Planar biaxial tensile testing of weft-knitted textiles with varying knit architectures

Textiles are widely used in tensile structures due to their low weight, flexibility, and ability to span large areas efficiently through membrane action. Weft-knitted textiles, in particular, offer customization at a unit level, enabling the creation of locally programmable, 3D-shaped, continuous membranes. However, their mechanical characterization remains challenging, despite its importance for structural applications such as flexible formwork. This study examines the biaxial elastic properties of CNC weft-knitted textiles, focusing on the influence of knit architecture on their mechanical response. A custom biaxial tensile testing setup was developed to test three knitting patterns – interlock, tuck, and hexagonal – under three strain ratios (1:2, 1:1, and 2:1). Results show that stiffness varies significantly with knitting pattern and direction, reflecting asymmetries in textile microstructure. Strain distribution was also found to be non-uniform, with lower strains at the core than on the edges, highlighting the role of boundary conditions. Beyond providing insights into weft-knitted textile behaviour, this study contributes to an experimental framework for biaxial stiffness evaluation. The methodology serves as a proof-of-concept framework for the biaxial testing, test preparation, and result interpretation for knitted textiles, as well as for developing low-cost biaxial testing setups. These findings are particularly relevant for architectural and construction applications, where understanding the mechanical behaviour of knitted textiles is essential for structural integrity and design optimization. • The biaxial tensile behaviour of CNC knitted textiles is experimentally evaluated. • A low-cost custom biaxial tensile testing setup for knitted textiles is developed. • Apparent tangent and elastic moduli describe stiffness in two deformation phases. • Knitting pattern and strain ratio strongly influence the textile biaxial stiffness. • The strain distribution is non-uniform, with lower strains recorded at the core.