Weight Functions for Edge Crack in Bilayer Material

The problem of weight functions for an edge crack in semi-infinite bilayer materials was revisited. The research aimed to develop the empirical equations for geometrical factors for reference SIFs associated with the weight functions, which covered a wider range of elastic mismatches. The weight functions in consideration covered the cases of a crack tip in a surface layer as well as in a substrate. The direct adjustment method was employed to derive the weight function coefficients. The reference SIFs for calculating the weight function coefficients were determined by finite element analysis with a systematic variation of the crack depth and the elastic mismatch parameters. The accuracies of the empirical equations for geometrical factors for the cases of a crack tip in coating and substrate were better than 1.3% and 4%, respectively. The weight functions were applied to bilayer materials with an edge crack under various crack face loading profiles. The SIFs predicted by the weight function method agreed with those from the FE method or the literature.