Dynamic Stress-strain Properties Research Articles

Effect of strain rate on transient local strain variations in articular cartilage

The non-homogeneous, anisotropic material properties, and triphasic nature of articular cartilage enables diarthrodial joints to withstand large and complex physiological loading conditions. To develop biomaterials that provide similar functional properties as those found in articular cartilage, it is vital to have knowledge of the strain distributions in cartilage for a large range of loading conditions. Applied stress vs. strain properties of articular cartilage have been measured primarily for static conditions, but the dynamic properties are thought to be more relevant for joint function and cartilage biosynthesis. Furthermore, the dynamic stress-strain properties are expected to vary significantly from those obtained for static, steady-state conditions. Here, we present a method for the determination of axial strain fields throughout the depth of articular cartilage for static loading conditions and dynamic conditions performed at different loading rates. For the conditions tested here, the strain distributions throughout the cartilage depth were more uniform for the dynamic than the static loading conditions, and more uniform for high compared to low strain rates.

Reduction of dynamic earth loads on flexible cantilever retaining walls by deformable geofoam panels

The potential application of geofoam in reducing the dynamic earth forces on flexible cantilever earth retaining walls was investigated through small-scale physical model tests. Tests were carried out using a state-of-the-art laminar container and a uniaxial shaking table. Deformable geofoam panels of low stiffness made from expanded polystyrene (EPS) and extruded polystyrene (XPS) geofoam were utilized as compressible inclusions in the present study. The dynamic stress-strain properties of these geomaterials are discussed based on results from laboratory cyclic triaxial tests. Lateral dynamic earth pressures and wall displacements at different elevations within the backfill were monitored during the application of various base excitations. The test results revealed that the presence of a deformable geofoam panel of low stiffness behind the flexible retaining wall will result in a reduction of the dynamic wall pressures and displacements. The geofoam efficiency in terms of load and displacement reduction decreases as the flexibility ratio of the model wall increases. On the other hand, load reduction efficiency of the geofoam increases as the amplitude and frequency ratio of the excitation increases. Load reduction efficiencies achieved in the tests were compared to those of the previous physical and numerical modeling studies available in the literature. Comparisons indicate that there is an agreement with the data presented in the previous modeling studies for low acceleration amplitudes and wall flexibility values, however, this agreement diminishes as wall flexibility begins to play role in reducing the earth pressures. Application point of the maximum dynamic thrust varies between 0.4H to 0.6H depending on the inclusion type, flexibility ratio of the wall and the characteristics of the harmonic motion applied to the base of the models.

Dynamic stress–strain properties of Ti–Al–V titanium alloys with various element contents

A series of Ti–Al–V titanium alloy bars with nominal composition Ti–7Al–5V ELI, Ti–5Al–3V ELI, commercial Ti–6Al–4V ELI and commercial Ti–6Al–4V were prepared. These alloys were then heat treated to obtain bimodal or equiaxed microstructures with various contents of primary α phase. Dynamic compression properties of the alloys above were studied by split Hopkinson pressure bar system at strain rates from 2,000 to 4,000 s−1. The results show that Ti–6Al–4V alloy with equiaxed primary α (αp) volume fraction of 45 vol% or 67 vol% exhibits good dynamic properties with high dynamic strength and absorbed energy, as well as an acceptable dynamic plasticity. However, all the Ti53ELI specimens and Ti64ELI specimens with αp of 65 vol% were not fractured at a strain rate of 4,000 s−1. It appears that the undamaged specimens still have load-bearing capability. Dynamic strength of Ti–Al–V alloy can be improved as the contents of elements Al, V, Fe, and O increase, while dynamic strain is not sensitive to the composition in the appropriate range. The effects of primary alpha volume fraction on the dynamic properties are dependent on the compositions of Ti–Al–V alloys.

Electrically conductive silicone rubber–steel fibre composites

Steel fibre–silicone rubber composites were prepared by two-roll mill method. Various weight fractions of fibres ranging from 20 phr (parts per hundred parts of rubber) to 90 phr, with a diameter of 7–8 μm and length of several metres were used and its influence on the surface resistance, physical properties, short-term and dynamic stress–strain properties of the composites were investigated. Addition of steel fibres renders a sharp decrease in resistance from MΩ to ~3–0.1 kΩ with the concentration from 20 phr to 90 phr, respectively. Addition of 20 phr of steel fibres yields composite with a resistance of 5–10 kΩ, other properties being negligibly altered.

Physically Based Model for Static and Dynamic Behaviour of TRIP Steel

Low alloy multiphase TRansformation Induced Plasticity (TRIP) steels offer an excellent combination of a large uniform elongation and a high strength. This results from the composite behaviour of the different phases that are present in these steels: polygonal ferrite, bainitic ferrite and a martensite/austenite constituent. In order to obtain a clear understanding of the behaviour of the different constituents within the multiphase steel, they were prepared separately. The stress-strain relationship of the different single phase and multiphase steels were simulated with physically based micromechanical models. The model used to describe the stress-strain curves of the separate phases is based on the Mecking-Kocks and Seeger-Kocks theories and uses physical properties such as the microstructural properties and the chemical composition of the different phases. Strain-induced transformation kinetics, based on a generalized form of the Olson-Cohen law, were used to include the influence of the transformation of the metastable austenite. Static stress-strain properties of multiphase steels were modelled by the successive application of a Gladman type mixture law for two-phase steels. The model yields detailed information of stress and strain partitioning between the different phases during a static tensile test. A model for the dynamic stress-strain properties of ferritic steels is also proposed.

Seismic p ∼ y Responses of Flexible Piles

The finite element method was designed to solve soil-pile-structure interaction under seismic excitation by introducing solid beam elements to reproduce beam flexure and soil-pile interaction. Dynamic lateral load-deflection relationships were characterized by ratio of soil reaction per unit pile length to product of pile displacement relative to free-field motion and dynamic stress-strain properties of soil. Three hetergeneous soil profiles with equivalent linear approximation of nonlinear stress-strain behavior were used with this new finite element method to study the characteristics of dynamic lateral load-deflection relationships. Results were compared with those by other investigators and showed that the proposed method provided improved means of evaluating load-deflection relationships of piles. Results of this study were used to compute discrete soil-pile springs and dashpots for use in a beam-on-Winkler foundation model. (ASCE)

Test procedures for characterising dynamic stress-strain properties of pavement materials : US Transportation Research Board special report 162, 1975, 40P

Test procedures for characterising dynamic stress-strain properties of pavement materials : US Transportation Research Board special report 162, 1975, 40P

Dynamic Stress—Strain Properties of a Steel and a Brass at Strain Rates up to 104 Per Second

Results of compression tests on 70:30 brass and a mild steel at strain rates from 10-3to 104per second are reported. The tests were carried out on a reactionless gas forging rig, using a high-frequency response piezo-electric load cell. The brass is shown to be relatively insensitive to strain rate over the range of the tests. The mild steel in the ‘as-received’ condition showed a marked increase in initial flow stress at high strain rates; pre-straining removed the phenomenon and ageing re-established it so that the rise in yield stress can be attributed to a ‘yield-point phenomenon’. The strain associated with the drop in stress following yielding is noted to be large and it is demonstrated that this results from the finite time for yielding to propagate along the specimen.

Effect of sampling on the dynamic stress-strain properties of till. Symposium. Summaries of papers : Silver, ML Univ. Illinois, Chicago, USA Faillace, GA Dames and Moore, Madrid, E Midland Soil Mech. Found. Engng Soc. Symp. on Engng Behaviour of Glacial Materials, Birmingham, April, 1975

Effect of sampling on the dynamic stress-strain properties of till. Symposium. Summaries of papers : Silver, ML Univ. Illinois, Chicago, USA Faillace, GA Dames and Moore, Madrid, E Midland Soil Mech. Found. Engng Soc. Symp. on Engng Behaviour of Glacial Materials, Birmingham, April, 1975

衝撃荷重を局部的に受ける場合の発ぽうスチロールの動的圧縮応力‐ひずみ特性

This paper presents the dynamic stress-strain properties of styrofoams under impact loading acting on a limited area. The specimens with the dimension of 100_??_mm×30tmm were bonded on the end of surface of the pendulum being impacted. The impact loading was applied to the center portion of the specimens by another impact pendulum with the diameter of 50φmm. The acceleration-time curves induced in the impacted pendulum were measured. The dynamic stress and strain were calculated by integrating these acceleration-time curves numerically. The effects of the strain rate and the number of impact loadings on the dynamic properties of styrofoams were examined in comparison with the results of the uniform impact loading on the whole_ surface area described in the previous report. The cushion factor-stress properties were also discussed. The results obtained are as follows:(1) Under localized impact loading, the strength and stiffness of styrofoams increase with increasing strain rate up to about 20/sec, beyond which they start to decrease.(2) A remarkable difference exists between the stress-strain properties under localized impact loading and those under uniform impact loading in the strain range beyond 20%.(3) The stiffness of styrofoams is remarkably reduced in the low strain range by the first application of localized impact loading, but the reduction becomes comparatively small in the higher strain range. The further reduction in stiffness is induced by the successive application of impact loadings.(4) The styrofoams seems to have the critical deformation rate at the strain rate of 35/sec under localized impact loading. In this strain rate, the dynamic stress-strain relationship becomes complicated because of the fracture in the vicinity of loading area.(5) The depth of the disintegration produced in styrofoams by localized impact loading can be indirectly estimated from the knee appeared on the cushion factor-stress curve.

Dynamic Stress-Strain Properties of Styrofoams

This paper presents the dynamic stress-strain properties of styrofoams. Two ballistic pendulums were used in this experiment. The specimens, which had been bonded on the end surface of the pendulum being impacted, were loaded by the impact pendulum. The acceleration-time curves induced in the impacted pendulum were measured. The dynamic stress and strain were calculated by integrating these acceleration-time curves numerically. The effects of the strain rates and the number of impact loadings on the dynamic properties of styrofoams were examined and the accuracy of the test result was also discussed. The results obtained are as follows:(1) The dynamic stress-strain properties of foamed plastics can be obtained with the accuracy of about 3 percent by this experimental method.(2) The strength and stiffness of styrofoams increase with increasing the strain rate up to about 20/sec, beyond which they start to decrease.(3) The stiffness of styrofoams is remarkably reduced by the first application of impact loading but does not change any more by its further successive applications.(4) At the strain rate of about 35∼40/sec, styrofoams disintegrate in an explosive manner. Therefore, the styrofoams seem to have the critical deformation rate in the vicinity of this strain rate.

Effective Stress Theory of Soil Compaction

The application of a compaction pressure to an unsaturated soil results in the development of shearing stresses at the points of contact between soil particles until the contacts fail. The particles then slide over one another with an increase in density. The compaction characteristics of soil are thus controlled by the shearing resistance of these contacts. The shearing strength is a function of the effective normal stress. When the compaction pressure is applied to a dry soil, the effective stress is approximately equal to the total stress, because the χ-coefficient is small. The addition of water increases the degree of saturation and increases the pore pressures, thus weakening the soil. Hence, the soil deforms more under stress, and higher densities result. The density must increase during compaction until the total stress, the pore-air pressure, and the pore-water pressure combine to give the required effective stresses. The theory is qualitative because little is known of the dynamic stress-strain properties of unsaturated soils.