The Influence of Peak Stress on the Mechanical Behavior and the Substructural Evolution in Shock-Prestrained Zirconium

2004 ◽  
Author(s):  
E. Cerreta
Keyword(s):  
Mechanical Behavior ◽  
Peak Stress

The Effect of Flash Freezing on Variability in Spinal Cord Compression Behavior

2009 ◽  
Vol 131 (11) ◽  
Author(s):  
Carolyn J. Sparrey ◽  
Tony M. Keaveny
Keyword(s):  
Spinal Cord ◽  
Mechanical Behavior ◽  
Mechanical Response ◽  
Peak Stress ◽  
Specimen Geometry ◽  
Specimen Preparation ◽  
Spinal Cord Tissue ◽  
Compression Behavior ◽  
Interface Friction ◽  
Cord Injury

The compression behavior of spinal cord tissue is important for understanding spinal cord injury mechanics but has not yet been established. Characterizing compression behavior assumes precise specimen geometry; however, preparing test specimens of spinal cord tissue is complicated by the extreme compliance of the tissue. The objectives of this study were to determine the effect of flash freezing on both specimen preparation and mechanical response and to quantify the effect of small deviations in specimen geometry on mechanical behavior. Specimens of porcine spinal cord white matter were harvested immediately following sacrifice. The tissue was divided into two groups: partially frozen specimens were flash frozen (60 s at −80°C) prior to cutting, while fresh specimens were kept at room temperature. Specimens were tested in unconfined compression at strain rates of 0.05 s−1 and 5.0 s−1 to 40% strain. Parametric finite element analyses were used to investigate the effect of specimen face angle, cross section, and interface friction on the mechanical response. Flash freezing did not affect the mean mechanical behavior of the tissue but did reduce the variability in the response across specimens (p<0.05). Freezing also reduced variability in the specimen geometry. Variations in specimen face angle (0–10 deg) resulted in a 34% coefficient of variation and a 60% underestimation of peak stress. The effect of geometry on variation and error was greater than that of interface friction. Taken together, these findings demonstrate the advantages of flash freezing in biomechanical studies of spine cord tissue.

scholarly journals Mechanical Behavior of Shale Rock under Uniaxial Cyclic Loading and Unloading Condition

2018 ◽  
Vol 2018 ◽  
pp. 1-8 ◽  
Author(s):  
Baoyun Zhao ◽  
Dongyan Liu ◽  
Ziyun Li ◽  
Wei Huang ◽  
Qian Dong
Keyword(s):  
Cyclic Loading ◽  
Mechanical Behavior ◽  
Creep Behavior ◽  
Peak Stress ◽  
Creep Model ◽  
Cycle Number ◽  
Shale Rock ◽  
Cyclic Loading And Unloading ◽  
Residual Strains ◽  
Loading And Unloading

In order to investigate the mechanical behavior of shale rock under cyclic loading and unloading condition, two kinds of incremental cyclic loading tests were conducted. Based on the result of the short-term uniaxial incremental cyclic loading test, the permanent residual strain, modulus, and damage evolution were analyzed firstly. Results showed that the relationship between the residual strains and the cycle number can be expressed by an exponential function. The deformation modulus E50 and elastic modulus ES first increased and then decreased with the peak stress under the loading condition, and both of them increased approximately linearly with the peak stress under the unloading condition. On the basis of the energy dissipation, the damage variables showed an exponential increasing with the strain at peak stress. The creep behavior of the shale rock was also analyzed. Results showed that there are obvious instantaneous strain, decay creep, and steady creep under each stress level and the specimen appears the accelerated creep stage under the 4th stress of 51.16 MPa. Based on the characteristics of the Burgers creep model, a viscoelastic-plastic creep model was proposed through viscoplastic mechanics, which agrees very well with the experimental results and can better describe the creep behavior of shale rock better than the Burgers creep model. Results can provide some mechanics reference evidence for shale gas development.

Numerical Brazilian split test of pre-cracked granite with randomly distributed micro-components

2020 ◽  
Vol 37 (8) ◽  
pp. 2641-2657
Author(s):  
Shiqi Liu ◽  
Huanling Wang ◽  
Weiya Xu ◽  
Xiao Qu ◽  
W.C. Xie
Keyword(s):  
Mechanical Behavior ◽  
Mineral Composition ◽  
Numerical Models ◽  
Strain Curve ◽  
Peak Stress ◽  
Simulation Method ◽  
Content Type ◽  
Rock Bridge ◽  
Split Test ◽  
Granite Samples

Purpose The purpose of this paper is to investigate the mechanical behavior and propagation of cracks of numerical granite samples through the Brazilian split test and to provide a reference for predicting the behavior of real granite samples. Design/methodology/approach The numerical models of granite containing two fissures are established using the parallel bond model (PBM) and the smooth joint model (SJM) in PFC2D. The peak stresses, number of cracks and anisotropic ratios are obtained to study the influence of the mineral composition and the angle of inclination of rock bridge on the strength, failure mode and deformation characteristics. Findings The numerical results obtained show that the mineral composition has a marginal influence on the peak stress. When the angle of inclination of rock bridge β increases, the peak stress drops to its minimum value at β = 90° and then gradually increases to a relatively low level. The behavior of cracks falls into three categories based on the distribution of cracks. By analyzing the stress–strain curve and the process of crack propagation for sample No. 4 with β = 60°, it is found that the process of failure can be divided into four stages and tensile cracks dominate. The anisotropic ratios of peak stress and a number of cracks obtained show that the peak stress is low anisotropic and the number of cracks is medium anisotropic. Originality/value This paper presents a numerical simulation method to analyze mechanical behavior and propagation of cracks under different conditions. The proposed method and the results obtained are useful for predicting the behavior of real granite samples in laboratory and engineering projects.

scholarly journals Experimental Investigation of the Mechanical Behavior of Layer-Crack Specimens under Cyclic Uniaxial Compression

Symmetry ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 465
Author(s):  
Wei-yao Guo ◽  
Feng-hai Yu ◽  
Yue Qiu ◽  
Tong-bin Zhao ◽  
Yun-liang Tan
Keyword(s):  
Cyclic Loading ◽  
Energy Density ◽  
Mechanical Behavior ◽  
Elastic Energy ◽  
Peak Stress ◽  
Dissipated Energy ◽  
Strengthening Effect ◽  
Input Energy ◽  
Rock Bursts ◽  
Number Of Cycles

It is generally acknowledged that the failure of the layer-crack structure is closely related to rock bursts (a layer-crack structure means a coal or rock rib that is cut by fractures that are parallel or sub-parallel to the surface of the rib). Understanding the mechanical behavior of the layer-crack structure under cyclic loading is beneficial for rock burst mitigation. This study experimentally investigated the influence of the geometry of vertical fissure (i.e., width, length and number) on the mechanical properties of layer-crack rock specimens. The results show that the sensitivity of parameters with respect to the geometry of the fissure from strong to weak is the number, length and width. First, the peak stress under cyclic loading increases by approximately 7.82%–17.35%, thereby exerting an obvious strengthening effect. Second, the fissure geometry slightly affects the energy evolution of the layer-crack specimen, i.e., the input energy density, elastic energy density and dissipated energy density all gradually increase with the increase of the number of cycles. However, when approaching a specimen failure, the increasing rates from quick to slow are the dissipated energy, input energy and elastic energy. Third, the damage variable of the layer-crack specimen shows a concave increasing trend with the increase of the number of cycles. When the number of cycles is equal, the damage increases with the increase of the number of fissures, but it decreases with the increase of the fissure length. Fourth, AE events occur shortly before specimen failures, but rapidly increase near the specimen failures. The accumulated AE events that lead to specimen failures decrease with the increase in the number of fissures. These results can provide some basic data for the research of rock bursts related to the failures of layer-crack structures.

Influence of Sulfate Attack and Drying-Wetting Cycle on Properties of Mortar

2012 ◽  
Vol 204-208 ◽  
pp. 3731-3735
Author(s):  
Da Chen ◽  
Na Wang ◽  
Chao Hua Jiang
Keyword(s):  
Mechanical Behavior ◽  
Peak Stress ◽  
Solution Concentration ◽  
Sulfate Attack ◽  
Peak Strain ◽  
High Concentration ◽  
Cycle Number ◽  
Change Rate ◽  
Mortar Specimen ◽  
High Concentration Solution

This paper presents the study on mortar specimens exposed to three kinds of Na2SO4 solution(0.5%,5%and10%)and different drying-wetting cycles(20,30,40and75). Influence of cycle number and solution concentration on mechanical behavior, mass and appearance of mortar specimen was analysis. The results show that surface of specimen in 5% and 10% solution shows obvious desizing, sandiness and some crack at 75 drying-wetting cycles. In different solution concentration, mass of specimen shows a trend to increase firstly then decrease lately. The increasing and declining separately of specimen mass are more obvious in high concentration solution. In three kinds concentration of solution, peak stress and modulus of elasticity of specimen show the same trend to increase in early erosion stage and decrease in late erosion stage. Change rate of mechanical behavior of specimen in high concentration solution is larger than that of in low concentration solution at early and later stage separately. On the contrary, peak strain show a trend to decline firstly then increase lately.

Nicotine Affects Murine Aortic Stiffness and Fatigue Response During Supraphysiological Cycling

2021 ◽  
Author(s):  
Elizabeth Ho ◽  
Joscha Mulorz ◽  
Jason Wong ◽  
Markus U. Wagenhäuser ◽  
Philip Tsao ◽  
...  
Keyword(s):  
Mechanical Behavior ◽  
Peak Stress ◽  
Uniaxial Tensile ◽  
Nicotine Exposure ◽  
Fatigue Cycling ◽  
Pathological Conditions ◽  
Induced Changes ◽  
Aortic Remodeling ◽  
Static And Dynamic Loading ◽  
Simple Stress

Abstract Nicotine exposure is a major risk factor for several cardiovascular diseases. Although the deleterious effects of nicotine on aortic remodeling processes have been studied to some extent, the biophysical consequences are not fully elucidated. In this investigation, we applied quasi-static and dynamic loading to quantify ways in which exposure to nicotine affects mechanical behavior of murine arterial tissue. Segments of thoracic aortas from C57BL/6 mice exposed to 25 mg/kg/day of subcutaneous nicotine for 28 days were subjected to uniaxial tensile loading in an open-circumferential configuration. Comparing aorta segments from nicotine-treated mice relative to an equal number of control counterparts, stiffness in the circumferential direction was nearly two-fold higher (377 kPa ± 165 kPa vs. 191 kPa ± 65 kPa, n = 5, p = 0.03) at 50% strain. Using a degradative power-law fit to fatigue data at supraphysiological loading, we observed that nicotine-treated aortas exhibited significantly higher peak stress, greater loss of tension, and wider oscillation band than control aortas (p = 0.01 for all three variables). Compared to simple stress relaxation tests, fatigue cycling is shown to be more sensitive and versatile in discerning nicotine-induced changes in mechanical behavior over many cycles. Supraphysiological fatigue cycling thus may have broader potential to reveal subtle changes in vascular mechanics caused by other exogenous toxins or pathological conditions.

Mechanical Behavior of Processed AZ91D by Equal Channel Angular Extrusion during Semi-Solid Isothermal Compression

2006 ◽  
Vol 116-117 ◽  
pp. 530-533 ◽  
Author(s):  
Ju Fu Jiang ◽  
Shou Jing Luo
Keyword(s):  
Plastic Deformation ◽  
Strain Rate ◽  
Mechanical Behavior ◽  
Equal Channel Angular Extrusion ◽  
Peak Stress ◽  
True Stress ◽  
Sudden Increase ◽  
Isothermal Compression ◽  
Angular Extrusion ◽  
Semi Solid

Mechanical behavior of processed AZ91D magnesium alloy by equal channel angular extrusion during semi-solid isothermal compression was investigated using semi-solid isothermal compression test. The results show that there are four stages, drastic increase of true stress, drastic falling of true stress, steady stage and increase of true stress. With the increase of holding time or deformation temperature, required true stress for obtaining same true strain falls evidently and peak stress and steady stress also fall in true stress-strain curve. With increasing strain rate, steady stress also increase. Peak stress will increase or decrease with the sudden increase or fall of strain rate. During semi-solid isothermal compression, plastic deformation of semi-solid billet mainly depends on plastic deformation of solid phases and their rotation and sliding. Coarse grains occur in upper position adjacent to compression die’s surface and fine grains occur in the central and free surface positions of billets.

scholarly journals Study on Macroscopic and Mesoscopic Mechanical Behavior of CSG based on Inversion of Mesoscopic Material Parameters

2020 ◽  
Vol 27 (1) ◽  
pp. 65-72
Author(s):  
Lixia Guo ◽  
Yanan Zhang ◽  
Ling Zhong ◽  
Minghua Wang ◽  
Xuanyi Zhu
Keyword(s):  
Numerical Simulation ◽  
Mechanical Behavior ◽  
Failure Time ◽  
Low Cost ◽  
Peak Stress ◽  
Simulation Method ◽  
Uniaxial Compression Test ◽  
Interface Unit ◽  
Mesoscopic Level ◽  
Sand And Gravel

AbstractCement Sand and Gravel (CSG) is a low-cost, environment-friendly composite material mixed of unscreened aggregate, cement, fly ash and water, and its properties differ from ordinary concrete due to different aggregate characteristics. In order to investigate the effect of aggregate characteristics on the mechanical behavior of CSG, this paper used numerical simulation method to divide the CSG into aggregate unit, cement mortar unit and interface unit at the mesoscopic level and randomly generate aggregate, then used laboratory uniaxial compression test results to inverse the said mesoscopic component parameters, and finally verified the rationality of mesoscopic numerical simulation. Based on the inversed parameters, the numerical simulation test of different aggregate grading was carried out and analyzed. The results showed that: (1) From the perspective of macroscopic mechanical properties, as the sand ratio increased, the aggregate occupancy and the peak stress decreased; under the same aggregate occupancy (the same sand ratio), the stress peak became higher with the improvement of aggregate grading (aggregates of small particle size increased); (2) At the mesoscopic level, the crack of CSG usually appeared on the interface and around the aggregate; the smaller the sand ratio was, the higher the aggregate occupancy was, the more obvious the stress concentration was, and the earlier the cracking of the test piece was, but there were many aggregates, so the eventual failure time was delayed. These research results can provide theoretical basis for engineering design and construction.

Application of TEM to Deformation, Wear, and Fracture of Ceramics

1974 ◽  
Vol 32 ◽  
pp. 472-473
Author(s):  
B. J. Hockey
Keyword(s):  
Wear Resistance ◽  
High Temperature ◽  
Mechanical Behavior ◽  
Brittle Materials ◽  
High Temperature Strength ◽  
Wide Range ◽  
Corrosive Environments ◽  
Further Development

Ceramics, such as Al2O3 and SiC have numerous current and potential uses in applications where high temperature strength, hardness, and wear resistance are required often in corrosive environments. These materials are, however, highly anisotropic and brittle, so that their mechanical behavior is often unpredictable. The further development of these materials will require a better understanding of the basic mechanisms controlling deformation, wear, and fracture.The purpose of this talk is to describe applications of TEM to the study of the deformation, wear, and fracture of Al2O3. Similar studies are currently being conducted on SiC and the techniques involved should be applicable to a wide range of hard, brittle materials.

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