On the mixed mode I/II delamination R-curve of E-glass/epoxy laminated composites

The main effort of the current study is to propose a procedure for prediction of delamination resistance curve (R-curve) of laminated composites under mixed mode I/II loading conditions based on the experimental observations. Hence, two material systems, i.e., E-glass/epoxy and E-glass/MWCNTs-toughened epoxy were tested at a wide range of mixed mode I/II delamination to present R-curves. Each R-curve was characterized by fiber-bridging zone (FBZ) length, critical strain energy release rate at delamination initiation (GTC) and stable propagation (GTR) states. It was manifested the magnitude of the FBZ length is constant at different mixed mode I/II loading states for a specific laminate system. Then, using the Benzeggagh and Kenane (B-K) criterion, two relations for computing the GTC and GTR were derived. Finally, according to these findings a relation was obtained to predict the delamination behavior of laminated composites (from delamination initiation to propagation states) under arbitrary mixed mode I/II loading condition.