A SIMPLE-MODEL FOR SIZING UNBONDS IN FOAM-ADHESIVE BONDED LAMINATES FROM SHEAROGRAPHIC FRINGES

This paper demonstrates the use of double-exposure shearography in det ecting and assessing unbonds in foam-adhesive bonded laminates. Unbond s are created artificially by placing mylar sheets between the foam ad hesive 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 bo undary of the perturbed fringes, is grossly larger than the actual siz e of the unbond. A simple model is developed, enabling a reasonably ac curate estimation of the unbond size. The findings also suggest that t he depth of an unbond may be estimated from shearograms of both sides of the laminate.