Bistable laminated composites are candidates for morphing structures as they are capable of large deflections without actuation and can exhibit drastic shape change when actuated. The coupled stable shapes of traditional thermally-cured fiber-reinforced polymeric laminates are the result of a globally-prestressed matrix and hence cannot be tailored independently. In this paper, we address this limitation by presenting an equivalent laminated composite in which mechanical prestress is applied to the matrix of selected laminae to achieve bistability; shapes are tailored individually by changing the magnitude of prestress in each lamina. The application of mechanical prestress is associated with an irreversible non-zero stress state which when combined with smart materials with controllable stress-states results in multifunctional morphing composites. The proposed bistable composite consists of a core that is sandwiched between two prestressed fiber-reinforced elastomers and is actuated by shape memory alloy wires. Composite mechanics is modeled analytically by incorporating the material and geometric nonlinearities of prestressed elastomers and the 1-D constitutive behavior of a shape memory alloy (SMA). The experimentally-validated model of the passive composite has an accuracy of 94%. A sensitivity study is conducted that shows the effects of prestress and SMA properties on composite curvature and serves as a guide for the design of active bistable composites. Simulations with the chosen parameter set resulted in the exact compensation of the nonlinear effects of applied stress and phase transformation kinetics to yield a linear response of composite curvature to Martensitic volume fraction.
Venkata Siva C. Chillara and Marcelo J. Dapino, "Bistable morphing composites with selectively pre-stressed laminae," Proc. SPIE 10165, Behavior and Mechanics of Multifunctional Materials and Composites 2017, 101650Y (Presented at SPIE Smart Structures and Materials + Nondestructive Evaluation and Health Monitoring: March 28, 2017; Published: 11 April 2017); https://doi.org/10.1117/12.2259787.
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