Wall made from a composite material reinforced so as to limit the spread of a crack in a direction

Abstract

The invention relates to a wall made from a composite material comprising at least two layers of fibers (18, 18) embedded in a resin matrix, a crack being able to spread in said wall in a direction of propagation, characterized in that it comprises at least one longilineal metal reinforcement (20), oriented in a direction secant to the direction of propagation, inserted between two layers of fibers (18, 18) of the wall.

Claims

1. A wall made from a composite material comprising: at least two layers of carbon fibers embedded in a resin matrix and the at least two layers of carbon fibers being in direct contact with each other over a majority of an area of each of the at least two layers of carbon fibers, wherein the at least two layers of carbon fibers have a crack propagation tendency direction; and at least one longilineal metal reinforcement oriented in a direction secant to the crack propagation tendency direction and the at least one longilineal metal reinforcement is inserted between the at least two layers of carbon fibers and is embedded in the resin matrix, wherein the at least one longilineal metal reinforcement is made from a material having an elongation at break that is 50% higher than that of the carbon fibers of the at least two layers, the at least one longilineal metal reinforcement has a cross section which varies in area along the length of the at least one longilineal metal reinforcement and the outer surface of the at least one longilineal metal reinforcement is not adhered to the at least two layers of carbon fibers.

2. The wall made from a composite material according to claim 1, wherein the at least one longilineal metal reinforcement is immobilized between the layers of carbon fibers while a tensile force is exerted at an end of the at least one longilineal metal reinforcement.

3. The wall made from a composite material according to claim 1, wherein the at least one metal reinforcement in shaped as at least one strip inserted between the at least two layers of carbon fibers.

4. The wall made from a composite material according to claim 3, wherein the at least one metal reinforcement is shaped as at least one metal strip including recesses each having a width narrower than that of the at least one metal reinforcement and the recesses are arranged symmetrically along the longitudinal median axis of the at least one metal reinforcement.

5. The wall made from a composite material according to claim 4, wherein the at least one metal reinforcement has a width of substantially 30 mm.

6. The wall made from a composite material according to claim 4, wherein the at least one metal reinforcement has a thickness of substantially 0.5 mm.

7. The wall made from a composite material according to claim 4, wherein the recesses are spaced apart by distances in a range of 2 to 4 mm and each of the recesses has a length of 30 to 35 mm and a width of substantially 25 mm.

8. The wall made from a composite material according to claim 1, wherein said at least one longilineal metal reinforcement comprises several reinforcements spaced apart by a distance greater than or equal to 5 times a width of each of the reinforcements.

9. The wall made from a composite material according to claim 1, wherein said wall includes sections arranged to form a closed perimeter, and said wall further comprises the composite material with the at least two layers of carbon fibers and at least one longilineal metal reinforcements regularly distributed over a surface of the sections forming the closed perimeter.

10. The wall made from a composite material according to claim 1, wherein said wall includes sections arranged in a closed perimeter and the composite material forms a cover over the sections and extending around the closed perimeter.

11. The wall made from a composite material according of claim 1 wherein the least one longilineal metal reinforcement is immobilized between the at least two layers of carbon fiber.

12. An acoustic wall at least partially made from a fiber reinforced composite material, said reinforced composite material comprising: at least two layers of carbon fibers embedded in a resin matrix and the at least two layers of carbon fibers in direct contact with each other over a majority of an area of each of the layers, wherein the at least two layers have a first direction aligned with the carbon fibers; and at least one longitudinally extending reinforcement embedded in the resin matrix and extending in a second direction which is at an acute angle or perpendicular to the first direction and the at least one longitudinally extending reinforcement is between the at least two layers of carbon fibers, wherein the at least one longitudinally extending reinforcement is made from a material having an elongation at break that is 50% higher than that of the carbon fibers of the at least two layers, the at least one longitudinally extending reinforcement has a cross section which varies in area along the length of the at least one longitudinally extending reinforcement and the outer surface of the at least one longitudinally extending reinforcement is not adhered to the at least two layers of carbon fibers.

13. The wall according to claim 12, wherein the at least one longitudinally extending reinforcement comprises a metal material.

14. The wall according to claim 12, wherein the at least one longitudinally reinforcement includes a metal strip with recesses, wherein each recess has a width narrower than that of the at least one longitudinally reinforcement, and said recesses are symmetrically arranged along a longitudinal axis of the at least one longitudinally reinforcement.

15. The wall according to claim 12, wherein said at least one longitudinally extending reinforcement comprises a plurality of longitudinally extending reinforcements spaced apart in the first direction by a distance greater than or equal to five times a width of the at least one longitudinally extending reinforcement.

16. The wall according to claim 12, wherein said wall further comprises wall sections arranged in a closed perimeter, and said wall sections comprise the reinforced composite material.

17. The acoustic wall of claim 12 wherein the at least one longitudinally extending reinforcement is immobilized between the at least two layers of carbon fiber.

18. An acoustic treatment panel comprising: layers of carbon fibers and at least two of the layers of carbon fibers are in direct contact with each other over a majority of an area of each of the two layers; reinforcement strips between the carbon fiber layers, wherein the reinforcement strips having a length dimension greater than five times of a width dimension, the reinforcement strips are made from a material having an elongation at break that is 50% higher than that of the carbon fibers, the reinforcement strips have a cross section which varies in area along the length of the reinforcement strips and the outer surfaces of the reinforcement strips are not adhered to the layers of carbon fibers; and a resin matrix embedding together the layers and the reinforcement strips, wherein the reinforcement strips are arranged at acute angles greater than zero or at right angles to a direction of potential crack propagation through the layers.

19. The acoustic treatment panel of claim 18 wherein the reinforcement strips are parallel to each other.

20. The acoustic treatment panel of claim 18 wherein the reinforcement strips include recesses symmetrically arranged along a length of each of the reinforcement strips.

21. The acoustic treatment panel of claim 18 wherein the reinforcement strips have a cross section varying in shape along a length of each of the reinforcement strips.

22. The acoustic treatment panel of claim 18 wherein a length of each of the reinforcement strips is greater than five times a width of the corresponding reinforcement strips.

23. The acoustic treatment panel of claim 18 wherein the panel is configured to be assembled with other acoustic treatment panels to form a wall having a closed perimeter.

24. The acoustic treatment panel of claim 18 wherein the at least one longitudinally extending reinforcement is immobilized between the at least two layers of the carbon fibers.

25. The acoustic treatment panel of claim 18 further comprising: an acoustically resistive porous layer, and a cellular layer having a honeycomb structure, wherein the cellular layer includes a first surface adjacent the acoustically resistive porous layer and a second surface adjacent one of the layers of the carbon fibers.

26. A panel having a width and a length, and comprising: overlapping layers of carbon fibers, wherein each of the layers extends the width and the length of the panel and wherein the overlapping layers of carbon fibers are in direct contact with each other over a majority of an area of the panel; at least one longilineal metal reinforcement between the overlapping layers of carbon fibers, having a length greater than a width, and the length is oriented parallel to the width or length of the panel, wherein the length and width of the at least one longilineal metal reinforcement are each smaller than the length and width, respectively, of the overlapping layers of carbon fibers, the at least one longilineal metal reinforcement is made from a material having an elongation at break that is 50% higher than that of the carbon fibers, the at least one longilineal metal reinforcement has a cross section which varies in area along the length of the at least one longilineal metal reinforcement and the outer surface of the at least one longilineal metal reinforcement is not adhered to the layers of carbon fibers; and a resin matrix embedding the overlapping layers of carbon fibers and the at least one longilineal metal reinforcement, wherein the resin matrix continues beyond sides of the at least one longilineal metal reinforcement.

27. The panel of claim 26 wherein the panel includes one or more of the panels arranged as a tube, and the length of the panel corresponds to a length of the tube and a width of the panel corresponds to a perimeter of the tube.

Description

SUMMARY OF THE DRAWINGS

(1) Other features and advantages will emerge from the following description of the invention, which is provided solely as an example, in light of the appended figures, in which:

(2) FIG. 1 is a cross-sectional view in a transverse plane of an acoustic treatment panel,

(3) FIG. 2 is a diagram illustrating a plate made from a reference composite material,

(4) FIG. 3A is a diagram illustrating a plate made from a composite material reinforced with additional plies of fabric in which a crack has spread,

(5) FIG. 3B is a diagram illustrating a plate in which a crack has spread made from a reinforced composite material with reinforcements in the form of Kevlar strips,

(6) FIG. 3C is a diagram illustrating a plate made from a composite material reinforced with metal reinforcements according to the invention that have made it possible to deflect the spread of a crack,

(7) FIG. 4 shows curves for tensile strength tests on plates in a direction parallel to the reinforcements respectively without reinforcements, with additional plies, with Kevlar reinforcements, and with metal reinforcements,

(8) FIG. 5 shows curves for tensile strength tests on plates in a direction perpendicular to the plates respectively without reinforcements, with additional plies, with Kevlar reinforcements, and with metal reinforcements,

(9) FIGS. 6A to 6G are lateral views of reinforcements according to various alternatives of the invention,

(10) FIG. 7 is a cross-sectional view of the reinforcement illustrated in FIG. 6B along cutting line VII-VII,

(11) FIG. 8 is a perspective illustration of a panel for the acoustic treatment of an air intake of an aircraft nacelle illustrating the installation of reinforcements,

(12) FIG. 9 is a transverse cross-sectional view of the panel of FIG. 8, and

(13) FIG. 10 is a transverse cross-sectional view of a wall according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

(14) FIG. 1 shows an acoustic treatment panel 10 including, from the outside toward the inside, an acoustically resistive porous layer 12, at least one cellular structure 14, and a reflective or impermeable wall 16.

(15) The acoustically resistive layer 12 and the cellular structure 14 are not described in more detail, as they are known by those skilled in the art and can be made in the same way as those of the acoustic treatment panels according to the prior art.

(16) The acoustically resistive layer 12 and the cellular structure 14 can be made from a composite material. The reflective wall 16 is made from a composite material. It comprises at least two layers of fibers 18, 18 oriented parallel to the plane of the panel and embedded in a resin matrix.

(17) According to one embodiment, the reflective wall 16 comprises at least two layers of fibers 18, 18, which may or may not be woven, and may or may not be pre-impregnated, the layers being draped on one another. The wall may comprise more than two layers of fibers. As illustrated in FIG. 10, the layers 18, 18 may intersect or be interwoven.

(18) According to one embodiment, these fibers can be made from carbon. As an example, to provide an order of magnitude, the carbon fibers have a diameter comprised between 0.005 mm and 0.015 mm, or a section smaller than 0.0002 mm.sup.2. The invention is applicable to all types of fibers: short fibers or long fibers.

(19) This wall 16 can be subjected to stresses that may cause a crack, also called a fissure, to appear.

(20) Crack refers to the break of at least one ply. It is called a through crack when it passes straight or obliquely through the entire thickness.

(21) In light of the stresses undergone, a crack may spread in a direction called the direction of propagation.

(22) According to the invention, the wall 16 comprises at least one longilineal metal reinforcement 20, arranged to be secant to the direction of propagation of the crack and inserted between two layers of fibers 18, 18. The reinforcement(s) 20 may be arranged between two parallel layers as shown in FIG. 1, or inserted between layers that intersect and pass above/below the reinforcements, as illustrated in FIG. 10.

(23) The reinforcement is metallic due to the ductile properties of metals, which can deform more than fibers can before breaking. Thus, the material used for the reinforcement must have an elongation at break 50% higher than that of fibers.

(24) Metal also encompasses metal alloys and metal matrix nanotechnologies.

(25) Longilineal means that the reinforcement has one dimension that is much larger than the other dimensions. As illustrated in FIGS. 6F and 6G, the reinforcement is not necessarily rectilinear, but can have a curved profile, for example such as corrugations.

(26) For the rest of the description, the longitudinal direction X refers to the direction corresponding to the largest dimension of the reinforcement, i.e. its length.

(27) When the reinforcement is not rectilinear, the longitudinal direction at a given point corresponds to the direction of the tangent to the reinforcement at the given point.

(28) Transverse plane refers to a plane perpendicular to the longitudinal direction.

(29) According to one important point of the invention, the metal reinforcement 20 must have shapes allowing it to be immobilized between the layers of fibers 18, 18 when a tensile force is exerted at one of its ends and preventing it from moving outward.

(30) To that end, as illustrated in FIGS. 6A to 6E, the reinforcement 20 does not have a constant section, that section varying in the longitudinal direction.

(31) Alternatively, as illustrated in FIGS. 6F and 6G, the reinforcement 20 has a non-rectilinear profile in the longitudinal direction, but for example describes corrugations.

(32) Alternatively, as illustrated in FIG. 6G, the reinforcement 20 comprises fastening points 22 to connect it to at least one of the adjacent layers 18, 18.

(33) The fact that the metal reinforcement 20 assumes forms allowing it to be immobilized between the layers of fibers 18, 18 when a tensile force is exerted at one of its ends makes it possible to limit the adhesion between the reinforcement 20 and the adjacent layers 18, 18. Optimally, the outer surface of the reinforcement 20 does not adhere to the adjacent layers 18, 18. This feature favors the deflection of the crack, which tends to spread in the direction of the reinforcement 20.

(34) According to the invention, the layers of fibers 18, 18 on either side of the metal reinforcement 20 are connected outside the surfaces covered by the reinforcement. In this way, the matrix in which the fibers of the layers and the metal reinforcement(s) are embedded is continuous on either side of the reinforcement(s) 20 and polymerized during a same polymerization phase. The wall does not comprise two distinct assembled matrices on either side of the plane of the reinforcement(s).

(35) Advantageously, the reinforcement 20 assumes the form of a strip, as shown in FIGS. 6A to 6E and 7. This feature makes it possible, at a constant section, for the reinforcement to have a reduced thickness for a reinforcement in strip form as compared to a reinforcement in the form of a cylindrical rod. It is possible to provide a strip with a thickness of 0.5 mm and a width in the vicinity of 0.7 mm, which corresponds to a section of 0.35 mm.sup.2. To obtain the same section, a cylindrical reinforcement must have a diameter in the vicinity of 0.65 mm. Providing a reinforcement in the form of a strip makes it possible to limit overthicknesses, and therefore the risks of breaking the fibers of the adjacent layers.

(36) According to another advantage, providing a reinforcement in the form of a strip makes it possible to limit the risks of shearing of the fibers relative to a reinforcement with a circular section, which may behave like a cutting thread.

(37) According to one preferred embodiment illustrated in FIGS. 6A and 6E, the reinforcement assumes the form of a metal strip with recesses 24 with a width smaller than that of the reinforcement and arranged symmetrically relative to the longitudinal median axis of the strip. These recesses define two posts 26, 26 at the strip, said posts being arranged at the longitudinal edges of the strip (parallel to the longitudinal direction) and connected by crosspieces 28. The adjacent layers 18 and 18 are embedded in the same matrix at the recesses.

(38) To provide an order of magnitude, a reinforcement has a width in the vicinity of 30 mm, as illustrated in FIGS. 6A and 6B, in the vicinity of 20 mm as illustrated in FIGS. 6D and 6E, or the vicinity of 10 mm as illustrated in FIG. 6C.

(39) The posts 26, 26 may or may not have the same width. The width of the posts may vary from 2 to 10 mm.

(40) The recesses 24 may be regularly spaced apart, as illustrated in FIGS. 6A to 6C and 6E, or may have different spaces between them, as illustrated in FIG. 6D.

(41) The recesses 24 may have a dimension L1 in the longitudinal direction that is identical or at most equal to two times the dimension L2 in the transverse direction, as illustrated in FIGS. 6B, 6D, 6E.

(42) Alternatively, as illustrated in FIGS. 6A and 6C, the dimension L1 of the recesses is larger than or equal to two times the dimension L2.

(43) Lastly, the posts 26, 26 and the crosspieces 28 may have substantially identical widths, as illustrated in FIGS. 6A to 6C, or certain crosspieces 28 may have a width much larger than that of the posts, as illustrated in FIGS. 6D and 6E.

(44) According to one preferred embodiment, a metal reinforcement 20 has a width in the vicinity of 30 mm and a thickness of the vicinity of 0.5 mm, the posts and the crosspieces have a width in the vicinity of 2 to 4 mm, the recesses are regularly spaced apart and have a dimension L1 of 30 to 35 mm and a dimension L2 in the vicinity of 25 mm.

(45) As illustrated in FIGS. 8 and 9, in the case of a reflective wall 16 of an acoustic treatment panel 10 in the form of a tube portion with an axis 30, reinforcements 20 should be provided oriented parallel to the axis 30, (preferably regularly) distributed over the circumference. Advantageously, in the case of a cylindrical wall of an air intake, 12 to 35 reinforcements should be provided regularly distributed over the periphery, which form an angle varying from approximately 10 to 30 between them. Advantageously, 16 to 18 reinforcement should be provided.

(46) In the case of a wall of a pressurized fuselage, not only should the spread of a crack be limited, but sealing of the wall should also be ensured. In that case, the reinforcements are arranged closer together and forming an angle varying from approximately 2 to 10 between them.

(47) More generally, in the case of a wall made from a composite material of an aircraft having sections in parallel planes with a closed perimeter, for example such as the fuselage or a wing, the reinforcements are arranged between the layers of the wall and oriented in a direction perpendicular to the section planes.

(48) When they are incorporated into a wall in which a crack may spread in a direction of propagation, the reinforcements 20 are spaced apart by a distance greater than or equal to 5 times the width of the reinforcement in the direction of propagation. Preferably, they are oriented perpendicular to the direction of propagation, which must be avoided as a priority.

(49) In FIG. 2, a test piece 32 is provided in the form of a plate made from a composite material, comprising at least two layers of fibers.

(50) This test piece 32 comprises a crack 34 and is subjected to tensile forces 36, 36 arranged on either side of the crack 34 oriented in opposite directions, in a direction Z that is perpendicular to the plane of the test piece, so as to cause the crack 34 to spread in a direction Y embodied by the arrow 38.

(51) The reference test piece 32 does not comprise any reinforcements and comprises a superposition of plies, for example 7 plies, certain plies having fibers oriented in the longitudinal direction, other fibers oriented at +/45 relative to the longitudinal direction. According to one embodiment, the fibers are made from carbon and embedded in an epoxy resin.

(52) In FIG. 3A, the test piece 32 has been reinforced by the addition of plies of the same nature. In this way, the test piece 32 comprises 20% additional plies, which amounts to a 20% increase in the mass of the test piece.

(53) The test piece 32 is subjected to the same stresses as the test piece 32. As illustrated in FIG. 3A, the crack tends to spread in the direction of propagation.

(54) As shown by the curves of FIG. 4, the tensile gain in the longitudinal direction X is 15% between the curve 40, which corresponds to the reference test piece 32, and the curve 42, which corresponds to the test piece 32.

(55) As illustrated in FIG. 5, the tensile gain in the perpendicular direction Z is 2% between the curve 44, which corresponds to the test piece 32, and the curve 46, which corresponds to the test piece 32.

(56) Thus, despite a 20% increase in the mass, a gain of only 2% is obtained regarding the limitation of the spread of the crack, which spreads identically to that of the test piece 32 without reinforcements.

(57) In FIG. 3B, the test piece 32 has been reinforced by adding reinforcements 48 in the form of Kevlar strips. The test piece 32 thus has a mass 5% higher compared to the reference test piece 32. As illustrated in FIG. 3B, the crack tends to spread in the direction of propagation Y.

(58) As shown by the curves of FIG. 4, the tensile gain in the longitudinal direction X is 15% between the curve 40, which corresponds to the reference test piece 32, and the curve 50, which corresponds to the test piece 32.

(59) As illustrated in FIG. 5, a tensile gain in the perpendicular direction Z is 50% between the curve 44, which corresponds to the test piece 32, and the curve 52, which corresponds to the test piece 32.

(60) In FIG. 3C, the test piece 32 has been reinforced by adding metal reinforcements 54 according to the invention, spaced apart in the direction of propagation Y. The test piece 32 has a mass 2% higher compared to the reference test piece 32. As illustrated in FIG. 3C, the crack tends to spread in the direction of propagation Y as far as the reinforcement, then is deflected and tends to spread in the longitudinal direction X.

(61) As shown by the curves of FIG. 4, the tensile gain in the longitudinal direction X is 30% between the curve 40, which corresponds to the referenced test piece 32, and the curve 56, which corresponds to the test piece 32.

(62) As illustrated in FIG. 5, a tensile gain in the perpendicular direction Z is 120% between the curve 44, which corresponds to the test piece 32, and the curve 58, which corresponds to the test piece 32.

(63) Thus, as shown by this trial, the crack does not spread in the direction of propagation, but is deflected owing to the reinforcements according to the invention. Furthermore, it will be noted for the test piece with metal reinforcements according to the invention that there is a much greater gain compared to the other test pieces with a more limited impact on the mass. These trials overcome a prejudice of those skilled in the art tending to think only of the iso-mass; composite materials have better mechanical properties than metals, with the result that metal aircraft parts are replaced by elements made from a composite material.