CN116595802A - DIC-based metal material high peripheral surface failure life prediction method - Google Patents
DIC-based metal material high peripheral surface failure life prediction method Download PDFInfo
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Abstract
The invention discloses a DIC-based metal material high peripheral surface failure life prediction method, which comprises the following steps: 1. obtaining the fatigue characteristics of the metal material under the condition of single-axis constant-amplitude loading of the material; 2. acquiring a load value of a plastic region of the crack tip; 3. obtaining the size of a plastic region of the split tip; 4. acquiring the fatigue crack growth rate from a small physical crack to a long crack growth stage; 5. establishing a model of a microscopic small crack expansion stage; 6. and obtaining a multi-scale life prediction model. According to the invention, the sizes of the stress field and the plastic region of the crack tip under the specific load condition are evaluated by combining DIC, and then the calculation model of the plastic region of the crack tip is built based on the crack closure effect, and then the multi-scale surface crack propagation life prediction model is built by combining the local yield strength theory on the basis of representing the stage from the physical small crack to the long crack propagation, so that the problem of separately considering the microscopic small crack and the physical small crack in the life prediction process is solved, and the method has more practical significance.
Description
Technical Field
The invention belongs to the technical field of fatigue failure of metal materials, and particularly relates to a DIC-based metal material high-peripheral surface failure life prediction method.
Background
A digital image correlation method (DIC), also called a digital speckle correlation method, is to obtain deformation information of a region of interest by correlation calculation of two digital images before and after deformation of a test piece; is a technique for tracking the strain change and displacement change of the surface of a test object. High cycle fatigue, also known as high cycle fatigue, has low stress level on parts and components, and the number of damage cycles is higher than 10 4 ～10 5 Fatigue of springs, drive shafts, etc. are among such. In damage tolerance designs, the original defect inside the material or component is considered an initial crack, and thus the life prediction model built based thereon does not take into account the crack initiation life. For long life fatigue, the small crack growth life occupies the majority of the total fatigue life, so the total fatigue life N f Can be divided into four parts, namely, initiating crack N ISC Microcosmic small crack N MSC Physical small crack N PSC And long crack N LC Number of cycles consumed by each of the four stages.
N will be in most studies MSC And N PSC Considered as a whole, the small crack propagation process is described based on crack tip displacement theory. But from a crack propagation perspective, both fall into the category of small cracks, but from a crack propagation rate perspective, exhibit distinct propagation modes. Therefore, it is more practical to consider the MSC phase separately from the PSC phase when modeling life prediction. From a crack length perspective, PSC can be considered as the conversion size between MSC and LC, i.e., from the PSC stage, the crack is controlled by Line Elastic Fracture Mechanics (LEFM), but at the same time is affected by microstructure. In addition, the relationship between crack length and stress intensity factor established in macroscopic fatigue test demonstrates the threshold value between PSC stage and LC stageAnd tend to be consistent. And most studies expect specific values for crack transformation size, which are typically related to average grain size. This indicates that under the combined action of factors such as material, grain size, microstructure, load, specimen morphology, etc., crack propagation processes of different scales are smoothly transited and do not occur suddenly. Thus, no clear limits for adjacent crack propagation phases can be given. Based on the above analysis, in order to predict the overall fatigue crack life with a unified model, a multi-scale life prediction model needs to be established to predict the fatigue life of the metal material.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a DIC-based metal material high peripheral surface failure life prediction method, which evaluates the sizes of a crack tip stress field and a plastic region under a specific load condition by combining a digital image correlation technique, establishes a crack tip plastic region calculation model based on a crack closure effect, and then establishes a multi-scale surface crack propagation life prediction model by combining a local yield strength theory on the basis of representing a physical small crack to a long crack propagation stage, thereby solving the problem of separately considering microscopic small cracks and physical small cracks in the life prediction process, and having more practical significance.
In order to solve the technical problems, the invention adopts the following technical scheme: the DIC-based metal material high peripheral surface failure life prediction method is characterized in that: the method comprises the following steps:
step one, obtaining fatigue characteristics of a metal material under the condition of uniaxial constant amplitude loading of the material: according to the fatigue test standard of the metal material, constant-amplitude fatigue tests under different conditions are carried out, the obtained test data are drawn in a coordinate system, and a stress-life curve and a fitting formula lgsigma of the metal material under the constant load loading condition are obtained through linear fitting a ＝A lg N f +B; wherein sigma a For loading stress amplitude, N f For the test fatigue life corresponding to the loaded stress amplitude, A and B are fitting parameters;
step two, obtaining a load value of a plastic zone of the crack tip, wherein the process is as follows:
step 201, applying a cyclic load with low stress amplitude to a test piece by using an in-situ fatigue test system, so that a crack is initiated at the tip of a notch of the test piece;
step 202, modifying the cyclic load amplitude according to the stress-life curve in the step one so as to observe crack expansion behavior in a high-cycle fatigue state;
in step 203, adjusting the load amplitude applied to the test piece, taking a micrograph by using an optical microscope every 5% of the load amplitude, and introducing the micrograph into a DIC analysis system for analysis;
204, taking the micrograph with the smallest load applied to the test piece as a reference, and comparing the micrograph with other load levels to calculate; starting from the position of the crack tip in calculation, measuring strain values at different positions along the crack propagation direction to obtain the size of a plastic region of the crack tip, and obtaining that the load value at the beginning of the plastic region of the crack tip is 53% of the maximum load value; the strain values at different positions need to be measured for multiple times to obtain an average value;
step three, obtaining the size of the plastic region of the split tip, wherein the process is as follows:
step 301, obtaining a calculation formula of a stress intensity factor of the plate-shaped test piece with the unilateral crack according to the Murakami theoryWherein K is stress intensity factor, sigma is stress value, a is crack length, F is sample geometric parameter, and +.>W is the width of the sample;
step 302, combining with crack closure effect, the theoretical calculation formula of the size of the plastic region of the crack tip is as followsWherein ρ is f Is the size of the plastic area of the crack tip, sigma y Is the yield strength, K of the material 0 Instantaneous opening of the tipA stress intensity factor between, and K 0 ≈0.53K max ，K max Is the maximum stress intensity factor in the loading process;
step four, obtaining the fatigue crack growth rate from a small physical crack to a long crack growth stage: combining Paris formula and Zheng-Hirt formula, santus and Taylor use small crack stress intensity factor range delta K th-small Substitution of DeltaK th-long For predicting small crack growth rates, i.eWherein (1)>C and m are fitting parameters for crack propagation rate, and are threshold values of long crack stages of the material; ΔK according to Murakami formula th-small Can be expressed asWherein HV is the microhardness of the material, about 342HV, lambda 1 And lambda is 2 All are fitting parameters, ++>Is crack length 2a;
establishing a model of a micro small crack expansion stage: combining LEFM conditions and Zheng-Hirt formula, chan and Lankford obtain corrected stress intensity factor range delta K for describing microscopic small crack stage by correcting delta K * I.e. ΔK * =Δk×q; wherein q is a correction coefficient, an Is the local yield strength;
step six, obtaining a multi-scale life prediction model; combining the formulas in the third step, the fourth step and the fifth step to obtain a prediction formula of the multi-scale crack growth rate covering the micro small crack, the physical small crack and the long crack process, wherein the prediction formula is as follows
；
Wherein n and m are both fitting parameters.
The DIC-based metal material high circumferential surface failure life prediction method described above is characterized in that: in step 201, the in-situ fatigue test system includes an in-situ fatigue test device, an optical microscope, an industrial camera, and a DIC analysis system, where the test piece is clamped on the in-situ fatigue test device, the optical microscope and the industrial camera are arranged above the test piece, and the in-situ fatigue test device is connected with the DIC analysis system.
The DIC-based metal material high circumferential surface failure life prediction method described above is characterized in that: in step 201, when the test piece is analyzed, the test piece is clamped on in-situ fatigue test equipment, cyclic loads with different stress ratios are applied to the test piece through compiling a load spectrum, a microscopic micrograph of an area around a crack tip is obtained through an optical microscope, a microscopic image at a specific moment in the cyclic loading process is collected through an industrial camera, and the collected microscopic image is uploaded to a DIC analysis system, so that a strain field, a displacement field and a plastic area size of the crack tip are obtained.
The DIC-based metal material high circumferential surface failure life prediction method described above is characterized in that: in step 502, local yield strengthWherein (1)>Is the initial value of the local yield strength, i.e. +.>d is the average grain size, k y Is a material constant.
The method has the advantages that the sizes of the stress field and the plastic region of the crack tip under the specific load condition are evaluated by combining the digital image related technology, the calculation model of the plastic region of the crack tip is built based on the crack closure effect, and then the multi-scale surface crack propagation life prediction model is built by combining the local yield strength theory on the basis of representing the stage from the physical small crack to the long crack propagation, so that the problem of separate consideration of the microscopic small crack and the physical small crack in the life prediction process is solved, and the method has more practical significance.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a schematic diagram of an in-situ fatigue testing system according to the present invention.
FIG. 2 is a graph showing the comparison of the measured and theoretical values of the plastic region of the metal material according to the present invention.
FIG. 3 is a graph comparing predicted fatigue life with experimental fatigue life for a metallic material of the present invention.
Fig. 4 is a flow chart of the method of the present invention.
Reference numerals illustrate:
1-in-situ fatigue testing equipment; 2-optical microscope; 3-industrial cameras;
4-DIC analysis system.
Detailed Description
A DIC-based metal material high circumferential surface failure lifetime prediction method as shown in fig. 1 to 4, the method comprising the steps of:
step one, obtaining fatigue characteristics of a metal material under the condition of uniaxial constant amplitude loading of the material: according to the fatigue test standard of the metal material, constant-amplitude fatigue tests under different conditions are carried out, the obtained test data are drawn in a coordinate system, and a stress-life curve and a fitting formula lgsigma of the metal material under the constant load loading condition are obtained through linear fitting a ＝A lg N f +B; wherein sigma a For loading stress amplitude, N f For the test fatigue life corresponding to the loaded stress amplitude, A and B are fitting parameters;
step two, obtaining a load value of a plastic zone of the crack tip, wherein the process is as follows:
step 201, applying a cyclic load with low stress amplitude to a test piece by using an in-situ fatigue test system, so that a crack is initiated at the tip of a notch of the test piece;
step 202, modifying the cyclic load amplitude according to the stress-life curve in the step one so as to observe crack expansion behavior in a high-cycle fatigue state;
in step 203, the load amplitude applied to the test piece is adjusted, and each time the load amplitude is increased by 5%, a photomicrograph is taken by using the optical microscope 2, and the photomicrograph is led into the DIC analysis system 4 for analysis;
204, taking the micrograph with the smallest load applied to the test piece as a reference, and comparing the micrograph with other load levels to calculate; starting from the position of the crack tip in calculation, measuring strain values at different positions along the crack propagation direction to obtain the size of a plastic region of the crack tip, and obtaining that the load value at the beginning of the plastic region of the crack tip is 53% of the maximum load value; the strain values at different positions need to be measured for multiple times to obtain an average value;
step three, obtaining the size of the plastic region of the split tip, wherein the process is as follows:
step 301, obtaining a calculation formula of a stress intensity factor of the plate-shaped test piece with the unilateral crack according to the Murakami theoryWherein K is stress intensity factor, sigma is stress value, a is crack length, F is sample geometric parameter, and +.>W is the width of the sample;
step 302, combining with crack closure effect, the theoretical calculation formula of the size of the plastic region of the crack tip is as followsWherein ρ is f Is the size of the plastic area of the fracture tip,σ y is the yield strength, K of the material 0 Is the stress intensity factor at the moment of opening the crack tip, and K 0 ≈0.53K max ，K max Is the maximum stress intensity factor in the loading process;
step four, obtaining the fatigue crack growth rate from a small physical crack to a long crack growth stage: combining Paris formula and Zheng-Hirt formula, santus and Taylor use small crack stress intensity factor range delta K th-small Substitution of DeltaK th-long For predicting small crack growth rates, i.eWherein (1)>C and m are fitting parameters for crack propagation rate, and are threshold values of long crack stages of the material; ΔK according to Murakami formula th-small Can be expressed asWherein HV is the microhardness of the material, about 342HV, lambda 1 And lambda is 2 All are fitting parameters, ++>Is crack length 2a;
establishing a model of a micro small crack expansion stage: combining LEFM conditions and Zheng-Hirt formula, chan and Lankford obtain corrected stress intensity factor range delta K for describing microscopic small crack stage by correcting delta K * I.e. ΔK * =Δk×q; wherein q is a correction coefficient, an Is the local yield strength;
step six, obtaining a multi-scale life prediction model; combining the third step, the fourth step and the stepThe formula in the fifth step is that a prediction formula of the multi-scale crack growth rate covering the micro-crack, the physical micro-crack and the long crack process is obtainedThe method comprises the steps of carrying out a first treatment on the surface of the Wherein n and m are both fitting parameters.
In actual use, the high cycle failure life of the metal material is divided into: surface failure and internal failure, the invention mainly predicts the high peripheral surface failure life of metal materials. In the stress-life curve in the first step, the test fatigue life is taken as an abscissa, and the stress amplitude is taken as an ordinate to establish a coordinate system.
In step 202, before formally taking the photo, the crack should be allowed to propagate forward for a certain distance, so as to ensure that the crack is stably propagated under the action of positive stress. The crack can be divided into three sections according to the shape, namely a notch section, an inclined crack section and a straight crack section. When the crack steadily propagates in a direction perpendicular to the load, it is indicated that the pre-crack is ended.
In step 204, to quantitatively measure the size of the plastic region of the crack tip, it is necessary to determine the strain values at different positions along the crack propagation direction from the crack tip position in the crack tip plastic strain region cloud chart, and then obtain the size of the plastic region by combining the stress-strain relationship. In order to ensure the accuracy of the test results, the average value is calculated by measuring for a plurality of times.
In the second step, the plastic zone of the crack tip refers to a zone where plastic deformation occurs at the crack tip after the crack body is stressed; i.e. crack opening is the occurrence of plastic deformation. The engineering material may have plastic regions at the crack tip as long as it has a slight ability to plastically deform. The presence of the plastic region will alleviate stress concentration at the crack tip. The larger the plastic deformation capability of the material is, the larger the stress is, the larger the plastic area of the fracture tip is, and the more easily the fracture tip is passivated. In general, fatigue failure can be classified into low cycle fatigue and high cycle fatigue according to the magnitude of the stress and cycle time that it is subjected to. The former refers to the circulation Zhou Ci of the metal material to fracture under higher alternating stress 4 The latter refers to the circulation of the metal material to fracture under lower alternating stressAt 10 cycles 5 ～10 7 The S-N curve and the fatigue limit have been the basis for fatigue design and the metal material has been subjected to 10 7 Fatigue strength without breaking after cycling is defined as the fatigue limit.
When the size of the plastic region of the fracture tip is obtained by adopting the method in the step two, the size of the plastic region of the fracture tip is 0 in the initial loading stage, but as the load continues to increase, the plastic region of the fracture tip starts to be generated and gradually increases, and the growth rate of the plastic region gradually decreases along with the increase of the load level. Because the sampling interval is limited, the load level of the plastic region of the crack tip at the beginning of generation cannot be accurately obtained, so that the load required by crack opening can be approximately obtained to be 53% of the maximum load value; as shown in the following table, the size of the plastic region of the fracture tip in the process of loading the constant amplitude load under the condition of r=0.1 is shown; wherein R is the stress ratio, i.e. the ratio of the minimum stress value to the maximum stress value.
In step three, the plastic zone starts to appear when the load is 53% of the maximum load, so K 0 ≈0.53K max 。
In step 302, residual stress is generated at the crack tip after the crack is closed, and the residual stress generated by unloading in the previous cycle can be offset by the tensile stress generated at the initial stage of the loading process of the next cycle, so that the influence of the crack closing effect should be considered when estimating the size of the plastic region of the crack tip.
In the fourth step, the earliest formula for predicting fatigue crack growth life is the pares formula; when the driving force is sufficiently large, the prediction results of the Paris equation, and the Zheng-Hirt equation are similar. Based on the Zheng-Hirt formula, santus and Taylor use a small crack stress intensity factor range DeltaK th-small Substitution of DeltaK th-long The method is used for predicting the small crack growth rate, and the Santus-Taylor formula corrected in the fourth step can be used for predicting the fatigue crack growth rate of the metal material in the physical small crack and long crack stages.
In step 501, the crack growth behavior cannot be described by ΔK during the microscopic small crack phase, so that further modification of the Zheng-Hirt equation is required to obtain a fatigue life prediction model that can describe the entire crack growth process. The study shows that the size of the plastic area of the crack tip at the stage of the micro-small crack is equivalent to the size of the crack, and the large-scale yield can be generated under the action of the cyclic stress, so that the crack is controlled to propagate forwards, and the size of the plastic area of the crack tip can be considered as the main control factor at the stage of the micro-small crack. At this time, the crack mainly propagates under the grain size, and the propagation rate changes more significantly. Therefore, the local yield strength should be adoptedTo describe the mechanical behavior of the crack tip plastic region. In the micro-crack stage, as the crack size increases, the crack size increases>The values also increase progressively until the crack is sufficiently long, the effect of the microstructure features on the crack growth rate is reduced. When the small-size yield condition is reached, i.e. the conditions of use of the LEFM are met, the local yield strength +.>Increase to and macroscopic yield strength sigma y Equal. Wherein ρ is f Is the cyclic plastic region size, which can be measured by in situ fatigue testing, or can be solved by the formula in step 302.
In step 502, the formula is used to predict the multi-scale crack growth rate covering both microscopic and macroscopic, where the microstructure differences are the determining factor of the growth behavior during microscopic microcracks, while the physical microcrack/long-crack stage is the dominant LEFM line elastic fracture mechanics. q determines the expansion mechanism of the material, since whenWhen 1, the applicable condition of LEFM is reached.
Step fiveWhere Δk cannot describe the crack propagation behavior MSC of the microcrack stage and the plastic zone size of the fracture tip is the dominant factor in the MSC stage, the local yield strength should be used to describe the plastic zone size of the fracture tip. ΔK * Is calculated by Δk and q, which in turn is calculated by the parameter local yield strength.
Assuming that the crack starts to propagate when the stress around the crack reaches the local yield strength, as the crack size increases, the more grain boundaries are covered by the plastic region around the crack, the local yield strength increases with it, i.e. the grain boundary strengthening criterion (Hall-Petch theory). The strain accumulation at the crack tip gradually accumulates with increasing cycles of fatigue, so it can be considered that a gradual accumulation process is exhibited during microscopic small cracks.
Furthermore, assuming that the material in the crack tip plastic region satisfies the Hall-Petch theory, the local yield strength can be expressed by the following formula:wherein (1)>Is the initial value of local yield strength, i.e. when the crack has just initiatedd is the average grain size, k y Is a material constant.
It should be noted that for single crystal materials, the initial local yield strength may be defined as the critical shear stress of the slip system. For polycrystalline materials, the initial local yield strength may be defined as the fatigue limit at a crack length of 0. And when the crack length is much greater than the grain size, the local yield strength is equal to the macroscopic yield strength of the material. However, for ultra-high cycle fatigue, it is believed that the material does not have a fatigue limit, where the initial local yield strength is 0, and here at 10 9 The fatigue strength corresponding to the cycle time was taken as the initial yield strength.
Ye and Zhang are based onEstablish->And->Relationship between them. When the crack starts to develop, it can be considered +.>And material fatigue limit sigma f Equal. Here specify sigma f Equal to the number of load cycles up to 10 9 Cyclic stress values at weeks, based on which:
where d is the average grain size and the coefficient α reflects the rate of transition from microscopic to physical small cracks, a smaller value means that the material will transition from microscopic to physical small cracks faster. It is clear from the definition that when the crack length increases to the transformation size of small and long cracks,/i>So the specific value of alpha can be obtained according to the conversion size from small crack to long crack.
And step six, fitting the C and m values under different conditions by utilizing the sizes of the surface failure fracture crack initiation area and the expansion area under different temperatures and different stress ratios based on the macroscopic fatigue test result, the in-situ fatigue test result and the DIC analysis result.
When the prediction model of the present invention is verified, the predicted fatigue life is taken as the abscissa and the predicted fatigue life is taken as the ordinate, a coordinate system is established, as shown in fig. 3, the predicted fatigue life result and the test result of the metal material under the conditions of two temperatures and two stress ratios are marked in the coordinate system, and the predicted values of the metal material are all located within the 3-time line boundary, so that the predicted fatigue life result is the life of the metal material when the high peripheral surface failure occurs
And D, integrating a prediction formula of the fatigue crack growth rate of the multi-scale surface of the alloy obtained in the step six to obtain a predicted fatigue life, and taking the predicted fatigue life into a coordinate system.
According to the invention, the sizes of the crack tip stress field and the plastic region under a specific load condition are evaluated by combining a digital image correlation technique, a crack tip plastic region calculation model is established based on a crack closure effect, and then a multi-scale surface crack propagation life prediction model is established by combining a local yield strength theory on the basis of representing a stage from a physical small crack to a long crack propagation, so that the problem of separate consideration of a microscopic small crack and a physical small crack in the life prediction process is solved, and the method has more practical significance.
In this embodiment, in step 201, the in-situ fatigue testing system includes an in-situ fatigue testing device 1, an optical microscope 2, an industrial camera 3, and a DIC analysis system 4, the test piece is clamped on the in-situ fatigue testing device 1, the optical microscope 2 and the industrial camera 3 are disposed above the test piece, and the in-situ fatigue testing device 1 is connected with the DIC analysis system 4.
In this embodiment, in step 201, when analyzing the test piece, the test piece is clamped on the in-situ fatigue testing device 1, cyclic loads with different stress ratios are applied to the test piece by compiling a load spectrum, a microscopic micrograph of an area around a crack tip is obtained by the optical microscope 2, a microscopic image at a specific moment in the cyclic load process is collected by the industrial camera 3, and the collected microscopic image is uploaded to the DIC analysis system 4, so as to obtain a strain field, a displacement field and a plastic region size of the crack tip.
The foregoing description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and any simple modification, variation and equivalent structural changes made to the above embodiment according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.
Claims (4)
1. A DIC-based metal material high circumferential surface failure life prediction method, comprising the steps of:
step one, obtaining fatigue characteristics of a metal material under the condition of uniaxial constant amplitude loading of the material: according to the fatigue test standard of the metal material, constant-amplitude fatigue tests under different conditions are carried out, the obtained test data are drawn in a coordinate system, and a stress-life curve and a fitting formula lgsigma of the metal material under the constant load loading condition are obtained through linear fitting a ＝AlgN f +B; wherein sigma a For loading stress amplitude, N f For the test fatigue life corresponding to the loaded stress amplitude, A and B are fitting parameters;
step two, obtaining a load value of a plastic zone of the crack tip, wherein the process is as follows:
step 201, applying a cyclic load with low stress amplitude to a test piece by using an in-situ fatigue test system, so that a crack is initiated at the tip of a notch of the test piece;
step 202, modifying the cyclic load amplitude according to the stress-life curve in the step one so as to observe crack expansion behavior in a high-cycle fatigue state;
in step 203, the load amplitude applied to the test piece is adjusted, and each time the load amplitude is increased by 5%, a photomicrograph is taken by using an optical microscope (2), and the photomicrograph is led into a DIC analysis system (4) for analysis;
204, taking the micrograph with the smallest load applied to the test piece as a reference, and comparing the micrograph with other load levels to calculate; starting from the position of the crack tip in calculation, measuring strain values at different positions along the crack propagation direction to obtain the size of a plastic region of the crack tip, and obtaining that the load value at the beginning of the plastic region of the crack tip is 53% of the maximum load value; the strain values at different positions need to be measured for multiple times to obtain an average value;
step three, obtaining the size of the plastic region of the split tip, wherein the process is as follows:
step 301, obtaining a calculation formula of a stress intensity factor of the plate-shaped test piece with the unilateral crack according to the Murakami theoryWherein K is stress intensity factor, sigma is stress value, a is crack length, F is sample geometric parameter, andw is the width of the sample;
step 302, combining with crack closure effect, the theoretical calculation formula of the size of the plastic region of the crack tip is as followsWherein ρ is f Is the size of the plastic area of the crack tip, sigma y Is the yield strength, K of the material 0 Is the stress intensity factor at the moment of opening the crack tip, and K 0 ≈0.53K max ，K max Is the maximum stress intensity factor in the loading process;
step four, obtaining the fatigue crack growth rate from a small physical crack to a long crack growth stage: combining Paris formula and Zheng-Hirt formula, santus and Taylor use small crack stress intensity factor range delta K th-small Substitution of DeltaK th-long For predicting small crack growth rates, i.eWherein (1)>C and m are fitting parameters for crack propagation rate, and are threshold values of long crack stages of the material; ΔK according to Murakami formula th-small Can be expressed asWherein HV is the microhardness of the material, about 342HV, lambda 1 And lambda is 2 All are fitting parameters, ++>Is crack lengthA degree 2a;
establishing a model of a micro small crack expansion stage: combining LEFM conditions and Zheng-Hirt formula, chan and Lankford obtain corrected stress intensity factor range delta K for describing microscopic small crack stage by correcting delta K * I.e. ΔK * =Δk×q; wherein q is a correction coefficient, an Is the local yield strength;
step six, obtaining a multi-scale life prediction model; combining the formulas in the third step, the fourth step and the fifth step to obtain a prediction formula of the multi-scale crack growth rate covering the micro small crack, the physical small crack and the long crack process, wherein the prediction formula is as follows
；
Where n is the fitting parameter.
2. The DIC-based metal-material high circumferential surface failure lifetime prediction method of claim 1, wherein: in step 201, the in-situ fatigue test system comprises in-situ fatigue test equipment (1), an optical microscope (2), an industrial camera (3) and a DIC analysis system (4), wherein the test piece is clamped on the in-situ fatigue test equipment (1), the optical microscope (2) and the industrial camera (3) are arranged above the test piece, and the in-situ fatigue test equipment (1) is connected with the DIC analysis system (4).
3. The DIC-based metal-material high-circumferential-surface failure lifetime prediction method of claim 2, wherein: in step 201, when analyzing the test piece, the test piece is clamped on an in-situ fatigue test device (1), cyclic loads with different stress ratios are applied to the test piece through compiling a load spectrum, a microscopic micrograph of a surrounding area of a crack tip is obtained through an optical microscope (2), a microscopic image at a specific moment in the cyclic load process is collected through an industrial camera (3), and the collected microscopic image is uploaded to a DIC analysis system (4) to obtain a strain field, a displacement field and a plastic area size of the crack tip.
4. The DIC-based metal-material high circumferential surface failure lifetime prediction method of claim 1, wherein: in step 502, local yield strengthWherein (1)>Is the initial value of the local yield strength, i.e. +.>d is the average grain size, k y Is a material constant.
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| CN117332688A (en) * | 2023-09-27 | 2024-01-02 | 中国石油大学(华东) | Method and system for predicting fatigue crack growth of X80 pipeline steel under random load effect |
| CN117954022A (en) * | 2024-03-25 | 2024-04-30 | 洛阳船舶材料研究所(中国船舶集团有限公司第七二五研究所) | Estimation method of fatigue crack growth rate of metal material under elastoplastic condition |
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| CN117332688A (en) * | 2023-09-27 | 2024-01-02 | 中国石油大学(华东) | Method and system for predicting fatigue crack growth of X80 pipeline steel under random load effect |
| CN117332688B (en) * | 2023-09-27 | 2024-04-16 | 中国石油大学(华东) | Method and system for predicting fatigue crack growth of X80 pipeline steel under random load effect |
| CN117954022A (en) * | 2024-03-25 | 2024-04-30 | 洛阳船舶材料研究所(中国船舶集团有限公司第七二五研究所) | Estimation method of fatigue crack growth rate of metal material under elastoplastic condition |
| CN117954022B (en) * | 2024-03-25 | 2024-06-07 | 洛阳船舶材料研究所(中国船舶集团有限公司第七二五研究所) | Estimation method of fatigue crack growth rate of metal material under elastoplastic condition |
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