Low velocity impact behavior of prestressed composite laminates

Composite materials remain extremely vulnerable to out-of-plane impact loads, which may lead to severe degradation in strength and stiffness. Many researchers have studied in this field, however, most of their papers only discussed the impact behavior of the specimens without in-plane forces. In reality, the aircraft parts made of composites were subjected to in-plane stresses during flight. In this study, an investigation was undertaken to evaluate the effect of in-plane stresses on the impact behavior of composite laminates. The low velocity drop-weight impact was conducted on T-300/976 quasi-isotropic graphite/epoxy laminates. Impacted composite specimens were examined by C-scanning ultrasonic inspection to quantify the damage size. The contact force during impact was measured with a piezoelectric force transducer and a digital oscilloscope. The experimental results showed that the impact behavior was highly related to birth pretension and precompression. Moreover, the pretension may induce the severe effect for impacted composite laminates.