ULTRASONIC MEASUREMENT OF YOUNGS MODULUS IN DOG-BONE-SHAPED SAMPLES SUBJECTED TO A TENSILE-STRESS

Thermostructural applications of fibrous ceramic composites require th e knowledge of their behavior in severe service conditions (high tempe rature, high stress, oxidizing atmosphere). Previous results have show n that ultrasonic measurements of Young's modulus are particularly sui table to monitor oxidation mechanisms at high temperature in these mat erials. Such measurements in materials subjected to tensile stress are possible by modeling the ultrasonic wave propagation in ''dog-bone'' specimens. The tensile specimens are modeled as a ''slender bar'' with two heads assumed to be thin plates (thickness less than the wave len gth). The frequency analysis of the signal allowed the determination o f the optimal dimensions of the specimen and the calculation of time c orrections in order to evaluate the real ultrasonic propagation time t 0 in the material. The ultrasonic wave velocity and the Young's modulu s are then derived from the knowledge of t0.