Saturation of the stress-strain behaviour of architectural fabrics

Abstract

The stress-strain characteristics of nonlinear visco-elastoplastic architectural fabrics show a mechanically saturating behaviour in cyclic tensile tests: stiffness changes decline, the increase of permanent strain decreases and the nonlinear material behaviour increasingly approaches a linear behaviour. Appropriate stress-strain paths for elastic material models for the structural analysis must be taken from load cycles in which the saturation processes are finished to a satisfactory degree. Generally, consistency of elastic analysis of fabric strutctures is achieved when it is based on the fabric's saturated state and the closely linked stable amount of presstress in the structure.To determine load cycles correlated to the saturated state, a new method is proposed here which considers three different inspection characteristics: irreversible strain increment, total strain increment and intensity of nonlinearity.Biaxial saturation tests with 1000 load cycles are performed on a PVC-coated polyester fabric. For each inspection characteristic, saturation development curves are generated. They are fitted by functions with horizontal asymptotes and are thereby extrapolated, revealing that for the tested polyster fabric tens of thousands of load cycles are required to achieve a satisfying state of saturation. The meaning and implications for biaxial testing and analysis of textile structures is discussed.