Prediction method and system for unified damage low-cycle fatigue life
By constructing a unified cohesive model, obtaining stress and strain information in the crack propagation region, constructing damage opening displacement, outputting monotonic and cyclic fatigue damage evolution, updating cohesive stiffness, and iteratively simulating the crack propagation process, the problem of dual-damage coupling characterization in existing technologies is solved, and high-precision crack propagation life prediction is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- BEIJING INST OF TECH
- Filing Date
- 2026-02-09
- Publication Date
- 2026-04-24
AI Technical Summary
Existing technologies struggle to achieve coupled characterization of monotonic damage and cyclic fatigue damage, and lack a unified modeling framework adapted to dual damage mechanisms, resulting in limited accuracy in predicting crack propagation processes under complex working conditions.
By constructing a unified cohesive model, the stress and strain states of the crack propagation region are obtained, the damage opening displacement is constructed, and the monotonic damage and cyclic fatigue damage evolution quantities are output for unified characterization. The cohesive stiffness is updated by combining the traction force-separation law, the crack propagation process is iteratively simulated, and the life curve of crack length changing with time is constructed.
It achieves integrated and accurate prediction of the entire process from evolution to failure of dual damage mechanisms within a unified framework, improving the prediction accuracy and reliability of crack propagation process.
Smart Images
Figure CN121920150A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of materials testing technology, and in particular to a method and system for predicting low-cycle fatigue life with uniform damage. Background Technology
[0002] In the safety design and life assessment of engineering structures, accurately predicting crack propagation behavior under cyclic loading is a core element in ensuring the reliable operation of equipment. Cohesion models, as macroscopic phenomenological models, have been widely used in simulating crack initiation and propagation behavior in materials due to their good adaptability and ability to avoid stress singularities. Predicting the crack propagation process from initial defect to critical size using this model provides a powerful analytical tool for achieving high-precision assessment of the remaining life of structures.
[0003] Significant progress has been made in fatigue crack propagation research based on cohesive models. The established cyclic cohesive models primarily focus on the impact of fatigue damage on material failure behavior and have been successfully applied to the effective simulation of crack propagation behavior under high-cycle fatigue conditions. This work lays an important theoretical foundation for understanding fatigue failure mechanisms and predicting lifespan, and promotes the application of computational fracture mechanics in engineering practice.
[0004] However, existing technologies struggle to achieve coupled characterization of monotonic damage and cyclic fatigue damage, and lack a unified modeling framework adapted to the dual damage mechanism, resulting in limited accuracy in predicting crack propagation processes under complex working conditions. Summary of the Invention
[0005] In view of the shortcomings of the prior art, the purpose of this invention is to provide a unified method for predicting low-cycle fatigue life of damage, which can solve the technical problems of the prior art being unable to achieve coupled characterization of monotonic damage and cyclic fatigue damage, lacking a unified modeling framework adapted to dual damage mechanisms, and thus limiting the prediction accuracy of crack propagation process under complex working conditions.
[0006] A first aspect of this invention proposes a method for predicting low-cycle fatigue life with uniform damage, comprising: 1. A method for predicting low-cycle fatigue life with uniform damage, characterized in that it includes: S1: Obtain stress and strain state information of the crack propagation region at the current increment step and the adjacent increment steps; S2: Construct the damage opening displacement based on the stress state and strain state information of the crack initiation location in the crack propagation region; S3: Input the damage opening displacement into the unified cohesive force model, and output the monotonic damage evolution and cyclic fatigue damage evolution respectively; S4: To uniformly characterize the monotonic damage evolution and the cyclic fatigue damage evolution, and determine the total cumulative damage value of the cohesive unit node under the current incremental step. S5: Based on the damage opening displacement and the damage opening displacement threshold, determine whether monotonic damage failure has occurred; if so, delete the cohesive element node that has experienced monotonic damage failure and record the corresponding time node; otherwise, proceed to S6. S6: Based on the total accumulated damage value and the total accumulated damage threshold, determine whether cyclic fatigue damage failure has occurred; if so, delete the cohesive element node that has experienced cyclic fatigue damage failure and record the corresponding time node; otherwise, update the cohesive stiffness of the next incremental step by combining the traction force-separation law of the coupling effect of monotonic damage failure and cyclic fatigue damage failure. S7: Based on the updated cohesive stiffness, update the boundary conditions of the unified cohesive model, and repeat S1 to S6 until the preset number of time increment steps is reached. S8: Extract the crack length change information corresponding to each incremental step during crack propagation, and construct the crack propagation life curve of crack length changing with time based on the crack length change information. S9: Determine the predicted low-cycle fatigue crack propagation life based on the crack propagation life curve.
[0007] A second aspect of the present invention provides a unified damage low-cycle fatigue life prediction system, comprising: a processor and a memory; The memory stores programs or instructions that can run on the processor, which, when executed by the processor, implement the steps of the method for predicting uniform damage low-cycle fatigue life as described in the first aspect.
[0008] A third aspect of the present invention provides a readable storage medium on which a program or instructions are stored, which, when executed by a processor, implement the steps of the method for predicting uniform damage low-cycle fatigue life as described in the first aspect.
[0009] The beneficial effects of the technical solutions provided by the embodiments of the present invention include at least the following: In this embodiment of the invention, a unified cohesive force model is constructed, and the damage opening displacement, based on mechanical information, is input into the model to directly output two types of damage evolution quantities. These evolution quantities are then uniformly characterized to determine the total cumulative damage value of the coupling. Through progressive failure judgment and stiffness updates based on the coupling traction force-separation law, the entire crack propagation process is simulated iteratively, ultimately constructing a lifetime curve. This method achieves integrated and accurate prediction of the entire process of dual damage mechanisms from evolution and coupling to failure within a unified framework. Attached Figure Description
[0010] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Obviously, the drawings described below are merely some embodiments of the present invention, and those skilled in the art can obtain other drawings based on these drawings without any creative effort.
[0011] Figure 1 This is a flowchart illustrating a method for predicting low-cycle fatigue life with uniform damage, provided in an embodiment of the present invention.
[0012] Figure 2 This is a schematic diagram of the structure of a crack propagation experimental finite element model provided in an embodiment of the present invention.
[0013] Figure 3 This is a comparison chart of fatigue crack propagation rate experiment and model life prediction provided by an embodiment of the present invention.
[0014] Figure 4 This is a comparison chart of fatigue crack prediction errors provided by an embodiment of the present invention.
[0015] Figure 5 This is a schematic diagram of the structure of a unified damage low-cycle fatigue life prediction system provided in an embodiment of the present invention. Detailed Implementation
[0016] To enable those skilled in the art to better understand the technical solutions in the embodiments of the present invention, the technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. It should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of the present invention.
[0017] The method for predicting the unified damage low-cycle fatigue life provided by the present invention will be described in detail below with reference to the accompanying drawings, through specific embodiments and application scenarios.
[0018] Reference manual attached Figure 1 The diagram shows a flowchart of a method for predicting low-cycle fatigue life of uniform damage provided by an embodiment of the present invention.
[0019] This invention provides a method for predicting low-cycle fatigue life with uniform damage, which may include the following steps: S1: Obtain the stress state and strain state information of the crack propagation region at the current increment step and the adjacent increment steps.
[0020] Among them, the current time increment step refers to the time interval unit for the current damage analysis, the adjacent time increment step refers to the previous or next time interval unit that is immediately adjacent to the current time interval unit, the crack propagation region refers to the specific region where crack initiation and propagation may occur and fatigue life prediction needs to be carried out, the stress state information reflects the distribution of the magnitude and direction of the force in the region, and the strain state information reflects the degree and distribution of deformation in the region.
[0021] Reference manual attached Figure 2 The diagram shows a structural schematic of a crack propagation experimental finite element model provided by an embodiment of the present invention.
[0022] Specifically, Figure 2 It comprises three parts: the overall finite element mesh model, magnified details of the crack region, and time-force load curves. Core elements include: the finite element mesh, the cohesive mesh, the pre-existing crack, the crack propagation direction, the external force load F, and the external force (in N) curve varying with time (in seconds) in the upper right subplot. The cohesive mesh serves as the numerical implementation of the unified cohesive model, the pre-existing crack represents the initial location of crack propagation, and the external force load F represents the model's loading conditions.
[0023] Furthermore, in terms of inclusion relationships, the overall finite element mesh model serves as the basic scenario for analysis. The magnified detail view focuses on the core crack region in the main image, while the upper right sub-image displays the quantified load curve. In terms of connectivity, the external force F in the main image directly corresponds to the "External Force" in the upper right sub-image. The magnified detail view is linked to the crack region in the main image, thus connecting the "overall modeling scenario - local crack structure - loading load pattern," fully presenting the numerical modeling and loading environment for crack propagation analysis.
[0024] It should be noted that, Figure 2 It provides a visual platform for finite element modeling and demonstrates the deployment method achieved through cohesive meshes. Simultaneously, it provides scenario support for the acquisition of mechanical state data (stress and strain information), intuitively verifying the feasibility of finite element analysis as a source of mechanical data, and clarifying the application of a unified cohesive model in numerical scenarios, thus helping to understand the basic modeling background for subsequent damage calculations and failure assessments.
[0025] It should be noted that the mechanical state data of the crack propagation region to be detected in this step is obtained based on finite element analysis, specifically the stress and strain information of the crack propagation region under the current time increment, and the stress and strain state information of adjacent time steps need to be introduced into a unified cohesive force model.
[0026] S2: Based on the stress state and strain state information of the crack initiation location in the crack propagation region, construct the damage opening displacement.
[0027] Among them, crack initiation location refers to the specific location where the crack initially occurs, and damage opening displacement refers to the core displacement parameter that comprehensively characterizes the degree of normal separation and tangential opening at the crack and is associated with the damage state.
[0028] In one possible implementation, S2 specifically includes sub-steps S201 to S203: S201: Define the load mixing ratio parameter through preset rules.
[0029] Among them, the preset rule is a standard or method that is set in advance to determine the value of the load mixing ratio parameter, which is a parameter that characterizes the ratio of normal load to tangential load.
[0030] S202: Extract features from the stress and strain state information of the crack propagation region at the current increment step and the adjacent increment steps to obtain the tangential damage displacement and normal separation damage displacement of the crack initiation location in the crack propagation region.
[0031] Feature extraction is a process of filtering and refining key information related to crack opening from the obtained stress and strain state information. Tangential damage displacement is a parameter that comprehensively reflects the degree of crack damage along the tangential direction, and normal separation damage displacement is a parameter that reflects the degree of crack separation damage along the normal direction.
[0032] S203: Calculate the damage opening displacement by combining the load mixing ratio parameter, tangential damage displacement, and normal separation damage displacement: in, Indicates damage opening displacement. Indicates the normal separation damage displacement. Indicates tangential damage displacement. β This represents the load mixing ratio parameter.
[0033] For example, the load mixing ratio parameter in this step β These are parameters related to fatigue characteristics and can be measured through standardized fatigue tests, or determined and calibrated based on matching analysis of experimental data and numerical simulation results. The calibrated parameters... β By substituting the extracted tangential damage displacement and normal separation damage displacement into the formula, the damage opening displacement can be accurately calculated.
[0034] It should be noted that by refining the calculation process of damage opening displacement, the load mixing ratio parameter is first defined to clarify the load ratio, then the core displacement parameters are obtained through feature extraction, and finally the damage opening displacement is accurately calculated by combining the formula. This not only takes into account the combined influence of normal and tangential loads, but also realizes the orderly transformation of raw data into crack characteristic parameters, providing accurate and targeted key basis for subsequent damage accumulation rate calculation.
[0035] S3: Input the damage opening displacement into the unified cohesive force model, and output the monotonic damage evolution and cyclic fatigue damage evolution respectively.
[0036] Among them, the unified cohesion model refers to an integrated modeling framework that integrates dual damage analysis functions and realizes damage evolution and failure judgment; the monotonic damage evolution refers to the cumulative change of damage over time under monotonic load; and the cyclic fatigue damage evolution refers to the cumulative change of damage over time under cyclic load.
[0037] Optionally, the process of outputting a monotonic damage evolution quantity from the unified cohesion model specifically includes: The damage opening displacement is input into the unified cohesive force model.
[0038] Based on preset damage initiation conditions and preset damage failure conditions, damage initiation displacement and damage failure displacement are extracted from the unified cohesive force model.
[0039] Among them, the preset damage initiation condition is a pre-set critical condition for determining the start of damage accumulation, the preset damage failure condition is a pre-set condition for determining the loss of bearing capacity of the cohesive unit due to monotonic damage, the damage initiation displacement is the critical value of the damage opening displacement corresponding to the start of damage accumulation, and the damage failure displacement is the critical value of the damage opening displacement corresponding to the failure of the cohesive unit due to monotonic damage.
[0040] By combining the damage opening displacement, damage initiation displacement, and damage failure displacement, the monotonic damage evolution quantity is calculated: in, Indicates the monotonic damage evolution amount. Indicates damage opening displacement. Indicates the initial displacement of the damage. Indicates the displacement due to damage and failure. D This represents the total cumulative damage value.
[0041] The monotonic damage evolution value calculated in this step is used for the subsequent coupling and superposition of the total damage accumulation value. D The initial value is 0, and as the load is applied cyclically, D Continuously accumulating, when D When the value increases to 1, it indicates that the corresponding cohesive unit has failed.
[0042] It should be noted that this step refines the calculation process of monotonic damage evolution. By clarifying the critical conditions for damage initiation and failure and the corresponding displacement parameters, and combining the formula to accurately solve the monotonic damage evolution, the damage evolution characteristics under monotonic load are fully considered, providing independent and accurate monotonic damage data support for dual-damage coupling analysis.
[0043] Optionally, the process of calculating the cyclic fatigue damage evolution in the unified cohesive model specifically includes: The damage opening displacement is input into the unified cohesive force model.
[0044] Based on the unified cohesive force model, the traction force of the cohesive unit node in the incremental step at the current time and the cohesive force intensity under the current damage state are obtained.
[0045] Among them, the traction force of the cohesive unit node in the current incremental step refers to the pulling force borne by the cohesive unit in the current incremental step, and the cohesive strength in the current damage state refers to the maximum traction force that the cohesive unit can withstand under the current cumulative damage level.
[0046] Input the damage opening displacement of the current increment step and the previous increment step into the unified cohesive force model to calculate the damage opening displacement increment.
[0047] Among them, the damage opening displacement increment is the difference between the damage opening displacement at the current moment and the previous moment, reflecting the magnitude of the displacement change.
[0048] The model control variables of the preset fatigue damage model are called from the unified cohesion model.
[0049] Among them, the preset fatigue damage model is a theoretical model that is pre-embedded in the module and used to analyze the evolution of cyclic fatigue damage. The model control variables are the key parameters in the preset fatigue damage model used to adjust the accuracy of damage calculation.
[0050] By combining traction force, cohesive strength, damage opening displacement increment, and model control variables, the cyclic fatigue damage evolution is calculated using a unified cohesive model. in, This represents the amount of cyclic fatigue damage evolution. Indicates the increment of damage opening displacement. Indicates the characteristic damage displacement parameters. This represents the traction force of the cohesive unit node in the incremental step at the current moment. This represents the cohesive strength under the current damage state. Represents the model control variables. H express Heaviside function, Indicates the initial displacement of the damage. This indicates the absolute value operation.
[0051] It should be noted that by refining the calculation of cyclic fatigue damage evolution through multiple steps, key factors such as displacement change, traction force, and cohesive strength under cyclic loading are comprehensively considered. Combined with the preset fatigue damage model, accurate solutions are achieved, providing accurate data that conforms to the characteristics of cyclic loading for dual-damage coupling analysis, and ensuring the comprehensiveness of damage assessment under complex loads.
[0052] In this embodiment of the invention, two damage evolution quantities are output synchronously by a unified model, which breaks through the limitations of traditional single damage analysis, realizes the synchronous quantification of dual damage mechanisms, and provides accurate data support for subsequent coupled characterization.
[0053] S4: To uniformly characterize the monotonic damage evolution and the cyclic fatigue damage evolution, and determine the total cumulative damage value of the cohesive unit node under the current incremental step.
[0054] Among them, unified characterization refers to the process of integrating two independent damage evolution quantities into a unified index that reflects the overall damage degree of the unit; cohesive unit node refers to the basic calculation node used to simulate crack propagation in the unified cohesive model; and total damage accumulation value refers to the comprehensive parameter that characterizes the cumulative damage degree of the cohesive unit node.
[0055] In one possible implementation, S4 specifically includes sub-steps S401 to S404: S401: Input the monotonic damage evolution quantity into the unified cohesion model, and calculate the monotonic damage integral through the unified cohesion model.
[0056] Among them, the monotonic damage integral is the cumulative sum of the monotonic damage accumulation rate over time, reflecting the degree of accumulation of monotonic damage.
[0057] S402: Input the cyclic fatigue damage evolution quantity into the unified cohesive model, and calculate the cyclic fatigue damage integral through the unified cohesive model.
[0058] Among them, the cyclic fatigue damage integral is the cumulative sum of the cyclic fatigue damage accumulation rate over time, reflecting the cumulative degree of cyclic fatigue damage.
[0059] S403: Calls the preset fatigue damage acceleration coefficient from the unified cohesion model.
[0060] Among them, the fatigue damage acceleration factor is a pre-set parameter used to improve the efficiency of prediction calculation.
[0061] It should be noted that those skilled in the art can set the preset fatigue damage acceleration coefficient according to actual needs, and this invention does not limit it.
[0062] S404: The monotonic damage integral, cyclic fatigue damage integral, and fatigue damage acceleration coefficient are coupled and superimposed to obtain the total cumulative damage value. in, D This represents the total cumulative damage value. Indicates the monotonic damage evolution amount. Indicates the fatigue damage acceleration factor. This represents the amount of cyclic fatigue damage evolution. This indicates an operation that accumulates and sums over increments of time.
[0063] Specifically, this step involves inputting the monotonic damage integral, cyclic fatigue damage integral, and fatigue damage acceleration coefficient into the coupling processing module. Through the unified characterization operation of coupling superposition, combined with the formula, the total cumulative damage value is calculated, with the initial value of the total cumulative damage value being 0.
[0064] Furthermore, the fatigue damage acceleration coefficient called in this step has a clear effect and can improve the calculation efficiency of fatigue life prediction without changing the coupling mechanism between monotonic damage and cyclic fatigue damage.
[0065] It should be noted that this step achieves the coupling and integration of dual damage through four ordered sub-steps. First, the cumulative integrals of the two types of damage are calculated separately, and then an acceleration coefficient is introduced for coupling superposition. This not only accurately obtains the total cumulative damage value that reflects the overall damage level, but also improves the computational efficiency without changing the coupling mechanism by using the acceleration coefficient, thus achieving a balance between accuracy and efficiency.
[0066] Optionally, after S4 and before S5, an adaptive degradation process of the unified cohesion model is also included.
[0067] Optionally, the adaptive degradation process of the unified cohesion model specifically includes: Calculate the contribution ratio of the monotonic damage integral and the cyclic fatigue damage integral to the total cumulative damage value, respectively.
[0068] The contribution ratio refers to the percentage of a single damage score in the total cumulative damage value, reflecting the degree of impact of that damage on the overall damage.
[0069] The dominant damage mechanism of the unified cohesion model is adaptively adjusted based on the contribution ratio and the preset ratio value.
[0070] Among them, the preset ratio values include monotonic preset ratio values and cyclic preset ratio values, which are pre-set critical values used to determine whether the damage contribution is negligible. The dominant damage mechanism refers to the damage type (monotonic damage or cyclic fatigue damage) that plays a major role in the overall damage.
[0071] It should be noted that those skilled in the art can set the preset ratio value according to actual needs, and this invention does not limit that.
[0072] If the contribution ratio of monotonic damage is lower than the preset monotonic ratio, the unified cohesion model degenerates into a cyclic fatigue damage model dominated by cyclic fatigue damage evolution calculation.
[0073] Among them, the cyclic fatigue damage model is a simplified model that only analyzes cyclic fatigue damage.
[0074] If the contribution ratio of cyclic fatigue damage is lower than the preset cyclic ratio, the unified cohesion model degenerates into a monotonic damage model dominated by monotonic damage evolution calculation.
[0075] Among them, the monotonic damage model is a simplified model that only analyzes monotonic damage.
[0076] Specifically, in addition to enabling the switching between dual-damage and single-damage models, this adaptive degradation process also allows the unified cohesive model to uniformly describe monotonic tensile separation failure, cyclic fatigue damage failure, and mixed failure behavior under the combined effect of the two, further expanding the application scenarios of the model.
[0077] Furthermore, the core of this adaptive degradation process is to compare the contribution ratio of the monotonic damage integral and the cyclic fatigue damage integral to the total cumulative damage value with a preset ratio value, thereby achieving adaptive adjustment of the damage mechanism dominated by the unified cohesion model. The adjusted model retains only the corresponding single damage calculation module.
[0078] It should be noted that the adaptive degradation process in this step allows the unified cohesion model to be flexibly adjusted according to the damage contribution characteristics. It can adapt to complex working conditions with the combined action of two damages, and simplify the model when a single damage dominates. This expands the application scenarios of the model and ensures the applicability, consistency and physical rationality of the predictions under different load conditions.
[0079] In this embodiment of the invention, the coupling and integration of the dual damage mechanisms are achieved through unified characterization operations, which solves the problem that the existing technology is difficult to quantify the joint effect of dual damage, making the damage assessment more comprehensive and providing a core basis for subsequent accurate judgment of failure status.
[0080] S5: Based on the damage opening displacement and the damage opening displacement threshold, determine whether monotonic damage failure has occurred. If so, delete the cohesive element node that has experienced monotonic damage failure and record the corresponding time node. Otherwise, proceed to S6.
[0081] Among them, the damage opening displacement threshold refers to the pre-set critical displacement value used to determine whether monotonic damage failure has occurred. Monotonic damage failure refers to the state in which the cohesive element node loses its bearing capacity under monotonic load. The time node refers to the time interval element corresponding to the occurrence of failure.
[0082] It should be noted that those skilled in the art can set the damage opening displacement threshold according to actual needs, and this invention does not limit it.
[0083] In this embodiment of the invention, this step enables accurate determination of monotonic failure and timely processing of failure nodes, realistically simulating the process of crack initiation due to monotonic damage, while recording failure time information to provide accurate data for subsequent crack propagation law analysis.
[0084] S6: Based on the total accumulated damage value and the total accumulated damage threshold, determine whether cyclic fatigue failure has occurred. If so, delete the cohesive element node that has experienced cyclic fatigue failure and record the corresponding time node. Otherwise, update the cohesive stiffness of the next incremental step by combining the traction force-separation law of the coupling effect of monotonic damage failure and cyclic fatigue failure.
[0085] Among them, the total damage accumulation threshold refers to the pre-set critical damage value used to determine whether cyclic fatigue damage failure has occurred; cyclic fatigue damage failure refers to the state in which the cohesive unit node loses its bearing capacity under cyclic load; the traction force-separation law refers to the theoretical criterion characterizing the relationship between the traction force and the opening displacement of the cohesive unit node; and the cohesive stiffness refers to the ability of the cohesive unit node to resist deformation.
[0086] Specifically, when a cohesive element is determined to have experienced monotonic or cyclic failure, in addition to recording the failure time and location information, the cohesive node that exhibited the failure behavior must also be deleted in order to accurately reflect the changes in the element state during the crack propagation process.
[0087] It should be noted that those skilled in the art can set the total damage accumulation threshold according to actual needs, and this invention does not limit it.
[0088] In one possible implementation, the traction-separation law in S6, which combines the coupling effects of monotonic damage failure and cyclic fatigue damage failure, specifically updates the cohesive stiffness of the next incremental step, including: S601: If it is determined that no cyclic fatigue damage failure has occurred, the maximum damage monotonic displacement of the current incremental step is obtained through the unified cohesive force model.
[0089] Among them, the maximum monotonic damage displacement is the maximum value of the damage opening displacement up to the current time step.
[0090] S602: Based on the damage opening displacement, maximum damage monotonic displacement, and damage failure displacement, and combined with the traction force-separation law of the coupling effect of monotonic damage failure and cyclic fatigue damage failure, the current traction force is determined: in, This represents the current traction force of the cohesive unit. Indicates damage opening displacement. Indicates the initial displacement of the damage. Indicates the displacement due to damage and failure. D This represents the total cumulative damage value. This represents the cohesive strength under the current damage state. This represents the maximum monotonic damage displacement at the current moment. This indicates the operation of taking the minimum value.
[0091] Among them, the unified traction force-separation law is a theoretical criterion for determining the traction force of cohesive units by comprehensively considering monotonic damage and cyclic fatigue damage.
[0092] It should be noted that the damage failure displacement in this step is the same physical quantity as the damage failure displacement in the monotonic damage calculation module sub-step, and the conditions for the value of the unified traction force-separation law completely correspond to those in the formula. The minimum value operation is performed on the traction force corresponding to the monotonic damage traction force-separation law and the cyclic fatigue damage traction force-separation law within the three interval ranges.
[0093] S603: Based on the current traction force, update the cohesive stiffness of the incremental step at the next moment.
[0094] In this embodiment of the invention, this step achieves accurate judgment of cyclic failure. At the same time, by updating the stiffness of the unfailed units, the impact of damage accumulation on the mechanical properties of the units can be truly reflected, ensuring the accuracy of subsequent cyclic calculations and forming a closed loop of "failure judgment - parameter update", thereby improving the coherence and accuracy of the prediction process.
[0095] S7: Based on the updated cohesive stiffness, update the boundary conditions of the unified cohesive model, and repeat S1 to S6 until the preset number of time increment steps is reached.
[0096] Among them, boundary conditions refer to the parameters that constrain the calculation range of the unified cohesive force model and the stress environment, and the preset time increment step refers to the total number of time interval units that are pre-set to terminate the iterative calculation.
[0097] It should be noted that those skilled in the art can set the preset number of time increment steps according to actual needs, and this invention does not limit this.
[0098] In this embodiment of the invention, dynamic simulation of the entire crack propagation cycle is achieved through iterative calculation and boundary condition update, which fully captures the damage accumulation and crack propagation process at different time stages, avoids missing key evolution information due to a single calculation, and ensures that the prediction results can fully reflect the laws of the entire crack propagation cycle.
[0099] S8: Extract the crack length change information corresponding to each incremental step during crack propagation, and construct the crack propagation life curve of crack length changing with time based on the crack length change information.
[0100] Among them, crack length variation information refers to the increase or decrease of crack length under different time interval units, and crack propagation life curve refers to a curve that intuitively presents the law of crack length variation over time.
[0101] In this embodiment of the invention, this step transforms scattered failure and damage data into intuitive life curves, visualizes the damage evolution process, provides clear data support for the final fatigue life prediction results, and improves the readability and practicality of the results.
[0102] S9: Determine the predicted low-cycle fatigue crack propagation life based on the crack propagation life curve.
[0103] Among them, the low-cycle fatigue crack propagation life prediction result refers to the final evaluation conclusion reflecting the entire life cycle of the component under low-cycle fatigue conditions, from crack initiation to failure.
[0104] It should be noted that after extracting crack length evolution information based on failure element information in this step, the final output fatigue life prediction result is specifically the crack propagation life curve under the current loading conditions. Furthermore, the unified traction force-separation law used in this method can degenerate into the corresponding basic cyclic fatigue damage model and monotonic damage model under high-cycle fatigue conditions and monotonic tensile conditions, respectively, ensuring applicability under various loading conditions.
[0105] In this embodiment of the invention, this step is based on the complete crack propagation law to obtain accurate prediction results, which provides a direct basis for the safety assessment of engineering components and the formulation of operation and maintenance plans, and effectively improves the engineering applicability and practical value of the technical solution.
[0106] Reference manual attached Figure 3 The figure shows a comparison between an experimental test and a model lifetime prediction of fatigue crack propagation rate provided by an embodiment of the present invention.
[0107] Specifically, Figure 3The core parameters include: the horizontal axis N (cycles), representing the number of cyclic load cycles; and the vertical axis Crack length (mm), representing the crack length. It also includes prediction results from both the conventional and proposed models, experimental results of crack propagation, and fitting curves for both the conventional and proposed models.
[0108] Furthermore, in terms of inclusion relationships, Figure 3 The overall graph compares the correlation curves between crack length and cycle count, integrating prediction data from two models, experimental data, and corresponding fitted curves. In terms of connectivity, the horizontal axis N (cycles) serves as a common variable, correlated with the vertical axis Crack length (mm) of the conventional model's prediction results, the proposed model's prediction results, and the crack propagation experimental results. Simultaneously, each prediction result corresponds to a fitted curve, linking the discrete prediction data into a continuous curve, thus providing a horizontal comparison with the experimental results curve.
[0109] It should be noted that, Figure 3 By comparing and correlating the prediction results and fitting curves of the proposed model with those of conventional models and experimental results, it is clearly shown that the prediction curves of the proposed model are closer to the experimental results, and the deviation between the discrete prediction data and the experimental data is smaller. This intuitively verifies the accuracy of the proposed model in predicting crack length evolution, provides data support for the reliability of subsequent fatigue life prediction results, highlights the predictive advantages of the proposed model compared with conventional models, and clarifies its practical value in crack propagation analysis.
[0110] Reference manual attached Figure 4 The diagram shows a comparison of fatigue crack prediction errors provided by an embodiment of the present invention.
[0111] Specifically, Figure 4 The core parameters include: the horizontal axis "crack propagation length," in mm, representing the length of crack propagation; and the vertical axis "prediction error," in %, representing the degree of deviation between the model's prediction and the actual result. Additionally, it includes two data series: "prediction error of the proposed model" and "prediction error of the classical model."
[0112] Furthermore, in terms of inclusion relationships, Figure 4 The overall graph is a comparison of the correlation curves between prediction error and crack propagation length, integrating the prediction error variation curves of the proposed model and the classical model. In terms of the connection relationship, the horizontal axis "crack propagation length" serves as a common correlation variable, corresponding to the vertical axis "prediction error" of the proposed model and the classical model, respectively. The two curves form a horizontal comparison with crack propagation length as the link, clearly showing the error differences of different models at various crack lengths.
[0113] It should be noted that, Figure 4 By comparing the prediction error curves of the proposed model and the classical model with the crack propagation length, it is evident that the overall prediction error of the proposed model is lower than that of the classical model, and it tends to stabilize more steadily with increasing crack propagation length. This strongly verifies the accuracy advantage of the proposed model in crack propagation prediction, provides direct data support for the reliability of subsequent fatigue life prediction results, highlights the performance improvement of the proposed model compared to the classical model, and clarifies its practical value in crack propagation analysis scenarios.
[0114] Reference manual attached Figure 5 The diagram shows a structural schematic of a unified damage low-cycle fatigue life prediction system provided by an embodiment of the present invention.
[0115] This invention provides a unified damage low-cycle fatigue life prediction system 20, comprising: a processor 201 and a memory 202; The memory 202 stores programs or instructions that can run on the processor 201. When the program or instructions are executed by the processor 201, they implement the steps of the above-described method for predicting the unified damage low-cycle fatigue life and achieve the same technical effect. To avoid repetition, the present invention will not elaborate further.
[0116] It should be understood that the processor 201 in this embodiment of the invention may be a central processing unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.
[0117] It should also be understood that the memory 202 in the embodiments of the present invention can be volatile memory or non-volatile memory, or may include both volatile and non-volatile memory. The non-volatile memory can be read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), or flash memory. The volatile memory can be random access memory (RAM), which is used as an external cache. By way of example, but not limitation, many forms of random access memory are available, such as static random access memory (SRAM), dynamic random access memory (DRAM), synchronous dynamic random access memory (SDRAM), double data rate synchronous dynamic random access memory (DDR SDRAM), enhanced synchronous dynamic random access memory (ESDRAM), synchronous link dynamic random access memory (SLDRAM), and direct memory bus RAM (DR RAM).
[0118] The above embodiments can be implemented, in whole or in part, by software, hardware (such as circuits), firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer instructions or computer programs. When the computer instructions or computer programs are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more sets of available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium. A semiconductor medium can be a solid-state drive.
[0119] It should be understood that, in various embodiments of the present invention, the sequence number of each process does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.
[0120] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.
[0121] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the devices, apparatuses, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.
[0122] In the several embodiments provided by this invention, it should be understood that the disclosed devices, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another device, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between devices or units may be electrical, mechanical, or other forms.
[0123] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.
[0124] In addition, the functional units in the various embodiments of the present invention can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit.
[0125] If the aforementioned functions are implemented as software functional units and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this invention, essentially, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this invention. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.
[0126] This invention provides a readable storage medium comprising: storing a program or instructions on the readable storage medium, wherein when the program or instructions are executed by a processor, the program or instructions implement the steps of the above-described method for predicting the unified damage low-cycle fatigue life, and can achieve the same technical effect. To avoid repetition, this invention will not elaborate further.
[0127] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the protection scope of the present invention.
Claims
1. A method for predicting low-cycle fatigue life with uniform damage, characterized in that, include: S1: Obtain stress and strain state information of the crack propagation region at the current increment step and the adjacent increment steps; S2: Based on the stress state information and strain state information of the crack initiation location in the crack propagation region, construct the damage opening displacement; S3: Input the damage opening displacement into the unified cohesive force model and output the monotonic damage evolution and cyclic fatigue damage evolution respectively; S4: The monotonic damage evolution quantity and the cyclic fatigue damage evolution quantity are uniformly characterized to determine the total cumulative damage value of the cohesive unit node under the incremental step at the current moment. S5: Based on the damage opening displacement and the damage opening displacement threshold, determine whether monotonic damage failure has occurred; if so, delete the cohesive element node that has experienced monotonic damage failure and record the corresponding time node; otherwise, proceed to S6. S6: Based on the total accumulated damage value and the total accumulated damage threshold, determine whether cyclic fatigue damage failure has occurred; if so, delete the cohesive unit node that has experienced cyclic fatigue damage failure and record the corresponding time node; otherwise, update the cohesive stiffness of the next incremental step by combining the traction force-separation law of the coupling effect of monotonic damage failure and cyclic fatigue damage failure. S7: Based on the updated cohesive stiffness, update the boundary conditions of the unified cohesive model, and repeat S1 to S6 until the preset number of time increment steps is reached. S8: Extract the crack length change information corresponding to each incremental step during crack propagation, and construct a crack propagation life curve of crack length changing with time based on the crack length change information. S9: Determine the low-cycle fatigue crack propagation life prediction result based on the crack propagation life curve.
2. The method for predicting low-cycle fatigue life of uniform damage according to claim 1, characterized in that, S2 specifically includes: S201: Define load mixing ratio parameters through preset rules; S202: Extract features from the stress state information and strain state information of the crack propagation region under the current time increment step and the adjacent time increment step to obtain the tangential damage displacement and normal separation damage displacement of the crack initiation position in the crack propagation region. S203: Calculate the damage opening displacement by combining the load mixing ratio parameter, the tangential damage displacement, and the normal separation damage displacement.
3. The method for predicting low-cycle fatigue life of uniform damage according to claim 1, characterized in that, The process by which the unified cohesive model outputs a monotonic damage evolution quantity specifically includes: The damage opening displacement is input into the unified cohesive force model; Based on preset damage initiation conditions and preset damage failure conditions, damage initiation displacement and damage failure displacement are extracted from the unified cohesive force model. The monotonic damage evolution quantity is calculated by combining the damage opening displacement, the damage initiation displacement, and the damage failure displacement.
4. The method for predicting low-cycle fatigue life of uniform damage according to claim 1, characterized in that, The process of calculating the cyclic fatigue damage evolution in the unified cohesive model specifically includes: The damage opening displacement is input into the unified cohesive force model; Based on the unified cohesive force model, the traction force of the cohesive force unit node at the current time increment step and the cohesive force intensity under the current damage state are obtained. The damage opening displacement of the current time increment step and the previous time increment step are input into the unified cohesive force model to calculate the damage opening displacement increment. The model control variables of the preset fatigue damage model are called from the unified cohesive force model; By combining the traction force, the cohesive strength, the damage opening displacement increment, and the model control variables, the cyclic fatigue damage evolution is calculated using the unified cohesive model.
5. The method for predicting low-cycle fatigue life of uniform damage according to claim 1, characterized in that, S4 specifically includes: S401: Calculate the monotonic damage integral based on the monotonic damage evolution quantity; S402: Calculate the cyclic fatigue damage integral based on the cyclic fatigue damage evolution amount; S403: Extract a preset fatigue damage acceleration coefficient from the unified cohesive force model; S404: The monotonic damage integral, the cyclic fatigue damage integral, and the fatigue damage acceleration coefficient are coupled and superimposed to obtain the total cumulative damage value.
6. The method for predicting low-cycle fatigue life of uniform damage according to claim 1, characterized in that, After S4 and before S5, the process also includes the adaptive degradation process of the unified cohesion model.
7. The method for predicting low-cycle fatigue life of uniform damage according to claim 6, characterized in that, The adaptive degradation process of the unified cohesion model specifically includes: Calculate the contribution ratios of the monotonic damage integral and the cyclic fatigue damage integral to the total cumulative damage value, respectively. The dominant damage mechanism of the unified cohesion model is adaptively adjusted based on the contribution ratio and the preset ratio value. If the contribution ratio of monotonic damage is lower than the preset monotonic ratio value, the unified cohesion model degenerates into a cyclic fatigue damage model dominated by cyclic fatigue damage evolution calculation. If the contribution ratio of cyclic fatigue damage is lower than the preset cyclic ratio value, the unified cohesion model degenerates into a monotonic damage model dominated by monotonic damage evolution calculation.
8. The method for predicting low-cycle fatigue life of uniform damage according to claim 1, characterized in that, The traction-separation law, which combines the coupling effects of monotonic damage failure and cyclic fatigue damage failure, in step S6, specifically updates the cohesive stiffness of the incremental step in the next moment, including: S601: If it is determined that no cyclic fatigue damage failure has occurred, the maximum monotonic displacement of the incremental step at the current moment is obtained through the unified cohesive force model. S602: Based on the damage opening displacement, the maximum damage monotonic displacement, and the damage failure displacement, and combined with the traction force-separation law of the coupling effect of the monotonic damage failure and the cyclic fatigue damage failure, determine the current traction force; S603: Based on the current traction force, update the cohesive stiffness of the incremental step at the next moment.
9. A unified system for predicting low-cycle fatigue life due to damage, characterized in that, include: Processor and memory; The memory stores programs or instructions that can run on the processor, which, when executed by the processor, implement the steps of the method for predicting uniform damage low-cycle fatigue life as described in any one of claims 1 to 8.
10. A readable storage medium, characterized in that, The readable storage medium stores a program or instructions that, when executed by a processor, implement the steps of the method for predicting uniform damage low-cycle fatigue life as described in any one of claims 1 to 8.