Special Considerations in Selection of Fabric Film Laminates for Use in Inflatable Structures

Inflatable structures are gaining wide support in planetary scientific missions as well as commercial applications. For such applications a new class of fabric/film laminates is being considered for use as a structural gas envelope. The emerging composite materials are a result of recent advances in the manufacturing of lightweight, high strength fibers, fabrics and scrims. The lamination of these load-carrying members with the proper gas barriers results in a wide range of materials suitable for various loading and environmental conditions. Polyester-based woven fabrics laminated to thin homogenous film of polyester are an example of this class. This fabric/film laminate is being considered for the development of a material suitable for building large gas envelopes for use in the NASA ultra long duration balloon program (ULDB). Compared to commercial homogenous films, the material provides relatively high strength to weight ratio as well as better resistance to crack and tear propagation, The mechanical, creep and viscoelastic properties of these fabric film laminates have been studied to form a material model. Preliminary analysis indicates that the material is highly viscoelastic. The mechanical properties of this class of materials will be discussed in some details.