CN113361183A - Method for forecasting ultimate bearing capacity of automobile half shaft - Google Patents

Method for forecasting ultimate bearing capacity of automobile half shaft Download PDF

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CN113361183A
CN113361183A CN202110799058.7A CN202110799058A CN113361183A CN 113361183 A CN113361183 A CN 113361183A CN 202110799058 A CN202110799058 A CN 202110799058A CN 113361183 A CN113361183 A CN 113361183A
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half shaft
shaft
forecasting
torque load
torque
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CN113361183B (en
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李俊楼
康一坡
朱学武
刘艳玲
张尤龙
闫博
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FAW Group Corp
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    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/20—Design optimisation, verification or simulation
    • G06F30/23—Design optimisation, verification or simulation using finite element methods [FEM] or finite difference methods [FDM]
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F30/00—Computer-aided design [CAD]
    • G06F30/10—Geometric CAD
    • G06F30/15—Vehicle, aircraft or watercraft design
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06F—ELECTRIC DIGITAL DATA PROCESSING
    • G06F2119/00—Details relating to the type or aim of the analysis or the optimisation
    • G06F2119/14—Force analysis or force optimisation, e.g. static or dynamic forces
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    • Y02T90/00—Enabling technologies or technologies with a potential or indirect contribution to GHG emissions mitigation

Abstract

The invention relates to the technical field of automobile research and development and manufacturing, and particularly discloses a method for forecasting the ultimate bearing capacity of an automobile half shaft. The method for forecasting the ultimate bearing capacity of the automobile half shaft is based on the real heat treatment state of the automobile half shaft, truly reproduces the static torsion test state of an automobile half shaft sample by building a material nonlinear and contact nonlinear CAE simulation model with a full-size structure, and forecasts the ultimate bearing torque of the half shaft by obtaining a high-precision relation curve of a half shaft corner and a torque load, so that the method for forecasting the ultimate bearing torque of the automobile half shaft with high speed and high precision is provided, the static torsion test of the automobile half shaft is replaced, and the product development cost is reduced; the method has the advantages of strong adaptability and wide application range, and the simulation efficiency is improved.

Description

Method for forecasting ultimate bearing capacity of automobile half shaft
Technical Field
The invention relates to the technical field of automobile research and development and manufacturing, in particular to a method for forecasting the ultimate bearing capacity of an automobile half shaft.
Background
Automobile half shafts are key parts for transmitting power from a differential side gear to a driving wheel, and the breakage and failure of the half shafts often cause serious injury. The ultimate bearing capacity of the automobile half shaft is the capacity of bearing the maximum load when the half shaft breaks and fails. The automobile half shaft is used as an important basic component and a force transmission component of a transmission system, the half shaft plays a role in limiting excessive loads which are not normally used except for transmitting normal use torque, if the transmission system encounters excessive impact loads, a part which is damaged firstly is the half shaft instead of other transmission system parts, so that the transmission system is protected from overload, and therefore the half shaft has proper limit bearing capacity and meets various requirements of the whole automobile through a refined structural design.
At present, in the design of the mechanical property of half-axle products, two technical means are generally adopted to obtain the ultimate bearing capacity of the half-axle products. Firstly, quiet torsional strength is experimental, fixes the semi-axis ring flange on the test bench, and the slow loading torque of department to the semi-axis fracture inefficacy in the spline department, the moment of torsion that corresponds is the limit and bears the moment of torsion promptly this moment, when the limit bears the moment of torsion and the ratio of the maximum rated torque of semi-axis is greater than given factor of safety, then deems the semi-axis and quiet torsional strength and satisfies the requirement. The half shaft limit bearing torque obtained by applying the test technical means is visual and real, but a physical prototype is required, the test period is long, and the half shaft limit bearing torque is relatively lagged compared with the product development, so that the product development requirement cannot be completely met. The ultimate bearing capacity test belongs to a destructive test, and a sample piece is scrapped after the test is finished, so that the test cost is high. And secondly, a CAE simulation technical means is adopted, a half shaft assembly finite element model is built, the required torque is loaded for simulation calculation, structural stress distribution is obtained, and when the stress value is lower than the required threshold value, the structural bearing capacity is judged to meet the requirement. Or further converting the stress evaluation into safety factor evaluation, and judging that the bearing capacity of the structure meets the requirement when the safety factor is higher than a required threshold value. On the basis, assuming that the stress or the static safety coefficient and the applied load are in a linear relation, and according to the threshold value requirement, the ultimate bearing load when the structure is broken is approximately calculated, and the following problems exist; stress has various forms, such as Mises stress, maximum main stress and the like, and also has various states of tension, bending and torsion and the like; the material strength is also of various types, such as tensile strength, compressive strength, bending strength and the like, and particularly, the ultimate bearing torque is calculated by adopting which stress and which material strength, so that the calculation of the ultimate bearing load is different, the precision is low, and the product development requirement cannot be met. Secondly, the influence of structural stress types, stress states and material strengths corresponding to different stress states and the like are comprehensively considered for evaluating the static safety coefficient, so that the subjectivity of people is avoided to a certain extent, but practice shows that the calculated ultimate bearing torque is far lower than a test value and is conservative, so that the half-axle strength backup coefficient is too large, the weight is heavy, the cost is high, and the product competitiveness is seriously influenced.
Disclosure of Invention
The invention aims to provide a forecasting method for the ultimate bearing capacity of an automobile half shaft, which can be used for quickly and accurately forecasting the ultimate bearing capacity of the automobile half shaft so as to realize the fine design and the light weight design of the automobile half shaft.
In order to achieve the purpose, the invention adopts the following technical scheme:
a forecasting method for the limit bearing capacity of an automobile half shaft comprises the following steps:
obtaining the size and hardness of each heat treatment affected area of the half shaft;
establishing a finite element model for half shaft assembly, and meshing the half shafts according to the size of each heat treatment affected area of the half shafts;
obtaining the material strength limit sigma of each heat treatment affected zone of the half shaft according to the hardness of each heat treatment affected zone of the half shaftb；
According to material strength limit σbObtaining stress-plastic strain (sigma-epsilon)p) Data defining material properties of the finite element model;
applying a torque load M and boundary conditions of the finite element model;
carrying out torsional elastoplasticity finite element analysis on the semi-axis finite element model, controlling time increment, applying the torque load M step by step, obtaining output displacement and plastic strain data by adopting a Newton-Lapton method, and obtaining a relation curve between the semi-axis corner alpha and the torque load M;
according to formula Ki＝(Mi+1-Mi)/(αi+1-αi) Calculating the slope K corresponding to the first point in the relation curve of the half-shaft rotation angle alpha and the torque load M1And slope K corresponding to other ith pointsiIf K isi/K1Greater than 5%, the torque load M of the half-shaft is multiplied by a factor x greater than 1 until Ki/K1Stopping when the concentration is less than or equal to 5%, wherein Mi、αiRespectively representing the torque load and the half shaft rotation angle corresponding to the ith point, wherein x is more than or equal to 3;
calculating the average slope of the initial linear stage of the relation curve of the half shaft rotation angle alpha and the torque load M
Figure BDA0003163930790000031
Get Ki/K1And performing polynomial fitting on data points between 5% and 25% to obtain a function M ═ f (alpha), and constructing a solving equation system of the limit bearing torque of the automobile half shaft:
Figure BDA0003163930790000032
wherein f' (α) is a derivative function of a fitting polynomial function;
and solving an equation set according to the automobile half-shaft limit bearing torque to obtain the limit bearing torque M of the half shaft.
As a preferable technical scheme of the forecasting method for the ultimate bearing capacity of the automobile half shaft, the forecasting method is based on the material strength limit sigmabObtaining stress-plastic strain (sigma-epsilon)p) The data specifically includes:
according to material strength limit σbDetermining the value range of the real stress sigma as (0-lambda multiplied by sigma)b) And uniformly taking N real stress sigma data sampling points in the range, and adopting a formula epsilonp＝(σ/k)1/nCalculation of the plastic Strain εpObtaining stress-plastic strain (sigma-epsilon)p) And in the formula, k is a material hardening coefficient, and n is a hardening index.
As a preferred technical solution of the method for forecasting the ultimate bearing capacity of the automotive half shaft, the defining of the material properties of the finite element model specifically includes:
defining the elastic modulus and Poisson's ratio of the finite element model;
and defining material properties according to each heat treatment influence area of the half shaft.
As a preferable technical solution of the method for forecasting the ultimate bearing capacity of the automotive axle shaft, the material property of the axle shaft is defined as a plastic property, and the material property of the side gear is defined as an elastic property.
As a preferred technical solution of the method for forecasting the ultimate bearing capacity of the half axle of the automobile,
at plastic strain εpLess than 1 x 10-4When is equal topAnd taking the value as 0, and taking the set of stress-plastic strain data as the initial value of the plastic property of the half-axle material.
As a preferred technical solution of the method for forecasting the ultimate bearing capacity of the half axle of the automobile, the applying the torque load M of the finite element model and the boundary conditions specifically include:
applying a torque load M to the side gear;
and applying boundary conditions to the half-shaft flange to fix the half-shaft flange.
As a preferable technical scheme of the forecasting method for the limit bearing capacity of the automobile half shaft, an RBE3 unit is established on the side gear, a slave point of the RBE3 unit is arranged at the central point of a spline of the side gear, and a master point of the RBE3 unit is a tooth surface unit node on the side gear.
As a preferable technical scheme of the forecasting method for the limit bearing capacity of the automobile half shaft, an RBE3 unit is established on the half shaft flange, a slave point of the RBE3 unit is arranged at the central point of the half shaft flange, and a master point of the RBE3 unit is a node of the inner surface of a bolt hole on the half shaft flange.
As a preferred technical solution of the method for predicting the ultimate bearing capacity of the automotive half shaft, performing torsional elastoplastic finite element analysis on a half shaft finite element model, controlling time increment, applying the torque load M step by step, acquiring output displacement and plastic strain data by a newton-raphson method, and acquiring a relationship curve between a half shaft corner α and the torque load M specifically includes:
setting a finite element simulation time period as 1, controlling time increment to be less than or equal to 0.02, outputting displacement and plastic strain data after each time increment is calculated, and acquiring data corresponding to the half shaft rotation angle alpha and time t, wherein the output frequency is greater than or equal to 50;
and multiplying the time t by the torque load M to obtain the torque corresponding to each time point, and acquiring a relation curve of the half-axle rotation angle alpha and the torque load M.
As an optimal technical scheme of the forecasting method for the ultimate bearing capacity of the automobile half shaft, K corresponding to the initial linear stage of the relation curve of the half shaft rotation angle alpha and the torque load MiIs Ki/K1Greater than 99% of the data.
The invention has the beneficial effects that:
the method for forecasting the ultimate bearing capacity of the automobile half shaft is based on the real heat treatment state of the automobile half shaft, truly reproduces the static torsion test state of an automobile half shaft sample by building a material nonlinear and contact nonlinear CAE simulation model with a full-size structure, and forecasts the ultimate bearing torque of the half shaft by obtaining a high-precision relation curve of a half shaft corner and a torque load, so that the method for forecasting the ultimate bearing torque of the automobile half shaft with high speed and high precision is provided, the static torsion test of the automobile half shaft is replaced, and the product development cost is reduced;
the forecasting method of the ultimate bearing capacity of the automobile half shaft can be applied to structural forms such as a full-floating half shaft, a semi-floating half shaft and the like, and has strong adaptability and wide application range; the standardized and streamlined forecasting method for the ultimate bearing capacity of the automobile half shaft greatly reduces the problem of large deviation of a calculation result caused by subjective judgment, reduces the time of artificial judgment and improves the simulation efficiency; in addition, the method for forecasting the ultimate bearing capacity of the automobile half shaft is in the early stage of product development, can realize a multi-wheel suboptimal structure, realizes a fine design and a lightweight design, effectively ensures that a product passes test examination once, shortens the product development period, and reduces the product development cost.
Drawings
FIG. 1 is a schematic view of a mounting structure of an automotive axle shaft provided by an embodiment of the invention;
FIG. 2 is a flow chart illustrating steps of a method for forecasting the ultimate bearing capacity of an automotive axle shaft according to an embodiment of the present invention;
FIG. 3 is a schematic structural view of the axle shaft of FIG. 1;
FIG. 4 is an enlarged view of the area A of the axle shaft spline of FIG. 3;
FIG. 5 is a schematic view of the grouping and meshing of the half-shaft splines at section E-E of FIG. 4 according to the size of the heat-treatment affected zone;
FIG. 6 is a schematic view of grouping and meshing the half-shaft rod portion B in the cross section of FIG. 3 according to the size of the heat treatment affected zone;
FIG. 7 is a schematic diagram of meshing at the axle diameter transition region C of the axle shaft of FIG. 3;
FIG. 8 is a schematic diagram of meshing at the half-axis fillet area D in FIG. 3;
FIG. 9 is a schematic illustration of an embodiment of the present invention establishing an RBE3 cell at the side gear;
FIG. 10 is a schematic illustration of an embodiment of the present invention establishing RBE3 cells at the half-shaft flanges;
FIG. 11 is a graph of half-axis rotation angle α versus torque load M provided by an embodiment of the present invention;
fig. 12 is a polynomial function expression and a curve fitted to the half-axis rotation angle α and the torque load M according to the embodiment of the present invention.
In the figure:
1-a half shaft gear; 2-half shaft; 3-half shaft flange;
11. 31-the slave point; 12. 32-principal point; 13. 33-RBE3 cell.
Detailed Description
In order to make the technical problems solved, technical solutions adopted and technical effects achieved by the present invention clearer, the technical solutions of the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
In the description of the present invention, unless expressly stated or limited otherwise, the terms "connected," "connected," and "fixed" are to be construed broadly, e.g., as meaning permanently connected, removably connected, or integral to one another; can be mechanically or electrically connected; either directly or indirectly through intervening media, either internally or in any other relationship. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
In the present invention, unless otherwise expressly stated or limited, "above" or "below" a first feature means that the first and second features are in direct contact, or that the first and second features are not in direct contact but are in contact with each other via another feature therebetween. Also, the first feature being "on," "above" and "over" the second feature includes the first feature being directly on and obliquely above the second feature, or merely indicating that the first feature is at a higher level than the second feature. A first feature being "under," "below," and "beneath" a second feature includes the first feature being directly under and obliquely below the second feature, or simply meaning that the first feature is at a lesser elevation than the second feature.
As shown in fig. 1, the mounting structure of the automobile half shaft includes a half shaft 3, one end of the half shaft 3 is mounted with a half gear 1, and the other end is a half shaft flange 3.
As shown in fig. 2, the present embodiment provides a method for forecasting the ultimate bearing capacity of an automotive axle shaft, where the method includes:
step one, obtaining the size and hardness of each heat treatment affected area of the half shaft 2.
Specifically, in the present embodiment, before obtaining each heat treatment influence size and hardness of the axle shaft 2, it is necessary to obtain a three-dimensional geometric model of the axle shaft 2, the side gear 1, and other relevant parts and the technical requirements of the heat treatment of the axle shaft 2. According to the technical requirements of heat treatment of the half shaft 2, the heat treatment influence size and hardness of the half shaft 2, the half gear 1 and other parts are obtained.
And step two, establishing a finite element model for assembling the half shaft 2, and meshing the half shaft 2 according to the size of each heat treatment affected area of the half shaft 2.
Specifically, as shown in fig. 3 to 8, in the present embodiment, the half shaft 2 is gridded in accordance with the size of each heat treatment affected zone of the half shaft 2, and the positional relationship of the parts such as the half shaft 2, the side gear 1, and the like defines the contact relationship, whereby the parts are assembled together.
When the half shaft 2, the half shaft gear 1 and other parts are subjected to grid division, grids need to be divided into regions according to the size of each heat treatment affected region of the half shaft 2, and the grids are classified into different finite element assemblies.
Thirdly, obtaining the material strength limit sigma of each heat treatment affected zone of the half shaft 2 according to the hardness of each heat treatment affected zone of the half shaft 2b。
Specifically, after the hardness of the material in each heat treatment affected zone of the half shaft 2 is obtained, the material strength limit sigma of each heat treatment affected zone of the half shaft 2 is obtained according to GB/T1172-1999 ferrous metal hardness and strength conversion valueb。
Step four, according to the material strength limit sigmabObtaining stress-plastic strain (sigma-epsilon)p) Data defining material properties of the finite element model.
In the present embodiment, the limit σ is determined according to the material strengthbDetermining the value range of the real stress sigma as (0-lambda multiplied by sigma)b) And uniformly taking N real stress sigma data sampling points in the range, and adopting a formula epsilonp＝(σ/k)1/nCalculation of the plastic Strain εpObtaining stress-plastic strain (sigma-epsilon)p) And in the formula, k is a material hardening coefficient, and n is a hardening index.
Further, λ is a material strength limit σbN is the number of data sampling points; the material hardening coefficient k and the hardening index n are empirical values.
In the present embodiment, the elastic modulus and poisson's ratio of the finite element model are defined, and the respective heat treatment influence regions are determined according to the half-axis 2, based on the material properties.
Further, the material property of the axle shaft 2 is defined as a plastic property, and the material property of the side gear 1 is defined as an elastic property. In the embodiment, the half shaft 2, the half shaft gear 1 and other parts are made of actual elastoplasticity, and the simulation precision is improved in a mode different from the mode that the constitutive relation of the materials is defined as sectional elastoplasticity in the prior art.
Further, at plastic strain εpLess than 1 x 10-4When is equal topThe value is 0, and the set of stress-plastic strain data is used as the initial value of the plastic property of the material of the half shaft 2.
And step five, applying the torque load M and the boundary conditions of the finite element model.
In the present embodiment, a torque load M is applied to the side gear 1. Specifically, as shown in fig. 9, RBE3 unit 13 is established on side gear 1, slave point 11 of RBE3 unit 13 is set at the center point of the splines of side gear 1, and master point 12 of RBE3 unit 13 is the tooth surface unit node on side gear 1.
A boundary condition is applied to the half-shaft flange 3 to fix the half-shaft flange 3. Specifically, as shown in fig. 10, RBE3 unit 33 is established on the half-shaft flange 3, the slave point 31 of RBE3 unit 33 is set at the center point of the half-shaft flange 3, the master point 32 of RBE3 unit 33 is the node of the inner surface of the bolt hole on the half-shaft flange 3, and the degree of freedom of the RBE3 unit 33 from the point 31 is restricted.
And sixthly, carrying out torsional elastoplastic finite element analysis on the half-axle finite element model, controlling time increment, applying the torque load M step by step, acquiring output displacement and plastic strain data by adopting a Newton-Lapton method, and acquiring a relation curve between the turning angle alpha of the half-axle 2 and the torque load M.
Specifically, as shown in fig. 11, in the present embodiment, the finite element simulation time period is set to 1, the control time increment is equal to or less than 0.02, displacement and plastic strain data are output after the calculation of each time increment is completed, the output frequency is equal to or greater than 50, and data corresponding to the half-axle rotation angle α and the time t are acquired.
And multiplying the time t by the torque load M to obtain the torque corresponding to each time point, and acquiring a relation curve of the half-axle rotation angle alpha and the torque load M.
Step seven, according to a formula Ki＝(Mi+1-Mi)/(αi+1-αi) Calculating the slope K corresponding to the first point in the relation curve of the half-shaft rotation angle alpha and the torque load M1And slope K corresponding to other ith pointsiIf K isi/K1Greater than 5%, the torque load M of the half-shaft is multiplied by a factor x greater than 1 until Ki/K1Stopping when the concentration is less than or equal to 5%, wherein Mi、αiRespectively representing the torque load and the half-shaft rotation angle corresponding to the ith point, wherein x is more than or equal to 3.
Step eight, calculating the average slope of the initial linear stage of the relation curve of the half-shaft rotation angle alpha and the torque load M
Figure BDA0003163930790000091
In the embodiment, the relationship curve of the half-axle rotation angle alpha and the torque load M corresponds to K in the initial linear stageiIs Ki/K1Greater than 99% of the data.
Step nine, as shown in FIG. 12, take Ki/K1And performing polynomial fitting on data points between 5% and 25% to obtain a function M ═ f (alpha), and constructing a solving equation system of the limit bearing torque of the automobile half shaft:
Figure BDA0003163930790000101
wherein f' (α) is a derivative function of a fitting polynomial function;
step ten, solving an equation set according to the automobile half-shaft limit bearing torque to obtain the limit bearing torque M of the half shaft 2.
Specifically, when the obtained limit bearing torque M of the half shaft 2 is larger than the target limit bearing torque, it indicates that the limit bearing capacity of the half shaft 2 satisfies the requirement. When the ultimate bearing torque M of the half shaft 2 is less than or equal to the target ultimate bearing torque, the ultimate bearing capacity of the half shaft 2 does not meet the requirement, and structural improvement is required.
The method for forecasting the ultimate bearing capacity of the automobile half shaft provided by the embodiment is based on the real heat treatment state of the automobile half shaft 2, the static torsion test state of the sample of the automobile half shaft 2 is truly reproduced by building a material nonlinear and contact nonlinear CAE simulation model of a full-size structure, the ultimate bearing torque of the half shaft is forecasted by obtaining a high-precision relation curve of a half shaft corner and a torque load, the method for forecasting the ultimate bearing torque of the automobile half shaft with high speed and high precision is provided, the static torsion test of the automobile half shaft is replaced, and the product development cost is reduced.
The forecasting method for the ultimate bearing capacity of the automobile half shaft can be applied to structural forms such as a full-floating half shaft and a semi-floating half shaft, and has strong adaptability and wide application range; the standardized and streamlined forecasting method for the ultimate bearing capacity of the automobile half shaft greatly reduces the problem of large deviation of a calculation result caused by subjective judgment, reduces the time of artificial judgment and improves the simulation efficiency; in addition, the method for forecasting the ultimate bearing capacity of the automobile half shaft is in the early stage of product development, can realize a multi-wheel suboptimal structure, realizes a fine design and a lightweight design, effectively ensures that a product passes test examination once, shortens the product development period, and reduces the product development cost.
For the convenience of understanding, the present invention will be described in further detail with reference to the following embodiments, but the present invention is not limited to the values shown in the following description in practical use.
Step one, obtaining the size and hardness of each heat treatment affected area of the half shaft 2.
Specifically, in the present embodiment, before obtaining each heat treatment influence size and hardness of the axle shaft 2, it is necessary to obtain a three-dimensional geometric model of the axle shaft 2, the side gear 1, and other relevant parts and the technical requirements of the heat treatment of the axle shaft 2. According to the technical requirements of heat treatment of the half shaft 2, the heat treatment influence size and hardness of the half shaft 2, the half gear 1 and other parts are obtained.
In the embodiment, the half shaft 2 adopts a surface induction quenching heat treatment process after pre-quenching and tempering, the hardness of a surface quenching layer is (52-58) HRC, the hardness of a core part is (25-32) HRC, and the depth of an effective hardening layer is (4.0-6.0) mm.
As shown in FIG. 3, the hardness of the surface quenching layer of the half-shaft spline A, the rod part B, the shaft diameter transition region C and the fillet region D is lower limit value 52HRC, the median value of the core hardness is 28.5HRC, and the median value of the effective hardening layer depth is 5 mm.
And step two, establishing a finite element model for assembling the half shaft 2, and meshing the half shaft 2 according to the size of each heat treatment affected area of the half shaft 2.
Specifically, as shown in fig. 3 to 8, in the present embodiment, the half shaft 2 is gridded in accordance with the size of each heat treatment affected zone of the half shaft 2, and the positional relationship of the parts such as the half shaft 2, the side gear 1, and the like defines the contact relationship, whereby the parts are assembled together.
Further, when meshing is performed on parts such as the half shaft 2 and the side gear 1, the side gear 1 is meshed by using a second-order tetrahedral unit, and the half shaft 2 is meshed by using a first-order hexahedral unit. The meshes need to be divided into regions according to the size of each heat treatment affected area of the half shaft 2, and the meshes are classified into different finite element assemblies. Exemplarily, as shown in fig. 4 and 5, the surface quenching layer Z01 and the core Z02 of the half-shaft spline a are meshed, and the meshes are respectively classified into a Z01 assembly and a Z02 assembly; as shown in fig. 6, the surface quenching layer Z03 and the core Z04 of the half-shaft rod part B are gridded, and the grids are classified into Z03 pieces and Z04 pieces, respectively. The radial grid distribution of the half-shaft spline A surface quenching layer Z01 and the half-shaft rod part B surface quenching layer Z03 is not less than 4 layers; the half-shaft spline A core part Z02 and the half-shaft rod part B core part Z04 outer grid are in one-to-one correspondence with the surface quenching layer inner grid nodes. As shown in FIGS. 7 and 8, the mesh distribution of the axle diameter transition region C and the fillet region D of the half axle 2 is not less than 3 rows.
Further, the contact relation is defined according to the position relation of the parts, all the parts are assembled together, and a finite element model is established, wherein the assembly relation of the parts is shown in table 1.
TABLE 1 Assemble relationship between parts
Figure BDA0003163930790000121
Thirdly, obtaining the material strength limit sigma of each heat treatment affected zone of the half shaft 2 according to the hardness of each heat treatment affected zone of the half shaft 2b。
Specifically, after the hardness of the material in each heat treatment affected zone of the half shaft 2 is obtained, the material strength limit sigma of each heat treatment affected zone of the half shaft 2 is obtained according to GB/T1172-1999 ferrous metal hardness and strength conversion valueb. Wherein the strength limit of the surface quenching layer Z01 and Z03 is 1825MPa, and the strength limit of the core Z02 and Z04 is 880 MPa.
Step four, according to the material strength limit sigmabObtaining stress-plastic strain (sigma-epsilon)p) Data defining material properties of the finite element model.
In the present embodiment, the limit σ is determined according to the material strengthbDetermining the value range of the real stress sigma as (0-lambda multiplied by sigma)b) And uniformly taking N real stress sigma data sampling points in the range, and adopting a formula epsilonp＝(σ/k)1/nCalculation of the plastic Strain εpObtaining stress-plastic strain (sigma-epsilon)p) And in the formula, k is a material hardening coefficient, and n is a hardening index.
Further, λ is a material strength limit σbThe amplification factor of (2) is 1.2, so the real stress value ranges of the surface quenching layers Z01 and Z03 are (0-2190 MPa), and the real stress value ranges of the core parts Z02 and Z04 are (0-1056 MPa).
Uniformly taking N real stress sigma data sampling points in a real stress sigma value range, wherein in the embodiment, for the materials of the surface quenching layers Z01 and Z03, the real stress sampling step length is 30MPa, and the number of the data sampling points N is 74; for the material of the core Z02, Z04, the true stress sampling step size is 20MPa, and the number of data sampling points N is 54.
Substituting the true stress sigma values into the equation epsilonp＝(σ/k)1/nMiddle calculation of plastic strain epsilonpAnd the true stress sigma and the plastic strain epsilonpThe data of (2) are recorded in data table 2, and are prepared for the plasticity data of the materials required by the finite element model. In the formula, the hardening coefficient k of the surface quenching layer material is 2938.25MPa, the hardening coefficient k of the core material is 1416.8MPa, and the hardening indexes n are both 0.11.
TABLE 2 data of plastic properties of materials
Figure BDA0003163930790000131
Figure BDA0003163930790000141
In the present embodiment, the elastic modulus and poisson's ratio of the finite element model are defined, and the material properties are defined according to the respective heat treatment affected zones of the axle shaft 2.
Exemplarily, the modulus of elasticity E of the side gear 1 is 210000MPa, and the poisson ratio μ is 0.3; each heat treatment affected zone (Z01, Z02, Z03, Z04) of the half shaft 2 is set to plastic properties, with an elastic modulus E of 212000MPa and a poisson ratio μ of 0.28. The stress-plastic strain data is shown in Table 2 and corresponds to the material value when the plastic strain epsilon of the material ispLess than 1 x 10-4When is equal topDirectly taking 0 and taking the set of stress-plastic strain data as the initial value of the plastic property of the material. The material properties of the half-shaft flange 3 are the same as the core material properties.
And finally, giving the material properties of each part or area to the corresponding component to complete the material property setting in the finite element model.
And step five, applying the torque load M and the boundary conditions of the finite element model.
In the present embodiment, a torque load M is applied to the side gear, for example, 15000 Nm. Specifically, as shown in fig. 9, RBE3 units 13 are established on the side gear 1, the slave point 11 of the RBE3 unit 13 is set at the center point of the splines of the side gear 1, the master point 12 of the RBE3 unit 13 is the tooth surface unit node on the side gear 1, and the torque load M is applied to the slave point 11 of the RBE3 unit 13.
A boundary condition is applied to the half-shaft flange 3 to fix the half-shaft flange 3. Specifically, as shown in fig. 10, RBE3 unit 33 is established on the half-shaft flange 3, the slave point 31 of RBE3 unit 33 is set at the center point of the half-shaft flange 3, the master point 32 of RBE3 unit 33 is the node of the inner surface of the bolt hole on the half-shaft flange 3, and the degree of freedom of the RBE3 unit 33 from the point 31 is restricted.
And sixthly, carrying out torsional elastoplastic finite element analysis on the half-axle finite element model, controlling time increment, applying the torque load M step by step, acquiring output displacement and plastic strain data by adopting a Newton-Lapson method, and acquiring a relation curve between the half-axle corner alpha and the torque load M.
In the present embodiment, the finite element simulation time period is set to 1, the control time increment is equal to or less than 0.02, displacement and plastic strain data are output after calculation of each time increment, the output frequency is equal to or greater than 50, displacement and plastic strain data are output after calculation of each time increment, the RBE3 unit 13 is output from the point 11 in the direction around the axis of the side gear 1 to obtain an accurate change history of the half shaft angle α with the time t, and the time t is multiplied by the torque load M to calculate the torque corresponding to each time point, so as to obtain the relationship curve between the half shaft angle α and the torque load M as shown in fig. 11.
Step seven, according to a formula Ki＝(Mi+1-Mi)/(αi+1-αi) Calculating the slope K corresponding to the first point in the relation curve of the half-shaft rotation angle alpha and the torque load M1And slope K corresponding to other ith pointsiIf K isi/K1Greater than 5%, the torque load M of the half-shaft is multiplied by a factor x greater than 1 until Ki/K1Stopping when the concentration is less than or equal to 5%, wherein Mi、αiRespectively representing the torque load and the half-shaft rotation angle corresponding to the ith point, wherein x is more than or equal to 3.
Specifically, the slope K of the half-shaft rotation angle alpha corresponding to the first point in the relation curve of the torque load M is calculated1And slope K corresponding to other ith pointsiAnd recorded in Table 3, starting with number 44, K in Table 3i/K1Less than or equal to 5%, so that the applied half-shaft torque load M value 15000Nm meets the requirement, and the ultimate bearing capacity of the half-shaft 2 can be continuously forecasted.
TABLE 3 torsion angle, Torque, Curve slope data for automotive axle shaft
Figure BDA0003163930790000161
Figure BDA0003163930790000171
Step eight, calculating the average slope of the initial linear stage of the relation curve of the half-shaft rotation angle alpha and the torque load M
Figure BDA0003163930790000176
In the embodiment, the relationship curve of the half-axle rotation angle alpha and the torque load M corresponds to K in the initial linear stageiIs Ki/K1Greater than 99% of the data. As can be seen from Table 3, the data points corresponding to the initial linear phase are numbered 1-25, thus
Figure BDA0003163930790000172
Step nine, as shown in FIG. 12, take Ki/K1And performing polynomial fitting on data points between 5% and 25% to obtain a function M ═ f (alpha), and constructing a solving equation system of the limit bearing torque of the automobile half shaft:
Figure BDA0003163930790000173
wherein f' (α) is a derivative function of a fitting polynomial function;
in particular, according to Table 3, Ki/K1Data points between 5% and 25% are numbered 31-44. Polynomial fitting is performed on 14 groups of data of half-shaft rotation angle alpha and torque M with serial numbers of 31-44, and R is performed during polynomial fitting of 2 th order as shown in FIG. 122The value is 0.9937, and good fitting results can be obtained. The polynomial function M is defined as f (α), the derivative function f' (α) of the polynomial function, and the average slope
Figure BDA0003163930790000174
Into the following system of equations
Figure BDA0003163930790000175
The following equation set for solving the limit bearing torque of the automobile half shaft can be obtained
Figure BDA0003163930790000181
Step ten, solving an equation set according to the automobile half-shaft limit bearing torque to obtain the limit bearing torque M of the half shaft 2.
Specifically, the half-shaft limit bearing torque M is 11756Nm obtained by solving the equation system, and the torque is higher than the automobile half-shaft target limit bearing torque 9200Nm, so that the automobile half-shaft limit bearing capacity is judged to meet the requirement.
It should be understood that the above-described embodiments of the present invention are merely examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Other variations and modifications will be apparent to persons skilled in the art in light of the above description. And are neither required nor exhaustive of all embodiments. Any modification, equivalent replacement, and improvement made within the spirit and principle of the present invention should be included in the protection scope of the claims of the present invention.

Claims (10)

1. A forecasting method for the limit bearing capacity of an automobile half shaft is characterized by comprising the following steps:
obtaining the size and hardness of each heat treatment affected area of the half shaft (2);
establishing a finite element model for assembling the half shaft (2), and meshing the half shaft (2) according to the size of each heat treatment affected area of the half shaft (2);
obtaining the material strength limit sigma of each heat treatment affected zone of the half shaft (2) according to the hardness of each heat treatment affected zone of the half shaft (2)b；
According to material strength limit σbObtaining stress-plastic strain (sigma-epsilon)p) Data defining material properties of the finite element model;
applying a torque load M and boundary conditions of the finite element model;
carrying out torsional elastoplasticity finite element analysis on the semi-axis finite element model, controlling time increment, applying the torque load M step by step, obtaining output displacement and plastic strain data by adopting a Newton-Lapton method, and obtaining a relation curve between the semi-axis corner alpha and the torque load M;
according to formula Ki＝(Mi+1-Mi)/(αi+1-αi) Calculating the slope K corresponding to the first point in the relation curve of the half-shaft rotation angle alpha and the torque load M1And slope K corresponding to other ith pointsiIf K isi/K1Greater than 5%, the torque load M of the half-shaft (2) is multiplied by a factor x greater than 1 until Ki/K1Stopping when the concentration is less than or equal to 5%, wherein Mi、αiRespectively representing the torque load and the half shaft rotation angle corresponding to the ith point, wherein x is more than or equal to 3;
calculating the average slope of the initial linear stage of the relation curve of the half shaft rotation angle alpha and the torque load M
Figure FDA0003163930780000011
Get Ki/K1And performing polynomial fitting on data points between 5% and 25% to obtain a function M ═ f (alpha), and constructing a solving equation system of the limit bearing torque of the automobile half shaft:
Figure FDA0003163930780000012
wherein f' (α) is a derivative function of a fitting polynomial function;
and solving an equation set according to the automobile half shaft limit bearing torque to obtain the limit bearing torque M of the half shaft (2).
2. A method for forecasting the ultimate bearing capacity of half-shafts of automobiles according to claim 1, characterized in that, the method is based on the material strength limit σbObtaining stress-plastic strain (sigma-epsilon)p) The data specifically includes:
according to material strength limit σbDetermining the value range of the real stress sigma as (0-lambda multiplied by sigma)b) And uniformly taking N real stress sigma data sampling points in the range, and adopting a formula epsilonp＝(σ/k)1/nCalculation of the plastic Strain εpObtaining stress-plastic strain (sigma-epsilon)p) And in the formula, k is a material hardening coefficient, and n is a hardening index.
3. A method as claimed in claim 1, wherein defining material properties of the finite element model specifically comprises:
defining the elastic modulus and Poisson's ratio of the finite element model;
the material properties are defined in terms of the heat treatment affected zones of the half-shaft (2).
4. A method for forecasting the ultimate load-bearing capacity of automotive axle half shafts as claimed in claim 3, characterized in that the material properties of the axle half shaft (2) are defined as plastic properties and the material properties of the side gear (1) are defined as elastic properties.
5. A method for forecasting the ultimate bearing capacity of axle shafts of automobiles as claimed in claim 4,
at plastic strain εpLess than 1×10-4When is equal topTaking the value as 0, and taking the set of stress-plastic strain data as the initial value of the plastic property of the material of the half shaft (2).
6. A method for forecasting the ultimate bearing capacity of automotive axle shafts as claimed in claim 1, wherein the applying the torque load M of the finite element model and the boundary conditions specifically include:
applying a torque load M to the side gear (1);
applying boundary conditions to the half-shaft flange (3) to fix the half-shaft flange (3).
7. The method for forecasting the ultimate bearing capacity of automotive axle shafts according to claim 6, characterized in that RBE3 units (13) are established on the side gear (1), the slave point (11) of the RBE3 unit (13) is arranged at the center point of the splines of the side gear (1), and the master point (12) of the RBE3 unit (13) is the tooth surface unit node on the side gear (1).
8. The forecasting method of the limit load-carrying capacity of the half shafts of the automobile according to claim 6, characterized in that RBE3 units (33) are established on the half shaft flange (3), the slave points (31) of the RBE3 units (33) are arranged at the center point of the half shaft flange (3), and the master points (32) of the RBE3 units (33) are nodes of the inner surface of the bolt holes on the half shaft flange (3).
9. The method for forecasting the ultimate bearing capacity of the automotive half shaft according to claim 1, wherein the method specifically comprises the steps of performing torsional elastoplastic finite element analysis on a half shaft finite element model, controlling time increment, applying the torque load M step by step, acquiring output displacement and plastic strain data by a Newton-Laptosen method, and acquiring a relation curve between a half shaft corner alpha and the torque load M:
setting a finite element simulation time period as 1, controlling time increment to be less than or equal to 0.02, outputting displacement and plastic strain data after each time increment is calculated, and acquiring data corresponding to the half shaft rotation angle alpha and time t, wherein the output frequency is greater than or equal to 50;
and multiplying the time t by the torque load M to obtain the torque corresponding to each time point, and acquiring a relation curve of the half-axle rotation angle alpha and the torque load M.
10. A prediction method for the limit bearing capacity of the half-axle of the car as claimed in claim 1, characterized in that the curve of the relationship between the half-axle rotation angle α and the torque load M is at the initial linear stage corresponding to KiIs Ki/K1Greater than 99% of the data.
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