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.
Prediction of fibre orientation and net shape definition of complex composite parts
Prediction of fibre orientation is important to assess the mechanical properties of a composite part. When the part is manufactured by a liquid moulding process, the resin flow through the preform depends also on local fibre orientation. In this article, a methodology based on dual kriging surface interpolation is presented for the prediction of fibre orientation in composite materials. By calculating the coordinates of each node of the fibre network, it is possible to determine the fibre orientation when the fabric is draped on a complex surface and to calculate the angle between two adjacent fibres. The methodology proposed here combines the definition of a parametric surface by dual kriging with a simple algorithm allowing free rotations of the fibres around the nodes of the fabric. Numerical results from simulations confirm the validity of this method to predict fibre orientation. The same approach can be used also for net shape definition of a fabric before draping on a complex surface. However, implementation of this methodology is computer-intensive and the accuracy is limited by round-off errors.
Turbulent boundary layer wall‐pressure fluctuations downstream from an abrupt change in surface roughness
Spectra of wall‐pressure fluctuations beneath a turbulent boundary layer have been investigated immediately downstream from an abrupt change in surface roughness, from slightly rough to very rough. Over the measurable frequency band (400 Hz to 7 kHz), the spectra in the first 150 mm scale on wall variables. This indicates that the motions responsible for the pressure fluctuations measured in this region are very close to the wall. Farther downstream this scaling procedure breaks down. It is suggested that the initially thin internal layer behaves independently of the flow external to it until it has grown appreciably and only then interacts with the outer boundary layer. It was found that, for all frequencies measured, the dimensional spectral level decreases initially then rises to a maximum at 250 mm from the roughness change before decreasing once more. The position of the maximum is close to where the internal layer ceases to have a distinct edge.