Date of Award

12-2006

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

William G. Davids

Second Committee Member

Michael L. Peterson

Third Committee Member

Eric N. Landis

Abstract

A key objective for military planners is reduced logistics cost for overseas deployments. Shelter continues to represent a significant factor in the weight, and volume required for forward military units. While inflatable fabric structures are not new, recent developments have vastly improved their load-carrying capability and durability which may allow them to replace traditional framed tent structures. The new inflated structures depend on improvements in the inflatable structural members called airbeams, which are essentially pressurized fabric tubes. Two major types of airbeam construction are; woven and braided. The woven beams are generally operated at lower pressures (50 to 85kPa), while the more recently developed braided beams operate at much higher pressures (276 to 552kPa). The internal pressure pre-tensions the fabric, effectively giving the fabric shear and compressive stiffness. Airbeams take the form of beams or arches and carry shear, moments and thrusts. Assessing the load-deformation response of an airbeam is essential in the design of an airbeam-supported tent. Modeling of the airbeams requires that fabric constitutive properties be available to obtain optimal design of airbeam structures. However, airbeam technology is relatively new; there are few standard tests for determining fabric constitutive properties and to be used for fabric quality control. This research reviews the current state of the art in textile testing and recommends test practices for accurately identifying the constitutive properties of the airbeam fabrics. Preliminary test results from loading of inflated airbeams have also been completed. These tests are critical to understanding the importance of fabric constitutive properties, operating pressure, and loading on airbeam load deformation response. Experimental test methods to determine constitutive properties of airbeam materials were developed for this thesis. The test methods were designed to incorporate the pressure effects on the constitutive properties. Tests performed included three and four point bend tests, tensile strip tests and tension-torsion testing. The elastic modulus E and shear modulus G were back calculated from the bend test data. This data was compared to the elastic and shear modulus directly calculated from the tension-torsion testing. Testing of airbeams and their components clearly showed the material property pressure dependence. The testing showed that the elastic modulus is less pressure dependent than the shear modulus. The higher initial the pre-strain, or internal pressure, the stiffer the response.

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