxial Behavior of Nitinol

NASA Astrophysics Data System (ADS)

Schlun, M.; Zipse, A.; Dreher, G.; Rebelo, N.

2011-07-01

The widespread development and use of implants made from NiTi is accompanied by the publication of many NiTi material characterization studies. These publications have increased significantly the knowledge about the mechanical properties of NiTi. However, this knowledge also increased the complexity of the numerical simulation of NiTi implants or devices. This study is focused on the uniaxial behavior of NiTi tubing due to cyclic loading and had the goal to deliver both precise and application-oriented results. Single aspects of this study have already been published (Wagner in Ein Beitrag zur strukturellen und funktionalen Ermüdung von Drähten und Federn aus NiTi-Formgedaechtnislegierungen, Ph.D. Thesis, 2005; Eucken and Duerig in Acta Metall 37:2245-2252, 1989; Yawny et al. in Z Metallkd 96:608-618, 2005); however, there is no publication known that shows all the single effects combined in a "duty cycle case." It was of particular importance to summarize the main effects of pre-strain and subsequent small or large strain amplitudes on the material properties. The phenomena observed were captured in an extended Abaqus® Nitinol material model, presented by Rebelo et al. (A Material Model for the Cyclic Behavior of Nitinol, SMST Extended Abstracts 2010). The cyclic tensile tests were performed using a video extensometer to obtain accurate strain measurement on small electro-polished dog-bone specimen that were incorporated into a stent framework so that standard manufacturing methods could be used for the fabrication. This study indicates that a prestrain beyond 6% strain alters the transformation plateaus and if the cyclic displacement amplitude is large enough, additional permanent deformations are observed, the lower plateau and most notably the upper plateau change. The changes to the upper plateau are very interesting in the sense that an additional stress plateau develops: its "start stress" is lowered thereby creating a new plateau up to the highest level of cyclic strain, followed by resuming the original plateau until full transformation. This study was conducted in the course of the work of a consortium of several stent manufacturers, SAFE Technology Limited and Dassault Systèmes Simulia Corp., dedicated to the development of fatigue laws suitable for life prediction of Nitinol devices.

In-situ TOF neutron diffraction studies of cyclic softening in superelasticity of a NiFeGaCo shape memory alloy

DOE PAGES

Yang, Hui; Yu, Dunji; Chen, Yan; ...

2016-10-24

Real-time in-situ neutron diffraction was conducted during uniaxial cycling compression of a Ni 49.3Fe 18Ga 27Co 5.7 shape memory alloy to explore the mechanism on its superelasticity at room temperature, which was manifested by the almost recoverable large strains and the apparent cyclic softening. Based on the Rietveld refinements, the real-time evolution of volume fraction of martensite was in-situ monitored, indicating the incremental amount of residual martensite with increasing load cycles. Real-time changes in intensities and lattice strains of { hkl} reflections for individual phase were obtained through fitting individual peaks, which reveal the quantitative information on phase transformation kineticsmore » as a function of grain orientation and stress/strain partitioning. Moreover, a large compressive residual stress was evidenced in the parent phase, which should be balanced by the residual martensite after the second unloading cycle. As a result, the large compressive residual stress found in the parent austenite phase may account for the cyclic effect on critical stress required for triggering the martensitic transformation in the subsequent loading.« less

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-01-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

Loading Path and Control Mode Effects During Thermomechanical Cycling of Polycrystalline Shape Memory NiTi

NASA Astrophysics Data System (ADS)

Nicholson, D. E.; Benafan, O.; Padula, S. A.; Clausen, B.; Vaidyanathan, R.

2018-03-01

Loading path dependencies and control mode effects in polycrystalline shape memory NiTi were investigated using in situ neutron and synchrotron X-ray diffraction performed during mechanical cycling and thermal cycling at constant strain. Strain-controlled, isothermal, reverse loading (to ± 4%) and stress-controlled, isothermal, cyclic loading (to ± 400 MPa for up to ten cycles) at room temperature demonstrated that the preferred martensite variants selected correlated directly with the macroscopic uniaxial strain and did not correlate with the compressive or tensile state of stress. During cyclic loading (up to ten cycles), no significant cycle-to-cycle evolution of the variant microstructure corresponding to a given strain was observed, despite changes in the slope of the stress-strain response with each cycle. Additionally, thermal cycling (to above and below the phase transformation) under constant strain (up to 2% tensile strain) showed that the martensite variant microstructure correlated directly with strain and did not evolve following thermal cycling, despite relaxation of stress in both martensite and austenite phases. Results are presented in the context of variant reorientation and detwinning processes in martensitic NiTi, the fundamental thermoelastic nature of such processes and the ability of the variant microstructure to accommodate irreversible deformation processes.

A simple approach for the modeling of an ODS steel mechanical behavior in pilgering conditions

NASA Astrophysics Data System (ADS)

Vanegas-Márquez, E.; Mocellin, K.; Toualbi, L.; de Carlan, Y.; Logé, R. E.

2012-01-01

The optimization of the forming of ODS tubes is linked to the choice of an appropriated constitutive model for modeling the metal forming process. In the framework of a unified plastic constitutive theory, the strain-controlled cyclic characteristics of a ferritic ODS steel were analyzed and modeled with two different tests. The first test is a classical tension-compression test, and leads to cyclic softening at low to intermediate strain amplitudes. The second test consists in alternated uniaxial compressions along two perpendicular axes, and is selected based on the similarities with the loading path induced by the Fe-14Cr-1W-Ti ODS cladding tube pilgering process. This second test exhibits cyclic hardening at all tested strain amplitudes. Since variable strain amplitudes prevail in pilgering conditions, the parameters of the considered constitutive law were identified based on a loading sequence including strain amplitude changes. A proposed semi automated inverse analysis methodology is shown to efficiently provide optimal sets of parameters for the considered loading sequences. When compared to classical approaches, the model involves a reduced number of parameters, while keeping a good ability to capture stress changes induced by strain amplitude changes. Furthermore, the methodology only requires one test, which is an advantage when the amount of available material is limited. As two distinct sets of parameters were identified for the two considered tests, it is recommended to consider the loading path when modeling cold forming of the ODS steel.

Uniaxial and Multiaxial Fatigue Life Prediction of the Trabecular Bone Based on Physiological Loading: A Comparative Study.

PubMed

Fatihhi, S J; Harun, M N; Abdul Kadir, Mohammed Rafiq; Abdullah, Jaafar; Kamarul, T; Öchsner, Andreas; Syahrom, Ardiyansyah

2015-10-01

Fatigue assessment of the trabecular bone has been developed to give a better understanding of bone properties. While most fatigue studies are relying on uniaxial compressive load as the method of assessment, in various cases details are missing, or the uniaxial results are not very realistic. In this paper, the effect of three different load histories from physiological loading applied on the trabecular bone were studied in order to predict the first failure surface and the fatigue lifetime. The fatigue behaviour of the trabecular bone under uniaxial load was compared to that of multiaxial load using a finite element simulation. The plastic strain was found localized at the trabecular structure under multiaxial load. On average, applying multiaxial loads reduced more than five times the fatigue life of the trabecular bone. The results provide evidence that multiaxial loading is dominated in the low cycle fatigue in contrast to the uniaxial one. Both bone volume fraction and structural model index were best predictors of failure (p < 0.05) in fatigue for both types of loading, whilst uniaxial loading has indicated better values in most cases.

Dependence of Microelastic-plastic Nonlinearity of Martensitic Stainless Steel on Fatigue Damage Accumulation

NASA Technical Reports Server (NTRS)

Cantrell, John H.

2006-01-01

Self-organized substructural arrangements of dislocations formed in wavy slip metals during cyclic stress-induced fatigue produce substantial changes in the material microelastic-plastic nonlinearity, a quantitative measure of which is the nonlinearity parameter Beta extracted from acoustic harmonic generation measurements. The contributions to Beta from the substructural evolution of dislocations and crack growth for fatigued martensitic 410Cb stainless steel are calculated from the Cantrell model as a function of percent full fatigue life to fracture. A wave interaction factor f(sub WI) is introduced into the model to account experimentally for the relative volume of material fatigue damage included in the volume of material swept out by an interrogating acoustic wave. For cyclic stress-controlled loading at 551 MPa and f(sub WI) = 0.013 the model predicts a monotonic increase in Beta from dislocation substructures of almost 100 percent from the virgin state to roughly 95 percent full life. Negligible contributions from cracks are predicted in this range of fatigue life. However, over the last five percent of fatigue life the model predicts a rapid monotonic increase of Beta by several thousand percent that is dominated by crack growth. The theoretical predictions are in good agreement with experimental measurements of 410Cb stainless steel samples fatigued in uniaxial, stress-controlled cyclic loading at 551 MPa from zero to full tensile load with a measured f(sub WI) of 0.013.

Engineering fibrin-based tissue constructs from myofibroblasts and application of constraints and strain to induce cell and collagen reorganization.

PubMed

de Jonge, Nicky; Baaijens, Frank P T; Bouten, Carlijn V C

2013-10-28

Collagen content and organization in developing collagenous tissues can be influenced by local tissue strains and tissue constraint. Tissue engineers aim to use these principles to create tissues with predefined collagen architectures. A full understanding of the exact underlying processes of collagen remodeling to control the final tissue architecture, however, is lacking. In particular, little is known about the (re)orientation of collagen fibers in response to changes in tissue mechanical loading conditions. We developed an in vitro model system, consisting of biaxially-constrained myofibroblast-seeded fibrin constructs, to further elucidate collagen (re)orientation in response to i) reverting biaxial to uniaxial static loading conditions and ii) cyclic uniaxial loading of the biaxially-constrained constructs before and after a change in loading direction, with use of the Flexcell FX4000T loading device. Time-lapse confocal imaging is used to visualize collagen (re)orientation in a nondestructive manner. Cell and collagen organization in the constructs can be visualized in real-time, and an internal reference system allows us to relocate cells and collagen structures for time-lapse analysis. Various aspects of the model system can be adjusted, like cell source or use of healthy and diseased cells. Additives can be used to further elucidate mechanisms underlying collagen remodeling, by for example adding MMPs or blocking integrins. Shape and size of the construct can be easily adapted to specific needs, resulting in a highly tunable model system to study cell and collagen (re)organization.

Empirical Measurements of Biomechanical Anisotropy of the Human Vocal Fold Lamina Propria

PubMed Central

Kelleher, Jordan E.; Siegmund, Thomas; Du, Mindy; Naseri, Elhum; Chan, Roger W.

2013-01-01

The vocal folds are known to be mechanically anisotropic due to the microstructural arrangement of fibrous proteins such as collagen and elastin in the lamina propria. Even though this has been known for many years, the biomechanical anisotropic properties have rarely been experimentally studied. We propose that an indentation procedure can be used with uniaxial tension in order to obtain an estimate of the biomechanical anisotropy within a single specimen. Experiments were performed on the lamina propria of three male and three female human vocal folds dissected from excised larynges. Two experiments were conducted: each specimen was subjected to cyclic uniaxial tensile loading in the longitudinal (i.e. anterior-posterior) direction, and then to cyclic indentation loading in the transverse (i.e. medial-lateral) direction. The indentation experiment was modeled as contact on a transversely isotropic half-space using the Barnett-Lothe tensors. The longitudinal elastic modulus EL was computed from the tensile test, and the transverse elastic modulus ET and longitudinal shear modulus GL were obtained by inverse analysis of the indentation force-displacement response. It was discovered that the average of EL/ET was 14 for the vocal ligament and 39 for the vocal fold cover specimens. Also, the average of EL/GL, a parameter important for models of phonation, was 28 for the vocal ligament and 54 for the vocal fold cover specimens. These measurements of anisotropy could contribute to more accurate models of fundamental frequency regulation and provide potentially better insights into the mechanics of vocal fold vibration. PMID:22886592

Quasi-static and ratcheting properties of trabecular bone under uniaxial and cyclic compression.

PubMed

Gao, Li-Lan; Wei, Chao-Lei; Zhang, Chun-Qiu; Gao, Hong; Yang, Nan; Dong, Li-Min

2017-08-01

The quasi-static and ratcheting properties of trabecular bone were investigated by experiments and theoretical predictions. The creep tests with different stress levels were completed and it is found that both the creep strain and creep compliance increase rapidly at first and then increase slowly as the creep time goes by. With increase of compressive stress the creep strain increases and the creep compliance decreases. The uniaxial compressive tests show that the applied stress rate makes remarkable influence on the compressive behaviors of trabecular bone. The Young's modulus of trabecular bone increases with increase of stress rate. The stress-strain hysteresis loops of trabecular bone under cyclic load change from sparse to dense with increase of number of cycles, which agrees with the change trend of ratcheting strain. The ratcheting strain rate rapidly decreases at first, and then exhibits a relatively stable and small value after 50cycles. Both the ratcheting strain and ratcheting strain rate increase with increase of stress amplitude or with decrease of stress rate. The creep model and the nonlinear viscoelastic constitutive model of trabecular bone were proposed and used to predict its creep property and rate-dependent compressive property. The results show that there are good agreements between the experimental data and predictions. Copyright © 2017 Elsevier B.V. All rights reserved.

Yield Behavior of Solution Treated and Aged Ti-6Al-4V

NASA Technical Reports Server (NTRS)

Ring, Andrew J.; Baker, Eric H.; Salem, Jonathan A.; Thesken, John C.

2014-01-01

Post yield uniaxial tension-compression tests were run on a solution treated and aged (STA), titanium 6-percent aluminum 4-percent vanadium (Ti-6Al-4V) alloy to determine the yield behavior on load reversal. The material exhibits plastic behavior almost immediately on load reversal implying a strong Bauschinger effect. The resultant stress-strain data was compared to a 1D mechanics model and a finite element model used to design a composite overwrapped pressure vessel (COPV). Although the models and experimental data compare well for the initial loading and unloading in the tensile regime, agreement is lost in the compressive regime due to the Bauschinger effect and the assumption of perfect plasticity. The test data presented here are being used to develop more accurate cyclic hardening constitutive models for future finite element design analysis of COPVs.

A comprehensive energy approach to predict fatigue life in CuAlBe shape memory alloy

NASA Astrophysics Data System (ADS)

Sameallah, S.; Legrand, V.; Saint-Sulpice, L.; Kadkhodaei, M.; Arbab Chirani, S.

2015-02-01

Stabilized dissipated energy is an effective parameter on the fatigue life of shape memory alloys (SMAs). In this study, a formula is proposed to directly evaluate the stabilized dissipated energy for different values of the maximum and minimum applied stresses, as well as the loading frequency, under cyclic tensile loadings. To this aim, a one-dimensional fully coupled thermomechanical constitutive model and a cycle-dependent phase diagram are employed to predict the uniaxial stress-strain response of an SMA in a specified cycle, including the stabilized one, with no need of obtaining the responses of the previous cycles. An enhanced phase diagram in which different slopes are defined for the start and finish of a backward transformation strip is also proposed to enable the capture of gradual transformations in a CuAlBe shape memory alloy. It is shown that the present approach is capable of reproducing the experimental responses of CuAlBe specimens under cyclic tensile loadings. An explicit formula is further presented to predict the fatigue life of CuAlBe as a function of the maximum and minimum applied stresses as well as the loading frequency. Fatigue tests are also carried out, and this formula is verified against the empirically predicted number of cycles for failure.

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

Kang, Guozheng, E-mail: guozhengkang@home.swjtu.edu.cn; Dong, Yawei; Liu, Yujie

The uniaxial ratchetting of Ti–6Al–4V alloy with two phases (i.e., primary hexagonal close packed (HCP) α and secondary body-centered cubic (BCC) β phases) was investigated by macroscopic and microscopic experiments at room temperature. Firstly, the effects of cyclic softening/hardening feature, applied mean stress and stress amplitude on the uniaxial ratchetting of the alloy were discussed. The macroscopic investigation of Ti–6Al–4V alloy presents obvious strain-amplitude-dependent cyclic softening, as well as a three-staged evolution curve with regard to the ratchetting strain rate. The ratchetting depends greatly on the applied mean stress and stress amplitude while the ratchetting strain increases with the increasingmore » applied mean stress and stress amplitude. Then, the evolution of dislocation patterns and deformation twinning during the uniaxial ratchetting of two-phase Ti–6Al–4V alloy were observed using transmission electron microscopy (TEM). The microscopic observation shows that deformation twinning occurs in the primary α phase and its amount increases gradually during the uniaxial ratchetting. Simultaneously, the planar dislocation evolves from discrete lines to some dislocation nets and parallel lines with the increasing number of cycles. The deformation twinning in the primary α phase is one of main contributions to the uniaxial ratchetting of Ti–6Al–4V alloy, and should be considered in the construction of corresponding constitutive model. - Highlights: • A three-staged ratchetting occurs in the stress-controlled cyclic tests of Ti–6Al–4V alloy. • Dislocation patterns change from discrete lines to nets and parallel lines. • Deformation twinning occurs during the uniaxial ratchetting. • Both dislocation slipping and twinning are the causes of ratchetting.« less

Constitutive modeling for isotropic materials (HOST)

NASA Technical Reports Server (NTRS)

Lindholm, Ulric S.; Chan, Kwai S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.

1984-01-01

The results of the first year of work on a program to validate unified constitutive models for isotropic materials utilized in high temperature regions of gas turbine engines and to demonstrate their usefulness in computing stress-strain-time-temperature histories in complex three-dimensional structural components. The unified theories combine all inelastic strain-rate components in a single term avoiding, for example, treating plasticity and creep as separate response phenomena. An extensive review of existing unified theories is given and numerical methods for integrating these stiff time-temperature-dependent constitutive equations are discussed. Two particular models, those developed by Bodner and Partom and by Walker, were selected for more detailed development and evaluation against experimental tensile, creep and cyclic strain tests on specimens of a cast nickel base alloy, B19000+Hf. Initial results comparing computed and test results for tensile and cyclic straining for temperature from ambient to 982 C and strain rates from 10(exp-7) 10(exp-3) s(exp-1) are given. Some preliminary date correlations are presented also for highly non-proportional biaxial loading which demonstrate an increase in biaxial cyclic hardening rate over uniaxial or proportional loading conditions. Initial work has begun on the implementation of both constitutive models in the MARC finite element computer code.

The Microstructure Evolution and Deformation Behavior of AZ80 During Gradient Increment Cyclic Loading

NASA Astrophysics Data System (ADS)

Ren, Lingbao; Quan, Gaofeng; Boehlert, Carl J.; Zhou, Mingyang; Guo, Yangyang; Fan, Lingling

2018-06-01

Cyclic loading-unloading uniaxial tension experiments were conducted at temperatures ranging between 293 K and 623 K and a strain rate of 10-3 s-1 to study the cyclic accumulated plastic deformation (CAP) behavior of extruded AZ80. The 673 K/4-h heat treatment to the as-extruded AZ80 led to a noticeable decrease in yield strength which was associated with both dissolution of the β-Mg17Al12 phase and growth of the matrix grain size. The critical number of cycles needed to soften the material (N c) decreased from 5 to 4 when the cyclic strain amplitude (ɛ a) increased from 3.3 to 5.0 pct for the as-extruded AZ80. The average cyclic hardening rate (Θ) increased from 11 to 23 MPa/cycle after heat treatment, and this was attributed to the more pronounced twinning process in the coarse-grained microstructure. During the 293 K to 473 K CAP deformation, the increasing accumulated cyclic tension strain may have accelerated the propagation of secondary twinning leading to the Lüders-like post-yield softening. Twinning was prevalent at low temperature (293 K to 473 K) in the ɛ a = 3.0 pct CAP deformation for the heat-treated alloy, and twin-assisted precipitation occurred during the 523 K CAP deformation, which implied that the high diffusivity in the twin boundary accelerated the heterogeneous nucleation of precipitates. The preferred cracking locations changed from twin boundaries to grain boundaries when the CAP deformation temperature increased from 473 K to 523 K. As for the 623 K CAP deformation, cavities initiated at the grain boundaries, and the volume fraction of the cracks/cavities increased from 0.01 to 0.05 with increasing temperature.

Evaluation of composite flattened tubular specimen. [fatigue tests

NASA Technical Reports Server (NTRS)

Liber, T.; Daniel, I. M.

1978-01-01

Flattened tubular specimens of graphite/epoxy, S-glass/epoxy, Kevlar-49/epoxy, and graphite/S-glass/epoxy hybrid materials were evaluated under static and cyclic uniaxial tensile loading and compared directly with flat coupon data of the same materials generated under corresponding loading conditions. Additional development for the refinement of the flattened specimen configuration and fabrication was required. Statically tested graphite/epoxy, S-glass/epoxy, and Kevlar 49/epoxy flattened tube specimens exhibit somewhat higher average strengths than their corresponding flat coupons. Flattened tube specimens of the graphite/S-glass/epoxy hybrid and the graphite/epoxy flattened tube specimens failed in parasitic modes with consequential lower strength than the corresponding flat coupons. Fatigue tested flattened tube specimens failed in parasitic modes resulting in lower fatigue strengths than the corresponding flat coupons.

Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

DOE PAGES

Hennessey, Conor; Castelluccio, Gustavo M.; McDowell, David L.

2017-02-01

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT)more » within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

Sensitivity of polycrystal plasticity to slip system kinematic hardening laws for Al 7075-T6

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

Hennessey, Conor; Castelluccio, Gustavo M.; McDowell, David L.

The prediction of formation and early growth of microstructurally small fatigue cracks requires use of constitutive models that accurately estimate local states of stress, strain, and cyclic plastic strain. However, few research efforts have attempted to systematically consider the sensitivity of overall cyclic stress-strain hysteresis and higher order mean stress relaxation and plastic strain ratcheting responses introduced by the slip system back-stress formulation in crystal plasticity, even for face centered cubic (FCC) crystal systems. This paper explores the performance of two slip system level kinematic hardening models using a finite element crystal plasticity implementation as a User Material Subroutine (UMAT)more » within ABAQUS, with fully implicit numerical integration. The two kinematic hardening formulations aim to reproduce the cyclic deformation of polycrystalline Al 7075-T6 in terms of both macroscopic cyclic stress-strain hysteresis loop shape, as well as ratcheting and mean stress relaxation under strain- or stress-controlled loading with mean strain or stress, respectively. The first formulation is an Armstrong-Frederick type hardening-dynamic recovery law for evolution of the back stress. This approach is capable of reproducing observed deformation under completely reversed uniaxial loading conditions, but overpredicts the rate of cyclic ratcheting and associated mean stress relaxation. The second formulation corresponds to a multiple back stress Ohno-Wang type hardening law with nonlinear dynamic recovery. The adoption of this back stress evolution law greatly improves the capability to model experimental results for polycrystalline specimens subjected to cycling with mean stress or strain. As a result, the relation of such nonlinear dynamic recovery effects are related to slip system interactions with dislocation substructures.« less

Effects of stress fiber contractility on uniaxial stretch guiding mitosis orientation and stress fiber alignment.

PubMed

Zhao, Lei; Sang, Chen; Yang, Chun; Zhuang, Fengyuan

2011-09-02

It has been documented that mitosis orientation (MO) is guided by stress fibers (SFs), which are perpendicular to exogenous cyclic uniaxial stretch. However, the effect of mechanical forces on MO and the mechanism of stretch-induced SFs reorientation are not well elucidated to date. In the present study, we used murine 3T3 fibroblasts as a model, to investigate the effects of uniaxial stretch on SFO and MO utilizing custom-made stretch device. We found that cyclic uniaxial stretch induced both SFs and mitosis directions orienting perpendicularly to the stretch direction. The F-actin and myosin II blockages, which resulted in disoriented SFs and mitosis directions under uniaxial stretch, suggested a high correlation between SFO and MO. Y27632 (10 μM), ML7 (50 μM, or 75 μM), and blebbistatin (50 μM, or 75 μM) treatments resulted in SFO parallel to the principle stretch direction. Upon stimulating and inhibiting the phosphorylation of myosin light chain (p-MLC), we observed a monotonic proportion of SFO to the level of p-MLC. These results suggested that the level of cell contraction is crucial to the response of SFs, either perpendicular or parallel, to the external stretch. Showing the possible role of cell contractility in tuning SFO under external stretch, our experimental data are valuable to understand the predominant factor controlling SFO response to exogenous uniaxial stretch, and thus helpful for improving mechanical models. Copyright © 2011 Elsevier Ltd. All rights reserved.

Nanoparticle amount, and not size, determines chain alignment and nonlinear hardening in polymer nanocomposites

PubMed Central

Varol, H. Samet; Meng, Fanlong; Hosseinkhani, Babak; Malm, Christian; Bonn, Daniel; Bonn, Mischa; Zaccone, Alessio

2017-01-01

Polymer nanocomposites—materials in which a polymer matrix is blended with nanoparticles (or fillers)—strengthen under sufficiently large strains. Such strain hardening is critical to their function, especially for materials that bear large cyclic loads such as car tires or bearing sealants. Although the reinforcement (i.e., the increase in the linear elasticity) by the addition of filler particles is phenomenologically understood, considerably less is known about strain hardening (the nonlinear elasticity). Here, we elucidate the molecular origin of strain hardening using uniaxial tensile loading, microspectroscopy of polymer chain alignment, and theory. The strain-hardening behavior and chain alignment are found to depend on the volume fraction, but not on the size of nanofillers. This contrasts with reinforcement, which depends on both volume fraction and size of nanofillers, potentially allowing linear and nonlinear elasticity of nanocomposites to be tuned independently. PMID:28377517

Modeling of long-term fatigue damage of soft tissue with stress softening and permanent set effects

PubMed Central

Martin, Caitlin; Sun, Wei

2012-01-01

One of the major failure modes of bioprosthetic heart valves is non-calcific structural deterioration due to fatigue of the tissue leaflets. Experimental methods to characterize tissue fatigue properties are complex and time-consuming. A constitutive fatigue model that could be calibrated by isolated material tests would be ideal for investigating the effects of more complex loading conditions. However, there is a lack of tissue fatigue damage models in the literature. To address these limitations, in this study, a phenomenological constitutive model was developed to describe the stress softening and permanent set effects of tissue subjected to long-term cyclic loading. The model was used to capture characteristic uniaxial fatigue data for glutaraldehyde-treated bovine pericardium and was then implemented into finite element software. The simulated fatigue response agreed well with the experimental data and thus demonstrates feasibility of this approach. PMID:22945802

Properties of a Ni(sub 19.5)Pd(sub 30)Ti(sub 50.5) high-temperature shape memory alloy in tension and compression

NASA Technical Reports Server (NTRS)

Noebe, Ronald; Padula, Santo, II; Bigelow, Glen; Rios, Orlando; Garg, Anita; Lerch, Brad

2006-01-01

Potential applications involving high-temperature shape memory alloys have been growing in recent years. Even in those cases where promising new alloys have been identified, the knowledge base for such materials contains gaps crucial to their maturation and implementation in actuator and other applications. We begin to address this issue by characterizing the mechanical behavior of a Ni19.5Pd30Ti50.5 high-temperature shape memory alloy in both uniaxial tension and compression at various temperatures. Differences in the isothermal uniaxial deformation behavior were most notable at test temperatures below the martensite finish temperature. The elastic modulus of the material was very dependent on strain level; therefore, dynamic Young#s Modulus was determined as a function of temperature by an impulse excitation technique. More importantly, the performance of a thermally activated actuator material is dependent on the work output of the alloy. Consequently, the strain-temperature response of the Ni19.5Pd30Ti50.5 alloy under various loads was determined in both tension and compression and the specific work output calculated and compared in both loading conditions. It was found that the transformation strain and thus, the specific work output were similar regardless of the loading condition. Also, in both tension and compression, the strain-temperature loops determined under constant load conditions did not close due to the fact that the transformation strain during cooling was always larger than the transformation strain during heating. This was apparently the result of permanent plastic deformation of the martensite phase with each cycle. Consequently, before this alloy can be used under cyclic actuation conditions, modification of the microstructure or composition would be required to increase the resistance of the alloy to plastic deformation by slip.

Fate of tenogenic differentiation potential of human bone marrow stromal cells by uniaxial stretching affected by stretch-activated calcium channel agonist gadolinium

PubMed Central

Balaji Raghavendran, Hanumantha Rao; Pingguan-Murphy, Belinda; Abbas, Azlina A.; Merican, Azhar M.; Kamarul, Tunku

2017-01-01

The role for mechanical stimulation in the control of cell fate has been previously proposed, suggesting that there may be a role of mechanical conditioning in directing mesenchymal stromal cells (MSCs) towards specific lineage for tissue engineering applications. Although previous studies have reported that calcium signalling is involved in regulating many cellular processes in many cell types, its role in managing cellular responses to tensile loading (mechanotransduction) of MSCs has not been fully elucidated. In order to establish this, we disrupted calcium signalling by blocking stretch-activated calcium channel (SACC) in human MSCs (hMSCs) in vitro. Passaged-2 hMSCs were exposed to cyclic tensile loading (1 Hz + 8% for 6, 24, 48, and 72 hours) in the presence of the SACC blocker, gadolinium. Analyses include image observations of immunochemistry and immunofluorescence staining from extracellular matrix (ECM) production, and measuring related tenogenic and apoptosis gene marker expression. Uniaxial tensile loading increased the expression of tenogenic markers and ECM production. However, exposure to strain in the presence of 20 μM gadolinium reduced the induction of almost all tenogenic markers and ECM staining, suggesting that SACC acts as a mechanosensor in strain-induced hMSC tenogenic differentiation process. Although cell death was observed in prolonged stretching, it did not appear to be apoptosis mediated. In conclusion, the knowledge gained in this study by elucidating the role of calcium in MSC mechanotransduction processes, and that in prolonged stretching results in non-apoptosis mediated cell death may be potential useful for regenerative medicine applications. PMID:28654695

Time- and temperature-dependent failures of a bonded joint

NASA Astrophysics Data System (ADS)

Sihn, Sangwook

This dissertation summarizes my study of time- and temperature-dependent behavior of a tubular lap bonded joint to provide a design methodology for windmill blade structures. The bonded joint is between a cast-iron rod and a GFRP composite pipe. The adhesive material is an epoxy containing chopped glass fibers. We proposed a new fabrication method to make concentric and void-less specimens of the tubular joint with a thick adhesive bondline to stimulate the root bond of a blade. The thick bondline facilitates the joint assembly of actual blades. For a better understanding of the behavior of the bonded joint, we studied viscoelastic behavior of the adhesive materials by measuring creep compliance at several temperatures during loading period. We observed that the creep compliance depends highly on the period of loading and the temperature. We applied time-temperature equivalence to the creep compliance of the adhesive material to obtain time-temperature shift factors. We also performed constant-rate of monotonically increased uniaxial tensile tests to measure static strength of the tubular lap joint at several temperatures and different strain-rates. We observed two failure modes from load-deflection curves and failed specimens. One is the brittle mode, which was caused by weakness of the interfacial strength occurring at low temperature and short period of loading. The other is the ductile mode, which was caused by weakness of the adhesive material at high temperature and long period of loading. Transition from the brittle to the ductile mode appeared as the temperature or the loading period increased. We also performed tests under uniaxial tensile-tensile cyclic loadings to measure fatigue strength of the bonded joint at several temperatures, frequencies and stress ratios. The fatigue data are analyzed statistically by applying the residual strength degradation model to calculate statistical distribution of the fatigue life. Combining the time-temperature equivalence and the residual strength degradation model enables us to estimate the fatigue life of the bonded joint at different load levels, frequencies and temperatures with a certain probability. A numerical example shows how to apply the life estimation method to a structure subjected to a random load history by rainflow cycle counting.

Mechanical characterization of human mesenchymal stem cells subjected to cyclic uniaxial strain and TGF-β1.

PubMed

Khani, Mohammad-Mehdi; Tafazzoli-Shadpour, Mohammad; Goli-Malekabadi, Zahra; Haghighipour, Nooshin

2015-03-01

Human mesenchymal stem cells (hMSCs) have shown promising potential in the field of regenerative medicine particularly in vascular tissue engineering. Optimal growing of MSCs into specific lineage requires a thorough understanding of the role of mechanobiology in MSC metabolism. Although effects of external physical cues (mechanical stimuli through external loading and scaffold properties) on regulation of MSC differentiation into Smooth muscle (SM) lineage have attracted widespread attention, fewer studies are available on mechanical characterization of single engineered MSCs which is vital in tissue development through proper mechanotransductive cell-environment interactions. In this study, we investigated effects of uniaxial tensile strain and transforming growth factor-β1 (TGF-β1) stimulations on mechanical properties of engineered MSCs and their F-actin cytoskeleton organization. Micropipette aspiration technique was used to measure mechanical properties of MSCs including mean Young׳s modulus (E) and the parameters of standard linear viscoelastic model. Compared to control samples, MSCs treated by uniaxial strain either with or without TGF-β1 indicated significant increases in E value and considerable drop in creep compliance curve, while samples treated by TGF-β1 alone met significant decreases in E value and considerable rise in creep compliance curve. Among treated samples, uniaxial tensile strain accompanied by TGF-β1 stimulation not only caused higher stimulation in MSC differentiation towards SM phenotype at transcriptional level, but also created more structural integrity in MSCs due to formation of thick bundled F-actin fibers. Results can be applied in engineering of MSCs towards functional target cells and consequently tissue development. Copyright © 2014 Elsevier Ltd. All rights reserved.

Proof test criteria for thin-walled 2219 aluminum pressure vessels. Volume 1: Program summary and data analysis

NASA Technical Reports Server (NTRS)

Finger, R. W.

1976-01-01

This experimental program was undertaken to investigate the crack growth behavior of deep surface flaws in 2219 aluminum. The program included tests of uniaxially loaded surface flaw and center crack panels at temperatures ranging from 20K (-423 F) to ambient. The tests were conducted on both the base metal and as-welded weld metal material. The program was designed to provide data on the mechanisms of failure by ligament penetration, and the residual cyclic life, after proof-testing, of a vessel which has been subjected to incipient penetration by the proof test. The results were compared and analyzed with previously developed data to develop guidelines for the proof testing of thin walled 2219 pressure vessels.

Flexor Tendon Repair With Looped Suture: 1 Versus 2 Knots.

PubMed

Gil, Joseph A; Skjong, Christian; Katarincic, Julia A; Got, Christopher

2016-03-01

To assess the strength of flexor tendon repair with looped suture. We hypothesized that, after passing the intact looped suture in the desired repair configuration, splitting the loop and tying 2 independent knots would increase the strength of flexor tendon repair. Thirty-two flexor tendons were harvested and were sharply transected in zone II. The tendons were repaired with a 4-strand core suture repair using 3-0 looped nonabsorbable nylon suture. The harvested tendons were randomly assigned and repaired with either a 1- or a 2-knot construct. The repaired flexor tendons were fixed in a servohydraulic material testing system and were loaded to failure either with uniaxial tension or cyclically. The average force at failure was 43 N for the 1-knot repair and 28 N for the 2-knot repair. The mode of failure of 15 of the flexor tendon repairs that were cyclically loaded to failure was suture pull-out. The average number of cycles and force in cyclic testing that caused failure of flexor tendon repairs was 134 cycles and 31 N for tendons repaired with looped 3-0 suture tied with 1 knot and 94 cycles and 33 N for tendons repaired with looped 3-0 suture tied with 2 knots. Our hypothesis was disproved by the results of this study. This study suggests that, when using looped suture, tying 2 independent knots instead of tying a single knot does not increase the strength of the flexor tendon repair. Copyright © 2016 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Constitutive modeling for isotropic materials (HOST)

NASA Technical Reports Server (NTRS)

Lindholm, U. S.; Chan, K. S.; Bodner, S. R.; Weber, R. M.; Walker, K. P.; Cassenti, B. N.

1985-01-01

This report presents the results of the second year of work on a problem which is part of the NASA HOST Program. Its goals are: (1) to develop and validate unified constitutive models for isotropic materials, and (2) to demonstrate their usefulness for structural analyses of hot section components of gas turbine engines. The unified models selected for development and evaluation are that of Bodner-Partom and Walker. For model evaluation purposes, a large constitutive data base is generated for a B1900 + Hf alloy by performing uniaxial tensile, creep, cyclic, stress relation, and thermomechanical fatigue (TMF) tests as well as biaxial (tension/torsion) tests under proportional and nonproportional loading over a wide range of strain rates and temperatures. Systematic approaches for evaluating material constants from a small subset of the data base are developed. Correlations of the uniaxial and biaxial tests data with the theories of Bodner-Partom and Walker are performed to establish the accuracy, range of applicability, and integability of the models. Both models are implemented in the MARC finite element computer code and used for TMF analyses. Benchmark notch round experiments are conducted and the results compared with finite-element analyses using the MARC code and the Walker model.

Thermal effects on the enhanced ductility in non-monotonic uniaxial tension of DP780 steel sheet

NASA Astrophysics Data System (ADS)

Majidi, Omid; Barlat, Frederic; Korkolis, Yannis P.; Fu, Jiawei; Lee, Myoung-Gyu

2016-11-01

To understand the material behavior during non-monotonic loading, uniaxial tension tests were conducted in three modes, namely, the monotonic loading, loading with periodic relaxation and periodic loading-unloadingreloading, at different strain rates (0.001/s to 0.01/s). In this study, the temperature gradient developing during each test and its contribution to increasing the apparent ductility of DP780 steel sheets were considered. In order to assess the influence of temperature, isothermal uniaxial tension tests were also performed at three temperatures (298 K, 313 K and 328 K (25 °C, 40 °C and 55 °C)). A digital image correlation system coupled with an infrared thermography was used in the experiments. The results show that the non-monotonic loading modes increased the apparent ductility of the specimens. It was observed that compared with the monotonic loading, the temperature gradient became more uniform when a non-monotonic loading was applied.

Modeling the mechanical response of PBX 9501

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

Ragaswamy, Partha; Lewis, Matthew W; Liu, Cheng

2010-01-01

An engineering overview of the mechanical response of Plastic-Bonded eXplosives (PBXs), specifically PBX 9501, will be provided with emphasis on observed mechanisms associated with different types of mechanical testing. Mechanical tests in the form of uniaxial tension, compression, cyclic loading, creep (compression and tension), and Hopkinson bar show strain rate and temperature dependence. A range of mechanical behavior is observed which includes small strain recoverable response in the form of viscoelasticity; change in stiffness and softening beyond peak strength due to damage in the form microcracks, debonding, void formation and the growth of existing voids; inelastic response in the formmore » of irrecoverable strain as shown in cyclic tests, and viscoelastic creep combined with plastic response as demonstrated in creep and recovery tests. The main focus of this paper is to elucidate the challenges and issues involved in modeling the mechanical behavior of PBXs for simulating thermo-mechanical responses in engineering components. Examples of validation of a constitutive material model based on a few of the observed mechanisms will be demonstrated against three point bending, split Hopkinson pressure bar and Brazilian disk geometry.« less

Modeling the viscoplastic behavior of Inconel 718 at 1200 F

NASA Technical Reports Server (NTRS)

Abdel-Kader, M. S.; Eftis, J.; Jones, D. L.

1988-01-01

A large number of tests, including tensile, creep, fatigue, and creep-fatigue were performed to characterize the mechanical properties of Inconel 718 (a nickel based superalloy) at 1200 F, the operating temperature for turbine blades. In addition, a few attempts were made to model the behavior of Inconel 718 at 1200 F using viscoplastic theories. The Chaboche theory of viscoplasticity can model a wide variety of mechanical behavior, including monotonic, sustained, and cyclic responses of homogeneous, initially-isotropic, strain hardening (or softening) materials. It is shown how the Chaboche theory can be used to model the viscoplastic behavior of Inconel 718 at 1200 F. First, an algorithm was developed to systematically determine the material parameters of the Chaboche theory from uniaxial tensile, creep, and cyclic data. The algorithm is general and can be used in conjunction with similar high temperature materials. A sensitivity study was then performed and an optimal set of Chaboche's parameters were obtained. This study has also indicated the role of each parameter in modeling the response to different loading conditions.

Law of damage accumulation and fracture criteria in highly filled polymer materials

NASA Astrophysics Data System (ADS)

Bykov, D. L.; Kazakov, A. V.; Konovalov, D. N.; Mel'nikov, V. P.; Milyokhin, Yu. M.; Peleshko, V. A.; Sadovnichii, D. N.

2014-09-01

We present the results of a large series of experiments aimed at the study of laws of damage accumulation and fracture in highly filled polymer materials under loading conditions of various types: monotone, repeated, low- and high-cycle, with varying type of stress state, dynamic (in general, more than 50 programs implemented on specimens from one lot of material). The data obtained in these test allow one to make conclusions about the constitutive role of the attained maximum of strain intensity when estimating the accumulated damage in the process of uniaxial tension by various programs (in particular, an additional cyclic deformation below the preliminary attained strain maximum does not affect the limit values of strain and stress in the subsequent active extension), about the strong influence of the stress state on the deformation and fracture, about the specific features of the nonlinear behavior of the material under the shock loading conditions and its influence on the repeated deformation. All tests are described (with an accuracy acceptable in practical calculations, both with respect to stresses and strains in the process of loading and at the moment of fracture) in the framework of the same model of nonlinear viscoelasticity with the same set of constants. The constants of the proposed model are calculated according to a relatively simple algorithm by using the results of standard uniaxial tension tests with constant values of the strain rate and hydrostatic pressure (each test for 2-3 levels of these parameters chosen from the ranges proposed in applications, each loading lasts until the fracture occurs, and one of the tests contains an intermediate interval of total loading and repeated loading) and one axial shock compression test if there are dynamic problems in the applications. The model is based on the use of the criterion fracture parameter which, in the class of proportional loading processes, is the sum of partial increments of the strain intensity on active segments of the process (where the strain intensity is at its historical maximum) with the form of the stress state and the intensity of strain rates taken into account.

Failure of composite plates under static biaxial planar loading

NASA Technical Reports Server (NTRS)

Waas, Anthony M.; Khamseh, Amir R.

1992-01-01

The project involved detailed investigations into the failure mechanisms in composite plates as a function of hole size (holes centrally located in the plates) under static loading. There were two phases to the project, the first dealing with uniaxial loads along the fiber direction, and the second dealing with coplanar biaxial loading. Results for the uniaxial tests have been reported and published previously, thus this report will place emphasis on the second phase of the project, namely the biaxial tests. The composite plates used in the biaxial loading experiments, as well as the uniaxial, were composed of a single ply unidirectional graphite/epoxy prepreg sandwiched between two layers of transparent thermoplastic. This setup enabled us to examine the failure initiation and propagation modes nondestructively, during the test. Currently, similar tests and analysis of results are in progress for graphite/epoxy cruciform shaped flat laminates. The results obtained from these tests will be available at a later time.

Mullins effect in a filled elastomer under uniaxial tension

DOE PAGES

Maiti, A.; Small, W.; Gee, R. H.; ...

2014-01-16

Modulus softening and permanent set in filled polymeric materials due to cyclic loading and unloading, commonly known as the Mullins effect, can have a significant impact on their use as support cushions. The quantitative analysis of such behavior is essential to ensure the effectiveness of such materials in long-term deployment. In this work we combine existing ideas of filler-induced modulus enhancement, strain amplification, and irreversible deformation within a simple non-Gaussian constitutive model to quantitatively interpret recent measurements on a relevant PDMS-based elastomeric cushion. Also, we find that the experimental stress-strain data is consistent with the picture that during stretching (loading)more » two effects take place simultaneously: (1) the physical constraints (entanglements) initially present in the polymer network get disentangled, thus leading to a gradual decrease in the effective cross-link density, and (2) the effective filler volume fraction gradually decreases with increasing strain due to the irreversible pulling out of an initially occluded volume of the soft polymer domain.« less

3D printed hierarchical honeycombs with shape integrity under large compressive deformations

DOE PAGES

Chen, Yanyu; Li, Tiantian; Jia, Zian; ...

2017-10-12

Here, we describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shapemore » integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment.« less

3D printed hierarchical honeycombs with shape integrity under large compressive deformations

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

Chen, Yanyu; Li, Tiantian; Jia, Zian

Here, we describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shapemore » integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment.« less

Uniaxial cyclic strain enhances adipose-derived stem cell fusion with skeletal myocytes

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

Andersen, Jens Isak; Juhl, Morten; Nielsen, Thøger

2014-07-25

Highlights: • Uniaxial cyclic tensile strain (CTS) applied to ASCs alone or in coculture with myogenic precursors. • CTS promoted the formation of a highly ordered array of parallel ASCs. • Without biochemical supplements, CTS did not support advanced myogenic differentiation of ASCs. • Mechanical stimulation of cocultures boosted fusion of ASCs with skeletal myoblasts. - Abstract: Although adult muscle tissue possesses an exceptional capacity for regeneration, in the case of large defects, the restoration to original state is not possible. A well-known source for the de novo regeneration is the adipose-derived stem cells (ASCs), which can be readily isolatedmore » and have been shown to have a broad differentiation and regenerative potential. In this work, we employed uniaxial cyclic tensile strain (CTS), to mechanically stimulate human ASCs to participate in the formation skeletal myotubes in an in vitro model of myogenesis. The application of CTS for 48 h resulted in the formation of a highly ordered array of parallel ASCs, but failed to support skeletal muscle terminal differentiation. When the same stimulation paradigm was applied to cocultures with mouse skeletal muscle myoblasts, the percentage of ASCs contributing to the formation of myotubes significantly exceeded the levels reported in the literature hitherto. In perspective, the mechanical strain may be used to increase the efficiency of incorporation of ASCs in the skeletal muscles, which could be found useful in diverse traumatic or pathologic scenarios.« less

Nonlinear finite element simulation of non-local tension softening for high strength steel material

NASA Astrophysics Data System (ADS)

Tong, F. M.

The capability of current finite element softwares in simulating the stress-strain relation beyond the elastic-plastic region has been limited by the inability for non- positivity in the computational finite elements' stiffness matrixes. Although analysis up to the peak stress has been proved adequate for analysis and design, it provides no indication of the possible failure predicament that is to follow. Therefore an attempt was made to develop a modelling technique capable of capturing the complete stress-deformation response in an analysis beyond the limit point. This proposed model characterizes a cyclic loading and unloading procedure, as observed in a typical laboratory uniaxial cyclic test, along with a series of material properties updates. The Voce equation and a polynomial function were proposed to define the monotonic elastoplastic hardening and softening behaviour respectively. A modified form of the Voce equation was used to capture the reloading response in the softening region. To accommodate the reduced load capacity of the material at each subsequent softening point, an optimization macro was written to control this optimum load at which the material could withstand. This preliminary study has ignored geometrical effect and is thus incapable of capturing the localized necking phenomenon that accompanies many ductile materials. The current softening model is sufficient if a global measure is considered. Several validation cases were performed to investigate the feasibility of the modelling technique and the results have been proved satisfactory. The ANSYS finite element software is used as the platform at which the modelling technique operates.

Experimental observations on uniaxial whole-life transformation ratchetting and low-cycle stress fatigue of super-elastic NiTi shape memory alloy micro-tubes

NASA Astrophysics Data System (ADS)

Song, Di; Kang, Guozheng; Kan, Qianhua; Yu, Chao; Zhang, Chuanzeng

2015-07-01

In this work, the low-cycle fatigue failure of super-elastic NiTi shape memory alloy micro-tubes with a wall thickness of 150 μm is investigated by uniaxial stress-controlled cyclic tests at human body temperature 310 K. The effects of mean stress, peak stress, and stress amplitude on the uniaxial whole-life transformation ratchetting and fatigue failure of the NiTi alloy are observed. It is concluded that the fatigue life depends significantly on the stress levels, and the extent of martensite transformation and its reverse play an important role in determining the fatigue life. High peak stress or complete martensite transformation shortens the fatigue life.

Experimental characterization of composites. [load test methods

NASA Technical Reports Server (NTRS)

Bert, C. W.

1975-01-01

The experimental characterization for composite materials is generally more complicated than for ordinary homogeneous, isotropic materials because composites behave in a much more complex fashion, due to macroscopic anisotropic effects and lamination effects. Problems concerning the static uniaxial tension test for composite materials are considered along with approaches for conducting static uniaxial compression tests and static uniaxial bending tests. Studies of static shear properties are discussed, taking into account in-plane shear, twisting shear, and thickness shear. Attention is given to static multiaxial loading, systematized experimental programs for the complete characterization of static properties, and dynamic properties.

Geomechanical rock properties of a basaltic volcano

NASA Astrophysics Data System (ADS)

Schaefer, Lauren; Kendrick, Jackie; Lavallée, Yan; Oommen, Thomas; Chigna, Gustavo

2015-06-01

In volcanic regions, reliable estimates of mechanical properties for specific volcanic events such as cyclic inflation-deflation cycles by magmatic intrusions, thermal stressing, and high temperatures are crucial for building accurate models of volcanic phenomena. This study focuses on the challenge of characterizing volcanic materials for the numerical analyses of such events. To do this, we evaluated the physical (porosity, permeability) and mechanical (strength) properties of basaltic rocks at Pacaya Volcano (Guatemala) through a variety of laboratory experiments, including: room temperature, high temperature (935 °C), and cyclically-loaded uniaxial compressive strength tests on as-collected and thermally-treated rock samples. Knowledge of the material response to such varied stressing conditions is necessary to analyze potential hazards at Pacaya, whose persistent activity has led to 13 evacuations of towns near the volcano since 1987. The rocks show a non-linear relationship between permeability and porosity, which relates to the importance of the crack network connecting the vesicles in these rocks. Here we show that strength not only decreases with porosity and permeability, but also with prolonged stressing (i.e., at lower strain rates) and upon cooling. Complimentary tests in which cyclic episodes of thermal or load stressing showed no systematic weakening of the material on the scale of our experiments. Most importantly, we show the extremely heterogeneous nature of volcanic edifices that arise from differences in porosity and permeability of the local lithologies, the limited lateral extent of lava flows, and the scars of previous collapse events. Input of these process-specific rock behaviors into slope stability and deformation models can change the resultant hazard analysis. We anticipate that an increased parameterization of rock properties will improve mitigation power.

The Microstructural Response of Granular Soil Under Uniaxial Strain

DTIC Science & Technology

1993-10-01

under uniaxial strains of up to 10 percent. The material tested was a poorly graded ottowa sand with specimens consisting of either 0.5- or 0.75-mm...microstructural effects in granular material under uniaxial strain of up to 10.0 percent. The relative influence of several microstructural effects (such as...uniaxial strain. The confinement vessel consisted of a base plate, four walls, and a loading cap. The sidewalls extended up beyond the specimen and served

Mechanics of instability-related delimination growth

NASA Technical Reports Server (NTRS)

Whitcomb, John D.

1988-01-01

Local buckling of a delaminated group of plies can lead to higher interlaminar stresses and delamination growth. The mechanics of instability-related delamination growth (IRDG) had been described previously for the through-width delamination. This paper describes the mechanics of IRDG for the embedded delamination subjected to either uniaxial or axisymmetric loads. The mechanics of IRDG are used to explain the dramatic differences in strain-energy release rates observed for the through-width, the axisymmetrically loaded embedded delamination, and the uniaxially loaded embedded delamination.

Improved Design Formulae for Buckling of Orthotropic Plates under Combined Loading

NASA Technical Reports Server (NTRS)

Weaver, Paul M.; Nemeth, Michael P.

2008-01-01

Simple, accurate buckling interaction formulae are presented for long orthotropic plates with either simply supported or clamped longitudinal edges and under combined loading that are suitable for design studies. The loads include 1) combined uniaxial compression (or tension) and shear, 2) combined pure inplane bending and 3) shear and combined uniaxial compression (or tension) and pure inplane bending. The interaction formulae are the results of detailed regression analysis of buckling data obtained from a very accurate Rayleigh-Ritz method.

Mechanical characterization of a short fiber-reinforced polymer at room temperature: experimental setups evaluated by an optical measurement system

NASA Astrophysics Data System (ADS)

Röhrig, C.; Scheffer, T.; Diebels, S.

2017-09-01

Composite materials are of great interest for industrial applications because of their outstanding properties. Each composite material has its own characteristics due to the large number of possible combinations of matrix and filler. As a result of their compounding, composites usually show a complex material behavior. This work is focused on the experimental testing of a short fiber-reinforced thermoplastic composite at room temperature. The characteristic behavior of this material class is often based on a superposition of typical material effects. The predicted characteristic material properties such as elasto-plasticity, damage and anisotropy of the investigated material are obtained from results of cyclic uniaxial tensile tests at constant strain rate. Concerning the manufacturing process as well as industrial applications, the experimental investigations are extended to multiaxial loading situations. Therefore, the composite material is examined with a setup close to a deep-drawing process, the Nakajima test (Nakazima et al. in Study on the formability of steel sheets. Yawate Technical Report No. 264, pp 8517-8530, 1968). The evaluation of the experimental investigations is provided by an optical analysis system using a digital image correlation software. Finally, based on the results of the uniaxial tensile tests, a one-dimensional macroscopic model is introduced and first results of the simulation are provided.

Morphology and contractile gene expression of adipose-derived mesenchymal stem cells in response to short-term cyclic uniaxial strain and TGF-β1.

PubMed

Rashidi, Neda; Tafazzoli-Shadpour, Mohammad; Haghighipour, Nooshin; Khani, Mohammad-Mehdi

2018-06-27

Previous studies have shown smooth muscle induction in adipose-derived mesenchymal stem cells (ASCs) caused by long-term cyclic stretch. Here we examined the capability of the short-term straining with time steps of 4, 8, 16 and 24 h alone or combined with TGF-β1 on smooth muscle induction of rabbit ASCs. Alterations in cell morphology were quantified through the cell shape index and orientation angle, and expression levels of α-SMA, SM22-α, h-caldesmon and calponin3 markers were examined using the real-time polymerase chain reaction (PCR) method. Moreover, F-actin cytoskeleton organization was observed by fluorescence staining. Mechanical strain either alone or combined with growth factor treatment caused significant up-regulation of both early and intermediate smooth muscle cells (SMCs) specific markers during the initial hours of stimulation peaking in 8 to 16 h. Furthermore, gradual alignment of cells perpendicular to the strain direction during loading time, and cell elongation resembling contractile SMC phenotype, together with alignment and reorganization of F-actin fibers were observed. Considering previously reported protein up-regulation in following days of straining, the effects of short-term cyclic stretch on smooth muscle induction of ASCs were revealed which can be helpful in achieving functional contractile SMCs through synergistic mechano-chemical regulation of ASCs as an appealing cell source for vascular tissue engineering.

Differentiation and Monitoring of Cells Using a Biochip for Regenerative Medicine

NASA Astrophysics Data System (ADS)

Uchida, Tomoyuki; Arai, Fumihito; Suzuki, Osamu; Ichikawa, Akihiko; Fukuda, Toshio; Katagiri, Takenobu; Kamijo, Ryutaro; Nakamura, Masanori; Numata, Mamoru; Watanabe, Naruaki

A novel biochip is developed for culturing stem cells. Biochip is made of Polymer (PDMS), and cells can be loaded by gradient strains in one chip. They grow well on a hydrophilic membrane and differentiation is promoted by cyclic strains. In this paper, we propose the method for culturing and monitoring of stem cells such as bone marrow stromal cells (ST2 cells) and myoblasts (C2C12 cells), and the results of culture. First we analyzed strains on a membrane when an air hole is decompressed, and clarified their range. From experiment, bone marrow stromal cells grew well in a narrow range, and we quantified their ALP activity as a measure of differentiation. As myoblasts, the direction of their differentiation was perpendicular to a groove, that is, the same direction of uniaxial strains.

Erythrocyte Membrane Failure by Electromechanical Stress.

PubMed

Du, E; Qiang, Yuhao; Liu, Jia

2018-01-01

We envision that electrodeformation of biological cells through dielectrophoresis as a new technique to elucidate the mechanistic details underlying membrane failure by electrical and mechanical stresses. Here we demonstrate the full control of cellular uniaxial deformation and tensile recovery in biological cells via amplitude-modified electric field at radio frequency by an interdigitated electrode array in microfluidics. Transient creep and cyclic experiments were performed on individually tracked human erythrocytes. Observations of the viscoelastic-to-viscoplastic deformation behavior and the localized plastic deformations in erythrocyte membranes suggest that electromechanical stress results in irreversible membrane failure. Examples of membrane failure can be separated into different groups according to the loading scenarios: mechanical stiffening, physical damage, morphological transformation from discocyte to echinocyte, and whole cell lysis. These results show that this technique can be potentially utilized to explore membrane failure in erythrocytes affected by other pathophysiological processes.

Estimation of fatigue life using electromechanical impedance technique

NASA Astrophysics Data System (ADS)

Lim, Yee Yan; Soh, Chee Kiong

2010-04-01

Fatigue induced damage is often progressive and gradual in nature. Structures subjected to large number of fatigue load cycles will encounter the process of progressive crack initiation, propagation and finally fracture. Monitoring of structural health, especially for the critical components, is therefore essential for early detection of potential harmful crack. Recent advent of smart materials such as piezo-impedance transducer adopting the electromechanical impedance (EMI) technique and wave propagation technique are well proven to be effective in incipient damage detection and characterization. Exceptional advantages such as autonomous, real-time and online, remote monitoring may provide a cost-effective alternative to the conventional structural health monitoring (SHM) techniques. In this study, the main focus is to investigate the feasibility of characterizing a propagating fatigue crack in a structure using the EMI technique as well as estimating its remaining fatigue life using the linear elastic fracture mechanics (LEFM) approach. Uniaxial cyclic tensile load is applied on a lab-sized aluminum beam up to failure. Progressive shift in admittance signatures measured by the piezo-impedance transducer (PZT patch) corresponding to increase of loading cycles reflects effectiveness of the EMI technique in tracing the process of fatigue damage progression. With the use of LEFM, prediction of the remaining life of the structure at different cycles of loading is possible.

Uniaxial experimental study of the acoustic emission and deformation behavior of composite rock based on 3D digital image correlation (DIC)

NASA Astrophysics Data System (ADS)

Cheng, Jian-Long; Yang, Sheng-Qi; Chen, Kui; Ma, Dan; Li, Feng-Yuan; Wang, Li-Ming

2017-12-01

In this paper, uniaxial compression tests were carried out on a series of composite rock specimens with different dip angles, which were made from two types of rock-like material with different strength. The acoustic emission technique was used to monitor the acoustic signal characteristics of composite rock specimens during the entire loading process. At the same time, an optical non-contact 3D digital image correlation technique was used to study the evolution of axial strain field and the maximal strain field before and after the peak strength at different stress levels during the loading process. The effect of bedding plane inclination on the deformation and strength during uniaxial loading was analyzed. The methods of solving the elastic constants of hard and weak rock were described. The damage evolution process, deformation and failure mechanism, and failure mode during uniaxial loading were fully determined. The experimental results show that the θ = 0{°}-45{°} specimens had obvious plastic deformation during loading, and the brittleness of the θ = 60{°}-90{°} specimens gradually increased during the loading process. When the anisotropic angle θ increased from 0{°} to 90{°}, the peak strength, peak strain, and apparent elastic modulus all decreased initially and then increased. The failure mode of the composite rock specimen during uniaxial loading can be divided into three categories: tensile fracture across the discontinuities (θ = 0{°}-30{°}), sliding failure along the discontinuities (θ = 45{°}-75{°}), and tensile-split along the discontinuities (θ = 90{°}). The axial strain of the weak and hard rock layers in the composite rock specimen during the loading process was significantly different from that of the θ = 0{°}-45{°} specimens and was almost the same as that of the θ = 60{°}-90{°} specimens. As for the strain localization highlighted in the maximum principal strain field, the θ = 0{°}-30{°} specimens appeared in the rock matrix approximately parallel to the loading direction, while in the θ = 45{°}-90{°} specimens it appeared at the hard and weak rock layer interface.

Fracture modes in off-axis fiber composites

NASA Technical Reports Server (NTRS)

Sinclair, J. H.; Chamis, C. C.

1978-01-01

Criteria were developed for identifying, characterizing, and quantifying fracture modes in high-modulus graphite-fiber/resin unidirectional composites subjected to off-axis tensile loading. Procedures are described which use sensitivity analyses and off-axis data to determine the uniaxial strength of fiber composites. It was found that off-axis composites fail by three fracture modes which produce unique fracture surface characteristics. The stress that dominates each fracture mode and the load angle range of its dominance can be identified. Linear composite mechanics is adequate to describe quantitatively the mechanical behavior of off-axis composites. The uniaxial strengths predicted from off-axis data are comparable to these measured in uniaxial tests.

Effect of Cr, Ti, V, and Zr Micro-additions on Microstructure and Mechanical Properties of the Al-Si-Cu-Mg Cast Alloy

NASA Astrophysics Data System (ADS)

Shaha, S. K.; Czerwinski, F.; Kasprzak, W.; Friedman, J.; Chen, D. L.

2016-05-01

Uniaxial static and cyclic tests were used to assess the role of Cr, Ti, V, and Zr additions on properties of the Al-7Si-1Cu-0.5Mg (wt pct) alloy in as-cast and T6 heat-treated conditions. The microstructure of the as-cast alloy consisted of α-Al, eutectic Si, and Cu-, Mg-, and Fe-rich phases Al2.1Cu, Al8.5Si2.4Cu, Al5.2CuMg4Si5.1, and Al14Si7.1FeMg3.3. In addition, the micro-sized Cr/Zr/Ti/V-rich phases Al10.7SiTi3.6, Al6.7Si1.2TiZr1.8, Al21.4Si3.4Ti4.7VZr1.8, Al18.5Si7.3Cr2.6V, Al7.9Si8.5Cr6.8V4.1Ti, Al6.3Si23.2FeCr9.2V1.6Ti1.3, Al92.2Si16.7Fe7.6Cr8.3V1.8, and Al8.2Si30.1Fe1.6Cr18.8V3.3Ti2.9Zr were present. During solution treatment, Cu-rich phases were completely dissolved, while the eutectic silicon, Fe-, and Cr/Zr/Ti/V-rich intermetallics experienced only partial dissolution. Micro-additions of Cr, Zr, Ti, and V positively affected the alloy strength. The modified alloy in the T6 temper during uniaxial tensile tests exhibited yield strength of 289 MPa and ultimate tensile strength of 342 MPa, being significantly higher than that for the Al-Si-Cu-Mg base. Besides, the cyclic yield stress of the modified alloy in the T6 state increased by 23 pct over that of the base alloy. The fatigue life of the modified alloy was substantially longer than that of the base alloy tested using the same parameters. The role of Cr, Ti, V, and Zr containing phases in controlling the alloy fracture during static and cyclic loading is discussed.

Experimental Studies on Strength Behaviour of Notched Glass/Epoxy Laminated Composites under Uni-axial and Bi-axial Loading

NASA Astrophysics Data System (ADS)

Guptha, V. L. Jagannatha; Sharma, Ramesh S.

2017-11-01

The use of FRP composite materials in aerospace, aviation, marine, automotive and civil engineering industry has increased rapidly in recent years due to their high specific strength and stiffness properties. The structural members contrived from such composite materials are generally subjected to complex loading conditions and leads to multi-axial stress conditions at critical surface localities. Presence of notches, much required for joining process of composites, makes it further significant. The current practice of using uni-axial test data alone to validate proposed material models is inadequate leading to evaluation and consideration of bi-axial test data. In order to correlate the bi-axial strengths with the uni-axial strengths of GFRP composite laminates in the presence of a circular notch, bi-axial tests using four servo-hydraulic actuators with four load cells were carried out. To determine the in-plane strength parameters, bi-axial cruciform test specimen model was considered. Three different fibre orientations, namely, 0°, 45°, and 90° are considered with a central circular notch of 10 mm diameter in the present investigation. From the results obtained, it is observed that there is a reduction in strength of 5.36, 2.41 and 13.92% in 0°, 45°, and 90° fibre orientation, respectively, under bi-axial loading condition as compared to that of uni-axial loading in laminated composite.

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...

Linking asphalt binder fatigue to asphalt mixture fatigue performance using viscoelastic continuum damage modeling

NASA Astrophysics Data System (ADS)

Safaei, Farinaz; Castorena, Cassie; Kim, Y. Richard

2016-08-01

Fatigue cracking is a major form of distress in asphalt pavements. Asphalt binder is the weakest asphalt concrete constituent and, thus, plays a critical role in determining the fatigue resistance of pavements. Therefore, the ability to characterize and model the inherent fatigue performance of an asphalt binder is a necessary first step to design mixtures and pavements that are not susceptible to premature fatigue failure. The simplified viscoelastic continuum damage (S-VECD) model has been used successfully by researchers to predict the damage evolution in asphalt mixtures for various traffic and climatic conditions using limited uniaxial test data. In this study, the S-VECD model, developed for asphalt mixtures, is adapted for asphalt binders tested under cyclic torsion in a dynamic shear rheometer. Derivation of the model framework is presented. The model is verified by producing damage characteristic curves that are both temperature- and loading history-independent based on time sweep tests, given that the effects of plasticity and adhesion loss on the material behavior are minimal. The applicability of the S-VECD model to the accelerated loading that is inherent of the linear amplitude sweep test is demonstrated, which reveals reasonable performance predictions, but with some loss in accuracy compared to time sweep tests due to the confounding effects of nonlinearity imposed by the high strain amplitudes included in the test. The asphalt binder S-VECD model is validated through comparisons to asphalt mixture S-VECD model results derived from cyclic direct tension tests and Accelerated Loading Facility performance tests. The results demonstrate good agreement between the asphalt binder and mixture test results and pavement performance, indicating that the developed model framework is able to capture the asphalt binder's contribution to mixture fatigue and pavement fatigue cracking performance.

Fibrocartilage tissue engineering: the role of the stress environment on cell morphology and matrix expression.

PubMed

Thomopoulos, Stavros; Das, Rosalina; Birman, Victor; Smith, Lester; Ku, Katherine; Elson, Elliott L; Pryse, Kenneth M; Marquez, Juan Pablo; Genin, Guy M

2011-04-01

Although much is known about the effects of uniaxial mechanical loading on fibrocartilage development, the stress fields to which fibrocartilaginous regions are subjected to during development are mutiaxial. That fibrocartilage develops at tendon-to-bone attachments and in compressive regions of tendons is well established. However, the three-dimensional (3D) nature of the stresses needed for the development of fibrocartilage is not known. Here, we developed and applied an in vitro system to determine whether fibrocartilage can develop under a state of periodic hydrostatic tension in which only a single principal component of stress is compressive. This question is vital to efforts to mechanically guide morphogenesis and matrix expression in engineered tissue replacements. Mesenchymal stromal cells in a 3D culture were exposed to compressive and tensile stresses as a result of an external tensile hydrostatic stress field. The stress field was characterized through mechanical modeling. Tensile cyclic stresses promoted spindle-shaped cells, upregulation of scleraxis and type one collagen, and cell alignment with the direction of tension. Cells experiencing a single compressive stress component exhibited rounded cell morphology and random cell orientation. No difference in mRNA expression of the genes Sox9 and aggrecan was observed when comparing tensile and compressive regions unless the medium was supplemented with the chondrogenic factor transforming growth factor beta3. In that case, Sox9 was upregulated under static loading conditions and aggrecan was upregulated under cyclic loading conditions. In conclusion, the fibrous component of fibrocartilage could be generated using only mechanical cues, but generation of the cartilaginous component of fibrocartilage required biologic factors in addition to mechanical cues. These studies support the hypothesis that the 3D stress environment influences cell activity and gene expression in fibrocartilage development.

Fibrocartilage Tissue Engineering: The Role of the Stress Environment on Cell Morphology and Matrix Expression

PubMed Central

Das, Rosalina; Birman, Victor; Smith, Lester; Ku, Katherine; Elson, Elliott L.; Pryse, Kenneth M.; Marquez, Juan Pablo; Genin, Guy M.

2011-01-01

Although much is known about the effects of uniaxial mechanical loading on fibrocartilage development, the stress fields to which fibrocartilaginous regions are subjected to during development are mutiaxial. That fibrocartilage develops at tendon-to-bone attachments and in compressive regions of tendons is well established. However, the three-dimensional (3D) nature of the stresses needed for the development of fibrocartilage is not known. Here, we developed and applied an in vitro system to determine whether fibrocartilage can develop under a state of periodic hydrostatic tension in which only a single principal component of stress is compressive. This question is vital to efforts to mechanically guide morphogenesis and matrix expression in engineered tissue replacements. Mesenchymal stromal cells in a 3D culture were exposed to compressive and tensile stresses as a result of an external tensile hydrostatic stress field. The stress field was characterized through mechanical modeling. Tensile cyclic stresses promoted spindle-shaped cells, upregulation of scleraxis and type one collagen, and cell alignment with the direction of tension. Cells experiencing a single compressive stress component exhibited rounded cell morphology and random cell orientation. No difference in mRNA expression of the genes Sox9 and aggrecan was observed when comparing tensile and compressive regions unless the medium was supplemented with the chondrogenic factor transforming growth factor beta3. In that case, Sox9 was upregulated under static loading conditions and aggrecan was upregulated under cyclic loading conditions. In conclusion, the fibrous component of fibrocartilage could be generated using only mechanical cues, but generation of the cartilaginous component of fibrocartilage required biologic factors in addition to mechanical cues. These studies support the hypothesis that the 3D stress environment influences cell activity and gene expression in fibrocartilage development. PMID:21091338

A investigation on unixial and quasi-biaxial tensile mechanical properties of aging HTPB propellant under dynamic loading at low temperature

NASA Astrophysics Data System (ADS)

Duan, Leiguang; Wang, Guang; Zhang, Guoxing; Sun, Xinya; Shang, Hehao

2018-06-01

In order to study the uniaxial and quasi-biaxial mechanical properties of aging solid propellants under low temperature and high strain rate, stress-strain curves and tensile fracture surfaces of HTPB propellant were obtained in a wide range of temperature (-30,25 °C) and strain rates (0.4,4.0 and 14.29 s-1), respectively, by means of uniaxial and biaxial tensile tests and electron microscopy scanning on the fracture cross section. The results indicate that the quasi-biaxial tensile mechanical properties of aging HTPB propellant is same as the uniaxial tensile mechanical properties influenced distinctly by temperature and strain rate. With decreasing temperature and increasing strain rate, the mechanical properties gradually strengthen. The damage for HTPB propellant changes from "dehumidification" to grain fracture. The initial elastic modulus E and maximum tensile stress σ of the uniaxial and biaxial tensile increase gradually with decreasing temperature and increasing strain rate, and well present linear-log function relation with strain rate. The ratio of quasi-biaxial and uniaxial stretching under different loading conditions was obtained so that the researchers could predict the quasi-biaxial tensile mechanical properties of the propellant based on the uniaxial test data.

Multi-scale mechanics of granular solids from grain-resolved X-ray measurements

NASA Astrophysics Data System (ADS)

Hurley, R. C.; Hall, S. A.; Wright, J. P.

2017-11-01

This work discusses an experimental technique for studying the mechanics of three-dimensional (3D) granular solids. The approach combines 3D X-ray diffraction and X-ray computed tomography to measure grain-resolved strains, kinematics and contact fabric in the bulk of a granular solid, from which continuum strains, grain stresses, interparticle forces and coarse-grained elasto-plastic moduli can be determined. We demonstrate the experimental approach and analysis of selected results on a sample of 1099 stiff, frictional grains undergoing multiple uniaxial compression cycles. We investigate the inter-particle force network, elasto-plastic moduli and associated length scales, reversibility of mechanical responses during cyclic loading, the statistics of microscopic responses and microstructure-property relationships. This work serves to highlight both the fundamental insight into granular mechanics that is furnished by combined X-ray measurements and describes future directions in the field of granular materials that can be pursued with such approaches.

Plastic Behavior of Metallic Damping Materials under Cyclical Shear Loading

PubMed Central

Zhang, Chaofeng; Wang, Longfei; Wu, Meiping; Zhao, Junhua

2016-01-01

Metallic shear panel dampers (SPDs) have been widely adopted in seismic engineering. In this study, axial and torsional specimens of four types of metallic damping materials, including three conventional metallic steels as well as low yield strength steel 160 (LYS160), were tested in order to investigate the material response under repeated large plastic strain and low cycle fatigue between 10 and 30 cycles. The present study demonstrated that both the deformation capacity and fatigue performance of LYS160 were underestimated by the conversion from the traditional uniaxial tensile test. The main difference in the failure mechanism between LYS160 and the three conventional materials was determined from the scanning electron microscopy data. The dominant failure mode in LYS160 is stable interlaminate slip and not bucking. Our results provide physical insights into the origin of the large deformation capacity, which is an important foundation for the lightweight design of SPDs. PMID:28773618

Micro-macro correlations and anisotropy in granular assemblies under uniaxial loading and unloading.

PubMed

Imole, Olukayode I; Wojtkowski, Mateusz; Magnanimo, Vanessa; Luding, Stefan

2014-04-01

The influence of contact friction on the behavior of dense, polydisperse granular assemblies under uniaxial (oedometric) loading and unloading deformation is studied using discrete element simulations. Even though the uniaxial deformation protocol is one of the "simplest" element tests possible, the evolution of the structural anisotropy necessitates its careful analysis and understanding, since it is the source of interesting and unexpected observations. On the macroscopic, homogenized, continuum scale, the deviatoric stress ratio and the deviatoric fabric, i.e., the microstructure behave in a different fashion during uniaxial loading and unloading. The maximal stress ratio and strain increase with increasing contact friction. In contrast, the deviatoric fabric reaches its maximum at a unique strain level independent of friction, with the maximal value decreasing with friction. For unloading, both stress and fabric respond to unloading strain with a friction-dependent delay but at different strains. On the micro-level, a friction-dependent non-symmetry of the proportion of weak (strong) and sliding (sticking) contacts with respect to the total contacts during loading and unloading is observed. Coupled to this, from the directional probability distribution, the "memory" and history-dependent behavior of granular systems is confirmed. Surprisingly, while a rank-2 tensor is sufficient to describe the evolution of the normal force directions, a sixth order harmonic approximation is necessary to describe the probability distribution of contacts, tangential force, and mobilized friction. We conclude that the simple uniaxial deformation activates microscopic phenomena not only in the active Cartesian directions, but also at intermediate orientations, with the tilt angle being dependent on friction, so that this microstructural features cause the interesting, nontrivial macroscopic behavior.

Monitoring microstructural evolution of alloy 617 with non-linear acoustics for remaining useful life prediction; multiaxial creep-fatigue and creep-ratcheting

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

Lissenden, Cliff; Hassan, Tasnin; Rangari, Vijaya

The research built upon a prior investigation to develop a unified constitutive model for design-­by-­analysis of the intermediate heat exchanger (IHX) for a very high temperature reactor (VHTR) design of next generation nuclear plants (NGNPs). Model development requires a set of failure data from complex mechanical experiments to characterize the material behavior. Therefore uniaxial and multiaxial creep-­fatigue and creep-­ratcheting tests were conducted on the nickel-­base Alloy 617 at 850 and 950°C. The time dependence of material behavior, and the interaction of time dependent behavior (e.g., creep) with ratcheting, which is an increase in the cyclic mean strain under load-­controlled cycling,more » are major concerns for NGNP design. This research project aimed at characterizing the microstructure evolution mechanisms activated in Alloy 617 by mechanical loading and dwell times at elevated temperature. The acoustic harmonic generation method was researched for microstructural characterization. It is a nonlinear acoustics method with excellent potential for nondestructive evaluation, and even online continuous monitoring once high temperature sensors become available. It is unique because it has the ability to quantitatively characterize microstructural features well before macroscale defects (e.g., cracks) form. The nonlinear acoustics beta parameter was shown to correlate with microstructural evolution using a systematic approach to handle the complexity of multiaxial creep-­fatigue and creep-­ratcheting deformation. Mechanical testing was conducted to provide a full spectrum of data for: thermal aging, tensile creep, uniaxial fatigue, uniaxial creep-­fatigue, uniaxial creep-ratcheting, multiaxial creep-fatigue, and multiaxial creep-­ratcheting. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM), and Optical Microscopy were conducted to correlate the beta parameter with individual microstructure mechanisms. We researched application of the harmonic generation method to tubular mechanical test specimens and pipes for nondestructive evaluation. Tubular specimens and pipes act as waveguides, thus we applied the acoustic harmonic generation method to guided waves in both plates and shells. Magnetostrictive transducers were used to generate and receive guided wave modes in the shell sample and the received signals were processed to show the sensitivity of higher harmonic generation to microstructure evolution. Modeling was initiated to correlate higher harmonic generation with the microstructure that will lead to development of a life prediction model that is informed by the nonlinear acoustics measurements.« less

A tensile machine with a novel optical load cell for soft biological tissues application.

PubMed

Faturechi, Rahim; Hashemi, Ata; Abolfathi, Nabiollah

2014-11-01

The uniaxial tensile testing machine is the most common device used to measure the mechanical properties of industrial and biological materials. The need for a low-cost uniaxial tension testing device for small research centers has always been the subject of research. To address this need, a novel uniaxial tensile testing machine was designed and fabricated to measure the mechanical properties of soft biological tissues. The device is equipped with a new low-cost load cell which works based on the linear displacement/force relationship of beams. The deflection of the beam load cell is measured optically by a digital microscope with an accuracy of 1 µm. The stiffness of the designed load cell was experimentally and theoretically determined at 100 N mm(-1). The stiffness of the load cell can be easily adjusted according to the tissue's strength. The force-time behaviour of soft tissue specimens was obtained by an in-house image processing program. To demonstrate the efficiency of the fabricated device, the mechanical properties of amnion tissue was measured and compared with available data. The obtained results indicate a strong agreement with that of previous studies.

The experimental research on response characteristics of coal samples under the uniaxial loading process

NASA Astrophysics Data System (ADS)

Jia, Bing; Wei, Jian-Ping; Wen, Zhi-Hui; Wang, Yun-Gang; Jia, Lin-Xing

2017-11-01

In order to study the response characteristics of infrasound in coal samples under the uniaxial loading process, coal samples were collected from GengCun mine. Coal rock stress loading device, acoustic emission tested system and infrasound tested system were used to test the infrasonic signal and acoustic emission signal under uniaxial loading process. The tested results were analyzed by the methods of wavelet filter, threshold denoise, time-frequency analysis and so on. The results showed that in the loading process, the change of the infrasonic wave displayed the characteristics of stage, and it could be divided into three stages: initial stage with a certain amount infrasound events, middle stage with few infrasound events, and late stage gradual decrease. It had a good consistency with changing characteristics of acoustic emission. At the same time, the frequency of infrasound was very low. It can propagate over a very long distance with little attenuation, and the characteristics of the infrasound before the destruction of the coal samples were obvious. A method of using the infrasound characteristics to predict the destruction of coal samples was proposed. This is of great significance to guide the prediction of geological hazards in coal mines.

Tension and fatigue behavior of 316LVM 1x7 multi-strand cables used as implantable electrodes.

PubMed

Lewandowski, John J; Varadarajan, Ravikumar; Smith, Brian; Tuma, Chris; Shazly, Mostafa; Vatamanu, Luciano O

2008-07-15

The mechanical behavior of 316LVM 1x7 cables were evaluated in uniaxial tension, and in cyclic strain-controlled fatigue with the use of a Flex tester operated to provide fully reversed bending fatigue. The magnitude of cyclic strains imparted to each cable tested was controlled via the use of different diameter mandrels. Smaller diameter mandrels produced higher values of cyclic strain and lower fatigue life. Multiple samples were tested and analyzed via scanning electron microscopy. The fatigue results were analyzed via a Coffin-Manson-Basquin approach and compared to fatigue data obtained from the literature where testing was conducted on similar materials, but under rotating bending fatigue conditions.

Effect of Stress Triaxiality on the Flow and Fracture of Mg Alloy AZ31

NASA Astrophysics Data System (ADS)

Kondori, Babak; Benzerga, A. Amine

2014-07-01

The microscopic damage mechanisms operating in a hot-rolled magnesium alloy AZ31B are investigated under both uniaxial and controlled triaxial loadings. Their connection to macroscopic fracture strains and fracture mode (normal vs shear) is elucidated using postmortem fractography, interrupted tests, and microscopic analysis. The fracture locus (strain-to-failure vs stress triaxiality) exhibits a maximum at moderate triaxiality, and the strain-to-failure is found to be greater in notched specimens than in initially smooth ones. A transition from twinning-induced fracture under uniaxial loading to microvoid coalescence fracture under triaxial loading is evidenced. It is argued that this transition accounts in part for the observed greater ductility in notched bars. The evolution of plastic anisotropy with stress triaxiality is also investigated. It is inferred that anisotropic plasticity at a macroscopic scale suffices to account for the observed transition in the fracture mode from flat (triaxial loading) to shear-like (uniaxial loading). Damage is found to initiate at second-phase particles and deformation twins. Fracture surfaces of broken specimens exhibit granular morphology, coarse splits, twin-sized crack traces, as well as shallow and deep dimples, in proportions that depend on the overall stress triaxiality and fracture mode. An important finding is that AZ31B has a greater tolerance to ductile damage accumulation than has been believed thus far, based on the fracture behavior in uniaxial specimens. Another finding, common to both tension and compression, is the increase in volumetric strain, the microscopic origins of which remain to be elucidated.

Experimental studies the evolution of stress-strain state in structured rock specimens under uniaxial loading

NASA Astrophysics Data System (ADS)

Oparin, Viktor; Tsoy, Pavel; Usoltseva, Olga; Semenov, Vladimir

2014-05-01

The aim of this study was to analyze distribution and development of stress-stress state in structured rock specimens subject to uniaxial loading to failure. Specific attention was paid to possible oscillating motion of structural elements of the rock specimens under constraints (pre-set stresses at the boundaries of the specimens) and the kinetic energy fractals. The detailed studies into the micro-level stress-strain state distribution and propagation over acting faces of rock specimens subject to uniaxial loading until failure, using automated digital speckle photography analyzer ALMEC-tv, have shown that: • under uniaxial stiff loading of prismatic sandstone, marble and sylvinite specimens on the Instron-8802 servohydraulic testing machine at the mobile grip displacement rate 0.02-0.2 mm/min, at a certain level of stressing, low-frequency micro-deformation processes originate in the specimens due to slow (quasi-static) force; • the amplitude of that deformation-wave processes greatly depends on the micro-loading stage: — at the elastic deformation stage, under the specimen stress lower than half ultimate strength of the specimen, there are no oscillations of microstrains; —at the nonlinearly elastic deformation stage, under stress varied from 0.5 to 1 ultimate strength of the specimens, the amplitudes of microstrains grow, including the descending stage 3; the oscillation frequency f=0.5-4 Hz; —at the residual strength stage, the amplitudes of the microstrains drop abruptly (3-5 times) as against stages 2 and 3; • in the elements of the scanned specimen surface in the region with the incipient crack, the microstrain rate amplitudes are a few times higher than in the undamged surface region of the same specimen. Sometimes, deformation rate greatly grows with increase in the load. The authors have used the energy scanning function of the deformation-wave processes in processing experimental speckle-photography data on the surface of the test specimen subject to loading until failure.

Observed physical processes in mechanical tests of PBX9501 and recomendations for experiments to explore a possible plasticity/damage threshold

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

Buechler, Miles A.

2012-05-02

This memo discusses observations that have been made in regards to a series of monotonic and cyclic uniaxial experiments performed on PBX9501 by Darla Thompson under Enhanced Surveilance Campaign support. These observations discussed in Section Cyclic compression observations strongly suggest the presence of viscoelastic, plastic, and damage phenomena in the mechanical response of the material. In Secton Uniaxial data analysis and observations methods are discussed for separating out the viscoelastic effects. A crude application of those methods suggests the possibility of a critical stress below which plasticity and damage may be negligible. The threshold should be explored because if itmore » exists it will be an important feature of any constitutive model. Additionally, if the threshold exists then modifications of experimental methods may be feasible which could potentially simplify future experiments or provide higher quality data from those experiments. A set of experiments to explore the threshold stress are proposed in Section Exploratory tests program for identifying threshold stress.« less

The Medial Stitch in Transosseous-Equivalent Rotator Cuff Repair: Vertical or Horizontal Mattress?

PubMed

Montanez, Anthony; Makarewich, Christopher A; Burks, Robert T; Henninger, Heath B

2016-09-01

Despite advances in surgical technique, rotator cuff repair retears continue to occur at rates of 10%, 22%, and 57% for small, medium, and large tears, respectively. A common mode of failure in transosseous-equivalent rotator cuff repairs is tissue pullout of the medial mattress stitch. While the medial mattress stitch has been studied extensively, no studies have evaluated a vertical mattress pattern placed near the musculotendinous junction in comparison with a horizontal mattress pattern. Vertical mattress stitches will have higher load to failure and lower gapping compared with horizontal mattress stitches in a transosseous-equivalent rotator cuff repair. Controlled laboratory study. Double-row transosseous-equivalent rotator cuff repairs were performed in 9 pairs of human male cadaveric shoulders (mean age ± SD, 58 ± 10 years). One shoulder in each pair received a medial-row suture pattern using a vertical mattress stitch, and the contralateral shoulder received a horizontal mattress. Specimens were mounted in a materials testing machine and tested in uniaxial tensile deformation for cyclic loading (500 cycles at 1 Hz to 1.0 MPa of effective stress), followed by failure testing carried out at a rate of 1 mm/s. Construct gapping and applied loads were monitored continuously throughout the testing. Vertical mattress sutures were placed in 5 right and 4 left shoulders. Peak cyclic gapping did not differ between vertical (mean ± SD, 2.8 ± 1.1 mm) and horizontal mattress specimens (3.0 ± 1.2 mm) (P = .684). Vertical mattress sutures failed at higher loads compared with horizontal mattress sutures (568.9 ± 140.3 vs 451.1 ± 174.3 N; P = .025); however, there was no significant difference in failure displacement (8.0 ± 1.6 vs 6.0 ± 2.1 mm; P = .092). Failure stiffness did not differ between the suture patterns (P = .204). In transosseous-equivalent rotator cuff repairs near the musculotendinous junction, a vertical mattress suture used as the medial stitch has a higher load to failure but no difference in gapping compared with a horizontal mattress pattern. A vertical mattress suture may offer enhanced strength of repair for transosseous-equivalent repairs. © 2016 The Author(s).

Macrodamage Accumulation Model for a Human Femur

PubMed Central

2017-01-01

The objective of this study was to more fully understand the mechanical behavior of bone tissue that is important to find an alternative material to be used as an implant and to develop an accurate model to predict the fracture of the bone. Predicting and preventing bone failure is an important area in orthopaedics. In this paper, the macrodamage accumulation models in the bone tissue have been investigated. Phenomenological models for bone damage have been discussed in detail. In addition, 3D finite element model of the femur prepared from imaging data with both cortical and trabecular structures is delineated using MIMICS and ANSYS® and simulated as a composite structure. The damage accumulation occurring during cyclic loading was analyzed for fatigue scenario. We found that the damage accumulates sooner in the multiaxial than in the uniaxial loading condition for the same number of cycles, and the failure starts in the cortical bone. The damage accumulation behavior seems to follow a three-stage growth: a primary phase, a secondary phase of damage growth marked by linear damage growth, and a tertiary phase that leads to failure. Finally, the stiffness of the composite bone comprising the cortical and trabecular bone was significantly different as expected. PMID:28951659

Time-dependent behavior of passive skeletal muscle

NASA Astrophysics Data System (ADS)

Ahamed, T.; Rubin, M. B.; Trimmer, B. A.; Dorfmann, L.

2016-03-01

An isotropic three-dimensional nonlinear viscoelastic model is developed to simulate the time-dependent behavior of passive skeletal muscle. The development of the model is stimulated by experimental data that characterize the response during simple uniaxial stress cyclic loading and unloading. Of particular interest is the rate-dependent response, the recovery of muscle properties from the preconditioned to the unconditioned state and stress relaxation at constant stretch during loading and unloading. The model considers the material to be a composite of a nonlinear hyperelastic component in parallel with a nonlinear dissipative component. The strain energy and the corresponding stress measures are separated additively into hyperelastic and dissipative parts. In contrast to standard nonlinear inelastic models, here the dissipative component is modeled using an evolution equation that combines rate-independent and rate-dependent responses smoothly with no finite elastic range. Large deformation evolution equations for the distortional deformations in the elastic and in the dissipative component are presented. A robust, strongly objective numerical integration algorithm is used to model rate-dependent and rate-independent inelastic responses. The constitutive formulation is specialized to simulate the experimental data. The nonlinear viscoelastic model accurately represents the time-dependent passive response of skeletal muscle.

High fidelity computational characterization of the mechanical response of thermally aged polycarbonate

NASA Astrophysics Data System (ADS)

Zhang, Zesheng; Zhang, Lili; Jasa, John; Li, Wenlong; Gazonas, George; Negahban, Mehrdad

2017-07-01

A representative all-atom molecular dynamics (MD) system of polycarbonate (PC) is built and conditioned to capture and predict the behaviours of PC in response to a broad range of thermo-mechanical loadings for various thermal aging. The PC system is constructed to have a distribution of molecular weights comparable to a widely used commercial PC (LEXAN 9034), and thermally conditioned to produce models for aged and unaged PC. The MD responses of these models are evaluated through comparisons to existing experimental results carried out at much lower loading rates, but done over a broad range of temperatures and loading modes. These experiments include monotonic extension/compression/shear, unilaterally and bilaterally confined compression, and load-reversal during shear. It is shown that the MD simulations show both qualitative and quantitative similarity with the experimental response. The quantitative similarity is evaluated by comparing the dilatational response under bilaterally confined compression, the shear flow viscosity and the equivalent yield stress. The consistency of the in silico response to real laboratory experiments strongly suggests that the current PC models are physically and mechanically relevant and potentially can be used to investigate thermo-mechanical response to loading conditions that would not easily be possible. These MD models may provide valuable insight into the molecular sources of certain observations, and could possibly offer new perspectives on how to develop constitutive models that are based on better understanding the response of PC under complex loadings. To this latter end, the models are used to predict the response of PC to complex loading modes that would normally be difficult to do or that include characteristics that would be difficult to measure. These include the responses of unaged and aged PC to unilaterally confined extension/compression, cyclic uniaxial/shear loadings, and saw-tooth extension/compression/shear.

Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading.

PubMed

Paepoemsin, T; Reichart, P A; Chaijareenont, P; Strietzel, F P; Khongkhunthian, P

2016-01-01

The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading. The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer's recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test. Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, P<.05). After cyclic loading, removal torque in all groups decreased significantly (P<.05). Group C revealed significantly less removal torque than groups A and B (P<.005). Tensile force in all groups significantly increased after cyclic loading (P<.05), group A had significantly less tensile force than groups B and C (P<.005). Removal torque reduced significantly after cyclic loading. Before cyclic loading, tapered screws maintained more preload than did flat head screws. After cyclic loading, tapered and flat head screws maintained even amounts of preload. The tensile force that dislodged abutment from implant fixture increased immensely after cyclic loading.

Removal torque evaluation of three different abutment screws for single implant restorations after mechanical cyclic loading

PubMed Central

PAEPOEMSIN, T.; REICHART, P. A.; CHAIJAREENONT, P.; STRIETZEL, F. P.; KHONGKHUNTHIAN, P.

2016-01-01

SUMMARY Purpose The aim of this study was to evaluate the removal torque of three different abutment screws and pull out strength of implant-abutment connection for single implant restorations after mechanical cyclic loading. Methods The study was performed in accordance with ISO 14801:2007. Three implant groups (n=15) were used: group A, PW Plus® with flat head screw; group B, PW Plus® with tapered screw; and group C, Conelog® with flat head screw. All groups had the same implant-abutment connection feature: cone with mandatory index. All screws were tightened with manufacturer’s recommended torque. Ten specimens in each group underwent cyclic loading (1×106 cycles, 10 Hz, and 250 N). Then, all specimens were un-tightened, measured for the removal torque, and underwent a tensile test. The force that dislodged abutment from implant fixture was recorded. The data were analysed using independent sample t-test, ANOVA and Tukey HSD test. Results Before cyclic loading, removal torque in groups A, B and C were significantly different (B> A> C, P<.05). After cyclic loading, removal torque in all groups decreased significantly (P<.05). Group C revealed significantly less removal torque than groups A and B (P<.005). Tensile force in all groups significantly increased after cyclic loading (P<.05), group A had significantly less tensile force than groups B and C (P<.005). Conclusions Removal torque reduced significantly after cyclic loading. Before cyclic loading, tapered screws maintained more preload than did flat head screws. After cyclic loading, tapered and flat head screws maintained even amounts of preload. The tensile force that dislodged abutment from implant fixture increased immensely after cyclic loading. PMID:28042450

Modeling of yield surface evolution in uniaxial and biaxial loading conditions using a prestrained large scale specimen

NASA Astrophysics Data System (ADS)

Zaman, Shakil Bin; Barlat, Frédéric; Kim, Jin Hwan

2018-05-01

Large-scale advanced high strength steel (AHSS) sheet specimens were deformed in uniaxial tension, using a novel grip system mounted on a MTS universal tension machine. After pre-strain, they were used as a pre-strained material to examine the anisotropic response in the biaxial tension tests with various load ratios, and orthogonal tension tests at 45° and 90° from the pre-strain axis. The flow curve and the instantaneous r-value of the pre-strained steel in each of the aforementioned uniaxial testing conditions were also measured and compared with those of the undeformed steel. Furthermore, an exhaustive analysis of the yield surface was also conducted and the results, prior and post-prestrain were represented and compared. The homogeneous anisotropic hardening (HAH) model [1] was employed to predict the behavior of the pre-strained material. It was found that the HAH-predicted flow curves after non-linear strain path change and the yield loci after uniaxial pre-strain were in good agreement with the experiments, while the r-value evolution after strain path change was qualitatively well predicted.

Analysis of Glenoid Fixation with Anatomic Total Shoulder Arthroplasty in an Extreme Cyclic Loading Scenario.

PubMed

Roche, Christopher P; Staunch, Cameron; Hahn, William; Grey, Sean G; Flurin, Pierre-Henri; Wright, Thomas W; Zuckerman, Joseph D

2015-12-01

ASTM F2028-14 was adopted to recom mend a cyclic eccentric glenoid edge loading test that simulates the rocking horse loading mechanism beleived to cause aTSA glenoid loosening. While this method accurately simulates that failure mechanism, the recommended 750 N load may not be sufficient to simulate worst-case loading magnitudes, and the recommended 100,000 cycles may not be sufficient to simulate device fatigue-related failure modes. Finally, if greater loading magnitude or a larger number of cycles is performed, the recommended substrate density may not be sufficiently strong to support the elevated loads and cycles. To this end, a new test method is proposed to supplement ASTM F2028-14. A series of cyclic tests were performed to evaluate the long-term fixation strength of two different hybrid glenoid designs in both low (15 pcf) and high (30 pcf) density polyurethane blocks at elevated loads relative to ASTM F2028-14. To simulate a worst case clinical condition in which the humeral head is superiorly migrated, a cyclic load was applied to the superior glenoid rim to induce a maximum torque on the fixation pegs for three different cyclic loading tests: 1. 1,250 N load for 0.75 M cycles in a 15 pcf block, 2. 1,250 N load for 1.5 M cycles in a 30 pcf block, and 3. 2,000 N load for 0.65 M cycles in a 30 pcf block. All devices completed cyclic loading without failure, fracture, or loss of fixation regardless of glenoid design, polyurethane density, loading magnitude, or cycle length. No significant difference in post-cyclic displacement was noted between designs in any of the three tests. Post-cyclic radiographs demonstrated that each device maintained fixa - tion with the metal pegs within the bone-substitute blocks with no fatigue related failures. These results demonstrate that both cemented hybrid glenoids maintained fixation when tested according to each cyclic loading scenario, with no difference in post-cyclic displacement observed between designs. The lack of fatigue-related failures in these elevated load and high cycle test scenarios are promising, as are the relatively low displacements given the extreme nature of each test. This cyclic loading method is intended to supplement the ASTM F2028-14 standard that adequately simulates the rocking horse loading mechanism but may not adequately simulate the fatigue-related failure modes.

The influence of thermal and cyclic stressing on the strength of rocks from Mount St. Helens, Washington

NASA Astrophysics Data System (ADS)

Kendrick, Jackie Evan; Smith, Rosanna; Sammonds, Peter; Meredith, Philip G.; Dainty, Matthew; Pallister, John S.

2013-07-01

Stratovolcanoes and lava domes are particularly susceptible to sector collapse resulting from wholesale rock failure as a consequence of decreasing rock strength. Here, we provide insights into the influence of thermal and cyclic stressing on the strength and mechanical properties of volcanic rocks. Specifically, this laboratory study examines the properties of samples from Mount St. Helens; chosen because its strength and stability have played a key role in its history, influencing the character of the infamous 1980 eruption. We find that thermal stressing exerts different effects on the strengths of different volcanic units; increasing the heterogeneity of rocks in situ. Increasing the uniaxial compressive stress generates cracking, the timing and magnitude of which was monitored via acoustic emission (AE) output during our experiments. AEs accelerated in the approach to failure, sometimes following the pattern predicted by the failure forecast method (Kilburn 2003). Crack damage during the experiments was tracked using the evolving static Young's modulus and Poisson's ratio, which represent the quasi-static deformation in volcanic edifices more accurately than dynamic elastic moduli which are usually implemented in volcanic models. Cyclic loading of these rocks resulted in a lower failure strength, confirming that volcanic rocks may be weakened by repeated inflation and deflation of the volcanic edifice. Additionally, volcanic rocks in this study undergo significant elastic hysteresis; in some instances, a material may fail at a stress lower than the peak stress which has previously been endured. Thus, a volcanic dome repeatedly inflated and deflated may progressively weaken, possibly inducing failure without necessarily exceeding earlier conditions.

Cyclic Load Effects on Long Term Behavior of Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Shah, A. R.; Chamis, C. C.

1996-01-01

A methodology to compute the fatigue life for different ratios, r, of applied stress to the laminate strength based on first ply failure criteria combined with thermal cyclic loads has been developed and demonstrated. Degradation effects resulting from long term environmental exposure and thermo-mechanical cyclic loads are considered in the simulation process. A unified time-stress dependent multi-factor interaction equation model developed at NASA Lewis Research Center has been used to account for the degradation of material properties caused by cyclic and aging loads. Effect of variation in the thermal cyclic load amplitude on a quasi-symmetric graphite/epoxy laminate has been studied with respect to the impending failure modes. The results show that, for the laminate under consideration, the fatigue life under combined mechanical and low thermal amplitude cyclic loads is higher than that due to mechanical loads only. However, as the thermal amplitude increases, the life also decreases. The failure mode changes from tensile under mechanical loads only to the compressive and shear at high mechanical and thermal loads. Also, implementation of the developed methodology in the design process has been discussed.

Effects of lateral cortical anchorage on the primary stability of implants subjected to controlled loads: an in vitro study.

PubMed

Xiao, Jian-rui; Li, Yong-Qi; Guan, Su-Min; Kong, Liang; Liu, Baolin; Li, Dehua

2012-03-01

Our aim was to evaluate the effects of lateral cortical anchorage on the primary stability of implants subjected to immediate loading. Implants were placed into bovine bones with monocortical anchorage (implant placed through the cortical bone of the crest) and bicortical anchorage (the crest cortical bone plus one cortical bone on the lateral side). Loads of 25N and 50N were applied to the implants in different cycles. The implant stability quotient (ISQ) was measured before and after the cyclic loadings. Under 25N load there was no difference in ISQ between 1800 cyclic loading and preloading, but the values decreased significantly after 3600 cyclic loading in both groups (p<0.05). Under a 50N load the ISQ value after 1800 and 3600 cyclic loading decreased in the monocortical group (p<0.05), but there was no difference between 1800 cyclic loading and preloading in the bicortical group, and the ISQ in the bicortical group was higher than in the monocortical group after 1800 cyclic loading (p<0.05). Our results suggest that the stability of implants with bicortical anchorage decreased more slowly under higher loads. Copyright © 2011 The British Association of Oral and Maxillofacial Surgeons. Published by Elsevier Ltd. All rights reserved.

Constitutive equations for the cyclic behaviour of short carbon fibre-reinforced thermoplastics and identification on a uniaxial database

NASA Astrophysics Data System (ADS)

Leveuf, Louis; Navrátil, Libor; Le Saux, Vincent; Marco, Yann; Olhagaray, Jérôme; Leclercq, Sylvain

2018-01-01

A constitutive model for the cyclic behaviour of short carbon fibre-reinforced thermoplastics for aeronautical applications is proposed. First, an extended experimental database is generated in order to highlight the specificities of the studied material. This database is composed of complex tests and is used to design a relevant constitutive model able to capture the cyclic behaviour of the material. A general 3D formulation of the model is then proposed, and an identification strategy is defined to identify its parameters. Finally, a validation of the identification is performed by challenging the prediction of the model to the tests that were not used for the identification. An excellent agreement between the numerical results and the experimental data is observed revealing the capabilities of the model.

Stress induced phase transitions in silicon

NASA Astrophysics Data System (ADS)

Budnitzki, M.; Kuna, M.

2016-10-01

Silicon has a tremendous importance as an electronic, structural and optical material. Modeling the interaction of a silicon surface with a pointed asperity at room temperature is a major step towards the understanding of various phenomena related to brittle as well as ductile regime machining of this semiconductor. If subjected to pressure or contact loading, silicon undergoes a series of stress-driven phase transitions accompanied by large volume changes. In order to understand the material's response for complex non-hydrostatic loading situations, dedicated constitutive models are required. While a significant body of literature exists for the dislocation dominated high-temperature deformation regime, the constitutive laws used for the technologically relevant rapid low-temperature loading have severe limitations, as they do not account for the relevant phase transitions. We developed a novel finite deformation constitutive model set within the framework of thermodynamics with internal variables that captures the stress induced semiconductor-to-metal (cd-Si → β-Si), metal-to-amorphous (β-Si → a-Si) as well as amorphous-to-amorphous (a-Si → hda-Si, hda-Si → a-Si) transitions. The model parameters were identified in part directly from diamond anvil cell data and in part from instrumented indentation by the solution of an inverse problem. The constitutive model was verified by successfully predicting the transformation stress under uniaxial compression and load-displacement curves for different indenters for single loading-unloading cycles as well as repeated indentation. To the authors' knowledge this is the first constitutive model that is able to adequately describe cyclic indentation in silicon.

Sensing human physiological response using wearable carbon nanotube-based fabrics

NASA Astrophysics Data System (ADS)

Wang, Long; Loh, Kenneth J.; Koo, Helen S.

2016-04-01

Flexible and wearable sensors for human monitoring have received increased attention. Besides detecting motion and physical activity, measuring human vital signals (e.g., respiration rate and body temperature) provide rich data for assessing subjects' physiological or psychological condition. Instead of using conventional, bulky, sensing transducers, the objective of this study was to design and test a wearable, fabric-like sensing system. In particular, multi-walled carbon nanotube (MWCNT)-latex thin films of different MWCNT concentrations were first fabricated using spray coating. Freestanding MWCNT-latex films were then sandwiched between two layers of flexible fabric using iron-on adhesive to form the wearable sensor. Second, to characterize its strain sensing properties, the fabric sensors were subjected to uniaxial and cyclic tensile load tests, and they exhibited relatively stable electromechanical responses. Finally, the wearable sensors were placed on a human subject for monitoring simple motions and for validating their practical strain sensing performance. Overall, the wearable fabric sensor design exhibited advances such as flexibility, ease of fabrication, light weight, low cost, noninvasiveness, and user comfort.

Apparatus for measurement of acoustic wave propagation under uniaxial loading with application to measurement of third-order elastic constants of piezoelectric single crystals.

PubMed

Zhang, Haifeng; Kosinski, J A; Karim, Md Afzalul

2013-05-01

We describe an apparatus for the measurement of acoustic wave propagation under uniaxial loading featuring a special mechanism designed to assure a uniform mechanical load on a cube-shaped sample of piezoelectric material. We demonstrate the utility of the apparatus by determining the effects of stresses on acoustic wave speed, which forms a foundation for the final determination of the third-order elastic constants of langasite and langatate single crystals. The transit time method is used to determine changes in acoustic wave velocity as the loading is varied. In order to minimize error and improve the accuracy of the wave speed measurements, the cross correlation method is used to determine the small changes in the time of flight. Typical experimental results are presented and discussed.

Structural phase transition of gold under uniaxial, tensile, and triaxial stresses: An ab initio study

NASA Astrophysics Data System (ADS)

Durandurdu, Murat

2007-07-01

The behavior of gold crystal under uniaxial, tensile, and three different triaxial stresses is studied using an ab initio constant pressure technique within a generalized gradient approximation. Gold undergoes a phase transformation from the face-centered-cubic structure (fcc) to a body-centered-tetragonal (bct) structure having the space group of I4/mmm with the application of uniaxial stress, while it transforms to a face-centered-tetragonal (fct) phase within I4/mmm symmetry under uniaxial tensile loading. Further uniaxial compression of the bct phase results in a symmetry change from I4/mmm to P1 at high stresses and ultimately structural failure around 200.0GPa . For the case of triaxial stresses, gold also converts into a bct state. The critical stress for the fcc-to-bct transformation increases as the ratio of the triaxial stress increases. Both fct and bct phases are elastically unstable.

Mechanical Stimulation of Stem Cells Using Cyclic Uniaxial Strain

PubMed Central

Kurpinski, Kyle; Li, Song

2007-01-01

The role of mechanical forces in the development and maintenance of biological tissues is well documented, including several mechanically regulated phenomena such as bone remodeling, muscular hypertrophy, and smooth muscle cell plasticity. However, the forces involved are often extremely complex and difficult to monitor and control in vivo. To better investigate the effects of mechanical forces on cells, we have developed an in vitro method for applying uniaxial cyclic tensile strain to adherent cells cultured on elastic membranes. This method utilizes a custom-designed bioreactor with a motorized cam-rotor system to apply the desired force. Here we present a step-by-step video protocol demonstrating how to assemble the various components of each "stretch chamber", including, in this case, a silicone membrane with micropatterned topography to orient the cells with the direction of the strain. We also describe procedures for sterilizing the chambers, seeding cells onto the membrane, latching the chamber into the bioreactor, and adjusting the mechanical parameters (i.e. magnitude and rate of strain). The procedures outlined in this particular protocol are specific for seeding human mesenchymal stem cells onto silicone membranes with 10 µm wide channels oriented parallel to the direction of strain. However, the methods and materials presented in this system are flexible enough to accommodate a number of variations on this theme: strain rate, magnitude, duration, cell type, membrane topography, membrane coating, etc. can all be tailored to the desired application or outcome. This is a robust method for investigating the effects of uniaxial tensile strain applied to cells in vitro. PMID:18997890

Impact of Intentional Overload on Joint Stability of Internal Implant-Abutment Connection System with Different Diameter.

PubMed

Lee, Ji-Hye; Lee, Won; Huh, Yoon-Hyuk; Park, Chan-Jin; Cho, Lee-Ra

2017-09-05

To evaluate the axial displacement of the implant-abutment assembly of different implant diameter after static and cyclic loading of overload condition. An internal conical connection system with three diameters (Ø 4.0, 4.5, and 5.0) applying identical abutment dimension and the same abutment screw was evaluated. Axial displacement of abutment and reverse torque loss of abutment screw were evaluated under static and cyclic loading conditions. Static loading test groups were subjected to vertical static loading of 250, 400, 500, 600, 700, and 800 N consecutively. Cyclic loading test groups were subjected to 500 N cyclic loading to evaluate the effect of excessive masticatory loading. After abutment screw tightening for 30 Ncm, axial displacement was measured upon 1, 3, 10, and 1,000,000 cyclic loadings of 500 N. Repeated-measure ANOVA and 2-way ANOVA were used for statistical analysis (α = 0.05). The increasing magnitude of vertical load and thinner wall thickness of implant increased axial displacement of abutment and reverse torque loss of abutment screw (p < 0.05). Implants in the Ø 5.0 diameter group demonstrated significantly low axial displacement, and reverse torque loss after static loading than Ø 4.0 and Ø 4.5 diameter groups (p < 0.05). In the cyclic loading test, all diameter groups of implant showed significant axial displacement after 1 cycle of loading of 500 N (p < 0.05). There was no significant axial displacement after 3, 10, or 1,000,000 cycles of loading (p = 0.603). Implants with Ø 5.0 diameter demonstrated significantly low axial displacement and reverse torque loss after the cyclic and static loading of overload condition. © 2017 by the American College of Prosthodontists.

3D printing of highly elastic strain sensors using polyurethane/multiwall carbon nanotube composites

NASA Astrophysics Data System (ADS)

Christ, Josef F.; Hohimer, Cameron J.; Aliheidari, Nahal; Ameli, Amir; Mo, Changki; Pötschke, Petra

2017-04-01

As the desire for wearable electronics increases and the soft robotics industry advances, the need for novel sensing materials has also increased. Recently, there have been many attempts at producing novel materials, which exhibit piezoresistive behavior. However, one of the major shortcomings in strain sensing technologies is in the fabrication of such sensors. While there is significant research and literature covering the various methods for developing piezoresistive materials, fabricating complex sensor platforms is still a manufacturing challenge. Here, we report a facile method to fabricate multidirectional embedded strain sensors using additive manufacturing technology. Pure thermoplastic polyurethane (TPU) and TPU/multiwall carbon nanotubes (MWCNT) nanocomposites were 3D printed in tandem using a low-cost multi-material FDM printer to fabricate uniaxial and biaxial strain sensors with conductive paths embedded within the insulative TPU platform. The sensors were then subjected to a series of cyclic strain loads. The results revealed excellent piezoresistive responses of the sensors with cyclic repeatability in both the axial and transverse directions and in response to strains as high as 50%. Further, while strain-softening did occur in the embedded printed strain sensors, it was predictable and similar to the results found in the literature for bulk polymer nanocomposites. This works demonstrates the possibility of manufacturing embedded and multidirectional flexible strain sensors using an inexpensive and versatile method, with potential applications in soft robotics and flexible electronics and health monitoring.

Microcracking and Healing in Semibrittle Salt-Rock: Elastic and Plastic Behavior

NASA Astrophysics Data System (ADS)

Ding, J.; Chester, F. M.; Chester, J. S.; Shen, X.; Arson, C. F.

2017-12-01

Microcracking and healing during semibrittle deformation are important processes that affect physical properties such as elastic moduli and permeability. We study these processes through triaxial compression tests involving cyclic differential loading and isostatic-holds on synthetic salt-rock at room temperature and low confining pressure (Pc, 1 to 4 MPa). The salt samples are produced by uniaxial pressing of granular (300 µm dia.) halite to 75 MPa at 150˚C for 10^3 s, to create low-porosity ( 5%) aggregates of nearly equant, work-hardened grains. Alternating large- and small-load cycles are performed to track the evolution of plastic and elastic properties, respecitively, with progressive strain to 8% axial shortening. 24-hour holds are carried out at about 4% axial shortening followed by renewed cyclic loading to investigate healing. During large load cycles samples yield and exhibit distributed flow with dilatancy and small work hardening. Young's Modulus (YM) decreases and then tends to stabilize, while Poisson's Ratio (PR) increases at a reducing rate, with progressive strain. Microstructures at sequential stages show that opening-mode grain-boundary cracking, grain-boundary sliding, and some intracrystalline plasticity are the dominant deformation processes. Opening and shear occur preferentially on boundaries that are parallel and inclined to the shortening axis, respectively, leading to progressive redistribution of porosity. Opening-mode grain-boundary cracks increase in number and aperature with strain, and are linked by sliding grain-boundaries to form en echelon arrays. After a 24-hour hold, samples show yielding and flow behavior consistent with that prior to the hold, whereas YM and PR are reset to the same values documented at zero strain and subsequently evolve with additional strain similar to that documented at smaller strains prior to the hold. Open grain-boundary cracks are not closed or healed during the hold. Observations suggest that changes in elastic properties in the semibrittle salt-rock reflect weakening and healing of grain-boundaries undergoing sliding rather than progressive dilatancy or healing of opening-mode cracks. Findings are being used to inform and develop continuum damage mechanics models of semibrittle deformation in polycrystalline aggregates

Cyclic strain increases protease-activated receptor-1 expression in vascular smooth muscle cells

NASA Technical Reports Server (NTRS)

Nguyen, K. T.; Frye, S. R.; Eskin, S. G.; Patterson, C.; Runge, M. S.; McIntire, L. V.

2001-01-01

Cyclic strain regulates many vascular smooth muscle cell (VSMC) functions through changing gene expression. This study investigated the effects of cyclic strain on protease-activated receptor-1 (PAR-1) expression in VSMCs and the possible signaling pathways involved, on the basis of the hypothesis that cyclic strain would enhance PAR-1 expression, reflecting increased thrombin activity. Uniaxial cyclic strain (1 Hz, 20%) of cells cultured on elastic membranes induced a 2-fold increase in both PAR-1 mRNA and protein levels. Functional activity of PAR-1, as assessed by cell proliferation in response to thrombin, was also increased by cyclic strain. In addition, treatment of cells with antioxidants or an NADPH oxidase inhibitor blocked strain-induced PAR-1 expression. Preincubation of cells with protein kinase inhibitors (staurosporine or Ro 31-8220) enhanced strain-increased PAR-1 expression, whereas inhibitors of NO synthase, tyrosine kinase, and mitogen-activated protein kinases had no effect. Cyclic strain in the presence of basic fibroblast growth factor induced PAR-1 mRNA levels beyond the effect of cyclic strain alone, whereas no additive effect was observed between cyclic strain and platelet-derived growth factor-AB. Our findings that cyclic strain upregulates PAR-1 mRNA expression but that shear stress downregulates this gene in VSMCs provide an opportunity to elucidate signaling differences by which VSMCs respond to different mechanical forces.

Creep crack growth by grain boundary cavitation under monotonic and cyclic loading

NASA Astrophysics Data System (ADS)

Wen, Jian-Feng; Srivastava, Ankit; Benzerga, Amine; Tu, Shan-Tung; Needleman, Alan

2017-11-01

Plane strain finite deformation finite element calculations of mode I crack growth under small scale creep conditions are carried out. Attention is confined to isothermal conditions and two time histories of the applied stress intensity factor: (i) a monononic increase to a plateau value subsequently held fixed; and (ii) a cyclic time variation. The crack growth calculations are based on a micromechanics constitutive relation that couples creep deformation and damage due to grain boundary cavitation. Grain boundary cavitation, with cavity growth due to both creep and diffusion, is taken as the sole failure mechanism contributing to crack growth. The influence on the crack growth rate of loading history parameters, such as the magnitude of the applied stress intensity factor, the ratio of the applied minimum to maximum stress intensity factors, the loading rate, the hold time and the cyclic loading frequency, are explored. The crack growth rate under cyclic loading conditions is found to be greater than under monotonic creep loading with the plateau applied stress intensity factor equal to its maximum value under cyclic loading conditions. Several features of the crack growth behavior observed in creep-fatigue tests naturally emerge, for example, a Paris law type relation is obtained for cyclic loading.

History-independent cyclic response of nanotwinned metals

NASA Astrophysics Data System (ADS)

Pan, Qingsong; Zhou, Haofei; Lu, Qiuhong; Gao, Huajian; Lu, Lei

2017-11-01

Nearly 90 per cent of service failures of metallic components and structures are caused by fatigue at cyclic stress amplitudes much lower than the tensile strength of the materials involved. Metals typically suffer from large amounts of cumulative, irreversible damage to microstructure during cyclic deformation, leading to cyclic responses that are unstable (hardening or softening) and history-dependent. Existing rules for fatigue life prediction, such as the linear cumulative damage rule, cannot account for the effect of loading history, and engineering components are often loaded by complex cyclic stresses with variable amplitudes, mean values and frequencies, such as aircraft wings in turbulent air. It is therefore usually extremely challenging to predict cyclic behaviour and fatigue life under a realistic load spectrum. Here, through both atomistic simulations and variable-strain-amplitude cyclic loading experiments at stress amplitudes lower than the tensile strength of the metal, we report a history-independent and stable cyclic response in bulk copper samples that contain highly oriented nanoscale twins. We demonstrate that this unusual cyclic behaviour is governed by a type of correlated ‘necklace’ dislocation consisting of multiple short component dislocations in adjacent twins, connected like the links of a necklace. Such dislocations are formed in the highly oriented nanotwinned structure under cyclic loading and help to maintain the stability of twin boundaries and the reversible damage, provided that the nanotwins are tilted within about 15 degrees of the loading axis. This cyclic deformation mechanism is distinct from the conventional strain localizing mechanisms associated with irreversible microstructural damage in single-crystal, coarse-grained, ultrafine-grained and nanograined metals.

Damage evolution analysis of coal samples under cyclic loading based on single-link cluster method

NASA Astrophysics Data System (ADS)

Zhang, Zhibo; Wang, Enyuan; Li, Nan; Li, Xuelong; Wang, Xiaoran; Li, Zhonghui

2018-05-01

In this paper, the acoustic emission (AE) response of coal samples under cyclic loading is measured. The results show that there is good positive relation between AE parameters and stress. The AE signal of coal samples under cyclic loading exhibits an obvious Kaiser Effect. The single-link cluster (SLC) method is applied to analyze the spatial evolution characteristics of AE events and the damage evolution process of coal samples. It is found that a subset scale of the SLC structure becomes smaller and smaller when the number of cyclic loading increases, and there is a negative linear relationship between the subset scale and the degree of damage. The spatial correlation length ξ of an SLC structure is calculated. The results show that ξ fluctuates around a certain value from the second cyclic loading process to the fifth cyclic loading process, but spatial correlation length ξ clearly increases in the sixth loading process. Based on the criterion of microcrack density, the coal sample failure process is the transformation from small-scale damage to large-scale damage, which is the reason for changes in the spatial correlation length. Through a systematic analysis, the SLC method is an effective method to research the damage evolution process of coal samples under cyclic loading, and will provide important reference values for studying coal bursts.

Effect of cyclic loading and retightening on reverse torque value in external and internal implants.

PubMed

Cho, Woong-Rae; Huh, Yoon-Hyuk; Park, Chan-Jin; Cho, Lee-Ra

2015-08-01

The aim of this study was to evaluate the effect of cyclic loading and screw retightening on reverse torque value (RTV) in external and internal type implants. Cement-retained abutments were connected with 30 Ncm torque to external and internal type implants. Experimental groups were classified according to implant connection type and retightening/loading protocol. In groups with no retightening, RTV was evaluated after cyclic loading for 100,000 cycles. In groups with retightening, RTV was measured after 3, 10, 100 cycles as well as every 20,000 cycles until 100,000 cycles of loading. Every group showed decreased RTV after cyclic loading. Before and after cyclic loading, external type implants had significantly higher RTVs than internal type implants. In external type implants, retightening did not affect the decrease in RTV. In contrast, retightening 5 times and retightening after 10 cycles of dynamic loading was effective for maintaining RTV in internal type implants. Retightening of screws is more effective in internal type implants than external type implants. Retightening of screws is recommended in the early stage of functional loading.

Compressive buckling analysis of hat-stiffened panel

NASA Technical Reports Server (NTRS)

Ko, William L.; Jackson, Raymond H.

1991-01-01

Buckling analysis was performed on a hat-stiffened panel subjected to uniaxial compression. Both local buckling and global buckling were analyzed. It was found that the global buckling load was several times higher than the buckling load. The predicted local buckling loads compared favorably with both experimental data and finite-element analysis.

Investigation of the mechanical properties of organoplastic under shock wave loading conditions

NASA Astrophysics Data System (ADS)

Bragov, A. M.; Igumnov, L. A.; Konstantinov, A. Yu; Lomunov, A. K.

2018-04-01

The paper presents results of dynamic tests of a typical representative of new composite and damping materials: organoplastics. Compression testing was performed using the traditional Kolsky method and its original modification. The strength and deformation properties of organoplastics under conditions of uniaxial stress and uniaxial deformation were studied. When the organoplastic is compressed transversely to the Kevlar fabric layers under conditions of a uniaxial stress state, the material begins to break down (to lose the layer cohesion) at a stress of about 200 MPa, while under the conditions of uniaxial strain, it retains its apparent integrity at stresses up to 500 MPa. The small value of the lateral thrust factor indicates a large internal strength of the material in tension in the radial direction.

Ultra High Strain Rate Nanoindentation Testing.

PubMed

Sudharshan Phani, Pardhasaradhi; Oliver, Warren Carl

2017-06-17

Strain rate dependence of indentation hardness has been widely used to study time-dependent plasticity. However, the currently available techniques limit the range of strain rates that can be achieved during indentation testing. Recent advances in electronics have enabled nanomechanical measurements with very low noise levels (sub nanometer) at fast time constants (20 µs) and high data acquisition rates (100 KHz). These capabilities open the doors for a wide range of ultra-fast nanomechanical testing, for instance, indentation testing at very high strain rates. With an accurate dynamic model and an instrument with fast time constants, step load tests can be performed which enable access to indentation strain rates approaching ballistic levels (i.e., 4000 1/s). A novel indentation based testing technique involving a combination of step load and constant load and hold tests that enables measurement of strain rate dependence of hardness spanning over seven orders of magnitude in strain rate is presented. A simple analysis is used to calculate the equivalent uniaxial response from indentation data and compared to the conventional uniaxial data for commercial purity aluminum. Excellent agreement is found between the indentation and uniaxial data over several orders of magnitude of strain rate.

Slow Crack Growth Behavior and Life/Reliability Analysis of 96 wt % Alumina at Ambient Temperature With Various Specimen/Loading Configurations

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Powers, Lynn M.; Nemeth, Noel N.

2000-01-01

Extensive constant stress-rate testing for 96 wt % alumina was conducted in room-temperature distilled water using four different specimen/loading configurations: rectangular beam test specimens under four-point uniaxial flexure, square plate test specimens in ring-on-ring biaxial flexure, square plate test specimens in ball-on-ring biaxial flexure, and dog-boned tensile test specimens in pure tension. The slow crack growth (SCG) parameter n was almost independent of specimen/loading configurations, in either four-point uniaxial flexure, ring-on-ring biaxial flexure, ball-on-ring biaxial flexure, or pure tension, ranging from n = 35 to 47 with an average value of n = 41.1 +/- 4.5. The prediction of fatigue strength/reliability based on the four-point uniaxial flexure data by using the CARES/Life design code as well as a simple PIA model was in good agreement with both the ring-on-ring biaxial and the ball-on-ring biaxial flexure data. A poor prediction using the PIA model was observed for the dog-boned tensile test specimens, presumably due to different flaw population involved in the tensile test specimens.

Cyclic load magnitude is a risk factor for a cumulative lower back disorder.

PubMed

Le, Peter; Solomonow, Moshe; Zhou, Bing-He; Lu, Yun; Patel, Vikas

2007-04-01

Epidemiological data suggest that high loads lifted by workers engaged in static and cyclic daily activities may be a risk factor for low back disorder. Our previous research provided physiological and biomechanical validation of the epidemiological data for static load conditions. The objective of this report was to provide physiological and biomechanical experimental validation to the epidemiological data in cyclic (repetitive) load conditions. Three groups of in vivo feline models were subjected to 3 cyclic load levels in a series of 6 periods of 10 minutes of work spaced by 10 minutes of rest followed by 7 hours of rest. Multifidus electromyography (EMG) and lumbar displacement were statistically analyzed after processing. Delayed muscular hyperexcitability was observed only in moderate (40 N) and high (60 N) loads (P<0.0001) but was absent in low (20 N) loads. The magnitude of the delayed hyperexcitability was found to be higher (P<0.0001) in the high (60 N) loads compared with the moderate (40 N) loads. Exposure to moderate and high loads in cyclic (repetitive) work results in an acute neuromuscular disorder indicative of soft tissue inflammation that may become chronic with further exposure.

Numerical simulation of the fatigue behavior of additive manufactured titanium porous lattice structures.

PubMed

Zargarian, A; Esfahanian, M; Kadkhodapour, J; Ziaei-Rad, S

2016-03-01

In this paper, the effects of cell geometry and relative density on the high-cycle fatigue behavior of Titanium scaffolds produced by selective laser melting and electron beam melting techniques were numerically investigated by finite element analysis. The regular titanium lattice samples with three different unit cell geometries, namely, diamond, rhombic dodecahedron and truncated cuboctahedron, and the relative density range of 0.1-0.3 were analyzed under uniaxial cyclic compressive loading. A failure event based algorithm was employed to simulate fatigue failure in the cellular material. Stress-life approach was used to model fatigue failure of both bulk (struts) and cellular material. The predicted fatigue life and the damage pattern of all three structures were found to be in good agreement with the experimental fatigue investigations published in the literature. The results also showed that the relationship between fatigue strength and cycles to failure obeyed the power law. The coefficient of power function was shown to depend on relative density, geometry and fatigue properties of the bulk material while the exponent was only dependent on the fatigue behavior of the bulk material. The results also indicated the failure surface at an angle of 45° to the loading direction. Copyright © 2015 Elsevier B.V. All rights reserved.

Effect of laser parameters on surface roughness of laser modified tool steel after thermal cyclic loading

NASA Astrophysics Data System (ADS)

Lau Sheng, Annie; Ismail, Izwan; Nur Aqida, Syarifah

2018-03-01

This study presents the effects of laser parameters on the surface roughness of laser modified tool steel after thermal cyclic loading. Pulse mode Nd:YAG laser was used to perform the laser surface modification process on AISI H13 tool steel samples. Samples were then treated with thermal cyclic loading experiments which involved alternate immersion in molten aluminium (800°C) and water (27°C) for 553 cycles. A full factorial design of experiment (DOE) was developed to perform the investigation. Factors for the DOE are the laser parameter namely overlap rate (η), pulse repetition frequency (f PRF) and peak power (Ppeak ) while the response is the surface roughness after thermal cyclic loading. Results indicate the surface roughness of the laser modified surface after thermal cyclic loading is significantly affected by laser parameter settings.

Deformation behavior of welded steel sandwich panels under quasi-static loading

DOT National Transportation Integrated Search

2011-03-01

This report describes engineering studies that were conducted to examine the deformation behavior of flat, welded steel sandwich panels under two quasi-static loading conditions: (1) uniaxial compression; and (2) bending with an indenter. Testing and...

Triple-loaded single-anchor stitch configurations: an analysis of cyclically loaded suture-tendon interface security.

PubMed

Coons, David A; Barber, F Alan; Herbert, Morley A

2006-11-01

This study evaluated the strength and suture-tendon interface security of different suture configurations from triple-suture-loaded anchors. A juvenile bovine infraspinatus tendon was detached and repaired by use of 4 different suture combinations from 2 suture anchors: 3 simple sutures in each anchor (ThreeVo anchor; Linvatec, Largo, FL); 2 peripheral simple stitches and 1 central horizontal mattress suture passed deeper into the tendon, creating a larger footprint (bigfoot-print anchor); 2 peripheral simple stitches with 1 central horizontal mattress stitch passed through the same holes as the simple sutures (stitch-of-Burns); and 2 simple stitches (TwoVo anchor; Linvatec). The constructs were cyclically loaded between 10 N and 180 N for 3,500 cycles and then destructively tested. The number of cycles required to create a 5-mm gap and a 10-mm gap and the ultimate load to failure and failure mode were recorded. The ThreeVo anchor was strongest and most resistant to cyclic loading (P < .01). The TwoVo anchor was least resistant to cyclic loading. The stitch-of-Burns anchor was more resistant to cyclic loading than both the bigfoot-print anchor and the TwoVo anchor (P < .03). The ThreeVo, stitch-of-Burns, and TwoVo anchors were stronger than the bigfoot-print anchor (P < .05). Three simple sutures in an anchor hold better than two simple sutures. Three simple sutures provide superior suture-tendon security than combinations of one mattress and two simple stitches subjected to cyclic loading. A central mattress stitch placed more medially than two peripheral simple stitches (bigfoot-print anchor) configured to enlarge the tendon-suture footprint was not as resistant to cyclic loading or destructive testing as three simple stitches (ThreeVo anchor). Placing a central mattress stitch more medially than 2 peripheral simple stitches to enlarge the tendon-suture footprint was not as resistant to cyclic loading or destructive testing as 3 simple stitches.

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.

Effect of Cyclic Thermo-Mechanical Loads on Fatigue Reliability in Polymer Matrix Composites

NASA Technical Reports Server (NTRS)

Shah, A. R.; Murthy, P. L. N.; Chamis, C. C.

1996-01-01

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multi-factor interaction relationship developed at NASA Lewis Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability- based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)(sub s) graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

A constitutive model for AS4/PEEK thermoplastic composites under cyclic loading

NASA Technical Reports Server (NTRS)

Rui, Yuting; Sun, C. T.

1990-01-01

Based on the basic and essential features of the elastic-plastic response of the AS4/PEEK thermoplastic composite subjected to off-axis cyclic loadings, a simple rate-independent constitutive model is proposed to describe the orthotropic material behavior for cyclic loadings. A one-parameter memory surface is introduced to distinguish the virgin deformation and the subsequent deformation process and to characterize the loading range effect. Cyclic softening is characterized by the change of generalized plastic modulus. By the vanishing yield surface assumption, a yield criterion is not needed and it is not necessary to consider loading and unloading separately. The model is compared with experimental results and good agreement is obtained.

A comparison of stress in cracked fibrous tissue specimens with varied crack location, loading, and orientation using finite element analysis.

PubMed

Peloquin, John M; Elliott, Dawn M

2016-04-01

Cracks in fibrous soft tissue, such as intervertebral disc annulus fibrosus and knee meniscus, cause pain and compromise joint mechanics. A crack concentrates stress at its tip, making further failure and crack extension (fracture) more likely. Ex vivo mechanical testing is an important tool for studying the loading conditions required for crack extension, but prior work has shown that it is difficult to reproduce crack extension. Most prior work used edge crack specimens in uniaxial tension, with the crack 90° to the edge of the specimen. This configuration does not necessarily represent the loading conditions that cause in vivo crack extension. To find a potentially better choice for experiments aiming to reproduce crack extension, we used finite element analysis to compare, in factorial combination, (1) center crack vs. edge crack location, (2) biaxial vs. uniaxial loading, and (3) crack-fiber angles ranging from 0° to 90°. The simulated material was annulus fibrosus fibrocartilage with a single fiber family. We hypothesized that one of the simulated test cases would produce a stronger stress concentration than the commonly used uniaxially loaded 90° crack-fiber angle edge crack case. Stress concentrations were compared between cases in terms of fiber-parallel stress (representing risk of fiber rupture), fiber-perpendicular stress (representing risk of matrix rupture), and fiber shear stress (representing risk of fiber sliding). Fiber-perpendicular stress and fiber shear stress concentrations were greatest in edge crack specimens (of any crack-fiber angle) and center crack specimens with a 90° crack-fiber angle. However, unless the crack is parallel to the fiber direction, these stress components alone are insufficient to cause crack opening and extension. Fiber-parallel stress concentrations were greatest in center crack specimens with a 45° crack-fiber angle, either biaxially or uniaxially loaded. We therefore recommend that the 45° center crack case be tried in future experiments intended to study crack extension by fiber rupture. Copyright © 2015 Elsevier Ltd. All rights reserved.

Axisymmetric micromechanics of elastic-perfectly plastic fibrous composites under uniaxial tension loading

NASA Technical Reports Server (NTRS)

Lee, Jong-Won; Allen, David H.

1993-01-01

The uniaxial response of a continuous fiber elastic-perfectly plastic composite is modeled herein as a two-element composite cylinder. An axisymmetric analytical micromechanics solution is obtained for the rate-independent elastic-plastic response of the two-element composite cylinder subjected to tensile loading in the fiber direction for the case wherein the core fiber is assumed to be a transversely isotropic elastic-plastic material obeying the Tsai-Hill yield criterion, with yielding simulating fiber failure. The matrix is assumed to be an isotropic elastic-plastic material obeying the Tresca yield criterion. It is found that there are three different circumstances that depend on the fiber and matrix properties: fiber yield, followed by matrix yielding; complete matrix yield, followed by fiber yielding; and partial matrix yield, followed by fiber yielding, followed by complete matrix yield. The order in which these phenomena occur is shown to have a pronounced effect on the predicted uniaxial effective composite response.

Effect of cyclic loading and retightening on reverse torque value in external and internal implants

PubMed Central

Cho, Woong-Rae; Huh, Yoon-Hyuk; Park, Chan-Jin

2015-01-01

PURPOSE The aim of this study was to evaluate the effect of cyclic loading and screw retightening on reverse torque value (RTV) in external and internal type implants. MATERIALS AND METHODS Cement-retained abutments were connected with 30 Ncm torque to external and internal type implants. Experimental groups were classified according to implant connection type and retightening/loading protocol. In groups with no retightening, RTV was evaluated after cyclic loading for 100,000 cycles. In groups with retightening, RTV was measured after 3, 10, 100 cycles as well as every 20,000 cycles until 100,000 cycles of loading. RESULTS Every group showed decreased RTV after cyclic loading. Before and after cyclic loading, external type implants had significantly higher RTVs than internal type implants. In external type implants, retightening did not affect the decrease in RTV. In contrast, retightening 5 times and retightening after 10 cycles of dynamic loading was effective for maintaining RTV in internal type implants. CONCLUSION Retightening of screws is more effective in internal type implants than external type implants. Retightening of screws is recommended in the early stage of functional loading. PMID:26330975

Experimental Results From Stitched Composite Multi-Bay Fuselage Panels Tested Under Uni-Axial Compression

NASA Technical Reports Server (NTRS)

Baker, Donald J.

2004-01-01

The experimental results from two stitched VARTM composite panels tested under uni-axial compression loading are presented. The curved panels are divided by frames and stringers into five or six bays with a column of three bays along the compressive loading direction. The frames are supported at the ends to resist out-of-plane translation. Back-to-back strain gages are used to record the strain and displacement transducers were used to record the out-of-plane displacements. In addition a full-field measurement technique that utilizes a camera-based-stero-vision system was used to record displacements. The panels were loaded in increments to determine the first bay to buckle. Loading was discontinued at limit load and the panels were removed from the test machine for impact testing. After impacting at 20 ft-lbs to 25 ft-lbs of energy with a spherical indenter, the panels were loaded in compression until failure. Impact testing reduced the axial stiffness 4 percent and less than 1 percent. Postbuckled axial panel stiffness was 52 percent and 70 percent of the pre-buckled stiffness.

Dislocation evolution in 316 L stainless steel during multiaxial ratchetting deformation

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

Dong Yawei; Kang Guozheng, E-mail: guozhengkang@yahoo.com.cn; Liu Yujie

2012-03-15

Dislocation patterns and their evolutions in 316 L stainless steel during the multiaxial ratchetting deformation were observed by transmission electron microscopy (TEM). The microscopic observations indicate that the dislocation evolution presented during the multiaxial ratchetting with four kinds of multiaxial loading paths is similar to that in the uniaxial case [G. Z. Kang et al., Mater Sci Eng A 527 (2010) 5952]. That is, dislocation networks and dislocation tangles are formed quickly by the multiple-slip and cross-slip of dislocation activated by applied multiaxial stress; and then polarized patterns such as dislocation walls and elongated incipient dislocation cells are formed atmore » the last stage of multiaxial ratchetting. The dislocation patterns evolve more quickly from the modes at low dislocation density to the ones at high density during the multiaxial ratchetting than that in the uniaxial case, and some traces of multiple-slip are observed in the multiaxial ones. The dislocation evolution during the multiaxial ratchetting deformation is summarized by comparing the observed dislocation patterns with those presented in the multiaxial strain-controlled and symmetrical stress-controlled cyclic tests. The multiaxial ratchetting of 316 L stainless steel can be microscopically and qualitatively explained by the observed evolution of dislocation patterns. - Highlights: Black-Right-Pointing-Pointer Dislocation patterns change from lines and nets to tangles, walls and cells. Black-Right-Pointing-Pointer Dislocation patterns evolve quicker in the multiaxial case. Black-Right-Pointing-Pointer Aligned dislocation arrays and some traces of multiple slips are observed. Black-Right-Pointing-Pointer Heterogeneous dislocation patterns result in the multiaxial ratchetting.« less

Deformation behavior of welded steel sandwich panels under quasi-static loading

DOT National Transportation Integrated Search

2011-03-16

This paper summarizes basic research (i.e., testing and analysis) : conducted to examine the deformation behavior of flat-welded : steel sandwich panels under two types of quasi-static loading: : (1) uniaxial compression; and (2) bending through an i...

Shape Optimisation of Holes in Loaded Plates by Minimisation of Multiple Stress Peaks

DTIC Science & Technology

2015-04-01

UNCLASSIFIED UNCLASSIFIED Shape Optimisation of Holes in Loaded Plates by Minimisation of Multiple Stress Peaks Witold Waldman and Manfred...minimising the peak tangential stresses on multiple segments around the boundary of a hole in a uniaxially-loaded or biaxially-loaded plate . It is based...RELEASE UNCLASSIFIED UNCLASSIFIED Shape Optimisation of Holes in Loaded Plates by Minimisation of Multiple Stress Peaks Executive Summary Aerospace

Effect of cyclic and static tensile loading on water content and solute diffusion in canine flexor tendons: an in vitro study.

PubMed

Hannafin, J A; Arnoczky, S P

1994-05-01

This study was designed to determine the effects of various loading conditions (no load and static and cyclic tensile load) on the water content and pattern of nutrient diffusion of canine flexor tendons in vitro. Region D (designated by Okuda et al.) of the flexor digitorum profundus was subjected to a cyclic or static tensile load of 100 g for times ranging from 5 minutes to 24 hours. The results demonstrated a statistically significant loss of water in tendons subjected to both types of load as compared with the controls (no load). This loss appeared to progress with time. However, neither static nor cyclic loading appeared to alter the diffusion of 3H-glucose into the tendon over a 24-hour period compared with the controls. These results suggest that any benefit in tendon repair derived from intermittent passive motion is probably not a result of an increase in the diffusion of small nutrients in response to intermittent tensile load.

Mechanical annealing under low-amplitude cyclic loading in micropillars

NASA Astrophysics Data System (ADS)

Cui, Yi-nan; Liu, Zhan-li; Wang, Zhang-jie; Zhuang, Zhuo

2016-04-01

Mechanical annealing has been demonstrated to be an effective method for decreasing the overall dislocation density in submicron single crystal. However, simultaneously significant shape change always unexpectedly happens under extremely high monotonic loading to drive the pre-existing dislocations out of the free surfaces. In the present work, through in situ TEM experiments it is found that cyclic loading with low stress amplitude can drive most dislocations out of the submicron sample with virtually little change of the shape. The underlying dislocation mechanism is revealed by carrying out discrete dislocation dynamic (DDD) simulations. The simulation results indicate that the dislocation density decreases within cycles, while the accumulated plastic strain is small. By comparing the evolution of dislocation junction under monotonic, cyclic and relaxation deformation, the cumulative irreversible slip is found to be the key factor of promoting junction destruction and dislocation annihilation at free surface under low-amplitude cyclic loading condition. By introducing this mechanics into dislocation density evolution equations, the critical conditions for mechanical annealing under cyclic and monotonic loadings are discussed. Low-amplitude cyclic loading which strengthens the single crystal without seriously disturbing the structure has the potential applications in the manufacture of defect-free nano-devices.

Elastic-plastic analysis of a propagating crack under cyclic loading

NASA Technical Reports Server (NTRS)

Newman, J. C., Jr.; Armen, H., Jr.

1974-01-01

Development and application of a two-dimensional finite-element analysis to predict crack-closure and crack-opening stresses during specified histories of cyclic loading. An existing finite-element computer program which accounts for elastic-plastic material behavior under cyclic loading was modified to account for changing boundary conditions - crack growth and intermittent contact of crack surfaces. This program was subsequently used to study the crack-closure behavior under constant-amplitude and simple block-program loading.

Determination of the critical plane and durability estimation for a multiaxial cyclic loading

NASA Astrophysics Data System (ADS)

Burago, N. G.; Nikitin, A. D.; Nikitin, I. S.; Yakushev, V. L.

2018-03-01

An analytical procedure is proposed to determine the critical plane orientation according to the Findley criterion for the multiaxial cyclic loading. The cases of in-phase and anti-phase cyclic loading are considered. Calculations of the stress state are carried out for the system of the gas turbine engine compressor disk and blades for flight loading cycles. The formulas obtained are used for estimations of the fatigue durability of this essential element of structure.

Compressive Properties of PTFE/Al/Ni Composite Under Uniaxial Loading

NASA Astrophysics Data System (ADS)

Wang, Huai-xi; Li, Yu-chun; Feng, Bin; Huang, Jun-yi; Zhang, Sheng; Fang, Xiang

2017-05-01

To investigate the mechanical properties of pressed and sintered PTFE/Al/Ni (polytetrafluoroethylene/aluminum/nickel) composite, uniaxial quasi-static and dynamic compression experiments were conducted at strain rates from 10-2 to 3 × 103/s. The prepared samples were tested by an electrohydraulic press with 300 kN loading capacity and a split Hopkinson pressure bar (SHPB) device at room temperature. Experimental results show that PTFE/Al/Ni composite exhibits evident strain hardening and strain rate hardening. Additionally, a bilinear relationship between stress and {{log(}}\\dot{ɛ} ) is observed. The experimental data were fit to Johnson-Cook constitutive model, and the results are in well agreement with measured data.

Substructure based modeling of nickel single crystals cycled at low plastic strain amplitudes

NASA Astrophysics Data System (ADS)

Zhou, Dong

In this dissertation a meso-scale, substructure-based, composite single crystal model is fully developed from the simple uniaxial model to the 3-D finite element method (FEM) model with explicit substructures and further with substructure evolution parameters, to simulate the completely reversed, strain controlled, low plastic strain amplitude cyclic deformation of nickel single crystals. Rate-dependent viscoplasticity and Armstrong-Frederick type kinematic hardening rules are applied to substructures on slip systems in the model to describe the kinematic hardening behavior of crystals. Three explicit substructure components are assumed in the composite single crystal model, namely "loop patches" and "channels" which are aligned in parallel in a "vein matrix," and persistent slip bands (PSBs) connected in series with the vein matrix. A magnetic domain rotation model is presented to describe the reverse magnetostriction of single crystal nickel. Kinematic hardening parameters are obtained by fitting responses to experimental data in the uniaxial model, and the validity of uniaxial assumption is verified in the 3-D FEM model with explicit substructures. With information gathered from experiments, all control parameters in the model including hardening parameters, volume fraction of loop patches and PSBs, and variation of Young's modulus etc. are correlated to cumulative plastic strain and/or plastic strain amplitude; and the whole cyclic deformation history of single crystal nickel at low plastic strain amplitudes is simulated in the uniaxial model. Then these parameters are implanted in the 3-D FEM model to simulate the formation of PSB bands. A resolved shear stress criterion is set to trigger the formation of PSBs, and stress perturbation in the specimen is obtained by several elements assigned with PSB material properties a priori. Displacement increment, plastic strain amplitude control and overall stress-strain monitor and output are carried out in the user subroutine DISP and URDFIL of ABAQUS, respectively, while constitutive formulations of the FEM model are coded and implemented in UMAT. The results of the simulations are compared to experiments. This model verified the validity of Winter's two-phase model and Taylor's uniform stress assumption, explored substructure evolution and "intrinsic" behavior in substructures and successfully simulated the process of PSB band formation and propagation.

Bond–Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading

PubMed Central

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-01-01

The objective of this paper was to explore the bond–slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond–slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond–slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond–slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond–slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond–slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results. PMID:29495383

Bond-Slip Relationship for CFRP Sheets Externally Bonded to Concrete under Cyclic Loading.

PubMed

Li, Ke; Cao, Shuangyin; Yang, Yue; Zhu, Juntao

2018-02-26

The objective of this paper was to explore the bond-slip relationship between carbon fiber-reinforced polymer (CFRP) sheets and concrete under cyclic loading through experimental and analytical approaches. Modified beam tests were performed in order to gain insight into the bond-slip relationship under static and cyclic loading. The test variables are the CFRP-to-concrete width ratio, and the bond length of the CFRP sheets. An analysis of the test results in this paper and existing test results indicated that the slope of the ascending segment of the bond-slip curve decreased with an increase in the number of load cycles, but the slip corresponding to the maximum shear stress was almost invariable as the number of load cycles increased. In addition, the rate of reduction in the slope of the ascending range of the bond-slip curve during cyclic loading decreased as the concrete strength increased, and increased as the load level or CFRP-to-concrete width ratio enhanced. However, these were not affected by variations in bond length if the residual bond length was longer than the effective bond length. A bilinear bond-slip model for CFRP sheets that are externally bonded to concrete under cyclic loading, which considered the effects of the cyclic load level, concrete strength, and CFRP-to-concrete ratio, was developed based on the existing static bond-slip model. The accuracy of this proposed model was verified by a comparison between this proposed model and test results.

Extracting material response from simple mechanical tests on hardening-softening-hardening viscoplastic solids

NASA Astrophysics Data System (ADS)

Mohan, Nisha

Compliant foams are usually characterized by a wide range of desirable mechanical properties. These properties include viscoelasticity at different temperatures, energy absorption, recoverability under cyclic loading, impact resistance, and thermal, electrical, acoustic and radiation-resistance. Some foams contain nano-sized features and are used in small-scale devices. This implies that the characteristic dimensions of foams span multiple length scales, rendering modeling their mechanical properties difficult. Continuum mechanics-based models capture some salient experimental features like the linear elastic regime, followed by non-linear plateau stress regime. However, they lack mesostructural physical details. This makes them incapable of accurately predicting local peaks in stress and strain distributions, which significantly affect the deformation paths. Atomistic methods are capable of capturing the physical origins of deformation at smaller scales, but suffer from impractical computational intensity. Capturing deformation at the so-called meso-scale, which is capable of describing the phenomenon at a continuum level, but with some physical insights, requires developing new theoretical approaches. A fundamental question that motivates the modeling of foams is `how to extract the intrinsic material response from simple mechanical test data, such as stress vs. strain response?' A 3D model was developed to simulate the mechanical response of foam-type materials. The novelty of this model includes unique features such as the hardening-softening-hardening material response, strain rate-dependence, and plastically compressible solids with plastic non-normality. Suggestive links from atomistic simulations of foams were borrowed to formulate a physically informed hardening material input function. Motivated by a model that qualitatively captured the response of foam-type vertically aligned carbon nanotube (VACNT) pillars under uniaxial compression [2011,"Analysis of Uniaxial Compression of Vertically Aligned Carbon Nanotubes," J. Mech.Phys. Solids, 59, pp. 2227--2237, Erratum 60, 1753-1756 (2012)], the property space exploration was advanced to three types of simple mechanical tests: 1) uniaxial compression, 2) uniaxial tension, and 3) nanoindentation with a conical and a flat-punch tip. The simulations attempt to explain some of the salient features in experimental data, like 1) The initial linear elastic response. 2) One or more nonlinear instabilities, yielding, and hardening. The model-inherent relationships between the material properties and the overall stress-strain behavior were validated against the available experimental data. The material properties include the gradient in stiffness along the height, plastic and elastic compressibility, and hardening. Each of these tests was evaluated in terms of their efficiency in extracting material properties. The uniaxial simulation results proved to be a combination of structural and material influences. Out of all deformation paths, flat-punch indentation proved to be superior since it is the most sensitive in capturing the material properties.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2011-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Probabilistic Simulation of Combined Thermo-Mechanical Cyclic Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2010-01-01

A methodology to compute probabilistically-combined thermo-mechanical fatigue life of polymer matrix laminated composites has been developed and is demonstrated. Matrix degradation effects caused by long-term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress-dependent multifactor-interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability-integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/-45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical-cyclic loads and low thermal-cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical-cyclic loads and high thermal-cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

The role of peel stresses in cyclic debonding

NASA Technical Reports Server (NTRS)

Everett, R. A., Jr.

1982-01-01

When an adhesively bonded joint is undergoing cyclic loading, one of the possible damage modes that occurs is called cyclic debonding - progressive separation of the adherends by failure of the adhesive bond under cyclic loading. In most practical structures, both peel and shear stresses exist in the adhesive bonding during cyclic loading. The results of an experimental and analytical study to determine the role of peel stresses on cyclic debonding in a mixed mode specimen are presented. Experimentally, this was done by controlling the forces that create the peel stresses by applying a clamping force to oppose the peel stresses. Cracked lap shear joints were chosen for this study. A finite element analysis was developed to assess the effect of the clamping force on the strain energy release rates due to shear and peel stresses. The results imply that the peel stress is the principal stress causing cyclic debonding.

A micro-mechanical model to determine changes of collagen fibrils under cyclic loading

NASA Astrophysics Data System (ADS)

Chen, Michelle L.; Susilo, Monica E.; Ruberti, Jeffrey A.; Nguyen, Thao D.

Dynamic mechanical loading induces growth and remodeling in biological tissues. It can alter the degradation rate and intrinsic mechanical properties of collagen through cellular activity. Experiments showed that repeated cyclic loading of a dense collagen fibril substrate increased collagen stiffness and strength, lengthened the substrate, but did not significantly change the fibril areal fraction or fibril anisotropy (Susilo, et al. ``Collagen Network Hardening Following Cyclic Tensile Loading'', Interface Focus, submitted). We developed a model for the collagen fibril substrate (Tonge, et al. ``A micromechanical modeling study of the mechanical stabilization of enzymatic degradation of collagen tissues'', Biophys J, in press.) to probe whether changes in the fibril morphology and mechanical properties can explain the tissue-level properties observed during cyclic loading. The fibrils were modeled as a continuous distribution of wavy elastica, based on experimental measurements of fibril density and collagen anisotropy, and can experience damage after a critical stress threshold. Other mechanical properties in the model were fit to the stress response measured before and after the extended cyclic loading to determine changes in the strength and stiffness of collagen fibrils.

Instantaneous angular speed monitoring of gearboxes under non-cyclic stationary load conditions

NASA Astrophysics Data System (ADS)

Stander, C. J.; Heyns, P. S.

2005-07-01

Recent developments in the condition monitoring and asset management market have led to the commercialisation of online vibration-monitoring systems. These systems are primarily utilised to monitor large mineral mining equipment such as draglines, continuous miners and hydraulic shovels. Online monitoring systems make diagnostic information continuously available for asset management, production outsourcing and maintenance alliances with equipment manufacturers. However, most online vibration-monitoring systems are based on conventional vibration-monitoring technologies, which are prone to giving false equipment deterioration warnings on gears that operate under fluctuating load conditions. A simplified mathematical model of a gear system was developed to illustrate the feasibility of monitoring the instantaneous angular speed (IAS) as a means of monitoring the condition of gears that are subjected to fluctuating load conditions. A distinction is made between cyclic stationary load modulation and non-cyclic stationary load modulation. It is shown that rotation domain averaging will suppress the modulation caused by non-cyclic stationary load conditions but will not suppress the modulation caused by cyclic stationary load conditions. An experimental investigation on a test rig indicated that the IAS of a gear shaft could be monitored with a conventional shaft encoder to indicate a deteriorating gear fault condition.

Constitutive relations describing creep deformation for multi-axial time-dependent stress states

NASA Astrophysics Data System (ADS)

McCartney, L. N.

1981-02-01

A THEORY of primary and secondary creep deformation in metals is presented, which is based upon the concept of tensor internal state variables and the principles of continuum mechanics and thermodynamics. The theory is able to account for both multi-axial and time-dependent stress and strain states. The wellknown concepts of elastic, anelastic and plastic strains follow naturally from the theory. Homogeneous stress states are considered in detail and a simplified theory is derived by linearizing with respect to the internal state variables. It is demonstrated that the model can be developed in such a way that multi-axial constant-stress creep data can be presented as a single relationship between an equivalent stress and an equivalent strain. It is shown how the theory may be used to describe the multi-axial deformation of metals which are subjected to constant stress states. The multi-axial strain response to a general cyclic stress state is calculated. For uni-axial stress states, square-wave loading and a thermal fatigue stress cycle are analysed.

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.

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

DOE PAGES

Cheng, G.; Choi, K. S.; Hu, X.; ...

2017-04-05

Here in this study, the deformation limits of various DP980 steels are examined with the deformation instability theory. Under uniaxial tension, overall stress–strain curves of the material are estimated based on a simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, an actual microstructure-based finite element (FE) method is used to resolve the deformation compatibilities explicitly between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for themore » various DP980 considered. Under complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Orthotropic Laminated Open-cell Frameworks Retaining Strong Auxeticity under Large Uniaxial Loading

NASA Astrophysics Data System (ADS)

Tanaka, Hiro; Suga, Kaito; Iwata, Naoki; Shibutani, Yoji

2017-01-01

Anisotropic materials form inside living tissue and are widely applied in engineered structures, where sophisticated structural and functional design principles are essential to employing these materials. This paper presents a candidate laminated open-cell framework, which is an anisotropic material that shows remarkable mechanical performance. Using additive manufacturing, artificial frameworks are fabricated by lamination of in-plane orthotropic microstructures made of elbowed beam and column members; this fabricated structure features orthogonal anisotropy in three-dimensional space. Uniaxial loading tests reveal strong auxeticity (high negative Poisson’s ratios) in the out-of-plane direction, which is retained reproducibly up to the nonlinear elastic region, and is equal under tensile and compressive loading. Finite element simulations support the observed auxetic behaviors for a unit cell in the periodic framework, which preserve the theoretical elastic properties of an orthogonal solid. These findings open the possibility of conceptual materials design based on geometry.

Rock physics properties of some lunar samples

NASA Technical Reports Server (NTRS)

Warren, N.; Trice, R.; Anderson, O. L.; Soga, N.

1973-01-01

Linear strains and acoustic velocity data for lunar samples under uniaxial and hydrostatic loading are presented. Elastic properties are presented for 60335,20; 15555,68; 15498,23; and 12063,97. Internal friction data are summarized for a number of artificial lunar glasses with compositions similar to lunar rocks 12009, 12012, 14305, 15021, and 15555. Zero porosity model-rock moduli are calculated for a number of lunar model-rocks, with mineralogies similar to Apollo 12, 14, and 16 rocks. Model-rock calculations indicate that rock types in the troctolitic composition range may provide reasonable modeling of the lunar upper mantle. Model calculations involving pore crack effects are compatible with a strong dependence of rock moduli on pore strain, and therefore of rock velocities on nonhydrostatic loading. The high velocity of rocks under uniaxial loading appears to be compatible with, and may aid in, interpretation of near-surface velocity profiles observed in the active seismic experiment.

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

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

Cheng, G.; Choi, K. S.; Hu, X.

The deformation limits of various DP980 steels are examined in this study with deformation instability theory. Under uniaxial tension, overall stress-strain curves of the material are estimated based on simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, actual microstructure-based finite element (FE) method is used to explicitly resolve the deformation incompatibilities between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for the various DP980 considered. Undermore » complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Predicting Deformation Limits of Dual-Phase Steels Under Complex Loading Paths

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

Cheng, G.; Choi, K. S.; Hu, X.

Here in this study, the deformation limits of various DP980 steels are examined with the deformation instability theory. Under uniaxial tension, overall stress–strain curves of the material are estimated based on a simple rule of mixture (ROM) with both iso-strain and iso-stress assumptions. Under complex loading paths, an actual microstructure-based finite element (FE) method is used to resolve the deformation compatibilities explicitly between the soft ferrite and hard martensite phases. The results show that, for uniaxial tension, the deformation instability theory with iso-strain-based ROM can be used to provide the lower bound estimate of the uniform elongation (UE) for themore » various DP980 considered. Under complex loading paths, the deformation instability theory with microstructure-based FE method can be used in examining the effects of various microstructural features on the deformation limits of DP980 steels.« less

Degradation forecast for PEMFC cathode-catalysts under cyclic loads

NASA Astrophysics Data System (ADS)

Moein-Jahromi, M.; Kermani, M. J.; Movahed, S.

2017-08-01

Degradation of Fuel Cell (FC) components under cyclic loads is one of the biggest bottlenecks in FC commercialization. In this paper, a novel experimental based algorithm is presented to predict the Catalyst Layer (CL) performance loss during cyclic load. The algorithm consists of two models namely Models 1 and 2. The Model 1 calculates the Electro-Chemical Surface Area (ECSA) and agglomerate size (e.g. agglomerate radius, rt,agg) for the catalyst layer under cyclic load. The Model 2 is the already-existing model from our earlier studies that computes catalyst performance with fixed structural parameters. Combinations of these two Models predict the CL performance under an arbitrary cyclic load. A set of parametric/sensitivity studies is performed to investigate the effects of operating parameters on the percentage of Voltage Degradation Rate (VDR%) with rank 1 for the most influential one. Amongst the considered parameters (such as: temperature, relative humidity, pressure, minimum and maximum voltage of the cyclic load), the results show that temperature and pressure have the most and the least influences on the VDR%, respectively. So that, increase of temperature from 60 °C to 80 °C leads to over 20% VDR intensification, the VDR will also reduce 1.41% by increasing pressure from 2 atm to 4 atm.

Evaluation of the base/subgrade soil under repeated loading : phase II, in-box and ALF cyclic plate load tests.

DOT National Transportation Integrated Search

2012-03-01

This research study aims at evaluating the performance of base and subgrade soil in flexible pavements under repeated loading test conditions. For this purpose, an indoor cyclic plate load testing equipment was developed and used to conduct a series ...

Particle loading time and humidity effects on the efficiency of an N95 filtering facepiece respirator model under constant and inhalation cyclic flows.

PubMed

Mahdavi, Alireza; Haghighat, Fariborz; Bahloul, Ali; Brochot, Clothilde; Ostiguy, Claude

2015-06-01

It is necessary to investigate the efficiencies of filtering facepiece respirators (FFRs) exposed to ultrafine particles (UFPs) for long periods of time, since the particle loading time may potentially affect the efficiency of FFRs. This article aims to investigate the filtration efficiency for a model of electrostatic N95 FFRs with constant and 'inhalation-only' cyclic flows, in terms of particle loading time effect, using different humidity conditions. Filters were exposed to generated polydisperse NaCl particles. Experiments were performed mimicking an 'inhalation-only' scenario with a cyclic flow of 85 l min(-1) as the minute volume [or 170 l min(-1) as mean inhalation flow (MIF)] and for two constant flows of 85 and 170 l min(-1), under three relative humidity (RH) levels of 10, 50, and 80%. Each test was performed for loading time periods of 6h and the particle penetration (10-205.4nm in electrical mobility diameter) was measured once every 2h. For a 10% RH, the penetration of smaller size particles (<80nm), including the most penetrating particle size (MPPS), decreased over time for both constant and cyclic flows. For 50 and 80% RH levels, the changes in penetration were typically observed in an opposite direction with less magnitude. The penetrations at MPPS increased with respect to loading time under constant flow conditions (85 and 170 l min(-1)): it did not substantially increase under cyclic flows. The comparison of the cyclic flow (85 l min(-1) as minute volume) and constant flow equal to the cyclic flow minute volume indicated that, for all conditions the penetration was significantly less for the constant flow than that of cyclic flow. The comparison between the cyclic (170 l min(-1) as MIF) and constant flow equal to cyclic flow MIF indicated that, for the initial stage of loading, the penetrations were almost equal, but they were different for the final stages of the loading time. For a 10% RH, the penetration of a wide range of sizes was observed to be higher with the cyclic flow (170 as MIF) than with the equivalent constant flow (170 l min(-1)). For 50 and 80% RH levels, the penetrations were usually greater with a constant flow (170 l min(-1)) than with a cyclic flow (170 l min(-1) as MIF). It is concluded that, for the tested electrostatic N95 filters, the change in penetration as a function of the loading time does not necessarily take place with the same rate under constant (MIF) and cyclic flow. Moreover, for all tested flow rates, the penetration is not only affected by the loading time but also by the RH level. Lower RH levels (10%) have decreasing penetration rates in terms of loading time, while higher RH levels (50 and 80%) have increasing penetration rates. Also, the loading of the filter is normally accompanied with a shift of MPPS towards larger sizes. © The Author 2015. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Investigation into the Cyclic Strength of the Bodies of Steam Shutoff Valves from 10Kh9MFB-Sh Steel

NASA Astrophysics Data System (ADS)

Skorobogatykh, V. N.; Kunavin, S. A.; Prudnikov, D. A.; Shchenkova, I. A.; Bazhenov, A. M.; Zadoinyi, V. A.; Starkovskii, G. L.

2018-02-01

Steam shutoff valves are operated under complex loading conditions at thermal and nuclear power stations. In addition to exposure to high temperature and stresses resulting in fatigue, these valves are subjected to cyclic loads in heating-up-cooling down, opening-closing, etc. cycles. The number of these cycles to be specified in designing the valves should not exceed the maximum allowable value. Hence, the problem of cyclic failure rate of steam shutoff valve bodies is critical. This paper continues the previous publications about properties of the construction material for steam shutoff valve bodies (grade 10Kh9MFB-Sh steel) produced by electroslag melting and gives the results of investigation into the cyclic strength of this material. Fatigue curves for the steal used for manufacturing steam shutoff valve bodies are presented. The experimental data are compared with the calculated fatigue curves plotted using the procedures outlined in PNAE G-002-986 and RD 10-249-98. It is confirmed that these procedures may be used in designing valve bodies from 10Kh9MFB-Sh steel. The effect of the cyclic damage after preliminary cyclic loading of the specimens according to the prescribed load conditions on the high-temperature strength of the steel is examined. The influence of cyclic failure rate on the long-term strength was investigated using cylindrical specimens with a smooth working section in the as-made conditions and after two regimes of preliminary cyclic loading (training) at a working temperature of 570°C and the number of load cycles exceeding the design value, which was 2 × 103 cycles. The experiments corroborated that the material (10Kh9MFB-Sh steel) of the body manufactured by the method of electroslag melting had high resistance to cyclic failure rate. No effect of cyclic damages in the metal of the investigated specimens on the high-temperature strength has been found.

Design and Use of a Novel Bioreactor for Regeneration of Biaxially Stretched Tissue-Engineered Vessels

PubMed Central

Huang, Angela Hai; Lee, Yong-Ung; Calle, Elizabeth A.; Boyle, Michael; Starcher, Barry C.; Humphrey, Jay D.

2015-01-01

Conventional bioreactors are used to enhance extracellular matrix (ECM) production and mechanical strength of tissue-engineered vessels (TEVs) by applying circumferential strain, which is uniaxial stretching. However, the resulting TEVs still suffer from inadequate mechanical properties, where rupture strengths and compliance values are still very different from native arteries. The biomechanical milieu of native arteries consists of both circumferential and axial loading. Therefore, to better simulate the physiological stresses acting on native arteries, we built a novel bioreactor system to enable biaxial stretching of engineered arteries during culture. This new bioreactor system allows for independent control of circumferential and axial stretching parameters, such as displacement and beat rate. The assembly and setup processes for this biaxial bioreactor system are reliable with a success rate greater than 75% for completion of long-term sterile culture. This bioreactor also supports side-by-side assessments of TEVs that are cultured under three types of mechanical conditions (static, uniaxial, and biaxial), all within the same biochemical environment. Using this bioreactor, we examined the impact of biaxial stretching on arterial wall remodeling of TEVs. Biaxial TEVs developed the greatest wall thickness compared with static and uniaxial TEVs. Unlike uniaxial loading, biaxial loading led to undulated collagen fibers that are commonly found in native arteries. More importantly, the biaxial TEVs developed the most mature elastin in the ECM, both qualitatively and quantitatively. The presence of mature extracellular elastin along with the undulated collagen fibers may contribute to the observed vascular compliance in the biaxial TEVs. The current work shows that biaxial stretching is a novel and promising means to improve TEV generation. Furthermore, this novel system allows us to optimize biomechanical conditioning by unraveling the interrelationships among the applied mechanical stress, the resulting ECM properties, and the mechanics of TEVs. PMID:25669988

Finite element analysis of the biaxial cyclic tensile loading of the elastoplastic plate with the central hole: asymptotic regimes

NASA Astrophysics Data System (ADS)

Turkova, Vera; Stepanova, Larisa

2018-03-01

For elastistoplastic structure elements under cyclic loading three types of asymptotic behavior are well known: shakedown, cyclic plasticity or ratcheting. In structure elements operating in real conditions ratcheting must always be excluded since it caused the incremental fracture of structure by means of the accumulation of plastic strains. In the present study results of finite-element (FEM) calculations of the asymptotical behavior of an elastoplastic plate with the central circular and elliptic holes under the biaxial cyclic loading for three different materials are presented. Incremental cyclic loading of the sample with stress concentrator (the central hole) is performed in the multifunctional finite-element package SIMULIA Abaqus. The ranges of loads found for shakedown, cyclic plasticity and ratcheting are presented. The results obtained are generalized and analyzed. Convenient normalization is suggested. The chosen normalization allows us to present all computed results, corresponding to separate materials, within one common curve with minimum scattering of the points. Convenience of the generalized diagram consists in a possibility to find an asymptotical behavior of an inelastic structure for materials for which computer calculations were not made.

Simulation of Texture Evolution during Uniaxial Deformation of Commercially Pure Titanium

NASA Astrophysics Data System (ADS)

Bishoyi, B.; Debta, M. K.; Yadav, S. K.; Sabat, R. K.; Sahoo, S. K.

2018-03-01

The evolution of texture in commercially pure (CP) titanium during uniaxial tension and compression through VPSC (Visco-plastic self-consistent) simulation is reported in the present study. CP-titanium was subjected to both uniaxial tension and compression upto 35% deformation. During uniaxial tension, tensile twin of \\{10\\bar{1}2\\}\\unicode{x003C;}\\bar{1}011\\unicode{x003E;} type and compressive twin of \\{11\\bar{2}2\\}\\unicode{x003C;}11\\bar{2}\\bar{3}\\unicode{x003E;} type were observed in the samples. However, only tensile twin of \\{10\\bar{1}2\\}\\unicode{x003C;}\\bar{1}011\\unicode{x003E;} type and compressive twin of type was observed in the samples during uniaxial compression. Volume fractions of the twins were increased linearly as a function of percentage deformation during uniaxial tension. Whereas, during uniaxial compression the twinning volume fraction was increased up to 20% deformation and then decreased rapidly on further increasing the percentage deformation. During uniaxial tension, the general t-type textures were observed in the samples irrespective of the percentage deformation. The initial non-basal texture was oriented to split basal texture during uniaxial compression of the sample. VPSC formulation was used for simulating the texture development in the material. Different hardening parameters were estimated through correlating the simulated stress-strain curve with the experimental stress-strain data. It was observed that, prismatic slip \\{10\\bar{1}0\\}\\unicode{x003C;}11\\bar{2}0\\unicode{x003E;} operated as the primary deformation mode during uniaxial tension whereas basal slip \\{0001\\}\\unicode{x003C;}11\\bar{2}0\\unicode{x003E;} acquired the leading role during deformation through uniaxial compression. It was also revealed that active deformation modes were fully depending on percentage deformation, loading direction, and orientation of grains.

Fatigue crack growth under general-yielding cyclic-loading

NASA Technical Reports Server (NTRS)

Minzhong, Z.; Liu, H. W.

1986-01-01

In low cycle fatigue, cracks are initiated and propagated under general yielding cyclic loading. For general yielding cyclic loading, Dowling and Begley have shown that fatigue crack growth rate correlates well with the measured delta J. The correlation of da/dN with delta J was also studied by a number of other investigators. However, none of thse studies have correlated da/dN with delta J calculated specifically for the test specimens. Solomon measured fatigue crack growth in specimens in general yielding cyclic loading. The crack tips fields for Solomon's specimens are calculated using the finite element method and the J values of Solomon's tests are evaluated. The measured crack growth rate in Solomon's specimens correlates very well with the calculated delta J.

{Linking permeability and mechanical damage for basalt from Mt Etna Volcano, Italy}

NASA Astrophysics Data System (ADS)

Faoro, I.; Vinciguerra, S.; Marone, C.; Elsworth, D.

2009-04-01

Volcanic edifices, such as Mt. Etna volcano (Italy), are affected from repeated episodes of pressurisation due to magma emplacement from deep reservoirs to shallow depths. This mechanism pressurizes the large aquifers within the edifice and increases the level of crack damage within the rocks of the edifice over extended periods of times. In order to improve our understanding of the complex coupling between circulating fluids and the development of crack damage, we performed flow-through tests using cylindrical cores of Etna Basalt (Etna, Italy) to evaluate permeabilty changes as a function of approach to failure under non-hydrostatic stresses at confining pressures from 5 to 60 MPa. Samples were loaded to failure by increasing increments of axial stress or by cyclic stresses of increasing amplitude. Both intact samples and pre-drilled samples (1.18mm) were tested. Under hydrostatic stresses, the permeability values of the intact sample decrease linearly with the increments of pressure and range between 5.2*10-17 m2and 1.5*10-17m2Under non-hydrostatic conditions, at low deviatoric stresses from (up to 18 MPa), the permeability values ranged between 5.5*10-17 m2and 4*10-17m2 and tended to completely recover the initial value each time the sample was unloaded, indicating an elastic regime. At higher deviatoric stresses (up to 60 MPa) the permeability values range between 2*10-17 m2 and 0.6*10-17m2. We hypothesize that from 5MPa to 40MPa axial stress, anelastic deformation mechanisms start to occur, with progressive pore collapse and opening of microfractures, resulting in a change of permeability. Under incremental uniaxial cyclic loading up to peak stresses of 160 MPa permeability decreases up to 2 orders of magnitude from initial values of 1*10-15 m2 to 2*10-14m2 Higher initial permeability values are related to the presence of an open fracture in the sample. We interpreted the reduction as a result of progressive closure of the voids space, as the axial load is incremented. Overall it is shown that permeability on Etna basalt rocks is strongly dependent on the loading conditions. Ongoing work is expected to elucidate the mechanisms relating increasing damage mechanical damage to changes of permeability.

An Investigation of SiC/SiC Woven Composite Under Monotonic and Cyclic Loading

NASA Technical Reports Server (NTRS)

Lang, J.; Sankar, J.; Kelkar, A. D.; Bhatt, R. T.; Singh, M.; Lua, J.

1997-01-01

The desirable properties in ceramic matrix composites (CMCs), such as high temperature strength, corrosion resistance, high toughness, low density, or good creep resistance have led to increased use of CMCs in high-speed engine structural components and structures that operate in extreme temperature and hostile aero-thermo-chemical environments. Ceramic matrix composites have been chosen for turbine material in the design of 21 st-century civil propulsion systems to achieve high fuel economy, improved reliability, extended life, and reduced cost. Most commercial CMCs are manufactured using a chemical vapor infiltration (CVI) process. However, a lower cost fabrication known as melt-infiltration process is also providing CMCs marked for use in hot sections of high-speed civil transports. The scope of this paper is to report on the material and mechanical characterization of the CMCs subjected to this process and to predict the behavior through an analytical model. An investigation of the SiC/SiC 8-harness woven composite is ongoing and its tensile strength and fatigue behavior is being characterized for room and elevated temperatures. The investigation is being conducted at below and above the matrix cracking stress once these parameters are identified. Fractography and light microscopy results are being studied to characterize the failure modes resulting from pure uniaxial loading. A numerical model is also being developed to predict the laminate properties by using the constituent material properties and tow undulation.

Probabilistic Simulation for Combined Cycle Fatigue in Composites

NASA Technical Reports Server (NTRS)

Chamis, Christos C.

2010-01-01

A methodology to compute probabilistic fatigue life of polymer matrix laminated composites has been developed and demonstrated. Matrix degradation effects caused by long term environmental exposure and mechanical/thermal cyclic loads are accounted for in the simulation process. A unified time-temperature-stress dependent multifactor interaction relationship developed at NASA Glenn Research Center has been used to model the degradation/aging of material properties due to cyclic loads. The fast probability integration method is used to compute probabilistic distribution of response. Sensitivities of fatigue life reliability to uncertainties in the primitive random variables (e.g., constituent properties, fiber volume ratio, void volume ratio, ply thickness, etc.) computed and their significance in the reliability-based design for maximum life is discussed. The effect of variation in the thermal cyclic loads on the fatigue reliability for a (0/+/- 45/90)s graphite/epoxy laminate with a ply thickness of 0.127 mm, with respect to impending failure modes has been studied. The results show that, at low mechanical cyclic loads and low thermal cyclic amplitudes, fatigue life for 0.999 reliability is most sensitive to matrix compressive strength, matrix modulus, thermal expansion coefficient, and ply thickness. Whereas at high mechanical cyclic loads and high thermal cyclic amplitudes, fatigue life at 0.999 reliability is more sensitive to the shear strength of matrix, longitudinal fiber modulus, matrix modulus, and ply thickness.

Influence of weld-induced residual stresses on the hysteretic behavior of a girth-welded circular stainless steel tube

NASA Astrophysics Data System (ADS)

Lee, Chin-Hyung; Nguyen Van Do, Vuong; Chang, Kyong-Ho; Jeon, Jun-Tai; Um, Tae-Hwan

2018-04-01

The present study attempts to characterize the relevance of welding residual stresses to the hysteretic behaviour of a girth-welded circular stainless steel tube under cyclic mechanical loadings. Finite element (FE) thermal simulation of the girth butt welding process is first performed to identify the weld-induced residual stresses by using the one-way coupled three-dimensional (3-D) thermo-mechanical FE analysis method. 3-D elastic-plastic FE analysis equipped with the cyclic plasticity constitutive model capable of describing the cyclic response is next carried out to scrutinize the effects that the residual stresses have on the hysteretic performance of the girth-welded steel tube exposed to cyclic axial loading, which takes the residual stresses and plastic strains calculated from the preceding thermo-mechanical analysis as the initial condition. The analytical results demonstrate that the residual stresses bring about premature yielding and deterioration of the load carrying capacity in the elastic and the transition load ranges, whilst the residual stress effect is wiped out quickly in the plastic load domain since the residual stresses are nearly wholly relaxed after application of the cyclic plastic loading.

Fatigue Behavior of Glass Fiber-Reinforced Polymer Bars after Elevated Temperatures Exposure.

PubMed

Li, Guanghui; Zhao, Jun; Wang, Zike

2018-06-16

Fiber-reinforced polymer (FRP) bars have been widely applied in civil engineering. This paper presents the results of an experimental study to investigate the tensile fatigue mechanical properties of glass fiber-reinforced polymer (GFRP) bars after elevated temperatures exposure. For this purpose, a total of 105 GFRP bars were conducted for testing. The specimens were exposed to heating regimes of 100, 150, 200, 250, 300 and 350 °C for a period of 0, 1 or 2 h. The GFRP bars were tested with different times of cyclic load after elevated temperatures exposure. The results show that the tensile strength and elastic modulus of GFRP bars decrease with the increase of elevated temperature and holding time, and the tensile strength of GFRP bars decreases obviously by 19.5% when the temperature reaches 250 °C. Within the test temperature range, the tensile strength of GFRP bars decreases at most by 28.0%. The cyclic load accelerates the degradation of GFRP bars after elevated temperature exposure. The coupling of elevated temperature and holding time enhance the degradation effect of cyclic load on GFRP bars. The tensile strength of GFRP bars after elevated temperatures exposure at 350 °C under cyclic load is reduced by 50.5% compared with that at room temperature and by 36.3% compared with that after exposing at 350 °C without cyclic load. In addition, the elastic modulus of GFRP bars after elevated temperatures exposure at 350 °C under cyclic load is reduced by 17.6% compared with that at room temperature and by 6.0% compared with that after exposing at 350 °C without cyclic load.

Cyclic mechanical loading promotes bacterial penetration along composite restoration marginal gaps

PubMed Central

Khvostenko, D.; Salehi, S.; Naleway, S. E.; Hilton, T. J.; Ferracane, J. L.; Mitchell, J. C.; Kruzic, J. J.

2015-01-01

Objectives Secondary caries is the most common reason for composite restoration replacement and usually forms between dentin and the filling. The objective of this study was to investigate the combined effect of cyclic loading and bacterial exposure on bacterial penetration into gaps at the interface between dentin and resin composite restorative material using a novel bioreactor system and test specimen design. Methods Human molars were machined into 3 mm thick disks with 2 mm deep × 5 mm diameter cavity preparations into which composite restorations were placed. A ∼15-30 micrometer (small) or ∼300 micrometer wide (large) dentin-restoration gap was introduced along half of the interface between the dentin and restoration. Streptococcus mutans UA 159 biofilms were grown on each sample prior to testing in a bioreactor both with and without cyclic loading. Both groups of samples were tested for 2 weeks and post-test biofilm viability was confirmed with a live-dead assay. Samples were fixed, mounted and cross-sectioned to reveal the gaps and observe the depth of bacterial penetration. Results It was shown that for large gap samples the bacteria easily penetrated to the full depth of the gap independent of loading or non-loading conditions. The results for all cyclically loaded small gap samples show a consistently deep bacterial penetration down 100% of the gap while the average penetration depth was only 67% for the non-loaded samples with only two of six samples reaching 100%. Significance A new bioreactor was developed that allows combining cyclic mechanical loading and bacterial exposure of restored teeth for bacterial biofilm and demineralization studies. Cyclic loading was shown to aid bacterial penetration into narrow marginal gaps, which could ultimately promote secondary caries formation. PMID:25900624

Stress-relaxation and fatigue behaviour of synthetic brow-suspension materials.

PubMed

Kwon, Kyung-Ah; Shipley, Rebecca J; Edirisinghe, Mohan; Rayment, Andrew W; Best, Serena M; Cameron, Ruth E; Salam, Tahrina; Rose, Geoffrey E; Ezra, Daniel G

2015-02-01

Ptosis describes a low position of the upper eyelid. When this condition is due to poor function of the levator palpebrae superioris muscle, responsible for raising the lid, "brow-suspension" ptosis correction is usually performed, which involves internally attaching the malpositioned eyelid to the forehead musculature using brow-suspension materials. In service, such materials are exposed to both rapid tensile loading and unloading sequences during blinking, and a more sustained tensile strain during extended periods of closure. In this study, various mechanical tests were conducted to characterise and compare some of commonly-used synthetic brow-suspension materials (Prolene(®), Supramid Extra(®) II, Silicone rods (Visitec(®) Seiff frontalis suspension set) and Mersilene(®) mesh) for their time-dependent response. At a given constant tensile strain or load, all of the brow-suspension materials exhibited stress-relaxation or creep, with Prolene(®) having a statistically different relaxation or creep ratio as compared with those of others. Uniaxial tensile cyclic tests through preconditioning and fatigue tests demonstrated drastically different time-dependent response amongst the various materials. Although the tests generated hysteresis force-strain loops for all materials, the mechanical properties such as the number of cycles required to reach the steady-state, the reduction in the peak force, and the cyclic energy dissipation varied considerably. To reach the steady-state, Prolene(®) and the silicone rod required the greatest and the least number of cycles, respectively. Furthermore, the fatigue tests at physiologically relevant conditions (15% strain controlled at 6.5 Hz) demonstrated that the reduction in the peak force during 100,000 cycles ranged from 15% to 58%, with Prolene(®) and the silicone rod exhibiting the greatest and the least value, respectively. Many factors need to be considered to select the most suitable brow-suspension material for ptosis correction. These novel data on the mechanical time-dependent performance could therefore help to guide clinicians in their decision-making process for optimal surgical outcome. Copyright © 2014 Elsevier Ltd. All rights reserved.

Electronic excitations and chemistry in Nitromethane and HMX

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

Reed, E J; Manaa, M R; Joannopoulos, J D

2001-06-19

The nature of electronic excitations in crystalline solid nitromethane under conditions of shock loading and static compression are examined. Density functional theory calculations are used to determine the crystal bandgap under hydrostatic stress, uniaxial strain, and shear strain. Bandgap lowering under uniaxial strain due to molecular defects and vacancies is considered. In all cases, the bandgap is not lowered enough to produce a significant population of excited states in the crystal. Preliminary simulations on the formation of detonation product molecules from HMX are discussed.

Nanoindentation cannot accurately predict the tensile strength of graphene or other 2D materials

NASA Astrophysics Data System (ADS)

Han, Jihoon; Pugno, Nicola M.; Ryu, Seunghwa

2015-09-01

Due to the difficulty of performing uniaxial tensile testing, the strengths of graphene and its grain boundaries have been measured in experiments by nanoindentation testing. From a series of molecular dynamics simulations, we find that the strength measured in uniaxial simulation and the strength estimated from the nanoindentation fracture force can differ significantly. Fracture in tensile loading occurs simultaneously with the onset of crack nucleation near 5-7 defects, while the graphene sheets often sustain the indentation loads after the crack initiation because the sharply concentrated stress near the tip does not give rise to enough driving force for further crack propagation. Due to the concentrated stress, strength estimation is sensitive to the indenter tip position along the grain boundaries. Also, it approaches the strength of pristine graphene if the tip is located slightly away from the grain boundary line. Our findings reveal the limitations of nanoindentation testing in quantifying the strength of graphene, and show that the loading-mode-specific failure mechanism must be taken into account in designing reliable devices from graphene and other technologically important 2D materials.Due to the difficulty of performing uniaxial tensile testing, the strengths of graphene and its grain boundaries have been measured in experiments by nanoindentation testing. From a series of molecular dynamics simulations, we find that the strength measured in uniaxial simulation and the strength estimated from the nanoindentation fracture force can differ significantly. Fracture in tensile loading occurs simultaneously with the onset of crack nucleation near 5-7 defects, while the graphene sheets often sustain the indentation loads after the crack initiation because the sharply concentrated stress near the tip does not give rise to enough driving force for further crack propagation. Due to the concentrated stress, strength estimation is sensitive to the indenter tip position along the grain boundaries. Also, it approaches the strength of pristine graphene if the tip is located slightly away from the grain boundary line. Our findings reveal the limitations of nanoindentation testing in quantifying the strength of graphene, and show that the loading-mode-specific failure mechanism must be taken into account in designing reliable devices from graphene and other technologically important 2D materials. Electronic ESI (ESI) available: Modelling of polycrystalline graphene, verification of loading speed, biaxial tensile simulations, comparison of stress distribution, size effects of indenter radius, force-deflection curves, and stability analysis of crack propagation. See DOI: 10.1039/c5nr04134a

Short rest between cyclic flexion periods is a risk factor for a lumbar disorder.

PubMed

Hoops, Heather; Zhou, Bing-He; Lu, Yun; Solomonow, Moshe; Patel, Vikas

2007-08-01

The epidemiology identifies cyclic lumbar loading as a risk factor for cumulative trauma disorder. Experimental biomechanical and physiological confirmation is lacking. The objective of this study was to asses the impact of different rest durations applied between periods of cyclic loading on the development of an acute lumbar disorder which, if continued to be subjected to loading, may develop into a cumulative disorder. Three groups of in vivo feline preparations were subjected to six sequential 10 min loading periods of cyclic lumbar flexion at 40 N with a frequency of 0.25 Hz applied to the L-4/5 level. The rest durations varied from 5 min in the first group, to 10 min in the second and to 20 min in the third. Reflexive EMG from the multifidi and lumbar displacement were used to identify significant (P<0.001) effects of time and rest duration for post-load EMG and displacement. Single-cycle test were performed hourly for 7 h post-loading to assess recovery. A model developed earlier was applied to represent the experimental data. The groups allowed 5 and 10 min rest exhibited an acute neuromuscular disorder expressed by a significant (P<0.001) delayed hyperexcitability 2-3 h into the 7 h recovery period with the intensity of the hyperexcitability significantly higher (P<0.001) for the group allowed only 5 min rest. The group allowed 20 min rest had a slow, uneventful recovery, free of delayed hyperexcitability. Occupational and sports activities requiring repetitive (cyclic) loading of the lumbar spine may be a risk factor for the development of a cumulative lumbar disorder and may require sufficient rest, as much as twice as long as the loading period, for prevention. Comparison to similar data for static lumbar loading shows that cyclic loading is more deleterious than static loading, requiring more rest to offset the negative effect of the repeated acts of stretch.

Thermomechanical fatigue life prediction for several solders

NASA Astrophysics Data System (ADS)

Wen, Shengmin

Since solder connections operate at high homologous temperature, solders are high temperature materials. This feature makes their mechanical behavior and fatigue phenomena unique. Based on experimental findings, a physical damage mechanism is introduced for solders. The mechanism views the damage process as a series of independent local damage events characterized by the failure of individual grains, while the structural damage is the eventual percolation result of such local events. Fine's dislocation energy density concept and Mura's microcrack initiation theory are adopted to derive the fatigue formula for an individual grain. A physical damage metric is introduced to describe the material with damage. A unified creep and plasticity constitutive model is adopted to simulate the mechanical behavior of solders. The model is cast into a continuum damage mechanics framework to simulate material with damage. The model gives good agreement with the experimental results of 96.5Pb-3.5Sn and 96.5Sn-3.5Ag solders under uniaxial strain-controlled cyclic loading. The model is convenient for implementation into commercial computational packages. Also presented is a fatigue theory with its failure criterion for solders based on physical damage mechanism. By introducing grain orientation into the fatigue formula, an m-N curve (m is Schmid factor) at constant loading condition is suggested for fatigue of grains with different orientations. A solder structure is defined as fatigued when the damage metric reaches a critical threshold, since at this threshold the failed grains may form a cluster and percolate through the structure according to percolation theory. Fatigue data of 96.5Pb-3.5Sn solder bulk specimens under various uniaxial tension tests were analyzed. Results show that the theory gives consistent predictions under broad conditions, while inelastic strain theory does not. The theory is anisotropic with no size limitation to its application, which could be suitable for anisotropic small-scale (micron or nano scale) solder joints. More importantly, the theory is materials science based so that the parameters of the fatigue formula can be worked out by testing of bulk specimens while the formula can be applicable to small-scale structures. The theory suggests metallurgical control in the manufacturing process to optimize the fatigue life of solder structures.

Life prediction methodology for thermal-mechanical fatigue and elevated temperature creep design

NASA Astrophysics Data System (ADS)

Annigeri, Ravindra

Nickel-based superalloys are used for hot section components of gas turbine engines. Life prediction techniques are necessary to assess service damage in superalloy components resulting from thermal-mechanical fatigue (TMF) and elevated temperature creep. A new TMF life model based on continuum damage mechanics has been developed and applied to IN 738 LC substrate material with and without coating. The model also characterizes TMF failure in bulk NiCoCrAlY overlay and NiAl aluminide coatings. The inputs to the TMF life model are mechanical strain range, hold time, peak cycle temperatures and maximum stress measured from the stabilized or mid-life hysteresis loops. A viscoplastic model is used to predict the stress-strain hysteresis loops. A flow rule used in the viscoplastic model characterizes the inelastic strain rate as a function of the applied stress and a set of three internal stress variables known as back stress, drag stress and limit stress. Test results show that the viscoplastic model can reasonably predict time-dependent stress-strain response of the coated material and stress relaxation during hold times. In addition to the TMF life prediction methodology, a model has been developed to characterize the uniaxial and multiaxial creep behavior. An effective stress defined as the applied stress minus the back stress is used to characterize the creep recovery and primary creep behavior. The back stress has terms representing strain hardening, dynamic recovery and thermal recovery. Whenever the back stress is greater than the applied stress, the model predicts a negative creep rate observed during multiple stress and multiple temperature cyclic tests. The model also predicted the rupture time and the remaining life that are important for life assessment. The model has been applied to IN 738 LC, Mar-M247, bulk NiCoCrAlY overlay coating and 316 austenitic stainless steel. The proposed model predicts creep response with a reasonable accuracy for wide range of loading cases such as uniaxial tension, tension-torsion and tension-internal pressure loading.

Effects of Cyclic Loading on the Deformation and Elastic-Plastic Fracture Behavior of a Cast Stainless Steel

DTIC Science & Technology

1991-10-01

23 8. High Cycle Fatigue Crack Growth Data for Cast Stainless Steel Showing Comparison with Rolfe and Barsom Fit .......... 24 9. Cyclic Load...compared to the Rolfe /Barsom4 fatigue crack propagation equation for austenitic stainless steels in Fig. 8. ELASTIC-PLASTIC Cyclic J-testing was...place during both the compression and tensile loadings. The J-integral was calculated on each cycle using the Merkle -Corten 9 J equation as modified by

Multi-scale Modeling of the Impact Response of a Strain Rate Sensitive High-Manganese Austenitic Steel

NASA Astrophysics Data System (ADS)

Önal, Orkun; Ozmenci, Cemre; Canadinc, Demircan

2014-09-01

A multi-scale modeling approach was applied to predict the impact response of a strain rate sensitive high-manganese austenitic steel. The roles of texture, geometry and strain rate sensitivity were successfully taken into account all at once by coupling crystal plasticity and finite element (FE) analysis. Specifically, crystal plasticity was utilized to obtain the multi-axial flow rule at different strain rates based on the experimental deformation response under uniaxial tensile loading. The equivalent stress - equivalent strain response was then incorporated into the FE model for the sake of a more representative hardening rule under impact loading. The current results demonstrate that reliable predictions can be obtained by proper coupling of crystal plasticity and FE analysis even if the experimental flow rule of the material is acquired under uniaxial loading and at moderate strain rates that are significantly slower than those attained during impact loading. Furthermore, the current findings also demonstrate the need for an experiment-based multi-scale modeling approach for the sake of reliable predictions of the impact response.

Local Mechanical Response of Superelastic NiTi Shape-Memory Alloy Under Uniaxial Loading

NASA Astrophysics Data System (ADS)

Xiao, Yao; Zeng, Pan; Lei, Liping; Du, Hongfei

2015-11-01

In this paper, we focus on the local mechanical response of superelastic NiTi SMA at different temperatures under uniaxial loading. In situ DIC is applied to measure the local strain of the specimen. Based on the experimental results, two types of mechanical response, which are characterized with localized phase transformation and homogenous phase transformation, are identified, respectively. Motivated by residual strain accumulation phenomenon of the superelastic mechanical response, we conduct controlled experiments, and infer that for a given material point, all (or most) of the irreversibility is accumulated when the transformation front is traversing the material point. A robust constitutive model is established to explain the experimental phenomena and we successfully simulate the evolution of local strain that agrees closely with the experimental results.

Redifferentiation of dedifferentiated bovine articular chondrocytes enhanced by cyclic hydrostatic pressure under a gas-controlled system.

PubMed

Kawanishi, Makoto; Oura, Atsuhiro; Furukawa, Katsuko; Fukubayashi, Toru; Nakamura, Kozo; Tateishi, Tetsuya; Ushida, Takashi

2007-05-01

Hydrostatic pressure is one of the most frequently used mechanical stimuli in chondrocyte experiments. A variety of hydrostatic pressure loading devices have been used in cartilage cell experiments. However, no gas-controlled system with other than a low pressure load was used up to this time. Hence we used a polyolefin bag from which gas penetration was confirmed. Chondrocytes were extracted from bovine normal knee joint cartilage. After 3 passages, dedifferentiated chondrocytes were applied to form a pellet. These pellets were cultured in chemically defined serum-free medium with ITS+Premix for 3 days. Then 5 MPa of cyclic hydrostatic pressure was applied at 0.5 Hz for 4 h per day for 4 days. Semiquantitative reverse transcriptase-polymerase chain reaction showed a 5-fold increase in the levels of aggrecan mRNA due to cyclic hydrostatic pressure load (p<0.01). Type II collagen mRNA levels were also upregulated 4-fold by a cyclic hydrostatic pressure load (p<0.01). Type I collagen mRNA levels were similarly reduced in the cyclic hydrostatic pressure load group and in the control group. The partial oxygen pressure (PO2) and partial carbon dioxide pressure (PCO2) of the medium in the bag reached equilibrium in 24 h, and no significant change was observed for 3 days afterwards. PO2 and PCO2 were very well controlled. The loaded pellet showed better safranin O/fast green staining than did the control pellet. Metachromatic staining by Alcian blue staining was found to be stronger in the loaded than in the control pellets. The extracellular matrices excretion of loaded pellets was higher than that of control pellets. These results suggest that gas-controlled cyclic hydrostatic pressure enhanced the cartilaginous matrix formation of dedifferentiated cells differentiated in vitro.

Study on Determination Method of Fatigue Testing Load for Wind Turbine Blade

NASA Astrophysics Data System (ADS)

Liao, Gaohua; Wu, Jianzhong

2017-07-01

In this paper, the load calculation method of the fatigue test was studied for the wind turbine blade under uniaxial loading. The characteristics of wind load and blade equivalent load were analyzed. The fatigue property and damage theory of blade material were studied. The fatigue load for 2MW blade was calculated by Bladed, and the stress calculated by ANSYS. Goodman modified exponential function S-N curve and linear cumulative damage rule were used to calculate the fatigue load of wind turbine blades. It lays the foundation for the design and experiment of wind turbine blade fatigue loading system.

Impact of tensile strain on the thermal transport of zigzag hexagonal boron nitride nanoribbon: An equilibrium molecular dynamics study

NASA Astrophysics Data System (ADS)

Navid, Ishtiaque Ahmed; Intisar Khan, Asir; Subrina, Samia

2018-02-01

The thermal conductivity of single layer strained hexagonal boron nitride nanoribbon (h-BNNR) has been computed using the Green—Kubo formulation of Equilibrium Molecular Dynamics (EMD) simulation. We have investigated the impact of strain on thermal transport of h-BNNR by varying the applied tensile strain from 1% upto 5% through uniaxial loading. The thermal conductivity of h-BNNR decreases monotonically with the increase of uniaxial tensile strain keeping the sample size and temperature constant. The thermal conductivity can be reduced upto 86% for an applied uniaxial tensile strain of 5%. The impact of temperature and width variation on the thermal conductivity of h-BNNR has also been studied under different uniaxial tensile strain conditions. With the increase in temperature, the thermal conductivity of strained h-BNNR exhibits a decaying characteristics whereas it shows an opposite pattern with the increasing width. Such study would provide a good insight on the strain tunable thermal transport for the potential device application of boron nitride nanostructures.

Experimental, numerical, and analytical studies on the seismic response of steel-plate concrete (SC) composite shear walls

NASA Astrophysics Data System (ADS)

Epackachi, Siamak

The seismic performance of rectangular steel-plate concrete (SC) composite shear walls is assessed for application to buildings and mission-critical infrastructure. The SC walls considered in this study were composed of two steel faceplates and infill concrete. The steel faceplates were connected together and to the infill concrete using tie rods and headed studs, respectively. The research focused on the in-plane behavior of flexure- and flexure-shear-critical SC walls. An experimental program was executed in the NEES laboratory at the University at Buffalo and was followed by numerical and analytical studies. In the experimental program, four large-size specimens were tested under displacement-controlled cyclic loading. The design variables considered in the testing program included wall thickness, reinforcement ratio, and slenderness ratio. The aspect ratio (height-to-length) of the four walls was 1.0. Each SC wall was installed on top of a re-usable foundation block. A bolted baseplate to RC foundation connection was used for all four walls. The walls were identified to be flexure- and flexure-shear critical. The progression of damage in the four walls was identical, namely, cracking and crushing of the infill concrete at the toes of the walls, outward buckling and yielding of the steel faceplates near the base of the wall, and tearing of the faceplates at their junctions with the baseplate. A robust finite element model was developed in LS-DYNA for nonlinear cyclic analysis of the flexure- and flexure-shear-critical SC walls. The DYNA model was validated using the results of the cyclic tests of the four SC walls. The validated and benchmarked models were then used to conduct a parametric study, which investigated the effects of wall aspect ratio, reinforcement ratio, wall thickness, and uniaxial concrete compressive strength on the in-plane response of SC walls. Simplified analytical models, suitable for preliminary analysis and design of SC walls, were developed, validated, and implemented in MATLAB. Analytical models were proposed for monotonic and cyclic simulations of the in-plane response of flexure- and flexure-shear-critical SC wall piers. The model for cyclic analysis was developed by modifying the Ibarra-Krawinler Pinching (IKP) model. The analytical models were verified using the results of the parametric study and validated using the test data.

Damage tolerance of pressurized graphite/epoxy tape cylinders under uniaxial and biaxial loading. M.S. Thesis

NASA Technical Reports Server (NTRS)

Priest, Stacy Marie

1993-01-01

The damage tolerance behavior of internally pressurized, axially slit, graphite/epoxy tape cylinders was investigated. Specifically, the effects of axial stress, structural anisotropy, and subcritical damage were considered. In addition, the limitations of a methodology which uses coupon fracture data to predict cylinder failure were explored. This predictive methodology was previously shown to be valid for quasi-isotropic fabric and tape cylinders but invalid for structurally anisotropic (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders. The effects of axial stress and structural anisotropy were assessed by testing tape cylinders with (90/0/+/-45)(sub s), (+/-45/90)(sub s), and (+/-45/0)(sub s) layups in a uniaxial test apparatus, specially designed and built for this work, and comparing the results to previous tests conducted in biaxial loading. Structural anisotropy effects were also investigated by testing cylinders with the quasi-isotropic (0/+/-45/90)(sub s) layup which is a stacking sequence variation of the previously tested (90/0/+/-45)(sub s) layup with higher D(sub 16) and D(sub 26) terms but comparable D(sub 16) and D(sub 26) to D(sub 11) ratios. All cylinders tested and used for comparison are made from AS4/3501-6 graphite/epoxy tape and have a diameter of 305 mm. Cylinder slit lengths range from 12.7 to 50.8 mm. Failure pressures are lower for the uniaxially loaded cylinders in all cases. The smallest percent failure pressure decreases are observed for the (+/-45/90)(sub s) cylinders, while the greatest such decreases are observed for the (+/-45/0)(sub s) cylinders. The relative effects of the axial stress on the cylinder failure pressures do not correlate with the degree of structural coupling. The predictive methodology is not applicable for uniaxially loaded (+/-45/90)(sub s) and (+/-45/0)(sub s) cylinders, may be applicable for uniaxially loaded (90/0/+/-45)(sub s) cylinders, and is applicable for the biaxially loaded (90/0/+/-45)(sub s) and (0/+/-45/90)(sub s) cylinders. This indicates that the ratios of D(sub 16) and D(sub 26) to D(sub 11), as opposed to the absolute magnitudes of D(sub 16) and D(sub 26), may be important in the failure of these cylinders and in the applicability of the methodology. Discontinuities observed in the slit tip hoop strains for all the cylinders tested indicate that subcritical damage can play an important role in the failure of tape cylinders. This role varies with layup and loading condition and is likely coupled to the effects of structural anisotropy. Biaxial failure pressures may exceed the uniaxial values because the axial stress contributes to the formation of 0 deg ply splitting (accompanied by delamination) or similar stress-mitigating subcritical damage. The failure behavior of similar cylinders can also vary as a result of differences in the role of subcritical damage as observed for the case of a biaxially loaded (90/0/+/-45)(sub s) cylinder with a 12.7 mm slit. For this case, the methodology is valid when the initial coupon and cylinder fracture modes agree. However, the methodology underpredicts the failure pressure of the cylinder when a circumferential fracture path, suggestive of a 0 deg ply split, occurs at one slit tip. Thus, the failure behavior of some tape cylinders may be highly sensitive to the initial subcritical damage mechanism. Finite element analyses are recommended to determine how structural anisotropy and axial stress modify the slit tip stress states in cylinders from those found in flat plates since similarity of these stress states is a fundamental assumption of the current predictive methodology.

The 4D evolution of porosity during ongoing pressure-solution processes in NaCl using x-ray microtomography

NASA Astrophysics Data System (ADS)

Macente, Alice; Fusseis, Florian; Butler, Ian; Tudisco, Erika; Hall, Stephen; Andò, Edward

2016-04-01

Pressure-solution creep is a common deformation mechanism in the upper crust. It represents a mass transfer via dissolution-reprecipitation that critically affects the hydraulic properties of rocks. Successful management of safe radioactive storage sites in rock-salt deposits critically depends on an accurate knowledge of the hydro-mechanical behaviour of salt deposits. Despite numerous lab experiments that have been conducted, many aspects of pressure-solution are still poorly understood. There is little knowledge about the spatio-temporal evolution of porosity and permeability during pressure-solution creep. While rates of pressure-solution creep in silicates and carbonates are slow, which makes laboratory investigations of these materials impractical, compaction experiments have demonstrated that NaCl samples deform sufficiently fast to study pressure-solution creep in a lab environment at room temperature and modest loads. We present results from novel experiments that quantify the 4-dimensional (three spatial dimensions plus time) evolution of pressure-solution processes using in-situ x-ray microtomography. Our experiments are performed in custom made x-ray transparent presses. 5 mm diameter NaCl powder samples with a grain size of 250-300 μm are loaded dry into the press and pre-compacted to produce a starting aggregated material. The sample is then flooded with saturated NaCl solution and loaded uniaxially by means of a pneumatic actuator to a constant uniaxial stress. Different sample mixtures were tested, as well as different uniaxial loads. The resulting deformation of the samples is documented in 3-dimensional microtomographic datasets, acquired at regular time intervals. Image analysis allowed characterization of the microstructural evolution of the NaCl grains and the spatio-temporal distribution of porosity during ongoing mechanical and chemical compaction. The microtomography data have also been analysed with 3D Digital Image Correlation (3D-DIC or DVC) to quantify the fields of displacements in each direction, as well as volumetric and maximum shear strain fields. Following the approach described above, we have been able to quantify and characterize in 4D the evolution of pressure-solution creep and porosity distribution in relation to different sample materials and increasing uniaxial load. The presence of phyllosilicates (biotite) and more competent materials (glass beads) allowed pressure-solution to develop in a much shorter time compared to pure halite sample. The same trend is observed in samples experiencing bigger uniaxial loads (6.6 MPa v 1.6 MPa). We also found that, in the presence of phyllosilicates (biotite), pore size distribution clearly reflects the localisation of pressure-solution processes, as for natural stylolites. In the presence of glass beads, pressure-solution has a greater effect on the pore orientations rather than pore sizes. Our results extend the current understanding of the effect of pressure-solution creep on the mechanical and hydraulic properties of rocks, with implications for natural rock-salt, salt-based repository systems (nuclear and chemical waste storage) and salt mining.

Variation of the uniaxial tensile behavior of ultrafine-grained pure aluminum after cyclic pre-deformation

NASA Astrophysics Data System (ADS)

Yan, Ying; Chen, Li-jia; Zhang, Guo-qiang; Han, Dong; Li, Xiao-wu

2018-06-01

To explore the influence of cyclic pre-deformation on the mechanical behavior of ultrafine-grained (UFG) materials with a high stacking fault energy (SFE), UFG Al processed by equal-channel angular pressing (ECAP) was selected as a target material and its tensile behavior at different pre-cyclic levels D ( D = N i / N f, where N i and N f are the applied cycles and fatigue life at a constant stress amplitude of 50 MPa, respectively) along with the corresponding microstructures and deformation features were systematically studied. The cyclic pre-deformation treatment on the ECAPed UFG Al led to a decrease in flow stress, and a stress quasi-plateau stage was observed after yielding for all of the different-state UFG Al samples. The yield strength σ YS, ultimate tensile strength σ UTS, and uniform strain ɛ exhibited a strong dependence on D when D ≤ 20%; however, when D was in the range from 20% to 50%, no obvious change in mechanical properties was observed. The micro-mechanism for the effect of cyclic pre-deformation on the tensile properties of the ECAPed UFG Al was revealed and compared with that of ECAPed UFG Cu through the observations of deformation features and microstructures.

Uniaxial, Pure Bending, and Column Buckling Experiments on Superelastic NiTi Rods and Tubes

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

Watkins, Ryan T.; Reedlunn, Benjamin; Daly, Samantha

Many existing shape memory alloy (SMA) devices consist of slender beams and frames. To better understand SMA beam behavior, we experimentally examined the isothermal, room temperature response of superelastic NiTi rods and tubes, of similar outer diameters, subjected to four different modes of loading. Pure tension, pure compression, and pure bending experiments were first performed to establish and compare the baseline uniaxial and bending behaviors of rods and tubes. Column buckling experiments were then performed on rod and tube columns of several slenderness ratios to investigate their mechanical responses, phase transformation kinetics under combined uniaxial and bending deformation, and themore » interaction between material and structural instabilities. In all experiments, stereo digital image correlation measured local displacement fields in order to capture phenomena such as strain localization and propagating phase boundaries. Superelastic mechanical behavior and the nature of stress-induced phase transformation were found to be strongly affected by specimen geometry and the deformation mode. Under uniaxial tension, both the rod and tube had well-defined loading and unloading plateaus in their superelastic responses, during which stress-induced phase transformation propagated along the length of the specimen in the form of a high/low strain front. Due to the dependence of strain localization on kinematic compatibility, the high/low strain front morphologies differed between the rod and tube: for the rod, the high/low strain front consisted of a diffuse “neck”, while the high/low strain front in the tube consisted of distinct, criss-crossing “fingers.” During uniaxial compression, both cross-sectional forms exhibited higher transformation stresses and smaller transformation strains than uniaxial tension, highlighting the now well-known tension-compression asymmetry of SMAs. Additionally, phase transformation localization and propagation were absent under compressive loading. During pure bending, the moment-curvature response of both forms exhibited plateaus and strain localization during forward and reverse transformations. Rod specimens developed localized, high-curvature regions that propagated along the specimen axis and caused shear strain near the high/low curvature interface; whereas, the tube specimens exhibited finger/wedge-like high strain regions over the tensile side of the tube which caused nonlinear strain profiles through the thickness of the specimen that did not propagate. Here, it was therefore found that classical beam theory assumptions did not hold in the presence of phase transformation localization (although, the assumptions did hold on average for the tube). During column buckling, the structures were loaded into the post-buckling regime yet recovered nearly-straight forms upon unloading. Strain localization was observed only for high aspect ratio (slender) tubes, but the mechanical responses were similar to that of rods of the same slenderness ratio. Also, an interesting “unbuckling” phenomenon was discovered in certain low aspect ratio (stout) columns, where late post-buckling straightening was observed despite continuous monotonic loading. Thus, these behaviors are some of the challenging phenomena which must be captured when developing SMA constitutive models and executing structural simulations.« less

Uniaxial, Pure Bending, and Column Buckling Experiments on Superelastic NiTi Rods and Tubes

DOE PAGES

Watkins, Ryan T.; Reedlunn, Benjamin; Daly, Samantha; ...

2018-03-23

Many existing shape memory alloy (SMA) devices consist of slender beams and frames. To better understand SMA beam behavior, we experimentally examined the isothermal, room temperature response of superelastic NiTi rods and tubes, of similar outer diameters, subjected to four different modes of loading. Pure tension, pure compression, and pure bending experiments were first performed to establish and compare the baseline uniaxial and bending behaviors of rods and tubes. Column buckling experiments were then performed on rod and tube columns of several slenderness ratios to investigate their mechanical responses, phase transformation kinetics under combined uniaxial and bending deformation, and themore » interaction between material and structural instabilities. In all experiments, stereo digital image correlation measured local displacement fields in order to capture phenomena such as strain localization and propagating phase boundaries. Superelastic mechanical behavior and the nature of stress-induced phase transformation were found to be strongly affected by specimen geometry and the deformation mode. Under uniaxial tension, both the rod and tube had well-defined loading and unloading plateaus in their superelastic responses, during which stress-induced phase transformation propagated along the length of the specimen in the form of a high/low strain front. Due to the dependence of strain localization on kinematic compatibility, the high/low strain front morphologies differed between the rod and tube: for the rod, the high/low strain front consisted of a diffuse “neck”, while the high/low strain front in the tube consisted of distinct, criss-crossing “fingers.” During uniaxial compression, both cross-sectional forms exhibited higher transformation stresses and smaller transformation strains than uniaxial tension, highlighting the now well-known tension-compression asymmetry of SMAs. Additionally, phase transformation localization and propagation were absent under compressive loading. During pure bending, the moment-curvature response of both forms exhibited plateaus and strain localization during forward and reverse transformations. Rod specimens developed localized, high-curvature regions that propagated along the specimen axis and caused shear strain near the high/low curvature interface; whereas, the tube specimens exhibited finger/wedge-like high strain regions over the tensile side of the tube which caused nonlinear strain profiles through the thickness of the specimen that did not propagate. Here, it was therefore found that classical beam theory assumptions did not hold in the presence of phase transformation localization (although, the assumptions did hold on average for the tube). During column buckling, the structures were loaded into the post-buckling regime yet recovered nearly-straight forms upon unloading. Strain localization was observed only for high aspect ratio (slender) tubes, but the mechanical responses were similar to that of rods of the same slenderness ratio. Also, an interesting “unbuckling” phenomenon was discovered in certain low aspect ratio (stout) columns, where late post-buckling straightening was observed despite continuous monotonic loading. Thus, these behaviors are some of the challenging phenomena which must be captured when developing SMA constitutive models and executing structural simulations.« less

Biomechanical evaluation of various suture configurations in side-to-side tenorrhaphy.

PubMed

Wagner, Emilio; Ortiz, Cristian; Wagner, Pablo; Guzman, Rodrigo; Ahumada, Ximena; Maffulli, Nicola

2014-02-05

Side-to-side tenorrhaphy is increasingly used, but its mechanical performance has not been studied. Two porcine flexor digitorum tendon segments of equal length (8 cm) and thickness (1 cm) were placed side by side. Eight tenorrhaphies (involving sixteen tendons) were performed with each of four suture techniques (running locked, simple eight, vertical mattress, and pulley suture). The resulting constructs underwent cyclic loading on a tensile testing machine, followed by monotonically increasing tensile load if failure during cyclic loading did not occur. Clamps secured the tendons on each side of the repair, and specimens were mounted vertically. Cyclic loading varied between 15 N and 35 N, with a distension rate of 1 mm/sec. Cyclic loading strength was determined by applying a force of 70 N. The cause of failure and tendon distension during loading were recorded. All failures occurred in the monotonic loading phase and resulted from tendon stripping. No suture or knot failure was observed. The mean loads resisted by the configurations ranged from 138 to 398 N. The mean load to failure, maximum load resisted prior to 1 cm of distension, and load resisted at 1 cm of distension were significantly lower for the vertical mattress suture group than for any of the other three groups (p < 0.031). All four groups sustained loads well above the physiologic loads expected to occur in tendons in the foot and ankle (e.g., in tendon transfer for tibialis posterior tendon insufficiency). None of the four side-to-side configurations distended appreciably during the cyclic loading phase. The vertical mattress suture configuration appeared to be weaker than the other configurations. For surgeons who advocate immediate loading or motion of a side-to-side tendon repair, a pulley, running locked, or simple eight suture technique appears to provide a larger safety margin compared with a vertical mattress suture technique.

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).

Effects of Simulated Functional Loading Conditions on Dentin, Composite, and Laminate Structures

PubMed Central

Walker, Mary P.; Teitelbaum, Heather K.; Eick, J. David; Williams, Karen B.

2008-01-01

Use of composite restorations continues to increase, tempered by more potential problems when placed in posterior dentition. Thus, it is essential to understand how these materials function under stress-bearing clinical conditions. Since mastication is difficult to replicate in the laboratory, cyclic loading is frequently used within in vitro evaluations but often employs traditional fatigue testing, which typically does not simulate occlusal loading because higher stresses and loading frequencies are used, so failure mechanisms may be different. The present investigation utilized relevant parameters (specimen size; loading frequency) to assess the effects of cyclic loading on flexural mechanical properties and fracture morphology of (coronal) dentin, composite, and dentin-adhesive-composite “laminate” structures. Incremental monitoring of flexural modulus on individual beams over 60,000 loading cycles revealed a gradual increase across materials; post-hoc comparisons indicated statistical significance only for 1 versus 60k cycles. Paired specimens were tested (one exposed to 60k loading cycles, one to static loading only), and comparisons of flexural modulus and strength showed statistically significantly higher values for cyclically-loaded specimens across materials, with no observable differences in fracture morphology. Localized reorganization of dentin collagen and polymer chains could have increased flexural modulus and strength during cyclic loading, which may have implications toward the life and failure mechanisms of clinical restorations and underlying tooth structure. PMID:18823019

Study on Energy Absorption Capacity of Steel-Polyester Hybrid Fiber Reinforced Concrete Under Uni-axial Compression

NASA Astrophysics Data System (ADS)

Chella Gifta, C.; Prabavathy, S.

2018-05-01

This work presents the energy absorption capacity of hybrid fiber reinforced concrete made with hooked end steel fibers (0.5 and 0.75%) and straight polyester fibers (0.5, 0.8, 1.0 and 2.0%). Compressive toughness (energy absorption capacity) under uni-axial compression was evaluated on 100 × 200 mm size cylindrical specimens with varying steel and polyester fiber content. Efficiency of the hybrid fiber reinforcement is studied with respect to fiber type, size and volume fractions in this investigation. The vertical displacement under uni-axial compression was measured under the applied loads and the load-deformation curves were plotted. From these curves the toughness values were calculated and the results were compared with steel and polyester as individual fibers. The hybridization of 0.5% steel + 0.5% polyester performed well in post peak region due to the addition of polyester fibers with steel fibers and the energy absorption value was 23% greater than 0.5% steel FRC. Peak stress values were also higher in hybrid series than single fiber and based on the results it is concluded that hybrid fiber reinforcement improves the toughness characteristics of concrete without affecting workability.

On the Interplay Between Adhesion Strength and Tensile Properties of Thermal Spray Coated Laminates—Part II: Low-Velocity Thermal Spray Coatings

NASA Astrophysics Data System (ADS)

Luo, Xiaotao; Smith, Gregory M.; Sampath, Sanjay

2018-02-01

In this two-part study, uniaxial tensile testing was used to evaluate coating/substrate bonding and compared with traditional ASTM C633 bond pull test results for thermal spray (TS) coated steel laminates. In Part I, the rationale, methodology, and applicability of the test to high-velocity TS coatings were demonstrated. In this Part II, the method was investigated for low-velocity TS processes (air plasma spray and arc spray) on equivalent materials. Ni and Ni-5wt.%Al coatings were deposited on steel substrates with three different roughness levels and tested using both uniaxial tensile and ASTM C633 methods. The results indicate the uniaxial tensile approach provides useful information about the nature of the coating/substrate bonding and goes beyond the traditional bond pull test in providing insightful information on the load sharing processes across the interface. Additionally, this proposed methodology alleviates some of the longstanding shortcomings and potentially reduces error associated with the traditional ASTM C633 test. The mechanisms governing the load transfer between the substrate and the coating were investigated, and the influence of Al in the coating material evaluated.

Validation of a New Elastoplastic Constitutive Model Dedicated to the Cyclic Behaviour of Brittle Rock Materials

NASA Astrophysics Data System (ADS)

Cerfontaine, B.; Charlier, R.; Collin, F.; Taiebat, M.

2017-10-01

Old mines or caverns may be used as reservoirs for fuel/gas storage or in the context of large-scale energy storage. In the first case, oil or gas is stored on annual basis. In the second case pressure due to water or compressed air varies on a daily basis or even faster. In both cases a cyclic loading on the cavern's/mine's walls must be considered for the design. The complexity of rockwork geometries or coupling with water flow requires finite element modelling and then a suitable constitutive law for the rock behaviour modelling. This paper presents and validates the formulation of a new constitutive law able to represent the inherently cyclic behaviour of rocks at low confinement. The main features of the behaviour evidenced by experiments in the literature depict a progressive degradation and strain of the material with the number of cycles. A constitutive law based on a boundary surface concept is developed. It represents the brittle failure of the material as well as its progressive degradation. Kinematic hardening of the yield surface allows the modelling of cycles. Isotropic softening on the cohesion variable leads to the progressive degradation of the rock strength. A limit surface is introduced and has a lower opening than the bounding surface. This surface describes the peak strength of the material and allows the modelling of a brittle behaviour. In addition a fatigue limit is introduced such that no cohesion degradation occurs if the stress state lies inside this surface. The model is validated against three different rock materials and types of experiments. Parameters of the constitutive laws are calibrated against uniaxial tests on Lorano marble, triaxial test on a sandstone and damage-controlled test on Lac du Bonnet granite. The model is shown to reproduce correctly experimental results, especially the evolution of strain with number of cycles.

The cell-stretcher: A novel device for the mechanical stimulation of cell populations

NASA Astrophysics Data System (ADS)

Seriani, S.; Del Favero, G.; Mahaffey, J.; Marko, D.; Gallina, P.; Long, C. S.; Mestroni, L.; Sbaizero, O.

2016-08-01

Mechanical stimulation appears to be a critical modulator for many aspects of biology, both of living tissue and cells. The cell-stretcher, a novel device for the mechanical uniaxial stimulation of populations of cells, is described. The system is based on a variable stroke cam-lever-tappet mechanism which allows the delivery of cyclic stimuli with frequencies of up to 10 Hz and deformation between 1% and 20%. The kinematics is presented and a simulation of the dynamics of the system is shown, in order to compute the contact forces in the mechanism. The cells, following cultivation and preparation, are plated on an ad hoc polydimethylsiloxane membrane which is then loaded on the clamps of the cell-stretcher via force-adjustable magnetic couplings. In order to show the viability of the experimentation and biocompatibility of the cell-stretcher, a set of two in vitro tests were performed. Human epithelial carcinoma cell line A431 and Adult Mouse Ventricular Fibroblasts (AMVFs) from a dual reporter mouse were subject to 0.5 Hz, 24 h cyclic stretching at 15% strain, and to 48 h stimulation at 0.5 Hz and 15% strain, respectively. Visual analysis was performed on A431, showing definite morphological changes in the form of cellular extroflections in the direction of stimulation compared to an unstimulated control. A cytometric analysis was performed on the AMVF population. Results show a post-stimulation live-dead ratio deviance of less than 6% compared to control, which proves that the environment created by the cell-stretcher is suitable for in vitro experimentation.

Life assessment of structural components using inelastic finite element analyses

NASA Technical Reports Server (NTRS)

Arya, Vinod K.; Halford, Gary R.

1993-01-01

The need for enhanced and improved performance of structural components subject to severe cyclic thermal/mechanical loadings, such as in the aerospace industry, requires development of appropriate solution technologies involving time-dependent inelastic analyses. Such analyses are mandatory to predict local stress-strain response and to assess more accurately the cyclic life time of structural components. The NASA-Lewis Research Center is cognizant of this need. As a result of concerted efforts at Lewis during the last few years, several such finite element solution technologies (in conjunction with the finite element program MARC) were developed and successfully applied to numerous uniaxial and multiaxial problems. These solution technologies, although developed for use with MARC program, are general in nature and can easily be extended for adaptation with other finite element programs such as ABAQUS, ANSYS, etc. The description and results obtained from two such inelastic finite element solution technologies are presented. The first employs a classical (non-unified) creep-plasticity model. An application of this technology is presented for a hypersonic inlet cowl-lip problem. The second of these technologies uses a unified creep-plasticity model put forth by Freed. The structural component for which this finite element solution technology is illustrated, is a cylindrical rocket engine thrust chamber. The advantages of employing a viscoplastic model for nonlinear time-dependent structural analyses are demonstrated. The life analyses for cowl-lip and cylindrical thrust chambers are presented. These analyses are conducted by using the stress-strain response of these components obtained from the corresponding finite element analyses.

Damage accumulation of bovine bone under variable amplitude loads.

PubMed

Campbell, Abbey M; Cler, Michelle L; Skurla, Carolyn P; Kuehl, Joseph J

2016-12-01

Stress fractures, a painful injury, are caused by excessive fatigue in bone. This study on damage accumulation in bone sought to determine if the Palmgren-Miner rule (PMR), a well-known linear damage accumulation hypothesis, is predictive of fatigue failure in bone. An electromagnetic shaker apparatus was constructed to conduct cyclic and variable amplitude tests on bovine bone specimens. Three distinct damage regimes were observed following fracture. Fractures due to a low cyclic amplitude loading appeared ductile ( 4000 μ ϵ ), brittle due to high cyclic amplitude loading (> 9000 μ ϵ ), and a combination of ductile and brittle from mid-range cyclic amplitude loading (6500 -6750 μ ϵ ). Brittle and ductile fracture mechanisms were isolated and mixed, in a controlled way, into variable amplitude loading tests. PMR predictions of cycles to failure consistently over-predicted fatigue life when mixing isolated fracture mechanisms. However, PMR was not proven ineffective when used with a single damage mechanism.

Phase Transformation Evolution in NiTi Shape Memory Alloy under Cyclic Nanoindentation Loadings at Dissimilar Rates

PubMed Central

Amini, Abbas; Cheng, Chun; Kan, Qianhua; Naebe, Minoo; Song, Haisheng

2013-01-01

Hysteresis energy decreased significantly as nanocrystalline NiTi shape memory alloy was under triangular cyclic nanoindentation loadings at high rate. Jagged curves evidenced discrete stress relaxations. With a large recovery state of maximum deformation in each cycle, this behavior concluded in several nucleation sites of phase transformation in stressed bulk. Additionally, the higher initial propagation velocity of interface and thermal activation volume, and higher levels of phase transition stress in subsequent cycles explained the monotonic decreasing trend of dissipated energy. In contrast, the dissipated energy showed an opposite increasing trend during triangular cyclic loadings at a low rate and 60 sec holding time after each unloading stage. Due to the isothermal loading rate and the holding time, a major part of the released latent heat was transferred during the cyclic loading resulting in an unchanged phase transition stress. This fact with the reorientation phenomenon explained the monotonic increasing trend of hysteresis energy. PMID:24336228

Effects of attrition, prior acid-etching, and cyclic loading on the bond strength of a self-etching adhesive system to dentin.

PubMed

Shinkai, Koichi; Ebihara, Takashi; Shirono, Manabu; Seki, Hideaki; Wakaki, Suguru; Suzuki, Masaya; Suzuki, Shiro; Katoh, Yoshiroh

2009-03-01

The purpose of this study was to evaluate the effects of dentin attrition, phosphoric acid etching, and cyclic loading on the microtensile bond strength (microTBS) of a self-etching adhesive system to dentin. Flat dentin surfaces of human molars were assigned to eight experimental groups based on those with or without attrition, prior acid-etching, and cyclic loading. Resin composite paste was placed and polymerized after the bonding procedure according to manufacturer's instructions. The specimens were subjected to microTBS testing at a crosshead speed of 0.5 mm/min. Results showed that the minimum mean value of microTBS was 14.9 MPa in the group without attrition and acid-etching but with loading, while the maximum mean value of microTBS was 40.0 MPa in the group without attrition and loading but with acid etching. Therefore, the value of microTBS to dentin without attrition was significantly decreased by cyclic loading but that to dentin with attrition was not affected.

The impact of posture and prolonged cyclic compressive loading on vertebral joint mechanics.

PubMed

Gooyers, Chad E; McMillan, Robert D; Howarth, Samuel J; Callaghan, Jack P

2012-08-01

An in vitro biomechanics investigation exposing porcine functional spinal units (FSUs) to submaximal cyclic or static compressive forces while in a flexed, neutral, or extended posture. To investigate the combined effect of cyclically applied compressive force (e.g., vibration) and postural deviation on intervertebral joint mechanics. Independently, prolonged vibration exposure and non-neutral postures are known risk factors for development of low back pain and injury. However, there is limited basic scientific evidence to explain how the risk of low back injury from vibration exposure is modified by other mechanical factors. This work examined the influence of static postural deviation on vertebral joint height loss and compressive stiffness under cyclically applied compressive force. Forty-eight FSUs, consisting of 2 adjacent vertebrae, ligaments, and the intervening intervertebral disc were included in the study. Each specimen was randomized to 1 of 3 experimental posture conditions (neutral, flexed, or extended) and assigned to 1 of 2 loading protocols, consisting of (1) cyclic (1500 ± 1200 N applied at 5 Hz using a sinusoidal waveform, resulting in 0.2 g rms acceleration) or (2) 1500 N of static compressive force. RESULTS.: As expected, FSU height loss followed a typical first-order response in both the static and cyclic loading protocols, with the majority (~50%) of the loss occurring in the first 20 minutes of testing. A significant interaction between posture and loading protocol (P < 0.001) was noted in the magnitude of FSU height loss. Subsequent analysis of simple effects revealed significant differences between cyclic and static loading protocols in both a neutral (P = 0.016) and a flexed posture (P < 0.0001). No significant differences (P = 0.320) were noted between pre/postmeasurements of FSU compressive stiffness. Posture is an important mechanical factor to consider when assessing the risk of injury from cyclic loading to the lumbar spine.

Cyclic stress effect on stress corrosion cracking of duplex stainless steel in chloride and caustic solutions

NASA Astrophysics Data System (ADS)

Yang, Di

Duplex stainless steel (DSS) is a dual-phase material with approximately equal volume amount of austenite and ferrite. It has both great mechanical properties (good ductility and high tensile/fatigue strength) and excellent corrosion resistance due to the mixture of the two phases. Cyclic loadings with high stress level and low frequency are experienced by many structures. However, the existing study on corrosion fatigue (CF) study of various metallic materials has mainly concentrated on relatively high frequency range. No systematic study has been done to understand the ultra-low frequency (˜10-5 Hz) cyclic loading effect on stress corrosion cracking (SCC) of DSSs. In this study, the ultra-low frequency cyclic loading effect on SCC of DSS 2205 was studied in acidified sodium chloride and caustic white liquor (WL) solutions. The research work focused on the environmental effect on SCC of DSS 2205, the cyclic stress effect on strain accumulation behavior of DSS 2205, and the combined environmental and cyclic stress effect on the stress corrosion crack initiation of DSS 2205 in the above environments. Potentiodynamic polarization tests were performed to investigate the electrochemical behavior of DSS 2205 in acidic NaCl solution. Series of slow strain rate tests (SSRTs) at different applied potential values were conducted to reveal the optimum applied potential value for SCC to happen. Room temperature static and cyclic creep tests were performed in air to illustrate the strain accumulation effect of cyclic stresses. Test results showed that cyclic loading could enhance strain accumulation in DSS 2205 compared to static loading. Moreover, the strain accumulation behavior of DSS 2205 was found to be controlled by the two phases of DSS 2205 with different crystal structures. The B.C.C. ferrite phase enhanced strain accumulation due to extensive cross-slips of the dislocations, whereas the F.C.C. austenite phase resisted strain accumulation due to cyclic strain hardening. Cyclic SSRTs were performed under the conditions that SCC occurs in sodium chloride and WL solutions. Test results show that cyclic stress facilitated crack initiations in DSS 2205. Stress corrosion cracks initiated from the intermetallic precipitates in acidic chloride environment, and the cracks initiated from austenite phase in WL environment. Cold-working has been found to retard the crack initiations induced by cyclic stresses.

Evaluation of Long Composite Struts

NASA Technical Reports Server (NTRS)

Jegley, Dawn C.; Wu, K. Chauncey; Phelps, James E.; McKenney, Martin J.; Oremont, Leonard; Barnard, Ansley

2011-01-01

Carbon-epoxy tapered struts are structurally efficient and offer opportunities for weight savings on aircraft and spacecraft structures. Seven composite struts were designed, fabricated and experimentally evaluated through uniaxial loading. The design requirements, analytical predictions and experimental results are presented. Struts with a tapered composite body and corrugated titanium end fittings successfully supported their design ultimate loads with no evidence of failure.

Dynamic strain aging in stress controlled creep-fatigue tests of 316L stainless steel under different loading conditions

NASA Astrophysics Data System (ADS)

Jiang, Huifeng; Chen, Xuedong; Fan, Zhichao; Dong, Jie; Jiang, Heng; Lu, Shouxiang

2009-08-01

Stress controlled fatigue-creep tests were carried out for 316L stainless steel under different loading conditions, i.e. different loading levels at the fixed temperature (loading condition 1, LC1) and different temperatures at the fixed loading level (loading condition 2, LC2). Cyclic deformation behaviors were investigated with respect to the evolutions of strain amplitude and mean strain. Abrupt mean strain jumps were found during cyclic deformation, which was in response to the dynamic strain aging effect. Moreover, as to LC1, when the minimum stress is negative at 550 °C, abrupt mean strain jumps occur at the early stage of cyclic deformation and there are many jumps during the whole process. While the minimum stress is positive, mean strain only jumps once at the end of deformation. Similar results were also found in LC2, when the loading level is fixed at -100 to 385 MPa, at higher temperatures (560, 575 °C), abrupt mean strain jumps occur at the early stage of cyclic deformation and there are many jumps during the whole process. While at lower temperature (540 °C), mean strain only jumps once at the end of deformation.

Experimental investigation of steel fiber-reinforced concrete beams under cyclic loading

NASA Astrophysics Data System (ADS)

Ranjbaran, Fariman; Rezayfar, Omid; Mirzababai, Rahmatollah

2018-03-01

An experimental study has been conducted to study the cyclic behavior of reinforced concrete beams in which steel fibers were added to the concrete mix. Seven similar geometrically specimens in full scale were studied under four- point bending test in the form of slow cyclic loading. One sample as a control specimen was made without steel fibers or 0% volume fraction (vf) and six other samples with 1, 2 and 4% vf of steel fibers in twin models. The maximum and ultimate resistance, ductility, degradation of loading and unloading stiffness, absorption and dissipation of energy and equivalent viscous damping were studied in this investigation and the effect of steel fibers on the cyclic behavior was compared with each other. Generally, the addition of steel fibers up to a certain limit value (vf = 2%) improves the cyclic behavior of reinforced concrete beams and results in the increase of maximum strength and ultimate displacement.

Mechanical behavior of NiTi arc wires under pseudoelastic cycling and cathodically hydrogen charging

NASA Astrophysics Data System (ADS)

Sarraj, R.; Hassine, T.; Gamaoun, F.

2018-01-01

NiTi wires are mainly used to design orthodontic devices. However, they may be susceptible to a delayed fracture while they are submitted to cyclic loading with the presence of hydrogen in the oral cavity. Hydrogen may cause the embrittlement of the structure, leading to lower ductility and to a change in transformation behavior. The aim of the present study is to predict the NiTi behavior under cyclic loading with hydrogen charging. One the one hand, samples are submitted to superelastic cyclic loading, which results in investigating their performance degradations. On the other hand, after hydrogen charging, cyclic tensile aging tests are carried out on NiTi orthodontic wires at room temperature in the air. During cyclic loading, we notice that the critical stress for the martensite transformation evolves, the residual strain is accumulated in the structure and the hysteresis loop changes. Thus, via this work, we can assume that the embrittlement is due to the diffusion of hydrogen and the generation of dislocations after aging. The evolution of mechanical properties of specimens becomes more significant with hydrogen charging rather than without it.

A nonlinear CDM based damage growth law for ductile materials

NASA Astrophysics Data System (ADS)

Gautam, Abhinav; Priya Ajit, K.; Sarkar, Prabir Kumar

2018-02-01

A nonlinear ductile damage growth criterion is proposed based on continuum damage mechanics (CDM) approach. The model is derived in the framework of thermodynamically consistent CDM assuming damage to be isotropic. In this study, the damage dissipation potential is also derived to be a function of varying strain hardening exponent in addition to damage strain energy release rate density. Uniaxial tensile tests and load-unload-cyclic tensile tests for AISI 1020 steel, AISI 1030 steel and Al 2024 aluminum alloy are considered for the determination of their respective damage variable D and other parameters required for the model(s). The experimental results are very closely predicted, with a deviation of 0%-3%, by the proposed model for each of the materials. The model is also tested with predictabilities of damage growth by other models in the literature. Present model detects the state of damage quantitatively at any level of plastic strain and uses simpler material tests to find the parameters of the model. So, it should be useful in metal forming industries to assess the damage growth for the desired deformation level a priori. The superiority of the new model is clarified by the deviations in the predictability of test results by other models.

Micromechanics of soil responses in cyclic simple shear tests

NASA Astrophysics Data System (ADS)

Cui, Liang; Bhattacharya, Subhamoy; Nikitas, George

2017-06-01

Offshore wind turbine (OWT) foundations are subjected to a combination of cyclic and dynamic loading arising from wind, wave, rotor and blade shadowing. Under cyclic loading, most soils change their characteristics including stiffness, which may cause the system natural frequency to approach the loading frequency and lead to unplanned resonance and system damage or even collapse. To investigate such changes and the underlying micromechanics, a series of cyclic simple shear tests were performed on the RedHill 110 sand with different shear strain amplitudes, vertical stresses and initial relative densities of soil. The test results showed that: (a) Vertical accumulated strain is proportional to the shear strain amplitude but inversely proportional to relative density of soil; (b) Shear modulus increases rapidly in the initial loading cycles and then the rate of increase diminishes and the shear modulus remains below an asymptote; (c) Shear modulus increases with increasing vertical stress and relative density, but decreasing with increasing strain amplitude. Coupled DEM simulations were performed using PFC2D to analyse the micromechanics underlying the cyclic behaviour of soils. Micromechanical parameters (e.g. fabric tensor, coordination number) were examined to explore the reasons for the various cyclic responses to different shear strain amplitudes or vertical stresses. Both coordination number and magnitude of fabric anisotropy contribute to the increasing shear modulus.

Unraveling cyclic deformation mechanisms of a rolled magnesium alloy using in situ neutron diffraction

DOE PAGES

Wu, Wei; An, Ke; Liaw, Peter K.

2014-12-23

In the current study, the deformation mechanisms of a rolled magnesium alloy were investigated under cyclic loading using real-time in situ neutron diffraction under a continuous-loading condition. The relationship between the macroscopic cyclic deformation behavior and the microscopic response at the grain level was established. The neutron diffraction results indicate that more and more grains are involved in the twinning and detwinning deformation process with the increase of fatigue cycles. The residual twins appear in the early fatigue life, which is responsible for the cyclic hardening behavior. The asymmetric shape of the hysteresis loop is attributed to the early exhaustionmore » of the detwinning process during compression, which leads to the activation of dislocation slips and rapid strain-hardening. The critical resolved shear stress for the activation of tensile twinning closely depends on the residual strain developed during cyclic loading. In the cycle before the sample fractured, the dislocation slips became active in tension, although the sample was not fully twinned. The increased dislocation density leads to the rise of the stress concentration at weak spots, which is believed to be the main reason for the fatigue failure. Furthermore, the deformation history greatly influences the deformation mechanisms of hexagonal-close-packed-structured magnesium alloy during cyclic loading.« less

Load-bearing capacity of screw-retained CAD/CAM-produced titanium implant frameworks (I-Bridge®2) before and after cyclic mechanical loading.

PubMed

Dittmer, Marc Philipp; Nensa, Moritz; Stiesch, Meike; Kohorst, Philipp

2013-01-01

Implant-supported screw-retained fixed dental prostheses (FDPs) produced by CAD/ CAM have been introduced in recent years for the rehabilitation of partial or total endentulous jaws. However, there is a lack of data about the long-term mechanical characteristics. The aim of this study was to investigate the failure mode and the influence of extended cyclic mechanical loading on the load-bearing capacity of these frameworks. Ten five-unit FDP frameworks simulating a free-end situation in the mandibular jaw were manufactured according to the I-Bridge®2-concept (I-Bridge®2, Biomain AB, Helsingborg, Sweden) and each was screw-retained on three differently angulated Astra Tech implants (30º buccal angulation/0º angulation/30º lingual angulation). One half of the specimens was tested for static load-bearing capacity without any further treatment (control), whereas the other half underwent five million cycles of mechanical loading with 100 N as the upper load limit (test). All specimens were loaded until failure in a universal testing machine with an occlusal force applied at the pontics. Load-displacement curves were recorded and the failure mode was macro- and microscopically analyzed. The statistical analysis was performed using a t-test (p=0.05). All the specimens survived cyclic mechanical loading and no obvious failure could be observed. Due to the cyclic mechanical loading, the load-bearing capacity decreased from 8,496 N±196 N (control) to 7,592 N±901 N (test). The cyclic mechanical loading did not significantly influence the load-bearing capacity (p=0.060). The failure mode was almost identical in all specimens: large deformations of the framework at the implant connection area were obvious. The load-bearing capacity of the I-Bridge®2 frameworks is much higher than the clinically relevant occlusal forces, even with considerably angulated implants. However, the performance under functional loading in vivo depends on additional aspects. Further studies are needed to address these aspects.

Load-bearing capacity of screw-retained CAD/CAM-produced titanium implant frameworks (I-Bridge®2) before and after cyclic mechanical loading

PubMed Central

DITTMER, Marc Philipp; NENSA, Moritz; STIESCH, Meike; KOHORST, Philipp

2013-01-01

Implant-supported screw-retained fixed dental prostheses (FDPs) produced by CAD/ CAM have been introduced in recent years for the rehabilitation of partial or total endentulous jaws. However, there is a lack of data about the long-term mechanical characteristics. Objective The aim of this study was to investigate the failure mode and the influence of extended cyclic mechanical loading on the load-bearing capacity of these frameworks. Material and Methods Ten five-unit FDP frameworks simulating a free-end situation in the mandibular jaw were manufactured according to the I-Bridge®2-concept (I-Bridge®2, Biomain AB, Helsingborg, Sweden) and each was screw-retained on three differently angulated Astra Tech implants (30º buccal angulation/0º angulation/30º lingual angulation). One half of the specimens was tested for static load-bearing capacity without any further treatment (control), whereas the other half underwent five million cycles of mechanical loading with 100 N as the upper load limit (test). All specimens were loaded until failure in a universal testing machine with an occlusal force applied at the pontics. Load-displacement curves were recorded and the failure mode was macro- and microscopically analyzed. The statistical analysis was performed using a t-test (p=0.05). Results All the specimens survived cyclic mechanical loading and no obvious failure could be observed. Due to the cyclic mechanical loading, the load-bearing capacity decreased from 8,496 N±196 N (control) to 7,592 N±901 N (test). The cyclic mechanical loading did not significantly influence the load-bearing capacity (p=0.060). The failure mode was almost identical in all specimens: large deformations of the framework at the implant connection area were obvious. Conclusion The load-bearing capacity of the I-Bridge®2 frameworks is much higher than the clinically relevant occlusal forces, even with considerably angulated implants. However, the performance under functional loading in vivo depends on additional aspects. Further studies are needed to address these aspects. PMID:24037068

Contact fatigue of human enamel: Experiments, mechanisms and modeling.

PubMed

Gao, S S; An, B B; Yahyazadehfar, M; Zhang, D; Arola, D D

2016-07-01

Cyclic contact between natural tooth structure and engineered ceramics is increasingly common. Fatigue of the enamel due to cyclic contact is rarely considered. The objectives of this investigation were to evaluate the fatigue behavior of human enamel by cyclic contact, and to assess the extent of damage over clinically relevant conditions. Cyclic contact experiments were conducted using the crowns of caries-free molars obtained from young donors. The cuspal locations were polished flat and subjected to cyclic contact with a spherical indenter of alumina at 2Hz. The progression of damage was monitored through the evolution in contact displacement, changes in the contact hysteresis and characteristics of the fracture pattern. The contact fatigue life diagram exhibited a decrease in cycles to failure with increasing cyclic load magnitude. Two distinct trends were identified, which corresponded to the development and propagation of a combination of cylindrical and radial cracks. Under contact loads of less than 400N, enamel rod decussation resisted the growth of subsurface cracks. However, at greater loads the damage progressed rapidly and accelerated fatigue failure. Overall, cyclic contact between ceramic appliances and natural tooth structure causes fatigue of the enamel. The extent of damage is dependent on the magnitude of cyclic stress and the ability of the decussation to arrest the fatigue damage. Copyright © 2016 Elsevier Ltd. All rights reserved.

Nonlinear behavior of shells of revolution under cyclic loading.

NASA Technical Reports Server (NTRS)

Levine, H. S.; Armen, H., Jr.; Winter, R.; Pifko, A.

1973-01-01

A large deflection elastic-plastic analysis is presented applicable to orthotropic axisymmetric plates and shells of revolution subjected to monotonic and cyclic loading conditions. The analysis is based on the finite-element method. It employs a new higher order, fully compatible, doubly curved orthotropic shell-of-revolution element using cubic Hermitian expansions for both meridional and normal displacements. Both perfectly plastic and strain hardening behavior are considered. Strain hardening is incorporated through use of the Prager-Ziegler kinematic hardening theory, which predicts an ideal Bauschinger effect. Numerous sample problems involving monotonic and cyclic loading conditions are analyzed.

Tensile loading modulates bone marrow stromal cell differentiation and the development of engineered fibrocartilage constructs.

PubMed

Connelly, John T; Vanderploeg, Eric J; Mouw, Janna K; Wilson, Christopher G; Levenston, Marc E

2010-06-01

Mesenchymal progenitors such as bone marrow stromal cells (BMSCs) are an attractive cell source for fibrocartilage tissue engineering, but the types or combinations of signals required to promote fibrochondrocyte-specific differentiation remain unclear. The present study investigated the influences of cyclic tensile loading on the chondrogenesis of BMSCs and the development of engineered fibrocartilage. Cyclic tensile displacements (10%, 1 Hz) were applied to BMSC-seeded fibrin constructs for short (24 h) or extended (1-2 weeks) periods using a custom loading system. At early stages of chondrogenesis, 24 h of cyclic tension stimulated both protein and proteoglycan synthesis, but at later stages, tension increased protein synthesis only. One week of intermittent cyclic tension significantly increased the total sulfated glycosaminoglycan and collagen contents in the constructs, but these differences were lost after 2 weeks of loading. Constraining the gels during the extended culture periods prevented contraction of the fibrin matrix, induced collagen fiber alignment, and increased sulfated glycosaminoglycan release to the media. Cyclic tension specifically stimulated collagen I mRNA expression and protein synthesis, but had no effect on collagen II, aggrecan, or osteocalcin mRNA levels. Overall, these studies suggest that the combination of chondrogenic stimuli and tensile loading promotes fibrochondrocyte-like differentiation of BMSCs and has the potential to direct fibrocartilage development in vitro.

Microleakage Evaluation at Implant-Abutment Interface Using Radiotracer Technique

PubMed Central

Siadat, Hakimeh; Arshad, Mahnaz; Mahgoli, Hossein-Ali; Fallahi, Babak

2016-01-01

Objectives: Microbial leakage through the implant-abutment (I-A) interface results in bacterial colonization in two-piece implants. The aim of this study was to compare microleakage rates in three types of Replace abutments namely Snappy, GoldAdapt, and customized ceramic using radiotracing. Materials and Methods: Three groups, one for each abutment type, of five implants and one positive and one negative control were considered (a total of 17 regular body implants). A torque of 35 N/cm was applied to the abutments. The samples were immersed in thallium 201 radioisotope solution for 24 hours to let the radiotracers leak through the I-A interface. Then, gamma photons received from the radiotracers were counted using a gamma counter device. In the next phase, cyclic fatigue loading process was applied followed by the same steps of immersion in the radioactive solution and photon counting. Results: Rate of microleakage significantly increased (P≤0.05) in all three types of abutments (i.e. Snappy, GoldAdapt, and ceramic) after cyclic loading. No statistically significant differences were observed between abutment types after cyclic loading. Conclusions: Microleakage significantly increases after cyclic loading in all three Replace abutments (GoldAdapt, Snappy, ceramic). Lowest microleakage before and after cyclic loading was observed in GoldAdapt followed by Snappy and ceramic. PMID:28392814

Cyclic mechanical loading enables solute transport and oxygen supply in bone healing: an in vitro investigation.

PubMed

Witt, Florian; Duda, Georg N; Bergmann, Camilla; Petersen, Ansgar

2014-02-01

Bone healing is a complex process with an increased metabolic activity and consequently high demand for oxygen. In the hematoma phase, inflammatory cells and mesenchymal stromal cells (MSCs) are initially cut off from direct nutritional supply via blood vessels. Cyclic mechanical loading that occurs, for example, during walking is expected to have an impact on the biophysical environment of the cells but meaningful quantitative experimental data are still missing. In this study, the hypothesis that cyclic mechanical loading within a physiological range significantly contributes to oxygen transport into the fracture hematoma was investigated by an in vitro approach. MSCs were embedded in a fibrin matrix to mimic the hematoma phase during bone healing. Construct geometry, culture conditions, and parameters of mechanical loading in a bioreactor system were chosen to resemble the in vivo situation based on data from human studies and a well-characterized large animal model. Oxygen tension was measured before and after mechanical loading intervals by a chemical optical microsensor. The increase in oxygen tension at the center of the constructs was significant and depended on loading time with maximal values of 9.9%±5.1%, 14.8%±4.9%, and 25.3%±7.2% of normal atmospheric oxygen tension for 5, 15, and 30 min of cyclic loading respectively. Histological staining of hypoxic cells after 48 h of incubation confirmed sensor measurements by showing an increased number of normoxic cells with intermittent cyclic compression compared with unloaded controls. The present study demonstrates that moderate cyclic mechanical loading leads to an increased oxygen transport and thus to substantially enhanced supply conditions for cells entrapped in the hematoma. This link between mechanical conditions and nutrition supply in the early regenerative phases could be employed to improve the environmental conditions for cell metabolism and consequently prevent necrosis.

Dynamic augmentation restores anterior tibial translation in ACL suture repair: a biomechanical comparison of non-, static and dynamic augmentation techniques.

PubMed

Hoogeslag, Roy A G; Brouwer, Reinoud W; Huis In 't Veld, Rianne; Stephen, Joanna M; Amis, Andrew A

2018-02-03

There is a lack of objective evidence investigating how previous non-augmented ACL suture repair techniques and contemporary augmentation techniques in ACL suture repair restrain anterior tibial translation (ATT) across the arc of flexion, and after cyclic loading of the knee. The purpose of this work was to test the null hypotheses that there would be no statistically significant difference in ATT after non-, static- and dynamic-augmented ACL suture repair, and they will not restore ATT to normal values across the arc of flexion of the knee after cyclic loading. Eleven human cadaveric knees were mounted in a test rig, and knee kinematics from 0° to 90° of flexion were recorded by use of an optical tracking system. Measurements were recorded without load and with 89-N tibial anterior force. The knees were tested in the following states: ACL-intact, ACL-deficient, non-augmented suture repair, static tape augmentation and dynamic augmentation after 10 and 300 loading cycles. Only static tape augmentation and dynamic augmentation restored ATT to values similar to the ACL-intact state directly postoperation, and maintained this after cyclic loading. However, contrary to dynamic augmentation, the ATT after static tape augmentation failed to remain statistically less than for the ACL-deficient state after cyclic loading. Moreover, after cyclic loading, ATT was significantly less with dynamic augmentation when compared to static tape augmentation. In contrast to non-augmented ACL suture repair and static tape augmentation, only dynamic augmentation resulted in restoration of ATT values similar to the ACL-intact knee and decreased ATT values when compared to the ACL-deficient knee immediately post-operation and also after cyclic loading, across the arc of flexion, thus allowing the null hypotheses to be rejected. This may assist healing of the ruptured ACL. Therefore, this study would support further clinical evaluation of dynamic augmentation of ACL repair.

Biomechanical Analysis of the Efficacy of Locking Plates during Cyclic Loading in Metacarpal Fractures

PubMed Central

Meffert, Rainer H.; Raschke, Michael J.; Blunk, Torsten; Ochman, Sabine

2014-01-01

Purpose. To analyse the biomechanical characteristics of locking plates under cyclic loading compared to a nonlocking plate in a diaphyseal metacarpal fracture. Methods. Oblique diaphyseal shaft fractures in porcine metacarpal bones were created in a biomechanical fracture model. An anatomical reduction and stabilization with a nonlocking and a comparable locking plate in mono- or bicortical screw fixation followed. Under cyclic loading, the displacement, and in subsequent load-to-failure tests, the maximum load and stiffness were measured. Results. For the monocortical screw fixation of the locking plate, a similar displacement, maximum load, and stiffness could be demonstrated compared to the bicortical screw fixation of the nonlocking plate. Conclusions. Locking plates in monocortical configuration may function as a useful alternative to the currently common treatment with bicortical fixations. Thereby, irritation of the flexor tendons would be avoided without compromising the stability, thus enabling the necessary early functional rehabilitation. PMID:24757429

In-situ neutron diffraction of LaCoO3 perovskite under uniaxial compression. I. Crystal structure analysis and texture development

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

Aman, Amjad; Chen, Yan; Lugovy, Mykola

2014-01-01

The dynamics of texture formation, changes in crystal structure and stress accommodation mechanisms are studied in R3c rhombohedral LaCoO3 perovskite during in-situ uniaxial compression experiment by neutron diffraction. The neutron diffraction revealed the complex crystallographic changes causing the texture formation and significant straining along certain crystallographic directions during in-situ compression, which are responsible for the appearance of hysteresis and non-linear ferroelastic deformation in LaCoO3 perovskite. The irreversible strain after the first loading was connected with the appearance of non-recoverable changes in the intensity ratio of certain crystallographic peaks, causing non-reversible texture formation. However in the second loading/unloading cycle the hysteresismore » loop was closed and no irreversible strain appears after deformation. The significant texture formation is responsible for increase in the Young s modulus of LaCoO3 at high compressive loads, where the reported values of Young s modulus increase from 76 GPa measured at the very beginning of the loading to 194 GPa at 900 MPa applied compressive stress measured at the beginning of the unloading curve.« less

A dynamic distention protocol for whole-organ bladder decellularization: histological and biomechanical characterization of the acellular matrix.

PubMed

Consolo, F; Brizzola, S; Tremolada, G; Grieco, V; Riva, F; Acocella, F; Fiore, G B; Soncini, M

2016-02-01

A combined physical-chemical protocol for whole full-thickness bladder decellularization is proposed, based on organ cyclic distention through repeated infusion/withdrawal of the decellularization agents through the urethra. The dynamic decellularization was intended to enhance cell removal efficiency, facilitating the delivery of detergents within the inner layers of the tissue and the removal of cell debris. The use of mild chemical detergents (hypotonic solution and non-ionic detergent) was employed to limit adverse effects upon matrix 3D ultrastructure. Inspection of the presence of residual DNA and RNA was carried out on decellularized matrices to verify effective cell removal. Histological investigation was focused on assessing the retention of adequate structural and functional components that regulate the biomechanical behaviour of the acellular tissue. Biomechanical properties were evaluated through uniaxial tensile loading tests of tissue strips and through ex vivo filling cystometry to evaluate the whole-organ mechanical response to a physiological-like loading state. According to our results, a dynamic decellularization protocol of 17 h duration with a 5 ml/min detergent infusion flow rate revealed higher DNA removal efficiency than standard static decellularization, resulting in residual DNA content < 50 ng/mg dry tissue weight. Furthermore, the collagen network and elastic fibres distribution were preserved in the acellular ECM, which exhibited suitable biomechanical properties in the perspective of its future use as an implant for bladder augmentation. Copyright © 2013 John Wiley & Sons, Ltd.

Uniaxial strain on graphene: Raman spectroscopy study and band-gap opening.

PubMed

Ni, Zhen Hua; Yu, Ting; Lu, Yun Hao; Wang, Ying Ying; Feng, Yuan Ping; Shen, Ze Xiang

2008-11-25

Graphene was deposited on a transparent and flexible substrate, and tensile strain up to approximately 0.8% was loaded by stretching the substrate in one direction. Raman spectra of strained graphene show significant red shifts of 2D and G band (-27.8 and -14.2 cm(-1) per 1% strain, respectively) because of the elongation of the carbon-carbon bonds. This indicates that uniaxial strain has been successfully applied on graphene. We also proposed that, by applying uniaxial strain on graphene, tunable band gap at K point can be realized. First-principle calculations predicted a band-gap opening of approximately 300 meV for graphene under 1% uniaxial tensile strain. The strained graphene provides an alternative way to experimentally tune the band gap of graphene, which would be more efficient and more controllable than other methods that are used to open the band gap in graphene. Moreover, our results suggest that the flexible substrate is ready for such a strain process, and Raman spectroscopy can be used as an ultrasensitive method to determine the strain.

Mechanical loading stimulates chondrogenesis via the PKA/CREB-Sox9 and PP2A pathways in chicken micromass cultures.

PubMed

Juhász, Tamás; Matta, Csaba; Somogyi, Csilla; Katona, Éva; Takács, Roland; Soha, Rudolf Ferenc; Szabó, István A; Cserháti, Csaba; Sződy, Róbert; Karácsonyi, Zoltán; Bakó, Eva; Gergely, Pál; Zákány, Róza

2014-03-01

Biomechanical stimuli play important roles in the formation of articular cartilage during early foetal life, and optimal mechanical load is a crucial regulatory factor of adult chondrocyte metabolism and function. In this study, we undertook to analyse mechanotransduction pathways during in vitro chondrogenesis. Chondroprogenitor cells isolated from limb buds of 4-day-old chicken embryos were cultivated as high density cell cultures for 6 days. Mechanical stimulation was carried out by a self-designed bioreactor that exerted uniaxial intermittent cyclic load transmitted by the culture medium as hydrostatic pressure and fluid shear to differentiating cells. The loading scheme (0.05 Hz, 600 Pa; for 30 min) was applied on culturing days 2 and 3, when final commitment and differentiation of chondroprogenitor cells occurred in this model. The applied mechanical load significantly augmented cartilage matrix production and elevated mRNA expression of several cartilage matrix constituents, including collagen type II and aggrecan core protein, as well as matrix-producing hyaluronan synthases through enhanced expression, phosphorylation and nuclear signals of the main chondrogenic transcription factor Sox9. Along with increased cAMP levels, a significantly enhanced protein kinase A (PKA) activity was also detected and CREB, the archetypal downstream transcription factor of PKA signalling, exhibited elevated phosphorylation levels and stronger nuclear signals in response to mechanical stimuli. All the above effects were diminished by the PKA-inhibitor H89. Inhibition of the PKA-independent cAMP-mediators Epac1 and Epac2 with HJC0197 resulted in enhanced cartilage formation, which was additive to that of the mechanical stimulation, implying that the chondrogenesis-promoting effect of mechanical load was independent of Epac. At the same time, PP2A activity was reduced following mechanical load and treatments with the PP2A-inhibitor okadaic acid were able to mimic the effects of the intervention. Our results indicate that proper mechanical stimuli augment in vitro cartilage formation via promoting both differentiation and matrix production of chondrogenic cells, and the opposing regulation of the PKA/CREB-Sox9 and the PP2A signalling pathways is crucial in this phenomenon. Copyright © 2014 Elsevier Inc. All rights reserved.

Self-aligning hydraulic piston assembly for tensile testing of ceramic

DOEpatents

Liu, Kenneth C.

1987-01-01

The present invention is directed to a self-aligning grip housing assembly that can transmit an uniaxial load to a tensil specimen without introducing bending stresses into the specimen. Disposed inside said grip housing assembly are a multiplicity of supporting pistons connected to a common source of pressurized oil that carry equal shares of the load applied to the specimen irregardless whether there is initial misalignment between the specimen load column assembly and housing axis.

Self-aligning hydraulic piston assembly for tensile testing of ceramic

DOEpatents

Liu, K.C.

1987-08-18

The present invention is directed to a self-aligning grip housing assembly that can transmit an uniaxial load to a tensile specimen without introducing bending stresses into the specimen. Disposed inside said grip housing assembly are a multiplicity of supporting pistons connected to a common source of pressurized oil that carry equal shares of the load applied to the specimen regardless whether there is initial misalignment between the specimen load column assembly and housing axis. 4 figs.

In vitro study of the impact of mechanical tension on the dermal fibroblast phenotype in the context of skin wound healing.

PubMed

Rolin, Gwenae L; Binda, Delphine; Tissot, Marion; Viennet, Céline; Saas, Philippe; Muret, Patrice; Humbert, Philippe

2014-11-07

Skin wound healing is finely regulated by both matrix synthesis and degradation which are governed by dermal fibroblast activity. Actually, fibroblasts synthesize numerous extracellular matrix proteins (i.e., collagens), remodeling enzymes and their inhibitors. Moreover, they differentiate into myofibroblasts and are able to develop endogenous forces at the wound site. Such forces are crucial during skin wound healing and have been widely investigated. However, few studies have focused on the effect of exogenous mechanical tension on the dermal fibroblast phenotype, which is the objective of the present paper. To this end, an exogenous, defined, cyclic and uniaxial mechanical strain was applied to fibroblasts cultured as scratch-wounded monolayers. Results showed that fibroblasts' response was characterized by both an increase in procollagen type-I and TIMP-1 synthesis, and a decrease in MMP-1 synthesis. The monitoring of scratch-wounded monolayers did not show any decrease in kinetics of the filling up when mechanical tension was applied. Additional results obtained with proliferating fibroblasts and confluent monolayer indicated that mechanical tension-induced response of fibroblasts depends on their culture conditions. In conclusion, mechanical tension leads to the differentiation of dermal fibroblasts and may increase their wound-healing capacities. So, the exogenous uniaxial and cyclic mechanical tension reported in the present study may be considered in order to improve skin wound healing. Copyright © 2014 Elsevier Ltd. All rights reserved.

NASTRAN forced vibration analysis of rotating cyclic structures

NASA Technical Reports Server (NTRS)

Elchuri, V.; Smith, G. C. C.; Gallo, A. M.

1983-01-01

Theoretical aspects of a new capability developed and implemented in NASTRAN level 17.7 to analyze forced vibration of a cyclic structure rotating about its axis of symmetry are presented. Fans, propellers, and bladed shrouded discs of turbomachines are some examples of such structures. The capability includes the effects of Coriolis and centripetal accelerations on the rotating structure which can be loaded with: (1) directly applied loads moving with the structure and (2) inertial loas due to the translational acceleration of the axis of rotation (''base' acceleration). Steady-state sinusoidal or general periodic loads are specified to represent: (1) the physical loads on various segments of the complete structure, or (2) the circumferential harmonic components of the loads in (1). The cyclic symmetry feature of the rotating structure is used in deriving and solving the equations of forced motion. Consequently, only one of the cyclic sectors is modelled and analyzed using finite elements, yielding substantial savings in the analysis cost. Results, however, are obtained for the entire structure. A tuned twelve bladed disc example is used to demonstrate the various features of the capability.

Effects of laboratory heating, cyclic pore pressure, and cyclic loading on fracture properties of asphalt mixture.

DOT National Transportation Integrated Search

2012-04-01

This study involved the identification and evaluation of laboratory conditioning methods and testing protocols considering heat oxidation, moisture, and load that more effectively simulate asphalt mixture aging in the field, and thereby help to prope...

Experimental and theoretical investigation of temperature-dependent electrical fatigue studies on 1-3 type piezocomposites

NASA Astrophysics Data System (ADS)

Mohan, Y.; Arockiarajan, A.

2016-03-01

1-3 type piezocomposites are very attractive materials for transducers and biomedical application, due to its high electromechanical coupling effects. Reliability study on 1-3 piezocomposites subjected to cyclic loading condition in transducer application is one of the primary concern. Hence, this study focuses on 1-3 piezocomposites for various PZT5A1 fiber volume fraction subjected to electrical fatigue loading up-to 106 cycles and at various elevated temperature. Initially experiments are performed on 1-3 piezocomposites, in order to understand the degradation phenomena due to various range in amplitude of electric fields (unipolar & bipolar), frequency of applied electric field and for various ambient temperature. Performing experiments for high cycle fatigue and for different fiber volume fraction of PZT5A1 is a time consuming process. Hence, a simplified macroscopic uni-axial model based on physical mechanisms of domain switching and continuum damage mechanics has been developed to predict the non-linear fatigue behaviour of 1-3 piezocomposites for temperature dependent electrical fatigue loading conditions. In this model, damage effects namely domain pinning, frozen domains and micro cracks, are considered as a damage variable (ω). Remnant variables and material properties are considered as a function of internal damage variable and the growth of the damage is derived empirically based on the experimental observation to predict the macroscopic changes in the properties. The measured material properties and dielectric hysteresis (electric displacement vs. electric field) as well as butterfly curves (longitudinal strain vs. electric field) are compared with the simulated results. It is observed that variation in amplitude of bipolar electric field and temperature has a strong influence on the response of 1-3 piezocomposites.

Load response and gap formation in a single-row cruciate suture rotator cuff repair.

PubMed

Huntington, Lachlan; Richardson, Martin; Sobol, Tony; Caldow, Jonathon; Ackland, David C

2017-06-01

Double-row rotator cuff tendon repair techniques may provide superior contact area and strength compared with single-row repairs, but are associated with higher material expenses and prolonged operating time. The purpose of this study was to evaluate gap formation, ultimate tensile strength and stiffness of a single-row cruciate suture rotator cuff repair construct, and to compare these results with those of the Mason-Allen and SutureBridge repair constructs. Infraspinatus tendons from 24 spring lamb shoulders were harvested and allocated to cruciate suture, Mason-Allen and SutureBridge repair groups. Specimens were loaded cyclically between 10 and 62 N for 200 cycles, and gap formation simultaneously measured using a high-speed digital camera. Specimens were then loaded in uniaxial tension to failure, and construct stiffness and repair strength were evaluated. Gap formation in the cruciate suture repair was significantly lower than that of the Mason-Allen repair (mean difference = 0.6 mm, P = 0.009) and no different from that of the SutureBridge repair (P > 0.05). Both the cruciate suture repair (mean difference = 15.7 N/mm, P = 0.002) and SutureBridge repair (mean difference = 15.8 N/mm, P = 0.034) were significantly stiffer than that of the Mason-Allen repair; however, no significant differences in ultimate tensile strength between repair groups were discerned (P > 0.05). The cruciate suture repair construct, which may represent a simple and cost-effective alternative to double-row and double-row equivalent rotator cuff repairs, has comparable biomechanical strength and integrity with that of the SutureBridge repair, and may result in improved construct longevity and tendon healing compared with the Mason-Allen repair. © 2017 Royal Australasian College of Surgeons.

Fracture toughness of Ti-Al3Ti-Al-Al3Ti laminate composites under static and cyclic loading conditions

NASA Astrophysics Data System (ADS)

Patselov, A. M.; Gladkovskii, S. V.; Lavrikov, R. D.; Kamantsev, I. S.

2015-10-01

The static and cyclic fracture toughnesses of a Ti-Al3Ti-Al-Al3Ti laminate composite material containing at most 15 vol % intermetallic compound are studied. Composite specimens are prepared by terminating reaction sintering of titanium and aluminum foils under pressure. The fracture of the titanium layers is quasi-cleavage during cyclic crack growth and is ductile during subsequent static loading.

A biomechanical analysis of sublaminar and subtransverse process fixation using metal wires and polyethylene cables.

PubMed

Fujita, Masaru; Diab, Mohammad; Xu, Zheng; Puttlitz, Christian M

2006-09-01

An in vitro biomechanical calf thoracic spine study. To evaluate the biomechanical stability of sublaminar and subtransverse process fixation using stainless steel wires and ultra-high molecular weight polyethylene (UHMWPE) cables. It is commonly held that transverse process fixation provides less stability than sublaminar fixation. To our knowledge, this is the first biomechanical study to compare the stability afforded by sublaminar fixation and subtransverse process fixation using metal wire and UHMWPE cable before and after cyclic loading. There were 6 fresh-frozen calf thoracic spines (T4-T9) used to determine the sublaminar fixation stiffness and subtransverse process fixation stiffness in each group. Double strands of 18-gauge stainless steel wire, 3 and 5 mm-width UHMWPE cable (Nesplon; Alfresa, Inc., Osaka, Japan) were applied to each spine. Cyclic pure flexion-extension moment loading (2 Nm, 0.5 Hz, 5000 cycles) was applied after the initial stability was analyzed by measuring the range of motion. Statistical analyses were used to delineate differences between the various experimental groups. Subtransverse process wiring was more stable than sublaminar wiring after cyclic loading in flexion-extension (P < 0.05). There were no significant differences between each group in lateral bending and axial rotation after cyclic loading. Sublaminar stainless steel wiring was more stable than sublaminar 3 and 5-mm cable before and after cyclic loading in axial rotation (P < 0.01). Acute subtransverse process fixation using 3-mm cable was less stable after cyclic loading in axial rotation (P < 0.05). All other groups did not produce statistically significant differences. Subtransverse process fixation provides at least as much stability as sublaminar fixation. A 5-mm UHMWPE cable and stainless steel wire result in equivalent sublaminar and subtransverse process stability.

Settling of abutments into implants and changes in removal torque in five different implant-abutment connections. Part 1: Cyclic loading.

PubMed

Kim, Ki-Seong; Han, Jung-Suk; Lim, Young-Jun

2014-01-01

The aim of this study was to evaluate and compare the settling of abutments into implants and the removal torque values (RTVs) before and after cyclic loading. Five different implant-abutment connections were tested: Ext = external butt joint + two-piece abutment; Int-H2 = internal hexagon + two-piece abutment; Int-H1 = internal hexagon + one-piece abutment; Int-O2 = internal octagon + two-piece abutment; and Int-O1 = internal octagon + one-piece abutment. Ten abutments from each group were secured to their corresponding implants (total n = 50). All samples were tested in a universal testing machine with a vertical load of 250 N for 100,000 cycles of 14 Hz. The amount of settling of the abutment into the implant was calculated from the change in the total length of the implant-abutment sample before and after loading, as measured with an electronic digital micrometer. The RTV after cyclic loading was compared to the initial RTV with a digital torque gauge. Statistical analysis was performed at a 5% significance level. A multiple-comparison test showed specific significant differences in settling values in each group after 250 N cyclic loading (Int-H1, Ext < Int-H2 < Int-O2 < Int-O1). There were statistically significant decreases in RTVs after loading compared to the initial RTVs in the Int-H2 and Int-O2 groups. No statistically significant differences were found in the Ext, Int-H1, and Int-O1 groups. The results of this study demonstrated that the settling amount and RTV (loss of preload) after cyclic loading were specific to the abutment type and related to the design characteristics of the implant-abutment connection.

Anisotropic deformation of extruded magnesium alloy AZ31 under uniaxial compression: A study with simultaneous in situ synchrotron x-ray imaging and diffraction

DOE PAGES

Lu, L.; Huang, J. W.; Fan, D.; ...

2016-08-29

In situ synchrotron x-ray imaging and diffraction are used to investigate anisotropic deformation of an extruded magnesium alloy AZ31 under uniaxial compression along two different directions, with the loading axis (LA) either parallel or perpendicular to the extrusion direction (ED), referred to as LA∥ED and LAED, respectively. Multiscale measurements including stress–strain curves (macroscale), x-ray digital image correlation (mesoscale), and diffraction (microscale) are obtained simultaneously. Electron backscatter diffraction is performed on samples collected at various strains to characterize deformation twins. The rapid increase in strain hardening rate for the LA∥ED loading is attributed to marked {101¯2} extension twinning and subsequent homogenizationmore » of deformation, while dislocation motion leads to inhomogeneous deformation and a decrease in strain hardening rate.« less

Test and Analyses of a Composite Multi-Bay Fuselage Panel Under Uni-Axial Compression

NASA Technical Reports Server (NTRS)

Li, Jian; Baker, Donald J.

2004-01-01

A composite panel containing three stringers and two frames cut from a vacuum-assisted resin transfer molded (VaRTM) stitched fuselage article was tested under uni-axial compression loading. The stringers and frames divided the panel into six bays with two columns of three bays each along the compressive loading direction. The two frames were supported at the ends with pins to restrict the out-of-plane translation. The free edges of the panel were constrained by knife-edges. The panel was modeled with shell finite elements and analyzed with ABAQUS nonlinear solver. The nonlinear predictions were compared with the test results in out-of-plane displacements, back-to-back surface strains on stringer flanges and back-to-back surface strains at the centers of the skin-bays. The analysis predictions were in good agreement with the test data up to post-buckling.

Slow Crack Growth of Brittle Materials With Exponential Crack-Velocity Formulation. Part 3; Constant Stress and Cyclic Stress Experiments

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Nemeth, Noel N.; Gyekenyesi, John P.

2002-01-01

The previously determined life prediction analysis based on an exponential crack-velocity formulation was examined using a variety of experimental data on advanced structural ceramics tested under constant stress and cyclic stress loading at ambient and elevated temperatures. The data fit to the relation between the time to failure and applied stress (or maximum applied stress in cyclic loading) was very reasonable for most of the materials studied. It was also found that life prediction for cyclic stress loading from data of constant stress loading in the exponential formulation was in good agreement with the experimental data, resulting in a similar degree of accuracy as compared with the power-law formulation. The major limitation in the exponential crack-velocity formulation, however, was that the inert strength of a material must be known a priori to evaluate the important slow-crack-growth (SCG) parameter n, a significant drawback as compared with the conventional power-law crack-velocity formulation.

Fracture Test Methods for Plastically Responding COPV Liners

NASA Technical Reports Server (NTRS)

Dawicke, David S.; Lewis, Joseph C.

2009-01-01

An experimental procedure for evaluating the validity of using uniaxial tests to provide a conservative bound on the fatigue crack growth rate behavior small cracks in bi-axially loaded Composite Overwrapped Pressure Vessel (COPV) liners is described. The experimental procedure included the use of a laser notch to quickly generate small surface fatigue cracks with the desired size and aspect ratios. An out-of-plane constraint system was designed to allow fully reversed, fully plastic testing of thin sheet uniaxial coupons. Finally, a method was developed to determine to initiate small cracks in the liner of COPVs.

Deformation behavior of micro-indentation defects under uniaxial and biaxial loads

NASA Astrophysics Data System (ADS)

Ma, Zhichao; Zhao, Hongwei; Lu, Shuai; Li, Hailian; Liu, Changyi; Liu, Xianhua

2015-09-01

The microdefects of structure frequently act as the source to generate initial cracks and lead to the fracture failure. Study on the deformation behaviors of embedded defects would be conducive to better understand the failure mechanisms of structural materials. Micro-indentation technique was applied to prepare the initial indentations as embedded surface defects at the gauge length section and central section of a cross-shaped AZ31B magnesium alloy specimen. A novel in situ biaxial tensile device was developed to apply the synchronous biaxial loads. Via the observation by an optical microscope with three-dimensional imaging and measurement functions, the changing laws of the indentation topographies under uniaxial and biaxial tensile loads were discussed. Compared with the gauge length section, the increasing trend of the indentation length of the central section was relatively flat, and the decreasing trend of the indentation depth was more significant. The changes of indentation topographies were explained by the Poisson effect, and the significant plastic tensile stress has led to the releasing of the residual stress around the indentation location and also promoted the planarization of the pileup.

Deformation behavior of micro-indentation defects under uniaxial and biaxial loads.

PubMed

Ma, Zhichao; Zhao, Hongwei; Lu, Shuai; Li, Hailian; Liu, Changyi; Liu, Xianhua

2015-09-01

The microdefects of structure frequently act as the source to generate initial cracks and lead to the fracture failure. Study on the deformation behaviors of embedded defects would be conducive to better understand the failure mechanisms of structural materials. Micro-indentation technique was applied to prepare the initial indentations as embedded surface defects at the gauge length section and central section of a cross-shaped AZ31B magnesium alloy specimen. A novel in situ biaxial tensile device was developed to apply the synchronous biaxial loads. Via the observation by an optical microscope with three-dimensional imaging and measurement functions, the changing laws of the indentation topographies under uniaxial and biaxial tensile loads were discussed. Compared with the gauge length section, the increasing trend of the indentation length of the central section was relatively flat, and the decreasing trend of the indentation depth was more significant. The changes of indentation topographies were explained by the Poisson effect, and the significant plastic tensile stress has led to the releasing of the residual stress around the indentation location and also promoted the planarization of the pileup.

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.

Tension degradation of anterior cruciate ligament grafts with dynamic flexion-extension loading: a biomechanical model in porcine knees.

PubMed

Dargel, Jens; Koebke, Jürgen; Brüggemann, Gert-Peter; Pennig, Dietmar; Schmidt-Wiethoff, Rüdiger

2009-10-01

This study investigates the influence of various femoral anterior cruciate ligament graft fixation methods on the amount of tension degradation and the initial fixation strength after cyclic flexion-extension loading in a porcine knee model. One hundred twenty porcine digital extensor tendons, used as 4-stranded free tendon grafts, were fixated within porcine femoral bone tunnels by use of extracortical button, cross-pin, or interference screw fixation. One hundred twenty porcine patellar tendon-bone grafts were fixated by use of cross-pin, interference screw, or press-fit fixation. Each femur-graft complex was submitted to cyclic flexion-extension loading for 1,000 cycles throughout different loading ranges, and the total loss of tension was determined. After cyclic testing, the grafts were loaded to failure, and the data were compared with a pullout series without cyclic loading. Tension degradation after 1,000 cycles of flexion-extension loading averaged 62.6% +/- 10.0% in free tendon grafts and 48.9% +/- 13.35% in patellar tendon-bone grafts. There was no influence of the loading range on the total amount of tension degradation. The total amount of tension degradation was the highest with interference screw fixation of free tendon and patellar tendon-bone grafts. Despite excessive loss of tension, the initial fixation strength of the femur-graft complex was not reduced. The method of femoral graft fixation significantly influenced tension degradation during dynamic flexion-extension loading. Femoral graft fixation methods that secure the graft close to the tunnel entrance and that displace the graft substance from the center of the bone tunnel show the largest amount of tension degradation during cyclic flexion-extension loading. The graft substance, not the fixation site, was the weakest link of the graft complex within this investigation. We believe that the graft fixation method should be considered when aiming to improve the precision of femoral graft placement in anterior cruciate ligament reconstruction.

Processing and characterization of unidirectional thermoplastic nanocomposites

NASA Astrophysics Data System (ADS)

Narasimhan, Kameshwaran

The manufacture of continuous fibre-reinforced thermoplastic nanocomposites is discussed for the case of E-Glass reinforced polypropylene (PP) matrix and for E-Glass reinforced Polyamide-6 (Nylon-6), with and without dispersed nanoclay (montmorillonite) platelets. The E-Glass/PP nanocomposite was manufactured using pultrusion, whereas the E-Glass/Nylon-6 nanocomposite was manufactured using compression molding. Mechanical characterization of nanocomposites were performed and compared with traditional microcomposites. Compressive as well as shear strength of nanocomposites was improved by improving the yield strength of the surrounding matrix through the dispersion of nanoclay. Significant improvements were achieved in compressive strength and shear strength with relatively low nanoclay loadings. Initially, polypropylene with and without nanoclay were melt intercalated using a single-screw extruder and the pultruded nanocomposite was fabricated using extruded pre-impregnated (pre-preg) tapes. Compression tests were performed as mandated by ASTM guidelines. SEM and TEM characterization revealed presence of nanoclay in an intercalated and partially exfoliated morphology. Mechanical tests confirmed significant improvements in compressive strength (˜122% at 10% nanoclay loading) and shear strength (˜60% at 3% nanoclay loading) in modified pultruded E-Glass/PP nanocomposites in comparison with baseline properties. Uniaxial tensile tests showed a small increase in tensile strength (˜3.4%) with 3% nanoclay loading. Subsequently, E-Glass/Nylon-6 nanocomposite panels were manufactured by compression molding. Compression tests were performed according to IITRI guidelines, whereas short beam shear and uni-axial tensile tests were performed according to ASTM standards. Mechanical tests confirmed strength enhancement with nanoclay addition, with a significant improvement in compressive strength (50% at 4% nanoclay loading) and shear strength (˜36% at 4% nanoclay loading) when compared with the baseline E-Glass/Nylon-6. Uni-axial tensile tests resulted in a small increase in tensile strength (˜3.2%) with 4% nanoclay loading. Also, hygrothermal aging (50°C and 100% RH) of baseline and nanoclay modified (4%) E-Glass/Nylon-6 was studied. It was observed that the moisture diffusion process followed Fickian diffusion. E-Glass/Nylon-6 modified with 4% nanoclay loading showed improved barrier performance with a significant reduction (˜30%) in moisture uptake compared to baseline E-Glass/Nylon-6 composites. Significant improvement in mechanical properties was also observed in hygrothermally aged nanocomposite specimens when compared with the aged baseline composite.

Nonlinear behavior of shells of revolution under cyclic loading

NASA Technical Reports Server (NTRS)

Levine, H. S.; Armen, H., Jr.; Winter, R.; Pifko, A.

1972-01-01

A large deflection elastic-plastic analysis is presented, applicable to orthotropic axisymmetric plates and shells of revolution subjected to monotonic and cyclic loading conditions. The analysis is based on the finite-element method. It employs a new higher order, fully compatible, doubly curved orthotropic shell-of-revolution element using cubic Hermitian expansions for both meridional and normal displacements. Both perfectly plastic and strain hardening behavior are considered. Strain hardening is incorporated through use of the Prager-Ziegler kinematic hardening theory, which predicts an ideal Bauschinger effect. Numerous sample problems involving monotonic and cyclic loading conditions are analyzed. The monotonic results are compared with other theoretical solutions.

Fatigue Damage in Notched Composite Laminates Under Tension-Tension Cyclic Loads

NASA Technical Reports Server (NTRS)

Stinchcomb, W. W.; Henneke, E. G.; Reifsnider, K. L.; Kress, G. R.

1985-01-01

The results are given of an investigation to determine the damage states which develop in graphite epoxy laminates with center holes due to tension-tension cyclic loads, to determine the influence of stacking sequence on the initiation and interaction of damage modes and the process of damage development, and to establish the relationships between the damage states and the strength, stiffness, and life of the laminates. Two quasi-isotropic laminates were selected to give different distributions of interlaminar stresses around the hole. The laminates were tested under cyclic loads (R=0.1, 10 Hz) at maximum stresses ranging between 60 and 95 percent of the notched tensile strength.

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.

Effects of cyclic fatigue stress-biocorrosion on noncarious cervical lesions.

PubMed

Grippo, John O; Chaiyabutr, Yada; Kois, John C

2013-08-01

Although there is a high prevalence of noncarious cervical lesions (NCCLs), the etiology of these lesions remains contentious. To evaluate the combined effects of cyclic fatigue stress and biocorrosion activity on NCCLs. Extracted premolar teeth were allocated into four groups (N = 10). Two groups were cyclically fatigue loaded (100 N; 72 cycles per minute; 9,200 cycles) and placed in either hydrochloric acid gel (pH = 0.1) or orange juice (pH = 4). The other two groups were stored in identical chemical solutions without fatigue load. The buccal-lingual width of each tooth was measured before and after testing. The depth of biocorrosion, normalized by the percentage change in buccolingual width, normalized by time (hour) was calculated. The data were analyzed using a two-way analysis of variance and Tukey's HSD multiple comparison test (α = 0.05). Mean (SD) of the depth of biocorrosion values were as follows: teeth receiving fatigue loading with hydrochloric acid gel exposure (1.003%/hour [0.063]) revealed a significantly higher depth of biocorrosion than the fatigue-loaded group with orange juice exposure (0.511%/hour [0.281]) (p < 0.01). For the groups without fatigue loading, those with hydrochloric acid gel (0.022%/hour [0.006]) had a significantly higher depth of biocorrosion than the group with orange juice (0.009%/hour [0.004]) (p < 0.01). The cyclically fatigue-loaded teeth with hydrochloric acid gel had a significantly greater depth of biocorrosion than either group without fatigue loading (p < 0.001). Cyclic fatigue stress-acidic biocorrosion had a significant effect on the depth of the NCCLs. In order to manage the destructive NCCLs lesions properly, it is essential to understand the etiology of these lesions. The present study indicated that the combined mechanisms of cyclic fatigue stress and biocorrosion could contribute to the formation of NCCLs. © 2013 Wiley Periodicals, Inc.

Effect of chlorhexidine and ethanol on push-out bond strength of fiber posts under cyclic loading.

PubMed

Cecchin, Doglas; Giacomin, Mateus; Farina, Ana Paula; Bhering, Cláudia Lopes; Mesquita, Marcelo Ferraz; Ferraz, Caio Cezar

2014-02-01

To investigate the effects of pretreatment with 2% chlorhexidine in a gel base (CHX) and 100% ethanol (EtOH) on the bond strength between fiber posts relined with resin composite and root dentin under cyclic loading. Forty bovine incisor roots were divided into four groups after phosphoric acid etching: group 1 (control), irrigation with physiological saline solution; group 2, 5 min pretreatment with CHX; group 3, 1 min pretreatment with EtOH; group 4, 5 min pretreatment with CHX followed by 1 min with EtOH. Fiber posts relined with resin composite were cemented with RelyX ARC and the etch-and-rinse adhesive system Scotchbond Multi-Purpose. Each group was randomly divided into two subgroups: 24 h of storage (immediate groups) and cyclic loading (loading groups) with 250,000 cycles in a controlled chewing simulator. All roots were sectioned transversely and push-out tests were performed. Failure modes were observed and the bond strength means were analyzed using ANOVA and Tukey's test (a = 0.05). The mean values for the bond strength test (MPa) in immediate groups were: group 1, 5.44 ± 1.48; group 2, 5.57 ± 1.41; group 3, 5.49 ± 1.48; group 4, 5.57 ± 1.42. Immediate groups showed similar bond strength values (p > 0.05). In the cyclic loading groups, the bond strength values were: group 1, 2.80 ± 0.79; group 2, 4.02 (1.30); group 3, 4.50 ± 1.67; group 4, 4.97 ± 2.00. After cyclic loading, a significant decrease in the control group was observed (p < 0.05), while CHX pretreatment resulted in intermediate values (p < 0.05) and EtOH alone or associated with CHX preserved the bond strength values (p > 0.05). Chlorhexidine and/or ethanol pretreatment preserved the bond strength of the fiber post after cyclic loading.

Plastic flow modeling in glassy polymers

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

Clements, Brad

2010-12-13

Glassy amorphous and semi-crystalline polymers exhibit strong rate, temperature, and pressure dependent polymeric yield. As a rule of thumb, in uniaxial compression experiments the yield stress increases with the loading rate and applied pressure, and decreases as the temperature increases. Moreover, by varying the loading state itself complex yield behavior can be observed. One example that illustrates this complexity is that most polymers in their glassy regimes (i.e., when the temperature is below their characteristic glass transition temperature) exhibit very pronounced yield in their uniaxial stress stress-strain response but very nebulous yield in their uniaxial strain response. In uniaxial compression,more » a prototypical glassy-polymer stress-strain curve has a stress plateau, often followed by softening, and upon further straining, a hardening response. Uniaxial compression experiments of this type are typically done from rates of 10{sup -5} s{sup -1} up to about 1 s{sup -1}. At still higher rates, say at several thousands per second as determined from Split Hopkinson Pressure Bar experiments, the yield can again be measured and is consistent with the above rule of thumb. One might expect that that these two sets of experiments should allow for a successful extrapolation to yet higher rates. A standard means to probe high rates (on the order of 105-107 S-I) is to use a uniaxial strain plate impact experiment. It is well known that in plate impact experiments on metals that the yield stress is manifested in a well-defined Hugoniot Elastic Limit (HEL). In contrast however, when plate impact experiments are done on glassy polymers, the HEL is arguably not observed, let alone observed at the stress estimated by extrapolating from the lower strain rate experiments. One might argue that polymer yield is still active but somehow masked by the experiment. After reviewing relevant experiments, we attempt to address this issue. We begin by first presenting our recently developed glassy polymer model. While polymers are well known for their non-equilibrium deviatoric behavior we have found the need for incorporating both equilibrium and non-equilibrium volumetric behavior into our theory. Experimental evidence supporting the notion of non-equilibrium volumetric behavior will be summarized. Our polymer yield model accurately captures the stress plateau, softening and hardening and its yield stress predictions agree well with measured values for several glassy polymers including PMMA, PC, and an epoxy resin. We then apply our theory to plate impact experiments in an attempt to address the questions associated with high rate polymer yield in uniaxial strain configurations.« less

High-repetition cyclic loading is a risk factor for a lumbar disorder.

PubMed

Navar, Daniel; Zhou, Bing-He; Lu, Yun; Solomonow, Moshe

2006-11-01

Epidemiological data suggest that prolonged exposure to cyclic lumbar flexion elicits a chronic neuromuscular disorder and disability in workers. This study provides a physiological and biomechanical assessment of various repetitions of cyclic lumbar flexion sessions as a risk factor for development of an acute neuromuscular disorder. An in vivo feline model was subjected to 10 minutes of cyclic (0.25-HZ) loading, followed by a 10-minute rest period, repeated three times in one experimental group, six times in a second group, and nine times in the third group, followed by rest for 7 hours. Displacement of the lumbar viscoelastic tissue and reflex electromyographic (EMG) activity from the lumbar multifidus muscle were monitored. Creep developed and accumulated during each load/rest period and partially recovered during the subsequent rest. Loading periods were characterized by a decrease in reflex EMG activity with superimposed spasms. In the 7-hour recovery period, initial hyperexcitability was present in all groups, whereas only the six- and nine-repetition groups displayed significant delayed hyperexcitability, indicating the presence of acute inflammation. The mathematical model developed fit the data reasonably well, as the R2 values were generally near 0.90. It was concluded that the resulting delayed muscular hyperexcitability constitutes an acute neuromuscular disorder associated with exposure to many repetitions of cyclic lumbar flexion. The acute disorder can become chronic if not allowed sufficient rest to resolve itself. Workers engaged in cyclic lumbar flexion (e.g., loading/unloading, assembly workers) should avoid long-term exposure in order to prevent the development of a chronic neuromuscular condition known as cumulative trauma disorder.

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.

Tensile Loading Modulates Bone Marrow Stromal Cell Differentiation and the Development of Engineered Fibrocartilage Constructs

PubMed Central

Connelly, John T.; Vanderploeg, Eric J.; Mouw, Janna K.; Wilson, Christopher G.

2010-01-01

Mesenchymal progenitors such as bone marrow stromal cells (BMSCs) are an attractive cell source for fibrocartilage tissue engineering, but the types or combinations of signals required to promote fibrochondrocyte-specific differentiation remain unclear. The present study investigated the influences of cyclic tensile loading on the chondrogenesis of BMSCs and the development of engineered fibrocartilage. Cyclic tensile displacements (10%, 1 Hz) were applied to BMSC-seeded fibrin constructs for short (24 h) or extended (1–2 weeks) periods using a custom loading system. At early stages of chondrogenesis, 24 h of cyclic tension stimulated both protein and proteoglycan synthesis, but at later stages, tension increased protein synthesis only. One week of intermittent cyclic tension significantly increased the total sulfated glycosaminoglycan and collagen contents in the constructs, but these differences were lost after 2 weeks of loading. Constraining the gels during the extended culture periods prevented contraction of the fibrin matrix, induced collagen fiber alignment, and increased sulfated glycosaminoglycan release to the media. Cyclic tension specifically stimulated collagen I mRNA expression and protein synthesis, but had no effect on collagen II, aggrecan, or osteocalcin mRNA levels. Overall, these studies suggest that the combination of chondrogenic stimuli and tensile loading promotes fibrochondrocyte-like differentiation of BMSCs and has the potential to direct fibrocartilage development in vitro. PMID:20088686

Does distal tibiofibular joint mobilization decrease limitation of ankle dorsiflexion?

PubMed

Fujii, Misaki; Suzuki, Daisuke; Uchiyama, Eiichi; Muraki, Takayuki; Teramoto, Atsushi; Aoki, Mitsuhiro; Miyamoto, Shigenori

2010-02-01

Limitation of ankle motion is in many cases treated by joint mobilization (JM), a kind of manual physical therapy technique. Until now, the JM approach has mainly focused on the talocrural joint, with less attention to the distal tibiofibular joint. We applied cyclic loading to the lateral malleolus as in JM in order to clarify the relationship between the dorsiflexion angle and the excursion of the lateral malleolus. Seven normal, fresh-frozen cadaver legs were used. To each specimen, cyclic loading with a 30N force was applied 1000 times to the lateral malleolus at a speed of 15N/s. The displacement of the lateral malleolus was measured with a magnetic tracking system. The maximum dorsiflexion angle was measured before and after cyclic loading. After the first 100 and 1000 times of cyclic loading, the tibia was displaced 0.44+/-0.30mm and 0.75+/-0.36mm, respectively, and the fibula was displaced 0.44+/-0.28mm and 0.92+/-0.39mm, respectively. The average dorsiflexion angle increased from 14.36+/-7.51 degrees to 16.74+/-7.21 degrees after cyclic loading (P<0.05). Movement of the distal tibiofibular joint led to a significant increase in the range of ankle dorsiflexion. These results suggest that tibiofibular JM would be effective for limitation of ankle dorsiflexion.

Abutments with reduced diameter for both cement and screw retentions: analysis of failure modes and misfit of abutment-crown-connections after cyclic loading.

PubMed

Moris, Izabela Cristina Maurício; Faria, Adriana Cláudia Lapria; Ribeiro, Ricardo Faria; Rodrigues, Renata Cristina Silveira

2017-04-01

The aim of this study was to analyze failure modes and misfit of abutments with reduced diameter for both cement and screw retentions after cyclic loading. Forty morse-taper abutment/implant sets of titanium were divided into four groups (N = 10): G4.8S-4.8 abutment with screw-retained crown; G4.8C-4.8 abutment with cemented crown; G3.8S-3.8 abutment with screw-retained crown; and G3.8C-3.8 abutment with cemented crown. Copings were waxed on castable cylinders and cast by oxygen gas flame and injected by centrifugation. After, esthetic veneering ceramic was pressed on these copings for obtaining metalloceramic crowns of upper canine. Cemented crowns were cemented on abutments with provisional cement (Temp Bond NE), and screw-retained crowns were tightened to their abutments with torque recommended by manufacturer (10 N cm). The misfit was measured using a stereomicroscope in a 10× magnification before and after cyclic loading (300,000 cycles). Tests were visually monitored, and failures (decementation, screw loosening and fractures) were registered. Misfit was analyzed by mixed linear model while failure modes by chi-square test (α = 0.05). Cyclic loading affected misfit of 3.8C (P ≤ 0.0001), 3.8S (P = 0.0055) and 4.8C (P = 0.0318), but not of 4.8S (P = 0.1243). No differences were noted between 3.8S with 4.8S before (P = 0.1550) and after (P = 0.9861) cyclic loading, but 3.8C was different from 4.8C only after (P = 0.0015) loading. Comparing different types of retentions at the same diameter abutment, significant difference was noted before and after cyclic loading for 3.8 and 4.8 abutments. Analyzing failure modes, retrievable failures were present at 3.8S and 3.8C groups, while irretrievable were only present at 3.8S. The cyclic loading decreased misfit of cemented and screw-retained crowns on reduced diameter abutments, and misfit of cemented crowns is greater than screw-retained ones. Abutments of reduced diameter failed more than conventional. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Crack Growth in Mercury Embrittled Aluminum Alloys under Cyclic and Static Loading Conditions

DTIC Science & Technology

1983-03-01

STATEMENT (ol the abalract entered In Block 20, It dlHerent from Report) 18. SUPPLEMENTARY NOTES This was a thesis in partial fulfillment of...argued that the strengthening that occurs from cold rolling suppresses crack nucleation at the surface under monotonlc loading. Under cyclic loading...precracking. Copper was chosen because It can be easily electrodeposited on aluminum, easily wet with mercury, and remains wet almost indefinitely

Optimizing an Intermittent Stretch Paradigm Using ERK1/2 Phosphorylation Results in Increased Collagen Synthesis in Engineered Ligaments

PubMed Central

Paxton, Jennifer Z.; Hagerty, Paul; Andrick, Jonathan J.

2012-01-01

Dynamic mechanical input is believed to play a critical role in the development of functional musculoskeletal tissues. To study this phenomenon, cyclic uniaxial mechanical stretch was applied to engineered ligaments using a custom-built bioreactor and the effects of different stretch frequency, amplitude, and duration were determined. Stretch acutely increased the phosphorylation of p38 (3.5±0.74-fold), S6K1 (3.9±0.19-fold), and ERK1/2 (2.45±0.32-fold). The phosphorylation of ERK1/2 was dependent on time, rather than on frequency or amplitude, within these constructs. ERK1/2 phosphorylation was similar following stretch at frequencies from 0.1 to 1 Hz and amplitudes from 2.5% to 15%, whereas phosphorylation reached maximal levels at 10 min of stretch and returned toward basal within 60 min of stretch. Following a single 10-min bout of cyclic stretch, the cells remained refractory to a second stretch for up to 6 h. Using the phosphorylation of ERK1/2 as a guide, the optimum stretch paradigm was hypothesized to be 10 min of stretch at 2.5% of resting length repeated every 6 h. Consistent with this hypothesis, 7 days of stretch using this optimized intermittent stretch program increased the collagen content of the grafts more than a continuous stretch program (CTL=3.1%±0.44%; CONT=4.8%±0.30%; and INT=5.9%±0.56%). These results suggest that short infrequent bouts of loading are optimal for improving engineered tendon and ligament physiology. PMID:21902469

Modelling of Fiber/Matrix Debonding of Composites Under Cyclic Loading

NASA Technical Reports Server (NTRS)

Naghipour, Paria; Pineda, Evan J.; Bednarcyk, Brett A.; Arnold, Steven M.

2013-01-01

The micromechanics theory, generalized method of cells (GMC), was employed to simulate the debonding of fiber/matrix interfaces, within a repeating unit cell subjected to global, cyclic loading, utilizing a cyclic crack growth law. Cycle dependent, interfacial debonding was implemented as a new module to the available GMC formulation. The degradation of interfacial stresses, with applied load cycles, was achieved via progressive evolution of the interfacial compliance. A periodic repeating unit cell, representing the fiber/matrix architecture of a composite, was subjected to combined normal and shear loadings, and degradation of the global transverse stress in successive cycles was monitored. The obtained results were compared to values from a corresponding finite element model. Reasonable agreement was achieved for combined normal and shear loading conditions, with minimal variation for pure loading cases. The local effects of interfacial debonding, and fatigue damage will later be combined as sub-models to predict the experimentally obtained fatigue life of Ti-15-3/Sic composites at the laminate level.

Strength degradation and lifetime prediction of dental zirconia ceramics under cyclic normal loading.

PubMed

Li, Wanzhong; Xu, Yingqiang; He, Huiming; Zhao, Haidan; Sun, Jian; Hou, Yue

2015-01-01

Clinical cases show that zirconia restoration could happen fracture by accident under overloading after using a period of time. The purpose of this study is to research mechanical behavior and predict lifetime of dental zirconia ceramics under cyclic normal contact loading with experiments. Cyclic normal contact loading test and three point bending test are carried on specimens made of two brands of dental zirconia ceramic to obtain flexure strength and damage degree after different number of loading cycles. By means of damage mechanics model, damage degree under different number of contact loading cycles are calculated according to flexure strength, and verified by SEM photographs of cross section morphology of zirconia ceramics specimen phenomenologically. Relation curve of damage degree and number of cycles is fitted by polynomial fitting, then the number of loading cycles can be concluded when the specimen is complete damage. Strength degradation of two brands dental zirconia ceramics are researched in vitro, and prediction method of contact fatigue lifetime is established.

Effect of Degeneration on Fluid-Solid Interaction within Intervertebral Disk Under Cyclic Loading - A Meta-Model Analysis of Finite Element Simulations.

PubMed

Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin

2015-01-01

The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid-fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid-solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid-fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk.

Effect of Degeneration on Fluid–Solid Interaction within Intervertebral Disk Under Cyclic Loading – A Meta-Model Analysis of Finite Element Simulations

PubMed Central

Nikkhoo, Mohammad; Khalaf, Kinda; Kuo, Ya-Wen; Hsu, Yu-Chun; Haghpanahi, Mohammad; Parnianpour, Mohamad; Wang, Jaw-Lin

2015-01-01

The risk of low back pain resulted from cyclic loadings is greater than that resulted from prolonged static postures. Disk degeneration results in degradation of disk solid structures and decrease of water contents, which is caused by activation of matrix digestive enzymes. The mechanical responses resulted from internal solid–fluid interactions of degenerative disks to cyclic loadings are not well studied yet. The fluid–solid interactions in disks can be evaluated by mathematical models, especially the poroelastic finite element (FE) models. We developed a robust disk poroelastic FE model to analyze the effect of degeneration on solid–fluid interactions within disk subjected to cyclic loadings at different loading frequencies. A backward analysis combined with in vitro experiments was used to find the elastic modulus and hydraulic permeability of intact and enzyme-induced degenerated porcine disks. The results showed that the averaged peak-to-peak disk deformations during the in vitro cyclic tests were well fitted with limited FE simulations and a quadratic response surface regression for both disk groups. The results showed that higher loading frequency increased the intradiscal pressure, decreased the total fluid loss, and slightly increased the maximum axial stress within solid matrix. Enzyme-induced degeneration decreased the intradiscal pressure and total fluid loss, and barely changed the maximum axial stress within solid matrix. The increase of intradiscal pressure and total fluid loss with loading frequency was less sensitive after the frequency elevated to 0.1 Hz for the enzyme-induced degenerated disk. Based on this study, it is found that enzyme-induced degeneration decreases energy attenuation capability of disk, but less change the strength of disk. PMID:25674562

Experimental and Numerical Studies on Development of Fracture Process Zone (FPZ) in Rocks under Cyclic and Static Loadings

NASA Astrophysics Data System (ADS)

Ghamgosar, M.; Erarslan, N.

2016-03-01

The development of fracture process zones (FPZ) in the Cracked Chevron Notched Brazilian Disc (CCNBD) monsonite and Brisbane tuff specimens was investigated to evaluate the mechanical behaviour of brittle rocks under static and various cyclic loadings. An FPZ is a region that involves different types of damage around the pre-existing and/or stress-induced crack tips in engineering materials. This highly damaged area includes micro- and meso-cracks, which emerge prior to the main fracture growth or extension and ultimately coalescence to macrofractures, leading to the failure. The experiments and numerical simulations were designed for this study to investigate the following features of FPZ in rocks: (1) ligament connections and (2) microcracking and its coalescence in FPZ. A Computed Tomography (CT) scan technique was also used to investigate the FPZ behaviour in selected rock specimens. The CT scan results showed that the fracturing velocity is entirely dependent on the appropriate amount of fracture energy absorbed in rock specimens due to the change of frequency and amplitudes of the dynamic loading. Extended Finite Element Method (XFEM) was used to compute the displacements, tensile stress distribution and plastic energy dissipation around the propagating crack tip in FPZ. One of the most important observations, the shape of FPZ and its extension around the crack tip, was made using numerical and experimental results, which supported the CT scan results. When the static rupture and the cyclic rupture were compared, the main differences are twofold: (1) the number of fragments produced is much greater under cyclic loading than under static loading, and (2) intergranular cracks are formed due to particle breakage under cyclic loading compared with smooth and bright cracks along cleavage planes under static loading.

Characterizing the Collagen Fiber Orientation in Pericardial Leaflets Under Mechanical Loading Conditions

PubMed Central

Alavi, S. Hamed; Ruiz, Victor; Krasieva, Tatiana; Botvinick, Elliot L.; Kheradvar, Arash

2014-01-01

When implanted inside the body, bioprosthetic heart valve leaflets experience a variety of cyclic mechanical stresses such as shear stress due to blood flow when the valve is open, flexural stress due to cyclic opening and closure of the valve, and tensile stress when the valve is closed. These types of stress lead to a variety of failure modes. In either a natural valve leaflet or a processed pericardial tissue leaflet, collagen fibers reinforce the tissue and provide structural integrity such that the very thin leaflet can stand enormous loads related to cyclic pressure changes. The mechanical response of the leaflet tissue greatly depends on collagen fiber concentration, characteristics, and orientation. Thus, understating the microstructure of pericardial tissue and its response to dynamic loading is crucial for the development of more durable heart valve, and computational models to predict heart valves’ behavior. In this work, we have characterized the 3D collagen fiber arrangement of bovine pericardial tissue leaflets in response to a variety of different loading conditions under Second-Harmonic Generation Microscopy. This real-time visualization method assists in better understanding of the effect of cyclic load on collagen fiber orientation in time and space. PMID:23180029

Experimental and numerical characterisation of the elasto-plastic properties of bovine trabecular bone and a trabecular bone analogue.

PubMed

Kelly, Nicola; McGarry, J Patrick

2012-05-01

The inelastic pressure dependent compressive behaviour of bovine trabecular bone is investigated through experimental and computational analysis. Two loading configurations are implemented, uniaxial and confined compression, providing two distinct loading paths in the von Mises-pressure stress plane. Experimental results reveal distinctive yielding followed by a constant nominal stress plateau for both uniaxial and confined compression. Computational simulation of the experimental tests using the Drucker-Prager and Mohr-Coulomb plasticity models fails to capture the confined compression behaviour of trabecular bone. The high pressure developed during confined compression does not result in plastic deformation using these formulations, and a near elastic response is computed. In contrast, the crushable foam plasticity models provide accurate simulation of the confined compression tests, with distinctive yield and plateau behaviour being predicted. The elliptical yield surfaces of the crushable foam formulations in the von Mises-pressure stress plane accurately characterise the plastic behaviour of trabecular bone. Results reveal that the hydrostatic yield stress is equal to the uniaxial yield stress for trabecular bone, demonstrating the importance of accurate characterisation and simulation of the pressure dependent plasticity. It is also demonstrated in this study that a commercially available trabecular bone analogue material, cellular rigid polyurethane foam, exhibits similar pressure dependent yield behaviour, despite having a lower stiffness and strength than trabecular bone. This study provides a novel insight into the pressure dependent yield behaviour of trabecular bone, demonstrating the inadequacy of uniaxial testing alone. For the first time, crushable foam plasticity formulations are implemented for trabecular bone. The enhanced understanding of the inelastic behaviour of trabecular bone established in this study will allow for more realistic simulation of orthopaedic device implantation and failure. Copyright © 2011 Elsevier Ltd. All rights reserved.

Differential expression of type X collagen in a mechanically active 3-D chondrocyte culture system: a quantitative study

PubMed Central

Yang, Xu; Vezeridis, Peter S; Nicholas, Brian; Crisco, Joseph J; Moore, Douglas C; Chen, Qian

2006-01-01

Objective Mechanical loading of cartilage influences chondrocyte metabolism and gene expression. The gene encoding type X collagen is expressed specifically by hypertrophic chondrocytes and up regulated during osteoarthritis. In this study we tested the hypothesis that the mechanical microenvironment resulting from higher levels of local strain in a three dimensional cell culture construct would lead to an increase in the expression of type X collagen mRNA by chondrocytes in those areas. Methods Hypertrophic chondrocytes were isolated from embryonic chick sterna and seeded onto rectangular Gelfoam sponges. Seeded sponges were subjected to various levels of cyclic uniaxial tensile strains at 1 Hz with the computer-controlled Bio-Stretch system. Strain distribution across the sponge was quantified by digital image analysis. After mechanical loading, sponges were cut and the end and center regions were separated according to construct strain distribution. Total RNA was extracted from the cells harvested from these regions, and real-time quantitative RT-PCR was performed to quantify mRNA levels for type X collagen and a housing-keeping gene 18S RNA. Results Chondrocytes distributed in high (9%) local strain areas produced more than two times type X collagen mRNA compared to the those under no load conditions, while chondrocytes located in low (2.5%) local strain areas had no appreciable difference in type X collagen mRNA production in comparison to non-loaded samples. Increasing local strains above 2.5%, either in the center or end regions of the sponge, resulted in increased expression of Col X mRNA by chondrocytes in that region. Conclusion These findings suggest that the threshold of chondrocyte sensitivity to inducing type X collagen mRNA production is more than 2.5% local strain, and that increased local strains above the threshold results in an increase of Col X mRNA expression. Such quantitative analysis has important implications for our understanding of mechanosensitivity of cartilage and mechanical regulation of chondrocyte gene expression. PMID:17150098

The effects of dynamic loading on the intervertebral disc.

PubMed

Chan, Samantha C W; Ferguson, Stephen J; Gantenbein-Ritter, Benjamin

2011-11-01

Loading is important to maintain the balance of matrix turnover in the intervertebral disc (IVD). Daily cyclic diurnal assists in the transport of large soluble factors across the IVD and its surrounding circulation and applies direct and indirect stimulus to disc cells. Acute mechanical injury and accumulated overloading, however, could induce disc degeneration. Recently, there is more information available on how cyclic loading, especially axial compression and hydrostatic pressure, affects IVD cell biology. This review summarises recent studies on the response of the IVD and stem cells to applied cyclic compression and hydrostatic pressure. These studies investigate the possible role of loading in the initiation and progression of disc degeneration as well as quantifying a physiological loading condition for the study of disc degeneration biological therapy. Subsequently, a possible physiological/beneficial loading range is proposed. This physiological/beneficial loading could provide insight into how to design loading regimes in specific system for the testing of various biological therapies such as cell therapy, chemical therapy or tissue engineering constructs to achieve a better final outcome. In addition, the parameter space of 'physiological' loading may also be an important factor for the differentiation of stem cells towards most ideally 'discogenic' cells for tissue engineering purpose.

Cyclic mechanical strain maintains Nanog expression through PI3K/Akt signaling in mouse embryonic stem cells

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

Horiuchi, Rie; Akimoto, Takayuki, E-mail: akimoto@m.u-tokyo.ac.jp; Institute for Biomedical Engineering, Consolidated Research Institute for Advanced Science and Medical Care, Waseda University, 513 Waseda-tsurumaki, Shinjuku, Tokyo 162-0041

2012-08-15

Mechanical strain has been reported to affect the proliferation/differentiation of many cell types; however, the effects of mechanotransduction on self-renewal as well as pluripotency of embryonic stem (ES) cells remains unknown. To investigate the effects of mechanical strain on mouse ES cell fate, we examined the expression of Nanog, which is an essential regulator of self-renewal and pluripotency as well as Nanog-associated intracellular signaling during uniaxial cyclic mechanical strain. The mouse ES cell line, CCE was plated onto elastic membranes, and we applied 10% strain at 0.17 Hz. The expression of Nanog was reduced during ES cell differentiation in responsemore » to the withdrawal of leukemia inhibitory factor (LIF); however, two days of cyclic mechanical strain attenuated this reduction of Nanog expression. On the other hand, the cyclic mechanical strain promoted PI3K-Akt signaling, which is reported as an upstream of Nanog transcription. The cyclic mechanical strain-induced Akt phosphorylation was blunted by the PI3K inhibitor wortmannin. Furthermore, cytochalasin D, an inhibitor of actin polymerization, also inhibited the mechanical strain-induced increase in phospho-Akt. These findings imply that mechanical force plays a role in regulating Nanog expression in ES cells through the actin cytoskeleton-PI3K-Akt signaling. -- Highlights: Black-Right-Pointing-Pointer The expression of Nanog, which is an essential regulator of 'stemness' was reduced during embryonic stem (ES) cell differentiation. Black-Right-Pointing-Pointer Cyclic mechanical strain attenuated the reduction of Nanog expression. Black-Right-Pointing-Pointer Cyclic mechanical strain promoted PI3K-Akt signaling and mechanical strain-induced Akt phosphorylation was blunted by the PI3K inhibitor and an inhibitor of actin polymerization.« less

Bond Capability of Universal Adhesive Systems to Dentin in Self-etch Mode after Short-term Storage and Cyclic Loading

PubMed Central

Costa, Daniele Morosini; Somacal, Deise Caren; Borges, Gilberto Antonio; Spohr, Ana Maria

2017-01-01

Objective: The aim was to evaluate, in vitro, the tensile bond strength to dentin of Scotchbond Universal (SU), All-Bond Universal (AU) and One Coat 7 Universal (OC7) adhesives applied in self-etch mode, after 24 h of storage and after 500,000 loading cycles, using Clearfil SE Bond (SE) as a control. Materials and Methods: The adhesives were applied on the dentin of bovine teeth, followed by the application of a composite resin. Thirty specimens were obtained for each adhesive. Half of the specimens were submitted to cyclic loading for 500,000 cycles. All specimens were submitted to a tensile bond strength test in a universal testing machine at a crosshead speed of 0.5 mm/minute. Results: According to two-way ANOVA and Tukey’s test (α=5%), the interaction between the adhesive and cyclic loading factors was significant (p=0.001). The means followed by the same letter represent no significant difference in the bond strength (MPa) after 24 h: OC7=7.86A (±2.90), SU=6.78AB (±2.03), AU=5.61BC (±2.32), and SE=3.53C (±1.89). After cyclic loading, SE, SU and AU maintained bond strength comparable to 24 h period. There was a significant decrease only for OC7. Conclusion: SU, AU and OC7 had bond strength to dentin comparable to that of SE. Only OC7 had decreased bond strength to dentin after cyclic loading. PMID:28839476

[Cyclic fatigue of Vita mark II machinable ceramics under Hertzian's contact].

PubMed

Liu, Wei-Cai; Zhang, Zhi-Shen; Huang, Cheng-Min; Chao, Yong-Lie; Wan, Qian-Bing

2006-08-01

To investigate the cyclic fatigue modes of Vita mark II machinable ceramics under Hertzian's contact. Hertzian's contact technique (WC spheres r = 3.18 mm) was used to investigate the cyclic fatigue of Vita mark II machinable ceramic. All specimens were fatigued by cyclic loading in moist environment, furthermore, surviving strength was examined by three point test and morphology damage observation. In homogeneous Vita mark II machinable ceramics, two fatigue damage modes existed after cyclic loading with spheres under moist environment, including conventional tensile-driven cone cracking (brittle mode) and shear-driven microdamage accumulation (quasi-plastic mode). The latter generated radial cracks and deeply penetrating secondary cone crack. Initial strength degradation were caused by the cone cracks, subsequent and much more deleterious loss was caused by radial cracks. Cyclic fatigue modes of Vita mark II machinable ceramics includes brittle and quasi-plastic mode.

Synchronous Measuring Techniques in Parallel to MRE: Study of Pressure, Pre-Tension, and Surface Dynamics

NASA Astrophysics Data System (ADS)

Brinker, Spencer Thomas

The contents of this dissertation include investigations in Magnetic Resonance Elastography (MRE) using a preclinical 9.4 Tesla small animal Magnetic Resonance Imaging (MRI) system along with synthetic materials that mimic the mechanical properties of soft human tissue. MRE is used for studying the mechanical behavior of soft tissue particularly applicable to medical applications. Wave motion induced by a mechanical driver is measured with MRI to acquire internal displacement fields over time and space within a material media. Complex shear modulus of the media is calculated from the response of mechanical wave transmission through the material. Changes in soft tissue stiffness is associated with disease progression and thus, is why assessing tissue mechanical properties with MRE has powerful diagnostic potential due to the noninvasive procedure of MRI. The experiments performed in this dissertation used elastic phantoms and specimens to observe the influence of pre-stress on MRE derived mechanical properties while additional mechanical measurements from other related material testing methods were synchronously collected alongside MRI scanning. An organ simulating phantom was used to explore changes in MRE stiffness in response to gas and liquid cyclic pressure loading. MRE stiffness increased with pressure and hysteresis was observed in cyclic pressure loading. The results suggest MRE is applicable to pressure related disease assessment. In addition, an interconnected porosity pressure phantom was constructed for future porous media investigations. A custom system was also built to demonstrate concurrent tensile testing during MRE for investigating homogeneous soft material media undergoing pre-tension. Stiffness increased with uniaxial tensile stress and strain. The tension and stiffness relationship explored can be related to the stress analysis of voluntary muscle. The results also offer prospective experimental strategies for community wide standards on MRE calibration methods. Lastly, a novel platform was developed for synchronous acquisition of Scanning Laser Doppler Vibrometry (SLDV) and MRE for examining surface wave dynamics related to internal media wave propagation in soft material experiencing sinusoidal mechanical excitation. The results indicate that optical displacement measurements of media on the surface are similar in nature to internal displacement measured from MRE. It is concluded that optical and MRI based elastography yield similar values of complex shear modulus.

Innovative design of composite structures: The use of curvilinear fiber format in structural design of composites

NASA Technical Reports Server (NTRS)

Charette, R. F.; Hyer, M. W.

1990-01-01

The influence is investigated of a curvilinear fiber format on load carrying capacity of a layered fiber reinforced plate with a centrally located hole. A curvilinear fiber format is descriptive of layers in a laminate having fibers which are aligned with the principal stress directions in those layers. Laminates of five curvilinear fiber format designs and four straightline fiber format designs are considered. A quasi-isotropic laminate having a straightline fiber format is used to define a baseline design for comparison with the other laminate designs. Four different plate geometries are considered and differentiated by two values of hole diameter/plate width equal to 1/6 and 1/3, and two values of plate length/plate width equal to 2 and 1. With the plates under uniaxial tensile loading on two opposing edges, alignment of fibers in the curvilinear layers with the principal stress directions is determined analytically by an iteration procedure. In-plane tensile load capacity is computed for all of the laminate designs using a finite element analysis method. A maximum strain failure criterion and the Tsai-Wu failure criterion are applied to determine failure loads and failure modes. Resistance to buckling of the laminate designs to uniaxial compressive loading is analyzed using the commercial code Engineering Analysis Language. Results indicate that the curvilinear fiber format laminates have higher in-plane tensile load capacity and comparable buckling resistance relative to the straightline fiber format laminates.

Fracture of Fiber-Reinforced Beams due to Impact Loading

DTIC Science & Technology

1975-03-01

high rates of tensile loading were made by Armenakas and Sciammarella [5, 6]. They found that the main contribution to the failure of the...2394, June 1974. Armenakas, A. E., and Sciammarella , C. A., "Experimental In- vestigation of the Failure Mechanisms of Fiber Reinforced Composites...Subjected to Uniaxial Tension," Technical Report AFML-TR-71-179, Air Force Materials Laboratory, August 1971. Armenakas, A. E., and Sciammarella , C. A

An analytical solution for the elastoplastic response of a continuous fiber composite under uniaxial loading

NASA Technical Reports Server (NTRS)

Lee, Jong-Won; Allen, David H.

1990-01-01

A continuous fiber composite is modelled by a two-element composite cylinder in order to predict the elastoplastic response of the composite under a monotonically increasing tensile loading parallel to fibers. The fibers and matrix are assumed to be elastic-perfectly plastic materials obeying Hill's and Tresca's yield criteria, respectively. Here, the composite behavior when the fibers yield prior to the matrix is investigated.

Multiaxial and Thermomechanical Fatigue of Materials: A Historical Perspective and Some Future Challenges

NASA Technical Reports Server (NTRS)

Kalluri, Sreeramesh

2013-01-01

Structural materials used in engineering applications routinely subjected to repetitive mechanical loads in multiple directions under non-isothermal conditions. Over past few decades, several multiaxial fatigue life estimation models (stress- and strain-based) developed for isothermal conditions. Historically, numerous fatigue life prediction models also developed for thermomechanical fatigue (TMF) life prediction, predominantly for uniaxial mechanical loading conditions. Realistic structural components encounter multiaxial loads and non-isothermal loading conditions, which increase potential for interaction of damage modes. A need exists for mechanical testing and development verification of life prediction models under such conditions.

A comprehensive study of layer-specific morphological changes in the microstructure of carotid arteries under uniaxial load.

PubMed

Krasny, Witold; Morin, Claire; Magoariec, Hélène; Avril, Stéphane

2017-07-15

The load bearing properties of large blood vessels are principally conferred by collagen and elastin networks and their microstructural organization plays an important role in the outcomes of various arterial pathologies. In particular, these fibrous networks are able to rearrange and reorient spatially during mechanical deformations. In this study, we investigate for the first time whether these well-known morphological rearrangements are the same across the whole thickness of blood vessels, and subsequently if the underlying mechanisms that govern these rearrangements can be predicted using affine kinematics. To this aim, we submitted rabbit carotid samples to uniaxial load in three distinct deformation directions, while recording live images of the 3D microstructure using multiphoton microscopy. Our results show that the observed realignment of collagen and elastin in the media layer, along with elastin of the adventitia layer, remained limited to small angles that can be predicted by affine kinematics. We show also that collagen bundles of fibers in the adventitia layer behaved in significantly different fashion. They showed a remarkable capacity to realign in the direction of the load, whatever the loading direction. Measured reorientation angles of the fibers were significantly higher than affine predictions. This remarkable property of collagen bundles in the adventitia was never observed before, it shows that the medium surrounding collagen in the adventitia undergoes complex deformations challenging traditional hyperelastic models based on mixture theories. The biomechanical properties of arteries are conferred by the rearrangement under load of the collagen and elastin fibers making up the arterial microstructure. Their kinematics under deformation is not yet characterized for all fiber networks. In this respect we have submitted samples of arterial tissue to uniaxial tension, simultaneously to confocal imaging of their microstructure. Our method allowed identifying for the first time the remarkable ability of adventitial collagen fibers to reorient in the direction of the load, achieving reorientation rotations that exceeded those predicted by affine kinematics, while all other networks followed the affine kinematics. Our results highlight new properties of the microstructure, which might play a role in the outcomes of vascular pathologies like aneurysms. Copyright © 2017 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Test method research on weakening interface strength of steel - concrete under cyclic loading

NASA Astrophysics Data System (ADS)

Liu, Ming-wei; Zhang, Fang-hua; Su, Guang-quan

2018-02-01

The mechanical properties of steel - concrete interface under cyclic loading are the key factors affecting the rule of horizontal load transfer, the calculation of bearing capacity and cumulative horizontal deformation. Cyclic shear test is an effective method to study the strength reduction of steel - concrete interface. A test system composed of large repeated direct shear test instrument, hydraulic servo system, data acquisition system, test control software system and so on is independently designed, and a set of test method, including the specimen preparation, the instrument preparation, the loading method and so on, is put forward. By listing a set of test results, the validity of the test method is verified. The test system and the test method based on it provide a reference for the experimental study on mechanical properties of steel - concrete interface.

Combining Dynamic Stretch and Tunable Stiffness to Probe Cell Mechanobiology In Vitro

PubMed Central

Throm Quinlan, Angela M.; Sierad, Leslie N.; Capulli, Andrew K.; Firstenberg, Laura E.; Billiar, Kristen L.

2011-01-01

Cells have the ability to actively sense their mechanical environment and respond to both substrate stiffness and stretch by altering their adhesion, proliferation, locomotion, morphology, and synthetic profile. In order to elucidate the interrelated effects of different mechanical stimuli on cell phenotype in vitro, we have developed a method for culturing mammalian cells in a two-dimensional environment at a wide range of combined levels of substrate stiffness and dynamic stretch. Polyacrylamide gels were covalently bonded to flexible silicone culture plates and coated with monomeric collagen for cell adhesion. Substrate stiffness was adjusted from relatively soft (G′ = 0.3 kPa) to stiff (G′ = 50 kPa) by altering the ratio of acrylamide to bis-acrylamide, and the silicone membranes were stretched over circular loading posts by applying vacuum pressure to impart near-uniform stretch, as confirmed by strain field analysis. As a demonstration of the system, porcine aortic valve interstitial cells (VIC) and human mesenchymal stem cells (hMSC) were plated on soft and stiff substrates either statically cultured or exposed to 10% equibiaxial or pure uniaxial stretch at 1Hz for 6 hours. In all cases, cell attachment and cell viability were high. On soft substrates, VICs cultured statically exhibit a small rounded morphology, significantly smaller than on stiff substrates (p<0.05). Following equibiaxial cyclic stretch, VICs spread to the extent of cells cultured on stiff substrates, but did not reorient in response to uniaxial stretch to the extent of cells stretched on stiff substrates. hMSCs exhibited a less pronounced response than VICs, likely due to a lower stiffness threshold for spreading on static gels. These preliminary data demonstrate that inhibition of spreading due to a lack of matrix stiffness surrounding a cell may be overcome by externally applied stretch suggesting similar mechanotransduction mechanisms for sensing stiffness and stretch. PMID:21858051

Hierarchical honeycomb auxetic metamaterials

NASA Astrophysics Data System (ADS)

Mousanezhad, Davood; Babaee, Sahab; Ebrahimi, Hamid; Ghosh, Ranajay; Hamouda, Abdelmagid Salem; Bertoldi, Katia; Vaziri, Ashkan

2015-12-01

Most conventional materials expand in transverse directions when they are compressed uniaxially resulting in the familiar positive Poisson’s ratio. Here we develop a new class of two dimensional (2D) metamaterials with negative Poisson’s ratio that contract in transverse directions under uniaxial compressive loads leading to auxeticity. This is achieved through mechanical instabilities (i.e., buckling) introduced by structural hierarchy and retained over a wide range of applied compression. This unusual behavior is demonstrated experimentally and analyzed computationally. The work provides new insights into the role of structural organization and hierarchy in designing 2D auxetic metamaterials, and new opportunities for developing energy absorbing materials, tunable membrane filters, and acoustic dampeners.

In situ neutron diffraction study of micromechanical interactions and phase transformation in Ni-Mn-Ga alloy under uniaxial and hydrostatic stress.

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

Peng, R. L.; Wang, Y. D.; Nie, Z. H.

2008-01-01

This paper deals with the experimental study of stress-induced phase transformation in a polycrystalline Ni-Mn-Ga alloy under uniaxial compression and its powder under hydrostatic compression. In situ neutron diffraction experiments were employed to follow changes in the structure and lattice strains caused by the applied stresses. Large lattice strains that are dependent on the lattice planes or grain orientations were observed in the parent Heusler phase for both the bulk material and the powder sample. The development of such anisotropic strains and the influence of external load conditions are discussed in the paper.

Computational study of dislocation based mechanisms in FCC materials

NASA Astrophysics Data System (ADS)

Yellakara, Ranga Nikhil

Understanding the relationships between microstructures and properties of materials is a key to developing new materials with more suitable qualities or employing the appropriate materials in special uses. In the present world of material research, the main focus is on microstructural control to cost-effectively enhance properties and meet performance specifications. This present work is directed towards improving the fundamental understanding of the microscale deformation mechanisms and mechanical behavior of metallic alloys, particularly focusing on face centered cubic (FCC) structured metals through a unique computational methodology called three-dimensional dislocation dynamics (3D-DD). In these simulations, the equations of motion for dislocations are mathematically solved to determine the evolution and interaction of dislocations. Microstructure details and stress-strain curves are a direct observation in the simulation and can be used to validate experimental results. The effect of initial dislocation microstructure on the yield strength has been studied. It has been shown that dislocation density based crystal plasticity formulations only work when dislocation densities/numbers are sufficiently large so that a statistically accurate description of the microstructure can be obtainable. The evolution of the flow stress for grain sizes ranging from 0.5 to 10 mum under uniaxial tension was simulated using an improvised model by integrating dislocation pile-up mechanism at grain boundaries has been performed. This study showed that for a same initial dislocation density, the Hall--Petch relationship holds well at small grain sizes (0.5--2 mum), beyond which the yield strength remains constant as the grain size increases. Various dislocation-particle interaction mechanisms have been introduced and investigations were made on their effect on the uniaxial tensile properties. These studies suggested that increase in particle volume fraction and decrease in particle size has contributed to the strength of these alloys. This work has been successful of capturing complex dislocation mechanisms that involves interactions with particles during the deformation of particle hardened FCC alloys. Finally, the DD model has been extended into studying the cyclic behavior of FCC metallic alloys. This study showed that the strength as well as the cyclic hardening increases due to grain refinement and increase in particle volume fraction. It also showed that the cyclic deformation of ultra-fine grained (UFG) material have undergone cyclic softening at all plastic strain amplitudes. The results provided very useful quantitative information for developing future fatigue models.

Mechanical Stimulation of Adipose-Derived Stem Cells for Functional Tissue Engineering of the Musculoskeletal System via Cyclic Hydrostatic Pressure, Simulated Microgravity, and Cyclic Tensile Strain.

PubMed

Nordberg, Rachel C; Bodle, Josie C; Loboa, Elizabeth G

2018-01-01

It is critical that human adipose stem cell (hASC) tissue-engineering therapies possess appropriate mechanical properties in order to restore function of the load bearing tissues of the musculoskeletal system. In an effort to elucidate the hASC response to mechanical stimulation and develop mechanically robust tissue engineered constructs, recent research has utilized a variety of mechanical loading paradigms including cyclic tensile strain, cyclic hydrostatic pressure, and mechanical unloading in simulated microgravity. This chapter describes methods for applying these mechanical stimuli to hASC to direct differentiation for functional tissue engineering of the musculoskeletal system.

Dynamic Torsional and Cyclic Fracture Behavior of ProFile Rotary Instruments at Continuous or Reciprocating Rotation as Visualized with High-speed Digital Video Imaging.

PubMed

Tokita, Daisuke; Ebihara, Arata; Miyara, Kana; Okiji, Takashi

2017-08-01

This study examined the dynamic fracture behavior of nickel-titanium rotary instruments in torsional or cyclic loading at continuous or reciprocating rotation by means of high-speed digital video imaging. The ProFile instruments (size 30, 0.06 taper; Dentsply Maillefer, Ballaigues, Switzerland) were categorized into 4 groups (n = 7 in each group) as follows: torsional/continuous (TC), torsional/reciprocating (TR), cyclic/continuous (CC), and cyclic/reciprocating (CR). Torsional loading was performed by rotating the instruments by holding the tip with a vise. For cyclic loading, a custom-made device with a 38° curvature was used. Dynamic fracture behavior was observed with a high-speed camera. The time to fracture was recorded, and the fractured surface was examined with scanning electron microscopy. The TC group initially exhibited necking of the file followed by the development of an initial crack line. The TR group demonstrated opening and closing of a crack according to its rotation in the cutting and noncutting directions, respectively. The CC group separated without any detectable signs of deformation. In the CR group, initial crack formation was recognized in 5 of 7 samples. The reciprocating rotation exhibited a longer time to fracture in both torsional and cyclic fatigue testing (P < .05). The scanning electron microscopic images showed a severely deformed surface in the TR group. The dynamic fracture behavior of NiTi rotary instruments, as visualized with high-speed digital video imaging, varied between the different modes of rotation and different fatigue testing. Reciprocating rotation induced a slower crack propagation and conferred higher fatigue resistance than continuous rotation in both torsional and cyclic loads. Copyright © 2017 American Association of Endodontists. Published by Elsevier Inc. All rights reserved.

Modeling of Micro Deval abrasion loss based on some rock properties

NASA Astrophysics Data System (ADS)

Capik, Mehmet; Yilmaz, Ali Osman

2017-10-01

Aggregate is one of the most widely used construction material. The quality of the aggregate is determined using some testing methods. Among these methods, the Micro Deval Abrasion Loss (MDAL) test is commonly used for the determination of the quality and the abrasion resistance of aggregate. The main objective of this study is to develop models for the prediction of MDAL from rock properties, including uniaxial compressive strength, Brazilian tensile strength, point load index, Schmidt rebound hardness, apparent porosity, void ratio Cerchar abrasivity index and Bohme abrasion test are examined. Additionally, the MDAL is modeled using simple regression analysis and multiple linear regression analysis based on the rock properties. The study shows that the MDAL decreases with the increase of uniaxial compressive strength, Brazilian tensile strength, point load index, Schmidt rebound hardness and Cerchar abrasivity index. It is also concluded that the MDAL increases with the increase of apparent porosity, void ratio and Bohme abrasion test. The modeling results show that the models based on Bohme abrasion test and L type Schmidt rebound hardness give the better forecasting performances for the MDAL. More models, including the uniaxial compressive strength, the apparent porosity and Cerchar abrasivity index, are developed for the rapid estimation of the MDAL of the rocks. The developed models were verified by statistical tests. Additionally, it can be stated that the proposed models can be used as a forecasting for aggregate quality.

Assessment of burned coal shale properties based on cyclic load

NASA Astrophysics Data System (ADS)

Grygierek, Marcin; Kalisz, Piotr; Pacześniowski, Krzysztof; Pytlik, Andrzej; Zięba, Magdalena

2018-04-01

Road surfaces that are subjected to cyclic loads generated by vehicle wheels must meet the requirements concerning the durability in the assumed period of use. The durability of the layered pavement construction systems depends on the value and frequency of the load as well as on the mechanical features of its individual layers. Layers of unbound, mechanically stabilized mixtures are a significant aspect of surfaces that are susceptible. Mixtures of this type can be applied both to the subgrade layers as well as to the bottom pavement layers, including the improved course. Considering the cyclic nature of the load on the surface of the entire system, mechanically stabilized layers are subject to continuous, but slow, densification during the period of use, which results in the formation of permanent deformations and so-called structural ruts. Post-mining waste is frequently used in road construction. which is the so-called burned shale that can be used for the bottom layers of the surface and layers of the improved subgrade (soil replacement). This material was the subject of the analysis. The evaluation was based mainly on the results of pilot studies covering cyclic loads of the layer/course made of the so-called red shale. The applied research method was aimed at preliminary assessment of its suitability for the assessment of the behaviour of the disintegrated medium under the conditions of test loads simulating the movement of vehicles.

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

Lu, Wei-Yang

Foam materials are used to protect sensitive components from impact loading. In order to predict and simulate the foam performance under various loading conditions, a validated foam model is needed and the mechanical properties of foams need to be characterized. Uniaxial compression and tension tests were conducted for different densities of foams under various temperatures and loading rates. Crush stress, tensile strength, and elastic modulus were obtained. A newly developed confined compression experiment provided data for investigating the foam flow direction. A biaxial tension experiment was also developed to explore the damage surface of a rigid polyurethane foam.

Quantification of Cyclic Ground Reaction Force Histories During Daily Activity in Humans

NASA Technical Reports Server (NTRS)

Breit, G. A.; Whalen, R. T.; Wade, Charles E. (Technical Monitor)

1994-01-01

Theoretical models and experimental studies of bone remodeling suggest that bone density and structure are influenced by local cyclic skeletal tissue stress and strain histories. Estimation of long-term loading histories in humans is usually achieved by assessment of physical activity level by questionnaires, logbooks, and pedometers, since the majority of lower limb cyclic loading occurs during walking and running. These methods provide some indication of the mechanical loading history, but fail to consider the true magnitude of the lower limb skeletal forces generated by various daily activities. These techniques cannot account for individual gait characteristics, gait speed, and unpredictable high loading events that may influence bone mass significantly. We have developed portable instrumentation to measure and record the vertical component of the ground reaction force (GRFz) during normal daily activity. This equipment allows long-term quantitative monitoring of musculoskeletal loads, which in conjunction with bone mineral density assessments, promises to elucidate the relationship between skeletal stresses and bone remodeling.

Mixed-mode cyclic debonding of adhesively bonded composite joints. M.S. Thesis

NASA Technical Reports Server (NTRS)

Rezaizadeh, M. A.; Mall, S.

1985-01-01

A combined experimental-analytical investigation to characterize the cyclic failure mechanism of a simple composite-to-composite bonded joint is conducted. The cracked lap shear (CLS) specimens of graphite/epoxy adherend bonded with EC-3445 adhesive are tested under combined mode 1 and 2 loading. In all specimens tested, fatigue failure occurs in the form of cyclic debonding. The cyclic debond growth rates are measured. The finite element analysis is employed to compute the mode 1, mode 2, and total strain energy release rates (i.e., GI, GII, and GT). A wide range of mixed-mode loading, i.e., GI/GII ranging from 0.03 to 0.38, is obtained. The total strain energy release rate, G sub T, appeared to be the driving parameter for cyclic debonding in the tested composite bonded system.

Study on stress-strain response of multi-phase TRIP steel under cyclic loading

NASA Astrophysics Data System (ADS)

Dan, W. J.; Hu, Z. G.; Zhang, W. G.; Li, S. H.; Lin, Z. Q.

2013-12-01

The stress-strain response of multi-phase TRIP590 sheet steel is studied in cyclic loading condition at room temperature based on a cyclic phase transformation model and a multi-phase mixed kinematic hardening model. The cyclic martensite transformation model is proposed based on the shear-band intersection, where the repeat number, strain amplitude and cyclic frequency are used to control the phase transformation process. The multi-phase mixed kinematic hardening model is developed based on the non-linear kinematic hardening rule of per-phase. The parameters of transformation model are identified with the relationship between the austenite volume fraction and the repeat number. The parameters in Kinematic hardening model are confirmed by the experimental hysteresis loops in different strain amplitude conditions. The responses of hysteresis loop and stress amplitude are evaluated by tension-compression data.

Matrix cracking in laminated composites under monotonic and cyclic loadings

NASA Technical Reports Server (NTRS)

Allen, David H.; Lee, Jong-Won

1991-01-01

An analytical model based on the internal state variable (ISV) concept and the strain energy method is proposed for characterizing the monotonic and cyclic response of laminated composites containing matrix cracks. A modified constitution is formulated for angle-ply laminates under general in-plane mechanical loading and constant temperature change. A monotonic matrix cracking criterion is developed for predicting the crack density in cross-ply laminates as a function of the applied laminate axial stress. An initial formulation for a cyclic matrix cracking criterion for cross-ply laminates is also discussed. For the monotonic loading case, a number of experimental data and well-known models are compared with the present study for validating the practical applicability of the ISV approach.

Static and cyclic loading of fiber-reinforced dental resin.

PubMed

Drummond, James L; Bapna, Mahendra S

2003-05-01

The aim of this study was to evaluate the flexure strength of unidirectional fiber-reinforced resins under static and cyclic loading with and without thermal cycling. The fiber-reinforced resin materials chosen for this project were commercially available endodontic posts and commercially procured bar samples. For all materials, controls for flexure strength were tested in air and in water using three-point loading. Specimens were thermal cycled between 7 and 63 degrees C for 6000 cycles. A staircase approach was used to determine the flexure fatigue limit and scanning microscopy was used to examine the microstructure. The carbon/graphite fiber-reinforced resin posts and the glass FiberKor posts were significantly stronger than the ceramic (zirconia) and the other glass-reinforced resin materials. Thermal cycling caused a significant lowering (11-24%) of the flexure strength for each resin based post system. The ceramic post system decreased only by 2%. Further, for standard size glass fiber-reinforced resin bars, no significant differences between testing in air and water was observed, but a significant difference between static and cyclic loading was noted. The decreases in the strength property due to thermal cycling and the cyclic loading of these materials indicates that their utilization in the oral environment enhances their degradation, and potentially shortens their clinical life.

Fatigue response of notched laminates subjected to tension-compression cyclic loads

NASA Technical Reports Server (NTRS)

Bakis, C. E.; Stinchcomb, W. W.

1986-01-01

The fatigue response of a ((0/45/90/-45)(sub s))(sub 4) T300-5208 graphite-epoxy laminate with a drilled center-hole subjected to various components of tensile and compressive cyclic loads was investigated. Damage evaluation techniques such as stiffness monitoring, penetrant-enhanced X-ray radiography, C-scan, laminate deply and residual strength measurement were used to establish the mechanisms of damage development as well as the effect of such damage on the laminate strength, stiffness and life. Damage modes consisted of transverse matrix cracks, initiating at the hole, in all plies, followed by delamination between plies of different orientation. A characteristic stiffness repsonse during cyclic loading at two load levels was identified and utilized a more reliable indicator of material and residual properties than accumulated cycles. For the load ratios of tension-compression loading, residual tensile strength increased significantly above the virgin strength early in the fatigue life and remained approximately constant to near the end of life. A technique developed for predicting delamination initiation sites along the hole boundary correlated well with experimental evidence.

Phase Transition of Single-Layer Molybdenum Disulfide Nanosheets under Mechanical Loading Based on Molecular Dynamics Simulations.

PubMed

Pang, Haosheng; Li, Minglin; Gao, Chenghui; Huang, Haili; Zhuo, Weirong; Hu, Jianyue; Wan, Yaling; Luo, Jing; Wang, Weidong

2018-03-27

The single-layer molybdenum disulfide (SLMoS2) nanosheets have been experimentally discovered to exist in two different polymorphs, which exhibit different electrical properties, metallic or semiconducting. Herein, molecular dynamics (MD) simulations of nanoindentation and uniaxial compression were conducted to investigate the phase transition of SLMoS2 nanosheets. Typical load-deflection curves, stress-strain curves, and local atomic structures were obtained. The loading force decreases sharply and then increases again at a critical deflection under the nanoindentation, which is inferred to the phase transition. In addition to the layer thickness, some related bond lengths and bond angles were also found to suddenly change as the phase transition occurs. A bell-like hollow, so-called residual deformation, was found to form, mainly due to the lattice distortion around the waist of the bell. The effect of indenter size on the residual hollow was also analyzed. Under the uniaxial compression along the armchair direction, a different phase transition, a uniformly quadrilateral structure, was observed when the strain is greater than 27.7%. The quadrilateral structure was found to be stable and exhibit metallic conductivity in view of the first-principle calculation.

Finite element modelling of creep crack growth in 316 stainless and 9Cr-1Mo steels

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

Krishnaswamy, P.; Brust, F.W.

1994-09-01

The failure behavior of steels under sustained and cyclic loads has been addressed. The constitutive behavior of the two steels have been represented by the conventional strain-hardening law and the Murakami-Ohno model for reversed and cyclic loads. The laws have been implemented into the research finite element code FVP. Post processors for FVP to calculate various path independent integral fracture parameters have been written. Compact tension C(T) specimens have been tested under sustained and cyclic loads with both the load point displacement and crack growth monitored during the tests. FE models with extremely refined meshes for the C(T) specimens weremore » prepared and the experiment simulated numerically. Results from this analysis focus on the differences between the various constitutive models as well as the fracture parameters in characterizing the creep crack growth of the two steels.« less

NASALIFE - Component Fatigue and Creep Life Prediction Program

NASA Technical Reports Server (NTRS)

Gyekenyesi, John Z.; Murthy, Pappu L. N.; Mital, Subodh K.

2014-01-01

NASALIFE is a life prediction program for propulsion system components made of ceramic matrix composites (CMC) under cyclic thermo-mechanical loading and creep rupture conditions. Although the primary focus was for CMC components, the underlying methodologies are equally applicable to other material systems as well. The program references empirical data for low cycle fatigue (LCF), creep rupture, and static material properties as part of the life prediction process. Multiaxial stresses are accommodated by Von Mises based methods and a Walker model is used to address mean stress effects. Varying loads are reduced by the Rainflow counting method or a peak counting type method. Lastly, damage due to cyclic loading and creep is combined with Minor's Rule to determine damage due to cyclic loading, damage due to creep, and the total damage per mission and the number of potential missions the component can provide before failure.

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

Jason Maung, K.; Hahn, H. Thomas; Ju, Y.S.

Multifunction integration of solar cells in load-bearing structures can enhance overall system performance by reducing parasitic components and material redundancy. The article describes a manufacturing strategy, named the co-curing scheme, to integrate thin-film silicon solar cells on carbon-fiber-reinforced epoxy composites and eliminate parasitic packaging layers. In this scheme, an assembly of a solar cell and a prepreg is cured to form a multifunctional composite in one processing step. The photovoltaic performance of the manufactured structures is then characterized under controlled cyclic mechanical loading. The study finds that the solar cell performance does not degrade under 0.3%-strain cyclic tension loading upmore » to 100 cycles. Significant degradation, however, is observed when the magnitude of cyclic loading is increased to 1% strain. The present study provides an initial set of data to guide and motivate further studies of multifunctional energy harvesting structures. (author)« less

Determination of babbit mechanical properties based on tin under static and cyclic loading

NASA Astrophysics Data System (ADS)

Zernin, M. V.

2018-03-01

Based on the results of studies of babbitt on the basis of tin under static loading under three types of stress state, the parameters of the criterion for the equivalence of stressed states were refined and a single diagram of the babbitt deformation was obtained. It is shown that the criterion of equivalence for static loading should contain the first principal stress and stress intensity. With cyclic loading, the first main voltage can be used as a criterion. The stages of development of fatigue cracks are described and it is logical to use a statistical approach to reveal the boundary of the transition from short cracks to macrocracks, based on a significant difference in the characteristics of the dispersion of the crack speeds at these two stages. The results of experimental studies of the cyclic crack resistance of babbitt are presented and the parameters of this boundary are obtained.

Cyclic loading increases friction and changes cartilage surface integrity in lubricin-mutant mouse knees

PubMed Central

Drewniak, Elizabeth I; Jay, Gregory D; Fleming, Braden C; Zhang, Ling; Warman, Matthew L; Crisco, Joseph J

2012-01-01

Objective To investigate the effects of lubricin gene dosage and cyclic loading on whole joint coefficient of friction and articular cartilage surface integrity in mouse knee joints. Methods Joints from mice with 2 (Prg4+/+), 1 (Prg4+/−), or no (Prg4−/−) functioning lubricin alleles were subjected to 26 hours of cyclic loading using a custom-built pendulum. Coefficient of friction values were measured at multiple time points. Contralateral control joints were left unloaded. Following testing, joints were examined for histologic evidence of damage and cell viability. Results At baseline, the coefficient of friction values in Prg4−/− mice were significantly higher than those in Prg4+/+ and Prg4+/− mice (P < 0.001). Cyclic loading continuously increased the coefficient of friction in Prg4−/− mouse joints. In contrast, Prg4+/− and Prg4+/+ mouse joints had no coefficient of friction increases during the first 4 hours of loading. After 26 hours of loading, joints from all genotypes had increased coefficient of friction values compared to baseline and unloaded controls. Significantly greater increases occurred in Prg4−/− and Prg4+/− mouse joints compared to Prg4+/+ mouse joints. The coefficient of friction values were not significantly associated with histologic evidence of damage or loss of cell viability. Conclusion Our findings indicate that mice lacking lubricin have increased baseline coefficient of friction values and are not protected against further increases caused by loading. Prg4+/− mice are indistinguishable from Prg4+/+ mice at baseline, but have significantly greater coefficient of friction values following 26 hours of loading. Lubricin dosage affects joint properties during loading, and may have clinical implications in patients for whom injury or illness alters lubricin abundance. PMID:21905020

Effect of Cyclic Loading on Micromotion at the Implant-Abutment Interface.

PubMed

Karl, Matthias; Taylor, Thomas D

2016-01-01

Cyclic loading may cause settling of abutments mounted on dental implants, potentially affecting screw joint stability and implant-abutment micromotion. It was the goal of this in vitro study to compare micromotion of implant-abutment assemblies before and after masticatory simulation. Six groups of abutments (n = 5) for a specific tissue-level implant system with an internal octagon were subject to micromotion measurements. The implant-abutment assemblies were loaded in a universal testing machine, and an apparatus and extensometers were used to record displacement. This was done twice, in the condition in which they were received from the abutment manufacturer and after simulated loading (100,000 cycles; 100 N). Statistical analysis was based on analysis of variance, two-sample t tests (Welch tests), and Pearson product moment correlation (α = .05). The mean values for micromotion ranged from 33.15 to 63.41 μm and from 30.03 to 42.40 μm before and after load cycling. The general trend toward reduced micromotion following load cycling was statistically significant only for CAD/CAM zirconia abutments (P = .036) and for one type of clone abutment (P = .012), with no significant correlation between values measured before and after cyclic loading (Pearson product moment correlation; P = .104). While significant differences in micromotion were found prior to load cycling, no significant difference among any of the abutment types tested could be observed afterward (P > .05 in all cases). A quantifiable settling effect at the implant-abutment interface seems to result from cyclic loading, leading to a decrease in micromotion. This effect seems to be more pronounced in low-quality abutments. For the implant system tested in this study, retightening of abutment screws is recommended after an initial period of clinical use.

Stress recovery and cyclic behaviour of an Fe-Mn-Si shape memory alloy after multiple thermal activation

NASA Astrophysics Data System (ADS)

Hosseini, E.; Ghafoori, E.; Leinenbach, C.; Motavalli, M.; Holdsworth, S. R.

2018-02-01

The stress recovery and cyclic deformation behaviour of Fe-17Mn-5Si-10Cr-4Ni-1(V,C) shape memory alloy (Fe-SMA) strips, which are often used for pre-stressed strengthening of structural members, were studied. The evolution of recovery stress under different constraint conditions was studied. The results showed that the magnitude of the tensile stress in the Fe-SMA member during thermal activation can have a signification effect on the final recovery stress. The higher the tensile load in the Fe-SMA (e.g., caused by dead load or thermal expansion of parent structure during heating phase), the lower the final recovery stress. Furthermore, this study investigated the cyclic behaviour of the activated SMA followed by a second thermal activation. Although the magnitude of the recovery stress decreased during the cyclic loading, the second thermal activation could retrieve a significant part of the relaxed recovery stress. This observation suggests that the relaxation of recovery stress during cyclic loading is due to a reversible phase transformation-induced deformation (i.e., forward austenite-to-martensite transformation) rather than an irreversible dislocation-induced plasticity. Retrieval of the relaxed recovery stress by the reactivation process has important practical implications as the prestressing loss in pre-stressed civil structures can be simply recovered by reheating of the Fe-SMA elements.

CARES/Life Ceramics Durability Evaluation Software Enhanced for Cyclic Fatigue

NASA Technical Reports Server (NTRS)

Nemeth, Noel N.; Powers, Lynn M.; Janosik, Lesley A.

1999-01-01

The CARES/Life computer program predicts the probability of a monolithic ceramic component's failure as a function of time in service. The program has many features and options for materials evaluation and component design. It couples commercial finite element programs--which resolve a component's temperature and stress distribution--to reliability evaluation and fracture mechanics routines for modeling strength-limiting defects. The capability, flexibility, and uniqueness of CARES/Life have attracted many users representing a broad range of interests and has resulted in numerous awards for technological achievements and technology transfer. Recent work with CARES/Life was directed at enhancing the program s capabilities with regards to cyclic fatigue. Only in the last few years have ceramics been recognized to be susceptible to enhanced degradation from cyclic loading. To account for cyclic loads, researchers at the NASA Lewis Research Center developed a crack growth model that combines the Power Law (time-dependent) and the Walker Law (cycle-dependent) crack growth models. This combined model has the characteristics of Power Law behavior (decreased damage) at high R ratios (minimum load/maximum load) and of Walker law behavior (increased damage) at low R ratios. In addition, a parameter estimation methodology for constant-amplitude, steady-state cyclic fatigue experiments was developed using nonlinear least squares and a modified Levenberg-Marquardt algorithm. This methodology is used to give best estimates of parameter values from cyclic fatigue specimen rupture data (usually tensile or flexure bar specimens) for a relatively small number of specimens. Methodology to account for runout data (unfailed specimens over the duration of the experiment) was also included.

Cyclic fatigue-crack propagation, stress-corrosion, and fracture-toughness behavior in pyrolytic carbon-coated graphite for prosthetic heart valve applications.

PubMed

Ritchie, R O; Dauskardt, R H; Yu, W K; Brendzel, A M

1990-02-01

Fracture-mechanics tests were performed to characterize the cyclic fatigue, stress-corrosion cracking, and fracture-toughness behavior of a pyrolytic carbon-coated graphite composite material used in the manufacture of cardiac valve prostheses. Testing was carried out using compact tension C(T) samples containing "atomically" sharp precracks, both in room-temperature air and principally in a simulated physiological environment of 37 degrees C Ringer's lactate solution. Under sustained (monotonic) loads, the composite exhibited resistance-curve behavior, with a fracture toughness (KIc) between 1.1 and 1.9 MPa square root of m, and subcritical stress-corrosion crack velocities (da/dt) which were a function of the stress intensity K raised to the 74th power (over the range approximately 10(-9) to over 10(-5) m/s). More importantly, contrary to common perception, under cyclic loading conditions the composite was found to display true (cyclic) fatigue failure in both environments; fatigue-crack growth rates (da/dN) were seen to be a function of the 19th power of the stress-intensity range delta K (over the range approximately 10(-11) to over 10(-8) m/cycle). As subcritical crack velocities under cyclic loading were found to be many orders of magnitude faster than those measured under equivalent monotonic loads and to occur at typically 45% lower stress-intensity levels, cyclic fatigue in pyrolytic carbon-coated graphite is reasoned to be a vital consideration in the design and life-prediction procedures of prosthetic devices manufactured from this material.

Effect of water temperature on cyclic fatigue properties of glass-fiber-reinforced hybrid composite resin and its fracture pattern after flexural testing.

PubMed

Kuroda, Soichi; Shinya, Akikazu; Vallittu, Pekka K; Nakasone, Yuji; Shinya, Akiyoshi

2013-02-01

To evaluate in vitro the influence of dynamic loading applied to a glass-fiber-reinforced hybrid composite resin on its flexural strength in a moist, simulated oral environment. Three-point flexural strength specimens were subjected to cyclic loading in water at 37°C and 55°C to investigate the influence of immersion temperature on impact fatigue properties. Specimens were subjected to cyclic impact loading at 1 Hz for up to 5 × 105 cycles to obtain the number of cycles to failure, the number of unbroken specimens after 5 × 105 cycles, and the residual flexural strength of unbroken specimens. Maximum loads of 100, 200, and 300 N were chosen for both the non-reinforced and the glass-fiber reinforced hybrid composite resins. The mean residual flexural strength for 100 N impact loading at temperatures of 37°C and 55°C was 634 and 636 MPa, respectively. All specimens fractured at fewer than 5 × 105 cycles for loads of 200 and 300 N. Reduced numbers of cycles to fracture and lower fatigue values were observed as both the maximum load and immersion temperature increased.

Biomechanical outcome of proximal femoral nail antirotation is superior to proximal femoral locking compression plate for reverse oblique intertrochanteric fractures: a biomechanical study of intertrochanteric fractures.

PubMed

Ma, Jian-Xiong; Wang, Jie; Xu, Wei-Guo; Yu, Jing-Tao; Yang, Yang; Ma, Xin-Long

2015-01-01

Reverse obliquity intertrochanteric fractures are a challenge for orthopedic surgeons. The optimal internal fixation for repairing this type of unstable intertrochanteric fractures remains controversial. This study aimed to compare the biomechanical properties in axial load and cyclical axial load of proximal femoral nail antirotation (PFNA) and proximal femoral locking compression plate (PFLCP) for fixation of reverse obliquity intertrochanteric fractures. Sixteen embalmed cadaver femurs were sawed to simulate reverse obliquity intertrochanteric fracture and instrumented with PFNA or PFLCP. Axial loads and axial cyclic loads were applied to the femoral head by an Instron tester. If the implant-femur constructs did not fail, axial failure load was added to the remaining implant-femur constructs. Mean axial stiffness for PFNA was 21.10% greater than that of PFLCP. Cyclic axial loading caused significantly less (p=0.022) mean irreversible deformation in PFNA (3.43 mm) than in PFLCP (4.34 mm). Significantly less (p=0.002) mean total deformation was detected in PFNA (6.16 mm) than in PFLCP (8.67 mm). For fixing reverse obliquity intertrochanteric fractures, PFNA is superior to PFLCP under axial load.

Fatigue effect in ferroelectric crystals: Growth of the frozen domains

NASA Astrophysics Data System (ADS)

Shur, V. Ya.; Akhmatkhanov, A. R.; Baturin, I. S.

2012-06-01

The model of the fatigue effect during cyclic switching caused by growth of the frozen domain area with charged domain walls has been proposed. It was claimed on the basis of the previous experimental results that for switching in increasing field the frozen domain area started to grow at the given sub-threshold field value and stopped at the threshold field. The influence of the shape and frequency of the field pulses used for cyclic switching has been considered. The uniaxial ferroelectric stoichiometric lithium tantalate single crystals produced by vapor transport equilibration with record low value of coercive field have been chosen as a model material for experimental verification of the model. The formation of the charged domain walls as a result of cyclic switching has been revealed by analysis of the domain images obtained by optical and Raman confocal microscopy. It has been shown that the fatigue degree is equal to the fraction of the frozen domain area. The experimental dependence of the switched charge on the cycle number has been successfully fitted by modified Kolmogorov-Avrami formula. The experimentally observed frequency independence of fatigue profile for rectangular pulses and frequency dependence for triangular pulses has been explained by proposed model.

An improved Armstrong-Frederick-Type Plasticity Model for Stable Cyclic Stress-Strain Responses Considering Nonproportional Hardening

NASA Astrophysics Data System (ADS)

Li, Jing; Zhang, Zhong-ping; Li, Chun-wang

2018-03-01

This paper modified an Armstrong-Frederick-type plasticity model for investigating the stable cyclic deformation behavior of metallic materials with different sensitivity to nonproportional loadings. In the modified model, the nonproportionality factor and nonproportional cyclic hardening coefficient coupled with the Jiang-Sehitoglu incremental plasticity model were used to estimate the stable stress-strain responses of the two materials (1045HR steel and 304 stainless steel) under various tension-torsion strain paths. A new equation was proposed to calculate the nonproportionality factor on the basis of the minimum normal strain range. Procedures to determine the minimum normal strain range were presented for general multiaxial loadings. Then, the modified model requires only the cyclic strain hardening exponent and cyclic strength coefficient to determine the material constants. It is convenient for predicting the stable stress-strain responses of materials in engineering application. Comparisons showed that the modified model can reflect the effect of nonproportional cyclic hardening well.

A constitutive material model for nonlinear finite element structural analysis using an iterative matrix approach

NASA Technical Reports Server (NTRS)

Koenig, Herbert A.; Chan, Kwai S.; Cassenti, Brice N.; Weber, Richard

1988-01-01

A unified numerical method for the integration of stiff time dependent constitutive equations is presented. The solution process is directly applied to a constitutive model proposed by Bodner. The theory confronts time dependent inelastic behavior coupled with both isotropic hardening and directional hardening behaviors. Predicted stress-strain responses from this model are compared to experimental data from cyclic tests on uniaxial specimens. An algorithm is developed for the efficient integration of the Bodner flow equation. A comparison is made with the Euler integration method. An analysis of computational time is presented for the three algorithms.

A comparative study of gold UCLA-type and CAD/CAM titanium implant abutments

PubMed Central

Park, Ji-Man; Lee, Jai-Bong; Heo, Seong-Joo

2014-01-01

PURPOSE The aim of this study was to evaluate the interface accuracy of computer-assisted designed and manufactured (CAD/CAM) titanium abutments and implant fixture compared to gold-cast UCLA abutments. MATERIALS AND METHODS An external connection implant system (Mark III, n=10) and an internal connection implant system (Replace Select, n=10) were used, 5 of each group were connected to milled titanium abutment and the rest were connected to the gold-cast UCLA abutments. The implant fixture and abutment were tightened to torque of 35 Ncm using a digital torque gauge, and initial detorque values were measured 10 minutes after tightening. To mimic the mastication, a cyclic loading was applied at 14 Hz for one million cycles, with the stress amplitude range being within 0 N to 100 N. After the cyclic loading, detorque values were measured again. The fixture-abutment gaps were measured under a microscope and recorded with an accuracy of ±0.1 µm at 50 points. RESULTS Initial detorque values of milled abutment were significantly higher than those of cast abutment (P<.05). Detorque values after one million dynamic cyclic loadings were not significantly different (P>.05). After cyclic loading, detorque values of cast abutment increased, but those of milled abutment decreased (P<.05). There was no significant difference of gap dimension between the milled abutment group and the cast abutment group after cyclic loading. CONCLUSION In conclusion, CAD/CAM milled titanium abutment can be fabricated with sufficient accuracy to permit screw joint stability between abutment and fixture comparable to that of the traditional gold cast UCLA abutment. PMID:24605206

Cyclic and Fatigue Behaviour of Rock Materials: Review, Interpretation and Research Perspectives

NASA Astrophysics Data System (ADS)

Cerfontaine, B.; Collin, F.

2018-02-01

The purpose of this paper is to provide a comprehensive state of the art of fatigue and cyclic loading of natural rock materials. Papers published in the literature are classified and listed in order to ease bibliographical review, to gather data (sometimes contradictory) on classical experimental results and to analyse the main interpretation concepts. Their advantages and limitations are discussed, and perspectives for further work are highlighted. The first section summarises and defines the different experimental set-ups (type of loading, type of experiment) already applied to cyclic/fatigue investigation of rock materials. The papers are then listed based on these different definitions. Typical results are highlighted in next section. Fatigue/cyclic loading mainly results in accumulation of plastic deformation and/or damage cycle after cycle. A sample cyclically loaded at constant amplitude finally leads to failure even if the peak load is lower than its monotonic strength. This subcritical crack is due to a diffuse microfracturing and decohesion of the rock structure. The third section reviews and comments the concepts used to interpret the results. The fatigue limit and S- N curves are the most common concepts used to describe fatigue experiments. Results published from all papers are gathered into a single figure to highlight the tendency. Predicting the monotonic peak strength of a sample is found to be critical in order to compute accurate S- N curves. Finally, open questions are listed to provide a state of the art of grey areas in the understanding of fatigue mechanisms and challenges for the future.

The failure mode of two reabsorbable fixation systems: Swivelock with Fibertape versus Bio-Corkscrew with Fiberwire in bovine rotator cuff.

PubMed

De Carli, Angelo; Lanzetti, Riccardo Maria; Monaco, Edoardo; Labianca, Luca; Mossa, Luigi; Ferretti, Andrea; Feretti, Andrea

2012-11-01

Despite technical advances in rotator cuff surgery, recurrent or persistent defects in the repaired tendon continue to occur. The improved strength of sutures and suture anchors has shown that the most common site of failure is the suture-tendon interface. The purpose of this study was to compare two different types of repair under both cyclic and load-to-failure conditions. The hypothesis is that the use of a fixation system with knotless anchor and taped suture results in better biomechanical performance, under both cyclic and load-to-failure conditions. Thirty bovine shoulder specimens were randomly assigned to two group tests: the Swivelock 5-mm anchor with Fibertape (Group A) and the Bio-Corkscrew 5 mm with Fiberwire (Group B). We simulated the reconstruction of a rotator cuff tear with a single-row technique, performing a tenodesis with types A and B fixation. Each specimen underwent cyclic testing from 5 to 30 N for 30 cycles, followed by load-to-failure testing, in order to calculate the ultimate failure load (UFL). Load-to-failure tests revealed a significantly higher UFL in Group A than in Group B. Wire fixing failed at the anchor loop whereas tape fixing failed at the sutures, suture-tendon interface, and anchors. Cyclic testing revealed no significantly greater slippage between the two groups. Stiffness values were not statistically significantly different. In all cases, tendons remained intact until the end of the cyclic testing. The tape structure is biomechanically stronger than the wire structure.

Cyclic Axial-Torsional Deformation Behavior of a Cobalt-Base Superalloy

NASA Technical Reports Server (NTRS)

Bonacuse, Peter J.; Kalluri, Sreeramesh

1995-01-01

The cyclic, high-temperature deformation behavior of a wrought cobalt-base super-alloy, Haynes 188, is investigated under combined axial and torsional loads. This is accomplished through the examination of hysteresis loops generated from a biaxial fatigue test program. A high-temperature axial, torsional, and combined axial-torsional fatigue database has been generated on Haynes 188 at 760 C. Cyclic loading tests have been conducted on uniform gage section tubular specimens in a servohydraulic axial-torsional test rig. Test control and data acquisition were accomplished with a minicomputer. The fatigue behavior of Haynes 188 at 760 C under axial, torsional, and combined axial-torsional loads and the monotonic and cyclic deformation behaviors under axial and torsional loads have been previously reported. In this paper, the cyclic hardening characteristics and typical hysteresis loops in the axial stress versus axial strain, shear stress ,versus engineering shear strain, axial strain versus engineering shear strain. and axial stress versus shear stress spaces are presented for cyclic in-phase and out-of-phase axial-torsional tests. For in-phase tests, three different values of the proportionality constant lambda (the ratio of engineering shear strain amplitude to axial strain amplitude, are examined, viz. 0.86, 1.73, and 3.46. In the out-of-phase tests, three different values of the phase angle, phi (between the axial and engineering shear strain waveforms), are studied, viz., 30, 60, and 90 degrees with lambda equals 1.73. The cyclic hardening behaviors of all the tests conducted on Haynes 188 at 760 C are evaluated using the von Mises equivalent stress-strain and the maximum shear stress-maximum engineering shear strain (Tresca) curves. Comparisons are also made between the hardening behaviors of cyclic axial, torsional, and combined in-phase (lambda = 1.73 and phi = 0) and out-of-phase (lambda = 1.73 and phi = 90') axial-torsional fatigue tests. These comparisons are accomplished through simple Ramberg-Osgood type stress-strain functions for cyclic, axial stress-strain and shear stress-engineering shear strain curves.

Cyclic Mechanical Loading Enhances Transport of Antibodies Into Articular Cartilage.

PubMed

DiDomenico, Chris D; Xiang Wang, Zhen; Bonassar, Lawrence J

2017-01-01

The goal of this study was to characterize antibody penetration through cartilage tissue under mechanical loading. Mechanical stimulation aids in the penetration of some proteins, but this effect has not characterized molecules such as antibodies (>100 kDa), which may hold some clinical value for treating osteoarthritis (OA). For each experiment, fresh articular cartilage plugs were obtained and exposed to fluorescently labeled antibodies while under cyclic mechanical load in unconfined compression for several hours. Penetration of these antibodies was quantified using confocal microscopy, and finite element (FE) simulations were conducted to predict fluid flow patterns within loaded samples. Transport enhancement followed a linear trend with strain amplitude (0.25-5%) and a nonlinear trend with frequency (0.25-2.60 Hz), with maximum enhancement found to be at 5% cyclic strain and 1 Hz, respectively. Regions of highest enhancement of transport within the tissue were associated with the regions of highest interstitial fluid velocity, as predicted from finite-element simulations. Overall, cyclic compression-enhanced antibody transport by twofold to threefold. To our knowledge, this is the first study to test how mechanical stimulation affects the diffusion of antibodies in cartilage and suggest further study into other important factors regarding macromolecular transport.

Influence of Different Screw Torque Levels on the Biomechanical Behavior of Tapered Prosthetic Abutments.

PubMed

Herbst, Paulo Eduardo; de Carvalho, Eduardo Bortolas; Salatti, Rafael C; Valgas, Laiz; Tiossi, Rodrigo

To study the force used for tightening tapered one-piece prosthetic abutments and their influence on the removal torque value and stress level of the prosthetic abutment after cyclic loading. Fourteen implants and prosthetic abutments were divided into two groups (n = 7): G1, 20 Ncm; and G2, 32 Ncm (manufacturer recommended). A 20-mm T-shaped horizontal bar was adapted to the abutments. A 12-Hz cyclic loading was applied to the specimens in an electrodynamic testing system with the maximum number of cycles set to 10 6 . Specimens were inclined by 15 degrees from the vertical axis, and a 5-mm off-center vertical load was applied to generate a combination of bending and torquing moments on the tapered connections. Progressive loads (from 164.85 to 362.85 N) were applied when the previous sample survived 10 6 cycles. The paired t test compared the screw removal torque with the initial tightening torque for each group (α = .05). A finite element analysis (FEA) of the mechanical testing analyzed the regions of stress concentration. No specimens failed after 10 6 cyclic loadings. The mean screw removal torque for both groups was similar to the initial abutment torque value applied for each group (G1, 20.36 ± 8.73 Ncm; and G2, 35.61 ± 6.99 Ncm) (P > .05). FEA showed similar stress behavior for both groups in the study despite the different simulated screw preloads (G1: 200 N; G2: 320 N). The coronal region of the implant body presented the highest strain values in both groups. Tightening tapered one-piece prosthetic abutments at 20 and 32 Ncm maintains a stable connection after cyclic loading. The stresses generated by the different tightening forces during cyclic loading are highest at the coronal level of the connection.

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.

Cyclic Mechanical Stretch Up-regulates Hepatoma-Derived Growth Factor Expression in Cultured Rat Aortic Smooth Muscle Cells.

PubMed

Kao, Ying-Hsien; Chen, Po-Han; Sun, Cheuk-Kwan; Chang, Yo-Chen; Lin, Yu-Chun; Tsai, Ming-Shian; Lee, Po-Huang; Cheng, Cheng-I

2018-02-21

Hepatoma-derived growth factor (HDGF) is a potent mitogen for vascular smooth muscle cells (SMCs) during embryogenesis and injury repair of vessel walls. Whether mechanical stimuli modulate HDGF expression remains unknown. This study aimed at investigating whether cyclic mechanical stretch plays a regulatory role in HDGF expression and regenerative cytokine production in aortic SMCs. A SMC cell line was grown on a silicone-based elastomer chamber with extracellular matrix coatings (either type I collagen or fibronectin) and received cyclic and uni-axial mechanical stretches with 10% deformation at frequency 1 Hz. Morphological observation showed that fibronectin coating provided better cell adhesion and spreading and that consecutive 6 hours of cyclic mechanical stretch remarkably induced reorientation and realignment of SMCs. Western blotting detection demonstrated that continuous mechanical stimuli elicited up-regulation of HDGF and PCNA, a cell proliferative marker. Signal kinetic profiling study indicated that cyclic mechanical stretch induced signaling activity in RhoA/ROCK and PI3K/Akt cascades. Kinase inhibition study further showed that blockade of PI3K activity suppressed the stretch-induced TNF-a, whereas RhoA/ROCK inhibition significantly blunted the IL-6 production and HDGF over-expression. Moreover, siRNA-mediated HDGF gene silencing significantly suppressed constitutive expression of IL-6, but not TNF-α, in SMCs. These findings support the role of HDGF in maintaining vascular expression of IL-6, which has been regarded a crucial regenerative factor for acute vascular injury. In conclusion, cyclic mechanical stretch may maintain constitutive expression of HDGF in vascular walls and be regarded an important biophysical regulator in vascular regeneration. ©2018 The Author(s).

Fatigue crack propagation in additively manufactured porous biomaterials.

PubMed

Hedayati, R; Amin Yavari, S; Zadpoor, A A

2017-07-01

Additively manufactured porous titanium implants, in addition to preserving the excellent biocompatible properties of titanium, have very small stiffness values comparable to those of natural bones. Although usually loaded in compression, biomedical implants can also be under tensional, shear, and bending loads which leads to crack initiation and propagation in their critical points. In this study, the static and fatigue crack propagation in additively manufactured porous biomaterials with porosities between 66% and 84% is investigated using compact-tension (CT) samples. The samples were made using selective laser melting from Ti-6Al-4V and were loaded in tension (in static study) and tension-tension (in fatigue study) loadings. The results showed that displacement accumulation diagram obtained for different CT samples under cyclic loading had several similarities with the corresponding diagrams obtained for cylindrical samples under compression-compression cyclic loadings (in particular, it showed a two-stage behavior). For a load level equaling 50% of the yield load, both the CT specimens studied here and the cylindrical samples we had tested under compression-compression cyclic loading elsewhere exhibited similar fatigue lives of around 10 4 cycles. The test results also showed that for the same load level of 0.5F y , the lower density porous structures demonstrate relatively longer lives than the higher-density ones. This is because the high bending stresses in high-density porous structures gives rise to local Mode-I crack opening in the rough external surface of the struts which leads to quicker formation and propagation of the cracks. Under both the static and cyclic loading, all the samples showed crack pathways which were not parallel to but made 45 ° angles with respect to the notch direction. This is due to the fact that in the rhombic dodecahedron unit cell, the weakest struts are located in 45 ° direction with respect to the notch direction. Copyright © 2017 Elsevier B.V. All rights reserved.

A Biomechanical Comparison of Distal Fixation for Bridge Plating in a Distal Radius Fracture Model.

PubMed

Alluri, Ram K; Bougioukli, Sofia; Stevanovic, Milan; Ghiassi, Alidad

2017-09-01

To compare the biomechanical properties of second versus third metacarpal distal fixation when using a radiocarpal spanning distraction plate in an unstable distal radius fracture model. Biomechanical evaluation of the radiocarpal spanning distraction plate comparing second versus third metacarpal distal fixation was performed using a standardized model of an unstable wrist fracture in 10 matched-pair cadaveric specimens. Each fixation construct underwent a controlled cyclic loading protocol in flexion and extension. The resultant displacement and stiffness were calculated at the fracture site. After cyclic loading, each specimen was loaded to failure. The stiffness, maximum displacement, and load to failure were compared between the 2 groups. Cyclic loading in flexion demonstrated that distal fixation to the third metacarpal resulted in greater stiffness compared with the second metacarpal. There was no significant difference between the 2 groups with regards to maximum displacement at the fracture site in flexion. Cyclic loading in extension demonstrated no significant difference in stiffness or maximum displacement between the 2 groups. The average load to failure was similar for both groups. Fixation to the third metacarpal resulted in greater stiffness in flexion. All other biomechanical parameters were similar when comparing distal fixation to the second or third metacarpal in distal radius fractures stabilized with a spanning internal distraction plate. The treating surgeon should choose distal metacarpal fixation primarily based on fracture pattern, alignment, and soft tissue integrity. If a stiffer construct is desired, placement of the radiocarpal spanning plate at the third metacarpal is preferred. Copyright © 2017 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Uniaxial Tensile Test for Soil.

DTIC Science & Technology

1987-04-01

2.0 by 5.0 cm. This test was also performed on a horizontal specimen; however loading was applied through small metal plates that were embedded in the 6...i. enlarged ends. The specimen was supported by a bed of mercury and had two small ceramic markers mounted in the gage length that were monitored...with a cathetometer to determine displacements. It was found that most tests failed near the location of the embedded metal loading plates making their

Mechanical Properties of a Unidirectional Basalt-Fiber-Reinforced Plastic Under a Loading Simulating Operation Conditions

NASA Astrophysics Data System (ADS)

Lobanov, D. S.; Slovikov, S. V.

2017-01-01

The results of experimental investigations of unidirectional composites based on basalt fibers and different marks of epoxy resins are presented. Uniaxial tensile tests were carried out using a specimen fixation technique simulating the operation conditions of structures. The mechanical properties of the basalt-fiber-reinforced plastics (BFRPs) were determined. The diagrams of loading and deformation of BFRP specimens were obtain. The formulations of the composites with the highest mechanical properties were revealed.

Analysis and Modeling of Small Crack Detection in Pressurized Fuselages for Structural Health Monitoring Applications (Preprint)

DTIC Science & Technology

2012-07-01

airframe failures resulting in the total loss of the aircraft [ Parton and Morozov (1978); Piascik (1999)]. More recently, in April 1988, the Aloha...a material [ Parton and Morozov (1978)]. The size of the region covered by the plastic flow depends on the material properties and the loading...crack length due to uniaxial loads applied normal to the crack orientation. The Griffith-Orowan-Irwin concept [ Parton (1992)] establishes that the

Coarse-grained molecular dynamics simulations of the tensile behavior of a thermosetting polymer.

PubMed

Yang, Shaorui; Qu, Jianmin

2014-07-01

Using a previously developed coarse-grained model, we conducted large-scale (∼ 85 × 85 × 85 nm(3)) molecular dynamics simulations of uniaxial-strain deformation to study the tensile behavior of an epoxy molding compound, epoxy phenol novolacs (EPN) bisphenol A (BPA). Under the uniaxial-strain deformation, the material is found to exhibit cavity nucleation and growth, followed by stretching of the ligaments separated by the cavities, until the ultimate failure through ligament scissions. The nucleation sites of cavities are rather random and the subsequent cavity growth accounts for much (87%) of the volumetric change during the uniaxial-strain deformation. Ultimate failure of the materials occurs when the cavity volume fraction reaches ∼ 60%. During the entire deformation process, polymer strands in the network are continuously extended to their linear states and broken in the postyielding strain hardening stage. When most of the strands are stretched to their taut configurations, rapid scission of a large number of strands occurs within a small strain increment, which eventually leads to fracture. Finally, through extensive numerical simulations of various loading conditions in addition to uniaxial strain, we find that yielding of the EPN-BPA can be described by the pressure-modified von Mises yield criterion.

Characteristics of Crushing Energy and Fractal of Magnetite Ore under Uniaxial Compression

NASA Astrophysics Data System (ADS)

Gao, F.; Gan, D. Q.; Zhang, Y. B.

2018-03-01

The crushing mechanism of magnetite ore is a critical theoretical problem on the controlling of energy dissipation and machine crushing quality in ore material processing. Uniaxial crushing tests were carried out to research the deformation mechanism and the laws of the energy evolution, based on which the crushing mechanism of magnetite ore was explored. The compaction stage and plasticity and damage stage are two main compression deformation stages, the main transitional forms from inner damage to fracture are plastic deformation and stick-slip. In the process of crushing, plasticity and damage stage is the key link on energy absorption for that the specimen tends to saturate energy state approaching to the peak stress. The characteristics of specimen deformation and energy dissipation can synthetically reply the state of existed defects inner raw magnetite ore and the damage process during loading period. The fast releasing of elastic energy and the work done by the press machine commonly make raw magnetite ore thoroughly broken after peak stress. Magnetite ore fragments have statistical self-similarity and size threshold of fractal characteristics under uniaxial squeezing crushing. The larger ratio of releasable elastic energy and dissipation energy and the faster energy change rate is the better fractal properties and crushing quality magnetite ore has under uniaxial crushing.

Coarse-grained molecular dynamics simulations of the tensile behavior of a thermosetting polymer

NASA Astrophysics Data System (ADS)

Yang, Shaorui; Qu, Jianmin

2014-07-01

Using a previously developed coarse-grained model, we conducted large-scale (˜85×85×85nm3) molecular dynamics simulations of uniaxial-strain deformation to study the tensile behavior of an epoxy molding compound, epoxy phenol novolacs (EPN) bisphenol A (BPA). Under the uniaxial-strain deformation, the material is found to exhibit cavity nucleation and growth, followed by stretching of the ligaments separated by the cavities, until the ultimate failure through ligament scissions. The nucleation sites of cavities are rather random and the subsequent cavity growth accounts for much (87%) of the volumetric change during the uniaxial-strain deformation. Ultimate failure of the materials occurs when the cavity volume fraction reaches ˜60%. During the entire deformation process, polymer strands in the network are continuously extended to their linear states and broken in the postyielding strain hardening stage. When most of the strands are stretched to their taut configurations, rapid scission of a large number of strands occurs within a small strain increment, which eventually leads to fracture. Finally, through extensive numerical simulations of various loading conditions in addition to uniaxial strain, we find that yielding of the EPN-BPA can be described by the pressure-modified von Mises yield criterion.

Multi-planar bending properties of lumbar intervertebral joints following cyclic bending.

PubMed

Chow, Daniel H K; Luk, Keith D K; Holmes, Andrew D; Li, Xing-Fei; Tam, Steven C W

2004-02-01

To assess the changes in the multi-planar bending properties of intervertebral joints following cyclic bending along different directions. An in vitro biomechanical study using porcine lumbar motion segments. Repeated bending has been suggested as part of the etiology of gradual prolapse of the intervertebral disc, but the multi-planar changes in bending properties following cyclic loading have not been examined in detail. Porcine lumbar motion segments were subject to 1500 cycles of bending along directions of 0 degrees (flexion), 30 degrees, 60 degrees, or 90 degrees (right lateral bending). The multi-planar bending moments and hysteresis energies were recorded before loading and after various cycle numbers. Repeated bending at 30 degrees and 60 degrees resulted in greater decreases in mean bending moment and hysteresis energy than bending at 0 degrees or 90 degrees. No significant differences were seen between loading groups for the change in bending moment along the anterior testing directions, but significant differences were observed in the posterior and lateral testing directions, with bending at 30 degrees causing a significantly greater decrease in bending moment in the postero-lateral directions. The change in mechanical properties of porcine intervertebral joints due to cyclic bending depend on the direction of loading and the direction in which the properties are measured. Loading at 30 degrees provokes the most marked changes in bending moment and hysteresis energy.

Analysis and Design of Connections, Openings and Attachments for Protective Construction

DTIC Science & Technology

1989-10-01

precast connection details were subjected to cyclic simulated earthquake loads . The detail... column and beam flexural steel. At the onset of flexural yield under cyclical loading , crack sizes at the face of the joint increase and reinforcement... beam / column connections may be a necessity and can be placed without a great deal of difficulty. However, their placement in slab/wall connections

Evaluating Daily Load Stimulus Formulas in Relating Bone Response to Exercise

NASA Technical Reports Server (NTRS)

Pennline, James A.; Mulugeta, Lealem

2014-01-01

Six formulas representing what is commonly referred to as "daily load stimulus" are identified, compared and tested in their ability to relate skeletal mechanical loading to bone maintenance and osteogenic response. Particular emphasis is placed on exercise- induced skeletal loading and whether or not the formulas can adequately capture the known experimental observations of saturation of continuous cyclic loading, rest insertion between repetitions (cycles), recovery of osteogenic potential following saturation, and multiple shorter bouts versus a single long bout of exercise. To evaluate the ability of the formulas to capture these characteristics, a set of exercise scenarios with type of exercise bout, specific duration, number of repetitions, and rest insertion between repetitions is defined. The daily load values obtained from the formulas for the loading conditions of the set of scenarios is illustrated. Not all of the formulas form estimates of daily load in units of stress or in terms of strain at a skeletal site due to the loading force from a specific exercise prescription. The comparative results show that none of the formulas are able to capture all of the experimentally observed characteristics of cyclic loading. However, the enhanced formula presented by Genc et al. does capture several characteristics of cyclic loading that the others do not, namely recovery of osteogenic potential and saturation. This could be a basis for further development of mathematical formulas that more adequately approximates the amount of daily stress at a skeletal site that contributes to bone adaptation.

A uniaxial cyclic compression method for characterizing the rheological and textural behaviors of mechanically dewatered sewage sludge.

PubMed

Liang, Fenglin; Sauceau, Martial; Dusserre, Gilles; Arlabosse, Patricia

2017-04-15

The mechanically dewatered sewage sludge with total solid content around 20% on a weight basis is very similar to yield stress fluid, its complex transition between solid and fluid states is not perfectly reversible and especially challenging in terms of pumping, land spreading and drying. To characterize the rheological and textural properties of highly concentrated sludge, a specific methodology based on uniaxial single and cyclic compression tests is developed. Three types of sludge samples (fresh original, fresh premixed and aged original ones) are extruded into cylinders and pressed between two parallel plates using a material testing machine. In single compression, the bioyield point beyond which the sludge fractures is around 7.3 kPa with true strain equal to 0.21. The cyclic compression tests reveal that the sludge behaves as a viscoelastic body when the true strain is smaller than 0.05 and as a visco-elasto-plastic once exceeding the yield stress. The elastic module is around 78 kPa; the viscosity is deduced, in the order of magnitude 10 4 -10 5  Pa·s and the yield stress is estimated about 4 kPa. In the unloading phase, the sludge behaves again as a viscoelastic body with clear hysteresis. With the increase of compression speed, the viscosity declines, which confirms that the sludge is a shear-thinning material. The yield stress and the bioyield increase with compression speed, but it does not induce extra internal damage in the samples since the resilience and the cohesiveness are unaltered. The reliability and sensitivity of the method is justified by highlighting the changes of sludge behavior due to aging and premixing effects: both decrease the strain energy density, but do aggravate the adhesiveness of the sludge; the aging makes the sludge less cohesive, while the premixing does not modify its cohesiveness. In spite of changes in test conditions, the elastic module of sludge samples remains unchanged. Copyright © 2017 Elsevier Ltd. All rights reserved.

Damage Model of Reinforced Concrete Members under Cyclic Loading

NASA Astrophysics Data System (ADS)

Wei, Bo Chen; Zhang, Jing Shu; Zhang, Yin Hua; Zhou, Jia Lai

2018-06-01

Based on the Kumar damage model, a new damage model for reinforced concrete members is established in this paper. According to the damage characteristics of reinforced concrete members subjected to cyclic loading, four judgment conditions for determining the rationality of damage models are put forward. An ideal damage index (D) is supposed to vary within a scale of zero (no damage) to one (collapse). D should be a monotone increasing function which tends to increase in the case of the same displacement amplitude. As for members under large displacement amplitude loading, the growth rate of D should be greater than that of D under small amplitude displacement loading. Subsequently, the Park-Ang damage model, the Niu-Ren damage model, the Lu-Wang damage model and the proposed damage model are analyzed for 30 experimental reinforced concrete members, including slabs, walls, beams and columns. The results show that current damage models do not fully matches the reasonable judgment conditions, but the proposed damage model does. Therefore, a conclusion can be drawn that the proposed damage model can be used for evaluating and predicting damage performance of RC members under cyclic loading.

Effect of cyclic load on vertical misfit of prefabricated and cast implant single abutment

PubMed Central

DE JESUS TAVAREZ, Rudys Rodolfo; BONACHELA, Wellington Cardoso; XIBLE, Anuar Antônio

2011-01-01

Objective The purpose of this in vitro study was to evaluate misfit alterations at the implant/abutment interface of external and internal connection implant systems when subjected to cyclic loading. Material and Methods Standard metal crowns were fabricated for 5 groups (n=10) of implant/abutment assemblies: Group 1, external hexagon implant and UCLA cast-on premachined abutment; Group 2, internal hexagon implant and premachined abutment; Group 3, internal octagon implant and prefabricated abutment; Group 4, external hexagon implant and UCLA cast-on premachined abutment; and Group 5, external hexagon implant and Ceraone abutment. For groups 1, 2, 3 and 5, the crowns were cemented on the abutments and in group 4 crowns were screwed directly on the implant. The specimens were subjected to 500,000 cycles at 19.1 Hz of frequency and non-axial load of 133 N in a MTS 810 machine. The vertical misfit (μm) at the implant/abutment interface was evaluated before (B) and after (A) application of the cyclic loading. Data were analyzed statistically by using two-away ANOVA and Tukey’s post-hoc test (p<0.05). Results Before loading values showed no difference among groups 2 (4.33±3.13), 3 (4.79±3.43) and 5 (3.86±4.60); between groups 1 (12.88±6.43) and 4 (9.67±3.08), and among groups 2, 3 and 4. However, groups 1 and 4 were significantly different from groups 2, 3 and 5. After loading values of groups 1 (17.28±8.77) and 4 (17.78±10.99) were significantly different from those of groups 2 (4.83±4.50), 3 (8.07±4.31) and 5 (3.81±4.84). There was a significant increase in misfit values of groups 1, 3 and 4 after cyclic loading, but not for groups 2 and 5. Conclusion The cyclic loading and type of implant/abutment connection may develop a role on the vertical misfit at the implant/abutment interface. PMID:21437464

Wear Behavior of an Ultra-High-Strength Eutectoid Steel

NASA Astrophysics Data System (ADS)

Mishra, Alok; Maity, Joydeep

2018-02-01

Wear behavior of an ultra-high-strength AISI 1080 steel developed through incomplete austenitization-based combined cyclic heat treatment is investigated in comparison with annealed and conventional hardened and tempered conditions against an alumina disk (sliding speed = 1 m s-1) using a pin-on-disk tribometer at a load range of 7.35-14.7 N. On a gross scale, the mechanism of surface damage involves adhesive wear coupled with abrasive wear (microcutting effects in particular) at lower loads. At higher loads, mainly the abrasive wear (both microcutting and microploughing mechanisms) and evolution of adherent oxide are observed. Besides, microhardness of matrix increases with load indicating substantial strain hardening during wear test. The rate of overall wear is found to increase with load. As-received annealed steel with the lowest initial hardness suffers from severe abrasive wear, thereby exhibiting the highest wear loss. Such a severe wear loss is not observed in conventional hardened and tempered and combined cyclic heat treatment conditions. Combined cyclic heat-treated steel exhibits the greatest wear resistance (lowest wear loss) due to its initial high hardness and evolution of hard abrasion-resistant tribolayer during wear test at higher load.

A method for continuous monitoring of the Ground Reaction Force during daily activity

NASA Technical Reports Server (NTRS)

Whalen, Robert; Quintana, Jason; Emery, Jeff

1993-01-01

Theoretical models and experimental studies of bone remodeling have identified peak cyclic force levels (or cyclic tissue strain energy density), number of daily loading cycles, and load (strain) rate as possible contributors to bone modeling and remodeling stimulus. To test our theoretical model and further investigate the influence of mechanical forces on bone density, we have focused on the calcaneus as a model site loaded by calcaneal surface tractions which are predominantly determined by the magnitude of the external ground reaction force (GRF).

Proceedings of the Third International Symposium on Ground Freezing Held at Hanover, New Hampshire on 22-24 June 1982.

DTIC Science & Technology

1982-01-01

The cyclicly changing axial stresses a . and a are leading to the dynamic stress path which loads the frozen soil [MN/m’) samples. It is obvious that...Fig. 5 are related to a sinoidal dynamic axial loading . Figure a sample temperature of T = -10*C, in 4 shows schematically a triaxial test re- Fig. 6...Czajkowski (1978), Behaviour of Fro-ry phase was not reached. zen Clay under Cyclic Axial Loading , Journal of the Geotechnical Engineer- ing Division

A new pressure chamber to study the biosynthetic response of articular cartilage to mechanical loading.

PubMed

Steinmeyer, J; Torzilli, P A; Burton-Wurster, N; Lust, G

1993-01-01

A prototype chamber was used to apply a precise cyclic or static load on articular cartilage explants under sterile conditions. A variable pressure, pneumatic controller was constructed to power the chamber's air cylinder, capable of applying, with a porous load platen, loads of up to 10 MPa at cycles ranging from 0 to 10 Hz. Pig articular cartilage explants were maintained successfully in this chamber for 2 days under cyclic mechanical loading of 0.5 Hz, 0.5 MPa. Explants remained sterile, viable and metabolically active. Cartilage responded to this load with a decreased synthesis of fibronectin and a small but statistically significant elevation in proteoglycan content. Similar but less extensive effects on fibronectin synthesis were observed with the small static load (0.016 MPa) inherent in the design of the chamber.

Axial displacement of external and internal implant-abutment connection evaluated by linear mixed model analysis.

PubMed

Seol, Hyon-Woo; Heo, Seong-Joo; Koak, Jai-Young; Kim, Seong-Kyun; Kim, Shin-Koo

2015-01-01

To analyze the axial displacement of external and internal implant-abutment connection after cyclic loading. Three groups of external abutments (Ext group), an internal tapered one-piece-type abutment (Int-1 group), and an internal tapered two-piece-type abutment (Int-2 group) were prepared. Cyclic loading was applied to implant-abutment assemblies at 150 N with a frequency of 3 Hz. The amount of axial displacement, the Periotest values (PTVs), and the removal torque values(RTVs) were measured. Both a repeated measures analysis of variance and pattern analysis based on the linear mixed model were used for statistical analysis. Scanning electron microscopy (SEM) was used to evaluate the surface of the implant-abutment connection. The mean axial displacements after 1,000,000 cycles were 0.6 μm in the Ext group, 3.7 μm in the Int-1 group, and 9.0 μm in the Int-2 group. Pattern analysis revealed a breakpoint at 171 cycles. The Ext group showed no declining pattern, and the Int-1 group showed no declining pattern after the breakpoint (171 cycles). However, the Int-2 group experienced continuous axial displacement. After cyclic loading, the PTV decreased in the Int-2 group, and the RTV decreased in all groups. SEM imaging revealed surface wear in all groups. Axial displacement and surface wear occurred in all groups. The PTVs remained stable, but the RTVs decreased after cyclic loading. Based on linear mixed model analysis, the Ext and Int-1 groups' axial displacements plateaued after little cyclic loading. The Int-2 group's rate of axial displacement slowed after 100,000 cycles.

Fracture resistance of computer-aided design and computer-aided manufacturing ceramic crowns cemented on solid abutments.

PubMed

Stona, Deborah; Burnett, Luiz Henrique; Mota, Eduardo Gonçalves; Spohr, Ana Maria

2015-07-01

Because no information was found in the dental literature regarding the fracture resistance of all-ceramic crowns using CEREC (Sirona) computer-aided design and computer-aided manufacturing (CAD-CAM) system on solid abutments, the authors conducted a study. Sixty synOcta (Straumann) implant replicas and regular neck solid abutments were embedded in acrylic resin and randomly assigned (n = 20 per group). Three types of ceramics were used: feldspathic, CEREC VITABLOCS Mark II (VITA); leucite, IPS Empress CAD (Ivoclar Vivadent); and lithium disilicate, IPS e.max CAD (Ivoclar Vivadent). The crowns were fabricated by the CEREC CAD-CAM system. After receiving glaze, the crowns were cemented with RelyX U200 (3M ESPE) resin cement under load of 1 kilogram. For each ceramic, one-half of the specimens were subjected to the fracture resistance testing in a universal testing machine with a crosshead speed of 1 millimeter per minute, and the other half were subjected to the fractured resistance testing after 1,000,000 cyclic fatigue loading at 100 newtons. According to a 2-way analysis of variance, the interaction between the material and mechanical cycling was significant (P = .0001). According to a Tukey test (α = .05), the fracture resistance findings with or without cyclic fatigue loading were as follows, respectively: CEREC VITABLOCKS Mark II (405 N/454 N) was statistically lower than IPS Empress CAD (1169 N/1240 N) and IPS e.max CAD (1378 N/1025 N) (P < .05). The IPS Empress CAD and IPS e.max CAD did not differ statistically (P > .05). According to a t test, there was no statistical difference in the fracture resistance with and without cyclic fatigue loading for CEREC VITABLOCS Mark II and IPS Empress CAD (P > .05). For IPS e.max CAD, the fracture resistance without cyclic fatigue loading was statistically superior to that obtained with cyclic fatigue loading (P < .05). The IPS Empress CAD and IPS e.max CAD showed higher fracture resistance compared with CEREC VITABLOCS Mark II. The cyclic fatigue loading negatively influenced only IPS e.max CAD. The CEREC VITABLOCS Mark II, IPS Empress CAD, and IPS e.max CAD ceramic crowns cemented on solid abutments showed sufficient resistance to withstand normal chewing forces. Copyright © 2015 American Dental Association. Published by Elsevier Inc. All rights reserved.

Effect of Restorative Configurations and Occlusal Schemes on Strain Levels in Bone Surrounding Implants.

PubMed

Block, Jonathan; Matalon, Shlomo; Tanase, Gabriela; Ormianer, Zeev

2017-08-01

This study investigated strain levels during and after implant insertion, and during and after simulated mastication, in splinted and nonsplinted restorations with different occlusal schemes. Fresh bovine bone resembling type I jawbone was collected. Strain gauges were placed at each implant's neck, one horizontally and one vertically. Strains at and after implant insertion were recorded. The restoration was loaded with cyclic load simulating mastication. Loading and residual strains were recorded for 6 experimental loading types. At and after implant insertion, high horizontal strains were measured. Full splint loading presented higher vertical compared with horizontal strains (P < 0.05). Segmented cross-arch splint showed higher horizontal strains (P < 0.05). Premolar loading guidance presented the most favorable loading and residual strain results (P < 0.05). Splinting implant restorations may reduce strain levels at implant neck area and provide preferable strain distribution during cyclic loading.

A Fatigue Life Prediction Model of Welded Joints under Combined Cyclic Loading

NASA Astrophysics Data System (ADS)

Goes, Keurrie C.; Camarao, Arnaldo F.; Pereira, Marcos Venicius S.; Ferreira Batalha, Gilmar

2011-01-01

A practical and robust methodology is developed to evaluate the fatigue life in seam welded joints when subjected to combined cyclic loading. The fatigue analysis was conducted in virtual environment. The FE stress results from each loading were imported to fatigue code FE-Fatigue and combined to perform the fatigue life prediction using the S x N (stress x life) method. The measurement or modelling of the residual stresses resulting from the welded process is not part of this work. However, the thermal and metallurgical effects, such as distortions and residual stresses, were considered indirectly through fatigue curves corrections in the samples investigated. A tube-plate specimen was submitted to combined cyclic loading (bending and torsion) with constant amplitude. The virtual durability analysis result was calibrated based on these laboratory tests and design codes such as BS7608 and Eurocode 3. The feasibility and application of the proposed numerical-experimental methodology and contributions for the technical development are discussed. Major challenges associated with this modelling and improvement proposals are finally presented.

Field testing of stiffened deep cement mixing piles under lateral cyclic loading

NASA Astrophysics Data System (ADS)

Raongjant, Werasak; Jing, Meng

2013-06-01

Construction of seaside and underground wall bracing often uses stiffened deep cement mixed columns (SDCM). This research investigates methods used to improve the level of bearing capacity of these SDCM when subjected to cyclic lateral loading via various types of stiffer cores. Eight piles, two deep cement mixed piles and six stiffened deep cement mixing piles with three different types of cores, H shape cross section prestressed concrete, steel pipe, and H-beam steel, were embedded though soft clay into medium-hard clay on site in Thailand. Cyclic horizontal loading was gradually applied until pile failure and the hysteresis loops of lateral load vs. lateral deformation were recorded. The lateral carrying capacities of the SDCM piles with an H-beam steel core increased by 3-4 times that of the DCM piles. This field research clearly shows that using H-beam steel as a stiffer core for SDCM piles is the best method to improve its lateral carrying capacity, ductility and energy dissipation capacity.

Deformation Behavior of Recycled Concrete Aggregate during Cyclic and Dynamic Loading Laboratory Tests

PubMed Central

Sas, Wojciech; Głuchowski, Andrzej; Gabryś, Katarzyna; Soból, Emil; Szymański, Alojzy

2016-01-01

Recycled concrete aggregate (RCA) is a relatively new construction material, whose applications can replace natural aggregates. To do so, extensive studies on its mechanical behavior and deformation characteristics are still necessary. RCA is currently used as a subbase material in the construction of roads, which are subject to high settlements due to traffic loading. The deformation characteristics of RCA must, therefore, be established to find the possible fatigue and damage behavior for this new material. In this article, a series of triaxial cyclic loading and resonant column tests is used to characterize fatigue in RCA as a function of applied deviator stress after long-term cyclic loading. A description of the shakedown phenomenon occurring in the RCA and calculations of its resilient modulus (Mr) as a function of fatigue are also presented. Test result analysis with the stress-life method on the Wohler S-N diagram shows the RCA behavior in accordance with the Basquin law. PMID:28773905

Experimental fatigue life investigation of cylindrical thrust chambers

NASA Technical Reports Server (NTRS)

Quentmeyer, R. J.

1977-01-01

Twenty-two cylindrical test sections of a cylindrical rocket thrust chamber were fabricated and 21 of them were cycled to failure to explore the failure mechanisms, determine the effects of wall temperature on cyclic life, and to rank the material life characteristics for comparison with results from isothermal tests of 12 alloys at 538 C. Cylinder liners were fabricated from OFHC copper, Amzirc, and NAR1loy-Z. Tests were conducted at a chamber pressure of 4.14 MW/sq m using hydrogen-oxygen propellants at an oxidant-fuel ratio of 6.0, which resulted in an average throat heat flux of 54 MW/sq m. The cylinders were cooled with liquid hydrogen at an average rate of 0.91 Kg/sec. All failures were characterized by a thinning of the cooling channel wall at the centerline and eventual failure by tensile rupture. Cyclic life rankings of the materials based on temperature do not agree with published rankings based on uniaxial, isothermal strain tests.

Strain-controlled fatigue behaviors of porous PLA-based scaffolds by 3D-printing technology.

PubMed

Gong, Baoming; Cui, Shaohua; Zhao, Yun; Sun, Yongtao; Ding, Qian

2017-12-01

In the study, the low-cycle fatigue behaviors of 3D-printed poly lactic acid (PLA) scaffolds with 60% porosity and two kinds of geometrical pores were investigated under strain-controlled loading. The obtained Δε a -N f curves were fitted by Coffin-Manson relation. The mechanical stability of the porous structure under cyclic loading was studied. Both kinds of specimens undergo the strain softening after the initial cyclic hardening. The scaffold with circular pore exhibits stable resistance to the fatigue damage which is desirable for bone repairing. Regarding to the accumulation of inelastic deformation, the triangular-scaffold is more sensitive to the cyclic load. The superior fatigue behaviors of the scaffold with circular pore is attributed to homogeneous distribution of the applied mechanical stress and diminishing stress concentration by the introduction of circular pore.

Biaxial fatigue loading of notched composites

NASA Technical Reports Server (NTRS)

Francis, P. H.; Walrath, D. E.; Sims, D. F.; Weed, D. N.

1977-01-01

Thin-walled, 2.54-cm diameter tubular specimens of graphite/epoxy were fatigue cycled in combinations of axial, torsional, and internal pressure loading. Two different four-ply layup configurations were tested: (0-90)s and (+ or- 45)s; each tube contained a 0.48-cm diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based on a plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experimental data proved to be remarkably good.

Dynamic Uniaxial Tensile Loading of Vector Polymers

DTIC Science & Technology

2011-11-01

to apply the loading velocity to the strip at x = 0 after impact by a steel slug projectile. The flange has two sets of grooves. One set, denoted as...travels down the barrel . The strip is clamped to the outside of the barrel at x = L. A Photron SA1 high-speed video camera with a framing rate of...nominal stress. Equation 1 is expressed in terms of particle displacement to obtain the wave equation Flange Gun Barrel Rubber Strip Clamp x = 0

Heavy Traffic Feasible Hybrid Intracycle and Cyclic Sleep for Power Saving in 10G-EPON

PubMed Central

Wang, Liqian; Zhang, Zhiguo; Chen, Xue

2014-01-01

Energy consumption in optical access networks costs carriers substantial operational expense (OPEX) every year and is one of contributing factors for the global warming. To reduce energy consumption in the 10-gigabit Ethernet passive optical network (10G-EPON), a hybrid intracycle and cyclic sleep mechanism is proposed in this paper. Under heavy traffic load, optical network units (ONUs) can utilize short idle slots within each scheduling cycle to enter intracycle sleep without postponing data transmission. In this way, energy conservation is achieved even under heavy traffic load with quality of service (QoS) guarantee. Under light traffic load, ONUs perform long cyclic sleep for several scheduling cycles. The adoption of cyclic sleep instead of intracycle sleep under light traffic load can reduce unnecessary frequent transitions between sleep and full active work caused by using intracycle sleep. Further, the Markov chain of the proposed mechanism is established. The performances of the proposed mechanism and existing approaches are analyzed quantitatively based on the chain. For the proposed mechanism, power saving ability with QoS guarantee even under heavy traffic and better power saving performance than existing approaches are verified by the quantitative analysis. Moreover, simulations validate the above conclusions based on the chain. PMID:25177727

Effect of loading speed on the stress-induced magnetic behavior of ferromagnetic steel

NASA Astrophysics Data System (ADS)

Bao, Sheng; Gu, Yibin; Fu, Meili; Zhang, Da; Hu, Shengnan

2017-02-01

The primary goal of this research is to investigate the effect of loading speed on the stress-induced magnetic behavior of a ferromagnetic steel. Uniaxial tension tests on Q235 steel were carried out with various stress levels under different loading speeds. The variation of the magnetic signals surrounding the tested specimen was detected by a fluxgate magnetometer. The results indicated that the magnetic signal variations depended not only on the tensile load level but on the loading speed during the test. The magnetic field amplitude seemed to decrease gradually with the increase in loading speed at the same tensile load level. Furthermore, the evolution of the magnetic reversals is also related to the loading speed. Accordingly, the loading speed should be considered as one of the influencing variables in the Jies-Atherton model theory of the magnetomechanical effect.

Buckling of Fiber Reinforced Composite Plates with Nanofiber Reinforced Matrices

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Murthy, Pappu L. N.

2010-01-01

Anisotropic composite plates were evaluated with nanofiber reinforced matrices (NFRM). The nanofiber reinforcement volumes ratio in the matrix was 0.01. The plate dimensions were 20 by 10 by 1.0 in. (508 by 254 by 25.4 mm). Seven different loading condition cases were evaluated: three for uniaxial loading, three for pairs of combined loading, and one with three combined loadings. The anisotropy arose from the unidirectional plates having been at 30 from the structural axis. The anisotropy had a full 6 by 6 rigidities matrix which were satisfied and solved by a Galerkin buckling algorithm. The buckling results showed that the NFRM plates buckled at about twice those with conventional matrix.

The viscoelastic standard nonlinear solid model: predicting the response of the lumbar intervertebral disk to low-frequency vibrations.

PubMed

Groth, Kevin M; Granata, Kevin P

2008-06-01

Due to the mathematical complexity of current musculoskeletal spine models, there is a need for computationally efficient models of the intervertebral disk (IVD). The aim of this study is to develop a mathematical model that will adequately describe the motion of the IVD under axial cyclic loading as well as maintain computational efficiency for use in future musculoskeletal spine models. Several studies have successfully modeled the creep characteristics of the IVD using the three-parameter viscoelastic standard linear solid (SLS) model. However, when the SLS model is subjected to cyclic loading, it underestimates the load relaxation, the cyclic modulus, and the hysteresis of the human lumbar IVD. A viscoelastic standard nonlinear solid (SNS) model was used to predict the response of the human lumbar IVD subjected to low-frequency vibration. Nonlinear behavior of the SNS model was simulated by a strain-dependent elastic modulus on the SLS model. Parameters of the SNS model were estimated from experimental load deformation and stress-relaxation curves obtained from the literature. The SNS model was able to predict the cyclic modulus of the IVD at frequencies of 0.01 Hz, 0.1 Hz, and 1 Hz. Furthermore, the SNS model was able to quantitatively predict the load relaxation at a frequency of 0.01 Hz. However, model performance was unsatisfactory when predicting load relaxation and hysteresis at higher frequencies (0.1 Hz and 1 Hz). The SLS model of the lumbar IVD may require strain-dependent elastic and viscous behavior to represent the dynamic response to compressive strain.

Biomechanical evaluation of different suture techniques for arthroscopic transtibial pull-out repair of posterior medial meniscus root tears.

PubMed

Feucht, Matthias J; Grande, Eduardo; Brunhuber, Johannes; Burgkart, Rainer; Imhoff, Andreas B; Braun, Sepp

2013-12-01

A tear of the posterior medial meniscus root (PMMR) is increasingly recognized as a serious knee joint injury. Several suture techniques for arthroscopic transtibial pull-out repair have been described; however, only limited data about the biomechanical properties of these techniques are currently available. There are significant differences between the tested suture techniques, with more complex suture configurations providing superior biomechanical properties. Controlled laboratory study. A total of 40 porcine medial menisci were randomly assigned to 1 of 4 groups (10 specimens each) according to suture technique: two simple stitches (TSS), horizontal mattress suture (HMS), modified Mason-Allen suture (MMA), and two modified loop stitches (TLS). Meniscus-suture constructs were subjected to cyclic loading followed by load-to-failure testing in a servohydraulic material testing machine. During cyclic loading, the HMS and TLS groups showed a significantly higher displacement after 100, 500, and 1000 cycles compared with the TSS and MMA groups. After 1000 cycles, the highest displacement was found for the TLS group, with significant differences compared with all other groups. During load-to-failure testing, the highest maximum load and yield load were observed for the MMA group, with statistically significant differences compared with the TSS and TLS groups. With regard to stiffness, the TSS and MMA groups showed significantly higher values compared with the HMS and TLS groups. The MMA technique provided the best biomechanical properties with regard to cyclic loading and load-to-failure testing. The TSS technique seems to be a valuable alternative. Both the HMS and TLS techniques have the disadvantage of lower stiffness and higher displacement during cyclic loading. Using a MMA technique may improve healing rates and avoid progressive extrusion of the medial meniscus after transtibial pull-out repair of PMMR tears. The TSS technique may be used as an alternative that is easier to perform, but a more careful rehabilitation program is possibly necessary to avoid early failure.

Normalized spectral damage of a linear system over different spectral loading patterns

NASA Astrophysics Data System (ADS)

Kim, Chan-Jung

2017-08-01

Spectral fatigue damage is affected by different loading patterns; the damage may be accumulated in a different manner because the spectral pattern has an influence on stresses or strains. The normalization of spectral damage with respect to spectral loading acceleration is a novel solution to compare the accumulated fatigue damage over different spectral loading patterns. To evaluate the sensitivity of fatigue damage over different spectral loading cases, a simple notched specimen is used to conduct a uniaxial vibration test for two representative spectral patterns-random and harmonic-between 30 and 3000 Hz. The fatigue damage to the simple specimen is analyzed for different spectral loading cases using the normalized spectral damage from the measured response data for both acceleration and strain. The influence of spectral loading patterns is discussed based on these analyses.

Dislocation density evolution of AA 7020-T6 investigated by in-situ synchrotron diffraction under tensile load

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

Zhong, Z.Y., E-mail: zhengye.zhong@hzg.de; Helmholtz-Zentrum Geesthacht, Max-Planck-Straße 1, D-21502 Geesthacht; Brokmeier, H.-G.

2015-10-15

The dislocation density evolution along the loading axis of a textured AA 7020-T6 aluminum alloy during uniaxial tension was investigated by in-situ synchrotron diffraction. The highly parallel synchrotron beam at the High Energy Materials Science beamline P07 in PETRA III, DESY, offers excellent conditions to separate different influences for line broadening from which micro-strains are obtained using the modified Williamson–Hall method which is also for defect density investigations. During tensile loading the dislocation density evolution was documented from the as-received material (initial micro-strain state) to the relaxation of the strains during elastic deformation. After yield, the increasing rate of dislocationmore » density growth was relatively fast till half-way between yield and UTS. After that, the rate started to decrease and the dislocation density fluctuated as the elongation increased due to the generation and annihilation of dislocations. When dislocation generation is dominant, the correlation between the flow stress and dislocation density satisfies the Taylor equation. Besides, a method to correct the thickness effect on peak broadening is developed in the present study. - Highlights: • In-situ synchrotron diffraction was applied to characterize peak broadening. • Dislocation evolution along the loading axis during uniaxial tension was investigated. • A method to correct the sample thickness effect on peak broadening was developed. • Dislocation density and flow stress satisfy the Taylor equation at a certain range. • The texture before load and after sample fracture was analyzed.« less

Thermo-elastic-plastic analysis for elastic component under high temperature fatigue crack growth rate

NASA Astrophysics Data System (ADS)

Ali, Mohammed Ali Nasser

The research project presents a fundamental understanding of the fatigue crack growth mechanisms of AISI 420 martensitic stainless steel, based on the comparison analysis between the theoretical and numerical modelling, incorporating research findings under isothermal fatigue loading for solid cylindrical specimen and the theoretical modelling with the numerical simulation for tubular specimen when subjected to cyclic mechanical loading superimposed by cyclic thermal shock.The experimental part of this research programme studied the fatigue stress-life data for three types of surface conditions specimen and the isothermal stress-controlled fatigue testing at 300 °C - 600 °C temperature range. It is observed that the highest strength is obtained for the polished specimen, while the machined specimen shows lower strength, and the lowest strength is the notched specimen due to the high effect of the stress concentration. The material behaviour at room and high temperatures shows an initial hardening, followed by slow extension until fully plastic saturation then followed by crack initiation and growth eventually reaching the failure of the specimen, resulting from the dynamic strain ageing occurred from the transformation of austenitic microstructure to martensite and also, the nucleation of precipitation at grain boundaries and the incremental temperature increase the fatigue crack growth rate with stress intensity factor however, the crack growth rate at 600 °C test temperature is less than 500 °C because of the creep-fatigue taking place.The theoretical modelling presents the crack growth analysis and stress and strain intensity factor approaches analysed in two case studies based on the addition of thermo-elastic-plastic stresses to the experimental fatigue applied loading. Case study one estimates the thermal stresses superimposed sinusoidal cyclic mechanical stress results in solid cylinder under isothermal fatigue simulation. Case study two estimates the transient thermal stresses superimposed on cyclic mechanical loading results in hollow cylinder under thermal shock in heating case and down shock cooling case. The combination of stress and strain intensity factor theoretical calculations with the experimental output recorded data shows a similar behaviour with increasing temperature, and there is a fair correlation between the profiles at the beginning and then divergence with increasing the crack length. The transient influence of high temperature in case two, giving a very high thermal shock stress as a heating or cooling effects, shifting up the combined stress, when applied a cyclic mechanical load in fraction of seconds, and the reputations of these shocks, causing a fast failure under high thermal shock stress superimposed with mechanical loading.Finally, the numerical modelling analyses three cases studied were solved due to the types of loading and types of specimen geometry by using finite element models constructed through the ANSYS Workbench version 13.0. The first case is a low cyclic fatigue case for a solid cylinder specimen simulated by applying a cyclic mechanical loading. The second is an isothermal fatigue case for solid cylinder specimen simulated by supplying different constant temperatures on the outer surface with cyclic mechanical loading, where the two cases are similar to the experimental tests and the third case, is a thermo-mechanical fatigue for a hollow cylinder model by simulating a thermal up-shock generated due to transient heating on the outer surface of the model or down shock cooling on the inner surface with the cyclic mechanical loading. The results show a good agreement with the experimental data in terms of alternative stress and life in the first case. In case two results show the strain intensity factor is increases with increasing temperature similar to the theoretical solution due to the influence of the modulus of elasticity and the difference in life estimation with the experimental output record is related to the input data made of theoretical physical properties and the experimental stress-life data.

Prediction and verification of creep behavior in metallic materials and components for the space shuttle thermal protection system. Volume 2: Phase 2 subsize panel cyclic creep predictions

NASA Technical Reports Server (NTRS)

Cramer, B. A.; Davis, J. W.

1975-01-01

A method for predicting permanent cyclic creep deflections in stiffened panel structures was developed. The resulting computer program may be applied to either the time-hardening or strain-hardening theories of creep accumulation. Iterative techniques were used to determine structural rotations, creep strains, and stresses as a function of time. Deflections were determined by numerical integration of structural rotations along the panel length. The analytical approach was developed for analyzing thin-gage entry vehicle metallic-thermal-protection system panels subjected to cyclic bending loads at high temperatures, but may be applied to any panel subjected to bending loads. Predicted panel creep deflections were compared with results from cyclic tests of subsize corrugation and rib-stiffened panels. Empirical equations were developed for each material based on correlation with tensile cyclic creep data and both the subsize panels and tensile specimens were fabricated from the same sheet material. For Vol. 1, see N75-21431.

A model of rotationally-sampled wind turbulence for predicting fatigue loads in wind turbines

NASA Technical Reports Server (NTRS)

Spera, David A.

1995-01-01

Empirical equations are presented with which to model rotationally-sampled (R-S) turbulence for input to structural-dynamic computer codes and the calculation of wind turbine fatigue loads. These equations are derived from R-S turbulence data which were measured at the vertical-plane array in Clayton, New Mexico. For validation, the equations are applied to the calculation of cyclic flapwise blade loads for the NASA/DOE Mod-2 2.5-MW experimental HAWT's (horizontal-axis wind turbines), and the results compared to measured cyclic loads. Good correlation is achieved, indicating that the R-S turbulence model developed in this study contains the characteristics of the wind which produce many of the fatigue loads sustained by wind turbines. Empirical factors are included which permit the prediction of load levels at specified percentiles of occurrence, which is required for the generation of fatigue load spectra and the prediction of the fatigue lifetime of structures.

The role of suture cutout in the failure of meniscal root repair during the early post-operative period: a biomechanical study.

PubMed

Perez-Blanca, Ana; Prado Nóvoa, María; Lombardo Torre, Maximiano; Espejo-Reina, Alejandro; Ezquerro Juanco, Francisco; Espejo-Baena, Alejandro

2018-04-01

To assess the role of suture cutout in the mechanics of failure of the repaired posterior meniscal root during the early post-operative period when using sutures of different shape. Twenty medial porcine menisci were randomized in two groups depending on the suture shape used to repair the posterior root: thread or tape. The sutured menisci were subjected to cyclic loading (1000 cycles, (10, 30) N) followed by load-to-failure testing. Residual displacements, stiffness, and ultimate failure load were determined. During tests, the tissue-suture interface was recorded using a high-resolution camera. In cyclic tests, cutout progression at the suture insertion points was not observed for any specimen of either group and no differences in residual displacements were found between use of thread or tape. In load-to-failure tests, suture cutout started in all menisci at a load close to the ultimate failure and all specimens failed by suture pullout. Suture tape had a greater ultimate load with no other differences. In a porcine model of a repaired posterior meniscal root subjected to cyclic loads representative of current rehabilitation protocols in the early post-operative period under restricted loading conditions, suture cutout was not found as a main source of permanent root displacement when using suture thread or tape. Suture cutout progression started at high loading levels close to the ultimate load of the construct. Tape, with a meniscus-suture contact area larger than thread, produced higher ultimate load.

Simulation of fatigue fracture of TiNi shape memory alloy samples at cyclic loading in pseudoelastic state

NASA Astrophysics Data System (ADS)

Belyaev, Fedor S.; Volkov, Aleksandr E.; Evard, Margarita E.; Khvorov, Aleksandr A.

2018-05-01

Microstructural simulation of mechanical behavior of shape memory alloy samples at cyclic loading in the pseudoelastic state has been carried out. Evolution of the oriented and scattered deformation defects leading to damage accumulation and resulting in the fatigue fracture has been taken into account. Simulations were performed for the regime of loading imitating that for endovascular stents: preliminary straining, unloading, deformation up to some mean level of the strain and subsequent mechanical cycling at specified strain amplitude. Dependence of the fatigue life on the loading parameters (pre-strain, mean and amplitude values of strain) has been obtained. The results show a good agreement with available experimental data.

Elastic-Plastic Finite Element Analysis of Fatigue Crack Growth in Mode 1 and Mode 2 Conditions

NASA Technical Reports Server (NTRS)

Nakagaki, M.; Atluri, S. N.

1978-01-01

Presented is an alternate cost-efficient and accurate elastic-plastic finite element procedure to analyze fatigue crack closure and its effects under general spectrum loading. Both Modes 1 and 2 type cycling loadings are considered. Also presented are the results of an investigation, using the newly developed procedure, of various factors that cause crack growth acceleration or retardation and delay effects under high-to-low, low-to-high, single overload, and constant amplitude type cyclic loading in a Mode 1 situation. Further, the results of an investigation of a centercracked panel under external pure shear (Mode 2) cyclic loading, of constant amplitude, are reported.

Fatigue induced changes in conical implant-abutment connections.

PubMed

Blum, Kai; Wiest, Wolfram; Fella, Christian; Balles, Andreas; Dittmann, Jonas; Rack, Alexander; Maier, Dominik; Thomann, Ralf; Spies, Benedikt Christopher; Kohal, Ralf Joachim; Zabler, Simon; Nelson, Katja

2015-11-01

Based on the current lack of data and understanding of the wear behavior of dental two-piece implants, this study aims for evaluating the microgap formation and wear pattern of different implants in the course of cyclic loading. Several implant systems with different conical implant-abutment interfaces were purchased. The implants were first evaluated using synchrotron X-ray high-resolution radiography (SRX) and scanning electron microscopy (SEM). The implant-abutment assemblies were then subjected to cyclic loading at 98N and their microgap was evaluated after 100,000, 200,000 and 1 million cycles using SRX, synchrotron micro-tomography (μCT). Wear mechanisms of the implant-abutment connection (IAC) after 200,000 cycles and 1 million cycles were further characterized using SEM. All implants exhibit a microgap between the implant and abutment prior to loading. The gap size increased with cyclic loading with its changes being significantly higher within the first 200,000 cycles. Wear was seen in all implants regardless of their interface design. The wear pattern comprised adhesive wear and fretting. Wear behavior changed when a different mounting medium was used (brass vs. polymer). A micromotion of the abutment during cyclic loading can induce wear and wear particles in conical dental implant systems. This feature accompanied with the formation of a microgap at the IAC is highly relevant for the longevity of the implants. Copyright © 2015 Academy of Dental Materials. Published by Elsevier Ltd. All rights reserved.

Phonon dispersion evolution in uniaxially strained aluminum crystal

NASA Astrophysics Data System (ADS)

Parthasarathy, Ranganathan; Misra, Anil; Aryal, Sitaram; Ouyang, Lizhi

2018-04-01

The influence of loading upon the phonon dispersion of crystalline materials could be highly nonlinear with certain particular trends that depend upon the loading path. In this paper, we have calculated the influence of [100] uniaxial strain on the phonon dispersion and group velocities in fcc aluminum using second moments of position obtained from molecular dynamics (MD) simulation at 300 K. In contrast to nonlinear monotonic variation of both longitudinal and transverse phonon frequencies along the Δ , Λ and Σ lines of the first Brillouin zone under tension, transverse phonon branches along the Λ line show inflection at specific wavevectors when the compressive strain exceeds 5%. Further, the longitudinal group velocities along the high-symmetry Δ line vary non-monotonically with strain, reaching a minimum at 5% compressive strain. Throughout the strain range studied, the equilibrium positions of atoms displace in an affine manner preserving certain static structural symmetry. We attribute the anomalies in the phonon dispersion to the non-affine evolution of second moments of atomic position, and the associated plateauing of force constants under the applied strain path.

Evolution of the plasma-sprayed microstructure in 7 wt% yttria-stabilized zirconia thermal barrier coatings during uniaxial stress relaxation and the concomitant changes in material properties

NASA Astrophysics Data System (ADS)

Petorak, Christopher

The understanding of failure mechanisms in plasma sprayed 7 wt% yttria stabilized zirconia (YSZ) is a key step toward optimizing thermal barrier coating (TBC) usage, design, and life prediction. The purpose of the present work is to characterize and understand the stress relaxation behavior occurring in plasma-sprayed YSZ coatings, so that the correlating magnitude of unfavorable tensile stress, which coatings experienced upon cooling, may be reduced through microstructural design. The microstructure and properties of as-sprayed coatings changes immensely during service at high temperature, and therefore the effects of long heat-treatment times, and the concomitant change within the microstructure, on the time-dependent mechanical behavior of stand-alone YSZ coatings was studied in parallel with the as-sprayed coating condition. Aside from influencing the mechanical properties, stress relaxation also affects the insulating efficiency of plasma-sprayed 7wt% YSZ coatings. Directionally dependent changes in microstructure due to stress relaxation of a uniaxially applied stress at 1200°C were observed in plasma-sprayed coatings. Small angle neutron scattering (SANS) investigation of coatings after stress relaxation displayed a 46% reduction in the specific surface area connected to the load-orientation dependent closure of void surface area perpendicular to the applied load when compared to coatings sintered in air, i.e. no applied load. These anisotropic microstructural changes were linked to the thermal properties of the coating. For example, a coating stress relaxed from 60 MPa for 5-min at 1200°C exhibited a thermal conductivity of 2.1 W/m-K. A coating that was only heat-treated for 5-min at 1200°C (i.e. no stress applied) exhibited a thermal conductivity of 1.7 W/m·K. In the current study, uniaxial stress relaxation in plasma-sprayed 7wt% YSZ coatings was determined the result of: (1) A more uniform distribution of the applied load with time, (2) A reduction in the SSA associated with void systems due to sintering, specifically the closing and healing of intralamellar cracks perpendicular to the applied stress, and (3) A compaction and closure of void systems under the applied load. These anisotropic changes in microstructure result in distinguishable changes in thermo-mechanical properties, with very minute changes to the overall bulk density.

Flexural creep of structural flakeboards under cyclic humidity

Treesearch

M.C. Yeh; R.C. Tang; Chung-Yun Hse

1990-01-01

Flexural creep behavior of randomly oriented structural flakeboards under cyclic humidity is presented. Specimens fabricated with 5 and 7 percent phenol-formaldehyde resin were subjected to constant concentrated load in bending under slow and fast cyclic relative humidity (RH) between 65 and 95 percent for 100 days. The temperature was set at a constant 75°F through...

A micromechanical constitutive model for anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals

NASA Astrophysics Data System (ADS)

Yu, Chao; Kang, Guozheng; Kan, Qianhua

2015-09-01

Based on the experimental observations on the anisotropic cyclic deformation of super-elastic NiTi shape memory alloy single crystals done by Gall and Maier (2002), a crystal plasticity based micromechanical constitutive model is constructed to describe such anisotropic cyclic deformation. To model the internal stress caused by the unmatched inelastic deformation between the austenite and martensite phases on the plastic deformation of austenite phase, 24 induced martensite variants are assumed to be ellipsoidal inclusions with anisotropic elasticity and embedded in the austenite matrix. The homogeneous stress fields in the austenite matrix and each induced martensite variant are obtained by using the Mori-Tanaka homogenization method. Two different inelastic mechanisms, i.e., martensite transformation and transformation-induced plasticity, and their interactions are considered in the proposed model. Following the assumption of instantaneous domain growth (Cherkaoui et al., 1998), the Helmholtz free energy of a representative volume element of a NiTi shape memory single crystal is established and the thermodynamic driving forces of the internal variables are obtained from the dissipative inequalities. The capability of the proposed model to describe the anisotropic cyclic deformation of super-elastic NiTi single crystals is first verified by comparing the predicted results with the experimental ones. It is concluded that the proposed model can capture the main quantitative features observed in the experiments. And then, the proposed model is further used to predict the uniaxial and multiaxial transformation ratchetting of a NiTi single crystal.

Life prediction of materials exposed to monotonic and cyclic loading: A new technology survey

NASA Technical Reports Server (NTRS)

Stuhrke, W. F.; Carpenter, J. L., Jr.

1975-01-01

Reviewed and evaluated technical abstracts for about 100 significant documents are reported relating primarily to life prediction for structural materials exposed to monotonic and cyclic loading, particularly in elevated temperature environments. The abstracts in the report are mostly for publications in the period April 1962 through April 1974. The purpose of this report is to provide, in quick reference form, a dependable source for current information

Preliminary analysis of dynamic stall effects on a 91-meter wind turbine rotor

NASA Technical Reports Server (NTRS)

Wilson, Robert E.

1995-01-01

Analytical investigation of dynamic stall on HAWT (horizontal-axis wind turbines) rotor loads was conducted. Dynamic stall was modeled using the Gormont approach on the MOD-2 rotor, treating the blade as a rigid body teetering about a fixed axis. Blade flapwise bending moments at station 370 were determined with and without dynamic stall for spatial variations in local wind speed due to wind shear and yaw. The predicted mean flapwise bending moments were found to be in good agreement with test results. Results obtained with and without dynamic stall showed no significant difference for the mean flapwise bending moment. The cyclic bending moments calculated with and without dynamic stall effects were substantially the same. None of the calculated cyclic loads reached the level of the cyclic loads measured on the MOD-2 using the Boeing five-minute-average technique.

Life prediction of materials exposed to monotonic and cyclic loading: Bibliography

NASA Technical Reports Server (NTRS)

Carpenter, J. L., Jr.; Moya, N.; Stuhrke, W. F.

1975-01-01

This bibliography is comprised of approximately 1200 reference citations related to the mechanics of failure in aerospace structures. Most of the references are for information on life prediction for materials exposed to monotonic and cyclic loading in elevated temperature environments such as that in the hot end of a gas turbine engine. Additional citations listed are for documents on the thermal and mechanical effects on solar cells in the cryogenic vacuum environment; radiation effects on high temperature mechanical properties; and high cycle fatigue technology as applicable to gas turbine engine bearings. The bibliography represents a search of the literature published in the period April 1962 through April 1974 and is largely limited to documents published in the United States. It is a companion volume to NASA CR-134750, Life Prediction of Materials Exposed to Monotonic and cyclic Loading - A Technology Survey.

Fine characterization rock thermal damage by acoustic emission technique

NASA Astrophysics Data System (ADS)

Kong, Biao; Li, Zenghua; Wang, Enyuan

2018-02-01

This paper examines the differences in the thermal mechanical properties and acoustic emission (AE) characteristics during the deformation and fracture of rock under the action of continuous heating and after high-temperature treatment. Using AE 3D positioning technology, the development and evolution of the internal thermal cracks and the time domain of AE signals in rock were analyzed. High-temperature treatment causes thermal damage to rock. Under the action of continuous heating, the phase characteristics of AE time series correspond to the five stages of rock thermal deformation and fracture, respectively: the micro-defect development stage, the threshold interval of rock micro-cracks, the crack initiation stage, the crack propagation stage, and the crack multistage propagation evolution. When the initial crack propagates, the crack initiation of the rock causes the AE signal to produce a sudden mutation change. Mechanical fraction characteristics during rock uniaxial compression after temperature treatment indicated that the decrease rate of the rock compressive strength, wave velocity, and elastic modulus are relatively large during uniaxial compression tests after high-temperature treatment. During the deformation and fracture of rock under loading, there is faster growth of AE counts and AE events, indicating an increase in the speed of rock deformation and fracture under loading. AE counts show obvious changes during the latter loading stages, whereas AE events show obvious changes during the loading process. The results obtained are valuable for rock thermal stability detection and evaluation in actual underground engineering.

Dynamic Microstructure Design Consortium

DTIC Science & Technology

2011-03-23

multiple realizations of polycrystalline microstructure. Cyclic microplasticity in favorably oriented martensite grains is the primary driver for the...can alter the residual stress distribution 13. The present work ex- plores how short-range microplastic deformation during cyclic loading promotes

Exploring the efficacy of cyclic vs static aspiration in a cerebral thrombectomy model: an initial proof of concept study.

PubMed

Simon, Scott; Grey, Casey Paul; Massenzo, Trisha; Simpson, David G; Longest, P Worth

2014-11-01

Current technology for endovascular thrombectomy in ischemic stroke utilizes static loading and is successful in approximately 85% of cases. Existing technology uses either static suction (applied via a continuous pump or syringe) or flow arrest with a proximal balloon. In this paper we evaluate the potential of cyclic loading in aspiration thrombectomy. In order to evaluate the efficacy of cyclic aspiration, a model was created using a Penumbra aspiration system, three-way valve and Penumbra 5Max catheter. Synthetic clots were aspirated at different frequencies and using different aspiration mediums. Success or failure of clot removal and time were recorded. All statistical analyses were based on either a one-way or two-way analysis of variance, Holm-Sidak pairwise multiple comparison procedure (α=0.05). Cyclic aspiration outperformed static aspiration in overall clot removal and removal speed (p<0.001). Within cyclic aspiration, Max Hz frequencies (∼6.3 Hz) cleared clots faster than 1 Hz (p<0.001) and 2 Hz (p=0.024). Loading cycle dynamics (specific pressure waveforms) affected speed and overall clearance (p<0.001). Water as the aspiration medium was more effective at clearing clots than air (p=0.019). Cyclic aspiration significantly outperformed static aspiration in speed and overall clearance of synthetic clots in our experimental model. Within cyclic aspiration, efficacy is improved by increasing cycle frequency, utilizing specific pressure cycle waveforms and using water rather than air as the aspiration medium. These findings provide a starting point for altering existing thrombectomy technology or perhaps the development of new technologies with higher recanalization rates. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.

Quantifying Residual Stresses by Means of Thermoelastic Stress Analysis

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.; Baaklini, George Y.

2001-01-01

This study focused on the application of the Thermoelastic Stress Analysis (TSA) technique as a tool for assessing the residual stress state of structures. TSA is based on the fact that materials experience small temperature changes when compressed or expanded. When a structure is cyclically loaded, a surface temperature profile results which correlates to the surface stresses. The cyclic surface temperature is measured with an infrared camera. Traditionally, the amplitude of a TSA signal was theoretically defined to be linearly dependent on the cyclic stress amplitude. Recent studies have established that the temperature response is also dependent on the cyclic mean stress (i.e., the static stress state of the structure). In a previous study by the authors, it was shown that mean stresses significantly influenced the TSA results for titanium- and nickel-based alloys. This study continued the effort of accurate direct measurements of the mean stress effect by implementing various experimental modifications. In addition, a more in-depth analysis was conducted which involved analyzing the second harmonic of the temperature response. By obtaining the amplitudes of the first and second harmonics, the stress amplitude and the mean stress at a given point on a structure subjected to a cyclic load can be simultaneously obtained. The experimental results showed good agreement with the theoretical predictions for both the first and second harmonics of the temperature response. As a result, confidence was achieved concerning the ability to simultaneously obtain values for the static stress state as well as the cyclic stress amplitude of structures subjected to cyclic loads using the TSA technique. With continued research, it is now feasible to establish a protocol that would enable the monitoring of residual stresses in structures utilizing TSA.

A biomechanical comparison of single and double-row fixation in arthroscopic rotator cuff repair.

PubMed

Smith, Christopher D; Alexander, Susan; Hill, Adam M; Huijsmans, Pol E; Bull, Anthony M J; Amis, Andrew A; De Beer, Joe F; Wallace, Andrew L

2006-11-01

The optimal method for arthroscopic rotator cuff repair is not yet known. The hypothesis of the present study was that a double-row repair would demonstrate superior static and cyclic mechanical behavior when compared with a single-row repair. The specific aims were to measure gap formation at the bone-tendon interface under static creep loading and the ultimate strength and mode of failure of both methods of repair under cyclic loading. A standardized tear of the supraspinatus tendon was created in sixteen fresh cadaveric shoulders. Arthroscopic rotator cuff repairs were performed with use of either a double-row technique (eight specimens) or a single-row technique (eight specimens) with nonabsorbable sutures that were double-loaded on a titanium suture anchor. The repairs were loaded statically for one hour, and the gap formation was measured. Cyclic loading to failure was then performed. Gap formation during static loading was significantly greater in the single-row group than in the double-row group (mean and standard deviation, 5.0 +/- 1.2 mm compared with 3.8 +/- 1.4 mm; p < 0.05). Under cyclic loading, the double-row repairs failed at a mean of 320 +/- 96.9 N whereas the single-row repairs failed at a mean of 224 +/- 147.9 N (p = 0.058). Three single-row repairs and three double-row repairs failed as a result of suture cut-through. Four single-row repairs and one double-row repair failed as a result of anchor or suture failure. The remaining five repairs did not fail, and a midsubstance tear of the tendon occurred. Although more technically demanding, the double-row technique demonstrates superior resistance to gap formation under static loading as compared with the single-row technique. A double-row reconstruction of the supraspinatus tendon insertion may provide a more reliable construct than a single-row repair and could be used as an alternative to open reconstruction for the treatment of isolated tears.

A Critical Assessment of Cyclic Softening and Hardening Behavior in a Near- α Titanium Alloy During Thermomechanical Fatigue

NASA Astrophysics Data System (ADS)

Prasad, Kartik; Sarkar, Rajdeep; Rao, K. Bhanu Sankara; Sundararaman, M.

2016-10-01

Thermomechanical fatigue behavior of Ti-alloy Timetal 834 has been studied at two temperature intervals viz. 573 K to 723 K (300 °C to 450 °C) and 723 K to 873 K (450 °C to 600 °C) under mechanical strain-controlled cycling. Among the temperatures studied, the alloy exhibited initial cyclic softening followed by cyclic hardening at 723 K (450 °C) in the temperature interval of 573 K to 723 K (300 °C to 450 °C). However, continuous cyclic hardening was observed at 723 K (450 °C) in 723 K to 873 K (450 °C to 600 °C). At 573 K (300 °C) and 873 K (600 °C), cyclic softening was observed in the cyclic stress response curves in both the temperature intervals. The dislocation substructure was observed to be planar in both the modes of TMF loading. Based on TEM microstructures and few unconventional fatigue tests, the observed cyclic hardening is attributed to dynamic strain aging. The reduced fatigue life at 723 K to 873 K (450 °C to 600 °C) under OP-TMF loading was attributed to the combined effect of cyclic hardening (leading to early strain localization and crack initiation), oxidation, and development of tensile mean stresses.

Cyclic debonding of adhesively bonded composites

NASA Technical Reports Server (NTRS)

Mall, S.; Johnson, W. S.; Everett, R. A., Jr.

1982-01-01

The fatigue behavior of a simple composite to composite bonded joint was analyzed. The cracked lap shear specimen subjected to constant amplitude cyclic loading was studied. Two specimen geometries were tested for each bonded system: (1) a strap adherend of 16 plies bonded to a lap adherend of 8 plies; and (2) a strap adherend of 8 plies bonded to a lap adherend of 16 plies. In all specimens the fatigue failure was in the form of cyclic debonding with some 0 deg fiber pull off from the strap adherend. The debond always grew in the region of adhesive that had the highest mode (peel) loading and that region was close to the adhesive strap interface.

Effect of phase lag on cyclic durability of laminated composite

NASA Astrophysics Data System (ADS)

Andersons, Janis; Limonov, V.; Tamuzs, Vitants

1992-07-01

Theoretical and experimental results on fatigue of laminated fiber reinforced composites under out-of-phase, biaxial cyclic loading are presented. Experiments were carried out on tubular filament wound samples of epoxy matrix/organic (Kevlar type) fiber composites. Fatigue strength under two different loading modes, namely cyclic torsion combined with axial tension or compression, was investigated for phase lags psi = 0, pi/2, and pi. Durability was shown to decrease with increasing phase shift both for axial tension (R = 0.1) and compression (R = 10). A matrix failure criterion was proposed for a unidirectionally reinforced ply, and the ply discount method was modified to account for phase lag. Calculated S-N curves agree reasonably well with experimental data.

Computational Simulation of Composite Structural Fatigue

NASA Technical Reports Server (NTRS)

Minnetyan, Levon; Chamis, Christos C. (Technical Monitor)

2005-01-01

Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic loads are included in the simulations. Results show the number of cycles to failure at different temperatures and the damage progression sequence during different degradation stages. A procedure is outlined for use of computational simulation data in the assessment of damage tolerance, determination of sensitive parameters affecting fracture, and interpretation of results with insight for design decisions.

Computational Simulation of Composite Structural Fatigue

NASA Technical Reports Server (NTRS)

Minnetyan, Levon

2004-01-01

Progressive damage and fracture of composite structures subjected to monotonically increasing static, tension-tension cyclic, pressurization, and flexural cyclic loading are evaluated via computational simulation. Constituent material properties, stress and strain limits are scaled up to the structure level to evaluate the overall damage and fracture propagation for composites. Damage initiation, growth, accumulation, and propagation to fracture due to monotonically increasing static and cyclic loads are included in the simulations. Results show the number of cycles to failure at different temperatures and the damage progression sequence during different degradation stages. A procedure is outlined for use of computational simulation data in the assessment of damage tolerance, determination of sensitive parameters affecting fracture, and interpretation of results with insight for design decisions.

Thermoelastic Stress Analysis: An NDE Tool for the Residual Stress Assessment of Metallic Alloys

NASA Technical Reports Server (NTRS)

Gyekenyesi, Andrew L.; Baaklini, George Y.

2000-01-01

During manufacturing, certain propulsion components that will be used in a cyclic fatigue environment are fabricated to contain compressive residual stresses on their surfaces because these stresses inhibit the nucleation of cracks. Overloads and elevated temperature excursions cause the induced residual stresses to dissipate while the component is still in service, lowering its resistance to crack initiation. Research at the NASA Glenn Research Center at Lewis Field has focused on employing the Thermoelastic Stress Analysis technique (TSA, also recognized as SPATE: Stress Pattern Analysis by Thermal Emission) as a tool for monitoring the residual stress state of propulsion components. TSA is based on the fact that materials experience small temperature changes when they are compressed or expanded. When a structure is cyclically loaded (i.e., cyclically compressed and expanded), the resulting surface-temperature profile correlates to the stress state of the structure s surface. The surface-temperature variations resulting from a cyclic load are measured with an infrared camera. Traditionally, the temperature amplitude of a TSA signal has been theoretically defined to be linearly dependent on the cyclic stress amplitude. As a result, the temperature amplitude resulting from an applied cyclic stress was assumed to be independent of the cyclic mean stress.

Biaxial fatigue loading of notched composites

NASA Technical Reports Server (NTRS)

Francis, P. H.; Walrath, D. E.; Sims, D. F.; Weed, D. N.

1977-01-01

Thin walled, 2.54-cm (1-in.) diameter tubular specimens of T300/934 graphite/epoxy were fabricated and fatigue cycled in combinations of axial, torsional, and internal pressure loading. Two different four-ply layup configurations were tested: (0/90)S and (+ or - 45)S; all tubes contained a 0.48-cm (3/16-in.) diameter circular hole penetrating one wall midway along the tube length. S-N curves were developed to characterize fatigue behavior under pure axial, torsional, or internal pressure loading, as well as combined loading fatigue. A theory was developed based on the Hill plane stress model which enabled the S-N curve for combined stress states to be predicted from the S-N data for the uniaxial loading modes. Correlation of the theory with the experimental data proved to be remarkably good.

Characterization of New PEEK/HA Composites with 3D HA Network Fabricated by Extrusion Freeforming.

PubMed

Vaezi, Mohammad; Black, Cameron; Gibbs, David M R; Oreffo, Richard O C; Brady, Mark; Moshrefi-Torbati, Mohamed; Yang, Shoufeng

2016-05-26

Addition of bioactive materials such as calcium phosphates or Bioglass, and incorporation of porosity into polyetheretherketone (PEEK) has been identified as an effective approach to improve bone-implant interfaces and osseointegration of PEEK-based devices. In this paper, a novel production technique based on the extrusion freeforming method is proposed that yields a bioactive PEEK/hydroxyapatite (PEEK/HA) composite with a unique configuration in which the bioactive phase (i.e., HA) distribution is computer-controlled within a PEEK matrix. The 100% interconnectivity of the HA network in the biocomposite confers an advantage over alternative forms of other microstructural configurations. Moreover, the technique can be employed to produce porous PEEK structures with controlled pore size and distribution, facilitating greater cellular infiltration and biological integration of PEEK composites within patient tissue. The results of unconfined, uniaxial compressive tests on these new PEEK/HA biocomposites with 40% HA under both static and cyclic mode were promising, showing the composites possess yield and compressive strength within the range of human cortical bone suitable for load bearing applications. In addition, preliminary evidence supporting initial biological safety of the new technique developed is demonstrated in this paper. Sufficient cell attachment, sustained viability in contact with the sample over a seven-day period, evidence of cell bridging and matrix deposition all confirmed excellent biocompatibility.

Fracture mode during cyclic loading of implant-supported single-tooth restorations.

PubMed

Hosseini, Mandana; Kleven, Erik; Gotfredsen, Klaus

2012-08-01

Fracture of veneering ceramics in zirconia-based restorations has frequently been reported. Investigation of the fracture mode of implant-supported ceramic restorations by using clinically relevant laboratory protocols is needed. This study compared the mode of fracture and number of cyclic loads until veneering fracture when ceramic and metal ceramic restorations with different veneering ceramics were supported by implants. Thirty-two implant-supported single-tooth restorations were fabricated. The test group was composed of 16 ceramic restorations of zirconia abutment-retained crowns with zirconia copings veneered with glass-ceramics (n=8) and feldspathic ceramics (n=8). The control group was composed of 16 metal ceramic restorations of titanium abutment-retained crowns with gold alloy copings veneered with glass (n=8) and feldspathic ceramics (n=8). The palatal surfaces of the crowns were exposed to cyclic loading of 800 N with a frequency of 2 Hz, which continued to 4.2 million cycles or until fracture of the copings, abutments, or implants. The number of cycles and the fracture modes were recorded. The fracture modes were analyzed by descriptive analysis and the Mann-Whitney test (α=.05). The differences in loading cycles until veneering fracture were estimated with the Cox proportional hazards analysis. Veneering fracture was the most frequently observed fracture mode. The severity of fractures was significantly more in ceramic restorations than in metal ceramic restorations. Significantly more loading cycles until veneering fracture were estimated with metal ceramic restorations veneered with glass-ceramics than with other restorations. The metal ceramic restorations demonstrated fewer and less severe fractures and resisted more cyclic loads than the ceramic restorations, particularly when the metal ceramic crowns were veneered with glass-ceramics. Copyright © 2012 The Editorial Council of the Journal of Prosthetic Dentistry. Published by Mosby, Inc. All rights reserved.

Fretting crevice corrosion of stainless steel stem-CoCr femoral head connections: comparisons of materials, initial moisture, and offset length.

PubMed

Gilbert, Jeremy L; Mehta, Manav; Pinder, Bryan

2009-01-01

Modular tapers continue to be used in a wide variety of orthopedic implants. In this study, stainless steel (ASTM F-1568) femoral hip stems combined with Co-Cr-Mo alloy heads (SS/CoCr) were tested in an in vitro fretting corrosion test set-up to assess the propensity for mechanically assisted corrosion. Three different aspects of the modular design were evaluated in this study: (1) material combination compared to CoCr/CoCr, (2) wet versus dry assembly for SS/CoCr couples, and (3) 0- and 6-mm head offset for SS/CoCr couples. Fretting corrosion tests over a range of cyclic loads up to 3300 N were performed, and continuous cyclic loading at 3300 N for 1 M cycles were performed on each group (n = 5). Fretting micromotion was measured as a function of cyclic load on select couples to detect the nature and extent of motion present. The results showed that SS/CoCr couples were more susceptible to fretting corrosion than CoCr/CoCr couples, that dry assembly does not prevent fretting corrosion from taking place but raises the onset load, and that 6-mm offset heads had higher visual evidence of fretting damage but showed mixed statistical results in terms of onset loads and OCP shifts and currents compared to the 0-mm offset samples. Current and voltage excursions over 1 million cycles tended to diminish towards their unloaded control levels but did not fully recover until cyclic loading ceased. Micromotion measurements indicated fretting motions in the range of 10-25 microm where 0-mm heads tended to piston on the trunion, while 6 mm heads tended to rock. (c) 2008 Wiley Periodicals, Inc.

Reverse Anterior Cruciate Ligament Reconstruction Fixation: A Biomechanical Comparison Study of Tibial Cross-Pin and Femoral Interference Screw Fixation.

PubMed

Lawley, Richard J; Klein, Samuel E; Chudik, Steven C

2017-03-01

To evaluate the biomechanical performance of tibial cross-pin (TCP) fixation relative to femoral cross-pin (FCP), femoral interference screw (FIS), and tibial interference screw (TIS) fixation. We randomized 40 porcine specimens (20 tibias and 20 femurs) to TIS fixation (group 1, n = 10), FIS fixation (group 2, n = 10), TCP fixation (group 3, n = 10), or FCP fixation (group 4, n = 10) and performed biomechanical testing to compare ultimate load, stiffness, yield load, cyclic displacement, and load at 5-mm displacement. We performed cross-pin fixation of the looped end and interference screw fixation of the free ends of 9-mm-diameter bovine extensor digitorum communis tendon grafts. Graft fixation constructs were cyclically loaded and then loaded to failure in line with the tunnels. Regarding yield load, FIS was superior to TIS (704 ± 125 N vs 504 ± 118 N, P = .002), TCP was superior to TIS (1,449 ± 265 N vs 504 ± 118 N, P < .001), and TCP was superior to FCP (1,449 ± 265 N vs 792 ± 397 N, P < .001). Cyclic displacement for FCP was superior to TCP. Cyclic displacement for TIS versus FIS showed no statistically significant difference (2.5 ± 1.0 mm vs 2.2 ± 0.6 mm, P = .298). Interference screw fixation consistently failed by graft slippage, whereas TCP fixation failed by tibial bone failure. FCP fixation failed by either femoral bone failure or failure elsewhere in the testing apparatus. Regarding yield load, TCP fixation performed biomechanically superior to the clinically proven FCP at time zero. Because TIS fixation shows the lowest yield strength, it represents the weak link, and combined TCP-FIS fixation theoretically would be biomechanically superior relative to combined FCP-TIS fixation with regard to yield load. Cyclic displacement showed a small difference in favor of FCP over TCP fixation and no difference between TIS and FIS. Time-zero biomechanics of TCP fixation paired with FIS fixation show that this method of fixation can be considered a potential alternative to current practice and may pose clinical benefits in different clinical scenarios of anterior cruciate ligament reconstruction. Copyright © 2016 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

[Expression of integrin alpha5 and actin in the cells of intervertebral disc under cyclic hydrostatic pressure in vitro].

PubMed

Yu, Sheng-ji; Qiu, Gui-xing; Burton, Yang; Sandra, Roth; Cari, Whyne; Albert, Yee

2005-12-15

To investigate the expression of integrin alpha5 and actin in the cells of intervertebral disc under cyclic hydrostatic pressure in vitro. The porcine lumbar intervertebral disc cells were isolated and cultured in vitro, and the cells underwent cyclic hydrostatic loading. After that, the expression of integrin alpha5 and actin in intervertebral disc cells were studied by means of morphology observing, Western blot and immunohistochemistry staining. The morphology of intervertebral disc cells were changed into smaller and flatten shape, and the expression of integrin alpha5 and actin were decreased after loading. The expression of integrin alpha5 decreases under cyclic hydrostatic pressure, and the actin is affected at the same time when signals are transferred into the cells by integrin alpha5. That may be one of the important mechanisms of the mechanotransduction in the cells of intervertebral disc.

Fatigue Lifetime of Ceramic Matrix Composites at Intermediate Temperature by Acoustic Emission

PubMed Central

Racle, Elie; Godin, Nathalie; Reynaud, Pascal; Fantozzi, Gilbert

2017-01-01

The fatigue behavior of a Ceramic Matrix Composite (CMC) at intermediate temperature under air is investigated. Because of the low density and the high tensile strength of CMC, they offer a good technical solution to design aeronautical structural components. The aim of the present study is to compare the behavior of this composite under static and cyclic loading. Comparison between incremental static and cyclic tests shows that cyclic loading with an amplitude higher than 30% of the ultimate tensile strength has significant effects on damage and material lifetimes. In order to evaluate the remaining lifetime, several damage indicators, mainly based on the investigation of the liberated energy, are introduced. These indicators highlight critical times or characteristic times, allowing an evaluation of the remaining lifetime. A link is established with the characteristic time around 25% of the total test duration and the beginning of the matrix cracking during cyclic fatigue. PMID:28773019

A Novel Repair Method for Radial Tears of the Medial Meniscus: Biomechanical Comparison of Transtibial 2-Tunnel and Double Horizontal Mattress Suture Techniques Under Cyclic Loading.

PubMed

Bhatia, Sanjeev; Civitarese, David M; Turnbull, Travis Lee; LaPrade, Christopher M; Nitri, Marco; Wijdicks, Coen A; LaPrade, Robert F

2016-03-01

Complete radial tears of the medial meniscus have been reported to be functionally similar to a total meniscectomy. At present, there is no consensus on an ideal technique for repair of radial midbody tears of the medial meniscus. Prior attempts at repair with double horizontal mattress suture techniques have led to a reportedly high rate of incomplete healing or healing in a nonanatomic (gapped) position, which compromises the ability of the meniscus to withstand hoop stresses. A newly proposed 2-tunnel radial meniscal repair method will result in decreased gapping and increased ultimate failure loads compared with the double horizontal mattress suture repair technique under cyclic loading. Controlled laboratory study. Ten matched pairs of male human cadaveric knees (average age, 58.6 years; range, 48-66 years) were used. A complete radial medial meniscal tear was made at the junction of the posterior one-third and middle third of the meniscus. One knee underwent a horizontal mattress inside-out repair, while the contralateral knee underwent a radial meniscal repair entailing the same technique with a concurrent novel 2-tunnel repair. Specimens were potted and mounted on a universal testing machine. Each specimen was cyclically loaded 1000 times with loads between 5 and 20 N before experiencing a load to failure. Gap distances at the tear site and failure load were measured. The 2-tunnel repairs exhibited a significantly stronger ultimate failure load (median, 196 N; range, 163-212 N) than did the double horizontal mattress suture repairs (median, 106 N; range, 63-229 N) (P = .004). In addition, the 2-tunnel repairs demonstrated decreased gapping at all testing states (P < .05) with a final measured gapping of 1.7 mm and 4.1 mm after 1000 cycles for the 2-tunnel and double horizontal mattress suture repairs, respectively. The 2-tunnel repairs displayed significantly less gapping distance after cyclic loading and had significantly stronger ultimate failure loads compared with the double horizontal mattress suture repairs. Complete radial tears of the medial meniscus significantly decrease the ability of the meniscus to dissipate tibiofemoral loads, predisposing patients to early osteoarthritis. Improving the ability to repair medial meniscal radial tears in a way that withstands cyclic loads and heals in an anatomic position could significantly improve patient healing rates and result in improved preservation of the articular cartilage of the medial compartment of the knee. The 2-tunnel repair may be a more reliable and stronger repair option for midbody radial tears of the medial meniscus. Clinical studies are warranted to further evaluate these repairs. © 2015 The Author(s).

Ratcheting Strain and Microstructure Evolution of AZ31B Magnesium Alloy under a Tensile-Tensile Cyclic Loading

PubMed Central

Wang, Denghui; Wang, Wenxian; Zhou, Jun; He, Xiuli; Dong, Peng; Zhang, Hongxia; Sun, Liyong

2018-01-01

In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material’s fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11−20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11−20} tensile twins. PMID:29597278

Analytical and experimental investigation of aircraft metal structures reinforced with filamentary composites. Phase 2: Structural fatigue, thermal cycling, creep, and residual strength

NASA Technical Reports Server (NTRS)

Blichfeldt, B.; Mccarty, J. E.

1972-01-01

Specimens representative of metal aircraft structural components reinforced with boron filamentary composites were manufactured and tested under cyclic loading, cyclic temperature, or continuously applied loading to evaluate some of the factors that affect structural integrity under cyclic conditions. Bonded, stepped joints were used throughout to provide composite-to-metal transition regions at load introduction points. Honeycomb panels with titanium or aluminum faces reinforced with unidirectional boron composite were fatigue tested at constant amplitude under completely reversed loading. Results indicated that the matrix material was the most fatigue-sensitive part of the design, with debonding initiating in the stepped joints. However, comparisons with equal weight all-metal specimens show a 10 to 50 times improved fatigue life. Fatigue crack propagation and residual strength were studied for several different stiffened panel concepts, and were found to vary considerably depending on the configuration. Composite-reinforced metal specimens were also subjected to creep and thermal cycling tests. Thermal cycling of stepped joint tensile specimens resulted in a ten percent decrease in residual strength after 4000 cycles.

Fatigue of the Resin-Enamel Bonded Interface and the Mechanisms of Failure

PubMed Central

Yahyazadehfar, Mobin; Mutluay, Mustafa Murat; Majd, Hessam; Ryou, Heonjune; Arola, Dwayne

2013-01-01

The durability of adhesive bonds to enamel and dentin and the mechanisms of degradation caused by cyclic loading are important to the survival of composite restorations. In this study a novel method of evaluation was used to determine the strength of resin-enamel bonded interfaces under both static and cyclic loading, and to identify the mechanisms of failure. Specimens with twin interfaces of enamel bonded to commercial resin composite were loaded in monotonic and cyclic 4-point flexure to failure within a hydrated environment. Results for the resin-enamel interface were compared with those for the resin composite (control) and values reported for resin-dentin adhesive bonds. Under both modes of loading the strength of the resin-enamel interface was significantly (p≤0.0001) lower than that of the resin composite and the resin-dentin bonded interface. Fatigue failure of the interface occurred predominately by fracture of enamel, adjacent to the interface, and not due to adhesive failures. In the absence of water aging or acid production of biofilms, the durability of adhesive bonds to enamel is lower than that achieved in dentin bonding. PMID:23571321

Ratcheting Strain and Microstructure Evolution of AZ31B Magnesium Alloy under a Tensile-Tensile Cyclic Loading.

PubMed

Yan, Zhifeng; Wang, Denghui; Wang, Wenxian; Zhou, Jun; He, Xiuli; Dong, Peng; Zhang, Hongxia; Sun, Liyong

2018-03-28

In this paper, studies were conducted to investigate the deformation behavior and microstructure change in a hot-rolled AZ31B magnesium alloy during a tensile-tensile cyclic loading. The relationship between ratcheting effect and microstructure change was discussed. The ratcheting effect in the material during current tensile-tensile fatigue loading exceeds the material's fatigue limit and the development of ratcheting strain in the material experienced three stages: initial sharp increase stage (Stage I); steady stage (Stage II); and final abrupt increase stage (Stage III). Microstructure changes in Stage I and Stage II are mainly caused by activation of basal slip system. The Extra Geometrically Necessary Dislocations (GNDs) were also calculated to discuss the relationship between the dislocation caused by the basal slip system and the ratcheting strain during the cyclic loading. In Stage III, both the basal slip and the {11-20} twins are found active during the crack propagation. The fatigue crack initiation in the AZ31B magnesium alloy is found due to the basal slip and the {11-20} tensile twins.

Proper Generalized Decomposition (PGD) for the numerical simulation of polycrystalline aggregates under cyclic loading

NASA Astrophysics Data System (ADS)

Nasri, Mohamed Aziz; Robert, Camille; Ammar, Amine; El Arem, Saber; Morel, Franck

2018-02-01

The numerical modelling of the behaviour of materials at the microstructural scale has been greatly developed over the last two decades. Unfortunately, conventional resolution methods cannot simulate polycrystalline aggregates beyond tens of loading cycles, and they do not remain quantitative due to the plasticity behaviour. This work presents the development of a numerical solver for the resolution of the Finite Element modelling of polycrystalline aggregates subjected to cyclic mechanical loading. The method is based on two concepts. The first one consists in maintaining a constant stiffness matrix. The second uses a time/space model reduction method. In order to analyse the applicability and the performance of the use of a space-time separated representation, the simulations are carried out on a three-dimensional polycrystalline aggregate under cyclic loading. Different numbers of elements per grain and two time increments per cycle are investigated. The results show a significant CPU time saving while maintaining good precision. Moreover, increasing the number of elements and the number of time increments per cycle, the model reduction method is faster than the standard solver.

Computational Modeling of Sinkage of Objects into Porous Bed under Cyclic Loading

NASA Astrophysics Data System (ADS)

Sheikh, B.; Qiu, T.; Liu, X.

2017-12-01

This work is a companion of another abstract submitted to this session on the computational modeling for the prediction of underwater munitions. In the other abstract, the focus is the hydrodynamics and sediment transport. In this work, the focus is on the geotechnical aspect and granular material behavior when the munitions interact with the porous bed. The final goal of the project is to create and utilize a comprehensive modeling framework, which integrates the flow and granular material models, to simulate and investigate the motion of the munitions. In this work, we present the computational modeling of one important process: the sinkage of rigid-body objects into porous bed under cyclic loading. To model the large deformation of granular bed materials around sinking objects under cyclic loading, a rate-independent elasto-plastic constitutive model is implemented into a Smoothed Particle Hydrodynamics (SPH) model. The effect of loading conditions (e.g., amplitude and frequency of shaking), object properties (e.g., geometry and density), and granular bed material properties (e.g., density) on object singkage is discussed.

Prediction and verification of creep behavior in metallic materials and components, for the space shuttle thermal protection system. Volume 1, phase 1: Cyclic materials creep predictions

NASA Technical Reports Server (NTRS)

Davis, J. W.; Cramer, B. A.

1974-01-01

Cyclic creep response was investigated and design methods applicable to thermal protection system structures were developed. The steady-state (constant temperature and load) and cyclic creep response characteristics of four alloys were studied. Steady-state creep data were gathered through a literature survey to establish reference data bases. These data bases were used to develop empirical equations describing creep as a function of time, temperature, and stress and as a basis of comparison for test data. Steady-state creep tests and tensile cyclic tests were conducted. The following factors were investigated: material thickness and rolling direction; material cyclic creep response under varying loads and temperatures; constant stress and temperature cycles representing flight conditions; changing stresses present in a creeping beam as a result of stress redistribution; and complex stress and temperature profiles representative of space shuttle orbiter trajectories. A computer program was written, applying creep hardening theories and empirical equations for creep, to aid in analysis of test data. Results are considered applicable to a variety of structures which are cyclicly exposed to creep producing thermal environments.

Off-Axis Ratcheting Behavior of Unidirectional Carbon/Epoxy Laminate under Asymmetric Cyclic Loading at High Temperature

DTIC Science & Technology

2011-11-01

ply unidirectional carbon/epoxy laminates [0]12 were fabricated from the prepreg tape of P3252-20 (TORAY). They were laid up by hand and cured in...Off-Axis Ratcheting Behavior of Unidirectional Carbon/Epoxy Laminate under Asymmetric Cyclic Loading at High Temperature Takafumi Suzuki 1 and...Development of an engineering model for predicting the off-axis ratcheting behavior of a unidirectional CFRP laminate has been attempted. For this purpose

Compressive Failure of Fiber Composites under Multi-Axial Loading

NASA Technical Reports Server (NTRS)

Basu, Shiladitya; Waas, Anthony M.; Ambur, Damodar R.

2006-01-01

This paper examines the compressive strength of a fiber reinforced lamina under multi-axial stress states. An equilibrium analysis is carried out in which a kinked band of rotated fibers, described by two angles, is sandwiched between two regions in which the fibers are nominally straight. Proportional multi-axial stress states are examined. The analysis includes the possibility of bifurcation from the current equilibrium state. The compressive strength of the lamina is contingent upon either attaining a load maximum in the equilibrium response or satisfaction of a bifurcation condition, whichever occurs first. The results show that for uniaxial loading a non-zero kink band angle beta produces the minimum limit load. For multi-axial loading, different proportional loading paths show regimes of bifurcation dominated and limit load dominated behavior. The present results are able to capture the beneficial effect of transverse compression in raising the composite compressive strength as observed in experiments.

Transitions from trees to cycles in adaptive flow networks

NASA Astrophysics Data System (ADS)

Martens, Erik A.; Klemm, Konstantin

2017-11-01

Transport networks are crucial to the functioning of natural and technological systems. Nature features transport networks that are adaptive over a vast range of parameters, thus providing an impressive level of robustness in supply. Theoretical and experimental studies have found that real-world transport networks exhibit both tree-like motifs and cycles. When the network is subject to load fluctuations, the presence of cyclic motifs may help to reduce flow fluctuations and, thus, render supply in the network more robust. While previous studies considered network topology via optimization principles, here, we take a dynamical systems approach and study a simple model of a flow network with dynamically adapting weights (conductances). We assume a spatially non-uniform distribution of rapidly fluctuating loads in the sinks and investigate what network configurations are dynamically stable. The network converges to a spatially non-uniform stable configuration composed of both cyclic and tree-like structures. Cyclic structures emerge locally in a transcritical bifurcation as the amplitude of the load fluctuations is increased. The resulting adaptive dynamics thus partitions the network into two distinct regions with cyclic and tree-like structures. The location of the boundary between these two regions is determined by the amplitude of the fluctuations. These findings may explain why natural transport networks display cyclic structures in the micro-vascular regions near terminal nodes, but tree-like features in the regions with larger veins.

Observation of Failure and Domain Switching in Lead Zirconate Titanate Ceramics

NASA Astrophysics Data System (ADS)

Okayasu, Mitsuhiro; Sugiyama, Eriko; Sato, Kazuto; Mizuno, Mamoru

The mechanical and electrical properties (electromechanical coupling coefficient, piezoelectric constant and dielectric constant) of lead zirconate titanate (PZT) ceramics are investigated during mechanical static and cyclic loading. There are several failure characteristics which can alter the material properties of PZT ceramics. The elastic constant increases and electrical properties decrease with increasing the applied load. This is due to the internal strain arising from the domain switching. In this case, 90° domain switching occurs anywhere in the samples as the sample is loaded. It is also apparent that electrogenesis occurs several times during cyclic loading to the final fracture. This occurrence is related to the domain switching. The elastic constant and electrical properties can decrease because of crack generation in the PZT ceramics. Moreover, the elastic constant increases with increase of the mechanical load and decreases with decrease of the load. On the contrary, the opposite sense of change of the electrical properties is observed.

Training and shape retention in conducting polymer artificial muscles

NASA Astrophysics Data System (ADS)

Tominaga, Kazuo; Hashimoto, Hikaru; Takashima, Wataru; Kaneto, Keiichi

2011-12-01

Electrochemomechanical deformation (ECMD) of the conducting polymer polyaniline film is studied to investigate the behaviour of actuation under tensile loads. The ECMD was induced by the strains due to the insertion of ionic species (cyclic strain) and a creep due to applied loads during the redox cycle. The cyclic strain was enhanced by the experience of high tensile loads, indicating a training effect. The training effect was explained by the enhanced electrochemical activity of the film. The creep was recovered by removal of the tensile load and several electrochemical cycles. This fact indicates that the creep results from the one-dimensional anisotropic deformation, and is retained (shape retention) by the ionic crosslink. The recovery of creep results from the elastic relaxation of the polymer conformation.

Cyclic crack growth behavior of reactor pressure vessel steels in light water reactor environments

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

Van Der Sluys, W.A.; Emanuelson, R.H.

1986-01-01

During normal operation light water reactor (LWR) pressure vessels are subjected to a variety of transients resulting in time varying stresses. Consequently, fatigue and environmentally assisted fatigue are growth mechanisms relevant to flaws in these pressure vessels. In order to provide a better understanding of the resistance of nuclear pressure vessel steels to flaw growth process, a series of fracture mechanics experiments were conducted to generate data on the rate of cyclic crack growth in SA508-2 and SA533b-1 steels in simulated 550/sup 0/F boiling water reactor (BWR) and 550/sup 0/F pressurized water reactor (PWR) environments. Areas investigated over the coursemore » of the test program included the effects of loading frequency and r ratio (Kmin-Kmax) on crack growth rate as a function of the stress intensity factor (deltaK) range. In addition, the effect of sulfur content of the test material on the cyclic crack growth rate was studied. Cyclic crack growth rates were found to be controlled by deltaK, R ratio, and loading frequency. The sulfur impurity content of the reactor pressure vessel steels studied had a significant effect on the cyclic crack growth rates. The higher growth rates were always associated with materials of higher sulfur content. For a given level of sulfur, growth rates were in a 550/sup 0/F simulated BWR environment than in a 550/sup 0/F simulated PWR environment. In both environments cyclic crack growth rates were a strong function of the loading frequency.« less

Cyclic compression maintains viability and induces chondrogenesis of human mesenchymal stem cells in fibrin gel scaffolds.

PubMed

Pelaez, Daniel; Huang, Chun-Yuh Charles; Cheung, Herman S

2009-01-01

Mechanical loading has long been shown to modulate cartilage-specific extracellular matrix synthesis. With joint motion, cartilage can experience mechanical loading in the form of compressive, tensile or shearing load, and hydrostatic pressure. Recent studies have demonstrated the capacity of unconfined cyclic compression to induce chondrogenic differentiation of human mesenchymal stem cell (hMSC) in agarose culture. However, the use of a nonbiodegradable material such as agarose limits the applicability of these constructs. Of the possible biocompatible materials available for tissue engineering, fibrin is a natural regenerative scaffold, which possesses several desired characteristics including a controllable degradation rate and low immunogenicity. The objective of the present study was to determine the capability of fibrin gels for supporting chondrogenesis of hMSCs under cyclic compression. To optimize the system, three concentrations of fibrin gel (40, 60, and 80 mg/mL) and three different stimulus frequencies (0.1, 0.5, and 1.0 Hz) were used to examine the effects of cyclic compression on viability, proliferation and chondrogenic differentiation of hMSCs. Our results show that cyclic compression (10% strain) at frequencies >0.5 Hz and gel concentration of 40 mg/mL fibrinogen appears to maintain cellular viability within scaffolds. Similarly, variations in gel component concentration and stimulus frequency can be modified such that a significant chondrogenic response can be achieved by hMSC in fibrin constructs after 8 h of compression spread out over 2 days. This study demonstrates the suitability of fibrin gel for supporting the cyclic compression-induced chondrogenesis of mesenchymal stem cells.

Impact tests on fibrous composite sandwich structures

NASA Technical Reports Server (NTRS)

Rhodes, M. D.

1978-01-01

The effect of low velocity impact on the strength of laminates fabricated from graphite/epoxy and Kevlar 49/epoxy composite materials was studied. The test laminates were loaded statically either in uniaxial tension or compression when impact occurred to evaluate the effect of loading on the initiation of damage and/or failure. Typical aircraft service conditions such as runway debris encountered during landing were simulated by impacting 1.27-cm-diameter projectiles normal to the plane of the test laminates at velocities between 5.2 and 48.8 m/s.

Investigation on local ductility of 6xxx-aluminium sheet alloys

NASA Astrophysics Data System (ADS)

Henn, P.; Liewald, M.; Sindel, M.

2017-09-01

Within the scope of this paper influence of localization of loading conditions on the ductility of two different 6xxx-aluminium sheet alloys is investigated. In order to improve the prediction of sheet material crash performance, material parameters based on uniaxial tensile and notched tensile tests are determined with varying consolidation areas. Especially evaluation methods based on the localized necking behaviour in tensile tests are investigated. The potential of local ductility characterisation is validated with results of Edge-Compression Tests (ECT) which applies load conditions that occur in actual crash events.

Tendon Contraction After Cyclic Elongation Is an Age-Dependent Phenomenon: In Vitro and In Vivo Comparisons.

PubMed

Lavagnino, Michael; Bedi, Asheesh; Walsh, Christopher P; Sibilsky Enselman, Elizabeth R; Sheibani-Rad, Shahin; Arnoczky, Steven P

2014-06-01

Tendons are viscoelastic tissues that deform (elongate) in response to cyclic loading. However, the ability of a tendon to recover this elongation is unknown. Tendon length significantly increases after in vivo or in vitro cyclic loading, and the ability to return to its original length through a cell-mediated contraction mechanism is an age-dependent phenomenon. Controlled laboratory study. In vitro, rat tail tendon fascicles (RTTfs) from Sprague-Dawley rats of 3 age groups (1, 3, and 12 months) underwent 2% cyclic strain at 0.17 Hz for 2 hours, and the percentages of elongation were determined. After loading, the RTTfs were suspended for 3 days under tissue culture conditions and photographed daily to determine the amount of length contraction. In vivo, healthy male participants (n = 29; age, 19-49 years) had lateral, single-legged weightbearing radiographs taken of the knee at 60° of flexion immediately before, immediately after, and 24 hours after completing eccentric quadriceps loading exercises on the dominant leg to fatigue. Measurements of patellar tendon length were taken from the radiographs, and the percentages of tendon elongation and subsequent contraction were calculated. In vitro, cyclic loading increased the length of all RTTfs, with specimens from younger (1 and 3 months) rats demonstrating significantly greater elongation than those from older (12 months) rats (P = .009). The RTTfs contracted to their original length significantly faster (P < .001) and in an age-dependent fashion, with younger animals contracting faster. In vivo, repetitive eccentric loading exercises significantly increased patellar tendon length (P < .001). Patellar tendon length decreased 24 hours after exercises (P < .001) but did not recover completely (P < .001). There was a weak but significant (R (2) = 0.203, P = .014) linear correlation between the amount of tendon contraction and age, with younger participants (<30 years) demonstrating significantly more contraction (P = .014) at 24 hours than older participants (>30 years). Cyclic tendon loading results in a significant increase in tendon elongation under both in vitro and in vivo conditions. Tendons in both conditions demonstrated an incomplete return to their original length after 24 hours, and the extent of this return was age dependent. The age- and time-dependent contraction of tendons, elongated after repetitive loading, could result in transient alterations in the mechanobiological environment of tendon cells. This, in turn, could induce the onset of catabolic changes associated with the pathogenesis of tendinopathy. These results suggest the importance of allowing time for contraction between bouts of repetitive exercise and may explain why age is a predisposing factor in tendinopathy. © 2014 The Author(s).

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

Monitoring of Failure Mechanisms in a Composite Bending Actuator during Cyclic Loading by Acoustic Emission

NASA Astrophysics Data System (ADS)

Woo, Sung-Choong; Goo, Nam Seo

The objective of this work is to investigate the influence of electromechanical cyclic loading on the performance of a bending piezoelectric composite actuator. We have analyzed the fatigue damage mechanisms in terms of the behavior of the AE event rate. It was found that whether the actuators are subjected to purely electric loading or electromechanical loading, the initial fatigue damage of the bending piezoelectric composite actuator was caused by the transgranular fracture in the PZT ceramic layer; the final failure was caused only in the case of PCAWB under electromechanical loading by a local discharge, which critically affected the performance reduction of the actuators. As the number of cycles increased, a large reduction in displacement performance coincided with a high AE event rate, which was identified via microscopic observations.

Does Abutment Collar Length Affect Abutment Screw Loosening After Cyclic Loading?

PubMed

Siadat, Hakimeh; Pirmoazen, Salma; Beyabanaki, Elaheh; Alikhasi, Marzieh

2015-07-01

A significant vertical space that is corrected with vertical ridge augmentation may necessitate selection of longer abutments, which would lead to an increased vertical cantilever. This study investigated the influence of different abutment collar heights on single-unit dental implant screw-loosening after cyclic loading. Fifteen implant-abutment assemblies each consisted of an internal hexagonal implant were randomly assigned to 3 groups: Group1, consisting of 5 abutments with 1.5 mm gingival height (GH); Group2, 5 abutments with 3.5 mm GH; and Group3, 5 abutments with 5.5 mm GH. Each specimen was mounted in transparent auto-polymerizing acrylic resin block, and the abutment screw was tightened to 35 Ncm with an electric torque wrench. After 5 minutes, initial torque loss (ITL) was recorded for all specimens. Metal crowns were fabricated with 45° occlusal surface and were placed on the abutments. A cyclic load of 75 N and frequency of 1 Hz were applied perpendicular to the long axis of each specimen. After 500 000 cycles, secondary torque loss (STL) was recorded. One-way ANOVA analysis was used to evaluate the effects of abutment collar height before and after cyclic loading. One-way ANOVA showed that ITL among the groups was not significantly different (P = .52), while STL was significantly different among the groups (P = .008). Post-hoc Tukey HSD tests showed that STL values were significantly different between the abutments with 1.5 mm GH (Group1) and with 5.5 mm GH (Group3) (P = .007). A paired comparison t-test showed that cyclic loading significantly influenced the STL in comparison with the ITL in each group. Within the limitations of this study, it can be concluded that increase in height of the abutment collar could adversely affect the torque loss of the abutment screw.

Comparison of cyclic and impact-based reference point indentation measurements in human cadaveric tibia.

PubMed

Karim, Lamya; Van Vliet, Miranda; Bouxsein, Mary L

2018-01-01

Although low bone mineral density (BMD) is strongly associated with increased fracture risk, up to 50% of those who suffer fractures are not detected as high-risk patients by BMD testing. Thus, new approaches may improve identification of those at increased risk for fracture by in vivo assessment of altered bone tissue properties, which may contribute to skeletal fragility. Recently developed reference point indentation (RPI) allows for assessment of cortical bone indentation properties in vivo using devices that apply cyclic loading or impact loading, but there is little information available to assist with interpretation of RPI measurements. Our goals were to use human cadaveric tibia to determine: 1) the associations between RPI variables, cortical bone density, and morphology; 2) the association between variables obtained from RPI systems using cyclic, slow loading versus a single impact load; and 3) age-related differences in RPI variables. We obtained 20 human tibia and femur pairs from female donors (53-97years), measured total hip BMD using dual-energy X-ray absorptiometry, assessed tibial cortical microarchitecture using high-resolution peripheral quantitative computed tomography (HR-pQCT), and assessed cortical bone indentation properties at the mid-tibial diaphysis using both the cyclic and impact-based RPI systems (Biodent and Osteoprobe, respectively, Active Life Scientific, Santa Barbara, CA). We found a few weak associations between RPI variables, BMD, and cortical geometry; a few weak associations between measurements obtained by the two RPI systems; and no age-related differences in RPI variables. Our findings indicate that in cadaveric tibia from older women RPI measurements are largely independent of age, femoral BMD, and cortical geometry. Furthermore, measurements from the cyclic and impact loading RPI devices are weakly related to each other, indicating that each device reflects different aspects of cortical bone indentation properties. Copyright © 2016. Published by Elsevier Inc.

The effect of cyclic feathering motions on dynamic rotor loads. [for helicopters

NASA Technical Reports Server (NTRS)

Harvey, K. W.

1974-01-01

The dynamic loads of a helicopter rotor in forward flight are influenced significantly by the geometric pitch angles between the structural axes of the hub and blade sections and the plane of rotation. The analytical study presented includes elastic coupling between inplane and out-of-plane deflections as a function of geometric pitch between the plane of rotation and the principal axes of inertia of each blade. The numerical evaluation is based on a transient analysis using lumped masses and elastic substructure techniques. A comparison of cases with and without cyclic feathering motion shows the effect on computed dynamic rotor loads.

Accelerated testing of composites

NASA Technical Reports Server (NTRS)

Papazian, H. A.

1983-01-01

It is shown that the Zhurkov method for testing the strength of solids can be applied to dynamic tension and to cyclic loading and provides a viable approach to accelerated testing of composites. Data from the literature are used to demonstrate a straightforward application of the method to dynamic tension of glass fiber and cyclic loading for glass/polymer, metal matrix, and graphite/epoxy composites. Zhurkov's equation can be used at relatively high loads to obtain failure times at any temperature of interest. By taking a few data points at one or two other temperatures the spectrum of failure times can be expanded to temperatures not easily accessible.

Strength of SiCf-SiCm composite tube under uniaxial and multiaxial loading

NASA Astrophysics Data System (ADS)

Shapovalov, Kirill; Jacobsen, George M.; Alva, Luis; Truesdale, Nathaniel; Deck, Christian P.; Huang, Xinyu

2018-03-01

The authors report mechanical strength of nuclear grade silicon carbide fiber reinforced silicon carbide matrix composite (SiCf-SiCm) tubing under several different stress states. The composite tubing was fabricated via a Chemical Vapor Infiltration (CVI) process, and is being evaluated for accident tolerant nuclear fuel cladding. Several experimental techniques were applied including uniaxial tension, elastomer insert burst test, open and closed end hydraulic bladder burst test, and torsion test. These tests provided critical stress and strain values at proportional limit and at ultimate failure points. Full field strain measurements using digital image correlation (DIC) were obtained in order to acquire quantitative information on localized deformation during application of stress. Based on the test results, a failure map was constructed for the SiCf-SiCm composites.

Cyclic strain alters the expression and release of angiogenic factors by human tendon cells.

PubMed

Mousavizadeh, Rouhollah; Khosravi, Shahram; Behzad, Hayedeh; McCormack, Robert G; Duronio, Vincent; Scott, Alex

2014-01-01

Angiogenesis is associated with the tissue changes underlying chronic overuse tendinopathy. We hypothesized that repetitive, cyclic loading of human tendon cells would lead to increased expression and activity of angiogenic factors. We subjected isolated human tendon cells to overuse tensile loading using an in vitro model (1 Hz, 10% equibiaxial strain). We found that mechanically stimulated human tendon cells released factors that promoted in vitro proliferation and tube formation by human umbilical vein endothelial cells (HUVEC). In response to cyclic strain, there was a transient increase in the expression of several angiogenic genes including ANGPTL4, FGF-2, COX-2, SPHK1, TGF-alpha, VEGF-A and VEGF-C, with no change in anti-angiogenic genes (BAI1, SERPINF1, THBS1 and 2, TIMP1-3). Cyclic strain also resulted in the extracellular release of ANGPTL4 protein by tendon cells. Our study is the first report demonstrating the induction of ANGPTL4 mRNA and release of ANGPTL4 protein in response to cyclic strain. Tenocytes may contribute to the upregulation of angiogenesis during the development of overuse tendinopathy.

Cyclic Strain Alters the Expression and Release of Angiogenic Factors by Human Tendon Cells

PubMed Central

Mousavizadeh, Rouhollah; Khosravi, Shahram; Behzad, Hayedeh; McCormack, Robert G.; Duronio, Vincent; Scott, Alex

2014-01-01

Angiogenesis is associated with the tissue changes underlying chronic overuse tendinopathy. We hypothesized that repetitive, cyclic loading of human tendon cells would lead to increased expression and activity of angiogenic factors. We subjected isolated human tendon cells to overuse tensile loading using an in vitro model (1 Hz, 10% equibiaxial strain). We found that mechanically stimulated human tendon cells released factors that promoted in vitro proliferation and tube formation by human umbilical vein endothelial cells (HUVEC). In response to cyclic strain, there was a transient increase in the expression of several angiogenic genes including ANGPTL4, FGF-2, COX-2, SPHK1, TGF-alpha, VEGF-A and VEGF-C, with no change in anti-angiogenic genes (BAI1, SERPINF1, THBS1 and 2, TIMP1-3). Cyclic strain also resulted in the extracellular release of ANGPTL4 protein by tendon cells. Our study is the first report demonstrating the induction of ANGPTL4 mRNA and release of ANGPTL4 protein in response to cyclic strain. Tenocytes may contribute to the upregulation of angiogenesis during the development of overuse tendinopathy. PMID:24824595

Hygrothermomechanical evaluation of transverse filament tape epoxy/polyester fiberglass composites

NASA Technical Reports Server (NTRS)

Lark, R. L.; Chamis, C. C.

1983-01-01

The static and cyclic load behavior of transverse filament tape (TFT) fiberglass/epoxy and TFY fiberglass/polyester composites, intended for use in the design of low-cost wind turbine blades, are presented. The data behavior is also evaluated with respect to predicted properties based on an integrated hygrothermomechanical response theory. Experimental TFT composite data were developed by the testing of laminates made by using composite layups typical of those used for the fabrication of TFT fiberglass wind turbine blades. Static properties include tension, compression, and interlaminar shear strengths at ambient conditions and at high humidity/elevated temperature conditions after a 500 hour exposure. Cyclic fatigue data were obtained using similar environmental conditions and a range of cyclic stresses. The environmental (temperature and moisture) and cyclic load effects on composite strength degradation are subsequently compared with the predictions obtained by using the composite life/durability theory. The results obtained show that the predicted hygrothermomechanical environmental effects on TFT composites are in good agreement with measured data for various properties including fatigue at different cyclic stresses.

Creep-Fatigue Interaction and Cyclic Strain Analysis in P92 Steel Based on Test

NASA Astrophysics Data System (ADS)

Ji, Dongmei; Zhang, Lai-Chang; Ren, Jianxing; Wang, Dexian

2015-04-01

This work focused on the interaction of creep and fatigue and cyclic strain analysis in high-chromium ferritic P92 steel based on load-controlled creep-fatigue (CF) tests and conventional creep test at 873 K. Mechanical testing shows that the cyclic load inhibits the propagation of creep damage in the P92 steel and CF interaction becomes more severe with the decrease in the holding period duration and stress ratio. These results are also verified by the analysis of cyclic strain. The fatigue lifetime reduces with the increasing of the holding period duration and it does not reduce much with the increasing stress ratio especially under the conditions of long holding period duration. The cyclic strains (i.e., the strain range and creep strain) of CF tests consist of three stages, which is the same as those for the conventional creep behavior. The microscopic fracture surface observations illustrated that two different kinds of voids are observed at the fracture surfaces and Laves phase precipitates at the bottom of the voids.

Cyclic Fatigue of Brittle Materials with an Indentation-Induced Flaw System

NASA Technical Reports Server (NTRS)

Choi, Sung R.; Salem, Jonathan A.

1996-01-01

The ratio of static to cyclic fatigue life, or 'h ratio', was obtained numerically for an indentation flaw system subjected to sinusoidal loading conditions. Emphasis was placed on developing a simple, quick lifetime prediction tool. The solution for the h ratio was compared with experimental static and cyclic fatigue data obtained from as-indented 96 wt.% alumina specimens tested in room-temperature distilled water.

Evaluating the damage of steel 09G2S under static and cyclic loading with regard for the level of residual stresses in the metal

NASA Astrophysics Data System (ADS)

Kuznetsov, A. V.; Kamantsev, I. S.; Zadvorkin, S. M.; Drukarenko, N. A.; Goruleva, L. S.; Veselova, V. E.

2017-12-01

An approach to the estimation of the residual durability of structural elements in view of their initial stress-strain state is proposed. The adequacy of the developed approach is confirmed by experiments on cyclic loading of specimens without pronounced stress concentrators simulating the work of real structural elements under conditions of overshooting the total stresses causing local plastic deformation of the material, with regard for residual stresses.

Addition of a suture anchor for coracoclavicular fixation to a superior locking plate improves stability of type IIB distal clavicle fractures.

PubMed

Madsen, Wes; Yaseen, Zaneb; LaFrance, Russell; Chen, Tony; Awad, Hani; Maloney, Michael; Voloshin, Ilya

2013-06-01

The purpose of this study was to determine the effect of coracoclavicular (CC) fixation on biomechanical stability in type IIB distal clavicle fractures fixed with plate and screws. Twelve fresh-frozen matched cadaveric specimens were used to create type IIB distal clavicle fractures. Dual-energy x-ray absorptiometry (DEXA) scans ensured similar bone quality. Group 1 (6 specimens) was stabilized with a superior precontoured distal clavicle locking plate and supplemental suture anchor CC fixation. Group 2 (6 specimens) followed the same construct without CC fixation. Each specimen was cyclically loaded in the coronal plane at 40 to 80 N for 17,500 cycles. Load-to-failure testing was performed on the specimens that did not fail cyclic loading. Outcome measures included mode of failure and the number of cycles or load required to create 10 mm of displacement in the construct. All specimens (12 of 12) completed cyclic testing without failure and underwent load-to-failure testing. Group 1 specimens failed at a mean of 808.5 N (range, 635.4 to 952.3 N), whereas group 2 specimens failed at a mean of 401.3 N (range, 283.6 to 656.0 N) (P = .005). Group 1 specimens failed by anchor pullout without coracoid fracture (4 of 6) and distal clavicle fracture fragment fragmentation (1 of 6); one specimen did not fail at the maximal load the materials testing machine was capable of exerting (1,000 N). Group 2 specimens failed by distal clavicle fracture fragment fragmentation (3 of 6) and acromioclavicular (AC) joint displacement (1 of 6); 2 specimens did not fail at the maximal load of the materials testing machine. During cyclic loading, type IIB distal clavicle fractures with and without CC fixation remain stable. CC fixation adds stability to type IIB distal clavicle fractures fixed with plate and screws when loaded to failure. CC fixation for distal clavicle fractures is a useful adjunct to plate-and-screw fixation to augment stability of the fracture. Copyright © 2013 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Influence of surface treatment and cyclic loading on the durability of repaired all-ceramic crowns

PubMed Central

ATTIA, Ahmed

2010-01-01

Objective This study investigated the durability of repaired all-ceramic crowns after cyclic loading. Material and methods Eighty In-ceram zirconia crowns were fabricated to restore prepared maxillary premolars. Resin cement was used for cementation of crowns. Palatal cusps were removed to simulate fracture of veneering porcelain and divided into 4 groups (n = 20). Fracture site was treated before repair as follows: roughening with diamond bur, (DB); air abrasion using 50 µm Al2O3, (AA) and silica coating using Cojet system followed by silane application, (SC). Control group (CG) 20 specimens were left without fracture. Palatal cusps were repaired using composite resin. Specimens were stored in water bath at 37°C for one week. Ten specimens of each group were subjected to cyclic loading. Fracture load (N) was recorded for each specimen using a universal testing machine. Two-way analysis of variance (ANOVA) and Tukey honestly significant difference (HSD) test (α=.05) were used for statistical analysis. Results There was statistically significant difference between control and tested groups, (p<0.001). Post Hoc analysis with the Tukey HSD test showed that cyclic loading fatigue significantly decreased means fracture load of control and test groups as follows (CG, 950.4±62.6 / 872.3±87.4, P = 0.0004), (DB, 624.2 ±38 / 425.5± 31.7, P <.001), (AA, 711.5 ±15.5 / 490 ± 25.2, p <0.001) and (SC, 788.7 ± 18.1 / 610.2 ± 25.2, P <.001), while silica coating and silane application significantly increased fracture load of repaired crowns (p<0.05). Conclusion Repair of fractured Inceram zirconia crowns after chairside treatment of the fracture site by silica coating and silane application could improve longevity of repaired In-ceram zirconia crowns. PMID:20485932

Cyclic Degradation Behavior of < 001 > -Oriented Fe-Mn-Al-Ni Single Crystals in Tension

NASA Astrophysics Data System (ADS)

Vollmer, M.; Kriegel, M. J.; Krooß, P.; Martin, S.; Klemm, V.; Weidner, A.; Chumlyakov, Y.; Biermann, H.; Rafaja, D.; Niendorf, T.

2017-12-01

In the present study, functional fatigue behavior of a near 〈001〉-oriented Fe-Mn-Al-Ni single crystal was investigated under tensile load. An incremental strain test up to 3.5% strain and cyclic tests up to 25 cycles revealed rapid pseudoelastic degradation. Progressive microstructural degradation was studied by in situ scanning electron microscopy. The results show a partially inhibited reactivation of previously formed martensite and proceeding activation of untransformed areas in subsequent cycles. The preferentially formed martensite variants were identified by means of Schmid factor calculation and the Kurdjumov-Sachs relationship. Post mortem transmission electron microscopy investigations shed light on the prevailing degradation mechanisms. Different types of dislocations were found promoting the progressive degradation during cyclic loading.

Intervertebral disc response to cyclic loading--an animal model.

PubMed

Ekström, L; Kaigle, A; Hult, E; Holm, S; Rostedt, M; Hansson, T

1996-01-01

The viscoelastic response of a lumbar motion segment loaded in cyclic compression was studied in an in vivo porcine model (N = 7). Using surgical techniques, a miniaturized servohydraulic exciter was attached to the L2-L3 motion segment via pedicle fixation. A dynamic loading scheme was implemented, which consisted of one hour of sinusoidal vibration at 5 Hz, 50 N peak load, followed by one hour of restitution at zero load and one hour of sinusoidal vibration at 5 Hz, 100 N peak load. The force and displacement responses of the motion segment were sampled at 25 Hz. The experimental data were used for evaluating the parameters of two viscoelastic models: a standard linear solid model (three-parameter) and a linear Burger's fluid model (four-parameter). In this study, the creep behaviour under sinusoidal vibration at 5 Hz closely resembled the creep behaviour under static loading observed in previous studies. Expanding the three-parameter solid model into a four-parameter fluid model made it possible to separate out a progressive linear displacement term. This deformation was not fully recovered during restitution and is therefore an indication of a specific effect caused by the cyclic loading. High variability was observed in the parameters determined from the 50 N experimental data, particularly for the elastic modulus E1. However, at the 100 N load level, significant differences between the models were found. Both models accurately predicted the creep response under the first 800 s of 100 N loading, as displayed by mean absolute errors for the calculated deformation data from the experimental data of 1.26 and 0.97 percent for the solid and fluid models respectively. The linear Burger's fluid model, however, yielded superior predictions particularly for the initial elastic response.

Mechanics Model for Simulating RC Hinges under Reversed Cyclic Loading

PubMed Central

Shukri, Ahmad Azim; Visintin, Phillip; Oehlers, Deric J.; Jumaat, Mohd Zamin

2016-01-01

Describing the moment rotation (M/θ) behavior of reinforced concrete (RC) hinges is essential in predicting the behavior of RC structures under severe loadings, such as under cyclic earthquake motions and blast loading. The behavior of RC hinges is defined by localized slip or partial interaction (PI) behaviors in both the tension and compression region. In the tension region, slip between the reinforcement and the concrete defines crack spacing, crack opening and closing, and tension stiffening. While in the compression region, slip along concrete to concrete interfaces defines the formation and failure of concrete softening wedges. Being strain-based, commonly-applied analysis techniques, such as the moment curvature approach, cannot directly simulate these PI behaviors because they are localized and displacement based. Therefore, strain-based approaches must resort to empirical factors to define behaviors, such as tension stiffening and concrete softening hinge lengths. In this paper, a displacement-based segmental moment rotation approach, which directly simulates the partial interaction behaviors in both compression and tension, is developed for predicting the M/θ response of an RC beam hinge under cyclic loading. Significantly, in order to develop the segmental approach, a partial interaction model to predict the tension stiffening load slip relationship between the reinforcement and the concrete is developed. PMID:28773430

Mechanics Model for Simulating RC Hinges under Reversed Cyclic Loading.

PubMed

Shukri, Ahmad Azim; Visintin, Phillip; Oehlers, Deric J; Jumaat, Mohd Zamin

2016-04-22

Describing the moment rotation (M/θ) behavior of reinforced concrete (RC) hinges is essential in predicting the behavior of RC structures under severe loadings, such as under cyclic earthquake motions and blast loading. The behavior of RC hinges is defined by localized slip or partial interaction (PI) behaviors in both the tension and compression region. In the tension region, slip between the reinforcement and the concrete defines crack spacing, crack opening and closing, and tension stiffening. While in the compression region, slip along concrete to concrete interfaces defines the formation and failure of concrete softening wedges. Being strain-based, commonly-applied analysis techniques, such as the moment curvature approach, cannot directly simulate these PI behaviors because they are localized and displacement based. Therefore, strain-based approaches must resort to empirical factors to define behaviors, such as tension stiffening and concrete softening hinge lengths. In this paper, a displacement-based segmental moment rotation approach, which directly simulates the partial interaction behaviors in both compression and tension, is developed for predicting the M/θ response of an RC beam hinge under cyclic loading. Significantly, in order to develop the segmental approach, a partial interaction model to predict the tension stiffening load slip relationship between the reinforcement and the concrete is developed.

Modeling of high-strength concrete-filled FRP tube columns under cyclic load

NASA Astrophysics Data System (ADS)

Ong, Kee-Yen; Ma, Chau-Khun; Apandi, Nazirah Mohd; Awang, Abdullah Zawawi; Omar, Wahid

2018-05-01

The behavior of high-strength concrete (HSC) - filled fiber-reinforced-polymer (FRP) tubes (HSCFFTs) column subjected to cyclic lateral loading is presented in this paper. As the experimental study is costly and time consuming, a finite element analysis (FEA) is chosen for the study. Most of the previous studies have focused on examining the axial load behavior of HSCFFT column instead of seismic behavior. The seismic behavior of HSCFFT columns has been the main interest in the industry. The key objective of this research is to develop a reliable numerical non-linear FEA model to represent the seismic behavior of such column. A FEA model was developed using the Concrete Damaged Plasticity Model (CDPM) available in the finite element software package (ABAQUS). Comparisons between experimental results from previous research and the predicted results were made based on load versus displacement relationships and ultimate strength of the column. The results showed that the column increased in ductility and able to deform to a greater extent with the increase of the FRP confinement ratio. With the increase of confinement ratio, HSCFFT column achieved a higher moment resistance, thus indicated a higher failure strength in the column under cyclic lateral load. It was found that the proposed FEA model can regenerate the experimental results with adequate accuracy.

Buckling and Vibration of Fiber Reinforced Composite Plates With Nanofiber Reinforced Matrices

NASA Technical Reports Server (NTRS)

Chamis, Christos C.; Murthy, Pappu L. N.

2011-01-01

Anisotropic composite plates were evaluated with nanofiber reinforced matrices (NFRM). The nanofiber reinforcement volumes ratio in the matrix was 0.01. The plate dimensions were 20 by 10 by 1.0 in. (508 by 254 by 25.4 mm). Seven different loading condition cases were evaluated for buckling: three for uniaxial loading, three for pairs of combined loading, and one with three combined loadings. The anisotropy arose from the unidirectional plates having been at 30 from the structural axis. The anisotropy had a full 6 by 6 rigidities matrix which were satisfied and solved by a Galerkin buckling algorithm. For vibration the same conditions were used with the applied cods about a small fraction of the buckling loads. The buckling and vibration results showed that the NFRM plates buckled at about twice those with conventional matrix.

Low-stress pressure solution experiments on halite single-crystals

NASA Astrophysics Data System (ADS)

Martin, Brigitte; Röller, Klaus; Stöckhert, Bernhard

1999-07-01

Pressure solution experiments on halite single-crystals in saturated solution were carried out at atmospheric pressure under uniaxial stress ranging from 0.1 to 2.0 MPa and at temperatures of 303 and 323 K. The experiments were performed in ceramic loading rigs with damp-proofed sample chambers. The low uniaxial stress is applied by loading the piston with steel weights ranging from 0.5 to 5.0 kg. The position of the piston is measured by an electronic displacement transducer, connected to a data acquisition system. Deviations caused by fluctuations of temperature and output voltage of the power supply are corrected after data acquisition. The halite cubes {100} with edge dimensions of 3-9 mm are prepared by cleaving and placed with a (100) cleavage face on the (001) face of a muscovite single-crystal (10×10×0.1 mm), a polished quartz (0001) plate, or another halite crystal oriented to form a 45° twist boundary. The four free (100) faces of the halite cube are in contact with the surrounding NaCl solution. The initial displacement rate of the piston after flooding of the system and loading is up to 50.0 μm/day, attributed to smoothing of the halite face and elimination of point contacts with high stress concentration. Within 2 to 3 days this stage grades into steady-state displacement with rates of 0.1-2.0 μm/day. In some experiments stages of higher displacement rates (2.0-5.0 μm/day) lasting for 3-5 days are observed episodically, with intervals of 10-15 days. These cycles appear not to be triggered by external events. Experiments with a dry mica-halite interface, carried out for comparison at the same temperature and at an uniaxial stress of 2 MPa, result in a displacement rate below the limits of detection. This rules out a significant contribution of crystal plastic deformation in the wet experiments. The experimental results show no simple correlation between displacement rate and magnitude of uniaxial stress, crystal size, type of the interface, and temperature. At the given conditions, convergence at a single interface due to pressure solution is apparently not a steady-state process. The alternating stages of lower and higher displacement rates observed in many experiments suggest that the mechanisms of transport or dissolution may change spontaneously during the experiment. It is possible that the process itself leads to an unstable configuration causing episodic changes.

Experimental verification of the Neuber relation at room and elevated temperatures. M.S. Thesis; [to predict stress-strain behavior in notched specimens of hastelloy x

NASA Technical Reports Server (NTRS)

Lucas, L. J.

1982-01-01

The accuracy of the Neuber equation at room temperature and 1,200 F as experimentally determined under cyclic load conditions with hold times. All strains were measured with an interferometric technique at both the local and remote regions of notched specimens. At room temperature, strains were obtained for the initial response at one load level and for cyclically stable conditions at four load levels. Stresses in notched members were simulated by subjecting smooth specimens to he same strains as were recorded on the notched specimen. Local stress-strain response was then predicted with excellent accuracy by subjecting a smooth specimen to limits established by the Neuber equation. Data at 1,200 F were obtained with the same experimental techniques but only in the cyclically stable conditions. The Neuber prediction at this temperature gave relatively accurate results in terms of predicting stress and strain points.

Modeling Strength Degradation of Fiber-Reinforced Ceramic-Matrix Composites Subjected to Cyclic Loading at Elevated Temperatures in Oxidative Environments

NASA Astrophysics Data System (ADS)

Longbiao, Li

2018-02-01

In this paper, the strength degradation of non-oxide and oxide/oxide fiber-reinforced ceramic-matrix composites (CMCs) subjected to cyclic loading at elevated temperatures in oxidative environments has been investigated. Considering damage mechanisms of matrix cracking, interface debonding, interface wear, interface oxidation and fibers fracture, the composite residual strength model has been established by combining the micro stress field of the damaged composites, the damage models, and the fracture criterion. The relationships between the composite residual strength, fatigue peak stress, interface debonding, fibers failure and cycle number have been established. The effects of peak stress level, initial and steady-state interface shear stress, fiber Weibull modulus and fiber strength, and testing temperature on the degradation of composite strength and fibers failure have been investigated. The evolution of residual strength versus cycle number curves of non-oxide and oxide/oxide CMCs under cyclic loading at elevated temperatures in oxidative environments have been predicted.

Resizing procedure for optimum design of structures under combined mechanical and thermal loading

NASA Technical Reports Server (NTRS)

Adelman, H. M.; Narayanaswami, R.

1976-01-01

An algorithm is reported for resizing structures subjected to combined thermal and mechanical loading. The algorithm is applicable to uniaxial stress elements (rods) and membrane biaxial stress members. Thermal Fully Stressed Design (TFSD) is based on the basic difference between mechanical and thermal stresses in their response to resizing. The TFSD technique is found to converge in fewer iterations than ordinary fully stressed design for problems where thermal stresses are comparable to the mechanical stresses. The improved convergence is demonstrated by example with a study of a simplified wing structure, built-up with rods and membranes and subjected to a combination of mechanical loads and a three dimensional temperature distribution.

Temperature-dependent mechanical properties of single-layer molybdenum disulphide: Molecular dynamics nanoindentation simulations

NASA Astrophysics Data System (ADS)

Zhao, Junhua; Jiang, Jin-Wu; Rabczuk, Timon

2013-12-01

The temperature-dependent mechanical properties of single-layer molybdenum disulphide (MoS2) are obtained using molecular dynamics (MD) nanoindentation simulations. The Young's moduli, maximum load stress, and maximum loading strain decrease with increasing temperature from 4.2 K to 500 K. The obtained Young's moduli are in good agreement with those using our MD uniaxial tension simulations and the available experimental results. The tendency of maximum loading strain with different temperature is opposite with that of metal materials due to the short range Stillinger-Weber potentials in MoS2. Furthermore, the indenter tip radius and fitting strain effect on the mechanical properties are also discussed.

Textile properties of synthetic prolapse mesh in response to uniaxial loading.

PubMed

Barone, William R; Moalli, Pamela A; Abramowitch, Steven D

2016-09-01

Although synthetic mesh is associated with superior anatomic outcomes for the repair of pelvic organ prolapse, the benefits of mesh have been questioned because of the relatively high complication rates. To date, the mechanisms that result in such complications are poorly understood, yet the textile characteristics of mesh products are believed to play an important role. Interestingly, the pore diameter of synthetic mesh has been shown to impact the host response after hernia repair greatly, and such findings have served as design criteria for prolapse meshes, with larger pores viewed as more favorable. Although pore size and porosity are well-characterized before implantation, the changes in these textile properties after implantation are unclear; the application of mechanical forces has the potential to greatly alter pore geometries in vivo. Understanding the impact of mechanical loading on the textile properties of mesh is essential for the development of more effective devices for prolapse repair. The objective of this study was to determine the effect of tensile loading and pore orientation on mesh porosity and pore dimensions. In this study, the porosity and pore diameter of 4 currently available prolapse meshes were examined in response to uniaxial tensile loads of 0.1, 5, and 10 N while mimicking clinical loading conditions. The textile properties were compared with those observed for the unloaded mesh. Meshes included Gynemesh PS (Ethicon, Somerville, NJ), UltraPro (Artisyn; Ethicon), Restorelle (Coloplast, Minneapolis, MN), and Alyte Y-mesh (Bard, Covington, GA). In addition to the various pore geometries, 3 orientations of Restorelle (0-, 5-, 45-degree offset) and 2 orientations of UltraPro (0-, 90-degree offset) were examined. In response to uniaxial loading, both porosity and pore diameter dramatically decreased for most mesh products. The application of 5 N led to reductions in porosity for nearly all groups, with values decreasing by as much as 87% (P < .05). On loading to 10 N of force, nearly all mesh products that were tested were found to have porosities that approached 0% and 0 pores with diameters >1 mm. In this study, it was shown that the pore size of current prolapse meshes dramatically decreases in response to mechanical loading. These findings suggest that prolapse meshes, which are more likely to experience tensile forces in vivo relative to hernia repair meshes, have pores that are unfavorable for tissue integration after surgical tensioning and/or loading in urogynecologic surgeries. Such decreases in pore geometry support the hypothesis that regional increases in the concentration of mesh leads to an enhanced local foreign body response. Although pore deformation in transvaginal meshes requires further characterization, the findings presented here provide a mechanical understanding that can be used to recognize potential areas of concern for complex mesh geometries. Understanding mesh mechanics in response to surgical and in vivo loading conditions may provide improved design criteria for mesh and a refinement of surgical techniques, ultimately leading to better patient outcomes. Copyright © 2016 Elsevier Inc. All rights reserved.

Data related to cyclic deformation and fatigue behavior of direct laser deposited Ti-6Al-4V with and without heat treatment.

PubMed

Sterling, Amanda J; Torries, Brian; Shamsaei, Nima; Thompson, Scott M

2016-03-01

Data is presented describing the strain-controlled, fully-reversed uniaxial cyclic deformation and fatigue behavior of Ti-6Al-4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) - a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their 'as-built', annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the mechanical integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti-6Al-4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their mechanical properties are understood with high certainty.

Data related to cyclic deformation and fatigue behavior of direct laser deposited Ti–6Al–4V with and without heat treatment

PubMed Central

Sterling, Amanda J.; Torries, Brian; Shamsaei, Nima; Thompson, Scott M.

2016-01-01

Data is presented describing the strain-controlled, fully-reversed uniaxial cyclic deformation and fatigue behavior of Ti–6Al–4V specimens additively manufactured via Laser Engineered Net Shaping (LENS) – a Direct Laser Deposition (DLD) process. The data was collected by performing multiple fatigue tests on specimens with various microstructural states/conditions, i.e. in their ‘as-built’, annealed (below the beta transus temperature), or heat treated (above the beta transus temperature) condition. Such data aids in characterizing the mechanical integrity and fatigue resistance of DLD parts. Data presented herein also allows for elucidating the strong microstructure coupling of the fatigue behavior of DLD Ti–6Al–4V, as the data trends were found to vary with material condition (i.e. as-built, annealed or heat treated) [1]. This data is of interest to the additive manufacturing and fatigue scientific communities, as well as the aerospace and biomedical industries, since additively-manufactured parts cannot be reliably deployed for public use, until their mechanical properties are understood with high certainty. PMID:26949728

Mechanical degradation of fuel cell membranes under fatigue fracture tests

NASA Astrophysics Data System (ADS)

Khorasany, Ramin M. H.; Sadeghi Alavijeh, Alireza; Kjeang, Erik; Wang, G. G.; Rajapakse, R. K. N. D.

2015-01-01

The effects of cyclic stresses on the fatigue and mechanical stability of perfluorosulfonic acid (PFSA) membranes are experimentally investigated under standard fuel cell conditions. The experiments are conducted ex-situ by subjecting membrane specimens to cyclic uniaxial tension at controlled temperature and relative humidity. The fatigue lifetime is measured in terms of the number of cycles until ultimate fracture. The results indicate that the membrane fatigue lifetime is a strong function of the applied stress, temperature, and relative humidity. The fatigue life increases exponentially with reduced stresses in all cases. The effect of temperature is found to be more significant than that of humidity, with reduced fatigue life at high temperatures. The maximum membrane strain at fracture is determined to decrease exponentially with increasing membrane lifetime. At a given fatigue life, a membrane exposed to fuel cell conditions is shown to accommodate more plastic strain before fracture than one exposed to room conditions. Overall, the proposed ex-situ membrane fatigue experiment can be utilized to benchmark the fatigue lifetime of new materials in a fraction of the time and cost associated with conventional in-situ accelerated stress testing methods.

Experimental Constraints on the Fatigue of Icy Satellite Lithospheres by Tidal Forces

NASA Astrophysics Data System (ADS)

Hammond, Noah P.; Barr, Amy C.; Cooper, Reid F.; Caswell, Tess E.; Hirth, Greg

2018-02-01

Fatigue can cause materials that undergo cyclic loading to experience brittle failure at much lower stresses than under monotonic loading. We propose that the lithospheres of icy satellites could become fatigued and thus weakened by cyclical tidal stresses. To test this hypothesis, we performed a series of laboratory experiments to measure the fatigue of water ice at temperatures of 198 K and 233 K and at a loading frequency of 1 Hz. We find that ice is not susceptible to fatigue at our experimental conditions and that the brittle failure stress does not decrease with increasing number of loading cycles. Even though fatigue was not observed at our experimental conditions, colder temperatures, lower loading frequencies, and impurities in the ice shells of icy satellites may increase the likelihood of fatigue crack growth. We also explore other mechanisms that may explain the weak behavior of the lithospheres of some icy satellites.

A tissue engineering approach to anterior cruciate ligament regeneration using novel shaped capillary channel polymer fibers

NASA Astrophysics Data System (ADS)

Sinclair, Kristofer D.

2009-12-01

Ruptures of the anterior cruciate ligament (ACL) are the most frequent of injuries to the knee due to its role in preventing anterior translation of the tibia. It is estimated that as many as 200,000 Americans per year will suffer from a ruptured ACL, resulting in management costs on the order of 5 billion dollars. Without treatment these patients are unable to return to normal activity, as a consequence of the joint instability found within the ACL deficient knee. Over the last thirty years, a variety of non-degradable, synthetic fibers have been evaluated for their use in ACL reconstruction; however, a widely accepted prosthesis has been unattainable due to differences in mechanical properties of the synthetic graft relative to the native tissue. Tissue engineering is an interdisciplinary field charged with the task of developing therapeutic solutions for tissue and organ failure by enhancing the natural wound healing process through the use of cellular transplants, biomaterials, and the delivery of bioactive molecules. The capillary channel polymer (CC-P) fibers used in this research were fabricated by melt extrusion from polyethylene terephthalate and polybutylene terephthalate. These fibers possess aligned micrometer scale surface channels that may serve as physical templates for tissue growth and regeneration. This inherent surface topography offers a unique and industrially viable approach for cellular contact guidance on three dimensional constructs. In this fundamental research the ability of these fiber channels to support the adhesion, alignment, and organization of fibroblasts was demonstrated and found to be superior to round fiber controls. The results demonstrated greater uniformity of seeding and accelerated formation of multi-layered three-dimensional biomass for the CC-P fibers relative to those with a circular cross-section. Furthermore, the CC-P geometry induced nuclear elongation consistent with that observed in native ACL tissue. Through the application of uniaxial cyclic strain the mechanical properties of the cell seeded CC-P fiber scaffold systems were shown to improve via the induction of increased cellular proliferation and extracellular matrix synthesis. Finally, unlike many studies examining the effects of cyclic strain on cellular behavior, the CC-P fiber geometry displayed the ability to maintain cellular alignment in the presence of an applied uniaxial cyclic strain.

Analytical and experimental evaluation of an aluminum bridge deck panel. Part 1, Service load performance.

DOT National Transportation Integrated Search

1999-01-01

Deck deterioration is responsible for the majority of deficient bridge ratings in the United States (Sotiropoulos & GangaRao, 1993). Subject to dynamic loading, cyclic loading, and occasional overloading, bridge decks are the most severely stressed e...

Achieving fixation in glenoids with superior wear using reverse shoulder arthroplasty.

PubMed

Roche, Christopher P; Stroud, Nicholas J; Martin, Brian L; Steiler, Cindy A; Flurin, Pierre-Henri; Wright, Thomas W; Zuckerman, Joseph D; Dipaola, Matthew J

2013-12-01

Superior glenoid wear is a common challenge with reverse shoulder arthroplasty and, if left uncorrected, can result in superior glenoid tilt, which increases the risk of aseptic glenoid loosening. This study evaluates the impact of an E2 superior defect on reverse shoulder glenoid fixation in composite scapulae after correction of glenoid tilt by use of 2 different glenoid reaming techniques: eccentric reaming and off-axis reaming. A superior glenoid defect was created in 14 composite scapulae. The superior defect was corrected by 2 different glenoid reaming techniques: (1) eccentric reaming with implantation of a standard glenoid baseplate and (2) off-axis reaming with implantation of a superior-augment glenoid baseplate. Each corrected superior-defect scapula was then cyclically loaded (along with a control group consisting of 7 non-worn scapulae) for 10,000 cycles at 750 N; glenoid baseplate displacement was measured for each group to quantify fixation before and after cyclic loading. Regardless of the glenoid reaming technique or the glenoid baseplate type, each standard and superior-augment glenoid baseplate remained well fixed in this superior-defect model scenario after cyclic loading. No differences in baseplate displacement were observed either before or after cyclic loading between groups. Our results suggest that either glenoid reaming technique may be used to achieve fixation in the clinically challenging situation of superior wear with reverse shoulder arthroplasty. Basic science, biomechanical study. Copyright © 2013 Journal of Shoulder and Elbow Surgery Board of Trustees. Published by Mosby, Inc. All rights reserved.

A simple model for indentation creep

NASA Astrophysics Data System (ADS)

Ginder, Ryan S.; Nix, William D.; Pharr, George M.

2018-03-01

A simple model for indentation creep is developed that allows one to directly convert creep parameters measured in indentation tests to those observed in uniaxial tests through simple closed-form relationships. The model is based on the expansion of a spherical cavity in a power law creeping material modified to account for indentation loading in a manner similar to that developed by Johnson for elastic-plastic indentation (Johnson, 1970). Although only approximate in nature, the simple mathematical form of the new model makes it useful for general estimation purposes or in the development of other deformation models in which a simple closed-form expression for the indentation creep rate is desirable. Comparison to a more rigorous analysis which uses finite element simulation for numerical evaluation shows that the new model predicts uniaxial creep rates within a factor of 2.5, and usually much better than this, for materials creeping with stress exponents in the range 1 ≤ n ≤ 7. The predictive capabilities of the model are evaluated by comparing it to the more rigorous analysis and several sets of experimental data in which both the indentation and uniaxial creep behavior have been measured independently.

Uniaxial and biaxial tensioning effects on thin membrane materials. [large space structures

NASA Technical Reports Server (NTRS)

Hinson, W. F.; Goslee, J. W.

1980-01-01

Thin laminated membranes are being considered for various surface applications on future large space structural systems. Some of the thin membranes would be stretched across or between structural members with the requirement that the membrane be maintained within specified limits of smoothness which would be dictated by the particular applications such as antenna reflector requirements. The multiaxial tensile force required to maintain the smoothness in the membrane needs to be determined for use in the structure design. Therefore, several types of thicknesses of thin membrane materials have been subjected to varied levels of uniaxial and biaxial tensile loads. During the biaxial tests, deviations of the material surface smoothness were measured by a noncontacting capacitance probe. Basic materials consisted of composites of vacuum deposited aluminum on Mylar and Kapton ranging in thickness from 0.00025 in (0.000635 cm) to 0.002 in (0.00508 cm). Some of the material was reinforced with Kevlar and Nomex scrim. The uniaxial tests determined the material elongation and tensile forces up to ultimate conditions. Biaxial tests indicated that a relatively smooth material surface could be achieved with tensile force of approximately 1 to 15 Newtons per centimeter, depending upon the material thickness and/or reinforcement.

Uniaxial Stretching of Poly(keto-ether-imide) Films

NASA Technical Reports Server (NTRS)

Hinkley, Jeffrey A.; Dezern, James F.; Feuz, L.; Klinedinst, D.

1999-01-01

Fully-cured aromatic polyimides were prepared from various combinations of five dianhydrides and six diamines. When heated progressively under constant load, most of the films elongated rapidly near their glass transition temperatures. In about half of the nineteen materials, the strain was self-limiting - a possible indication of strain-induced crystallinity. The presence of crystallinity was established unambiguously for one material.

On the Use of Biaxial Properties in Modeling Annulus as a Holzapfel–Gasser–Ogden Material

PubMed Central

Momeni Shahraki, Narjes; Fatemi, Ali; Goel, Vijay K.; Agarwal, Anand

2015-01-01

Besides the biology, stresses and strains within the tissue greatly influence the location of damage initiation and mode of failure in an intervertebral disk. Finite element models of a functional spinal unit (FSU) that incorporate reasonably accurate geometry and appropriate material properties are suitable to investigate such issues. Different material models and techniques have been used to model the anisotropic annulus fibrosus, but the abilities of these models to predict damage initiation in the annulus and to explain clinically observed phenomena are unclear. In this study, a hyperelastic anisotropic material model for the annulus with two different sets of material constants, experimentally determined using uniaxial and biaxial loading conditions, were incorporated in a 3D finite element model of a ligamentous FSU. The purpose of the study was to highlight the biomechanical differences (e.g., intradiscal pressure, motion, forces, stresses, strains, etc.) due to the dissimilarity between the two sets of material properties (uniaxial and biaxial). Based on the analyses, the biaxial constants simulations resulted in better agreements with the in vitro and in vivo data, and thus are more suitable for future damage analysis and failure prediction of the annulus under complex multiaxial loading conditions. PMID:26090359

A 12 year EDF study of concrete creep under uniaxial and biaxial loading

DOE PAGES

Charpin, Laurent; Le Pape, Yann; Coustabeau, Eric; ...

2017-11-04

This paper presents a 12-year-long creep and shrinkage experimental campaign on cylindrical and prismatic concrete samples under uniaxial and biaxial stress, respectively. The motivation for the study is the need for predicting the delayed strains and the pre-stress loss of concrete containment buildings of nuclear power plants. Two subjects are central in this regard: the creep strain's long-term evolution and the creep Poisson's ratio. A greater understanding of these areas is necessary to ensure reliable predictions of the long-term behavior of the concrete containment buildings.Long-term basic creep appears to evolve as a logarithm function of time in the range ofmore » 3 to 10 years of testing. Similar trends are observed for drying creep, autogenous shrinkage, and drying shrinkage testing, which suggests that all delayed strains obtained using different loading and drying conditions originate from a common mechanism.The creep Poisson's ratio derived from the biaxial tests is approximately constant over time for both the basic and drying creep tests (creep strains corrected by the shrinkage strain).It is also shown that the biaxial non-drying samples undergo a significant increase in Young's modulus after 10 years.« less

A 12 year EDF study of concrete creep under uniaxial and biaxial loading

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

Charpin, Laurent; Le Pape, Yann; Coustabeau, Eric

This paper presents a 12-year-long creep and shrinkage experimental campaign on cylindrical and prismatic concrete samples under uniaxial and biaxial stress, respectively. The motivation for the study is the need for predicting the delayed strains and the pre-stress loss of concrete containment buildings of nuclear power plants. Two subjects are central in this regard: the creep strain's long-term evolution and the creep Poisson's ratio. A greater understanding of these areas is necessary to ensure reliable predictions of the long-term behavior of the concrete containment buildings.Long-term basic creep appears to evolve as a logarithm function of time in the range ofmore » 3 to 10 years of testing. Similar trends are observed for drying creep, autogenous shrinkage, and drying shrinkage testing, which suggests that all delayed strains obtained using different loading and drying conditions originate from a common mechanism.The creep Poisson's ratio derived from the biaxial tests is approximately constant over time for both the basic and drying creep tests (creep strains corrected by the shrinkage strain).It is also shown that the biaxial non-drying samples undergo a significant increase in Young's modulus after 10 years.« less

Investigation of hyperelastic models for nonlinear elastic behavior of demineralized and deproteinized bovine cortical femur bone.

PubMed

Hosseinzadeh, M; Ghoreishi, M; Narooei, K

2016-06-01

In this study, the hyperelastic models of demineralized and deproteinized bovine cortical femur bone were investigated and appropriate models were developed. Using uniaxial compression test data, the strain energy versus stretch was calculated and the appropriate hyperelastic strain energy functions were fitted on data in order to calculate the material parameters. To obtain the mechanical behavior in other loading conditions, the hyperelastic strain energy equations were investigated for pure shear and equi-biaxial tension loadings. The results showed the Mooney-Rivlin and Ogden models cannot predict the mechanical response of demineralized and deproteinized bovine cortical femur bone accurately, while the general exponential-exponential and general exponential-power law models have a good agreement with the experimental results. To investigate the sensitivity of the hyperelastic models, a variation of 10% in material parameters was performed and the results indicated an acceptable stability for the general exponential-exponential and general exponential-power law models. Finally, the uniaxial tension and compression of cortical femur bone were studied using the finite element method in VUMAT user subroutine of ABAQUS software and the computed stress-stretch curves were shown a good agreement with the experimental data. Copyright © 2016 Elsevier Ltd. All rights reserved.

Development and evaluation of a device for simultaneous uniaxial compression and optical imaging of cartilage samples in vitro

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

Steinert, Marian; Kratz, Marita; Jones, David B.

2014-10-15

In this paper, we present a system that allows imaging of cartilage tissue via optical coherence tomography (OCT) during controlled uniaxial unconfined compression of cylindrical osteochondral cores in vitro. We describe the system design and conduct a static and dynamic performance analysis. While reference measurements yield a full scale maximum deviation of 0.14% in displacement, force can be measured with a full scale standard deviation of 1.4%. The dynamic performance evaluation indicates a high accuracy in force controlled mode up to 25 Hz, but it also reveals a strong effect of variance of sample mechanical properties on the tracking performancemore » under displacement control. In order to counterbalance these disturbances, an adaptive feed forward approach was applied which finally resulted in an improved displacement tracking accuracy up to 3 Hz. A built-in imaging probe allows on-line monitoring of the sample via OCT while being loaded in the cultivation chamber. We show that cartilage topology and defects in the tissue can be observed and demonstrate the visualization of the compression process during static mechanical loading.« less

The role of biaxial stresses in discriminating between meaningful and illusory composite failure theories

NASA Technical Reports Server (NTRS)

Hart-Smith, L. J.

1992-01-01

The irrelevance of most composite failure criteria to conventional fiber-polymer composites is claimed to have remained undetected primarily because the experiments that can either validate or disprove them are difficult to perform. Uniaxial tests are considered inherently incapable of validating or refuting any composite failure theory because so much of the total load is carried by the fibers aligned in the direction of the load. The Ten-Percent Rule, a simple rule-of-mixtures analysis method, is said to work well only because of this phenomenon. It is stated that failure criteria can be verified for fibrous composites only by biaxial tests, with orthogonal in-plane stresses of the same as well as different signs, because these particular states of combined stress reveal substantial differences between the predictions of laminate strength made by various theories. Three scientifically plausible failure models for fibrous composites are compared, and it is shown that only the in-plane shear test (orthogonal tension and compression) is capable of distinguishing between them. This is because most theories are 'calibrated' against the measured uniaxial tension and compression tests and any cross-plied laminate tests dominated by those same states of stress must inevitably 'confirm' the theory.

Multiaxial mechanical response and constitutive modeling of esophageal tissues: Impact on esophageal tissue engineering.

PubMed

Sommer, Gerhard; Schriefl, Andreas; Zeindlinger, Georg; Katzensteiner, Andreas; Ainödhofer, Herwig; Saxena, Amulya; Holzapfel, Gerhard A

2013-12-01

Congenital defects of the esophagus are relatively frequent, with 1 out of 2500 babies suffering from such a defect. A new method of treatment by implanting tissue engineered esophagi into newborns is currently being developed and tested using ovine esophagi. For the reconstruction of the biological function of native tissues with engineered esophagi, their cellular structure as well as their mechanical properties must be considered. Since very limited mechanical and structural data for the esophagus are available, the aim of this study was to investigate the multiaxial mechanical behavior of the ovine esophagus and the underlying microstructure. Therefore, uniaxial tensile, biaxial tensile and extension-inflation tests on esophagi were performed. The underlying microstructure was examined in stained histological sections through standard optical microscopy techniques. Moreover, the uniaxial ultimate tensile strength and residual deformations of the tissue were determined. Both the mucosa-submucosa and the muscle layers showed nonlinear and anisotropic mechanical behavior during uniaxial, biaxial and inflation testing. Cyclical inflation of the intact esophageal tube caused marked softening of the passive esophagi in the circumferential direction. The rupture strength of the mucosa-submucosa layer was much higher than that of the muscle layer. Overall, the ovine esophagus showed a heterogeneous and anisotropic behavior with different mechanical properties for the individual layers. The intact and layer-specific multiaxial properties were characterized using a well-known three-dimensional microstructurally based strain-energy function. This novel and complete set of data serves the basis for a better understanding of tissue remodeling in diseased esophagi and can be used to perform computer simulations of surgical interventions or medical-device applications. Copyright © 2013 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

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

NASA Astrophysics Data System (ADS)

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

2016-03-01

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

Biomechanical testing of circumferential instrumentation after cervical multilevel corpectomy.

PubMed

Hartmann, Sebastian; Thomé, Claudius; Keiler, Alexander; Fritsch, Helga; Hegewald, Aldemar Andres; Schmölz, Werner

2015-12-01

Biomechanical investigation. This study describes ex vivo evaluation of the range of motion (ROM) to characterize the stability and need for additional dorsal fixation after cervical single-level, two-level or multilevel corpectomy (CE) to elucidate biomechanical differences between anterior-only and supplemental dorsal instrumentation. Twelve human cervical cadaveric spines were loaded in a spine tester with pure moments of 1.5 Nm in lateral bending (LB), flexion/extension (FE), and axial rotation (AR), followed by two cyclic loading periods for three-level corpectomies. After each cyclic loading session, flexibility tests were performed for anterior-only instrumentation (group_1, six specimens) and circumferential instrumentation (group_2, six specimens). The flexibility tests for all circumferential instrumentations showed a significant decrease in ROM in comparison with the intact state and anterior-only instrumentations. In comparison with the intact state, supplemental dorsal instrumentation after three-level CE reduced the ROM to 12% (±10%), 9% (±12%), and 22% (±18%) in LB, FE, and AR, respectively. The anterior-only construct outperformed the intact state only in FE, with a significant ROM reduction to 57% (±35 %), 60% (±27%), and 62% (±35%) for one-, two- and three-level CE, respectively. The supplemental dorsal instrumentation provided significantly more stability than the anterior-only instrumentation regardless of the number of levels resected and the direction of motion. After cyclic loading, the absolute differences in stability between the two instrumentations remained significant while both instrumentations showed a comparable increase of ROM after cyclic loading. The large difference in the absolute ROM of anterior-only compared to circumferential instrumentations supports a dorsal support in case of three-level approaches.

Biomechanical Performance of Medial Row Suture Placement Relative to the Musculotendinous Junction in Transosseous Equivalent Suture Bridge Double-Row Rotator Cuff Repair.

PubMed

Virk, Mandeep S; Bruce, Benjamin; Hussey, Kristen E; Thomas, Jacqueline M; Luthringer, Tyler A; Shewman, Elizabeth F; Wang, Vincent M; Verma, Nikhil N; Romeo, Anthony A; Cole, Brian J

2017-02-01

To compare the biomechanical performance of medial row suture placement relative to the musculotendinous junction (MTJ) in a cadaveric transosseous equivalent suture bridge (TOE-SB) double-row (DR) rotator cuff repair (RCR) model. A TOE-SB DR technique was used to reattach experimentally created supraspinatus tendon tears in 9 pairs of human cadaveric shoulders. The medial row sutures were passed either near the MTJ (MTJ group) or 10 mm lateral to the MTJ (rotator cuff tendon [RCT] group). After the supraspinatus repair, the specimens underwent cyclic loading and load to failure tests. The localized displacement of the markers affixed to the tendon surface was measured with an optical tracking system. The MTJ group showed a significantly higher (P = .03) medial row failure (5/9; 3 during cyclic testing and 2 during load to failure testing) compared with the RCT group (0/9). The mean number of cycles completed during cyclic testing was lower in the MTJ group (77) compared with the RCT group (100; P = .07) because 3 specimens failed in the MTJ group during cyclic loading. There were no significant differences between the 2 study groups with respect to biomechanical properties during the load to failure testing. In a cadaveric TOE-SB DR RCR model, medial row sutures through the MTJ results in a significantly higher rate of medial row failure. In rotator cuff tears with tendon tissue loss, passage of medial row sutures through the MTJ should be avoided in a TOE-SB RCR technique because of the risk of medial row failure. Copyright © 2016. Published by Elsevier Inc.

Comparable biomechanical results for a modified single-row rotator cuff reconstruction using triple-loaded suture anchors versus a suture-bridging double-row repair.

PubMed

Lorbach, Olaf; Kieb, Matthias; Raber, Florian; Busch, Lüder C; Kohn, Dieter; Pape, Dietrich

2012-02-01

To compare the biomechanical properties and footprint coverage of a single-row (SR) repair using a modified suture configuration versus a double-row (DR) suture-bridge repair in small to medium and medium to large rotator cuff tears. We created 25- and 35-mm artificial defects in the rotator cuff of 24 human cadaveric shoulders. The reconstructions were performed as either an SR repair with triple-loaded suture anchors (2 to 3 anchors) and a modified suture configuration or a modified suture-bridge DR repair (4 to 6 anchors). Reconstructions were cyclically loaded from 10 to 60 N. The load was increased stepwise up to 100, 180, and 250 N. Cyclic displacement and load to failure were determined. Furthermore, footprint widths were quantified. In the 25-mm rupture, ultimate load to failure was 533 ± 107 N for the SR repair and 681 ± 250 N for the DR technique (P ≥ .21). In the 35-mm tear, ultimate load to failure was 792 ± 122 N for the SR reconstruction and 891 ± 174 N for the DR reconstruction (P ≥ .28). There were no statistically significant differences for both tested rupture sizes. Cyclic displacement showed no significant differences between the tested configurations at 60 N (P = .563), 100 N (P = .171), 180 N (P = .211), and 250 N (P = .478) for the 25-mm tear. For the 35-mm tear, cyclic displacement showed significantly lower gap formation for the SR reconstruction at 180 N (P = .037) and 250 N (P = .020). No significant differences were found at 60 N (P = .296) and 100 N (P = .077). A significantly greater footprint width (P = .028) was seen for the DR repair (16.2 mm) compared with the SR repair (13.8 mm). However, both reconstructions were able to achieve complete footprint coverage compared with the initial footprint. The tested SR repair using a modified suture configuration was similar in load to failure and cyclic displacement to the DR suture-bridge technique independent of the tested initial sizes of the rupture. The tested DR repair consistently restored a larger footprint than the SR method. However, both constructs achieved complete footprint coverage. SR repairs with modified suture configurations might combine the biomechanical advantages and increased footprint coverage that are described for DR repairs without increasing the overall costs of the reconstruction. Copyright © 2012 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Effectiveness of a Load-Imposing Device for Cyclic Stretching of Isolated Human Bronchi: A Validation Study

PubMed Central

Le Guen, Morgan; Naline, Emmanuel; Grassin-Delyle, Stanislas; Devillier, Philippe; Faisy, Christophe

2015-01-01

Background Mechanical ventilation may induce harmful effects in the airways of critically ill patients. Nevertheless, the effects of cyclic stretching caused by repetitive inflation-deflation of the bronchial compartment have not been well characterized in humans. The objective of the present study was to assess the effectiveness of a load-imposing device for the cyclic stretching of human bronchi. Methods Intact bronchial segments were removed from 128 thoracic surgery patients. After preparation and equilibration in an organ bath, bronchi were stretched repetitively and cyclically with a motorized transducer. The peak force imposed on the bronchi was set to 80% of each individual maximum contraction in response to acetylcholine and the minimal force corresponded to the initial basal tone before stretching. A 1-min cycle (stretching for 15 sec, relaxing for 15 sec and resting for 30 sec) was applied over a time period ranging from 5 to 60 min. The device's performance level was assessed and the properties of the stretched bronchi were compared with those of paired, non-stretched bronchi. Results Despite the intrinsic capacities of the device, the targets of the tension adjustments remained variable for minimal tension (156–178%) while the peak force set point was unchanged (87–115%). In the stretched bronchi, a time-dependent rise in basal tone (P <.05 vs. non-stretched) was apparent after as little as 5 min of cyclic stretching. The stretch-induced rise in basal tone continued to increase (P <.01) after the stretching had ended. Only 60 min of cyclic stretching was associated with a significant (P <.05) increase in responsiveness to acetylcholine, relative to non-stretched bronchi. Conclusions Low-frequency, low-force, cyclic loading of human bronchi is associated with elevated basal tone and acetylcholine responsiveness. The present experimental model is likely to be a useful tool for future investigations of the bronchial response to repetitive stress during mechanical ventilation. PMID:26011598

Beta-tricalcium phosphate plugs for press-fit fixation in ACL reconstruction--a mechanical analysis in bovine bone.

PubMed

Mayr, Hermann O; Hube, Robert; Bernstein, Anke; Seibt, Alexander B; Hein, Werner; von Eisenhart-Rothe, Ruediger

2007-06-01

The goal of this study was to test fixation properties of microporous pure beta-tricalcium phosphate (TCP) plugs (porosity 40%) for press-fit fixation of the ACL graft using patellar tendons with and without bone blocks. We set out to establish whether it is possible, in this way, to obtain results comparable with those of interference screw fixation of bone-tendon-bone (BTB) grafts in terms of cyclic loading and load-to-failure. In a bovine model 30 ACL grafts were fixed in tibial drill holes, divided into three groups: 10 BTB grafts fixed with TCP press-fit plugs (7x25 mm), 10 pure patellar tendon grafts with TCP press-fit plugs (7x25 mm), and 10 BTB grafts with metal interference screws (7x25 mm). All grafts were tested by cyclic loading (50-200 N) and loaded until failure in a tensiometer. Under cyclic loading one interference screw fixation failed. None of the TCP plug fixations failed. After 1500 cycles the displacement of the graft in the drill hole for BTB fixed with screws was 3.6+/-7.8 mm, for BTB/TCP plugs 1.6+/-3.4 mm, and for the pure tendon/TCP grafts 1.4+/-0.4 mm. Regarding cyclic loading the pure tendon/TCP system was significantly superior to BTB (p=0.007). The load-to-failure for the BTB/interference screw group was 908+/-539 N with a stiffness of 94+/-36 N/mm, 936+/-245 N for the BTB/TCP cylinder group with a stiffness of 98+/-12 N/mm, and 673+/-159 N for the pure tendon/TCP group with a stiffness of 117+/-9 N/mm. In terms of pull-out load the BTB/TCP system was significantly better than the pure tendon/TCP group (p=0.011). However, pure tendon/TCP grafts achieved significantly greater stiffness (p=0.002) than the BTB system. Press-fit fixation with microporous pure beta-TCP plugs of BTB grafts or patellar tendon grafts without bone blocks for ACL reconstruction leads to primary stability comparable with that achieved by fixation with metal interference screws in case of BTB grafts.

Effects of laboratory heating, cyclic pore pressure, and cyclic loading on fracture properties of asphalt mixture [summary].

DOT National Transportation Integrated Search

2012-04-01

Asphalt pavement ages continuously, beginning with production and construction and thoughout its service life. "Aging" refers to many changes in asphalt properties over time that generally result in increased pavement damage. Because aging is often a...

Large-displacement structural durability analyses of simple bend specimen emulating rocket nozzle liners

NASA Technical Reports Server (NTRS)

Arya, Vinod K.; Halford, Gary R.

1994-01-01

Large-displacement elastic and elastic-plastic, finite-element stress-strain analyses of an oxygen-tree high-conductivity (OFHC) copper plate specimen were performed using an updated Lagrangian formulation. The plate specimen is intended for low-cost experiments that emulate the most important thermomechanical loading and failure modes of a more complex rocket nozzle. The plate, which is loaded in bending at 593 C, contains a centrally located and internally pressurized channel. The cyclic crack initiation lives were estimated using the results from the analyses and isothermal strain-controlled low-cycle fatigue data for OFHC copper. A comparison of the predicted and experimental cyclic lives showed that an elastic analysis predicts a longer cyclic life than that observed in experiments by a factor greater than 4. The results from elastic-plastic analysis for the plate bend specimen, however, predicted a cyclic life in close agreement with experiment, thus justifying the need for the more rigorous stress-strain analysis.

Hierarchical poroelasticity: movement of interstitial fluid between porosity levels in bones.

PubMed

Cowin, Stephen C; Gailani, Gaffar; Benalla, Mohammed

2009-09-13

The governing equations for the theory of poroelastic materials with hierarchical pore space architecture and compressible constituents undergoing small deformations are developed. These equations are applied to the problem of determining the exchange of pore fluid between the vascular porosity (PV) and the lacunar-canalicular porosity (PLC) in bone tissue due to cyclic mechanical loading and blood pressure oscillations. The result is basic to the understanding of interstitial flow in bone tissue that, in turn, is basic to understanding of nutrient transport from the vasculature to the bone cells buried in the bone tissue and to the process of mechanotransduction by these cells. A formula for the volume of fluid that moves between the PLC and PV in a cyclic loading is obtained as a function of the cyclic mechanical loading and blood pressure oscillations. Formulas for the oscillating fluid pore pressure in both the PLC and the PV are obtained as functions of the two driving forces, the cyclic mechanical straining and the blood pressure, both with specified amplitude and frequency. The results of this study also suggest a PV permeability greater than 10(-9) m(2) and perhaps a little lower than 10(-8) m(2). Previous estimates of this permeability have been as small as 10(-14) m(2).

In-Plane Anisotropy in Mechanical Behavior and Microstructural Evolution of Commercially Pure Titanium in Tensile and Cyclic Loading

NASA Astrophysics Data System (ADS)

Sinha, Subhasis; Gurao, N. P.

2017-12-01

Tensile and cyclic deformation behavior of three samples oriented at 0, 45, and 90 deg to the rolling direction in the rolling direction-transverse direction (RD-TD) plane of cold-rolled and annealed plate of commercially pure titanium is studied in the present investigation. The sample along the RD (R0) shows the highest strength but lowest ductility in monotonic tension. Although ultimate tensile strength (UTS) and elongation of samples along 45 and 90 deg to the RD (R45 and R90, respectively) are similar, the former has significantly higher yield strength than the latter, indicating different strain-hardening behavior. It is found that the R90 sample exhibits the highest monotonic ductility as well as fatigue life. This is attributed to a higher propensity for twinning in this sample with the presence of multiple variants and twin intersections. Cyclic life is also influenced by the high tendency for detwinning of contraction twins in this orientation. Elastoplastic self-consistent (EPSC) simulations of one-cycle tension-compression load reversal indicate that the activity of pyramidal 〈 c + a〉 slip and extension twinning oscillates during cyclic loading that builds up damage in a cumulative manner, leading to failure in fatigue.

Factors affecting the mechanical behavior of collagen hydrogels for skin tissue engineering.

PubMed

Pensalfini, Marco; Ehret, Alexander E; Stüdeli, Silvia; Marino, Daniela; Kaech, Andres; Reichmann, Ernst; Mazza, Edoardo

2017-05-01

The effect of the production factors yielding a functional dermal substitute was investigated by means of monotonic and cyclic uniaxial tensile tests, as well as electron microscopy visualizations. The role of (i) plastic compression, (ii) product incubation, and (iii) cell permanence in the collagenous matrix in order to achieve a skin-like behavior were characterized in terms of material and structural stiffness, in-plane kinematics, and cyclic response, as well as pore size and network density. The plastic compression resulted in a denser and stiffer material, while no corresponding change was observed in the behavior of the entire structure. This was related to the progressive reduction in product thickness and amount of excess water, rather than to formation of new crosslinks between fibers. Contrary, irrespective of the presence of human fibroblasts, the product incubation induced both material and structural stiffening, indicating the formation of a denser network. These results were confirmed by similar evolutions in the construct in-plane kinematics and cyclic stress reduction. Finally, comparison of constructs incubated in different culture media indicated a determinant contribution of the biochemical environment, rather than of the seeded cells, to the achieved mechanical properties. The observed features are relevant in terms of mechanical biocompatibility of the implant and might direct future optimizations of the production process in order to rapidly attain the desired mechanical properties. Copyright © 2016 Elsevier Ltd. All rights reserved.

Dynamic strain aging behavior of 10Cr steel under low cycle fatigue at 650°C

NASA Astrophysics Data System (ADS)

Mishnev, Roman; Dudova, Nadezhda; Kaibyshev, Rustam

2017-12-01

The low cycle fatigue behavior of a 10Cr-2W-0.7Mo-3Co-NbV steel with 80 ppm of B additions was studied at elevated temperatures of 600 and 650°C. The steel after normalizing and tempering at 770°C was tested under fully reversed tension-compression loading with the total strain amplitude controlled from ±0.2 to ±1.0% at temperatures of 600 and 650°C. It was revealed that the steel exhibits a positive temperature dependence of both the cyclic strain hardening exponent n' and the cyclic strength coefficient K ' during cyclic loading at 650°C. It was suggested that dynamic strain aging causes fatigue resistance degradation through facilitating microcrack initiation.

Assessment of Multiaxial Mechanical Response of Rigid Polyurethane Foams

NASA Astrophysics Data System (ADS)

Pettarin, Valeria; Fasce, Laura A.; Frontini, Patricia M.

2014-02-01

Multiaxial deformation behavior and failure surface of rigid polyurethane foams were determined using standard experimental facilities. Two commercial foams of different densities were assayed under uniaxial, biaxial, and triaxial stress states. These different stress states were reached in a uniaxial universal testing machine using suitable testing configurations which imply the use of special grips and lateral restricted samples. Actual strains were monitored with a video extensometer. Polyurethane foams exhibited typical isotropic brittle behavior, except under compressive loads where the response turned out to be ductile. A general failure surface in the stress space which accounts for density effects could be successfully generated. All of failure data, determined at the loss of linear elasticity point, collapsed in a single locus defined as the combination of a brittle crushing of closed-cell cellular materials criterion capped by an elastic buckling criterion.

Experimental characterization and constitutive modeling of the mechanical behavior of molybdenum under electromagnetically applied compression-shear ramp loading

DOE PAGES

Alexander, C. Scott; Ding, Jow -Lian; Asay, James Russell

2016-03-09

Magnetically applied pressure-shear (MAPS) is a new experimental technique that provides a platform for direct measurement of material strength at extreme pressures. The technique employs an imposed quasi-static magnetic field and a pulsed power generator that produces an intense current on a planar driver panel, which in turn generates high amplitude magnetically induced longitudinal compression and transverse shear waves into a planar sample mounted on the drive panel. In order to apply sufficiently high shear traction to the test sample, a high strength material must be used for the drive panel. Molybdenum is a potential driver material for the MAPSmore » experiment because of its high yield strength and sufficient electrical conductivity. To properly interpret the results and gain useful information from the experiments, it is critical to have a good understanding and a predictive capability of the mechanical response of the driver. In this work, the inelastic behavior of molybdenum under uniaxial compression and biaxial compression-shear ramp loading conditions is experimentally characterized. It is observed that an imposed uniaxial magnetic field ramped to approximately 10 T through a period of approximately 2500 μs and held near the peak for about 250 μs before being tested appears to anneal the molybdenum panel. In order to provide a physical basis for model development, a general theoretical framework that incorporates electromagnetic loading and the coupling between the imposed field and the inelasticity of molybdenum was developed. Based on this framework, a multi-axial continuum model for molybdenum under electromagnetic loading is presented. The model reasonably captures all of the material characteristics displayed by the experimental data obtained from various experimental configurations. Additionally, data generated from shear loading provide invaluable information not only for validating but also for guiding the development of the material model for multiaxial loadings.« less

Inverse Slip Accompanying Twinning and Detwinning during Cyclic Loading of Magnesium Single Crystal

DOE PAGES

Yu, Qin; Wang, Jian; Jiang, Yanyao

2013-01-01

In situ , observation of twinning and detwinning in magnesium single crystals during tension-compression cyclic loading was made using optical microscopy. A quantitative analysis of plastic strain indicates that twinning and detwinning experience two stages, low and high work hardening de-twinning, and pure re-twinning and fresh twinning combined with retwinning. Slip is always activated. For the first time, inverse slip accompanying with pure retwinning and high work hardening detwinning was experimentally identified, which provides insights in better understanding of the activity of twining, detwinning, and slips.

Design Considerations for Thermally Insulating Structural Sandwich Panels for Hypersonic Vehicles

NASA Technical Reports Server (NTRS)

Blosser, Max L.

2016-01-01

Simplified thermal/structural sizing equations were derived for the in-plane loading of a thermally insulating structural sandwich panel. Equations were developed for the strain in the inner and outer face sheets of a sandwich subjected to uniaxial mechanical loads and differences in face sheet temperatures. Simple equations describing situations with no viable solution were developed. Key design parameters, material properties, and design principles are identified. A numerical example illustrates using the equations for a preliminary feasibility assessment of various material combinations and an initial sizing for minimum mass of a sandwich panel.

Behavior of nonplastic silty soils under cyclic loading.

PubMed

Ural, Nazile; Gunduz, Zeki

2014-01-01

The engineering behavior of nonplastic silts is more difficult to characterize than is the behavior of clay or sand. Especially, behavior of silty soils is important in view of the seismicity of several regions of alluvial deposits in the world, such as the United States, China, and Turkey. In several hazards substantial ground deformation, reduced bearing capacity, and liquefaction of silty soils have been attributed to excess pore pressure generation during dynamic loading. In this paper, an experimental study of the pore water pressure generation of silty soils was conducted by cyclic triaxial tests on samples of reconstituted soils by the slurry deposition method. In all tests silty samples which have different clay percentages were studied under different cyclic stress ratios. The results have showed that in soils having clay content equal to and less than 10%, the excess pore pressure ratio buildup was quicker with an increase in different cyclic stress ratios. When fine and clay content increases, excess pore water pressure decreases constant cyclic stress ratio in nonplastic silty soils. In addition, the applicability of the used criteria for the assessment of liquefaction susceptibility of fine grained soils is examined using laboratory test results.

Behavior of Nonplastic Silty Soils under Cyclic Loading

PubMed Central

Ural, Nazile; Gunduz, Zeki

2014-01-01

The engineering behavior of nonplastic silts is more difficult to characterize than is the behavior of clay or sand. Especially, behavior of silty soils is important in view of the seismicity of several regions of alluvial deposits in the world, such as the United States, China, and Turkey. In several hazards substantial ground deformation, reduced bearing capacity, and liquefaction of silty soils have been attributed to excess pore pressure generation during dynamic loading. In this paper, an experimental study of the pore water pressure generation of silty soils was conducted by cyclic triaxial tests on samples of reconstituted soils by the slurry deposition method. In all tests silty samples which have different clay percentages were studied under different cyclic stress ratios. The results have showed that in soils having clay content equal to and less than 10%, the excess pore pressure ratio buildup was quicker with an increase in different cyclic stress ratios. When fine and clay content increases, excess pore water pressure decreases constant cyclic stress ratio in nonplastic silty soils. In addition, the applicability of the used criteria for the assessment of liquefaction susceptibility of fine grained soils is examined using laboratory test results. PMID:24672343

Effect of Repeated Screw Joint Closing and Opening Cycles and Cyclic Loading on Abutment Screw Removal Torque and Screw Thread Morphology: Scanning Electron Microscopy Evaluation.

PubMed

Arshad, Mahnaz; Mahgoli, Hosseinali; Payaminia, Leila

To evaluate the effect of repeated screw joint closing and opening cycles and cyclic loading on abutment screw removal torque and screw thread morphology using scanning electron microscopy (SEM). Three groups (n = 10 in each group) of implant-abutment-abutment screw assemblies were created. There were also 10 extra abutment screws as new screws in group 3. The abutment screws were tightened to 12 Ncm with an electronic torque meter; then they were removed and removal torque values were recorded. This sequence was repeated 5 times for group 1 and 15 times for groups 2 and 3. The same screws in groups 1 and 2 and the new screws in group 3 were then tightened to 12 Ncm; this was also followed by screw tightening to 30 Ncm and retightening to 30 Ncm 15 minutes later. Removal torque measurements were performed after screws were subjected to cyclic loading (0.5 × 10⁶ cycles; 1 Hz; 75 N). Moreover, the surface topography of one screw from each group before and after cyclic loading was evaluated with SEM and compared with an unused screw. All groups exhibited reduced removal torque values in comparison to insertion torque in each cycle. However, there was a steady trend of torque loss in each group. A comparison of the last cycle of the groups before loading showed significantly greater torque loss value in the 15th cycle of groups 2 and 3 compared with the fifth cycle of group 1 (P < .05). Nonetheless, torque loss values after loading were not shown to be significantly different from each other. Using a new screw could not significantly increase the value of removal torque. It was concluded that restricting the amount of screw tightening is more important than replacing the screw with a new one when an abutment is definitively placed.

Short bursts of cyclic mechanical compression modulate tissue formation in a 3D hybrid scaffold.

PubMed

Brunelli, M; Perrault, C M; Lacroix, D

2017-07-01

Among the cues affecting cells behaviour, mechanical stimuli are known to have a key role in tissue formation and mineralization of bone cells. While soft scaffolds are better at mimicking the extracellular environment, they cannot withstand the high loads required to be efficient substitutes for bone in vivo. We propose a 3D hybrid scaffold combining the load-bearing capabilities of polycaprolactone (PCL) and the ECM-like chemistry of collagen gel to support the dynamic mechanical differentiation of human embryonic mesodermal progenitor cells (hES-MPs). In this study, hES-MPs were cultured in vitro and a BOSE Bioreactor was employed to induce cells differentiation by mechanical stimulation. From day 6, samples were compressed by applying a 5% strain ramp followed by peak-to-peak 1% strain sinewaves at 1Hz for 15min. Three different conditions were tested: unloaded (U), loaded from day 6 to day 10 (L1) and loaded as L1 and from day 16 to day 20 (L2). Cell viability, DNA content and osteocalcin expression were tested. Samples were further stained with 1% osmium tetroxide in order to investigate tissue growth and mineral deposition by micro-computed tomography (µCT). Tissue growth involved volumes either inside or outside samples at day 21 for L1, suggesting cyclic stimulation is a trigger for delayed proliferative response of cells. Cyclic load also had a role in the mineralization process preventing mineral deposition when applied at the early stage of culture. Conversely, cyclic load during the late stage of culture on pre-compressed samples induced mineral formation. This study shows that short bursts of compression applied at different stages of culture have contrasting effects on the ability of hES-MPs to induce tissue formation and mineral deposition. The results pave the way for a new approach using mechanical stimulation in the development of engineered in vitro tissue as replacement for large bone fractures. Copyright © 2017 Elsevier Ltd. All rights reserved.

Mechanical properties of cancellous bone in the human mandibular condyle are anisotropic.

PubMed

Giesen, E B; Ding, M; Dalstra, M; van Eijden, T M

2001-06-01

The objective of the present study was (1) to test the hypothesis that the elastic and failure properties of the cancellous bone of the mandibular condyle depend on the loading direction, and (2) to relate these properties to bone density parameters. Uniaxial compression tests were performed on cylindrical specimens (n=47) obtained from the condyles of 24 embalmed cadavers. Two loading directions were examined, i.e., a direction coinciding with the predominant orientation of the plate-like trabeculae (axial loading) and a direction perpendicular to the plate-like trabeculae (transverse loading). Archimedes' principle was applied to determine bone density parameters. The cancellous bone was in axial loading 3.4 times stiffer and 2.8 times stronger upon failure than in transverse loading. High coefficients of correlation were found among the various mechanical properties and between them and the apparent density and volume fraction. The anisotropic mechanical properties can possibly be considered as a mechanical adaptation to the loading of the condyle in vivo.

Load partitioning between the bcc-iron matrix and NiAl-type precipitates in a ferritic alloy on multiple length scales

PubMed Central

Sun, Zhiqian; Song, Gian; Sisneros, Thomas A.; Clausen, Bjørn; Pu, Chao; Li, Lin; Gao, Yanfei; Liaw, Peter K.

2016-01-01

An understanding of load sharing among constituent phases aids in designing mechanical properties of multiphase materials. Here we investigate load partitioning between the body-centered-cubic iron matrix and NiAl-type precipitates in a ferritic alloy during uniaxial tensile tests at 364 and 506 °C on multiple length scales by in situ neutron diffraction and crystal plasticity finite element modeling. Our findings show that the macroscopic load-transfer efficiency is not as high as that predicted by the Eshelby model; moreover, it depends on the matrix strain-hardening behavior. We explain the grain-level anisotropic load-partitioning behavior by considering the plastic anisotropy of the matrix and elastic anisotropy of precipitates. We further demonstrate that the partitioned load on NiAl-type precipitates relaxes at 506 °C, most likely through thermally-activated dislocation rearrangement on the microscopic scale. The study contributes to further understanding of load-partitioning characteristics in multiphase materials. PMID:26979660

Load partitioning between the bcc-iron matrix and NiAl-type precipitates in a ferritic alloy on multiple length scales

DOE PAGES

Sun, Zhiqian; Song, Gian; Sisneros, Thomas A.; ...

2016-03-16

An understanding of load sharing among constituent phases aids in designing mechanical properties of multiphase materials. Here we investigate load partitioning between the body-centered-cubic iron matrix and NiAl-type precipitates in a ferritic alloy during uniaxial tensile tests at 364 and 506 C on multiple length scales by in situ neutron diffraction and crystal plasticity finite element modeling. Our findings show that the macroscopic load-transfer efficiency is not as high as that predicted by the Eshelby model; moreover, it depends on the matrix strain-hardening behavior. We explain the grain-level anisotropic load-partitioning behavior by considering the plastic anisotropy of the matrix andmore » elastic anisotropy of precipitates. We further demonstrate that the partitioned load on NiAl-type precipitates relaxes at 506 C, most likely through thermally-activated dislocation rearrangement on the microscopic scale. Furthermore, the study contributes to further understanding of load-partitioning characteristics in multiphase materials.« less

Triple-Loaded Suture Anchors Versus a Knotless Rip Stop Construct in a Single-Row Rotator Cuff Repair Model.

PubMed

Noyes, Matthew P; Lederman, Evan; Adams, Christopher R; Denard, Patrick J

2018-05-01

To compare the biomechanical properties of single-row repair with triple-loaded (TL) anchor repair versus a knotless rip stop (KRS) repair in a rotator cuff repair model. Rotator cuff tears were created in 8 cadaveric matched-pair specimens and repaired with a TL anchor or KRS construct. In the TL construct, anchors were placed in the greater tuberosity and then all suture limbs were passed through the rotator cuff as simple sutures and tied. In the KRS construct, a 2-mm suture tape was passed through the tendon in an inverted mattress fashion, and a free suture was passed medial to the suture tape to create a rip-stop. Then, the suture tape and free suture were secured with knotless anchors. Displacement was observed with video tracking after cyclic loading, and specimens were loaded to failure. The mean load to failure was 438 ± 59 N in TL anchor repairs compared with 457 ± 110 N in KRS repairs (P = .582). The mean displacement with cyclic loading was 3.8 ± 1.6 mm in TL anchor repairs versus 4.3 ± 1.8 mm in the KRS group (P = .297). Mode of failure was consistent in both groups, with 6 of 8 failures in the TL anchor group and 7 of 8 failures in KRS group occurring from anchor pullout. There is no statistical difference in load to failure and cyclic loading between TL anchor and KRS single-row repair techniques. KRS repair technique may be an alternative method of repairing full-thickness supraspinatus tendon tears with a single-row construct. Copyright © 2018 Arthroscopy Association of North America. Published by Elsevier Inc. All rights reserved.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants.

PubMed

Mohammed, Hnd Hadi; Lee, Jin-Han; Bae, Ji-Myung; Cho, Hye-Won

2016-02-01

The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading.

Effect of abutment screw length and cyclic loading on removal torque in external and internal hex implants

PubMed Central

Mohammed, Hnd Hadi; Lee, Jin-Han; Bae, Ji-Myung

2016-01-01

PURPOSE The purpose of this study was to evaluate the effects of abutment screw length and cyclic loading on the removal torque (RTV) in external hex (EH) and internal hex (IH) implants. MATERIALS AND METHODS Forty screw-retained single crowns were connected to external and internal hex implants. The prepared titanium abutment screws were classified into 8 groups based on the number of threads (n = 5 per group): EH 12.5, 6.5, 3.5, 2.5 and IH 6.5, 5, 3.5, 2.5 threads. The abutment screws were tightened with 20 Ncm torque twice with 10-minute intervals. After 5 minutes, the initial RTVs of the abutment screws were measured with a digital torque gauge (MGT12). A customized jig was constructed to apply a load along the implant long axis at the central fossa of the maxillary first molar. The post-loading RTVs were measured after 16,000 cycles of mechanical loading with 50 N at a 1-Hz frequency. Statistical analysis included one-way analysis of variance and paired t-tests. RESULTS The post-loading RTVs were significantly lower than the initial RTVs in the EH 2.5 thread and IH 2.5 thread groups (P<.05). The initial RTVs exhibited no significant differences among the 8 groups, whereas the post-loading RTVs of the EH 6.5 and EH 3.5 thread groups were higher than those of the IH 3.5 thread group (P<.05). CONCLUSION Within the limitations of this study, the external hex implants with short screw lengths were more advantageous than internal hex implants with short screw lengths in torque maintenance after cyclic loading. PMID:26949489

The Assessing of the Failure Behavior of Glass/Polyester Composites Subject to Quasi Static Stresses

NASA Astrophysics Data System (ADS)

Stanciu, M. D.; Savin, A.; Teodorescu-Drăghicescu, H.

2017-06-01

Using glass fabric reinforced composites for structure of wind turbine blades requires high mechanical strengths especially to cyclic stresses. Studies have shown that approximately 50% of composite material failure occurs because of fatigue. Composites behavior to cyclic stresses involves three stages regarding to stiffness variation: the first stage is characterized by the accelerated decline of stiffness with micro-cracks, the second stage - a slight decrease of stiffness characterized by the occurrence of delamination and third stage characterized by higher decreases of resistance and occurrence of fracture thereof. The aim of the paper is to analyzed the behavior of composites reinforced with glass fibers fabric type RT500 and polyester resin subjected to tensile cyclic loading with pulsating quasi-static regime with asymmetry coefficient R = 0. The samples were tested with the universal tensile machine LS100 Lloyd Instruments Plus, with a load capacity of 100 kN. The load was applied with different speeds of 1 mm/min, 10 mm/min and 20 mm/min. After tests, it was observed that the greatest permanent strains were recorded in the first load cycles when the total energy storage by material was lost due to internal friction. With increasing number of cycles, the glass/polyester composites ability to store energy of deformation decreases, the flow phenomenon characterized by large displacements to smaller loading forces appearing.

Quasi-Static Viscoelasticity Loading Measurements of an Aircraft Tire

NASA Technical Reports Server (NTRS)

Mason, Angela J.; Tanner, John A.; Johnson, Arthur R.

1997-01-01

Stair-step loading, cyclic loading, and long-term relaxation tests were performed on an aircraft tire to observe the quasi-static viscoelastic response of the tire. The data indicate that the tire continues to respond viscoelastically even after it has been softened by deformation. Load relaxation data from the stair-step test at the 15,000-lb loading was fit to a monotonically decreasing Prony series.

Viscoelasticity and Creep Recovery of Polyimide Thin Films

DTIC Science & Technology

1990-06-01

3931; (617) 253-0292. Accesion For NTIS CRA&I DTIC TAB Unannounced 0 JuslfIcation .... ’ ry (I’. . ,* VISCOELASTICITY AND CREEP RECOVERY OF POLYIMIDE...polyimide is subjected to sustained loads. Viscoelastic properties of materials are traditionally measured by uniaxial tests [4]. Creep, stress...structure The membrane fabrication and analysis is implemented in the environment of a previously reported CAD architecture [7,81, which uses a

Relating Ab Initio Mechanical Behavior of Intergranular Glassy Films in Γ-Si3N4 to Continuum Scales

NASA Astrophysics Data System (ADS)

Ouyang, L.; Chen, J.; Ching, W.; Misra, A.

2006-05-01

Nanometer thin intergranular glassy films (IGFs) form in polycrystalline ceramics during sintering at high temperatures. The structure and properties of these IGFs are significantly changed by doping with rare earth elements. We have performed highly accurate large-scale ab initio calculations of the mechanical properties of both undoped and Yittria doped (Y-IGF) model by theoretical uniaxial tensile experiments. Uniaxial strain was applied by incrementally stretching the super cell in one direction, while the other two dimensions were kept constant. At each strain, all atoms in the model were fully relaxed using Vienna Ab initio Simulation Package VASP. The relaxed model at a given strain serves as the starting position for the next increment of strain. This process is carried on until the total energy (TE) and stress data show that the "sample" is fully fractured. Interesting differences are seen between the stress-strain response of undoped and Y-doped models. For the undoped model, the stress-strain behavior indicates that the initial atomic structure of the IGF is such that there is negligible coupling between the x- and the y-z directions. However, once the behavior becomes non- linear the lateral stresses increase, indicating that the atomic structure evolves with loading [1]. To relate the ab initio calculations to the continuum scales we analyze the atomic-scale deformation field under this uniaxial loading [1]. The applied strain in the x-direction is mostly accommodated by the IGF part of the model and the crystalline part experiences almost negligible strain. As the overall strain on the sample is incrementally increased, the local strain field evolves such that locations proximal to the softer spots attract higher strains. As the load progresses, the strain concentration spots coalesce and eventually form persistent strain localization zone across the IGF. The deformation pattern obtained through ab initio calculations indicates that it is possible to construct discrete grain-scale models that may be used to bridge these calculations to the continuum scale for finite element analysis. Reference: 1. J. Chen, L. Ouyang, P. Rulis, A. Misra, W. Y. Ching, Phys. Rev. Lett. 95, 256103 (2005)

Centrifuge modeling of cyclic lateral response of pile-cap systems and seat-type abutments in dry sands

DOT National Transportation Integrated Search

1998-10-02

This report presents the results of slow, cyclic, lateral-loading centrifuge tests performed on models of pile-cap foundation systems and seat-type bridge abutements in dry Neveda sand of 75% relative density to study the lateral response of these sy...

Biomechanical evaluation of a transtibial pull-out meniscal root repair: challenging the bungee effect.

PubMed

Cerminara, Anthony J; LaPrade, Christopher M; Smith, Sean D; Ellman, Michael B; Wijdicks, Coen A; LaPrade, Robert F

2014-12-01

A common treatment for posterior meniscal root tears is transtibial pull-out repair, which has been biomechanically reported to restore tibiofemoral contact mechanics to those of the intact knee. Biomechanical data suggest that there is significant displacement of the repaired meniscal root with cyclic loading, which may be responsible for the poor healing and meniscal extrusion demonstrated in some clinical studies. The purpose of this study was to quantify the time-zero displacement of the posterior meniscal root in response to cyclic loading after transtibial pull-out repair and to quantify the individual contributions to displacement of the following: (1) suture elongation, (2) button-bone interface, and (3) meniscus-suture interface. The meniscus-suture interface was hypothesized to result in significantly more displacement than the button-bone interface or suture elongation. Descriptive laboratory study. Transtibial pull-out repair of the posterior medial meniscal root was performed in 6 porcine knees, and cyclic displacement was measured using a loading protocol representative of postoperative rehabilitation. Displacement from (1) suture elongation, (2) the button-bone interface, and (3) the meniscus-suture interface was determined by cyclically loading 6 specimens for each construct using the same loading protocol to determine the contribution of each component to the overall displacement of the repair construct. After 1000 cycles, the repair construct displaced by a mean of 3.28 mm (95% CI, 2.07-4.49). The meniscus-suture component (mean, 2.52 mm; 95% CI, 2.21-2.83) displaced significantly more than the button-bone component (mean, 0.90 mm; 95% CI, 0.64-1.15; P = .006) and suture elongation component (mean, 0.71 mm; 95% CI, 0.36-1.06; P = .006) after 1000 cycles. Displacement of the button-bone and suture elongation components was not significantly different after 1000 cycles (P = .720). There was substantial displacement of the posterior medial meniscal root repaired with the transtibial pull-out technique under a cyclic loading protocol simulating postoperative rehabilitation. The meniscus-suture interface contributed to significantly more displacement than the button-bone interface and suture elongation in the transtibial pull-out repair construct. The results provide a framework for optimizing the transtibial pull-out repair technique. Future studies should focus on improving suture fixation strength within the meniscus-suture interface. © 2014 The Author(s).

Nonlinear effects on composite laminate thermal expansion

NASA Technical Reports Server (NTRS)

Hashin, Z.; Rosen, B. W.; Pipes, R. B.

1979-01-01

Analyses of Graphite/Polyimide laminates shown that the thermomechanical strains cannot be separated into mechanical strain and free thermal expansion strain. Elastic properties and thermal expansion coefficients of unidirectional Graphite/Polyimide specimens were measured as a function of temperature to provide inputs for the analysis. The + or - 45 degrees symmetric Graphite/Polyimide laminates were tested to obtain free thermal expansion coefficients and thermal expansion coefficients under various uniaxial loads. The experimental results demonstrated the effects predicted by the analysis, namely dependence of thermal expansion coefficients on load, and anisotropy of thermal expansion under load. The significance of time dependence on thermal expansion was demonstrated by comparison of measured laminate free expansion coefficients with and without 15 day delay at intermediate temperature.

Thermal and Structural Performance of Woven Carbon Cloth For Adaptive Deployable Entry and Placement Technology

NASA Technical Reports Server (NTRS)

Arnold, James O.; Peterson, Keith H.; Yount, Bryan C.; Schneider, Nigel; Chavez-Garcia, Jose

2013-01-01

Arcjet testing and analysis of a three-dimensional (3D) woven carbon fabric has shown that it can be used as a thermal protection system and as a load bearing structural component for a low ballistic coefficient hypersonic decelerator called ADEPT (Adaptive Deployable Entry and Placement Technology). Results of arcjet tests proved that the 3D woven carbon fabric can withstand flight-like heating while under flight-like biaxial mechanical loads representative of those encountered during shallow entry flight path angles into the atmosphere of Venus. Importantly, the arcjet test results have been used to extend a preliminary material thermal response model based on previous testing of the same 3D woven carbon fabric under uni-axial mechanical loading.

Analytical Modelling of Transverse Matrix Cracking of [plus or minus Theta/90(sub n)](sub s) Composite Laminates Under Multiaxial Loading

NASA Technical Reports Server (NTRS)

Mayugo, J A.; Camanho, P. P.; Maimi, P.; Davila, C. G.

2010-01-01

An analytical model based on the analysis of a cracked unit cell of a composite laminate subjected to multiaxial loads is proposed to predict the onset and accumulation of transverse matrix cracks in the 90(sub n) plies of uniformly stressed [plus or minus Theta/90(sub n)](sub s) laminates. The model predicts the effect of matrix cracks on the stiffness of the laminate, as well as the ultimate failure of the laminate, and it accounts for the effect of the ply thickness on the ply strength. Several examples describing the predictions of laminate response, from damage onset up to final failure under both uniaxial and multiaxial loads, are presented.

i RadMat: A thermo-mechanical testing system for in situ high-energy X-ray characterization of radioactive specimens

DOE PAGES

Zhang, Xuan; Xu, Chi; Wang, Leyun; ...

2017-01-27

Here, we present an in situ Radiated Materials (iRadMat) experimental module designed to interface with a servo-hydraulic load frame for X-ray measurements at beamline 1-ID at the Advanced Photon Source. This new capability allows in situ studies of radioactive specimens subject to thermo-mechanical loading using a suite of high-energy X-ray scattering and imaging techniques. The iRadMat is a radiation-shielded vacuum heating system with the sample rotation-under-load capability. We describe the design features and performances of the iRadMat and present a dataset from a 300 °C uniaxial tensile test of a neutron-irradiated pure Fe specimen to demonstrate its capabilities.

Deformability of shredded tires

DOT National Transportation Integrated Search

1999-01-01

This report describes three separate studies that examine the deformability of shredded tire fill material. The first study determined the response of shredded tires to cyclic loading. These tests were conducted in a load frame on both constrained an...

A Cyclic-Plasticity-Based Mechanistic Approach for Fatigue Evaluation of 316 Stainless Steel Under Arbitrary Loading

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

Barua, Bipul; Mohanty, Subhasish; Listwan, Joseph T.

In this paper, a cyclic-plasticity based fully mechanistic fatigue modeling approach is presented. This is based on time-dependent stress-strain evolution of the material over the entire fatigue life rather than just based on the end of live information typically used for empirical S~N curve based fatigue evaluation approaches. Previously we presented constant amplitude fatigue test based related material models for 316 SS base, 508 LAS base and 316 SS- 316 SS weld which are used in nuclear reactor components such as pressure vessels, nozzles, and surge line pipes. However, we found that constant amplitude fatigue data based models have limitationmore » in capturing the stress-strain evolution under arbitrary fatigue loading. To address the above mentioned limitation, in this paper, we present a more advanced approach that can be used for modeling the cyclic stress-strain evolution and fatigue life not only under constant amplitude but also under any arbitrary (random/variable) fatigue loading. The related material model and analytical model results are presented for 316 SS base metal. Two methodologies (either based on time/cycle or based on accumulated plastic strain energy) to track the material parameters at a given time/cycle are discussed and associated analytical model results are presented. From the material model and analytical cyclic plasticity model results, it is found that the proposed cyclic plasticity model can predict all the important stages of material behavior during the entire fatigue life of the specimens with more than 90% accuracy« less

A Cyclic-Plasticity-Based Mechanistic Approach for Fatigue Evaluation of 316 Stainless Steel Under Arbitrary Loading

DOE PAGES

Barua, Bipul; Mohanty, Subhasish; Listwan, Joseph T.; ...

2017-12-05

In this paper, a cyclic-plasticity based fully mechanistic fatigue modeling approach is presented. This is based on time-dependent stress-strain evolution of the material over the entire fatigue life rather than just based on the end of live information typically used for empirical S~N curve based fatigue evaluation approaches. Previously we presented constant amplitude fatigue test based related material models for 316 SS base, 508 LAS base and 316 SS- 316 SS weld which are used in nuclear reactor components such as pressure vessels, nozzles, and surge line pipes. However, we found that constant amplitude fatigue data based models have limitationmore » in capturing the stress-strain evolution under arbitrary fatigue loading. To address the above mentioned limitation, in this paper, we present a more advanced approach that can be used for modeling the cyclic stress-strain evolution and fatigue life not only under constant amplitude but also under any arbitrary (random/variable) fatigue loading. The related material model and analytical model results are presented for 316 SS base metal. Two methodologies (either based on time/cycle or based on accumulated plastic strain energy) to track the material parameters at a given time/cycle are discussed and associated analytical model results are presented. From the material model and analytical cyclic plasticity model results, it is found that the proposed cyclic plasticity model can predict all the important stages of material behavior during the entire fatigue life of the specimens with more than 90% accuracy« less

Hysteretic Models Considering Axial-Shear-Flexure Interaction

NASA Astrophysics Data System (ADS)

Ceresa, Paola; Negrisoli, Giorgio

2017-10-01

Most of the existing numerical models implemented in finite element (FE) software, at the current state of the art, are not capable to describe, with enough reliability, the interaction between axial, shear and flexural actions under cyclic loading (e.g. seismic actions), neglecting crucial effects for predicting the nature of the collapse of reinforced concrete (RC) structural elements. Just a few existing 3D volume models or fibre beam models can lead to a quite accurate response, but they are still computationally inefficient for typical applications in earthquake engineering and also characterized by very complex formulation. Thus, discrete models with lumped plasticity hinges may be the preferred choice for modelling the hysteretic behaviour due to cyclic loading conditions, in particular with reference to its implementation in a commercial software package. These considerations lead to this research work focused on the development of a model for RC beam-column elements able to consider degradation effects and interaction between the actions under cyclic loading conditions. In order to develop a model for a general 3D discrete hinge element able to take into account the axial-shear-flexural interaction, it is necessary to provide an implementation which involves a corrector-predictor iterative scheme. Furthermore, a reliable constitutive model based on damage plasticity theory is formulated and implemented for its numerical validation. Aim of this research work is to provide the formulation of a numerical model, which will allow implementation within a FE software package for nonlinear cyclic analysis of RC structural members. The developed model accounts for stiffness degradation effect and stiffness recovery for loading reversal.