Characteristics of interface cracks in creep regime

In this study, the growth behavior of interface cracks in bimaterials and in graded/layered materials at creep regime was studied. In the first part of the study, the evolution of the time-dependent stress states ahead of the stationary interface cracks was elucidated using a finite element model. In the second part, the observed stress states were incorporated into a creep crack growth model resulting from the growth of creep cavities ahead of the interface cracks. The growth model includes the effects of material deposition resulting from the growth of creep cavities on the crack tip stress fields. The results indicate that in graded/layered materials under identical applied loading, both the location of the interface crack and the extent of the transitional layer strongly influence the amplitude of the stress field (C*) at steady state. Also, the time required to achieve the steady state varies considerably with these parameters. The growth rates of the interface cracks are much faster than the growth rate of a homogeneous crack in the fastest creeping sector of that interface. Due to large variation in the distribution of the stresses ahead of the interface cracks at creep regime, depending upon the location, the creep crack growth rates will be significantly different from each other under identical loading for a given graded/layered material.