Decrimping Behavior of Uncoated Plain-woven Fabrics Subjected to Combined Biaxial Tension and Shear Stresses

Abstract

Tension structures continue to be of increasing importance to military applications requiring minimal weight, small packaging volumes and enhanced deployment operations. Presently, design methods for inflated fabric structures are not well established. Analysis tools for their efficient design lag behind those for conventional structures, partly because woven fabrics do not behave as a continuum. Changes in fabric architecture occur with loading and lead to several sources of nonlinear response. In particular, effective constitutive relationships must be developed that institute the combined effects of biaxial tensile stresses from inflation and shear stresses from bending for use in structural models. Through analysis and experiment, this study addressed these architectural changes, such as crimp interchange, and their effects on the mechanical properties of uncoated plain-woven fabrics. This was accomplished through meso-scale finite element analyses and material tests using a recently developed experimental fixture. The fixture facilitated testing of a wide variety of fabrics (woven, braided, knitted, etc.) subjected to combined biaxial tensile and shear stresses. The meso-scale models and swatch-level test results confirmed that: (1) crimp interchange profoundly influenced the fabric elastic and shear stiffnesses, as changes in crimp heights occurred with increasing biaxial tensions, (2) the shear modulus was highly dependent upon the biaxial tensions and compaction of the tows at the crossover points and (3) the shear modulus was highly nonlinear and was not monotonic with rotation and shear force. This study also presents analytical and experimental methods to ascertain the elastic and shear moduli of woven fabrics for use in evaluating the performance of air beams.