On imperfections and stowage creases in aluminum-rigidized inflated cylinders

Due to their thin and flexible constituent walls, the stiffness and stability performance of inflatable structures is highly sensitive to geometric and material imperfections. For aluminum-rigidized inflatables, crease lines associated with stowage and deployment represent a well pronounced and easily identifiable source of imperfections. However, the mechanics of creases is not understood well enough to enable design to quantitatively assess their effects and/or optimize their configuration. To enhance this understanding, the present paper addresses some aspects of creases and crease-induced imperfections, with special attention paid to longitudinal fold lines in the walls of pressurized cylinders. The fundamental concepts of metal plasticity are interpreted in the context of an inflatable cylinder. Common characteristics between the evolution of a plastic fold in a planar aluminum strip of constrained width under uniaxial tension and one longitudinally oriented on an inflated cylinder are identified. A simple formulae is presented to assess the alleviating effect of plastic straining on smooth shape imperfections of small magnitude. The flattening of a crease via stretching is numerically and experimentally studied.