A reliability-based method for stage fatigue life prediction of structural components

Abstract

The application discloses a kind of based on reliability structural member stage fatigue life prediction method, whether structural member contains crack and crack characteristic is divided fatigue life stage;A plurality of fatigue data is used, and the crack initiation-small crack propagation life of structural member under given survival rate is solved by combining probability control volume method, critical plane method and the like, if structural member has multiple high stress zones or dangerous zones, take the minimum life of multiple zones;Initial macro crack is established in high stress zone or dangerous zone, and crack driving force is characterized by using fracture mechanics parameters and the like, and macro crack propagation life under given survival rate is obtained by combining statistical analysis and finite element simulation;Superimposed stage life obtains structural member reliable life.The application is finely segmented modeling, and material data dispersion, scale effect and multi-region competitive failure are considered, standardized analysis process is output structural member reliable life, and it is strong in universality, suitable for aerospace, deep sea, rail transit and other fields structural member fatigue design and life evaluation.

Description

Technical Field

[0001] This invention belongs to the field of mechanical structure fatigue reliability analysis and life prediction technology, and particularly relates to a reliability-based method for predicting the staged fatigue life of structural components. Background Technology

[0002] In aerospace, deep-sea, and rail transportation fields, many load-bearing structural components are subjected to cyclic loads for extended periods, with fatigue failure being the primary failure mode. Accurate prediction of the fatigue life of these components is crucial for equipment reliability design. Existing prediction methods suffer from four core shortcomings:

[0003] The first problem is that there is usually a significant difference between the fatigue performance of material-level specimens and actual structural components. Without correcting for the effects of material dimensions and stress state, and ignoring the competitive failure of high-stress areas in the structure, directly using material-level fatigue performance to predict the fatigue performance of structural components often yields dangerous results.

[0004] The second problem is that due to the dispersion of fatigue data, especially the even greater dispersion of fatigue life during the crack initiation and small crack propagation stages, traditional methods usually do not combine probability statistics, multi-scale analysis and other means, making it difficult to give reliable life prediction results.

[0005] The third problem is that macroscopic crack propagation usually uses standard specimen propagation rate data and crack propagation equivalent mechanical parameters in simulation software without conducting relevant experimental verification for the structural components and their service conditions, making it difficult to guarantee the applicability and accuracy of the model; the initial crack morphology, size, and location rely heavily on experience and lack targeted material-level or local equivalent specimen test data support.

[0006] The fourth problem is that existing technologies usually do not distinguish between the damage evolution differences of structural components with no initial cracks and those with initial small cracks. The single superposition logic is difficult to match with the actual damage and crack behavior, making it difficult to accurately characterize the fatigue life at each stage and the life of the structural component.

[0007] In summary, existing methods suffer from four major problems: failure to consider the differences in fatigue data between material-level specimens and structural components; insufficient consideration of the reliability of the small crack initiation stage; lack of a standardized process for macroscopic crack simulation; and poor adaptability of the total life superposition model. There is an urgent need to develop a phased, reliability-based method for predicting the fatigue life of structural components. Summary of the Invention

[0008] This invention addresses the problems existing in the prior art by proposing a reliability-based method for predicting the staged fatigue life of structural components. The aim is to solve the problems of missing stage division, insufficient consideration of reliability in the small crack initiation stage, lack of standardized process for macro crack simulation, and poor adaptability of the total life superposition model.

[0009] To solve its technical problem, the present invention adopts the following technical solution:

[0010] A reliability-based method for predicting the staged fatigue life of structural components, characterized by the following steps:

[0011] Step 1: Based on whether the structural component contains cracks and the characteristics of the cracks, the fatigue life is segmented. Structural components without cracks are divided into the stages of crack initiation, small crack propagation, and macro crack propagation. Structural components with initial small cracks are divided into the stages of small crack propagation and macro crack propagation.

[0012] Step 2: Obtain multiple fatigue life data for the crack initiation and small crack propagation stages. Use methods including probabilistic control volume method and critical plane method to solve the stage life under a given survival rate. If the structural component has multiple high stress areas or dangerous areas, the life of the crack initiation and small crack propagation stages is the minimum life of these areas.

[0013] Step 3: Obtain test data of multiple macroscopic crack propagation specimens, determine the crack propagation driving force using equivalent stress intensity factor, energy release rate, etc., construct an initial macroscopic crack in the minimum lifetime region, and calculate the lifetime of the macroscopic crack propagation stage under a given survival rate by combining statistical analysis and finite element simulation.

[0014] Step 4: Based on whether the structural component contains initial cracks or other types of defects, the corresponding stage lifespans are superimposed to obtain the reliable fatigue life of the structural component.

[0015] Furthermore, in step 2, multiple fatigue life data for the crack initiation and small crack propagation stages are obtained through material-level specimen fatigue tests or multi-scale simulations combined with test data. The data takes into account the statistical characteristics of the material microstructure and the influence of specimen size and stress state. When there are multiple high-stress areas or dangerous areas in the structural component, the minimum value of the life of the crack initiation and small crack propagation stages in each area is selected as the life of that stage.

[0016] Furthermore, in step 3, obtaining test data of multiple macroscopic crack propagation specimens involves obtaining test data of multiple specimens through material-grade specimens or material-grade crack propagation specimens with certain structural characteristics. Then, by using parameters such as equivalent stress intensity factor and energy release rate, the driving force parameters for macroscopic crack propagation of structural components under the same survival rate are obtained, taking into account the influence of specimen size, stress state, etc. Then, by combining relevant fatigue theories, an initial macroscopic crack is established for the minimum life region of the structural component in step 2, and the fatigue life of the macroscopic crack propagation stage is obtained through finite element simulation.

[0017] Furthermore, step 3, constructing the initial macroscopic crack in the minimum lifespan region, involves providing the morphology and specific location of the initial macroscopic crack, and determining it in conjunction with the geometric characteristics, loading characteristics, and relevant fatigue theories of the component. The size of the initial macroscopic crack needs to be determined by considering the size of the material-grade specimen or the material-grade specimen with certain structural characteristics used in the crack initiation and small crack propagation stages of the structural component, as well as the crack initiation and small crack propagation lifespans. For example, if the material-grade specimen or the material-grade specimen with certain structural characteristics used is not very small and the proportion of macroscopic crack propagation life to the total lifespan is very small, the size of the initial macroscopic crack can be the crack size corresponding to the long crack propagation threshold value or the equivalent long crack propagation threshold value. Furthermore, step 4, superimposing the corresponding stage lifespans based on whether the structural component contains initial cracks, etc., to obtain the reliable fatigue life of the structural component, specifically involves: distinguishing the total lifespan composition based on whether the structural component contains initial small cracks and macroscopic cracks; the fatigue life is the sum of the crack initiation, small crack propagation, and macroscopic crack propagation stages, or the sum of the small crack propagation and macroscopic crack propagation stages, or only the lifespan of the macroscopic crack propagation stage. Advantages and effects of the present invention

[0018] 1. By classifying different fatigue stages based on whether structural components contain cracks and the characteristics of the cracks, the existing unified model for life estimation does not distinguish between damage evolution differences such as no initial cracks and those with initial small cracks, thus achieving a more accurate reflection of the actual damage evolution characteristics and improving prediction performance from the source.

[0019] 2. By combining multiple fatigue test data with probabilistic control volume method and critical plane method, the life of crack initiation and small crack propagation stages under a given survival rate is calculated. For multiple high-stress areas or dangerous areas, the minimum life is taken to solve the problem of traditional methods ignoring the influence of material size and stress state and the competitive failure of multiple high-stress areas or dangerous areas, thereby improving the accuracy of prediction.

[0020] 3. The initial macroscopic crack morphology, size, and location are based on material-level or locally equivalent test data considering the structural components and their service conditions. This solves the problem that the initial macroscopic crack setting in existing macroscopic fracture mechanics simulations often relies on experience, and achieves the effect of standardizing the macroscopic crack propagation calculation process.

[0021] 4. By superimposing corresponding life stages according to the differences in whether the structural component contains cracks and the type of initial cracks, the existing unified model life estimation is difficult to accurately predict the life of structural components, and outputs the effect of life with reliability index. Attached Figure Description

[0022] Figure 1 This is a flowchart of the reliability-based phased fatigue life prediction method for structural components according to the present invention. Detailed Implementation Innovation of this invention

[0023] 1. Innovative division of different fatigue stages: Based on whether the structural component contains cracks and the differences in crack characteristics, fatigue stages are divided into three stages: crack initiation, small cracks, and macroscopic crack propagation for crack-free components, and two stages for components containing initial small cracks. This replaces the existing unified life estimation model that usually does not distinguish the differences in damage evolution at different stages of structural components.

[0024] 2. Innovation in the crack initiation-small crack stage: Using material-level or locally equivalent specimen fatigue tests, combined with multi-scale simulation, probabilistic controlled volume method, critical plane method, etc., to correct the influence of specimen size and stress state, and to solve the stage fatigue life under a given survival rate by traversing multiple high stress regions or dangerous regions.

[0025] 3. Innovation in the macroscopic crack propagation stage: Initial macroscopic cracks are constructed in the minimum life region. The size, morphology, and specific location of the initial macroscopic cracks are determined by combining targeted material-grade specimens or material-grade specimens with certain structural characteristics and relevant fatigue theories. The driving force of crack propagation is characterized by equivalent stress intensity factor and energy release rate. The macroscopic crack propagation life is calculated under a given survival rate by combining statistical analysis and finite element simulation.

[0026] Solution of the present invention

[0027] Technical Challenge 1: Multi-dimensional variable coupling makes it difficult to simultaneously quantify scale effects, stress states, and competing failures in multiple critical areas. Existing technologies typically rely solely on material specimen lifetimes, directly applying them to structural components without correcting for the influence of specimen size and stress states; they also tend to overestimate lifetimes by considering only local stress. Solution of this invention: ① Conduct and obtain fatigue data of material-level or locally equivalent specimens based on the characteristics of the structural component and its service load features; ② Use probabilistic controlled volume methods and critical plane methods to correct for the influence of specimen size effects and stress states, completing the conversion of small specimen fatigue data to structural component fatigue data; ③ Traverse high-stress or critical areas of the structural component, taking the minimum lifetime of each area as the lifetime for that stage, considering competing failure scenarios at multiple locations or in multiple areas.

[0028] Technical Challenge 2: Modeling the full life reliability of structural components across crack initiation, small crack propagation, and long crack propagation stages is challenging, especially the crack initiation and small crack propagation stages, which exhibit strong dispersion. Existing technologies typically use a uniform model for full life estimation, outputting a single lifespan without considering reliability. Our solution: ① Divide the structural component's lifespan into different fatigue stages, for example, dividing the lifespan of a structural component with initial small cracks into two stages; ② Conduct targeted material-level or locally equivalent specimen tests for different stages to obtain fatigue data, then use methods such as probabilistic controlled volume method, critical plane method, and finite element simulation to solve for the stage fatigue life under a given survival rate; ③ Use a uniform survival rate throughout the fatigue life prediction across different stages, superimpose the segmented lives to obtain the structural component's fatigue life under a given survival rate.

[0029] Based on the above principles, this invention designs a staged fatigue life prediction method for structural components based on reliability, characterized by the following steps: Step 1: Based on whether the structural component contains cracks and the characteristics of the cracks, the fatigue life is segmented. Structural components without cracks are divided into the stages of crack initiation, small crack propagation, and macro crack propagation. Structural components with initial small cracks are divided into the stages of small crack propagation and macro crack propagation. Step 2: Obtain multiple fatigue life data for the crack initiation and small crack propagation stages. Use methods including probabilistic control volume method and critical plane method to solve the stage life under a given survival rate. If the structural component has multiple high stress areas or dangerous areas, the life of the crack initiation and small crack propagation stages is the minimum life of these areas. The acquisition of multiple fatigue life data for the crack initiation and small crack propagation stages is achieved through material-level specimen fatigue tests or multi-scale simulations combined with test data. The data takes into account the statistical characteristics of the material microstructure and the influence of specimen size and stress state. When there are multiple high-stress areas or dangerous areas in the structural component, the minimum value of the life of the crack initiation and small crack propagation stages in each area is selected as the life of that stage.

[0030] Step 3: Obtain test data of multiple macroscopic crack propagation specimens, determine the crack propagation driving force using equivalent stress intensity factor, energy release rate, etc., construct an initial macroscopic crack in the minimum lifetime region, and calculate the lifetime of the macroscopic crack propagation stage under a given survival rate by combining statistical analysis and finite element simulation. The acquisition of test data for multiple macroscopic crack propagation specimens involves obtaining test data for multiple specimens through material-grade specimens or material-grade crack propagation specimens with certain structural characteristics. Then, by using parameters such as equivalent stress intensity factor and energy release rate, the driving force parameters for macroscopic crack propagation of structural components under the same survival rate are obtained, taking into account the influence of specimen size, stress state, etc. Then, by combining relevant fatigue theories, an initial macroscopic crack is established for the minimum life region of the structural component in step 2, and the fatigue life of the macroscopic crack propagation stage is obtained through finite element simulation. The construction of the initial macroscopic crack in the minimum lifespan region involves providing the morphology and specific location of the initial macroscopic crack, and determining it in conjunction with the geometric characteristics, loading characteristics, and relevant fatigue theories of the component. The size of the initial macroscopic crack needs to be determined by combining the size of the material-grade specimen or the material-grade specimen with certain structural characteristics used in the crack initiation and small crack propagation stages of the structural component, as well as the crack initiation and small crack propagation lifespans. For example, if the material-grade specimen or the material-grade specimen with certain structural characteristics used is not very small and the proportion of macroscopic crack propagation life to total lifespan is very small, the size of the initial macroscopic crack can be the crack size corresponding to the long crack propagation threshold value or the equivalent long crack propagation threshold value.

[0031] Step 4: Based on whether the structural component contains initial cracks or other types of defects, the corresponding stage lifespans are superimposed to obtain the reliable fatigue life of the structural component. Specifically: the total lifespan is determined by whether the structural component contains initial small cracks or macroscopic cracks. The fatigue life is the sum of the crack initiation, small crack propagation, and macroscopic crack propagation stages, or the sum of the small crack propagation and macroscopic crack propagation stages, or only the lifespan of the macroscopic crack propagation stage.

[0032] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for predicting the staged fatigue life of structural components based on reliability, characterized in that, Includes the following steps: Step 1: Based on whether the structural component contains cracks and the characteristics of the cracks, the fatigue life is segmented. Structural components without cracks are divided into the stages of crack initiation, small crack propagation, and macro crack propagation. Structural components with initial small cracks are divided into the stages of small crack propagation and macro crack propagation. Step 2: Obtain multiple fatigue life data for the crack initiation and small crack propagation stages. Use methods including probabilistic control volume method and critical plane method to solve the stage life under a given survival rate. If the structural component has multiple high stress areas or dangerous areas, the life of the crack initiation and small crack propagation stages is the minimum life of these areas. Step 3: Obtain test data of multiple macroscopic crack propagation specimens, determine the crack propagation driving force using equivalent stress intensity factor, energy release rate, etc., construct an initial macroscopic crack in the minimum lifetime region, and calculate the lifetime of the macroscopic crack propagation stage under a given survival rate by combining statistical analysis and finite element simulation. Step 4: Based on whether the structural component contains initial cracks or other types of defects, the corresponding stage lifespans are superimposed to obtain the reliable fatigue life of the structural component.

2. The method for predicting the staged fatigue life of structural components based on reliability according to claim 1, characterized in that: Step 2 involves obtaining multiple fatigue life data for the crack initiation and small crack propagation stages. This is achieved through material-level specimen fatigue tests or multi-scale simulations combined with test data. The data takes into account the statistical characteristics of the material microstructure and the influence of specimen size and stress state. When there are multiple high-stress areas or dangerous areas in the structural component, the minimum value of the life of the crack initiation and small crack propagation stages in each area is selected as the life of that stage.

3. The method for predicting the staged fatigue life of structural components based on reliability according to claim 1, characterized in that: Step 3 involves obtaining test data from multiple macroscopic crack propagation specimens. This means obtaining test data from multiple specimens, either material-grade specimens or material-grade crack propagation specimens with certain structural characteristics. Then, by using parameters such as equivalent stress intensity factor and energy release rate, the driving force parameters for macroscopic crack propagation of structural components under the same survival rate are obtained, taking into account the influence of specimen size, stress state, and other factors. Finally, by combining relevant fatigue theories, an initial macroscopic crack is established for the minimum life region of the structural component in step 2, and the fatigue life of the macroscopic crack propagation stage is obtained through finite element simulation.

4. The method for predicting the staged fatigue life of structural components based on reliability according to claim 1, characterized in that: Step 3, constructing the initial macroscopic crack in the minimum lifespan region, involves providing the morphology and specific location of the initial macroscopic crack, and determining it in conjunction with the geometric characteristics, loading characteristics, and relevant fatigue theories of the component. The size of the initial macroscopic crack needs to be determined by combining the size of the material-grade specimen or the material-grade specimen with certain structural characteristics used in the crack initiation and small crack propagation stages of the structural component, as well as the crack initiation and small crack propagation lifespans. For example, if the material-grade specimen or the material-grade specimen with certain structural characteristics used is not very small and the proportion of macroscopic crack propagation life to total lifespan is very small, the size of the initial macroscopic crack can be the crack size corresponding to the long crack propagation threshold value or the equivalent long crack propagation threshold value.

5. The method for predicting the staged fatigue life of structural components based on reliability according to claim 1, characterized in that: Step 4 involves superimposing the corresponding stage lifespans based on whether the structural component contains initial cracks, etc., to obtain the reliable fatigue life of the structural component. Specifically, the total lifespan is determined by whether the structural component contains initial small cracks or macroscopic cracks. The fatigue life is the sum of the crack initiation, small crack propagation, and macroscopic crack propagation stages, or the sum of the small crack propagation and macroscopic crack propagation stages, or only the lifespan of the macroscopic crack propagation stage.

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