FEM analysis of failure process in thin film during wear test

The semi-circular parallel cracks appeared on the film surface with the angles of 45 degree to the sliding direction of SiC ball and the delamination of film quickly occurred after cracking by using a “ball-on-disk” type testing machine. Stress distribution before and after cracking in the film was calculated by FEM analysis. The maximum tensile stress existing in the film at the back-contact edge of ball is the reason for the initiation of semi-circular parallel cracks. The tensile stress normal to interface as well as the shear stress along interface appears at crack tip, and the alternate generation of these two stresses is the main reason for the delamination. The longitudinal normal stress σxx and the maximum principal stress σ1 become bigger after cracking, so that the crack propagation is faster.