Moisture transport in unidirectional carbon/vinylester panels with imperfect fiber/matrix interface

The objective of this work is to characterize the moisture transport in a unidirectional carbon/vinylester composite. The moisture uptake is analyzed by superposition of Fickian diffusion through the matrix, and capillary transport of water through gaps between fiber and matrix, known as “wicking,” modeled using Darcy’s law. A neat resin vinylester 510A panel and a set of different size unidirectional carbon/vinylester 510A panels were immersed in seawater at 40℃. The moisture content was monitored beyond saturation. The experimentally determined saturation time increased with increased size of the composite panels. Both the diffusion and capillary flow models predict increased time of saturation with increasing panel size, although the diffusion model predicts much longer times, and the capillary model much shorter times than observed experimentally. The diffusion model assumes a perfect fiber/matrix interface while the capillary model assumes the capillaries running along the entire panel without obstructions. In reality, fiber/matrix interface voids are most likely isolated, and regions of adequate bonding will interrupt the capillary flow.