Analysis of multistable variable stiffness composite plates

This paper presents a new concept for morphing composite structures based on variable stiffness composite plates. The variable stiffness morphing laminate proposed in this paper consists in a modified version of a straight fiber laminate composed of two regions, one with symmetric and the other with unsymmetric stacking sequence. Since there is a lay-up mismatch where the two regions meet, stress concentrations are expected to occur when straight fibers are used. A solution to mitigate this effect in which the fibers are allowed to vary smoothly along the plane from one region to the other is analyzed. The particular trajectories followed by the curved fibers were designed such that the plate can be manufactured using Advanced Fiber Placement technology (AFP). A finite element analysis of the laminate is performed to predict its out-of-plane displacements for the two possible stable configurations that may be obtained after the curing process. Then, the plate may be snapped from one shape to the other with the application of a force. This snap-through behavior is analyzed and compared with the original straight fiber laminate. The concept of a bistable Variable Stiffness Panel (VSP) composed of regions of symmetric and unsymmetric lay-ups that preserve the tangential continuity of the fibers could be of great importance in morphing or shape-adaptable structures for aerospace applications, such as winglets or flaps.