Shearography is a double-exposure optical method which reveals defects in components from anomalies in interferometric fringe patterns. In this paper, disbonds of known shapes and sizes are deliberately created at different layers of glassfibre-reinforced plastic (GRP) laminates which are subsequently “vacuum-stressed” during the test. Experimental results show that both the shape and size of disbonds can be deduced easily from the boundaries of the anomalous fringe patterns; the depth of disbonds can also be estimated by counting the number of fringes appearing within these boundaries. The results also correlate well with those predicted from thin plate theory, suggesting that the response of disbonds in GRP plates during vacuum-stressing may be modelled with this theory.

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