Correlation of fracture processes and damage mechanisms of armor structural materials under high strain rates with acoustic emission characteristics

Abstract

Methodology for the monitoring of an acoustic emission (AE) signal was employed to investigate the deformation and/or fracture processes together with damage mechanisms for RHA steel and WHA in high-strain-rate compressive loadings. Cylindrical test specimens were loaded with an incident bar and the AE activity was monitored in real time during the entire impact by using a resonant type AE sensor connected to the specimen with a waveguide. Post-failure observations were conducted to correlate the particular features in the acoustic emission signal that corresponded to the specific types of damage mechanisms. AE characteristics from the specimens were firstly examined to distinguish the different AE signals from various possible damage mechanisms. AE signals were analyzed in terms of AE amplitude and normalized cumulative AE energy, and were classified into three different signal types based on the waveform and the peak frequency which was obtained by a short time Fourier transform (STFT). Furthermore the behavior of RA (ratio of rise time to amplitude) value was used for characterization of the damage mechanisms which could be confirmed by the SEM observation after the test. As a result, the behavior of the three classified different AE signal types according to the waveform and the peak frequency successfully represented the deformation/fracture processes of the armor materials exhibiting various and multiple damage mechanisms. It was elucidated that each classified signal type was associated with the specific damage mechanism within the specimen, and the AE characteristics were summarized in association with the individual damage mechanism of the armor materials.