ANALYSIS OF SUBSURFACE CRACK-PROPAGATION AND IMPLICATIONS FOR WEAR OF ELASTICALLY DEFORMING MATERIALS

Photoelastic methods are used to analyze the stress intensity factors and crack trajectories for subsurface cracks that are relevant to the process of wear particle generation. The specimen represents a half-plane with a shallow subsurface crack oriented parallel to the boundary. A concentrated load is applied to the boundary of the half-plane in close proximity to the crack tip. Three different series of experiments were conducted and results for the stress intensity factors for both the opening (K(I)) and shearing (K(II)) modes were determined. The mixed-mode stress intensity factors were combined to give the magnitude of an effective stress intensity factor which drives the subsurface crack. It was determined that the magnitude of K(II) was much smaller than K(I). The relative signs of K(I) and K(II), which depend on the location of crack tip with respect to the point of load application, were used to predict the crack trajectory.