Effect of time-dependent material properties on the crack behavior in the interface of two polymeric materials

Crack penetration through the bimaterial interface of two polymers is investigated numerically. Due to the practical importance of the problem, a crack in a three-layer pipe consisting of a main and two, inner and outer, protective layers is analyzed in this paper. The prime aim is to formulate the conditions under which the crack stays arrested at the interface between the protective layer and the main pipe or penetrates into the interface and causes failure of the main pipe and consequently of the entire pipe system. The crack tip stress field is described by using a generalized stress intensity factor for cases where the crack touches the interface and the stress singularity exponent differs from 1/2. In the case of short-term applications, the stress state on the interface is given simply by a combination of the elastic properties of materials of the main pipe and the protective layers. In long-term applications, the time-dependent properties of the materials can significantly influence the stress state of the interface and can lead to considerable changes in failure conditions. The results presented here may contribute to a more accurate estimation of the residual lifetime of multilayer pipes.