Displacement Rate Effects on the Mode II Shear Delamination Behavior of Carbon Fiber/Epoxy Composites

This paper studies the influence of displacement rate on mode II delamination of unidirectional carbon/epoxy composites. End-notched flexure test is performed at displacement rates of 1, 10, 100 and 500 mm/min. Experimental results reveal that the mode II fracture toughness G(IIC) increases with the displacement, with a maximum increment of 45% at 100 mm/min. In addition, scanning electron micrographs depict that fiber/matrix interface debonding is the major damage mechanism at 1 mm/min. At higher speeds, significant matrix-dominated shear cusps are observed contributing to higher G(IIC). Besides, it is demonstrated that the proposed rate-dependent model is able to fit the experimental data from the current study and the open literature generally well. The mode II fracture toughness measured from the experiment or deduced from the proposed model can be used in the cohesive element model to predict failure. Good agreement is found between the experimental and numerical results, with a maximum difference of 10%. The numerical analyses indicate crack jump occurs suddenly after the peak load is attained, which leads to the unstable crack propagation seen in the experiment.

Automated summary

This study investigates the effect of displacement rate on mode II delamination in unidirectional carbon/epoxy composites. It is found that the fracture toughness increases with displacement, and different damage mechanisms are observed at different rates. The proposed rate-dependent model fits well with the experimental data, and good agreement is found between experimental and numerical results.