Hyperelastic membrane approach for macroscopic forming simulations of unidirectional non-crimp fabrics (UD-NCF)

Unidirectional non-crimp fabrics (UD-NCFs) provide an excellent lightweight potential for high-performance components due to their straight fibers. However, during forming they are prone to wrinkling and gapping compared to woven or biaxial textiles. The unidirectional reinforcement direction requires the consideration of different deformation modes during modeling besides shear, which is the main deformation mode of most models for woven or biaxial textiles [1]. A hyperelastic model is proposed to describe the membrane behavior of UD-NCFs based on superimposed shear, transverse tension and compression perpendicular to the fiber rovings [2]. The membrane deformation modes are related to suitable invariants based on principle material directions of the UD-NCF.
Experimental off-axis tension tests with bias angles of 30°, 45° and 60° are used to impose different ratios of superimposed strains [3] and subsequently parameterize the model, cf. Figure 1b. The resulting approach is validated by forming simulations of a hemisphere and tetrahedron geometry, cf. Figure 1c. Good qualitative and quantitative agreement with experimental tests is achieved for the outer contour after forming as well as the strains measured by digital image correlation.