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Stress-biased laminated composites for smooth folds in origami structures

Origami folding principles are attractive for morphing structures due to their potential for realizing drastic changes in shape. Laminated composites enable adaptive lightweight solutions for the implementation of rigid origami structures. This paper presents a strategy for the creation of smooth folds in finite-thickness laminated composites; the approach is applicable to smart folding structures with reconfigurable creases. An analytical laminated-plate model, based on strain energy minimization, is presented to calculate fold angle as a function of laminate parameters. Folds, realized as localized curvature at a crease, are modeled using piecewise displacement polynomials. Folded composites, created using prestressed elastomers with zero in-plane Poisson's ratio, are fabricated for demonstration and model validation. The calculated out-of-plane deflection of the curved creases is in agreement with measurements. A parametric study is conducted to characterize the sensitivity of fold angle and sharpness to variations in laminate modulus and thickness, crease width, and prestrain orientation. Narrow creases require higher prestress for a given fold angle than wider creases. Fold sharpness can be maximized by minimizing crease width and thickness. Anisotropy in the prestressed elastomer is a tradeoff between achieving zero in-plane Poisson’s ratio for unidirectional prestress and maximizing the range of crease orientations for foldability.