An investigation of combined biaxial tensile and shear deformations in textile woven fabrics

Abstract

Textile fabrics undergo complex deformation during processing, wear and use. Determining how a fabric behaves is important for understanding its performance. While traditional testing methods focus on evaluating a fabric’s mechanical properties, usually along one axis, this study considers the measurement of combined forces which is more realistic under real life conditions. A new apparatus has been constructed named IrisTex inspired by the iris movement of the human eye, capable of applying and measuring combined tensile and shear forces simultaneously in biaxial and uniaxial formats. The current study focuses on the application of low stresses, as typically found in fabrics used for garment making, and hence aims the use of the machine to establish the deformation behaviour during processing and wear. The apparatus is equipped with 4 load cells of 111N maximum capacity to measure low tensile and shear forces. Deformations of 2°, 4° and 8° are applied at 0,24 °/sec by four stepper motors at speeds up to 50 mm/sec and 250 N thrust. The apparatus is specially constructed for low noise, where friction in the bearings is only 1% of the forced applied, and hence it is capable of measuring forces as low as 0,1 N/cm and producing complete force-recovery curves representing combined bi-shear and bi-tensile behaviour from which mechanical values can be obtained. The interface of the apparatus to the computer is done using LabVIEW and the testing procedure allows for changing of the testing conditions and datalogging. Initially, one cotton fabric was tested to set the testing protocols, examine limitations and to analyse and understand the combined tensile and shear curves. Once completed, four more commercially available fabrics were tested and analysed. Meaningful hysteresis curves for combined tensile and shear have been produced for all tested fabrics. The curves were interpreted and characterised to enable fabric to fabric comparison. For the combined tensile curve, properties such as Initial Combined Tensile Modulus (TMint) and Maximum Force (Fmax) were calculated. While for the combined shear curves, values such as Transverse Maximum Force (Fsmax) and Combined Shear Rigidity between 0,5° and 4° (Gc), that represent the ease with which the yarns bend and rotate inside the fabric under the combined deformation were also measured and reported. The results of the combined mechanical properties were meaningful in terms of measuring the combined tensile and shear properties of the fabrics.