Ultrasonic characterization of compressional and shear wave properties for additively manufactured photopolymers

Advanced applications of polymer additive manufacturing (AM) require knowledge of the material acoustic and complex elastic properties. Recently, ultrasonic nondestructive evaluation (NDE) has been applied to the characterization of AM polymers; however, the available information is limited and there are little data on shear‐wave and complex elastic properties. In this study, a two‐sample method using ultrasonic measurements of compressional and shear phase velocity and attenuation was used to experimentally determine the complex elastic properties of 14 AM photopolymers manufactured using PolyJet systems. In this method, two samples of identical material properties but different thicknesses are measured using ultrasonic contact transducers, with the change in the time of arrival and amplitude providing the phase speed and attenuation. In order to determine the optimal thickness difference between the two samples, preliminary sets of samples were printed in a range of thicknesses, without a priori knowledge of the material properties of the AM polymers. Using a subset of these results, further analysis and optimization was conducted to better select the two thicknesses to use for each material sample. The results provided here are expected to aid in experimental design for characterization of polymers. [Work supported by the Office of Naval Research.]