Method for evaluating residual fatigue strength of friction type high-strength bolt connection after corrosion

Abstract

The application discloses a kind of evaluation methods of the remaining fatigue strength of friction type high-strength bolt connection after corrosion, for the bolt connection joint commonly used in civil engineering, first, dismantle appearance corrosion serious bolt, calculate the bolt mass loss rate by corrosion product cleaning, obtain the remaining average bolt pretightening force and the friction coefficient of plate after corrosion;Second, check the corrosion state of base metal at the opening of plate, determine the fatigue life calculation stage of connection;Then, the finite element method is used to establish the solid model of friction type high-strength bolt connection, and the stress field distribution of the key parts of the connection under different fatigue stress amplitudes is extracted;Generate the fatigue crack plane stress intensity correction coefficient table, calculate the cycle number under the given material parameters and initial crack, obtain the fatigue data curve of the connection after corrosion;Finally, the remaining fatigue strength of friction type high-strength bolt connection after corrosion is evaluated, and used to guide the subsequent maintenance and reinforcement work.

Description

Technical Field

[0001] This invention belongs to the field of structural fatigue life prediction and fatigue strength assessment, and relates to a method for assessing the residual fatigue strength of friction-type high-strength bolted connectors after corrosion. Background Technology

[0002] Friction-type high-strength bolt connections are an important type of steel structure joint connection, offering advantages such as high connection strength, convenient construction, and high installation reliability, and are widely used in civil engineering structures such as bridges and buildings. In marine or industrial atmospheric environments, structures inevitably experience environmental corrosion over decades of use, leading to a degradation of the fatigue strength of the bolt connections. When the fatigue strength of the bolt connections fails to meet the structural stress requirements, connection failure occurs, resulting in overall structural damage. However, as connection nodes, replacing bolts is difficult and costly. Therefore, considering the unavoidable nature of bolt corrosion, accurately assessing the remaining fatigue strength of the bolt connections after corrosion is crucial for ensuring the safety of the connection nodes and the overall structure, and for the proper maintenance and repair of the connection nodes. However, there are currently few reports on methods for assessing the fatigue strength of friction-type high-strength bolt connections after considering the effects of corrosion. Existing research on friction-type high-strength bolt connections mainly focuses on static mechanical properties such as slip load, ultimate bearing capacity, and tensile failure mode; the established methods and models are not applicable to dynamic fatigue analysis. Existing research on the fatigue performance of steel structures after corrosion has mainly focused on components such as steel plates and steel wires, and the relevant methods and models cannot be applied to bolted connections.

[0003] Friction-type high-strength bolted connections consist of high-strength bolts and connecting plates. Due to the complexity of actual structures and the destructive effects of corrosion, it is difficult to install sensors to measure the contact state between plates and the stress state at openings. Furthermore, actual connection nodes are difficult to disassemble for fatigue testing. Therefore, it is challenging to effectively study and analyze the fatigue performance of bolted connections in in-service structures after corrosion. How to develop a practical evaluation method for bolted connections based on existing corrosion and fatigue test data of friction-type high-strength bolted connections, combined with finite element analysis, is a problem that urgently needs further resolution. This invention addresses these issues by establishing an analytical method. Summary of the Invention

[0004] Technical Problem: To fill the gap in the evaluation method for the fatigue strength of friction-type high-strength bolted connections after corrosion, this invention provides an evaluation method for the residual fatigue strength of friction-type high-strength bolted connections based on experimental data and finite element simulation, taking into account the influence of environmental corrosion. This method is highly operable, accurate, and easy to implement, and can be used to evaluate the residual fatigue strength of friction-type high-strength bolted connections in steel structures under operating conditions, thereby providing guidance for subsequent structural maintenance and repair work.

[0005] Technical Solution: The present invention provides a method for evaluating the residual fatigue strength of friction-type high-strength bolt connectors after corrosion. This method assesses the residual fatigue strength of friction-type high-strength bolt connectors after corrosion. The friction-type high-strength bolt connector includes a connecting plate and several high-strength bolts mounted on the connecting plate. The evaluation method specifically includes the following steps:

[0006] Step 1: Calculate the average mass loss rate η of high-strength bolts after corrosion.

[0007] The average mass loss rate η of the high-strength bolts removed from the connecting plate after corrosion is calculated using the following formula:

[0008]

[0009] In the formula: m0 represents the original mass of the high-strength bolt; m1 represents the average remaining mass of the high-strength bolt after cleaning following corrosion.

[0010] Step 2: Calculate the remaining preload P of the high-strength bolt after corrosion. c The coefficient of friction μ with the connecting plate c

[0011] Residual preload P of high-strength bolts after corrosion c The calculation formula is:

[0012] P c =P0(1-1.748η) 1.337 )

[0013] The coefficient of friction μ of the connecting plates after corrosion c The calculation formula is:

[0014] μ c =μ0(0.357ηe -0.233η +1)

[0015] In the above formula, P0 represents the design preload of the high-strength bolt; μ0 represents the design friction coefficient of the connecting plates.

[0016] Step 3: Determine whether to conduct a residual fatigue strength assessment of the high-strength bolts.

[0017] Inspect the corrosion status of the base material at the edge of the opening after removing the high-strength bolts on the connecting plate to determine whether a residual fatigue strength assessment is required. If a residual fatigue strength assessment is required, proceed to step four.

[0018] Step 4: Finite element simulation evaluation of the residual fatigue strength of friction-type high-strength bolted connections after corrosion.

[0019] The finite element method is used to assess the residual fatigue strength of friction-type high-strength bolted connections after corrosion. The specific steps include:

[0020] Step 4.1: Establish a three-dimensional finite element model of the friction-type high-strength bolt connection and determine the stress ratio R based on the actual stress state of the structure. Simultaneously, set n calculated stress amplitudes, with the maximum fatigue loading stress corresponding to the i-th calculated stress amplitude being S. i ; i represents the index of the calculated stress amplitude, i = 1, 2, 3...n;

[0021] In the three-dimensional finite element model, both the connecting plates and the high-strength bolts are built using solid elements, and preload elements are built inside the bolts of the high-strength bolts. A Coulomb contact model is used to simulate the contact friction between the plates and between the high-strength bolts and the plates in the three-dimensional finite element model. The slip coefficient of this Coulomb contact model is the friction coefficient μ calculated in step two. c ;

[0022] Step 4.2: Finite Element Loading Analysis. The three-dimensional finite element model of the friction-type high-strength bolt connection established in Step 4.1 is used to solve and extract the planar two-dimensional tensile stress field distribution of the minimum cross-section at the opening edge of the connecting plate. Loading of the three-dimensional finite element model includes bolt preload loading and fatigue stress loading. Bolt preload loading is achieved by applying the residual preload P obtained in Step 2 to the preload element of the three-dimensional finite element model. c To achieve this, fatigue stress loading is achieved by applying the maximum fatigue loading stress S obtained in step 4.1 through a three-dimensional finite element model. i And achieve;

[0023] Step 4.3: Generate a table of plane stress intensity correction coefficients based on the two-dimensional tensile stress field distribution obtained in Step 4.2.

[0024] Step 4.4: Calculate the stress intensity factor K of the crack in the depth and width directions respectively. a With K c :

[0025]

[0026]

[0027] In the above formula: β a The stress intensity correction factor in the depth direction of the crack is obtained from the plane stress intensity correction factor table obtained in step 4.3; β c The stress intensity correction factor in the width direction of the crack is obtained from the plane stress intensity correction factor table obtained in step 4.3; Y represents the uniaxial tensile geometry factor of the crack; S i This represents the maximum fatigue loading stress corresponding to the i-th calculated stress amplitude applied to the three-dimensional finite element model; a j c represents the crack depth after the j-th crack propagation.j This represents the crack width after the j-th crack propagation; j represents the number of crack propagation cycles, with values ​​of 0, 1, 2...N; when j = 0, a0 and c0 represent the initial crack depth and initial crack width, respectively, which are determined based on the local corrosion of the base material at the edge of the opening in the connecting plate.

[0028] Step 4.5: Apply the stress intensity factor K calculated in Step 4.4. a With K c The fracture toughness K of the connecting plate material is respectively related to the fracture toughness. r Compare the results, and when the judgment result is K a ≥K r And K c ≥K r At that time, output pairs (S) i T j ), and proceed to step 4.7, T j T0 represents the fatigue life of the crack. When j = 0, T0 represents the fatigue life of the initial crack, and its value is 0. Otherwise, proceed to step 4.6.

[0029] Step 4.6: Calculate the crack depth and crack width after the current crack propagation:

[0030] The current crack propagation is simulated using a crack propagation rate model. In this model, after the current crack has undergone ΔT cycles, the crack depth increases by Δa, and the crack width increases by Δc. The crack depth, crack width, and fatigue life after propagation are calculated using the following formula:

[0031] a j+1 =a j +Δa

[0032] c j+1 =c j +Δc

[0033] T j+1 =T j +ΔT

[0034] In the above formula: a j Indicates the current crack depth, a j+1 This indicates the crack depth after crack propagation.

[0035] Step 4.7: Pair each number (S) i T j By fitting the data, the fatigue strength corresponding to 2 million fatigue cycles is obtained. This strength is then compared with the actual structural stress to evaluate the corrosion of friction-type high-strength bolt connections.

[0036] Preferably, the average remaining mass m1 is obtained in the following way:

[0037] Step 1.1: Remove the high-strength bolts from the connecting plate that show corrosion products on their surface or whose diameter shrinkage exceeds the preset value 'a'.

[0038] Step 1.2: Clean the corrosion products from the high-strength bolts removed in Step 1.1;

[0039] Step 1.3: Weigh the high-strength bolts after cleaning in step 1.2 to obtain the average remaining mass m1 of the high-strength bolts.

[0040] Preferably, in step three, the criterion for determining whether a residual fatigue strength assessment is required is: whether corrosion damage to the base material occurs at the edge of the opening in the connecting plate.

[0041] Preferably, in step 4.1, the number of calculated stress amplitudes i ≥ 5, and the minimum cross-sectional area of ​​the opening edge is finely meshed to a size of 0.2 mm.

[0042] Preferably, in step 4.3, the plane stress intensity correction coefficient table is obtained by inputting the two-dimensional tensile stress field distribution into the fatigue analysis software AFGROW; or by solving the two-dimensional tensile stress field distribution using the Gaussian integration method.

[0043] Preferably, in step 4.6, the number of cycles ΔT is set to 100.

[0044] Preferably, in step 4.2, the loading of the three-dimensional finite element model is static hierarchical loading.

[0045] This invention is used to predict the residual fatigue strength of friction-type high-strength bolted connections in in-service structures after corrosion, accurately assess the reliability of bolted joints under environmental corrosion, and provide a reasonable and effective reference for assessing the condition of joints and arranging maintenance, upkeep and reinforcement of connection joints.

[0046] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0047] Existing technologies cannot assess the fatigue strength of friction-type high-strength bolted connections after corrosion in engineering structures. The "Method for Evaluating the Residual Fatigue Strength of Friction-Type High-Strength Bolted Connections after Corrosion" proposed in this application fills this technological gap. By combining experimental data with finite element simulation, it considers the changes in bolt preload and plate friction coefficient, the influence of the base material anti-corrosion coating, and the complex stress state at the plate openings, thereby achieving the assessment of the fatigue strength of friction-type high-strength bolted connections after corrosion.

[0048] Existing technologies for assessing corrosion fatigue strength generally require disassembling components from the structure and conducting experimental studies. The "Method for Assessing Residual Fatigue Strength of Friction-Type High-Strength Bolt Connections After Corrosion" proposed in this application does not require disassembling the bolt joints or conducting time-consuming and labor-intensive fatigue tests. It only requires calculating the mass loss rate by disassembling the bolts, establishing a finite element model, and iterative calculations to assess the residual fatigue strength, thus saving on structural maintenance costs.

[0049] Existing technologies for assessing corrosion fatigue strength mostly focus on plates, failing to consider the combined effects of bolt preload, openings, and plate contact. The "Method for Assessing Residual Fatigue Strength of Friction-Type High-Strength Bolt Connections After Corrosion" proposed in this application, through the combination of a finite element model and a stress intensity correction coefficient, avoids the simulation of fatigue crack propagation under complex stress states, effectively improving simulation and prediction efficiency and showing broad application prospects. Attached Figure Description

[0050] Figure 1 This is a typical 1 / 4 finite element model of a friction-type high-strength bolt connection.

[0051] Figure 2 A schematic diagram showing the direction of the crack plane in the minimum cross-section of the opening edge;

[0052] Figure 3 This is a two-dimensional tensile stress field distribution diagram;

[0053] Figure 4 This is a schematic diagram of a crack.

[0054] Figure 5 The graph shows the relationship between crack length and number of cycles. In the graph: (a) represents the relationship between crack depth and number of cycles, and (b) represents the relationship between crack width and number of cycles.

[0055] Figure 6 This is a schematic diagram showing the stress amplitude and corresponding fatigue life points under a double logarithmic curve.

[0056] Figure 7 This is a data flow diagram for evaluating the residual fatigue strength of friction-type high-strength bolted connections after corrosion. Detailed Implementation

[0057] The present invention will be further described below with reference to the embodiments and the accompanying drawings.

[0058] The method for evaluating the residual fatigue strength of friction-type high-strength bolted connections after corrosion, as described in this invention, is as follows: Figure 7 As shown, it includes the following steps:

[0059] Step 1: Disassemble severely corroded bolts and clean the corrosion products from the high-strength bolts according to the procedure specified in GB / T 16545-2015 "Corrosion of Metals and Alloys - Removal of Corrosion Products from Corrosion Specimens". This includes soaking in pickling solution (various pickling solution formulas can be substituted for each other and do not need to be specifically specified), brushing off the corrosion products with a soft brush, rinsing with water and ethanol at room temperature, and drying. Obtain the average remaining mass m1 and the original mass m0 of the high-strength bolts, and determine the average mass loss rate η of the high-strength bolts after corrosion.

[0060]

[0061] Step 2: Determine the type of high-strength bolt and the surface treatment method of the connecting plate, determine the design preload P0 of the high-strength bolt and the design friction coefficient μ0 of the connecting plate as specified in the standard, and calculate the remaining preload P of the bolt after corrosion based on the model fitted by the experimental data. c The coefficient of friction μ between the corroded plate and the plate c .

[0062] Based on experimental statistics, the remaining preload P of the bolt after corrosion is calculated using the following formula. c The coefficient of friction μ between the corroded plate and the plate c :

[0063] P c =P0(1-1.748η) 1.337 )

[0064] μ c =μ0(0.357ηe -0.233η +1)

[0065] The calculation formula can be updated as experimental statistics are increased.

[0066] Step 3: Inspect the corrosion status of the base material at the edge of the plate opening after bolt removal to determine the fatigue life calculation stage of the connector. If the base material corrosion protection layer (zinc-rich coating, protective paint, etc.) is present and there is no base material corrosion damage, the remaining fatigue strength is considered to meet the requirements. If some of the base material corrosion protection layer (zinc-rich coating, protective paint, etc.) disappears and there is localized base material corrosion damage, the remaining fatigue strength is assessed. In short, whether there is base material corrosion damage at the edge of the plate opening is the criterion for this step.

[0067] Step 4: Based on the structural design drawings, establish a three-dimensional finite element model of the friction-type high-strength bolt connection (see attached document). Figure 1 The mesh is refined to a size of 0.2 mm on the plane of the minimum cross-section at the opening edge. The stress ratio R is determined according to the actual stress state of the structure. At the same time, n calculated stress amplitudes (n≥5) are set, and the maximum fatigue loading stress corresponding to the i-th calculated stress amplitude is S. i .

[0068] In the established three-dimensional finite element model, both the plate and bolt components are simulated using solid elements. The linear elastic material constitutive relations are defined according to the elastic modulus and Poisson's ratio of each material and assigned to the corresponding elements in the model. Contact relationships between plates and between bolts and plates are simulated using contact elements. The minimum cross-sectional plane of the opening edge is refined into a mesh with a size of 0.2 mm.

[0069] The material constitutive model of the three-dimensional finite element model is a general linear elastic constitutive model, and a 1 / 2 or 1 / 4 model can be established according to the model symmetry.

[0070] Step 5: For the i-th maximum fatigue loading stress S i Finite element loading analysis was performed, which consisted of two steps: bolt preload loading and fatigue stress loading. The load was applied in a static, graded manner. After loading, the two-dimensional tensile stress field distribution in the plane with the minimum cross-section of the opening edge was solved and extracted.

[0071] Step 6: Generate a table of plane stress intensity correction coefficients based on the two-dimensional tensile stress field distribution. According to the local corrosion of the base material at the edge of the opening in the plate, set the initial crack depth *a* and initial crack width *c*, and simultaneously set material parameters, including the material fracture toughness *K*. r Crack propagation rate model, etc.

[0072] The initial crack size can be obtained from on-site testing or by using the general macroscopic crack initiation length under drilling method, and is set to 0.05 mm.

[0073] The table of plane stress intensity correction coefficients can be obtained by inputting the two-dimensional tensile stress field distribution in the fatigue analysis software AFGROW, or by consulting the "Stress Analysis Handbook - Third Edition" (edited by Tada, Paris, and Irwin) and solving the two-dimensional tensile stress field distribution using the Gaussian integration method.

[0074] Step 7: Obtain the stress intensity correction factor β corresponding to the two directions of the current crack from the table. a With β c At this point, the initial fatigue life T i =0, based on the uniaxial tensile geometry factor Y, the stress intensity factor K in the crack depth and width directions is calculated. a With K c :

[0075]

[0076]

[0077] If K a With K c Greater than or equal to fracture toughness K rThe output stress amplitude is related to the corresponding fatigue life (S). i T i After calculating and outputting the average of n calculated stress amplitudes, proceed to step nine;

[0078] The crack stress intensity factor is corrected by the stress intensity correction coefficient to take into account the complex stress state at the edge of the hole in the bolted connection.

[0079] Step 8: Determine the crack depth and width growth Δa and Δc under 100 cycles based on the crack propagation rate model. Calculate the crack depth a = a + Δa and crack width c = c + Δc after propagation. At this point, the fatigue life T... i =T i +100, return to step 7;

[0080] Step 9: Based on n stress amplitudes and corresponding fatigue life points, fit the fatigue strength corresponding to 2 million fatigue lifespans, compare it with the actual structural stress, and realize the evaluation of corrosion of friction-type high-strength bolt connections.

[0081] Example

[0082] Based on the above-mentioned method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion, the present invention provides a specific embodiment as follows:

[0083] Step 1: Severe corrosion was found in the friction-type high-strength bolt connections at the crossbeam of a steel bridge tower. A total of three bolts with severe external corrosion were disassembled. Following the procedures specified in the standard GB / T 16545-2015 "Corrosion of Metals and Alloys - Removal of Corrosion Products from Corrosion Specimens", the corrosion products on the high-strength bolts were cleaned. This included soaking in pickling solution, brushing off the corrosion products with a soft brush, rinsing with water and ethanol at room temperature, and drying. The average mass loss rate η of the high-strength bolts after corrosion was found to be 8.2%.

[0084] Step 2: According to the bridge steel tower structural design drawings, the bolts used are determined to be 10.9 grade M24 high-strength bolts with a bolt hole diameter of 26.5mm. The method involves first drilling 24.5mm holes and then cutting and enlarging them. According to the specifications, the design preload of the 10.9 grade M24 high-strength bolts is 230kN. The steel plate surface is a clean, untreated rolled surface. According to the specifications, the coefficient of friction of the plate contact surface is 0.35. The remaining bolt preload P after corrosion is calculated using the formula. c The coefficient of friction μ of the steel plate contact surface after corrosion is 163.1 kN. c It is 0.49.

[0085] Step 3: After the bolts were removed, the corrosion status of the base material at the edge of the hole in the plate was checked. It was found that the local corrosion protection layer of the base material at the edge of the hole in the plate had been completely consumed, and local steel showed corrosion damage. There was reddish-brown rust at the edge of the hole, and the remaining fatigue strength assessment was required.

[0086] Step 4: According to the structural design drawings, the plate thickness is 20mm, the vertical bolt spacing is 120mm, and the bolt-to-hole spacing is 50mm. The plate steel is Q345D steel, and the high-strength bolt material is 20MnTiB alloy steel. Establish a three-dimensional finite element model of the friction-type high-strength bolt connection, such as... Figure 1 As shown. All plates and bolts are built using Solid 185 solid elements. Bolt preload is achieved by creating PRETS179 preload elements inside the bolt. TARGE 170 target elements and CONTA174 contact elements are used to simulate the contact between the tension plate and connecting plate, the connecting plate and gasket, and the bolt and the opening in the plate. Friction in the contact is simulated using the Coulomb model, and the friction coefficient of the plate is the slip coefficient. The contact between the gasket and the nut and bolt is simulated using coupled nodes. The element size is 1 mm, with the element size of the plate and bolt components near the opening edge refined to 0.2 mm. Considering the symmetry of the loading direction, a 1 / 4 scale model is created.

[0087] The stress ratio R is determined to be 0.1 based on the actual stress state of the structure. At the same time, five calculated stress amplitudes (110, 120, 130, 140 and 150 MPa) are set. The maximum fatigue loading stresses corresponding to the calculated stress amplitudes are 122.2, 133.3, 144.4, 155.6 and 166.7 MPa, respectively.

[0088] Step 5: The nonlinear solution of the finite element model consists of two steps. The first step applies bolt preload to the model. The second step applies the maximum fatigue load to the model. After loading, the two-dimensional tensile stress field distribution in the plane of the minimum cross-section at the opening edge is solved and extracted. The minimum cross-section at the opening edge is divided into two directions: depth and width. Figure 2 As shown, the two-dimensional tensile stress field distribution is expressed using the stress concentration factor, such as... Figure 3 As shown.

[0089] Step 6: By consulting the "Stress Analysis Handbook - Third Edition" (edited by Tada, Paris, and Irwin) and using the Gaussian integration method, the two-dimensional tensile stress field distribution is solved to obtain a table of plane stress intensity correction coefficients. Based on the local corrosion of the base material at the edge of the plate opening, the initial crack depth a = 0.4 mm and the initial width c = 0.4 mm are set, as follows: Figure 4 As shown, material parameters are set simultaneously, including the material fracture toughness K. r Crack propagation rate models, etc. The crack propagation rate model uses the Paris formula.

[0090] Step 7: Obtain the stress intensity correction factor β corresponding to the two directions of the current crack from the table. a With β c At this point, the initial fatigue life T i =0, based on Figure 4 The uniaxial tensile geometry factor Y of the crack shown is used to calculate the stress intensity factors K in the crack depth and width directions. a With K c :

[0091]

[0092]

[0093] If K a With K c Greater than or equal to fracture toughness K r The output stress amplitude is related to the corresponding fatigue life (S). i T i After calculating and outputting all n calculated stress amplitudes, proceed to step nine.

[0094] Step 8: Set the number of calculation cycles to 100. Based on the crack propagation rate model, determine the crack depth and width growth Δa and Δc after 100 cycles. Calculate the crack depth a = a + Δa and crack width c = c + Δc after propagation. At this point, the fatigue life T corresponding to the i-th calculated stress amplitude is determined. i =T i +100, return to step 7, and repeat the process to obtain the relationship between crack length and number of iterations, as shown below. Figure 5 As shown.

[0095] Step 9: Following steps 7-8, obtain 5 stress amplitudes and their corresponding fatigue life points, plot them on a double logarithmic curve and fit the curve, as shown below. Figure 6 As shown, the fatigue strength corresponding to 2 million fatigue cycles is 105 MPa, meaning the residual fatigue strength of this friction-type high-strength bolt connector after corrosion is 105 MPa. The standard GB50017-2017 "Standard for Design of Steel Structures" specifies a value of 144 MPa. The actual equivalent stress amplitude of the bolted joints on the crossbeams of the steel bridge tower is 35 MPa. Therefore, although the residual fatigue strength of this friction-type high-strength bolt connector after corrosion does not meet the standard requirements, it does meet the structural service requirements. The data flow of the above method for evaluating the residual fatigue strength of friction-type high-strength bolt connectors after corrosion is as follows: Figure 7 As shown in the figure, the assessment results indicate that node maintenance only requires removing rust from plates and bolts, reapplying anti-corrosion coating, and retightening bolts, providing a reference for the reasonable maintenance and reinforcement of bridge steel towers.

[0096] The above embodiments are merely preferred embodiments of the present invention. It should be noted that those skilled in the art can make several improvements and equivalent substitutions without departing from the principle of the present invention. All such improvements and equivalent substitutions to the claims of the present invention fall within the protection scope of the present invention.

Claims

1. A method for evaluating the residual fatigue strength of a friction-type high-strength bolt connector after corrosion, used to evaluate the residual fatigue strength of the friction-type high-strength bolt connector after corrosion; the friction-type high-strength bolt connector includes a connecting plate and a plurality of high-strength bolts mounted on the connecting plate, characterized in that, The evaluation method specifically includes the following steps: Step 1: Calculate the average mass loss rate η of high-strength bolts after corrosion. The average mass loss rate η of the high-strength bolts removed from the connecting plate after corrosion is calculated using the following formula: In the formula: m0 represents the original mass of the high-strength bolt; m1 represents the average remaining mass of the high-strength bolt after cleaning following corrosion. Step 2: Calculate the remaining preload P of the high-strength bolt after corrosion. c The coefficient of friction μ with the connecting plate c Residual preload P of high-strength bolts after corrosion c The calculation formula is: P c =P0(1-1.748η 1.337 ) The coefficient of friction μ of the connecting plates after corrosion c The calculation formula is: m c =μ0(0.357ηe -0.233η +1) In the above formula, P0 represents the design preload of the high-strength bolt; μ0 represents the design friction coefficient of the connecting plates. Step 3: Determine whether to conduct a residual fatigue strength assessment of the high-strength bolts. Inspect the corrosion status of the base material at the edge of the opening after removing the high-strength bolts on the connecting plate to determine whether a residual fatigue strength assessment is required. If a residual fatigue strength assessment is required, proceed to step four. Step 4: Finite element simulation evaluation of the residual fatigue strength of friction-type high-strength bolted connections after corrosion. The finite element method is used to assess the residual fatigue strength of friction-type high-strength bolted connections after corrosion. The specific steps include: Step 4.1: Establish a three-dimensional finite element model of the friction-type high-strength bolt connection and determine the stress ratio R based on the actual stress state of the structure. Simultaneously, set n calculated stress amplitudes, with the maximum fatigue loading stress corresponding to the i-th calculated stress amplitude being S. i ; i represents the index of the calculated stress amplitude, i = 1, 2, 3...n; In the three-dimensional finite element model, both the connecting plates and the high-strength bolts are built using solid elements, and preload elements are built inside the bolts of the high-strength bolts. A Coulomb contact model is used to simulate the contact friction between the plates and between the high-strength bolts and the plates in the three-dimensional finite element model. The slip coefficient of this Coulomb contact model is the friction coefficient μ calculated in step two. c ; Step 4.2: Finite Element Loading Analysis. The three-dimensional finite element model of the friction-type high-strength bolt connection established in Step 4.1 is used to solve and extract the planar two-dimensional tensile stress field distribution of the minimum cross-section at the opening edge of the connecting plate. Loading of the three-dimensional finite element model includes bolt preload loading and fatigue stress loading. Bolt preload loading is achieved by applying the residual preload P obtained in Step 2 to the preload element of the three-dimensional finite element model. c To achieve this, fatigue stress loading is achieved by applying the maximum fatigue loading stress S obtained in step 4.1 through a three-dimensional finite element model. i And achieve; Step 4.3: Generate a table of plane stress intensity correction coefficients based on the two-dimensional tensile stress field distribution obtained in Step 4.

2. Step 4.4: Calculate the stress intensity factor K of the crack in the depth and width directions respectively. a With K c : In the above formula: β a The stress intensity correction factor in the depth direction of the crack is obtained from the plane stress intensity correction factor table obtained in step 4.3; β c The stress intensity correction factor in the width direction of the crack is obtained from the plane stress intensity correction factor table obtained in step 4.3; Y represents the uniaxial tensile geometry factor of the crack; S i This represents the maximum fatigue loading stress corresponding to the i-th calculated stress amplitude applied to the three-dimensional finite element model; a j c represents the crack depth after the j-th crack propagation. j This represents the crack width after the j-th crack propagation; j represents the number of crack propagation cycles, with values ​​of 0, 1, 2...N; when j = 0, a0 and c0 represent the initial crack depth and initial crack width, respectively, which are determined based on the local corrosion of the base material at the edge of the opening in the connecting plate. Step 4.5: Apply the stress intensity factor K calculated in Step 4.

4. a With K c The fracture toughness K of the connecting plate material is respectively related to the fracture toughness. r Compare the results, and when the judgment result is K a ≥K r And K c ≥K r At that time, output pairs (S) i T j ), and proceed to step 4.7, T j T0 represents the fatigue life of the crack. When j = 0, T0 represents the fatigue life of the initial crack, and its value is 0. Otherwise, proceed to step 4.

6. Step 4.6: Calculate the crack depth and crack width after the current crack propagation: The current crack propagation is simulated using a crack propagation rate model. In this model, after the current crack has undergone ΔT cycles, the crack depth increases by Δa, and the crack width increases by Δc. The crack depth, crack width, and fatigue life after propagation are calculated using the following formula: in j+1 = yes j +Δa c j+1 =c j +Δc T j+1 =T j +ΔT In the above formula: a j Indicates the current crack depth, a j+1 This indicates the crack depth after crack propagation. Step 4.7: Pair each number (S) i T j By fitting the data, the fatigue strength corresponding to 2 million fatigue cycles is obtained. This strength is then compared with the actual structural stress to evaluate the corrosion of friction-type high-strength bolt connections.

2. The method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion according to claim 1, characterized in that, The specific method for obtaining the average remaining mass m1 is as follows: Step 1.1: Remove the high-strength bolts from the connecting plate that show corrosion products on their surface or whose diameter shrinkage exceeds the preset value 'a'. Step 1.2: Clean the corrosion products from the high-strength bolts removed in Step 1.1; Step 1.3: Weigh the high-strength bolts after cleaning in step 1.2 to obtain the average remaining mass m1 of the high-strength bolts.

3. The method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion according to claim 1, characterized in that, In step three, the criterion for determining whether a residual fatigue strength assessment is needed is to determine whether corrosion damage to the base material occurs at the edge of the opening in the connecting plate.

4. The method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion according to claim 1, characterized in that, In step 4.1, the number of stress amplitude calculations is set to n≥5, and the minimum cross-sectional plane of the opening edge is refined to a size of 0.2mm.

5. The method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion according to claim 1, characterized in that, In step 4.3, the plane stress intensity correction coefficient table is obtained by inputting the two-dimensional tensile stress field distribution in the fatigue analysis software AFGROW; or by solving the two-dimensional tensile stress field distribution using the Gaussian integration method.

6. The method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion according to claim 1, characterized in that, In step 4.6, the number of loops ΔT is set to 100.

7. The method for evaluating the residual fatigue strength of friction-type high-strength bolt connections after corrosion according to claim 1, characterized in that, In step 4.2, the loading of the three-dimensional finite element model is static hierarchical loading.

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