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In order to facilitate the prediction of some physical properties, we propose several simple formulas based on two parameters only, the metallic valence and metallic atomic radii. Knowing the composition, for single-phase alloys, the average parameters can be calculated by the rule of mixture. The input parameters can be obtained from tabulated databases. Adopting from the literature the results of Coulomb crystal model for metals and single-phase high-entropy alloys, we have derived formulas for the shear modulus (G) and the cohesion energy (Ecoh). Based on these parameters separately, we set up two formulas to estimate the hardness in the case of pure metals. For single-phase (solid-solution) HEAs, by simplifying the Maresca and Curtin model, we obtained a formula for estimating the hardness, which takes into account the atomic misfit in addition to G. The maximal hardness for single-phase HEA is approximately 600 kg/mm2 and is obtained for a composition with a valence electron concentration of approximately 6 ÷ 7. [ABSTRACT FROM AUTHOR]

Tissue susceptibility to histotripsy disintegration has been reported to depend on its elastic properties. This work was aimed at investigation of histotripsy efficiency for liquefaction of human hematomas, depending on their stiffness and degree of retraction over time (0–10 d). As an in vitro hematoma model, anticoagulated human blood samples (200 mL) were recalcified at different temperatures. In one set of samples, the shear modulus was measured by shear wave elastography during blood clotting at 10℃, 22℃ and 37℃, and then daily during further aging. The ultrastructure of the samples was analyzed daily with scanning electron microscopy (SEM). Another set of blood samples (50–200 mL) were recalcified at 37℃ for density and retraction measurements over aging and exposed to histotripsy at varying time points. Boiling histotripsy (2.5 ms pulses) and hybrid histotripsy (0.2 ms pulses) exposures (2 MHz, 1% dc, P +/ P –/ A s = 182/–27/207 MPa in situ) were used to produce either individual cigar-shaped or volumetric (0.8–3 mL) lesions in samples incubated for 3 h, 5 d and 10 d. The obtained lesions were sized, then the lysate aspirated under B-mode guidance was analyzed ultrastructurally and diluted in distilled water for sizing of residual fragments. It was found that clotting time decreased from 113 to 25 min with the increase in blood temperature from 10℃ to 37℃. The shear modulus increased to 0.53 ± 0.17 kPa during clotting and remained constant within 8 d of incubation at 2℃. Sample volumes decreased by 57% because of retraction within 10 d. SEM revealed significant echinocytosis but unchanged ultrastructure of the fibrin meshwork. Liquefaction rate and lesion dimensions produced with the same histotripsy protocols correlated with the increase in the degree of retraction and were lower in retracted samples versus freshly clotted samples. More than 80% of residual fibrin fragments after histotripsy treatment were shorter than 150 µm; the maximum length was 208 µm, allowing for unobstructed aspiration of the lysate with most clinically used needles. The results indicate that hematoma susceptibility to histotripsy liquefaction is not entirely determined by its stiffness, and correlates with the retraction degree. [ABSTRACT FROM AUTHOR]

A series of shaking table tests were performed on reduced-scale models of helical soil-nailed walls (HSNWs) to evaluate the effect of the nail arrangement and nail inclination on the failure mechanisms and dynamic characteristics of this type of retaining structures under seismic conditions. The results of particle image velocimetry (PIV) showed that the potential failure surfaces in the helical soil-nailed walls were parabolic ones with an inflection point and the dimensions of failure wedge increased as the length and inclination of the nails increased. A combination of overturning and base sliding was identified as the predominant deformation mode in the HSNWs and that base sliding faded with an increase in the nail inclination. It was found that horizontal helical nails located in the lower half of the wall played a more effective role in reducing lateral displacement, but the opposite was true for HSNWs with inclined nails. The use of inclined nails instead of horizontal ones was found to be an efficient solution for increasing the shear modulus in HSNWs. The efficiency of this solution decreased with the use of shorter nails in the upper half of the walls and was eventually minimized by increasing the length of the nails across the wall height. It was found that, although the use of helical nails instead of grouted ones reduced wall damping, it could be a good solution for increasing the stiffness of the soil-nailed walls. [ABSTRACT FROM AUTHOR]

The empirical expressions for predicting the small-strain shear modulus (G0) of granular soils in current engineering practice are established mainly on experimental data under isotropic stress conditions. In most geotechnical applications, however, soils are subjected to anisotropic stress conditions. The impact of stress anisotropy on G0 is a critical concern but is not yet fully understood. In this paper, we present a specifically designed experimental study to address the question. Various principal stress ratios were applied to isotropically consolidated sand specimens in a triaxial apparatus, and the elastic shear waves were generated by the bender elements installed in the apparatus such that the variations of G0 from isotropic stress states to anisotropic stress states were determined. Three quartz sands with different particle shapes were tested under a range of states in terms of void ratio, axial stress, and radial stress. The study shows that the impact of stress anisotropy is much more complicated than commonly thought. It depends on the magnitude of the stress ratio and the loading mode. A simple model that accounts for two primary mechanisms associated with the impact of stress anisotropy is proposed, and its performance is evaluated using various sources of data in the literature. [ABSTRACT FROM AUTHOR]

This study investigated the effect of gradation, especially of mean particle size and uniformity of gradation, on the shear modulus degradation of natural marine sands compared to regraded clean sands. A series of fixed-free resonant column tests were performed on graded clean sands and marine sands having similar uniformity coefficient values, Cu. It is observed that the modulus degradation of both clean sands and marine sands increased with the increase in Cu. However, the marine sands have degraded less than clean sands for the same Cu and effective confining stress. The reasons can be attributed to the nonlinearity in the grain size distribution of marine sands above 60% finer and mean particle size, D50 , compared to graded clean sands. The overestimation of the modulus degradation of marine sands by the existing empirical equations is demonstrated. Considering the effects of uniformity coefficient, Cu , and mean particle diameter, D50 , a generalized calibrated modulus degradation model for a wide range of clean sands and marine sands is proposed with a high coefficient of determination. Good agreement is demonstrated between the estimated and experimental data from the literature. [ABSTRACT FROM AUTHOR]

To describe the evolution of residual stresses in epoxy resin during the curing process, a more detailed characterization of its viscoelastic properties is necessary. In this study, we have devised a simplified apparatus for assessing the viscoelastic properties of epoxy resin. This apparatus employs a confining cylinder to restrict the circumferential and radial deformations of the material. Following the application of load by the testing machine, the epoxy resin sample gradually reduces the gap between its surface and the inner wall of the confining cylinder, ultimately achieving full contact and establishing a continuous interface. By recording the circumferential stress–strain on the outer surface of the confining cylinder, we can deduce the variations in material bulk and shear moduli with time. This characterization spans eight temperature points surrounding the glass transition temperature, revealing the bulk and shear relaxation moduli of the epoxy resin. Throughout the experiments, the epoxy resin's viscoelastic response demonstrated a pronounced time-temperature dependency. Below the glass transition temperature, the stress relaxation response progressively accelerated with increasing temperature, while beyond the glass transition temperature, the stress relaxation time underwent a substantial reduction. By applying the time-temperature superposition principle, it is possible to construct the relaxation master curves for the bulk and shear moduli of the epoxy resin. By fitting the data, we can obtain expressions for the constitutive model describing the viscoelastic behavior of the epoxy resin. In order to validate the reliability of the test results, a uniaxial tensile relaxation test was conducted on the epoxy resin casting body. The results show good agreement between the obtained uniaxial relaxation modulus curves and those derived from the bulk and shear relaxation modulus equations, confirming the validity of both the device design and the testing methodology. [ABSTRACT FROM AUTHOR]

Establishing the influence of sample preparation method on shear wave velocity or associated small-strain shear modulus (G0) of silty sands is a subject of considerable interest. This paper presents an attempt to address this topic through a comprehensive experimental programme covering four sample preparation methods. The experiments were conducted on clean Toyoura sand and its mixtures with two types of fines of different sizes. For each sample preparation method, a range of void ratio and confining stress was investigated to obtain a comprehensive view of the influence of sample preparation and its interplay with other factors. One of the notable findings is that, compared with clean sand, the difference of G0 induced by different sample reconstitution methods can be much enlarged for silty sand, and the influence is coupled with the size disparity ratio of the mixtures. The reduction of G0 due to the presence of fines also depends on sample preparation method and for smaller fines the reduction is more significant. A careful examination of the X-ray images of the specimens made by different methods suggests that the observed effects are mainly associated with the different contact conditions of coarse and fine grains. [ABSTRACT FROM AUTHOR]

An ultrasonic-wave system was developed to measure the rheological properties of non-Newtonian materials based on their responses to shear and pressure waves. This system was composed of a commercial shear wave transducer and various homemade devices, including a signal generator, a signal conditioner, and a transmission/receiving switch. The shear wave reflections at the interface between the delay line and the unknown test materials can be interpreted by the signals measured with calibration materials (e.g. air, water, olive oil and honey) that have well-known rheological properties. If the Voigt viscoelastic model is used to describe the dynamic behaviour of these test materials, the interpreted data can be used to determine the acoustic impedances, and thus solve for their shear moduli (G), kinematic viscosities (ν) and bulk densities (ρ). After the calibration procedures, the proposed system was used to test a consolidating kaolinite slurry with zero salinity and an initial suspended sediment concentration of 420 g l–1. The measurements showed that the shear modulus G is developed until consolidation for approximately 100 h. Afterward, the G gradually approached a value on the order of 500 N m–2 after approximately 200 h. This corresponded to an initial viscosity of approximately 7 × 10−5 m2 s–1, which decreased slowly over time to approximately 4 × 10−6 m2 s–1 after 300 h. With minor modification to capture pressure waves from the shear wave transducer, the bulk density can also be measured. The integrated system offers a non-invasive and efficient method for characterizing non-Newtonian fluids, providing valuable insights into their rheological properties, which are crucial for a wide range of industrial and scientific applications. [ABSTRACT FROM AUTHOR]

In the aging of oil-contaminated soils, the ambient conditions that the soils are naturally exposed to can affect soil properties over time while most studies stored the prepared samples in the laboratory with well-controlled environments. The tests on samples kept in the laboratory cannot thus reflect the actual behavior. This study compares the time-dependent characteristics of static and dynamic parameters of crude oil-contaminated sands stored in the laboratory and left in natural conditions using cyclic simple shear tests. Crude oil-contaminated samples prepared from sands with various gradations with 6% crude oil contamination were held in natural and laboratory environments for up to 24 months and tested at 3-month intervals under a constant void ratio and relative density of 60% to highlight the impacts of stored conditions of the samples in conjunction with the aging on shear modulus, damping ratio, and friction angle of sands. With the long investigation period in the study, the fluctuation of properties during the first year due to seasonal change can be seen. The testing results indicate that the impact of contaminants in the sands reduces with the aging effect. Both aging and stored conditions had the greatest effect on the static and dynamic parameters of coarse sand. While the smallest effect is seen for dynamic parameters of fine sand. The study provides useful information and necessary considerations for using oil-contaminated soils safely. [ABSTRACT FROM AUTHOR]

The bulk production of fly ash from the primary source requirement brings the attention of the geotechnical engineers for the recommendation of mass utilization in a different area of civil engineering. The application of waste materials is normally done in stratified form, and their performance must be examined in static as well as dynamic conditions. The behavior of the waste material under static condition has been done in considerable amounts; therefore, in the present study, the shear modulus assessment of the homogeneous and stratified soil-ash deposits has been carried out. In addition, the strain energy per unit volume required for the liquefaction has also been investigated for the present combinations. The stratified soil shows higher shear modulus than that of the fly ash and local soil for shear strain of 0.3% and 0.6% and beyond 0.6%; it shows a comparable shear modulus as compared to the homogeneous one. The shear modulus versus shear strain variation of the present materials was comparable with the sand having higher fine content (or categorized as SP). The energy required for liquefaction is dependent on all the considered parameters, whereas it is independent of the cycle needed to liquefy. In addition to that, the excess pore pressure model has been developed for the homogeneous and stratified soil-ash deposit using a strain energy ratio as an independent parameter. [ABSTRACT FROM AUTHOR]

Assessing the dynamic properties of rocks remains a foundational pursuit in the field of rock engineering, providing crucial insights into their mechanical behaviors across a spectrum of loading conditions, including static, cyclic, and dynamic scenarios. This paper expounds upon the utilization of the nonresonance (NR) torsional shear test and its implications for understanding rock responses, particularly in the context of low and medium loading rates. The NR method serves as a pivotal tool for investigating model rock materials subjected to loading conditions characterized by low frequencies and amplitudes. Renowned for its efficacy, this method allows the simultaneous determination of two critical dynamic parameters: shear modulus (G) and damping ratio (D), all at a specific loading frequency. It has been ascertained that the loading rate increased as the loading frequency and applied amplitude of loading increased. With increasing loading rate, the shear modulus consequently increased while the damping ratio decreased. It is observed that the dynamic responses of both ramp and sinusoidal loading waveforms increase concurrently with the amplitudes of the applied torque and loading frequencies. The sinusoidal waveform exhibits greater dynamicity than the ramp waveform at a certain loading rate. Furthermore, this study delves into the intricate analysis of the nonlinear viscoelastic dynamic response exhibited by rocks, utilizing the modified hyperbolic (MH) model and the Ramberg–Osgood (RO) model as analytical tools. The findings derived from curve fitting exercises unequivocally underscore the superior applicability of the Ramberg–Osgood model, particularly in characterizing modulus reduction behavior. Conversely, the modified hyperbolic model emerges as the preferred choice for comprehensive damping ratio analyses. This study enhances the comprehension of rock dynamics and responses under diverse loading conditions, contributing valuable understanding to rock engineering. Insights into loading and strain rate effects aid informed decisions and preventive measures for rock deformation and collapse risks. Practical Applications: This research suggests vital findings regarding the response of intact model materials to various dynamic loading conditions, providing significant insights for comprehending the mechanical response of rock structures exposed to cyclic loading conditions, which have the potential to create weaknesses in rocks resulting in untimely failures. The research can be utilized to assess the response of rocks in the context of seismic incidents, specifically those characterized by shear waves at particular frequencies. This study evaluates the response of rocks during earthquakes by establishing a correlation between the amplitude of torsional shear loading and the peak ground displacement linked to seismic events. In addition to its seismic implications, this research aids in advancing accurate predictive models and instruments that assess the stability and integrity of rock formations under different loading rates—a consequence of the symbiosis between frequency and amplitude. Professionals may ensure efficient risk mitigation, make well-informed decisions, and execute preventative measures concerning rock collapse and deformation by virtue of their comprehensive awareness of the delicate relationship between loading rate and dynamic rock properties. Incorporating the findings into engineering design standards and codes can bring about substantial improvements, augmenting the overall reliability and protection of rock structures. [ABSTRACT FROM AUTHOR]

Porosity has an important influence on the elastic properties of tight sandstone. Using acoustic models to study the matrix mineral modulus of tight sandstone reservoirs can provide an important reference for tight sandstone reservoir evaluation. In this paper, taking tight sandstone as an example, starting from the microscopic pore scale and considering the heterogeneity of the rock skeleton, the effect of the effective stress coefficient of porosity (n) on the elastic properties of tight sandstone was discussed. In addition, the acoustic model was used to construct the calculation method of the matrix mineral shear modulus. The research results showed that the porosity disturbance model can better describe the change law of the elastic properties of the tight sandstone. As the value of n decreases from 1 to 0, the bulk modulus (Kφ) of the unencapsulated rock gradually decreases. In the process of increasing from n=0 to n=4, the rock Kud has a slight increase trend. The fluid pressure does not produce a reverse stress effect on the movement of the rock pore boundary, that is, the fluid pressure does not have any effect on the change of the rock porosity. When n>0, the pore fluid pressure will affect the movement of the rock pore boundary to a certain extent. When the porosity disturbance is not considered, the Kφ value of the formation rock will be overestimated. The Ko of tight sandstone can be obtained using Gassmann fluid substitution equation. The calculation results of modulus parameters accord with the internal mineral composition and structural characteristics of tight sandstone, which shows the effectiveness of the method. [ABSTRACT FROM AUTHOR]

Expanded polystyrene (EPS) beads mixed with soil and cement are a new type of artificial lightweight fill material used in geotechnical practices. Hence, it is necessary to adopt an exhaustive procedure for evaluating the EPS composite attributes. In this study, Firoozkuh No. 161 sand was treated with portland cement and EPS beads, and the results of the two types of tests were combined to recommend the best mix ratio for geotechnical applications. Unconfined compression tests were carried out to investigate the mechanical characteristics of EPS composite and specify the optimum scope for EPS, cement, and water contents that were used in the strain-controlled cyclic experiments. Moreover, cyclic triaxial tests were conducted to evaluate the influence of mixing ratios, confining pressure, strain level, and the development of modulus reduction curves. The results indicate that increasing the cement content by 4%–6%, along with EPS beads up to 10% in volume, significantly enhances the composite's uniaxial compressive strength and shear modulus at higher strain levels. According to the results, there is a small variation in the damping ratio caused by cementation, which indicates that cement percentage has a greater impact on the damping ratio of the mixture than EPS beads. [ABSTRACT FROM AUTHOR]

The low-frequency (74 kHz) shear elasticity of the homologous series of normal hydrocarbons (alkanes) is studied using acoustic resonance. The shear modulus and mechanical loss tangent are measured, and the relaxation frequency and effective viscosity are calculated. The dependences of these parameters on homologue viscosity are established. It is shown that the mechanical loss tangent of all studied liquids is less than 1, demonstrating that the relaxation frequency is below the experimental frequency. [ABSTRACT FROM AUTHOR]

An analytical solution was obtained for seismic wave fields in a spherically symmetric Earth. Asymptotics is used for stable calculation of wave fields. It is shown that the classical asymptotics in the case of a sphere of large (in wavelengths) dimensions gives an error in the solution. The original asymptotics is used for efficient calculation of a solution without errors with great detail. Software has been created that makes it possible to carry out calculations for high-frequency (1 Hz and more) teleseismic wave fields in a discrete (layered) sphere of planetary dimensions. Calculations can be carried out on personal computers with OpenMP parallelization. V.Yu. Burmin (2010, 2019) proposed a spherically symmetric model of the Earth. It is characterized by the fact that the outer core in this model has viscosity and, therefore, an effective shear modulus other than zero. For this model of the Earth, a highly detailed calculation was carried out with a carrier frequency of 1 Hz. As a result of the analytical calculation, it was found that low-amplitude high-frequency oscillations, so-called "precursors," appear ahead of the PKP waves. An analytical calculation showed that the theoretical seismograms for this model of the Earth is in many respects similar to the experimental data. This confirms the correctness of the ideas that form the basis of the model. [ABSTRACT FROM AUTHOR]

In this paper, we consider the inverse coefficients problem of recovering a shear modulus μ and density ρ of a medium from the Neumann-to-Dirichlet map. This inverse problem is motivated by the reconstruction of mechanical properties of tissues in non-destructive testing. We prove Lipschitz stability results for any dimension $ d \geq 2 $ d ≥ 2 , provided that the parameters μ and ρ have upper and lower bounds and belong to a known finite dimensional subspace. The proofs rely on monotonicity relations between the parameters and the Neumann-to-Dirichlet operator, combined with the techniques of localized potentials. [ABSTRACT FROM AUTHOR]

The shear modulus and damping ratio are arguably the two most crucial soil parameters to be used in seismic site-response analyses and a wide variety of other geotechnical engineering applications involving soil materials subjected to dynamic loading. The dependency of these parameters on the level of load-induced shear strains in the field has been investigated rather extensively for different types of soils. Most experimental studies, however, have relied on a limited set of controlled environmental factors and stress variables, mainly soil moisture and confinement. The present work is an attempt to gain further insights into the possible impact of an additional critical factor: soil temperature. A resonant column apparatus was upgraded to assess the dynamic response of three types of cohesive–frictional soils as they transitioned from linear to nonlinear behavior under thermo-controlled cyclic torsional loading. Emphasis was placed on shear modulus degradation, and hence variation in damping ratio, with increasing shear strain amplitude (cyclic torque magnitude). Results showed a mostly detrimental effect of increasing soil temperature on the normalized shear modulus, damping ratio, and threshold shear strain of clayey, silty, and sandy soils when subject to small to medium shear strain levels. [ABSTRACT FROM AUTHOR]

The aim of this study was to compare the viscoelastic properties of a decellularized mesh from the porcine esophagus, prepared by our group, with two commercial acellular tissues derived from porcine small intestine submucosa and bovine pericardium for use in medical devices. The tissues' viscoelastic properties were characterized by creep tests in tension, applying the load in the direction of the fibers or the transverse direction, and also by dynamic-shear mechanical tests between parallel plates or in tension at frequencies between 0.1 and 35 Hz. All the tests were performed in triplicate at a constant temperature of 37 °C immersed in distilled water. The tissues' surface and cross-sectional microstructure were observed by scanning electron microscopy (SEM) to characterize the orientation of the fibers. The matrices of the porcine esophagus present an elastic modulus in the order of 60 MPa when loaded in the longitudinal direction while those of the porcine intestine submucosa and bovine pericardium have an elastic modulus below 5 MPa. Nevertheless, the shear modulus of bovine pericardium nearly triplicates that of the esophageal matrix. The viscoelasticity of decellularized esophageal mucosa is characterized by a fast change in the creep compliance with time. The slope of the creep curve in the double logarithmic plot is twice that of the control samples. These results are consistent with the microstructure observed under electron microscopy regarding the orientation of the fibers that make up the matrices. [ABSTRACT FROM AUTHOR]

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]

Background: There are several techniques to characterize the mechanical properties of soft materials, such as the indentation method and the method based on the application of a spherical object placed inside the sample. The indentation systems usually yield the elastic properties of materials and their mathematical models do not consider the inertia of the sample involved in motion and radiation damping, while placing an object inside the sample is not practical and this procedure can alter the mechanical properties of the sample for the method based on the application of a bubble/sphere placed inside the sample. Objective: A new approach for the identification of the viscoelastic properties of soft materials using the dynamic response of a spherical object placed at the sample interface was proposed. Methods: The spherical object placed at the sample interface was pressed using an electromagnet and the dynamic response of the spherical object was tracked using a high-speed camera, while the dynamic response of the spherical object placed at the sample interface was estimated using a comprehensive analytical model. The effects of the shear modulus, viscosity, Poisson's ratio and density of the soft sample, the radius and density of the spherical object and the damping due to radiation were considered in this mathematical model. The shear modulus and viscosity of the soft sample were determined by matching the experimentally identified and theoretically estimated responses of the spherical object. Results: The shear moduli and viscosities of the three phantoms with the gelatin mass ratios of 0.20, 0.25 and 0.29 were measured to be 3450, 4300 and 4950 Pa and 12.5, 14.0 and 15.0 Pa⋅s, respectively. The shear modulus and viscosity of the phantom increases as the gelatin mass ratio increases. The frequency of oscillations of the hemisphere placed at the phantom interface increases as the gelatin mass ratio increases due to stiffness increase. Conclusions: After matching the experimental and theoretical steady-state displacements and amplitudes of oscillations of the hemisphere at the sample interface, the comparison of the experimentally identified and theoretically predicted frequency of oscillations further confirmed the identified material properties of the samples. The approach presented here is expected to provide valuable information on material properties in biomedical and industrial applications. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this preliminary study was to compare the effects of 1-h sitting with and without short active breaks on muscle stiffness as measured by shear-wave elastography (SWE). Methods: The participants (7 females, 3 males; age: 24.9 ± 1.2 years) completed two (with and without active breaks) 1-h sitting exposures on separate days. Active breaks (2–3 min) were performed at 20 min and 40 min time marks and comprised simple stretching and activation exercises. Before, during (30 min) and after (1 h) of sitting, shear modulus of upper trapezius, lumbar region of erector spinae and rectus femoris muscles was measured with SWE. Results: Statistically significant effects of sitting exposure in erector spinae muscle stiffness were noted (p = 0.041; η2 = 0.38). There were no other statistically significant effects of sitting exposure or condition (with/without breaks). Conclusions: Although few statistically significant effects were detected, the trends in this preliminary trial suggest that prolonged sitting increases muscle stiffness and warrants further investigation of short active breaks with larger sample sizes. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to determine whether mild to moderate muscle damage accumulates on the knee extensors after two bouts of maximal eccentric contractions performed over two consecutive days. Methods: Thirty participants performed an initial bout of maximal eccentric contractions of knee extensors during the first day of the protocol (ECC1). Then, they were separated in two groups. The Experimental (EXP) group repeated the eccentric bout 24 h later (ECC2) while the Control (CON) group did not. Indirect markers of muscle damage (i.e., strength loss, muscle soreness, and shear modulus) were measured to quantify the amount of muscle damage and its time course. Results: Two days after the initial eccentric session, participants from EXP had a higher strength deficit (− 14.5 ± 10.6%) than CON (− 6.6 ± 8.7%) (P = 0.017, d = 0.9). Although both groups exhibited an increase in knee extensors shear modulus after ECC1, we found a significant increase in muscle shear modulus (+ 13.3 ± 22.7%; P < 0.01; d = 0.5) after ECC2 for the EXP group, despite the presence of mild to moderate muscle damage (i.e., strength deficit about 16%). Conclusion: Although the markers of muscle damage used in the current study were indirect, they suggest that the repetition of two bouts of maximal eccentric contractions with 24 h apart induces additional muscle damage in the knee extensors in presence of mild to moderate muscle damage. [ABSTRACT FROM AUTHOR]

In this study, a series of undrained cyclic torsional shear tests were conducted to investigate the effect of cyclic loading frequency f on the pre-liquefaction (shearing contractive (SC) period and initial shearing dilative (ISD) period) and post-liquefaction (late shearing dilative (LSD) period) deformation properties of saturated Fujian sand. The secant shear modulus G and damping ratio k in the entire cyclic loading process, and the unloading tangent shear modulus GL1 and flow deformation tangent shear modulus GL2 in the ISD and LSD periods were adopted to quantitatively characterize the evolution of hysteresis loop with an increase in shear strain amplitude γa. The test results show that the effect of f on G of saturated Fujian sand in the SC period is not apparent. However, all the G-γa, GL1-γa, and GL2-γa curves in the ISD and LSD periods showed a downward trend with an increase in f. This study also proposes a modified method for calculating λ to compensate for the analytical error caused by the non-closure of hysteresis loop. Compared with the classical curves that mainly applied in geotechnical engineering, the λ first increases and then decreases with the increase of γa. Furthermore, the λ evaluated by the modified method is approximately 10%-15% more than the λ evaluated by the traditional method when the λ reaches its peak value. [ABSTRACT FROM AUTHOR]

Ground response analysis (GRA) requires the use of dynamic soil property curves (DSPCs). However, because regional DSPCs are not always available, globally recorded DSPCs are utilized in regional GRA the majority of the time. For those regions where regional DSPCs, based on laboratory estimations, exist, the DSPCs are affected in a variety of ways. For this reason, inverse GRA (IGRA), performed on instrumented earthquake (EQ) data, appears to be a realistic alternative for determining in situ DSPCs. Existing IGRA studies, based on downhole EQ data from around the world, show constraints, particularly in determining damping ratio (β) properties. Furthermore, previous frequency domain IGRA studies have only detected DSPCs for the surficial layer. Whereas a few of the frequency domain IGRA studies have determined the shear modulus degradation (G/Gmax) curve for multiple soil layers, they have been unable to determine the β curve for those layers. In the current study, we propose a novel frequency domain framework for determining the G/Gmax and β curves for a two-layered soil system positioned between successive accelerometer levels. The proposed framework was applied to 28 EQ records from the Lotung downhole array in Taiwan to determine the G/Gmax, β, and shear strain (γ) values for the top two layers from the ground surface. In addition, average DSPCs for the two layers are proposed. The effectiveness of the proposed DSPCs was tested by using them in a GRA and comparing them with recorded ground motions. It has been noted that, at present, there are limited downhole array records available. Therefore, there is ambiguity involved in applying the proposed framework presented in this paper to a larger number of records from downhole arrays. However, physical modeling of the wave propagation mechanism through layered media can be done on a smaller scale to determine dynamic soil properties in the future. Several attempts have been made to estimate the G/Gmax and β based on centrifuge testing using recorded acceleration time histories at different levels in the centrifuge model. In addition, the one-dimensional propagation of shear waves could be determined in those studies by taking special measures. However, these studies were based on a stress–strain imaging method in the time domain, which has its own limitations. However, recently, a frequency domain method was used to determine the G/Gmax and β from centrifuge modeling for a single soil layer. In that study, the β values obtained were scattered. Thus, the frequency domain framework proposed herein could be a viable alternative for determining the G/Gmax and β of a multilayered soil profile (here, two layers) when used in centrifuge testing. [ABSTRACT FROM AUTHOR]

The objective of this work was to evaluate the effect of growth ring number (specimens including 2, 4, and 6 rings from the bark) and growth ring width on elastic constants in the radial direction of Populus x canadensis, which has not been revealed before. The longitudinal (2.25 MHz) and transverse (1 MHz) ultrasonic waves were propagated to calculate the longitudinal (VRR) and shear (VRL, VLR, VTR, and VRT) wave velocities and used to determine the elasticity modulus (ER), and shear moduli (GRL and GRT). The average growth ring widths of specimens including 2, 4, and 6 rings were 17.0 mm, 17.8 mm, and 18.2 mm, respectively. According to the results, only VRL steadily increased with increased ring number, while other velocities fluctuated. The same fluctuations were observed for moduli except for GLR, which constantly increased with ring number. The influence of ring number on velocity was statistically significant only for VRL and VRT. However, all moduli were significantly affected by ring number. Linear regression statistics revealed that there were significant relations between the ring width and density, VRL, VLR, VRT, GRL, and GRT. [ABSTRACT FROM AUTHOR]

The elastic modulus, shear modulus, and Poisson's ratio of timber are the elastic constants characterizing its material properties. In this paper, the transient excitation method was used to dynamically measure the 10 elastic constants of the falling larch wood under the condition of the free board and cantilever board, that is, 3 elastic moduli E, 3 shear moduli G, and 4 Poisson's ratios μ. The other two Poisson's ratios μ were derived using the principle of orthogonality. At the same time, the elastic modulus, shear modulus, and Poisson's ratio under static conditions were tested and verified by symmetrical four-point bending, asymmetrical four-point bending, and tensile methods. This study is expected to have good application value and practical significance for timber as an engineering structural material, which is widely used in architecture, decoration, furniture, transportation, musical instruments, and in other fields. [ABSTRACT FROM AUTHOR]

The response of soil beds reinforced with multi-layer geocell systems that support machine foundations is investigated by laboratory testing that incorporates vertical machine vibrations of a square concrete foundation (400 × 400 mm) resting on soil that is unreinforced or reinforced with single-, double- or triple geocell layers. The tests are performed under three different vibration moment levels and three static force levels using a mechanical oscillator and concrete blocks, respectively. The vibration responses are studied in terms of resonant amplitude, resonant frequency, shear modules and damping coefficient. The results reveal that the resonant amplitude significantly reduced in the presence of geocell reinforcement whereas the resonant frequency, shear modulus and damping coefficient increased. In the range of applied vibration load and frequency, and hence the induced amplitude, maximum improvement (i.e., the greatest reduction in vibration amplitude) was observed in the presence of the triple-layer geocell reinforcement. Since the rate of improvement decreases steadily with an increase in the number of geocell layers, thus, further geocell layers would deliver little further benefit. The optimum placement depth of the first geocell layer and vertical spacing of the geocell layers were found to be 0.1 and 0.05 of the foundation's width respectively. • Laboratory tests to investigate the vibration response of machine foundations over multi-layer geocells are conducted. • The effect of static force levels and vibration moment levels on vibration responses is investigated. • The effect of the number of geocell layers on vibration responses is evaluated. • Shear modulus (G), damping coefficient (ζ) and damping ratio (η) in all tests are evaluated. [ABSTRACT FROM AUTHOR]

In this work, the influence of lignosulfonate (LS), which is a by-product of timber and paper industries, on the cyclic characteristics of expansive clay was investigated by conducting cyclic triaxial tests. Test findings showed that cyclic stress ratio (CSR) substantially influenced liquefaction resistance of treated soil samples such that, at CSR = 0.2, none of the specimens were liquefied, whereas, at CSR = 0.4, all of the specimens were liquefied. Furthermore, liqueaction resistance was enhanced by decreasing the sample moisture content. Due to a stabilisation effect, the secant shear modulus increased by up to about 64%, and the damping ratio decreased by up to about 22%. [ABSTRACT FROM AUTHOR]

The literature confirms that fine recycled concrete aggregate (fRCA) can be used as a replacement for natural soil in new concrete, offering many advantages. Despite these advantages, there are also critical barriers to the development of fRCA in new mixes. Among these, the first challenge is the variability of fRCA properties, in both physical, chemical, and mechanical terms. Many individual studies have been carried out on different RCA or fRCA properties, but little investigative work has been performed to analyze their dynamic properties. Therefore, the influence of the non-cohesive fine fraction content of RCA on the dynamic properties of this waste material, when used as a specific anthropogenic soil, has been studied in laboratory conditions, employing a standard resonant column apparatus, as well as piezoelectric elements. In the present research, special emphasis has been placed on the dynamic shear modulus, dynamic damping ratio, small-strain shear modulus, and small-strain damping ratio, as well as shear modulus degradation G(γ)/Gmax, the damping ratio increase D(γ)/Dmin, and the threshold shear strain amplitudes γtl and γtv. Artificially prepared fRCAs with varying fine fraction contents (0% ≤ FF ≤ 30%, within increments of 5%) have been tested at different pressures (p′ = 90, 180, and 270 kPa) and relative densities of Dr > 65%. This study also examined the effect of two tamping-based sample preparation methods, i.e., dry and wet tamping. The results presented herein indicate that the analyzed anthropogenic material, although derived from concrete and produced by human activities, behaves very similarly to natural aggregate when subjected to dynamic loading. The introduction of a fine fraction content to fRCA leads to changes in the dynamic properties of the tested mixture. Concrete material with lower stiffness but, at the same time, with stronger damping properties can be obtained. A fine fraction content of at least 30% is sufficient to cause a significant loss of stiffness and, at the same time, a significant increase in the damping properties of the mixture. This study can serve as a reference for designing fRCA mixtures in engineering applications. [ABSTRACT FROM AUTHOR]

Bamboo curtain plywood is made of equal-thickness slotted bamboo slivers as its constituent units and is formed into boards with high pressure. In this paper, rectangular plates, beam specimens, and two sizes of square plates were tested to determine the elastic modulus and shear modulus of bamboo curtain plywood quickly, easily, and accurately. The free square board torsional vibration method was used to test the shear modulus of the square plates. The dynamic test results were also verified by means of the static four-point bending method. The main conclusions show that the dynamic elastic modulus, shear modulus and Poisson's ratio of this bamboo curtain plywood are 0.7 GPa, 1300 MPa and 0.12, respectively. The values of the elastic constants of these bamboo curtain plywood specimens measured by dynamic and static methods are consistent, and this dynamic test method has the advantages of fast, easy, good repeatability and high accuracy. [ABSTRACT FROM AUTHOR]

The complete characterization of wood, with the determination of the 12 elastic constants that represent its orthotropy, is greatly relevant in applications employing structural calculation software programs. Ultrasound allows for such characterization with relative simplicity when compared to other methods. The polyhedron is considered the most appropriate specimen format for allowing the 12 constants to be calculated with a single specimen, and the traditionally used one is the 26-sided polyhedron, which, to be produced manually with more precision in directing the main directions of the wood, needs larger faces. The accuracy of this technique tends to be reduced when increasing the growth rings' inclination since the waves deviate from the main directions of orthotropy. This research aimed to verify whether it is possible to reduce the polyhedra dimension without affecting the results of the elastic parameters obtained in wood characterization by ultrasound. The results indicate that the dimension of the polyhedron can be reduced without prejudice to the results of the elastic parameters obtained by the ultrasound test and that, in the manual production process of the specimen, the best way to make this reduction is to eliminate the faces unused in the test, changing the polyhedron to 18 faces instead of 26. Reducing the number of faces simplifies the manufacturing process and thus increases the possibility of producing specimens with straighter growth rings and better-directed symmetry axes. [ABSTRACT FROM AUTHOR]

This study investigated a new predictive model of the shear modulus reduction ( G G max − Log (γ c)) and damping ratio (ξ − Log (γc)) curves for sensitive eastern Canada clays. The model was established based on experimental measurements of G G max and ξ performed on 69 sensitive clay specimens from eastern Canada. The compiled database was first analyzed to qualitatively assess the influences of different soil parameters on the measurements. Next, statistical analyses using regression analysis and the modified hyperbolic model were performed. It was found that the G G max and ξ values of sensitive eastern Canada clays were influenced mainly by the plasticity index (Ip), mean effective stress (σ m ′) , and structure, which was quantified by the liquidity index (IL). Based on the statistical analysis performed, new equations for G G max and ξ were proposed. The newly proposed model was compared with previously published models. The comparison clearly showed that the proposed model was more representative of sensitive eastern Canada clays. Consequently, it is suggested that the proposed model is more appropriate for use in the dynamic analysis of sensitive eastern Canada clay deposits as well as other similar soils. [ABSTRACT FROM AUTHOR]

• The dynamic characteristics of MBT waste were investigated. • The dynamic shear modulus increases with increasing confining pressure. • The damping ratio increases with the increase in the strain amplitude. • The modified Devidenkov model considering the confining pressure was applied. • MBT waste exhibits a higher dynamic shear modulus but lower damping ratio. The dynamic characteristics of landfills under seismic loading and their stability strongly depend on the cyclic stress-strain characteristics of the waste. An accurate assessment of the dynamic characteristics of mechanically – biologically treated (MBT) waste is crucial to the construction and safe operation of landfills. Considering the effects of the confining pressure, strain amplitude, and loading frequency, 72 sets of consolidated undrained cyclic triaxial (CTX) tests were conducted on MBT waste. Our results showed that the dynamic stress amplitude of MBT waste increases with increasing strain amplitude and decreases with increasing number of cycles. Furthermore, the shear modulus of MBT waste increases with the increase in the confining pressure and decreases with the increase in the strain amplitude. By increasing the strain amplitude, the damping ratio of MBT waste increases. However, the shear modulus and damping ratio of MBT waste are less affected by the loading frequency. A modified Davidenkov model is presented, which describes the correlations among the normalized shear modulus of MBT waste, shear strain, and confining pressure. The fitting parameters are discussed, and the correlation between the normalized shear modulus and shear strain of MBT waste and that between the normalized shear modulus and shear strain of municipal solid waste were compared. The results of this study can be used as references for analyses of the dynamic stability of MBT landfills. [ABSTRACT FROM AUTHOR]

Purpose: This study aimed to examine the effect of age on the mechanical properties, muscle size, and muscle quality in the upper and lower limb and trunk muscles. Methods: We evaluated the shear modulus (G), muscle thickness (MT), and echo intensity (EI) of the upper and lower limb and trunk muscles of 83 healthy women (21–83-year-old). The G values of some limb muscles were measured in relaxed and stretched positions. Results: Regarding the effect of age on G at the distinct positions, the G of the upper limb muscles were not significantly correlated with age in the relaxed and stretched positions. In contrast, the G of the iliacus showed a significant negative correlation in both positions. Additionally, the G of the rectus femoris had a significant negative correlation only in the relaxed position. Regarding differences among body parts, the G of the lower limb and oblique abdominal muscles showed a significant negative correlation, but no correlation in the upper limb, rectus abdominis, and back muscles. Moreover, MT showed a significant negative correlation with age in the lower limb, abdominal, and erector spinae muscles, but no correlation was detected in the upper limb and lumbar multifidus muscles. EI had a significant positive correlation in all the muscles. Conclusion: The effect of age on G depended on body parts, and the G of the lower limb and oblique abdominal muscles negatively associated with age. Additionally, G in the relaxed position may be more susceptible to aging than G in the stretched position. [ABSTRACT FROM AUTHOR]

The soil nonlinear hysteretic behaviour is usually described, in the moderate strain range, through the shear modulus reduction and material damping ratio (MRD) curves. In common practice, in absence of specific laboratory tests, the curves are estimated by employing empirical regression models. Such predictive models, typically calibrated on large experimental datasets, correlate the soil response to its physical properties. This research fits within this context, presenting a comprehensive database of cyclic and dynamic laboratory tests conducted on natural Italian soils. The database, publicly available as supplementary data of the paper, contains the results of the tests conducted by the geotechnical laboratories of the Politecnico di Torino (Turin, Italy) and the Sapienza Università di Roma (Rome, Italy) over the past 30 years. The experimental data are employed to assess the performance of some widely used empirical models in predicting the MRD curves of natural uncemented fine-grained soils, emphasizing the importance of using an independent dataset for conducting a reliable statistical analysis. The results show that the use of many soil parameters as proxies for predicting the soil response does not necessarily lead to an improvement in the performance of the model. Therefore, according to Occam's razor principle, simple models are to be preferred. [ABSTRACT FROM AUTHOR]

To establish an equivalent model of the core layer of the grid beetle elytron plate (GBEP) and perfect the bionic system of the beetle elytron plate (BEP), the in-plane and out-of-plane equivalent shear moduli of the basic unit of the GBEP core layer are calculated by the energy method, and the accuracy of the expressions is verified by comparison with the results obtained with the finite element method and experiments. The results show that the in-plane and out-of-plane shear moduli can be expressed as functions of η , the ratio of trabecula radius to unit width, and the trends of the in-plane and out-of-plane shear moduli of the GBEP core unit with η are discussed. The concept of stiffness per unit volume (SPUV, k) is proposed, and the difference in shear performance (in-plane and out-of-plane) between the GBEP and grid plate (GP) core layer is theoretically revealed for the first time. The SPUV of the GBEP is slightly less than that of the GP for out-of-plane shearing but far better than that of the GP for in-plane shearing. According to the values of the in-plane and out-of-plane SPUVs of the GBEP and GP, a theoretical explanation is given for why the shear performance of the GBEP core is better than that of the GP, and the shear moduli of GBEP core equivalent model are obtained. From the point of view of shear properties, the theoretical basis that the in-plane stiffness of GBEP core cannot be ignored is given for the first time. This paper lays a theoretical foundation for exploring the shear properties of GBEP and its application in practical engineering. [ABSTRACT FROM AUTHOR]

Purpose: A previous study revealed that resistance exercise with eccentric contraction and a wide range of motion (ROM) can acutely decrease muscle stiffness of a specific muscle. To explore further approaches to decrease the stiffness, we examined the acute changes in passive stiffness of the individual hamstring muscles after eccentric-only resistance exercise with different combinations of muscle lengths and exercise durations. Methods: Thirteen healthy young male participants performed three sessions of eccentric-only exercises that comprised stiff-leg deadlift with different muscle lengths and exercise durations (duration per repetition × the total number of repetitions) on separate days as follows: (1) short muscle lengths with a short duration (SS); (2) long muscle lengths with a short duration (LS); and (3) long muscle lengths with a long duration (LL). Maximal joint ROM, passive torque, shear modulus of each hamstring muscle, and maximal isometric torque of knee flexion were measured before, and at 3, 30, and 60 min after each session. Results: The shear modulus of the semimembranosus was significantly lower at 3 min post-exercise (129.8 ± 22.7 kPa) than at pre-exercise (140.5 ± 19.1 kPa, p < 0.01) in LL, but not in SS or LS. No significant differences were observed in the shear moduli of the biceps femoris long head or semitendinosus between pre-exercise and 3 min post-exercise in any session. Conclusion: The combination of long muscle lengths and a long duration during eccentric-only resistance exercise is important to immediately decrease the stiffness (shear modulus) of a specific muscle. [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]

Wood is a non-homogeneous and orthotropic natural polymer material. It is important to test the wood shear modulus and elastic constants accurately and reliably using dynamic methods. Based on the introduction of the advantages of six common methods for dynamic testing of wood shear modulus, such as free plate torsional mode method, free bar torsional vibration method, and Timoshenko beam iterative method, issues associated with the applicability and accuracy of these methods are also pointed out. Recent methods, such as the free square plate torsional mode method and the square plate static torsional strain method, that were developed to dynamically test the shear modulus of wood and wood composite materials, are presented as effective ways to tackle these issues. These new approaches are expected to provide beneficial technical support for using small specimens, overcoming the size effect of specimens, simplifying the testing procedures, improving the test accuracy, and expanding the application range in the dynamic testing of wood shear modulus. These approaches have practical significance in promoting the industrialization and development of structural engineering, furniture and interior decoration, transportation, military, and musical instrument industries. [ABSTRACT FROM AUTHOR]

In order to reduce material costs, a simple and economical method without the use of strain gages was chosen, which is not widespread in practical implementations due to the high spread of the characteristic determined and its instability. It is based on the three-point transverse bending of specimens and measuring the deflection under the load applied. In this case, the shear modulus is calculated in two different ways. The tests were carried out on isotropic and on three types of composite materials with different reinforcement schemes. The control of the results obtained was carried out by testing similar samples in tension and bending by other proven methods. The main factors preventing the obtaining of stable and reliable values of shear moduli were established, one of which is the neglect of angular displacements of cross sections of the sample during calculation of the desired characteristics. It is shown that both the ways give very underestimated values of shear modulus for both isotropic and composite materials, with a very significant spread, which does not allow one to use the method considered in the presented form without corrections. It was established, that deflection under the load is determined by the rotation angles of sample cross sections and by the span, and its value is equal to the product of the maximal cross-sectional rotation angle and one third of the span length. It is shown that, taking into account the identified factors and some adjustment, this method is suitable for determining the shear modulus by the first or second way for both isotropic and composite materials. [ABSTRACT FROM AUTHOR]

A comparative analysis of typical stress-strain diagrams obtained for in-plain shear of 25 unidirectional and cross-ply reinforced polymer matrix composites under quasistatic loading was carried out. Three of them were tested within the framework of this study, and the experimental data on other materials were taken from the literature. The analysis of the generalized shear-strength curves showed that most of the tested materials exhibit a similar deformation pattern depending on their initial shear modulus: a linear section is observed at the beginning of loading, whereas further increase in the load decreases the slope of the curve, reaching the minimum at the failure point. For three parameters (end point of the linear part, maximum reduced deviation of the diagram, tangent shear modulus at the failure point) characterizing the individual features of the presented stress-strain diagrams, approximating dependences on the values of the reduced initial shear modulus are obtained. At the characteristic points of the deformation diagrams, boundary conditions are determined that can be used to find the parameters of the approximating functions. A condition is proposed for determination of the end point of the linear section on the experimental stress-strain curve, according to which the maximum deviation between the experimental and calculated (according to Hooke's law) values of the shear stress in this section is no more than 1%, thus ensuring rather high accuracy of approximation in the linear section of the diagram. It is recommended to use the results of this study when developing universal and approximating functions relatively simple in structure that take into account the characteristic properties of the experimental curves of deformation of polymer composite materials under in-plane shear of the sheet. The minimum set of experimental data is required to determine the parameters of these functions. [ABSTRACT FROM AUTHOR]

The dynamic behavior of saturated sands has been sufficiently studied from different points of view, but in laboratory tests only the stress conditions, prior to dynamic stress, are reproduced at the level of the surface; that is, for conditions of zero static shear stresses (τo). For this reason, the main objective of this research is to reveal the influence that static shear stresses (τo) have on the response of the dynamically saturated sands. The experimental phase included: identification and classification tests and six monotonic simple shear tests and 17 cyclic simple shear tests with different combinations of monotonic (τo) and cyclic shear stresses (τc) and in undrained conditions. The tested samples were extracted from the 'La Bocana Norte' sector of the Port of Barcelona–Spain. The samples were taken at depths between 31 m and 55 m, with a corresponding effective vertical stress (σ'ov) between 290 kPa and 421 kPa, respectively. Based on the results of the tests, a detailed analysis was carried out on the influence of the combination of monotonic (τo) and cyclic (τc) shear stresses on the variation of the dynamic shear modulus (G). Specifically: in the stress–strain behavior, the development of both permanent (γp) and cyclic (γc) shear strain and the reduction of the effective stresses (σ′v) as a consequence of the generation of pore water pressure (u). The results of the laboratory tests generally show that: (a) the combination of τo and τc controls the stress–strain behavior, the degradation of the cyclic shear modulus, the development of permanent and cyclic shear strain, the generation of pore water pressures and the liquefaction risk, (b) in the monotonic case, an empirical function was established to evaluate the internal friction angle (ϕ') as a function of the shear strain (γm) (mobilized friction angle), (c) in the combined case of monotonic and cyclical stress, it was possible to establish an empirical function among the G/σ′ov ratio, the cyclic strain (γc) and the number of cycles (N) and among the σ′v/σ′ov ratio, the cyclic strain (γc) and the number of cycles (N), (d) based on empirical functions, a simple methodology can be proposed to assess liquefaction risk and (e) it is not always true that the liquefaction phenomenon occurs when the effective vertical stress (σ'v) is reduced to zero. Depending on the cyclic stress ratio (τc/σ'ov) liquefaction can occur in the first cycle with a reduction in vertical effective stress of just 70%. [ABSTRACT FROM AUTHOR]

Characterization of shear moduli of composite lamina by existing methods such as rail shear test, Arcan shear test, Iosipescu shear test, etc. has their disadvantages. Developing a simple and efficient method for characterizing the shear moduli of the composite lamina is the objective of this work. A composite specimen of unidirectional laminate clamped and suspended from one end and with a rod weight attached horizontally at the lower end was tested simply by twisting and releasing as a torsional pendulum. By measuring the period of the twisting oscillation, the shear modulus of the laminae can then be calculated via a theoretical relationship. Experiments were conducted on specimens with different widths and rod weights with different lengths. Data of period were fitted simultaneously, and the shear modulus was obtained with less than 4% errors in comparison with that offered by the material manufacturer. The sensitivities of the shear moduli to the measured period are discussed and evaluated. This work presents the technique of the torsional pendulum, a very simple and efficient technique for measuring the shear modulus of the composite lamina. [ABSTRACT FROM AUTHOR]

Muscle stiffness has been implicated as a possible factor in low back pain risk. There are few studies on the effects of isometric fatigue on the shear modulus of trunk muscles. This study aimed to investigate the effects of trunk isometric fatigue on the passive and active (during low and high-level contractions) shear moduli of the erector spinae (ES) and superficial and deep multifidus (MF) muscles. We assessed passive and active shear modulus using shear-wave elastography in healthy young participants (n = 22; 11 males, 11 females), before and after an isometric trunk extension fatigue protocol. Maximal voluntary force decreased from 771.2 ± 249.8 N before fatigue to 707.3 ± 204.1 N after fatigue (−8.64%; p = 0.003). Passive shear modulus was significantly decreased after fatigue in the MF muscle (p = 0.006–0.022; Cohen's d = 0.40–46), but not the ES muscle (p = 0.867). Active shear modulus during low-level contraction was not affected by fatigue (p = 0.697–0.701), while it was decreased during high-level contraction for both muscles (p = 0.011; d = 0.29–0.34). Sex-specific analysis indicated the decrease in ES shear modulus was significant in males (p = 0.015; d = 0.31), but not in females (p = 0.140). Conversely, the shear modulus in superficial MF had a statistically significant decrease in females (p = 0.002; d = 0.74) but not in males (p = 0.368). These results have important implications for further investigations of the mechanistic interaction between physical workloads, sex, muscle stiffness (and other variables affecting trunk stability and neuromuscular control), and the development/persistence of low back pain. [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]

Benign and malignant lesions in tissues or organs can be detected by elastographic investigations in which pathological regions are spotted from local alterations of the stiffness. As is known, the shear modulus provides a measure of the stiffness of an elastic material. Based on the classical theory of linear elasticity, an elastogram yields estimations of the linear shear modulus from measurements of the speed of small-amplitude transverse waves propagating in the medium tested. In this paper, we show that the estimation of the shear modulus can be improved significantly by employing the fourth-order weakly nonlinear theory of elasticity (FOE), and indicate how the stiffness can be assessed more precisely with the use of FOE. We discuss also why FOE provides more reliable results than the fully nonlinear theory of elasticity. This article is part of the theme issue 'The Ogden model of rubber mechanics: Fifty years of impact on nonlinear elasticity'. [ABSTRACT FROM AUTHOR]

To consider the influence of the quality of the accelerometer and the installation position on the test frequency, a test scheme was designed to identify the first-order bending frequency with free and cantilever beams as well as the first-order torsion frequency with free plates. According to the energy method and mode shape, the correction relationship between the elastic modulus and the first-order bending frequency of free and cantilever beams is derived alongside the relationship between the shear modulus and first-order torsion frequency of a free plate. These relationships are suitable for informing the influence of the accelerometer mass and installation. The first-order bending frequency and the first-order torsion frequency of Sitka spruce beams, slabs, and oriented strand board have been measured along the length, which verifies the effectiveness of the derived relation in testing the elastic modulus and shear modulus of wood materials. Taking the ratio m/M between the mass of the accelerometer and the mass of the test specimen as a parameter, the scope of application of the modified relation is discussed. [ABSTRACT FROM AUTHOR]

Using tire waste rubber reinforced expansive soil (ESR) can modify its poor engineering characteristics. The damping properties of ESR at different temperatures may vary dramatically. Two kinds of rubber Ra (large particle size) and Rb (small particle size) are mixed with expansive soil according to gradient ratio. The backbone curves, dynamic shear modulus, and damping ratio of expansive soil in varying temperature fields of 20 °C, −5 °C, and −15 °C are investigated. The Hardin-Drnevich model can well fit the backbone curves of ESR specimens in various temperature fields. Dynamic triaxial results show that 5–10% Ra rubber can withstand higher shear stress in all temperature fields; Rb rubber can increase the dynamic shear modulus of expansive soil and reach the peak value with 10% rubber content. The damping ratio can be significantly improved by using 10% Ra rubber at room temperature, while the ESR damping ratio in a temperature field of −5 °C does not change significantly with increasing shear strain or even decreases; Ra increases the damping ratio of expansive soils in the temperature field of 15 °C while small particle size Rb decreases the damping ratio of expansive soils. The experimental results validate the effectiveness of ESR in the frozen soil area. In an engineering sense, local temperature needs to be considered to use an appropriate ESR, which can provide effective seismic isolation and damping. [ABSTRACT FROM AUTHOR]

Shear-wave elastography is a method that is increasingly used to assess muscle stiffness in clinical practice and human health research. Recently, shear-wave elastography has been suggested and used to assess exercise-induced muscle damage. This review aimed to summarize the current knowledge of the utility of shear-wave elastography for assessment of muscle damage. In general, the literature supports the shear-wave elastography as a promising method for assessment of muscle damage. Increases in shear modulus are reported immediately and up to several days after eccentric exercise, while studies using shear-wave elastography during and after endurance events are showing mixed results. Moreover, it seems that shear modulus increases are related to the decline in voluntary strength loss. We recommend that shear modulus is measured at multiple muscles within a muscle group and preferably at longer muscle lengths. While further studies are needed to confirm this, the disruption of calcium homeostasis seems to be the primary candidate for the underlying mechanism explaining the increases in shear modulus observed after eccentric exercise. It remains to be investigated how well the changes in shear modulus correlate with directly assessed amount of muscle damage (biopsy). [ABSTRACT FROM AUTHOR]