A hinge effect that anomalously decreases the stiffness of slender fiber-reinforced composite structures

TL;DR

This paper uncovers a novel hinge effect in fiber-reinforced composites that reduces stiffness and enhances flexibility, supported by experiments, modeling, and potential applications in origami and deployable structures.

Contribution

It introduces the hinge effect as a new phenomenon explaining anomalous flexibility in fiber composites, supported by experimental and analytical evidence.

Findings

Embedded fibers cause a 20% reduction in stiffness.

The fiber-matrix interface remains strong, ruling out debonding.

The hinge effect enables design of foldable and deployable structures.

Abstract

We present experimental evidence for an anomalous decrease in stiffness in a fiber-reinforced polymer composite because of the embedded fiber. A shell with carbon fiber showed about 20% less stiffness and 100% more strength under compressive loading. We ruled out the role of debonding of fiber due to imperfect impregnation by using a fiber-pullout test, which revealed that the fiber-matrix interface is strong in the direction of the fiber. Therefore, we hypothesize that a fiber allows the matrix material to rotate around it as in a hinge. We corroborate this phenomenon, which we call the hinge effect, with analytical modelling and experimental data for small and large deformations of a fiber embedded in slender composite beams. We also demonstrate the design of foldable and deployable sheets with hill and valley folds enabled by the embedded fibers. Moreover, the hinge effect warrants further research into physics of how fibers in slender composite structures give rise to the anomalous flexibility. This effect can be gainfully used in designing novel origami structures and compliant mechanisms should be flexible and strong.