Slip-bias extension test: A characterization tool for understanding and modeling the effect of clamping conditions in forming of woven fabrics

It has been well recognized that intra-ply shear and inter-ply slippage are the principal mechanisms allowing the woven fabrics to conform to doubly-curved geometries. The implication of boundary conditions on the forming response of this class of reinforcements is complex in nature, and time-consuming simulations are often needed during process optimization. This study aims to better understand the influence of sliding boundary conditions during forming process of woven fabrics, via a new well-controlled 2D characterization test (termed Slip-bias Extension test). Thereby, a modified shear stress formulation has been developed for the sake of faster 3D simulations, while accounting for the effect of frictional interactions between the fabric and blank holder at different shear angles, normal pressures, and under asymmetric gripping conditions. A key advantage of the new equivalent formulation is that the frictional contact between the ply and the tool at various shear angles and normal pressures does not need to be explicitly modeled in the simulations. The overall applicability of the proposed test and modeling framework is validated against a hemispherical forming of a plain carbon woven fabric. Results suggested an improved modeling accuracy under different forming configurations while reducing the run time by 20%.