Solid-mechanics finite element simulations of the draping of fabrics: a sensitivity analysis
Abstract This paper covers numerical investigations of the draping of woven fabrics into a “hat” shape, combining a hemispherical cup with a wide flat rim. A mechanical approach is adopted using finite element analysis (FEA) methodology. In this, the fabric is considered as a solid sheet with mechanical properties and friction properties. In this study, a linear elastic anisotropic material model describes the deformation of fabrics. An explicit dynamic finite element analysis is applied and systematic parametric numerical studies are presented, which incorporate investigations of the effects of numerical parameters, material properties and processing conditions on the draping of fabrics. More specifically, the effects of the following variables and parameters are included: number of elements, number of time increments in the dynamic FEA analysis, punch speed, shear and tensile moduli of fabric, coefficient of friction for all interfaces and level of load on the fabric holder.
Characterising and Modelling Tool-ply Friction of Viscous Textile Composites (CD-rom)
The first part of the paper describes two experimental methods for measuring the tool-ply friction behaviour of impregnated thermoplastic textile composites. These include the so-called pull through test and tests conducted using a commercial rheometer using a custom designed platen. Results from the two techniques are compared and the relative advantages and disadvantages of the different test methods are discussed. Data produced over a range of temperatures, normal pressures and shear rates using the rheometer are employed to produce a master equation for the steady state friction. The method of shifting the data to produce this empirically determined equation is described. In the second part of the paper, a predictive meso-scale model is presented that incorporates parameters such as fabric architecture, tow geometry and matrix viscosity. The model is based on lubrication theory and can predict steady state friction. Predictions from the model are compared with experimental results.
The kinematics for forming ideal aligned fibre composites into complex shapes
Abstract In this paper we present a framework to analyse the kinematics for forming aligned fibre composites into complex shapes. We identify the ideal process endpoint, with equal fibre spacing and uniform part thickness, as the goal for all processes. Furthermore, we show that this ideal mapping is obtainable for a large group of ‘topologically equivalent’ parts by using only two deformation modes: shear in-the-plane and out-of-plane bending (which leads to shear between plies for a laminate). In addition, we show how in-plane shear is related to the instrinsic attributes of the part geometry. Example solutions are derived for a variety of shapes. Then it is shown how the kinematic analysis can be used for the development of forming limit diagrams for composites. One example of this approach is given for a vacuum forming process.