Shear-bending interaction in textile composite reinforcements during forming: Experimental characterisation and modelling insights

This study examines the interaction between in-plane shear and bending in flax/PA12 commingled textile reinforcements during forming. Although these deformation modes are often treated as independent in simulations, their interaction is closely related to the onset of wrinkling. A modified experimental approach based on the Kawabata Evaluation System (KES-FB2) was developed to perform bending tests on pre-sheared specimens. This method allows the respective contributions of yarns and sheared fabric regions to be distinguished. A normalisation framework accounting for shear-induced geometric changes was also introduced. The results show that the apparent bending stiffness increases with shear angle. This increase is mainly attributed to yarn reorientation and associated torsional effects, rather than structural locking of the fabric. The evolution is approximately linear up to the locking angle. An improved Dahl-based model is proposed to reproduce the nonlinear and hysteretic bending response, providing better agreement with experiments than the classical Grosberg model. The findings clarify the origin of the apparent shear-bending coupling and support the use of decoupled energy contributions in forming simulations. This work contributes to improving the prediction of wrinkling defects in textile composite forming.