ATTACHMENTS

Abstract

Mechanically attaching articles made from composites has problems due to the difference in properties of the composite in the x, y planar direction and the z perpendicular direction, this results in different properties between the composite and the attachment member such as differences in coefficients of thermal expansion which can weaken the joint further leading to differences in moisture uptake which can further reduce the strength and robustness of the joint. The invention relates to the selection of the position of a joint in order to reduce such problems and to operating the moulding process in a way that improves the provision of mechanical attachments such as bolt holes.

Claims

1. A method of selecting a bolt line in a composite part comprising the steps of: a) obtaining the strain characteristics of the composite; b) selecting a bolt line, wherein the bolt line is selected such that the strain and/or associated stress along the bolt line is within a desired range.

2. (canceled)

3. A method according to claim 1, wherein the strain characteristics comprise thermal expansion strain, moisture induced strain and/or combinations thereof.

4. A method according to claim 1, wherein the composite is an anisotropic composite material.

5. (canceled)

6. A method according to claim 1, wherein the composite material has isotropic strain in a plane.

7. A method according to claim 6, wherein the bolt line is in the isotropic plane.

8. A method according to claim 1, wherein the fastener is arranged parallel to the bolt line.

9. A method according to claim 1, wherein the fastener is arranged perpendicular to the bolt line.

10. A moulding process in which the orientation of fibres in a moulding compound is controlled to provide a volume in an article cured from the moulding compound that optimises the location of a mechanical attachment within the article.

11. A moulding process according to claim 10 performed in a press in which the conditions optimise the orientation of the fibres in a plane.

12. A method of connecting one or more parts, at least one part comprising a composite, by means of a metal fastener, comprising providing a line for the fastener in the composite part in accordance with claim 1.

13. A method according to claim 12, wherein the one or more parts are connected in combination with an adhesive.

14. A composite part comprising an aperture positioned along a bolt line selected by means of a method as set forth in claim 1.

15. (canceled)

16. (canceled)

17. A composite part comprising a cured moulding material in which the fibres lie substantially in a x, y plane of the part and comprising a metal fastener said fastener being arranged along a bolt line, said bolt line extending substantially perpendicular to the x, y plane.

18. A composite part according to claim 17, wherein the fastener is threaded and the composite part comprises corresponding threaded fastener receiving means for receiving the fastener.

19. A part according to claim 17 wherein the fastener is additionally secured by an adhesive comprising a methacrylate based adhesive composition, preferably a poly(methyl methacrylate) based composition.

Description

EXAMPLE 1

[0066] HexMC® M77 and HexMC® M81 laminates were manufactured and cured. HexMC® as supplied by Hexcel Corporation is a moulding material containing discrete unidirectional fiber elements which are impregnated with a resin matrix, in this case M77 and M81 resins also available from Hexcel Corporation. The cure/post cure cycles used are as follows. [0067] M77: 2 min/150° C. under 100 bar pressure, no post cure [0068] M81: ageing step in oven 7 min/170° C., cure 1 h/150° C. under 100 bar pressure+post cure 2 h/180° C.

[0069] Different laminates were prepared in which the orientation of the fiber elements was varied so that some laminates were isotropic (same distribution of elements in x, y and z direction), whilst other laminates were anisotropic so that the elements were distributed isotropically in the x-y direction, but not in the z direction.

[0070] Two laminates were made for each material to allow both in-plan and through thickness measurements to be made. In plan samples could be cut from relatively thin laminates (x=2.3 mm), however through thickness samples required a thicker laminate (x=25 mm). All samples were cut using a diamond tipped water cooled wheel saw. Samples of the cured composite materials were placed in a vacuum oven overnight at 90° C. to remove any moisture.

[0071] The reduction in bolted torque performance of bolted HexMC® samples which were subjected to ageing/conditioning cycles was evaluated to determine any detrimental effect on composite thermal expansion coefficient and/or Tg caused by moisture uptake during the cycling. The thermal cycling was found to have minimal effect on the glass transition temperature of both materials. The moisture conditioning was found to degrade both materials performance significantly. However, the samples having a greater alignment of the fibres in the x, y plane as opposed to the z plane were found to enable a more robust and longer lasting mechanical attachment to be obtained.

EXAMPLE 2

[0072] Two HexMC® M81 laminates were manufactured and cured using the same cure schedule as defined in Example 1.

[0073] In the first laminate the fiber elements were distributed to form a laminate which was an isotropic laminate (Laminate 1). In the second laminate, the fiber elements were distributed to form a laminate in which the elements were anisotropic in the z-direction but isotropic in the x-y direction (Laminate 2).

[0074] Each laminate was drilled to a depth of 22 mm and threaded to accept 5 rows of 6 bolts and washers (so 30 bolts and washers in total for each laminate). The bolts were M8 bolts of 16 mm length manufactured from zinc plated steel (grade 10.9). The washers were 1 mm thick and also manufactured from zinc plated steel (grade 10.). The washer had an inner aperture of 8.4 mm and an outer diameter of 17 mm.

[0075] The bolts were applied to the laminates at different torque settings as set out in Table 1 as follows:

TABLE-US-00003 TABLE 1 Bolt torque settings before temperature/moisture cycles Bolt row Torque setting (N .Math. m) 1 10 2 15 3 20 4 25 5 30

[0076] The laminates were then each exposed to the temperature and relative humidity cycle variations as shown in FIG. 1. The relative humidity is the ratio of the amount of water vapor in the air at a specific temperature to the maximum amount that the air could hold at that temperature, expressed as a percentage.

[0077] The torque settings of the M8 bolts were then checked for each of the laminates. The results are presented in the below Table 2.

TABLE-US-00004 TABLE 2 Bolt torque settings after temperature/moisture cycle of FIG. 1 Laminate 1 - number of Laminate 2 - number of Bolt row bolts with reduced torque bolts with reduced torque 1 0 0 2 0 0 3 0 0 4 0 0 5 2 6