Geometric modelling of industrial preforms: warp-knitted textiles

Abstract: The processing properties of fibrous preforms and the final properties of liquid moulded composite parts are strongly related to the internal architecture of the preforms. The architecture of a preform is determined by the individual textile layers from which it is made. In order to calculate the processing and final properties in the same way over all the volume of a preform or part made from different types of textile, some sets of equations that generate similar definitions of the textiles from their manufacturing parameters are required. The similarity of these definitions is assessed through a series of criteria stated in a previous paper by the present authors; definition modules for woven and braided textiles were also presented in that paper. This paper presents a definition module, or a set of equations, that generates similar definitions for non-crimp reinforcements assembled by warp knitting; the equations also apply for the stitched threads used to assemble multiple-layer preforms. The definitions obtained from this module obey the criteria mentioned previously. The sets of equations presented in both papers cover most technical textiles; similar sets of equations can be created for speciality reinforcements and applied to the calculation of diverse physical properties of the preforms and parts. As an example, this paper discusses the mapping of the voids which are defined between the tows and threads of non-crimp stitched reinforcements