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.

During bone's fatigue process, cracks generally initiate from inherent defects existing in the bone. Fatigue lives of bone specimens at different stress frequencies as well as at different stress ratios (R) were evaluated using a computer simulation under the assumption that the cracks initiated from the inherent defects in the bone. The S-N curves as well as the distributions of fatigue lives obtained by the simulations accurately conform with the experimental results. As strain thresholds representing fatigue failure of the bone specimens, values of 1500 µε for R = -1,2500 µε for R = 0.1 and 4000 µε for R = 10 were extrapolated from the simulations. These values are in good agreement with experimental values reported in the literature. Such conformity indicates that the strain threshold for fatigue failure is associated with the threshold value for crack propagation.