Recent studies have exemplified the potential for curved origami-inspired acoustic arrays to focus waves. Yet, reconfigurable structures that adopt curvatures are often difficult to translate to practice due to mechanical deformation of the facets that inhibit straightforward folding. In addition, not all tessellations that curve upon folding are also flat-foldable, which is a key advantage of portability inherent to many origami-inspired structures. This research introduces a new concept of partially activated reconfigurable acoustic arrays as a means to mitigate these drawbacks. Here, tessellations are studied where a subset of the facet surfaces are considered to radiate acoustic waves. The analytical results reveal focusing behaviors in such arrays that are otherwise not manifest for the array when fully activated. The focused waves are more intense in amplitude and space for partially activated arrays than fully activated counterparts. These trends are verified by experiment and are also found to be applicable to multiple reconfigurable array geometries. The results encourage broader study of the design space accessible in reconfigurable arrays to capitalize on all of the functionality afforded by origami-inspired wave guiding structures.
Curved surfaces are often used to radiate and focus acoustic waves. Yet, when tessellated into reconfigurable surfaces for sake of deployability needs, origami-inspired acoustic arrays may be challenging to hold into curved shape and may not retain flat-foldability. On the other hand, deployable mechanisms such as the Hoberman ring are as low-dimensional as many origami-tessellations and may maintain curved shape with ease due to ideal rigid bar compositions. This research explores an interface between a Hoberman ring and Miura-ori tessellation that maintain kinematic and geometric compatibility for sake of maintaining curved shapes for sound focusing. The Miura-ori facets are considered to vibrate like baffled pistons and generate acoustic waves that radiate from the ring structure. An analytical model is built to reveal the near field acoustic behavior of acoustic arrays resulting from a Hoberman-Miura system synthesis. Acoustic wave focusing capability is scrutinized and validated through proof-of-principle experiments. Studies reveal wave focusing phenomena distinct to this manifestation of acoustic array and uncover design and operational influences on wave focusing effectiveness. The results encourage exploration of new interfaces between reconfigurable mechanisms and origami devices where low-dimensional shape change is desired.
Previous research has developed a process for producing strong fiber reinforced polymers (FRP)-metal joints via ultrasonic additive manufacturing (UAM), and structural tests have been conducted to characterize the mechanical properties of the joints. In this research, an analytical model and a finite element analysis (FEA) model are developed for UAM-produced FRP-metal joints to provide better joint design and application insights. The analytical model applies both the thick-wall cylindrical pressure vessel theory and Tsai-Wu failure criterion to characterize the stress condition in the embedded fibers and the failure mode when tension is applied to the joint. Comparing the analytical model and experimental results of two different sample configurations, the model is able to predict the peak load of the joint with given material properties and joint geometries. Based on the analytical model, an FEA model is built using LS-DYNA to simulate the tensile testing of FRP-metal joint using shell mesh by homogenizing the hybrid portion of the joint. The stress maps obtained from the FEA model for two joint designs show similar distributions when compared to measured digital image correlation (DIC) strain maps, indicating that the failure modes match the experimental results. The FEA simulation results agree well with the experimental result for peak load and displacement at fracture, with an error of less than 5%.
Tessellated acoustic arrays inspired by origami structures are suggested to enable wave focusing by exploiting curvatures realized by folded configurations of the array transducer elements. The use of origami-inspired folding patterns also cultivates great portability for space-limited applications. Yet, maintaining curvatures may prohibit feasible implementation of a tessellated been studied for the acoustic energy focusing usage. This research proposes an alternative technique to achieve wave focusing with tessellated arrays that do not realize curvatures upon folding. Here, the partial activation of a tessellated array is exploited to result in constructive interference that realizes a nearfield focal region. The modeling approach to examine partially activated arrays is presented and verified against numerical simulations. Then, the changes in nearfield focusing characteristics are correlated with corresponding changes in partial activation and array folding extent. The opportunities to exploit the partial activation of relatively simple origami-inspired array structures are examined to identify strategies to simplify implementation of portable, folding acoustic arrays in applications.
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