Mechanical characterization of additively manufactured polymers using ultrasonic nondestructive testing

Ultrasonic nondestructive testing (NDT) can be used to relate the print settings of additively manufactured polymers to their macroscopic elastic properties. We present a comparison of the measurement of angle- and frequency-dependent ultrasonic transmission through a flat plate to predictions using a multiscale model that considers infill geometry and constitutive material properties. The experiment is an immersion test that uses a point source and synthetic linear array to measure the transmission coefficient from 0.2 to 1 MHz over a wide range of incident angles. Samples were fabricated using fused deposition modeling (FDM) to print infilled plates with polylactic acid (PLA) filament. Transmission measurements were compared to predictions from a multiscale model consisting of a finite element model to predict the effective anisotropic stiffness based on an assumed infill geometry and PLA material properties and an acoustic reflection-transmission model for an anisotropic elastic plate submerged in water based on the work of Rokhlin and Wang [J. Acoust. Soc. Am. 112, 822 (2002)]. Minimization of the difference between the measured and modeled transmission coefficient for all angles and frequencies by varying model inputs provides an improved understanding of the effects of the print settings on the as-built mechanical properties for 3D-printed materials.