Mixed-Mode (I+II) Fracture Toughness and Rate Dependent Fracture Behavior of Interlayer-Toughened Composite Laminate

摘要

Mixed mode (I + II) fracture toughness of the interlayer-toughened composite laminates, T800H/3900-2 (Toray), which is a newly developed composite material having a tough 'interlayer' containing fine polyamide particles, was investigated over a very wide range of loading rate from static to impact The MMF (Mixed Mode Flexure) specimen and SHPB (Split Hopkinson Pressure Bar) system were employed for measuring the mixed mode fracture toughness under impact loading. The strain rate dependence of fracture behavior was also studied from both macro- and microscopic aspects to clarify the mesoscopic fracture mechanism of the material. The experimental results showed the crack path was inside the toughened interlayer during the initial stage of crack growth, however, it moved from the toughened interlayer to the carbon/epoxy base lamina during the propagation stage of crack growth. The mixed mode fracture toughness was sensitive to loading rate; the impact fracture toughness for the toughened interlayer was about 23 percent lower than the maximum value under static loading, and the impact fracture toughness for the carbon/epoxy base lamina was about 11 percent lower than the maximum value under static loading. The effects of mode mixture varied with loading rate for interlayer fracture, though they did not varied for base-lamina fracture. Microscopic observation showed that the fracture morphology was sensitive to loading rate.