MFC-actuated snap-through in bi-stable VAT composites for enhanced energy harvesting bandwidth

Abstract Composite laminates with unsymmetric layups can exhibit two stable equilibrium states at room temperature, known as bi-stability, due to residual thermal or hygrothermal stresses. Transition between these states occurs via snap-through actuation, which can be triggered by external excitation, shape memory alloys, or voltages applied to piezoelectric layers. While many factors such as fiber profile, geometry, actuator placement, and environmental conditions influence bi-stable behavior, limited research has explored the role of variable angle tow (VAT) composites in this context. This study addresses this gap by investigating the bi-stable response of VAT laminates, with a particular focus on the slip-strain effects introduced during actuator bonding, an often-overlooked factor that does not contribute to active deformation but affects stability. A large deformation kinematic model is developed, with transverse displacement and in-plane strains expressed using polynomial functions. The governing equations, accounting for thermal and hygrothermal residual strains, are derived using the principle of minimum potential energy and solved via the Rayleigh–Ritz method. Stability is assessed using the Jacobian matrix derived from the second-order potential energy. The influence of fiber angle profiles on snap-through loads, transverse displacements, and the frequency bandwidth of cross-well oscillations is systematically studied under both thermal loading and macro-fiber composite actuation. Comparative analyses between constant stiffness and curvilinear fiber laminates reveal that VAT configurations can significantly broaden the oscillation bandwidth, an essential factor for effective energy harvesting. These findings demonstrate the potential of VAT composites for advanced multifunctional structures and provide quantitative guidance for their application in bi-stable energy harvesting systems.