Structure stability fatigue life prediction method and system based on critical plane stress damage parameter

Abstract

The invention belongs to the technical field of metal structure fatigue life prediction, and discloses a structure stability fatigue life prediction method and system based on a critical plane stress damage parameter, and the method comprises the steps: obtaining a material shear fatigue strength coefficient and a shear fatigue strength index based on fatigue test data, a Manson-Coffin elastic strain line expression and a Kim conversion formula; based on the material shear fatigue strength coefficient, the shear fatigue strength index and the Dang Van fatigue criterion, constructing a stable fatigue life prediction model; acquiring stress process data of the structural dangerous unit body in a complete period in the stability cycle process; based on the stress process data, critical damage plane damage parameters are obtained; and obtaining a structural stability fatigue life value based on the stability fatigue life prediction model and the critical damage plane damage parameter. The method is simple in structure fatigue life prediction operation, simple and understandable in calculation and wide in application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of fatigue life prediction of metal structures, and relates to a method and system for predicting structural stability fatigue life based on critical plane stress damage parameters. Background Art

[0002] For giant hydraulic presses, due to the discontinuity of their own structure, there will inevitably be local high stress areas with "extremely small areas and extremely high stress". The current methods to solve local high stress are mainly to increase the size or extreme manufacturing, but neither can completely eliminate the impact of local high stress. The local high stress area of ​​the giant hydraulic press will undergo plastic deformation due to high stress and then reach a stable state. After reaching the stable state, the press will not be damaged due to the accumulation of plastic deformation under the subsequent cyclic load, but high-cycle fatigue failure will occur because of the high local stress level. At the same time, the residual stress generated by local plastic deformation may also change the stress cycle type, thereby affecting the fatigue life of the press structure after stabilization. Therefore, it is very necessary to study the prediction of high-cycle fatigue life after the local structure of the giant hydraulic press enters the stable state.

[0003] Since the 20th century, people have continuously studied and proposed various fatigue prediction methods. Fatigue prediction methods can be divided into high-cycle fatigue prediction and low-cycle fatigue prediction. The most widely used and representative criteria are Basquin stress-life prediction method and Coffin-Manson strain-life prediction method. Basquin prediction method mainly uses stress amplitude as damage criterion and is mostly used for fatigue life greater than 10 4 The Coffin-Manson prediction method mainly uses strain amplitude as the damage criterion and is mostly used for high-cycle fatigue life prediction with a fatigue life of less than 10 4 The low-cycle fatigue life prediction of the structure is carried out. After the structure reaches the stable state, it is always in the elastic response state, but it will still suffer high-cycle fatigue damage under high stress cycles. Therefore, when constructing the stable fatigue life prediction model, the stress amplitude is considered as the damage criterion. However, the general stress-life prediction model with stress amplitude as the damage criterion can only be used to predict the structural life under low stress cycles. Under the action of low stress amplitude cyclic loads, the local high stress area of ​​the structure does not undergo plastic deformation and is always in an elastic state. At this time, the damage judgment is sensitive to the stress amplitude, so the stress-life method is used. For the prediction of structural stable fatigue life, the general stress-life method and strain-life method have obvious limitations, and the stress-life method and strain-life method mostly define the damage parameter through a single variable, which will lead to inaccurate life prediction results and cannot meet the current engineering needs. Summary of the invention

[0004] The purpose of the present invention is to solve the problem that the existing fatigue life prediction technology cannot predict the fatigue life of the structure after it reaches a stable state and the damage parameter is defined by a single variable, resulting in inaccurate prediction results that cannot meet current engineering needs, and to provide a structural stable fatigue life prediction method and system based on critical plane stress damage parameters.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] The structural stability fatigue life prediction method based on critical plane stress damage parameters includes:

[0007] Conduct symmetrical tension-compression cycle fatigue tests under strain control on national standard fatigue rod specimens to obtain fatigue test data;

[0008] Based on the acquired fatigue test data, Manson-Coffin elastic strain line expression and Kim conversion formula, the shear fatigue strength coefficient and shear fatigue strength index of the material are obtained;

[0009] Based on the material shear fatigue strength coefficient, shear fatigue strength index and Dang Van fatigue criterion, a shakedown fatigue life prediction model is constructed;

[0010] Perform cyclic simulation on the target structural parts under steady state load to obtain the stress history data of the dangerous structural unit in a complete cycle during the steady state cycle;

[0011] Based on the stress history data, the damage parameters of the critical damage plane are obtained;

[0012] Based on the shakedown fatigue life prediction model and the damage parameters of the critical damage plane, the structural shakedown fatigue life value is obtained.

[0013] A further improvement of the present invention is:

[0014] Further, fatigue test data, including: elastic strain amplitude ε e,a And the fatigue life of the national standard fatigue standard rod specimen N f .

[0015] Furthermore, based on the acquired fatigue test data, the Manson-Coffin elastic strain line expression and the Kim conversion formula, the shear fatigue strength coefficient and shear fatigue strength index of the material are obtained, specifically:

[0016]

[0017] Among them, σ′ f is the material fatigue strength coefficient, unit MPa; b is the material fatigue strength index, which is a dimensionless parameter; E is the elastic modulus, unit MPa; εe,a is the elastic strain amplitude, dimensionless; N f is the fatigue life of the national standard fatigue standard rod specimen, that is, the number of cycles when fatigue failure occurs;

[0018] In the absence of torsion fatigue test conditions, the shear fatigue strength coefficient and shear fatigue strength index are obtained according to Kim's conversion formula;

[0019] τ′ f =0.63σ′ f

[0020] b0=b

[0021] Among them, τ′ f is the shear fatigue strength coefficient, and b0 is the shear fatigue strength index.

[0022] Furthermore, based on the material shear fatigue strength coefficient, shear fatigue strength index and Dang Van fatigue criterion, a shakedown fatigue life prediction model is constructed, specifically:

[0023]

[0024] Among them, τ a,max is the maximum shear stress amplitude, unit: MPa; α DV is the Dang Van coefficient, a dimensionless constant; σ H is the hydrostatic stress, in MPa; a,max +α DV σ H is the damage parameter defined by the model; τ′ f is the shear fatigue strength coefficient, unit MPa; b0 is the shear fatigue strength index, which is a dimensionless material parameter; N sf is the structural stability fatigue life value;

[0025] Based on the torsional fatigue limit and tensile and compressive fatigue limit of the material, the Dang Van coefficient is obtained, which is:

[0026]

[0027] Among them, τ -1 is the torsional fatigue limit of the material; σ -1 is the tensile and compressive fatigue limit of the material;

[0028] The Dang Van fatigue criterion assumes that fatigue corresponds to the limit of elastic stability possibility of structural materials, assumes that elastic stability occurs at the macroscopic and microscopic scales, and believes that the elastic stability limit depends on the hydrostatic tension that occurs in the loading cycle; the Dang Van fatigue criterion believes that at the microscopic scale, the plastic deformation of grains on the characteristic slip bands in the critical volume inside the material leads to fatigue crack initiation, and shear stress and hydrostatic stress accelerate slip band generation and crack propagation; therefore, it is believed that the Dang Van fatigue criterion is not only very consistent with the critical plane stress method, but also applicable to the elastic stability state; the Dang Van fatigue criterion is specifically:

[0029] τ a,max +α DV σ H <τ -1

[0030] Among them, τ a,max is the maximum shear stress amplitude, unit: MPa; σ H is the hydrostatic stress, unit: MPa; τ -1 is the torsional fatigue limit of the material, unit: MPa; α DV is the Dang Van coefficient, dimensionless;

[0031] The left side of the inequality τ a,max +α DV σ H Can be regarded as equivalent stress, denoted as σ eq ; σ eq From the shear stress amplitude τ a and hydrostatic stress σ H Combined with the critical plane stress method, σ eq Defined as the damage parameter of the structural stability fatigue life prediction model.

[0032] Furthermore, a cyclic simulation is performed on the target structural part under a stable load to obtain the stress history data of the dangerous unit body of the structure within a complete cycle during the stable cycle. Specifically, when a cyclic simulation is performed on the target structural part under a stable load, the value range of the stable load Fn is between the yield load of the dangerous point of the structure and the stable limit load of the dangerous point of the structure; the stress history data of the dangerous unit body of the structure within a complete cycle during the stable cycle are extracted, including: S11, S22, S33, S12, S13, S23; wherein, S11, S22, S33, S12, S13, S23 are six independent stress components of the dangerous unit body; and then the stress history data of the independent stress components within a stable cycle period are obtained.

[0033] Furthermore, based on the stress history data, the damage parameters of the critical damage plane are obtained. Specifically, in a stable cycle, the maximum damage parameter values ​​of different damage planes are different; the damage plane is determined by Definition, the value range is as follows: θ∈[0°,180°]; where θ are the angles between the normal line of the damage plane and the Z axis and X axis respectively; There are 181×181 different combinations of , so the number of damage planes to be calculated is 181×181; in a stable cycle, the damage parameter value of each damage plane is related to time and reaches a maximum value at a certain moment. The maximum damage parameter value is taken as the representative value of the damage plane, and the representative values ​​of all damage planes are calculated in this way, totaling 181×181; finally, the size of the 181×181 representative values ​​is compared again, and the largest representative value is taken as the critical damage parameter of the dangerous unit of the structure under the stable cycle, denoted as σ eq,max .

[0034] Furthermore, based on the shakedown fatigue life prediction model and the critical damage plane damage parameters, the structural shakedown fatigue life value is obtained, specifically:

[0035] σ eq,max Substituting into the shakedown fatigue life prediction model, we have:

[0036]

[0037] The final calculated structural stability fatigue life value N sf .

[0038] The structural stability fatigue life prediction system based on critical plane stress damage parameters includes:

[0039] A test module, wherein the test module performs a symmetrical tension-compression cycle fatigue test under strain control on a national standard fatigue standard rod-shaped specimen to obtain fatigue test data;

[0040] A first acquisition module, which acquires a shear fatigue strength coefficient and a shear fatigue strength index of a material based on the acquired fatigue test data, a Manson-Coffin elastic strain line expression, and a Kim conversion formula;

[0041] A construction module, wherein the construction module constructs a shakedown fatigue life prediction model based on a material shear fatigue strength coefficient, a shear fatigue strength index and a DangVan fatigue criterion;

[0042] A cycle simulation module, wherein the cycle simulation module performs a cycle simulation on the target structural member under a stable load, and obtains stress history data of the structural dangerous unit body in a complete cycle during the stable cycle process;

[0043] A second acquisition module, wherein the second acquisition module acquires a critical damage plane damage parameter based on the stress history data;

[0044] The third acquisition module acquires the structural stability fatigue life value based on the stability fatigue life prediction model and the critical damage plane damage parameter.

[0045] Compared with the prior art, the present invention has the following beneficial effects:

[0046] The fatigue life prediction model constructed by the present invention takes into account the influence of structural stability on fatigue life, and is suitable for fatigue life prediction after the structure reaches a stable state, filling the gap in fatigue life prediction in the field of stability. At the same time, the present invention combines the critical plane stress method and the Dang Van fatigue criterion to define the damage parameter σ for the structural stability eq , the damage parameter includes the maximum shear stress amplitude τ a,max and hydrostatic stress σ H Compared with the traditional fatigue life prediction model that defines the damage parameter with a single variable, the present invention has higher calculation accuracy and avoids the limitations of the traditional model. The present invention is simple to operate in predicting the stable fatigue life of the structure. It only needs to use the relevant simulation software to perform a stable cycle on the target structural part and derive the stress history data of the six independent stress components of a complete cycle of the dangerous unit body, which can be imported into the program to calculate the critical damage parameter σ eq,max The specific fatigue life value can be calculated quickly and accurately, which is suitable for practical engineering applications and has broad application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0048] Figure 1 It is a schematic flow chart of the method for predicting structural stability fatigue life based on critical plane stress damage parameters of the present invention;

[0049] Figure 2 It is a structural schematic diagram of the structural stability fatigue life prediction system based on critical plane stress damage parameters of the present invention;

[0050] Figure 3 (a) is a schematic diagram of the target structural component dimensions;

[0051] Figure 3 (b) is the side view of the target structure;

[0052] Figure 4 is the force diagram of the target structural member;

[0053] Figure 5 This is a schematic diagram of the Manson-Coffin elastic-plastic line fitting results;

[0054] Figure 6 It is a schematic diagram of the cyclic loading path;

[0055] Figure 7 It is a schematic diagram of the simulation of the steady state load cycle of the target structural component;

[0056] Figure 8 Schematic diagram of the relationship between equivalent plastic strain and period;

[0057] Fig. 9 It is a schematic diagram of the change of stress history data in a stable cycle;

[0058] Fig.10 Schematic diagram of arbitrary damage plane. DETAILED DESCRIPTION

[0059] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions 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 part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0060] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0061] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0062] In the description of the embodiments of the present invention, it should be noted that if the terms "upper", "lower", "horizontal", "inner", etc. indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use, it is only for the convenience of describing the present invention and simplifying the description, and does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention. In addition, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0063] In addition, if the term "horizontal" appears, it does not mean that the component must be absolutely horizontal, but can be slightly tilted. For example, "horizontal" only means that its direction is more horizontal than "vertical", which does not mean that the structure must be completely horizontal, but can be slightly tilted.

[0064] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "install", "connect", and "connect" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0065] The present invention is further described in detail below in conjunction with the accompanying drawings:

[0066] See also Figure 1 The present invention discloses a method for predicting structural stability fatigue life based on critical plane stress damage parameters, comprising:

[0067] S101, perform a symmetrical tension-compression cycle fatigue test under strain control on a national standard fatigue standard rod specimen to obtain fatigue test data;

[0068] Fatigue test data include: elastic strain amplitude ε e,a And the fatigue life of the national standard fatigue standard rod specimen N f .

[0069] S102, obtaining a shear fatigue strength coefficient and a shear fatigue strength index of a material based on the obtained fatigue test data, the Manson-Coffin elastic strain line expression and the Kim conversion formula;

[0070]

[0071] Among them, σ′ f is the material fatigue strength coefficient, unit MPa; b is the material fatigue strength index, which is a dimensionless parameter; E is the elastic modulus, unit MPa; ε e,a is the elastic strain amplitude, dimensionless; N f is the fatigue life of the national standard fatigue standard rod specimen, that is, the number of cycles when fatigue failure occurs;

[0072] In the absence of torsion fatigue test conditions, the shear fatigue strength coefficient and shear fatigue strength index are obtained according to Kim's conversion formula;

[0073] τ′ f =0.63σ′ f

[0074] b0=b

[0075] Among them, τ′ f is the shear fatigue strength coefficient, and b0 is the shear fatigue strength index.

[0076] S103, based on the material shear fatigue strength coefficient, shear fatigue strength index and Dang Van fatigue criterion, a shakedown fatigue life prediction model is constructed;

[0077]

[0078] Among them, τ a,max is the maximum shear stress amplitude, unit: MPa; α DV is the Dang Van coefficient, a dimensionless constant; σ H is the hydrostatic stress, in MPa; a,max +α DV σ H is the damage parameter defined by the model; τ′ f is the shear fatigue strength coefficient, unit MPa; b0 is the shear fatigue strength index, which is a dimensionless material parameter; N sf is the structural stability fatigue life value;

[0079] Based on the torsional fatigue limit and tensile and compressive fatigue limit of the material, the Dang Van coefficient is obtained, which is:

[0080]

[0081] Among them, τ -1 is the torsional fatigue limit of the material; -1 is the tensile and compressive fatigue limit of the material;

[0082] The Dang Van fatigue criterion assumes that fatigue corresponds to the limit of elastic stability possibility of structural materials, assumes that elastic stability occurs at the macroscopic and microscopic scales, and believes that the elastic stability limit depends on the hydrostatic tension that occurs in the loading cycle; the Dang Van fatigue criterion believes that at the microscopic scale, the plastic deformation of grains on the characteristic slip bands in the critical volume inside the material leads to fatigue crack initiation, and shear stress and hydrostatic stress accelerate slip band generation and crack propagation; therefore, it is believed that the Dang Van fatigue criterion is not only very consistent with the critical plane stress method, but also applicable to the elastic stability state; the Dang Van fatigue criterion is specifically:

[0083] τ a,max +α DV σ H <τ -1

[0084] Among them, τa,max is the maximum shear stress amplitude, unit: MPa; σ H is the hydrostatic stress, unit: MPa; τ -1 is the torsional fatigue limit of the material, unit: MPa; α DV is the Dang Van coefficient, dimensionless;

[0085] The left side of the inequality τ a,max +α DV σ H Can be regarded as equivalent stress, denoted as σ eq ; σ ep From the shear stress amplitude τ a and hydrostatic stress σ H Combined with the critical plane stress method, σ ep Defined as the damage parameter of the structural stability fatigue life prediction model.

[0086] S104, performing a cyclic simulation on the target structural component under a shakedown load to obtain stress history data of the structural dangerous unit body in a complete cycle during the shakedown cycle process;

[0087] When performing cyclic simulation on the target structural member under the shakedown load, the shakedown load Fn takes a value range from the yield load of the structural dangerous point to the shakedown limit load of the structural dangerous point; the stress history data of the structural dangerous unit body in a complete cycle during the shakedown cycle are extracted, including: S11, S22, S33, S12, S13, S23; among them, S11, S22, S33, S12, S13, S23 are six independent stress components of the dangerous unit body; and then the stress history data of the independent stress components in a shakedown cycle period are obtained.

[0088] S105, obtaining damage parameters of a critical damage plane based on the stress history data;

[0089] In a stable cycle, the maximum damage parameter values ​​of different damage planes are different; the damage plane is Definition, the value range is as follows: θ∈[0°,180°]; where θ are the angles between the normal line of the damage plane and the Z axis and X axis respectively; There are 181×181 different combinations of , so the number of damage planes to be calculated is 181×181; in a stable cycle, the damage parameter value of each damage plane is related to time and reaches a maximum value at a certain moment. The maximum damage parameter value is taken as the representative value of the damage plane, and the representative values ​​of all damage planes are calculated in this way, totaling 181×181; finally, the size of the 181×181 representative values ​​is compared again, and the largest representative value is taken as the critical damage parameter of the dangerous unit of the structure under the stable cycle, denoted as σeq,max .

[0090] S106, obtaining a structural stability fatigue life value based on the stability fatigue life prediction model and the critical damage plane damage parameter.

[0091] σ eq,max Substituting into the shakedown fatigue life prediction model, we have:

[0092]

[0093] The final calculated structural stability fatigue life value N sf .

[0094] See also Figure 2 The present invention discloses a structural stability fatigue life prediction system based on critical plane stress damage parameters, comprising:

[0095] A test module, wherein the test module performs a symmetrical tension-compression cycle fatigue test under strain control on a national standard fatigue standard rod-shaped specimen to obtain fatigue test data;

[0096] A first acquisition module, which acquires a shear fatigue strength coefficient and a shear fatigue strength index of a material based on the acquired fatigue test data, a Manson-Coffin elastic strain line expression, and a Kim conversion formula;

[0097] A construction module, wherein the construction module constructs a shakedown fatigue life prediction model based on a material shear fatigue strength coefficient, a shear fatigue strength index and a DangVan fatigue criterion;

[0098] A cycle simulation module, wherein the cycle simulation module performs a cycle simulation on the target structural member under a stable load, and obtains stress history data of the structural dangerous unit body in a complete cycle during the stable cycle process;

[0099] A second acquisition module, wherein the second acquisition module acquires a critical damage plane damage parameter based on the stress history data;

[0100] The third acquisition module acquires the structural stability fatigue life value based on the stability fatigue life prediction model and the critical damage plane damage parameter.

[0101] Example:

[0102] The present invention predicts the stability fatigue life of specific structural parts through the structural stability fatigue life prediction model. The structural part is a plate-like structural part with a hollow center and a thickness of 2mm. The specific dimensions are as follows: Figure 3 (a) and Figure 3 (b) as shown:

[0103] The material of this structure is 20MnNiMo. The basic material parameters are obtained from the single tensile test. The yield limit is about 847MPa, the elastic modulus is about 201Gpa, and the tensile strength is about 1084MPa. Figure 4 As shown:

[0104] The specific steps for predicting the stable fatigue life value of the structural component are as follows:

[0105] 1. Clarify the prediction model of stable fatigue life. The stable fatigue life model is as follows:

[0106]

[0107] Among them, τ a,max is the maximum shear stress amplitude, unit: MPa; α DV is the Dang Van coefficient, a dimensionless constant; σ H is the hydrostatic stress, unit: MPa; τ′ f is the shear fatigue strength coefficient, unit MPa; b0 is the shear fatigue strength index, which is a dimensionless material parameter; N sf is the structural stability fatigue life value;

[0108] 2. Calculate critical plane model parameters for predicting structural stability fatigue life;

[0109] The national standard fatigue standard rod specimen was subjected to a symmetrical tension-compression cycle fatigue test under strain control. Four groups were conducted with strain amplitudes of 0.4%, 0.6%, 0.8%, and 1.0%, respectively. Finally, fatigue test data were obtained. The fatigue test data include: elastic strain amplitude ε e,a And the fatigue life of the national standard fatigue standard rod specimen N f .

[0110] Fitting σ′ via the Manson-Coffin elastic strain line expression f and b;

[0111]

[0112] Among them, σ′ f is the material fatigue strength coefficient, unit MPa; b is the material fatigue strength index, which is a dimensionless parameter; E is the elastic modulus, unit MPa; ε e,a is the elastic strain amplitude, dimensionless; the fitting results are shown in Figure 5 shown.

[0113] By calculation Figure 5 The vertical intercept and slope of the elastic strain line can be obtained as σ′ f =1970.64(MPa); b=-0.09;

[0114] Calculation of τ′ using Kim's transformation formula in the absence of torsional fatigue test conditions f , b0;

[0115] τ′ f =0.63σ′ f =1241.50 (MPa);

[0116] b0=b=-0.09;

[0117] The Dang Van coefficient was calculated by the following formula;

[0118]

[0119] Among them, τ -1 is the torsional fatigue limit of the material, in MPa; σ -1 is the tensile and compressive fatigue limit of the material, in MPa;

[0120] 3. Extract the stress history data of a complete cycle of the structural dangerous unit during the stability cycle; first use the simulation software to simulate the target structural part under the stability load for 50 cycles. Since the analyzed structural part is symmetrical up and down and left and right, a 1 / 4 model is used for simulation. The loading path is as follows: Figure 6 As shown in the figure, Fn is the peak value of the loading load, and its value range is from the yield load of the structural dangerous point to the stable limit load of the structural dangerous point. Within this range, it can ensure that the structural dangerous point reaches a stable state during the cycle. Here, the peak value of the loading load is 16000N, recorded as Fn = 16000N; the simulation results are shown in the figure. Figure 7 shown.

[0121] Depend on Figure 7 It can be seen that the structural danger point is located at the arc transition, and the maximum stress is 859MPa, which is greater than the material yield limit of 847MPa. At this time, the structural danger point enters the yield state and plastic deformation occurs. In order to ensure that the structural danger point reaches a stable state at this time, the equivalent plastic strain history data of the danger point in the unloading step (F=0N) is extracted. The results are as follows: Figure 8 As shown:

[0122] Depend on Figure 8It can be seen that after the structural danger point enters the yield stage, the equivalent plastic strain value first increases and then remains unchanged, and finally stabilizes at about 0.003. It can be seen that the structural danger point reaches a stable state in 50 cycles with a peak load of Fn=16000N, and Fn=16000N is the stable cycle load. Next, the stress history data of a complete cycle during the stability cycle of the structural dangerous unit body is extracted (here the 8th to 10th steps are extracted as a complete cycle), including: S11, S22, S33, S12, S13, S23. Among them, S11, S22, S33, S12, S13, S23 are six independent stress components of the dangerous unit body; the extraction results are as follows Fig. 9 shown.

[0123] 4. Calculate the critical damage parameter value and calculate the structural stability fatigue life;

[0124] The extracted stress history data is imported into the critical plane damage parameter calculation program to calculate the critical damage parameter value. The shakedown fatigue life model is as follows:

[0125]

[0126] Among them, the left side of the equation is τ a,max +α DV σ H The value of is the damage parameter, also known as the equivalent stress, denoted as σ eq ;

[0127] In a cycle, the maximum damage parameter values ​​of different damage planes are different. The damage plane is Definition, the value range is as follows: θ∈[0°,180°]; the damage plane and the coordinate axis are as follows Fig.10 As shown. Among them, θ are the angles between the normal line of the damage plane and the Z axis and X axis respectively; There are 181×181 different combinations of , so the number of damage planes to be calculated is 181×181; in one cycle, the damage parameter value of each damage plane is related to time and reaches a maximum value at a certain moment. The maximum damage parameter value is taken as the representative value of the damage plane, and so on to calculate the representative values ​​of all damage planes, a total of 181×181; finally, the size of the 181×181 representative values ​​is compared again, and the largest representative value is taken as the critical damage parameter of the structural dangerous unit under the stability cycle, recorded as σ eq,max , σ eq,max The damage plane where it is located is the critical plane; the above calculation characteristics are large amount of calculation and strong regularity, which can be realized through the calculation program; the stress history data of the structural dangerous unit extracted in step 3 in a complete cycle during the stability cycle are calculated and the results are as follows:

[0128] σ eq,max =393.98 (MPa);

[0129]

[0130] θ = 3°;

[0131] Finally, σ eq,max Bringing back the stable fatigue life prediction model, we have:

[0132] σ eq,max =τ a,max +α DV σ H =393.98=1241.50×(2N sf ) -0.09

[0133] The final calculated structural stability fatigue life value is:

[0134] N sf =10 5.2

[0135] The terminal device provided in an embodiment of the present invention. The terminal device of this embodiment includes: a processor, a memory, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, the steps in the above-mentioned method embodiments are implemented. Alternatively, when the processor executes the computer program, the functions of the modules / units in the above-mentioned device embodiments are implemented.

[0136] The computer program may be divided into one or more modules / units, and the one or more modules / units are stored in the memory and executed by the processor to accomplish the present invention.

[0137] The terminal device may be a computing device such as a desktop computer, a notebook, a PDA, a cloud server, etc. The terminal device may include, but is not limited to, a processor and a memory.

[0138] The processor can be a central processing unit (CPU), or other general-purpose processors, digital signal processors (DSP), application-specific integrated circuits (ASIC), field-programmable gate arrays (FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0139] The memory may be used to store the computer programs and / or modules, and the processor implements various functions of the terminal device by running or executing the computer programs and / or modules stored in the memory and calling the data stored in the memory.

[0140] If the module / unit integrated in the terminal device is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present invention implements all or part of the processes in the above-mentioned embodiment method, and can also be completed by instructing the relevant hardware through a computer program. The computer program can be stored in a computer-readable storage medium, and the computer program can implement the steps of the above-mentioned various method embodiments when executed by the processor. Among them, the computer program includes computer program code, and the computer program code can be in source code form, object code form, executable file or some intermediate form. The computer-readable medium may include: any entity or device capable of carrying the computer program code, recording medium, U disk, mobile hard disk, disk, optical disk, computer memory, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), electric carrier signal, telecommunication signal and software distribution medium. It should be noted that the content contained in the computer-readable medium can be appropriately increased or decreased according to the requirements of legislation and patent practice in the jurisdiction. For example, in some jurisdictions, according to legislation and patent practice, computer-readable media do not include electric carrier signals and telecommunication signals.

[0141] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, 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 structural stability fatigue life based on critical plane stress damage parameters, characterized in that: include: Conduct symmetrical tension-compression cycle fatigue tests under strain control on national standard fatigue rod specimens to obtain fatigue test data; Based on the acquired fatigue test data, Manson-Coffin elastic strain line expression and Kim conversion formula, the shear fatigue strength coefficient and shear fatigue strength index of the material are obtained; Based on the material shear fatigue strength coefficient, shear fatigue strength index and Dang Van fatigue criterion, a shakedown fatigue life prediction model is constructed; Perform cyclic simulation on the target structural parts under steady state load to obtain the stress history data of the dangerous structural unit in a complete cycle during the steady state cycle; Based on the stress history data, the damage parameters of the critical damage plane are obtained; Based on the shakedown fatigue life prediction model and the damage parameters of the critical damage plane, the structural shakedown fatigue life value is obtained.

2. The method for predicting structural stability fatigue life based on critical plane stress damage parameters according to claim 1 is characterized in that: The fatigue test data include: elastic strain amplitude ε e,a And the fatigue life of the national standard fatigue standard rod specimen N f .

3. The method for predicting structural stability fatigue life based on critical plane stress damage parameters according to claim 2 is characterized in that: Based on the obtained fatigue test data, the Manson-Coffin elastic strain line expression and the Kim conversion formula, the shear fatigue strength coefficient and the shear fatigue strength index of the material are obtained, specifically: Among them, σ′ f is the material fatigue strength coefficient, unit MPa; b is the material fatigue strength index, which is a dimensionless parameter; E is the elastic modulus, unit MPa; ε e,a is the elastic strain amplitude, dimensionless; N f is the fatigue life of the national standard fatigue standard rod specimen, that is, the number of cycles when fatigue failure occurs; In the absence of torsion fatigue test conditions, the shear fatigue strength coefficient and shear fatigue strength index are obtained according to Kim's conversion formula; the f =0.63σ′ f b0=b Among them, τ′ f is the shear fatigue strength coefficient, and b0 is the shear fatigue strength index.

4. The method for predicting structural stability fatigue life based on critical plane stress damage parameters according to claim 1, characterized in that: The shakedown fatigue life prediction model is constructed based on the material shear fatigue strength coefficient, shear fatigue strength index and Dang Van fatigue criterion, specifically: Among them, τ a,max is the maximum shear stress amplitude, unit: MPa; α DV is the Dang Van coefficient, a dimensionless constant; σ H is the hydrostatic stress, in MPa; a,max +α DV σ H is the damage parameter defined by the model; τ′ f is the shear fatigue strength coefficient, unit MPa; b0 is the shear fatigue strength index, which is a dimensionless material parameter; N sf is the structural stability fatigue life value; Based on the torsional fatigue limit and tensile and compressive fatigue limit of the material, the Dang Van coefficient is obtained, which is: Among them, τ -1 is the torsional fatigue limit of the material; -1 is the tensile and compressive fatigue limit of the material; The Dang Van fatigue criterion assumes that fatigue corresponds to the limit of elastic stability possibility of structural materials, assumes that elastic stability occurs at the macroscopic and microscopic scales, and believes that the elastic stability limit depends on the hydrostatic tension that occurs in the loading cycle; the Dang Van fatigue criterion believes that at the microscopic scale, the plastic deformation of grains on the characteristic slip bands in the critical volume inside the material leads to fatigue crack initiation, and shear stress and hydrostatic stress accelerate slip band generation and crack propagation; therefore, it is believed that the Dang Van fatigue criterion is not only very consistent with the critical plane stress method, but also applicable to the elastic stability state; the Dang Van fatigue criterion is specifically: t a,max +a DV s H <t -1 Among them, τ a,max is the maximum shear stress amplitude, unit: MPa; σ H is the hydrostatic stress, unit: MPa; τ -1 is the torsional fatigue limit of the material, unit: MPa; α DV is the Dang Van coefficient, dimensionless; The left side of the inequality τ a,max +α DV σ H Can be regarded as equivalent stress, denoted as σ eq ; σ eq From the shear stress amplitude τ a and hydrostatic stress σ H Combined with the critical plane stress method, σ eq Defined as the damage parameter of the structural stability fatigue life prediction model.

5. The method for predicting structural stability fatigue life based on critical plane stress damage parameters according to claim 4 is characterized in that: The method comprises performing a cyclic simulation under a shakedown load on a target structural part to obtain stress history data of a dangerous unit body of the structure in a complete cycle during the shakedown cycle, specifically: when performing a cyclic simulation under a shakedown load on a target structural part, a shakedown load Fn takes a value range from a yield load at a dangerous point of the structure to a shakedown limit load at a dangerous point of the structure; extracting stress history data of a dangerous unit body of the structure in a complete cycle during the shakedown cycle, including: S11, S22, S33, S12, S13, S23; wherein S11, S22, S33, S12, S13, S23 are six independent stress components of the dangerous unit body; and then obtaining stress history data of the independent stress components in a shakedown cycle period.

6. The method for predicting structural stability fatigue life based on critical plane stress damage parameters according to claim 5 is characterized in that: The damage parameters of the critical damage plane are obtained based on the stress history data, specifically: in a stable cycle, the maximum damage parameter values ​​of different damage planes are different; the damage plane is Definition, the value range is as follows: θ∈[0°,180°]; where θ are the angles between the normal line of the damage plane and the Z axis and X axis respectively; There are 181×181 different combinations of , so the number of damage planes to be calculated is 181×181; in a stable cycle, the damage parameter value of each damage plane is related to time and reaches a maximum value at a certain moment. The maximum damage parameter value is taken as the representative value of the damage plane, and the representative values ​​of all damage planes are calculated in this way, totaling 181×181; finally, the size of the 181×181 representative values ​​is compared again, and the largest representative value is taken as the critical damage parameter of the dangerous unit of the structure under the stable cycle, denoted as σ eq,max .

7. The method for predicting structural stability fatigue life based on critical plane stress damage parameters according to claim 6, characterized in that: The structure stability fatigue life value is obtained based on the stability fatigue life prediction model and the critical damage plane damage parameter, specifically: σ eq,max Substituting into the shakedown fatigue life prediction model, we have: The final calculated structural stability fatigue life value N sf .

8. A structural stability fatigue life prediction system based on critical plane stress damage parameters, characterized in that: include: A test module, wherein the test module performs a symmetrical tension-compression cycle fatigue test under strain control on a national standard fatigue standard rod-shaped specimen to obtain fatigue test data; A first acquisition module, which acquires a shear fatigue strength coefficient and a shear fatigue strength index of a material based on the acquired fatigue test data, a Manson-Coffin elastic strain line expression, and a Kim conversion formula; A construction module, wherein the construction module constructs a shakedown fatigue life prediction model based on a material shear fatigue strength coefficient, a shear fatigue strength index and a Dang Van fatigue criterion; A cycle simulation module, wherein the cycle simulation module performs a cycle simulation on the target structural member under a stable load, and obtains stress history data of the structural dangerous unit body in a complete cycle during the stable cycle process; A second acquisition module, wherein the second acquisition module acquires a critical damage plane damage parameter based on the stress history data; The third acquisition module acquires the structural stability fatigue life value based on the stability fatigue life prediction model and the critical damage plane damage parameter.

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