Influence of the Matrix Toughness in Carbon-Epoxy Composites Subjected to Delamination under Modes I, II, and Mixed I/II

Abstract In this work, the fracture behavior under modes I, II, and mixed mode I/II has been studied for two different AS4 carbon fiber epoxy laminates. One of the laminates was produced with a Hexcel 3501-6 epoxy resin while the other was laminated with a tougher modified Hexcel 8552 epoxy resin. Both laminates were experimentally tested in modes I, II, and mixed I/II with different mixity ratios by means of DCB (double cantilever beam), ENF (end notch flexure), and MMB (mixed mode bending) specimens, respectively. Finite element modeling (FEM) was used in order to analyze modes I, II, and mixed I/II and to compare experimental and numerical results. The modified 8552 resin matrix presented the best behavior in mode I and mixed mode I/II as the critical energy release rate was higher than that for the 3501-6 matrix composites. In mode II, the best performance was reached for the 3501-6 matrix laminates. It was also found that the critical energy Gc and the scatter increased as the mode ratio GII/Gc increased. Finally, experimental and numerical results showed a good agreement as the differences obtained from both procedures were generally lower than 10%. Keywords: delaminationfracturemixed modeMMBDCBFEM Acknowledgment The authors are indebted to the Spanish Ministry of Science and Innovation (Project MAT2010-14943) for the funding of this work.