Low‐velocity impact behavior of a carbon/bismaleimide composite proposed for supersonic flight simulation after hygrothermal cycling

The combined high temperature oxidation, humidity exposure, thermal cycling, and a low temperature period were simultaneously performed on a carbon fiber‐reinforced bismaleimide (C/BMI) composite to simulate the supersonic hygrothermal flight‐cycles on long durability of the C/BMI applied in supersonic aircraft. After a hygrothermal cycling for 300 times, the drop‐weight impact test and ultrasonic analysis were carried out to evaluate low‐velocity impact damage behavior of the composite caused by foreign objects during service. The fiber/matrix interface degradation caused by hygrothermal cycling was demonstrated through a parameter proposed by Sarasua (parameter b), which is shown to reflect the level of the interfacial bond by estimating the contribution of the interphase on the damping properties of composites through the dynamic thermomechanical analysis (DMA) test. A secondary increase of delamination area initiated from one long edge was detected for the first time in the hygrothermal cycled C/BMI composite impacted by energy higher than 20 J. After experiencing 300 combined ageing cycles, the damage model of C/BMI composite impacted by more than 20 J changes from the pine tree model to gyro model because of free‐edge delamination, resulting in a serious potential risk to the application of C/BMI composite laminates in aeronautics. POLYM. COMPOS., 40:E1588–E1599, 2019. © 2018 Society of Plastics Engineers