Reducing Stress Concentration in the Transition Region of Coilable Ultra-Thin-Shell Booms

High stress concentrations leading to material failure have been observed in TRAC booms coiled under tension around a circular hub. The stress concentrations are typically observed in the transition region between the fully deployed and coiled sections of the boom. A numerical simulation framework is proposed to model the coiling process analyses the stress distribution in the transition region. Isotropic booms are first studied to understand the effects of the cross-section geometry and the boundary conditions during coiling. Compressive stress is reduced by 13% and 26% by using a variable curvature cross-section and adding nip rollers in the coiling mechanism respectively. For an ultra-thin glass fiber-carbon fiber composite laminate, the compressive stress is similarly reduced by 24% and 11%. The variable curvature cross-section is shown to eliminate the stress concentration in the transition region.