Modelling the waviness of the fibres in non-crimp fabric composites using 3D finite element models with straight tows

A new approach to efficiently model the waviness of the fibres in non-crimp fabric (NCF) composites using mesoscale 3D finite element (FE) models with straight tows is presented. This approach omits the geometric curvature of the tows allowing the use of a straight 3D FE mesh, the waviness of the fibres being taken into account with the definition of the mechanical properties of each element according to the actual direction of the fibres. A representative unit cell (RUC) of a single NCF lamina with fibre crimp has been developed following this approach. The RUC has been used to predict the stiffness properties and to study the stresses/strains that develop along the length of the tows. To ensure the validity of the new modelling approach, the results obtained with its use have been compared with the results obtained from an equivalent RUC in which the FE mesh follows the actual curvature of the tows, in accordance with the classical modelling approach. The results show that the new approach is a valid alternative to model the waviness of the fibres, both in terms of simplicity in modelling and accuracy of the results, opening up the possibility of studying damage mechanisms more efficiently.