Quantifying the anisotropic elasticity of 3D printed phononic artifacts with ultrasound for process monitoring

The layer-wise additive building technique utilized by 3D Printing (3DP)/Additive Manufacturing (AM) processes results in builds and parts with strong anisotropy. Also, with 3DP/AM, the intentional creation of intricate internal geometries and regulated compositions is possible, leading to exciting opportunities for generating anisotropic structures at the material level with optimized properties and superior performance. Accurate characterization of these anisotropic properties for specific applications is essential for optimizing their design and performance, as well as monitoring their quality in real-time during production. The current study introduces a new monitoring mechanism to evaluate the anisotropic characteristics of a build by examining the ultrasonic responses of Phononic Crystal Artifacts (PCAs), which are specially designed calibration pieces that represent the geometric and mechanical complexities of the build. But the PCAs are much simpler and smaller in size, making them easier and more cost-effective to manufacture, monitor, and assess compared to the actual build. Based on the Christoffel equation, the proposed monitoring approach extracts the elastic coefficients from the ultrasonically acquired waveforms and their corresponding speeds in three principal (one build-up and two lateral) and two additional (diagonal) wave propagation directions. The printed Polylactic Acid (PLA) material exhibits anisotropy of 3.07 % to 8.91 % in the reported experiments. The extracted directional elastic parameters are determined as the directional Young's moduli E1 = E2 = 2.59 GPa, E3 = 2.22 GPa; shear modulus, G13 = 0.94 GPa, and Poisson's ratios, υ12 = 0.29, and υ13 = 0.34. The obtained elastic parameters show that the lateral directions dominate the elasticity of the printed material in the build-up direction. The presented approach for non-destructive ultrasonic characterization, which is used to investigate the directional mechanical properties, can also be beneficial in developing a real-time quality monitoring system for 3DP/AM.