Thermal ageing effects on mechanical properties and barely visible impact damage behavior of a carbon fiber reinforced bismaleimide composite

Effects of ageing at 200 degrees C in air for up to 1000 h on static mechanical properties and low velocity impact behavior of a carbon fiber (T700) reinforced modified bismaleimide (BMI) composite have been investigated. A new C-scan data process method was applied to determine the variation in impact damage model and related failure mechanism due to thermal ageing, and attention was paid mainly to the barely visible impact damage. The transverse tensile strength and interlaminar-shear strength of the composite were found to decrease progressively with increase in ageing time, resulting from degradation of BMI matrix, damage of fiber/matrix interface and formation of microcracks caused by thermal ageing. It was shown that after thermal ageing, the impact damage model of the composite varied from a barely visible impact damage to a visually detectable impact damage as the impact energy reached the range from 20 J to 30 J. The employed C-scan data process method was proven to be more effective in revealing variation of impact failure mechanisms. It was deduced that the internal delamination dominated the barely visible impact damage model, and fiber breakage became more important in the aged composite as impact energy higher than 20 J. (C) 2016 Elsevier Ltd. All rights reserved.