Mechanical and elastic wave responses of rocks subjected to cyclic tensile stresses

Abstract

Rock masses are frequently subjected to cyclic tensile stresses associated with engineering operations, such as repeated pressurization and depressurization, around underground compressed air energy storage caverns and cyclic fluid injection in petroleum or geothermal reservoirs. Despite their significance, rocks' mechanical responses and elastic wave behaviors under cyclic tensile loading remain poorly understood. This study investigates these responses by performing ultrasonic measurements on diabase and quartz diorite rock samples subjected to progressive cyclic direct tensile loading using a custom-built test system. Results reveal that quartz diorite exhibits pronounced nonlinearity and significant hysteresis in its stress–strain behavior, while diabase shows nearly linear stress–strain relations with negligible hysteresis. Elastic wave properties, including wave velocity, peak-to-peak amplitude, maximum spectral amplitude, and dominant frequency, generally decrease with increasing tensile stress/strain upon loading, followed by significant recovery during unloading, exhibiting hysteresis. Quartz diorite demonstrates greater hysteresis and irreversible decrements in elastic wave properties than diabase, linked to its microstructural characteristics. Repeated tensile loading induces progressive microcrack damage, reflected in residual strain and degraded wave signatures. The increases in residual strain and irreversible wave signature decrements suggest that the cumulative tension cycles cause accumulated microscopic damage in rocks, which the increasing crack density upon loading predicted by the constitutive model can explain. A differential scheme-based constitutive model successfully describes the nonlinear loading and nearly linear unloading stress–strain behaviors, capturing the evolution of microcrack density with tensile strain.