Increasing Shear Strain Research Articles

Load plate rigidity and scale effects on the frictional behavior of sand/geomembrane interfaces

The possible load plate rigidity and scale effects on the frictional behavior of the interface between a quartz sand and high-density polyethylene (HDPE) geomembranes was investigated. The test materials included a quartz sand against smooth and textured HDPE geomembranes. The American Society for Testing and Materials D-5321 standard test method is adopted for measuring the shear strength of the interface between the test soil and geomembranes. The dimensions of the shear boxes are 100×100, 200×200, 300×300 and 400×400 mm 2 . In addition to the use of conventional rigid load plates to transfer applied load to the test specimens, a silicon-membrane-type water bladder was also designed to attach at the bottom of the conventional rigid load plate to form a flexible load plate. Moreover, a measuring device was used to replace the lower shear box for measuring the variation of normal pressures at the shearing plane. The results of the study indicated that the use of conventional rigid load plate to perform direct shear test results in a concave pressure distribution at the shearing plane. A minimum of 5 cm thickness of soil in upper shear box is recommended in order to ensure the reproduction of normal pressures at the shearing plane when a rigid load plate is used for applying the normal load. The use of flexible load plate for large-scale direct shear test machine would provide an anticipated uniform pressure distribution at interface shearing plane. A thickness of 2– 3 cm of sand layer in the upper shear box should be enough if loading is applied using a flexible load plate. The shear resistance associated with flexible and rigid load plate is quite similar to each other under same test conditions. However, the direct shear test performed using flexible load plate showed a better reproducibility of test data than that using rigid load plate. The size of shear box has an effect on the shear strength at the interface of sand/geomembrane systems. In general, the shear strength for larger shear box is greater than that associated with smaller shear box. However, the shear strength associated with 300×300 and 400×400 mm 2 shear boxes is almost identical to one another. Thus, it is recommended that minimum dimension of 300×300 mm 2 direct shear box should be used for determining the shear strength at the interface of a sand/geomembrane system. The shearing resistance associated with textured HDPE geomembrane is greater than that associated with a smooth-surfaced geomembrane. The shear strength associated with textured HDPE geomembranes increases with increasing shear strain. No peak values were observed. Stress–strain curves with peak values only occur for sand/smooth geomembrane system under high normal stress conditions. The friction angle for sand/textured geomembrane combinations is about 12° greater than that for sand/smooth geomembrane combinations.

Ligament material behavior is nonlinear, viscoelastic and rate-independent under shear loading

The material behavior of ligament is determined by its constituents, their organization and their interaction with each other. To elucidate the origins of the multiaxial material behavior of ligaments, we investigated ligament response to shear loading under both quasi-static and rate-dependent loading conditions. Stress relaxation tests demonstrated that the tissue was highly viscoelastic in shear, with peak loads dropping over 40% during 30 min of stress relaxation. The stress relaxation response was unaffected by three decades of change in shear strain rate (1.3, 13 and 130%/s). A novel parameter estimation technique was developed to determine material coefficients that best described the experimental response of each test specimen to shear. The experimentally measured clamp displacements and reaction forces from the simple shear tests were used with a nonlinear optimization strategy based around function evaluations from a finite element program. A transversely isotropic material with an exponential matrix strain energy provided an excellent fit to experimental load–displacement curves. The shear modulus of human MCL showed a significant increase with increasing shear strain ( p<0.001), reaching a maximum of 1.72±0.4871 MPa. The results obtained from this study suggest that viscoelasticity in shear does not likely result from fluid flow. Gradual loading of transversely oriented microstructural features such as intermolecular collagen crosslinks or collagen-proteoglycan crosslinking may be responsible for the stiffening response under shear loading.

ELECTRORHEOLOGICAL FLUIDS UNDER SHEAR

The behavior of an electrorheological (ER) chain under a shear force is investigated theoretically and experimentally. Contrary to the conventional assumption that the ER chain under a shear force becomes slanted and breaks at the middle, we have found that there is symmetry breaking. When the shear strain is small, the chain becomes slanted with a space gap between the first and second particles (or between the last and next last particles). As the shear strain increases, the gap becomes wider and wider. When the shear strain exceeds a critical value, the chain breaks at the gap. The experiment also confirms that an ER chain under the shear breaks at either end, not at the middle. This symmetry breaking reflects the space's anisotropy, which is the result of the applied electric field.

3-D rock salt fabrics in a shear zone (Súria Anticline, South-Pyrenees)

The internal geometry of the evaporitic horizons serves as a good indicator of their large-scale behaviour. However, the determination of the strain ellipsoid inside the deformed salt bodies can often be difficult. Moreover, the relationship between the bulk strain ellipsoid and the grain shape ellipsoid is not straightforward, and two parameters, orientation and the dimension of the grain shape ellipsoid, need evaluation. The grain shape ellipsoid is not an indicator of the dimensions of the bulk strain ellipsoid. The increase in shear strain led initially to a growth in grain volume followed by a reduction to a value near the original volume, specifically due to the long axis change. The orientation of the grain shape ellipsoid runs parallel to that of the strain ellipsoid after a certain amount of deformation. These changes were accompanied by the growth of a new tectonically oriented grain population. The rapid spatial changes in morphology contrast with the constant and strong {100} texture. The intracrystalline deformation mechanism consistent with this texture is the {110}〈1 1 0〉 slip system. Nevertheless, a mechanism such as fluid assisted grain boundary migration might have also taken place to account for the grain volume changes.

Effect of phyllosilicates on fluid-assisted healing of gouge-bearing faults

On the basis of both experimental and field studies, it is widely accepted that solution transfer processes are important in controlling fault strength recovery (healing) in the hydrothermal reaches of the seismogenic zone. Fluid-assisted healing of fault gouge may be strongly influenced by phyllosilicate content and spatial arrangement, but little is known about such effects. To study these effects, we have performed slide–hold–slide experiments using simulated faults containing gouges of halite+kaolinite saturated with brine. In this system, solution transfer processes are extremely fast. The results show rapid healing in the case of pure halite gouge, whereas almost no such effects were observed in foliated, clay-bearing gouge under otherwise identical conditions. The degree of healing increased with increasing shear strain in monomineralic gouge, whereas the opposite was observed in clay-bearing gouge. The above effects are interpreted to be due to phyllosilicates inhibiting halite–halite grain contact healing processes, an effect which becomes more prominent as on-going shear deformation leads to foliation development. The results raise questions regarding recent application of laboratory-derived healing data for monomineralic gouge to natural fault rocks, since these generally contain significant amounts of phyllosilicates and are often foliated.

Small Strain Stiffness of Natural Granitic Saprolite in Hong Kong

Nonlinear stress-strain characteristics and shear stiffness-shear strain relationships of sedimentary soils and recompacted sands at small strains have been reported by many researchers. However, research work on the behavior of granitic soils at small strains has not attracted much attention, despite the fact that many countries around the world are underlain by granitic saprolites. In the study reported in this paper, shear stiffness of a natural granitic saprolite from Hong Kong has been investigated in the field, using the self-boring pressuremeter and geophysical techniques such as the suspension P-wave and S-wave logging method, and in the laboratory, using a triaxial apparatus equipped with internal displacement measuring devices. The observed stiffness-strain relationships of the natural granitic saprolite are highly nonlinear at small strains. Shear stiffness decreases significantly as shear strain increases. At very small shear strains (in the order of 0.001%), the elastic shear moduli deduced f...

Analysis of the billet deformation behaviour in equal channel angular extrusion

Equal channel angular extrusion is a relatively novel method for deforming materials to very high plastic strains, with no net change in the billet's shape. However, before the technique can be exploited it is important to understand the deformation behaviour within the die and its relationship to the tooling configuration and friction conditions. Billets containing scribed grids, simple finite element analysis, and microstructural evidence have been used to investigate this issue. It has been found that the strain achieved is sensitive to the die angle, friction conditions, and the application of a back-pressure, all of which can have a large effect on the microstructure and strain inhomogeneity within the processed billet. The distribution of strain is most uniform, and approximates most closely to a simple shear, if the deformation zone is constrained to be as narrow as possible. The best processing conditions appear to be obtained with a sharp die corner, low friction, and a constraining back-pressure. Embedded marker wire experiments have shown that on repeatedly extruding a billet with a constant strain path rotation of material occurs around the billet's ends. This results in the sheared billet wrapping around on itself during the process and thus maintaining the billet's shape, despite the increasing shear strain in each extrusion cycle.

Evolution of Kink Bands and Tilt Boundaries in Block Copolymers at Large Shear Strains

The evolution of kink bands and kink band boundaries in a prealigned poly(styrene-b-ethylene propylene) lamellar diblock copolymer was investigated by applying steady shear at strains in the range of 1−10 strain units. Boundary morphologies were characterized using transmission electron microscopy. As the shear strain increases, both the kink bands and the lamellae within the kink bands rotate continuously toward the shearing direction, leading to a decrease in the tilt boundary angle and the kink band boundary angle. Simultaneously, the nature of the kink band boundary transforms. The chevron boundaries present at low strains, and thus large tilt angles, become omega boundaries as the strain increases to ∼3 strain units. At higher strains (∼5 strain units), the tilt angle further decreases, and the omega boundaries start to break, preferentially in the PS microdomains. Delamination of the PS microdomains was also observed at the highest strain amplitude (10 strain units), which was associated with the limited extent of entanglement across the PS microdomains.

A New Model and Analysis of Orthogonal Machining With an Edge-Radiused Tool

A new machining process model that explicitly includes the effects of the edge hone is presented. A force balance is conducted on the lower boundary of the deformation zone leading to a machining force model. The machining force components are an explicit function of the edge radius and shear angle. An increase in edge radius leads to not only increased ploughing forces but also an increase in the chip formation forces due to an average rake angle effect. Previous attempts at assessing the ploughing components as the force intercept at zero uncut chip thickness, which attribute to the ploughing mechanism all the changes in forces that occur with changes in edge radius, are seen to be erroneous in view of this model. Calculation of shear stress on the lower boundary of the deformation zone using the new machining force model indicates that the apparent size effect when cutting with edge radiused tools is due to deformation below the tool (ploughing) and a larger chip formation component due to a lower shear angle. Increases in specific energy and shear stress are also due to shear strain and strain rate increases. A consistent material behavior model that does not vary with process input conditions like uncut chip thickness, rake angle and edge radius can be developed based on the new model. [S1087-1357(00)01302-2]

Dynamic recrystallization in deformed plagioclase during progressive shear deformation

Grain size reduction of plagioclase accompanied with progressive ductile deformation was investigated in a centimeter-scale small shear zone, collected from the Hatagawa shear zone, northeast Japan. The angle θ between the foliation and the shear zone boundary decreases from the margin to the center of the shear zone, indicating an increase of shear strain toward the center. The volume fraction of fine plagioclase grains X pl ( diameter <15 μm) increases with progressive shear strain. The value of X pl increases steeply from 30% to 60% between the angles θ=23° and θ=20°, and then it gradually increases from 60% to 90% toward θ≈0°. The fine plagioclase grains have a variable dislocation density and a crystallographic preferred orientation, suggesting that recrystallization accommodated dislocation creep. Transmission electron microscopy (TEM) observations revealed that strain-induced grain boundary bulging occurred along the grain boundaries of plagioclase porphyroclasts. Thus the grain size of plagioclase was reduced by strain-induced grain boundary bulging. The kinetic theory of dynamic recrystallization approximately predicts the formation of the above-mentioned X pl– θ curve, and suggests that the inflection point of X pl at θ=23–20° is probably due to site saturation in which all of the original grain boundaries are covered by the recrystallized grains. The kinetic theory of dynamic recrystallization also gives a physical basis for the classification of mylonite on the basis of the volume fraction of fine grains.

Mechanical considerations in impaction bone grafting.

In impaction grafting of contained bone defects after revision joint arthroplasty the graft behaves as a friable aggregate and its resistance to complex forces depends on grading, normal load and compaction. Bone mills in current use produce a distribution of particle sizes more uniform than is desirable for maximising resistance to shear stresses. We have performed experiments in vitro using morsellised allograft bone from the femoral head which have shown that its mechanical properties improve with increasing normal load and with increasing shear strains (strain hardening). The mechanical strength also increases with increasing compaction energy, and with the addition of bioglass particles to make good the deficiency in small and very small fragments. Donor femoral heads may be milled while frozen without affecting the profile of the particle size. Osteoporotic femoral heads provide a similar grading of sizes, although fewer particles are obtained from each specimen. Our findings have implications for current practice and for the future development of materials and techniques.

Mechanical considerations in impaction bone grafting

In impaction grafting of contained bone defects after revision joint arthroplasty the graft behaves as a friable aggregate and its resistance to complex forces depends on grading, normal load and compaction. Bone mills in current use produce a distribution of particle sizes more uniform than is desirable for maximising resistance to shear stresses. We have performed experiments in vitro using morsellised allograft bone from the femoral head which have shown that its mechanical properties improve with increasing normal load and with increasing shear strains (strain hardening). The mechanical strength also increases with increasing compaction energy, and with the addition of bioglass particles to make good the deficiency in small and very small fragments. Donor femoral heads may be milled while frozen without affecting the profile of the particle size. Osteoporotic femoral heads provide a similar grading of sizes, although fewer particles are obtained from each specimen. Our findings have implications for current practice and for the future development of materials and techniques.

Simulation of the influence of ice rheology on velocity profiles and ice-sheet mass balance

Assessment of the effect of the Antarctic ice sheet on sea level requires an accurate determination of its current state of balance. This is usually done by comparing the ice net accumulation for an area with the net outward flow of the ice. To obtain the net outward flux to better than 20% accuracy the relationship between the column-integrated ice flux and measurements of ice-sheet thickness and surface velocity must be considered. That relationship is summarised by the ratio of depth-averaged velocity ϒ to surface velocity γs in areas where ice sliding can be neglected, this ratio strongly reflects the rheological properties of the ice and depends on the shear strain-rate profile through the ice column, which is influenced by profiles of stress, temperature and ice-crystal fabric. We present calculations from a flowline model of a hypothetical large ice sheet to demonstrate how development of an anisotropic ice-crystal fabric can influence the depth profile of horizontal velocity. The temperature dependence of ice rheology, combined with typical ice-sheet temperature profiles, yields a more block-like velocity profile with increasing to values in the range 0.89-0.96 from the isothermal rheology value of 0.8. Our results show that the onset of enhanced shear flow with increasing shear strain, as a consequence of anisotropy, and then a reduction of enhancement nearer the bedrock, can modify the velocity profile, giving values typically in the range 0.86-0.91. Smaller values than these may also occur for rougher bedrock or thinner ice.

Anisotropic and enhanced self-diffusion of a macromolecular chain under simple shear flow as revealed by Monte Carlo simulation on lattices

Two-dimensional simple shear flow of a self-avoiding macromolecular chain is simulated by a lattice Monte Carlo (MC) method with a pseudo-potential describing the flow field. The simulated velocity profile satisfies the requirements of simple shear flow unless the shear rate is unreasonably high. Some diffusion problems for a free-draining bead-spring chain with excluded volume interaction are then investigated at low and relatively high shear rates. Three diffusion coefficients are defined and examined in this paper: the conventional self-diffusivity in zero field, Dself, the apparent self-diffusivity in flow field, Dapp, and the flow diffusivity in simulation, Dflow reflecting actually the transport coefficient. It is found that these three diffusivities for a flexible chain are different from each other. What is more important is that self-diffusion exhibits a high anisotropy in the flow field. The apparent self-diffusion along the flow direction is enhanced to a large extent. It is increased monotonically with the increase of shear time or shear strain, whereas the chain configuration can achieve a stationary anisotropic distribution following an interesting overshoot of the coil shape and size. Besides a single self-avoiding chain, an isolated Brownian bead and a group of self-avoiding beads with a quasi-Gaussian spatial distribution are also simulated. According to the comparison, the effects of the connectivity of the chain on the diffusion behavior are revealed. Some scaling relations of Dapp versus t are consistent with the theoretical analyses in the pertinent literature.

Proteolysis and gelation of fish proteins under ohmic heating.

Pacific whiting surimi gels heated slowly in a water bath exhibited poor gel quality, while the ohmically heated gels without holding at 55 degrees C showed more than a twofold increase in shear stress and shear strain over conventionally heated gels. Degradation of myosin and actin was minimized by ohmic heating, resulting in a continuous network structure. Ohmic heating with a rapid heating rate was an effective method for maximizing gel functionality of Pacific whiting surimi without enzyme inhibitors. In linear heating, slow heating rates increased proteolysis in Pacific whiting surimi as shown by degradation of myosin heavy chain and low shear stress and shear strain. Proteolysis of whiting surimi was decreased by the presence of beef plasma protein (BPP) to a greater extent at rapid heating rates (20 and 30 degrees C/min) than at slow heating rates (1 and 5 degrees C/min). Shear stress of Alaska pollock surimi gels with or without BPP increased as heating rate decreased, but shear strain was unaffected. An increase in shear stress was accompanied by an increase of cross-linked myosin heavy chain.

Anisotropic and enhanced self-diffusion of a macromolecular chain under simple shear flow as revealed by Monte Carlo simulation on lattices

Two-dimensional simple shear flow of a self-avoiding macromolecular chain is simulated by a lattice Monte Carlo (MC) method with a pseudo-potential describing the flow field. The simulated velocity profile satisfies the requirements of simple shear flow unless the shear rate is unreasonably high. Some diffusion problems for a free-draining bead-spring chain with excluded volume interaction are then investigated at low and relatively high shear rates. Three diffusion coefficients are defined and examined in this paper: the conventional self-diffusivity in zero field, Dself, the apparent self-diffusivity in flow field, Dapp, and the flow diffusivity in simulation, Dflow reflecting actually the transport coefficient. It is found that these three diffusivities for a flexible chain are different from each other. What is more important is that self-diffusion exhibits a high anisotropy in the flow field. The apparent self-diffusion along the flow direction is enhanced to a large extent. It is increased monotonically with the increase of shear time or shear strain, whereas the chain configuration can achieve a stationary anisotropic distribution following an interesting overshoot of the coil shape and size. Besides a single self-avoiding chain, an isolated Brownian bead and a group of self-avoiding beads with a quasi-Gaussian spatial distribution are also simulated. According to the comparison, the effects of the connectivity of the chain on the diffusion behavior are revealed. Some scaling relations of Dapp versus t are consistent with the theoretical analyses in the pertinent literature.

Cell concentration dependence of dynamic viscoelasticity of Escherichia coli culture suspensions

The viscoelastic properties of Escherichia coli culture suspensions of various cell concentrations were studied in terms of relation to shear strain amplitude and angular frequency dependence. Samples of the suspensions were prepared by resuspension of a concentrated suspension obtained by centrifugation. Dynamic viscoelasticity for all cell concentrations at an angular frequency of ω=0.1 rad·s −1 exhibited linear behavior up to a shear strain amplitude of about 0.02. The storage modulus decreased with an increase in shear strain amplitude above 0.02, while dynamic viscosity was not so noticeably influenced. Further, for samples of very high cell concentrations in particular, the dynamic viscosity increased with increasing shear strain amplitude, in parallel with the decrease in storage modulus. The angular frequency dependence of the storage modulus for samples of high cell concentrations was very low, since the network of the suspension behaved as a relaxation mechanism having a long relaxation time. Marked dependence of viscoelasticity on cell concentration was observed, and considered to be caused by the development of a network structure composed of microbial floccules interacting wigh one another.

Active structural acoustic control of a thin plate with a hybrid sandwich actuating mechanism

The objective of this research is to control the acoustic radiation of thin plates with hybrid active–passive actuating mechanisms. The hybrid mechanism consists of a piezoelectric actuator and viscoelastic and piezoelastic active constrained layers in a sandwich configuration, with the viscoelastic core layer in between the piezoelastic components. The actuator end of the hybrid mechanism is attached to a host structure. The main purpose of the proposed hybrid mechanism is to enhance the damping characteristics of the system while maintaining sufficient control authority. The damping characteristic of the hybrid mechanism is maximized by applying opposite voltages to the actuator and the active constrained layers, thus inducing a significant increase in shear strain within the viscoelastic layer. The general goal of this study is to evaluate the performance of the hybrid mechanism with some of the previously published actuating systems. Initial comparison results indicate that the proposed hybrid active–passive sandwich mechanism is more efficient than the actuating devices in comparison.

Solid-Like Director Reorientation in Sheared Hexagonal Lyotropic Liquid Crystals as Studied by Nuclear Maginetic Resonance

The shear-induced reorientation of the hexagonal surfactant mesophase is investigated by deuterium nuclear magnetic resonance spectroscopy. The NMR spectra of the sheared samples, measured in situ with two different shear geometries, either cone and plate or coaxial cylinders, prove that the hexagonal axis (the director) aligns parallel to the flow. Shear experiments starting from a monodomain sample, with the director initially aligned along the velocity gradient, exhibit an increasing tilt of the director as the shear strain γ grows. The tilt angle is given by arctan γ. This makes evident that the hexagonal lyomesophase behaves like a solid. The analysis of nuclear magnetic resonance spectra and textures observed by polarizing microscopy shows an undulation of the columns in both the quiescent and the sheared state. The amplitude of the undulations decreases with increasing shear strain.

CONDUCTIVITY AND FORCE BETWEEN PARTICLES IN A MODEL ELECTRORHEOLOGICAL FLUID II: INTERACTION FORCE

The interaction force between humidified glass spheres forming a single-row chain in silicone oil was determined in shear as a function of the number of particles in the chain, the electric field and the shear strain (separation of the particles). The measured values of the interaction force vs the average distance of separation of the particles and the electric field exponent were in accord with the conductivity model for ER response. With increase in shear strain the separation of the particles soon became localized and one or both of the particles next to the gap began oscillating back-and-forth leading ultimately to rupture of the chain with increased shear.