A steel structure fatigue life evaluation method and system based on multi-level load

Abstract

This invention discloses a method and system for assessing the fatigue life of steel structures based on multi-level loads. The method includes: constructing a normalized constitutive model that uniformly characterizes the material damage evolution under static, dynamic, and vibration loads by integrating damage mechanisms under these three types of loads; establishing a segmented fatigue life assessment sub-model based on the detailed fatigue rating (DFR) method to distinguish the differences in fatigue characteristics between the medium-to-long life range and the long life range; and combining the normalized constitutive model, the life assessment sub-model, and the Miner linear cumulative damage criterion to complete the dynamic correction of load spectrum data and accurate calculation of cumulative damage, ultimately outputting the cumulative damage degree, fatigue life, and health status level of the structure. This invention solves the problems of poor adaptability to complex multi-level load conditions, incomplete damage characterization, and insufficient prediction accuracy across the entire life range in existing assessment methods. It can improve the engineering applicability of steel structures for special equipment in complex service environments and provide reliable technical support for the safe operation and maintenance of special equipment.

Description

Technical Field

[0001] This invention relates to the field of health monitoring and fatigue damage prediction technology for special steel structures, specifically to a method and system for assessing the fatigue life of steel structures based on multi-level loads. Background Technology

[0002] In key sectors such as infrastructure construction, aerospace, shipbuilding, and steel metallurgy in my country, steel structural components of special equipment like cranes, bridges, and offshore platforms serve as core load-bearing units, operating under complex and variable load environments for extended periods and continuously enduring the coupling effects of alternating loads. With increasing service life, these components accumulate microscopic damage due to factors such as micro-dislocations and irregular metallographic structures, potentially leading to structural failure and seriously threatening engineering safety and the lives and property of personnel. As modern engineering demands for the service safety and durability of special steel structures continue to rise, the importance of fatigue damage assessment technology is becoming increasingly prominent.

[0003] Current fatigue damage theories largely focus on damage mechanisms under single load conditions, failing to fully characterize the nonlinear and cumulative characteristics of damage evolution under multi-level load coupling. This leads to significant discrepancies between assessment results and actual service conditions under complex working conditions. Traditional damage detection for special steel structures primarily relies on manual visual inspection and non-destructive testing for periodic verification and specialized inspections. This not only consumes substantial manpower, material resources, and time but also has fixed inspection cycles, making it difficult to achieve real-time early warning of sudden damage and failing to meet the dynamic safety management requirements of special steel structures. Furthermore, current research on life assessment of special steel structures under multi-level loads is limited. Some related studies concentrate on single load characteristics, mechanical strength calculations, or overall structural macroscopic assessments, lacking an integrated assessment scheme that balances model accuracy and engineering practicality, making it difficult to adapt to the application needs of complex engineering scenarios. Summary of the Invention

[0004] The main objective of this invention is to address the aforementioned problems. This invention proposes a method and system for assessing the fatigue life of steel structures based on multi-level loads. By integrating the cumulative damage mechanism and constitutive model of special steel structures under static, dynamic, and vibration loads, a normalized constitutive model of damage to special steel structures under multi-level load conditions is constructed. This model is then combined with the detailed fatigue rating (DFR) fatigue life model to design an integrated life assessment system for special steel structures, thereby ensuring the service safety of special steel structures.

[0005] This invention can integrate multi-source information and adapt to various types of loads, overcoming the limitations of traditional fatigue damage theory which is limited to a single load, and fully considering the complex damage evolution process.

[0006] On the other hand, while retaining the multi-level load damage modeling framework, this invention introduces load spectrum characteristics and material mechanical property parameters under actual working conditions to improve the engineering applicability of steel structure evaluation results.

[0007] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0008] A method for optimizing the fatigue life of steel structures based on multi-level loads includes the following steps: S1 constructs a normalized constitutive model of steel structure damage under static load, dynamic load and vibration load. This model comprehensively considers damage variables and damage evolution process, and can uniformly characterize the damage behavior of steel structure under different loads. S2 acquires the material parameters, load spectrum data and working condition parameters of the target steel structure, and establishes a high-quality dataset through data preprocessing. S3 Based on the Detailed Fatigue Rating (DFR) method, fatigue life assessment sub-models applicable to the medium-to-long life range and the long life range are established respectively, and the relationship between DFR value and stress amplitude and fatigue life is quantified. S4 corrects the load spectrum data based on the damage normalization constitutive model, and calculates the cumulative damage and fatigue life of the steel structure under multi-level loads by combining the fatigue life assessment sub-model and the Miner linear cumulative damage criterion. S5 constructs a fatigue life assessment system that outputs the cumulative damage degree, fatigue life, health status level and assessment report of steel structures in real time, providing accurate decision support for the operation and maintenance of special equipment.

[0009] In the above technical solution, in step S1, when constructing the steel structure damage constitutive equation under static load, the problem of only considering material hardening and ignoring the damage decline stage in the traditional constitutive equation is corrected. Now, based on the Lemaitre strain equivalence principle, Von Mises yield criterion and isotropic damage theory, the damage evolution process of steel after the ultimate strength is incorporated for correction.

[0010] In the above technical solution, in step S1, the maximum inter-story displacement and hysteresis energy consumption of the vibration disturbance are used to establish a damage model under vibration disturbance, and then the model is integrated with the overall structural damage model to calculate the damage index of the overall structure.

[0011] In the above technical solution, in step S1, a normalized constitutive model of steel structure damage is constructed by combining factors such as static, dynamic and vibration loads, and a temperature-dependent damage function and a corrosion fatigue damage model are introduced to enhance applicability.

[0012] In the above technical solution, in step S2, the material parameters, load spectrum data and working condition parameters of the steel structure are obtained, and after data preprocessing, a high-quality dataset that meets the requirements of damage prediction accuracy is constructed.

[0013] In the above technical solution, in step S3, fatigue life assessment models for the medium-to-long life range and the long life range are established based on the DFR method, and the fatigue life of steel structures is accurately predicted by quantifying the relationship equation.

[0014] In the above technical solution, in step S4, the cumulative damage degree under multi-level loads is calculated by combining the Miner linear cumulative damage criterion, and the fatigue failure critical point of the steel structure is determined.

[0015] In the above technical solution, in step S5, a fatigue life assessment system for steel structures is designed based on the multi-level load damage model and the DFR method evaluation model, providing a health status level and maintenance recommendations.

[0016] In summary, the fatigue life assessment method for steel structures based on multi-level loads of the present invention relies on the service condition monitoring system for steel structures of special equipment to comprehensively collect multi-dimensional mechanical parameters and material property parameters related to static loads, dynamic loads, and vibration loads; the collected raw data is systematically preprocessed, including outlier removal, data standardization, and load spectrum regularization, to construct a high-quality dataset that meets the requirements of damage modeling and life assessment.

[0017] Based on the preprocessed dataset, specific damage constitutive models were constructed to address the differences in damage mechanisms under different load types. Under static loads, the Lemaitre strain equivalence principle, Von Mises yield criterion, and isotropic damage theory were introduced to characterize the damage evolution behavior of steel after reaching its ultimate strength. Under dynamic loads, the strain rate effect was introduced based on the CS model to correct the material strength and damage evolution process. Under vibration disturbance conditions, a vibration damage model was established based on the nonlinear combination relationship between the maximum inter-story displacement and the maximum hysteretic energy dissipation of the layered structure, and the overall structural damage index was calculated.

[0018] Based on this, by adding a unified damage variable and load coupling coefficient, the damage evolution behavior under different load forms is normalized, and a constitutive model that can characterize the damage evolution of multi-level loads is constructed. At the same time, temperature-related damage functions and corrosion fatigue damage models are introduced to expand the model's adaptability to complex environmental conditions and improve the versatility of engineering applications.

[0019] Based on the Detailed Fatigue Rating (DFR) method, and considering the differences in fatigue characteristics between long-life ranges in steel structures, a segmented modeling strategy is adopted to establish quantitative relationship equations between DFR values, stress amplitude, and fatigue life. Combined with the Miner linear cumulative damage criterion, a damage accumulation calculation model under multi-level loads is constructed to achieve accurate quantification of damage evolution at different load levels and different life stages.

[0020] Based on the aforementioned multi-level load damage model and DFR method fatigue life assessment model, an integrated steel structure fatigue life assessment system is designed, integrating core functional modules for material and parameter setting, dynamic strength correction, and life assessment. The system supports the import, generation, and clearing of load spectrum data, can automatically switch between medium- and long-life assessment models, and outputs multi-dimensional visualized analysis results and assessment reports, forming a complete technical system of "data acquisition - model calculation - result output - operation and maintenance decision-making," providing precise technical support for the safe operation and maintenance of special equipment steel structures.

[0021] Based on the above methods, the present invention also provides an electronic device or system, including a processor, a memory, and a program stored in the memory and executable on the processor, wherein the program, when executed by the processor, implements the steps of any of the above methods.

[0022] The present invention also provides a computer-readable storage medium storing a program that, when executed by a processor, implements the steps of any of the methods described above.

[0023] Compared with the prior art, the beneficial effects of this invention are:

[0024] This invention constructs a constitutive model for the full-process damage of steel under static loads, overcoming the limitations of traditional models. Addressing the shortcomings of traditional models that assume damage stops after steel reaches its ultimate strength and fail to accurately reflect the actual mechanical response during service, this invention integrates damage variables and evolution laws into the constitutive relation based on the Lemaitre strain equivalence principle, the Von Mises yield criterion, and isotropic damage theory. By modifying the softening stage after the ultimate strength on the basis of an ideal elastoplastic model, it achieves a continuous characterization of the damage development process before and after the ultimate strength of steel, significantly improving the rationality and accuracy of damage analysis and prediction of steel structures under static loads.

[0025] This invention systematically expands the damage modeling method under dynamic loads and vibration disturbances. Addressing the significant strain rate sensitivity of steel under dynamic conditions, a strain rate correction mechanism based on the CS model is introduced. This mechanism comprehensively considers the coupled effects of strain rate, strain hardening, strain stiffening, and damage evolution to accurately describe the material's dynamic mechanical response. For vibration disturbances, based on the nonlinear combination relationship between the maximum inter-story displacement and hysteretic energy dissipation in layered structures, and combining a column bilinear restoring force model with an inter-story weighted superposition strategy, a multi-level damage quantification system is constructed from component layers, floor layers to the overall structural layers, realistically reflecting the effect of vibration on structural damage evolution.

[0026] This invention innovatively constructs a multi-level load damage normalized constitutive model to achieve a unified representation of complex working conditions. By introducing a unified damage variable and load coupling mechanism, the damage evolution behavior under static, dynamic, and vibration loads is incorporated into the same theoretical framework, achieving integrated modeling of steel structure damage under complex service conditions. For special environments such as high temperature and corrosion, temperature-related damage functions and corrosion fatigue damage models are further integrated, significantly improving the model's applicability and scalability in complex environments.

[0027] This invention proposes a segmented fatigue life assessment method and integrated system, providing precise operation and maintenance support. It introduces the Detailed Fatigue Rating (DFR) theory and establishes a segmented life assessment model based on the differences in fatigue characteristics between the medium-to-long life and long life ranges. Combined with the Miner linear cumulative damage criterion, it achieves damage accumulation calculation and life prediction under multi-level loads. The constructed assessment system can intuitively output core results such as fatigue life and damage status, providing a reliable technical basis for the safe operation, life management, and maintenance decisions of special equipment steel structures. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0029] Figure 1 This is a flowchart of the fatigue life assessment method for multi-level load steel structures according to an embodiment of the present invention. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0031] Example 1:

[0032] like Figure 1 As shown, the fatigue life optimization method for multi-level load steel structures according to the present invention includes the following steps:

[0033] Based on the Lemaitre strain equivalence principle, Von Mises yield criterion, and isotropic damage theory, S1 establishes a damage constitutive equation for steel under static load. By introducing the CS model and incorporating the strain rate effect, the constitutive equation under static load is modified to construct a damage constitutive equation under dynamic load. Combining the nonlinear combination relationship between the maximum inter-story displacement and hysteretic energy consumption under vibration, a damage constitutive equation under vibration load is established. Integrating the damage evolution mechanisms of static, dynamic, and vibration loads, load type coefficients and damage variables are introduced to construct a normalized constitutive model that can uniformly characterize the damage behavior of steel structures under multiple load levels.

[0034] S2 acquires material parameters, load spectrum data, and operating condition parameters of the steel structure of special equipment. The material parameters include the stress of the damaged material. Ultimate strength of materials Material fracture strength Material strain Strain at ultimate strength of material Strain at fracture Maximum hysteresis energy consumption of the structure Load spectrum data includes stress amplitude Static stress components The data includes parameters such as the number of cycles, strain hardening index, strain rate, and vibration displacement. The acquired raw data undergoes preprocessing, including outlier removal, data standardization, and load spectrum normalization, to construct a high-quality dataset for model training and evaluation.

[0035] Based on the detailed fatigue rating method, S3 establishes relationship equations between DFR values, stress amplitude, and fatigue life to address the differences in fatigue characteristics between the medium-to-long life range and the long life range. Combined with the Miner linear cumulative damage criterion, a damage accumulation calculation model under multi-level loads is constructed to quantify fatigue damage and predict the life of steel structures under variable amplitude load spectra.

[0036] S4 constructs a fatigue life assessment system for steel structures based on the established damage normalization constitutive model and the DFR method segmented life assessment model. The system includes: a material and parameter setting module, a dynamic strength correction module, and a life assessment module.

[0037] The S5 system takes steel structure material parameters and load spectrum data as input and maps each load cycle to the corresponding nominal life. It automatically switches between medium- and long-life or long-life assessment models based on the life range. It supports the import, generation, clearing, and dynamic updating of load spectrum data. The system outputs stress amplitude distribution histograms, damage accumulation curves, historical trends of health status, and structural assessment reports to support operation and maintenance decisions for special equipment steel structures.

[0038] According to the above technical solution, the specific steps in step S1 are as follows:

[0039] When constructing the constitutive equation for steel structure damage under static load in S11, addressing the issue that traditional constitutive equations only consider material hardening but not the damage degradation stage, we now apply the Lemaitre strain equivalence principle: by defining a damage variable that can equivalently link the constitutive relations of damaged and undamaged materials, the damage variable adjusts the stress-strain relationship of the material when damage occurs, simulating the strength degradation process of the material; the Von Mises yield criterion: when the internal shape change energy of the material reaches a certain critical value, the material begins to yield, comprehensively considering the influence of all stresses on yielding; and the isotropic damage theory: the isotropic damage theory equates the influence of internal defects of the material on macroscopic mechanical properties as a scalar damage variable, the increase of which leads to a decrease in material stiffness.

[0040] By coupling damage variables with damage evolution and modifying the softening stage after the ultimate strength, the damage process of steel after the ultimate strength is considered, resulting in the following damage constitutive model for steel after reaching the ultimate strength:

[0041]

[0042] in: To account for the stress on the damaged material; The ultimate strength of the material; For the material's fracture strength; Strain at the material's ultimate strength; In response to the situation; The strain hardening index represents the degree of hardening of a material during the plastic deformation stage, which is related to the material's deformability.

[0043] The expression for the steel structure damage variable D in the isotropic damage model is as follows:

[0044]

[0045] in: For damage variables; This is the initial elastic modulus of the material; For damage parameters; The damage threshold strain is denoted as .

[0046] Under S12 dynamic load, select Model:

[0047]

[0048] in: The dynamic strength of steel; This refers to the static strength of the steel. This is the equivalent rate of change; and for The strain rate parameters of the model.

[0049] Considering the effects of strain rate, ultimate strength, fracture strength, and strain on the material, the damage constitutive model under static loading is revised accordingly. The model is:

[0050]

[0051] Combining this with the model under static load, we get:

[0052] ;

[0053] Based on the nonlinear combination relationship between the maximum inter-story displacement and the maximum hysteretic energy dissipation of the structure under vibration, the damage model of the steel structure under vibration disturbance is set as follows:

[0054]

[0055] in: This represents the maximum inter-story displacement of the structure under vibration. This represents the maximum hysteretic energy dissipation of the substructure under vibration. The ultimate displacement of the structure; The ultimate hysteresis energy dissipation of the layered structure; For nonlinear combination coefficients, the general structure is taken as follows: Important structures are taken .

[0056] To ensure the accuracy of the analysis, the yield deformation of the layered structure. and limit deformation The yield deformation of all columns within the same layer is used. and limit deformation The minimum value in the calculation is used to determine the yield shear force of the layered structure. and ultimate shear force The yield shear force of each column in the same story and ultimate shear force The superposition of these factors. Based on low-cycle fatigue tests of steel structures, the ultimate hysteresis energy dissipation can be determined. for:

[0057]

[0058] in: This is a constant coefficient related to the material or loading conditions used to adjust the proportion of energy consumption.

[0059] Then, the limiting hysteresis energy dissipation is combined with the overall structural damage model. By analyzing the damage of each layer of the structure separately, the damage index of each layer can be obtained. Based on certain weighting coefficients, the damage indices of each layer are weighted and combined to finally calculate the damage index of the overall structure.

[0060]

[0061] in, For the first Damage weighting of the layer structure, where the weighting value represents the damage weight of the first layer. The contribution of each layer to the damage to the entire structure is determined by weighting the values. Take as This indicates that the more severe the damage to a component, the greater its contribution to the overall structural damage.

[0062] By combining the above-mentioned static loads, dynamic loads, and vibration disturbance factors, S14 can construct a damage-normalized constitutive model for the steel structure of special equipment:

[0063]

[0064] in: ;when At that time, the steel structure was operating under dynamic loads; At that time, the steel structure is only subjected to static loads; .

[0065] At the same time, regarding The value needs to be considered in two cases. First, when under vibration disturbance, its value is:

[0066]

[0067] When there is no vibration disturbance, its value is:

[0068]

[0069] Under high-temperature conditions (S15), the plasticity of the steel increases, and the damage mechanism changes from fatigue crack propagation to the combined effect of fatigue damage and creep damage. Therefore, a temperature-dependent damage function can be introduced.

[0070]

[0071]

[0072] in: Thermal stress; It is the elastic modulus; The coefficient of thermal expansion; For temperature change; Temperature-related damage factors; It is a temperature-sensitive parameter; For temperature; This is a strain rate sensitivity parameter; The current strain rate; The reference strain rate is used.

[0073] The total stress is obtained by combining thermal stress with external load. The total stress is used to replace the individual mechanical stress. Combined with the multi-level load damage normalized constitutive model, the corresponding high-temperature damage factor is calculated.

[0074] In the S16 corrosion environment, pitting corrosion and intergranular corrosion lead to concentrated damage and abrupt changes, which contradicts the uniform accumulation assumption of the linear model. Therefore, a corrosion fatigue damage model can be used.

[0075]

[0076]

[0077] in: This represents the ultimate stress after corrosion. Indicates the number of load cycles; and It is a fitting parameter related to the degree of corrosion and needs to be determined through fatigue test data of different corrosion levels; Corrosion-related damage factors; It is the corrosion rate constant; It's time.

[0078] Considering the impact of corrosion on the ultimate strength of steel structures, the ultimate strength after corrosion can be obtained by subtracting the stress loss caused by corrosion from the original stress. Combined with the normalized constitutive model of multi-level load damage, the corresponding corrosion damage factor can be calculated.

[0079] According to the above technical solution, the specific steps in step S2 are as follows:

[0080] S21 Obtain material parameters for the steel structure of special equipment: damaged material stress Ultimate strength of materials Material fracture strength Material strain Strain at ultimate strength of material Strain at fracture Maximum hysteresis energy consumption of the structure The ultimate displacement of the structure Limiting hysteresis energy dissipation of layered structures ;

[0081] S22 Obtain load spectrum data of special equipment steel structure: stress amplitude Static stress components Number of loops;

[0082] S23 obtains the operating parameters of special equipment steel structures: strain hardening index, strain rate. strain rate parameters of the model and Vibration displacement;

[0083] After obtaining the material parameters, load spectrum, and operating condition parameters of the steel structure of special equipment, S24 needs to preprocess the raw data, specifically including removing outliers, standardizing the data, and regularizing the load spectrum sequence. This process can effectively improve the accuracy and consistency of the data, thereby constructing a high-quality dataset suitable for subsequent model training and performance evaluation.

[0084] According to the above technical solution, the specific steps in step S3 are as follows:

[0085] S31 Detail Fatigue Rating (DFR) refers to the fatigue rating (DFR) at a stress ratio of... Under conditions of 95% confidence level and 95% reliability, the structure can withstand... The maximum stress value corresponding to the second cycle is a measure of the fatigue quality of the structure.

[0086] In fatigue life assessment of steel structures, particularly in the medium-to-long life and long life ranges, the relationship between the DFR value and other fatigue parameters shows significant differences. In the medium-to-long life range, the main characteristic of fatigue damage is the gradual accumulation of material damage. However, in the long life range, as the structure approaches the critical damage point, various properties gradually deteriorate, and the risk of failure increases significantly. Therefore, discussing and calculating these two ranges separately not only more accurately reflects the fatigue characteristics of the structure at different life stages but also improves the accuracy and reliability of life prediction.

[0087] The long lifespan range of S33 is defined as the number of lifespan cycles within a certain range. Between, when When it is a constant, the medium-to-long lifespan range The relationship between them is a straight line with a slope of ,have:

[0088]

[0089] in: This represents the number of loops that failed. This represents the applied stress amplitude; A and B are constants.

[0090] Will The DFR term was introduced and the number of iterations was expressed as DFR and The function. To complete the transformation, assuming A can be represented as a function of DFR, convert A to: The constant A in the formula has an empirical relationship with the dynamic fatigue resistance (DFR), which includes a factor of 0.47, and B is applied to DFR, so we get:

[0091]

[0092] For any equal lifetime curve, we have:

[0093]

[0094] in: It is the stress amplitude of the isolife curve, in a given isolife curve (usually ). In this context, the alternating stress amplitude of the material at a specific lifetime is considered. The x-coordinate of the common intersection point among all life curves is usually the static strength or ultimate stress of the material. The static stress component in cyclic loading affects fatigue life.

[0095] Rearranging the terms and combining the two formulas above, we obtain the expression for the DFR method evaluation model in the medium-to-long lifespan range as follows:

[0096]

[0097] in: For fatigue life; Static strength of the material; Static stress components; This refers to the stress amplitude. This represents the slope of the medium-to-long lifespan range.

[0098] S34 Assumption It is a known constant and hour, If the relationship between them is a straight line, then:

[0099]

[0100] Statistical analysis greater than The slope of the SN curve for the number of iterations can be obtained when... At that time, the slope parameter of the SN curve ,but Here It is a parameter related to the slope of the SN curve, representing the value at a distance greater than... The stress amplitude value within the next cycle range. This is obtained through regression analysis of the SN curve. The value of , and from this, the calculation of .

[0101] The intersection of the SN curve and the horizontal axis in the long-life range is: We can obtain:

[0102]

[0103] in: Long lifespan region The slope of the curve.

[0104] Will Substitution and Substituting the values, the DFR method evaluation model expression for the long lifespan range is:

[0105]

[0106] S35Miner's linear cumulative damage theory defines the following: If a component, under cyclic loading at a stress level S below a certain constant amplitude, has a lifespan of N at failure, then its damage after n cycles can be defined as follows:

[0107]

[0108] If n=0, then D=0, and the component has not experienced fatigue failure; if n=N, then D=1, corresponding to fatigue failure of the component. If the component is subjected to n cycles under k stress levels G, the total damage can be defined as:

[0109]

[0110] Where: n is the number of cycles under stress level G given by the load spectrum; N is the cycle life under stress level S determined by the SN curve.

[0111] Damage is calculated at each loading cycle, and the damage from each cycle is accumulated using Miner's rule, i.e., the damage is summed over each cycle. The component is under pressure level... The damage after n cycles is Then at the stress level After undergoing n cycles, the damage is If total damage If fatigue failure occurs, the component will fail, thus enabling damage accumulation calculation under multi-level loads.

[0112] S36 combines the damage normalization constitutive model with the DFR life assessment model and integrates them through the Miner linear cumulative damage criterion, thereby effectively quantifying the fatigue damage state of steel structures under multi-level loads and achieving reliable prediction of their service life.

[0113] According to the above technical solution, the specific steps in step S4 are as follows:

[0114] S41 designs a fatigue life assessment system for steel structures under specific conditions based on a multi-level load damage model and a DFR method fatigue life assessment model.

[0115] S42 Material and Parameter Setting Module: This module defines the mechanical property parameters of materials, clarifying their strength characteristics and fatigue behavior under cyclic loading, thus providing the necessary physical basis for subsequent fatigue life prediction. It includes commonly used steels or custom materials, containing fatigue-related parameters. Parameters are extracted from the material library or user input and instantiated into a material object for calculation; all subsequent stress-life mapping calls this object.

[0116] S43 Dynamic Strength Correction Module: When loading rate effects exist, it performs an equivalent correction to the nominal stress amplitude, making the fatigue assessment compatible with the strain rate under actual working conditions. Input strain rate Static strength The CS model parameters M and n are used to calculate the correction factor k, and the original stress amplitude is adjusted. Mapped to corrected .right The available range is limited to prevent extrapolation in high / low speed domains where experimental support is lacking. A rate-dependent correction term is used to parametrically transform the stress amplitude to characterize the strength evolution of the material under different loading rates. This treatment effectively improves the extrapolation stability and engineering applicability of the model to real working conditions.

[0117] S44 Life Assessment Module: Outputs single-block spectrum damage, total life, remaining life, current damage level, and condition classification, categorized as: Good - Continue normal use, periodic inspections; Caution - Increase inspection frequency, consider planned maintenance; Dangerous - Conduct immediate detailed inspection, develop maintenance or decommissioning plan.

[0118] According to the above technical solution, the specific steps in step S5 are as follows:

[0119] S51, based on the DFR method, performs cyclic lifetime and damage accumulation assessments on a given load spectrum, automatically switching between the medium-to-long lifetime and long-life domains. It takes material parameters, stress spectrum, and the number of load applications as input, and calculates the cumulative damage at the cyclic level based on material parameters and mean stress correction rules. Mapped to nominal lifespan ,when Exceeding the tolerance or When the value is below the effective threshold, a distinction is made between "rapid failure" and "ignoring damage". If the calculated value is... It automatically switches to a long-life model to avoid extrapolation errors. Based on Miner's linear cumulative damage, when When this occurs, a failure (or danger) alarm is triggered, and the extent of the over-limit is quantified;

[0120] S52 Click to perform a life assessment, which will eventually generate a stress amplitude distribution histogram, damage analysis, K-model assessment, historical trends, historical records, and a report preview.

[0121] Example 2

[0122] Based on Example 1, this example integrates the method into a portable system or an online control system to adapt to the on-site operation and maintenance monitoring and real-time management needs of special equipment steel structures, and realizes the steps of the method in Example 1.

[0123] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A method for optimizing the fatigue life of steel structures based on multi-level loads, characterized in that... Includes the following steps: S1 constructs a normalized constitutive model of steel structure damage under static load, dynamic load and vibration load. This model comprehensively considers damage variables and damage evolution process, and can uniformly characterize the damage behavior of steel structure under different loads. S2 acquires the material parameters, load spectrum data and working condition parameters of the target steel structure, and establishes a high-quality dataset through data preprocessing. S3 Based on the Detailed Fatigue Rating (DFR) method, fatigue life assessment sub-models applicable to the medium-to-long life range and the long life range are established respectively, and the relationship between DFR value and stress amplitude and fatigue life is quantified. S4 corrects the load spectrum data based on the damage normalization constitutive model, and calculates the cumulative damage and fatigue life of the steel structure under multi-level loads by combining the fatigue life assessment sub-model and the Miner linear cumulative damage criterion. S5 constructs a fatigue life assessment system that outputs the cumulative damage degree, fatigue life, health status level and assessment report of steel structures in real time, providing accurate decision support for the operation and maintenance of special equipment.

2. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that, In step S1, when constructing the constitutive equation for steel structure damage under static load, the problem of only considering material hardening and ignoring the damage decline stage in the traditional constitutive equation is corrected. Now, based on the Lemaitre strain equivalence principle, Von Mises yield criterion and isotropic damage theory, the damage evolution process of steel after ultimate strength is incorporated for correction.

3. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S1, for dynamic loads, the CS model is used, and the damage constitutive model under static loads is adaptively modified by combining key factors such as strain rate, ultimate strength, and fracture strength.

4. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S1, the maximum inter-story displacement and hysteresis energy consumption of the vibration disturbance are used to establish a damage model under vibration disturbance, and then the model is integrated with the overall structural damage model to calculate the damage index of the overall structure.

5. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S1, a normalized constitutive model for steel structure damage is constructed by combining factors such as static, dynamic, and vibration loads. Temperature-dependent damage functions and corrosion fatigue damage models are introduced to enhance applicability.

6. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S2, the material parameters, load spectrum data and working condition parameters of the steel structure are obtained. After data preprocessing, a high-quality dataset that meets the requirements for damage prediction accuracy is constructed.

7. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S3, fatigue life assessment models for the medium-to-long life range and the long life range are established based on the DFR method, and the fatigue life of steel structures is accurately predicted by quantifying the relationship equations.

8. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S4, the cumulative damage degree under multi-level loads is calculated by combining the Miner linear cumulative damage criterion, and the fatigue failure critical point of the steel structure is determined.

9. The method for optimizing the fatigue life of steel structures under multi-level loads according to claim 1, characterized in that... In step S5, based on the multi-level load damage model and the DFR method evaluation model, a fatigue life assessment system for steel structures is designed to provide health status levels and maintenance recommendations.

10. An electronic device comprising a processor, a memory, and a program stored in the memory and executable on the processor, characterized in that: When the program is executed by the processor, it implements the steps of the method according to any one of claims 1-9.

11. A computer-readable storage medium, characterized in that, The storage medium stores a program that, when executed by a processor, implements the steps of the method described in any one of claims 1-9.

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