Thermally induced multistability in cured shapes of hybrid composite laminates

Compliant structures derived from multistable laminates have attracted significant research interest due to their ability to transition between multiple equilibrium shapes. However, most existing designs are limited to bistable behavior or rely on the assembly of multiple elements to achieve higher-order multistability, which restricts their applicability in continuous morphing structures. These structures can exhibit symmetrically or antisymmetrically curved configurations depending on geometry and layup, with square laminates typically showing symmetrically curved bistable shapes and rectangular laminates exhibiting antisymmetrically curved bistable shapes. Symmetric curved shapes in rectangular bistable laminates can be achieved by tailoring the stiffness distribution through additional plies. Laminates designed with such customized layups are referred to as hybrid bistable symmetric laminates (HBSLs). Most center-fixed HBSLs reported in the literature exhibit two symmetric stable shapes, along with several intermediate unstable configurations influenced by boundary conditions and material properties. However, bistable behavior alone does not satisfy the requirements of continuous shape-changing structures, which demand more than two stable configurations. This study investigates selected HBSL layups with a center-fixed boundary condition that exhibit more than two equilibrium configurations, enabled by a tailored hybrid composite–aluminum layup. A fully nonlinear finite element framework is first employed to characterize the cured multistable shapes. The presence of multistability is then further confirmed using a Rayleigh–Ritz-based semi-analytical approach. Finally, experimental results are used to validate the predicted multistable behavior of HBSLs through comparisons of displacement profiles. The results demonstrate that the proposed laminates can achieve up to four stable configurations, with good agreement between numerical, semi-analytical, and experimental predictions, showing discrepancies generally within 6% for the primary shapes, with slightly larger errors observed for the intermediate shapes. The findings highlight the potential of HBSLs for highly flexible morphing structures with smooth shape transitions, offering promising applications in adaptive structures, deployable systems, and advanced shape-morphing components.