A lattice-based theory for kinematics and constitutive responses of warp-knitted textiles under multiaxial loading

Warp-knitted textiles often exhibit an effectively isotropic mechanical response under multiaxial loading despite their anisotropic knitting architectures, yet a quantitative theoretical explanation remains lacking. In this work, we proposed a lattice-based kinematics and constitutive theory that directly links warp-knitted architecture to macroscopic uniaxial and biaxial mechanical behavior. The fabric is modeled as a two-dimensional lattice of looped yarns, from which uniaxial and biaxial constitutive responses are derived based on yarn extension between neighboring looped braids. Systematic uniaxial and biaxial tensile experiments, combined with surface-resolved digital image correlation, verify the theoretical predictions and reveal an effectively isotropic biaxial response across loading orientations. Full-field strain measurements further confirm that deformation is governed by loop rotation and interlocked entanglement between neighboring wale braids. These results establish an architecture-driven framework for understanding the mechanics of warp-knitted textiles and provide a foundation for modeling multiaxial deformation in knitted fabrics.