A fatigue fracture prediction method and system applicable to complex structures

Abstract

This invention discloses a fatigue fracture prediction method and system applicable to complex structures. The method includes: dividing the working condition of the region to be predicted into multiple sub-processes to obtain a sub-process set; determining the crack size at the current sub-process iteration number using the equivalent stress intensity factor and crack increment number at the current sub-process iteration number; updating the sub-process set; and performing the next iteration calculation on the sub-process set until the sub-process set is empty. This invention divides the working condition of the entire region to be predicted into multiple sub-processes and performs update and iteration calculations, thereby achieving the prediction of the fracture situation of complex structural regions under the entire working condition, filling the gap in existing technologies that cannot predict the fracture situation of complex structural regions.

Description

Technical Field

[0001] This invention relates to the field of fracture prediction and assessment technology, and in particular to a fatigue fracture prediction method and system applicable to complex structures. Background Technology

[0002] During the manufacturing, transportation, installation, and commissioning of nuclear power plants and chemical equipment, micro-cracks or defects may develop inside the equipment due to sand inclusions, impacts, and human-caused damage. During operation, the equipment is subjected to factors such as high temperature, high pressure, radiation, and corrosion, resulting in material damage, crack initiation, and propagation, such as fatigue crack propagation, ductile and brittle damage and crack propagation, and stress corrosion crack propagation. Simultaneously, as the equipment operates, the materials undergo aging and degradation. All of these factors can lead to service defects in nuclear power and chemical equipment. Whether initial defects before commissioning or cracks developed during service, both can affect the safe operation of the equipment, necessitating fracture prediction.

[0003] Currently, for simple structural regions, the stress intensity factor can be quickly calculated by looking up the influence coefficient and stress coefficient in tables, allowing for a single calculation to predict whether the structure will fracture. However, actual operating conditions are generally more complex. For nuclear power equipment such as steam generators (SG), the operation often involves multiple sub-processes such as heating, cooling, pressurization, and depressurization, each with multiple runs. For example, the heating sub-process may involve multiple heating operations. Cracks can propagate during these sub-processes, requiring analysis of crack propagation and fracture mechanics analysis and evaluation, which is currently lacking in technology. Therefore, existing technology cannot meet the requirements for predicting fracture conditions in complex structural regions. Summary of the Invention

[0004] The purpose of this invention is to provide a fatigue fracture prediction method and system applicable to complex structures, so as to fill the gap in the existing technology that cannot predict the fracture situation in complex structural regions.

[0005] To achieve the above objectives, the present invention provides the following solution:

[0006] A fatigue fracture prediction method applicable to complex structures, the method comprising:

[0007] Determine the set of subprocesses for the region to be predicted at the current subprocess iteration number;

[0008] Determine the equivalent stress intensity factor of each subprocess in the subprocess set under the current subprocess iteration number; the equivalent stress intensity factor includes: the first equivalent stress intensity factor of the deepest point of the crack front and the second equivalent stress intensity factor of the surface point of the crack front;

[0009] The first subprocess and the second subprocess are determined based on the equivalent stress intensity factor; the first subprocess is the subprocess with the largest first equivalent stress intensity factor, and the second subprocess is the subprocess with the smallest first equivalent stress intensity factor.

[0010] Determine the number of crack increments; the number of crack increments is the number of runs of the smaller subprocess; the smaller subprocess is the subprocess with the smaller number of runs between the first subprocess and the second subprocess;

[0011] The crack size under the current sub-process iteration number is determined based on the first sub-process, the second sub-process, and the crack increment number;

[0012] The smaller subprocess is removed from the subprocess set, and the execution count of the larger subprocess in the subprocess set is updated according to the number of crack increments; the larger subprocess is the subprocess with the larger execution count between the first subprocess and the second subprocess.

[0013] Determine whether the updated set of subprocesses is empty to obtain the first determination result;

[0014] If the first judgment result is yes, then determine whether the region to be predicted has fractured based on the crack size under the current subprocess iteration number;

[0015] If the first judgment result is negative, the updated subprocess set is used as the subprocess set for the next subprocess iteration number and iterated until the subprocess set is empty.

[0016] Optionally, determining the equivalent stress intensity factor of each subprocess in the subprocess set at the current subprocess iteration number specifically includes:

[0017] Obtain the constant properties of the region to be predicted; the constant properties include: structural dimensions, load, and material properties.

[0018] Based on the aforementioned constant properties, the stress coefficient is calculated using the finite element method;

[0019] Obtain the crack size after the previous sub-process iteration number; the crack size includes the first crack size at the deepest point and the second crack size at the surface point;

[0020] Based on the constant properties, the first crack size under the previous subprocess iteration number, and the second crack size under the previous subprocess iteration number, the influence coefficient of the deepest point and the influence coefficient of the surface point under the current subprocess iteration number are determined using the finite element method.

[0021] The first equivalent stress intensity factor for the current subprocess iteration number is determined based on the stress coefficient and the influence coefficient of the deepest point for the current subprocess iteration number, and the second equivalent stress intensity factor for the current subprocess iteration number is determined based on the stress coefficient and the influence coefficient of the surface point for the current subprocess iteration number.

[0022] Optionally, determining the crack size at the current sub-process iteration number based on the first sub-process, the second sub-process, and the crack increment number specifically includes:

[0023] The first equivalent stress intensity factor of the first sub-process is determined as the first maximum equivalent stress intensity factor, and the second equivalent stress intensity factor of the second sub-process is determined as the first minimum equivalent stress intensity factor;

[0024] The amplitude of the first equivalent stress intensity factor is determined based on the first maximum equivalent stress intensity factor and the first minimum equivalent stress intensity factor;

[0025] The first plastic equivalent stress intensity factor amplitude is obtained by plastic correction of the first equivalent stress intensity factor amplitude;

[0026] The first effective stress intensity factor amplitude is calculated based on the first maximum equivalent stress intensity factor, the first minimum equivalent stress intensity factor, and the first plastic equivalent stress intensity factor amplitude;

[0027] The first crack propagation rate is calculated based on the first effective stress intensity factor amplitude.

[0028] The first crack propagation amount under the current subprocess iteration number is determined based on the first propagation rate and the crack increment number;

[0029] The first crack size at the deepest point at the current subprocess iteration number is determined based on the first crack propagation amount at the current subprocess iteration number.

[0030] The second equivalent stress intensity factor of the first subprocess is determined as the second maximum equivalent stress intensity factor, and the second equivalent stress intensity factor of the second subprocess is determined as the second minimum equivalent stress intensity factor;

[0031] The amplitude of the second equivalent stress intensity factor is determined based on the second maximum equivalent stress intensity factor and the second minimum equivalent stress intensity factor;

[0032] The second equivalent stress intensity factor amplitude is obtained by plastic correction of the second equivalent stress intensity factor amplitude;

[0033] The second effective stress intensity factor amplitude is calculated based on the second maximum equivalent stress intensity factor, the second minimum equivalent stress intensity factor, and the second plastic equivalent stress intensity factor amplitude;

[0034] The second crack propagation rate is calculated based on the second effective stress intensity factor amplitude.

[0035] The second crack propagation amount under the current subprocess iteration number is determined based on the second propagation rate and the crack increment number;

[0036] The second crack size of the surface point at the current subprocess iteration number is determined based on the second crack propagation amount at the current subprocess iteration number.

[0037] Optionally, determining whether the region to be predicted has fractured based on the crack size at the current sub-process iteration number specifically includes:

[0038] Based on the constant attribute and the first crack size under the current subprocess iteration number, determine the first final influence coefficient of the deepest point; based on the constant attribute and the second crack size under the current subprocess iteration number, determine the second final influence coefficient of the surface point.

[0039] The first final equivalent stress intensity factor of the deepest point is determined based on the stress coefficient and the first final influence coefficient, and the second final equivalent stress intensity factor of the surface point is determined based on the stress coefficient and the second final influence coefficient.

[0040] The first final equivalent stress intensity factor is plastically corrected to obtain the first final plastic equivalent stress intensity factor, and the second final equivalent stress intensity factor is plastically corrected to obtain the second final plastic equivalent stress intensity factor.

[0041] Determine whether the first final plastic equivalent stress intensity factor and the second final plastic equivalent stress intensity factor meet the preset standard to obtain a second determination result;

[0042] If the second judgment result is yes, then the region to be predicted has not been broken;

[0043] If the second judgment result is negative, then the region to be predicted is fractured.

[0044] Optionally, the step of calculating the stress coefficient using the finite element method based on the constant property specifically includes:

[0045] Based on the constant properties, the stress is determined using the finite element method; the stress includes: normal stress, depth shear stress, and length shear stress.

[0046] The stress coefficient is obtained based on the stress fitting.

[0047] Optionally, determining the first equivalent stress intensity factor for the current subprocess iteration number based on the stress coefficient and the influence coefficient of the deepest point for the current subprocess iteration number specifically includes:

[0048] The first normal stress intensity factor is determined based on the stress coefficient of the normal stress at the deepest point and the influence coefficient of the deepest point; the first depth shear stress intensity factor is determined based on the stress coefficient of the depth shear stress at the deepest point and the influence coefficient of the deepest point; and the first length shear stress intensity factor is determined based on the stress coefficient of the length shear stress at the deepest point and the influence coefficient of the deepest point.

[0049] The first equivalent stress intensity factor is calculated based on the first normal stress intensity factor, the first depth shear stress intensity factor, and the first length shear stress intensity factor for the current subprocess iteration number.

[0050] Optionally, determining the second equivalent stress intensity factor for the current subprocess iteration number based on the stress coefficient and the influence coefficient of the surface point for the current subprocess iteration number specifically includes:

[0051] The second normal stress intensity factor is determined based on the stress coefficient of the normal stress at the surface point and the influence coefficient of the surface point; the second depth shear stress intensity factor is determined based on the stress coefficient of the depth shear stress at the surface point and the influence coefficient of the surface point; and the second length shear stress intensity factor is determined based on the stress coefficient of the length shear stress at the surface point and the influence coefficient of the surface point.

[0052] The second equivalent stress intensity factor is calculated based on the second normal stress intensity factor, the second depth shear stress intensity factor, and the second length shear stress intensity factor.

[0053] A fatigue fracture prediction system applicable to complex structures, the system comprising:

[0054] The subprocess set determination module is used to determine the subprocess set of the region to be predicted at the current subprocess iteration number;

[0055] The equivalent stress intensity factor determination module is used to determine the equivalent stress intensity factor of each subprocess in the subprocess set under the current subprocess iteration number; the equivalent stress intensity factor includes: the first equivalent stress intensity factor of the deepest point of the crack front and the second equivalent stress intensity factor of the surface point of the crack front;

[0056] The subprocess determination module is used to determine a first subprocess and a second subprocess based on the equivalent stress intensity factor; the first subprocess is the subprocess with the largest first equivalent stress intensity factor, and the second subprocess is the subprocess with the smallest first equivalent stress intensity factor;

[0057] A crack increment count determination module is used to determine the crack increment count; the crack increment count is the number of times the smaller subprocess is run; the smaller subprocess is the subprocess with the smaller number of runs between the first subprocess and the second subprocess;

[0058] A crack size determination module is used to determine the crack size under the current sub-process iteration number based on the first sub-process, the second sub-process, and the crack increment number;

[0059] The subprocess set update module is used to delete the smaller subprocess from the subprocess set and update the execution count of the larger subprocess in the subprocess set according to the number of crack increments; the larger subprocess is the subprocess with the larger execution count between the first subprocess and the second subprocess.

[0060] The first judgment module is used to determine whether the updated sub-process set is an empty set and obtain the first judgment result;

[0061] The fracture determination module is used to determine whether the region to be predicted has fractured based on the crack size under the current subprocess iteration number if the first judgment result is yes.

[0062] An iteration module is used to iterate the updated subprocess set as the subprocess set for the next subprocess iteration number if the first judgment result is negative, until the subprocess set is empty.

[0063] Optionally, the equivalent stress intensity factor determination module specifically includes:

[0064] A constant attribute acquisition unit is used to acquire the constant attributes of the region to be predicted; the constant attributes include: structural dimensions, load, and material properties.

[0065] The stress coefficient calculation unit is used to calculate the stress coefficient using the finite element method based on the constant properties.

[0066] A crack size acquisition unit is used to acquire the crack size after the previous subprocess iteration number; the crack size includes the first crack size at the deepest point and the second crack size at the surface point;

[0067] The influence coefficient determination unit is used to determine the influence coefficient of the deepest point and the influence coefficient of the surface point at the current subprocess iteration number based on the constant attribute, the first crack size at the previous subprocess iteration number, and the second crack size at the previous subprocess iteration number, using the finite element method.

[0068] The equivalent stress intensity factor determination unit is used to determine the first equivalent stress intensity factor under the current subprocess iteration number based on the stress coefficient and the influence coefficient of the deepest point under the current subprocess iteration number, and to determine the second equivalent stress intensity factor under the current subprocess iteration number based on the stress coefficient and the influence coefficient of the surface point under the current subprocess iteration number.

[0069] Optionally, the crack size determination module specifically includes:

[0070] The first maximum equivalent stress intensity factor determination unit is used to determine the first equivalent stress intensity factor of the first subprocess as the first maximum equivalent stress intensity factor, and the second equivalent stress intensity factor of the second subprocess as the first minimum equivalent stress intensity factor;

[0071] The first equivalent stress intensity factor amplitude determination unit is used to determine the first equivalent stress intensity factor amplitude based on the first maximum equivalent stress intensity factor and the first minimum equivalent stress intensity factor;

[0072] The first correction unit is used to plastically correct the first equivalent stress intensity factor amplitude to obtain the first plastic equivalent stress intensity factor amplitude.

[0073] The first effective stress intensity factor amplitude calculation unit is used to calculate the first effective stress intensity factor amplitude based on the first maximum equivalent stress intensity factor, the first minimum equivalent stress intensity factor and the first plastic equivalent stress intensity factor amplitude.

[0074] The first crack propagation rate calculation unit is used to calculate the first crack propagation rate based on the first effective stress intensity factor amplitude.

[0075] The first crack propagation determination unit is used to determine the first crack propagation amount under the current subprocess iteration number based on the first propagation rate and the number of crack increments.

[0076] The first crack size determination unit is used to determine the first crack size of the deepest point at the current subprocess iteration number based on the first crack propagation amount at the current subprocess iteration number.

[0077] The second maximum equivalent stress intensity factor determination unit is used to determine the second equivalent stress intensity factor of the first subprocess as the second maximum equivalent stress intensity factor and to determine the second equivalent stress intensity factor of the second subprocess as the second minimum equivalent stress intensity factor.

[0078] The second equivalent stress intensity factor amplitude determination unit is used to determine the second equivalent stress intensity factor amplitude based on the second maximum equivalent stress intensity factor and the second minimum equivalent stress intensity factor;

[0079] The second correction unit is used to plastically correct the second equivalent stress intensity factor amplitude to obtain the second plastic equivalent stress intensity factor amplitude;

[0080] The second effective stress intensity factor amplitude calculation unit is used to calculate the second effective stress intensity factor amplitude based on the second maximum equivalent stress intensity factor, the second minimum equivalent stress intensity factor and the second plastic equivalent stress intensity factor amplitude;

[0081] The second crack propagation rate calculation unit is used to calculate the second crack propagation rate based on the second effective stress intensity factor amplitude.

[0082] The second crack propagation determination unit is used to determine the second crack propagation amount under the current subprocess iteration number based on the second propagation rate and the crack increment number.

[0083] The second crack size determination unit is used to determine the second crack size of the surface point at the current subprocess iteration number based on the second crack propagation amount at the current subprocess iteration number.

[0084] According to specific embodiments provided by the present invention, the present invention discloses the following technical effects:

[0085] This invention discloses a fatigue fracture prediction method and system applicable to complex structures. The method divides the working conditions of the entire region to be predicted into multiple sub-processes and performs update and iterative calculations, thereby realizing the prediction of the fracture situation of the complex structural region under the entire working conditions, filling the gap in the existing technology that cannot predict the fracture situation of complex structural regions. Attached Figure Description

[0086] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0087] Figure 1This is a schematic diagram of the fatigue fracture prediction method for complex structures provided in an embodiment of the present invention;

[0088] Figure 2 A structural diagram of a fatigue fracture prediction system for complex structures provided in an embodiment of the present invention. Detailed Implementation

[0089] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0090] The purpose of this invention is to provide a fatigue fracture prediction method and system applicable to complex structures, aiming to fill the gap in the existing technology that cannot predict the fracture situation in complex structural regions, and can be applied to the field of fracture prediction and evaluation technology.

[0091] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0092] Figure 1 This is a schematic diagram of a fatigue fracture prediction method for complex structures provided in an embodiment of the present invention. Figure 1 As shown in this embodiment, the fatigue fracture prediction method applicable to complex structures includes:

[0093] Step 101: Determine the set of subprocesses for the region to be predicted at the current subprocess iteration number.

[0094] Step 102: Determine the equivalent stress intensity factor of each subprocess in the subprocess set under the current subprocess iteration number. The equivalent stress intensity factor includes: the first equivalent stress intensity factor at the deepest point of the crack front and the second equivalent stress intensity factor at the surface point of the crack front.

[0095] Step 103: Determine the first subprocess and the second subprocess based on the equivalent stress intensity factor. The first subprocess is the one with the largest first equivalent stress intensity factor, and the second subprocess is the one with the smallest first equivalent stress intensity factor.

[0096] Step 104: Determine the number of crack increments. The number of crack increments is the number of times the smaller subprocess is run; the smaller subprocess is the subprocess with the fewer runs in the first and second subprocesses.

[0097] Step 105: Determine the crack size under the current sub-process iteration number based on the first sub-process, the second sub-process, and the crack increment number.

[0098] Step 106: Remove the smaller subprocess from the subprocess set, and update the execution count of the larger subprocess in the subprocess set according to the number of crack increments. The larger subprocess is the one that has the larger execution count among the first and second subprocesses.

[0099] Step 107: Determine whether the updated subprocess set is an empty set to obtain the first judgment result.

[0100] If the first judgment result is yes, then determine whether the region to be predicted has fractured based on the crack size under the current subprocess iteration number.

[0101] If the first judgment result is negative, the updated subprocess set will be used as the subprocess set for the next subprocess iteration number and iterated until the subprocess set is empty.

[0102] As an optional implementation, step 102 specifically includes:

[0103] Obtain the constant properties of the region to be predicted; constant properties include: structural dimensions, loads, and material properties.

[0104] The stress coefficient is calculated using the finite element method based on constant properties.

[0105] Obtain the crack size after the previous subprocess iteration number; the crack size includes the first crack size at the deepest point and the second crack size at the surface point.

[0106] Based on constant properties, the first crack size under the previous subprocess iteration number, and the second crack size under the previous subprocess iteration number, the influence coefficient of the deepest point and the influence coefficient of the surface point under the current subprocess iteration number are determined using the finite element method.

[0107] In existing technologies, for simple structural regions, the stress intensity factor can be quickly calculated by looking up the influence coefficient and stress coefficient in a table, thus predicting whether the structure will fracture after a single calculation. However, for complex regions, such as discontinuous structural regions, there is a lack of records for the influence coefficient. This invention solves the problem of the lack of application of influence coefficients for complex structural regions in existing technologies.

[0108] The first equivalent stress intensity factor for the current subprocess iteration number is determined based on the stress coefficient and the influence coefficient of the deepest point under the current subprocess iteration number. The second equivalent stress intensity factor for the current subprocess iteration number is determined based on the stress coefficient and the influence coefficient of the surface point under the current subprocess iteration number.

[0109] Specifically, within the same region, the stress coefficient is the same at any location. Therefore, the stress coefficient at the deepest point is the same as the stress coefficient at the surface point, and both are calculated using the following formula:

[0110]

[0111] Where t is the wall thickness, u is the distance from the test point to the surface, 0≤u≤t, σ is the stress at the test point, and σ0, σ1, σ2 and σ3 are stress coefficients.

[0112] Specifically, the calculation steps for the first and second equivalent stress intensity factors are as follows:

[0113] The first stress intensity factor is determined based on the stress coefficient and the influence coefficient of the deepest point, and the second stress intensity factor is determined based on the stress coefficient and the influence coefficient of the surface point.

[0114] First stress intensity factor K A Second stress intensity factor K C The calculation formulas are as follows:

[0115]

[0116]

[0117] Where a is the crack depth, c is the crack half-width, t is the wall thickness, and i 0A i 1A i 2A and i 3A All are the influence coefficients of the deepest point, i 0C i 1C i 2C and i 3C All are influence coefficients for surface points.

[0118] Because the stress at each location includes normal stress, depth shear stress, and length shear stress, therefore, when σ is the normal stress perpendicular to the crack surface, i.e., the normal stress, K A =K A1 K C =K C1 .

[0119] When σ is the shear stress parallel to the crack surface and pointing towards the crack depth, i.e., the depth shear stress, K A =K A2 K C =K C2 .

[0120] When σ is the shear stress parallel to the crack surface and pointing towards the crack length, i.e., the length shear stress, K A =K A3 KC =K C3 .

[0121] Among them, K A1 K is the first normal stress intensity factor. C1 K is the second normal stress intensity factor. A2 K is the shear stress intensity factor at the first depth. C2 K is the second depth shear stress intensity factor. A3 K is the first length shear stress intensity factor. C3 This is the second length shear stress intensity factor.

[0122] The first equivalent stress intensity factor K is calculated using the following two formulas. eqA Second equivalent stress intensity factor K eqC :

[0123]

[0124] Where v is Poisson's ratio.

[0125] As an optional implementation, step 105 specifically includes:

[0126] The first equivalent stress intensity factor of the first subprocess is determined as the first maximum equivalent stress intensity factor, and the second equivalent stress intensity factor of the second subprocess is determined as the first minimum equivalent stress intensity factor.

[0127] The amplitude of the first equivalent stress intensity factor is determined based on the first maximum equivalent stress intensity factor and the first minimum equivalent stress intensity factor.

[0128] The first plastic equivalent stress intensity factor amplitude is obtained by plastic correction of the first equivalent stress intensity factor amplitude.

[0129] The first effective stress intensity factor amplitude is calculated based on the first maximum equivalent stress intensity factor, the first minimum equivalent stress intensity factor, and the first plastic equivalent stress intensity factor amplitude.

[0130] The first crack propagation rate is calculated based on the first effective stress intensity factor amplitude.

[0131] The first crack propagation amount is determined based on the first propagation rate and the number of crack increments.

[0132] The size of the first crack at the deepest point is determined based on the first crack propagation amount at the current subprocess iteration number.

[0133] The second equivalent stress intensity factor of the first subprocess is determined as the second maximum equivalent stress intensity factor, and the second equivalent stress intensity factor of the second subprocess is determined as the second minimum equivalent stress intensity factor.

[0134] The amplitude of the second equivalent stress intensity factor is determined based on the second maximum equivalent stress intensity factor and the second minimum equivalent stress intensity factor.

[0135] The second plastic equivalent stress intensity factor amplitude is obtained by plastic correction of the second equivalent stress intensity factor amplitude.

[0136] The second effective stress intensity factor amplitude is calculated based on the second maximum equivalent stress intensity factor, the second minimum equivalent stress intensity factor, and the second plastic equivalent stress intensity factor amplitude.

[0137] The second crack propagation rate is calculated based on the second effective stress intensity factor amplitude.

[0138] The second crack propagation amount is determined based on the second propagation rate and the number of crack increments, according to the current number of subprocess iterations.

[0139] The second crack size at the surface point is determined based on the second crack propagation amount at the current subprocess iteration number.

[0140] Specifically, the first crack size at the deepest point and the second crack size at the surface point under the current subprocess iteration number constitute the crack size under the current subprocess iteration number.

[0141] Specifically, the following two formulas are used to apply the first final equivalent stress intensity factor K′. eqA Second final equivalent stress intensity factor K′ eqC Plasticity correction is performed to obtain the first final plastic equivalent stress intensity factor K. cpA Second final plastic equivalent stress intensity factor K cpC :

[0142]

[0143] Where, r yA The radius of the first plastic zone at the deepest point. S yA α is the yield stress value at the crack tip, and α is the first correction factor, obtained from Table 1.

[0144] Table 1α Lookup Table

[0145]

[0146] Specifically, the first maximum equivalent stress intensity factor K eqAmax The corresponding first maximum normal stress intensity factor, first maximum depth shear stress intensity factor, and first maximum length shear stress intensity factor are denoted as K. A1max K A2max and KA3max The first minimum equivalent stress intensity factor K eqAmin The corresponding first minimum normal stress intensity factor, first minimum depth shear stress intensity factor, and first minimum length shear stress intensity factor are denoted as K. A1min K A2min and K A3min Therefore, the amplitude of the first normal stress intensity factor ΔK at the deepest point is... A1 First depth shear stress intensity factor amplitude ΔK A2 and the amplitude of the first length shear stress intensity factor ΔK A3 They are respectively:

[0147] ΔK A1 =|K A1max -K A1min |,ΔK A2 =|K A2max -K A2min |,ΔK A3 =|K A3max -K A3min |

[0148] Therefore, the amplitude of the first equivalent stress intensity factor ΔK at the deepest point eqA The calculation formula is:

[0149]

[0150] The second maximum equivalent stress intensity factor K eqCmax The corresponding second maximum normal stress intensity factor, second maximum depth shear stress intensity factor, and second maximum length shear stress intensity factor are denoted as K, respectively. C1max K C2max and K C3max The second minimum equivalent stress intensity factor K eqCmin The corresponding second minimum normal stress intensity factor, second minimum depth shear stress intensity factor, and second minimum length shear stress intensity factor are denoted as K, respectively. C1min K C2min and K C3min Therefore, the amplitude of the second normal stress intensity factor ΔK at the surface point C1 Second depth shear stress intensity factor amplitude ΔK C2 Second length shear stress intensity factor amplitude ΔK C3 They are respectively:

[0151] ΔK C1 =|K C1max -K C1min |,ΔK C2 =|K C2max -K C2min |,ΔK A3 =|KC3max -K C3min |

[0152] Therefore, the second equivalent stress intensity factor amplitude ΔK at the surface point eqC The calculation formula is:

[0153]

[0154] For the first equivalent stress intensity factor amplitude ΔK eqA Plastic correction yields the amplitude ΔK of the first plastic equivalent stress intensity factor at the deepest point. cpA for: For the second equivalent stress intensity factor amplitude ΔK eqC The second plastic equivalent stress intensity factor amplitude ΔK is obtained by performing plastic correction on the surface points. cpC for:

[0155] Where, r′ yA The radius of the second plastic zone at the deepest point. S yA (m) and S yA (n) represents the yield stress value of the material at the crack tip temperature in the first subprocess m and the second subprocess n, respectively. This temperature depends on the temperature corresponding to the extreme moment in the calculation in the first subprocess m and the second subprocess n.

[0156] β is the second correction coefficient, obtained from Table 2.

[0157] Table 2 shows the β lookup table.

[0158]

[0159] First effective stress intensity factor amplitude ΔK effA Second effective stress intensity factor amplitude ΔK effC The calculation formulas are as follows:

[0160] ΔK effA =f(R) A )ΔK cpA ΔK effC =f(R) C )ΔK cpC .

[0161] Where, f(R) A ) represents the first coefficient of the deepest point. f(R C ) is the second coefficient of the surface point.

[0162] First crack propagation rate Second crack propagation rate The calculation formulas are as follows:

[0163]

[0164] Where Q and n are constants related to materials and environment, and N is the number of cross-loops between the first subprocess m and the second subprocess n, i.e., the current loop count, N = min(N m N n ), N m and N n These are the number of iterations for the first sub-process m and the second sub-process n, respectively. The current iteration count is the smaller of the number of iterations for the first sub-process m and the second sub-process n.

[0165] The formulas for calculating the first crack propagation Δa and the second crack propagation Δc are as follows:

[0166]

[0167] The update formulas for the first crack size and the second crack size are as follows:

[0168] a′=a+Δa,c'=c+Δc.

[0169] Where a' is the updated first crack size, and c' = c + Δc is the updated second crack size.

[0170] The update formulas for the number of iterations in the first and second cycles are:

[0171] N″ m =N' m -N',N″ n =N' n -N″.

[0172] Among them, N' m N' represents the number of the first loop before the update. m The initial value is N m N' is the number of crossover loops before the first loop count is updated, N″ m N' represents the number of the first iteration after the update. n N' is the number of the second loop before the update. n The initial value is N n N″ is the number of crossover iterations after the first iteration count is updated. n This represents the number of iterations in the updated second loop.

[0173] As an optional implementation, step 108 specifically includes:

[0174] Based on the constant properties and the first crack size under the current subprocess iteration number, determine the first final influence coefficient of the deepest point; based on the constant properties and the second crack size under the current subprocess iteration number, determine the second final influence coefficient of the surface point.

[0175] The first final equivalent stress intensity factor of the deepest point is determined based on the stress coefficient and the first final influence coefficient, and the second final equivalent stress intensity factor of the surface point is determined based on the stress coefficient and the second final influence coefficient.

[0176] The first final equivalent stress intensity factor is obtained by plastic correction of the first final equivalent stress intensity factor, and the second final equivalent stress intensity factor is obtained by plastic correction of the second final equivalent stress intensity factor.

[0177] Determine whether the first final plastic equivalent stress intensity factor and the second final plastic equivalent stress intensity factor meet the preset standard, and obtain the second judgment result.

[0178] If the second judgment result is yes, then the region to be predicted has not been broken.

[0179] If the second judgment result is negative, then the region to be predicted will be fractured.

[0180] Specifically, the criteria for determining whether a breakage has occurred are as follows:

[0181] As long as K′ eqA ≤K IC / SF or K′ eqC ≤K IC If any one of the formulas in / SF is not satisfied, the structure will break. Where K... IC SF represents fracture toughness, and SF is the safety factor.

[0182] As an optional implementation method, the stress coefficient is calculated using the finite element method based on constant properties, specifically including:

[0183] Based on constant properties, stress is determined using the finite element method; stress includes: normal stress, depth shear stress, and length shear stress.

[0184] The stress coefficients are obtained by stress fitting.

[0185] As an optional implementation, the first equivalent stress intensity factor for the current subprocess iteration number is determined based on the stress coefficient and the influence coefficient of the deepest point at the current subprocess iteration number, specifically including:

[0186] The first normal stress intensity factor is determined based on the stress coefficient of the normal stress at the deepest point and the influence coefficient of the deepest point. The first depth shear stress intensity factor is determined based on the stress coefficient of the depth shear stress at the deepest point and the influence coefficient of the deepest point. The first length shear stress intensity factor is determined based on the stress coefficient of the length shear stress at the deepest point and the influence coefficient of the deepest point.

[0187] The first equivalent stress intensity factor is calculated based on the first normal stress intensity factor, the first depth shear stress intensity factor, and the first length shear stress intensity factor for the current subprocess iteration number.

[0188] As an optional implementation, the second equivalent stress intensity factor for the current subprocess iteration number is determined based on the stress coefficient and the influence coefficient of the surface point for the current subprocess iteration number, specifically including:

[0189] The second normal stress intensity factor is determined based on the stress coefficient of the normal stress at the surface point and the influence coefficient of the surface point. The second depth shear stress intensity factor is determined based on the stress coefficient of the depth shear stress at the surface point and the influence coefficient of the surface point. The second length shear stress intensity factor is determined based on the stress coefficient of the length shear stress at the surface point and the influence coefficient of the surface point.

[0190] The second equivalent stress intensity factor is calculated based on the second normal stress intensity factor, the second depth shear stress intensity factor, and the second length shear stress intensity factor.

[0191] Figure 2 A structural diagram of a fatigue fracture prediction system suitable for complex structures provided in an embodiment of the present invention. Figure 2 As shown, the present invention also provides a fatigue fracture prediction system suitable for complex structures, the system comprising:

[0192] The subprocess set determination module 201 is used to determine the subprocess set of the region to be predicted at the current subprocess iteration number.

[0193] The equivalent stress intensity factor determination module 202 is used to determine the equivalent stress intensity factor of each subprocess in the subprocess set under the current subprocess iteration number; the equivalent stress intensity factor includes: the first equivalent stress intensity factor of the deepest point of the crack front and the second equivalent stress intensity factor of the surface point of the crack front.

[0194] The subprocess determination module 203 is used to determine the first subprocess and the second subprocess based on the equivalent stress intensity factor; the first subprocess is the subprocess with the largest first equivalent stress intensity factor, and the second subprocess is the subprocess with the smallest first equivalent stress intensity factor.

[0195] The crack increment count determination module 204 is used to determine the crack increment count; the crack increment count is the number of times the smaller subprocess runs; the smaller subprocess is the subprocess with the smaller number of runs in the first subprocess and the second subprocess.

[0196] The crack size determination module 205 is used to determine the crack size under the current subprocess iteration number based on the first subprocess, the second subprocess, and the crack increment number;

[0197] The subprocess set update module 206 is used to delete smaller subprocesses from the subprocess set and update the number of runs of larger subprocesses in the subprocess set according to the number of crack increments; the larger subprocess is the subprocess with the larger number of runs in the first and second subprocesses.

[0198] The fracture determination and return module 207 is used to determine whether the updated subprocess set is an empty set and obtain the first determination result.

[0199] If the first judgment result is negative, then the crack size under the current subprocess iteration number determines whether the region to be predicted has fractured.

[0200] If the first judgment result is negative, the updated subprocess set will be used as the subprocess set for the next subprocess iteration number and iterated until the subprocess set is empty.

[0201] As an optional implementation, the equivalent stress intensity factor determination module 202 specifically includes:

[0202] The constant attribute acquisition unit is used to acquire the constant attributes of the region to be predicted; the constant attributes include: structural dimensions, loads, and material properties.

[0203] The stress coefficient calculation unit is used to calculate the stress coefficient using the finite element method based on constant properties.

[0204] The crack size acquisition unit is used to acquire the crack size after the previous subprocess iteration number; the crack size includes the first crack size at the deepest point and the second crack size at the surface point.

[0205] The influence coefficient determination unit is used to determine the influence coefficient of the deepest point and the influence coefficient of the surface point at the current subprocess iteration number based on constant properties, the first crack size at the previous subprocess iteration number, and the second crack size at the previous subprocess iteration number, using the finite element method.

[0206] The equivalent stress intensity factor determination unit is used to determine the first equivalent stress intensity factor under the current subprocess iteration number based on the stress coefficient and the influence coefficient of the deepest point under the current subprocess iteration number, and to determine the second equivalent stress intensity factor under the current subprocess iteration number based on the stress coefficient and the influence coefficient of the surface point under the current subprocess iteration number.

[0207] As an optional implementation, the crack size determination module 205 specifically includes:

[0208] The first maximum equivalent stress intensity factor determination unit is used to determine the first equivalent stress intensity factor of the first subprocess as the first maximum equivalent stress intensity factor and the second equivalent stress intensity factor of the second subprocess as the first minimum equivalent stress intensity factor.

[0209] The first equivalent stress intensity factor amplitude determination unit is used to determine the first equivalent stress intensity factor amplitude based on the first maximum equivalent stress intensity factor and the first minimum equivalent stress intensity factor.

[0210] The first correction unit is used to plastically correct the first equivalent stress intensity factor amplitude to obtain the first plastic equivalent stress intensity factor amplitude.

[0211] The first effective stress intensity factor amplitude calculation unit is used to calculate the first effective stress intensity factor amplitude based on the first maximum equivalent stress intensity factor, the first minimum equivalent stress intensity factor, and the first plastic equivalent stress intensity factor amplitude.

[0212] The first crack propagation rate calculation unit is used to calculate the first crack propagation rate based on the first effective stress intensity factor amplitude.

[0213] The first crack propagation determination unit is used to determine the first crack propagation amount under the current subprocess iteration number based on the first propagation rate and the number of crack increments.

[0214] The first crack size determination unit is used to determine the first crack size of the deepest point under the current subprocess iteration number based on the first crack propagation amount under the current subprocess iteration number.

[0215] The second maximum equivalent stress intensity factor determination unit is used to determine the second equivalent stress intensity factor of the first subprocess as the second maximum equivalent stress intensity factor and to determine the second equivalent stress intensity factor of the second subprocess as the second minimum equivalent stress intensity factor.

[0216] The second equivalent stress intensity factor amplitude determination unit is used to determine the second equivalent stress intensity factor amplitude based on the second maximum equivalent stress intensity factor and the second minimum equivalent stress intensity factor.

[0217] The second correction unit is used to plastically correct the second equivalent stress intensity factor amplitude to obtain the second plastic equivalent stress intensity factor amplitude.

[0218] The second effective stress intensity factor amplitude calculation unit is used to calculate the second effective stress intensity factor amplitude based on the second maximum equivalent stress intensity factor, the second minimum equivalent stress intensity factor, and the second plastic equivalent stress intensity factor amplitude.

[0219] The second crack propagation rate calculation unit is used to calculate the second crack propagation rate based on the second effective stress intensity factor amplitude.

[0220] The second crack propagation determination unit is used to determine the second crack propagation amount under the current subprocess iteration number based on the second propagation rate and the number of crack increments.

[0221] The second crack size determination unit is used to determine the second crack size of the surface point at the current subprocess iteration number based on the second crack propagation amount at the current subprocess iteration number.

[0222] In practical use, the number of times each subprocess is run can be set according to actual needs, and the lifespan of complex structures can be evaluated based on the fracture prediction results.

[0223] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the systems disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the descriptions are relatively simple; relevant parts can be referred to the method section.

[0224] This document uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the device and core ideas of the present invention. Furthermore, those skilled in the art will recognize that, based on the ideas of the present invention, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for fatigue fracture prediction suitable for complex structures, characterized by, The method comprises: determining a sub-process set of a current sub-process iteration number of a region to be predicted; determining equivalent stress intensity factors of each sub-process in the sub-process set of the current sub-process iteration number; the equivalent stress intensity factors comprise a first equivalent stress intensity factor of a deepest point of a crack front and a second equivalent stress intensity factor of a surface point of the crack front; determining a first sub-process and a second sub-process according to the equivalent stress intensity factors; the first sub-process is a sub-process with the maximum first equivalent stress intensity factor, and the second sub-process is a sub-process with the minimum first equivalent stress intensity factor; determining a crack increment number; the crack increment number is a running number of a smaller sub-process; the smaller sub-process is a sub-process with a smaller running number in the first sub-process and the second sub-process; determining a crack size of the current sub-process iteration number according to the first sub-process, the second sub-process and the crack increment number; deleting the smaller sub-process from the sub-process set and updating a running number of a larger sub-process in the sub-process set according to the crack increment number; the larger sub-process is a sub-process with a larger running number in the first sub-process and the second sub-process; judging whether the updated sub-process set is an empty set to obtain a first judgment result; if the first judgment result is yes, determining whether the region to be predicted is fractured according to the crack size of the current sub-process iteration number; if the first judgment result is no, iterating the updated sub-process set as a sub-process set of a next sub-process iteration number until the sub-process set is empty.

2. The fatigue fracture prediction method for complex structures according to claim 1, characterized in that, The determination of the equivalent stress intensity factors of each sub-process in the sub-process set of the current sub-process iteration number specifically comprises: obtaining constant attributes of the region to be predicted; the constant attributes comprise structure size, load and material attribute; calculating a stress coefficient by using a finite element method according to the constant attributes; obtaining a crack size of a previous sub-process iteration number; the crack size comprises a first crack size of the deepest point and a second crack size of the surface point; determining an influence coefficient of the deepest point of the current sub-process iteration number and an influence coefficient of the surface point of the current sub-process iteration number by using the finite element method according to the constant attributes, the first crack size of the previous sub-process iteration number and the second crack size of the previous sub-process iteration number; determining the first equivalent stress intensity factor of the current sub-process iteration number according to the stress coefficient and the influence coefficient of the deepest point of the current sub-process iteration number, and determining the second equivalent stress intensity factor of the current sub-process iteration number according to the stress coefficient and the influence coefficient of the surface point of the current sub-process iteration number.

3. The fatigue fracture prediction method for complex structures according to claim 1, characterized in that, The determination of the crack size of the current sub-process iteration number according to the first sub-process, the second sub-process and the crack increment number specifically comprises: determining the first equivalent stress intensity factor of the first sub-process as a first maximum equivalent stress intensity factor, and determining the second equivalent stress intensity factor of the second sub-process as a first minimum equivalent stress intensity factor; determining a first equivalent stress intensity factor amplitude according to the first maximum equivalent stress intensity factor and the first minimum equivalent stress intensity factor; performing plastic correction on the first equivalent stress intensity factor amplitude to obtain a first plastic equivalent stress intensity factor amplitude; calculating a first effective stress intensity factor amplitude according to the first maximum equivalent stress intensity factor, the first minimum equivalent stress intensity factor and the first plastic equivalent stress intensity factor amplitude; calculating a first crack propagation rate according to the first effective stress intensity factor amplitude; determining a first crack propagation amount at the current sub-process iteration number according to the first propagation rate and the crack increment number; determining a first crack size of the deepest point at the current sub-process iteration number according to the first crack propagation amount at the current sub-process iteration number; determining a second equivalent stress intensity factor of the first sub-process as a second maximum equivalent stress intensity factor and determining a second equivalent stress intensity factor of the second sub-process as a second minimum equivalent stress intensity factor; determining a second equivalent stress intensity factor amplitude according to the second maximum equivalent stress intensity factor and the second minimum equivalent stress intensity factor; performing plastic correction on the second equivalent stress intensity factor amplitude to obtain a second plastic equivalent stress intensity factor amplitude; calculating a second effective stress intensity factor amplitude according to the second maximum equivalent stress intensity factor, the second minimum equivalent stress intensity factor and the second plastic equivalent stress intensity factor amplitude; calculating a second crack propagation rate according to the second effective stress intensity factor amplitude; determining a second crack propagation amount at the current sub-process iteration number according to the second propagation rate and the crack increment number; determining a second crack size of the surface point at the current sub-process iteration number according to the second crack propagation amount at the current sub-process iteration number.

4. The fatigue fracture prediction method for complex structures according to claim 2, characterized in that, The determining whether the region to be predicted is fractured according to the crack size at the current sub-process iteration number specifically comprises: determining a first final influence coefficient of the deepest point according to the constant attribute and the first crack size at the current sub-process iteration number, and determining a second final influence coefficient of the surface point according to the constant attribute and the second crack size at the current sub-process iteration number; determining a first final equivalent stress intensity factor of the deepest point according to the stress coefficient and the first final influence coefficient, and determining a second final equivalent stress intensity factor of the surface point according to the stress coefficient and the second final influence coefficient; performing plastic correction on the first final equivalent stress intensity factor to obtain a first final plastic equivalent stress intensity factor, and performing plastic correction on the second final equivalent stress intensity factor to obtain a second final plastic equivalent stress intensity factor; judging whether the first final plastic equivalent stress intensity factor and the second final plastic equivalent stress intensity factor satisfy a preset standard to obtain a second judgment result; if the second judgment result is yes, the region to be predicted is not fractured; if the second judgment result is no, the region to be predicted is fractured.

5. The fatigue fracture prediction method for complex structures according to claim 2, characterized in that, The stress coefficient is calculated according to the constant property by using the finite element method, and specifically includes the following steps. The stress is determined according to the constant property by using the finite element method; the stress includes normal stress, depth shear stress and length shear stress; The stress coefficient is fitted according to the stress.

6. The fatigue fracture prediction method for complex structures according to claim 5, characterized in that, The first equivalent stress intensity factor at the current sub-process iteration number is determined according to the stress coefficient and the influence coefficient of the deepest point at the current sub-process iteration number, and specifically includes the following steps. The first normal stress intensity factor is determined according to the stress coefficient of the normal stress of the deepest point and the influence coefficient of the deepest point, the first depth shear stress intensity factor is determined according to the stress coefficient of the depth shear stress of the deepest point and the influence coefficient of the deepest point, and the first length shear stress intensity factor is determined according to the stress coefficient of the length shear stress of the deepest point and the influence coefficient of the deepest point. The first equivalent stress intensity factor at the current sub-process iteration number is calculated according to the first normal stress intensity factor, the first depth shear stress intensity factor and the first length shear stress intensity factor.

7. The fatigue fracture prediction method for complex structures according to claim 5, characterized in that, The second equivalent stress intensity factor is determined according to the stress coefficient and the influence coefficient of the surface point at the current sub-process iteration number, and specifically includes the following steps. The second normal stress intensity factor is determined according to the stress coefficient of the normal stress of the surface point and the influence coefficient of the surface point, the second depth shear stress intensity factor is determined according to the stress coefficient of the depth shear stress of the surface point and the influence coefficient of the surface point, and the second length shear stress intensity factor is determined according to the stress coefficient of the length shear stress of the surface point and the influence coefficient of the surface point. The second equivalent stress intensity factor is calculated according to the second normal stress intensity factor, the second depth shear stress intensity factor and the second length shear stress intensity factor.

8. A fatigue fracture prediction system suitable for complex structures, characterized by, The system includes: A sub-process set determination module is configured to determine a sub-process set of a to-be-predicted region at a current sub-process iteration number. An equivalent stress intensity factor determination module is configured to determine an equivalent stress intensity factor of each sub-process in the sub-process set at the current sub-process iteration number; the equivalent stress intensity factor includes a first equivalent stress intensity factor of a deepest point of a crack front and a second equivalent stress intensity factor of a surface point of the crack front. A sub-process determination module is configured to determine a first sub-process and a second sub-process according to the equivalent stress intensity factor; the first sub-process is a sub-process with the largest first equivalent stress intensity factor, and the second sub-process is a sub-process with the smallest first equivalent stress intensity factor. A crack increment number determination module is configured to determine a crack increment number; the crack increment number is a running number of a smaller sub-process; the smaller sub-process is a sub-process with a smaller running number in the first sub-process and the second sub-process. A crack size determination module is configured to determine a crack size at the current sub-process iteration number according to the first sub-process, the second sub-process and the crack increment number. The sub-process set updating module is configured to delete the smaller sub-process from the sub-process set and update the running times of larger sub-processes in the sub-process set according to the crack increment times; the larger sub-processes are sub-processes with larger running times among the first sub-process and the second sub-process; The crack determination and return module is configured to determine whether the updated sub-process set is empty, and obtain a first determination result; If the first determination result is yes, it is determined whether the crack occurs in the to-be-predicted region according to the crack size under the current sub-process iteration times; If the first determination result is no, the updated sub-process set is taken as a sub-process set under a next sub-process iteration times for iteration until the sub-process set is empty.

9. The fatigue crack prediction system suitable for complex structures according to claim 8, wherein, The equivalent stress intensity factor determination module specifically comprises: The constant attribute acquisition unit is configured to acquire constant attributes of the to-be-predicted region; the constant attributes include structure size, load, and material attribute; The stress coefficient calculation unit is configured to calculate a stress coefficient by using a finite element method according to the constant attributes; The crack size acquisition unit is configured to acquire a crack size under a previous sub-process iteration times; the crack size includes a first crack size of the deepest point and a second crack size of the surface point; The influence coefficient determination unit is configured to determine an influence coefficient of the deepest point under the current sub-process iteration times and an influence coefficient of the surface point under the current sub-process iteration times by using the finite element method according to the constant attributes, the first crack size under the previous sub-process iteration times, and the second crack size under the previous sub-process iteration times; The equivalent stress intensity factor determination unit is configured to determine a first equivalent stress intensity factor under the current sub-process iteration times according to the stress coefficient and the influence coefficient of the deepest point under the current sub-process iteration times, and determine a second equivalent stress intensity factor under the current sub-process iteration times according to the stress coefficient and the influence coefficient of the surface point under the current sub-process iteration times.

10. The fatigue fracture prediction method for complex structures according to claim 8, characterized in that, The crack size determination module specifically comprises: The first maximum and minimum equivalent stress intensity factor determination unit is configured to determine that the first equivalent stress intensity factor of the first sub-process is a first maximum equivalent stress intensity factor, and the second equivalent stress intensity factor of the second sub-process is a first minimum equivalent stress intensity factor; The first equivalent stress intensity factor amplitude determination unit is configured to determine a first equivalent stress intensity factor amplitude according to the first maximum equivalent stress intensity factor and the first minimum equivalent stress intensity factor; The first correction unit is configured to perform plastic correction on the first equivalent stress intensity factor amplitude to obtain a first plastic equivalent stress intensity factor amplitude; The first effective stress intensity factor amplitude calculation unit is configured to calculate a first effective stress intensity factor amplitude according to the first maximum equivalent stress intensity factor, the first minimum equivalent stress intensity factor, and the first plastic equivalent stress intensity factor amplitude; The first crack propagation rate calculation unit is configured to calculate a first crack propagation rate according to the first effective stress intensity factor amplitude. a first crack extension amount determining unit configured to determine a first crack extension amount at the current sub-process iteration number according to the first extension rate and the crack increment number; a first crack size determining unit configured to determine a first crack size of the deepest point at the current sub-process iteration number according to the first crack extension amount at the current sub-process iteration number; a second maximum and minimum equivalent stress intensity factor determining unit configured to determine a second equivalent stress intensity factor of the first sub-process as a second maximum equivalent stress intensity factor and a second equivalent stress intensity factor of the second sub-process as a second minimum equivalent stress intensity factor; a second equivalent stress intensity factor amplitude determining unit configured to determine a second equivalent stress intensity factor amplitude according to the second maximum equivalent stress intensity factor and the second minimum equivalent stress intensity factor; a second correction unit configured to perform plastic correction on the second equivalent stress intensity factor amplitude to obtain a second plastic equivalent stress intensity factor amplitude; a second effective stress intensity factor amplitude calculating unit configured to calculate a second effective stress intensity factor amplitude according to the second maximum equivalent stress intensity factor, the second minimum equivalent stress intensity factor and the second plastic equivalent stress intensity factor amplitude; a second crack extension rate calculating unit configured to calculate a second crack extension rate according to the second effective stress intensity factor amplitude; a second crack extension amount determining unit configured to determine a second crack extension amount at the current sub-process iteration number according to the second extension rate and the crack increment number; a second crack size determining unit configured to determine a second crack size of the surface point at the current sub-process iteration number according to the second crack extension amount at the current sub-process iteration number.

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