ABSTRACT
Despite the sensitivity of acoustical nonlinear techniques to the presence and evolution of the microstructure of materials, they still need to be quantified. The desired quantification aims to link the changes observed on nonlinear parameters to the remaining lifetime of materials. In that sense, one of the proposed methods is the application of acoustic emission, which can separate damage
1 INTRODUCTION
Acoustic nonlinearity corresponding to microcracked, or micro-inhomogeneous materials has increased considerably during the last years. It has been established that the classical Landau theory cannot describe the dynamic behavior of these materials since it does not take into account the influence of strain on the elastic constants (Bentahar et al. 2006, McCall et al. 1994). In resonance experiments, many measurements made on micro-cracked materials have shown that real and imaginary components of the elastic modulus are strain dependent. Indeed, resonance frequency and quality factor of the followed resonance modes have proved to be able to monitor damage as a function of the induced dynamic strain. In the nonlinear resonant approach, two hysteretic nonlinear parameters are defined, where the first is related to frequency (elastic modulus) and the second to quality factor (damping). However, the abovementioned NLH parameters are defined for one resonance mode i.e. in a very narrow frequency domain. In order to broaden the frequency domain, we recently developed an experimental method in which we considered different flexural resonances generated in composite plates. In harmonic generation experiments, one can
mechanisms and determine their respective energies. Therefore, correlation between nonlinear acoustics parameters of micro-cracked materials and acoustic emission signals is able to bring the necessary information related to the critical damage mechanisms whose presence lead to the failure of the material.
