A Plasticity Index, a Plasticity Number, and the Distribution of the Plastic Deformation Depth Based on a Fractal-Regular Contact Model

A plasticity index and a plasticity number were proposed to indicate the severity of plastic deformation by considering the multi-scale and hierarchical nature of surface roughness. A distribution density function of the plastic deformation depth was introduced to characterize the evolution of plastic deformation with increasing load. By integrating this function, the fraction of the real contact area where plastic deformation depths are within any given range can be calculated.