Fatigue delamination, initiation, and growth, under mode I and II of fracture in a carbon‐fiber epoxy composite

In this article, interlaminar crack initiation and propagation under mode I and II dynamic loading of an epoxy matrix reinforced with unidirectional carbon fibers were evaluated. Delamination in mode I was carried out employing the DCB test (Double Cantilever Beam). In mode II, the ENF test (End Notched Flexure) was used. The fracture toughness in mode I was obtained using the methods of the ASTM D5528 Standard, whereas in mode II, the methods were applied in accordance with the ESIS (European Structural Integrity Society) Protocol. Employing this experimental program, the fatigue curves (ΔG,N) and growth rate curves (ΔG, da/dN) in both fracture modes were determined for an asymmetry ratio R = 0.2. The influence of the manufacturing process of the material on its behavior with respect to crack growth onset may be deduced from the experimental results, mainly the presence of resin bags. Moreover, as the crack growth rate decreases for large crack lengths, crack growth may even cease if the critical fracture energy does not increase above the values obtained in the static characterization of the material. POLYM. COMPOS., 2010.