Curvature determination in the bending test of continuous fibre reinforcements

Bending deformation is one of the main deformation modes in the forming of continuous fibre reinforcements. It is very specific compared to the classical continuous materials. In most textile material forming simulation models, bending stiffness is neglected, but taking into account it would give a more accurate predication, particularly the shape of wrinkles. In the deformation, fibres constituting the reinforcement can slide to each other, resulting in the bending stiffness of reinforcement is not directly related to its in-plane tensile modulus as the classical continuous materials. Consequently, it is necessary to determine the bending stiffness by the experimental method. A cantilever bending stiffness test approach was proposed to measure the bending stiffness of continuous fibre reinforcements. A CCD camera was used to take the bending deflection shape. To calculate the curvature of bending deflection curve, uniform quartic B-spline curve was chosen. A detailed process of curvature calculating of deflection curve was given in this paper. A single bending test gives the bending moment as a function of curvature from zero to the maximum value. Bending tests were conducted to validate the capacity of the proposed approach. A smooth curvature plot along the bending deflection curve was obtained for different types of reinforcements, and the non-linear bending deformation behaviour can be identified with the proposed bending test method.