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 differences are quantified by an objective function, which is minimized using a numerical optimization technique. When the difference between the analytically produced modal parameters and those measured experimentally is minimized, the 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 the effective shear rigidity of the delaminated area, and this is incorporated into the dynamic stiffness method. The damage is located using a two-stage optimization process. First, the differences in the analytical and experimental bending frequencies and mode shapes are minimized by altering the material properties and boundary conditions of the model. Once the differences have been minimized for an undamaged beam, damage is located by altering the number, size, and location of delaminations within the beams. Results are obtained and compared using two different optimization procedures: a gradient-based optimization procedure and a genetic algorithm.