Bending of unidirectional non-crimp-fabrics: experimental characterization, constitutive modeling and application in finite element simulation

Carbon fiber reinforced plastic (CFRP) shell structures are often manufactured from a textile structure. Compared to the tensile stiffness of the fibers, textile structures have a low bending stiffness. This low bending stiffness strongly affects the deformation behavior of textile structures, as small bending loads are sufficient for causing significant deformations: e.g. placing the textile structure into a forming tool under gravity. The resulting deformation generally affects the subsequent forming operation. Further, the onset and formation of wrinkles during the forming operation is also influenced by the bending stiffness. For ensuring the manufacturability of CFRP shell structures using finite element based process simulation, the textile specific bending behavior has to be taken into account. For this purpose, a two point bending test is carried out for characterizing the bending behavior of a unidirectional (UD) non-crimp-fabric (NCF). Based on this, the bending stiffness as well as the deflection behavior of the fibrous material is analyzed and compared to a continuous material. For describing this fiber specific material behavior in a FE simulation, a constitutive model is calibrated by applying analytical beam theories. To demonstrate the validity of this straight forward calibration procedure, a gravity load case for placing UD NCF into a forming tool is carried out, both numerically and experimentally.