An Energy Release Rate Approach For Stable Crack Growth in the Free-Edge Delamination Problem

An experimental and analytical study was conducted to examine the free-edge delamination mode of failure in a (±30/±30/90/90) _S Boron/ Epoxy laminate. The initiation and stable growth of the delamination for static tension loading conditions were identified using ultrasonic tech niques. A finite element representation for the test specimen was con structed using conventional elements. The interlaminar stress distribution at the laminate midplane was found to be in agreement with published results. The finite element representation was used to model the initiation and stable growth of the delamination. An applied force versus longitudinal strain curve was obtained from the model based on the data for the longi tudinal strain versus the extent of the delamination. The applied force versus longitudinal strain curve obtained from the model was between the two sets of data obtained from the specimens. The model also predicted the strain level at which the laminate showed a marked decrease in stiff ness. Energy release rates were evaluated by a simple computational scheme that does not require a special singular element or knowledge of the existence of a stress singularity in the solution. The results of these computations are combined with the experimental data and discussed in terms of the initiation and stable crack growth characteristics of the delamination.