Calculation of energy release rates for delaminations in composite materials using phase shifting Moiré interferometry
An experimental technique was developed to measure the energy release rate for delaminations in composite materials. The method can be used in cases where conventional methods may not be applicable, such as problems involving multidirectional laminates or arbitrary specimen geometry. The work involved the experimental and computational enhancement of the optical technique of moirâe interferometry, including alternative grating technology, image processing of fringe patterns, the implementation of phase shifting and the automation of the data reduction process. The improvements provided a practical experimental means for determining full-field displacement fields surrounding delaminations, together with a convenient method for using these displacement fields to calculate energy release rates via the J-integral. Three types of experiments were performed on carbon-fibre/epoxy unidirectional laminates to validate the new approach. The results compared favourably to those obtained by conventional methods. Several experiments were also performed on multidirectional laminates to demonstrate the extended capabilities of the new method. It was concluded that the new method is not particularly well suited to the measurement of critical energy release rates, but it should be a valuable tool in the validation of computational methods.