Effect of Microvoids on Anomalous Moisture Absorption of Quartz/BMI Composite Laminates

Abstract

The focus of this paper was to investigate the effects of microvoid content in quartz/BMI laminates on both short and long-term moisture absorption dynamics. The moisture absorption characteristics for the laminates were experimentally obtained by water immersion tests at 25°C of three-ply quartz/BMI samples that contain voids, ranging from 8.6% to 13.7% by volume. The void levels were obtained by conditioning the prepreg at different moisture levels for 48 hours in an environmental chamber before curing in a hot press. The curing process was carried out at 69 kPa, which leads to a more uniform fiber volume fraction for the laminates. Having a constant fiber volume fraction ensures the same amount of fiber-matrix interface present in all the test samples, therefore eliminating the effect of fiber-matrix interface as an experimental variable. It is shown that the presence of microvoids leads to an increased non-Fickian absorption behavior. Hence, the anomalous, non-Fickian absorption parameters are obtained by using a one-dimensional absorption model that accounts for both bound and unbound free water within the laminate. It is shown that the microvoids act as storage sites for moisture which can be described by the one-dimensional, non-Fickian absorption model. Finally, possible relationships between the four absorption model parameters and the process-induced microvoid content are discussed.

Temperature and anisotropy effects in the application of the hindered diffusion model to composite laminates

“…The exact nature of these interactions is still a source of debate, and likely involves both physical (i.e. voids/porosity 45 ) and chemical (van der Waals, hydrogen bonds) elements. While the geometric distribution of these interactions, which can be considered sources and sinks of diffusing molecules, is likely not homogenous in fiber-reinforced laminates, the effect of this non-homogeneity has not yet been considered.…”