Toward Enhanced Forming Simulation of Woven Fabrics Using a Coupled Non-Orthogonal Hypoelastic Constitutive Model, Integrated with a New Wrinkling Onset Criterion

Abstract

One of the advantages of woven fabrics over unidirectional prepregs is their superior formability thanks to the large shear deformation capability. There exists, however, a limit on the shear deformation of woven fabrics, namely the wrinkling. Applying tension to delay wrinkling during forming processes, a consequence of the inherent coupling in woven fabrics, is widely known to the industry. Yet, inherent coupling – change in the effective material properties of a given direction of the fabric due to the applied deformation in other directions - has not been fully understood and implemented in the forming simulations of fabric reinforcements. Coupling should be incorporated in numerical optimization routines to accurately predict the deformation of the material under complex forming set-ups, and more importantly to predict a realistic yarn tension level that can suppress wrinkles. Towards this goal, the present study proposes and implements a new coupled non-orthogonal model which predicts not only the stress-strain path, but also the critical point (shear wrinkling) of the woven fabrics, under combined loading conditions similar to the draping processes. Furthermore, the study reveals that the concept of inherent coupling raises a new issue in fabric forming simulations; the load history dependency of the fabric. Accordingly, the constitutive model has been enhanced to a hypoelastic form to capture the load path dependency of the forming material. Finally, the constitutive model has been integrated with a newly developed analytical fabric instability criterion by authors to account for the occurrence of wrinkling, based on the fabric properties and the level of tension applied during forming. To show its application, the model has been implemented in ABAQUS via a UMAT code to predict the stress and strain fields as well as the onset of wrinkling under large shear deformations.