Effect of Hot-Wet Conditioning on the Mechanical and Thermal Properties of IM7/ 8552 Carbon Fiber Composite

Carbon fiber composite IM7/8552 laminates with unidirectional (UD) and quasi isotropic (QI) lay-up sequence were fabricated by autoclave process. Standard test specimens for compression and thermal tests as well as traveler coupons for hygrothermal aging were cut and prepared from these laminates. Prior to testing, hot-wet specimens along with traveler coupons were hygrothermally aged in a chamber maintained at 70ºC and 85% relative humidity (RH) until moisture absorption saturation was attained. Compression properties and glass transition temperature (Tg) of composites were determined in both room temperature and in hot-wet conditions. Moisture absorption rate and maximum moisture content was observed to depend on the lay-up sequence. UD laminate absorbed moisture at a higher rate than that of QI. Also the diffusion coefficient (Dc) was observed to be higher in UD than in QI laminate. Compressive strength was observed to decrease by about 28%- 37%.whereas compression modulus was unaffected due to moisture absorption. The Tg was observed to reduce by about 17% due to moisture. The mechanisms of moisture absorption behavior and the consequent degradation in the mechanical properties are discussed