The effect of curing schedules on fiber-matrix adhesion in carbon fiber–epoxy resin composites

Abstract

Fiber-reinforced polymeric composites are used in a large and growing number of applications, all requiring different property sets including the nature of the fiber-matrix adhesion to which the present work is addressed. Specifically, the number of curing cycles, curing temperature and schedule, degree of cure, use of accelerants, annealing, and the use of fiber handling agents are investigated for systems of Hexcel IM7 carbon fibers embedded in Epon862 (resin) and Epikure Curing Agent W (hardener) using the single-fiber fragmentation method. The fractional extent of cure is monitored using differential scanning calorimetry (DSC), so that comparisons are made at the same degree of cure (99%). Single-stage curing at the highest temperature produces the highest apparent adhesion, and the use of accelerants significantly increases the curing rate while maintaining the same level of adhesion. Accelerants in some cases, however, decrease the plastic yield strength of the specimens. Annealing reduces induced residual stress and apparent adhesion, but not below the baseline achieved at lower curing temperatures. Plastic yield strength and apparent adhesion decrease for any degree of cure lower than 95%, while the use of handling agents shows no effect on adhesion.