Experimental Study of the Acoustoelastic Effect on Woven Carbon/Epoxy Composites

The acoustoelastic effect relates the variation of the velocity of a wave propagating in an elastic body with the variation of stress in the same body. Using the acoustoelastic effect, the state of stress of a mechanical component can be evaluated nondestructively by measuring variations of ultrasonic wave velocity. In practical terms, the relation between wave velocity and stress is determined by a constant commonly referred to as acoustoelastic constant. The aim of this work is to experimentally determine the acoustoelastic constant of a woven carbon/epoxy laminate. In tensile tests, predetermined load values were applied to the samples at the same time the time-of-flight (TOF) variation of the ultrasonic wave traveling in the sample was measured. In the experiments, the ultrasonic wave traveled along one of the main fiber directions of the sample and the load was applied in the same direction. The value of the acoustoelastic constant obtained for the laminate was −0.37 ns/MPa with standard deviation of 0.07 ns/MPa. Knowing the acoustoelastic constant of a material, it allows evaluation of the state of stress of the material in question using ultrasonic waves.