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Morphing structures, defined as body panels that are capable of a drastic autonomous shape transformation, have gained importance in the aerospace, automotive, and soft robotics industries since they address the need to switch between shapes for optimal performance over the range of operation. Laminated composites are attractive for morphing because multiple laminae, each serving a specific function, can be combined to address multiple functional requirements such as shape transformation, structural integrity, safety, aerodynamic performance, and minimal actuation energy. This paper presents areview of laminated composite designs for morphing structures. The trends in morphing composites research are outlined and the literature on laminated composites is categorized based on deformation modes and multifunctional approaches. Materials commonly used in morphing structures are classified based on their properties. Composite designs for various morphing modes such as stretching, flexure, and folding are summarized and their performance is compared. Based on the literature, the laminae in an n-layered com-posite are classified based on function into three types: constraining, adaptive, and pre-stressed. A general analytical modeling framework is presented for composites comprising the three types of functional laminae. Modeling developments for each morphing mode and for actuation using smart material-based active layers are discussed. Results, presented for each deformation mode, indicate that the analytical modeling cannot only provide insight into the structure’s mechanics but also serve as a guide for geometric design and material selection.

V.S.C. CHILLARA and M.J. Dapino, “Review of morphing laminated composites,” Applied Mechanics Reviews, 72(1): 010801.2020. doi:10.1115/1.4044269

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Continuous layer jamming is an effective tunable stiffness mechanism that utilizes vacuum to vary friction between laminates enclosed in a membrane. In this paper, we present a discrete layer jamming mechanism that is composed of a multilayered beam and multiple variable pressure clamps placed discretely along the beam; system stiffness can be varied by changing the pressure applied by the clamps. In comparison to continuous layer jamming, discrete layer jamming is simpler as it can be implemented with dynamic variable pressure actuators for faster control, better portability, and no sealing issues due to no need for an air supply. Design and experiments show that discrete layer jamming can be used for a variable stiffness co-robot arm. The concept is validated by quasi-static cantilever bending experiments. The measurements show that clamping 10% of the beam area with two clamps increases the bending stiffness by around 17 times when increasing the clamping pressure from 0 to 3 MPa. Computational case studies using finite element analysis for the five key parameters are presented, including clamp location, clamp width, number of laminates, friction coefficient, and number of clamps. Clamp location, number of clamps, and number of laminates are found to be most useful for optimizing a discrete layer jamming design. Actuation requirements for a variable pressure clamp are presented based on results from laminate beam compression tests.

Y. ZHOU, L.M. Headings, and M.J. Dapino, “Discrete layer jamming for variable stiffness co-robot arms,” ASME Journal of Mechanisms and Robotics. Vol. 12(1): 015001, 2020.  doi.org/10.1115/1.4044537

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Fe-Ga alloys (Galfenol) are structural magnetostrictive materials which undergo magnetization changes when subjected to mechanical stress. They are machinable and can withstand large normal or shear stresses. Based on these unique features, this study develops an impact force sensor which consists of an electromagnet, magnetic circuit, cantilevered Fe-Ga alloy beam, and pickup coil. The external impact force generates a stress-induced flux density that is measured by the pickup coil. An axial impact sensor based on a FeGa rod is constructed for comparison. Analytical modeling shows that the sensitivity of the cantilevered beam configuration is 11.27 times higher than that of the rod configuration. Three different geometries, including a rectangular beam, a uniform I beam, and a tapered I beam, are designed and compared. Analytical modeling shows that the tapered I beam exhibits maximum sensitivity. The optimized tapered I beam-based sensor is constructed experimentally and benchmarked against a similar sensor based on a Fe-Ga rod. A nonlinear Levenberg-Marquardt fitting method is used to correlate the input impact force with the resulting flux density variation. Experimental results show that the measurement error is within 5.8% for various impact amplitudes.

L. SHU, J. Yang, B. Li, Z. DENG, and M.J. Dapino, “Impact force sensing with magnetostrictive Fe-Ga alloys,” Mechanical Systems and Signal Processing, Vol.139, 106418, May 2020.