Investigation of compression after impact failure in carbon fiber reinforced polymers using acoustic emission

Although several studies have been performed, the compression after impact (CAI) failure of CFRP is still not entirely understood. It is still unclear what sequence of events determines the onset of failure in CAI tests and how the different damage modes are involved in this process. To experimentally investigate this matter, the present work relies on acoustic emission (AE) monitoring and advanced acoustic signal analysis. A series of preliminary tests was conducted to correlate damage modes with recorded acoustic waveforms. Four types of waveforms were separated and associated to different damage modes. Following the preliminary tests, AE was monitored in actual CAI tests. A damage accumulation study was conducted combining three indicators, namely wavelet packet components, sentry function and energy b-value. The results evidence different phases in the damage accumulation process that were not shown in previous literature. In all specimens, the onset of the unstable damage accumulation appeared to be triggered by an intermediate frequency acoustic event associated to a combination of matrix cracking and fiber-matrix debonding, occurring at 80% of failure displacement.