Composite materials

Details Composite materials Composite materials

1997-11-18

1999-08-03

Zirker, Daniel

Fabric (woven, knitted, or nonwoven textile or cloth, etc.)

Woven fabric

Including a free metal or alloy constituent

442228, 442229, 442230, 442231, 205114, 205125, 427437, B32B 1514, C25D 502

Patent

active

059324961

DESCRIPTION:

BRIEF SUMMARY
The invention relates to composite materials having patterned conductors integral to their structure, and to composite materials comprising embedded electronic devices utilizing such patterned conductors.
In many modern structures use is made of fibre polymeric matrix composite materials and in particular fibre resin composite materials. These are frequently fabricated from one or more cloth layers of a fibre, such as glass or carbon fibres, formed into a woven fabric or a mat, together with some permeating polymeric matrix. Considerable potential utility has been seen in the embedding electronic devices within such materials. Such devices might include strain gauges, temperature sensors and similar sensing devices, embedded identification tags, and also aerials and the like.
Problems are encountered however in effecting electrical contact between embedded devices and the outside world. Structures are known which employ fine conductors such as thin wires which trail through the laminate to an edge. Such connections present potential points of weakness at the conductor matrix interface, which is prone to separation, have a tendency to break easily during fabrication, and only allow a connection to be made at an edge of the composite laminate. The wires take an essentially arbitrary path which allows the possibility of short-circuits in multiwire systems. The position of wires at the edge of the panel is also difficult to control, making the use of multi plug connectors virtually impossible. A further problem in that has been encountered is that the wires tend to break at the edge of the panel during autoclaving. It is clear that the trailed wire technique has limited application to embedded devices.
In more conventional situations multiple electronic devices are mounted on a printed circuit board, a board coated with a patterned layer of electrical conductor, which much simplifies the task of connecting a large number of devices. The principle can be applied to produce printed circuits either on rigid substrates or in a flexible form by coating the conductor layer onto a thin polymeric substrate. Neither type of conventional printed circuit board, however, is readily suitable for incorporation into laminated composites as they would represent a significant plane of weakness in the composite structure exhibiting a tendency to delamination at the interface with the resin matrix. Printed circuits comprising a conductive pattern on reticulated or foraminous bases are known from, for example, U.S. Pat. No. 3,053,929, but the conducting strip so formed in the conducting regions of the pattern remains a potential zone of weakness producing a tendency to delamination.
It is an object of the invention to provide a composite material incorporating a connection system with the case of connection and use of printed circuits which is more compatible with use in laminated composites.
According to an aspect of the invention there is provided a composite prepreg comprising a cloth layer formed from fibres of a material suitable for incorporation into a fibre and polymeric matrix composite having deposited thereon a patterned layer of electrical conductor, the electrical conductor being deposited to such a thickness that individual fibres of the cloth are coated but that permeation of the cloth by resin remains possible in the conducting regions, and the cloth being impregnated with an uncured, curable polymeric composite matrix material.
The invention enables complex patterns of conductors, analogous to those which can be produced on printed circuit boards, to be laid down onto the cloth allowing ready connection of a plurality of devices in a format which is suitable for incorporation into a resin matrix composite. Such complex and precisely ordered patterns could not practicably be incorporated using wires.
The cloth material may comprise woven or laid fibres or an otherwise partially porous web-like structure, provided that it is susceptible to penetration by matrix material. Since matrix material is able to penetrate b

REFERENCES:
patent: 2806509 (1957-09-01), Bozzacco et al.
patent: 3053929 (1962-05-01), Friedman
patent: 4201825 (1980-05-01), Ebneth
patent: 4882089 (1989-11-01), Iwaskow et al.
patent: 5681441 (1997-10-01), Svendsen et al.

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