Design and optimization of high strain composite tube flexures

Abstract

Deployable tube flexures are components designed to fold and be compactly stowed during transport, later expanding into a configuration larger than existing launcher fairings upon deployment. By introducing a cut-out geometry, they can elastically fold and deploy without experiencing material failure. The inherent viscoelasticity can gradually reduce load-carrying capacity and possibly lead to anomalous deployment. This research proposes a design methodology for ultra-thin carbon fiber composite tube flexures, introducing a novel cut-out parameterization to enhance performance and incorporating viscoelasticity to assess stowage effects on deployment.

The cut-out in tube flexures is parameterized using generalized spline-based geometries. Bayesian optimization technique is utilized to determine optimal cut-out geometries considering folding characteristics and Hashin failure criteria. The objective function aims to achieve a constant moment, maximize peak moment, and prevent material failure. Results show significant improvement in folding performance using spline-based cut-outs, allowing smooth-transition curves and reducing localized failure on edges compared to a rectangle slot with circular ends.

Time-dependent behavior is incorporated into the cut-out design process with the goal of enhancing viscoelastic resilience after prolonged stowage. Viscoelasticity is experimentally characterized to establish a Prony series master curve. Bayesian optimization is then applied to determine cut-out shapes with the objective of minimizing both recovery time and material failure. The interpretation of Partial Dependent plots offers a design guideline for cut-out formations related to key operational performance including recovery time, Hashin failure, peak moment, and constant moment.

Finally, the efficiency of the proposed design methodology for three operations is validated through a series of experiments, , including folding experiment to assess moment-rotation behavior and dynamic deployment to examine viscoelastic effect on long-term stowage. The Finite Element simulations show a good correlations with the observed experiment results.