Increasing Shear Strain Research Articles

Study on Thermal Cycling of Sn0.7Cu Solder

Thermal cycling of a unit Sn0.7Cu solder was studied based on the steady-state creep constitutive equation and Matlab software. The results show that there is a steady-state cycle for the thermal cycling of unit Sn0.7Cu eutectic solder. In steady-state thermal cycling, the shear stress is increased with the increase of temperature. There is a stage of stress relaxation during high temperature. A liner relationship between maximum shear stress and maximum shear strain is observed during thermal cycling. The metastable cycle number is declined greatly with the increase of maximum shear strain.

Mapping cyclic stretch in the postpneumonectomy murine lung

In many mammalian species, the removal of one lung [pneumonectomy (PNX)] is associated with the compensatory growth of the remaining lung. To investigate the hypothesis that parenchymal deformation may trigger lung regeneration, we used respiratory-gated micro-computed tomography scanning to create three-dimensional finite-element geometric models of the murine cardiac lobe with cyclic breathing. Models were constructed of respiratory-gated micro-computed tomography scans pre-PNX and 24 h post-PNX. The computational models demonstrated that the maximum stretch ratio map was patchy and heterogeneous, particularly in subpleural, juxta-diaphragmatic, and cephalad regions of the lobe. In these parenchymal regions, the material line segments at peak inspiration were frequently two- to fourfold greater after PNX; some regions of the post-PNX cardiac lobe demonstrated parenchymal compression at peak inspiration. Similarly, analyses of parenchymal maximum shear strain demonstrated heterogeneous regions of mechanical stress with focal regions demonstrating a threefold increase in shear strain after PNX. Consistent with previously identified growth patterns, these subpleural regions of enhanced stretch and shear strain are compatible with a mechanical signal, likely involving cyclic parenchymal stretch, triggering lung growth.

Rheological contrast between serpentine species and implications for slab–mantle wedge decoupling

Serpentine is considered the main hydrous mineral to cause significant weakening at the slab–mantle interface; however, despite the possible presence of lizardite/chrysotile (liz/ctl) and antigorite (i.e., low- and high-temperature serpentine species, respectively) at the base of the mantle wedge, the differences in rheological properties between these two serpentine types are poorly understood. To investigate the effect of serpentine speciation on slab–mantle decoupling, we performed a series of two-layer shear deformation experiments on liz/ctl, antigorite, and olivine at P = 1 GPa and T = 250–300 °C, using a Griggs-type solid-medium apparatus. With increasing shear strain (γ up to ~ 5), the liz/ctl and antigorite samples evolved to deform predominantly by slip or glide on the (001) basal plane, whereas the olivine sample deformed by a combination of brittle and crystal-plastic mechanisms. The contrasting amount of rotation of strain markers between layers demonstrates that the shear strain of liz/ctl is significantly lower than that of antigorite, possibly arising from differences in interlayer bond strength. The strain contrasts between serpentines and olivine were γliz/ctl/γol = 9–12 and γatg/γol = 1–2. Our results indicate that assuming a thin, serpentinized layer upon a subducting slab, significant decoupling can occur only where liz/ctl is stable in the layer. Thus, the distribution of serpentine species in the hydrated mantle wedge is a critical factor that controls the degree of decoupling along the slab–wedge interface, at depths below the seismogenic zone.

Discrete modeling of granular soils reinforcement by plant roots

The analysis of the influence of the roots on the shear resistance of the soil requires identifying the effect of the different root–soil interaction processes depending on soil and roots properties. For that purpose, a numerical model of direct shear tests of non-rooted and rooted granular soils based on the Discrete Element Method was developed. The soil is modeled as an assembly of locally interacting spheres and the roots are modeled as deformable cylinders in the soil matrix. The model allows accounting for the root tensile loading until breakage, the root bending loading, the root–soil adhesive links until adhesion breakage, the root slippage associated with a frictional resistance at the root–soil interface.The study focuses on identifying the different root–soil interaction mechanisms depending on the soil type. Both frictional and cohesive granular soil types were used in the simulations. The effects of the roots mechanical properties – tensile, bending modulus and root–soil interfacial friction angle – and of the root number were also analyzed for the different soil types.The results first show that the effect of the roots strongly depends on the shear strain for any soil type. For frictional soils, an increasing shear strain induces progressively a pure tensile loading of the roots until slippage of the root–soil interface. For cohesive granular soils, the pure tensile loading of the roots is followed by a progressive breakage of the adhesive root–soil links and by a complete slippage of the roots. The results show that the influence of the root number is significant if the prevailing processes are root tensile loading combined with slippage whereas it is less important if root loading is combined with progressive breakage of the adhesive links for the root configurations explored. Finally, the results show that the shear strain range associated with the different processes strongly depends on the relative rigidities of the roots and soil matrix.The model developed was shown of great interest to analyze the shear resistance of the rooted soil assemblies depending on the shear strain. Such an approach could therefore be used to test the different assumptions done in the analytical models. Developing analytical models of slope stability based on the calculation of the shear resistance of rooted soil depending not only on soil and root properties but also on shear strain intensity also constitutes a perspective for the use of the model developed.

Influence of shear deformation on the normal force of magnetorheological elastomer

The influence of shear deformation on the normal force of magnetorheological elastomer was investigated. In quasi-static shear, the normal force decreases with increasing shear strain at low magnetic field, while increases with increasing shear strain when the magnetic field exceeds 452mT. In oscillatory shear, the normal force shows similar trend. However, it decreases sharply when the strain amplitude exceeds 7%. A microstructure based theory was proposed to investigate this phenomenon. Under shearing, the elastic modulus decreases while the magnetic torque increases, which lead to the different trends of normal force at different magnetic fields. This mechanism agrees well with the experimental results.

Graphite as a lubricating agent in fault zones: An insight from low‐ to high‐velocity friction experiments on a mixed graphite‐quartz gouge

Graphite is a very low friction material, often enriched within fault zones due to mechanical or chemical processes. The effects of weak minerals on the strength of faults have been examined by friction experiments on bimineralic mixtures. However, previous experiments were conducted with limited shear strains, even though applied shear strains and textural developments had already been signaled as significant factors in the weakening of faults. We therefore conducted large‐displacement, low‐ to high‐velocity friction experiments with graphite‐quartz gouges, to determine how much graphite is needed to reduce frictional strength, and to examine how textures contribute to the strength reduction of a mature fault at various slip rates. We found that the coefficients of friction of the gouges decrease nonlinearly with increasing graphite fraction for any given shear strain and slip rate, decreasing first with 5–20 vol% graphite, then reaching similar frictional levels to pure graphite with 30–50 vol% graphite. The nonlinear weakening trends can be fitted by sigmoidal curves. The weakening with 10–30 vol% graphite is associated with zones of slip‐localization and the development of a graphite‐lubricated penetrative slip surface(s). With increasing shear strain, the relationship between strength and graphite fraction evolves abruptly from an early gentle curve to a sigmoidal curve, and the frictional strength drops significantly even with small amounts of graphite (~10 vol%). Our results highlight the importance of shear strain and textural developments on weak faults, not only with respect to graphite, but also other fault lubricants such as the phyllosilicates.

Evaluation of Transfer Function and Dynamic Properties from Strain-Controlled Resonant Column Tests

Abstract Dynamic properties of soils can be inferred via curve fitting of the transfer function between the excitation and the induced strain using a resonant column device. The shape of the measured transfer function is distorted and differs from that of the theoretical transfer function because of different shear strain levels at different frequencies in the specimen. The difference becomes more pronounced with increasing shear strain levels. This study presents a new methodology for the evaluation of dynamic properties from an improved transfer function. In this methodology, the soil specimen is excited using a sinusoidal carrier excitation at the desired strain level coupled with simultaneous excitation of a very small strain random noise. The desired strain level induced by the fixed sine controls the resonant frequency of the specimen, whereas the small strain random noise (always kept small) determines the shape of the transfer function and thus the damping coefficient. The results indicate excellent matching of the transfer function obtained from the proposed method and the theoretical transfer function at all shear strain levels. The new methodology also shows good potential for the evaluation of dynamic properties of soils as a function of frequency in resonant column testing.

Structural Constraints and Numerical Simulation of Strain Localization in the Bendigo Goldfield, Victoria, Australia

Strain localization and fluid flow patterns adjacent to the massive quartz-hosted reefs of the Bendigo gold-field have been investigated using new structural observations, three-dimensional geometry of fold-fault relationships, and gold distribution. Quartz reef and vein formation in the Bendigo goldfield is associated with an initial E-W compression event that produced a penetrative upright cleavage and N-S–trending fold hinges. In the immediate hanging wall of quartz reefs with high gold grades, the S1 cleavage is locally deformed by an E-W–trending S2 cleavage that is attributed to a low-strain N-S–oriented compressive event. Further evidence of this low-strain event is provided by gently S plunging quartz-carbonate slickenline lineations on S1 cleavage surfaces and the reef margin surfaces and visible gold within the outer portions of the reef. The reefs are commonly situated on or immediately to the south of a left-flex (sinistral) change in strike of the axial surface of the folds, and the flexure occurs close to an anticlinal culmination defined by the double-plunging N-S–striking folds. The folds become deformed with meter to decimeter wavelengths, which generally affect the stiff units, in a disharmonic style. Accompanying this is a reactivation of reef margins by oblique slip and the formation of dilational sites and tensional vein arrays that provide the conduits for fluid flow and gold deposition. Numerical models that best simulate the observed distribution of strain, based upon the location of quartz reefs, involve NW-SE–oriented contraction with a significant sinistral strike-slip component. This contraction event has an overall N-S–sense orientation and is therefore consistent with deformation features in the immediate hanging wall of quartz reefs. The models also demonstrate a geometrical dependence on the localization of strain and, thus, the potential localization of fluid flow. Volume and shear strain increase with the flex angle, and variations in the magnitude of strain are also associated with variations in the strike angle of the flexure. This analysis highlights that the modification of preexisting fold structures and quartz veins by a low-strain event may enhance the localization of dilation sites within individual quartz reefs where there are subtle changes in the orientation of the reef margins. Such numerical modeling can also improve ranking of exploration targets based on fold geometry and provide a better understanding of fluid flow in hydrothermal mineral systems.

Depth-dependent strain fields of articular cartilage under rolling load by the optimized digital image correlation technique

It is significant to investigate the depth-dependent mechanical behaviors of articular cartilage under rolling load since considerable rolling occurs for cartilage joint in activities of daily living. In this study, the rolling experiments of articular cartilage were conducted by applying an optimized digital image correlation (DIC) technique for the first time and the depth-dependent normal strain and shear strain of cartilage were analyzed. It is found that the normal strain and shear strain values of different layers increase firstly and then decrease with rolling time, and they increase with increasing compressive strains. The normal strain and shear strain values decrease along cartilage depth with constant compressive strain. The normal strain values of different normalized depth decrease with increasing rolling rates. The shear strain values of superficial layer and middle layer decrease; however there are no major changes for the shear strain values of deep layer with increasing rolling rates. The normal strain values with different rolling time increase with increasing rolling numbers and the 30.6% increase in initial normal strain is observed from 1st to 99th cycle. The fitting relationship of the normal strain and normalized depth was obtained considering the effects of compressive strain and rolling rate and the fitting curves agree with the experimental results for cartilage very well.

Electrical conductivity of magnetite‐bearing serpentinite during shear deformation

Electrical conductivity of serpentinite with various amounts of magnetite was measured during shear deformation at high pressure and temperatures (P = 1.0 GPa, T = 750 K) corresponding to mantle wedge conditions to evaluate the contribution of aligned magnetite to the bulk conductivity of serpentinite. Under hydrostatic conditions, the sample conductivity considerably increases when the magnetite volume fraction exceeds 25% in volume, suggesting the presence of the percolation threshold for magnetite interconnection. During shear deformation, the conductivity for the samples with less than 25 vol.% magnetite increased by an order of magnitude or higher with increasing shear strain up to 9, which is likely a result of the clustering or realignment of magnetite grains in the serpentinites. However, activation enthalpy was nearly constant before and after deformation experiments, suggesting that shear deformation is unlikely to enhance establishment of interconnection of magnetite. Consequently, more than 25 vol.% magnetite is needed to establish connectivity of magnetite in serpentinite. On the other hand, the conductivity of serpentinite with low volume fraction of magnetite (5%), which is typical concentration of natural serpentinites, is almost similar to that of magnetite‐free serpentinites. The present results show that the interconnection of magnetite in serpentinites by shear deformation is not expected as an origin of the high conductivity anomaly occasionally observed at the slab interface in the mantle wedge. The origin of high conductivity, therefore, indicates the presence of aqueous fluid with high salinity rather than the magnetite interconnection.

Petrofabric and strength of SiO2 near the quartz‐coesite phase boundary

AbstractQuartz and coesite constitute an important portion of deep subducted continental upper crust. However, the rheology and petrofabric of quartz and coesite are not well constrained under high‐pressure (HP)/ultrahigh‐pressure (UHP) metamorphic conditions both in laboratory and in nature. We report here the first deformation microstructure and lattice preferred orientations of garnet, omphacite, interstitial coesite, quartz and rutile in UHP eclogites from the Yangkou Bay, Sulu UHP terrane, as well as fabric development of quartz and coesite in shear experiments at P–T conditions near the quartz‐coesite phase boundary. Our results show: (i) garnet and coesite develop weak to random fabric while omphacite, quartz and rutile develop pronounced fabrics in deformed natural eclogites; (ii) quartz develops fabrics in responding to a dominant c‐slip with increasing shear strain under HP/UHP conditions; (iii) coesite develops fabrics in responding to a dominant [100](010) slip with increasing shear strain under UHP conditions; and (iv) the relative strengths of major constituent minerals in continental deep subduction zones are quartz < omphacite < coesite. These results are consistent with the rheology determined in the laboratory for quartz, jadeite/omphacite and coesite. We propose that jadeite/omphacite dominates the rheology and seismic anisotropy of deeply subducted continental crust.

An Investigation into Nonlinearity of Foundation Soil of Gravity Retaining Wall Based on an Inversion Method

Strong earthquake ground motion leads to residual displacements of gravity retaining walls. Since large deformation occurs in foundation soil, nonlinear mechanical behavior should not be neglected in numerical modeling. The inversion methodology in geophysics is borrowed here to study the nonlinearity, i.e. the variation of shear modulus and damping ratio with the increase of shear strain of soil. A simplified model for the seismic displacement of retaining walls is combined with a genetic algorithm for the inversion. The dynamic shear modulus and damping ratio curves, representing the nonlinear property of foundation soil in a centrifuge test for gravity retaining walls, is obtained by the use of an inversion scheme. The result indicates that, for low level of shear strain, the shear modulus is larger than that used in the literature, implying that the model ground may be stiffer than expectation. For high level of shear strain, the inverted damping ratio is larger than the conventional one, which has efficiently suppressed an overestimation of seismic displacements. It is also displayed that the inversion method is an effective way to obtain quantitatively the dynamic nonlinearity of foundation soil of gravity retaining walls.

An analytical model for shear-enhanced adhesiveless transfer printing

Transfer printing is an important technique for assembling micro/nanomaterials on unusual substrates, with promising applications in the fabrication of stretchable and flexible electronics designed for use in areas such as biomedicine. The process involves retrieval of structures (e.g., micro-devices) from their growth (donor) substrate via an elastomeric stamp (i.e., an element with posts on its surface), and then delivers them onto a different (receiver) substrate. An analytical mechanics model is developed to identify the key parameters for a shear-enhanced mode for transfer printing. The results predict that the pull-off force decreases linearly with increasing shear strain in the post, or with shear displacement across the stamp. This prediction agrees well with the experiments.

Characterization of chip formation during machining 1045 steel

A deep understanding of the generation and characterization of chip formation can result for practical advices of chip type controlling in engineering applications. The chip formation is divided into the continuous chip and the serrated one in this study. The characterization of the continuous chip formation is expressed as the chip deformation and that of the serrated chip formation is expressed as the frequency of serration, the degree of segmentation, and the deformation of serrated chip. The chips of 1045 steel under different cutting speeds (100–3,600 m/min) are collected during machining. After inlay and polishing of the collected chips, the chip morphology is observed with VHX-600 ESO digital microscope. It is found that at the cutting speeds of 100–400 m/min, the chip type is continuous, at the cutting speeds of 600–2,200 m/min the chip type is serrated, and at the cutting speeds of 2,500–3,600 m/min the chip type is segmented. The quantitative relations between the characterization parameters of chip formation and the cutting speed are obtained. The chip deformation increases with the cutting speed, and the influence of the cutting speed on the shear strain rate is more sensitive than that on the shear strain during the continuous chip formation. All the characterization parameters including the shear strain rate, the frequency of serration, the degree of segmentation, and the shear strain increase with the cutting speed during the serrated chip formation. The sensitivity of influence of the cutting speed on these parameters is in the following: the shear strain rate, the degree of segmentation, the frequency of serration, and the shear strain.

How does muscle stiffness affect the internal deformations within the soft tissue layers of the buttocks under constant loading?

Mechanical loading of soft tissues covering bony prominences can cause skeletal muscle damage, ultimately resulting in a severe pressure ulcer termed deep tissue injury (DTI). Deformation plays an important role in the aetiology of DTI. Therefore, it is essential to minimise internal muscle deformations in subjects at risk of DTI. As an example, spinal cord-injured (SCI) individuals exhibit structural changes leading to a decrease in muscle thickness and stiffness, which subsequently increase the tissue deformations. In the present study, an animal-specific finite element model, where the geometry and boundary conditions were derived from magnetic resonance images, was developed. It was used to investigate the internal deformations in the muscle, fat and skin layers of the porcine buttocks during loading. The model indicated the presence of large deformations in both the muscle and the fat layers, with maximum shear strains up to 0.65 in muscle tissue and 0.63 in fat. Furthermore, a sensitivity analysis showed that the tissue deformations depend considerably on the relative stiffness values of the different tissues. For example, a change in muscle stiffness had a large effect on the muscle deformations. A 50% decrease in stiffness caused an increase in maximum shear strain from 0.65 to 0.99, whereas a 50% increase in stiffness resulted in a decrease in maximum shear strain from 0.65 to 0.49. These results indicate the importance of restoring tissue properties after SCI, with the use of, for example, electrical stimulation, to prevent the development of DTI.

First-principles study of the transport behavior of zigzag graphene nanoribbons tailored by strain

The charge transport properties of zigzag graphene nanoribbons (ZGNRs) under uniaxial and shear strains are theoretically studied. Although all strained ZGNRs have similar metallic band structures, they show four types of transport behavior under bias voltages that depend on the type of strain and the mirror symmetry of the ZGNR. Under an applied uniaxial strain, the current of symmetric ZGNRs is consistently small, while for asymmetric ZGNRs it is large. In contrast, the current increases with increasing shear strain for symmetric ZGNRs while it decreases for asymmetric ZGNRs. The current properties merge when the shear strain exceeds a critical value, and the two systems then show similar behavior. Our results suggest that strained ZGNRs with an appropriate applied shear are ideal conducting wires.

Microstructure Development and Lateral Distribution of Defects in Ultra-fine Grained Copper Prepared by High-pressure Torsion

A defect study of ultra-fine grained (UFG) Cu prepared by high-pressure torsion (HPT) will be reported. Conventional positron annihilation spectroscopy (PAS) including positron lifetime (PLT) and Doppler broadening (DB) techniques was employed as the main experimental tool. PAS was combined with transmission electron microscopy, X-ray diffraction and Vickers microhardness (HV) measurements. First, lattice defects introduced by HPT were characterized. A very high concentration of defects created during HPT deformation was observed and the two kinds of defects could be identified: dislocations and small vacancy clusters (microvoids). Further investigations were focused on (i) the radial distributions of defects and (ii) the evolution of microstructure during HPT processing. The results of the present study are consistent with an increase of shear strain from the sample centre toward its periphery. Extended lateral mapping of microstructure was performed using HV and DB techniques. The latter one reveals a significant non-uniformity of defect distribution which was less pronounced in the HV measurements.

Effects of Strain Rate and Temperature on Shear Properties and Fracture Characteristics of 316L Stainless Steel

The dynamic shear deformation behaviour and fracture characteristics of 316L stainless steel are investigated using a split-Hopkinson torsional bar system at temperatures of ¹150, 25 and 300°C and strain rates ranging from 1000 to 3000s ¹1 . The results show that the flow stress, shear fracture strain, work hardening rate, and strain rate sensitivity all increase with increasing strain rate for a given temperature, but decrease with increasing temperature given a constant strain rate. The activation energy decreases with increasing shear stress for a constant shear strain, but increases with increasing shear strain given a constant shear stress. Optical microscopy observations reveal that localized plastic flows occur in the shear deformation region. Moreover, the flow angle increases with increasing strain rate and temperature. Scanning electron microscopy observations show that the fracture surfaces are characterized by a dimple-like structure, which indicates a ductile failure mode. The morphology and density of the dimple-like structures are highly sensitive to the strain rate and temperature conditions. Overall, the microstructural observations show that the shear response of 316L stainless steel is directly related to the effects of the strain rate and temperature on the evolution of the sheared microstructure. [doi:10.2320/matertrans.M2011274]

Longitudinal displacement and intramural shear strain of the porcine carotid artery undergo profound changes in response to catecholamines

The effects of catecholamines on longitudinal displacements and intramural shear strain of the arterial wall are unexplored. Therefore, the common carotid artery of five anaesthetized pigs was investigated using an in-house developed noninvasive ultrasonic technique. The study protocol included intravenous infusion of low-dose epinephrine (β-adrenoceptor activation), as well as intravenous boluses of norepinephrine (α-adrenoceptor activation). Further, the effects of β-blockade (metoprolol) were studied. There were significant positive correlations between pulse pressure and longitudinal displacement of the intima-media complex (r = 0.72; P < 0.001), as well as between pulse pressure and intramural shear strain (r = 0.48; P < 0.001). Following administration of norepinephrine, the longitudinal displacement of the intima-media complex and intramural shear strain profoundly increased (median 190%, range 102-296%, and median 141%, range 101-182%, respectively, compared with baseline), also when given during β-blockade (median 228%, range 133-266%, and median 158%, range 152-235%, respectively). During infusion of low-dose epinephrine, the longitudinal displacement of the intima-media complex and intramural shear strain decreased (median 88%, range 69-122%, and median 69%, range 47-117%, respectively, compared with baseline). In conclusion, the present study shows, for the first time, that the longitudinal displacement and intramural shear strain of the porcine carotid artery undergo profound changes in response to catecholamines. Increase in longitudinal displacements seems to be strongly related to α-adrenoceptor activation. Thus metoprolol is insufficient to counteract a profound increase in longitudinal displacement and intramural shear strain following a surge of norepinephrine.

Macro-micromechanical approaches for non-coaxiality of coarse grained soils

For coarse grained soils, their principal stress directions may change when the water level of embankment dam varies instantaneously. In this loading case, the principal directions of stress and strain rate will become non-coaxial. In an effort to model non-coaxial behavior, a modified three-dimensional non-coaxial model is developed in the context of vertex yield (tangent plasticity) theory. Discrete Element Method (PFC) incorporating user-defined interparticle contact models is also employed to gain an insight into microscopic mechanism of non-coaxiality. The analysis focuses on non-coaxial behaviors under simple shear condition. It has been shown that the proposed non-coaxial model gives good predictions for non-coaxiality with reference to microscopic observations while the classical coaxial model fails to simulate the non-coaxial behaviors. In general, non-coaxiality as a result of the rotation of principal stress, is large at a small shear strain, and inclined to become negligible with increasing shear strain. For coarse grained soils, their non-coaxiality tends to largely depend on the initial normal pressure, where a larger degree of non-coaxiality can be observed at a higher pressure.