A simple model for sizing unbonds in foam-adhesive bonded laminates from shearographic fringes

Abstract

This paper demonstrates the use of double-exposure shearography in detecting and assessing unbonds in foam-adhesive bonded laminates. Unbonds are created artificially by placing mylar sheets between the foam adhesive and the adherends. When the laminates are vacuum-stressed, the unbonds are revealed from perturbations in the fringe patterns. As the foam is highly elastic, the apparent unbond size, described by the boundary of the perturbed fringes, is grossly larger than the actual size of the unbond. A simple model is developed, enabling a reasonably accurate estimation of the unbond size. The findings also suggest that the depth of an unbond may be estimated from shearograms of both sides of the laminate. © 1994.