Morphing panels offer opportunities as adaptive control surfaces for optimal system performance over a broad range of operating conditions. This work presents a design framework for multifunctional composites based on three types of laminae, viz., constraining, adaptive, and prestressed. Based on this framework, laminate configurations are designed to achieve multiple morphing modes such as stretching, flexure, and folding in a given composite structure. Multiple functions such as structural integrity, bistability, and self-actuation are developed. The composites are developed through a concurrent focus on mathematical modeling and experiments.
This research shows that curvature can be created in a composite structure by applying mechanical prestress to one or more of its laminae. Cylindrical curvature can be tailored using a prestressed lamina with zero in-plane Poisson's ratio. Analytical laminated-plate models, based on strain energy minimization, are presented in multiple laminate configurations to characterize composites with curvature, bistability, folding, and embedded smart material-driven actuation. Fabrication methods are also presented for these composite configurations. The mathematical models are validated experimentally using tensile tests and 3D motion capture.
The mechanics of an n-layered composite is explained through modeling of all the stacking sequences of the three generic laminae. Actuation energy requirement is found to be minimal in the constraining-prestressed-adaptive layer configuration. Bistable curved composites are developed using asymmetric prestressed laminae on either face of a core layer; these composites address the drawbacks of thermally-cured bistable fiber-reinforced polymeric composites. When the prestressed directions are orthogonal, the stable curvatures are weakly-coupled. The composite's domain of bistability and actuation requirements are quantified using a non-dimensional high-order strain model.
Active bistable composites are modeled and demonstrated using shape memory alloy (SMA) actuators in a push-pull configuration. Experiments show that the unactuated SMA dampens the composite's post-transition vibrations. Folds are created by laminating a prestressed layer across a crease. Fold angle is modeled using piecewise displacement functions to account for the low stiffness of a crease relative to its faces. Extensive model-based parametric studies are conducted in various laminate configurations to study the effect of laminae properties, dimensions, and prestress magnitude and orientation, on the composite's shape, stiffness, and actuation energy.
A thorough literature survey is conducted on the effect of various aerodynamic treatments on effective vehicle drag. A morphing fender skirt is demonstrated since it provides a good trade-off between drag reduction (0.038 points) and practical implementation. Through design, manufacturing, and testing, a lightweight, self-supported, and self-actuated morphing fender skirt is developed based on the multifunctional composites characterized at the coupon scale.
Intellectual Merit: Innovative stress-biased curved composites with an irreversible non-zero stress state are presented through this work. A framework for multifunctional composites, backed by analytical modeling tools and fabrication methods, is presented for the design of generic laminated composite-based morphing structures.
Broader Impact: Morphing structures can effectively contribute to the improved fuel economy in automobiles through reductions in aerodynamic drag and vehicle weight. The multifunctional composites, demonstrated using relatively inexpensive materials, are suitable for mass-market products. The composite framework enables applications in the fields of morphing aircraft and automobiles, soft robotics, and biomimetics.