Origami-inspired self-sensing foldable composite structures: Experiments and modeling

• Developed a FE modeling framework for fold-state monitoring in foldable structures. • Validated the model for a single fold structure and a two-fold auxetic structure experiments. • Numerical simulations of waterbomb structure with a complex multi-fold pattern. • Piezoresistivity, folding stages, moment and curvature were predicted closely to the tests. Origami-inspired self-sensing foldable structures made from fiber-reinforced polymer composites (FRPCs) can be created using piezoresistive fabric laminates. These foldable structures enable real-time monitoring of the state of folds throughout the folding and unfolding processes. This study develops a simplified finite element (FE) modeling framework to predict the piezoresistive-mechanical response of the origami-inspired foldable structures. The model, implemented via UMATHT in ABAQUS®, leverages the analogy between electrical conduction and steady-state heat conduction. The piezoresistive-mechanical response of a simple folding hinge was predicted using the model and compared with the electromechanical folding experimental results. For this purpose, the hinge was manufactured by embedding rGO-coated fabric as a substrate for prepreg patches, which were consolidated using hot compression molding with varying sizes of the folding regions (3, 6, 9, and 12 mm). The folding tests revealed that the moment (M) and curvature (k) during bending depend on the fold region size (b), which in turn affects piezoresistivity, quantified as the fractional change in resistance (FCR). An inverse relationship was observed between moment, curvature, and piezoresistivity as the fold region size varied. Finally, the model was applied to predict piezoresistivity in two structures: a waterbomb base structure and an auxetic structure. We concluded that this modeling framework can be effectively used to predict the electromechanical response of full-scale foldable structures, calibrated with the experimental results of a simple folding hinge with a specific folding size.