Interferometric measurement of inhomogeneous swelling

Abstract Differential thermal contraction between matrix and fiber materials in composites and between adhesive and adherend materials in adhesive joints occurs during cooling from the resin cure temperature and gives rise to non‐uniform internal stress fields. Resin swelling associated with water uptake during service gives rise to inhomogeneous stress, the magnitude and distribution of which is the subject of the present investigation. Thin layers of cured epoxy resin have been allowed to absorb water at their edges only, and the swelling normal to these layer planes has been measured by studying optical interference patterns. The stresses resulting from inhomogeneous swelling, a few tens of bars, are of similar magnitude to those resulting from inhomogeneous shrinkage during cooling from resin cure temperatures.