Narrow Results

This study aims to evaluate the impacts of initial stress anisotropy on the variation of elastic shear stiffness of silica sand through the application of continuous shear wave velocity measurements during two distinct compression and extension loading paths. Besides, the validation of existing empirical models during both the consolidation and shearing stages is assessed. The specimens were prepared using the water sedimentation (WS) method and then consolidated with different stress ratios ($\eta =q∕p^{\prime }$) from $-0.6$ to $+0.6$. Afterward, they were subjected to strain-controlled axial compression and axial extension shear in the drained condition. The shear wave velocities in the triaxial specimen were measured continuously during the consolidation and shearing stages by employing an automated small strain system. The results indicate the significant impacts of the initial stress anisotropy on the small strain shear stiffness of sand. The study also revealed that while the existing empirical correlations can be suitably applied within the elastic zone, the precision of these models in predicting the shear modulus during the shear loading when the soil’s behavior enters the plastic zone is not reliable.

The elastic constants are paramount to determine the strength of alloys. The elastic constants of $M$–Ir, $M_3$–Ir, and $M$–Ir₃ where $M$ represents $\mathrm{\text{Cu}}$, $\mathrm{\text{Au}}$, $\mathrm{\text{Ni}}$, $\mathrm{\text{Ag}}$, $\mathrm{\text{Pt}}$, $\mathrm{\text{Al}}$, $\mathrm{\text{Pd}}$ and $\mathrm{\text{Rh}}$ were computed at room temperature using the embedded atom method (EAM) and the alloy mixing potentials. The potential parameters of the selected pure metals were fitted to the experimental values to compute some properties of Ni–Al, Ni₃–Al, Ni–Al₃, Cu–Au, Cu₃–Au and Cu–Au₃, and by comparing the experimental data with our predictions, the employed potential predicted some results in reasonable agreement to available experimental data with discrepancies in some cases, and these discrepancies linked to the dependence of the computed elastic constants on the fitting parameters. The potential with the metallic parameters was used as alloy parameters in computing the elastic constants, bulk modulus, and the shear modulus of the iridium binary alloy. It was generally observed that, the selected metals improve the ductility of Iridium with the highest value, recorded for Pd–Ir, and consequently the minimum value for Al–Ir, and Rh–Ir which characterized them to be ductile. The balance orders for the binary alloys were provided through the formation enthalpy.

Ground state of interlayer Josephson vortex systems is investigated on the basis of the Lawrence-Doniach model. For low fields, the ground state is characterized by various rotated-lattice configurations, and inhomogeneity of the internal field and superconducting amplitude plays little role. For intermediate fields, the ground state is characterized by continuously-varying shearing angle of vortex lattices, and the shear instability field is enhanced by inhomogeneity of the internal field. For high fields, the upper critical field H_c2 is determined by inhomogeneity of the superconducting amplitude. For material parameters of cuprate high-T_c superconductors, the shear instability field is significantly increased, and H_c2 becomes infinite. These results are compared with the elastic theory and the London theory with respect to field dependence of the shear modulus c₆₆.

Steinberg-Guinan constitutive model is widely used in impact engineering simulations. Shock wave profile measurements of Al, Cu, and W under shock pressures ranging from 4 GPa to 200 GPa were analyzed, and shear modulus G and yield strength Y of these materials were obtained by using the high-pressure sonic velocities and rate independent Lagrange analysis results. Then values of derivatives of G and Y with respect to pressure or temperature at the reference state of these three metals were determined. By analyzing the pressure and temperature dependence of shear modulus and yield strength, we conclude that the relations of Steinberg-Guinan constitutive model, Y/G=constant, are approximately correct on Hugoniot state for these materials. So this is a probable approach to solve the difficulty of measurement of Y under high-pressure and high-temperature directly.

Since carbon nanotubes were discovered, till now no definitive formulation for computing the shear modulus of them was presented. To develop a theoretically rigorous and mathematically elegant expression for the shear modulus, thus, we initially propound a new small-strain theory in which merely small strain will arise when small-diameter carbon nanotubes are formed and thereby conclude the total potential energy including bond elongation and bond angle variation will suffice and the utilization of Quantum Mechanics and certain far complicated potential functions is unnecessary. Then based on it, a closed-form expression derived entirely from the "definition" of shear modulus, which was never published in all other literature, will be evolved. It should be noted that previously there was only one formula by which the shear moduli for all carbon nanotubes with diverse diameters and configurations could be predicted. By comparing the values calculated by the expression in this paper with those reckoned from the article mentioned above, it is obvious that both classes of quantities are similar to each other. It should also be noted that because the expression in this paper is the first (really having no precedent in related study fields) to be derived entirely according to the definition of shear modulus, perhaps this paper can be used as a useful theoretical tool for further study.

Erosion corrosion is encountered in many areas of industry and is a very complex phenomenon. In this study, it is aimed to investigate the effects of erosion corrosion in elbow pipes with different shear moduli, velocities of fluid, density of pipe using Ansys Workbench Explicit Dynamics module which is computer-aided and based on finite element. Statistical analyses were also performed to obtain the best flow parameters. SolidWorks program was used for three-dimensional studies considering elbow pipe design. The fluid properties and physical conditions were applied to the three-dimensional solid model in the pipe flow analysis. At the end of the dynamic analysis, erosion values (deformation) occurring in the elbow pipes were statistically compared to each other.

Recently, composites have attracted many researchers, which have advanced favored properties compared to metallic materials, such as high strength with lightweight as well as corrosion and erosion resistance and others. However, these resources are exposed to yield during the working life. For these new products and their employing in different applications, and for the mentioned importance, this study has investigated the mechanical characteristics of these structures to avoid potential failure. An investigation of Arcan (shear $V$-notch test) procedure has been conducted for epoxy resin which is used for reimpregnations with Eglass and compared with lightweight metal of Aluminum as a benchmark to show the shear behavior for the composite one under shear load experimentally and numerically. The butterfly-shaped sample was modeled and tested accordingly with Arcan (shear $V$-notch test) numerically in order to produce pure shear force by tensile subjection condition using ANSYS software. The test verified that a state of pure shear was present during the testing on each ± 45^∘ inclined from the axis of subjection although the changes recorded as G magnitude of shear modulus between Aluminum and the thermoplastic of Epoxy resin is nearby 94%, which may be because of the effect of material nature (i.e. mechanical properties) for the selected materials. The mentioned novel constituent shear behaviors have been investigated and compared expediently. These novel constituents can be adopted in different applications of shear loads.

Bi-modulus materials exhibit the different modulus in tension and compression. The value of elastic modulus and Poisson ratio of every point in the bi-modulus elastic body not only depend on the material itself, but also the stress state and the strain state of the point. The uncertainty and nonlinearity of the elastic constitutive relation result in that the bi-modulus elastic problem is the complicated nonlinear problem This paper aims at studying the bi-modulus elastic constitutive equation employed in the bi-modulus finite element numerical method (FEM). The new elastic matrix model is proposed based on Ye’s principal strain criterion with the assumption that the Poisson ratio maintain constant whenever in tension or in compression, and the elastic matrix is symmetric by equivalent transmitting. The shear modulus expression of this elastic matrix model is derived to enable the elastic matrix completely and improve the convergence of the FEM calculation. The statically indeterminate bi-modulus beam is analyzed by means of FEM employing the proposed elastic matrix model. The effects of the tensile modulus to compressive modulus ratio and the boundary condition on the stress and deflection of the bi-modulus beam is studied.

A series of cyclic triaxial tests on clayey sands was carried out and attempts were made to evaluate the strain dependency of shear modulus and damping. Although the strain dependency of the shear modulus of clayey sands was similar to that of clay in the low strain range, G/G₀ became close to that of clean sand in the high strain range. The damping ratio was less for the clayey sand containing more fines, especially in the medium to large strain range. It was shown that the change in the effective confining stress with loading cycles in the undrained shear test needed to be considered, particularly in the large strain range. The consideration can be made by normalising G with G′₀ instead of using G₀. When an initial shear stress was applied to the specimen, the amount of residual strain, which was induced with cycles, had to be added to the normal strain amplitude in order to determine the shear modulus. If the effects of excess pore pressure and the amount of residual strain were taken into account properly, it was suggested that the shear modulus of clayey sand in irregular loading could be evaluated reasonably well by using the average G/G′₀-γ curve obtained by cyclic loading tests on isotropically-consolidated specimens.

Adequate information on dynamic soil properties, especially strain dependent shear modulus (G) and damping ratio (ξ) for each soil layer are the essential input data for seismic ground response analysis and soil-structure interaction studies. In the present study, the shear modulus and damping ratio of sand are estimated for a wide range of strains based on undrained strain-controlled cyclic triaxial tests. The bender elements are also utilized in the cyclic triaxial test to estimate the low strain shear modulus. For this purpose, the soil samples are taken from a nuclear power plant site located at the south-east coastal region of India. Based on the experimental results, an empirical expression is developed to calculate the maximum shear modulus, G_max as function of void ratio and effective confining stress. Predictive relationships are also developed for estimating normalized shear modulus and damping ratio curves for the sand. The predictive relationships are based on the hyperbolic model and cyclic triaxial test results. The developed modulus reduction and damping ratio curves from the predictive relationships are compared with the previously available curves in the literature.

The dynamic behavior of lightly cemented sand under long-term seawater attack was evaluated in this study. Resonant column and cyclic triaxial tests were employed to investigate the evolution of the shear modulus and damping ratio of cemented sand with respect to soaking period (SP), confining pressure, and cement content (CC). The results of this study show that the cementation of the sand is affected by soaking in seawater to a greater extent than by soaking in tap water. The shear modulus of the cemented sand soaked in seawater was smaller than that of the cemented sand soaked in tap water. The damping ratio increased significantly, as the SP increased and was greater for the cemented sand soaked in seawater than for the cemented sand soaked in tap water. The dynamic behavior of nonhomogenous specimens was examined. Crystallization of salts could be clearly observed and probably explains the evolution of the dynamic behavior of the cemented sand. Finally, the shear modulus was fitted using Rollins' Law [Rollins et al., 1998], which demonstrates that the parameters used in the equation can be reasonably fitted linearly over a range of SPs.

The objective of this study was to investigate the liquefaction response of soil using the spatial variability of the shear modulus by considering different values of the coefficient of variation (COV) and the horizontal scale of fluctuation (SOF). For this purpose, a Monte Carlo simulation, combining the digital generation of a non-Gaussian random field with finite difference analyses, was utilized. Parametric studies were performed from the perspectives of the liquefaction area, excess pore water pressure (EPWP), and displacement at the ground surface. We found that a larger COV of the soil shear modulus was correlated with a slower reduction of liquefaction area and a lower EPWP ratio. To explain the influence from the perspective of the spatial distribution characteristics of the shear modulus, a deterministic model test was carried out. Additionally, it was found that the displacement history and the differential settlement at the end of shaking were regularly affected by the COV and the horizontal SOF, especially for large COV and horizontal SOF.

Continuous shear wave velocity measurements are conducted on cylindrical triaxial sandy specimens consolidated with isotropic and anisotropic stress histories to characterize the evolution of the elastic shear modulus under different stress paths. The shear wave velocity is measured using an automatic device capable of consecutive measurements of travel time. All specimens were prepared using the Water Sedimentation (WS) method, and after undergoing a stress-controlled path representing the stress history of the specimens, they were subjected to stress-controlled drained shearing along eight different paths. The stress components used in the existing correlations estimating the shear moduli are specified under different stress paths. The results demonstrate that the existing empirical correlations can appropriately be used within the elastic region or the loading surface. However, the accuracy of such models estimating shear moduli might be depreciated as shearing commences, particularly if the stress path involves deviatoric stress, diverging from the expected trends at a specific stress ratio, which is strongly linked to the consolidation stress state. A criterion at which the shear modulus is diverted is also suggested, found to be directly related to the initial stress anisotropy.

The aim of this study is to investigate the rheological properties of three grades of virgin bitumen 40/50pen, 60/70pen and 80/100pen using the frequency sweep strain control. Several road pavement distresses are related to rheological properties of bitumen. Rutting and fatigue cracking are the major distresses that lead to permanent failures in pavement construction. There is thus growing demand for the study the rheological properties of bitumen using high accuracy device such as Dynamic Shear Rheometer (DSR). Frequency sweep strain controlled test and penetration test has been conducted to investigate the rheological properties of the three grades of bitumen. The results shows that value of G*, G′, G″ and the viscosity are higher in harder bitumen and its match with the penetration tests results.

A two-dimensional porous-elastoplastic model, in which the influence of the reduction of the effective stress on the soil strength has been considered, is proposed to investigate the accumulation of pore water pressure under standing wave. The simulation results show that the liquefaction is likely to occur around the node due to the accumulation of pore water pressure. The liquefaction leads to the decrease of soil resistance, which has great effect on the development of the residual pore pressure. The simulation demonstrates that if the decrease of soil resistance is not considered, the soil liquefaction depth will be overestimated.