WO2006123928A1

WO2006123928A1 - Fibre metal laminates and constructions provided therewith

Info

Publication number: WO2006123928A1
Application number: PCT/NL2006/000255
Authority: WO
Inventors: Reinout Gummaris Jacobus Van Rooijen; Sybrand Van Der Zwaag
Original assignee: Netherlands Institute For Metals Research (Nimr)
Priority date: 2005-05-20
Filing date: 2006-05-19
Publication date: 2006-11-23
Also published as: NL1029088C2

Abstract

A fibre metal laminate (FML) provided with at least two metal layers and at least one fibre layer glued between said two metal layers, wherein said laminate has a length and width which are in two directions at right angles to each other, which extend at right angles to a through thickness of the laminate, while in through thickness, viewed between said at least two metal layers, a strip of material is provided, preferably substantially isotropic material, in particular metal, with a relatively high elastic modulus and/or high strength with respect to the metal of the metal layers, which strip has a width which is smaller than the width of the laminate and/or has a length which is smaller than the length of the laminate.

Description

Title: Fibre metal laminates and constructions provided therewith.

The invention relates to fibre metal laminates. The invention further relates to fibre metal laminate connections.

Fibre metal laminates, internationally referred to as, inter alia, Fibre Metal Laminates (FMLs) are hybrid materials built up from thin metal plates, glued to one or more layers of fibres. In each layer of fibres, each time, the fibres are preferably in one orientation, while the relative orientations of the fibres in the different layers are preferably different, are, in particular, at right angles to each other.

FMLs have as an advantage over metal plates such as, for instance, aluminum plates, that the fatigue strength is many times greater. This appears to be the result of the fibres which bridge the fatigue cracks in the metal layers in an efficient manner, so that the growth of these cracks is considerably retarded, or can even be prevented. A drawback is that the fibres can adversely affect static properties, in particular at the location of connections such as connecting bolts, rivet connections and the like.

The invention contemplates providing a fibre metal laminate or a connection for fibre metal laminate with improved static properties.

With a laminate according to the invention, a strip of material is included between two metal layers of the laminate which extend approximately parallel to each other, which strip has a relatively high elastic modulus and/or strength, preferably both, with respect to the metal layers. Through the use of such a strip, the fatigue strength can be maintained to be, at least approximately, equal to that of a comparable laminate without this strip of material, while the static strength can be considerably improved, in particular the capacity to absorb surface pressure.

It is then preferred that the material of this strip is substantially isotropic. As a result, a greater insensitivity to direction of forces acting on the laminate is obtained. The, a or each fibre layer in the laminate is preferably built up from at least two layers of fibres, while in each layer, the fibres are oriented substantially uniformly. It is preferred that the orientations of the fibres in these layers in the or each respective fibre layer mutually include an angle, in particular an angle of between 45 and 135 degrees, more particularly preferably approximately a right angle. As a result, the load bearing capacity in the different directions is improved even further.

Preferably, the laminate has a longitudinal direction and a transverse direction, which directions are preferably at right angles to each other, while layers of fibres with a main orientation in longitudinal direction as well as layers of fibres with a main orientation in transverse direction are provided, preferably in each fibre layer.

The strip of material is preferably embedded in the at least one fibre layer mentioned, more particularly between two layers of fibres in the respective fibre layer. As a result, in a simple manner, a good connection can be obtained between the strip and further layers of the laminate, in particular through gluing. Including the strip of material between two fibre layers, at least layers of fibres, allows optimal utilization of the glue present in and/or on the fibre layers. If the strip is glued between a fibre layer and the metal of the laminate, additional glue is to be utilized.

Particularly advantageous is an embodiment in which the or a strip extends in a zone of the laminate where a connection is formed or is to be formed to another part, for instance another plate of laminate, a fastening element, a frame part, an assembly part or the like. As a result, a particularly suitable, local reinforcement of the laminate is obtained, at the location where the greatest local forces and/or the highest fatigue can be expected. Preferably, the surface of the strip or of the strips jointly, is considerably smaller than the surface of the laminate. This prevents the weight of the laminate from increasing to an undesirably large extent while still, the desired improvements can be obtained. Particularly advantageous is an embodiment with which the elastic modulus and/or the tensile strength and/or the yield point of the material of the strip are higher than those of the metal of the laminate. The thickness of the strip is preferably in the order of the thickness of the metal layers, or smaller. The thickness of the strip can even be considerably smaller than that of the metal layers. As a result, the or each strip contributes little to the weight of the laminate and, nevertheless, ensures a great improvement in the mechanical properties thereof.

The or each strip is preferably manufactured from metal with a rigidity greater than approximately 150 GPa, a strength of, for instance, at least 800 MPa, high ductility and corrosion-proofness. Examples thereof that are especially advantageous are types of corrosion resistant steel, in particular a nickel-steel alloy (maraging steel). Corrosion resistant steel is advantageous because of the high rigidity with respect to aluminum, high corrosion resistance with respect to regular steel, great strength and high ductility.

The invention further relates to a construction or part thereof as described in claim 15.

Such a construction has the advantage that it can be of particularly light design while it still has superior mechanical properties compared to, for instance, a completely metal or completely plastic construction of the same type. Fastening elements such as pins, bolts and nuts, blind rivets, rivets and such fastening means which reach through holes in the construction can then, in a known manner, be used without this causing undesirably low yield points. Moreover, the mechanical strength of the construction is increased.

A construction according to the invention can comprise, for instance, two laminates according to the invention, which are secured one on top of the other by edge zones, while in the respective edge zones, the strips are provided such that fastening means extend through openings in these edge zones and hence, through these strips. Naturally, also a butt joint can be manufactured with which two edge zones of two laminates are laid against each other instead of on top of each other, and are mutually connected by, for instance, a further plate or frame part provided in a manner so as to cover both edge zones at least partly, and secured on these edge zones with, for instance, the fastening means mentioned through these edge zones and hence, through the strips.

The invention further relates to a method for manufacturing fibre metal laminates (FMLs) characterized by the features according to Fig. 18.

Such a method offers the advantage that laminates can be manufactured which are relatively light and still particularly strong compared to traditional FMLs without the at least one strip, in particular when used in constructions in which fastening means are connected to the laminate in or through this strip. The mechanical properties of the obtained laminate and constructions manufactured therewith can be improved therewith without the weight thereof being undesirably increased.

The or each strip is preferably completely glued to at least two layers of fibres or a layer of fibres and a metal layer in this laminate, so that the connection is further optimized and the mechanical properties are further improved.

Without wishing to be bound to any theory, the improvement of the mechanical properties of a laminate according to the invention with respect to a similar laminate without this at least one strip of metal appears to be the result of at least an increase of the yield point around openings in which the fastening means are secured, while use of the fibres prevents the formation of fatigue cracks or fractures in a usual manner, at least decelerates growth of fatigue cracks or fractures considerably.

In clarification of the invention, embodiments thereof will be further elucidated on the basis of the drawing. In the drawing:

Fig. 1 schematically shows, in partly exploded condition, a strip of fibre metal laminate (FML) according to the state of the art; Fig. 2 schematically shows, in perspective view, a strip of laminate according to the invention, provided with two metal layers and two layers of fibre with an intermediate strip of material;

Figs. 3A and B schematically show, in partly cross-sectioned side view, a connection between two plates of laminate according to the invention, in two alternative embodiments;

Fig. 4 shows a graphic representation of the 2% bearing yield and the first bearing ultimate of a laminate without the strip, compared to a similar laminate with this strip, upon loading;

Fig. 5 shows, in side view, schematically, a laminate according to the invention in an alternative embodiment; and

Fig. 6 schematically shows, in side view, a set-up for a bolt bearing test as used for the test of a laminate according to the invention.

The embodiments shown and described are merely shown by way of illustration and should not be construed to be limitative in any manner. Many variations thereon are possible within the inventive concept as set forth in the claims. In this description, identical or corresponding parts have identical or corresponding reference numerals.

In Fig. 1, in partly exploded condition, the structure of a fibre metal laminate (Fibre Metal Laminate; FML) known from the state of the art is shown, which will further be indicated as "laminate" or "FML". Such laminates are known and are commercially available as, for instance, Glare® or Arall®. As a rule, such a laminate is built up from, alternately, metal layers and synthetic fibre layers, mutually glued together. In the example shown in Fig. 1, the laminate 1 comprises a first layer of metal 2, a first fibre layer 3 glued thereon, a second metal layer 4 glued thereon, and, glued thereon, a second fibre layer 5 and, finally, a third metal layer 6 glued thereon. Preferably, the different layers 2 — 6 are completely glued together. The metal layers may be formed from rolled or extruded aluminum or an aluminum alloy, the layers of fibres are for instance formed from aramid and/or glass fibres embedded in plastic or resin. In the exemplary embodiment shown, the fibre layers 3, 5 are substantially built up from two layers 7, 8 of fibres 9. Each layer of fibres 7, 8 has a substantially uniform distribution of elongated fibres 9 with a longitudinal orientation such that they extend with this longitudinal orientation substantially in a main orientation 10 or 11, respectively. The main orientation 10, 11 mutually include an angle, in particular an angle between approximately 45 and 135 degrees. In the exemplary embodiment shown, the included angle α is approximately 90 degrees. As a result, the fibres are optimally utilized in different directions.

In comparison to similar, completely metal plates, the fatigue properties such a structure offers are superior, but a number of static properties thereof are not. It has appeared that in particular there where connections are to be formed to, for instance, other plate parts or construction parts, for instance with bolt connections or nail connections, static properties can be insufficient.

Fig. 2 shows a perspective view of a laminate 1 according to the invention, built up from, substantially, a first metal layer 2 and a second metal layer 4 and, therebetween, a fibre layer 3 comprising a first layer 7 and a second layer 8 of fibres 9, with main orientations 11, 10 which include an angle α of approximately 90 degrees. The laminate 1 has a transverse direction B and a longitudinal direction L, of which only a part is shown in Fig. 2. The longitudinal direction L and the transverse direction B are approximately at right angles to each and to the through thickness D of the laminate 1. Parallel to the longitudinal direction L extends a longitudinal edge 12 of the laminate 1. Along the longitudinal edge 12, an edge zone 13 is defined having a width Bi parallel to the transverse direction B. In the edge zone 13 are provided a number of holes 14 extending through the entire laminate 1, at right angles to the surface 15 of the laminate defined by the transverse and longitudinal direction. In the exemplary embodiment shown, three (rows of) holes 14 are provided, side by side. The centre line M of the hole 14A closest to the longitudinal edge is at a distance E from the longitudinal edge, which distance is indicated as edge distance. Preferably, this is selected to be approximately twice as large as the diameter of the respective opening 14A, at least of a connecting element to be fittingly included therein. Naturally however, this can be chosen to be different.

In the exemplary embodiment shown, in the edge zone 13, a strip of material 16 is included, between the two layers 7, 8 of fibres 9. This strip 16 has a width B2 which substantially corresponds to the width Bi of the edge zone 13, at least a width such that the relevant openings 14 extend through this strip. The length of the strip, viewed in the longitudinal direction L of the laminate, can be chosen such that all openings 14 in this edge zone 13 extend therethrough and can, for instance, be equal to the length of the laminate. It is preferred that the strip 16 be manufactured from an isotropic material. Preferably, the material of the strip 16 is chosen such that this has an elastic modulus and/or tensile strength higher than that of the metal used for the metal layers of the laminate. Preferably, both the elastic modulus and the tensile strength are higher.

In a particularly advantageous embodiment, the strip is manufactured from nickel-steel alloy, while the thickness di thereof is not greater than the thickness d2 of the metal layers 2, 4. Preferably, the thickness di is smaller than the thickness d2 of the metal layers.

In Fig. 3A, a first embodiment of a connection 17 between two laminates IA, IB is shown, in cross-section parallel to the transverse direction B. Here, the edge zone 13A of the first laminate IA (the upper one in Fig. 3A) is laid on the edge zone 13B of the second laminate IB. A connecting element 18 in the form of a rivet or bolt connection is secured in the two edge zones 13A,B, through openings 14 extending one over the other. As can be clearly seen, the strips 16 are one above the other.

Fig. 3B shows a second embodiment of a connection 17 between two laminates IA, IB, in a butt joint, which are, furthermore, connected to a frame part 19, for instance a beam of a vehicle or other construction part. Here, the longitudinal edges 12A, B of the two laminates 1A,B are slid together on a surface 20 of the frame part 19 such that the edge zones 13 A, B of the laminates rest on this surface 20. Then, the bolt connections are formed through openings 14 in the edge zones, which extend through the strips 16 provided therein, and through holes in the frame part 19 so that that a fixed connection is obtained.

It will be clear that also other forms of connections can be formed between laminates according to the invention, to each other and/or to other artefacts such as construction parts, fastening elements, bearing constructions, frames and the like.

In order to test the invention, two types of laminate 1 are manufactured, viz. Glare 2-2/1-0.4 and Glare3-3/2-0.4, both with and without the strip 16 mentioned (comparable to Fig. 2). Glare 2-2/1-0.4 is formed from two aluminum layers 2, 4 with a thickness of approximately 0.4 mm. Therebetween is glued a fibre layer 3 with one layer of glass fibres 9 extending substantially uniformly and in one direction, in the rolling direction of the aluminum, with a thickness of approximately 0.25 mm. Glare 3-3/2-0.4 has a similar structure (comparable to Fig. 1) in which three layers 2, 4, 6 of aluminum are utilized with a thickness of approximately 0.4 mm with, therebetween, two fibre layers 3, 5, each built up from two layers of fibres 7, 8, each with a uniform distribution of glass fibres with a longitudinal orientation 10, 11 which cross, in particular at an angle of approximately 90 degrees.

The laminates with the strip 16 had a similar structure, while with the Glare 2-2/1-0.4, the strip 16 was manufactured from a nickel-steel with a thickness of 0.08 mm and was glued into the fibre layer 3, by splitting this partly. With the Glare 3-3/2-0.4, identical strips 16 of nickel-steel were used, while in each fibre layer 3, 5 between the respective layers of fibres 7, 8, a strip was provided. The strips 16 have a rigidity of approximately 210 GPa and a strength of approximately 1500 MPa. In the edge zone 13 of each laminate, a hole 14 was provided. Each hole 14 had a diameter of approximately 4.8 mm, as did a pin 18 which was inserted therethrough, with an accurate fit. The edge distance E was approximately 9.6 mm, while the width of the or each strip, respectively, was approximately equal to six times the pin diameter. This was therefore approximately 28.8 mm.

The laminates were all subjected to the same standard bolt bearing test, with lateral clamping of the laminate as shown in Fig. 6 in order to test the load bearing capacity. In Fig. 6, a test strip of laminate 1 is placed by an edge strip 13 between two plates 21 of a test block 22, which plates 21 have been secured with the aid of filler plates 23 against a drawing plate 24, such that the distance between the plates 21 was equal to the thickness of the edge zone 13, without clamping occurring. A pin 18 was inserted through the plates 21 and through the hole 14 in the edge zone. The side of the laminate opposite the edge zone 13 was clamped in a claw 25 of a test bench, as was the drawing plate 24, whereupon a tensile load could be applied to the laminate. The Glare2-2/l-0.4 was measured both in the fibre orientation (hence in the rolling direction) and at right angles thereto. The Glare 3-3/2-0.4 was measured in the rolling direction of the metal layers only.

Fig. 4 shows a graphic representation of the difference in Bearing Yield and Bearing Ultimate between Glare 2-2/1-0.4 without the strip 16 and Glare 2-2/2.0-4 according to the invention with the strip 16. Here, Bearing Yield is defined as a load causing a 2% permanent deformation of the holes, comparable to tensile strength. Bearing Ultimate is defined as the stress at which the first maximum load peak occurs, normally at maximum stress. In Fig. 4, along the vertical axis, the values for the bearing strength Ob are given in MPa. Side by side, two times two beams are shown, from the left to the right Bearing Yield for Glare 2-2/1-0.4 without strip 16 and Glare 2-21-0.4 with strip 16 according to the invention, and Bearing Ultimate of Glare 2-2/1-0.4 without strip 16 and Glare 2-2/1-0.4 with strip 16 according to the invention, respectively. It is clear that adding the relatively thin, slim and narrow strip has effected an increase of the load bearing capacity of approximately 20%. Here, it should be noted that the gluing of the strip 16 to the fibres in the test laminates was suboptimal, and that therefore an even greater improvement is to be expected if the gluing is further optimized. For Glare 3-3/2-0.4, comparable results were found.

In Fig. 5, in side view, schematically, a further embodiment of a laminate according to the invention is shown. Here, both an edge zone 13A and a zone 21 located at distance from the longitudinal edge 12 are provided with a strip 16 of material between the first and second metal layer 2, 4 in the fibre layer 3, so that on the surface of the laminate a construction part can be fastened.

The invention is not limited in any manner to the exemplary embodiments represented in the description and the drawings. Many variations thereon are possible within the framework of the invention as outlined by the claims. For instance, other forms, lengths, widths, thicknesses and/or numbers of strips 16 can be utilized, while the strip can furthermore be glued between a fibre layer or layer of fibres and an adjoining metal layer. The laminate 1 can be built up from more layers, while other materials can be utilized, in particular aluminum alloys and other light metals and light metal alloys for the metal layers and other plastics, in particular fibre reinforced plastic as fibre layers. Two or more strips 16 can be provided between two metal layers, the laminate can be designed in a different way than flat, for instance single-curved or double-curved. The, a or each strip 16 can be manufactured from a different material, as long as this has a higher tensile strength and/or a higher elastic modulus than the other metal used for the laminate such as, in particular, aluminum. It will be directly clear to the skilled person that for composition and structure, choices can be made in the customary manner.

Claims

1. A fibre metal laminate (FML) provided with at least two metal layers and at least one fibre layer glued between said two metal layers, wherein said laminate has a length and width which are in two directions at right angles to each other, which extend at right angles to a through thickness of the laminate, while in through thickness, viewed between said at least two metal layers, a strip of material is provided, preferably substantially isotropic material, in particular metal, with a relatively high elastic modulus and/or high strength with respect to the metal of the metal layers, which strip has a width which is smaller than the width of the laminate and/or has a length which is smaller than the length of the laminate.

2. A fibre metal laminate according to claim 1, wherein said fibre layer comprises at least one first and one second layer of substantially uniformly oriented fibres.

3. A fibre metal laminate according to claim 2, wherein, in the first layer of fibres, the fibres have a first main orientation and, in the second layer of fibres, have a second main orientation, which main orientations mutually include an angle such that said orientations do not run parallel and preferably include an angle of approximately 90°.

4. A fibre metal laminate according to claim 3, wherein the first and second orientation are substantially parallel to the longitudinal direction and the transverse direction, respectively, of the laminate.

5. A fibre metal laminate according to any one of the preceding claims, wherein said strip of material is embedded in said at least one fibre layer.

6. A fibre metal laminate according to claim 5, wherein said strip of material is included between the said first and second layer of fibres.

7. A fibre metal laminate according to any one of the preceding claims, wherein the strip of material extends along an edge of the laminate in a longitudinal direction, while the width of the strip is smaller than the width of the laminate.

8. A fibre metal laminate according to any one of the preceding claims, wherein said strip of material is manufactured from a material with an elastic modulus which is higher than that of the metal of the metal layers.

9. A fibre metal laminate according to any one of the preceding claims, wherein said strip of material is manufactured from a material with a strength that is higher than that of the metal of the metal layers.

10. A fibre metal laminate according to any one of the preceding claims, wherein said strip of material has a thickness which is in the order of the thickness of the metal layers, in particular has approximately a similar thickness or a smaller thickness.

11. A fibre metal laminate according to any one of the preceding claims, wherein said strip is manufactured from steel, a steel alloy or a steel laminate.

12. A fibre metal laminate according to claim 11, wherein said strip comprises as steel-nickel alloy.

13. A fibre metal laminate according to any one of the preceding claims, wherein said at least two metal layers are manufactured from aluminum or an aluminum alloy and wherein said at least one fibre layer comprises glass fibres embedded in a resin, plastic or similar filling material.

14. A fibre metal laminate according to any one of the preceding claims, wherein adjacent at least one longitudinal edge, an edge zone is provided in which holes are provided extending through the laminate, while said strip extends over at least the edge zone.

15. A construction, comprising at least one fibre metal laminate according to any one of the preceding claims, wherein said laminate is connected to a further construction part via a connection formed in or on a part of said laminate comprising this said at least one strip of material.

16. A construction, comprising a fibre metal laminate according to claim 14, wherein through said openings, fastening pins such as bolts or nails extend with which a further construction part is secured to said laminate.

17. A construction according to any one of claims 15 or 16, wherein said construction part is a further fibre metal laminate according to any one of claims 1 — 15.

18. A method for manufacturing a fibre metal laminate, wherein, on a first layer of metal, a first fibre layer is glued and, on a second layer of metal, a second fibre layer is glued, the first and the second fibre layer being interconnected, while between said first and second fibre layer at least one strip of material is provided having a relatively high elastic modulus and/or tensile strength with respect to the metal of at least one of the metal layers.

19. A method according to claim 18, wherein the metal layers have a through thickness and a strip is used with a through thickness approximately parallel to the through thickness of the metal layers and a surface, viewed at right angles to said thickness, which is considerably smaller than the surface of said metal layers viewed approximately at right angles to the through thickness of the respective metal layers.