Comparison of Constant-Force Increment and Constant-Rate Loading Protocols in Biaxial Tests of Coated Fabrics

Abstract

Biaxial tension testing is an increasingly accepted tool to understand the mechanical behavior of architectural coated fabric membrane materials. However, different loading protocols in biaxial tests result in diverse results. This study investigates the different results between constant-force increment (CFI) and constant-rate (CR) loading protocols. Different loading procedures were proposed on a self-made biaxial tension tester to conduct systematic experiments. The mechanical behavior of a typical fabric was investigated by both CFI and CR loading. The stress-strain curves and their mechanical characteristics were compared. On the basis of test data, the authentic weft stress values in the CR loading protocol were observed to be 20% lower than the nominal load value. The elastic modulus determined by CR loading was significantly larger than that acquired by CFI loading. An obvious viscous effect is seen in the unloading stage under CFI loading. This did not arise under CR loading. Future work might focus on material to further strengthen the conclusion.