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MULTIWEAVE Report Summary

Project ID: 508125
Funded under: FP6-SME
Country: Portugal

Final Report Summary - MULTIWEAVE (Weaving machine for producing multiaxial fabric)

The aim of the project MULTIWEAVE was to investigate the feasibility of a multiaxial two-dimensional (2D) interlaced woven structure able to provide specified strengths in different directions and the development of its manufacturing process. This structure can be obtained by the insertion of interlaced yarns at approximately 45 degrees between the weft and warp.

The main objective was the design and development of a weaving system able to produce a multiaxial fabric. The applied methodology consisted in the study of a principle for the insertion and interlacing of yarns in bias directions. A multiaxial weaving system was designed comprising the following systems: warp feeding, bias yarns feeding and criss-cross insertion, shedding, incorporating one heddle, weft feeding and insertion, beating-up mechanism, incorporating the reed, fabric taking-up and winding mechanisms. The solution incorporates the use of conventional weaving elements but also completely new mechanisms or modifications of existing ones.

Multilayer fabrics have the following main advantages and disadvantages:
the two key improvements with stitched multilayer fabrics over woven types are:
- better mechanical properties, primarily from the fact that the fibres are always straight and non-crimped, and that more orientations of fibre are available from the increased number of layers of fabric;
- improved component build speed based on the fact that fabrics can be made thicker and with multiple fibre orientations so that fewer layers need to be included in the laminate sequence.

- polyester fibre does not bond very well to some resin systems and so the stitching can be a starting point for wicking or other failure initiation.
- the fabric production process can also be slow and the cost of the machinery high. This, together with the fact that the more expensive, low Tex fibres are required to get good surface coverage for the low weight fabrics, means the cost of good quality, stitched fabrics can be relatively high compared to wovens.
- extremely heavy weight fabrics, while enabling large quantities of fibre to be incorporated rapidly into the component, can also be difficult to impregnate with resin without some automated process.
- the stitching process, unless carefully controlled, can bunch together the fibres, particularly in the 0 degree direction, creating resin-rich areas in the laminate
- poor delamination strength due to non-interlacement between layers.

The use and impact of the multiaxial fabric may be found in two different products:
- technical textiles, such as composites for car and aircraft industry, conveyor belts, inflatable boats, sails, boat hulls, air inflated houses, geotextiles, wall coverings, sport devices, tarpaulins, tents, grinding and lapping disks and many other applications on products that still use traditional technology of gluing together several layers of fabrics, differently oriented;
- garments designed to be resistant to tear, with an original texture, easily conformable and dimensionally stable could have a big impact on very different articles such as military and protective clothing. Although the application on conventional clothing looks considerably out of the way, possible applications on tennis and other sports shoes and some sportswear seems a possibility to further explore.

During this period, the following work packages (WPs) took place:
WP1 - Identification of requirements;
WP2 - Design of the weaving machine;
WP3 - Providing the weaving machine components;
WP4 - Design of the electronic and control system;
WP5 - Prototype assembly;
WP6 - Tests on processing of the weaving machine and in the fabric's mechanical properties;
WP7 - Product tests, market validation and improvements. Field tests and analysis of results;
WP8 - Project management and exploitation.

The working principle of the MULTIWEAVE development prototype is as follows. The bias yarns are feed from two bias beams through a tension compensation device and stepwise moved in two very close and parallel layers in opposite directions by means of an appropriate mechanism. The heddle and the reed are in their lower and backward positions, out of the plane of the bias yarns, allowing their free criss-crossing. The heddle rises forming the shed and the warps interlace with the bias. The shed is formed between the warp and the two very close parallel layers of the bias yarns. A first (false) beating takes place to clear the shed; this was found necessary as when the warp yarns are raised by the heddle, they are partially held up by the criss-crossing effect of the bias, preventing from obtaining a clear shed which caused difficulties for the insertion of the weft yarn; The weft yarn is then inserted across the shed to be interlaced with the warps and bias yarns. A second (real) beating operation takes place which pushes the weft forward and compacts with the fabric, at the same time that the heddle moves down to its rest position closing the shed and holding the weft. The taking-up mechanism advances one step and the fabric is wound up.

Fabric samples of different fibres have been manufactured using the MULTIWEAVE development prototype. As there are no standards for multiaxial fabric tests, a new procedure had to be developed in order to test the mechanical properties of the multiweave fabrics. So far, conventional strip and grab tensile tests were carried out. To keep the multiaxial structure fixed and to produce a first multiaxial composite, a multiweave fabric has been laminated in a polyester resin. Having both fabric and resin made of the same material, no dissolving of the fabric structure can occur.

The main objectives of this research have been achieved The multiaxial concept was embodied in a development prototype which proved the feasibility of the concept. The most significant innovation of this idea is concerned with the characteristics of the fabric structure where there is criss-crossing between all sets of yarns, which increases the capability for supporting more severe mechanical loads without failure, namely without delaminating.

Simultaneously, the strength-weight ratio is expected to increase, which, for applications such as in the aircraft and car industries, can be very advantageous. Other important applications are in marine textiles, such as composites for boat and shipbuilding, which are products submitted to severe stressing conditions.

The MULTIWEAVE prototype developed within this work is being used to produce different types of 'directionally oriented structures' (DOS), using various types of fibres (HT polyester, aramide, carbon and glass) and yarn counts. The present development prototype has to be seen as a learning tool from where much know-how has been acquired. Some mechanisms and details need reviewing and optimisation.

However, some aspects could already be identified:
- when moving to a larger fabric width, for example 500 mm or 1000 mm, extra problems will be raised by the extra complexity of the bias yarns feeding system;
- the fabric being produced presents a structure which is not yet very dense, mainly due to the limitations imposed by the relatively high bias pitch; more research and development is required in order to find the appropriate solutions.

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