Distributed sensing using piezoelectric sensors have been widely studied on shell-type structures. Usually, sensing signals by piezoelectric sensors are contributed by both membrane and bending strains which are always closely coupled so that either of them is not easy to be extracted from the physical output signal. Based on the direct flexoelectric effect, flexoelectric materials are promising transducers with capability of monitoring the structural vibration especially the bending behavior. In this study, a hybrid flexoelectric-piezoelectric configuration based on a cylindrical shell is proposed to separately monitor its membrane and bending behaviors. A five-layer composite cylindrical shell is established. A piezoelectric layer is embedded in the neutral surface of the shell and flexoelectric layers are laminated on the inner and outer surfaces. The piezoelectric layer and the flexoelectric layers are segmented into a number of patches serving as distributed sensors. Results show that for piezoelectric sensors, only the membrane strain component is detected while the flexoelectric sensing signals are only contributed by the bending strain component. In order to further obtain signal information respectively indicating the longitudinal and the circumferential bending strains, an orthogonal lamination scheme of flexoelectric layers was proposed. Signal modulate circuits with different flexoelectric material constants were also designed in order to directly achieve on-line monitoring. Spatial distributions of hybrid flexoelectric-piezoelectric sensing signals were evaluated and analyzed in case studies. Results show that by implementing the orthogonal lamination scheme, the flexoelectric sensors can individually predict the longitudinal and circumferential bending behaviors. Such a hybrid configuration is also applicable to other structures.

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