Rb Ramgulam

Comprehensive drape modelling for moulding 3D textile preforms

A comprehensive drape model has been developed to deal with a range of 3D surfaces, from simple open surfaces to closed tubular sections with 3D bends. Existing drape algorithms, developed mainly for broadcloth composites, cannot cope with closed sections. These algorithms consider the woven fabric as a network of linkages with pin joints and perform kinematic mapping by solving a set of sphere-intersection equations. This method of kinematic drape assumes only in-plane shear deformation and hence cannot be readily applied to a number of 3D shapes, involving other modes of deformation. In the present work, a kinematic mapping algorithm was implemented at first and subsequently modified to drape two-layer tapered preforms to open surfaces. Following this work, a more general algorithm was developed to drape closed preforms on bent tubes, which the authors believe to be the first such attempt.

Tow-Scale Mechanics for Composite Forming Simulations

Abstract. Composites are processed by a variety of forming techniques at both preforming and consolidation stages; ranging from hand draping, diaphragm forming, vacuum infusion to Resin Transfer Molding. During these processes, individual fabric or prepreg layers are subjected to inplane tension and shear, inter-ply shear, transverse compression and out-of-plane bending forces. These forming forces are translated into individual tow-level forces leading to tow deformations. Each tow is subjected to tension, transverse compaction (in the plane of the fabric due to shear and normal to the fabric plane due to consolidation force), bending and torsion. The resulting tow geometry and local fibre volume fractions (within a tow) would have a significant impact on resin flow as well as mechanical properties of the composite. In this paper, we present computational as well as experimental approaches to predicting tow deformations, when subjected to various loading conditions. The test rigs, shown in figure 1, can measure stress-strain behaviour of a tow in bending, torsion and transverse compression respectively. Figure shows buckling of carbon tow – bending stiffness can be computed from the post-buckling behavior. Torsional moments at monotonically increased twist angle were measured using a very sensitive torque sensor. An anvil, nearly same size as a tow, is used to compress a tow (under controlled axial tension) and the cross-sectional shape is computed from the flattened image (recorded using a high resolution camera). A mechanics-based model has been developed to predict tow-scale deformations under transverse compression, tension, bending and torsion modes of deformation. Individual fibres in a tow are modeled as ‘3D elastica’ and a simple inter-fibre friction model has been incorporated. Initially developed for twisted fibre bundles, the elastic-based model works reasonably well for untwisted fibre tows (by assuming an extremely small twist level for convergence). Full paper will present comparison between experimental and theoretical results.

Mechanics of woven fabrics using cruciform elements

This paper presents a cruciform element for finite element modelling of woven fabrics. Unlike shell elements, cruciform elements do not need special forms near curved boundaries. Additionally, cruciform elements represent the discrete nature of textile structures and ensure that the arms of the cruciform are parallel to the warp and weft directions. In this paper, stiffness matrices for three types of loading, biaxial tensile, in-plane shear and in-plane bending, have been derived. FE modelling with cruciform elements has been demonstrated for bias extension of a woven fabric near the fixed clamp region.

Three-dimensional Elastica for Modelling Fibre Assemblies

In knitted and woven fabrics, inter-yarn forces at the crossover regions tend to compress the yarns thus affecting their mechanical properties. Hence the need to relate lateral forces and yarn cross-sectional deformation. Some theoretical analysis [1, 2] assumed filaments are elasticas and forces are applied at discrete points [1, 2] or uniformly distributed [3] on the filaments. Harwood et al. [4] have proposed a model of yarn compressibility by extending the work of van Wyk [5] to oriented fibres. The present chapter is concerned with compression of continuous filament yarns. The filaments are assumed to be elasticas and follow helical paths in the yarn. The theory of three-dimensional elastica is developed from differential geometry of curves and is applied to lateral deformation of a single helix. Finally, a yarn geometrical model and the algorithm for yarn compression are described.

Mechanics of Flexible Sheet Materials during Draping on Complex Surfaces

The tensile behaviour of a flexible sheet, for example a woven fabric, draped on a complex surface is modelled based on the knowledge of the geometry of the deformed object. A draping simulation is used to determine the coordinates of the material as it is deformed to conform to a complex surface. The simulation in turn is based on the local geometry of the surface. To conform to a doubly curved surface a flat flexible material will bend and shear. The degree of bending and shearing at different locations on the surface will depend on the local Gaussian curvature. The geometry of the deformed material is used to calculate local tow or yarn displacements. The strain energy in each segment of the material is then calculated based on a shear model that assumes no slippage at crossover points. Finally the forces required in each yarn are calculated from the total strain energy in the yarn as well as the total displacement the forces have to undergo to drape the fabric.