Ultrasonic Characterization of Damage in Thick FRP Composites

This paper presents the results of an investigation into the applicability of ultrasonic techniques for obtaining quantitative measures of changes in effective properties of glass-fiber reinforced polyester composite structural members manufactured by the pultrusion process. Immersion techniques were used to measure the through-thickness ultrasonic velocities, as a function of input frequency, in pristine specimens, as well as after the same specimens had been damaged; damage was induced by three-point bending. Specimens were evaluated in an unloaded condition, and distinct changes were observed between the measured velocities of the pristine sample and those after the introduction of damage. The measured changes were found to be greater than the experimental error associated with the test procedure.