CRACK DEFLECTION AT AN INTERFACE BETWEEN DISSIMILAR ELASTIC-MATERIALS- ROLE OF RESIDUAL-STRESSES

A crack intersecting an interface between two dissimilar materials may advance by either penetrating through the interface or deflecting int o the interface. The competition between deflection and penetration ca n be assessed by comparison of two ratios: (i) the ratio of the energy release rates for interface cracking and crack penetration; and (ii) the ratio of interface to material fracture energies. Residual stresse s caused by thermal expansion misfit can influence the energy release rates of both the deflected and penetrating crack. This paper analyses the role of residual stresses. The results reveal that expansion misf it can be profoundly important in systems with planar interfaces (such as layered materials, thin film structures, etc.), but generally can be expected to be of little significance in fiber composites. This pap er corrects an earlier result for the ratio of the energy release rate for the doubly deflected crack to that for the penetrating crack in t he absence of residual stress.