A scale effect analysis method for creep strain measurement of metallic materials

Abstract

The present invention discloses a method for analyzing the scale effect of creep strain measurement of metal materials, comprising the following steps: Step 001, dividing a creep specimen test section S under a certain stress state into reference test sections C composed of multiple materials and the same process under the same stress state, assuming that the creep strain of the test section S at a given creep time is approximately n S The method of the present invention is used to quantify the difference between creep strains or creep curves measured on specimens of different sizes under the same stress state, thereby better understanding the creep properties of materials.

Description

Technical Field

[0001] The present invention relates to the technical field of material testing and analysis, and in particular to a method for analyzing scale effects of creep strain measurement of metallic materials. Background Art

[0002] It is well known that heterogeneous material microstructures can lead to differences in macroscopic creep deformation. In creep testing of metallic materials, creep strain is calculated by comparing the overall deformation of the specimen's test section with the initial test section length. This creep strain calculation method results in differences in creep strain measurement and dispersion for specimens of different sizes.

[0003] Due to limitations in test materials and equipment, it is difficult to use a single specimen size or form for creep performance testing. Therefore, it is necessary to understand the differences between creep strains or creep curves obtained using specimens of different sizes in order to study the relationship between creep strains of specimens of different sizes. Summary of the Invention

[0004] The purpose of the present invention is to provide a method for analyzing the scale effect of creep strain measurement of metal materials to solve the technical problems existing in the prior art.

[0005] In order to solve the above technical problems, the present invention specifically provides the following technical solutions:

[0006] A method for analyzing scale effects of creep strain measurement in metal materials, comprising the following steps:

[0007] Step 001: Divide the creep specimen test section S under a certain stress state into reference test sections C composed of multiple materials and the same process under the same stress state. Assume that the creep strain of the test section S at a given creep time is approximately n S The average value of creep strain of the reference test section C at the same creep time;

[0008] Step 002, based on the assumptions in step 001 and the normal distribution, derive the relationship between the creep strains measured on specimens of different sizes at the same probability under the same stress state.

[0009] Furthermore, in step 001, the reference test section C is the minimum scale at which the creep strain measurement result of the material has statistical distribution characteristics.

[0010] Furthermore, in step 001, n S yes V S / V C The integer part of V S andV C are the volumes of the test section S and the reference test section C, respectively.

[0011] Furthermore, the step 002 includes the following steps:

[0012] Step 0021, calculate the creep strain of reference test section C e C The probability of not exceeding a certain value, that is, the survival rate;

[0013] Step 0022, calculating the relationship between the creep strain of the test section S and the creep strain of the reference test section C under the same survival rate;

[0014] Step 0023, calculating the relationship between the creep strain of the test section L and the creep strain of the reference test section C under the same survival rate;

[0015] Step 0024: Calculate the relationship between the creep strains of the test section S and the test section L under the same survival rate.

[0016] Furthermore, in step 0021, it is assumed that the creep strain of the reference test section C is e C Is subject to the mean m C and standard deviation s C The normal distribution is:

[0017] ;

[0018] Where Φ() is the standard normal distribution function;

[0019] According to formula (1), the creep strain of the reference test section C is calculated as e C The probability of not exceeding a certain value is the survival rate.

[0020] Furthermore, in step 0022, according to the statistical analysis theory, the creep strain of the creep specimen test section S is The measurement results obey the normal distribution and satisfy:

[0021] ;

[0022] ;

[0023] From formulas (2) and (3), we can get:

[0024] ;

[0025] Under the same survival rate, the creep strain of the test section S and the creep strain of the reference test section C satisfy:

[0026] ;

[0027] Right now .

[0028] Furthermore, in step 0023, according to the calculation method of step 0022, the creep strain of the test section L and the creep strain of the reference test section C satisfy the following relationship:

[0029] ;

[0030] in, V L is the volume of the test section L.

[0031] Furthermore, in step 0024, from equations (6) and (7), we can obtain:

[0032] ;

[0033] From formula (2), we can know that , so we have:

[0034] ;

[0035] Equation (9) gives the relationship between the creep strains of the test section S and the test section L when the survival rate is the same under the same stress state.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] The method provided by the present invention is used to quantify the differences between creep strains or creep curves measured by different specimens under the same stress state, so as to better understand the creep properties of materials. It is of great significance for understanding the differences between creep strains of metal materials measured using different specimens.

[0038] The method provided by the present invention not only gives the difference between the creep strains of metal materials measured by different samples, but also can predict the average creep strain of different samples under the same stress state based on the creep strain of metal materials measured by one sample. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for the embodiments or the description of the prior art. Obviously, the drawings described below are merely illustrative, and those skilled in the art can derive other implementation drawings based on the provided drawings without inventive effort.

[0040] Figure 1 Schematic diagram of the shape and size of the Ti-6Al-4V titanium alloy compression creep specimen;

[0041] Figure 2 The compressive creep strain measurement results of Ti-6Al-4V titanium alloy specimens with a test section of 25 mm are used to predict the compressive creep strain of Ti-6Al-4V titanium alloy specimens with a test section of 12.5 mm at different survival rates. DETAILED DESCRIPTION

[0042] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0043] like Figure 1 As shown, the present invention provides a method for analyzing the scale effect of creep strain measurement of metal materials, and the specific steps are as follows:

[0044] Step 001: Assume that a creep specimen test section S under a certain stress state (such as uniaxial tension or compression) can be regarded as a reference test section C composed of multiple materials and processes under the same stress state.

[0045] The reference test section C is the minimum scale at which the creep strain measurement results of the material have statistical distribution characteristics (such as the length of cylindrical specimens with the same cross-section, the cross-sectional area of ​​specimens with the same height). The creep strain of the test section S at a given creep time is approximately: n S The average value of creep strain of the reference test section C at the same creep time.

[0046] in, n S yes V S / V C The integer part of V S and V C are the volumes of the test section S and the reference test section C, respectively.

[0047] Step 002, assuming the creep strain of the reference test section C e C Is subject to the mean m C and standard deviation s CThe normal distribution is:

[0048] ;

[0049] Where Φ() is the standard normal distribution function.

[0050] From formula (1), the creep strain of the reference test section C can be calculated: e C The probability of not exceeding a certain value is the survival rate.

[0051] According to the statistical analysis theory, the creep strain of the creep specimen test section S is The measurement results obey the normal distribution and satisfy:

[0052] ;

[0053] ;

[0054] From formulas (2) and (3), we can get:

[0055] ;

[0056] Then, under the same probability (survival rate), the creep strain of the test section S and the creep strain of the reference test section C satisfy:

[0057] ;

[0058] Right now:

[0059] ;

[0060] Similarly, the creep strain of the test section L and the creep strain of the reference test section C satisfy:

[0061] ;

[0062] in, V L is the volume of the test section L.

[0063] From formula (6) and formula (7), we can get:

[0064] ;

[0065] From formula (2), we can know that , so we have:

[0066] ;

[0067] Equation (9) gives the relationship between the creep strains measured for specimens of different sizes under the same stress state and with the same probability (survival rate).

[0068] From equations (2) and (3), it can be seen that the creep strain dispersion measured using large-size specimens (i.e., specimens with large test section volumes) is smaller than that measured using small-size specimens, but their mean values ​​are the same.

[0069] Step 003, the following is a specific description of the compression creep strain prediction of a Ti-6Al-4V titanium alloy specimen with a test section of 12.5 mm at different survival rates, taking the compression creep strain measurement results of a Ti-6Al-4V titanium alloy specimen with a test section of 25 mm at room temperature as an example.

[0070] First, the MTS Landmark test machine was used to Figure 1 The titanium alloy specimen shown was subjected to a compression creep test at room temperature for 50 h. The stress level was selected as the compressive yield strength of 912 MPa. A total of three parallel experiments were carried out, and all experiments were completed on the same machine.

[0071] During the test, an extensometer with a gauge length of 25 mm was used to record the deformation. The relationship between the creep strain and time of the titanium alloy specimens was obtained as shown in the figure. Figure 2 As shown by the solid line in the middle, it can be seen that under a given creep time, the compressive creep strain of the titanium alloy specimen shows obvious dispersion.

[0072] choose Figure 2 The creep strains of different samples at 0.1 h, 0.2 h, 0.3 h, ..., 50 h were fitted to obtain the normal distribution parameters; among them, the mean of the normal distribution function is m and standard deviation s Calculate according to formula (10) and (11):

[0073] ;

[0074] ;

[0075] in, n is the total number of test specimens, x i The sample is sampled at a typical time i Creep strain data.

[0076] The creep strains of the 25 mm specimen at 50% and 90% survival rates at 0.1 h, 0.2 h, 0.3 h, ..., 50 h were calculated according to the normal distribution function. The creep strains of the 12.5 mm specimen at 50% and 90% survival rates were then predicted according to formula (9). The creep strains at different times and the same survival rate were connected to obtain the predicted PCT (Probabilistic-Creep strain-Time) curve as shown in the figure: Figure 2Indicated by the dotted line.

[0077] It can be seen that the predicted creep curve of the 12.5 mm test section specimen at a survival rate of 50% is the average of the creep curves of the three tested specimens with a 25 mm test section; the predicted creep curve of the 12.5 mm test section specimen at a survival rate of 90% is higher than the creep curve of the tested specimen with a 25 mm test section.

[0078] Figure 2 The results show that the dispersion of the compressive creep strain measurement results of the 12.5 mm test section specimens is higher than that of the 25 mm test section specimens.

[0079] During the experimental verification process for different sizes and different experimental environments, it was found that the scale effect analysis method for creep strain measurement of metal materials disclosed in this application mainly targets the overall creep deformation difference of metal materials in the initial and slow growth stages of creep deformation, among which the high-temperature surface oxidation generated during the creep deformation process should not have a large impact or can be ignored.

[0080] However, for the third stage of tensile creep of metal materials, the analysis method disclosed in this application may not be applicable.

[0081] The above embodiments are merely exemplary embodiments of the present application and are not intended to limit the scope of the present application. The scope of protection of the present application is defined by the claims. Those skilled in the art may make various modifications or equivalent substitutions to the present application within the essence and scope of protection of the present application, and such modifications or equivalent substitutions shall also be deemed to fall within the scope of protection of the present application.

Claims

1. A method for analyzing the scale effect of creep strain measurement in metal materials, characterized in that: The following steps are involved: Step 001: Divide the creep specimen test section S under a certain stress state into reference test sections C composed of multiple materials and the same process under the same stress state. Assume that the creep strain of the test section S at a given creep time is approximately n S The average value of creep strain of the reference test section C at the same creep time; n S yes V S / V C The integer part of V S and V C are the volumes of the test section S and the reference test section C, respectively; Step 002, based on the assumptions in step 001 and based on the normal distribution, derives the relationship between creep strains measured on specimens of different sizes under the same stress state and with the same probability, including the following steps: Step 0021, calculate the creep strain of reference test section C ε C The probability of not exceeding a certain value, that is, the survival rate; Step 0022, calculating the relationship between the creep strain of the test section S and the creep strain of the reference test section C under the same survival rate; Step 0023, calculating the relationship between the creep strain of the test section L and the creep strain of the reference test section C under the same survival rate; Step 0024: Calculate the relationship between the creep strains of the test section S and the test section L under the same survival rate.

2. The metal material creep strain measurement scale effect analysis method according to claim 1, characterized in that: In step 001, the reference test section C is the minimum scale at which the creep strain measurement result of the material has statistical distribution characteristics.

3. The metal material creep strain measurement scale effect analysis method according to claim 2, characterized in that: In step 0021, it is assumed that the creep strain of the reference test section C ε C Is subject to the mean μ C and standard deviation σ C The normal distribution is: ； Where Φ() is the standard normal distribution function; According to formula (1), the creep strain of the reference test section C is calculated as ε C The probability of not exceeding a certain value is the survival rate.

4. The method for analyzing the scale effect of creep strain measurement of metal materials according to claim 3, characterized in that: In step 0022, according to the statistical analysis theory, the creep strain of the creep specimen test section S is The measurement results obey the normal distribution and satisfy: ； ； From formulas (2) and (3), we can get: ； Under the same survival rate, the creep strain of the test section S and the creep strain of the reference test section C satisfy: ； Right now .

5. The metal material creep strain measurement scale effect analysis method according to claim 4, characterized in that: In step 0023, according to the calculation method of step 0022, the creep strain of the test section L and the creep strain of the reference test section C satisfy the following relationship: ； in, V L is the volume of the test section L.

6. The metal material creep strain measurement scale effect analysis method according to claim 5, characterized in that: In step 0024, the equations (6) and (7) yield: ； From formula (2), we can know that , so we have: ； Equation (9) gives the relationship between the creep strains of the test section S and the test section L when the survival rate is the same under the same stress state.

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