MEASUREMENT BY LASER-GENERATED ULTRASOUND OF 4 STIFFNESS COEFFICIENTSOF AN ANISOTROPIC MATERIAL AT ELEVATED-TEMPERATURES

Ultrasonic waves are generated through a composite material by means o f a noncontact technique. It uses a Nd:Yag LASER for the generation an d an interferometric probe for the detection of acoustic waveforms. Fr om a suitable set of experimental data, an inversion scheme is used fo r the recovering of four stiffness coefficients. They characterize the elasticity in a principal plane of symmetry of the material which exh ibits an orthorhombic symmetry. The measurements are performed at vari ous temperatures, elevated by steps up to 300 degrees C for two specim en. The sensitivity of the method appears convenient to measure the te mperature induced stiffness changes. The anisotropic degradation of th e material properties are then pointed out.