Detection and sizing of delamination cracks in composite panels using speckle interferometry and genetic algorithms

Abstract

A real-time system for analysing data from speckle interferometers, and speckle shearing interferometers, has been applied to the problem of detecting and sizing sub-surface delamination cracks in carbon fiber composite panels subjected to vacuum loading. Interferograms are continuously recorded by a CCD camera at a rate of 60 frames s -1 with temporal phase shifting carried out at the same rate. Wrapped phase maps are calculated and displayed at 15 frames s -1 . These are unwrapped using a temporal phase unwrapping algorithm to provide a real-time display of the relevant displacement component. The damage identification procedure is formulated as an input output inverse problem through which system parameters are identified. The input of the inverse problem, the geometric moments (GM), is calculated from the surface displacement fields. The objective function of the optimization algorithm is defined as the squared difference between the GM obtained from the sample under test and that from a finite element (FE) model with a trial debonding. The optimum crack parameters are found by minimizing the objective function through the use of a novel implementation of real-coded genetic algorithms (ARGAs). The performance of the measurement procedure and analysis algorithms is evaluated using a set of carbon-fiber epoxy composite samples with systematically-varying and well-characterized defect geometries.