# Fabric material behavior

 The fabric material model: is anisotropic and nonlinear; is a phenomenological model that captures the mechanical response of a woven fabric made of yarns in the fill and the warp directions; is valid for materials that exhibit two “structural” directions that may not be orthogonal to each other with deformation; defines the local fabric stresses as a function of change in angle between the fibers (shear strain) and the nominal strains along the yarn directions; allows for the computation of local fabric stresses based on test data or through user subroutine VFABRIC, which can be used to define a complex constitutive model; and requires that geometric nonlinearity be accounted for during the analysis step (General and perturbation procedures), since it is intended for finite-strain applications. The fabric material model defined based on test data: assumes that the responses along the fill and the warp directions are independent of each other and that the shear response is independent of the direct response along the yarns; can include separate loading and unloading responses; can exhibit nonlinear elastic behavior, damaged elastic behavior, or elastic-plastic type behavior with permanent deformation upon complete unloading; can deform elastically to large tensile and shear strains; and can have properties that depend on temperature and/or other field variables. The following topics are discussed: