Evaluation of the water content in phenolic resin plates via nonlinear ultrasonic measurements

In this study, we dispose of 12 phenolic resin samples at the diffusion process equilibrium with a water content controlled (from 0% to 5% of the dry mass). In these samples, celerity, attenuation and nonlinear coefficient β behaviour with water content is estimated. Nonlinear coefficient is evaluated with a contact phase modulation method. This method is based on parametric interaction between two waves with very different frequencies. It induces a phase variation of the high frequency toneburst which is proportional to the nonlinear coefficient β. The nonlinear coefficient exhibits a non monotonous behaviour with the water content and a better sensitivity than the linear parameters in a restricted range of water content.Complementary series of experiments have been conducted in order to study non homogeneous water content situations. Linear and nonlinear parameters are measured. The theoritical water profile through the sample thickness is known and used in a pseudo‐spectral numerical code, in wich the ...