High strain-rate failure in carbon/Kevlar hybrid woven composites via a novel SHPB-AE coupled test

The high strain-rate induced failure characteristics in a carbon/Kevlar hybrid composite subjected to high strain-rate compressive loading were studied using a novel SHPB-AE coupled test. The tests were performed based on a split-Hopkinson pressure bar (SHPB) apparatus and an acoustic emission (AE) technique, respectively. Within the strain-rate range of 1002-1941 s(-1), a high strain-rate compressive test was conducted on the cylindrical carbon/Kevlar hybrid composite specimens located between the incident and transmitted bars. A wide bandwidth type AE sensor was connected to the specimen with a fine copper waveguide to monitor the AE signals in real time during the test. Specific types of failure mechanisms were observed with optical microscopy and scanning electron microscopy. First, AE characteristics originating from the specimens were investigated profoundly to distinguish the AE signals from diverse damage or failure sources. AE signals were then analyzed in terms of the AE amplitude, the AE count, the slope of cumulative AE count and the peak frequency. Finally, signals were classified into four types based on the waveform and corresponding peak frequency by a short time Fourier transforms (SIFT). As a result, under high strain-rate compressive loading, the strain level at the damage initiation was shortened with increasing strain-rate. The failure process of the carbon/Kevlar hybrid woven composite showed initial matrix fracture and then brittle carbon fiber breakage. Subsequently, multiple failure mechanisms appeared, such as fiber-matrix debonding, fiber pull-out, excessive deformation and breakage in the Kevlar fiber tips including splitting and fibrillation. The application of the novel SHPB-AE coupled test to the carbon/Kevlar hybrid composite was discussed in depth for characterizing the failure process, and it was an effective and relevant methodology to grasp in situ information on the failures under high strain-rate compressive loading. (C) 2016 Elsevier Ltd. All rights reserved.