Morphing of Bistable Composite Laminates Using Distributed Piezoelectric Actuators

The use of bistable unsymmetric cross-ply laminates for morphing application has received growing attention in the last few years. So far, most studies use large rectangular piezoelectric Macro Fiber Composite (MFC) patches bonded at the center of the laminate to induce snap-through. However, the use of large rectangular MFC patches bonded in the center of the laminates significantly influences the shape of the laminate by greatly reducing the curvature at the midsection of the laminate where the MFC patches are bonded. This paper presents a study where narrow cocured MFC strips distributed over the entire surface are used to induce snap-through of unsymmetric cross-ply laminates. This MFC configuration allows having a more uniform curvature in the laminate. Since the strips are bonded on both sides, reverse snap-through should be obtained. The study was both theoretical and experimental. A finite element nonlinear analysis was used to predict the two stable cylindrical configurations and the snap-through induced by MFC actuation. For the experimental study, a laminate-MFC structure was manufactured and tested. The shapes were measured using a 3D image correlation system as a function of applied voltage. Good correlations for the cylindrical shape and displacement field were observed. 1. Introduction The use of bistable composites for morphing application has received growing attention the last few years. The key characteristic of bistable structures is that they possess two stable equilibrium shapes and that they can be changed from one shape to the other by a simple snap-through action. Morphing can be obtained by alternating between these two shapes. Well-known bistable structures are unsymmetrically laminated composite plates [1–4]. For example, a two-layer [0/90]T laminate that is flat at its elevated cure temperature, as in Figure 1(a), cools from its cure temperature to have two equilibrium configurations. One configuration is cylindrical with a large curvature in the -direction, Figure 1(b). The other configuration is cylindrical with a large curvature in the -direction, Figure 1(c). The curvatures for the two configurations are equal but of opposite signs, and the laminate can be changed from one configuration to the other by a simple snap-through action initiated by applying equal and opposite moments to the edges of the laminate. Analysis indicates that there is a third equilibrium configuration which is a saddle shape, Figure 1(d). However, this shape is unstable and is not observed in practice. Due to their bi stability, unsymmetric