Assessment of residual composite properties as influenced by thermal mechanical aging

In this study two quasi-isotropic carbon fiber-reinforced polyimide materia l systems, IM7/K3B and IM7/PETI-5, were thermally aged at 163 degrees C (32 5 degrees F) for up to 10 000 hours under a static compressive load (contro lled at 2000 mu epsilon). The compressive load was applied using steel fixt ures supplied by The Boeing Company. Back-to-back gages on the aging panels monitored compressive strain as well as bending strain. Following aging at 1500, 3000, and 10 000 hours, ambient residual compression properties were assessed using the IITRI compression test method. Unexposed specimens were also tested to obtain baseline properties for comparison. These results sh owed that 10 000 hours of stressed isothermal aging did not significantly a ffect the compressive properties of the two composite systems. However, the re was one exception. A slight increase in scatter of the residual strength , was observed. Statistical evaluation of the results provided guidelines f or the development of A-basis and B-basis values and assessing significant property changes following aging. Differential scanning calorimetry (DSC) f ound the glass transition temperatures for the two material systems to be u naffected by 3000 and 10 000 hours of aging. The combined results of these experiments provide valuable information on the effects of physical and che mical aging on the long-term thermal mechanical behavior of these materials .