Characterization of temperature-induced stiffness changes in a C-PMR15 composite material by means of laser generated and detected ultrasound

Nine stiffness coefficients of a polymer-matrix composite material have been measured by a contactless process method which consists in the focusing of a pulsed laser beam on one side of a sample to generate acoustic waves through the material. A laser interferometric probe is used on the other side to detect the acoustic wavefronts. These devices are associated with a specific oven allowing the transmission of the optical beams. The nine coefficients are measured for several temperatures increased by steps up to the matrix glass-transition temperature. The changes of coefficients with temperature show anisotropic decreases of the stiffness properties. It is worth noting the changes of the shear coefficients that are associated with the decrease of the matrix properties.