Acoustic emission to probe slow dynamics in complex materials

Abstract

Acoustic emission has already been applied to give complementary information on the evolution of nonlinear behavior microcracked materials. In particular, energies of elastic waves emitted during the creation and propagation of microcracks in composites revealed to be in good correlation with relaxation time [1]. However, it remains important to study the relaxation (and/or conditioning) of complex materials as a function of mechanisms that lie behind the experimental observations. In this contribution, composite and concrete samples taken at microcracked states are submitted to slow dynamics experiments. Acoustic emission hits recorded during conditioning are first presented. During the high level excitation, the pump signal is at a very low frequency (few hundreds of hertz) in order to separate clearly the acoustic emission activity (> 50 kHz) and the low frequency excitation. Relaxation of complex materials has been realized with and without a probing ultrasonic wave. Results revealed that despite the weak acoustic emission activity, recorded acoustic emission hits contain enough information in order to improve our understanding of relaxation probed in complex materials. [1] M. Bentahar, R. El Guerjouma, “Monitoring progressive damage in polymer-based composite using nonlinear dynamics and acoustic émission.” Acoust. Soc. Am. 125, EL39 (2009).