INTERMEDIATE DEFORMATION LAYER WITH ADJUSTABLE MACROSCOPIC STIFFNESS FOR BONDED ASSEMBLY

Abstract

Disclosed is a bonded assembly comprising at least: a first substrate, a second substrate, an intermediate deformation layer secured to the first substrate, the intermediate deformation layer comprising a material in which cavities are provided so that the intermediate deformation layer has a stiffness which is variable along a direction parallel to the intermediate deformation layer, an adhesive between the intermediate layer and the second substrate.

Claims

1: A bonded assembly comprising at least: a first substrate, a second substrate, an intermediate deformation layer secured to the first substrate, the intermediate deformation layer comprising a material in which cavities not compartmentalized from each other are provided so that the intermediate deformation layer has a stiffness which is variable along a direction parallel to the intermediate deformation layer, an adhesive between said intermediate layer and the second substrate.

2: The bonded assembly according to claim 1, wherein one or more of a first face of the intermediate deformation layer or a second face of the intermediate deformation layer respectively have shapes complementary to the first substrate and/or to the second substrate.

3: The bonded assembly according to claim 1, wherein the intermediate deformation layer comprises elements of elongated shape connecting two faces of the intermediate deformation layer.

4: The bonded assembly according to claim 3, wherein the elongated elements form a lattice structure.

5: The bonded assembly according to claim 3, wherein the elongated elements are aligned in a direction orthogonal to the intermediate deformation layer.

6: The bonded assembly according to claim 3, wherein the stiffness of the intermediate deformation layer along one direction is adapted by adapting cross-sections of the elements and/or spacings between the elements and/or directions of the elements.

7: The bonded assembly according to claim 1, wherein the material has the same Young's modulus value as the Young's modulus value of the adhesive.

8: The bonded assembly according to claim 1, wherein the stiffness of the intermediate layer varies gradually.

9: The bonded assembly according to claim 1, wherein the intermediate layer comprises a portion arranged at the edge of the intermediate layer and having a lower stiffness along one direction than the stiffness along said direction of another portion of the intermediate layer.

10: The bonded assembly according to claim 1, wherein the intermediate deformation layer comprises a portion covering one or more of an area of weakness of the second substrate, a crack in the second substrate, or an area of high stress, said portion of the intermediate deformation layer having a lower stiffness along one direction than the stiffness along said direction of another portion of the intermediate deformation layer.

11: The bonded assembly according to claim 1, wherein one or more of a mechanical resistance of the intermediate deformation layer to tensile stress or a mechanical resistance of the intermediate deformation layer to shear stress is lower than the mechanical resistance of at least one of the first substrate or the second substrate.

12: The bonded assembly according to claim 1, wherein the intermediate deformation layer is formed of a material that is homogeneous in composition.

13: A method for manufacturing an element of a bonded assembly, the method comprising: the formation of an intermediate deformation layer comprising a material, said formation being carried out so as to obtain cavities in the material such that the intermediate deformation layer has a stiffness which is variable along a direction parallel to the intermediate deformation layer; securing together the formed intermediate layer and a first substrate.

14: The manufacturing method according to claim 13, wherein the formation of the intermediate layer is carried out by an additive manufacturing technique.

15: The manufacturing method according to claim 13, the method further comprising: the obtaining of data relating to a shape of a surface of a second substrate; wherein the formation of the intermediate deformation layer is carried out so as to obtain a surface of the intermediate deformation layer having a shape complementary to the shape of the surface of the second substrate.

16: A method for manufacturing a bonded assembly, comprising: the manufacturing of an element of a bonded assembly, according to claim 13, the method further comprising the bonding of the intermediate deformation layer to a second substrate by means of an adhesive.

17: The manufacturing method according to claim 19, wherein the bonding of the intermediate deformation layer to the second substrate by means of the adhesive is carried out so that said surface of the intermediate deformation layer is secured to the surface of the second substrate in a complementary manner.

18: A method for reinforcing a structure comprising at least one substrate to be reinforced, the method comprising: securing together a reinforcing substrate and an intermediate layer comprising a material in which cavities not compartmentalized from each other are provided such that the intermediate deformation layer has a stiffness which is variable along a direction parallel to the intermediate deformation layer, holding the reinforcing substrate and the intermediate deformation layer on the substrate to be reinforced, by means of an adhesive.

19: The method for manufacturing the bonded assembly of claim 16, the method further comprising: obtaining of data relating to a shape of a surface of the second substrate; wherein the formation of the intermediate deformation layer is carried out so as to obtain a surface of the intermediate deformation layer having a shape complementary to the shape of the surface of the second substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0113] Other features and advantages of the disclosure will become apparent upon examining the detailed description below and the appended drawings, in which:

[0114] FIGS. 1A-1C illustrate examples of typical embodiments of a bonded assembly, and show the deformations and shear stresses conventionally undergone by the adhesive, in particular at its edges.

[0115] FIGS. 2A-2C illustrate examples of embodiments of a reinforcing element bonded to a structure, generating deformations and stresses similar to the examples of FIGS. 1A to 1C.

[0116] FIG. 3 represents the evolution, as a function of the overlapping length of two substrates of the adhesion interface of the adhesive, of the ultimate force to be applied in order to obtain rupture of the adhesive in a conventional bonded assembly.

[0117] FIGS. 4A-4B illustrate examples of a bonded assembly according to the disclosure.

[0118] FIGS. 5A-5G illustrate examples of the intermediate deformation layer according to the disclosure.

[0119] FIG. 6 illustrates a method for manufacturing a bonded assembly AC according to the disclosure.

DETAILED DESCRIPTION

[0120] We now refer to FIGS. 4A and 4B in which are illustrated examples of a bonded assembly AC according to the disclosure. The assembly includes a first substrate S1 and a second substrate S2.

[0121] In the example shown in FIG. 4A, a mechanical connector (CM) is secured to the first substrate S1; the second substrate may be a wall. Once the first substrate (S1) has been fixed to the second substrate (S2), the bonded assembly (AC) forms an attachment means on the wall.

[0122] In the example represented in FIG. 4B, the first substrate S1 is a reinforcing element intended to repair, protect, and/or reinforce a structure comprising the second substrate S2. The reinforcing element may take the form of a rigid plate superimposed on a wall of the structure, typically a plate made of metal, composite, or any other material of sufficient rigidity to reinforce the structure. This reinforcement may be used in particular to reinforce: [0123] concrete structures in seismic zones which can cause cracks that are millimetric in magnitude; [0124] metal structures undergoing significant cyclic loads; [0125] metal or concrete structures undergoing instantaneous or long-term deformations (shrinkage, damage, creep, corrosion).

[0126] The assembly AC comprises an intermediate deformation layer, CID, called “deformation”, and an adhesive AD. The adhesive AD is placed between substrates S1 and S2 and is intended to secure them to one another via the CID. The CID comprises a first securing interface INT1 with the substrate S1, and a second securing interface INT2 with the adhesive AD. The CID has variable stiffness along interfaces INT1 and INT2.

[0127] The CID and the adhesive AD may be made from the same material. The CID may in particular have a Young's modulus close to that of the adhesive AD.

[0128] The material used for the CID may in particular be selected among the following list of polymers: [0129] an epoxide; [0130] an elastomer; [0131] a plastic; [0132] polyurethane; or [0133] a composite.

[0134] The use of epoxy and/or polyurethane proves to be particularly effective. Indeed, the adhesive affinities between the CID and the adhesive AD are then improved.

[0135] The stiffness R.sub.vector(v)(x.sub.1,y.sub.1) of the CID at a point (x.sub.1;y.sub.1) thereof along vector(v) expresses the proportionality relationship between the force F applied at that point and along the same direction as vector(v) and the resulting deflection at that point. When the vector(v) is perpendicular to the CID we use the term tension-compression stiffness; when the vector(v) is parallel to the CID we use the term shear stiffness. This is expressed in newtons per meter (N/m).

[0136] The adhesive AD may be relatively rigid and has good capacities for adhesion: [0137] with the substrate S2, due to its rigidity; and [0138] with the CID because of the adhesive affinities of their material and possibly because of the Young's modulus of the CID which may be similar to that of the adhesive AD.

[0139] The intermediate deformation layer CID makes it possible to improve: [0140] the absorption of differential deformations at the periphery of the adhesive layer AD (by means of the CID); and [0141] the general adhesion capacities at the interfaces INT1 and INT2 with the substrates via the adhesive AD in which the stresses are distributed more evenly.

[0142] In this case, the CID of variable stiffness makes it possible to obtain a controlled behavior which more evenly distributes the shear and peel stresses generated by external forces applied to the bonded assembly AC.

[0143] The deformation absorption behavior of the CID makes it possible to reduce or even eliminate the edge effects which usually occur at the adhesive AD in the prior art.

[0144] The desired value of the stiffness of the CID along one direction and the variation in stiffness along the CID are obtained via cavities within the layer, as specified above. Thus, to reduce stiffness R.sub.vector(v)(x.sub.1,y.sub.1) at point (x.sub.1,y.sub.1) it is possible for example to: [0145] reduce the number and/or the cross-section of the microstructures (elongated elements) oriented along the direction of vector(v); and/or [0146] increase the density of the cavities around point (x.sub.1,y.sub.1); and/or [0147] orient the elongated elements advantageously.

[0148] Examples of CIDs with different microstructures are presented below.

[0149] In the case of FIG. 4A, a portion P1 arranged at the edge of the CID is represented. This portion of the CID has a lower stiffness level than that of the portion P2 arranged in a central part of the CID. Portion P1 may be for example the peripheral part of the CID, namely the part representing the 20% of the CID at the edge in the longitudinal direction. More specifically, edge effects are greatly reduced when reducing, in P1: [0150] the stiffness in a direction perpendicular to the CID (vector(v)=vector(z)) in order to reduce the edge effects relating to peel stresses; and/or [0151] the stiffness, in the vicinity of a point on the edge, along a direction perpendicular to the edge at this point of the CID and parallel to the plane of the CID (i.e. the radial direction from the edge in the plane of the CID, vector(v)=vector(r) for a polar reference system of the CID when it is a disk) to reduce the edge effects relating to shear.

[0152] Because the edge effects are reduced (limit length L.sub.max is substantially increased), the breaking strength of the CID is improved.

[0153] In the case of FIG. 4B, a portion P3 is shown arranged at an area of weakness of the CID, namely a crack in the wall. Portion P3 of the CID has a lower stiffness level than that of portion P2.

[0154] More specifically, the transfer of stresses between the first substrate (S1) and the second substrate (S2) in the vicinity of the crack is greatly reduced when the stiffness in P3 is reduced along the direction(s) in which the stresses are applied at P3 (namely along the direction perpendicular to the CID if the stresses are peel stresses and/or along one or more longitudinal directions if the stresses are shear stresses).

[0155] Although the example of FIG. 4A concerns a mechanical connector and that of FIG. 4B concerns a reinforcement, the CID described in FIG. 4A may also comprise a portion P3 as described in FIG. 4B when the second substrate (S2) has areas of weakness. Similarly, the CID described in FIG. 4B may also comprise a portion P1 as described in FIG. 4A when the bonded assembly (AC) is subjected to high stresses leading to edge effects.

[0156] Reference is now made to FIGS. 5A to 5G in which embodiments of the intermediate deformation layer (CID) of variable stiffness have been represented. All of these CIDs can be used in the embodiment of FIG. 4A as well as in that of FIG. 4B. FIG. 5A is a cross-sectional view of the CID shown in FIG. 5B.

[0157] The CID comprises a first outer layer CEx1 which is secured to the first substrate S1, and a second layer CEx2 which is secured to the second substrate S2 via the adhesive AD.

[0158] Microstructures, MS, connect the two outer layers CEx1 and CEx2. The MS form spacers between the two outer layers CEx1 and CEx2. The cavities, EV, are the spaces not occupied by the MS between CEx1 and CEx2 of the CID. Each CID, and in particular its stiffness and the variation thereof within the plane of the CID, are characterized by the material used to form the CID and the structure formed by the MS or, equivalently, the structure formed by the cavities.

[0159] The MS of FIGS. 5A and 5B are elongated elements of rectangular cross-section. The MS form a lattice. The stiffness of the CID can be adapted to obtain the desired properties as described in FIGS. 4A and 4B. For example, to reduce the stiffness at the edge of the CID in all directions: [0160] the MS at the edge of the layer, for example MS1, can have a smaller cross-section than the MS at the heart of the CID, for example MS2; [0161] it is possible to have fewer MS at the edge of the CID.

[0162] To reduce the stiffness in the direction orthogonal to the CID at the edge of the CID and increase the stiffness in a direction parallel to the CID, it is possible to: [0163] reduce the angle of inclination of the MS at the edge of the CID relative to CEx1 and CEx2.

[0164] Conversely, when the angle of inclination of the MS at the edge of the CID relative to CEx1 and CEx2 is increased, the stiffness in the direction orthogonal to the CID is increased at the edge of the CID and the stiffness in a direction parallel to the CID is reduced. More generally, when the MS are modified inversely to what is described above, an inverse modification of the stiffness is obtained.

[0165] The MS which are not located at the edge of the CID, for example MS2, can also be adapted in the same manner to vary the stiffness, in particular in the case where the second substrate S2 has areas of weakness, for example at MS2.

[0166] Such a lattice structure of the MS makes it possible to adapt the stiffness along the direction orthogonal to the CID and the stiffness along a direction parallel to the CID without relative constraints between them.

[0167] The MS of FIGS. 5C and 5D are elongated elements of rectangular cross-section. The MSs are substantially aligned in the direction orthogonal to the CID. The stiffness of the CID can be adapted to obtain the desired properties as described in FIGS. 4A and 4B. For example, to reduce the stiffness at the edge of the CID in all directions: [0168] the MS at the edge of the layer, for example MS3, can have a smaller cross-section than the MS at the heart of the CID, for example MS4; [0169] it is possible to have fewer MS at the edge of the CID.

[0170] In the case of FIG. 5C, it is also possible to reduce the stiffness along the direction orthogonal to the CID at the edge of the CID by modifying the shape of the MSs at the edge of the CID, for example by increasing the curvature of the MS.

[0171] When the MS are modified in an inverse manner to what is described above, an inverse modification of the stiffness is obtained.

[0172] The MS which are not located at the edge of the CID, for example MS4, can also be adapted in the same manner to vary the stiffness, in particular in the case where the second substrate S2 has areas of weakness, for example at MS4.

[0173] Such a structure where the MS are aligned in the direction orthogonal to the CID makes it possible to obtain a high stiffness along this same direction, while allowing the stiffness to be varied along the CID.

[0174] The MS of FIG. 5E are elongated elements of rectangular cross-section. The embodiment of FIG. 5E combines MS substantially aligned in the direction orthogonal to the CID and MS that are inclined relative to CEx1 and CEx2. The stiffness of the CID in FIG. 5E can be adapted to achieve the desired properties, as depicted in FIGS. 4A and 4B.

[0175] For example, to reduce the stiffness at the edge of the CID in all directions: [0176] the MS at the edge of the layer, for example MS5, can have a smaller cross-section than the MS at the heart of the CID, for example MS6; [0177] it is possible to have fewer MS at the edge of the CID.

[0178] To reduce the stiffness along the direction orthogonal to the CID at the edge of the CID and increase the stiffness along a direction parallel to the CID, it is possible to: [0179] reduce the angle of inclination of the MS at the edge of the CID relative to CEx1 and CEx2.

[0180] It is also possible to reduce the stiffness along the direction orthogonal to the CID at the edge of the CID by modifying the shape of the MS at the edge of the CID, for example by increasing the curvature of the MS.

[0181] When the MS are modified in an inverse manner to what is described above, an inverse modification of the stiffness is obtained.

[0182] The MS which are not located at the edge of the CID, for example MS6, can also be adapted in the same manner to vary the stiffness, in particular in the case where the second substrate S2 has areas of weakness, for example at MS6.

[0183] Such a structure with MS for which the inclination varies greatly relative to CEx1 and CEx2 makes it possible to obtain stiffnesses of the CID along the orthogonal direction and along the directions parallel to the CID which vary greatly and independently of each other.

[0184] The embodiment of FIG. 5F is an alternative to the embodiment of FIG. 5D, where the MS are elongated elements aligned in the direction orthogonal to the CID. However, here the MS are of circular cross-section.

[0185] In the embodiment of FIG. 5G, the MSs are free-form, allowing great adaptability of the stiffness within the CID. These free forms may be obtained by numerical simulation.

[0186] In addition, it is possible to provide a crack in P3, i.e. the portion of the CID which is facing the area of weakness. This makes it possible to reduce the forces imposed by the possible appearance of a crack in the second substrate S2.

[0187] The thickness of the CID is for example between 2 and 20 mm. The material of the CID, namely CEx1 and CEx2 as well as the MS, are of a material homogeneous in composition with a Young's modulus value that is between 1000 and 5000 MPa. The CID may be of the same material as the adhesive or may have a Young's modulus comparable to that of the adhesive AD. This stiffness homogeneity between the CID and the adhesive ensures good adhesion conditions between the CID and the adhesive AD.

[0188] In FIG. 6 a method for manufacturing a bonded assembly AC as described above is illustrated.

[0189] In a first step ST1, data relating to the shape of the surface of the second substrate are obtained. For example, the second substrate S2 is scanned by means of a 3D laser scanner or structured-light scanner, or by photogrammetry.

[0190] In a second step ST2, the CID is formed. Its stiffness is obtained by an appropriate arrangement of the MS as described above.

[0191] The CID may in particular be formed by an additive manufacturing technique, for example by photopolymerization. Since the cavities do not form an enclosure, it is possible to extract the unsolidified polymer.

[0192] On the basis of the data obtained in step ST1, CEx2 is formed so that its surface forming the outer face of the CID is complementary to the second substrate S2.

[0193] In a third step ST3, the CID is secured (for example by means of an adhesive) to the first substrate (this securing may be carried out in the factory). This step is not performed when the CID is formed directly on the first substrate.

[0194] In a fourth step ST4, the assembly formed by the CID and the first substrate S1 is bonded to the second substrate S2 by means of the adhesive AD. The second substrate S2 is prepared for this beforehand (cleaning, surface finishing, etc.). A knob of adhesive is placed on the CID, more precisely on the securing interface INT2. The CID is then positioned facing the second substrate S2 so that the surfaces face each other in a complementary manner. The assembly composed of the first substrate S1, the CID, and the knob of adhesive is transposed onto the second substrate S2 and held in position during the application time.

[0195] In a fifth step ST5, in the case where the bonded assembly AC forms an attachment means on the wall, a device may be fixed to the bonded assembly AC via the mechanical connector, for example by bolting.

[0196] One will note that the applications for the bonded assembly AC according to the disclosure are not limited to the embodiment described above, and can also serve for: [0197] repairing a structural area that is damaged (typically by corrosion); [0198] repairing a pipeline; [0199] repairing, reinforcing, and/or connecting to industrial structures, aircraft, ships, vehicles, or other.

[0200] Of course, the disclosure is not limited to the embodiments described above by way of example and they extend to other variants. In this respect, according to another embodiment, the layers comprised in the intermediate deformation layer may have, for example, a beveled profile in which air cells are also provided. Such an implementation of the bonded assembly may make it possible in particular to refine control of the deformation behavior of the adhesive, in particular at the edges.