An experimental investigation was performed to determine the behavior of an open-hole tension (OHT) graphite/bismaleimide composite specimen loaded in tension-tension fatigue under isothermal, fixed-frequency conditions. A range of stress levels and temperature levels was chosen to assess performance. These loads and elevated temperatures ranged from relatively benign conditions (low stress, room temperature) up through aggressive conditions (high stress, high temperature). Measurements were made of stiffness, edge crack density, residual strength, weight loss, and changes in glass transition temperature (Tg).
Results from this work will help explain the roles of aging and fatigue damage in the performance of graphite/bismaleimide OHT specimens as well as providing insights into the individual and synergistic contributions of each of these processes. Contributions of aging and microcrack formation during elevated temperature fatigue of OHT specimens may result in a net stiffness increase in the gage section and a decrease in residual strength. The magnitude of changes in stiffness or strength is determined by the time at temperature and the chosen stress level.