EFFECT OF DELAMINATION FACE OVERLAPPING ON STRAIN-ENERGY RELEASE RATE CALCULATIONS

The strain energy release rate is often used as a fracture mechanics parameter to describe delamination propagation and onset in composites, and is conveniently evaluated using finite element analysis. A common problem encountered in analysis is overlapping (interpenetration) of the delamination faces if these faces are not constrained. This paper examines the effect of overlapping on strain energy release rate calculated using the virtual crack closure method in conjunction with 3-dimensional anisotropic finite element analysis. A bilinear gap element was used between the delamination faces to prevent these faces from overlapping. Three problems were studied: (1) laminates with an embedded crack and embedded delaminations; (2) laminates with free edge delaminations; and (3) end-notched flexure specimens. The results of this investigation indicated that overlapping has a significant effect on the component values of G(I) and G(II), as well as on the total strain energy release rate. It was also found that end effects can create non-uniform energy release rates along the crack front in edge delamination problems due to twisting of the sublaminate with unsymmetrical lay-up, so that 3-dimensional finite element analysis is required.