Preliminary investigation of self-sensing in piezoelectric bistable laminates

Abstract

Bistable laminated composites are attractive for morphing structures because they can hold deformed stable shapes without any external energy and require actuation only to switch between shapes. They offer opportunities for shape morphing, energy harvesting, and flow control devices. Piezoelectric macrofiber composites (MFC) embedded in bistable laminates have been demonstrated for actuation and energy harvesting. However, their relatively high stiffness, relatively complex architecture, and arbitrary fiber orientation limit their ability to sense shape change in bistable laminates. There has been little work on the integration of sensing methods to monitor an adaptive structure’s shape; shape sensing has been investigated mainly for the detection of snap-through events. In this paper, we present self-sensing curved bistable laminates layered with piezoelectric PVDF films that can sense smooth changes as well as abrupt snap-through transitions. Measurement of smooth changes in the laminate’s curvature is enabled by an automated drift compensation charge amplifier with an extremely low cutoff frequency of 0.01 mHz. The sensing function is demonstrated on bistable laminates created using mechanical prestress. Two sensor layers are configured in the composite such that one measures change in curvature and the other measures snap-through response. The shapes measured by the sensor in terms of voltage correlate well with the shapes measured with a 3D motion capture system. An analytical model is developed to relate curvature change to voltage output and is found to be in good agreement with the measured curvature-voltage sensitivities. The weakly coupled shapes of the laminate and the low cross sensitivity of PVDF enable real-time measurement of the principal curvatures.