Macroscopic Forming Simulation for a Unidirectional Non-crimp Fabric Using an Anisotropic Hyperelastic Material Model

A macroscopic forming simulation model employing the anisotropic hyperelastic material model *MAT_249 (LS-DYNA) was developed for a binder stabilized carbon fiber unidirectional non-crimp fabric (UD-NCF). A new in-depth approach was devised to calibrate the nonlinear membrane deformation response of the UD-NCF using tabulated experimental data, where the extension of the carbon fiber tows, supporting glass fibers, and the stitching and the in-plane shear deformation were captured. Predicted force-displacement responses and shear angle contours for 30° and 60° off-axis extension tests correlated well with available experimental data (R2 > 0.90). This result provided verification, for the first time, that the model was able to accurately capture in-plane shear-extension coupling for UD-NCFs, which is often neglected by other macroscopic forming models. Performed hemispherical forming experiments revealed that out-of-plane wrinkling occurred in the regions near the die along directions slightly biased to the tows due to notable shear deformations. Wrinkling was less pronounced for the case when a blank holder was used due to the tension imposed on the fabric specimen. The macroscopic forming model accurately predicted the force-displacement response (R2 > 0.97) and the locations of wrinkling for the hemispherical tests. This important result demonstrates the ability of the model to capture high in-plane shear deformations and low out-of-plane bending stiffness promoting wrinkling in UD-NCFs, which is often not captured by other models. However, the magnitude of predicted shear angle diverged from those measured during the experiments using digital image correlation, which may be due to the inability of continuum-based material models to explicitly capture local deformations such as tow/stitch interactions. Nevertheless, this study represents an important first step in developing a robust and efficient macroscopic forming model for UD-NCFs. The unique data set presented for the binder stabilized UD-NCF can be used for future macroscopic forming simulations.