Full-strain range characteristics of the Poisson’s ratio for coated biaxial warp-knitted fabrics under bias tensile loading

Abstract

It is undeniable that full-strain range characteristics of Poisson’s ratios on the behaviors of a fabric composite are crucial. However, there have been relatively few papers devoted to this subject. In this study, tensile tests of seven bias angles with a 15° increment are conducted on a typical coated biaxial warp-knitted fabric (BWKF) to estimate the Poisson’s ratios in full-strain range. By utilizing the digital image correlation technique, experimental results are processed, and detailed responses of strain contours and Poisson’s ratios are determined for specific strain states. Then, two typical types, that is recession and peak types, of the Poisson’s ratio strain curves are proposed and their characteristics evolving with the strain, bias angle and stress state are discussed. Results show that characteristics of Poisson’s ratios and strain contours vary noticeably with the yarn orientations, strain and stress levels. As the strain increases, the Poisson’s ratio of peak type first ascends markedly, and then descends moderately after arriving at a peak, generating three distinct stages: the ascending, peak and post-peak stages; in contrast, the recession type only experiences a downward trend, resulting in two characteristic stages: the recession and stable stages. In addition, there is an M-shaped relationship between the Poisson’s ratio and bias angle, with a local valley at 45°, which is not consistent with results in previous works. This investigation could provide new insights into the orientation dependence, Poisson effect and warp–weft interaction mechanism of BWKFs.