SHEAROGRAPHIC AND HOLOGRAPHIC ASSESSMENT OF DEFECTIVE LAMINATES WITH BOND-LINES OF DIFFERENT ELASTICITIES

While defects in laminated plates are readily revealed using double-exposure shearography and holography, when an incremental vacuum pressure is applied between the exposures, the apparent defect size, measured from the boundary of the perturbed fringes, may over-estimate the actual defect size depending on the elasticity of the bond-life. In this paper, the perturbed fringes were described by a mathematical model derived from the theory of thin plates supported by a Winkler type elastic foundation which takes into consideration the elasticity of the bond-line. Am iterative technique is subsequently presented for estimating the size and depth of the defect from the fringe pattern without the need to pre-determine the current elasticity of the bond-line. Laminates with a thick and highly elastic bond-line found in foam-adhesive bonded metal laminates, and those with a thin and brittle bond-line, found in multi-layered glassfibre reinforced plastic plates, were tested Results have shown that the defects in these laminates were accurately assessed.