Thermosetting SMC resin characterization using linear and nonlinear ultrasonics

The material properties of viscous pastes used for the fabrication of thermosetting SMC (Sheet Molding Compound) have been investigated with ultrasonic spectroscopy working in linear and nonlinear modes. Attenuation versus frequency curves exhibit variations due to the time evolution of unsaturated polyester (UP) resin. A power amplifier was needed because of the high attenuation coefficient of resins. Different ultrasonic responses were measured versus the age and the proportion of gas bubbles and clusters in the paste. We present experimental results and show the interest of using nonlinear acoustics for nondestructive characterization of SMC.