Tensile and compression analyses to investigate the mesoscale mechanical characteristics influential for press formability of CFRP sheets

Carbon fiber reinforced plastic (CFRP) is applied in various fields such as automobile and aerospace industry due to high specific strength and rigidity than metals. However, since its ductility is poor, there are problems that it is difficult to perform press forming and the production cost increases. In recent years, studies on improving the ductility of CFRP for realizing press forming are gradually increasing. Experiments to obtain the mechanical properties of CFRP are costly and time consuming. Although there are several test standards in the compression test for CFRP, none of them evaluates mesoscale compression characteristics, and it is difficult to capture the deformation of internal fibers and resins when the sheet is subjected to forming. Therefore, establishing an analytical model that expresses the deformation of CFRP by evaluating mesoscale mechanical characteristics would be important to meet the increasing demand for the press forming of CFRP sheets. In this research, by modeling and analyzing CFRP sheets in microscale, the influence of the interaction between resin and fiber within a CFRP during plastic deformation was evaluated. The carbon fiber was modeled to observe its kink behavior based on an orthotropic elastic material model. The epoxy resin was regarded as a ductile material and a Gurson-Tvergaard-Needleman (GTN) model was applied, which represent a viscoelastic plastic material considering damage by void generation, growth and coalescence. Simulations were performed by changing the GTN parameters, and this paper explains the influence of each parameter on formability based on the analysis result.