Effect of inflation pressure on the constitutive response of coated woven fabrics used in airbeams

Textile fabrics have gained considerable attention as reinforcement for inflatable structures. A natural challenge arising from their implementation is the proper characterization of their constitutive behavior, which involves complex inter-tow contact interactions under different loading conditions, and the effect of inflation pressure on the fabric stiffness. This paper presents an experimental investigation aimed to independently quantify the effective constitutive properties of coated, woven textile fabrics used as reinforcement for pressurized fabric tubes. When used as structural members, these tubes are commonly known as airbeams. To investigate the influence of inflation pressure on the effective fabric properties, tension/torsion experiments of airbeams were performed at various inflation pressures and under various applied axial and torsional load conditions. Good test repeatability was achieved and the results showed that the effective fabric moduli increase with internal pressure. Effective constitutive properties obtained from these experiments were used as material inputs for beam finite element models to predict the load-deflection response of woven airbeams loaded in four-point bending. The FE model results correlated well with the experimental data over the full range of loading, thus demonstrating that the test method presented is well-suited to determine independent material-level fabric properties which account for the effect of inflation pressure. Additionally, tension/torsion results of braided fabric tubes tests are presented, where good repeatability of the material properties was obtained, highlighting that the test procedure can be extended to different fabric architectures.