Method for predicting fatigue crack growth rate of metal material

Abstract

The invention relates to the technical field of metal material fatigue crack prediction, in particular to a method for predicting a metal material fatigue crack growth rate. The method comprises the following steps: introducing an equivalent factor # imgabs0 # to obtain a fatigue crack propagation rate model; the method comprises the following steps: carrying out a fatigue crack growth rate test on a metal material at room temperature, measuring a fatigue crack growth curve under a stress ratio # imgabs1 # in a steady-state stage, and fitting the obtained fatigue crack growth curve based on a Paris formula to obtain values # imgabs2 # and # imgabs3 # and an equivalent factor # imgabs6 # corresponding to stress intensity factor change ranges # imgabs4 # and # imgabs5 #; the # imgabs7 # is multiplied by the # imgabs8 #, and the # imgabs10 # when the stress ratio of the # imgabs9 # is obtained; the # imgabs 11 # is divided by the # imgabs 13 # under the target stress ratio # imgabs 12 #, and the fatigue crack growth rate under the stress ratio # imgabs 14 # is obtained. According to the method, the technical problem of large prediction result error caused by large calculation amount and complex steps of a metal material fatigue crack propagation prediction method in the prior art is effectively solved.

Description

Technical Field

[0001] The invention relates to the technical field of fatigue crack prediction of metal materials, and in particular to a method for predicting the growth rate of fatigue crack of metal materials. Background Art

[0002] Fatigue cracks in metal materials are a phenomenon in which cracks slowly form on the surface and inside of metals and gradually expand due to stress in different directions and internal defects of the materials during long-term use. In order to timely discover potential crack expansion risks and avoid safety accidents caused by fatigue fracture of metal structures, the method of establishing crack expansion types is often used to predict the expansion of metal cracks.

[0003] For example, a patent document with authorization announcement number CN107506544B discloses a method for predicting fatigue crack growth of metal materials. The method first uses a finite element analysis method to obtain the residual stress field distribution at the crack tip under cyclic loading; then the residual stress intensity factor is calculated to determine the residual stress influence range of the cyclic load, and the residual stress intensity factor is filtered. The influence range of any residual stress intensity factor is compared with the influence range of the stress intensity factor generated by all previous cyclic loads, and it is concluded that the residual stress that affects crack growth is the linear superposition of the residual stress intensity factors generated by all previously applied cyclic loads starting from the residual stress intensity factor; then the influence range of any residual stress intensity factor is compared with the influence range of the stress intensity factor generated by all previous cyclic loads. If the influence range of the residual stress intensity factor exceeds the influence range of the residual stress intensity factor generated by all previous cyclic loads, it is determined that only the influence of the residual stress intensity factor on crack growth is considered. Finally, a fatigue crack growth model is established, and the fatigue crack growth of the metal material can be predicted based on the fatigue crack growth model.

[0004] It can be seen that the above prediction method mainly reflects the contribution of residual stress to crack propagation by quantitatively characterizing the distribution of residual stress caused by overload during crack propagation, and combines the residual stress intensity factor to establish a fatigue crack propagation prediction method under variable amplitude load. Although this method can predict the fatigue crack propagation of metal materials, its steps are complicated and require complex mathematical calculations and numerical integration. The amount of calculation is large, which greatly increases the prediction cost and prediction time. In addition, there will be certain errors in the calculation and measurement of each step. These errors gradually accumulate during the prediction process, resulting in a large deviation between the final prediction result and the actual result. Summary of the invention

[0005] The present invention provides a method for predicting the fatigue crack growth rate of a metal material, so as to solve the technical problem that the method for predicting the fatigue crack growth rate of a metal material in the prior art has large calculation amount and complicated steps, resulting in large errors in the prediction results.

[0006] In order to solve the above problems, the method for predicting the fatigue crack growth rate of metal materials provided by the present invention adopts the following technical solution: A method for predicting fatigue crack growth rate of a metal material comprises the following steps: S1: Introducing equivalence factors , and the fatigue crack growth rate model is obtained: , where: - crack depth or width, - Number of stress cycles, - equivalence factor, , - parameters related to the material, - Range of stress intensity factor; Definition , where: - equivalence factor, - equivalent stress factor, - Stress Factor Equivalent stress factor when The calculation formula is: , where: - equivalence factor, -Cyclic stress is The turning point of - stress ratio; S2: Fatigue crack growth rate test of metal materials at room temperature, and the stress ratio of the steady state stage is measured The fatigue crack growth curve under the condition of , and the fatigue crack growth curve obtained is fitted based on the Paris formula to obtain the stress ratio Next , Value and stress intensity factor range , the stress ratio is The corresponding equivalent factor is ; S3: Change the stress intensity factor range Multiply by the stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor when ; S4: Change the stress intensity factor range Divide by the target stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor ,Will Substitute into the Paris formula obtained in step S2, where the and The value remains unchanged, and the stress ratio is Fatigue crack growth rate.

[0007] The beneficial effects of the method for predicting fatigue crack growth rate of metal materials provided by the present invention are: 1. Based on the principle that fatigue crack growth behavior under different stress ratios is determined by the energy consumed during the growth process, a new method is proposed that is independent of the material and only depends on the stress ratio. Equivalence factors , and introduce it into the Paris formula to construct a new fatigue crack growth rate model, which can more comprehensively consider the effect of stress on fatigue crack growth rate, thereby improving the accuracy of fatigue crack growth prediction; 2. Establishing Equivalence Factors Ratio to stress The relationship is due to the equivalence factor It is a parameter that has nothing to do with the material. Therefore, the new fatigue crack growth rate model can be applied to a variety of materials and has a wider applicability. 3. When actually predicting the fatigue crack growth rate of metal materials, it is only necessary to convert any stress ratio The fatigue crack growth curve under the condition of φ is fitted based on the Paris formula to obtain the material-related parameters , and stress intensity factor range , and then Multiply by the stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor when , and then Divide by the target stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor ,Will , and Substituting into the Paris formula, we can get the stress ratio: The fatigue crack growth rate at the time of the test is simple and the calculation amount is small. Only one multiplication and one division operation are required for the initial stress intensity factor variation range obtained by the test to obtain the stress intensity factor variation range under the target stress ratio, which is then compared with the fitted and By bringing them into the Paris formula, the fatigue crack growth rate under the target stress ratio can be predicted, which greatly saves the test time and cost.

[0008] Through the above settings, the present invention completes the improvement and upgrading of the existing metal fatigue crack growth rate prediction method, and effectively solves the technical problems of the existing metal material fatigue crack growth prediction method having large calculation amount and complex steps, resulting in large errors in its prediction results.

[0009] Furthermore, the equivalent stress factor The calculation formula is: , where: - equivalent stress factor, - energy consumption per unit time, - crack surface area, - The elastic modulus of the material.

[0010] Furthermore, the energy consumption per unit time The calculation formula is: , where: - energy consumption per unit time, - total energy consumption per cycle, - Loading time per cycle.

[0011] Furthermore, the total energy consumption per cycle The calculation formula is: , where: - total energy consumption per cycle, - energy dissipation during crack tip opening, - Loading time per cycle, -Cyclic stress is The turning point of -Hysteresis coefficient.

[0012] Furthermore, the hysteresis coefficient The calculation formula is: , where: - hysteresis coefficient, -Cyclic stress is The turning point of time.

[0013] Furthermore, the cyclic stress is The turning point The calculation formula is: , where: -Cyclic stress is The turning point of -Stress ratio.

[0014] Furthermore, the energy consumption when the crack tip opens is The calculation formula is: , where: - energy dissipation during crack tip opening, -Energy release rate, -Crack surface area.

[0015] Furthermore, the energy release rate The calculation formula is: , where: -Energy release rate, - stress intensity factor, - The elastic modulus of the material.

[0016] Furthermore, the stress intensity factor The calculation formula is: , where: - stress intensity factor, - maximum value of the stress intensity factor, - stress ratio, - Loading time per cycle, its value range is .

[0017] Furthermore, the Paris formula is: , where: - crack depth or width, - Number of stress cycles, , - parameters related to the material, -The range of stress intensity factors. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] By reading the following detailed description with reference to the accompanying drawings, the above and other objects, features and advantages of the exemplary embodiments of the present invention will become readily understood. In the accompanying drawings, several embodiments of the present invention are shown in an exemplary and non-limiting manner, and the same or corresponding reference numerals represent the same or corresponding parts, wherein: Figure 1 A flow chart of a method for predicting metal fatigue crack growth rate provided by the present invention; Figure 2 The equivalent factor in the method for predicting the metal fatigue crack growth rate provided by the present invention is With stress ratio ; Figure 3 The stress ratio in the method for predicting the metal fatigue crack growth rate provided by the present invention is Comparison of the fatigue crack growth rate prediction curve and the experimental curve obtained when . DETAILED DESCRIPTION

[0019] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Those skilled in the art should know that the embodiments described below are part of the embodiments of the present disclosure, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0020] It should be noted that the main concept of the method for predicting fatigue crack growth rate of metal materials provided by the present invention is: Based on the principle that fatigue crack growth behavior under different stress ratios is determined by the energy consumed during the growth process, a new method is proposed that is independent of the material and only depends on the stress ratio. Equivalence factors , establish the equivalent factor Ratio to stress The relationship is due to the equivalence factor is a material-independent parameter. Therefore, the new fatigue crack growth rate model can be applied to a variety of materials and has a wider applicability. Introducing the Paris formula to construct a new fatigue crack growth model can more comprehensively consider the effect of stress on fatigue crack growth rate, thereby improving the accuracy of fatigue crack growth rate prediction; when actually predicting the fatigue crack growth rate of metal materials, it is only necessary to convert any stress ratio The fatigue crack growth curve under the condition of φ is fitted based on the Paris formula to obtain the material-related parameters , and stress intensity factor range , and then Multiply by the stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor when , and then Divide by the target stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor ,Will , and Substituting into the Paris formula, we can get the stress ratio: The fatigue crack growth rate at this time is simple in steps and small in calculation, which saves test time and test costs to a great extent.

[0021] From the above analysis of the concept, it can be seen that the method for predicting the fatigue crack growth rate of metal materials provided by the present invention simplifies the steps of predicting the fatigue crack growth rate of metal materials, reduces the amount of calculation, and can guarantee the accuracy of the prediction results to a large extent. Therefore, it can effectively solve the technical problems of the existing method for predicting fatigue crack growth rate of metal materials, which has large amount of calculation and complex steps, resulting in large errors in the prediction results.

[0022] After introducing the basic principle of the present invention, various non-limiting embodiments of the present invention are described in detail below. The number of any element in the drawings is for illustration and not for limitation, and any naming is only for distinction and does not have any limiting meaning.

[0023] The prediction of fatigue crack growth rate of metal materials is crucial in engineering, as it is directly related to the safety and reliability of the structure. Fatigue of metal materials refers to the process in which the material gradually produces local permanent cumulative damage under the action of cyclic stress or cyclic strain, and cracks or sudden complete fracture occur after a certain number of cycles; fatigue crack growth is the development stage of fatigue damage, which usually originates from high stress areas or material defects, and gradually expands with the continuous action of cyclic stress, eventually leading to complete fracture of the material.

[0024] In the process of exploring the fatigue crack growth of materials, the Paris formula introduced fracture mechanics into the field of fatigue crack growth for the first time, which well described the fatigue crack growth behavior of materials in the steady-state stage, and was helpful in exploring fatigue damage mechanisms and predicting fatigue life. However, the fatigue of engineering components is actually always under variable amplitude loads. For example, high-speed trains and airplanes are often subjected to random loads during operation. Therefore, it is far from enough to use the Paris formula to predict the fatigue life of engineering components. It is a crucial challenge to expand the knowledge of constant amplitude fatigue to more realistic situations, including variable amplitude cyclic stress and strain.

[0025] The principle and spirit of the present invention are explained in detail below with reference to several representative embodiments of the present invention.

[0026] Embodiment 1 of the method for predicting fatigue crack growth rate of metal materials provided by the present invention: like Figure 1 As shown, the method for predicting the fatigue crack growth rate of metal materials includes the following steps: S1: Introducing equivalence factors , and the fatigue crack growth rate model is obtained: , where: - crack depth or width, - Number of stress cycles, - equivalence factor, , - parameters related to the material, - Range of stress intensity factor; Definition , where: - equivalence factor, - equivalent stress factor, - Stress Factor Equivalent stress factor when The calculation formula is: , where: - equivalence factor, -Cyclic stress is The turning point of - stress ratio; S2: Fatigue crack growth rate test of metal materials at room temperature, and the stress ratio of the steady state stage is measured The fatigue crack growth curve under the condition of , and the fatigue crack growth curve obtained is fitted based on the Paris formula to obtain the stress ratio Next , Value and stress intensity factor range , the stress ratio is The corresponding equivalent factor is ; S3: Change the stress intensity factor range Multiply by the stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor when ; S4: Change the stress intensity factor range Divide by the target stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor ,Will Substitute into the Paris formula obtained in step S2, where the formula obtained in step S2 is and The value remains unchanged, and the stress ratio is Fatigue crack growth rate.

[0027] In step S1, the equivalent stress factor The calculation formula is: , where: - equivalent stress factor, - energy consumption per unit time, - crack surface area, - The elastic modulus of the material.

[0028] In the above formula, the energy consumption per unit time is The calculation formula is: , where: - energy consumption per unit time, - total energy consumption per cycle, - Loading time per cycle.

[0029] In the above formula, the total energy consumption per cycle is The calculation formula is: , where: - total energy consumption per cycle, - energy dissipation during crack tip opening, - Loading time per cycle, -Cyclic stress is The turning point of -Hysteresis coefficient.

[0030] In the above formula, the hysteresis coefficient The calculation formula is: , where: - hysteresis coefficient, -Cyclic stress is The turning point of time.

[0031] In the above formula, the cyclic stress is The turning point The calculation formula is: , where: -Cyclic stress is The turning point of -Stress ratio.

[0032] In the above formula, the energy consumption when the crack tip opens is The calculation formula is: , where: - energy dissipation during crack tip opening, -Energy release rate, -Crack surface area.

[0033] In the above formula, the energy release rate The calculation formula is: , where: -Energy release rate, - stress intensity factor, - The elastic modulus of the material.

[0034] In the above formula, the stress intensity factor The calculation formula is: , where: - stress intensity factor, - maximum value of the stress intensity factor, - stress ratio, - Loading time per cycle, its value range is By adjusting the stress intensity factor By analyzing the calculation formula, it can be found that the average stress increases with the stress ratio increases with the increase of .

[0035] In calculation When the stress ratio When it is greater than 0, it is the stress intensity factor In the calculation formula When the stress ratio is greater than 0, the value is integrated; When it is less than 0, due to the existence of compressive stress, the compressive stress will delay the expansion of the crack. The hysteresis factor is introduced .

[0036] It should be noted that the Paris formula is: , where: - crack depth or width, - Number of stress cycles, , - parameters related to the material, -The range of stress intensity factor. For the same metal material, the parameters in the Paris formula is approximately a constant value, so in the new model, the formula To predict the fatigue crack growth rate under different stress ratios.

[0037] In addition, it should be noted that the formula In the equivalent factor With stress ratio Changes such as Figure 2 shown.

[0038] In addition, it should be noted that the Paris formula was proposed by American Paris in 1963 based on the fracture mechanics method. The Paris formula provides a new method for estimating crack propagation life for fatigue research. On this basis, damage tolerance design was developed, thus gradually combining the two disciplines of fracture mechanics and fatigue.

[0039] Paris believed that the stress field intensity at the crack tip can be expressed by the stress intensity factor To express it, then only the stress intensity factor is the real driving force of crack extension, so it is proposed to directly change the range of stress intensity factor The crack growth formula.

[0040] When the crack front Then the cracks started to expand. and It is a linear relationship, which is called the first stage of fatigue crack growth. is the stress intensity factor range threshold, that is, the minimum value of the stress intensity factor range required for cracks to start to propagate.

[0041] when Continue to increase, after passing the turning point B1, enter the second stage, the crack growth rate slows down, and It is still a linear relationship. When it increases to exceed the turning point B2 of stage II, Close to the material , the crack propagation speed increases sharply until it breaks. is the maximum stress intensity factor, that is, the maximum stress intensity factor experienced by the crack front during crack propagation; It is the fracture toughness, a measure of a material's ability to resist crack growth under plane strain conditions.

[0042] Since stages I and II are straight lines in double logarithmic coordinates, it means and There is an exponential relationship between them, so Paris proposed an empirical formula for crack growth rate, namely the Paris formula: .

[0043] Next, we use 300M steel at a stress ratio of Prediction of fatigue crack growth curve at Taking the fatigue crack growth curve of the embodiment as an example, the method for predicting the crack growth rate of metal materials provided by the present invention is introduced.

[0044] First, the stress ratio was performed at room temperature. The fatigue crack growth rate test under stress ratio was carried out, and the data obtained from the test were fitted based on the Paris formula to obtain of and The value of and the range of stress intensity factor at this stress ratio ,because , so, Substitute into the formula ,get The equivalent factor , the fitted Paris formula is: ; Then, yes Based on the formula ,formula and formula Normalize the stress ratio The stress intensity factor variation range obtained when and The equivalent factor Multiply them to get the stress ratio The range of stress intensity factor when , the calculation formula is: ; Then, the stress ratio The range of stress intensity factor when Divide by the target stress ratio The corresponding equivalent factor , and the stress ratio The range of stress intensity factor when , the calculation formula is: ; Finally, the stress ratio The range of stress intensity factor when Substitute into the stress ratio In the Paris formula obtained by fitting, Value and The value remains unchanged, only Replace with , and the stress ratio Paris formula when: , the stress ratio can be predicted Fatigue crack growth rate.

[0045] Based on stress ratio Paris formula , make a fatigue crack growth rate prediction curve and compare it with the stress ratio By comparing the experimental curve obtained by fitting the measured data, it can be found that the fitting degree of the fatigue crack growth rate prediction curve and the experimental curve is It can be seen from the results that the curve calculated by the prediction method of the present invention is highly consistent with the test results. The fatigue crack growth rate prediction curve obtained when the test curve is compared with Figure 3 shown.

[0046] According to the above description of this specification, those skilled in the art may also understand that the terms used below, such as "up", "down", "front", "back", "left", "right", "width", "horizontal", "top", "bottom", "inside", "outside" and the like, which indicate orientation or positional relationships, are based on the orientation or positional relationships shown in the drawings of this specification, and are only for the purpose of facilitating the explanation of the scheme of the present invention and simplifying the description, rather than explicitly or implicitly indicating that the devices or elements involved must have the specific orientation, be constructed and operated in a specific orientation. Therefore, the above-mentioned orientation or positional relationship terms cannot be understood or interpreted as limitations on the scheme of the present invention.

[0047] In addition, in the description of this specification, “plurality” means at least two, for example, two, three or more, etc., unless otherwise clearly and specifically defined.

Claims

1. A method for predicting fatigue crack growth rate of metal materials, characterized in that: The steps include: S1: Introducing equivalence factors , and the fatigue crack growth rate model is obtained: , where: - crack depth or width, - Number of stress cycles, - equivalence factor, , - parameters related to the material, - Range of stress intensity factor; Definition , where: - equivalence factor, - equivalent stress factor, - Stress Factor Equivalent stress factor when Equivalence Factor The calculation formula is: , where: - equivalence factor, -Cyclic stress is The turning point of - stress ratio; S2: Fatigue crack growth rate test of metal materials at room temperature, and the stress ratio of the steady state stage is measured The fatigue crack growth curve under the condition of , and the fatigue crack growth curve obtained is fitted based on the Paris formula to obtain the stress ratio Next , Value and stress intensity factor range , the stress ratio is The corresponding equivalent factor is ; S3: Change the stress intensity factor range Multiply by the stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor when ; S4: Change the stress intensity factor range Divide by the target stress ratio The equivalent factor of , and the stress ratio The range of stress intensity factor ,Will Substitute into the Paris formula obtained in step S2, where the and The value remains unchanged, and the stress ratio is Fatigue crack growth rate.

2. The method for predicting fatigue crack growth rate of metal materials according to claim 1, characterized in that: The equivalent stress factor The calculation formula is: , where: - equivalent stress factor, -Energy consumption per unit time, - crack surface area, - The elastic modulus of the material.

3. The method for predicting fatigue crack growth rate of metal materials according to claim 2, characterized in that: The energy consumption per unit time The calculation formula is: , where: -Energy consumption per unit time, - total energy consumption per cycle, - Loading time per cycle.

4. The method for predicting fatigue crack growth rate of metal materials according to claim 3, characterized in that: The total energy consumption per cycle The calculation formula is: , where: - total energy consumption per cycle, - energy dissipation during crack tip opening, - Loading time per cycle, -Cyclic stress is The turning point of -Hysteresis coefficient.

5. The method for predicting fatigue crack growth rate of metal materials according to claim 4, characterized in that: The hysteresis coefficient The calculation formula is: , where: - hysteresis coefficient, -Cyclic stress is The turning point of time.

6. The method for predicting fatigue crack growth rate of metal materials according to claim 5, characterized in that: The cyclic stress is The turning point The calculation formula is: , where: -Cyclic stress is The turning point of -Stress ratio.

7. The method for predicting fatigue crack growth rate of metal materials according to any one of claims 4 to 6, characterized in that: The energy consumption when the crack tip opens is The calculation formula is: , where: - energy dissipation during crack tip opening, -Energy release rate, -Crack surface area.

8. The method for predicting fatigue crack growth rate of metal materials according to claim 7, characterized in that: The energy release rate The calculation formula is: , where: -Energy release rate, - stress intensity factor, - The elastic modulus of the material.

9. The method for predicting fatigue crack growth rate of metal materials according to claim 8, characterized in that: The stress intensity factor The calculation formula is: , where: - stress intensity factor, - maximum value of the stress intensity factor, - stress ratio, - Loading time per cycle, its value range is .

10. The method for predicting fatigue crack growth rate of metal materials according to any one of claims 1 to 6, characterized in that: The Paris formula is: , where: - crack depth or width, - Number of stress cycles, , - parameters related to the material, -The range of stress intensity factors.

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