Moisture Diffusion in Impact Damaged Face Sheets of Composite Sandwich Materials.

Moisture permeation can weaken composite sandwich material structures. This report describes an investigation of the change in moisture diffusion coefficients in composite sandwich face sheet material which has sustained moderate damage. Sandwich panels were subjected to impacts of 50, 75 and 100 foot-pounds using a one-inch diameter instrumented impact head. After the panels were subjected to the impacts, the core and rear face material were removed, leaving only the impacted face sheet. In the analysis, a sufficient undamaged area of the composite was retained in order to prevent further damage to the impact area. Small squares of damaged and undamaged face sheet material were then dried in a vacuum oven and exposed to 80 percent RH at 22 deg C for a period of seven months. The diffusion coefficients were determined through the damaged area and compared with that of undamaged face sheets. The sorption curves of the damaged specimens were analyzed to estimate the moisture diffusion coefficients. It was determined that small damage, barely noticeable, increased the diffusion coefficients of the damaged area by about two orders of magnitude.