On energy release rates in heterogeneous composite laminates

Composite laminates are usually assumed to be homogeneous when determining the energy release rates (ERRs) associated with inter-ply delamination. This short paper discusses the effect of neglecting this assumption by accounting for inter-ply interface layer thickness and the resulting influence that this may have on the ERRs. A global approach is used to analytically determine ERRs for delaminations subject to mixed mode loading in symmetric double cantilever beam (DCB) samples of a material formed of alternating stiff and compliant layers. In contrast to their homogeneously determined counterparts these ERRs and their mixity are dependent on both sample depth and interface thickness and when compared the conditions under which obvious differences become apparent can be explicitly identified. Some brief conclusions on the application of the analysis to the prescription of practical delamination testing protocols for composite laminates are drawn.