Prediction method for fatigue strengths of metal materials with different strengths under average stresses

Abstract

The present invention relates to the technical field of metal material property testing, and in particular to a prediction method for fatigue strengths of metal materials with different strengths under average stresses. On the basis of Walker and P-C models, the prediction method of the present invention well describes changes of the fatigue strengths of the metal materials with different strengths under the average stresses. The prediction method comprises: firstly, describing a relationship between a tensile strength and a fatigue strength of a metal material on the basis of the P-C model; then using the Walker model to analyze change parameters of the fatigue strength of the material under different average stresses; and establishing a relationship among the average stresses, the tensile strength and the fatigue strength by combining the two models. The method reduces the design costs of the material and trial and error during process selection, thereby truly realizing efficient prediction of the materials with different strengths under different average stresses.

Description

A method for predicting fatigue strength of metal materials with different strengths under various mean stresses

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. 2024100187312, filed on January 5, 2024, entitled “A method for predicting fatigue strength of metal materials with different strengths under various average stresses”, and Chinese patent application No. 2023114072042, filed on October 27, 2023, entitled “A method for predicting fatigue strength of metal materials with different strengths under various average stresses”, and both applications are included herein by reference. Technical Field

[0003] The present invention relates to the technical field of metal material performance testing, in particular to a method for predicting the fatigue strength of metal materials with different strengths under various average stresses. Background Art

[0004] Metal fatigue is the most common form of component failure. Statistics show that over 80% of mechanical part failures are attributable to fatigue. However, components exhibit no noticeable macroscopic deformation prior to fatigue failure, and fracture occurs suddenly. This makes fatigue failure difficult to detect and often leads to unexpected accidents. Therefore, predicting the fatigue strength of component materials is of great significance to industrial production.

[0005] Patent application CN 110069858 A discloses a method for predicting the high-cycle fatigue performance of metal 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. The method then uses the Basquin relationship to establish the relationship between the fatigue strength coefficient σ′f and the fatigue strength exponent b, respectively, and the temperature T, obtaining relevant parameters. This established relationship is then substituted 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 the metal material at different temperatures. However, this method is inefficient and produces inaccurate predictions.

[0006] Patent application CN 116359035 A discloses a method and system for predicting the creep fatigue behavior of martensitic heat-resistant steel, which relates to the technical field of high-temperature creep fatigue performance evaluation. The method comprises: collecting the microstructural evolution of copper-containing martensitic heat-resistant steel during the test, obtaining the cyclic strength change rate based on the microstructural evolution, and calculating the creep rate of the copper-containing martensitic heat-resistant steel during dislocation climb in the 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 and strain evolution of the copper-containing martensitic heat-resistant steel under cyclic loading conditions according to the elastic modulus tensor; however, the method fails to effectively address the limitations of the macroscopic creep fatigue behavior prediction method.

[0007] Patent application CN111044349A discloses a method for predicting the low-temperature ultra-high cycle fatigue life of high-strength steel. This method uses low-temperature ultrasonic fatigue testing, based on fracture mechanics theory, and introduces parameters reflecting the low-temperature environment to establish a low-temperature ultra-high cycle fatigue life equation for the material. This method quantitatively evaluates the ultra-high cycle fatigue life of high-strength steel under different low-temperature environments. However, this method cannot accurately assess the low-temperature ultra-high cycle fatigue life of high-strength steel.

[0008] In the engineering field, components in service are constantly subjected to loading forces, and they experience varying stresses under different operating conditions. Therefore, the impact of mean stress on component performance is unavoidable, particularly on fatigue strength. As early as the 1870s, scholars and engineers recognized this issue and, based on experience, developed a series of models to describe the effect of mean stress on material fatigue properties. In 1970, Waler proposed a more accurate model that, by introducing parameters, better predicted the fatigue strength of materials at different mean stresses.

[0009] With the development of the times and advancements in technology, ultra-high-strength materials and advanced manufacturing processes have emerged. Scholars have discovered that models that only describe the relationship between mean stress and fatigue strength are insufficient. Recently, Pang et al. proposed the PC model based on tensile properties. This model effectively describes the changes in tensile and fatigue strength of materials under the same mean stress conditions. It has a wide range of applications and can effectively predict materials with ultra-high strength levels. Therefore, it is of great significance to combine the PC model to establish a relationship between the tensile and fatigue strength of materials under a variety of different mean stress conditions.

[0010] Because fatigue testing, especially high-temperature fatigue testing, is time-consuming, labor-intensive, and expensive, the failure to utilize comprehensive and accurate fatigue data or constitutive relationships for fatigue performance prediction during component design and fabrication can significantly increase component service costs, reduce component service safety, and result in irreparable losses. Therefore, a truly efficient prediction method for materials of varying strengths under varying mean stresses is urgently needed.

[0011] Summary of the Invention

[0012] The present invention aims to address the shortcomings of existing technologies. To reduce costs and improve efficiency, it provides a method for predicting the fatigue strength of metal materials of varying strengths under various mean stresses. This method leverages the intrinsic relationship between tensile strength and fatigue strength from the PC model and the relationship between mean stress and fatigue strength from the Walker model, enabling effective predictions using only a small amount of test data. This method reduces material design costs and the trial-and-error process in process selection, enabling efficient predictions of fatigue strength for materials of varying strengths under varying mean stresses.

[0013] In order to achieve the above object, the technical solution adopted by the present invention is:

[0014] The present invention provides a method for predicting the fatigue strength of metal materials with different strengths under various average stresses, the method specifically comprising the following steps:

[0015] (1) Test samples of different strengths or structures of the metal material to be tested to obtain the tensile strength value;

[0016] (2) testing multiple groups of materials with different strengths or structures of the metal material to be tested, and obtaining fatigue strength values ​​of each group of materials under symmetrical axial loads and at least one fatigue strength value under asymmetrical axial loads;

[0017] (3) calculating the ratio of fatigue strength to tensile strength of multiple groups of materials with different strengths under symmetrical axial loads, fitting them with the tensile strength values ​​of the corresponding materials, and obtaining the first parameter and the second parameter;

[0018] (4) Calculate the ratio of the fatigue strength under asymmetric axial load to the fatigue strength under symmetric axial load of the same group of strength under stress ratio, fit it with the corresponding stress ratio, and obtain the third parameter;

[0019] (5) fitting the third parameter values ​​of multiple groups of materials with different strengths with the fatigue strength / tensile strength values ​​under symmetrical axial load to obtain the fourth parameter and the fifth parameter;

[0020] (6) The fatigue strength value of the metal material with the tensile strength to be measured under the stress ratio is calculated using the first parameter, the second parameter, the fourth parameter and the fifth parameter obtained in steps (3) and (5).

[0021] As one of the improvements to the above technical solution, in step (1), at least two samples with different strengths are selected from the same category of metal materials to be tested for testing; materials of the same category are materials with different strengths after the same metal is processed by different heat treatments and preparation processes; at least three samples are required for each strength material to obtain the tensile strength.

[0022] As one of the improvements 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).

[0023] As one of the improvements to the above technical solution, in step (2), materials of the same strength require fatigue strength of 1-2 asymmetric axial loads; and fatigue strength testing requires more than 3 pairs of stress amplitudes of the lifting method to participate in the calculation.

[0024] As one of the improvements to the above technical solution, in step (1), an axial tensile test is performed on samples of different strengths or structures of the metal material to be tested to obtain the tensile strength σ b .

[0025] As one of the improvements to the above technical solution, in step (2), fatigue strength tests are performed on multiple groups of materials with different strengths or structures of the metal material to be tested, and the fatigue strength σ of each group of materials under symmetrical axial load is obtained. -1 , where the stress ratio R = -1, and at least one fatigue strength σ under asymmetric axial load conditions w , where the stress ratio R≠-1.

[0026] As one of the improvements to the above technical solution, in step (3), σ of multiple groups of materials with different strengths is calculated separately. -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;

[0027] As one of the improvements to the above technical solution, in step (4), the σ of the same group intensity under R is calculated w / σ -1 The value is fitted with the corresponding R using formula (2) to obtain the third parameter m;

[0028] As one of the improvements to the above technical solution, step (5) compares the m values ​​of multiple groups of materials with different strengths with σ -1 / σ b Fitting is performed through formula (3) to obtain the fourth parameter m0 and the fifth parameter k;

[0029] As one of the improvements 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), and the intensity to be measured can be calculated as σ b The fatigue strength value σ of the metal material under the stress ratio R w ;

[0030] 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 at various average stresses; according to the changes in parameters C and P, the relationship between fatigue strength and tensile strength can be described.

[0031] The prediction method of the present invention is applicable to multiple loading environments and can describe the relationship between the stress ratio and fatigue strength of the material under ultra-high cycles, high temperature and high stress concentration according to the changes in m0 and k.

[0032] Compared with the prior art, the advantages of the present invention are:

[0033] 1. The prediction method of the present invention, based on the Walker and PC models, effectively describes the variation in fatigue strength of metal materials of varying strengths under various mean stresses. This prediction method first describes the relationship between the tensile strength and fatigue strength of a metal material using the PC model. It then uses the Waler model to analyze the variation in fatigue strength parameters of the material under various mean stresses. By combining these two models, the relationship between mean stress, tensile strength, and fatigue strength is established. This method can address the important issue of the impact of load characteristics on component fatigue performance in the engineering field. It is applicable to high-strength materials and some extreme environments, and has the potential to be applied to component life prediction.

[0034] 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 at various average stresses; based on the changes in the first parameter and the second parameter, the relationship between fatigue strength and tensile strength can be described.

[0035] 3. The prediction method of the present invention is applicable to many loading environments. According to the changes of the fourth parameter and the fifth parameter, the relationship between the stress ratio and fatigue strength of the material under ultra-high cycles, high temperature and high stress concentration can be described.

[0036] 4. The prediction method of the present invention has the advantages of high precision and low cost. It can perform effective predictions through a small amount of tensile and fatigue tests and has potential application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 is a flow chart of the fatigue strength prediction method for the same type of metal materials at various stress ratios.

[0038] Figure 2 shows the σ of 18Ni maraging steel -1 / σ b –σ bRelationship diagram.

[0039] Figure 3 shows the σ of 18Ni maraging steel in two states m / σ b –σ w / σ -1 Relationship diagram.

[0040] Figure 4 shows the m–σ of 18Ni maraging steel -1 / σ b Relationship diagram.

[0041] Figure 5 shows the accuracy verification of the prediction results of 18Ni martensite. DETAILED DESCRIPTION

[0042] The present invention is further described below with reference to the embodiments and accompanying drawings. In order 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 are clearly and completely described below. Obviously, the described embodiments are only part of the embodiments of this application, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of this application.

[0043] The present invention provides a method for predicting the fatigue strength of metal materials with different strengths under various average stresses, the method specifically comprising the following steps:

[0044] (1) Perform axial tensile tests on samples of different strengths or structures of the metal material to be tested to obtain the tensile strength σ b ;

[0045] (2) Fatigue strength tests are performed on multiple groups of materials with different strengths or structures of the metal material to be tested, and the fatigue strength σ of each group of materials under symmetrical axial load (stress ratio R = -1) is obtained. -1 and at least one fatigue strength σ under asymmetric axial load (R≠-1) w ;

[0046] (3) Calculate 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;

[0047] (4) Calculate the σ of the same group strength under R w / σ -1 The value is fitted with the corresponding R using formula (2) to obtain the third parameter m;

[0048] (5) Compare the m values ​​of multiple groups of materials with different strengths with σ -1 / σ b Fitting is performed through formula (3) to obtain the fourth parameter m0 and the fifth parameter k;

[0049] (6) Substitute the parameters C, P, m0 and k obtained in steps (3) and (5) into formula (4) to calculate the intensity to be measured as σ b The fatigue strength value σ of the metal material under the stress ratio R w .

[0050] FIG1 is an operational flow of the fatigue strength prediction method for the same type of metal materials under various average stresses according to the present invention. The specific process is shown in the examples.

[0051] Example:

[0052] This embodiment predicts the fatigue strength of 18Ni maraging steels of different strengths at various stress ratios.

[0053] Step 1: Obtain the tensile properties of 18Ni maraging steel at 500°C / 5h and 630°C / 3h, with the tensile strengths being 1939 MPa and 1358 MPa, respectively.

[0054] In step 2, fatigue strength test was performed on 18Ni maraging steel. The fatigue strength at 500℃ / 5h at R=-1 and 0.1 was 595MPa and 475MPa, respectively; the fatigue strength at 630℃ / 3h at R=-1 and 0.1 was 588MPa and 386MPa, respectively, as shown in Table 1.

[0055] Step 3: Calculate the σ of 18Ni maraging steel at 500℃ / 5h and 630℃ / 3h -1 / σ b , and its tensile strength is expressed by the formula The fitting was performed (as shown in Figure 2), and the parameters C and P were obtained to be 0.728 and 2.171×10 -4 (See Table 1).

[0056] Step 4: Calculate the σ of 18Ni maraging steel at 500℃ / 5h and 630℃ / 3h under R=-1 and 0.1 respectively. w / σ -1 Value, and R using the formula Fitting,(as shown in Figure 3), the parameter m values ​​are 2.282 and 0.527 respectively (see Table 1).

[0057] Step 5: Compare the m values ​​of the two intensities in step 4 with their σ -1 / σb By formula After fitting, the parameters m0 and k were obtained as -0.314 and 1.943, respectively, as shown in Figure 4.

[0058] Step 6: Substitute the C, P, m0 and k values ​​obtained in steps 3 and 5 into the formula In the equation, the intensity to be measured can be calculated as σ b Fatigue strength σ of metal materials under other R w .

[0059] Step 7: To evaluate the accuracy of the prediction results, the fatigue strength of 18Ni maraging steel at 550°C / 5h and 600°C / 3h at various mean stresses was measured and predicted using the above method. The prediction accuracy is shown in Table 1, and a comparison of the calculated and experimental values ​​is shown in Figure 5. (This step verifies the accuracy of the method and can be ignored in actual operation.)

[0060] Table 1 Summary of prediction data for 18Ni maraging steel

[0061] Finally, it should be noted that the above embodiments are intended only to illustrate the technical solutions of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the embodiments, it should be understood by those skilled in the art 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 are intended to be encompassed by the claims of the present invention.

Claims

1. A method for predicting fatigue strength of metal materials of different strengths under various average stresses, the method specifically comprising the following steps: (1) Test samples of different strengths or structures of the metal material to be tested to obtain the tensile strength value; (2) testing multiple groups of materials with different strengths or structures of the metal material to be tested, and obtaining the fatigue strength value of each group of materials under a symmetrical axial load and at least one fatigue strength value under an asymmetrical axial load; (3) respectively calculating the ratio of fatigue strength to tensile strength of multiple groups of materials with different strengths under symmetrical axial loads, and fitting them with the tensile strength values ​​of the corresponding materials to obtain a first parameter and a second parameter; (4) calculating the ratio of the fatigue strength under asymmetric axial load to the fatigue strength under symmetric axial load of the same group of strengths under stress ratio, fitting it with the corresponding stress ratio, and obtaining the third parameter; (5) fitting the third parameter values ​​of multiple groups of materials with different strengths with the symmetrical axial load fatigue strength / tensile strength values ​​to obtain the fourth parameter and the fifth parameter; (6) The fatigue strength value of the metal material with the tensile strength to be measured under the stress ratio is calculated by using the first parameter, the second parameter, the fourth parameter and the fifth parameter obtained in steps (3) and (5).

2. The method for predicting fatigue strength of metal materials of different strengths under various average stresses according to claim 1, characterized in that: In step (1), at least two samples with different strengths are selected from the same category of metal materials to be tested for testing; materials of the same category are materials with different strengths after the same metal has been processed by different thermal processes and preparation processes; at least three samples are required for each strength material to obtain the tensile strength.

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

4. The method for predicting fatigue strength of metal materials with different strengths under various average stresses according to claim 1, characterized in that: In step (2), materials of the same strength require 1-2 fatigue strength tests under asymmetric axial loads; fatigue strength tests require more than 3 pairs of stress amplitudes using the lifting and lowering method to participate in the calculation.

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

6. The method for predicting fatigue strength of metal materials with 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 or structures of the metal material to be tested, and the fatigue strength σ of each group of materials under symmetrical axial load is obtained. -1 , where the stress ratio R = -1, and at least one fatigue strength σ under asymmetric axial load conditions w , where the stress ratio R≠-1.

7. The method for predicting fatigue strength of metal materials with different strengths under various average stresses according to claim 6, characterized in that: In step (3), σ of multiple groups of materials with different strengths are calculated separately. -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; 8. The method for predicting fatigue strength of metal materials with different strengths under various average stresses according to claim 7, characterized in that: In step (4), calculate the σ of the same group strength under R w / σ -1 The value is fitted with the corresponding R using formula (2) to obtain the third parameter m; 9. The method for predicting fatigue strength of metal materials with different strengths under various average stresses according to claim 8, characterized in that: Step (5) compares the m values ​​of multiple groups of materials with different strengths with σ -1 / σ b Fitting is performed through formula (3) to obtain the fourth parameter m0 and the fifth parameter k; 10. The method for predicting fatigue strength of metal materials with different strengths under various average stresses according to claim 9, characterized in that: 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 of metal materials under stress ratio R is σ w ;

Images