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Multiaxial Textile Performs for Complex Structural Composite Parts

Exploitable results

MULTEXCOMP started April 1996 and was completed September 1999. The project was defined as a matrix of textile technology development combined with application part development. This way, textile / textile machine industry could benefit from end-user feedback while at the same time, the composite processing / composite part end-user industries learned how to apply advanced textile preforms cost-effectively. For both types of industries, the project helps to minimize the time-to-market of new technologies, and thus maximizes the return on development. Two Universities (K.U.Leuven and Zaragoza) supported both categories of partners by developing modelling, design and testing tools that predict specific characteristics of the composites on a micromechanical (within a unit cell) and macromechanical (whole part) level. The results can be industrially applied within 1-3 years. Textile technologies: The multilayer 2-D robot-assisted 'braiding around a complex shaped core' process machine and robot offers potential for volume production of high performance composite preforms. The even more innovative true-3-D braiding technology is currently in a demonstrator stage, and will be developed further. A fully CAD/CAM linked weft knitting process was developed which allows to transfer a 3-d CAD file of a complex shaped part to a knitting file that results in a 3-d shaped glassfibre preform with straight inlay yarns for added stiffness. The warp-knitting process results in extremely open and drapable glassfibre fabrics that can also include a sandwich structure. The technology is now available to produce cost effective 3-d open warp knits in glassfibre or glassfibre / polyester mixes. Sports industry is especially interested in the stiffness combined with breathability of the composite parts that can be made of this preform fabric. Next generation production equipment for stitched multi-axials is planned to be operational in the first quarter of 2000. The Aerotiss 4/5 D process results in carbon multi-axials, showing excellent material characteristics. The technology produces panels with four directions of yarns, linked by a fifth one. Each of the yarns, especially also the stitching yarn, can be 100% carbon fibre. Fabrics can have thicknesses up to 40mm of very high density (>60% fibre volume in the finished part).The Aerotiss O3S technology is a cost effective way to join preforms using again carbon or glass stitching yarn. It's very cost effective and chosen on the Airbus A340-500/600 program. A portable stitching machine, developed to do manual stitching, has also been developed. Finally a 'next generation' multiaxial non-crimp fabric was also developed offering smoother surfaces, more flexibility in layers directions (0 layer in the middle), possibility to make sandwich preforms and a lower price and higher performance. The technology will be further developed into commercial availability. Composite parts: Targeting automotive frame applications, a range of T-shaped joining elements and A-pillars were developed using the new preforms and their combinations. The project proved that these complex shaped parts can be produced in composites, offering a substantial weight saving while maintaining the energy absorption of accepted traditional materials / constructions. Further development will focus on integration of different shaped inserts and breakthroughs in the preforms. For helicopters, a conical gearbox housing was prototyped. The final solution tested in the project is however not considered today in production, further studies need to be done. Other helicopter parts, which were not considered before to be made with the 3-D preforms, have been identified as more suitable applications. Marine applications have been developed and tested, such as a sonar dome, a hull and various underwater appendages. Sports applications that have been prototyped and tested include bicycle wheel rims, backpack frames and shin guards. The interest from the sporting goods industry is clearly growing as processes become more suitable for mass production. Software tools: The TOAN-MULTEXCOMP PC-based tool provides a user-friendly and fast tool for composite structures. It uses the results of elaborate FEM analyses in a very intelligent way, resulting in predictions that have less than 10% deviation (in more than 90% of the conditions: less than 5%) compared with results of the very calculation intensive FEM tools such as e.g. ABAQUS or DYNA3D. The work on micro-mechanical models has resulted in unique models capable of predicting the stiffness and strength coefficients for most textile reinforced composites, using as input the textile process and the parameters of raw materials (yarns and matrix). Work is under way towards developing a novel Textile Composite Analysis Tool (to run on Win9x and WinNT platforms) which will further improve accuracy of these models (especially on strength predictions) and the suitability for knitted fabrics. There is clearly a challenge remaining in this area.