Delamination failure of a woven glass fiber composite

Delamination fracture of a woven glass fiber composite was studied with the double cantilever beam (DCB) test. The mechanism of stop-start crack propagation was determined by direct observation of the crack front, complemented by fractographic analysis. The results were compared with an earlier study of interlaminar fracture that considered the effect of yarn undulation without the effect of weave. The constraint imposed by the interwoven fill yarns forced the fracture from an intrayarn path to an interply path which approximately doubled the interlaminar fracture toughness. Increasing the matrix toughness by increasing the amount of soft segment in the urethane methacrylate resin translated directly to increased composite toughness. The resin-rich regions, especially the interstitial areas where four yarns intersected, strongly influenced the mechanism of stop-start crack propagation. In the most brittle matrix, these regions fractured ahead of the crack front and thus served as internal flaws or weak points that facilitated crack propagation. With a tougher matrix, the interstitial areas were points of increased toughness and functioned as pinning points that temporarily arrested crack growth.