Delamination R-curve phenomena due to damage

Resistance to delamination in composites can be enhanced by a variety of bridging mechanisms. The bridging zone size is usually several times the lamina thickness, so it is questionable to think of delamination resistance as a material property independent of specimen size and geometry. When measured with slender beams, the plateau resistance is found to be independent of the beam thickness. However, the steady-state bridging zone size increases with the beam thickness. Further implications of the large-scale bridging are studied using a family of steady-state, mixed-mode delamination beams, in conjunction with an idealized damage response. The complete solution is obtained for the model, which allows the R-curves to be constructed for given model parameters. The significance of the steady-state cracking, which is crucial in understanding delamination R-curves, is elucidated by contrasting double-cantilever beams loaded by moments and by wedge forces. As an inverse process, it is recommended that R-curves be used as an experimental probe to study localized damage response, such as polymer craze and interface separation.