Displacement rate effects on mixed-mode I/II delamination of laminated carbon/epoxy composites

Mixed-mode delamination is one of the common failures composites which has not been studied under low-impact loading. This paper studies influence displacement rate on mixed-mode I/II unidirectional carbon/epoxy composites. Single leg bending test performed at rates 1, 10, 100, and 500 mm/min. Experimental results reveal that fracture toughness invariant with rate. In addition, scanning electron micrographs shows shear cusps are more obvious 100 At mm/min, significant matrix debris noticed. Furthermore, proposed three-dimensional rate-dependent criterion found to well predict toughness. Numerical simulation using cohesive zone model suggests lower numerical peak load due damage dissipated energy. theoretical traction-separation responses show differences, also reflected in phase angle. implies local ratio constant throughout process.