Advanced Structures & Composites Center

Published: 2020

Publication Name: Maine State Government

Publication URL: https://digitalcommons.library.umaine.edu/etd/3473/

Abstract:

Inflatable beams, arches and panels have become increasingly popular for load-bearing applications and have a variety of military and civil applications. The popularity of these structures comes from being lightweight, easy to transport, and being able to regain shape after the structure has been overloaded and the load is removed. The majority of inflatable beams and arches – commonly termed “airbeams” – are cylindrical pressure vessels with a circular cross-section. In contrast, drop-stitch panels incorporate yarns that connect the top and bottom surfaces, giving a wide, shallow cross-section with parallel top and bottom surfaces. Unlike airbeams, drop-stich panels do not incorporate a bladder due to the presence of drop-yarns. Therefore, the majority of drop-stich panels use a coated fabric. The primary objective of this research was to develop testing procedures to determine the constitutive properties of orthotropic neoprene/nylon drop-stitch inflatable panel fabric, and to quantify panel bending load-deflection response. This was done through panel inflation and skin coupon testing, large-scale torsion tests, and full-scale four-point bend tests. Panel inflation and skin coupon testing was done to determine the effective panel orthotropic constitutive properties in the longitudinal/warp and transverse/weft directions of the panel. Torsion testing was performed to determine the membrane shear modulus. Full-scale panel bending tests to large displacements were used to quantify panel bending load-deflection response and the effect of inflation pressure on panel stiffness and capacity. The large-scale bend test load-deflection behavior was compared to the response estimated using the experimentally-determined skin constitutive properties. The bend test results indicated that there were likely significant shear deformations in the panel during bending, which was supported by the fact that the membrane shear modulus determined from the torsion tests was a small fraction of the membrane elastic moduli. While the actual response of the panel was softer than predicted using Euler beam theory, significantly stiffer response and higher capacities were observed at higher pressures as expected. It was also observed that with an increase in pressure, there is an increase in the membrane modulus. Prior literature has observed that the pressure-volume work effectively increases the shear rigidity (Davids and Zhang, 2008) (Davids, 2009). The increase in shear modulus with inflation pressure also contributes to the increase in panel bending stiffness.