The deployment repeatability of a high stiffness folded composite hinge

Abstract

A new type of folded composite hinge is investigated for its use in precision deployable spacecraft structures. The hinge is an integral feature of a composite tube intended for use as a structural truss member. The flexure design of the hinge allows the tube to be elastically folded for stowage in spite of tube wall thicknesses from 0.4 to 1.7 millimeters (0.02 to 0.065 inches). This paper experimentally assesses whether the large but elastic folding stresses impart permanent deformations to the tube after it is deployed. The data shows that any such permanent strain induces no more than 2.5 microns axially and 9 microns laterally of tip deformation, depending on the composite layup. This is comparable deployment repeatability to prior measurements of mechanical deployables. Moreover, stow duration and number of stows have no effect, once the initial stow-deploy cycle has been completed. There is always a significant viscoelastic creep recovery following deployment that increases with stowage time. However, this viscoelastic creep is recovered to within the total error of the experiment. An analysis of the creep shows that the viscoelastic recovery is more complex than simple viscoelastic models would predict.