Decrease In Shear Modulus Research Articles

Role of the coefficient of uniformity on the California bearing ratio, penetration resistance, and small strain stiffness of coarse arctic soils

For seasonally frozen-thawed Arctic soils, soil properties are significantly affected by the particle size distribution. The objective of this study is to study the role of the coefficient of uniformity (Cu) on the California bearing ratio (CBR), strength, and stiffness. Six poorly-graded sand (SP) samples with various Cu are collected from a depth from 20 cm to 120 cm in the active layer. The amounts of the organic matter range from 0.22% to 2.11%. Specimens are prepared with each natural water content into a CBR mold, and the CBR, mini-cone tip resistance (qc), and shear wave velocity (Vs) are measured. Field tests using an instrumented dynamic cone penetrometer (IDCP), which can gather force and acceleration signals at the cone tip, are performed. The IDCP index (IDCPI), energy-corrected DCPI (EDCPI), and dynamic cone resistance (qd) are estimated during penetration. Test results show that the CBR, qc, qd, Vs, and maximum shear modulus (Gmax) decrease with increasing Cu value. The IDCPI and EDCPI increase according to the Cu value. Thus, CBR is inversely proportional to the DCPI, and linearly proportional to the qd and Gmax. This study demonstrates that the CBR, strength, and stiffness of Arctic soils are affected by the particle size distribution because the main skeleton comprised of large particles can be disrupted by small particles.

Mechanical properties of 65Mn chiral structure with three ligaments

Chiral honeycomb structures have been developed in recent years, showing excellent mechanical properties, including in-plane deformation and out-of-plane bearing and vibration isolation. In this study, the 65Mn chiral structure with three ligaments was modeled and analyzed using the finite element (FE) method. The effects of the dimensionless ligament length and dimensionless ligament thickness on the in-plane equivalent elastic modulus, equivalent Poisson’s ratio, and out-of-plane shear modulus were studied. The numerical results indicate that increase of the dimensionless ligament length leads to decrease of the equivalent elastic modulus and increase of the equivalent Poisson’s ratio, whereas the out-of-plane equivalent shear modulus decreases. The results also indicate that increase of the dimensionless ligament thickness leads to increase of the equivalent elastic modulus, whereas the equivalent Poisson’s ratio remains nearly unchanged and the out-of-plane equivalent shear modulus shows a linear increase. The numerical results are verified by comparison with published experimental data. These results will provide a reference for the application of chiral structures with three ligaments in the aerospace field.

Relationship between pre-exercise muscle stiffness and muscle damage induced by eccentric exercise

This study aimed to determine whether pre-exercise muscle stiffness is related to the amount of muscle damage induced by an eccentric exercise and to determine whether the post-exercise increase in stiffness is homogenously distributed between the synergist muscles. Fifty healthy participants were randomly assigned to an eccentric exercise group or a control group. The shear modulus (an index of stiffness) of rectus femoris (RF), vastus lateralis (VL) and vastus medialis oblique (VMO) was measured before, immediately after and at 48 h after eccentric exercise. The maximal isometric voluntary knee extension (MVC) torque was also measured. Significant reduction in MVC torque was observed in the eccentric group both at post and 48 H when compared with pre-exercise (both p < .001). RF shear modulus increased significantly when assessed at 90° of knee flexion at post and 48 H after the eccentric exercise (p = .004 and .005, respectively). Slight but significant decrease in VL shear modulus was observed at post-exercise for the eccentric group (p = .002). No change was observed in VMO. The decrease in MVC at 48 H was negatively correlated with the RF shear modulus measured at 90° of knee flexion before the exercise. Eccentric exercise induced a wide range of peak torque reduction and muscle-head specific modulation on muscle stiffness. Participants with stiffer RF muscles exhibited greater decrease in force generating capacity at 48 H after eccentric exercise.

Effect of hydrothermal treatment of microfibrillated cellulose on rheological properties and formation of hydrolysis products

The aim of this study was to determine the effects of hydrothermal treatment of microfibrillated cellulose (MFC) on its gel stability, water retention and rheological behavior. MFC gel was prepared by fibrillating endoglucanase pre-treated, never-dried dissolving pulp. The MFC gel samples were then exposed in a static chamber for different times at different temperatures. At temperatures of 120–150 °C, the viscosity profile of the gels was not significantly changed and a characteristic series of 3 successive regimes in the course of increasing shear rate, showing different behavior was revealed. The amount of water released by the samples under pressure, on the other hand, was notably increased after hydrothermal treatment. After further exposure to prolonged treatment times (24 h) and higher temperature (180 °C), a significant decrease in viscosity and shear modulus was observed. Analysis of filtrates revealed the formation of cello-oligosaccharides, glucose and HMF and a decrease in surface tension indicating peeling and molecular degradation of the sample matrice. The microfibralled cellulose sample decomposition and gel network structure breakdown on a molecular level is discussed.

Different metastable equilibrium states in metallic glasses occurring far below and near the glass transition

Precise measurements of the high-frequency shear modulus of two bulk Zr- and Pd-based glasses in the initial and strongly preannealed states in a wide temperature range are performed. Isothermal structural relaxation of preannealed samples leads to either decrease or increase of the shear modulus. At temperatures below particular temperature Tpc, one observes cross-over relaxation (decrease→increase) of the shear modulus. The minimal shear modulus attained upon relaxation corresponds to the quasi-metastable equilibrium, which depends both on temperature and thermal prehistory. At higher temperatures T >Tpc, the relaxation always leads to shear modulus decrease towards the “true” metastable equilibrium, which depends only on temperature. The temperature Tpc for both glasses is by ≈ 25 K smaller than the calorimetric glass transition temperature. It is shown that this temperature constitutes the low temperature limit of the linear extrapolation of the shear modulus from the supercooled liquid state. By definition, the temperature Tpc corresponds to the pseudocritical temperature introduced by Kauzmann in 1948 (W. Kauzmann, Chem. Rev. 43 (1948) 219).A detailed discussion of the microscopic relaxation mechanism below and above Tpc based on the Interstitialcy theory is presented.

Manipulation and control of instabilities for surfactant-laden liquid film flowing down an inclined plane using a deformable solid layer

We analyzed the linear stability of surfactant-laden liquid film with a free surface flowing down an inclined plane under the action of gravity when the inclined plane is coated with a deformable solid layer. For a flow past a rigid incline and in the presence of inertia, the gas-liquid (GL) interface is prone to the free surface instability and the presence of surfactant is known to stabilize the free surface mode when the Marangoni number increases above a critical value. The rigid surface configuration also admits a surfactant induced Marangoni mode which remains stable for film flows with a free surface. This Marangoni mode was observed to become unstable for a surfactant covered film flow past a flexible inclined plane in a creeping flow limit when the wall is made sufficiently deformable. In view of these observations, we investigate the following two aspects. First, what is the effect of inertia on Marangoni mode instability induced by wall deformability? Second, and more importantly, whether it is possible to use a deformable solid coating to obtain stable flow for the surfactant covered film for cases when the Marangoni number is below the critical value required for stabilization of free surface instability. In order to explore the first question, we continued the growth rates for the Marangoni mode from the creeping flow limit to finite Reynolds numbers (Re) and observed that while the increase in Reynolds number has a small stabilizing effect on growth rates, the Marangoni mode still remains unstable for finite Reynolds numbers as long as the wall is sufficiently deformable. The Marangoni mode remains the dominant mode for zero and small Reynolds numbers until the GL mode also becomes unstable with the increase in Re. Thus, for a given set of parameters and beyond a critical Re, there is an exchange of dominant mode of instability from the Marangoni to free surface GL mode. With respect to the second important aspect, our results clearly demonstrate that for cases when the stabilizing contribution of surfactant is not sufficient for suppressing GL mode instability, a deformable solid coating could be employed to suppress free surface instability without triggering Marangoni or liquid-solid interfacial modes. Specifically, we have shown that for a given solid thickness, as the shear modulus of the solid layer decreases (i.e., the solid becomes more deformable) the GL mode instability is suppressed. With further decrease in shear modulus, the Marangoni and liquid-solid interfacial modes become unstable. Thus, there exists a stability window in terms of shear modulus where the surfactant-laden film flow remains stable even when the Marangoni number is below the critical value required for free surface instability suppression. Further, when the Marangoni number is greater than the critical value so that the GL mode remains stable in the rigid limit or with the deformable wall, the increase in wall deformability or solid thickness triggers Marangoni mode instability and, thus, renders a stable flow configuration into an unstable one. Thus, we show that the soft solid layer can be used to manipulate and control the stability of surfactant-laden film flows.

Structural, mechanical and electronic properties of two-dimensional structure of III-arsenide (1 1 1) binary compounds: An ab-initio study

Structural, mechanical and electronic properties of two-dimensional single-layer hexagonal structures in the (111) crystal plane of IIIAs-ZnS systems (III = B, Ga and In) are studied by first-principles calculations based on density functional theory (DFT). Elastic and phonon dispersion relation display that 2D h-IIIAs systems (III = B, Ga and In) are both mechanical and dynamically stable. Electronic structures analysis show that the semiconducting nature of the 3D-IIIAs compounds is retained by their 2D single layer counterpart. Furthermore, density of states reveals the influence of σ and π bonding in the most stable geometry (planar or buckled) for 2D h-IIIAs systems. Calculations of elastic constants show that the Young’s modulus, bulk modulus and shear modulus decrease for 2D h-IIIAs binary compounds as we move down on the group of elements of the periodic table. In addition, as the bond length between the neighboring cation-anion atoms increases, the 2D h-IIIAs binary compounds display less stiffness and more plasticity. Our findings can be used to understand the contribution of the σ and π bonding in the most stable geometry (planar o buckled) for 2D h-IIIAs systems. Structural and electronic properties of h-IIIAs systems as a function of the number of layers have been also studied. It is shown that h-BAs keeps its planar geometry while both h-GAs and h-InAs retained their buckled ones obtained by their single layers. Bilayer h-IIIAs present the same bandgap nature of their counterpart in 3D. As the number of layers increase from 2 to 4, the bandgap width for layered h-IIIAs decreases until they become semimetal or metal. Interestingly, these results are different to those found for layered h-GaN. The results presented in this study for single and few-layer h-IIIAs structures could give some physical insights for further theoretical and experimental studies of 2D h-IIIV-like systems.

A hybrid damage assessment for E-and S-glass reinforced laminated composite structures under in-plane shear loading

Micro-damage initiation and accumulation in two different Glass Fiber Reinforced -E-glass and S-glass- Laminated Composite Structures (LCS) subjected to in-plane shear stressing are monitored with Acoustic Emission (AE) and thermography methods. AE signals caused by micro-damage formation are graphed as a scatter plot of Weighted Peak Frequency (WPF) versus Partial Power 2 (PP2) features and clustered using the K-means algorithm with Bray Curtis dissimilarity function thus resulting in three different well-separated clusters. Each of these clusters corresponds to different micro damages, i.e., transverse cracks, delaminations, or fiber ruptures. It is observed that the E-glass reinforced LCS has higher numbers of AE hits. Thus, the total amount of micro-damage incurred as well as the average temperature change measured by thermography is higher for the E-glass reinforced LCS. It is shown that due to the curing induced residual tensile stress in E-glass reinforced LCS, the initial formation of delamination in E-glass reinforced LCS starts at higher load level. Under the applied shear load, a significant reduction in in-plane shear modulus is observed both for the E-glass and S-glass-reinforced LCS where the E-glass reinforced LCS shows greater reduction. The decrease in in-plane shear modulus is attributed to micro-damage accumulated in the LCS.

Cyclic behavior of saturated soft clay under stress path with bidirectional shear stresses

Under seismic loading, soil layers experience multidirectional cyclic shear stresses with different amplitudes and frequencies. Therefore, the deformation behavior of soft clay under complex stress paths is practically relevant. In this study, cyclic tests are performed on normally consolidated soft clay. To simulate the situation induced by seismic load, the complex figure-eight-shaped stress path is realized by applying shear stresses in two directions simultaneously. Under the figure-eight-shaped shear stress path, the cyclic strain, cyclic modulus, and cyclic strength of soft clay are found to be significantly dependent on the CSR (cyclic shear stress ratio) and the bidirectional shear frequencies. With an increase in the CSR and a decrease in the shear frequency, the dynamic shear modulus decreases and cyclic strain accumulation increases with an increasing number of cycles. Based on the test results, an empirical formula was presented to predict the cyclic strength under different shear frequencies.

Effect of ripples on the finite temperature elastic properties of hexagonal boron nitride using strain-fluctuation method

This work intents to put forth the results of a classical molecular dynamics study to investigate the temperature dependent elastic constants of monolayer hexagonal boron nitride (h-BN) between 100 and 1000 K for the first time using strain fluctuation method. The temperature dependence of out-of-plane fluctuations (ripples) is quantified and is explained using continuum theory of membranes. At low temperatures, negative in-plane thermal expansion is observed and at high temperatures, a transition to positive thermal expansion has been observed due to the presence of thermally excited ripples. The decrease of Young's modulus, bulk modulus, shear modulus and Poisson's ratio with increase in temperature has been analyzed. The thermal rippling in h-BN leads to strong anharmonic behaviour that causes large deviation from the isotropic elasticity. A detailed study shows that the strong thermal rippling in large systems is also responsible for the softening of elastic constants in h-BN. From the determined values of elastic constants and elastic moduli, it has been elucidated that 2D h-BN sheets meet the Born's mechanical stability criterion in the investigated temperature range. The variation of longitudinal and shear velocities with temperature is also calculated from the computed values of elastic constants and elastic moduli.

Preliminary examination of soybean oil derived material as a potential rejuvenator through Superpave criteria and asphalt bitumen rheology

The increased use of recycled asphalt materials in bituminous mixtures has led to increasing interest in rejuvenators. Rejuvenators are primarily used to restore the rheological properties of aged bitumens to their unaged state. In this work, the effect of adding a soybean-derived biomaterial at a 0.75% by mass of bitumen to a polymer modified PG64-28 and a neat PG58-28 is studied. Dynamic Shear Rheometer, Bending Beam Rheometer, and Rotational Viscometer are used to characterize the bitumens rheology. The effect of aging on the longevity of the soybean additive is examined. It was revealed that this material is a viable candidate as a rejuvenator. At such low dosage, it had a remarkable effect on the fatigue and low temperature properties of both bitumens. It also led to a notable decrease in the complex shear modulus accompanied by an increase in the phase angle, which is essentially reversing the effect of aging.

Elastic moduli and Poisson's ratio of 2-dimensional magnetic skyrmion lattice

By analyzing the magnetic energy, we investigated the deformation of magnetic chiral structures and derived estimates of the skyrmion lattice (SkL) elastic moduli and SkL Poisson's ratio. We verified that the SkL system is close to an elastically isotropic system in which skyrmions display a particle behavior with only nearest-neighbor interactions. We found that with the applied external field, the SkL shear modulus decreases and SkL Poisson's ratio increases. We also obtained an estimate for the critical energy required for the crystal axis reorientation of the SkL, which like the SkL shear modulus also decreases with the external field. These trends indicate that the SkL becomes soft and less solid as the external field increases until the chiral structures disappear at the critical field.

Maximum Shear Modulus of Cement-Treated Singapore Marine Clay

In this study, bender element was adopted to test the maximum shear modulus of cement-treated Singapore marine clay. The effects of factors such as cement content and total water content on the maximum shear modulus of cement-treated clay was evaluated. The maximum shear modulus of cementtreated clay is governed by cement content and total water content. At constant total water content, higher cement content will result in higher value of maximum shear modulus. However, when cement content is fixed, increase in total water content will result in decrease of maximum shear modulus.

Cyclic Direct Simple Shear Test to Measure Strain-Dependent Dynamic Properties of Unsaturated Sand

The dynamic properties of a clean sand under different degrees of saturation were investigated using a modified custom built Direct Simple Shear (DSS) apparatus at the University of New Hampshire. The specific characteristics of the DSS were presented, and the testing procedures were discussed. The device used the axis translation and tensiometric techniques to control the matric suction in the soil specimen. The investigation on F75 Ottawa Sand showed a decrease in shear modulus and an increase in damping by increasing the shear strain over the tested range of strains for various degrees of saturation: dry, saturated, and partially saturated. The modulus reduction in the applied range of medium shear strains regardless of the degree of saturation demonstrated the capability of the DSS in consistently capturing the changes of dynamic properties. Experimental results indicated that the matric suction can have a substantial effect on the stiffness of the soil. However, the extent of this effect may depend on the induced strain level of the effective stress in unsaturated soil. In addition, partially saturated specimens resulted in lower dynamic compression.

The competitive nucleation of misfit dislocation dipole and misfit extended dislocation dipole in nanocomposites

Nanocomposites have shown excellent mechanical and physical properties; however, their properties are seriously affected by the nucleation of misfit defects at the interfaces between the inclusion and the matrix. Based on the energy rule, the nucleation criteria for a misfit extended dislocation dipole (MEDD) and a misfit screw dislocation dipole (MSDD) are analytically given. Furthermore, we systematically investigate the effects of the geometrical and mechanical factors, such as the radius of the inclusion, the misfit strain, the shear modulus ratio and the stacking fault energy, on the competitive nucleation between MEDD and MSDD. It is found that the stacking fault energy has a decisive effect on the competitive nucleation of MEDD and MSDD. The critical stacking fault energy for the nucleation transferring from MSDD to MEDD increases with the increase of the shear modulus ratio and decrease of the misfit strain, while it is almost not affected by the inclusion radius.

Effects of Ga content on the stability of Fe-X (X = 6.25, 12.5, 18.75, 25 at.% Ga) alloys from first-principles calculations

First-principles calculations based on density functional theory (DFT) were employed to investigate the influence of Ga concentration on the stability of binary Fe–Ga alloy. The contents of Ga element are 6.25, 12.5, 18.75 and 25 at.% for Fe[Formula: see text]Ga, Fe[Formula: see text]Ga, Fe[Formula: see text]Ga[Formula: see text] and Fe[Formula: see text]Ga alloys, respectively. Cohesive energy, elastic properties, electronic structures and phonon properties of optimized Fe–Ga models were calculated. Our results of calculated elastic constants and elastic moduli are in good accordance with the determined available literature. Our study shows that with increasing Ga content, the absolute value of cohesive energy of Fe–Ga alloy is decreasing. From the calculations of elastic constants, we found that the value of [Formula: see text] decreases with the increasing Ga content, which indicates that the stability of Fe–Ga along the [001] direction is decreasing with the increasing Ga content. The calculated bulk moduli of Fe–Ga alloys increase with increasing Ga content because of the increase of the average bonding number evaluated by our calculations of densities of states. Conversely, the shear moduli decrease with increasing Ga content, which indicates that the stability of Fe–Ga is decreasing with the increasing Ga content. Tetragonal shear elastic constant [Formula: see text] almost decreases linearly with increasing Ga content, which follows the same decreasing trend as the cohesive energy and the shear modulus. It is worth noting that with the increasing Ga content, the pseudogap between two major peaks in the minority-spin state became softer. The softness brings the Fermi level into a high state, which lowers the stability of the Fe–Ga alloy. According to the phonon calculations, the acoustic mode of Fe-25 at.% Ga appeared to be softening along the [001] direction, which is in good accordance with the direction predicted by the calculations of elastic constant. But this softening trend cannot be observed in the phonon dispersion spectrum of Fe-6.25 at.% Ga, which proved that Fe-6.25 at.% Ga is more stable than the Fe-25 at.% Ga alloy.

Nonlinear shear behavior and failure of composite materials under plane stress conditions

Most of laminated composites used in modern structures exhibit nonlinearity even under elastic conditions. Probably, the most evident case that reveals this effect is the plane shear experiment, where the stress strain diagram is apparently nonlinear directly from low values of load. This experiment demonstrates the decrease in shear modulus during increase of shear stress and strain. The aim of the research is the analysis of shear nonlinear response of the composite material with stress concentrator, and its influence on stress distribution and damage evaluation during specimen loading. An example problem of an open hole composite plate under compression loading is studied. The comparison of experimental and numerical results is performed with reasonable proximity. It was shown that in spite of equal limit loads of the nonlinear elastic model and linear one, the stress and damage distributions are significantly different.

Investigation of the micro-mechanics of sand–rubber mixtures at very small strains

This study presents a series of discrete element method (DEM) simulations consisting of mixtures of stiff (sand) and soft (rubber) particles, subjected to monotonic triaxial shearing under constant volume at very small strains where pure elasticity governs the behaviour of the samples. The elastic shear moduli of the simulated pure sand and pure rubber samples were first calibrated to values reported in previous experimental works. Sand–rubber mixtures were then simulated with a focus on small-strain stiffness to examine the role of rubber content on the prevailed micro-mechanisms of the samples. The macro-mechanical response of the numerical mixtures showed a decrease in the elastic shear modulus and the deviatoric stress as the soft particle content increased, in line with observations from laboratory tests. Micro-scale information including coordination number, fabric tensor and normal contact force anisotropy was obtained for all tests and the contribution of each type of contact, i.e. sand–sand, rubber–sand or rubber–rubber, in the overall response of the samples, was analysed. The contact force network in the mixtures changed from being sand-dominated to rubber-dominated, with the presence of an intermediate zone in between rubber and sand particles forming a stable contact force network mainly by sand–rubber contacts. Each type of contact was seen to contribute differently to the deviatoric stress in the system as the rubber content increased.

Effects of warm-up on hamstring muscles stiffness: Cycling vs foam rolling.

This study investigated the effects of active and/or passive warm-up tasks on the hamstring muscles stiffness through elastography and passive torque measurements. On separate occasions, fourteen males randomly completed four warm-up protocols comprising Control, Cycling, Foam rolling, or Cycling plus Foam rolling (Mixed). The stiffness of the hamstring muscles was assessed through shear wave elastography, along with the passive torque-angle relationship and maximal range of motion (ROM) before, 5, and 30minutes after each experimental condition. At 5minutes, Cycling and Mixed decreased shear modulus (-10.3%±5.9% and -7.7%±8.4%, respectively; P≤.0003, effect size [ES]≥0.24) and passive torque (-7.17%±8.6% and -6.2%±7.5%, respectively; P≤.051, ES≥0.28), and increased ROM (+2.9%±2.9% and +3.2%±3.5%, respectively; P≤.001, ES≥0.30); 30minutes following Mixed, shear modulus (P=.001, ES=0.21) and passive torque (P≤.068, ES≥0.2) were still slightly decreased, while ROM increased (P=.046, ES=0.24). Foam rolling induced "small" immediate short-term decreases in shear modulus (-5.4%±5.7% at 5minutes; P=.05, ES=0.21), without meaningful changes in passive torque or ROM at any time point (P≥.12, ES≤0.23). These results suggest that the combined warm-up elicited no acute superior effects on muscle stiffness compared with cycling, providing evidence for the key role of active warm-up to reduce muscle stiffness. The time between warm-up and competition should be considered when optimizing the effects on muscle stiffness.

An autonomous self‐healing hydrogel based on surfactant‐free hydrophobic association

ABSTRACTSelf‐healing hydrogels are attractive for a variety of applications including wound dressings and coatings. This paper describes the facile preparation and characterization of an autonomous self‐healing hydrogel system comprising surfactant‐free hydrophobic associations. The hydrogel comprised a copolymer of benzyl methacrylate (B), octadecyl methacrylate (O), and methacrylic acid (MA). The hydrogels were prepared via a controlled dehydration procedure to achieve the formation of strong intermolecular hydrophobic associations of the octadecyl groups above a critical polymer concentration. Fractured hydrogels healed within 30 min without any external intervention. Increasing hydrogel polymer content from 31 wt % to 39 wt % resulted in a threefold increase in the shear modulus and 50% reduction of the relaxation time. Addition of 4 mM NaCl to a hydrogel of 31 wt % polymer content resulted in 2.5 times longer relaxation time and 24% decrease in shear modulus. The hydrogels swelled up water by up to four times its weight, which corroborates the robustness of the hydrophobic association crosslinks. The bulk properties of the hydrogels are discussed in terms of the hydrophobic associations of the O‐groups and the electrostatic interaction of the MA‐groups in the polymer chains. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44800.