ANALYSING CREASE-WRINKLE BEHAVIOUR OF THIN-FILM INFLATABLE SPACE STRUCTURE

Abstract

Today, the space technology aims to enhance the gossamer structures by operating them at higher orbits for an improved performance. The increasing number of space explorations and communication launches demand more compact and reliable solutions without compromising hardware mass, stowage volume, and structural size. Deployable structures, one of the promising approach, offer higher packaging efficiency and lower stowage requirements. They are suitable for various applications such as reconfigurable antennae, solar-sails and de-orbiters. In recent time, the concept of inflatable space structures has gained attention due to their exceptional performance in weight reduction, stowage volume, structural efficiency, and overall mission cost. These ultra-light membrane-based structures can be deployed or inflated to a larger volume in space from a compactly packed configuration during launch. However, these flexible membrane structures’ poor post-deployment static properties, inflation-deployment dynamic qualities, and limited bandwidth for larger focal lengths demand extensive testing and analysis in both ambient and space conditions. The reflector, one of the three basic components of an Inflatable Antenna Structure(IAS), acts as a radiating element. The torus, an outer frame, supports the reflector from edges/corners by tensioning forces to achieve the desired aperture surface flatness. However, in-depth study of various failure modes is required for efficient shape transformation. This thesis aims to demonstrate the capabilities of systematic fold arrangements in developing an inflatable rim-reflector assembly by analyzing crease-wrinkle interaction behavior, inflationdeployment, and post-deployment surface flatness followed by wrinkle alleviation procedure. Adopting any folding method introduces permanent folds in the thin-films. These inevitable creases modify the mechanical response of the compactly packed membrane, and hence fold-line mechanics and their influence on stretched ultra-thin Kapton film have been examined. A hyper-elastic material model with integrated fold-line stiffness and constant crease curvature is suggested for membrane adopting the zig-zag folding. Selection depends on its appropriateness over pinned, fixed hinge and connector based element techniques. Real-world behaviour of crease relaxation and fold-region properties help in computing the crease curvature. Experimentation quantify the material parameters like crease relaxation (captures the neutral angle), effective modulus, and induced residual stresses. These material parameters are essential for an analytical crease profile formulation to characterize the 1D zig-zag fold arrangement with membrane shortening & constant crease curvature. Later, a fully folded component profile is modeled and analyzed in FE package using explicit time integration method. It was observed that mechanical response might vary depending on the form of a fold. A proposed approach is compared against test cases under different loading conditions for its modeling complexity and wrinkling behaviour.