A method for analyzing the connecting bolts of gearbox housing based on finite element simulation

Abstract

The present invention provides a gearbox housing connecting bolt analysis method based on finite element simulation, which belongs to the field of electrical digital data processing technology, including: establishing a geometric model of the gearbox housing connecting bolt; meshing, so that the threaded rod and the bolt hole node are completely merged; analyzing the static strength limit, applying a load to obtain the Mises stress of the first thread meshing unit of different structures and connecting bolts; analyzing fatigue strength, applying a load, calculating the unit stress and further extracting the axial force and bending moment; finite element analysis, according to the established geometric model of the gearbox housing connecting bolt, setting the connection mode in the finite element analysis model; and loading the obtained stress into the finite element analysis model as a boundary condition to calculate the fatigue damage of the connecting bolt. The present invention can not only simulate the actual meshing condition of the thread position, reflect the performance of the bolt itself, but also verify the fatigue strength to ensure that the structure will not be damaged under the operating state.

Description

Technical Field

[0001] The invention relates to the technical field of electrical digital data processing, and in particular to a gear box body connecting bolt analysis method based on finite element simulation. Background Art

[0002] Gearboxes are the core components of wind turbine equipment, and manufacturers have increasingly higher requirements for the strength verification of their components. Among them, high-strength bolts are the most commonly used parts in wind turbine equipment. In order to accurately simulate the thread engagement state, it is necessary to establish the thread detail features and set the thread engagement contact relationship. If a finite element model is established for each bolt in this way, the calculation scale is huge and difficult to achieve. Therefore, the thread engagement relationship is simplified to a rigid coupling, which verifies the feasibility of Beam188 beam element simulation of bolt connections;

[0003] At present, the strength check of gearbox housing bolts is carried out by using solid bolt modeling, which has the following disadvantages:

[0004] 1. Solid modeling can only simulate the results of the gearbox bolt joint surface, and cannot accurately simulate the actual meshing conditions of the thread position, so it cannot accurately check the actual ultimate strength and fatigue damage of the thread.

[0005] 2. Solid modeling cannot reflect the performance of the bolt itself, and cannot perform fatigue strength verification.

[0006] 3. The calculation results of solid modeling will show stress concentration in fillets, resulting in unrealistic results of the bonding surface.

[0007] 4. The number of solid modeling grids is large, which affects the calculation efficiency. Summary of the invention

[0008] According to the technical problems raised above, a gearbox housing connection bolt analysis method based on finite element simulation is provided. The present invention simplifies the housing bolt thread meshing relationship into a rigid coupling calculation method, and the calculation speed caused by the thread meshing relationship of the method is applied to verify the feasibility of Beam188 beam element simulation of bolt connection.

[0009] The technical means adopted by the present invention are as follows:

[0010] A gearbox housing connection bolt analysis method based on finite element simulation, comprising:

[0011] S1. Establish the geometric model of the gearbox housing connecting bolts;

[0012] S2, meshing to completely merge the threaded rod and bolt hole nodes;

[0013] S3, analyze the static strength limit, apply load, and obtain the Mises stress of the unit at the first thread engagement of different structures and connecting bolts;

[0014] S4, analyze fatigue strength, apply load, calculate unit stress and further extract axial force and bending moment;

[0015] S5. Perform finite element analysis. During the finite element analysis, according to the geometric model of the gear box housing connecting bolts established in step S1, set the connection mode in the finite element analysis model; and load the stress obtained in step S4 into the finite element analysis model as a boundary condition to calculate the fatigue damage of the connecting bolts.

[0016] Furthermore, step S1 specifically includes:

[0017] S11. Build the overall model of the gearbox housing connecting bolts, including the front end cover, the upwind bearing outer ring, the front housing first-stage gear ring, the middle housing and the downwind bearing inner ring. The housing is made of QT400-18AL material, and the structural parts are all made of structural steel.

[0018] S12, select the bolts connecting the front cover and the front box, the front box and the first gear ring, and the first gear ring and the middle box for verification, among which the screw, nut and thread are all modeled and simulated by Beam unit;

[0019] S13, Beam unit modeling is used. Multiple Beam units are used to model the thread and screw head in the form of a load umbrella. The entire thread is divided into several equal parts. At the same time, each screw hole is divided into several equal parts, and the contact relationship is accurately set.

[0020] Furthermore, in step S13, the cross-sectional properties of the Beam unit are set as follows:

[0021] The beam units are all given a circular cross-section, where the diameter of the screw is the bolt mid-diameter, and the diameter at the thread is calculated based on the stress cross-sectional area of ​​the bolt.

[0022] Further, step S2 specifically includes:

[0023] S21, control the mesh size of the joint surface;

[0024] S22, simultaneously controlling the mesh size of the bolt holes on the nut, the housing and the gear ring;

[0025] S23. Ensure that the rod unit is aligned with the nut and bolt hole nodes so that the threaded rod and bolt hole nodes are completely merged.

[0026] Furthermore, step S3 specifically includes:

[0027] S31. For static strength analysis, a preload is applied to the screw before the working load is applied;

[0028] S32, the working load is applied to the simplified upwind bearing outer ring surface and the downwind bearing inner ring surface, and the working load includes the bearing force, the tangential force of the gear ring, the torque of the middle box and the axial force;

[0029] S33. Analyze the ultimate strength results. The location with the maximum stress is the location of the maximum damage to the bolt, which is the first thread root unit or adjacent unit where the nut and the bolt are meshed. Check the Mises stress of the first thread meshing unit of different structures and connecting bolts.

[0030] Further, step S4 specifically includes:

[0031] S41. Apply preload before bearing the working unit load. The working unit load is 70% of the maximum load amplitude of the hub center extracted for each working condition and applied to the bearing as the unit load. The load for each working condition is divided into several levels.

[0032] S42. Locate each bolt unit:

[0033] Set the global coordinate system csys,1;

[0034] Define the variable bolt_num= n ;

[0035] Define the distance between the first bolt and the global coordinate system RC_in= r ;

[0036] Define the work plane coordinate system WPCSYS,-1,2: -1 means use the global Z Axis, 2 means use global X Axis, where 2 is the position of the first bolt, and the coordinates of other bolts are defined in sequence;

[0037] Define the bolt_angles.csv file and reference it in the APDL file to determine the position of each bolt;

[0038] S43. Define .dat file:

[0039] Define the array bolt_force. Since it is divided into 4 levels this time, the data will be 10 rows and bolt_num*3+1 columns.

[0040] Define character array load_direction, M x / M y / Mz / F x / F y / F z ;

[0041] Define a loop do,j,1,bolt_num,1, select a single element set named element, find the element to extract forces and moments;

[0042] Define a table named ssx, extract the data with the highest value and put it in the first column F x ; Similarly, define a table named bsy, the first column of data M y , define a table named bsz, the first column of data M z ;

[0043] definition i Cycle, from 1 to 6, step size is 1, 6 working condition cycles are defined;

[0044] S44. Generate .dat file:

[0045] definition i Loop do,i,2,49,1: from step 2 to step 49, the step length is 1;

[0046] definition j Loop do,j,1,4,1: from step 1 to step 4, the step length is 1;

[0047] Read the unit stress result file and extract F x , M y , M z , and store it in a table.

[0048] Furthermore, step S5 specifically includes:

[0049] S51, according to the geometric model of the gearbox housing connecting bolts established in step S1, setting the connection mode in the finite element analysis model, including: a friction connection between the front end cover and the front housing, a friction connection between the front housing and the primary gear ring, and a friction connection between the primary gear ring and the middle housing;

[0050] S52, obtaining a load-stress nonlinear relationship curve at the maximum stress position of each bolt;

[0051] S53, interpolate the fatigue time series load into the load-time curve, generate the .inp file for the working condition and time distribution, and prepare the load file for easy reading by Matlab;

[0052] S54, obtaining a stress-time series curve of the bolt through a load-stress curve relationship and a time series load group;

[0053] S55, bolt calculation uses SN curve, and the stress calculation formula corresponding to the inflection point is as follows:

[0054]

[0055] In the above formula, represents the fatigue limit, represents the stress range, Represents the slope. When the number of cycles corresponding to the inflection point is less than hour, , when the number of cycles corresponding to the inflection point is not less than hour, , represents the safety factor, , Indicates the number of permissible load cycles, represents the number of cycles corresponding to the inflection point, , Indicates impact factor; number of cycles The fatigue strength is ; Indicates the maximum bolt internal force under the ultimate load, It indicates the minimum bolt internal force corresponding to the elastic strain limit of 0.2%. For bolts with a diameter greater than M30, considering the factors affecting the SN curve, the calculation formula is as follows:

[0056]

[0057] In the above formula, Indicates nominal diameter;

[0058] S56, loading the data obtained from step S52 to step S55 into matlab software, extracting the stress array at the target node of the bolt, sequentially calculating the distributed stress of each bolt evenly spaced 30°, and then generating the load stress array load_stress of each bolt under multiple working conditions;

[0059] S57, according to the generated load stress array load_stress, the stress time series array stress_time of each bolt at different angles is obtained by extended interpolation;

[0060] S58, using the three-peak-valley value cycle counting method, filtering and splicing the stress time series array stress_time, eliminating unreasonable data, so that the stress time series array stress_time only contains alternately appearing peaks and troughs;

[0061] S59. Based on the synthetic S / N curve of the bearing material, the rain flow counting method is used to obtain the actual stress amplitude, and then the fatigue damage of each bolt in each group of the box is calculated according to Miner's linear cumulative damage theory.

[0062] Compared with the prior art, the present invention has the following advantages:

[0063] 1. The present invention provides a gearbox housing connecting bolt analysis method based on finite element simulation, and its calculation results are reliable. It not only takes into account the results at the thread meshing point (usually the maximum result value appears at the meshing point) but also takes into account the influence of the thread meshing on the housing. That is, it can not only simulate the actual meshing situation of the thread position and reflect the performance of the bolt itself, but also perform fatigue strength verification to ensure that the structure will not be damaged when in operation.

[0064] 2. The present invention provides a gearbox housing connecting bolt analysis method based on finite element simulation, which has high modeling accuracy, strict mesh control, and efficient simulation calculation, that is, all unit types are low-order units (rod units and mass units).

[0065] 3. The present invention provides a gearbox housing connecting bolt analysis method based on finite element simulation, which avoids stress concentration at the chamfer of the bolt.

[0066] 4. The present invention provides a gearbox housing connecting bolt analysis method based on finite element simulation, which calculates bolt damage through MATLAB software, has high calculation efficiency, can perform rain flow processing on stress amplitude, and achieves consistency with commercial software fatigue damage calculation methods; at the same time, the load does not require secondary processing.

[0067] Based on the above reasons, the present invention can be widely promoted in the fields of gear box body bolt modeling method and fatigue damage calculation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0068] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0069] Figure 1The present invention is a flow chart of the method for calculating the ultimate and fatigue strength of box bolts based on finite element simulation.

[0070] Figure 2 A solid bolt model of a gearbox housing provided in an embodiment of the present invention.

[0071] Figure 3 A gearbox housing rod unit bolt model provided in an embodiment of the present invention.

[0072] Figure 4 A schematic diagram of a bolt entity provided in an embodiment of the present invention.

[0073] Figure 5 A schematic diagram of a rod unit model provided in an embodiment of the present invention.

[0074] Figure 6 An overall schematic diagram of a box finite element mesh model provided in an embodiment of the present invention.

[0075] Figure 7 A local detailed schematic diagram of a bolt hole mesh unit model provided in an embodiment of the present invention.

[0076] Figure 8 The contact relationship between the thread and the screw hole provided in the embodiment of the present invention.

[0077] Fig. 9 A schematic diagram of applying a working load provided in an embodiment of the present invention.

[0078] Fig.10 A schematic diagram of applying bolt pre-tightening force provided in an embodiment of the present invention.

[0079] Fig.11 Bolts between the front cover and the front box body provided in the embodiment of the present invention M y _min limit condition calculation result cloud chart.

[0080] Fig.12 The unit load input file provided by the embodiment of the present invention.

[0081] Fig.13 A table of calculation results of the maximum damage of each bolt provided in an embodiment of the present invention. DETAILED DESCRIPTION

[0082] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0083] It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0084] like Figure 1 As shown, the present invention provides a gearbox housing connecting bolt analysis method based on finite element simulation, comprising:

[0085] S1. Establish the geometric model of the gearbox housing connecting bolts;

[0086] S2, meshing to completely merge the threaded rod and bolt hole nodes;

[0087] S3, analyze the static strength limit, apply load, and obtain the Mises stress of the unit at the first thread engagement of different structures and connecting bolts;

[0088] S4, analyze fatigue strength, apply load, calculate unit stress and further extract axial force and bending moment;

[0089] S5. Perform finite element analysis. During the finite element analysis, according to the geometric model of the gear box housing connecting bolts established in step S1, set the connection mode in the finite element analysis model; and load the stress obtained in step S4 into the finite element analysis model as a boundary condition to calculate the fatigue damage of the connecting bolts.

[0090] In specific implementation, as a preferred embodiment of the present invention, step S1 specifically includes:

[0091] S11. Build the overall model of the gearbox housing connecting bolts, including the front end cover, the upwind bearing outer ring, the front housing first-stage gear ring, the middle housing and the downwind bearing inner ring. The housing is made of QT400-18AL material, and the structural parts are all made of structural steel.

[0092] S12, select the bolts connecting the front cover and the front box, the front box and the first gear ring, and the first gear ring and the middle box for verification, among which the screw, nut and thread are all modeled and simulated by Beam unit;

[0093] S13, Beam unit modeling is adopted. Multiple beam units are adopted to model the thread and screw head in the form of load umbrella. The whole thread is divided into several equal parts (such as 4, 5 or more parts, which can be divided according to the pitch or thread length). At the same time, each screw hole is divided into several equal parts, and the contact relationship is accurately set.

[0094] In this embodiment, two groups of bolt connections and one group of stud connection are included. Two types of bolts, M30 and M42, are selected for simulation calculation.

[0095] Basic parameters of bolts

[0096]

[0097] Figure 2 What is shown is the solid model of the box bolts. This model has no threads. To accurately simulate the thread engagement state, it is necessary to establish the thread detail features and set the thread engagement contact relationship. If a finite element model is established in this way for each bolt, the calculation scale will be huge and difficult to achieve. Figure 3 The bar element model of the box bolt is shown, which simplifies the thread engagement relationship into a rigid coupling, verifying that the Beam188 beam element can simulate the bolt connection; Figure 4 and Figure 5 It is a model of solid bolts and rod unit bolts, in which the screw diameter part is given the screw mean diameter (i.e. d2), and the thread diameter part is calculated according to the stress cross-sectional area of ​​the bolt model. As shown in the table above, the stress cross-sectional area of ​​the M30 bolt is A=561mm2, and the thread diameter is calculated to be 2*(561 / PI)^0.5=26.73mm. Similarly, the calculated equivalent diameter of the M42 bolt is 37.76mm.

[0098] In specific implementation, as a preferred embodiment of the present invention, in step S13, the cross-sectional properties of the Beam unit are set as follows:

[0099] The beam units are all given a circular cross-section, where the diameter of the screw is the bolt mid-diameter, and the diameter at the thread is calculated based on the stress cross-sectional area of ​​the bolt.

[0100] In specific implementation, as a preferred embodiment of the present invention, step S2 specifically includes:

[0101] S21, control the mesh size of the joint surface;

[0102] S22, simultaneously controlling the mesh size of the bolt holes on the nut, the housing and the gear ring;

[0103] S23. Ensure that the rod unit is aligned with the nut and bolt hole nodes so that the threaded rod and bolt hole nodes are completely merged.

[0104] In this embodiment, the node merging model obtained is as follows: Figure 6-7 shown. Figure 6 It is the finite element model of the entire box, all of which use tetrahedral meshes. Figure 7 This is the mesh control requirement at the threaded load parachute. The load parachute node and the bolt hole node need to be completely overlapped and contact settings (Node Merge) must be performed. The mesh settings here must be error-free, otherwise the nodes cannot be merged successfully, affecting the size of the contact surface and, in turn, the calculation results.

[0105] In this embodiment, the thread and the screw hole surface of the box body are bound and contacted through Node Merge, such as Figure 8 The figure shows the node merging of the entire bolt thread and the bolt hole of the box body, so the meshing requirements here are relatively high. The same is true for the screw head. The general contact mode is adopted between the components, and the friction coefficient is 0.15. If required, other friction coefficients can be used.

[0106] In specific implementation, as a preferred embodiment of the present invention, step S3 specifically includes:

[0107] S31. For static strength analysis, a preload is applied to the screw before the working load is applied;

[0108] S32, the working load is applied to the simplified upwind bearing outer ring surface and the downwind bearing inner ring surface, and the working load includes the bearing force (force and moment), the tangential force of the gear ring, the torque and axial force of the middle box;

[0109] S33. Analyze the ultimate strength results. The location with the maximum stress is the location of the maximum damage to the bolt, which is the first thread root unit or adjacent unit where the nut and the bolt are meshed. Check the Mises stress of the first thread meshing unit of different structures and connecting bolts.

[0110] In this embodiment, Fig. 9 and Fig.10 The working load and preload force of the bolts are applied to the box body. The grade of the M30 bolt is 10.9, and the preload force is F =Tightening torque M / diameter D / Friction coefficient f ,Right now F = M / D / f However, the preload applied by the bolt will have different coefficients. This calculation coefficient is 0.9, which is the preload force of the M30 bolt. F =427.543 KN , preload force of M42 bolt F =871.312 KN . Fig.11 is the calculation result of the bolts connecting the front housing and the first gear ring, and the first gear ring and the middle housing, because M y The calculation result of the _min condition is the largest, so this time only the calculation result of this condition is explained. The tensile strength of the 10.9 grade bolt is 1040MPa, of which the stress of non-proportional extension of 0.2% is 940Mpa; the equivalent stress of the front cover and the front box body when the bolt is used is 752.92MPa, which is less than the allowable stress of 940MPa; the equivalent stress of the front box body and the first gear ring is 761.55MPa, which is less than the allowable stress of 940MPa; the equivalent stress of the first gear ring and the middle box body is 776.71MPa, which is less than the allowable stress of 940MPa.

[0111] In specific implementation, as a preferred embodiment of the present invention, step S4 specifically includes:

[0112] S41. Apply preload before bearing the working unit load. The working unit load is 70% (empirical value) of the maximum load amplitude of the hub center extracted for each working condition and applied to the bearing as the unit load. The load for each working condition is divided into several levels.

[0113] In this embodiment, the levels can be 4, 6, 8, 10, etc. This time, it is divided into 4 levels, and 6 working conditions are generated respectively ( M x / M y / M z / F x / F y / F z ),in, M x First negative then positive working condition, M y / M z / F x / F y / F z The working condition is the same. The first step is the preload condition, so the calculation is divided into 49 steps (49=1+12*4). Fig.12 As shown, the load applied to calculate the unit stress of the bolt, such as bending moment M y Working condition, its limit load is M y =-12565.3KNm, select 70% of it, that is M1= M *0.7=-8795.71KNm, approximately equal to M 2=8800KNm (take the absolute value), then M 2 Divide into four equal parts according to the positive and negative directions, namely (-8800, -6600, -4400, -2200, 2200, 4400, 6600, 8800), and the same applies to the other five working conditions ( M x / M z / F x / F y / F z ),like Fig.12 The data on the left is then converted into equivalent bearing loads. The results are as follows Fig.12 Data shown on the right.

[0114] S42. Locate each bolt unit:

[0115] Set the global coordinate system csys,1;

[0116] Define the variable bolt_num= n ;

[0117] Define the distance between the first bolt and the global coordinate system RC_in= r ;

[0118] Define the work plane coordinate system WPCSYS,-1,2: -1 means use the global Z Axis, 2 means use global X Axis, where 2 is the position of the first bolt, and the coordinates of other bolts are defined in sequence;

[0119] Define the bolt_angles.csv file and reference it in the APDL file to determine the position of each bolt;

[0120] S43. Define .dat file:

[0121] Define the array bolt_force. Since it is divided into 4 levels this time, the data will be 10 rows and bolt_num*3+1 columns.

[0122] Define character array load_direction, M x / M y / M z / F x / F y / F z ;

[0123] Define a loop do,j,1,bolt_num,1, select a single element set named element, find the element to extract force and moment;

[0124] Define a table named ssx, extract the data with the highest value and put it in the first column ( F x ); Similarly, define a table named bsy, the first column of data ( M y ), define a table named bsz, the first column of data ( M z );

[0125] definition i Cycle, from 1 to 6, step size is 1, 6 working condition cycles are defined;

[0126] S44. Generate .dat file:

[0127] definition i Loop do,i,2,49,1: from step 2 to step 49, the step length is 1;

[0128] definition j Loop do,j,1,4,1: from step 1 to step 4, the step length is 1;

[0129] Read the unit stress result file and extract F x , M y , M z , and store it in a table.

[0130] In this example, check the location where the maximum principal stress results appear, and extract the axial force and bending moment of the maximum stress unit of each bolt. Use the APDL command to extract forces and moments in the ANSYS Mechanical module. According to the GL gearbox coordinate system standard, extract the axial force F x and bending moment M y , M z , generate 6 working conditions respectively ( M x / M y / M z / F x / F y / F z ) of the loads, forces and moments.dat files.

[0131] In specific implementation, as a preferred embodiment of the present invention, step S5 specifically includes:

[0132] S51, according to the geometric model of the gearbox housing connecting bolts established in step S1, setting the connection mode in the finite element analysis model, including: a friction connection between the front end cover and the front housing, a friction connection between the front housing and the primary gear ring, and a friction connection between the primary gear ring and the middle housing;

[0133] S52, obtaining a load-stress nonlinear relationship curve at the maximum stress position of each bolt;

[0134] S53, Time series load spectrum: If the load time history is used as the load input, the stress time history data is obtained through finite element calculation, and the amount of calculation is extremely large. The fatigue time series load is interpolated in the load-time curve, and the working condition and time distribution are generated into an .inp file. At the same time, the load file is prepared for easy reading by Matlab;

[0135] S54, obtaining a stress-time series curve of the bolt through a load-stress curve relationship and a time series load group;

[0136] S55, bolt calculation uses SN curve, and the stress calculation formula corresponding to the inflection point is as follows:

[0137]

[0138] In the above formula, represents the fatigue limit, represents the stress range, Represents the slope. When the number of cycles corresponding to the inflection point is less than hour, , when the number of cycles corresponding to the inflection point is not less than hour, , represents the safety factor, , Indicates the number of permissible load cycles, represents the number of cycles corresponding to the inflection point, , Indicates impact factor; number of cycles The fatigue strength is ; Indicates the maximum bolt internal force under the ultimate load, It indicates the minimum bolt internal force corresponding to the elastic strain limit of 0.2%. For bolts with a diameter greater than M30, considering the influencing factors affecting the SN curve, the calculation formula is as follows:

[0139]

[0140] In the above formula, Indicates the nominal diameter;

[0141] S56, loading the data obtained from step S52 to step S55 into matlab software, extracting the stress array at the target node of the bolt, and sequentially calculating the distributed stress of each bolt evenly spaced 30° (i.e. extracting a bolt into 12 equal parts, the number of parts has been tested to meet the calculation accuracy while taking into account the calculation efficiency), and then generating the load stress array load_stress (load_stress=6×9×12n, n is the number of bolts) of each bolt under multiple working conditions;

[0142] S57, according to the generated load stress array load_stress, the stress time series array stress_time of each bolt at different angles is obtained by extended interpolation;

[0143] S58, using the three-peak-valley value cycle counting method, filtering and splicing the stress time series array stress_time, eliminating unreasonable data, so that the stress time series array stress_time only contains alternately appearing peaks and troughs;

[0144] S59. Based on the synthetic S / N curve of the bearing material, the rain flow counting method is used to obtain the actual stress amplitude, and then the fatigue damage of each bolt in each group of the box is calculated according to Miner's linear cumulative damage theory.

[0145] In this embodiment, MATLAB software is used to calculate the fatigue damage of the bolt extraction unit. The results are as follows: Fig.13 As shown, the maximum fatigue damage value of the bolt is D =0.2941, which is less than the allowable damage value of 1. Therefore, the structure meets the fatigue life requirements of the material.

[0146] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A gearbox housing connection bolt analysis method based on finite element simulation, characterized in that: include: S1. Establish the geometric model of the gearbox housing connecting bolts; Step S1 specifically includes: S11. Build the overall model of the gearbox housing connecting bolts, including the front end cover, the upwind bearing outer ring, the front housing first-stage gear ring, the middle housing and the downwind bearing inner ring. The housing is made of QT400-18AL material, and the structural parts are all made of structural steel. S12, select the bolts connecting the front cover and the front box, the front box and the first gear ring, and the first gear ring and the middle box for verification, among which the screw, nut and thread are all modeled and simulated by Beam unit; S13, using Beam unit modeling, the thread and screw head are modeled in the form of a load umbrella using multiple Beam units. The entire thread is divided into several equal parts, and each screw hole is divided into several equal parts, and the contact relationship is accurately set; S2, meshing to completely merge the threaded rod and bolt hole nodes; S3, analyze the static strength limit, apply load, and obtain the Mises stress of the unit at the first thread engagement of different structures and connecting bolts; S4, analyze fatigue strength, apply load, calculate unit stress and further extract axial force and bending moment; Step S4 specifically includes: S41. Apply preload before bearing the working unit load. The working unit load is 70% of the maximum load amplitude of the hub center extracted for each working condition and applied to the bearing as the unit load. The load for each working condition is divided into several levels. S42. Locate each bolt unit: Set the global coordinate system csys,1; Define the variable bolt_num= n ; Define the distance between the first bolt and the global coordinate system RC_in= r ; Define the work plane coordinate system WPCSYS,-1,2: -1 means use the global Z Axis, 2 means use global X Axis, where 2 is the position of the first bolt, and the coordinates of other bolts are defined in sequence; Define the bolt_angles.csv file and reference it in the APDL file to determine the position of each bolt; S43. Define .dat file: Define the array bolt_force. Since it is divided into 4 levels this time, the data will be 10 rows and bolt_num*3+1 columns. Define character array load_direction, M x / M y / M z / F x / F y / F z ; Define a loop do,j,1,bolt_num,1, select a single element set named element, find the element to extract forces and moments; Define a table named ssx, extract the data with the highest value and put it in the first column F x ; Similarly, define a table named bsy, the first column of data M y , define a table named bsz, the first column of data M z ; definition i Cycle, from 1 to 6, step size is 1, 6 working condition cycles are defined; S44. Generate .dat file: definition i Loop do,i,2,49,1: from step 2 to step 49, the step length is 1; definition j Loop do,j,1,4,1: from step 1 to step 4, the step length is 1; Read the unit stress result file and extract F x , M y , M z , and store it in a table; S5, performing finite element analysis. During the finite element analysis, according to the geometric model of the gear box housing connecting bolts established in step S1, a connection mode is set in the finite element analysis model; and the stress obtained in step S4 is loaded into the finite element analysis model as a boundary condition to calculate the fatigue damage of the connecting bolts; Step S5 specifically includes: S51, according to the geometric model of the gearbox housing connecting bolts established in step S1, setting the connection mode in the finite element analysis model, including: a friction connection between the front end cover and the front housing, a friction connection between the front housing and the primary gear ring, and a friction connection between the primary gear ring and the middle housing; S52, obtaining a load-stress nonlinear relationship curve at the maximum stress position of each bolt; S53, interpolate the fatigue time series load into the load-time curve, generate the .inp file for the working condition and time distribution, and prepare the load file for easy reading by Matlab; S54, obtaining a stress-time series curve of the bolt through a load-stress curve relationship and a time series load group; S55, bolt calculation uses SN curve, and the stress calculation formula corresponding to the inflection point is as follows: In the above formula, represents the fatigue limit, represents the stress range, Indicates the slope. When the number of cycles corresponding to the inflection point is less than hour, , when the number of cycles corresponding to the inflection point is not less than hour, , represents the safety factor, , Indicates the number of permissible load cycles, represents the number of cycles corresponding to the inflection point, , Indicates impact factor; number of cycles The fatigue strength is ; Indicates the maximum bolt internal force under the ultimate load, It indicates the minimum bolt internal force corresponding to the elastic strain limit of 0.2%. For bolts with a diameter greater than M30, considering the factors affecting the SN curve, the calculation formula is as follows: In the above formula, Indicates the nominal diameter; S56, loading the data obtained from step S52 to step S55 into matlab software, extracting the stress array at the target node of the bolt, sequentially calculating the distributed stress of each bolt evenly spaced 30°, and then generating the load stress array load_stress of each bolt under multiple working conditions; S57, according to the generated load stress array load_stress, the stress time series array stress_time of each bolt at different angles is obtained by extended interpolation; S58, using the three-peak-valley value cycle counting method, filtering and splicing the stress time series array stress_time, eliminating unreasonable data, so that the stress time series array stress_time only contains alternately appearing peaks and troughs; S59. Based on the synthetic S / N curve of the bearing material, the rain flow counting method is used to obtain the actual stress amplitude, and then the fatigue damage of each bolt in each group of the box is calculated according to Miner's linear cumulative damage theory.

2. The gearbox housing connection bolt analysis method based on finite element simulation according to claim 1 is characterized in that: In step S13, the cross-sectional properties of the Beam element are set as follows: The beam units are all given a circular cross-section, where the diameter of the screw is the bolt mid-diameter, and the diameter at the thread is calculated based on the stress cross-sectional area of ​​the bolt.

3. The gearbox housing connection bolt analysis method based on finite element simulation according to claim 1 is characterized in that: Step S2 specifically includes: S21, control the mesh size of the joint surface; S22, simultaneously controlling the mesh size of the bolt holes on the nut, the housing and the gear ring; S23. Ensure that the rod unit is aligned with the nut and bolt hole nodes so that the threaded rod and bolt hole nodes are completely merged.

4. The gearbox housing connection bolt analysis method based on finite element simulation according to claim 1 is characterized in that: Step S3 specifically includes: S31. For static strength analysis, a preload is applied to the screw before the working load is applied; S32, the working load is applied to the simplified upwind bearing outer ring surface and the downwind bearing inner ring surface, and the working load includes the bearing force, the tangential force of the gear ring, the torque of the middle box and the axial force; S33. Analyze the ultimate strength results. The location with the maximum stress is the location of the maximum damage to the bolt, which is the first thread root unit or adjacent unit where the nut and the bolt are meshed. Check the Mises stress of the first thread meshing unit of different structures and connecting bolts.

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