Mechanical modelling of a sheared textile composite unit cell

Abstract

Composites made using carbon fibre textile reinforcement give an anisotropic material with directional mechanical properties that are dependent on the fabric architecture. The directional properties of a 2D textile are primarily based on weave pattern: The direction of warp and weft yarns, undulation of the tows, and the change in fibre orientation during dry fabric forming process.During dry fabric forming processes, shear is the dominant deformation mechanism as the 2D fabric conforms to 3D shapes. As the fabric changes its shape to match that of the tool, the fibres rotate away from the orthogonal axes as a function of the shear angle. The modified fibre orientation is carried through the curing process and ends up in the finished composite component. This has an influence on the mechanical properties of a cured composite in localised regions of high deformation. Currently the effect of shear during fabric forming is not usually taken into account when modelling the performance of the finished composite at the macro-scale. Through the development of a novel, robust virtual tool, it is possible to identify the change in mechanical properties for a given shear angle. This will allow the macro FE models to give more accurate results. High deformation regions can be identified from a forming simulation (e.g. a sheet of fabric draped over a tetrahedron tool and causes severe shear near the intrusion) and the change in mechanical properties of these local regions can be adjusted accordingly.Using the digital element method previously developed in University of Bristol, the dry fabric architecture can be accurately predicted. The current work has created the ability to shear this virtual unit cell to update the unit cell geometry. This deformed woven geometry is then mapped onto a sheared voxel mesh and combined with an epoxy resin matrix to obtain the meso-scale Representative Volume Element (RVE) model. By applying periodic load cases to the model, the stiffness matrix and therefore the mechanical properties of the composite can be determined. This tool is applicable for any 2D woven resin-infused composite.