Automated dynamic fracture procedure for explicit time integration brick finite elements

Abstract

An elastodynamic fracture model has been implemented in the explicit finite element software DYNA3D that predicts energy release rates of stationary, through-thickness, 3-D cracks in linearly elastic materials. This work is part of an on-going effort to investigate implementation of automated fracture models in DYNA3D. It follows the implementation of a linear elastic fracture model that is capable of simulating automatic crack propagation without user intervention. The current model uses a path- independent volume integral expression obtained by modifying an expression developed earlier for 2-D crack problems to compute the dynamic energy release rate. It is implemented for 3-D solid (brick) elements. Domain integral method is used to develop the volume integral expression. Domain integral form of the expression is particularly well- suited for applications with the finite element method as it overcomes the difficulty associated with defining contours around the crack tip. Also, it does not involve elements around the crack front, thereby leading to better accuracy when using the finite element method for crack analysis. The implementation of the model has two basic steps - search for elements in a chosen integration volume, and numerical evaluation of the integral expression. The integration volume to be used is input by means of two values - one for number of rings of elements around the crack front to be ignored, and the other for outer limit of the volume. Some mechanical field quantities in the integral expression are not available in DYNA3D’s brick element implementation. These values are determined for the integration volume elements and stored as additional history variables, if needed, during the numerical evaluation phase. Numerical examples to verify the accuracy of the current model are presented.