An analysis method for predicting cracking of a substation support porcelain insulator

Abstract

The application discloses a kind of analysis methods for predicting substation support post porcelain insulator cracking, comprising the following steps: step S1: construct support post porcelain insulator three-dimensional model, and set reference point mark to displacement monitoring point;Step S2: for the region needing to embed cohesive interface unit, insert cohesive force unit in batches, mesh division is carried out to component;Step S3: define material attribute, and give component;Step S4: assemble support post porcelain insulator three-dimensional model;Step S5: set boundary condition, top and bottom constrain y direction degree of freedom;Step S6: by self-defined amplitude curve, analysis step thermal cycle load is applied;Step S7: cycle step S6, complete preset number of thermal cycle load, output result cloud picture, record reference point mark displacement and generate displacement monitoring matrix, carry out thermal-boundary coupling analysis.The application can effectively predict support post porcelain insulator crack nucleation position and expansion.

Description

Technical Field

[0001] This invention relates to the field of porcelain insulators for substation posts, specifically an analytical method for predicting cracking in porcelain insulators for substation posts. Background Technology

[0002] Insulators are widely used in power transmission and transformation projects due to their high strength, excellent insulation, and strong resistance to degradation. However, with increasing service life, the risk of insulator fracture due to inherent manufacturing defects, improper installation, and inadequate operation and maintenance measures is increasing. Porcelain insulator fractures pose a significant safety hazard to power grid operation, causing minor power outages and potentially leading to regional power grid collapse. In recent years, with the shift in power grid construction strategies from robust to highly resilient grids, effectively reducing power grid failures has become an important research topic.

[0003] In power equipment, porcelain insulators primarily serve insulation and support functions, and are the most widely used insulating components in power transmission and transformation projects. They are typically composed of ceramics, cast iron (or aluminum alloy) flanges, and cement, and can be considered a broadly defined brittle composite material and structure. With increasing service life, the spatial geometry and boundary conditions (such as uneven settlement) of the post insulators have a crucial impact on their stress levels during service. Combined with environmental factors, this makes them prone to fracture accidents.

[0004] Currently, the power grid system industry lacks targeted and easy-to-use analysis and monitoring prediction methods to address the cracking problem of porcelain insulators. Summary of the Invention

[0005] To address the shortcomings of the existing technologies, this invention provides an analytical method for predicting cracking of post porcelain insulators in substations. This method aims to reduce the risk of insulator breakage caused by inherent manufacturing defects, improper installation, and inadequate operation and maintenance measures as the service life increases. It also solves the problem of predicting cracking of post porcelain insulators, a problem that is currently lacking both domestically and internationally.

[0006] To achieve the above objectives, the present invention provides the following technical solution: an analytical method for predicting cracking of porcelain insulators used as support posts in substations, comprising:

[0007] Step S1: Construct a three-dimensional model of the post porcelain insulator. The components in the model include the upper part of the porcelain post, the lower part of the porcelain post, the metal flange, the cement adhesive, the outer asphalt buffer layer, the inner asphalt buffer layer, the bolts and nuts, and set reference point markers for the displacement monitoring points.

[0008] Step S2: Create a set-cohesive for the region where cohesive elements need to be embedded, insert the cohesive elements, and mesh the component;

[0009] Step S3: Define material properties, create assigned sections, and assign them to the upper ceramic column, lower ceramic column, metal flange, cement adhesive, outer asphalt buffer layer, inner asphalt buffer layer, bolts, nuts, and cohesive elements. Material properties include elastic modulus, coefficient of thermal expansion, Poisson's ratio, density, conductivity, and specific heat capacity.

[0010] Step S4: Assemble the three-dimensional model of the post porcelain insulator and set the viscous analysis step to one thermal cycle load period of T;

[0011] Step S5: Set boundary conditions, constraining the y-direction degrees of freedom at the top and bottom;

[0012] Step S6: Set the initial temperature to C, and apply the analysis step thermal cycle load through a custom amplitude curve;

[0013] Step S7: Repeat step S6 to complete the preset number of thermal cycle loads, output the result cloud map, record the displacement of the reference point marker and generate the displacement monitoring matrix, and perform thermal-boundary coupling analysis by combining the result cloud map and the displacement monitoring matrix to obtain the cracking prediction result of the substation support porcelain insulator.

[0014] Furthermore, in step S1, the displacement monitoring is multi-point boundary displacement monitoring, with monitoring points set at the upper and lower metal flanges and the metal flange at the connection between the two support porcelain insulators.

[0015] Furthermore, in step S2, the cohesive unit type is an eight-node three-dimensional bonding unit COH3D8, the unit type of the upper part of the ceramic column, the metal flange and the inner asphalt buffer layer is a ten-node tetrahedral unit C3D10M, and the unit type of the lower part of the ceramic column, the cement adhesive, the outer asphalt buffer layer, the bolt and nut is an eight-node linear hexahedral unit C3D8R.

[0016] Furthermore, a bilinear cohesive constitutive model based on the bilinear tension-displacement method is used to simulate the cracking of the post porcelain insulator. The cohesive unit is based on the traction separation damage law, the initial damage criterion of the cohesive unit is the maximum nominal stress criterion, and the critical fracture energy is selected to simulate damage propagation.

[0017] Furthermore, the governing equations of the bilinear tension displacement method are:

[0018]

[0019]

[0020] In the formula, σ is the normal stress component, and τ s The tangential stress component along the crack depth direction, τ tThese are the tangential stress components along the crack width direction. The three stress components correspond to the three common crack propagation modes: Type I, Type II, and Type III. max τ max These are the limit stress values ​​in the normal and tangential directions, respectively, corresponding to the tensile strength of the material; δ represents the crack opening displacement. and These are the opening displacements corresponding to the normal stress value, the tangential stress value along the crack depth direction, and the tangential stress value along the crack width direction when they reach the ultimate stress value, respectively. and These are the normal critical opening displacement value, the tangential critical opening displacement value along the crack depth direction, and the tangential critical opening displacement value along the crack width direction, respectively.

[0021] Furthermore, the maximum nominal stress criterion is that damage occurs at the element interface when the ratio of the maximum nominal stress to its corresponding ultimate stress is 1, as detailed below:

[0022]

[0023] In the formula: σ′ n,max ,τ′ s,max ,τ′ t,max σ′ represents the normal ultimate strength, the tangential ultimate strength along the crack depth direction, and the tangential ultimate strength along the crack width direction, respectively. n ,τ′ s ,τ′ t These represent the normal cohesive component, the tangential cohesive component along the crack depth direction, and the tangential cohesive component along the crack width direction, respectively. The meanings of < and > in the formula are:

[0024]

[0025] Furthermore, the interface stiffness of the cohesive element depends on the slope of the bilinear tension-displacement relationship graph.

[0026] Furthermore, the normal critical fracture energy value Tangential critical fracture energy along the crack depth direction and the critical tangential fracture energy along the crack width direction The specific calculation formula is as follows:

[0027]

[0028] In the formula, τ s,max τ t,max These are the tangential ultimate stress values ​​along the crack depth direction and along the crack width direction, respectively; These are the critical tangential opening displacements along the crack depth direction and along the crack width direction, respectively; KIC ν represents the fracture toughness of the material; E represents the elastic modulus of the material; and ν represents the Poisson's ratio of the material.

[0029] Furthermore, in step S6, the initial temperature is set to -30°C, heated to 70°C after 1200 equivalent time, and then cooled to -30°C after 1200 equivalent time.

[0030] Furthermore, in step S7, the resulting contour map is an SDEG contour map, from which the permissible triaxial displacement [δ] of each reference point at the nodal temperature is obtained. ij [] and comprehensive allowable displacement [δ]. The displacement monitoring matrix is ​​a set of matrices of three-dimensional displacement at different monitoring points under different temperature nodes. Every 100 equivalent time is selected as a temperature node to simulate the temperature change in twelve months of a year.

[0031] T i The displacement monitoring matrix at nodal temperatures is as follows:

[0032]

[0033] Where, δ 1i δ represents the displacement in the X direction at different monitoring points at this node temperature. 2i δ represents the displacement in the Y direction at different monitoring points at this node temperature. 3i This represents the displacement in the Z direction at different monitoring points under this node temperature;

[0034] Compare the displacement monitoring matrix and the allowable triaxial displacement [δ] of the reference point. ij The allowable displacement [δ] is calculated using the following formula:

[0035] T i At node temperatures: {δ ij}<[δ ij (5)

[0036] T i At node temperatures:

[0037] In the formula, {δ ij} is T i The corresponding values ​​of the displacement monitoring matrix at nodal temperatures, [δ j ] represents the comprehensive allowable displacement of monitoring point j.

[0038] Compared with existing technologies, this invention has the following advantages: It can effectively predict the nucleation location and propagation of cracks in substation post porcelain insulators. This invention reduces the risk of insulator breakage due to inherent manufacturing defects, improper installation, and inadequate operation and maintenance measures as the service life increases, solving the current problem of predicting cracks in post porcelain insulators, which is lacking both domestically and internationally. Attached Figure Description

[0039] Figure 1 This is a diagram showing the normal stress-displacement relationship of the present invention;

[0040] Figure 2 This is a diagram showing the tangential stress-displacement relationship of the present invention.

[0041] Figure 3 This is a flowchart illustrating the embedding of zero-thickness cohesive units in an embodiment of the present invention.

[0042] Figure 4 This is the cohesive traction-separation curve in an embodiment of the present invention;

[0043] Figure 5 This is a distribution map of monitoring points in an embodiment of the present invention;

[0044] Figure 6 This is a diagram of the on-site instrument testing in an embodiment of the present invention;

[0045] Figure 7 This is a schematic diagram of the displacement monitoring matrix in an embodiment of the present invention. Detailed Implementation

[0046] To better demonstrate the feasibility of the present invention, the present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0047] This invention provides an analytical method for predicting cracking in porcelain insulators used as support posts in substations, comprising:

[0048] Step S1: Construct a three-dimensional model of the ceramic insulator for the support column. The components in the model include the upper part of the ceramic column, the lower part of the ceramic column, the metal flange, the cement adhesive, the outer asphalt buffer layer, the inner asphalt buffer layer, the bolts and nuts, and set reference point markers for the displacement monitoring points.

[0049] Step S2: Create a set-cohesive for the region where cohesive elements need to be embedded, insert the cohesive elements, and mesh the component.

[0050] Step S3: Define material properties, create assigned sections, and assign them to the upper ceramic column, lower ceramic column, metal flange, cement adhesive, outer asphalt buffer layer, inner asphalt buffer layer, bolts, nuts, and cohesive elements. Material properties include elastic modulus, coefficient of thermal expansion, Poisson's ratio, density, conductivity, and specific heat capacity.

[0051] Step S4: Assemble the three-dimensional model of the post porcelain insulator and set the viscous analysis step to one thermal cycle load period of T.

[0052] Step S5: Set boundary conditions, constraining the y-direction degrees of freedom at the top and bottom.

[0053] Step S6: Set the initial temperature to C and apply the analysis step thermal cycle load through a custom amplitude curve.

[0054] Step S7: Repeat step S6 to complete the preset number of thermal cycle loads, output the result cloud map, record the displacement of the reference point marker and generate the displacement monitoring matrix, and perform thermal-boundary coupling analysis by combining the result cloud map and the displacement monitoring matrix to obtain the cracking prediction result of the substation support porcelain insulator.

[0055] Specifically, in step S1, the displacement monitoring is multi-point boundary displacement monitoring, with monitoring points set at the upper and lower metal flanges and the metal flange at the connection between the two support porcelain insulators.

[0056] Specifically, in step S2, the cohesive unit type is an eight-node three-dimensional bonding unit COH3D8, the unit type of the upper part of the ceramic column, the metal flange and the inner asphalt buffer layer is a ten-node tetrahedral unit C3D10M, and the unit type of the lower part of the ceramic column, the cement adhesive, the outer asphalt buffer layer, the bolt and nut is an eight-node linear hexahedral unit C3D8R.

[0057] Specifically, a bilinear cohesive constitutive model based on the bilinear tension-displacement method is used to simulate the cracking of the post porcelain insulator. The cohesive unit is based on the traction separation damage law, the initial damage criterion of the cohesive unit is the maximum nominal stress criterion, and the critical fracture energy is selected to simulate damage propagation.

[0058] The governing equations of the bilinear tension displacement method are:

[0059]

[0060]

[0061] In the formula, σ is the normal stress component, and τ s The tangential stress component along the crack depth direction, τ t These are the tangential stress components along the crack width direction. The three stress components correspond to the three common crack propagation modes: Type I, Type II, and Type III. max τ max These are the limit stress values ​​in the normal and tangential directions, respectively, corresponding to the tensile strength of the material; δ represents the crack opening displacement. and These are the opening displacements corresponding to the normal stress value, the tangential stress value along the crack depth direction, and the tangential stress value along the crack width direction when they reach the ultimate stress value, respectively. and These are the normal critical opening displacement value, the tangential critical opening displacement value along the crack depth direction, and the tangential critical opening displacement value along the crack width direction, respectively.

[0062] Specifically, the maximum nominal stress criterion is that damage occurs at the element interface when the ratio of the maximum nominal stress to its corresponding ultimate stress is 1, as follows:

[0063]

[0064] In the formula: σ′ n,max ,τ′ s,max ,τ′ t,max σ′ represents the normal ultimate strength, the tangential ultimate strength along the crack depth direction, and the tangential ultimate strength along the crack width direction, respectively. n ,τ′ s ,τ′ t These represent the normal cohesive component, the tangential cohesive component along the crack depth direction, and the tangential cohesive component along the crack width direction, respectively. The meanings of < and > in the formula are:

[0065]

[0066] Specifically, the interface stiffness of the cohesive element depends on the slope of the bilinear tension-displacement graph, such as... Figure 1-2 As shown.

[0067] Specifically, the normal critical fracture energy value Tangential critical fracture energy along the crack depth direction and the critical tangential fracture energy along the crack width direction The specific calculation formula is as follows:

[0068]

[0069] In the formula, τ s,max τ t,max These are the tangential ultimate stress values ​​along the crack depth direction and along the crack width direction, respectively; These are the critical tangential opening displacements along the crack depth direction and along the crack width direction, respectively; K IC ν represents the fracture toughness of the material; E represents the elastic modulus of the material; and ν represents the Poisson's ratio of the material.

[0070] Specifically, in step S6, the initial temperature is set to -30°C, heated to 70°C over a period of 1200 equivalent time, and then cooled to -30°C over a period of 1200 equivalent time.

[0071] Specifically, in step S7, the resulting contour map is the SDEG contour map, from which the allowable triaxial displacement [δ] of each reference point at the nodal temperature is obtained. ij[] and comprehensive allowable displacement [δ]. The displacement monitoring matrix is ​​a set of matrices of three-dimensional displacement at different monitoring points under different temperature nodes. Every 100 equivalent time is selected as a temperature node to simulate the temperature change in twelve months of a year.

[0072] T i The displacement monitoring matrix at nodal temperatures is as follows:

[0073]

[0074] Where, δ 1i δ represents the displacement in the X direction at different monitoring points at this node temperature. 2i δ represents the displacement in the Y direction at different monitoring points at this node temperature. 3i This represents the displacement in the Z direction at different monitoring points under this node temperature;

[0075] Compare the displacement monitoring matrix and the allowable triaxial displacement [δ] of the reference point. ij The allowable displacement [δ] is calculated using the following formula:

[0076] T i At node temperatures: {δ ij}<[δ ij (5)

[0077] T i At node temperatures:

[0078] In the formula, {δ ij} is T i The corresponding values ​​of the displacement monitoring matrix at nodal temperatures, [δ j ] represents the comprehensive allowable displacement of monitoring point j.

[0079] Example

[0080] This embodiment provides an analytical method for predicting cracking of porcelain insulators on substation posts, including the following steps:

[0081] Step S1: Construct a three-dimensional model of the ceramic insulator for the support column. The components in the model include the upper part of the ceramic column, the lower part of the ceramic column, the metal flange, the cement adhesive, the outer asphalt buffer layer, the inner asphalt buffer layer, the bolts and nuts, and set reference point markers for the displacement monitoring points.

[0082] In this embodiment, a three-dimensional model of the post porcelain insulator is established using ABAQUS software. The components in the model include two upper porcelain posts, two lower porcelain posts, four metal flanges, four cement adhesives, four outer asphalt buffer layers, four inner asphalt buffer layers, three bolts, and three nuts.

[0083] Step S2: Create a set-cohesive for the regions where cohesive interface units need to be embedded in batches. Output a .inp file in the job module. Process the .inp file using Python, batch processing the node information of the set-cohesive set within the .inp file. After processing, a new .inp file is obtained, containing the generated new nodes, sets, and other information. Import the newly generated .inp file into ABAQUS, following the procedure below. Figure 3 As shown, each component in the model is meshed, and cohesive elements are inserted. The type of cohesive element is an eight-node three-dimensional bonding element COH3D8. The element type of the upper part of the ceramic column, the metal flange, and the internal asphalt buffer layer is a ten-node tetrahedral element C3D10M. The element type of the lower part of the ceramic column, the cement adhesive, the external asphalt buffer layer, the bolts, and the nuts is an eight-node linear hexahedral element C3D8R.

[0084] Step S3: Set material properties for the upper and lower parts of the ceramic column, the metal flange, the cement adhesive, the outer asphalt buffer layer, the inner asphalt buffer layer, the bolts, nuts, and the cohesive unit, including elastic modulus, coefficient of thermal expansion, Poisson's ratio, density, conductivity, and specific heat capacity, as shown in Table 1. For the bolts and nuts, the density, elastic modulus, and Poisson's ratio are selected from the cast iron flange parameters in Table 1. For the cohesive unit, the density, elastic modulus, and Poisson's ratio are selected from the ceramic column parameters in Table 1. The cohesive unit is based on the traction separation damage law, as shown in Table 1. Figure 4 As shown, the initial damage criterion for cohesive elements is the maximum nominal stress criterion, and the critical fracture energy is selected to simulate damage propagation.

[0085] Table 1. Main material performance parameters of insulator porcelain bushings

[0086]

[0087] Step S4: Assemble the three-dimensional model of the post porcelain insulator and set the viscous analysis step to one thermal cycle load period of T.

[0088] Step S5: Set boundary conditions, constrain the y-direction degrees of freedom at the top and bottom, and simulate the constraints of an actual support porcelain insulator during service.

[0089] Step S6: Apply a thermal cycling load to the model using a predefined field. The initial temperature of the thermal cycling load is -10℃, which is heated to 70℃ after 1200s, and then cooled to -10℃ after 1200s.

[0090] Step S7: Repeat step S6 to complete the preset number of thermal load cycles and output the SDEG cloud map. The damage factor SDEG is an indicator for judging the degree of damage to the interface cohesive units. When SDEG is 1, the interface cohesive units are completely damaged, and the deletion of cohesive units represents the nucleation and propagation of interface cracks. The displacement monitoring matrix is ​​a set of displacement column vectors at different monitoring points at temperature nodes. A temperature node is selected every 100 seconds to simulate the temperature changes over twelve months of a year. In actual operation, the boundary displacement is obtained by a displacement monitoring system composed of a telescope and a CCD optical testing element. The sensor composed of the telescope and the CCD optical testing element is installed on a measuring tripod, and the CCD camera is aimed at the monitoring points. The monitoring points are set on the upper and lower flanges and the flange at the connection between the two pillar porcelain insulators, as shown below. Figure 5 As shown, the camera will capture speckle images of the test piece before and after deformation, and store the images in the control computer, such as... Figure 6 As shown. After image acquisition is complete, the DIC testing system will use corresponding algorithms to process the information, that is, after performing mathematical calculations on the acquired digital information of the images before and after deformation, it will output a displacement monitoring matrix.

[0091] In this embodiment, by combining the SDEG damage factor cloud map, the allowable triaxial displacement [δ] of the reference point at this node temperature can be obtained. ij The displacement monitoring matrix is ​​a set of matrices representing the triaxial displacements at different monitoring points under different temperature nodes, and the allowable displacement is [δ]. Figure 7 As shown, a temperature node is selected every 100 equivalent time periods to simulate the temperature changes over twelve months of a year. By coupling the displacement monitoring matrix and the damage factor SDEG results together using the following formula, the location and propagation of cracks in the porcelain insulators of substation supports can be effectively predicted.

[0092] T i At node temperatures: {δ ij}<[δ ij (5)

[0093] T i At node temperatures:

[0094] In the formula, [δ ij ] is T i The corresponding values ​​of the displacement monitoring matrix at nodal temperatures, [δ j ] represents the comprehensive allowable displacement of monitoring point j.

[0095] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An analytical method for predicting cracking of porcelain insulators on substation posts, characterized in that, include: Step S1: Construct a three-dimensional model of the post porcelain insulator. The components in the model include the upper part of the porcelain post, the lower part of the porcelain post, the metal flange, the cement adhesive, the outer asphalt buffer layer, the inner asphalt buffer layer, the bolts and nuts, and set reference point markers for the displacement monitoring points. Step S2: Create a set-cohesive for the region where cohesive elements need to be embedded, insert the cohesive elements, and mesh the component; Step S3: Define material properties, create assigned sections, and assign them to the upper ceramic column, lower ceramic column, metal flange, cement adhesive, outer asphalt buffer layer, inner asphalt buffer layer, bolts, nuts, and cohesive elements. Material properties include elastic modulus, coefficient of thermal expansion, Poisson's ratio, density, conductivity, and specific heat capacity. Step S4: Assemble the three-dimensional model of the post porcelain insulator and set one thermal cycle load period of the viscous analysis step to T; Step S5: Set boundary conditions, constraining the y-direction degrees of freedom at the top and bottom; Step S6: Set the initial temperature to C, and apply the analysis step thermal cycle load through a custom amplitude curve; Step S7: Repeat step S6 to complete the preset number of thermal cycle loads, output the result cloud map, record the displacement of the reference point marker and generate the displacement monitoring matrix, and perform thermal-boundary coupling analysis by combining the result cloud map and the displacement monitoring matrix to obtain the cracking prediction result of the substation support porcelain insulator.

2. The analytical method for predicting cracking of porcelain insulators on substation posts according to claim 1, characterized in that, In step S1, the displacement monitoring is multi-point boundary displacement monitoring, with monitoring points set at the upper and lower flanges and the flange at the connection between the two support porcelain insulators.

3. The analytical method for predicting cracking of porcelain insulators on substation posts according to claim 1, characterized in that, In step S2, the cohesive unit type is an eight-node three-dimensional bonding unit COH3D8, the unit type of the upper part of the ceramic column, the metal flange and the inner asphalt buffer layer is a ten-node tetrahedral unit C3D10M, and the unit type of the lower part of the ceramic column, the cement adhesive, the outer asphalt buffer layer, the bolt and nut is an eight-node linear hexahedral unit C3D8R.

4. The analytical method for predicting cracking of porcelain insulators for substation supports according to claim 1, characterized in that, A bilinear cohesive constitutive model based on the bilinear tension-displacement method was used to simulate the cracking of the post porcelain insulator. The cohesive element was based on the traction separation damage law, and the initial damage criterion of the cohesive element was the maximum nominal stress criterion. The critical fracture energy was selected to simulate the damage propagation.

5. The analytical method for predicting cracking of porcelain insulators for substation supports according to claim 4, characterized in that, The governing equations of the bilinear tension displacement method are: (1) ， (2) In the formula, For the normal stress component, The tangential stress component along the crack depth direction, These are the tangential stress components along the crack width direction. The three stress components correspond to common... type, Type and Three types of crack propagation modes; , These are the limit stress values ​​in the normal and tangential directions, respectively, corresponding to the tensile strength of the material; This indicates the displacement of the crack opening. , and These are the opening displacements corresponding to the normal stress value, the tangential stress value along the crack depth direction, and the tangential stress value along the crack width direction when they reach the ultimate stress value, respectively. , and These are the normal critical opening displacement value, the tangential critical opening displacement value along the crack depth direction, and the tangential critical opening displacement value along the crack width direction, respectively.

6. The analytical method for predicting cracking of porcelain insulators on substation posts according to claim 5, characterized in that, The maximum nominal stress criterion is that damage occurs at the element interface when the ratio of the maximum nominal stress to its corresponding ultimate stress is 1, as detailed below: (3) In the formula: , , These represent the normal ultimate strength, the tangential ultimate strength along the crack depth direction, and the tangential ultimate strength along the crack width direction, respectively. , , represent the normal cohesive component, the tangential cohesive component along the crack depth direction, and the tangential cohesive component along the crack width direction, respectively. The meaning is: 。 7. The analytical method for predicting cracking of porcelain insulators for substation supports according to claim 4, characterized in that, The interface stiffness of cohesive elements depends on the slope of the bilinear tension-displacement relationship graph.

8. The analytical method for predicting cracking of porcelain insulators for substation supports according to claim 4, characterized in that, Normal critical fracture energy value Tangential critical fracture energy along the crack depth direction and the critical tangential fracture energy along the crack width direction The specific calculation formula is as follows: (4) In the formula, , These are the tangential ultimate stress values ​​along the crack depth direction and along the crack width direction, respectively; , These are the critical tangential opening displacement values ​​along the crack depth direction and along the crack width direction, respectively. For the fracture toughness of the material; The elastic modulus of the material; Let be the Poisson's ratio of the material.

9. The analytical method for predicting cracking of porcelain insulators for substation supports according to claim 1, characterized in that, In step S6, the initial temperature is set to -30℃, heated to 70℃ after 1200 equivalent time, and then cooled to -30℃ after 1200 equivalent time.

10. The analytical method for predicting cracking of porcelain insulators for substation supports according to claim 1, characterized in that, In step S7, the resulting contour map is the SDEG contour map, from which the allowable triaxial displacement [δ] of each reference point at the nodal temperature is obtained. ij [] and comprehensive allowable displacement [δ]. The displacement monitoring matrix is ​​a set of matrices of three-dimensional displacement at different monitoring points under different temperature nodes. Every 100 equivalent time is selected as a temperature node to simulate the temperature change in twelve months of a year. T i The displacement monitoring matrix at nodal temperatures is as follows: Where, δ 1i δ represents the displacement in the X direction at different monitoring points at this node temperature. 2i δ represents the displacement in the Y direction at different monitoring points at this node temperature. 3i This represents the displacement in the Z direction at different monitoring points under this node temperature; Compare the displacement monitoring matrix and the allowable triaxial displacement [δ] of the reference point. ij The allowable displacement [δ] is calculated using the following formula: T i At node temperatures: { δ ij } < [ δ ij (5) T i At node temperatures: (6) In the formula, {δ ij } For T i The corresponding values ​​of the displacement monitoring matrix at nodal temperatures, [ δ j ] represents the comprehensive allowable displacement of monitoring point j.

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