Energy release rate calculations for the compact tension specimen using brittle orthotropic materials

An energy release rate calculation is performed using the modified crack closure integral (MCCI) method applied to the compact tension (CT) specimen. Mechanical properties used are typical of short-fiber sheet molding compound (SMC) materials. Using orthotropic linear constant strain finite elements, the classical solution is closely approximated with a relatively coarse grid. The wedge opening of the CT specimen is shown to lower the expected energy release rate by 6·1%, introducing a systematic error. Orientation of the SMC material near the load application point perpendicular to the applied load will raise the energy release rate by 12·0%. The CT specimen results are shown to be insensitive to the distribution of the applied load around the hole periphery. A probabilistic method is developed for converting the distribution of applied failure load to the distribution of critical energy release rate. This method is applied to predict the distribution of failure load for other geometries.