Shear Mechanical Behavior of Lunar Regolith Simulant with Different Relative Densities Under Thermal–Mechanical Coupling

The mechanical behavior of lunar regolith is crucial for lunar exploration projects, particularly drilling and sampling equipment. However, the extremely limited quantity of returned lunar regolith is insufficient for systematic macroscopic mechanical testing. Lunar regolith simulants are therefore widely used to investigate the macroscopic mechanical behavior of lunar regolith. Most previous studies were conducted under ambient laboratory conditions, with limited consideration of temperature effects. In this study, direct shear tests were conducted on lunar regolith simulant specimens with relative densities Dr of 75%, 90%, and 100% under normal stresses of 50, 100, and 150 kPa and at temperatures of 25, 60, 120 and 180 °C. The effects of relative density, normal stress, and temperature on the shear response were systematically evaluated. The results showed that the peak and residual shear strengths generally increased with normal stress, whereas the effect of temperature on peak strength depended on relative density and normal stress. Three-dimensional laser scanning was used to reconstruct and quantitatively characterize the post-shear surface morphology, and its relationship with the measured shear response was examined. A damage-based phenomenological formulation incorporating a log-logistic function was used to parameterize the shear stress–displacement responses and to examine the fitted shear-stiffness parameter and phenomenological damage variable. The implications of the measured shear behavior for lunar drilling and sampling were also discussed. The study can provide laboratory-scale insights into the shear behavior of lunar regolith simulant relevant to lunar drilling and sampling.