Experimental and numerical study of specific bending behavior of tufted multilayered reinforcements and effects of tufting density

The tufting technology enhances the delamination and impact resistance of composites. The presence of tufting yarns leads to a modification of the structure of the fabric, which affects the bending behavior of tufted reinforcements. Tufted reinforcements experience significant slippage during bending, challenging classical plate and shell theories. Therefore, the bending behavior of tufted reinforcement is investigated and a specific fibrous shell approach is proposed, assuming quasi-inextensibility of fibers and potential slippage between them. The influence of tufting yarns on the bending behavior is integrated into the constitutive model. The experimental results show that the bending stiffness of reinforcements can be increased by tufting density. The simulations exhibit a good agreement with experiments, demonstrating that the proposed approach can accurately capture not only the bending deflections of tufted reinforcements, but also the rotation of material direction indicators. Using the proposed numerical method, the prediction accuracy for deflection and rotation angle of tufted reinforcements reaches 90% in cantilever bending tests and 85% in three-point bending tests. These novel insights can deepen the understanding of the bending behavior of tufted reinforcements and be an asset of the developing numerical model for the forming simulation.