ASSESSMENT OF STRUCTURAL INTEGRITY AND INTERFACIAL DEBONDING IN CARBON FIBER/EPOXY COMPOSITES UNDERGOING HYGROTHERMAL AGING

Adverse environmental conditions, characterized by elevated moisture levels and high temperatures, can profoundly affect the structural integrity of polymer matrix composites over extended periods of service. This study employs a combination of microstructural analysis and analytical modeling to quantify the extent of interfacial debonding induced by hygrothermal aging in carbon fiber reinforced polymer (CFRP) composites. Moisture is absorbed concurrently through the matrix and microvoids, leading to interfacial debonding at the fiber/matrix interfaces. While only a limited number of preexisting microvoids were observed in the unaged composite through field-emission scanning electron microscope (FESEM) micrographs, the average number and volume of these debonded regions increased with aging duration. This interfacial debonding, even without external loading, creates mesoscopic "free volume," which is conducive to moisture diffusion. To assess and quantify this interfacial debonding, we employ an established theoretical model based on the principles of free volume theory. The experimental results align closely with the theoretical calculations for the thickness of the interfacial debonding.