Joining method of composite parts having a thermoset matrix, and wind turbine blade manufactured using this said method

Abstract

A method of fabricating a composite joint from a first cured composite component (13) and a second cured composite component (14), the first and second cured composite components (13, 14) comprising fiber elements embedded in a thermoset resin matrix; the method comprising the steps of providing an adhesive (15) on at least one of the first and/or second composite components (13, 14); forming a joint region between the first and second composite component by bringing the first and second composite component into contact with each other with the adhesive (15) therebetween; applying a force to the joint region (16, 17); and heating the first composite component in the joint region to a temperature above the glass transition temperature of the thermoset resin matrix of the first composite component.

Claims

1. A method of fabricating a composite joint from a first cured composite component and a second cured composite component, the first and second cured composite components comprising fibre elements embedded in a thermoset resin matrix, the method comprising: forming a joint region between the first and second composite components by bringing the first and second composite component into contact with each other; applying a force to the joint region; reducing variations in fit between the first and second composite components by heating the first composite component in the joint region to a temperature above the glass transition temperature of the thermoset resin matrix of the first composite component when force is being applied to the joint region; selecting a predetermined amount of adhesive based on the variation in fit between the first and second composite components being reduced; applying the predetermined amount of adhesive on at least one of the first and second composite component; and coupling the first and second composite components together at the joint region using the predetermined amount of adhesive.

2. A method of fabricating a composite joint in accordance with claim 1, further comprising heating the second composite component in the joint region to a temperature above the glass transition temperature of the thermoset resin matrix of the second composite component.

3. A spar for a wind turbine blade, the spar comprising a composite joint fabricated according to the method of claim 1.

4. A wind turbine blade comprising a spar according to claim 3.

5. A wind turbine having at least one wind turbine blade according to claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described by way of example only, with reference to the following Figures in which:

(2) FIG. 1 is a perspective view of a spar for a wind turbine blade.

(3) FIG. 2 is a cross sectional view of a spar for a wind turbine blade.

(4) FIG. 3 is a schematic view of a joint according to an example of the present invention.

DETAILED DESCRIPTION

(5) FIG. 1 shows a spar 10 for a wind turbine blade (not shown). Although the invention is applicable to the joining of any two cured composite parts, this example is described with reference to a wind turbine blade component. The spar 10 is a structural member that extends along the length of a wind turbine blade from a root end of the blade to a tip end of the blade. In use, an aerodynamic shell is fixed to the spar to create the wind turbine blade.

(6) The spar 10 comprises two spar caps 11 and two shear webs 12 arranged in a box shape. The spar caps 11 are fixed to the aerodynamic shells (not shown) and the shear webs 12 maintain the distance between the two spar caps.

(7) The spar caps 11 and the shear webs 12 are pre-manufactured in a mould prior to being assembled into the spar 10. In this example, the spar caps 11 are formed from carbon fibre embedded in a thermoset resin matrix and the shear webs 12 are formed from glass fibre embedded in a thermoset resin matrix. The spar caps 11 and the shear webs 12 are fabricated in a mould and then cured so that they are solid components prior to being assembled into the spar 10. The fabrication of the spar caps 11 and the shear webs 12 can be done by any well known composite manufacturing method known in the art, i.e. using prepreg technology or resin infusion.

(8) As shown in FIG. 2, the shear webs 12 are fixed to the spar caps 11 in a joint region J which extends along the length of the spar. Owing to the large size of the spar caps 11 and the shear webs 12, which may be up to 50 m in length, there may be variations in the fits of the components when they are assembled as described above, which may create stress concentrations in the joint region J.

(9) FIG. 3 shows a schematic view of a joint region according to the invention. In this example, a first cured composite component 13 is being joined to a second cured composite component 14. Due to the manufacture of the composite components 13, 14, there are variations in fit between the two parts as can be seen in an exaggerated form in FIG. 3.

(10) The first and second component 13, 14 are arranged next to each other in the joint region and a predetermined amount of adhesive 15 is placed between them. The adhesive may be, for example, epoxy or polyurethane. The joint is formed by applying heat and pressure at the joint region as indicated by the arrows 16 and 17.

(11) By heating the composite component to above the glass transition temperature (Tg) of the thermoset matrix allows the stiffness of the composite component to reduce. This results in a reduced force required to fit the two composite components together. When the composite component is heated to above the glass transition temperature of the thermoset matrix, the polymer chains of the thermoset resin are allowed to move, which relaxes the preloads caused by the pressure required to force the composite components 13, 15 together. This results in a reduced likelihood of a stress concentration and allows a predetermined amount of adhesive to be used.

(12) In this embodiment, the first composite component 13 is a cured spar cap formed from carbon fibre embedded in a matrix of epoxy resin which has a Tg of 130 degrees centigrade, and the second composite component 14 is a cured shear web formed from glass fibre embedded in a matrix of epoxy resin which has a Tg of 60 degrees centigrade.

(13) In a first example, the second cured composite component 14 is heated to above the glass transition temperature of the thermoset resin of the second composite component 14. Heat is applied as indicated at 17 at a temperature of 70 degrees centigrade. The heat may be applied from a hot air blower or a heat mat. The application of heat reduces the stiffness of the second composite component 14 which results in a reduced force required to fit the two composite components together as described above.

(14) In a second example, both composite components 13, 14 are heated to above the glass transition temperature of the thermoset resin of each composite component. Heat is applied as indicated at 16 at a temperature of 140 degrees centigrade and heat is applied as indicated at 17 at a temperature of 70 degrees centigrade. In this example, the stiffness of both composite components will be reduced and the clamps, which force the components 13, 14 together may determine the final shape of the joint.

(15) In a third example, heat is applied only as indicated at 16 at a temperature of 140 degrees and the heat will transfer from the first composite component 13 to the second composite component 14. As the applied heat is at a temperature higher than the Tg of both thermoset resins of each composite component, the stiffness of both composite components will be reduced.