Variable stiffness characteristics of embeddable multi-stable composites

The possibility to achieve shape adaptation provides structural systems with the potential to adjust for optimal operation in a wide range of conditions. The formidable challenges posed by shape adaptation, and particularly in morphing applications, can be potentially addressed through the development of distributed compliance systems featuring highly directional structural properties. These characteristics can be further enhanced by embedding in such systems elements featuring variable stiffness. In this paper, a novel type of embeddable variable stiffness elements exploiting thermally-induced multi-stability in unsymmetrically laminated composites is presented. A tailored lay-up exhibiting spatially distirbuted stacking sequences is implemented to achieve multi-stability even when restricting two opposing edges. The difference between the structural responses leading exhibited by the multiple stable shapes of the designed composites are numerically investigated. The restoring force for each stable state is examined yielding a significant variability in the stiffness. Experimental specimens are manufactured and tested showing good agreement with the numerical results, validating the proposed variable stiffness implementation.