RJTA Vol. 11 No. 4 2007
Finite Element Modelling of the Warp Knitted Structure Argyro Kallivretaki1*, Savvas Vassiliadis2 , Mirela Blaga3 and Christopher Provatidis1 1 National Technical University of Athens, School of Mechanical Engineering 2 TEI Piraeus, Department of Electronics 3 Gh. Asachi Technical University, Faculty of Textiles and Leather Engineering
ABSTRACT The finite element modelling of the Charmeuse warp knitted fabrics is the main subject of this paper. The proposed model consists of a three-dimensional representation of the warp knitted fabric microstructure and a mechanical analysis of the defined unit cell. An iterative calculation procedure was used for the definition of the geometrical representation of the structure. The parametric modelling is based on the main structural parameters: yarn crosssection, warp density, course density, and yarn consumption of the front and the back bar. The flattening of the yarn cross-section has been introduced in the undeformed state of the model for the realistic approach of the authentic situation. The Finite Element Method (FEM) with contact analysis was implemented for a mechanical analysis of the multi-body structural unit. The appropriate contact algorithm was defined for fast convergence during the solution. Although the complexity of the unit cell was high, the modelling was possible and it can become a tool for the mechanical analysis of warp knitted fabrics. Keywords: Computer Aided Engineering (CAE), Numerical Methods, Finite Element Method (FEM), Textile Fabrics
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structures produced by high performance fibers made from glass or carbon are used for composite reinforcement. The increasing requirements of the industry for high performance technical textiles demand an accurate definition of their properties. Thus realistic modelling and mechanical analyses of warp knitted structures are of great importance.
Introduction
In the warp knitting technology, warp yarn is introduced in the longitudinal fabric direction. The characteristic feature of the warp knitted structure is the formation of adjacent loops in the course direction by the separate warp. Usually the basic lapping structures are used in combination producing more than one warp sheet. The considered structure, Charmeuse or Locknit, is a combination of tricot and 2×1 plain stitches. Thus two guide bars are used for the manufacturing of the structure under consideration.
Several research studies have been reported concerning the micromechanical analysis of the basic warp knitted structures. The geometrical representation of the structure comprised obviously the starting point for researchers. The representations were based mainly on the division of the loop configuration into discernible parts as loop’s head and arms, root of the loop and underlapping sections. Depending on the approach and complexity, two- and threedimensional models have been proposed including or ignoring the loop inclination. Convenient geometrical shapes as straight lines and circular parts and in some cases complicated geometries based on empirical assumptions were used for the representation of the defined partitions (Dalidovici, 1940; Allison, 1958; Grosberg, 1964; Korlinski, 1981; Raz, 1987; Vékássy, 1960). There was a different approach
Warp knitted fabrics have a limited range of applications in apparel fabrics and household textiles. However, their continuously widespread use in technical applications attracts increasing research interest. The technological advantages of warp knitted fabrics as formability, contourability, dynamic mechanical properties along with easy and rapid manufacturability are essential reasons for their establishment in composite manufacturing. Nowadays the warp knitted ____________________ * Corresponding author. E-mail address:
[email protected] (Argyro Kallivretaki)
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