Multiscale analysis of the formability of CFRP sheets subjected to warm forming with a temperature-dependent epoxy model

The press formability of cured CFRP (carbon fiber reinforced plastic) sheets composed of a thermoset polymer and continuous fibers was examined in this study. Press forming requires large plastic deformation, but CFRP is not sufficiently ductile in general. Therefore, it has been considered that CFRP is not suitable for press forming. However, recent experimental research has shown that the press formability of CFRP sheets is improved at 100 °C compared with that at room temperature. This finding indicates the possibility of the press forming of CFRP, but the temperature dependence of its formability has yet to be shown. To establish a press forming method for CFRP, an analytical study of its plastic deformation is essential. To determine the temperature dependence of the formability of CFRP, the strain-softening behavior of epoxy at warm temperatures was focused on in this study. This is because the mechanical characteristics of the polymer have a strong effect on the plastic deformation of CFRP. An approximated curve based on the temperature parameters was constructed to express the stress–strain relationship at different forming temperatures. Then, a model for press forming simulation was constructed to consider the effect of the mechanical characteristics of epoxy in CFRP. The approximated stress–strain curves at room temperature and 100 °C were applied to the model. Using this model, the stress distribution in CFRP sheets formed at each temperature has been shown, and the results clearly demonstrate that the formability of CFRP sheets is improved at higher temperatures.