Acoustic Nondestructive Characterization of Metal Pantographs for Material and Defect Identification

Mechanical metamaterials offer an approach to design materials beyond bulk properties by changing their geometry. Due to the complex architecture, the fabrication of these material systems is often enabled by additive manufacturing. However, production-related defects can occur and affect the material functionality, so that rapid and reliable characterization methods are required. In this work, we studied acoustic analysis, specifically a combination of classical resonance analysis and decay time observation, for nondestructive characterization of metamaterials. We focused on metallic pantographs which are metamaterials with high elongation. All samples were manufactured by laser powder bed fusion with three different base materials: NiTi, Fe-based, and Ti6Al4V. Experiments complimented by simulations were carried out to evaluate vibration behavior stimulated by a low energy impact. Geometrical design parameters and major defects such as missing elements resulted in changes in the acoustic spectrum as well as the decay time of the signal. Simulations enable the interpretation of the occurring modes and offer a possibility to study a much wider parameter space. Acoustic characterization of metamaterials is promising for scaling the technology of metamaterials for industrial applications due to the simplicity and low costs. In the future, further investigations are needed to optimize the simulations for complex geometries and evaluate alternatives for the acoustic stimulation of the samples.