Moisture Effects on the Dimensional Stability of Bistable Carbon/Epoxy Laminates

ABSTRACT Bistable composite laminates are attractive because they can switch between two stable shapes without continuous energy input, enabling applications in morphing structures and energy harvesting devices. However, moisture significantly affects their mechanical response, potentially modifying curvature, snap‐through behavior, and even suppressing bistability. This study investigates the effects of moisture absorption on the shape change and bistable behavior of carbon fiber/epoxy laminates through a combined experimental and numerical approach. Laminates with different stacking sequences were manufactured and exposed to controlled moisture environments. Diffusion coefficient, moisture expansion, and resulting deflection were measured under both symmetric and asymmetric absorption conditions. To analyze the transient behavior, a finite element model was developed to simulate moisture diffusion and deformation. Moisture transport was modeled as a time‐dependent process governed by the mass diffusion equation, producing concentration gradients within the laminate. The deformation was related to the local moisture concentration through the elastic equilibrium equations for transversely isotropic laminates. The numerical predictions showed good agreement with measurements of water uptake and deflection. Results indicate that moisture absorption generally reduces the curvature of bistable laminates, while asymmetric absorption can initially increase curvature in unidirectional laminates, providing a predictive tool for analyzing moisture‐driven shape changes in composites.