Simulation of the tensile behaviour of biaxial knitted fabrics produced based on rib structure using a macro constitutive model

This study presents a macro-scale constitutive model to simulate the tensile behaviour of biaxial weft knitted fabrics produced based on a 1 × 1 rib structure. Fabrics were produced using polyester yarns as stitch yarns and nylon yarns as straight yarns in a modern flat knitting machine. Stress–strain curves of 1 × 1 rib structure and corresponding biaxial knitted fabric were measured in three different directions (course, wale and 45 degrees) on a tensile tester. Based on extracted results, a constitutive equation was proposed for macro modelling of biaxial knitted fabrics. The stiffness matrix of the biaxial knitted fabrics was assumed to be a combination of the stiffness matrix of 1 × 1 rib and reinforcement yarns. A UMAT subroutine was provided to implement the constitutive behaviour in Abaqus software. To evaluate the accuracy of the proposed model, fabric tensile behaviour in 22.5° and 67.5° directions were simulated and compared with experimental results. The results showed that the macro model can successfully predict the tensile behaviour of the biaxial weft knitted fabric in different directions.