Locating delaminations in composite beams using gradient techniques and a genetic algorithm

A method of locating delaminations within composite beams is presented. The method compares the experimental natural frequencies and mode shapes of a delaminated beam with those predicted by an analytical model. The differenc es are quantified by an objective function, which is minimized using a nume rical optimization technique. When the difference between the analytically produced modal parameters and those measured experimentally is minimized, t he damage is said to have been located. A simple model. based on the static deflection of a cantilever beam, is developed to obtain an estimate for th e effective shear rigidity of the delaminated area, and this is incorporate d into the dynamic stiffness method. The damage is located using a two-stag e optimization process. First, the differences in the analytical and experi mental bending frequencies and mode shapes are minimized by altering the ma terial properties and boundary conditions of the model. Once the difference s have been minimized for an undamaged beam, damage is located by altering the number, size, and location of delaminations within the beams. Results a re obtained and compared using two different optimization procedures: a gra dient-based optimization procedure and a genetic algorithm.