Morphing structures, defined as body panels that are capable of a drastic autonomous shape transformation, have gained importance in the aerospace, automotive, and soft robotics industries since they address the need to switch between shapes for optimal performance over the range of operation. Laminated composites are attractive for morphing because multiple laminae, each serving a specific function, can be combined to address multiple functional requirements such as shape transformation, structural integrity, safety, aerodynamic performance, and minimal actuation energy. This paper presents a review of laminated composite designs for morphing structures. The trends in morphing composites research are outlined and the literature on laminated composites is categorized based on deformation modes and multifunctional approaches. Materials commonly used in morphing structures are classified based on their properties. Composite designs for various morphing modes such as stretching, flexure, and folding are summarized and their performance is compared. Based on the literature, the laminae in an n-layered composite are classified based on function into three types: constraining, adaptive, and prestressed. A general analytical modeling framework is presented for composites comprising the three types of functional laminae. Modeling developments for each morphing mode and for actuation using smart material-based active layers are discussed. Results, presented for each deformation mode, indicate that the analytical modeling can not only provide insight into the structure's mechanics but also serve as a guide for geometric design and material selection.

Fiber-reinforced asymmetric laminates fabricated at elevated temperatures may exhibit bistability at room temperature. The magnitude of deformation in each shape depends primarily on the curing temperature. This paper presents a novel asymmetric bistable laminate that is fabricated at room temperature and whose stable shapes are analogous to those of a fiber-reinforced laminate. The proposed laminate is composed of a stress-free isotropic core layer sandwiched between two asymmetric, mechanically-prestressed, fiberreinforced elastomeric layers. Its stable shapes can be independently tuned by varying the prestress in each elastomeric layer. The mechanics of the laminate are studied using an analytical laminated-plate model that includes the geometric and material nonlinearities associated with large deformations caused by highly-strained elastomers. The effect of core modulus, core thickness, elastomer-core width ratio, and laminate size is examined through a parametric study. Laminate samples are fabricated in the 90 • /core/0 • configuration for model validation. The simulated stable shapes of the laminate are in agreement with the measured shapes. The dynamic response of the laminate during shape transition is measured using a motion capture system.

This work presents smart laminated composites that enable morphing vehicle structures. Morphing panels can be effective for drag reduction, for example, adaptive fender skirts. Mechanical prestress provides tailored curvature in composites without the drawbacks of thermally induced residual stress. When driven by smart materials such as shape memory alloys, mechanically-prestressed composites can serve as building blocks for morphing structures. An analytical energy-based model is presented to calculate the curved shape of a composite as a function of force applied by an embedded actuator. Shape transition is modeled by providing the actuation force as an input to a one-dimensional thermomechanical constitutive model of a shape memory alloy wire. A design procedure, based on the analytical model, is presented for morphing fender skirts comprising radially configured smart composite elements. A half-scale fender skirt for a compact passenger car is designed, fabricated, and tested. The demonstrator has a domed unactuated shape and morphs to a flat shape when actuated using shape memory alloys. Rapid actuation is demonstrated by coupling shape memory alloys with integrated quick-release latches; the latches reduce actuation time by 95%. The demonstrator is 62% lighter than an equivalent dome-shaped steel fender skirt.

Pressure-actuated elements can be embedded in morphing panels to achieve continuous control of shape and stiffness. This paper presents a multifunctional laminated composite that exhibits a curved geometry due to intrinsic mechanical prestress and a change in curvature when fluid (liquid or gas) contained in one of its laminae is pressurized. The composite is composed of a mechanically-prestressed layer, a fluidic layer, and a constraining layer. The composite can be driven to any desired shape up to a flat limiting shape through modulation of pressure in its fluidic layer. An analytical model is developed to characterize the quasi-static response of such a composite to the applied fluid pressure for various laminate stacking sequences. A parametric study is also conducted to study the effects of the dimensions of the fluid channel and its spatial location. Composite beams are fabricated in the laminate configuration that requires the least actuation effort for a given change in curvature. Pneumatic pressure is applied to the composite in an open-loop setup and its response is measured using a motion capture system. The simulated response of the composite is in agreement with the measured response.

Bistable laminates offer opportunities for shape morphing, energy harvesting, and flow control devices. Smart materials such as piezoelectric macrofiber composites and shape memory alloys have been embedded in bistable laminates to actuate or harvest energy. However, sensor systems capable of measuring bistable shapes and snap-through events are lacking. In this paper, we present curved bistable laminates layered with piezoelectric PVDF films that can sense smooth shape changes as well as abrupt snap-through transitions. Near-static measurement is facilitated by a drift compensated charge amplifier with a large time constant that converts the sensor's charge output into a measurable voltage with minimal drift error. The sensing function is demonstrated on mechanically-prestressed bistable laminates. The laminated composites include two sensor layers such that one measures the changes in curvature and the other measures snap-through events. An analytical model is presented in which strains and curvatures calculated using a laminated-plate model are fed into a linear piezoelectric model to calculate voltage. Shapes measured by the sensors correlate well with shapes measured using a 3D motion capture system. A model-based analysis is performed to understand the laminates' design space.