High-strain-rate impact in Kevlar-woven composites and fracture analysis using acoustic emission

Abstract

Characteristics of the failure progress in plain weave Kevlar composite under high-strain-rate impact loading has been investigated by using an acoustic emission (AE) technique. Cylindrical specimens were loaded with an incident bar, and the corresponding AE activity was monitored in real time during the entire impact by using an AE sensor connected to the specimen with a waveguide. Post-failure observations were conducted to correlate the particular features in the acoustic emission signal corresponding to the specific types of failure mechanisms. AE characteristics from the specimens were first examined to distinguish the different AE signals from various possible damage mechanisms. AE signals were then analyzed in terms of the AE amplitude, the normalized cumulative AE energy, ratio of rise time to amplitude (RA) and the peak frequency. Finally, signals were classified into four types based on the peak frequency and the magnitude obtained by a fast Fourier transform (FFT). As a result, the peak stress and toughness of the Kevlar-woven fabric specimen increased by as much as two times, with increasing strain rate in a range of 1182-1460 s(-1), whereas the strain at peak stress decreased by approximately 16%. The application of combined AE techniques and SHPB tests was discussed for characterizing the failure process which resulted in failure of the plain weave Kevlar composite, thereby enabling fracture analysis in the materials.