IT201900009915A1 - COMPOSITE-METAL JOINT BASED ON ENGINEERED SURFACE AND RELEVANT MANUFACTURING METHOD - Google Patents

Description

Description of the Industrial Invention entitled:

"COMPOSITE-METAL JOINT BASED ON ENGINEERED SURFACE AND RELATIVE METHOD OF CONSTRUCTION"

DESCRIPTION

The present invention relates to a joint between fiber composite materials and metallic materials, in accordance with the preamble of claim 1. In particular, a joint between fiber composite materials and metallic materials and a method for making such a joint is illustrated. The joint, object of the present invention, can be used in complex structures obtained from the assembly of different materials for functional and / or aesthetic needs, such as for example in the aeronautical, space, energy (in wind generators, turbine blades), automotive ( racing vehicles) and in the medical sector.

In current joints, composite and metal materials are glued using various types of single or double component adhesives, using or not passages in a controlled temperature oven. To facilitate the adhesion of the resin in the joint, additional techniques are also used, such as mechanical abrasion of the metal surfaces of the joint, or the surface metal oxide of the joint is mechanically removed. These additional techniques make the process of making these joints more complex and inefficient.

The gluing techniques have a series of drawbacks illustrated below.

A first drawback is due to the limited mechanical properties of adhesion of the adhesive which consequently entail limited mechanical properties, such as elasticity and resistance to the stresses of the joint.

Another problem is due to the different thermal expansion between the two materials of the joint which, in case of heating, are able to cause residual stresses at the interface of the bonded joint and therefore to produce the failure of the adhesive.

A further problem is due to the aging of the adhesive as a result of its mechanical wear, making the joint less durable and less reliable.

Another drawback is due to the influence of UV radiation which contribute to deteriorate the adhesive and reduce its performance, making the joint less reliable.

The purpose of the present invention is therefore to solve these and other problems of the known art, in particular to indicate a junction between fiber composite materials and metal materials without using adhesives between the two materials.

A further object of the present invention is to indicate a junction between fiber composite materials and metallic materials with high resistance to mechanical stresses due, for example, to the presence of static and cyclic loads.

Another object of the present invention is to indicate a junction between fiber composite materials and metallic materials capable of distributing any residual thermal expansion stresses in a much more efficient way.

Another object of the present invention is to indicate a junction with high reliability between fiber composite materials and metallic materials.

A further object of the present invention is to indicate a UV radiation resistant junction between fiber composite materials and metallic materials.

The objects indicated above apply equally to a method for making a joint between fiber composite materials and metallic materials.

The invention described consists of a joint comprising long or short fiber composite materials and metallic materials, and related method of making said joint.

A fiber composite material and a metal material are connected at the level of their internal structure by means of a suitable geometry of the metal surface, which can be achieved through additive manufacturing processes, such as for example by casting a powder bed. The present invention allows to obtain a joint with high mechanical strength and prolonged reliability between the two materials. The presence of a controlled and inert atmosphere, typical of metal additive manufacturing processes, is also exploited to prevent surface oxidation of the metal, obtaining an improved joint.

A technique for the production of composite materials, which does not use adhesives, is discussed for example in the document "A HYBRID METAL-TO-COMPOSITE JOINT FABRICATED THROUGH ADDITIVE MANUFACTURING PROCESSES" by Thomas J. Whitney and collaborators, presented at IMECE2012 (International Mechanical Engineering Congress & Exposition), November 9-15, 2012 in Houston, Texas (USA).

This document illustrates the application of additive technology for the casting of metal, such as titanium, on a substrate of carbon fibers, in order to obtain a composite material.

The technical solution proposed by said document does not describe a junction between composite materials and metallic materials, as typically the additive processes from precision casting of powders have very stringent process specifications that do not allow their combination with other technologies, such as that of materials composites. Therefore, in general, it is very difficult to make joints between composite materials and metals without the use of adhesives.

Further advantageous features of the present invention are the subject of the attached claims which form an integral part of the present description.

The invention will be described in detail below through non-limiting embodiments with particular reference to the attached figures, in which:

Figures 1a and 1b schematically show the structure of some fiber composite materials usable in a junction between fiber composite materials and metal materials according to an embodiment of the present invention;

Figure 2 schematically represents a junction between a fiber composite material of Figure 1 and a metallic material according to an embodiment of the present invention;

Figure 3 represents an exemplary flow chart of a method for producing the junction between fiber composite materials and metallic materials of Figure 2;

Figure 4 schematically exemplifies a structure comprising at least one joint between a fiber composite material and a metallic material according to an embodiment of the present invention.

With reference to Figure 1, a composite material is characterized by the presence of at least two constituents (or phases), namely a continuous phase (or matrix) and a dispersed phase (reinforcement or filler). Generally, the matrix is made up of a continuous and homogeneous material, which has the function of enclosing the reinforcement, in order to guarantee the cohesion of the composite material and to ensure that the reinforcing particles, or fibers, have the right dispersion at the inside the composite and there is no segregation. The matrix can be, for example, a polymer-based compound (Nylon, epoxy resins) or it can be a metal-based (aluminum, titanium), carbon-based (graphitic or amorphous) or ceramic-based (alumina) compound. The reinforcement is dispersed through various techniques inside the matrix and has the task of ensuring the rigidity and mechanical resistance of the composite material, taking on itself most of the external load. The reinforcement can be made from particles, fibers or laminar structures (panels, sandwiches). The reinforcements with fibers can be long or short fibers, the fibers can be made up of glass, carbon (graphitic or amorphous), ceramics (alumina) and Aramid fibers (Kevlar). The fibers can be intertwined to create a more or less extended two-dimensional structure within the matrix, such as a fabric made with carbon fibers.

Figure 1a schematically represents a long fiber composite material 140 usable in a junction between fiber composite materials and metallic materials, according to an embodiment of the present invention. Long fibers 120 are arranged in an orderly manner in one or more directions in a matrix 110, so that the macroscopic mechanical characteristics of the long fiber composite material 140 are globally anisotropic. Figure 1b schematically represents a short fiber composite material 150 usable in a junction between composite materials and metallic materials, according to an embodiment of the present invention. Short fibers 130 are arranged in a disordered manner in the matrix 110, so that the macroscopic mechanical characteristics of the short fiber composite material 150 are globally isotropic. Alternatively, the short fibers 130 can be arranged in an orderly manner along one or more directions in the matrix 110, in which case the macroscopic mechanical characteristics of the short fiber composite material 150 are globally anisotropic.

Figure 2 schematically represents a junction 200 between the long fiber composite material 140 and a metallic material 210, such as aluminum alloys, titanium, steels and nickel based alloys, according to an embodiment of the present invention. As described above, the long fiber composite material 140 comprises the long fibers 120, which are arranged in an orderly manner in one or more directions in the matrix 110.

The present invention is based on the engineering of at least one interface surface 215 of the metallic material 210 in contact with the fiber composite material, such as the long fiber composite material 140. The interface surface 215 is designed and manufactured by means of processes of additive manufacturing. Among these we cite, by way of example, and not exhaustively, the technology of precision casting of metal powders. The precision casting processes of powders are based on the localized concentration of a heat source, such as LASER or electron beams, capable of producing a change of state of the metal with a high degree of dimensional detail. The starting metal powder undergoes a process of fusion and subsequent solidification according to successive and superimposed layers, until the desired final geometry is obtained. Appropriate systems currently on the market are able to manage the entire process starting from the supply of powder, to the movement of this powder, to the regulation of the controlled atmosphere, to the regulation of the thermal source and to the movement of the junction 200 under construction. . Powder casting technologies are aimed at metallic materials, typically aluminum alloys, titanium, steels and nickel-based alloys. Their diffusion has increased in the last decade thanks to the development of the supply chain linked to additive manufacturing including dedicated design systems, such as software for topological optimization and plant equipment, refinement of production techniques and dust control. , stabilization of plant processes and machines, fine-tuning of post-production heat treatments and growing awareness of end users about the new technology. Among the main advantages associated with components obtained from precision casting of powders is the geometric complexity (freeform) in the face of reduced or non-existent complications of the production process of the junction 200. This characteristic meets the needs of lightening, local control of stresses, local control of the forced refrigeration, increase in the versatility of molds and prototypes. The aforementioned processes take place in the presence of an inert atmosphere including, for example, argon or other gases, to prevent oxidation of the powder during the casting phases. The process takes place in sealed chambers with gas insufflation.

The interface surface 215 comprises at least one anchoring means 220 adapted to receive at least one fiber of a composite material, such as for example the long fiber 120 of the long fiber composite material 140.

Said at least one anchoring means is made by means of a growth process deriving from additive manufacturing techniques, such as for example the micro-casting technology of metal powders. For this growth process, the starting metal powder undergoes a process of fusion and subsequent solidification according to successive and superimposed layers, until the desired final geometry of the interface surface 215 is obtained.

Said anchoring means 220 may comprise at least one hollow structure (or cell) which may comprise at least one hook-shaped or ring-shaped structure and / or comprise one or more protruding or cantilevered elements and / or comprise at least one cavity and / or at least a cavity. Said at least one hollow structure can be of variable dimensions depending on the dimensions of the fibers of a composite material, such as for example the long fiber 120 of the long fiber composite material 140. A hollow structure not protruding from the interface surface 215, such as for example a cavity or a cavity can be made for example by means of said growth process, deriving from additive manufacturing techniques, carried out before making a hollow structure protruding from the interface surface 215, such as for example a hook-shaped structure.

Said anchoring means 220 is able to receive inside it one or more fibers of a composite material of the joint, such as for example the long fibers 120 of the long fiber composite material 140 of the joint 200, so as to make one or more fibers mechanically integral. to the anchoring means 220. One or more anchoring means 220 can be arranged repetitively or periodically on the interface surface 215 until it totally or partially covers the surface itself.

In another embodiment of the invention, the anchoring means 220 can receive one or more fibers of a composite material, such as the short fibers 130 of the short fiber composite material 150. In this embodiment of the invention , one or more anchoring means 220 can be arranged aperiodically on the interface surface 215 until it totally or partially covers the surface itself. Alternatively, if the short fibers 130 are arranged in an orderly manner along one or more directions in the matrix 110, one or more anchoring means 220 can be periodically arranged on said interface surface 215.

In a further embodiment of the invention, one or more anchoring means 220 can be arranged periodically or aperiodically according to the type of fibers, short or long, oriented or non-oriented, comprised in a composite material of an object junction of the present invention.

In another embodiment of the invention, at least one anchoring means 220 can be of a different shape than a further anchoring means 220 based on the type of fibers, short or long, oriented or non-oriented. Said at least one anchoring means 220 can be arranged according to a predefined pattern on the interface surface 215, until it totally or partially covers the surface itself. Said predefined scheme can be determined on the basis of the type of fiber composite material of the junction 200.

In a further embodiment of the invention, said at least one anchoring means 220 can receive groups of short or long fibers, oriented or non-oriented. Said groups of fibers can be, for example, bundles of fibers or weaves of fibers or a two-dimensional fabric of fibers.

The present invention can be used in structures comprising at least one joint between fiber composite materials and metallic materials, such as the joint 200. These structures can be obtained by assembling different materials for functional and / or aesthetic needs, such as for example in the aeronautics, space, energy (in wind generators, turbine blades), automotive (racing vehicles) and in the medical sector. With reference to Figure 4, a structure 400 is described comprising at least one junction 200 according to an embodiment of the present invention. Said structure 400 can be for example a sandwich panel consisting of walls in composite fiber material 410 and a core 420 in different materials such as foams, polymers, honeycomb structures and so on. Said structure 400 can comprise, for example, a metal insert 405. In this embodiment, the present invention is applied to the surfaces of the metal insert 405 in contact with the composite fiber material 410 of the structure 400, i.e. in the interface area of the insert metal 405. The junctions according to the present invention, such as the junction 200, are made at this interface.

With reference to Figure 3, an exemplary method for producing the junction 200 between fiber composite materials and metallic materials according to an embodiment of the present invention is described.

At step 310, an initialization phase is carried out, in which a production plant of the junction 200 is initialized, for example the plant is supplied with the metal powders for the realization of said plurality of anchoring means. In this phase, and in the subsequent phases, the volume in which the junction 200 is produced is filled with an inert atmosphere, including for example a gas such as argon, so as to preserve the interface surface 215 and said at least one means of anchoring from oxidation processes.

At step 320, a first growth step is carried out in which a first layer of fibers, such as for example a layer comprising the long fibers 120, is positioned on the interface surface 215 comprising said at least one anchoring means, so that said at least one anchoring means 220 is adapted to receive at least one or more fibers, such as for example the long fibers 120, of said first layer of fibers. In this way one or more fibers, such as for example said long fibers 120, are mechanically integral with the anchoring means 220.

Said at least one anchoring means is made by means of a growth process deriving from additive manufacturing techniques, such as for example the micro-casting technology of metal powders.

During said growth process, said at least one anchoring means 220 is made in such a way as to comprise at least one hollow structure (or cell) which can comprise at least one hook-shaped or ring-shaped structure and / or comprise one or more protruding elements or overhang and / or comprise at least one interspace and / or at least one cavity. Said at least one hollow structure can be of variable dimensions depending on the dimensions of the fibers of a composite material, such as for example the long fiber 120 of the long fiber composite material 140. A hollow structure not protruding from the interface surface 215, such as for example a cavity or a cavity can be made for example by means of said growth process, deriving from additive manufacturing techniques, carried out before making a hollow structure protruding from the interface surface 215, such as for example a hook-shaped structure.

In this way, the anchoring means 220 is able to receive inside it one or more fibers of a composite material of the joint, such as for example the long fibers 120 of the long fiber composite material 140 of the joint 200, so as to make one or more a plurality of fibers mechanically integral with the anchoring means 220. During said growth process, one or more anchoring means 220 can be arranged repetitively or periodically on the interface surface 215 until it totally or partially covers the surface itself. In another embodiment of the invention, during said growth process, one or more anchoring means 220 can be made of a different shape with respect to a further anchoring means 220 according to the type of fibers, short or long, oriented or not oriented. Said at least one anchoring means 220 can be arranged according to a predefined pattern on the interface surface 215, until it totally or partially covers the surface itself. Said predefined scheme can be determined on the basis of the type of fiber composite material of the junction 200.

In another embodiment of the invention, said first layer of fibers is positioned on the interface surface 215 before carrying out said growth process to achieve said plurality of anchoring means. In this case, said at least one anchoring means 220 is adapted to receive at least one or more fibers, such as for example the long fibers 120, of said first layer of fibers.

During the first growth phase, after receiving the first layer of fibers, as described above, a first layer of matrix is deposited, for example a liquid polymeric matrix, so that it can incorporate both said fibers and said plurality of anchoring means. In this way, a first layer of fibers and matrix is formed in contact with a metal material, such as the metal material 210. During the first growth phase, said anchoring means 220 is able to receive the matrix of said first matrix layer, if it has not received at least one fiber of said first fiber layer, so as to favor the adhesion between said first fiber layer and matrix in contact with a metallic material.

In one embodiment of the invention, instead of fibers and matrix in separate form, it is possible to use special components, called prepregs, to make a composite material, such as the composite material with long fiber 140.

At step 330, a second growth step is carried out in which at least one further layer of fibers and matrix is deposited on the first layer of fibers and matrix, described in the previous step, so as to obtain an assembly comprising said first layer of fibers and matrix and at least one further layer of fibers and matrix.

At step 340, a hardening step is carried out in which said assembly, obtained in the previous step, is subjected to a hardening process of the matrix of said first layer of fibers and matrix and at least one further layer of fibers and matrix, for example by means of processes heating and / or pressing and so on.

At step 340, a finalization phase is carried out, in which the production plant of the junction 200 reaches a state of rest. During this phase it is possible to carry out a quality control of the junction 200 obtained through the previous steps.

From the above description the advantages of the present invention are therefore evident.

The method according to the present invention advantageously allows to realize the junction between fiber composite materials and metallic materials, described in the present invention, advantageously having an integration method between fiber composite materials and structural metallic materials, without using of adhesives, compared to the solution with gluing currently practiced.

The junction between fiber composite materials and metallic materials, described in the present invention, advantageously has a high resistance to mechanical stresses through direct interaction between the fibers of the composite material and the metallic material by means of at least one interface surface between the fiber composite materials and metallic materials. The interface surface is specially engineered and can advantageously comprise hollow structures (or cells), such as for example hooks or rings or similar elements, within which one or more fibers of the composite are received.

The junction between fiber composite materials and metal materials, described in the present invention, advantageously allows any residual thermal expansion stresses to be distributed much more efficiently, since the fibers and the cell structures create a solid and inseparable mechanical connection, of far more robust and reliable than a bonded connection.

Another advantage of the junction between fiber composite materials and metal materials, described in the present invention, is a high reliability, advantageously exploiting the inert atmosphere of the powder casting process to prevent surface oxidation of the metal during the production of the metal part. and the creation of the junction. In fact, surface oxidation causes greater brittleness of the chemical adhesion layer between the materials: in current solutions this involves disadvantageously eliminating the oxidized material by abrasion or grinding.

Naturally, the principle of the invention remaining the same, the embodiments and construction details may be widely varied with respect to what has been described and illustrated purely by way of non-limiting example, without thereby departing from the scope of protection of the present document. invention defined by the appended claims.

Claims (19)

CLAIMS 1. Junction (200) between fiber composite materials and metallic materials comprising: - a fiber composite material (140; 150), - a metallic material (210), - at least one interface surface (215) of said metal material (210) in contact with said fiber composite material (140; 150), said junction (200) being characterized in that said interface surface (215) comprises at least one anchoring means (220) able to receive at least one fiber of said fiber composite material (140; 150). Joint (200) according to claim 1, wherein said anchoring means (220) comprises at least one hollow structure of variable dimensions depending on the dimensions of the fibers of said fiber composite material (140; 150). 3. Joint (200) according to claim 2, wherein said anchoring means (220) is adapted to receive inside it one or more fibers of said fiber composite material (140; 150) so as to make one or more fibers of said fiber composite material (140; 150) mechanically integral with said anchoring means (220). Joint (200) according to one or more of claims 2 to 3, wherein said at least one hollow structure comprises at least one hook-shaped or ring-shaped structure and / or comprises one or more protruding or cantilevered elements and / or comprises at least one cavity and / or at least one cavity. Joint (200) according to one or more of claims 1 to 4, wherein at least one anchoring means (220) is of a different shape than a further anchoring means (220), according to the type of fibers, short or long, oriented or undirected of said fiber composite material (140; 150). 6. Joint (200) according to one or more of claims 1 to 5, wherein said at least one anchoring means (220) is arranged according to a predefined pattern on the interface surface (215), until it totally or partially covers said interface surface (215), said predefined pattern being determined on the basis of the type of fiber composite material (140; 150). Joint (200) according to one or more of claims 1 to 6, wherein said at least one anchoring means (220) can receive groups of short or long fibers, oriented or non-oriented, said groups of fibers being bundles of fibers or weaves of fibers or a two-dimensional fabric of fibers. Structure comprising at least one joint (200) according to one or more of claims 1 to 7. 9. Method for producing a joint (200) between fiber composite materials and metallic materials, called joint (200) comprising: - a fiber composite material (140; 150), - a metallic material (210), - at least one interface surface (215) of said metal material (210) in contact with said fiber composite material (140; 150), said method comprising: - a first growth step in which a first layer of fibers of said fiber composite material (140; 150) is positioned on said interface surface (215), in which a first layer of matrix is deposited so as to form a first layer of fibers and matrix in contact with said metallic material (210), said method being characterized in that during said first growth step at least one fiber of said first fiber layer of said fiber composite material (140; 150) is received in at least one anchoring means (220) of said interface surface ( 215). Method according to claim 9, wherein said at least one anchoring means is made by means of a growth process deriving from additive manufacturing techniques. 11. Method according to claim 10, wherein said growth process is carried out by means of the micro-casting technology of metal powders. Method according to one or more of claims 10 to 11, wherein said first layer of fibers is positioned on the interface surface (215) before carrying out said growth process to realize said plurality of anchoring means, so that said at least one anchoring means (220) is adapted to receive at least one or more fibers of said first layer of fibers. Method according to one or more of claims 10 to 12, wherein during said growth process, said anchoring means (220) is made to comprise at least one hollow structure of variable dimensions depending on the size of the fibers of said composite material fiber (140; 150). Method according to claim 13, wherein during said growth process, said anchoring means (220) is made so as to receive inside it one or more fibers of said fiber composite material (140; 150) so as to make one or more fibers of said fiber composite material (140; 150) mechanically integral with said anchoring means (220). Method according to one or more of claims 13 to 14, wherein during said growth process, said at least one hollow structure comprises at least one hook-shaped or ring-shaped structure and / or comprises one or more protruding or cantilevered elements and / or comprises at least one cavity and / or at least one cavity. Method according to one or more of claims 10 to 15, wherein during said growth process, said at least one anchoring means (220) is made of a different shape with respect to a further anchoring means (220) according to the type of fibers, short or long, oriented or non-oriented, of said fiber composite material (140; 150). Method according to one or more of claims 10 to 16, wherein during said growth process, said at least one anchoring means (220) is arranged according to a predefined pattern on the interface surface (215), until it totally covers or in part said interface surface (215), said predefined pattern being determined on the basis of the type of fiber composite material (140; 150). Method according to one or more of claims 9 to 17 comprising: - a second growth phase in which at least one further layer of fibers and matrix is deposited on said first layer of fibers and matrix, so as to obtain an assembly comprising said first layer of fibers and matrix and at least one further layer of fibers and matrix , - a hardening step in which said assembly is subjected to a hardening process of the matrix of said first layer of fibers and matrix and of said at least one further layer of fibers and matrix, by means of thermal heating and / or pressing processes. 19. Method according to one or more of claims 9 to 18, in which said first growth phase, said second growth phase and said hardening phase are carried out in a volume filled with an inert atmosphere so as to preserve the interface surface (215) and said plurality of anchoring means from oxidation processes.