Laminated structure and differentiated hole machining method of laminated structure

Abstract

The invention discloses a laminated structure and a differentiated hole machining method of the laminated structure, and relates to the technical field of machining, the method comprises the steps that S1, first reaming is conducted on the laminated structure, and the laminated structure comprises two or more layers of laminated plates; s2, linings made of matched materials are selected according to the material characteristics of different plates; s3, bushings made of different materials are installed in the reamed holes of the matched plates by pulling the core rod; s4, the linings made of the different materials are extruded, so that the linings made of the different materials are in interference fit with the matched plates; and S5, secondary reaming is conducted on the laminated structure according to the assembly requirement, so that the inner diameters of the deformed bushings made of different materials are the same. According to the method, the fatigue performance of plates made of different materials is coordinated through a differential hole machining method, and the fatigue life of the laminated structure is remarkably prolonged; and it is guaranteed that hole machining of different machining amounts is conducted on the laminated structure under one-time hole forming, the continuity of the hole forming technology is guaranteed, and the hole position precision is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of mechanical processing, in particular to a laminated structure and a differential hole processing method of the laminated structure. BACKGROUND

[0002] The existing technology composite material plate assembly hole processing method includes: a, providing a bushing, the bushing can be installed in the assembly hole; b, providing a metal core rod with a taper, and inserting the core rod into the bushing; c, installing the bushing into the assembly hole; d, applying axial force to the core rod by processing equipment to process the maximum diameter part of the core rod to the bushing; e, removing the core rod, and the bushing is held in the assembly hole.

[0003] The existing technology is a hole processing method for a single composite material plate, while in large aircraft, CFRP single material laminated plate is less used, and more laminated structures are used, and the common laminated structure is CFRP / Ti (composite material plate / titanium alloy material plate) composite / titanium laminated structure, and the component is often applied to important load-bearing parts through mechanical connection. In large aircraft structures, the composite / titanium laminated structure is generally mechanically connected by high-lock bolts. These laminated structures have large sizes, and usually use multiple bolts or bolt groups for fastening and load transfer. The composite material plate and the titanium alloy material plate constituting the laminated structure generally adopt a laminated one-time hole processing technology to ensure the position accuracy of the processed bolt hole and meet the assembly requirements. When the laminated structure is processed according to the existing technology, an initial hole is formed on the laminated structure, which penetrates the composite material plate and the titanium alloy material plate. When the initial hole on the composite material plate is installed with a bushing, the hole wall will be severely damaged due to the large processing amount, affecting its mechanical properties. When the initial hole on the titanium alloy material plate is installed with a bushing, a relatively large processing amount is required to generate obvious hole peripheral residual stress to improve the fatigue performance. Therefore, when the initial hole penetrating the laminated structure is processed, the processing amount is difficult to unify.

[0004] Therefore, it is urgent to provide a laminated structure and a differential hole processing method of the laminated structure to realize the coordinated processing of the connecting holes on the laminated structure, which is a technical problem to be solved by the person skilled in the art. SUMMARY

[0005] The present application aims at the defects and deficiencies in the prior art, and provides a laminated structure and a differential hole processing method of the laminated structure. The differential hole processing method coordinates the fatigue performance of different material plates, significantly improves the fatigue life of the laminated structure, ensures the differential processing amount of the laminated structure under one-time hole processing, guarantees the continuity of the hole processing technology, and improves the hole position accuracy.

[0006] To achieve the above-mentioned purpose, the technical scheme adopted by the present application is:

[0007] This invention provides a method for processing differentiated holes in a laminated structure, comprising: S1, performing a first reaming on the laminated structure, wherein the laminated structure comprises two or more layers of plates stacked together;

[0008] S2, Select bushings of suitable materials according to the material properties of different plates, and set the inner diameter of the corresponding bushings according to the amount of hole extrusion that the plate can withstand.

[0009] S3, Bushings of different materials are placed on tapered mandrels according to the stacking order of the plates. An axial force is applied to the tapered mandrels using an extrusion device, and the mandrels are pulled through the hinge holes of the stacked structure in sequence to install bushings of different materials into the hinge holes of the matching plates.

[0010] S4, using an extrusion device to apply axial force to a tapered mandrel, pulling the mandrel to extrude bushings of different materials, so that the bushings of different materials are interference-fitted with the appropriate plate.

[0011] S5. According to the assembly requirements, the stacked structure is reamed a second time to make the inner diameter of the bushings of different materials the same after deformation.

[0012] In one embodiment, the outer diameter of the bushing is smaller than the inner diameter of the corresponding hinge hole.

[0013] In one embodiment, the bushing is a seamless bushing.

[0014] In one embodiment, the laminated structure includes two stacked plates, comprising a first material plate and a second material plate. When the first material plate is a composite material plate and the second material plate is a titanium alloy material plate, the first bushing is a titanium alloy bushing and the second bushing is a stainless steel bushing.

[0015] In one embodiment, the mandrel includes a guide section and a pressing section connected in sequence, the guide section and the pressing section passing through the first bushing and the second bushing in sequence; the diameter of the guide section is smaller than the inner diameter of the first bushing and the inner diameter of the second bushing, the diameter of the pressing section gradually increases along the axis away from the guide section, the minimum diameter of the pressing section is the same as the diameter of the guide section, and the maximum diameter of the pressing section is larger than the inner diameter of the second bushing and smaller than the outer diameter of the second bushing.

[0016] In one embodiment, the mandrel further includes a calibration section, the end of the extrusion section away from the guide section being connected to the calibration section, the diameter of the calibration section being the same as the maximum diameter of the extrusion section.

[0017] In one embodiment, the extrusion section of the mandrel has a length of 1 mm, a front cone angle of 3°, and a rear cone angle of 9°.

[0018] In one embodiment, the mandrel is made of a rigid material.

[0019] In one embodiment, the inner walls of the first bushing and the second bushing are lubricated before deformation.

[0020] The present invention also provides a laminated structure, comprising a laminated structure made by a differentiated hole processing method of the laminated structure, the laminated structure comprising two or more layers of plates stacked together, the laminated structure having hinge holes, the hinge holes on plates with different material properties being fitted with bushings of a matching material, the hinge holes on plates with different material properties being interference-fitted with bushings of a matching material, and all bushings in the same hinge hole on the laminated structure having the same centerline and inner diameter.

[0021] The present invention achieves the following technical effects compared to the prior art:

[0022] This invention involves creating holes in a laminated structure, then placing the laminated plates sequentially onto a tapered mandrel. An extrusion device applies axial force to the tapered mandrel, pulling it through the hinge holes of the laminated structure. Bushings of different materials are then installed into the hinge holes of the corresponding plates. The mandrel is then pulled further to extrude the bushings of different materials, ensuring an interference fit between the bushings and the corresponding plates. This allows for processing with varying extrusion amounts, coordinating the fatigue performance of the laminated structure and significantly improving its fatigue life. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the process flow for a differentiated hole processing method for a stacked structure disclosed in a specific embodiment of the present invention.

[0025] Figure 2 This is a cross-sectional view of the laminated structure (when the bushing is not deformed) disclosed in a specific embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the structure of the mandrel disclosed in a specific embodiment of the present invention;

[0027] Figure 4 This is a schematic diagram of the drilling of a stacked three-nail connection sample disclosed in a specific embodiment of the present invention (A, B, and C represent different holes);

[0028] Figure 5 This is a schematic diagram of the fatigue life of a stacked three-nail connection specimen under different loads in a specific embodiment of the present invention.

[0029] Figure 6 This is a schematic diagram of the fatigue life of a laminated three-nail connection specimen disclosed in a specific embodiment of the present invention at 29.8 kN.

[0030] Figure 7 This is a schematic diagram of the fatigue life of a laminated three-nail connection specimen disclosed in a specific embodiment of the present invention at 29.8 kN.

[0031] Among them, 1. Composite material plate; 2. Titanium alloy material plate; 3. Titanium alloy bushing; 4. Stainless steel bushing; 5. Mandrel; 51. Guide section; 52. Extrusion section; 53. Calibration section; 6. Drill bit; 7. Reamer; 8. Compensation plate. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0034] like Figures 1-3 As shown, the present invention provides a method for processing differentiated holes in a laminated structure, comprising: S1, performing a first reaming on the laminated structure, wherein the laminated structure comprises two or more layers of stacked plates; S2, selecting bushings of suitable materials according to the material characteristics of different plates, and setting the inner diameter of the bushings according to the hole extrusion amount that the plates can withstand; S3, placing bushings of different materials onto a tapered mandrel in the order of plate stacking, applying axial force to the tapered mandrel using an extrusion device, pulling the mandrel through the reaming holes of the laminated structure in sequence, and installing bushings of different materials into the reaming holes of the suitable plates; S4, continuing to apply axial force to the tapered mandrel using an extrusion device, pulling the mandrel to extrude bushings of different materials, so that the bushings of different materials are interference-fitted with the suitable plates; S5, performing a second reaming on the laminated structure according to assembly requirements, so that the inner diameters of the bushings of different materials are the same after deformation.

[0035] When the laminated structure includes two layers of plates, a first material plate and a second material plate, S1, the laminated structure is first reamed, the hole on the first material plate is the first initial hole, and the hole on the second material plate is the second initial hole; S2, a first bushing adapted to the first initial hole is set according to the hole compression amount that the first material plate can withstand; a second bushing adapted to the second initial hole is set according to the hole compression amount that the second material plate can withstand; when the hole compression amount that the first material plate can withstand is less than the hole compression amount that the second material plate can withstand, the outer diameter of the first bushing is the same as the outer diameter of the second bushing, and the inner diameter of the first bushing is greater than the inner diameter of the second bushing. S3, A second bushing and a first bushing with the same outer diameter but different inner diameters are sequentially fitted onto the tapered mandrel 5. An axial force is applied to the tapered mandrel 5 using a pressing device, pulling the mandrel 5 through the second initial hole and the first initial hole in sequence, and installing the first bushing and the second bushing of different materials into the first initial hole and the second initial hole respectively; S4, An axial force is applied to the tapered mandrel 5 using a pressing device, pulling the mandrel 5 through the first bushing and the second bushing in sequence and pressing the first bushing and the second bushing, causing the first bushing and the second bushing to deform under compression, and making the first bushing interference fit with the first initial hole of the first material plate, and the second bushing interference fit with the second initial hole of the second material plate; S5, the laminated structure is reamed for the second time according to the assembly requirements, so that the inner diameter of the first bushing and the inner diameter of the second bushing are the same after deformation.

[0036] It is understandable that by drilling holes in the laminated structure (including the first material plate and the second material plate), the first bushing and the second bushing with the same outer diameter but different inner diameter are respectively installed in the first initial hole in the first material plate and the second initial hole in the second material plate. Then, the mandrel 5 is pulled to pass through the first bushing and the second bushing in sequence and to compress the first bushing and the second bushing, so that the first bushing and the second bushing undergo extrusion deformation, and the first bushing is interference-fitted with the first initial hole of the first material plate, and the second bushing is interference-fitted with the second initial hole of the second material plate. This achieves processing with different extrusion amounts, coordinates the fatigue performance of the laminated structure, and significantly improves the fatigue life of the laminated structure.

[0037] It should be noted that a laminated structure includes two or more layers of sheet materials stacked together. When a laminated structure is made of two layers of sheet materials, the two layers can be composite material sheet 1 and titanium alloy sheet 2, or composite material sheet 1 and aluminum alloy sheet, with the sheet materials selected according to actual needs. When a laminated structure is made of three layers of sheet materials, the three layers can be composite material sheet 1, titanium alloy sheet 2, and composite material sheet 1.

[0038] In some specific embodiments, the outer diameter of the bushing is smaller than the inner diameter of its corresponding reamed hole.

[0039] It is understandable that when the laminated structure includes two layers of plates, a first material plate and a second material plate, the outer diameter of the first bushing is smaller than the inner diameter of the first initial hole, and the outer diameter of the second bushing is smaller than the inner diameter of the second initial hole. This facilitates the installation of the first bushing and the second bushing, which have the same outer diameter but different inner diameters, into the first initial hole and the second initial hole, respectively.

[0040] In some specific embodiments, the bushing is a seamless bushing. When the laminated structure includes two layers of sheet metal, a first material plate and a second material plate, both the first bushing and the second bushing are seamless bushings.

[0041] In some specific embodiments, the laminated structure includes two stacked plates. The laminated structure includes two plates: a first material plate and a second material plate. When the first material plate is a composite material plate 1 and the second material plate is a titanium alloy material plate 2, the first bushing is a titanium alloy bushing 3 and the second bushing is a stainless steel bushing 4.

[0042] Understandably, the selection of bushing materials needs to comprehensively consider the elastic modulus of the plate and the assembly potential difference. For composite material plate 1, titanium alloy bushing 3 is preferred, while for titanium alloy plate 2, materials with relatively high elastic modulus, such as stainless steel bushing 4, can be selected. When the first material plate is composite material plate 1 and the second material plate is titanium alloy plate 2, the first bushing is selected as titanium alloy bushing 3 based on the material characteristics of the first material plate; and the second bushing is selected as stainless steel bushing 4 based on the material characteristics of the second material plate. Specifically, composite material plate 1 is made of carbon fiber reinforced polymer (CFRP), which refers to a new type of fiber material with a carbon content of over 95% and high strength and high modulus. CFRP material plates have a high elastic modulus but poor plastic deformation capacity. During processing, CFRP material plates mainly undergo elastic deformation. Therefore, placing titanium alloy bushing 3 in the first initial hole of composite material plate 1 ensures that titanium alloy bushing 3 can smoothly pass through mandrel 5 and achieve the required deformation during processing, while protecting the hole wall of the first initial hole of composite material plate 1 from damage. The titanium alloy plate 2 is made of titanium alloy (such as Ti6Al4V). Titanium alloy has high strength and good elastic-plastic deformation capacity, and can withstand large processing stress without excessive deformation or damage. Stainless steel has high strength and good wear resistance, and can withstand large frictional forces during processing without wear. Therefore, placing the stainless steel bushing 4 into the second initial hole of the titanium alloy plate 2 can ensure that the stainless steel bushing 4 can pass smoothly through the mandrel 5 and achieve the required deformation during processing, while reducing wear between the stainless steel bushing 4 and the mandrel 5.

[0043] To enable the mandrel 5 to compress and deform the bushing, in some embodiments, the mandrel 5 includes a guide section 51 and a compression section 52 connected in sequence, passing through the first bushing and the second bushing respectively. The diameter of the guide section 51 is smaller than the inner diameter of the first bushing, and the diameter of the compression section 52 gradually increases along the axis away from the guide section 51. The minimum diameter of the compression section 52 is the same as the diameter of the guide section 51, and the maximum diameter of the compression section 52 is larger than the inner diameter of the second bushing but smaller than the outer diameter of the second bushing. In some embodiments, the mandrel 5 also includes a calibration section 53, with the end of the compression section 52 away from the guide section 51 connected to the calibration section 53. The diameter of the calibration section 53 is the same as the maximum diameter of the compression section 52. In some embodiments, the mandrel 5 is made of a hard material. Specifically, the hard material of the mandrel 5 can be high-speed steel (W6Mo5Cr4V2 steel).

[0044] In some specific embodiments, the inner wall of the bushing is lubricated before deformation.

[0045] It is understandable that when the laminated structure includes two layers of plates, a first material plate and a second material plate, the inner walls of the first bushing and the second bushing are lubricated before deformation. A solid lubricant is applied to the inner wall of the bushing for lubrication to prevent excessive friction from causing the mandrel 5 to scratch the bushing.

[0046] The present invention also provides a stacked structure, including a stacked structure made by a differentiated hole processing method for stacked structures. The stacked structure includes two or more layers of plates stacked together. Reamed holes are opened on the stacked structure. Bushings of suitable materials are installed in the reamed holes on the plates with different material properties. The reamed holes on the plates with different material properties are interference-fitted with the bushings of suitable materials. The center lines and inner diameters of all bushings in the same reamed hole on the stacked structure are the same.

[0047] When the laminated structure includes a first material plate and a second material plate, a deformed first bushing is installed inside the first material plate, and a deformed second bushing is installed inside the second material plate. The center lines and inner diameters of the first bushing and the second bushing are the same.

[0048] In one embodiment:

[0049] In laminated structures, the fatigue properties of composite materials and titanium alloys differ significantly. Using existing technologies for hole machining presents the problem of inconsistent machining amounts, which may cause the composite material to suffer severe damage to the hole wall due to excessive machining, affecting its mechanical properties; or the machining amount may be insufficient to generate significant residual stress around the hole to improve fatigue performance.

[0050] To address this, a laminated structure made of composite materials and titanium alloys was selected, and differentiated hole processing was employed. To investigate the influence of hole processing technology on the mechanical properties of the composite / titanium laminated multi-nail connection structure using a three-nail connection structure, T800 / X850 carbon fiber reinforced resin matrix composite laminate was used. (See specific references.) Figure 4 The composite material sample has dimensions of 200×30×3.5mm, hole edge distance of 15mm, hole spacing of 36mm, hole diameter of 7.6mm, and 3 holes.

[0051] Differentiated hole machining of the composite / titanium laminate structure includes: S1, performing the first reaming of the composite / titanium laminate structure (using drill bit 6): The composite / titanium laminate structure includes a stacked composite material plate 1 and a titanium alloy material plate 2. The hole on the composite material plate 1 is the first initial hole, and the hole on the titanium alloy plate 2 is the second initial hole. Specifically, the composite / titanium laminate structure is machined as a whole before hole machining to avoid the positional accuracy of hole machining affecting or even causing the composite / titanium laminate structure to be unable to be assembled, so that the first and second initial holes meet the initial hole size requirements of hole machining.

[0052] S2, a titanium alloy bushing 3 (Ti6Al4V bushing) adapted to the first initial hole is set according to the hole extrusion amount that the composite material plate 1 can withstand; a stainless steel bushing 4 adapted to the second initial hole is set according to the hole extrusion amount that the titanium alloy material plate 2 can withstand; the hole extrusion amount that the composite material plate 1 can withstand is less than the hole extrusion amount that the titanium alloy material plate 2 can withstand, the outer diameter of the titanium alloy bushing 3 and the outer diameter of the stainless steel bushing 4 are the same, and the inner diameter of the titanium alloy bushing 3 is greater than the inner diameter of the stainless steel bushing 4.

[0053] Specifically, to enhance the residual stress field generated during the machining of two holes in the titanium alloy plate, stainless steel PH13-8Mo, with higher elastic modulus and strength, was selected as the material for the titanium alloy hole machining bushing. The outer diameter of the titanium alloy bushing 3 is consistent with that of the stainless steel bushing 4. Different hole extrusion amounts are achieved by controlling the inner diameter. Specifically, the outer diameter of both bushings is set to 7.58 mm, the inner diameter of the titanium alloy bushing 3 is set to 6.20 mm, and the inner diameter of the stainless steel bushing 4 is set to 6.08 mm.

[0054] S3, stainless steel bushing 4 and titanium alloy bushing 3 with the same outer diameter but different inner diameter are sequentially fitted onto the tapered mandrel. An axial force is applied to the tapered mandrel 5 using a pressing device, and the mandrel 5 is pulled through the second initial hole and the first initial hole in sequence. The titanium alloy bushing 3 and stainless steel bushing 4 of different materials are respectively installed in the first initial hole and the second initial hole.

[0055] S4, continue using the extrusion equipment to apply axial force to the tapered mandrel 5, pulling the mandrel 5 through the titanium alloy bushing 3 and stainless steel bushing 4 in sequence, and extruding the titanium alloy bushing 3 and stainless steel bushing 4, causing them to deform under extrusion. This results in an interference fit between the titanium alloy bushing 3 and the first initial hole of the composite material plate 1, and an interference fit between the stainless steel bushing 4 and the second initial hole of the titanium alloy material plate 2. Specifically, during the processing, to prevent excessive friction from causing the mandrel 5 to scratch the bushings, a solid lubricant is applied to the inner wall of the bushing for lubrication. By pulling the mandrel 5, the maximum diameter of the extrusion section 52 of the mandrel 5 passes through the titanium alloy bushing 3 and stainless steel bushing 4 respectively. Under the extrusion of the mandrel 5, the titanium alloy bushing 3 and stainless steel bushing 4 are completely machined into the inner wall of the first and second initial holes, thus fixing the titanium alloy bushing 3 and stainless steel bushing 4 onto the composite material plate 1 and the titanium alloy material plate 2 respectively.

[0056] It should be noted that the mandrel 5 is made of W6Mo5Cr4V2 steel, oil-quenched at 1150℃, and tempered twice at 210℃ to ensure that the hardness of the extrusion section 52, guide section 51, and calibration section 53 reaches HRC62~66. The length of the extrusion section 52 of the mandrel 5 is 1mm, and the maximum diameter of the extrusion section 52 is 6.38mm; the front cone angle of the mandrel 5 is 3°, and the rear cone angle is 9°.

[0057] S5. According to the assembly requirements, the titanium / titanium laminate structure is reamed a second time (using reamer 7 to make the hole) so that the inner diameter of the deformed titanium alloy bushing 3 and stainless steel bushing 4 is the same, and their hole diameter is 6.35mm.

[0058] Tensile fatigue performance tests were performed on the processed three-pronged nail connection specimens of the composite / titanium laminate structure, specifically including:

[0059] Reference Figure 4 A three-bolt connection specimen of the composite / titanium laminate structure was obtained by connecting the composite / titanium laminate structure with high-strength bolts, and attaching compensation plates 8 (including aluminum alloy compensation plates) to the clamping section of the composite / titanium laminate structure (the part clamped by the fatigue testing machine). The aluminum alloy compensation plates were attached to prevent off-center loading during fatigue testing clamping and loading, thus avoiding affecting the accuracy of the test. (Refer to...) Figure 4 An aluminum alloy compensation sheet is attached to the exposed upper surface of the composite material plate 1, and an aluminum alloy compensation sheet is attached to the exposed lower surface of the titanium alloy material plate 2. Figure 4 In the diagram, A, B, and C represent different holes;

[0060] To test the fatigue performance of three-pronged joint specimens with a composite / titanium laminate structure, the influence of hole processing technology on the joint performance was investigated. Tensile-tensile fatigue tests were conducted on the machined specimens using an electro-hydraulic servo fatigue testing machine (W+BLFV-100HH) at room temperature. During the fatigue tests, the stress level q was selected as 65% and 80% of the maximum static tensile load, the loading frequency was 5 Hz, the stress ratio R was 0.1, and the loading waveform was a sine wave. Three parallel tests were performed for each parameter, and the average value was taken to represent the fatigue life under that parameter.

[0061] All holes in the three-pronged connection specimens of the titanium / tanium laminated structure were machined, and tensile-tensile fatigue performance tests were conducted on the machined specimens under different loads. Five parallel specimens were tested in each group, and the average life was taken as the fatigue life under that condition. The results were compared with those of the previous tests. Figure 5 As shown.

[0062] This embodiment selected two different loads, 80% and 65% of the maximum static tensile load, with loads of 36.7 and 29.8 kN respectively. The results show that the hole-making process can effectively improve the fatigue performance of the three-pronged joint specimens of the titanium / laminated composite structure. The fatigue life of the unprocessed specimen at 36.7 kN was 1.22 × 10⁴ cycles, while that of the processed specimen was 1.75 × 10⁴ cycles, an improvement of approximately 43%. The strengthening effect of hole-making becomes more pronounced as the load decreases; at a load of 29.8 kN, the specimen life is improved by approximately 67%.

[0063] The failure modes of three-pronged joint specimens with different composite / titanium laminate structures under fatigue loading were analyzed. The fatigue failure modes of the three-pronged joint specimens with composite / titanium laminate structures were basically the same before and after hole machining, both resulting in fracture of the titanium alloy plate 2 at hole C. The damage tolerance of titanium alloy plate 2 was smaller than that of composite plate 1, making it more prone to fatigue failure under higher stress levels. Although titanium alloy plate 2 could undergo plastic deformation under load, resulting in almost equal distribution of the nail load, the load at hole C was the greatest due to factors such as bending deformation of the specimen, thus making it more susceptible to fatigue fracture. The fracture surface of the unstrengthened specimen without hole machining was relatively flat, while the fracture surface of the strengthened specimen after hole machining was uneven. This indicates that the gradient structure on the titanium alloy surface formed after hole machining, combined with residual compressive stress, makes fatigue fracture more difficult, requires greater tip stress for crack propagation, and improves the fatigue life of the specimen.

[0064] It should be noted that "before hole machining" in the three-pin connection specimen of the composite / titanium laminated structure refers to the connection specimen that has undergone direct hole machining, while "after hole machining" refers to the connection specimen after installing bushings of different materials according to the differentiated hole machining method in this embodiment.

[0065] The fatigue fracture surface of a three-pronged nail-connected specimen with a composite / titanium laminate structure under a fatigue load of 29.8 kN is shown below. Figure 6 As shown, two specific specimen types were included: THE-S specimens (smooth specimens) and NTHE specimens (notched specimens). The fracture morphology of each region of the titanium alloy and the crack propagation process consisted of a stable crack propagation stage, a rapid crack propagation stage, and the final instantaneous fracture region. In the stable crack propagation stage I, the unprocessed specimen showed obvious river-like features (a), the processed specimen showed obvious river-like features (d), and the processed specimen showed small tear ridges in some areas. In the stable crack propagation stage II, the typical feature of this stage was fatigue banding. The average width of the fatigue band (b) at a distance of 2 mm from the hole in the unprocessed specimen was 531 nm, while the width of the band (e) in the processed specimen was even smaller, only 327 nm. The smaller fatigue band spacing also indicated a lower crack propagation rate. In the final instantaneous fracture region, the dimples (c) in the unprocessed specimen were more uniform and flatter, while the dimples (f) in the processed specimen varied in depth, which also proved that the stress required for instantaneous fracture of the specimen after hole processing was greater. Its (a), (b), (c), (d), (e), and (f) are Figure 6 Small pictures in the image.

[0066] The fatigue fracture surface of the three-pin joint specimen of the titanium / tanium laminate under a fatigue load of 36.7 kN is shown in the figure. Figure 7 As shown, two specific specimen designs are included: THE-S specimens (smooth specimens) and NTHE specimens (notched specimens). On the NTHE fracture surfaces 1 mm and 2 mm from the hole edge, the average width of the fatigue bands was 504 nm (a) and 1214 nm (b), while that of the THE-S specimens was 279 nm (d) and 618 nm (e), representing reductions of 45% and 49%, respectively. The reduced fatigue band width of the hole-machined specimens demonstrates a lower crack propagation rate in this region, resulting in a corresponding increase in fatigue life. Simultaneously, more secondary cracks were observed in the THE-S specimens. The formation of secondary cracks can reduce the tip stress during the main crack propagation process, inhibiting the increase in crack propagation rate. (a), (b), (c), and (d) are... Figure 7 Small pictures in the image.

[0067] In summary, this embodiment, by designing bushings with different inner diameters, creates beneficial residual compressive stresses in the composite material holes and titanium alloy holes respectively, significantly improving their fatigue strength and matching them, thus solving the problem of fatigue performance differences. By precisely controlling the inner diameters of the first and second bushings, appropriate elastoplastic deformation is ensured during processing, reducing stress concentration and local deformation, and improving processing accuracy and quality.

[0068] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

[0069] It should be noted that, for those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for fabricating differentiated holes in a stacked structure, characterized in that, include: S1, perform the first boring of the stacked structure, the stacked structure comprising two or more layers of plates stacked together; S2, Select bushings of suitable materials according to the material properties of different plates, and set the inner diameter of the corresponding bushings according to the amount of hole extrusion that the plate can withstand. S3, Bushings of different materials are placed on tapered mandrels according to the stacking order of the plates. An axial force is applied to the tapered mandrels using an extrusion device, and the mandrels are pulled through the hinge holes of the stacked structure in sequence to install bushings of different materials into the hinge holes of the matching plates. S4, continue to use the extrusion equipment to apply axial force to the tapered mandrel, pull the mandrel to extrude bushings of different materials, so that the bushings of different materials are interference-fitted with the appropriate plate. S5. According to the assembly requirements, the stacked structure is reamed a second time to make the inner diameter of the bushings of different materials the same after deformation.

2. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The outer diameter of the bushing is smaller than the inner diameter of the corresponding hinge hole.

3. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The bushing is a seamless bushing.

4. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The laminated structure includes two stacked plates, comprising a first material plate and a second material plate. When the first material plate is a composite material plate and the second material plate is a titanium alloy material plate, the first bushing is a titanium alloy bushing and the second bushing is a stainless steel bushing.

5. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The mandrel includes a guide section and a pressing section connected in sequence, the guide section and the pressing section passing through the first bushing and the second bushing in sequence; the diameter of the guide section is smaller than the inner diameter of the first bushing, the diameter of the pressing section gradually increases along the axis away from the guide section, the minimum diameter of the pressing section is the same as the diameter of the guide section, and the maximum diameter of the pressing section is larger than the inner diameter of the second bushing and smaller than the outer diameter of the second bushing.

6. The method for processing differentiated holes in a stacked structure according to claim 5, characterized in that, The mandrel further includes a calibration section, and the end of the extrusion section away from the guide section is connected to the calibration section. The diameter of the calibration section is the same as the maximum diameter of the extrusion section.

7. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The extrusion section of the mandrel is 1 mm long, with a front cone angle of 3° and a rear cone angle of 9°.

8. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The core rod is made of a rigid material.

9. The method for processing differentiated holes in a stacked structure according to claim 1, characterized in that, The inner wall of the bushing before deformation is lubricated.

10. A layered structure, characterized in that, The stacked structure includes a stacked structure made by the differential hole processing method of any one of claims 1-9, wherein the stacked structure comprises two or more layers of plates stacked together, the stacked structure has a hinge hole, the hinge hole on the plates with different material properties is fitted with a bushing of a suitable material, the hinge hole on the plates with different material properties is interference-fitted with the bushing of the suitable material, and all bushings in the same hinge hole on the stacked structure have the same center line and inner diameter.

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