Measurements of elastic properties and their dependencies within a damage mechanics workflow

Abstract

Experimental rock mechanics testing provides a controlled and effective method for measuring physical properties, their dependencies, and their evolution due to the addition of localized microcracks. To understand the contributions of microcracks to first order changes in compliance, the behavior of initial undamaged properties of a material should be comprehensively investigated as a function of stress, load path, and load history. We perform a comprehensive study of elastic properties and their dependence on a variety of materials exhibiting nonlinearity, and varying levels of anisotropy in elastic stiffnesses. We programmatically perturb the testing environment of the specimens under triaxial stresses. Elastic moduli are measured within each test, and along multiple discrete loading paths for multistage tests as a function of stress, focusing on a set launch point. Four single stage triaxial tests per rock type are performed to calculate Mohr-Coulomb failure criteria, and ultrasonic velocities are captured during compression for establishing the upper bound of elastic behavior. Shear wave velocity for granite experiences a maximum value at a lower differential stress than maximum volumetric strain. Sandstone displays a similar trend at the highest confining pressure, while these two maxima converge under the lowest confining pressure.

Keywords

• Triaxial test
• Elastic moduli
• Ultrasonic measurements
• Damage mechanics
• Rock nonlinear behavior