Overall dropper fatigue life prediction method and system considering crimping process

Abstract

The invention belongs to the technical field of dropper fatigue life prediction, and particularly relates to an integral dropper fatigue life prediction method and system considering a crimping process, and the method comprises the steps: constructing a Chboch follow-up hardening constitutive model, a crimping damage model and a multi-axial fatigue damage evolution model of a dropper, parameters in all the models are calibrated; establishing a local simulation model of the dropper crimping process, acquiring plastic deformation and residual stress at the crimping part of the dropper according to a simulation result of the local simulation model of the dropper crimping process, and calculating initial damage D0 generated by the dropper in the crimping process according to the crimping damage model and the plastic deformation and residual stress at the crimping part of the dropper; and taking D0 as an initial condition of a multi-axial fatigue damage evolution model of the dropper, and predicting the fatigue life of the dropper according to the multi-axial fatigue damage evolution model. The dropper fatigue life prediction method is more accurate in dropper fatigue life prediction.

Description

Technical Field

[0001] The present invention belongs to the technical field of catenary fatigue life prediction, and particularly relates to a method for predicting the fatigue life of an integral catenary considering the crimping process. Background Technique

[0002] The integral catenary is a key component of the high-speed railway catenary. In practical engineering applications, the catenary structure not only bears the self-weight of the contact wire but also bears the impact vibration caused by the high-speed movement of the pantograph. Under the long-term action of such cyclic loads, the catenary will have a failure problem of fatigue damage.

[0003] The fatigue life of the catenary is closely related to the material and the form of the load it bears, but other factors also need to be considered, that is, the one-time damage that may occur during the production process, forming a slight pit defect in the local part of the component, thereby reducing the fatigue life of the component. For example, the crimping process experienced by the catenary during production and manufacturing causes certain damage to it. Therefore, it is necessary to predict the fatigue life of the integral catenary after crimping.

[0004] At present, there are mainly two methods for predicting fatigue life: (1) predicting the fatigue life of the catenary based on experiments and statistics, but this method is time-consuming and laborious and requires specific experimental devices; (2) analyzing the fatigue life of the catenary through the nominal stress method and fatigue analysis software, but both are based on the linear damage accumulation theory, which not only cannot consider the influence of the crimping process on the catenary life but also has lower accuracy.

[0005] Therefore, it is necessary to establish a method for predicting the fatigue life of an integral catenary considering the crimping process to provide assistance for the improvement of the integral catenary crimping process and installation and maintenance. Summary of the Invention

[0006] The purpose of the present invention is to provide a method and system for predicting the fatigue life of an integral catenary considering the crimping process, which considers the influence of the crimping process, the non-linear damage accumulation of the material, and the decrease of the elastic modulus on the fatigue life of the integral catenary, making the prediction of the catenary fatigue life more accurate and having important theoretical significance and engineering value.

[0007] To achieve the above object, in the first aspect, the present invention provides a method for predicting the fatigue life of an integral catenary considering the crimping process, including:

[0008] Construct a Chaboche kinematic hardening constitutive model, a crimping damage model, and a multiaxial fatigue damage evolution model of the catenary, and calibrate the parameters in each model;

[0009] Establish a local simulation model of the suspension string crimping process, obtain the plastic deformation and residual stress at the crimping location of the suspension string according to the simulation results of the local simulation model of the suspension string crimping process, and calculate the initial damage D generated by the suspension string during the crimping process according to the crimping damage model and the plastic deformation and residual stress at the crimping location of the suspension string 0 ;

[0010] Take D 0 as the initial condition of the multiaxial fatigue damage evolution model of the suspension string, and predict the fatigue life of the suspension string according to the multiaxial fatigue damage evolution model

[0011] In some embodiments, the method for predicting the fatigue life of the suspension string according to the multiaxial fatigue damage evolution model includes:

[0012] The damage of the suspension string is manifested as a change in the elastic modulus. The elastic modulus E at the crimping location of the suspension string after the crimping process (0) = E(1 - D 0 ), where E is the initial elastic modulus of the suspension string, calculate the damage and elastic modulus at the crimping location of the suspension string after n cycles of cyclic loading E (n) = E (n-1) (1 - D n ), where D n is the damage of the suspension string after n cycles of cyclic loading, D n-1 is the damage of the suspension string after n - 1 cycles of cyclic loading is the damage generated during the nth cycle of cyclic loading, N represents the life of the suspension string. If D n ≥ D C , then record the number of cycles n at this time to achieve the prediction of the fatigue life of the suspension string, where D C is the damage threshold σ u is the tensile strength of the suspension string, σ R is the nominal stress when the suspension string is finally broken

[0013] In some embodiments, the cyclic loading is a constant amplitude load, and the amplitude of the cyclic loading is the maximum peak value in the actual service load of the suspension string

[0014] In some embodiments, the method for constructing the Chaboche kinematic hardening constitutive model of the suspension string includes:

[0015] According to the generalized Hooke's law and considering the influence of damage, the relationship between the deviatoric stress tensor, the deviatoric strain and the plastic strain is:

[0016]

[0017] In the formula S ijis the deviatoric stress tensor; D is the damage parameter; G is the shear modulus; is the plastic strain, e ij is the deviatoric strain tensor, e ij is the component of the deviatoric strain tensor, ε ij the component of the total strain tensor, ε 11 、ε 22 、ε 33 are the diagonal components of the total strain tensor, representing the principal strains along the x-axis, y-axis, and z-axis directions respectively;

[0018] Then the yield potential function can be rewritten as:

[0019]

[0020] where, is the strain hardening function, which is the yield strength after considering hardening and is related to the equivalent plastic strain; α ij is the back stress, and the expression form of the back stress is as follows:

[0021]

[0022] where, α ij is the total back stress; is the plastic strain rate; is the equivalent plastic strain rate; is the back stress evolution rate, indicating the change speed of the back stress during the plastic flow process of the material; C k and γ k are the kinematic hardening constant and the kinematic hardening index respectively, controlling the growth rate and dissipation rate of the back stress respectively, and are calibrated through experimental data.

[0023] In some embodiments, the method for calibrating the parameters in the Chaboche kinematic hardening constitutive model of the suspension wire includes:

[0024] Through the tensile test of the suspension wire material at room temperature, obtain the stress-strain curve of the suspension wire material, determine the elastic modulus and initial yield stress of the suspension wire material, calculate the elastic strain in the elastic stage during the tensile process of the suspension wire material, and subtract the elastic strain from the total strain to obtain the stress-plastic strain curve of the suspension wire material;

[0025] Integrate the back stress α ij to obtain the relationship between the stress σ and the plastic strain ε p :

[0026]

[0027] where, σ y ′ is the initial yield stress, C k, γ k are the kinematic hardening constant and the kinematic hardening index respectively. According to the stress - plastic strain curve, data fitting is carried out to obtain the parameters C k , γ k .

[0028] In some embodiments, the method for constructing the crimping damage model of the dropper includes:

[0029] The damage to the dropper caused by the crimping process is mainly plastic damage. The crimping damage model adopts a non - linear fatigue damage evolution model considering the plastic strain increment:

[0030]

[0031] S ij S ij represents the dot product of the stress tensor S ij with itself. Actually:

[0032]

[0033]

[0034] In the formula, is the plastic damage generated in a single cycle; is the equivalent plastic strain in a single cycle; M and m are the material parameters of the dropper, which are calibrated through experimental data; σ eq is the Von Mises equivalent stress; R V is the stress triaxiality function, σ H is the hydrostatic pressure; ν is the Poisson's ratio; E is the elastic modulus.

[0035] Assume that for the maximum stress in each cycle, the material is completely plastic, and we get Integrating within one load cycle, we obtain:

[0036]

[0037] In the formula, Δε p is the equivalent plastic strain increment corresponding to a half - cycle.

[0038] In some embodiments, the method for calibrating the parameters in the crimping damage model of the dropper includes:

[0039] Integrate D p to obtain the relationship between the life N and the plastic strain:

[0040]

[0041] Utilize the relationship between cyclic stress and strain Convert the above formula to:

[0042]

[0043] In the formula, n' and K′ are strain fatigue parameters;

[0044] According to the strain-life curve, Perform data fitting to obtain parameters M and m.

[0045] The strain-life curve (i.e., the ε-N curve) can be obtained through fatigue tests under strain control;

[0046] In the absence of test data, it can be estimated through the static tensile properties of the suspension string material: elastic modulus E, tensile strength σ b , true fracture strain ε f , true fracture strength σ f The expressions are as follows:

[0047]

[0048] In the formula, ε f ′ and c can be estimated using the general slope method or the four-point correlation method, combined with the true fracture strain ε f , which is related to the static tensile property parameters. Among them, c = -0.6, ε f ′ = 0.5ε f 0.6 .

[0049] In some embodiments, the method for constructing the multiaxial fatigue damage evolution model of the suspension string includes:

[0050] The damage to the suspension string caused by cyclic loading is mainly elastic damage. Considering that the suspension string is a stranded structure, a multiaxial fatigue damage evolution model is used to calculate the elastic damage of the suspension string. The expression is as follows:

[0051]

[0052]

[0053] In the formula, is the elastic damage generated by a single cycle; A II is the octahedral shear stress amplitude; S ij,max and S ij,min are the maximum and minimum values of the deviatoric stress tensor components in a load cycle, respectively; σ H,m is the mean hydrostatic pressure; σ H is the hydrostatic pressure, σ 11 , σ 22 , σ 33 represent the principal stresses along the x, y, and z directions, respectively; σeq,max is the maximum equivalent stress within a load cycle; σ u is the ultimate stress; is the Sines fatigue limit criterion, σ l0 is the fatigue limit when the stress ratio is -1; a, b 1 、b 2 、β、M 0 are parameters to be calibrated.

[0054] In some embodiments, the method for calibrating the parameters in the multiaxial fatigue damage evolution model of the suspension insulator string includes:

[0055] Integrate D e to obtain the following expression:

[0056]

[0057] According to the stress-life curve, fit using the least squares method to obtain the value of the parameter β and the overall value of , b 1 , b 2 is determined by the relationship of the Goodman curve. Combining the damage data, the parameter a is comprehensively optimized using the least squares method.

[0058] In a second aspect, the present invention provides an overall suspension insulator string fatigue life prediction system considering the crimping process, including:

[0059] Model construction module: used to establish the Chaboche kinematic hardening constitutive model, crimping damage model, and multiaxial fatigue damage evolution model of the suspension insulator string, and calibrate the parameters in each model;

[0060] Crimping damage calculation module: used to establish a local simulation model of the suspension insulator string crimping process, and calculate the initial damage D 0 ;

[0061] Fatigue life calculation module: used to take D 0 as the initial condition of the multiaxial fatigue damage evolution model of the suspension insulator string, and predict the fatigue life of the suspension insulator string according to the multiaxial fatigue damage evolution model.

[0062] Compared with the prior art, the present invention can achieve the following beneficial effects:

[0063] 1. The present invention considers the single damage during the crimping process as the initial condition for fatigue damage accumulation, making the prediction of the suspension insulator string fatigue life more accurate.

[0064] 2. The present invention takes into account the effects of non-linear damage accumulation of materials and the decrease in elastic modulus on the fatigue life of integral suspension strings, further improving the accuracy of fatigue life prediction of suspension strings. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 FIG. is a schematic flow chart of a method for predicting the fatigue life of an integral suspension string considering the crimping process provided by an embodiment of the present invention;

[0066] Figure 2 FIG. is a schematic flow chart of the basic calculation of the VUMAT subroutine in an embodiment of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0067] The following further describes the present invention in detail with reference to the accompanying drawings and specific embodiments, but the embodiments should not be construed as limiting the present invention.

[0068] As Figure 1 shown, this embodiment provides a method for predicting the fatigue life of an integral suspension string considering the crimping process, including:

[0069] S1. Construct a Chaboche kinematic hardening constitutive model, a crimping damage model, and a multiaxial fatigue damage evolution model for the suspension string; S1 specifically includes:

[0070] S11. Construct a Chaboche kinematic hardening constitutive model for the suspension string:

[0071] Under the action of external loads, the damage of metal materials is manifested as internal microvoids and microcracks and other microscopic defects, and the damage situation of materials can be characterized by the degree of stiffness degradation, represented by the damage parameter D, and the formula is as follows:

[0072]

[0073] In the formula, E is the initial elastic modulus, and E' is the elastic modulus with damage.

[0074] According to the generalized Hooke's law and considering the influence of damage, the relationship between the deviatoric stress tensor, the deviatoric strain, and the plastic strain is:

[0075]

[0076] In the formula, S ij is the deviatoric stress tensor; D is the damage parameter; G is the shear modulus; is the plastic strain, e ij is the deviatoric strain tensor, e ij is the component of the deviatoric strain tensor, ε ij is the component of the total strain tensor, ε 11 、ε22 , ε 33 are the diagonal components of the total strain tensor, representing the principal strains along the x-axis, y-axis, and z-axis, respectively;

[0077] Then the yield potential function can be rewritten as:

[0078]

[0079] This formula describes the condition for whether the material reaches yield in damage mechanics considering the damage variable; in the formula, is the strain hardening function, which is the yield strength considering hardening and is related to the equivalent plastic strain; α ij is the back stress; for the construction of the constitutive model of the catenary wire material, the Chaboche kinematic hardening model can accurately represent the characteristics of the plastic stage of metallic materials and is more in line with the nonlinear stress change process of metallic materials. Its expression form of the back stress is as follows:

[0080]

[0081]

[0082] In the formula, α ij is the total back stress; is the plastic strain rate; is the equivalent plastic strain rate; is the back stress evolution rate, representing the change speed of the back stress during the plastic flow process of the material; C k and γ k are the kinematic hardening constant and the kinematic hardening index, respectively, which control the growth rate and dissipation rate of the back stress and are calibrated through experimental data.

[0083] By constructing the Chaboche kinematic hardening constitutive model of the catenary wire, the mechanical properties of the catenary wire are determined.

[0084] S12. Construct the crimping damage model and the multiaxial fatigue damage evolution model of the catenary wire:

[0085] The crimping process causes obvious plastic deformation to the catenary wire, mainly plastic damage; under the action of subsequent cyclic loads, it is mainly elastic damage. Therefore, the damage parameter of the overall catenary wire is divided into two components, that is, the damage parameter of the overall catenary wire = elastic damage + plastic damage.

[0086] The crimping damage model adopts a nonlinear fatigue damage evolution model considering the plastic strain increment:

[0087]

[0088] S ij S ij represents the stress tensor Sij The dot product with itself, actually:

[0089]

[0090]

[0091] In the formula, is the plastic damage generated in a single cycle; is the equivalent plastic strain in a single cycle; N represents the life of the catenary wire; M, m are the material parameters of the catenary wire, calibrated through test data; σ eq is the Von Mises equivalent stress; R V is the stress triaxiality function, σ H is the hydrostatic pressure; ν is the Poisson's ratio; E is the elastic modulus.

[0092] Assume that for the maximum stress σ max in each cycle, the material is completely plastic, and we get σ eq R v 1 / 2 = σ max , and integrating within one load cycle, we get:

[0093]

[0094] In the formula, Δε p is the increment of the equivalent plastic strain corresponding to a half-cycle. The load cycle of the material includes the processes of tension and compression, and the stress-strain of the whole process forms a hysteresis curve. Assume that the material is an isotropic hardening material, and the plastic strains generated by tension and compression are equal. The increment of the equivalent plastic strain corresponding to a half-cycle is the equivalent plastic strain generated during the tension process.

[0095] The elastic damage of the catenary wire is calculated using a multiaxial fatigue damage evolution model, and its expression is as follows:

[0096]

[0097]

[0098]

[0099] In the formula, is the elastic damage generated in a single cycle; A II is the octahedral shear stress amplitude; S ij,max and S ij,min are respectively the maximum and minimum values of the deviatoric stress tensor components in a load cycle; σ H,m is the mean hydrostatic pressure; σ H is the hydrostatic pressure, σ 11 、σ22 , σ 33 respectively represent the principal stresses in the x, y, and z directions; σ eq,max is the maximum equivalent stress within a load cycle; σ u is the limit stress; is the Sines fatigue limit criterion, σ l0 is the fatigue limit when the stress ratio is -1; a, b 1 , b 2 , β, M 0 are the parameters to be calibrated.

[0100] S2. Calibrate the parameters in each model; S2 specifically includes:

[0101] S21. Calibrate the parameters in the Chaboche kinematic hardening constitutive model of the suspension string:

[0102] Through the tensile test of the suspension string material at room temperature, obtain the stress-strain curve of the suspension string material, determine the elastic modulus and initial yield stress of the suspension string material, calculate the elastic strain in the elastic stage during the tensile process of the suspension string material, and subtract the elastic strain from the total strain to obtain the stress-plastic strain curve of the suspension string material;

[0103] Integrate the back stress α ij to obtain the relationship between the stress σ and the plastic strain ε p :

[0104]

[0105] In the formula, σ y ′ is the initial yield stress, C k , γ k are the kinematic hardening constant and kinematic hardening index respectively. According to the stress-plastic strain curve, perform data fitting on to obtain the parameters C k , γ k .

[0106] S22. The method for calibrating the parameters in the crimping damage model of the suspension string includes:

[0107] Integrate D p to obtain the relationship between the life N and the plastic strain:

[0108]

[0109] Utilize the relationship between the cyclic stress and strain to transform the above formula into:

[0110]

[0111] In the formula, n' and K′ are strain fatigue parameters;

[0112] According to the strain-life curve, data fitting is carried out to obtain the parameters M and m. The strain-life curve (i.e., the ε-N curve) can be obtained through fatigue tests under strain control;

[0113] In the case of no test data, the static tensile properties of the suspension string material: elastic modulus E, tensile strength σ b and true fracture strain ε f , true fracture strength σ f can be used for estimation, and the expression is as follows:

[0114]

[0115] In the formula, ε f ′ and c can be estimated by the general slope method or the four-point correlation method, combined with the true fracture strain ε f , which is related to the static tensile property parameters. Among them, c = -0.6, ε f ′ = 0.5ε f 0.6 .

[0116] S23. The method for calibrating the parameters in the multiaxial fatigue damage evolution model of the suspension string includes:

[0117] Integrate D e to obtain the following expression:

[0118]

[0119] According to the stress-life curve, perform least squares fitting to obtain the value of the parameter β and the overall value of , b 1 , b 2 is determined by the relationship of the Goodman curve. Combining the damage data, the parameter a is obtained by comprehensive optimization using the least squares method.

[0120] S3. Establish a local simulation model of the suspension string crimping process and calculate the initial damage D 0 generated by the suspension string during the crimping process. S3 specifically includes:

[0121] The actual length of the suspension string is about 1 m. To improve the calculation efficiency and refine the mesh model, the simulation model was simplified accordingly. A local simulation model including the crimping position was established. At the same time, the crimping die was regarded as a rigid body model without considering its stress and strain conditions, and the crimping process was input in the form of displacement load. By observing the simulation results of the suspension string crimping, it was found that obvious plastic deformation occurred at the position where the crimping side of the suspension string was close to the tooth shape of the crimping die. The mesh elements at this position were selected as the extraction points for the plastic deformation field and the residual stress field, and the plastic deformation and residual stress at the crimping position of the suspension string were extracted. At the same time, the crimping force was calculated by extracting the reaction force, and the effects of different crimping methods and the form of the crimping force on the crimping damage and damage evolution of the suspension string could be comprehensively investigated.

[0122] Based on the Lemaitre plastic damage theory, combined with the plastic deformation and residual stress at the crimping position of the suspension string, according to calculate the initial damage generated during the crimping process of the suspension string. Among them, is the equivalent plastic strain of a single cycle, and the integral of is equal to the plastic deformation at the crimping position of the suspension string, and σ eq is equal to the residual stress at the crimping position of the suspension string.

[0123] S4. Take D 0 as the initial condition of the multiaxial fatigue damage evolution model of the suspension string, and predict the fatigue life of the suspension string according to the multiaxial fatigue damage evolution model. S4 specifically includes:

[0124] Apply cyclic loads to the local simulation model of the overall suspension string. Since the actual service load of the suspension string is relatively complex with frequent peak fluctuations, considering that the actual fatigue life of the suspension string is up to tens of thousands or even hundreds of thousands of times, it is not only difficult to obtain the actual service load, but also the calculation efficiency is slow when importing it into the finite element software. Therefore, the load value of the maximum peak can be selected as the amplitude of the cyclic load, and a constant amplitude load spectrum can be compiled for solution. When the total damage of the suspension string reaches a certain threshold, record the number of load cycles, and the conservative value of the fatigue life prediction of the overall suspension string can be obtained.

[0125] Among them, the fatigue life prediction of the suspension string is completed by using the VUMAT subroutine. The VUMAT subroutine is a secondary development based on ABAQUS, which can write the damage constitutive model, the damage evolution model and predict the fatigue life of the overall suspension string.

[0126] As Figure 2 shown, the steps of using the VUMAT subroutine to predict the fatigue life of the overall suspension string include:

[0127] The failure of the suspension string is mainly reflected in the fracture of the stranded wire at the crimping position. Therefore, the finite element elements at this position are used as the data extraction object.

[0128] The initial damage parameters of the finite element are all 0, indicating that the suspension string is intact, and the initial elastic modulus is E.

[0129] In the crimping stage, the VUMAT subroutine automatically calculates the initial damage D of the crimping 0 , and reconstructs the element model (updates the material properties and stiffness matrix). The damage of the suspension string is manifested as a change in the elastic modulus. The elastic modulus E at the crimping position of the suspension string after the crimping process (0) = E(1 - D 0 );

[0130] Calculate the damage and elastic modulus at the crimping position of the suspension string after n cycles of cyclic loading, E (n) = E (n-1) (1 - D n ), where D n is the damage of the suspension string after n cycles of cyclic loading, D n-1 is the damage of the suspension string after n - 1 cycles of cyclic loading, is the damage generated during the nth cycle of cyclic loading. If D n ≥ D C , then record the number of cycles n at this time to achieve the fatigue life prediction of the suspension string. Among them, D C is the damage threshold, σ u is the tensile strength of the suspension string, and σ R is the nominal stress when the suspension string is finally broken.

[0131] The VUMAT subroutine of the present invention can achieve the fatigue life prediction of structural components considering single crimping and impact, which has important theoretical significance.

[0132] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for predicting fatigue life of an integral suspension string considering the crimping process, characterized in that: include: The Chaboche kinematic hardening constitutive model, crimping damage model and multiaxial fatigue damage evolution model of the suspension string are constructed, and the parameters in each model are calibrated. A local simulation model of the suspension string crimping process is established, and the plastic deformation and residual stress at the suspension string crimping point are obtained according to the simulation results of the local simulation model of the suspension string crimping process. The initial damage D0 generated by the suspension string in the crimping process is calculated according to the crimping damage model and the plastic deformation and residual stress at the suspension string crimping point. D0 is used as the initial condition of the multiaxial fatigue damage evolution model of the suspension string, and the fatigue life of the suspension string is predicted based on the multiaxial fatigue damage evolution model.

2. The method for predicting fatigue life of an integral suspension string considering the crimping process according to claim 1 is characterized in that: The methods for predicting the fatigue life of suspension strings based on the multiaxial fatigue damage evolution model include: The damage of the suspension string is manifested as a change in the elastic modulus. The elastic modulus E of the suspension string at the crimping point after the crimping process is (0) =E(1-D0), where E is the initial elastic modulus of the suspension string. The damage and elastic modulus of the suspension string crimping after n cycles of cyclic loading are calculated. E (n) =E (n-1) (1-D n ), where D n is the damage of the suspension string after n cycles of cyclic loading, D n-1 is the damage of the suspension string after n-1 cycles of cyclic loading, is the damage caused by the nth cycle of cyclic loading, N is the life of the suspension string, if D n ≥D C , then record the number of cycles n at this time to achieve the fatigue life prediction of the suspension string, where D C is the damage threshold, σ u is the tensile strength of the suspension string, σ R is the nominal stress when the suspension string finally breaks.

3. The method for predicting fatigue life of an integral suspension string considering the crimping process according to claim 2 is characterized in that: The cyclic load is a constant amplitude load, and the amplitude of the cyclic load is the maximum peak value in the actual service load of the suspension string.

4. The method for predicting fatigue life of an integral suspension string considering the crimping process according to any one of claims 1 to 3, characterized in that: The method of constructing the Chaboche kinematic hardening constitutive model of the suspension string includes: According to the generalized Hooke's law and considering the effect of damage, the relationship between the deviatoric stress tensor and the deviatoric strain and plastic strain is: In the formula, S ij is the deviatoric stress tensor; D is the damage parameter; G is the shear modulus; is the plastic strain, e ij is the deviatoric strain tensor, e ij are the components of the deviatoric strain tensor, ε ij Components of the total strain tensor, ε 11 , ε 22 , ε 33 are the diagonal components of the total strain tensor, representing the principal strains along the x-axis, y-axis, and z-axis respectively; Then the yield potential function can be rewritten as: In the formula, is the strain hardening function, which is the yield strength after hardening and is related to the equivalent plastic strain; α ij is the back stress, and the expression of back stress is as follows: In the formula, α ij is the total back stress; is the plastic strain rate; is the equivalent plastic strain rate; is the back stress evolution rate, which indicates the speed of change of back stress during the plastic flow process of the material; C k and γ k are the kinematic hardening constant and kinematic hardening exponent, which control the growth rate and dissipation rate of back stress respectively and are calibrated by experimental data.

5. The method for predicting fatigue life of an integral suspension string considering the crimping process according to claim 4 is characterized in that: The method for calibrating the parameters in the Chaboche kinematic hardening constitutive model of the dropper string includes: Through the tensile test of the suspension string material at room temperature, the stress-strain curve of the suspension string material is obtained, the elastic modulus and initial yield stress of the suspension string material are determined, the elastic strain in the elastic stage during the tensile process of the suspension string material is calculated, and the stress-plastic strain curve of the suspension string material is obtained by subtracting the elastic strain from the total strain; Back stress α ij Integrate to obtain stress σ and plastic strain ε p The relationship between: In the formula, σ y ′ is the initial yield stress, C k , γ k are the kinematic hardening constant and kinematic hardening exponent, respectively. Perform data fitting and obtain parameter C k , γ k .

6. The method for predicting fatigue life of an integral suspension string considering the crimping process according to any one of claims 1 to 3, characterized in that: The methods for constructing the crimping damage model of the dropper string include: The damage caused by the crimping process to the suspension string is mainly plastic damage. The crimping damage model adopts a nonlinear fatigue damage evolution model that considers the plastic strain increment: In the formula, Plastic damage caused by a single cycle; is the equivalent plastic strain of a single cycle; M and m are the material parameters of the suspension string, which are calibrated by test data; σ eq is VonMise equivalent stress; R V is the stress triaxiality function, σ H is the hydrostatic pressure; ν is the Poisson's ratio; E is the elastic modulus; Assuming that the material is completely plastic for the maximum stress in each load cycle, σ eq R v 1 / 2 =σ max , integrated within one load cycle, we get: In the formula, Δε p is the equivalent plastic strain increment corresponding to half a branch cycle.

7. The method for predicting fatigue life of an integral suspension string considering the crimping process according to claim 6 is characterized in that: The method for calibrating the parameters in the crimping damage model of the suspension string includes: Right D p By integrating, we can obtain the relationship between life span N and plastic strain: Using the cyclic stress-strain relationship Convert the above formula into: Where n' and K' are strain fatigue parameters; According to the strain-life curve Perform data fitting to obtain parameters M and m; strain-life curve can be obtained through fatigue test under strain control; In the absence of fatigue test data under strain control, the static tensile properties of the suspension string material can be used: elastic modulus E, tensile strength σ b , true fracture strain ε f , true breaking strength σ f To estimate, the expression is as follows: In the formula, ε f ′ and c can be calculated by using the general slope method or the four-point correlation method, combined with the true fracture strain ε f Estimation is related to the static tensile performance parameters, where c = -0.6, ε f ′=0.5ε f 0.6 .

8. The method for predicting fatigue life of an integral suspension string considering the crimping process according to any one of claims 1 to 3, characterized in that: The methods for constructing the multiaxial fatigue damage evolution model of the suspension string include: The damage of the suspension string caused by cyclic load is mainly elastic damage. Considering that the suspension string is a twisted wire structure, the elastic damage of the suspension string is calculated using the multi-axial fatigue damage evolution model, and its expression is as follows: In the formula, It is the elastic damage produced by a single cycle; is the octahedral shear stress amplitude; S ij,max and S ij,min are the maximum and minimum values ​​of the deviator stress tensor components in a load cycle; σ H,m is the average hydrostatic pressure; σ H is the hydrostatic pressure, σ 11 , σ 22 , σ 33 Respectively represent the principal stresses along the x, y, and z directions; σ eq,max is the maximum equivalent stress within a load cycle; σ u is the ultimate stress; is the Sines fatigue limit criterion, σ l0 is the fatigue limit when the stress ratio is -1; a, b1, b2, β, M0 are the parameters to be calibrated.

9. The method for predicting fatigue life of an integral suspension string considering the crimping process according to claim 8 is characterized in that: The method for calibrating the parameters in the multiaxial fatigue damage evolution model of the suspension string includes: Right D e Integrate and get the following expression: According to the stress-life curve The least squares method is used to fit the value of parameter β and The overall value of b1 and b2 are determined by the relationship of the Goodman curve. Combined with the damage data, the least squares method is used to comprehensively optimize the parameter a.

10. A system for predicting fatigue life of an integral suspension string considering the crimping process, characterized in that: include: Model building module: used to establish the Chaboche kinematic hardening constitutive model, crimping damage model and multiaxial fatigue damage evolution model of the suspension string, and calibrate the parameters in each model; Crimping damage calculation module: used to establish a local simulation model of the hanging string crimping process and calculate the initial damage D0 of the hanging string in the crimping process; Fatigue life calculation module: It is used to use D0 as the initial condition of the multi-axial fatigue damage evolution model of the suspension string, and predict the fatigue life of the suspension string according to the multi-axial fatigue damage evolution model.

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