High temperature joint evaluation method and system considering stress relaxation

Abstract

The application provides a high-temperature connecting piece evaluation method and system considering stress relaxation, and relates to the technical field of connecting piece performance detection, and comprises the following steps: determining the type of complex load according to the pre-tightening force of the connecting piece; determining the attribute value of the connecting piece according to the complex load type; obtaining the initial equivalent stress level calculation equation under the type of the complex load according to the attribute value and the stress distribution characteristics of the complex load type; determining the Norton-Bailey constitutive equation coefficients A, stress index m and time index n, establishing the equivalent relaxation theory equation, and obtaining the axial average stress of the connecting piece after relaxation in combination with the composition working condition characteristics of each load in the complex load type; and comparing the axial average stress of the connecting piece after relaxation with the preset minimum clamping limit value to evaluate the connecting piece. The application solves the problem of lacking a stress relaxation calculation method for high-temperature connecting pieces under complex load in the prior art.

Description

Technical Field

[0001] This invention relates to the technical field of performance testing of connectors, and in particular to a method and system for evaluating high-temperature connectors that takes stress relaxation into account. Background Technology

[0002] Connectors are commonly used for installation connections between equipment. Among connectors, bolts, in particular, are widely used in various scenarios due to their simple structure and ease of installation. Therefore, the strength, deformation, and clamping force of bolts have become the main indicators for evaluating the effectiveness of bolted connection structures. In high-temperature environments, metal bolts with preload will exhibit creep behavior over time, leading to failures such as leakage and connector opening due to reduced clamping force. Regarding this type of failure, international design standards related to high-temperature bolts (such as ASME, RCC-MR, and VDI) all require attention to the stress relaxation behavior of bolts in high-temperature environments, but none provide detailed prediction and evaluation methods. With the development of fourth-generation nuclear power and related high-parameter technologies, the operating temperature of components such as high-temperature bolted connectors is increasing, even reaching or exceeding 550°C, making stress relaxation of bolts in high-temperature environments increasingly significant.

[0003] Although researchers have derived a high-temperature bolt stress relaxation prediction model based on the constitutive equation of creep in metallic materials, they have only conducted extensive research on the creep behavior of metallic materials under axial tensile loads.

[0004] However, since high-temperature connecting bolts, in addition to bearing the axial tensile load that plays their main functional role, also bear bending, torsion, shear, and even combinations of these loads caused by the structure, installation, and operation of the connected components, there are still no reports on the prediction and evaluation of the axial clamping force after high-temperature relaxation of the bolt structure under combined loads. In other words, there is a lack of reasonable design and prediction methods for stress relaxation of high-temperature bolts under complex load conditions.

[0005] Therefore, it is particularly necessary to construct a reasonable, reliable and accurate method for calculating the stress relaxation of high-temperature bolts under the above-mentioned complex loads in order to meet the design requirements of bolts in high-temperature environments. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method and system for evaluating high-temperature connectors that consider stress relaxation, thus solving the problem of the lack of a method for calculating stress relaxation of high-temperature connectors under complex loads in existing technologies.

[0007] At least one embodiment of the present invention provides a method for evaluating high-temperature connectors considering stress relaxation, comprising the following steps:

[0008] The type of complex load is determined based on the preload of the connector;

[0009] Based on the complex load type, the attribute values ​​of the connector are determined, which characterize the deformation parameters and shear loads generated by the force on the connector.

[0010] Based on the attribute values ​​and the stress distribution characteristics of the complex load type, the initial equivalent stress level calculation equation under the complex load type is obtained. The initial equivalent stress level calculation equation represents the functional relationship between the equivalent stress and the attribute values ​​when the connector is initially loaded with the complex load.

[0011] The Norton-Bailey constitutive equation coefficients A, stress exponent m, and time exponent n were determined by conducting high-temperature creep fracture tests on the connector. Based on the coefficients A, stress exponent m, time exponent n, and the initial equivalent stress level calculation equation, an equivalent relaxation theory equation was established. The equivalent relaxation theory equation characterizes the functional relationship between the equivalent stress of the connector after a preset relaxation time period and the equivalent stress of the connector when initially loaded with the complex load.

[0012] Based on the initial equivalent stress level calculation equation and the equivalent stress relaxation theory equation, combined with the composition characteristics of each load in the complex load type, the axial average stress after relaxation of the connector is obtained.

[0013] The average axial stress after the connector is relaxed is compared with the preset minimum clamping limit to evaluate the connector.

[0014] An embodiment of the present invention provides a high-temperature connector evaluation system that considers stress relaxation, comprising:

[0015] The load type determination module is used to determine the complex load type of the connector based on the preload of the connector.

[0016] The parameter determination module receives the complex load type and determines the attribute values ​​of the connector, which characterize the deformation parameters and shear loads generated by the connector under stress.

[0017] The initial equivalent stress calculation module receives the attribute value and, based on the stress distribution characteristics of the complex load type, obtains the initial equivalent stress level calculation equation for the element point. The initial equivalent stress level calculation equation represents the functional relationship between the equivalent stress and the attribute value when the connector is initially loaded with the complex load.

[0018] The equivalent stress relaxation theory equation acquisition module receives the initial equivalent stress level calculation equation, and combines the Norton-Bailey constitutive equation coefficients A, stress exponent m and time exponent n obtained from the high temperature creep fracture test of the connector to establish the equivalent stress relaxation theory equation. The equivalent relaxation theory equation is characterized as the functional relationship between the equivalent stress of the connector after a preset relaxation time period and the equivalent stress of the connector when the complex load is initially applied.

[0019] The axial average stress calculation module receives the equivalent stress relaxation theoretical equation and the initial equivalent stress level calculation equation, and calculates the axial average stress of the connector after relaxation based on the composition characteristics of each load in the complex load type.

[0020] The evaluation module is used to input the required minimum clamping force limit and receive the axial average stress after relaxation, determine the magnitude of the axial average stress after relaxation and the minimum clamping force limit, and evaluate the connector based on the determination result.

[0021] The technical solution disclosed in this invention has at least the following beneficial effects:

[0022] By conducting high-temperature creep fracture tests on the connectors, the coefficients A, stress exponent m, and time exponent n of the Norton-Bailey constitutive equations were obtained. Based on the fastening method of the connector preload, the type of complex load that the connectors are subjected to was determined, and the initial equivalent stress level calculation equation and the equivalent stress relaxation equation were established. By combining the characteristics of the combined working conditions of various loads under complex loads, the axial stress of the corresponding connectors after relaxation at each time point can be calculated.

[0023] This provides a more reasonable, reliable, and accurate method for the design of stress relaxation and prediction of residual preload in high-temperature connectors under complex loads, and has good development prospects. It also provides theoretical support for the safe design, installation, and maintenance of high-temperature connectors under high-parameter complex loads. Attached Figure Description

[0024] Figure 1 This is a flowchart illustrating the implementation of an evaluation method for high-temperature connectors that takes stress relaxation into account, as per the present invention.

[0025] Figure 2-1 This is a schematic diagram of the bending load-related parameters involved in this invention.

[0026] Figure 2-2 This is a schematic diagram of the torsional load-related parameters involved in this invention.

[0027] Figure 3-1 This is a schematic diagram showing the model load and boundary conditions when the complex loads are axial tensile loads and bending loads.

[0028] Figure 3-2 This is a schematic diagram showing the model load and boundary conditions when the complex loads are axial tensile loads and torsional loads.

[0029] Figure 3-3 This is a schematic diagram showing the model load and boundary conditions when the complex loads are axial tensile loads and shear loads.

[0030] Figure 3-4 This is a schematic diagram showing the application of loads and boundaries to a model when the complex loads are axial tensile loads, bending loads, and torsional loads.

[0031] Figure 4-1 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and bending load (σT=0.5σy,(σM)max=0.1σy).

[0032] Figure 4-2 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and bending load (σT=0.5σy,(σM)max=0.3σy).

[0033] Figure 4-3 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and bending load (σT=0.5σy,(σM)max=0.4σy).

[0034] Figure 4-4 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and bending load (σT=0.3σy,(σM)max=0.1σy).

[0035] Figure 4-5 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and bending load (σT=0.4σy,(σM)max=0.1σy).

[0036] Figure 5-1 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and torsional load (σT=0.5σy,(τR)max=0.3σy).

[0037] Figure 5-2 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and torsional load (σT=0.5σy,(τR)max=0.5σy).

[0038] Figure 5-3 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and torsional load (σT=0.5σy,(τR)max=0.6σy).

[0039] Figure 5-4Comparison of predicted results and finite element results for complex loads, namely axial tensile load and torsional load (σT=0.3σy,(τR)max=0.3σy).

[0040] Figure 5-5 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and torsional load (σT=0.6σy,(τR)max=0.3σy).

[0041] Figure 6-1 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and shear load (σT=0.55σy, Fs=400N).

[0042] Figure 6-2 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and shear load (σT=0.55σy, Fs=300N).

[0043] Figure 6-3 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and shear load (σT=0.55σy,Fs=800N).

[0044] Figure 6-4 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and shear load (σT=0.4σy, Fs=400N).

[0045] Figure 6-5 Comparison of predicted results and finite element results for complex loads, namely axial tensile load and shear load (σT=0.3σy, Fs=400N).

[0046] Figure 7-1 Comparison of predicted results and finite element results for complex loads such as axial tensile load, bending load, and torsional load (σT=0.5σy, (σM)max=0.3σy, (τR)max=0.5σy).

[0047] Figure 7-2 Comparison of predicted results and finite element results for complex loads such as axial tensile load, bending load, and torsional load (σT=0.5σy, (σM)max=0.3σy, (τR)max=0.3σy).

[0048] Figure 7-3 Comparison of predicted results and finite element results for complex loads such as axial tensile load, bending load, and torsional load (σT=0.5σy, (σM)max=0.3σy, (τR)max=0.7σy).

[0049] Figure 7-4Comparison of predicted results and finite element results for complex loads such as axial tensile load, bending load, and torsional load (σT=0.5σy, (σM)max=0.1σy, (τR)max=0.5σy).

[0050] Figure 7-5 Comparison of predicted results and finite element results for complex loads such as axial tensile load, bending load, and torsional load (σT=0.5σy, (σM)max=0.1σy, (τR)max=0.7σy).

[0051] Figure 8 This is a flowchart illustrating another embodiment of the present invention regarding an evaluation method for high-temperature connectors that takes stress relaxation into account.

[0052] Figure 9 This is a block diagram of an evaluation system for high-temperature connectors that takes stress relaxation into account, according to the present invention. Detailed Implementation

[0053] The principles and features of the present invention are described below. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0054] In this invention, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0055] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0056] This invention provides a method for evaluating high-temperature connectors that takes stress relaxation into account; please refer to [link / reference here]. Figure 1 As shown, it includes:

[0057] The type of complex load is determined based on the preload of the connector;

[0058] Specifically, the type of complex load is determined by the magnitude of the preload applied to the connector and the tightening direction of the preload; it should also be understood that the connector involved in this invention can be specifically referred to as a bolt.

[0059] Based on the complex load type, the property values ​​of the connector are determined. The property values ​​characterize the deformation parameters and shear loads generated by the connector under stress.

[0060] Based on the determined attribute values ​​and the stress distribution characteristics of complex load types, the initial equivalent stress level calculation equation for the element point under complex load types is obtained. The initial equivalent stress level calculation equation is characterized as the functional relationship between the equivalent stress and attribute values ​​when the connector is initially loaded with a complex load.

[0061] The Norton-Bailey constitutive equation coefficients A, stress exponent m, and time exponent n were determined by conducting high-temperature creep fracture tests on the connector. Based on the coefficients A, stress exponent m, time exponent n, and the initial equivalent stress level calculation equation, the equivalent relaxation theory equation was established. The equivalent relaxation theory equation represents the functional relationship between the equivalent stress of the connector after a preset relaxation time period and the equivalent stress of the connector when initially loaded with a complex load.

[0062] Based on the initial equivalent stress level calculation equation and the equivalent stress relaxation theory equation, combined with the composition characteristics of each load in the complex load type, the relaxed axial average stress is obtained.

[0063] The average axial stress after the connector is relaxed is compared with the preset minimum clamping limit to evaluate the connector.

[0064] By conducting high-temperature creep fracture tests on the connectors, the coefficients A, stress exponent m, and time exponent n of the Norton-Bailey constitutive equations were obtained. Based on the fastening method of the connector preload, the type of complex load that the connectors bear was determined, and the initial equivalent stress level calculation equation and the equivalent stress relaxation equation were established. By combining the composition characteristics of each load under complex loads, the axial stress of the corresponding connector after relaxation at each time point can be calculated.

[0065] This provides a more reasonable, reliable, and accurate method for the design of stress relaxation and prediction of residual preload in high-temperature connectors under complex loads, and has good development prospects. It also provides theoretical support for the safe design, installation, and maintenance of high-temperature connectors under high-parameter complex loads.

[0066] Specifically, the elastic modulus of the connector at a preset temperature is obtained, which is the elastic modulus of the connector at the corresponding temperature under service conditions. Based on the coefficient A, stress exponent m, time exponent n, and the initial equivalent stress level calculation equation, an equivalent relaxation theory equation is established. This equation is:

[0067]

[0068] Where, σ r The equivalent stress of the connector after relaxation time t, where t represents the preset time period, σ0 is the equivalent stress of the connector when initially subjected to a complex load, A is the Norton-Bailey constitutive equation coefficient, n is the stress exponent in the Norton-Bailey constitutive equation, m is the time exponent in the Norton-Bailey constitutive equation, and E is the elastic modulus.

[0069] Specifically, the attribute values ​​include axial elongation, planar bending radius, planar torsional radius, and shear load;

[0070] Among them, the axial elongation, planar bending arc and planar torsional arc can all be measured by finite element analysis, RCC-MRx-III-Part1-Z-AppendixA6 or engineering testing, which are existing technologies and will not be elaborated on here; since no deformation occurs when shear load is applied to the connector, it cannot be measured, and it is only necessary to determine the magnitude of the shear load applied manually.

[0071] Complex loads consist of at least two superimposed loads, including axial tensile loads caused by the axial elongation of the connector, bending loads caused by the planar bending curvature of the connector, torsional loads caused by the planar torsional curvature of the connector, and shear loads on the connector.

[0072] In this embodiment, there are four types of complex loads: a complex load consisting of axial tensile load and bending load, a complex load consisting of axial tensile load and torsional load, a complex load consisting of planar tensile load and shear load, and a complex load consisting of axial tensile load, bending load and torsional load.

[0073] Based on the attribute values ​​and the stress distribution characteristics of complex load types, an initial equivalent stress level calculation equation is established. The specific steps are as follows:

[0074] First, assuming that there is only one type of load on the connector, the initial stress on the middle cross section of the connector caused by the load is obtained based on the stress distribution characteristics of the load.

[0075] When the above load is an axial tensile load, it results in:

[0076]

[0077] σ T L represents the initial axial stress on the intermediate cross-section of the connector caused by axial tensile load, and L is the initial shaft length of the connector. T E represents the axial elongation of the connector, and E represents the elastic modulus of the connector at the corresponding service temperature.

[0078] When the above load is a bending load, it results in:

[0079]

[0080] σ M This refers to the initial axial stress on the intermediate cross-section of the connector caused by bending load; please refer to [reference needed]. Figure 2-1 As shown, y is the planar bending radius caused by the bending load on the cross section, and y is the distance from the corresponding point to the neutral axis of the middle cross section of the connector.

[0081] When the above load is a torsional load, it results in:

[0082]

[0083] τ R This refers to the initial tangential stress on the intermediate cross-section of the connector caused by torsional load. Please refer to [reference needed]. Figure 2-2 As shown, R represents the planar torsional curvature caused by torsional load on the intermediate cross-section of the connector, where R is the distance from the corresponding point to the center of the intermediate cross-section of the connector. Please refer to [reference needed]. Figure 2-2 As shown, G is the shear modulus of the connector at a preset temperature;

[0084] When the above load is a shear load, it results in:

[0085]

[0086] τ s F is the initial tangential stress on the intermediate cross-section of the connector caused by shear load. S The load is shear load, and r represents the radius of the cross-section at the middle of the connector;

[0087] Using the calculation principle of von Mises equivalent stress, the stress distribution characteristics of different complex load types are obtained. Based on the calculation formula of the initial stress on the middle cross section of the connector caused by the corresponding load, the calculation equation of the initial equivalent stress level under complex load type is derived.

[0088] When the complex load is an axial tensile load and a bending load, the initial shaft length of the connector and the distance from the element point to the neutral axis of the cross section are obtained. Combining formulas (2) and (3), the initial equivalent stress level calculation equation is as follows:

[0089]

[0090] σ0 represents the equivalent stress when the connector is initially loaded with a complex load;

[0091] When the complex load is an axial tensile load and a torsional load, the distance from the element point to the center of the cross-section of the connector and the shear modulus of the connector at a preset temperature (i.e., the temperature during service) are obtained. Combining formula (2) and formula (4), the initial equivalent stress level calculation equation is obtained as follows:

[0092]

[0093] When the complex load is an axial tensile load and a shear load, the radius of the middle cross section of the connector is obtained. Combining formula (2) and formula (5), the initial equivalent stress level calculation equation is obtained as follows:

[0094]

[0095] When the complex load is an axial tensile load, bending load, and torsional load, the angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis is obtained. Combining formulas (2), (3), and (4), the initial equivalent stress level calculation equation is obtained as follows:

[0096]

[0097] Where θ is the angle between the line connecting the unit point on the middle cross section of the connector to the circle and the positive horizontal axis.

[0098] Specifically, by combining the characteristics of the combined working conditions of various loads in different complex load types, the equivalent stress level calculation equation and the equivalent relaxation stress equation, the axial average stress relaxation equation is derived.

[0099] For example, when a complex load includes both axial tensile load and bending load, the characteristics of each load's composition are that both axial tensile load and bending load cause the axial stress on the intermediate cross-section of the connecting part to relax. Combining formulas (1) and (6), the integral equation of the equivalent load after relaxation is obtained as follows:

[0100]

[0101] Wherein, F represents the remaining axial stress of the connector after a preset stress relaxation time period;

[0102] According to formula (10), the average axial stress of the connector after relaxation is calculated by dividing by the cross-sectional area of ​​the connector. The calculation equation is as follows:

[0103]

[0104] in, This represents the axial average stress after relaxation.

[0105] For example, when a complex load includes both axial tensile load and torsional load, the characteristic of each load's constituent working condition is that the ratio of the axial stress on the intermediate cross-section of the connector caused by the axial tensile load to the tangential stress on the intermediate cross-section of the connector caused by the torsional load remains constant. That is, throughout the entire relaxation process, the ratio of the initial axial stress on the intermediate cross-section of the connector caused by the axial tensile load to the initial tangential stress on the intermediate cross-section of the connector caused by the torsional load is equal to the ratio of the equivalent axial stress after a preset time period t to the equivalent tangential stress after a preset time period t. The specific relationship is as follows:

[0106]

[0107] Where, σ y τ is the equivalent axial stress of the connector after a preset time period t. x The connecting component experiences the equivalent tangential stress after a preset time t;

[0108] Based on the stress distribution characteristics of complex load types, we also obtain:

[0109]

[0110] By combining equations (1), (2), (4), (12), and (13), the equivalent axial stress σ of the connector after a preset time period t is derived. y The calculation formula is as follows:

[0111]

[0112] At this point, the equivalent axial stress at each point on the middle cross-section of the connector after a preset time period t is integrated to obtain the remaining axial stress F of the connector after the preset stress relaxation time period. The above integral equation is:

[0113]

[0114] By dividing by the cross-sectional area of ​​the connector in the middle using formula (15), the axial average stress relaxation equation is obtained as follows:

[0115]

[0116] in, This represents the axial average stress after relaxation.

[0117] For example, when the complex load is an axial tensile load and a shear load, the characteristics of the working conditions of each load are that the axial tensile load causes the axial stress on the middle cross section of the connector to relax, and the shear load does not affect the relaxation of the connector.

[0118] According to formula (13), under a preset time period, when the complex load is an axial tensile load and a shear load, and the following conditions are met:

[0119]

[0120] The equivalent axial stress of the connector after a preset time period t is 0, which means that the remaining axial stress of the connector after a preset stress relaxation time period is also 0, and correspondingly, the average axial stress after relaxation is also 0.

[0121] According to formula (13), under a preset time period, when the complex load is an axial tensile load and a shear load, and the following conditions are met:

[0122]

[0123] Then you can continue with the following calculations:

[0124] Considering that the tangential stress remains constant during the overall relaxation process of the connector, by combining formulas (1) and (13), the equivalent axial stress σ of the connector after a preset time period t is derived. y The calculation formula is as follows:

[0125]

[0126] At this point, the equivalent axial stress at each point on the middle cross-section of the connector after a preset time period t is integrated to obtain the remaining axial stress F of the connector after the preset stress relaxation time period. The above integral equation is:

[0127]

[0128] By dividing by the cross-sectional area of ​​the connector in the middle using formula (20), the axial average stress relaxation equation is obtained as follows:

[0129]

[0130] in, This represents the axial average stress after relaxation.

[0131] Specifically, when the complex load includes axial tensile load, bending load, and torsional load, the characteristic of each load's composition is that the ratio of the axial stress on the intermediate cross-section of the connector caused by the axial tensile load and bending load to the tangential stress on the intermediate cross-section of the connector caused by the torsional load remains constant. Therefore, during the entire relaxation process, the ratio of the initial axial stress on the intermediate cross-section of the connector caused by the axial tensile load and bending load to the initial tangential stress on the intermediate cross-section of the connector caused by the torsional load is equal to the ratio of the equivalent axial stress after a preset time period t to the equivalent tangential stress after a preset time period t. The specific formula is as follows:

[0132]

[0133] By combining formulas (1), (2), (3), (4), (13), and (22), the equivalent axial stress σ of the connector after a preset time period t is derived. y The calculation formula is as follows:

[0134]

[0135] At this point, the equivalent axial stress at each point on the middle cross-section of the connector after a preset time period t is integrated to obtain the remaining axial stress F of the connector after the preset stress relaxation time period. The above integral equation is:

[0136]

[0137] By dividing by the cross-sectional area of ​​the connector in the middle using formula (24), the axial average stress relaxation equation is obtained as follows:

[0138]

[0139] in, This represents the axial average stress after relaxation.

[0140] The present invention also provides another embodiment, which is described herein. Figure 8 As shown, it includes:

[0141] The type of complex load is determined based on the preload of the connector;

[0142] Based on the complex load type, determine the property values ​​of the connector. The property values ​​characterize the deformation parameters and shear loads generated by the connector under stress.

[0143] Based on the determined attribute values ​​and the stress distribution characteristics of complex load types, the initial equivalent stress level calculation equation for the element point under complex load types is obtained. The initial equivalent stress level calculation equation is characterized as the functional relationship between the equivalent stress and attribute values ​​when the connector is initially loaded with a complex load.

[0144] The Norton-Bailey constitutive equation coefficients A, stress exponent m, and time exponent n were determined by conducting high-temperature creep fracture tests on the connector. Based on the coefficients A, stress exponent m, time exponent n, and the calculation equation of the initial equivalent stress level, the equivalent relaxation theory equation was established. The equivalent relaxation theory equation is characterized as a functional relationship between the equivalent stress of the connector after a preset relaxation time period and the equivalent stress of the connector when initially loaded with a complex load.

[0145] Based on the initial equivalent stress level calculation equation and the equivalent stress relaxation theory equation, combined with the composition characteristics of each load in the complex load type, the relaxed axial average stress is obtained.

[0146] The average axial stress of the connector after relaxation is compared with the preset minimum clamping limit to evaluate the connector.

[0147] The preload design of the connector meets the requirements when the minimum clamping force limit is not greater than the average axial stress after relaxation.

[0148] When the minimum clamping force limit is greater than the axial average stress after relaxation, the new preload of the connector is determined and the connector is re-evaluated until the minimum clamping force limit is not greater than the new axial average stress after relaxation.

[0149] In the above steps, the new preload can be achieved by changing the magnitude of the preload tightening force or the tightening method;

[0150] By redesigning the new preload and re-evaluating the connection until the minimum clamping force limit is no greater than the new axial average stress after relaxation, it can be ensured that the designed connection meets the service requirements.

[0151] Furthermore, the Norton-Bailey constitutive equation coefficients A, stress exponent m, and time exponent n were determined by conducting high-temperature creep rupture tests on the connectors, including:

[0152] High-temperature creep fracture test was conducted on the connector under the load stress to obtain the creep stress-strain curve corresponding to the high-temperature creep fracture test as a function of time.

[0153] The creep stress-strain curve is fitted using the Norton-Bailey constitutive equation to determine the coefficients A, stress exponent m, and time exponent n corresponding to the creep stress-strain curve.

[0154] The Norton-Bailey constitutive equation is:

[0155] ε c =Aσ n t m (26)

[0156] In formula (26), ε c σ is the strain generated during creep in a creep-connected joint, and σ is the load-bearing stress.

[0157] The following section describes the stress relaxation simulation and calculation of 316SS material in ASME III HBB-T at an operating temperature of 566°C under four different complex loads, using a high-temperature connector evaluation method considering stress relaxation as described in this invention. The results are compared with those obtained by traditional finite element analysis methods. Specific results are as follows:

[0158] Firstly, when the bolted connection is subjected to complex loads, namely deformation-controlled axial tensile loads and bending loads:

[0159] It should be understood that this example is not based on a real engineering case and does not specify a minimum bolt clamping force limit σ according to the functional requirements of the bolted connection equipment during service. LB This is mainly used to illustrate the application process and prediction accuracy of the stress relaxation prediction model in this method.

[0160] Material parameters of 316SS material at 566℃ were obtained according to ASME standards. The material's elastic modulus is 186846 MPa, Poisson's ratio is 0.3, and yield strength is 140.5 MPa. The creep stress-strain relationship of the material was fitted using the Norton-Bailey equation, yielding: A = 3.35E-15, n = 4.9, m = 0.4833. Since stress relaxation in bolted connections is mainly caused by deformation in the bolt shank region, a cylindrical finite element model of the bolt shank was established. Based on GB / T 5782-2000 Class A and Class B hexagonal head bolts, the bolt shank radius was selected as 13.5 mm, and the initial shaft length was 80 m. The bolt shank is subjected to axial displacement loads and bending loads about the neutral axis of the bolt cross-section. The load application methods are as follows: Figure 3-1 As shown in the figure, the bottom surface of the bolt is fully constrained, and a reference point RF is established on the upper end face, with the reference point coupled to the upper end face. Axial tensile and bending loads are applied to the reference point RF. Based on this method, the axial average stress after relaxation for different times under the corresponding complex loads is obtained, and the axial average stress relaxation curve changing with time is plotted accordingly. The results obtained by the finite element analysis method are compared, and the bolt attribute values ​​and result comparison diagram are shown in Table 1.

[0161] Table 1 Comparison of Load Levels and Results

[0162]

[0163] Secondly, when the bolted connection is subjected to complex loads, namely deformation-controlled axial tensile loads and torsional loads:

[0164] It should be understood that this example is not based on a real engineering case and does not specify a minimum bolt clamping force limit σ according to the functional requirements of the bolted connection equipment during service. LB This is mainly used to illustrate the application process and prediction accuracy of the stress relaxation prediction model in this method.

[0165] Material parameters of 316SS material at 566℃ were obtained according to ASME standards. The material's elastic modulus is 186846 MPa, Poisson's ratio is 0.3, and yield strength is 140.5 MPa. The creep stress-strain relationship of the material was fitted using the Norton-Bailey equation, yielding: A = 3.35E-15, n = 4.9, m = 0.4833. Since bolt stress relaxation is mainly caused by deformation in the bolt shank region, a cylindrical finite element model of the bolt shank was established. The bolt, selected according to GB / T 5782-2000 Class A and Class B hexagonal head bolts, has a radius of 13.5 mm and an initial axial length of 80 mm. The bolt shank is subjected to axial tensile load and torsional load about the bolt's central axis, with the load application methods as follows: Figure 3-2 As shown in the figure, the bottom surface of the bolt shank is fully constrained, and a reference point RF is established on the upper end face, with the reference point coupled to the upper end face. Axial tensile and torsional loads are applied to the reference point RF. Based on this method, the axial average stress at different relaxation times under the corresponding complex loads is obtained, and the axial average stress relaxation curve over time is plotted accordingly, and compared with the results obtained by the finite element analysis method. The bolt property values ​​and result comparison diagram are shown in Table 2.

[0166] Table 2 Comparison of Attribute Values ​​and Results

[0167]

[0168] Third, when the bolted connection is subjected to complex loads, namely deformation-controlled axial tensile loads and shear loads:

[0169] It should be understood that this example is not based on a real engineering case and does not specify a minimum bolt clamping force limit σ according to the functional requirements of the bolted connection equipment during service. LBThis section primarily illustrates the application process and prediction accuracy of the stress relaxation prediction model in this method. Basic material parameters of 316SS material at 566℃ were obtained according to ASME standards. The material's elastic modulus is 186846 MPa, Poisson's ratio is 0.3, and yield strength is 140.5 MPa. The creep stress-strain relationship of the material was fitted using the Norton-Bailey equation, yielding: A = 3.35E-15, n = 4.9, m = 0.4833. Bolts selected according to GB / T5782-2000 (Grade A and B hexagonal head bolts) have a radius of 13.5 mm and an axial length of 80 mm. Since the shear load is mainly caused by friction between the nut and bolt head and the connected parts, the clamped parts, nuts, and bolt heads need to be established during modeling. The end face dimensions of the clamped parts are 100 × 40 mm. The bolt bears axial bolt load, and the connecting parts bear constant tangential tensile force. There is no friction between the clamped parts in the model. The specific load application method is as follows... Figure 3-3 As shown, the bottom surface of the bolt is subject to displacement constraints in the Y-axis direction (Uy), and the corresponding end faces of the clamping member are subject to displacement constraints in the X (Ux) and Z (Uz) axes. An axial tensile load, Bolt force, is applied to the cross-section of the bolt, and a uniformly distributed stress, with a total force of Fs, is applied to the corresponding end faces of the clamping member. An axial displacement load is applied to the upper end face. Based on this method, the axial average stress at different relaxation times under the corresponding complex load is obtained, and the axial average stress relaxation curve over time is plotted and compared with the results obtained by the finite element analysis method. The bolt attribute values ​​and result comparison diagram are shown in Table 3.

[0170] Table 3 Comparison of Load Levels and Results

[0171]

[0172] Fourth, when the bolted connection is subjected to complex loads such as deformation-controlled axial tensile loads, bending loads, and torsional loads:

[0173] It should be understood that this example is not based on a real engineering case and does not specify a minimum bolt clamping force limit σ according to the functional requirements of the bolted connection equipment during service. LB This is mainly used to illustrate the application process and prediction accuracy of the stress relaxation prediction model in this method.

[0174] The basic material parameters of 316SS material at 566℃ were obtained according to ASME standards. The material's elastic modulus is 186846 MPa, Poisson's ratio is 0.3, and yield strength is 140.5 MPa. The creep stress-strain relationship of the material was fitted using the Norton-Bailey equation, yielding: A = 3.35E-15, n = 4.9, m = 0.4833. Since bolt stress relaxation is mainly caused by deformation in the bolt shank region, a cylindrical finite element model of the bolt shank was established. The bolt, selected according to GB / T 5782-2000 Class A and Class B hexagonal head bolts, has a radius of 13.5 mm and an initial axial length of 80 mm. The bolt shank is subjected to axial tensile load, bending load about the neutral axis of the bolt cross-section, and torsional load about the central axis of the bolt. The load application methods are as follows: Figure 3-4 As shown in the figure, the bottom surface of the bolt shank is fully constrained, and a reference point RF is established on the upper end face, with the reference point coupled to the upper end face. Axial tensile and torsional loads are applied to the reference point RF. Based on this method, the axial average stress at different relaxation times under the corresponding complex loads is obtained, and the axial average stress relaxation curve over time is plotted accordingly, and compared with the results obtained by the finite element analysis method. The bolt property values ​​and result comparison diagram are shown in Table 4.

[0175] Table 4 Comparison of Load Levels and Results

[0176]

[0177] As can be seen from the comparison of the results above, the method of the present invention has prediction results that are close to those of finite element analysis, and can effectively predict and evaluate the relaxation behavior of high-temperature connectors under different composite loads.

[0178] This invention also provides a high-temperature connector evaluation system that takes stress relaxation into account, please refer to [link / reference here]. Figure 9 As shown, it includes:

[0179] The load type determination module is used to determine the complex load type of the connector based on the preload of the connector.

[0180] The parameter determination module receives complex load types and determines the attribute values ​​of the connectors. The attribute values ​​characterize the deformation parameters and shear loads generated by the force on the connectors.

[0181] The initial equivalent stress calculation module receives attribute values ​​and, based on the stress distribution characteristics of complex load types, obtains the initial equivalent stress level calculation equation. The initial equivalent stress level calculation equation represents the functional relationship between the equivalent stress and attribute values ​​when the connector is initially loaded with a complex load.

[0182] The equivalent stress relaxation theory equation acquisition module receives the initial equivalent stress level calculation equation, and combines the Norton-Bailey constitutive equation coefficients A, stress exponent m and time exponent n obtained from the high temperature creep fracture test of the connector to establish the equivalent stress relaxation theory equation. The equivalent relaxation theory equation is characterized as the functional relationship between the equivalent stress of the connector after the relaxation preset time period and the equivalent stress of the connector when initially loaded with complex load.

[0183] The axial average stress calculation module receives the equivalent stress relaxation theory equation and the initial equivalent stress level calculation equation, and calculates the axial average stress after relaxation of the connecting parts according to the composition characteristics of each load in the complex load type.

[0184] The evaluation module is used to input the required minimum clamping force limit and the received axial average stress after relaxation, to determine the magnitude of the axial average stress after relaxation and the minimum clamping force limit, and to evaluate the connector based on the judgment result.

[0185] Optionally, when the equivalent stress relaxation theory equation acquisition module establishes the equivalent stress relaxation theory equation, it acquires the elastic modulus of the connector at a preset temperature, and establishes the equivalent relaxation theory equation based on the coefficient A, stress exponent m, time exponent n, and the initial equivalent stress level calculation equation. This equation is:

[0186]

[0187] Where, σ r The equivalent stress of the connector after relaxation time t, where t represents the preset time period, σ0 is the equivalent stress of the connector when initially subjected to a complex load, A is the Norton-Bailey constitutive equation coefficient, n is the stress exponent in the Norton-Bailey constitutive equation, m is the time exponent in the Norton-Bailey constitutive equation, and E is the elastic modulus.

[0188] Optionally, when the initial equivalent stress calculation module establishes the initial equivalent stress calculation equation, the attribute values ​​include axial elongation, planar bending radius, planar torsional radius, and shear load.

[0189] Complex loads consist of at least two superimposed loads, including axial tensile loads caused by the axial elongation of the connector, bending loads caused by the planar bending curvature of the connector, torsional loads caused by the planar torsional curvature of the connector, and shear loads on the connector.

[0190] Based on the attribute values ​​and the stress distribution characteristics of complex load types, an initial equivalent stress level calculation equation is established, including:

[0191] When the complex load is an axial tensile load and a bending load, the initial shaft length of the connector and the distance from the element point to the neutral axis of the cross section are obtained. The initial equivalent stress level calculation equation is as follows:

[0192]

[0193] Where σ0 represents the equivalent stress when the connector is initially loaded with a complex load, and L T L represents the axial elongation, and L is the initial shaft length. Let y be the planar bending radius caused by the bending load on the intermediate cross-section of the connector, and y be the distance from the element point to the neutral axis of the intermediate cross-section of the connector.

[0194] When the complex load includes both axial tensile load and torsional load, the distance from the element point to the center of the cross-section of the connector and the shear modulus of the connector at a preset temperature are obtained. The initial equivalent stress level calculation equation is as follows:

[0195]

[0196] in, R is the planar torsional curvature caused by torsional load on the middle cross section of the connector, R is the distance from the element point to the center of the middle cross section of the connector, and G is the shear modulus.

[0197] When the complex load includes both axial tensile load and shear load, the radius of the intermediate cross-section of the connector is obtained, and the initial equivalent stress level is calculated using the following equation:

[0198]

[0199] Among them, F S For shear load, r represents the radius of the cross-section at the middle of the connector;

[0200] When complex loads include axial tensile loads, bending loads, and torsional loads, the angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis is obtained. The initial equivalent stress level calculation equation is as follows:

[0201]

[0202] Where θ is the angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis.

[0203] Optionally, when the axial average stress calculation module calculates the relaxed axial average stress, if the complex load consists of axial tensile load and bending load, and the characteristics of each load condition are that the axial tensile load and bending load cause the axial stress on the middle cross section of the connector to relax, then the calculation equation for the relaxed axial average stress is:

[0204]

[0205] in, This represents the axial average stress after relaxation.

[0206] Optionally, when the axial average stress calculation module calculates the relaxed axial average stress, if the complex load includes both axial tensile load and torsional load, and the characteristic of each load's composition is that the axial tensile load causes axial stress on the intermediate cross-section of the connector, and the ratio of this stress to the torsional load causing tangential stress on the intermediate cross-section of the connector remains constant, then the equation for calculating the relaxed axial average stress is:

[0207]

[0208] in, This represents the average axial stress after the connector has relaxed.

[0209] Optionally, when the axial average stress calculation module calculates the relaxed axial average stress, if the complex load includes both axial tensile load and shear load, and the characteristics of each load's composition are that the axial tensile load causes relaxation of the axial stress on the intermediate cross-section of the connector, and the shear load does not affect the relaxation of the connector, then the equation for calculating the relaxed axial average stress is:

[0210]

[0211] in, This represents the axial average stress after relaxation.

[0212] Optionally, when the axial average stress calculation module calculates the relaxed axial average stress,

[0213] When complex loads include axial tensile loads, bending loads, and torsional loads, the characteristic of each load component is that the axial tensile load and bending load cause axial stress on the intermediate cross-section of the connector, and the ratio of this stress to the tangential stress on the intermediate cross-section of the connector caused by the torsional load remains constant. Therefore, the equation for calculating the relaxed axial average stress is:

[0214]

[0215] in, This represents the axial average stress after relaxation.

[0216] Optionally, when the evaluation module evaluates the connector, if the minimum clamping force limit is not greater than the average axial stress after relaxation, the preload design of the connector meets the requirements.

[0217] When the minimum clamping force limit is greater than the axial average stress after relaxation, a new preload force is determined for the connector, and the connector is re-evaluated until the minimum clamping force limit is not greater than the new axial average stress after relaxation.

[0218] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A method for evaluating high-temperature connectors considering stress relaxation, characterized in that, include: The type of complex load is determined based on the preload of the connector; Based on the complex load type, the attribute values ​​of the connector are determined, which characterize the deformation parameters and shear loads generated by the force on the connector. Based on the attribute values ​​and the stress distribution characteristics of the complex load type, the initial equivalent stress level calculation equation under the complex load type is obtained. The initial equivalent stress level calculation equation represents the functional relationship between the equivalent stress and the attribute values ​​when the connector is initially loaded with the complex load. The connection was determined by conducting a high-temperature creep rupture test on the connector. Norton-Bailey Constitutive equation coefficients A Stress index m With time index n and according to the coefficient A Stress index m Time index n The initial equivalent stress level calculation equation is used to establish the equivalent relaxation theory equation, which characterizes the functional relationship between the equivalent stress of the connector after a preset relaxation time period and the equivalent stress of the connector when the complex load is initially applied. Based on the initial equivalent stress level calculation equation and the equivalent relaxation theory equation, and combined with the composition characteristics of each load in the complex load type, the axial average stress after relaxation of the connector is obtained. The average axial stress after the connector is relaxed is compared with the preset minimum clamping force limit to evaluate the connector; The attribute values ​​include axial elongation, planar bending radius, planar torsional radius, and shear load; The complex load is composed of at least two superimposed loads, including the axial tensile load caused by the axial elongation of the connector, the bending load caused by the planar bending curvature of the connector, the torsional load caused by the planar torsional curvature of the connector, and the shear load on the connector. Based on the attribute values ​​and the stress distribution characteristics of the complex load type, the initial equivalent stress level calculation equation is established, including: When the complex load is an axial tensile load and a bending load, the initial shaft length of the connector and the distance from the element point to the neutral axis of the cross section are obtained. The initial equivalent stress level calculation equation is as follows: in, This represents the equivalent stress when the connector is initially loaded with the complex load. L T This refers to the axial elongation of the connector. L This is the initial shaft length of the connector. The curvature of the plane caused by the bending load on the intermediate cross-section of the connector. y This is the distance from the element point to the neutral axis of the middle cross section of the connector; When the complex load is an axial tensile load and a torsional load, the distance from the unit point to the center of the cross-section of the connector and the shear modulus of the connector at a preset temperature are obtained. The initial equivalent stress level calculation equation is as follows: in, This refers to the planar torsional curvature caused by torsional load on the intermediate cross-section of the connector. R This represents the distance from the unit point to the center of the cross-section of the connector. G Shear modulus; When the complex load is an axial tensile load and a shear load, the radius of the intermediate cross-section of the connector is obtained, and the initial equivalent stress level is calculated using the following equation: in, For shear load, r represents the radius of the cross-section at the middle of the connector; When the complex load is an axial tensile load, bending load, or torsional load, the angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis is obtained. The initial equivalent stress level calculation equation is as follows: in, The angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis.

2. The method for evaluating high-temperature connectors considering stress relaxation according to claim 1, characterized in that, Obtain the elastic modulus of the connector at a preset temperature, and based on the coefficient... A Stress index m Time index n And the equivalent relaxation theory equation is established based on the initial equivalent stress level calculation equation. The equation is as follows: in, Loosen the connector t Equivalent stress after time, t Indicates a preset time period. The equivalent stress when the complex load is initially applied to the connector. A for Norton-Bailey Constitutive equation coefficients n for Norton-Bailey Stress exponent in constitutive equations m for Norton-Bailey The time exponent in the constitutive equation E It is the elastic modulus.

3. The method for evaluating high-temperature connectors considering stress relaxation according to claim 1, characterized in that: When the complex load consists of axial tensile load and bending load, the characteristic of each load condition is that both the axial tensile load and bending load cause relaxation of the axial stress on the intermediate cross-section of the connector. Therefore, the equation for calculating the relaxed average axial stress is: in, This represents the axial average stress after relaxation.

4. The method for evaluating high-temperature connectors considering stress relaxation according to claim 1, characterized in that: When the complex load includes both axial tensile load and torsional load, the characteristic of each load's constituent working condition is that the ratio of the axial stress caused by the axial tensile load to the tangential stress caused by the torsional load on the intermediate cross-section of the connector remains constant. Therefore, the equation for calculating the relaxed axial average stress is: in, This represents the average axial stress after the connector has relaxed.

5. The method for evaluating high-temperature connectors considering stress relaxation according to claim 1, characterized in that: When the complex load includes both axial tensile load and shear load, the characteristic of each load's working condition is that the axial tensile load causes relaxation of the axial stress on the intermediate cross-section of the connector, and the shear load has no effect on the relaxation of the connector. Therefore, the equation for calculating the relaxed axial average stress is: in, This represents the axial average stress after relaxation.

6. The method for evaluating high-temperature connectors considering stress relaxation according to claim 1, characterized in that: When the complex load includes axial tensile load, bending load, and torsional load, the characteristic of each load's constituent working condition is that the ratio of the axial stress on the intermediate cross-section of the connector caused by the axial tensile load and bending load to the tangential stress on the intermediate cross-section of the connector caused by the torsional load remains constant. Therefore, the equation for calculating the relaxed axial average stress is: in, This represents the axial average stress after relaxation.

7. A method for evaluating high-temperature connectors considering stress relaxation according to any one of claims 1 to 6, characterized in that, The average axial stress of the connector after relaxation is compared with a preset minimum clamping force limit to evaluate the connector, including: The preload design of the connector meets the requirements when the minimum clamping force limit is not greater than the average axial stress after relaxation. When the minimum clamping force limit is greater than the relaxed axial average stress, a new preload force is determined for the connector, and the connector is re-evaluated until the minimum clamping force limit is not greater than the new relaxed axial average stress.

8. A method for evaluating high-temperature connectors considering stress relaxation according to any one of claims 1 to 6, characterized in that, The connection was determined by conducting a high-temperature creep rupture test on the connector. Norton-Bailey Constitutive equation coefficients A Stress index m With time index n ,include: A high-temperature creep rupture test was conducted on the connector to obtain the creep stress-strain curves that change with time corresponding to the high-temperature creep rupture test. use Norton-Bailey The constitutive equation is fitted to the creep stress-strain curve to determine the coefficients corresponding to the creep stress-strain curve. A Stress index m With time index n .

9. A high-temperature connector evaluation system considering stress relaxation, characterized in that, include: The load type determination module is used to determine the complex load type of the connector based on the preload of the connector. The parameter determination module receives the complex load type and determines the attribute values ​​of the connector. The attribute values ​​characterize the deformation parameters and shear loads generated by the force on the connector. The attribute values ​​include axial elongation, planar bending curvature, planar torsional curvature, and shear load. The complex load is composed of at least two superimposed loads, including the axial tensile load caused by the axial elongation of the connector, the bending load caused by the planar bending curvature of the connector, the torsional load caused by the planar torsional curvature of the connector, and the shear load experienced by the connector. The initial equivalent stress calculation module receives the attribute value and, based on the stress distribution characteristics of the complex load type, obtains the initial equivalent stress level calculation equation. The initial equivalent stress level calculation equation represents the functional relationship between the equivalent stress and the attribute value when the connector is initially loaded with the complex load. Based on the attribute values ​​and the stress distribution characteristics of the complex load type, the initial equivalent stress level calculation equation is established, including: When the complex load is an axial tensile load and a bending load, the initial shaft length of the connector and the distance from the element point to the neutral axis of the cross section are obtained. The initial equivalent stress level calculation equation is as follows: in, This represents the equivalent stress when the connector is initially loaded with the complex load. L T This refers to the axial elongation of the connector. L This is the initial shaft length of the connector. The curvature of the plane caused by the bending load on the intermediate cross-section of the connector. y This is the distance from the element point to the neutral axis of the middle cross section of the connector; When the complex load is an axial tensile load and a torsional load, the distance from the unit point to the center of the cross-section of the connector and the shear modulus of the connector at a preset temperature are obtained. The initial equivalent stress level calculation equation is as follows: in, The planar torsional curvature caused by torsional load on the intermediate cross-section of the connector. R This represents the distance from the unit point to the center of the cross-section of the connector. G Shear modulus; When the complex load is an axial tensile load and a shear load, the radius of the intermediate cross-section of the connector is obtained, and the initial equivalent stress level is calculated using the following equation: in, For shear load, r represents the radius of the cross-section at the middle of the connector; When the complex load is an axial tensile load, bending load, or torsional load, the angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis is obtained. The initial equivalent stress level calculation equation is as follows: in, The angle between the line connecting the unit point on the middle cross section of the connector to the center of the circle and the positive horizontal axis; The equivalent relaxation theory equation acquisition module receives the initial equivalent stress level calculation equation and combines it with the equation obtained from the high-temperature creep fracture test of the connector. Norton-Bailey Constitutive equation coefficients A Stress index m With time index n An equivalent relaxation theory equation is established, which represents the functional relationship between the equivalent stress of the connector after a preset relaxation time period and the equivalent stress of the connector when the complex load is initially applied. The axial average stress calculation module receives the equivalent relaxation theory equation and the initial equivalent stress level calculation equation, and calculates the axial average stress of the connector after relaxation based on the composition characteristics of each load in the complex load type. The evaluation module is used to input the required minimum clamping force limit and receive the axial average stress after relaxation, determine the magnitude of the axial average stress after relaxation and the minimum clamping force limit, and evaluate the connector based on the determination result.

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