Improved fatigue life of adhesive joints

Abstract

A method of manufacturing an adhesive structure is provided, the adhesive structure comprising first and second components, each including first and second outer surfaces, at least the first component being a first metal component, the first and second outer surfaces facing each other and partially overlapping, and the adhesive structure including an adhesive layer received between the overlapping portions of the first and second outer surfaces. The method includes deforming a first outer surface of the first metal component along a first isolation path extending alongside a first edge of the adhesive layer for at least a substantial length.

Description

Technical Field

[0001] This disclosure relates to adhesive structures and methods for manufacturing adhesive structures. Background Technology

[0002] Bonding is a low-cost, simple manufacturing method commonly used for thin metal components. Advantages include bonding and sealing in a single step, reduced noise transmission, low cost of bonding mixed materials, long fatigue life, and high impact resistance.

[0003] However, adhesive bonding has its limitations. Like many other joining methods, adhesive joints have a finite lifespan when subjected to cyclic loading. This is especially true when the number of failure cycles is low (i.e., the load is very high). High loads lead to crack initiation and propagation, while low loads cause creep in the adhesive layer. Fatigue life and ultimate joint strength are directly related to the steel thickness and plateau at a given thickness. Methods to improve strength and / or fatigue life include adding material (by extending the overlap) or fixing the edges of the overlap (by spot welding). These methods increase the cost and weight of the assembly.

[0004] In the case of bonded joints, the stress distribution is relatively more uniform compared to other conventional joining methods, resulting in weight reduction. However, even in bonded joints, the stress distribution is not perfectly uniform (due to localized stress). From a joint mechanics perspective, the main limiting factor for bonded joints is peel or cleavage stress. To design robust joints, peel or cleavage stress should be minimized. This high peel stress concentration at the edges of the overlap is exacerbated in components with unbalanced adherent stiffness. Fatigue cracks almost always initiate at the high-stress edges of bonded joints.

[0005] Figure 1 The illustration schematically depicts a typical prior art bonded metal structure 100, comprising a first sheet metal 102 and a second sheet metal 104 bonded together by an adhesive layer 106. The application of tensile force on the joint is schematically indicated by arrow F, and the load is typically applied in the direction of the dashed line 108.

[0006] Figure 2 schematically shown Figure 1 The same structure after the load F is sufficient to deform the joint. Figure 2 This is a superimposed illustration of the stress distribution within the adhesive layer 106. High-amplitude tensile stresses peak at the edges 110 and 112 of the overlap, while small compressive stresses are located in region 114 near the center of the overlap. In prior art structures, fatigue cracks typically initiate in these regions 110 and 112.

[0007] Therefore, there is a continued need for improved methods to manufacture bonded metal structures with improved strength and fatigue life at low cost without increasing the weight of the structure. Summary of the Invention

[0008] In one embodiment, a method of manufacturing an adhesive structure is provided, the adhesive structure comprising a first component and a second component, each including a first outer surface and a second outer surface, at least the first component being a first metal component, the first and second outer surfaces facing each other and partially overlapping, and the adhesive metal structure including an adhesive layer received between the overlapping portions of the first and second outer surfaces. The method may include the following steps:

[0009] (a) Deform the first outer surface of the first metal component along the first isolation path;

[0010] (b) Adheding the overlapping portions of the first outer surface and the overlapping portions of the second outer surface to form an adhesive layer, such that the adhesive layer includes a first edge laterally facing the non-overlapping portion of the first outer surface, and the adhesive layer includes a second edge laterally facing the non-overlapping portion of the second outer surface; and

[0011] (c) wherein the first isolation path extends along at least a majority of the length of the first edge of the adhesive layer alongside the first edge of the adhesive layer.

[0012] In another embodiment, the adhesive structure may include a first metal component and a second metal component, each including a first outer surface and a second outer surface, which face each other and partially overlap. An adhesive layer may be received between the overlapping portions of the first and second outer surfaces, the adhesive layer including a first edge laterally facing a non-overlapping portion of the first outer surface and a second edge laterally facing a non-overlapping portion of the second outer surface. The first outer surface of the first metal component may be deformable along a first isolation path extending adjacent to the first edge of the adhesive layer for at least a majority of its length. The second outer surface of the second metal component may be deformable along a second isolation path extending adjacent to the second edge of the adhesive layer for at least a majority of its length.

[0013] Many objects, features and advantages of the present invention will be apparent to those skilled in the art from the following description taken in conjunction with the accompanying drawings. Attached Figure Description

[0014] Figure 1 This is a schematic diagram of an existing adhesive joint.

[0015] Figure 2 yes Figure 1A schematic diagram of an existing adhesive joint under load, wherein the superimposed diagram represents the stress distribution within the adhesive layer.

[0016] Figure 3 This is a schematic perspective view of the bonded metal structure formed by the method of the present invention.

[0017] Figure 4 This is a schematic diagram of an adhesive metal structure, in which the deformation of the metal structure adjacent to the adhesive layer is carried out after the adhesive metal structure is constructed.

[0018] Figure 5 This is a schematic diagram of an adhesive metal structure, in which the deformation of the metal structure adjacent to the adhesive layer is carried out before the adhesive metal structure is constructed.

[0019] Figure 6 Is implementation and Figure 4 A schematic diagram of a high-frequency impact tool that causes deformation similar to that of sheet metal.

[0020] Figure 7 Is implementation and Figure 5 A schematic diagram of a high-frequency impact tool that causes deformation similar to that of sheet metal.

[0021] Figure 8 This is a diagram illustrating fatigue test data using a 4.5mm thick steel sample with a first exemplary adhesive.

[0022] Figure 9 This is a diagram illustrating fatigue test data showing the adverse results of using a bonded joint with relatively thin 1.0 mm thick sheet metal.

[0023] Figure 10 This is a diagram illustrating fatigue test data using a 3.0 mm thick steel sample with a second exemplary adhesive.

[0024] Figure 11 This is a diagram illustrating fatigue test data using the first exemplary adhesive, in this case using a 3.0 mm thick steel sample. Detailed Implementation

[0025] Now refer to the accompanying drawings and specifically to... Figure 3 The adhesive structure 200 includes a first component 202 and a second component 204. The first component includes a first outer surface 206, and the second component 204 includes a second outer surface 208. The first outer surface 206 and the second outer surface 208 face each other and at least partially overlap. The first outer surface may include an overlapping portion 212 and a non-overlapping portion 213. The second outer surface 208 may include an overlapping portion 214 and a non-overlapping portion 215. The adhesive structure 200 includes an adhesive layer 210 received between the overlapping portion 212 of the first outer surface 206 and the overlapping portion 214 of the second outer surface 208.

[0026] At least the first component 202 can be a first metallic component 202. In one embodiment, the first component 202 can be a metallic component, and the second component 204 can be a non-metallic component. In another embodiment, both the first and second components can be metallic components. In one embodiment, one or both of the metallic components can be steel plate material having a thickness of at least about 2.0 mm.

[0027] The adhesive layer 210 includes a first edge 230 of a non-overlapping portion 213 facing the first outer surface 206 and a second edge 232 of a non-overlapping portion 215 facing the second outer surface 208.

[0028] exist Figure 3 In the accompanying drawings, the geometry and dimensions of components 202 and 204 can be described in the x, y, z coordinate system. These components can be described as having a length along the x-axis, a width along the y-axis, and a thickness along the z-axis.

[0029] Therefore, the first component 202 has a length of 216, a width of 218, and a thickness of 220. The second component 204 has a length of 222, a width of 224, and a thickness of 226. The overlapping portions 212 and 214 have an overlapping length of 228.

[0030] We have discovered surprising results that certain surface treatments on metal parts 202 and 204 can improve the fatigue life of the adhesive joint 210 between these metal parts.

[0031] In one embodiment, the first outer surface 206 of the first metal component 202 may be deformed along a first isolation path 234, which extends alongside the first edge 230 of the adhesive layer 210 for at least a majority of its length. The second outer surface 208 of the second metal component 204 may be deformed along a second isolation path 236, which extends alongside the second edge 232 of the adhesive layer 210 for at least a majority of its length. In the example shown, the lengths of the first edge 230 and the second edge 232 are equal to the widths 218 and 224 of the adjacent component 202.

[0032] As used herein, the term "isolation path" refers to a path of deformable metal between non-deformable metal regions located on either side of the path. Therefore, a metal component 202, for example, whose entire outer surface 206 is deformed by shot peening, does not have an isolation path of deformable metal.

[0033] The deformation of the metal component forming the isolation path 234 can be achieved, for example, by using an impact tool (such as a HiFit pneumatic tool available from HiFIT Vertriebs GmbH, 4D-38112 Adam OPEC Road, Braunschweig, Germany) via high-frequency mechanical impact. Such a pneumatic tool... Figure 6 and Figure 7 The pneumatic tool 242 is schematically shown and identified by the number 242. The pneumatic tool 242 includes a pneumatic actuator 244 that causes an impact tool 246 to reciprocate, the impact tool having a tip 248 which may typically be hemispherical in shape.

[0034] The isolation paths 234 and 236 can be in the shape of a circular groove formed by the hemispherical tip 248 of the impact tool (like the HiFit tool mentioned above). Figure 4 and Figure 5 Two embodiments of the isolation path 234 are schematically shown. The groove may have a groove depth 238 of at least about 0.1 mm and a groove width 240 ranging from about 1.0 mm to about 3.0 mm.

[0035] exist Figure 4 In this process, the isolation path 234 is formed after the adhesive joint 200 is formed by bonding the two components 202 and 204 together with the adhesive layer 210. Therefore, the isolation path 234 has been formed as close as possible to the first edge 230 as it actually is. Figure 4 The isolation path can be described as being laterally located outside the adhesive layer. Preferably, the isolation path 204 is either in contact with the edge 230 or spaced from the edge 230 by a thickness 220 perpendicular to the first outer surface 206 of the first metal component 202.

[0036] exist Figure 5 In this process, the isolation path is formed before the adhesive joint 200 is created, so the adhesive layer 210 can partially or completely overlap with the isolation path 234. Figure 5 In the diagram, adhesive layer 210 is shown as partially overlapping isolation path 234.

[0037] In general, such as Figure 4 and Figure 5 The isolation path 234 shown can be described as at least partially in, as Figure 5 Below the adhesive layer 210, or laterally located as... Figure 4 The distance beyond the visible adhesive layer 210 and laterally located beyond the adhesive layer 210 does not exceed the thickness 220 of the first metal component 202 perpendicular to the first outer surface 206.

[0038] Figure 6 and Figure 7The diagram schematically illustrates how the pneumatic tool 242 can be used to form an isolation path 234 before or after forming the adhesive joint 200, thereby corresponding to respectively Figure 4 and Figure 5 The structure that is seen and obtained.

[0039] If an isolation path 234 is formed in the metal component 202 after the adhesive joint 200 is formed, the impact actuator is preferably angled (such as 250) to the tip 248, as close as practically possible to the edge 230 of the adhesive layer 210. The angle 250 can range from 30 to 80 degrees. In one embodiment, the angle 250 can range from 60 to 75 degrees. In another embodiment, the angle can be approximately 67 degrees. The isolation path 234 extends along most of the length of the edge 230, and preferably along the entire length of the edge 230, adjacent to the edge 230. In one embodiment, the isolation path 234 may contact the edge 230, or along most of the length of the edge 230, and preferably along the entire length of the edge 230, separated from the edge 230 by a distance no greater than the thickness 220 of the component 202.

[0040] If the isolation path 234 is formed in the metal component 202 prior to the formation of the adhesive joint 200, the impact actuator is preferably at an angle (such as 252) to the tip 248, substantially perpendicular to the surface 206. The angle 252 can be in the range of 80 to 100 degrees. When the isolation path is formed prior to the construction of the adhesive joint 200, the adhesive layer 210 can extend into the isolation path, such as... Figure 5 As shown. Figure 5 As shown, edge 230 may be located within adhesive path 234, or edge 230 may even be located on the far side of isolation path 234. If edge 230 is indeed located on the far side of isolation path 234 such that path 234 is completely covered, preferably edge 230 extends along most of the length of edge 230, and preferably extends beyond isolation path 234 and not exceed width 220 of part 202 along the entire length of edge 230.

[0041] use Figure 6 Alternatively, as shown in 7, there may be preferred parameters for the operation of the pneumatic tool 242.

[0042] Tip 248 may have a tip diameter ranging from about 0.5 mm to about 3 mm.

[0043] The pneumatic actuator 244 can be operated to apply a force to the impact tool 246 ranging from about 0.5 pounds to about 15.0 pounds.

[0044] The pneumatic tool 242 can move along the isolation path at a travel speed ranging from about 0.1 inches per second to about 20.0 inches per second. In another embodiment, the pneumatic tool 242 can move along the isolation path at a travel speed ranging from about 0.1 inches per second to about 10.0 inches per second.

[0045] The isolation path 234 can be formed in a single pass or multiple passes of the pneumatic tool 242.

[0046] In one example, the HiFit tool is oriented perpendicular to the steel plate, such as... Figure 7 As shown, the material was applied to the part before the adhesive was applied. The HiFit tool has a 1.5mm tip diameter. The steel plate is 3mm thick 350MPa yield strength steel. Three passes were used. The first pass produced a rough groove with a depth of 322 microns and an interpeak width of approximately 1mm. The second pass increased the depth to 338 microns and the width to approximately 2mm. The third pass resulted in a depth of approximately 514 microns and a width of approximately 2.4mm.

[0047] In another example, the HiFit tool is applied after the adhesive joint is formed. The HiFit tool is as follows: Figure 6 The orientation is shown at an angle of approximately 67 degrees (250°). The HiFit tool has a tip diameter of 1.5 mm. The steel plate is 3 mm thick and made of 350 MPa yield strength steel. A single pass results in an asymmetrical groove or recess with a peak of 349 micrometers on one side closest to the adhesive layer 210 and a peak of 186 micrometers on the other side. The groove has a width of approximately 2.6 mm (240°).

[0048] The pneumatic tool 242 can operate at a tip impact frequency ranging from approximately 100 impacts per second to approximately 400 impacts per second. In one embodiment, the tip impact frequency is in the range of approximately 150 impacts per second to approximately 300 impacts per second. In another embodiment, the tip impact frequency is in the range of approximately 200 impacts per second to approximately 250 impacts per second.

[0049] The action of the pneumatic tool 242 impacting the surface 206 of the metal part 202 with its tip 248 generates compressive residual stress in the metal below and near the isolation path 234. Localized work hardening and / or strain hardening of the metal are present. How this deformed metal region of the isolation path 234 interacts with the adhesive layer 210 to increase its fatigue life is not fully understood, but test data discussed below indicate that such improved fatigue life exists in some cases.

[0050] Furthermore, when the isolation path 234 is combined with the adhesive layer 210 formed of a preferred adhesive material, the improvement in fatigue life is more stable. In one embodiment, the adhesive material may be selected from the group consisting of epoxy adhesives, polyurethane adhesives, and acrylic adhesives. In another embodiment, the adhesive may be a high-impact epoxy adhesive.

[0051] Manufacturing method:

[0052] In one embodiment, a method for manufacturing an adhesive structure 200 is provided, the adhesive structure including a first component 202 and a second component 204, each including a first outer surface 206 and a second outer surface 208, wherein at least the first component 202 is a first metal component, the first outer surface 206 and the second outer surface 208 face each other and partially overlap, and the adhesive structure includes an adhesive layer 210 received between an overlapping portion 212 of the first outer surface and the second outer surface 204, the method comprising:

[0053] (a) Deform the first outer surface 206 of the first metal component 202 along the first isolation path 234;

[0054] (b) Adheding the overlapping portion 212 of the first outer surface 206 and the overlapping portion 214 of the second outer surface 208 to form an adhesive layer 210, such that the adhesive layer includes a first edge 230 laterally facing the non-overlapping portion 213 of the first outer surface 206, and the adhesive layer includes a second edge 232 laterally facing the non-overlapping portion 215 of the second outer surface 208; and

[0055] (c) wherein the first isolation path 234 extends 234 along at least a majority of the length of the first edge of the adhesive layer next to the first edge 230 of the adhesive layer 210.

[0056] In one embodiment, step (a) can be performed before step (b), such as Figure 7 As illustrated. In another embodiment, step (b) may be performed before step (a), as shown below. Figure 6 As shown schematically.

[0057] When the second component 204 is also a metal component, the method may further include deforming the second outer surface 208 of the second metal component 204 along the second isolation path 236, wherein the second isolation path 236 extends alongside the second edge 232 of the adhesive layer 210 along at least a majority of its length.

[0058] In one embodiment, in step (a), deformation can be performed by high-frequency mechanical impact using a tool such as a pneumatic impact tool 242.

[0059] In another embodiment, in step (a), a high-frequency mechanical impact can be performed using an impact tool 246 having a tip diameter ranging from about 0.5 mm to about 3.0 mm.

[0060] In another embodiment, in step (a), a high-frequency mechanical impact can be performed using an impact tool having an impact force ranging from about 0.5 lbs to about 15 lbs.

[0061] In another embodiment, in step (a), a high-frequency mechanical impact can be performed using an impact tool having a travel speed ranging from about 0.1 inches / second to about 20 inches / second.

[0062] In another embodiment, in step (a), high-frequency mechanical impact can be performed by multiple passes of the impact tool.

[0063] In another embodiment, in step (a), the deformation may create a groove 230 in the first outer surface. The groove 230 may have a depth of at least 0.1 mm and a width ranging from about 1.0 mm to about 3.0 mm.

[0064] In one embodiment, in step (a), deformation of the first outer surface 206 of the first metal component 202 can increase the fatigue life of the adhesive layer 210.

[0065] In one embodiment, in step (b), the adhesive material may be selected from the group consisting of epoxy adhesives, polyurethane adhesives and acrylic adhesives.

[0066] Example:

[0067] Numerous fatigue tests were conducted to evaluate the disclosed method for manufacturing bonded joints. In the fatigue tests, the samples were always under tension (both at high and low stress levels during the cycles). Two different load levels (minimum 5% / maximum 50% or minimum 4% / maximum 40%) were investigated for static joint strength. This implies an R-ratio of 0.1. The test frequency was 5 Hz. The tests were performed using a closed-loop servo-hydraulic 100 kN dual-column frame on an Instron Model 8801 fatigue testing machine. The bonded joints are essentially as follows: Figure 3 The shape shown is approximately 38 mm wide (218, 200) and approximately 25 mm overlapping length (228). The adhesive layer 210 has a thickness of approximately 0.25 mm.

[0068] Figure 8The graph illustrates the fatigue life of a type of adhesive (named epoxy resin 1) with and without deformation of the metallic component when using a HiFit impact tool at two different load levels. HiFit was applied after bonding 4.5 mm thick steel specimens. At a 40% load level, the fatigue life of the HiFit-treated specimens increased by an average of 3.5 times, and at a 50% load level, it increased by an average of 2 times.

[0069] Figure 11 The fatigue life of epoxy resin 1 adhesive (named epoxy resin 1) with and without metal part deformation under HiFit impact tooling at two different load levels, this time using 3.0 mm thick steel specimens. At the lower load level, the fatigue life of the HiFit-treated specimens increased by an average of 3.3 times, and at the higher load level, by an average of 1.5 times.

[0070] Epoxy Resin 1 is a one-component epoxy adhesive available from Henkel under the trade name Teroson EP 5089. Henkel describes Teroson EP 5089 as having high impact resistance greater than 20 N / mm at temperatures up to -40°C. Teroson EP 5089 is described as having a nano-dispersion embedded in an epoxy resin matrix. Teroson EP 5089 is described as having very high static strength, an elastic modulus greater than 1600 MPa, and low-temperature curing ability.

[0071] Figure 9 This refers to a test run used to determine the suitability of the process for very thin steel sheets. Figure 9 In our tests, the HiFit process was applied to bonded structures made of 1mm thick steel plates. A significant reduction in fatigue life was observed after HiFit treatment. For this reason, we have concluded that this process should only be applied to steel plates with a thickness of at least approximately 2.0mm.

[0072] Figure 10 The fatigue life of a type of adhesive (named epoxy resin 2) with and without deformation of the metallic component is shown when using a HiFit impact tool at a single load level. HiFit was applied before bonding to a 3.0 mm thick steel specimen. The fatigue life of the HiFit-treated specimens increased by an average of 7.5 times. Epoxy resin 2 is a two-component epoxy adhesive available from Henkel under the trade name Teroson 5065.

[0073] On the other hand, note that, similar to Figure 10The tests were conducted using several other adhesives that did not result in an increase in fatigue life for the HiFit-treated samples. These other adhesives included: (1) a two-component epoxy adhesive available from Sika Corporation under the trade name Sikapower 1277; (2) a two-component methyl methacrylate adhesive available from Lord Corporation under the trade name 850 / 25GB; and (3) a two-component methyl methacrylate adhesive available from ITW Corporation under the trade name Plexus MA422.

[0074] It is not yet understood why the disclosed process of deforming the metal components leads to an increase in the fatigue life of the adhesive layer. Furthermore, it is not understood why this improvement in fatigue life occurs with some adhesives but not with others. However, any suggested combination of metal components and adhesive materials used for bonding joints can be readily tested using the techniques disclosed herein to determine the applicability of the disclosed methods.

[0075] Therefore, it can be seen that the apparatus and methods of this disclosure readily achieve the stated objectives and advantages, as well as those inherent therein. Although certain preferred embodiments of the invention have been shown and described for the purposes of this invention, various changes in the arrangement and construction of components and steps can be made by those skilled in the art, and these changes are covered within the scope and spirit of the invention as defined by the appended claims. Each disclosed feature or embodiment may be combined with any of the other disclosed features or embodiments.

Claims

1. A method of manufacturing an adhesive structure (200), the adhesive structure comprising a first component (202) and a second component (204), the first component (202) comprising a first outer surface (206), and the second component (204) comprising a second outer surface (208), at least the first component being a first metal component, the first and second outer surfaces facing each other and partially overlapping, and the adhesive structure comprising an adhesive layer (210) received between an overlapping portion (212) of the first outer surface and an overlapping portion (214) of the second outer surface, the method comprising: (a) Deform the first outer surface of the first metal component along the first isolation path (234); (b) Adheding the overlapping portions of the first outer surface and the second outer surface to form the adhesive layer, such that the adhesive layer includes a first edge (230) laterally facing the non-overlapping portion (213) of the first outer surface, and the adhesive layer includes a second edge (232) laterally facing the non-overlapping portion (215) of the second outer surface, the adhesive layer being formed by an adhesive selected from the group consisting of: epoxy adhesives; polyurethane adhesives and acrylic adhesives; and (c) wherein the first isolation path extends along at least a majority of the length of the first edge of the adhesive layer adjacent to the first edge of the adhesive layer, and wherein the deformation of the first outer surface of the first metal component increases the fatigue life of the adhesive layer.

2. The method according to claim 1, wherein: The first isolation path (234) is either at least partially located under the adhesive layer (210) or laterally located outside the adhesive layer, and the distance laterally located outside the adhesive layer does not exceed the thickness (220) of the first metal component perpendicular to the first outer surface (206).

3. The method according to claim 1, wherein, Step (a) is performed before step (b).

4. The method according to claim 1, wherein, Step (b) is performed before step (a).

5. The method according to claim 1, wherein, The second component (204) is a second metal component, and the method further includes: The second outer surface (208) of the second metal component is deformed along the second isolation path (236), wherein the second isolation path extends along at least a majority of the length of the second edge of the adhesive layer (210) alongside the second edge (232) of the adhesive layer.

6. The method according to claim 1, wherein, The first component (202) is a first sheet metal, and the second component (204) is a second sheet metal.

7. The method according to claim 6, wherein, The first sheet metal and the second sheet metal are steel plates with a thickness of at least 2.0 mm (220, 226).

8. The method according to claim 1, wherein: In step (a), the deformation is performed by high-frequency mechanical impact.

9. The method according to claim 8, wherein: In step (a), the high-frequency mechanical impact is carried out using an impact tool (246) having a tip diameter in the range of 0.5 mm to 3.0 mm.

10. The method according to claim 8, wherein: In step (a), the high-frequency mechanical impact is carried out using an impact tool (246) having an impact force in the range of 0.5 lbs to 15 lbs.

11. The method according to claim 8, wherein: In step (a), the high-frequency mechanical impact is carried out using an impact tool (246) having a travel speed in the range of 0.1 inches / second to 20 inches / second.

12. The method according to claim 8, wherein: In step (a), the high-frequency mechanical impact is performed by multiple passes of the impact tool (246).

13. The method according to claim 1, wherein: In step (a), the deformation creates a groove in the first outer surface (206) having a depth (238) of at least 0.1 mm.

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