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Rotator cuff tear is a common shoulder injury that causes shoulder dysfunction and pain. Although surgical repair is the primary treatment for rotator cuff tear, it is well recognized that impaired force exertion of muscles connecting to the involved tendon and subsequent complemental change in the force exertion of synergist muscles persist even after repair. This study aimed to identify the compensation strategy of shoulder abductors by examining how synergist muscles respond to supraspinatus (SSP) muscle force deficit in patients with rotator cuff repair. Muscle shear modulus, an index of muscle force, was assessed for SSP, infraspinatus, upper trapezius, and middle deltoid muscles in repaired and contralateral control shoulders of 15 patients with unilateral tendon repair of the SSP muscle using ultrasound shear wave elastography while the patients passively or actively held their arm in shoulder abduction. In the repaired shoulder, the shear modulus of the SSP muscle declined, whereas that of other synergist muscles did not differ relative to that of the control. To find the association between the affected SSP and each of the synergist muscles, a regression analysis was used to assess the shear moduli at the population level. However, no association was observed between them. At the individual level, there was a tendency of variation among patients with regard to a specific muscle whose shear modulus complementarily increased. These results suggest that the compensation strategy for SSP muscle force deficit varies among individuals, being nonstereotypical in patients with rotator cuff injury. [ABSTRACT FROM AUTHOR]

Determining proper strain‐dependent shear modulus and damping ratio for soils is of utmost importance when investigating their response to cyclic loads. Experimental studies on the effect of the degree of saturation and suction on the shear modulus at large strain amplitudes are scarce due to the complexities involved in testing such soils. Furthermore, the previously presented micromechanical models for the cyclic behavior of unsaturated soils lack some of the required features of soil pore skeleton essential to model unsaturated soils' hydromechanical behavior. This paper is, thus, aimed at addressing this shortcoming by incorporating a pore‐scale numerical method that couples the discrete element simulation of the solid phase and the fluid pore network to capture the cyclic behavior of unsaturated sands. To this end, the model is first calibrated to determine the micro‐scale parameters using experimental results from static drained triaxial compression tests on dry and saturated sand samples. Next, the coupled model is employed to simulate the observed behavior during cyclic triaxial tests on unsaturated sands. A linear dependence of the plastic rolling coefficient and the interparticle friction angle on the degree of saturation is proposed from simulations of suction‐controlled cyclic triaxial tests. Variation of shear modulus with shear strain amplitude and degree of saturation indicates a continuous increase in the shear modulus with the decrease in saturation. In contrast, the trend for the damping ratio is the opposite. Finally, closed‐form relationships are proposed based on the simulation results for the shear modulus and damping ratio of unsaturated soils. [ABSTRACT FROM AUTHOR]

Strong earthquakes with larger magnitude and longer durations trigger many landslides, however, how magnitude and duration affect landslides is still unclear. Many factors could contribute to this, including additional shear stress provided by strong ground motion, or "seismogenic liquefaction"; herein, we hypothesize that the dynamic weakening of sliding zone gouge is important. We explored the influence of earthquake magnitude and duration on landslide triggering by simulating the seismic response of sliding zone gouge using a dynamic ring‐shear device and glass spheres. The experiments showed that vibration with larger amplitudes and longer durations more easily trigger deformation and even instability in dry granular materials. We used a dynamic triaxial‐bender system to find that the shear modulus of these materials decreased with the increase in duration and amplitude of cyclic loading. We suggest that this universal decrease in shear modulus is an important landslide‐trigger mechanism. Our results revealed how magnitude and duration of earthquakes affect co‐seismic landslides and why earthquakes with larger magnitude and long durations can trigger more co‐seismic landslides. Plain Language Summary: Strong earthquakes with larger magnitudes and longer durations trigger many landslides. Some mechanisms have been proposed to explain the triggering, for example, seismic waves provide additional driving force which increases the shear stress on the sliding plane. Earthquakes may cause an increase of pore pressure, which reduces the effective normal stress on the sliding plane. However, the mechanisms that apply to wet and dry conditions are not fully understood. We hypothesize that the dynamic weakening of sliding zone gouge caused by earthquakes is an important mechanism. We used a dynamic ring shear device and glass spheres to simulate the seismic response of sliding zone gouge, and our experiments show that larger amplitudes and longer durations more easily trigger deformation and even instability. Using a dynamic triaxial‐bender system, we found that the shear modulus decreased with the increase in duration and amplitude of vibration. Our results reveal how earthquakes with larger magnitudes and long durations trigger more co‐seismic landslides. Our experimental method may be helpful for monitoring and early warning of earthquake‐triggered landslides in the future. Key Points: Dynamic ring shear tests show the deformation characteristics of granular materials under vibrationLonger durations and larger amplitudes of vibration are more likely to trigger slip and shear modulus weakeningThe reduction and recovery of shear modulus is an important mechanism for triggering failure of earthquake‐triggered landslides [ABSTRACT FROM AUTHOR]

Dynamic mechanical properties of natural gas hydrate (NGH) reservoirs are extremely important owing to their critical role in drilling safety and reservoir stability during NGH development. However, the comprehensive influence of reservoir skeleton and hydrate status on the dynamic mechanical properties of hydrate‐bearing sediments (HBS) has rarely been reported. In this study, three types of sandy sediments with different particle size were simulated. A customized resonant column system was used to synthesize HBS and to test the dynamic mechanical properties of the HBS under the conditions of different confining pressures and shear strains. In addition, the dynamic mechanical responses of the hydrate‐free and hydrate‐dissociated specimens were comprehensively studied to further demonstrate the dominant role of hydrate status and skeleton‐hydrate interactions on the dynamic mechanical properties of HBS. The results show that the shear moduli of the HBS specimens increase exponentially with an increase in confining pressure and decrease in amplitude strain. However, the damping ratios decreases with an increase in confining pressure and decrease in amplitude strain. With an increase in the median particle size (D50) of the simulated sediments, the shear moduli tend to increase, whereas the damping ratios decreas. In addition, the hydrate occurrence decreases differences in moduli between fine‐, medium‐ and coarse‐skeleton specimens, and the enhancement effect of hydrate on the mechanical properties of the specimen is the maximum for the fine sediment specimens. Interestingly, we find that the modulus of the hydrate‐dissociated specimen is relatively smaller than that of the hydrate‐free specimen, which implies that the structure of the sediments could be rearranged and weakened due to the hydrate formation‐dissociation processes. [ABSTRACT FROM AUTHOR]

Temperature‐dependent viscosity is critical to decipher two profound questions in condensed matter physics, namely the glass transition and the relaxation of amorphous solids. However, direct measurement of viscosity over a large temperature range is extremely difficult. Here, using classical molecular dynamics (MD) simulations, we report a novel method to calculate the equilibrium viscosity of supercooled liquid both above and below the glass transition temperature (Tg) and to estimate the nonequilibrium viscosity of glass down to room temperature. Based on the shoving model, we derived an analytical formula showing that the shear viscosity in logarithmic scale changes linearly with the shear‐induced variation in shear modulus or potential energy of the glass‐forming system. The shear viscosity as a function of steady‐state potential energy of liquid under different shear strain rates can be directly calculated in MD simulations; together with its equilibrium potential energy, one can extrapolate the zero‐strain‐rate equilibrium viscosity. We verified the proposed model by reliably calculating equilibrium viscosity near Tg of four glass‐forming systems (Kob–Andersen system, silica, Cu45.5Zr45.5Al9, and silicon) with different fragilities. Furthermore, our model can estimate the nonequilibrium viscosity of glass below Tg; the upper‐bound nonequilibrium viscosity of amorphous silica and silicon at room temperature are calculated to be ~1032 and 1025 Pa·s, respectively. [ABSTRACT FROM AUTHOR]

Soft materials such as hydrogels and elastomers exhibit very low stiffness and strength as well as large deformations, which makes their mechanical characterisation extremely difficult through conventional methods. This paper presents a novel experimental technique for the mechanical shear property characterisation of these materials. Agarose hydrogels were chosen as a model material for this study. The new in‐plane shear test method incorporates 3‐D‐printed acrylonitrile butadiene styrene (ABS) grips for specimen mounting and digital image correlation (DIC) for full‐field strain measurement on both sides of the specimen gauge section. These grips utilise barb‐like pegs to secure the specimen while load is applied. In order to evaluate the methodology, four concentrations of agarose hydrogel (4.0%, 2.5%, 1.5%, and 0.5% wt./solvent volume) were tested. Results for the agarose hydrogel demonstrated excellent repeatability. The obtained shear moduli show a monotonic increase with gel concentration. Furthermore, the range of shear moduli applicable to the novel testing method was determined. [ABSTRACT FROM AUTHOR]

Intra‐ply shear is the most important deformation mode in composite sheet forming. In this study, the intra‐ply shear behaviors of cross‐ply unidirectional carbon fiber/epoxy prepregs under double diaphragm compaction at different temperatures and cross‐head rates were investigated by a home‐made testing system. The experimental test results indicate that uniform temperature distribution and low forming speed in double diaphragm process help to obtain high‐quality products. A modified model based on the temperature, cross‐head rate and the level of compaction was proposed for shear angle prediction. Then fifth‐degree polynomial and power functions combined with two rate‐independent theories were used to calculate the shear force and modulus. The shear force and shear modulus are strongly influenced by the function that describing the relationship between the shear force and shear angle. [ABSTRACT FROM AUTHOR]

Summary: Purpose: Shear modulus (μ) is directly correlated to the tissue stiffness and can predict the tendon ultimate force to failure. With the knee extended 0° (K0), semitendinosus tendon (ST) is tensioned while patellar tendon (PT) is relaxed. At 80o, knee flexion (K80) tendons present an opposite stress pattern; however, the relation between ST and PT μ in both situations was not studied yet. Method: We accessed the μ of the ST and PT at 0o and 80o knee flexion by supersonic shear wave imaging (SSI) elastography from 18 healthy males. Relative μ indexes were calculated for relaxed and tensioned conditions. Result: The average μ for ST was μST‐K0 = 197·62 ± 31·93 kPa and μST‐K80 = 77·76 ± 30·08. For TP, values were μTP‐K0 = 23·45 ± 5·89 and μTP‐K80 = 113·92 ± 57·23 kPa. Relative μ indexes were calculated for relaxed (IR = μST‐K80/μTP‐K0) and tensioned conditions (IT = μST‐K0/μPT‐K80). The relative μ indexes were IR = 3·63 ± 1·50 and IT = 2·00 ± 0·96 (P<0·05). Conclusion: Semitendinosus tendon μ was significantly higher than PT μ in both tensioned and relaxed positions. This can predict a higher ultimate force to failure and a less elastic behaviour in ST grafts when compared to PT grafts. This new parameter could aid physicians in graft choice previous to anterior cruciate ligament reconstruction. [ABSTRACT FROM AUTHOR]

The mechanical behaviour of non-chiral and chiral single-walled carbon nanotubes under torsional loading is studied. For this purpose, three-dimensional finite element modelling is used in order to evaluate the torsional rigidity and shear modulus. It is shown that the evolution of torsional rigidity as a function of nanotube diameter can be described by a unique function for non-chiral and chiral single-walled nanotubes. A comprehensive study to evaluate the Poisson's ratio of single-walled carbon nanotubes is also carried out. Two robust methodologies, one for evaluating the shear modulus from results of tensile, bending and torsion tests, and the other to assess Poisson's ratio from results of bending and torsion tests, are recommended. [ABSTRACT FROM AUTHOR]