Additive manufacturing (AM) is rapidly becoming a local manufacturing modality in fabricating complex, custom-designed parts, providing an unprecedented form-free flexibility for custom products. However, significant variability in part geometric quality and mechanical strength due to the shortcomings of AM processes has often been reported. Presently, AM generally lacks in situ quality inspection capability, which seriously hampers the realization of its full potential in delivering qualified practical parts. Here, we present a monitoring approach and a periodic structure design for developing test artifacts for in situ real-time monitoring of the material and bonding properties of a part at fiber/bond-scale. While the production method used in current work is filament based, the proposed approach is generic as defects are always due to materials in a bonding zone and their local bonding attributes in any production modality. The artifact design detailed here is based on ultrasonic wave propagation in phononic coupons consisting of repeating substructures to monitor and eventually to assess the bond quality and placement uniformity—not only for geometry but also for defect states. Periodicity in a structure leads to the dispersion of waves, which is sensitive to geometric/materials properties and irregularities. In this proof-of-concept study, an experimental setup and basic artifact designs are described and off-line/real-time monitoring data are presented. As a model problem, the effects of printing speed on the formation of stop bands, wave propagation speeds and fiber placement accuracy in samples are detected and reported.
At the micrometer-scale and below, particle adhesion becomes particularly relevant as van der Waals force often dominates volume and surface proportional forces. The rolling resistance of microparticles and their critical rolling angles prior to the initiation of free-rolling and/or complete detachment are critical in numerous industrial processes and natural phenomenon involving particle adhesion and granular dynamics. The current work describes a non-contact measurement approach for determining the critical rolling angle of a single microparticle under the influence of a contact-point base-excitation generated by a transient displacement field of a prescribed surface acoustic wave pulse and reports the critical rolling angle data for a set of polystyrene latex microparticles.
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