Capabilities and limitations of pure-shear based macroscopic forming simulations for 0°/90° biaxial non-crimp fabrics

Macroscopic modeling of a non-crimp fabric’s (NCF’s) forming behavior is challenging as it strongly depends on the textile architecture, fiber type, and stitching type. While shear is the main deformation mode of woven fabrics, membrane modeling approaches for NCFs should also consider stitching deformation and roving slippage. However, for 0°/90° biaxial NCFs (Biax-NCF) with a symmetrical stitching pattern and high stitch pretension, deviations from a pure-shear assumption in coupon tests are only observed at higher shear angles due to limited roving slippage. In this work, a hyperelastic approach initially proposed for unidirectional NCFs is adopted for a tricot stitched 0°/90° Biax-NCF based on a pure-shear assumption. The shear behavior is experimentally characterized through 45° off-axis-tension tests, and the parameterization is derived from energetic approaches originally developed for woven fabrics. This approach efficiently and adequately describes the general behavior in forming simulations of different geometries. Fiber orientation and location of areas with high shear angles are predicted well, but the peak shear angles are overestimated due to the neglected roving slippage.