Effects of mixed-mode ratio and step-shaped micro pattern surface on crack-propagation resistance of carbon-fiber-reinforced plastic/adhesive interface

This study investigated the effects of the mixed-mode ratio of applied loads (GII/G) and aspect ratio A of step-shaped micro patterns on the crack-propagation resistance of a carbon-fiber-reinforced plastic (CFRP)/adhesive interface fabricated by in-mold surface modification. Experiments showed that the fracture behaviors change and that the apparent mixed mode fracture toughness GC increases with GII/G and A. We used the Benzeggagh-Kenane (B-K) failure criterion for the mixed-mode fracture toughness considering the transition of the failure mode of the step-shaped micro patterns. The B-K criterion agreed well with the improvement of GC due to an increase in GII/G for various fixed values of A. We clarified the relationship between the aspect ratio A and the parameter η, which is required to describe the B-K criterion, and therefore, η can be estimated from A. Consequently, it was verified that GC of the CFRP/adhesive interface with step-shaped micro patterns can be predicted for arbitrary GII/G and A values by substituting the η-A relationship in the B-K criterion.