A method for constructing a compressive creep constitutive model for metal materials

Abstract

The present invention provides a method for constructing a compressive creep constitutive model of a metal material, which comprises: 1) constructing a constitutive model of the metal material under nominal compressive stress; 2) determining the creep time threshold of the metal material; 3) determining the creep characteristic constant of the material A and B and creep time influencing parameters n and m ;4) Determine the material parameters A 、 n 、 m and B Substituting this into the constitutive model under nominal compressive stress yields a compressive creep constitutive model for metal materials. This method can describe the temporal relationship between creep strain and deformation under constant compressive loads, and can also predict the creep deformation behavior of metal materials under long-term compressive loads, thereby optimizing the design of structural components and improving their service reliability.

Description

Technical Field

[0001] The present invention relates to the technical field of material and component testing and analysis, and in particular to a method for constructing a compression creep constitutive model of a metal material. Background Art

[0002] In recent years, with the application of titanium alloys in the main pressure-resistant structures of major deep-sea equipment, the compressive creep behavior of titanium alloys has gradually become a hot topic in creep research. However, there is currently a lack of effective mathematical models to describe the compressive creep deformation behavior of titanium alloys, namely, compressive creep constitutive models. Using creep constitutive models, it is possible to simulate or predict the deformation and life of materials under long-term actual service conditions, thereby reducing the risk of failure of engineering structural components caused by long-term deformation. Therefore, establishing compressive creep constitutive models for metallic materials has important scientific significance and engineering application value. Summary of the Invention

[0003] In response to the technical problems existing in the above-mentioned background technology, the present invention proposes a method for constructing a compressive creep constitutive model of metal materials, which can describe the relationship between the strain of metal materials changing with time under constant compressive load, and can also predict the deformation behavior of metal materials under long-term compressive load, thereby optimizing the design of structural parts and improving their service reliability.

[0004] To solve the above technical problems, the present invention provides a method for constructing a compressive creep constitutive model of a metal material, which mainly includes the following steps:

[0005] Step 1: Construct a constitutive model of the metal material under nominal compressive stress. The specific process is as follows:

[0006] Ignoring the change in the mechanical properties of metal materials during compression creep, a s Related creep time threshold , exceeds the creep time threshold It is assumed that creep deformation no longer occurs under this compressive load, and it is further assumed that the compressive creep constitutive model is expressed as:

[0007] ;

[0008] in, s pc is the compressive yield strength of the material, e is the creep strain, t is the creep time, The nominal compressive stress s Lower creep time reaches time threshold The accumulated creep strain of the material is A 、 n 、 m and Bis the material parameter;

[0009] When only a certain nominal compressive stress is considered, the above formula (1) can be simplified to:

[0010] ;

[0011] in, is the creep time threshold associated with this nominal compressive stress;

[0012] Step 2: Determine the creep time threshold of the metal material;

[0013] Step 3: Determine the creep characteristic constants of the material A and B and creep time influencing parameters n and m ;

[0014] Step 4: Determine the material parameters A 、 n 、 m and B Substitute it into the constitutive model under nominal compressive stress to obtain the compressive creep constitutive model of metal materials.

[0015] The method for constructing a compressive creep constitutive model of a metal material, wherein: the creep time threshold in step 2 It is determined based on the test results of creep strain-time, or estimated based on the changing trend of creep strain-time.

[0016] The method for constructing a compressive creep constitutive model of a metal material, wherein: in the step 3, if it is necessary to obtain a constitutive model under different nominal compressive stresses, that is, the above formula (1), creep strain-time test data under no less than two stress levels are selected, and the creep strain-time test data under the preset parameter value range are calculated. A 、 n 、 m and B Discretize, for any A 、 n 、 m and B Combine and calculate the sum of square errors between the model prediction value and the test value under the selected stress level, and select the one with the smallest sum of square errors. A 、 n 、 m and B Combination, as a parameter A 、 n 、 m and B The numerical value of .

[0017] The method for constructing a compressive creep constitutive model of a metal material, wherein: in the step 3, if only a constitutive model under a certain nominal compressive stress is required, that is, the above formula (2), within the range of the preset parameter values, A 、 n and m Discretize, for any A 、 n and m Combine the two and calculate the sum of square errors between the model prediction value and the test value at the stress level, and select the one with the smallest sum of square errors. A 、 n and m Combination, as a parameter A 、 n and m The numerical value of .

[0018] The method for constructing a compressive creep constitutive model of a metal material, wherein the formula for the sum of squares of the errors between the model prediction value and the experimental value at the calculated stress level is:

[0019] ;

[0020] In the above formula (3), y ( s i , t k ) indicates the stress s i and time t k The creep strain measured by the test is f ( s i , t k ) represents the stress predicted by formula (1) s i and time t k The creep strain value at M is the number of creep stress levels selected, N is the total number of moments used to calculate creep strain.

[0021] The method for constructing a compressive creep constitutive model of a metal material, wherein: in step 4, the material parameters determined by the constitutive model under different nominal compressive stresses are A 、 n 、 m and B Substituting into the above formula (1), the compressive creep constitutive model of metal materials can be obtained.

[0022] The method for constructing a compressive creep constitutive model of a metal material, wherein: in step 4, the material parameters determined according to the constitutive model under a certain nominal compressive stress are A 、 n and m Substituting into the above formula (2), we can obtain the compression creep constitutive model of metal materials.

[0023] By adopting the above technical solution, the present invention has the following beneficial effects:

[0024] The method for constructing a compressive creep constitutive model for metallic materials disclosed herein can describe the temporal relationship between creep strain under a constant compressive load. The method can also predict the temporal relationship between creep strain under other different compressive loads using test data from two compressive loads, significantly reducing testing costs. Furthermore, the method can predict the creep deformation behavior of materials under long-term compressive loads, thereby optimizing the design of structural components and improving their service reliability. The model incorporates a creep time threshold related to the nominal compressive stress. Beyond this threshold, creep deformation ceases under this compressive load, enabling a better description of creep test results for metallic materials under constant compressive loads. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 This is a comparison diagram of the Ti-6Al-4V ELI titanium alloy compression creep constitutive model involved in the method for constructing a compression creep constitutive model of metal materials of the present invention and the test results. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] The present invention will be further explained below with reference to specific embodiments.

[0029] This embodiment provides a method for constructing a compressive creep constitutive model of a metal material, which includes the following steps:

[0030] 1) Ignoring the change in the mechanical properties of metal materials during compression creep, a s Related creep time threshold , exceeding time , it is assumed that creep deformation no longer occurs under the compressive load, and it is further assumed that the compressive creep constitutive model can be expressed as:

[0031] ;

[0032] in, s pc is the compressive yield strength of the material, e is the creep strain, t is the creep time, The nominal compressive stress s Lower creep time reaches time threshold The accumulated creep strain of the material is A 、 n 、 m and B is the material parameter.

[0033] When only a certain nominal compressive stress is considered, formula (1) can be simplified as:

[0034] ;

[0035] in, is the creep time threshold associated with this nominal compressive stress.

[0036] 2) Determine the creep time threshold

[0037] Creep time threshold It is determined based on the test results of creep strain-time, or estimated based on the changing trend of creep strain-time.

[0038] 3) Determine the creep characteristic constant of the material A and B and creep time influencing parameters n and m

[0039] If it is necessary to obtain the constitutive model under different nominal compressive stresses, that is, formula (1), select creep strain-time test data under no less than two stress levels, and calculate the creep strain-time data within the range of the preset parameters. A 、 n 、 m and B Discretize, for any A 、 n 、 m and BCombine and calculate the sum of square errors between the model prediction value and the test value under the selected stress level, and select the one with the smallest sum of square errors. A 、 n 、 m and B Combination, as a parameter A 、 n 、 m and B If we only need to obtain the constitutive model under a certain nominal compressive stress, that is, formula (2), within the range of the preset parameters, A 、 n and m Discretize, for any A 、 n and m Combine the two and calculate the sum of square errors between the model prediction value and the test value at the stress level, and select the one with the smallest sum of square errors. A 、 n and m Combination, as a parameter A 、 n and m The numerical value of .

[0040] 4) Obtained material parameters A 、 n 、 m and B Substitute into formula (1) or material parameters A 、 n and m Substituting into formula (2), the compression creep constitutive model is obtained.

[0041] The following is a detailed explanation of the compression creep constitutive model of Ti-6Al-4V ELI titanium alloy obtained from the literature (Wang et al. Journal of Ship Mechanics, 2018, 22(4):464-474).

[0042] Figure 1 The “○” in the figure represents the creep strain-time test data of Ti-6Al-4V ELI titanium alloy under different compressive stresses. It can be seen that for 0.7 s pc Compressive creep stress, when the creep time is about 1000 h, the creep strain no longer increases with the increase of creep time, that is, at 0.7 s pc The creep time threshold of Ti-6Al-4V ELI titanium alloy under compressive creep stress is 1000h. s pc , 0.85 spc and 0.9 s pc During the test, the creep strain still tends to increase with time. According to the trend of creep strain changing with time, it is estimated that 0.8 s pc , 0.85 s pc and 0.9 s pc The creep time thresholds under compressive creep stress are 2000 h, 2500 h and 5000 h, respectively.

[0043] Here, 0.7 is used s pc and 0.9 s pc Parameters of test data under compressive creep stress A 、 n 、 m and B Preset parameters A 、 n 、 m and B The parameter ranges are [-0.1:0.1], [-0.9:0], [-0.1:0.1] and [1.4:1.8], and the parameters A 、 n 、 m and B Discretize with step sizes of 0.01, 0.01, 0.02, and 0.01 respectively. A 、 n 、 m and B Combination, calculate 0.7 s pc and 0.9 s pc The sum of squares of the errors between the model's predicted value and the experimental value under compressive creep stress is given by formula (3), namely:

[0044] ;

[0045] Among them, in the above formula (3), y ( s i , t k ) indicates the stress s i and time t k The creep strain measured by the test is f ( s i ,t k ) represents the stress predicted by formula (1) s i and time t k The creep strain value at M is the number of creep stress levels selected (here M =2), N is the total number of moments used to calculate creep strain.

[0046] When the above formula (3) is minimum, the corresponding A 、 n 、 m and B They are 0.03, -0.57, 0.06 and 1.48 respectively. Substituting these parameters and the creep time thresholds under different compressive creep stresses into Equation (1), the compressive creep constitutive model of Ti-6Al-4V ELI titanium alloy is obtained.

[0047] Figure 1 The lines in the figure are given using 0.7 s pc and 0.9 s pc The compressive creep constitutive model of Ti-6Al-4V ELI titanium alloy obtained by fitting the creep-time test data under compressive creep stress and the 0.8 s pc and 0.85 s pc Creep constitutive prediction results under compressive creep stress. It can be seen that the constitutive model proposed in this invention can well describe the relationship between the creep strain and time of Ti-6Al-4V ELI titanium alloy under different stress levels.

[0048] The method for constructing a compressive creep constitutive model for metallic materials disclosed herein can describe the temporal relationship between creep strain under a constant compressive load. The method can also predict the temporal relationship between creep strain under other different compressive loads using test data from two compressive loads, significantly reducing testing costs. Furthermore, the method can predict the creep deformation behavior of materials under long-term compressive loads, thereby optimizing the design of structural components and improving their service reliability. The model incorporates a creep time threshold related to the nominal compressive stress. Beyond this threshold, creep deformation ceases under this compressive load, enabling a better description of creep test results for metallic materials under constant compressive loads.

[0049] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for constructing a compressive creep constitutive model of a metal material, characterized in that: The main steps include: Step 1: Construct a constitutive model of the metal material under nominal compressive stress. The specific process is as follows: Ignoring the change in the mechanical properties of metal materials during compression creep, a σ Related creep time threshold , exceeds the creep time threshold The nominal compressive stress is considered σ Creep deformation no longer occurs, and it is further assumed that the compressive creep constitutive model is expressed as: (1)； in, σ pc is the compressive yield strength of the material, ε is the creep strain, t is the creep time, The nominal compressive stress σ Lower creep time reaches time threshold The accumulated creep strain of the material is A 、 n 、 m and B is the material parameter; When only a certain nominal compressive stress is considered, the above formula (1) can be simplified to: (2)； in, is the creep time threshold associated with this nominal compressive stress; Step 2: Determine the creep time threshold of the metal material; Step 3: Determine the creep characteristic constants of the material A and B and creep time influencing parameters n and m If you need to obtain the constitutive model under different nominal compressive stresses, that is, the above formula (1), select creep strain-time test data under no less than two nominal compressive stress levels, and calculate the creep strain-time test data within the range of the preset parameters. A 、 n 、 m and B Discretize, for any A 、 n 、 m and B Combine and calculate the sum of square errors between the model prediction value and the test value under at least two selected nominal compressive stress levels, and select the one with the smallest sum of square errors. A 、 n 、 m and B Combination, as a parameter A 、 n 、 m and B If only the constitutive model under a certain nominal compressive stress is needed, that is, the above formula (2), within the range of the preset parameters, A 、 n and m Discretize, for any A 、 n and m Combine the two, calculate the sum of square errors between the model prediction value and the test value at a certain nominal compressive stress level, and select the one with the smallest sum of square errors. A 、 n and m Combination, as a parameter A 、 n and m The value of Step 4: Determine the material parameters A 、 n 、 m and B Substitute it into the constitutive model under nominal compressive stress to obtain the compressive creep constitutive model of metal materials.

2. The method for constructing a compressive creep constitutive model of a metal material according to claim 1, wherein: The creep time threshold in step 2 It is determined based on the test results of creep strain-time, or estimated based on the changing trend of creep strain-time.

3. The method for constructing a compressive creep constitutive model of a metal material according to claim 1, wherein: The calculation of the sum of squares of the errors between the model prediction value and the test value at at least two nominal compressive stress levels selected, or the calculation of the sum of squares of the errors between the model prediction value and the test value at a certain nominal compressive stress level is performed using the following formula: （3）； In the above formula (3), y ( σ i , t k ) indicates the stress σ i and time t k The creep strain measured by the test is f ( σ i , t k ) represents the stress predicted by formula (1) or formula (2) σ i and time t k The creep strain value at M is the number of creep stress levels selected, N is the total number of moments used to calculate creep strain.

4. The method for constructing a compressive creep constitutive model of a metal material according to claim 1, wherein: In step 4, the material parameters determined by the constitutive model under different nominal compressive stresses are A 、 n 、 m and B Substituting into the above formula (1), the compressive creep constitutive model of metal materials can be obtained.

5. The method for constructing a compressive creep constitutive model of a metal material according to claim 1, wherein: In step 4, the material parameters determined by the constitutive model under a certain nominal compressive stress are A 、 n and m Substituting into the above formula (2), we can obtain the compression creep constitutive model of metal materials.

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