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Steady-state traveling waves in structures have been previously investigated for a variety of purposes including propulsion of objects and agitation of a surrounding medium. In the field of additive manufacturing, powder bed fusion (PBF) is a commonly used process that uses heat to fuse regions of metallic or polymer powders within a loose bed. PBF processes require post-process removal of loose powder, which can be difficult when blind holes or complex internal geometry are present in the fabricated part. Here, a preliminary investigation of a simple part is conducted examining the use of traveling waves for post-process de-powdering of additively manufactured specimens. The generation of steady-state traveling waves in a structure is accomplished through excitation at a frequency between two adjacent resonant frequencies of the structure, resulting in two-mode excitation. This excitation can be generated by bonded piezoceramic elements actuated by a sinusoidal voltage signal. The response of the structure is affected by the parameters of the excitation, such as the particular frequency of the voltage signal, the placement of the piezoceramic actuators, and the phase difference in the signals applied to different actuators. Careful selection of these parameters allows adjustment of the quality, wavelength, and wave speed of the resulting traveling waves. In this work, open-top rectangular box specimens composed of sintered nylon powder and coated with fine sand are used to represent freshly fabricated parts yet-to-be cleaned of un-sintered powder. Steady-state traveling waves are excited in the specimens while variations in the frequency content and phase differences between actuation points of the excitation are used to affect the characteristics of the dynamic response. The effectiveness of several response types for the purpose of moving un-sintered nylon powder within the specimens is investigated. 

The flexibility offered by additive manufacturing (AM) technologies to fabricate complex geometries poses several challenges to non-destructive evaluation (NDE) and quality control (QC) techniques. Existing NDE and QC techniques are not optimized for AM processes, materials, or parts. Such lack of reliable means to verify and qualify AM parts is a significant barrier to further industrial adoption of AM technologies. Electromechanical impedance measurements have been recently introduced as an alternative solution to detect anomalies in AM parts. With this approach, piezoelectric wafers bonded to the part under test are utilized as collocated sensors and actuators. Due to the coupled electromechanical characteristics of piezoelectric materials, the measured electrical impedance of the piezoelectric wafer depends on the mechanical impedance of the part under test, allowing build defects to be detected. This paper investigates the effectiveness of impedance-based NDE approach to detect internal porosity in AM parts. This type of build defects is uniquely challenging as voids are normally embedded within the structure and filled with unhardened model or supporting material. The impact of internal voids on the electromechanical impedance of AM parts is studied at several frequency ranges.