Quasi-static subinterfacial crack propagation.

摘要

Quasi-static propagation of subinterfacial cracks near an interface between dissimilar materials was investigated by mapping the near-tip stress fields using a Polariscope/Shearing Interferometer (PSI). The PSI is a combination of a polariscope and a shearing interferometer that can be used on optically isotropic and optically birefringent materials. The subinterfacial crack problem is first analyzed using a dislocation-based approach. By using a numerical procedure to evaluate coupled Cauchy-type singular integral equations, the dislocation distribution functions are extracted and these functions are used for the calculation of stress intensity factors and dislocation crack extension and deflection forces. The "equilibrium" positions where subinterfacial cracks might propagate parallel to the material interface and for which the crack deflection force is zero are obtained and the stability of such "equilibrium" positions are discussed. Additionally, the inner crack based dislocation analysis is extended to the case of an edge crack in a PMMA/Al 6061 bimaterial. three-point bend specimen.; From experiments on quasi-static propagation of subinterfacial cracks in PMMA/Al6061 specimens, it is observed that when the crack propagates outward and parallel to the interface seeking a path leading to zero mode II, the agreement with numerical simulations based on maximum tangential stress criterion is good. However at very close distances to the interface, the results of the experiments diverge from those predicted by numerical simulations. It appears that in this case subinterfacial crack propagation is governed by a different mechanism arising from the rather large mode mixities that prevail here.