Measurement of energy release rates for delaminations in composite materials

Conventional measurements of energy release rates,GI andGII, for delaminations in composite materials, generally utilize loads, crack lengths and simple standard specimen geometries. In this work, a more widely applicable measurement method, using phase shifting moiré and the J integral, is presented. The experimental technique described requires only fringe-pattern information and the elastic constants for the measurements—thus it can be used when the standard methods are inapplicable. Using conventional double-cantilever beam and end-notched flexure specimens, the energy release rate has been measured simultaneously by the moiré method and the standard methods, with good agreement found between the two. This development will for the first time permit the experimental validation of new finite-element routines as they are developed.