Numerical modelling of quasi-static and dynamic compact tension tests for obtaining the translaminar fracture toughness of CFRP

In the recent past, several studies have been undertaken to characterise the loading rate dependency of the translaminar fracture toughness GIcf+, however, no consensus has yet been reached. In an attempt to make a first step towards resolving this inconsistency, this work employed a modelling campaign based on the experimental data generated in Hoffmann et al. [Compos Sci Technol 164 (2018) 110–119] in order to identify the driving mechanism behind the negative loading rate trend observed in said study. The numerical analysis employed detailed FE models of the quasi-static and high-rate experiments, as well as a high-fidelity strain-rate- and pressure-dependent user material model to represent the intralaminar behaviour of the composite material. This study found the energy release rate along the macroscopic crack to be practically rate-insensitive. Loading rate, however, was shown to have a pronounced effect on the extent of “secondary” energy dissipation mechanisms away from the macroscopic crack in the form of matrix damage and plasticity. This damage zone was significantly larger under quasi-static than under high-rate loading, thus providing an explanation for the observed drop of GIcf+ under elevated loading rates in Hoffmann et al. (2018).