Microcracking and Compressive Strength Degradation of Carbon Fiber/Polyimide Resin Composites by Thermal Cycling
Hisaya KATOH, Toshiyuki SHIMOKAWA, Yasumasa HAMAGUCHI, Hiroshi MIZUNO, Hroyuki NAKAMURA and Ryoji ASAGUMO
Abstract:The objective of this study was to investigate the effect of thermal cycles, encountered by an Super Sonic Transport (SST) in service, on the cumulative frequency of microcracks and the degradation of compressive strength in carbon fiber/polyimide resin composite materials. One cycle of thermal cycling was designated as a sequence from room temperature (RT) to -54, and then to +177, finally back to RT. Transverse microcracks initiated on the sectional free edge surface of the laminates were observed and counted by using an optical microscope. Approximate 10,000 thermal cycles were given for five kinds of carbon fiber/polyimide composite material: IM7/PIXA, IM600/PIXA-M, IM600/PIXA-MT3, IM7/K3B, IM7/R1-16, as well as a Ti/Gr (polyimide CFRP) fiber metal laminate. For IM7/R1-16 thermal cycling tests were conducted up to 40,000 cycles. Transverse microcracks were observed not only on the sectional free edge surface but also on the inside cross section of specimens cut after thermal cycling tests for IM7/R1-16. Static open-hole-compressive (OHC) strength was measured at RT before and after thermal cycling tests on the five kinds of material except for IM7/PETI-5. Static non-hole-compressive (NHC) strength was measured at RT on IM600/PIXA-M and IM600/PIXA-MT3. In addition, in order to know the estimates of thermal stress generated by the thermal cycles, the thermal stresses were calculated by the classical lamination theory (CLT) using basic lamina data given in a reference. Key Words:Polyimide resin, CFRP, Ti/Gr fiber metal laminate, Thermal cycles, SST, Microcracking, Compressive strength, Thermal stress calculation