Composite storable tubular extendable members (STEMs) have been attached to cylindrical drums to deploy deorbiting sails, sensors and other instruments in space. Attaching STEMs in this way causes the cross section to flatten at the root reducing the structural performance. This reduction in properties needs to be quantified before future high risk applications can be considered. A beam model and finite element model (FEM) are presented here to quantify the detrimental effects of attaching a STEM to a cylindrical drum by way of the rotational stiffness. The beam model is derived using a finite difference approach to numerically solve for the curvature field in the transition from the root to the free end. The FEM produced in ABAQUS uses a contact simulation to deform a composite STEM. The beam model is unable to capture the crucial partially clamped root condition, but does give a qualitative understanding of the layup effects on the stiffness. The FEM shows a significant reduction in the rotational stiffness, from 88.1Nm/rad to 14.3Nm/rad for a [±45°/0°/±45°] layup once the STEM is attached to the drum. The braid angle of a [±θ°/0°/±θ°] layup is shown to have a lesser effect on the stiffness with larger braid angles increasing the rotational stiffness by 2Nm/rad due to the shorter transition length.
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