A method for predicting notched tensile strength from material hardness

Abstract

The application discloses a simple method for predicting notched tensile strength through material hardness, and belongs to the technical field of material science and engineering. bn The method uses the hardness value H of the material and the notched tensile strength σ bn to fit the relationship between H and σ bn , thereby establishing a formula for predicting the notched tensile strength of other metal materials in the same series. The method is simple and fast in data acquisition, effectively improves the efficiency of obtaining the notched tensile strength of the material, guarantees the integrity of the equipment structure, and can be applied in the fields of manufacturing, nuclear power and aviation.

Description

Technical Field

[0001] This invention relates to the field of materials science and engineering application technology, specifically a method for predicting notched tensile strength by material hardness. Background Technology

[0002] With the advancement of industrial technology and the improvement of productivity, equipment structures in many fields are becoming increasingly complex and larger in size. However, this structural complexity and large-scale nature bring significant challenges to strength testing. The increased structural complexity of components often leads to stress concentration at notches, further complicating strength prediction. Therefore, considering structural integrity and safe service operation, exploring the strength prediction of notched components is of great significance.

[0003] In recent years, with breakthroughs in nanometer testing theory, the method of obtaining material mechanical properties through indentation has become increasingly mature, solving the problem of difficulty in obtaining strength during in-service testing. However, the notched tensile strength of structural components has not yet been effectively predicted. Therefore, using material hardness to reflect notched tensile strength would be a simple and rapid evaluation method, greatly ensuring the safety and reliability of the structure during service. Summary of the Invention

[0004] The purpose of this invention is to provide a method for predicting notched tensile strength through material hardness. By obtaining the material's hardness value and notched tensile strength, the relationship between the ratio of hardness to notched tensile strength and hardness is fitted using the least squares method, establishing a formula for predicting notched tensile strength based on hardness. This formula demonstrates a non-linear relationship between hardness and notched tensile strength, possessing scientific rationality. This method can easily and quickly predict the notched tensile strength of parts while ensuring the structural integrity of in-service equipment. The method is simple to apply, greatly reducing the amount of experimentation required.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for predicting notched tensile strength based on material hardness, the method specifically includes the following steps:

[0007] (1) Hardness test:

[0008] Hardness tests (at least two) are performed on several metallic materials of the same series to obtain the hardness H of several materials;

[0009] (2) Tensile test of notched sample:

[0010] Select 2 to 4 materials from the same series of metallic materials to prepare the stress concentration (stress concentration factor K) to be predicted. t A notched sample was subjected to a tensile test to obtain the stress concentration factor K. t Notched tensile strength σbn ;

[0011] (3) Parameter fitting:

[0012] Calculate the value of σ bn / H, and fit M with H to obtain formula (1),

[0013]

[0014] In formula (1), a and b are material-related constants obtained by fitting.

[0015] (4) Notch part tensile strength prediction:

[0016] Transform formula (1) to formula (2), that is, the notch tensile strength prediction formula of the same series of metal materials, and calculate the corresponding material notch tensile strength σ bn prediction value under stress concentration K t ;

[0017] σ bn = (a + b·H)·H (2).

[0018] In the above step (1), the plurality of metal materials of the same series have different strengths or different microstructures.

[0019] In the above step (1), the metal materials of the same series have the same chemical composition, but are samples prepared by different processing treatments, have different organizational characteristics or different strength levels; the hardness value of each sample is the average value of the hardness of at least 5 different positions; the hardness value can be Vickers hardness, Brinell hardness and Rockwell hardness, etc., and the hardness test method is selected according to the microstructure characteristics to represent the overall hardness of the material.

[0020] In the above step (2), characterized in that: in step (2), the strain rate and temperature atmosphere conditions of the notch sample tensile test of the same series of materials need to be consistent; in order to ensure the repeatability of the experiment, at least 3 samples of each material need to be tested.

[0021] In the above step (3), formula (2) is a linear fitting of σ bn / H and H using the least square method.

[0022] The advantages and beneficial effects of the present application are as follows:

[0023] 1. The present application provides a method for quickly predicting the notch tensile strength of metal materials, which solves the problems of difficult design of notch radius in notch test, and inability to sample large in-service components.

[0024] 2、The hardness of the application can be obtained by the indentation experiment method, the data acquisition is simple, and the damage is small, which ensures the structural integrity of the in-service equipment, and can be popularized and applied in manufacturing, nuclear power and aviation fields.

[0025] 3、The notch tensile strength prediction method of the application has good universality, especially for metal materials with different hardness after heat treatment.

[0026] 4、The prediction method of the application is simple to apply and has high accuracy, by establishing the relationship between static performance (hardness) and notch tensile strength, the notch tensile strength of the same series of metal materials is predicted. The hardness test operation is simple, the required time is less, and the time and money cost is greatly saved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the relationship between σ t and HV under the condition of K bn =3.

[0028] Figure 2 is the relationship between σ t and HV under the condition of K bn =5.

[0029] Figure 3 is the relationship between σ t and HV under the condition of K bn =3.

[0030] Figure 4 is the relationship between σ t and HV under the condition of K bn =5.

[0031] Figure 5 is the accuracy verification of the notch tensile strength prediction result of SAE 4135 steel under the conditions of K t =3 and K t =5.

[0032] Figure 6 is the relationship between σ and HB under the condition of K t =2.8. bn

[0033] Figure 7 is the relationship between σ and HB under the condition of K t =9. bn

[0034] Figure 8 is​​ Martensitic steel in K t = 2.8 σ bn vs HB.

[0035] Figure 9 is Martensitic steel in K t = 9 σ bn vs HB.

[0036] Figure 10 is Martensitic steel in K t = 2.8 and K t = 9 accuracy verification of the prediction of the notched tensile strength. DETAILED DESCRIPTION

[0037] The application will be further described below in connection with examples and drawings.

[0038] Example 1

[0039] This example is the prediction of the notched tensile strength of SAE 4135 steels with different hardness under K t = 3 and K t = 5, two different hardness SAE 4135 steels are tested (experimental data) and used to predict the remaining two SAE 4135 steels which are not tested (verification data).

[0040] Step one, hardness test of SAE 4135 steels with different hardness in the same series, the Vickers hardness HV of the two experimental samples of SAE 4135 steels used is 466 kgf / mm 2 and 562 kgf / mm 2 , the Vickers hardness HV of the two samples to be tested is 518 kgf / mm 2 and 552 kgf / mm 2 (see Table 1).

[0041] Step two, prepare K t = 3 and K t = 5 notched samples for the two experimental samples, and perform tensile test, the notched tensile strength of K t = 3 is 2213 MPa and 2337 MPa respectively; the notched tensile strength of K t = 5 is 2141 MPa and 2164 MPa respectively (see Table 1).

[0042] Step three, calculate the value of σ bn / H of the experimental samples, the value under K t = 3 is 4.749 and 4.158 respectively, the value under K tThe values ​​under condition =5 are 4.597 and 3.851 respectively, and are fitted with the hardness value (K t =3 and K t The fitting relationships for =5 are as follows: Figure 1 and 2 As shown), formulas (1) and (2) are obtained as follows:

[0043]

[0044]

[0045] Step four, transform the above formulas (1) and (2) to obtain the following formulas for predicting notched tensile strength: (3) and (4), K t =3 and K t The relationship between a hardness of 5 and its notched tensile strength is as follows: Figure 3 and 4 As shown. The K value of the SAE 4135 steel to be tested is calculated using formula (3). t The notched tensile strengths under the condition of 3 are 2294 MPa and 2329 MPa, respectively; the tensile strengths of the SAE 4135 steel under the condition of K are calculated by formula (4). t The notched tensile strengths under the condition of 5 are 2188 MPa and 2187 MPa, respectively (see Table 1).

[0046] σ bn = (7.618 - 6.156 × 10) -3 HV)·HV (3)

[0047] σ bn = (8.218 - 7.771 × 10) -3 HV)·HV (4)

[0048] Step 5: To verify the accuracy of the predicted data, the SAE 4135 steel to be tested is placed in a K... t =3 and K t The experimental and calculated values ​​under condition 5 were compared, and the accuracy of the prediction was as follows: Figure 5 As shown, the deviation is within 12%. (This step is for verification of the method and can be omitted in actual operation).

[0049] Table 1. Summary of relevant data for predicting the notched tensile strength of SAE 4135 steel

[0050]

[0051] Example 2:

[0052] This embodiment applies to different hardness levels. Martensitic steel (hereinafter referred to as martensitic steel) in K t= 2.8 and K t = 9, the notched tensile strength of two different hardness martensitic steels were tested (experimental data) and used to predict the notched tensile strength of the remaining four martensitic steels (validation data).

[0053] Step one, the hardness of the same series of different hardness martensitic steels was tested, the Vickers hardness HV of the two experimental samples of martensitic steels used was 305 kgf / mm 2 and 475 kgf / mm 2 , respectively, and the Vickers hardness HV of the four samples to be tested was 270 kgf / mm 2 , 340 kgf / mm 2 , 370 kgf / mm 2 and 420 kgf / mm 2 , respectively (see Table 2).

[0054] Step two, two K t = 2.8 and K t = 9 notched samples were prepared from the two experimental samples, and tensile tests were performed, the K t = 2.8 notched tensile strength was 1834 MPa and 2614 MPa, respectively; the K t = 5 notched tensile strength was 1688 MPa and 1891 MPa, respectively (see Table 2).

[0055] Step three, the value of σ bn / H of the experimental samples was calculated, the value under K t = 2.8 was 6.013 and 5.503, respectively, and the value under K t = 9 was 5.534 and 3.981, respectively, which was fitted with the hardness value (the fitting relationship of K t = 2.8 and K t = 9 is shown in Figure 6 and Figure 7 , respectively), and formulas (5) and (6) were obtained as follows, respectively:

[0056]

[0057]

[0058] Step four, the above formulas (5) and (6) were transformed, and the following notched tensile strength prediction formulas (7) and (8) were obtained, respectively, the hardness and notched tensile strength relationship of K t = 2.8 and K t = 9 is shown in Figure 8 and Figure 9 , respectively. The notched tensile strength of the martensitic steels to be tested was calculated by formula (7) under K tThe notched tensile strengths of the martensitic steels under K t = 9 were 1580 MPa, 1773 MPa, 1828 MPa and 1883 MPa, respectively (see Table 2).

[0059] σ bn = (6.928 - 3.000 x 10 -3 HB) · HB (7)

[0060] σ bn = (8.320 - 9.135 x 10 -3 HB) · HB (8)

[0061] Step five, to verify the accuracy of the predicted data, the experimental values of the martensitic steels under K t = 2.8 and K t = 9 were compared with the calculated values, and the degree of accuracy of the prediction was shown in Table 2, with a deviation of less than 10% (this step is a verification of the method, and can be omitted in actual operation). Figure 10

[0062] Table 2 Summary of data related to the prediction of the notched tensile strength of the martensitic steels

[0063]

[0064] The above examples only illustrate the principles and performance of the present application, and are not exhaustive. Other examples can be obtained by a person skilled in the art based on the above examples without creative labor, and these examples all belong to the protection scope of the present application.​

Claims

1. A method for predicting notched tensile strength by material hardness, characterized in that: The method specifically includes the following steps: (1) Hardness test: Hardness tests are performed on at least two metallic materials of the same series to obtain the hardness of each material. H ; (2) Tensile test of notched sample: Two to four different metallic materials from the same series are selected to prepare notched samples for predicting stress concentration. The stress concentration factor of the notched sample is... K t Tensile tests were performed on the notched sample to obtain the stress concentration factor. K t Notch tensile strength σ bn ; (3) Parameter fitting: calculate σ bn / H The value M, and M with H Perform linear fitting to obtain formula (1); (1) In formula (1), a and b These are material-related constants, obtained through linear fitting using the least squares method; (4) Prediction of tensile strength of notched parts: Equation (1) is transformed to obtain the formula for predicting the notched tensile strength of the same series of metallic material components, namely formula (2). The stress concentration factor of the corresponding material can be calculated from formula (2). K t Notched tensile strength σ bn Predicted value; (2)。 2. The method for predicting notched tensile strength by material hardness according to claim 1, characterized in that: In step (1), the at least two metal materials of the same series have different strengths or different microstructures.

3. The method for predicting notched tensile strength by material hardness according to claim 1 or 2, characterized in that: In step (1), the metal materials of the same series have the same chemical composition but are samples processed by different preparation processes and / or processing processes. Each sample has different microstructure characteristics or different strength levels. The hardness value of each sample is the average of the hardness at at least 5 different locations. The hardness value is Vickers hardness, Brinell hardness or Rockwell hardness. The hardness test method is selected according to the microstructure characteristics to represent the overall hardness of the material.

4. The method for predicting notched tensile strength by material hardness according to claim 1, characterized in that: In step (2), the strain rate and temperature atmosphere conditions of the tensile test of notched specimens of the same series of metal materials must be consistent; in order to ensure the repeatability of the experiment, at least 3 specimens of each material are required for the experiment.

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