Hygrothermal aging of polyimide matrix composite laminates

Two polyimide-matrix systems (Avimid(R) K3B/IM7 and PETI-5/IM7) were subjected to a series of hygrothermal aging experiments at various temperatures and relative humidities. For each aging condition, we measured the water absorption rate and the microcracking toughness as a function of aging time. The toughness decreased with time. The rate of decrease increased with temperature and relative humidity. All experimental results could be fit to a simple first-order kinetics analysis where the degradation rate was assumed to be proportional to the total exposure to water above a threshold water level. Below the water threshold, no degradation occurred. The kinetics analysis was used to construct a hygrothermal aging master plot that can be used to make predictions of toughness degradation due to arbitrary hygrothermal environments. The master plot can be constructed from a few experiments on specimens immersed in water and thus is a potential accelerated test method for characterizing hygrothermal stability of composite laminates. (C) 2003 Elsevier Ltd. All rights reserved.