Corrosion fatigue evaluation method based on coupling degradation and multi-crack stage evolution law

Abstract

The invention belongs to the technical field of corrosion fatigue testing, and particularly relates to a corrosion fatigue evaluation method based on a coupling degradation and multi-crack stage evolution law. The method comprises the following steps: establishing a three-stage crack evolution model of the steel according to a corrosion fatigue test and a classical theory; according to existing corrosion test data or empirical formulas, natural corrosion behaviors of corresponding structural members are deduced in combination with geographic positions and service environments of the members; deducing the coupling effect of corrosion and fatigue by combining the environmental corrosivity and the service load frequency, and performing equivalent conversion on the loss of corrosion and fatigue; deriving node stress amplitude according to the stress time history of the structural member; building a probabilistic corrosion fatigue model; and verifying the model, and performing probability evaluation on the corrosion fatigue coupling degradation performance by using the model. According to the method, the coupling effect between the corrosion effect and the fatigue effect is quantified, and the problem that corrosion fatigue coupling degradation cannot be considered in a steel structural component bearing environmental corrosion and fatigue loads at the same time is solved.

Description

Technical Field

[0001] This invention belongs to the field of corrosion fatigue testing technology, specifically relating to a corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution laws. Background Technology

[0002] During service, steel structures are subjected to alternating stresses such as vehicle dynamic loads, wind loads, and wave loads, making fatigue failure a particularly prominent issue. Especially in harsh corrosive environments such as coastal areas, steel structural components exhibit significant time-varying degradation characteristics, namely, coupled corrosion-fatigue (CF) degradation. On the one hand, steel structural components face escalating loads from wind-wave coupling effects and improved air-servo dynamic loads; on the other hand, the marine environment, characterized by strong sunlight, high humidity, and high chloride ion concentration, makes the servo environment of the components extremely corrosive. Therefore, for steel structural components simultaneously subjected to environmental corrosion and fatigue loads, the adverse effects of coupled corrosion-fatigue degradation must be considered to accurately assess their corrosion fatigue performance. Current methods for assessing the corrosion fatigue performance of steel structural components fail to consider the multi-stage crack evolution characteristics of coupled corrosion-fatigue degradation, which differs significantly from actual CF degradation behavior. Furthermore, the coupling effect between corrosion and fatigue effects has not been clearly quantified, leading to an unsafe assessment of the corrosion fatigue performance of steel structural components. Summary of the Invention

[0003] To address the problems existing in the prior art, this invention provides a corrosion fatigue assessment method that considers the coupled degradation of corrosion and fatigue and the multi-stage evolution of multiple cracks. This method can take into account the adverse effects of coupled corrosion and fatigue degradation to accurately assess its corrosion fatigue performance. It can also take into account the multi-stage crack evolution characteristics of coupled corrosion and fatigue degradation. At the same time, it quantifies the coupling effect between corrosion effect and fatigue action, thus solving the problem that coupled corrosion and fatigue degradation cannot be considered in steel structural members that are simultaneously subjected to environmental corrosion and fatigue loads.

[0004] The corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution law provided by this invention includes the following steps: S1. Based on corrosion fatigue tests and classical theories, a three-stage crack evolution model for steel is established. S2. Based on existing corrosion test data or empirical formulas, and combined with the geographical location and service environment of the component, deduce the natural corrosion behavior of the corresponding structural component. S3. The coupling effect of corrosion fatigue is derived by combining environmental corrosion and service load frequency, and the losses from corrosion and fatigue are converted into equivalent values. S4. Derive the nodal stress amplitude based on the stress time history of structural members; S5. Construct a probabilistic corrosion fatigue model; S6. The probabilistic crack evolution model was verified from both pure fatigue and corrosion fatigue perspectives, and this model was used to probabilistically evaluate the coupled degradation performance of corrosion fatigue.

[0005] Preferably, in step S1, the three-stage crack evolution model includes the evolution from corrosion-driven crack initiation to corrosion fatigue-competitive crack driving, and the subsequent continuous propagation of cracks is mainly driven by fatigue until final fracture failure occurs; wherein, the initiation of short cracks in the early stage is quantified by corrosion loss and damage accumulation, and the propagation of subsequent long cracks is characterized by fracture mechanics; and equivalent initial defects are used to delineate this boundary.

[0006] Preferably, in step S1, the initiation of short cracks is calculated considering damage mechanics. ;in, It is a short crack. As damage accumulates, Corrosion damage; long crack propagation is characterized by the propagation rate using fracture mechanics; based on ( - The equivalent initial defect EIFS derived from the curve is used to define the starting point of the long crack stage, i.e.: ;in, It is the stress intensity factor threshold in fracture mechanics. It is the ultimate fatigue strength, represented by the SN curve at 10. 8 The intensity value at that location.

[0007] Preferably, in step S3, when corrosion plays a dominant role in the early stage, corrosion loss and fatigue damage are superimposed when calculating the total loss; when fatigue plays a dominant role in the later stage, the increase in crack propagation rate under strong corrosion environment is also considered; and the corrosion loss represented by time and the fatigue crack propagation represented by the number of cycles are replaced by the load frequency.

[0008] Preferably, in step S4, the stress time history spectrum of the steel structure component is processed by rainflow counting, and the stress spectrum is statistically analyzed to obtain the stress amplitude of the component, thereby conducting analysis of the corresponding component.

[0009] Preferably, in step S5, the Monte Carlo sampling method is used for probabilistic modeling, and the three-stage crack propagation model in S1 is further developed into a probabilistic corrosion fatigue model by sampling material parameters. This model takes into account the overlapping and aggregation effect during the propagation of multiple cracks.

[0010] This invention can take into account the adverse effects of corrosion-fatigue coupled degradation to accurately assess its corrosion-fatigue performance. It can also take into account the multi-stage crack evolution characteristics of corrosion-fatigue coupled degradation. At the same time, it quantifies the coupling effect between corrosion effect and fatigue action, thus solving the problem that corrosion-fatigue coupled degradation cannot be considered in steel structural members that are simultaneously subjected to environmental corrosion and fatigue load. Attached Figure Description

[0011] Figure 1 The flowchart illustrates the implementation of the corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution provided by this invention. Figure 2 A schematic diagram of the three-stage evolution of corrosion fatigue (CF) cracks; Figure 3 Corrosion performance derived from existing corrosion test data; Figure 4 The solution process for the proposed probabilistic corrosion fatigue (PCF) model; Figure 5 The derivation and verification of the PSN curve for the PCF model; (a) pure fatigue verification; (b) corrosion fatigue verification; Figure 6 The probability of crack growth is statistically calculated for the PCF model. Detailed Implementation

[0012] To facilitate understanding of the present invention, a more detailed description is provided below with reference to the accompanying drawings and specific embodiments. Preferred embodiments of the invention are shown in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0013] This invention provides a corrosion fatigue assessment method based on the coupled degradation of corrosion fatigue (CF) and the multi-stage evolution of multiple cracks. The specific process is as follows: Figure 1 As shown, the main steps include:

[0014] Step S1: Based on corrosion fatigue tests and classical theory, establish a CF crack evolution model for steel structural members. Combining electrochemical, damage mechanics, and fracture mechanics theories with corrosion fatigue tests, establish a three-stage corrosion fatigue crack evolution model for steel structural members, such as... Figure 2 As shown in the figure. The CF crack evolution model conservatively calculates the crack initiation increment during the early short crack stage based on the superposition of corrosion and fatigue. , For short cracks, subscript Indicates corrosion, subscript This indicates fatigue; simultaneously, as long crack propagation fatigue gradually becomes dominant in the later stages, crack calculations are performed according to the competition mechanism between the two. , It is a long crack. This is an environmental auxiliary coefficient.

[0015] According to the classical formula, based on ( - The equivalent initial defect EIFS derived from the curve can be used to define the starting point of the long crack stage, i.e.: Among them, the initiation of short cracks is calculated considering damage mechanics. Meanwhile, the propagation rate of fatigue cracks during long crack propagation is calculated using fracture mechanics, i.e.: , This represents the change in stress intensity factor along the crack depth direction. It is the stress ratio. and These are the crack propagation coefficient and the exponent, respectively; The load frequency, i.e. .

[0016] Step S2: Based on the service environment of the steel structure components, combined with existing corrosion test data and empirical formulas, deduce the natural corrosion behavior of the corresponding structure, using the annual loss rate based on the steel plate thickness. Characterization, , This refers to the thickness loss of carbon steel in its first year. This is a materials-related index. It considers the actual changes in corrosion degree of structural components over time under real engineering service environments. This process can be determined through the National Data Center for Materials Corrosion and Protection and existing corrosion test data under similar service environments. Its corrosion performance is as follows: Figure 3 As shown.

[0017] Step S3: When corrosion plays a dominant role in the early stage, corrosion loss and fatigue damage are superimposed when calculating the total loss; when fatigue plays a dominant role in the later stage, the increase in crack propagation rate under strong corrosion environment is also considered. This not only quantifies the acceleration of fatigue crack propagation by corrosion, but also reflects the contribution of fatigue to corrosion loss.

[0018] An environmental auxiliary coefficient is introduced based on the empirical formula in the standard to account for the accelerated fatigue crack propagation of carbon steel caused by increased corrosion, namely: This accelerating effect can be calculated using the first-year corrosion rate.

[0019] By load frequency Corrosion equivalent per unit time Converted to fatigue loss equivalent .

[0020] Step S4: Perform rainflow counting on the stress time history spectrum of the steel structure component, and statistically analyze the stress spectrum to obtain the stress amplitude of the component.

[0021] Step S5: Considering the huge uncertainties in the coupled corrosion fatigue degradation process and the uncertainty of the existing CF test in understanding the coupled degradation behavior, the aforementioned CF crack propagation model is upgraded to a probabilistic corrosion fatigue (PCF) model using the probabilistic modeling method of Monte Carlo sampling. This model also specifically considers the overlapping and aggregation effect when multiple cracks propagate.

[0022] The specific probabilistic crack propagation process is as follows: Figure 4 As shown. The proposed PCF model solution process includes two main stages: parameter sampling and failure life calculation. The first stage, sampling, involves generating a list of key parameters, including aspect ratio, based on the probability distribution of actual steel structural members. Expansion rate Extended threshold and fatigue strength level It is important to note that the variable parameters at different crack initiation locations are still treated as independent and identically distributed during the Monte Carlo simulation (MCS). Based on the sampled values, the EIFS for each defect can be determined. Then, a deterministic simulation of the CF degradation for each sample is performed, including three stages of crack evolution until the critical crack occurs, leading to failure fracture, i.e., reaching (…). > ,or > )hour, and These refer to the failure values ​​in the crack depth and length directions, respectively. and These represent the current crack depth and length, respectively. It's worth noting that multi-crack coagulation is performed after each solution step. Finally, the failure lifetime of each sample is recorded. .

[0023] Step S6: Based on existing pure fatigue and corrosion fatigue test data of steel structure components, the PCF model was systematically validated under different environmental corrosion levels and load frequencies. Figure 5 As shown. Then, using the validated PCF model, different service environments ( and ) and load spectrum effects ( and Crack propagation behavior ( or Predictions and statistics are performed to determine the failure life of components. The precise calculation of ), such as Figure 6 As shown.

Claims

1. A corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution, characterized in that, Includes the following steps: S1. Based on corrosion fatigue tests and classical theories, a three-stage crack evolution model for steel is established. S2. Based on existing corrosion test data or empirical formulas, and combined with the geographical location and service environment of the component, deduce the natural corrosion behavior of the corresponding structural component. S3. The coupling effect of corrosion fatigue is derived by combining environmental corrosion and service load frequency, and the losses from corrosion and fatigue are converted into equivalent values. S4. Derive the nodal stress amplitude based on the stress time history of structural members; S5. Construct a probabilistic corrosion fatigue model; S6. The probabilistic crack evolution model was verified from both pure fatigue and corrosion fatigue perspectives, and this model was used to probabilistically evaluate the coupled degradation performance of corrosion fatigue.

2. The corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution law according to claim 1, characterized in that, In step S1, the three-stage crack evolution model includes the evolution from corrosion-driven crack initiation to corrosion fatigue-competitive crack driving, and the subsequent continuous propagation of cracks is mainly driven by fatigue until final fracture failure. Among them, the initiation of short cracks in the early stage is quantified by corrosion loss and damage accumulation, and the propagation of long cracks in the later stage is characterized by fracture mechanics. An equivalent initial defect is used to delineate this boundary.

3. The corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution law according to claim 2, characterized in that, Short crack initiation is calculated considering damage mechanics. ;in, It is a short crack. As damage accumulates, Corrosion damage; long crack propagation is characterized by the propagation rate using fracture mechanics; based on ( - The equivalent initial defect EIFS derived from the curve is used to define the starting point of the long crack stage, i.e.: ;in, It is the stress intensity factor threshold in fracture mechanics. It is the ultimate fatigue strength, represented by the SN curve at 10. 8 The intensity value at that location.

4. The corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution law according to claim 1, characterized in that, In step S3, when corrosion plays a dominant role in the early stage, corrosion loss and fatigue damage are superimposed when calculating the total loss; when fatigue plays a dominant role in the later stage, the increase in crack propagation rate under strong corrosion environment is also considered; the corrosion loss represented by time and the fatigue crack propagation represented by the number of cycles are replaced by the load frequency.

5. The corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution law according to claim 1, characterized in that, In step S4, the stress time history spectrum of the steel structure component is processed by rainflow counting, and the stress spectrum is statistically analyzed to obtain the stress amplitude of the component, thereby conducting analysis of the corresponding component.

6. The corrosion fatigue assessment method based on coupled degradation and multi-crack stage evolution law according to claim 1, characterized in that, In step S5, a probabilistic modeling method is used to further sample material parameters of the three-stage crack propagation model in step S1, and develop it into a probabilistic corrosion fatigue model through Monte Carlo simulation. This model takes into account the overlapping and aggregation effect during the propagation of multiple cracks.

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