A method for predicting fatigue strength of different strength metallic materials under various mean stresses

Abstract

The present application relates to the technical field of metal material performance testing, in particular to a method for predicting fatigue strength of different strength metal materials under various average stresses. The prediction method is based on Walker and P-C models, which better describes the change of fatigue strength of different strength metal materials under various average stresses. The prediction method first describes the relationship between tensile strength and fatigue strength of the metal material according to the P-C model, and then analyzes the change parameters of the fatigue strength of the material under different average stresses by using the Waler model, and establishes the relationship among the average stress, the tensile strength and the fatigue strength by combining the two models. The method reduces the trial and error in the process of material design cost and process selection, and can truly realize efficient prediction of various strength materials under different average stresses.

Description

Technical Field

[0001] This invention relates to the field of metal material performance testing technology, specifically a method for predicting the fatigue strength of metal materials of different strengths under various average stresses. Background Technology

[0002] Metal fatigue is the most common failure mode of components. Statistics show that over 80% of mechanical part failures are fatigue failures. Since components do not exhibit obvious macroscopic deformation before fatigue failure, and the fracture is sudden, fatigue failure is difficult to detect and accidents often occur unexpectedly. Therefore, predicting the fatigue strength of component materials is of great significance for industrial production.

[0003] Patent application CN 110069858 A discloses a method for predicting the high-cycle fatigue performance of metallic materials under different temperature conditions, belonging to the field of materials science and engineering application technology. This method first conducts high-cycle fatigue tests at different temperatures to obtain SN curves; then, it establishes the relationship between the fatigue strength coefficient σ′f and the fatigue strength index b and temperature T through Basquin equation fitting, obtaining relevant parameters; finally, it substitutes the established relationships into the Basquin equation to establish a quantitative relationship between stress amplitude σa, fatigue life Nf, and temperature, thereby predicting the high-cycle fatigue performance of metallic materials at different temperatures. However, this method is inefficient and inaccurate in its predictions.

[0004] Patent application CN 116359035 A discloses a method and system for predicting the creep fatigue behavior of martensitic heat-resistant steel, relating to the field of high-temperature creep fatigue performance evaluation technology. The method includes: acquiring the microstructure evolution of copper-containing martensitic heat-resistant steel during the test process, obtaining the cyclic strength change rate based on the microstructure evolution, and calculating the creep rate of the copper-containing martensitic heat-resistant steel in the dislocation climb hard phase, as well as the dislocation density under cyclic loading conditions; based on the cyclic strength change rate, creep rate, and dislocation density, obtaining the elastic strain tensor, plastic strain tensor, and creep strain tensor of the copper-containing martensitic heat-resistant steel, and predicting the stress-strain evolution of the copper-containing martensitic heat-resistant steel under cyclic loading conditions based on the elastic modulus tensor; however, it fails to adequately address the limitations of macroscopic creep fatigue behavior prediction methods.

[0005] Patent application CN111044349A discloses a method for predicting the low-temperature ultra-high cycle fatigue life of high-strength steel. This invention employs low-temperature ultrasonic fatigue testing, based on fracture mechanics theory, introduces parameters reflecting the low-temperature environment, establishes a low-temperature ultra-high cycle fatigue life equation for the material, and quantitatively evaluates the ultra-high cycle fatigue life of high-strength steel under different low-temperature environments. However, it cannot accurately assess the low-temperature ultra-high cycle fatigue life of high-strength steel.

[0006] In engineering, in-service components are constantly subjected to loading forces, and under different working conditions, they will also be subjected to different stresses. Therefore, the influence of mean stress on component performance is an unavoidable issue, especially its significant impact on fatigue strength. As early as the 1870s, scholars and engineers recognized this problem and, based on experience, successively established a series of models describing the influence of mean stress on the fatigue performance of materials. In 1970, Waler proposed a more accurate model, which, by introducing parameters, better predicted the fatigue strength of materials under different mean stresses.

[0007] With the development of the times and the advancement of technology, ultra-high strength materials and advanced manufacturing processes have emerged. Scholars have found that models describing only the relationship between mean stress and fatigue strength are insufficient to meet the demands. In recent years, Pang et al. proposed the PC model based on tensile properties, which can effectively describe the changes in tensile strength and fatigue strength of materials under the same mean stress conditions. It has a wide range of applicable strengths and can still effectively predict the strength of ultra-high-strength materials. Therefore, combining the PC model to establish a description of the relationship between tensile strength and fatigue strength of materials under various mean stress conditions will be of great significance.

[0008] Fatigue testing, especially high-temperature fatigue testing, is time-consuming, labor-intensive, and expensive. If comprehensive and accurate fatigue data or constitutive relationships for fatigue performance prediction cannot be used in component design and fabrication, it will significantly increase the service cost of components, reduce their service safety, and cause irreparable losses. Therefore, there is an urgent need for a truly efficient prediction method for materials of various strengths under different mean stresses. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of existing technologies. To reduce costs and improve efficiency, this invention provides a method for predicting the fatigue strength of metallic materials of different strengths under various mean stresses. This method utilizes the intrinsic relationship between tensile strength and fatigue strength in the PC model and the influence of mean stress on fatigue strength in the Walker model, enabling effective prediction with only a small amount of test data. This method reduces material design costs and trial-and-error in process selection, truly achieving efficient prediction of materials of various strengths under different mean stresses.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] This invention provides a method for predicting the fatigue strength of metallic materials of different strengths under various average stresses. The method specifically includes the following steps:

[0012] (1) Test samples of different strengths or structures of the metal material to be tested to obtain tensile strength values;

[0013] (2) Test multiple groups of materials with different strengths or structures to obtain the fatigue strength value of each group of materials under symmetrical axial load and at least one fatigue strength value under asymmetrical axial load.

[0014] (3) Calculate the ratio of fatigue strength to tensile strength of symmetrical axial load for multiple groups of materials with different strengths, and fit it with the tensile strength value of the corresponding material to obtain the first parameter and the second parameter;

[0015] (4) Calculate the ratio of the fatigue strength of the same group of strengths under asymmetric axial load to the fatigue strength under symmetric axial load, and fit it with the corresponding stress ratio to obtain the third parameter;

[0016] (5) Fit the third parameter values ​​of multiple sets of materials with different strengths to the fatigue strength / tensile strength values ​​under symmetrical axial load to obtain the fourth and fifth parameters;

[0017] (6) Using the first, second, fourth and fifth parameters obtained in steps (3) and (5), calculate the fatigue strength value of the metal material with the tensile strength to be tested under the stress ratio.

[0018] As one of the improvements to the above technical solution, in step (1), at least two samples of different strengths are selected for testing of the same type of metal material to be tested; the same type of material refers to materials of different strengths after the same metal has been processed by different heat treatment and preparation processes; at least three samples are required for each strength material to obtain tensile strength.

[0019] As an improvement to the above technical solution, in step (2), the fatigue strength test needs to maintain the same environmental conditions as the tensile test in step (1).

[0020] As one of the improvements to the above technical solution, in step (2), the fatigue strength of materials with the same strength requires 1-2 asymmetric axial loads; the fatigue strength test requires the stress amplitude of more than 3 pairs of lifting and lowering methods to participate in the calculation.

[0021] As an improvement to the above technical solution, in step (1), axial tensile tests are performed on samples of different strengths or structures of the metal material to be tested to obtain the tensile strength σ. b .

[0022] As an improvement to the above technical solution, in step (2), fatigue strength tests are performed on multiple groups of materials with different strengths or structures to be tested to obtain the fatigue strength σ of each group of materials under symmetrical axial load. -1 Wherein, the stress ratio R = -1, and at least one fatigue strength σ under asymmetric axial loading conditions. w , where the stress ratio R≠-1.

[0023] As one of the improvements to the above technical solution, step (3) calculates σ for multiple groups of materials with different strengths. -1 / σ b Value, and the corresponding material's σ b The values ​​are fitted using formula (1) to obtain the first parameter C and the second parameter P;

[0024]

[0025] As one of the improvements to the above technical solution, step (4) calculates the σ of the same group of strengths under R. w / σ -1 The value is fitted with the corresponding R using formula (2) to obtain the third parameter m;

[0026]

[0027] As an improvement to the above technical solution, step (5) compares the m values ​​of multiple sets of materials with different strengths and σ. -1 / σ b By fitting the data using formula (3), the fourth parameter m0 and the fifth parameter k are obtained;

[0028]

[0029] As an improvement to the above technical solution, in step (6), the parameters C, P, m0 and k obtained in steps (3) and (5) are substituted into formula (4) to calculate the strength to be measured as σ. b The fatigue strength value σ of metallic materials under stress ratio R w ;

[0030]

[0031] The prediction method of this invention is applicable to a wide range of material strengths and can predict the fatigue strength of ultra-high strength alloy materials under various average stresses. Based on the changes in parameters C and P, the relationship between fatigue strength and tensile strength can be described.

[0032] The prediction method of this invention is applicable to a wide range of loading environments. Based on the changes in m0 and k, it can describe the relationship between the stress ratio and fatigue strength of materials under ultra-high cycle counts, high temperatures, and high stress concentrations.

[0033] Compared with the prior art, the advantages of the present invention are:

[0034] 1. The prediction method of this invention is based on the Walker and PC models, which effectively describe the variation of fatigue strength of metallic materials with different strengths under various mean stresses. This method first describes the relationship between tensile strength and fatigue strength of metallic materials using the PC model, then analyzes the variation parameters of fatigue strength under different mean stresses using the Walker model. By combining the two models, the relationship between mean stress, tensile strength, and fatigue strength is established. This method can solve the important problem of the influence of load characteristics on the fatigue performance of components in engineering fields, and is applicable to high-strength materials and some extreme environments, and is expected to be applied to component life prediction.

[0035] 2. The prediction method of the present invention is applicable to a wide range of material strengths and can predict the fatigue strength of ultra-high strength alloy materials under various average stresses; based on the changes of the first parameter and the second parameter, the relationship between fatigue strength and tensile strength can be described.

[0036] 3. The prediction method of the present invention is applicable to a variety of loading environments. Based on the changes in the fourth and fifth parameters, it can describe the relationship between the stress ratio and fatigue strength of the material under ultra-high cycle, high temperature and high stress concentration.

[0037] 4. The prediction method of the present invention has advantages such as high accuracy and low cost. It can make effective predictions with a small number of tensile and fatigue tests and has potential application value. Attached Figure Description

[0038] Figure 1 This is a flowchart illustrating the method for predicting fatigue strength at various stress ratios for the same type of metallic materials.

[0039] Figure 2 σ for 18Ni martensitic aging steel -1 / σ b –σ b Relationship diagram.

[0040] Figure 3 σ for two states of 18Ni martensitic aging steel m / σ b –σ w / σ -1 Relationship diagram.

[0041] Figure 4 m–σ for 18Ni martensitic aging steel -1 / σ b Relationship diagram.

[0042] Figure 5 To verify the accuracy of the predicted results for 18Ni martensite. Detailed Implementation

[0043] The present invention will be further described below with reference to embodiments and accompanying drawings. To enable those skilled in the art to better understand the technical solutions in this application, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. 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 this application.

[0044] This invention provides a method for predicting the fatigue strength of metallic materials of different strengths under various average stresses. The method specifically includes the following steps:

[0045] (1) Perform axial tensile tests on specimens of different strengths or structures of the metallic material to be tested to obtain the tensile strength σ. b ;

[0046] (2) Perform fatigue strength tests on multiple groups of materials with different strengths or microstructures to obtain the fatigue strength σ of each group of materials under symmetrical axial load (stress ratio R = -1). -1 and at least one fatigue strength σ under asymmetric axial load (R≠-1) conditions. w ;

[0047] (3) Calculate the σ of multiple groups of materials with different strengths respectively. -1 / σ b Value, and the corresponding material's σ b The values ​​are fitted using formula (1) to obtain the first parameter C and the second parameter P;

[0048]

[0049] (4) Calculate the σ of the same group of strengths under R. w / σ -1 The value is fitted with the corresponding R using formula (2) to obtain the third parameter m;

[0050]

[0051] (5) The m values ​​of multiple groups of materials with different strengths are compared with σ -1 / σ b By fitting the data using formula (3), the fourth parameter m0 and the fifth parameter k are obtained;

[0052]

[0053] (6) Substitute the parameters C, P, m0 and k obtained in steps (3) and (5) into formula (4) to calculate the strength to be measured as σ. b The fatigue strength value σ of metallic materials under stress ratio R w .

[0054]

[0055] Figure 1 The following is the operational procedure for predicting the fatigue strength of the same type of metallic materials under various average stresses according to the present invention. The specific procedure is shown in the embodiment.

[0056] Example:

[0057] This embodiment predicts the fatigue strength of 18Ni martensitic aging steel with different strengths at various stress ratios.

[0058] Step 1: Obtain the tensile properties of 18Ni martensitic aging steel at 500℃ / 5h and 630℃ / 3h, with tensile strengths of 1939MPa and 1358MPa, respectively.

[0059] Step 2: Fatigue strength tests were conducted on the 18Ni martensitic aging steel. The fatigue strengths at 500℃ / 5h with R=-1 and 0.1 were 595MPa and 475MPa, respectively; the fatigue strengths at 630℃ / 3h with R=-1 and 0.1 were 588MPa and 386MPa, respectively, as shown in Table 1.

[0060] Step 3: Calculate the σ of 18Ni martensitic aging steel at 500℃ / 5h and 630℃ / 3h. -1 / σ b Its tensile strength is obtained through the formula Perform fitting (e.g.) Figure 2 As shown in the figure, the parameters C and P were obtained as 0.728 and 2.171 × 10⁻⁶, respectively. -4 (See Table 1).

[0061] Step four: Calculate the σ values ​​of 18Ni martensitic aging steel at 500℃ / 5h and 630℃ / 3h under conditions of R = -1 and 0.1, respectively. w / σ -1 Value, and R using the formula Fitting, (e.g.) Figure 3 As shown in Table 1, the parameter m values ​​were 2.282 and 0.527 respectively.

[0062] Step 5, combine the m values ​​of the two intensities from Step 4 with their σ values. -1 / σ b Through formula The fitting yielded parameters m0 and k of -0.314 and 1.943, respectively. Figure 4 As shown.

[0063] Step six: Substitute the C, P, m0, and k values ​​obtained in steps three and five into the formula. From this, the strength to be measured, σ, can be calculated.b Fatigue strength σ of metallic materials under other values ​​of R w .

[0064] Step 7: To evaluate the accuracy of the prediction results, the fatigue strength of 18Ni martensitic aging steel at various average stresses was measured in two states: 550℃ / 5h and 600℃ / 3h. The predicted strength was then calculated using the method described above. The accuracy of the predictions is shown in Table 1, and a comparison between the calculated and experimental values ​​is provided. Figure 5 As shown (this step is to verify the accuracy of the method and can be ignored in actual operation).

[0065] Table 1. Summary of Relevant Data for Prediction of 18Ni Martensitic Aging Steel

[0066]

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for predicting the fatigue strength of metallic materials with different strengths under various average stresses, the method specifically including the following steps: (1) Test specimens of different strengths of the metal material to be tested to obtain the tensile strength. σ b ; (2) Test multiple groups of materials with different strengths to obtain the fatigue strength of each group of materials under symmetrical axial load. σ -1 and at least one fatigue strength under asymmetric axial load σ w ; (3) Calculate the ratio of fatigue strength to tensile strength of multiple groups of materials with different strengths under symmetrical axial loads, and fit it with the tensile strength value of the corresponding material to obtain the first parameter and the second parameter; (4) Calculate the strength of the same group under stress ratio R The ratio of fatigue strength under asymmetric axial load to fatigue strength under symmetric axial load is fitted with the corresponding stress ratio to obtain the third parameter; (5) Fit the third parameter values ​​of multiple sets of materials with different strengths to the fatigue strength / tensile strength values ​​under symmetrical axial load to obtain the fourth and fifth parameters; (6) Using the first, second, fourth and fifth parameters obtained in steps (3) and (5), calculate the fatigue strength value of the metal material with the tensile strength to be tested under the stress ratio. In step (3), multiple groups of materials with different strengths are calculated respectively. σ -1 / σ b Value, and corresponding material σ b The first parameter is obtained by fitting the value using formula (1). C Second parameter P ; （1）； In step (4), the intensity of the same group is calculated. R Below σ w / σ -1 Value, and corresponding R The third parameter is obtained by fitting using formula (2). m ; （2）； Step (5) combine multiple groups of materials with different strengths m Value and σ -1 / σ b The fourth parameter is obtained by fitting using formula (3). m 0 and the fifth parameter k ; （3）； In step (6), the parameters obtained in steps (3) and (5) are... C , P , m 0 and k Substituting into formula (4), the tensile strength to be tested can be calculated as follows: σ b Metal materials in stress ratio R Fatigue strength under asymmetric axial loading conditions σ w ; （4）。 2. The method for predicting the fatigue strength of metallic materials of different strengths under various average stresses according to claim 1, characterized in that: In step (1), at least two samples of different strengths should be selected for testing of the same type of metal material; materials of the same type are materials of different strengths after being treated by different heat processing and preparation processes; at least three samples are required for each strength material to obtain tensile strength.

3. The method for predicting the fatigue strength of metallic materials of different strengths under various average stresses according to claim 1, characterized in that: In step (2), the fatigue strength test must be conducted under the same environmental conditions as the tensile test in step (1).

4. The method for predicting the fatigue strength of metallic materials of different strengths under various average stresses according to claim 1, characterized in that: In step (2), the fatigue strength of materials with the same strength requires 1-2 asymmetric axial loads; the fatigue strength test requires the stress amplitude of more than 3 pairs of lifting and lowering methods to be included in the calculation.

5. The method for predicting the fatigue strength of metallic materials of different strengths under various average stresses according to claim 1, characterized in that: In step (1), axial tensile tests are performed on specimens of different strengths of the metal material to be tested to obtain the tensile strength. σ b .

6. The method for predicting the fatigue strength of metallic materials of different strengths under various average stresses according to claim 5, characterized in that: In step (2), fatigue strength tests are performed on multiple groups of materials with different strengths to be tested to obtain the fatigue strength of each group of materials under symmetrical axial load. σ -1 Among them, stress ratio R = -1, and at least one fatigue strength under asymmetric axial loading conditions. σ w Among them, stress ratio R ≠ -1.

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