Rate-Dependent Characteristics of Damage and Roughness Degradation of Three-Dimensional Artificial Joint Surfaces

A series of direct shear tests on specimens with artificial joints were performed to investigate the rate-dependent characteristics of damage and roughness degradation of three-dimensional joint surfaces under different normal stresses and shear velocities. A novel method was proposed to identify and extract the damaged area of joint surfaces based on the combination of the three-dimensional scanning technology and the color image segmentation method. Based on the proposed method, two main failure modes were identified on the joint surface, including asperity wear and debris backfilling. By controlling different shear displacements and shear velocities, the rate-dependent damage evolution of the joint surface during shearing was revealed. Four damage states are defined to better understand the local damage mechanism of joints. The statistical results indicate that the damage area ratio increases with increasing normal stress and shear velocity. The damage develops more rapidly at a higher shear velocity during progressive shearing. Furthermore, the three-dimensional roughness parameter theta(max)*/(C + 1) is measured in 36 analysis directions on the sheared joint surfaces to quantitatively describe the asperity degradation. It is observed that the average roughness parameter increases with increasing shear velocity under the same normal stress but decreases with increasing shear displacement. The results in the present study may provide some references for revealing the mechanical behavior and damage state of joints subjected to dynamic loads.