Holographic determination of the residual strength of arbitrarily clamped, centrally thinned circular plates

In holographic inspection, the perturbed fringe patterns which reveal internal defects in components are generally distinct. However, in the case of a uniformly loaded circular flat plate containing a central circular defect, distinct fringe perturbation is not visually obvious except through quantitative analysis of the fringe pattern. During the analysis, ambiguities frequently arise in correctly assigning the fringe order, which is often fractional, at the centre of the plate. With the use of carrier fringes, accurate fringe orders at the central region of the plate can be determined. These, together with an iterative procedure, enable accurate estimation of both the size and depth of the defect. As the present method also determines the actual clamping condition along the plate boundary, the use of the von Mises yield criterion enables estimation of the residual strength, expressed in terms of the proportional reduction in the allowable pressure which can be applied to the defective plate.