INVARIANT POINTS ON ENERGY CONTOURS AROUND A CRACK-TIP UNDER MIXED-MODE LOADING

The locus of points around a crack tip where the strain energy density is set equal to a critical value reveals interesting features. It is seen that, for certain cases, two points on this locus remain invarian t with respect to the phase of the applied loads. The existence of the se invariant points is examined for different configurations - a crack in a homogeneous isotropic medium, an interface crack and an inclined interface crack. This analysis is extended to the two components of s train energy density - volumetric (VSED) and distortional (DSED).