A three-dimensional crack tip element for energy release rate determination in layered elastic structures

A three-dimensional crack tip element is presented and used to determine en ergy release rate and mode mix for different types of laminated plates cont aining delaminations. These results are then compared to predictions by thr ee-dimensional finite element analyses. For all cases, total energy release rates as predicted by the two methods are in good agreement. For delaminat ions between plies at the same orientation, energy release rate components are determined by the crack tip element using both classical and non-classi cal definitions. The non-classical definition is one that has been derived in a previous work and, compared to the classical result, is shown to provi de superior capability for predicting delamination growth in some graphite/ epoxy composites. The classical energy release rate components predicted by the crack tip element are compared to results by three-dimensional finite element analyses and the virtual crack closure technique and good agreement is obtained. For delaminations between plies at different orientations, th e crack tip element is used to predict non-classical energy release rate co mponents as well as components based on a finite amount of crack closure. T hese latter quantities are compared to results by three dimensional finite element analyses and the virtual crack closure technique, and good correlat ion is obtained. These results indicate that the crack tip element may be u sed to accurately determine energy release rate components in practical pro blems of delamination where these components are defined classically, defin ed by commonly used approaches such as finite crack closure, or defined usi ng a non-classical approach. As such, the element provides a powerful yet a daptable technique for predicting delamination growth in a wide variety of materials.