Evaluation of the moisture content in phenolic resin via acoustic measurements

Abstract

Moisture absorption is a water diffusion process known to alter many of the mechanical properties of polymers and polymer-based composites. Ultrasonic waves are sensitive to such changes of properties and allow in situ measurements to be performed. This paper presents linear and nonlinear ultrasonic measurements on 12 phenolic resin plates with water contents ranging from 0% to 5% of their dry mass. Linear parameters are evaluated by an insertion/ substitution spectroscopy method yielding to a representation of the evolution, with frequency, of the attenuation and of the phase velocity of acoustic waves propagating in each sample. Nonlinear Β coefficient of each sample is determined by a contact phase modulation method. The evolution, with moisture content, of acoustic parameters such as the attenuation and the phase velocity of acoustic waves propagating at a given frequency, the slope of their attenuation with frequency, and the Β coefficient of each sample is then studied. Results are discussed in terms of sensitivity. © 2006 American Institute of Physics.