Mechanical adhesion among lunar regolith particles significantly influences the shear characteristics of lunar regolith. However, experimental limitations on Earth and challenges in capturing particle-scale information obscure the microscopic mechanisms of adhesion and its interaction with other particle properties, such as shape. This study employs the Discrete Element Method to bridge this gap by incorporating mechanical adhesion and simplifying the particle shape effect. Numerical triaxial shear tests were performed on representative volume elements under densities representative of lunar surface. The study introduced a simplified shape parameter, the rolling friction coefficient mu r, r , representing particle 3D sphericity, which ranged from 0.025 to 1.6. Additionally, the particle surface energy density gamma was adjusted from 0 to 1.28 x 10-- 2 J/m2 2 to model the effects of mechanical adhesion. Stress-strain relationships, friction angles, and microscale mechanics parameters were thoroughly analyzed. Simulation results reveal that under low stress, the e c-ln p relationship remains linear, consistent with critical state sand theory. Significant variability in macro properties is influenced by micro-Newton adhesive forces and rolling friction coefficients (0.1-0.8), particularly in particles with notable irregularities, where adhesion profoundly affects mechanical properties, requiring precise calibration. This research advances the understanding of the shear behavior of lunar regolith, providing critical insights for future simulations and experimental designs.

In this work, we numerically investigate the quasi -static shear behavior of ellipsoids under triaxial compression using the level set discrete element method (LS-DEM). Assemblies composed of ellipsoids with various aspect ratios are prepared at the densest states and then sheared to the critical state. Macroscopically, the stress and dilation behaviors are strongly affected by the particle shape, with the spheres having the least shear strength and dilatancy. At the particle scale, more ellipsoidal particles are more resistant to particle rotations and can effectively increase friction mobilizations.We identify the clusters in assemblies via the three-dimensional cluster labeling algorithm and then analyze the structural and mechanical properties of clusters. Based on our analysis, we find that the clusters exhibit the power -law decay in the cluster size distribution and have fractal structures. Upon shearing, the clusters tend to self -organize to gain mechanical stability, indicated by the increasing cluster stress ratio, and mainly support the deviatoric stresses in the assemblies. The mean cluster stress ratio is found to be linearly related to the macroscopic shear strength at the critical state, where more ellipsoidal shapes can gain higher cluster stress ratios, contributing to higher shear strength for the granular assembly. Microscopically, the cluster contributes more significantly to geometrical anisotropy terms while comparably to mechanical ones compared to the non -cluster.