Constitutive modelling for composite forming

Fibre reorientation occurs when forming a reinforced structure such as a fabric onto a doubly curved surface. This leads to a change in the angle between warp and fill yarns. The composite properties change inhomogeneously, corresponding to the varying angle between warp and fill yarns. Many composite properties are determined by the angle between the warp and fill yarns, such as the mechanical properties, the coefficients of thermal expansion, the local fibre volume fractions, the local thickness and the permeability. The extent of the fibre reorientation is affected by the product shape and the forming process. The forming process may cause tensile stresses in the fabric yarns, causing subsequent product distortions. Also, wrinkling risks are present due to the incapability of the fabric to deform beyond a maximum shear deformation. The local change in composite properties must be taken into account to predict the properties of a product. Drape modelling can predict the process induced fibre orientations and stresses, which can speed up the product development process compared with trial-and-error development. The constitutive model for these bi-axially reinforced composite materials is the primary element of these process simulations.