Thermally driven morphing and snap-through behavior of hybrid laminate shells

Analytical and experimental results are presented regarding the nonlinear temperature-curvature relationship displayed by composite bimorph shells. Snap-through action, driven solely by temperature change, is demonstrated using fiberCmetal hybrid laminates.These laminates exploit the high coefficient of thermal expansionmismatch between composites and metals to yield thermal bimorphs with tailorable properties. To predict the potentially nonlinear response of these laminates, an energy-based multistability model is developed and made available online. The model utilizes experimentally measured one-dimensional thermally induced curvatures as input parameters to predict a corresponding shell's two-dimensional flexural behavior. Initial curvature is found to be a critical component in enabling snap-through behavior, especially when partnered with highly orthotropic internal moments. Interestingly, the 0_n-90_n-class of unsymmetric laminates popular in the study of thermally induced bistability are shown to be inherently incapable of displaying thermally driven snap-through behavior, regardless of initial curvature. Modeling results compare well with experiments for a square-planform hybrid laminate. The potential impact of this work is the realization of passively controlled, variable geometry structures that can be triggered to change shape at certain temperatures or within specified temperature ranges. Applications include flow and cooling control of gas turbine engines, spacecraft passive thermal control systems, and bimorph-based micro-electromechanical systems.