Metal material creep strain measurement scale effect analysis method

Abstract

The invention discloses a metal material creep strain measurement scale effect analysis method which comprises the following steps: step 001, dividing a creep sample test section S in a certain stress state into a plurality of reference test sections C which are made of a plurality of materials and have the same process in the same stress state, assuming that the creep strain of the test section S at the given creep time is approximate to the average value of the creep strains of nS reference test sections C at the same creep time; and step 002, on the basis of the assumption of the step 001, based on normal distribution, obtaining the relationship between the creep strains measured by the samples with different sizes under the same stress state and the same probability. The method provided by the invention is used for quantifying the difference between the creep strain or the creep curve measured by the samples with different sizes in the same stress state, so that the creep property of the material can be better known.

Description

Technical Field

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

[0002] As is well known, the inhomogeneity of the microstructure of materials will lead to differences in macroscopic creep deformation. In the creep test of metal materials, the creep strain is obtained by the overall deformation of the test section of the specimen and the initial test section length. This method of calculating creep strain results in differences in the measurement and its dispersion of creep strain for specimens of different sizes.

[0003] Due to limitations such as test materials and equipment, it is difficult to conduct creep performance tests using a single specimen size or form; therefore, it is necessary to master the differences between creep strains or creep curves obtained from specimens of different sizes 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] To solve the above technical problems, the present invention specifically provides the following technical solutions: A method for analyzing the scale effect of creep strain measurement of metal materials, comprising the following steps: Step 001: Divide the test section S of the creep specimen under a certain stress state into reference test sections C composed of multiple materials with the same stress state and the same process. Assume that the creep strain of the test section S at a given creep time is approximately n S the average value of the creep strains of the reference test sections C at the same creep time; Step 002: Based on the assumption in Step 001 and the normal distribution, obtain the relationship between the creep strains measured from specimens of different sizes at the same probability under the same stress state.

[0006] Further, in Step 001, the reference test section C is the smallest scale with statistical distribution characteristics of the creep strain measurement results of the material.

[0007] Further, in Step 001, n S is 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.

[0008] Further, in step 002, the following steps are included: Step 0021, calculate the creep strain of the reference test section C ε C The probability when it does not exceed a certain value, that is, the survival rate; Step 0022, calculate 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, calculate 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.

[0009] Further, in step 0021, assume that the creep strain of the reference test section C ε C obeys a normal distribution with a mean value μ C and a standard deviation σ C , that is: ; where Φ() is the standard normal distribution function; From equation (1), calculate the probability that the creep strain of the reference test section C ε C does not exceed a certain value, that is, the survival rate.

[0010] Further, in step 0022, according to the statistical analysis theory, the measured creep strain of the creep specimen test section S obeys a normal distribution and satisfies: ; ; From equations (2) and (3), it can be obtained that ; Then, under the same survival rate, the relationship between the creep strain of the test section S and the creep strain of the reference test section C satisfies: ; That is .

[0011] Further, in step 0023, according to the calculation method of step 0022, the relationship between the creep strain of the test section L and the creep strain of the reference test section C satisfies: ; where VL is the volume of the test section L.

[0012] Furthermore, in step 0024, from equations (6) and (7), we get: ; From equation (2), we know that , so we get: ; Equation (9) gives the relationship between the creep strains of test section S and test section L at the same survival rate under the same stress state.

[0013] The present invention has the following beneficial effects compared with the prior art: The method provided by the present invention is used to quantify the differences between the creep strains or creep curves measured from different specimens under the same stress state, so as to better understand the creep properties of materials. It is of great significance for grasping the differences between the creep strains of metal materials measured from different specimens.

[0014] The method provided by the present invention not only gives the differences between the creep strains of metal materials measured from different specimens, but also can predict the average creep strain of different specimens under the same stress state based on the creep strain of the metal materials measured from one specimen. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only exemplary, and for those of ordinary skill in the art, without creative efforts, other implementation drawings can also be obtained according to the provided drawings.

[0016] Figure 1 is a schematic diagram of the shape and dimensions of a Ti-6Al-4V titanium alloy compression creep specimen; Figure 2 is the prediction result of the compression creep strain of a Ti-6Al-4V titanium alloy specimen with a test section of 12.5 mm under different survival rates based on the measurement result of the compression creep strain of a Ti-6Al-4V titanium alloy specimen with a test section of 25 mm. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0018] As Figure 1 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: Step 001: Assume that the test section S of a creep specimen under a certain stress state (such as uniaxial tension, compression) can be regarded as composed of multiple reference test sections C of the same material and process under the same stress state.

[0019] The reference test section C is the smallest scale for which the creep strain measurement results of this material have statistical distribution characteristics (such as the length of a cylindrical specimen with the same cross-section, the cross-sectional area of a specimen with the same height), then the creep strain of the test section S at a given creep time is approximately n S the average value of the creep strains of

[0020] Among them, n S is 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.

[0021] Step 002: Assume that the creep strain ε C of the reference test section C follows a normal distribution with a mean μ C and a standard deviation σ C , that is: ; where Φ() is the standard normal distribution function.

[0022] From equation (1), the probability that the creep strain ε C of the reference test section C does not exceed a certain value, that is, the survival rate, can be calculated.

[0023] According to the statistical analysis theory, the creep strain measurement results of the test section S of the creep specimen follow a normal distribution and satisfy: ; ; From equations (2) and (3), it can be obtained that ; 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: ; That is: ; Similarly, the creep strain of the test section L and the creep strain of the reference test section C satisfy: ; Wherein, V L is the volume of the test section L.

[0024] From equations (6) and (7), we get: ; It can be seen from equation (2) that , so there is: ; Equation (9) gives the relationship between the creep strains measured from specimens of different sizes under the same stress state and the same probability (survival rate).

[0025] It can be seen from equations (2) and (3) that the creep strain measured using a large-size specimen (i.e., a specimen with a large test section volume) has relatively less dispersion than that of a small-size specimen, but their means are the same.

[0026] Step 003, taking the compressive 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 to predict the compressive creep strain of a Ti-6Al-4V titanium alloy specimen with a test section of 12.5 mm under different survival rates, a specific description is given as follows.

[0027] First, use an MTS Landmark testing machine to Figure 1 perform a 50-hour compressive creep experiment on the titanium alloy specimen shown at room temperature. The stress level is selected as the compressive yield strength of 912 MPa, and a total of 3 parallel experiments are carried out. All experiments are completed on the same machine.

[0028] During the experiment, an extensometer with a gauge length of 25 mm is used to record the deformation. The relationship between the creep strain and time of the titanium alloy specimen obtained is as shown by the solid line in Figure 2 ; it can be seen that at a given creep time, the compressive creep strain of the titanium alloy specimen shows obvious dispersion.

[0029] Select Figure 2 the creep strains of different specimens at 0.1 h, 0.2 h, 0.3 h,..., 50 h in to perform fitting to obtain the normal distribution parameters; among them, the mean μ and standard deviationσ Calculate according to formulas (10) and (11): ; ; wherein, n is the total number of test specimens, x i is the creep strain data of the specimen i at a certain typical time.

[0030] Calculate the creep strains of the specimens with a test section of 25 mm at 0.1 h, 0.2 h, 0.3 h, ……, 50 h under 50% and 90% survival rates according to the normal distribution function, and then predict the creep strains of the specimens with a test section of 12.5 mm under 50% and 90% survival rates according to formula (9). Connect the creep strains at the same survival rate at different times to obtain the predicted P-C-T (Probabilistic-Creep strain-Time) curve as shown by the dashed line in Figure 2 the figure.

[0031] It can be seen that the predicted creep curve of the specimen with a 12.5 mm test section under a 50% survival rate is the average of the creep curves of the 3 specimens with a 25 mm test section; the predicted creep curve of the specimen with a 12.5 mm test section under a 90% survival rate is higher than the creep curve of the specimen with a 25 mm test section.

[0032] Figure 2 It shows that the dispersion of the measured results of the compressive creep strain of the specimen with a 12.5 mm test section is higher than that of the specimen with a 25 mm test section.

[0033] During the experimental verification for different sizes and different experimental environments, it is found that the method for analyzing the scale effect of creep strain measurement of the metal materials disclosed in this application mainly focuses on the overall creep deformation difference at the beginning and slow growth stage of the creep deformation of the metal materials. Among them, the influence of high-temperature surface oxidation generated during the creep deformation process should not be too large or can be ignored.

[0034] For the third stage of the tensile creep of metal materials, the analysis method disclosed in this application may not be applicable.

[0035] The above embodiments are only exemplary embodiments of this application and are not used to limit this application. The protection scope of this application is defined by the claims. Those skilled in the art can make various modifications or equivalent replacements within the essence and protection scope of this application, and such modifications or equivalent replacements should also be regarded as falling within the protection scope of this application.

Claims

1. A method for analyzing the scale effect of creep strain measurement of 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 reference test section C at the same creep time; Step 002, based on the assumptions in step 001 and based on normal distribution, derive the relationship between creep strains measured on specimens of different sizes at the same probability under the same stress state.

2. The method for analyzing the scale effect of creep strain measurement of metal materials 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 method for analyzing the scale effect of creep strain measurement of metal materials according to claim 1, characterized in that: In step 001, 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.

4. The method for analyzing the scale effect of creep strain measurement of metal materials according to claim 1, characterized in that: The step 002 includes 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, calculating the relationship between the creep strains of the test section S and the test section L under the same survival rate.

5. The method for analyzing the scale effect of creep strain measurement of metal materials according to claim 4, 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 reference test section C is calculated as ε C The probability of not exceeding a certain value is the survival rate.

6. The method for analyzing the scale effect of creep strain measurement of metal materials according to claim 4, 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 equations (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 .

7. The method for analyzing the scale effect of creep strain measurement of metal materials 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.

8. The method for analyzing the scale effect of creep strain measurement of metal materials according to claim 4, characterized in that: In step 0024, equations (6) and (7) yield: ； From formula (2), we can know , so we get: ； Formula (9) gives the relationship between the creep strains of test section S and test section L when the survival rate is the same under the same stress state.

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