Delamination growth behavior of a woven E-glass/bismaleimide composite in seawater environment

This study investigated the effects of seawater immersion at different temperatures on the delamination behavior of a woven E-glass/Bismaleimide (BMI) composite under mode I, mode II and mixed-mode I/II loadings. Delamination tests were conducted to characterize the fracture toughness and the resistance curve (R-curve) of the composite material before and after ageing. The fracture toughness was found to decrease monotonically with seawater exposure and increasing immersion temperature except for pure mode II results, where it surged up nearly 20% compared with the results of dry specimen. However, most specimens with seawater absorption exhibited increasing resistance with the delamination growth. This is mainly due to the plasticization of the matrix and higher ductility of the specimen after immersion. The experimental results were correlated with existing delamination criteria to determine the parameters for numerical models. An experimental procedure based on J-integral was used to characterize the delamination behavior, and the result of the J-integral method was compared with that of well-established ASTM methods. The J-integral method is very attractive as it has a wider selection of materials without the restrictions of linear elastic fracture mechanics (LEFM). Moreover, it provides a simpler experimental procedure and avoids the ambiguity of visual measurements for delamination length.