Computational models for mode I composite fracture failure: the virtual crack closure technique versus the two-step extension method

This paper deals with the numerical determination of the energy release rate under mode I in carbon fibre reinforced composites (CFRC). Two different models are reviewed: the virtual crack closure technique (VCCT) and the Two-step extension method. The Two-step extension method needs two computational steps in order to calculate the energy release rate (G). The VCCT method is able to provide ERR value only from one computational step. Results were compared with empirical data obtained from double cantilever beam (DCB) tests carried out on unidirectional AS4/8552 carbon/epoxy laminates. This study showed that, in a pure mode I state, results obtained via the Two-step extension method were in agreement with a straightforward calculation of the elastic energy variation in the system. As expected, results obtained from VCCT and Two-step extension models converge as element length decreases. Regarding the comparison between experimental and numerical results, the study showed that a correction for testing devices compliance was needed to match both models.