Metal material strain rate effect measurement method based on multiple stress relaxation
By employing a multiple stress relaxation method, the challenge of measuring strain rate effects in single-sample testing was solved, and stress-strain curves within the quasi-static range were obtained. This approach avoids material property dispersion and transient effects, thereby improving the accuracy and efficiency of the measurement.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-30
- Publication Date
- 2026-04-10
AI Technical Summary
Existing technologies make it difficult to obtain the strain rate effect measurement results of metallic materials under different strain rates through single-sample testing, and the traditional jump strain rate method is affected by transient effects.
By employing a multiple stress relaxation method, standard tests are conducted at a constant strain rate, stress-strain curves are recorded, the number of stress relaxations and strain value sequences are determined, multiple stress relaxations and strain tests are performed, and stress-time and plastic strain rate curves are analyzed to obtain stress-strain curves at different strain rates.
This method enables the acquisition of stress-strain curves within the quasi-static range using a single specimen, avoiding the influence of material property dispersion in multi-specimen methods and the transient effects of traditional single-specimen methods, thus improving the accuracy and efficiency of measurements.
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Figure CN121830261A_ABST
Abstract
Description
TECHNICAL FIELD
[0001] The present application relates to the field of mechanical property testing of metallic materials. In particular, it relates to a method for measuring strain rate effect of metallic materials based on multiple stress relaxations. BACKGROUND
[0002] Metallic materials usually have strain rate effect, that is, the flow stress changes with the change of deformation rate during deformation. Therefore, when predicting and analyzing the process of plastic forming of metallic materials and other processes with strain rate change, the strain rate effect of the material needs to be measured in advance.
[0003] Traditional strain rate effect testing methods include two types: one is the multi-sample method, which takes multiple samples to carry out tensile or compression tests at different strain rates. This method has material microstructure dispersion, which leads to material strength dispersion. The dispersion is close to the strength change caused by strain rate effect, and the two are mixed together. Therefore, multiple sample tests need to be carried out at each strain rate, and then the average curve is analyzed to obtain statistically meaningful results, which is time-consuming and costly. The other method is the single sample jump strain rate method, which takes a single sample to change the strain rate rapidly during tensile process at different strains, and analyzes the strain rate effect of the material by the sudden change of flow stress caused by strain rate jump. This method overcomes the influence of material performance dispersion in the multi-sample method, but it is difficult to obtain the measurement results of strain rate effect corresponding to different strains due to the small number of jump strains and strain rates, and the transient change in the jump process will lead to an overestimation of the rate effect. The transient change refers to the phenomenon that when the strain rate is suddenly changed, the corresponding flow stress is higher or lower than that under the stable strain rate after the jump due to the influence of the dynamic response characteristics of the testing machine and the dynamic response characteristics of the material sample.
[0004] Therefore, how to obtain the stress-strain curve of the material at different strain rates through single sample test and avoid the transient effect of the traditional jump strain rate method is a problem that needs to be solved. SUMMARY
[0005] The present application provides a method for measuring strain rate effect of metallic materials based on multiple stress relaxations to solve the problem that it is difficult to obtain the measurement results of strain rate effect corresponding to different strains, and the transient effect of the traditional jump strain rate method in the prior art.
[0006] To achieve the above-mentioned purpose, in a first aspect, the present application relates to a method for measuring strain rate effect of metallic materials based on multiple stress relaxations, comprising: step 1: carrying out a standard quasi-static tensile or compression test on a material sample at a constant strain rate to obtain a stress-strain curve;
[0007] Step 2: Analyze the strain range based on the stress-strain curve, determine the number of stress relaxation cycles N to be performed, and the corresponding relaxation strain value sequence ε. i , i=1...N;
[0008] Step 3: Take a material sample and perform a tensile or compressive test at a set strain rate. When the strain reaches each value in the relaxation strain sequence, continue stress relaxation for a relaxation time Δt. After each stress relaxation, perform a tensile or compressive test again at the set strain rate until the Nth strain sequence value ε is reached. N The stress relaxation process corresponding to the continuous relaxation time Δt is stopped during the tensile or compression test.
[0009] Step 4: Analyze the stress-time curve for each stress relaxation process to obtain the relaxation strain ε for each stress relaxation process. i The corresponding stress-plastic strain rate curve;
[0010] Step 5: From each relaxation strain ε i The stress-strain curves corresponding to each strain rate are obtained by analyzing the stress-plastic strain rate curves.
[0011] Preferably, the data recorded during the test process includes at least time, strain, and stress, and the data acquisition frequency is greater than or equal to 1 Hz.
[0012] Preferably, the relaxation strain value sequence ε i The strain values are selected within the range of maximum force-to-total elongation strain in the stress-strain curve of the material, and the number N is greater than or equal to 5; the relaxation strain value sequence ε i The distribution is selected at equal intervals or with increased relaxation strain density in a portion of the strain range.
[0013] Preferably, the stress relaxation time Δt is set according to the strain rate range, and the value range is greater than or equal to 10s.
[0014] Preferably, step 4 specifically involves: for each relaxation strain value ε i The corresponding stress relaxation stress-time curve is differentiated to obtain the stress rate-time curve; further, the stress rate is divided by the Young's modulus of the material and multiplied by -1 to obtain the plastic strain rate-time curve; based on the stress relaxation stress-time curve and the plastic strain rate-time curve, the stress and plastic strain rate data corresponding to the same time are taken to obtain the relaxation strain value ε. i The corresponding stress-plastic strain rate curve.
[0015] Preferably, step 5 specifically involves: [details of step 5, which are defined as follows: each relaxation strain ε] i The corresponding stress-plastic strain rate curve yields the stress value σ corresponding to any plastic strain rate.i ; the data set (sigma i , epsilon i ) is curve fitted to obtain the stress-strain curve corresponding to this plastic strain rate.
[0016] The metal material strain rate effect measurement method based on multiple stress relaxations has the following beneficial effects compared with the prior art:
[0017] Compared with the prior art, the beneficial effect of the present application is that the stress-strain curve corresponding to different plastic strain rates in the quasi-static range can be obtained by a single sample, avoiding the shortcomings of the traditional multiple sample method that the number of samples is large and is easily affected by material performance dispersion. At the same time, compared with the traditional single sample jump strain rate method, the rate effect of the jump point can be obtained, and the deficiency of being easily affected by transient effect is avoided. BRIEF DESCRIPTION OF DRAWINGS
[0018] Figure 1 The method flowchart of the metal material strain rate effect measurement method based on multiple stress relaxations in the first embodiment of the present application is shown in the figure;
[0019] Figure 2 The strain-time curve schematic diagram for test process control of the metal material strain rate effect measurement method based on multiple stress relaxations in the first embodiment of the present application is shown in the figure;
[0020] Figure 3 The stress-time curve schematic diagram for test process measurement of the metal material strain rate effect measurement method based on multiple stress relaxations in the first embodiment of the present application is shown in the figure;
[0021] Figure 4 The stress-strain curve schematic diagram for test process measurement of the metal material strain rate effect measurement method based on multiple stress relaxations in the first embodiment of the present application is shown in the figure;
[0022] Figure 5 The schematic diagram of superimposing the stress-strain curves corresponding to different strain rates obtained by analysis and the test stress-strain curve of the metal material strain rate effect measurement method based on multiple stress relaxations in the embodiment of the present application is shown in the figure;
[0023] Figure 6 The quasi-static tensile curve diagram of the titanium alloy in Example 1 of the present application is shown in the figure;
[0024] Figure 7 The engineering stress / engineering strain-time curve diagram in Example 1 of the present application is shown in the figure;
[0025] Figure 8 The engineering stress-engineering strain curve diagram in Example 1 of the present application is shown in the figure;
[0026] Figure 9True stress-time curve diagram corresponding to relaxation strain 0.01 in Example 1 of the present application;
[0027] Figure 10 True plastic strain rate-time curve diagram corresponding to relaxation strain 0.01 in Example 1 of the present application;
[0028] Figure 11 True stress-true plastic strain rate curve diagram corresponding to relaxation strain 0.01 in Example 1 of the present application;
[0029] Figure 12 True stress-true plastic strain rate curve diagram corresponding to relaxation strain 0.01 in Example 1 of the present application;
[0030] Figure 13 True stress-true plastic strain rate curve diagram corresponding to relaxation strain 0.01 in Example 1 of the present application; DETAILED DESCRIPTION
[0031] The present application will be further described below in conjunction with the accompanying drawings and examples. It should be understood that the specific examples described herein are intended to be illustrative only and are not in any way limiting of the present application. Furthermore, it should be understood that, for ease of description, only the parts related to the present application are shown in the drawings.
[0032] Example 1
[0033] A metal material strain rate effect measurement method based on multiple stress relaxations, please refer to Figures 1-5 , comprising the following steps:
[0034] Step 1: Perform a standard quasi-static tensile or compression test on the material sample at a constant strain rate to obtain a stress-strain curve.
[0035] Step 2: Analyze the strain range based on the stress-strain curve to determine the number of stress relaxations N to be performed and the corresponding relaxation strain value sequence ε i , i = 1... N.
[0036] Step 3: Take a material sample and perform a tensile or compression test at a set strain rate. When the strain reaches each value in the relaxation strain value sequence, perform a stress relaxation for a duration of Δt. After each stress relaxation, perform a tensile or compression test at the set strain rate until the Nth stress relaxation process corresponding to the duration of Δt is completed, and stop the tensile or compression test. N
[0037] As shown in Figure 2 , the loading process is performed at different relaxation strains ε i , so there are different εi The platform indicates that the strain remains constant during the relaxation time Δt.
[0038] like Figure 3 As shown, under different relaxation strains ε i Stress relaxation is performed, and within the relaxation time Δt, the stress decreases as time increases.
[0039] like Figure 4 As shown, under different relaxation strains ε i During stress relaxation, the stress decreases with increasing time, so the stress-strain curve will drop vertically at this point. After stress relaxation ends, the stress increases with increasing strain.
[0040] Specifically, step 3 includes steps 31-33.
[0041] Step 31: Take a material sample and begin a tensile or compressive test at the set strain rate. When the strain reaches the first value ε1 of the relaxation strain value sequence, perform the first stress relaxation for a duration Δt. Step 32: Continue the tensile or compressive test at the set strain rate. When the strain reaches the second value ε2 of the relaxation strain value sequence, perform the second stress relaxation for a duration Δt. Step 33: Continue the test as described in Step 32 until the last strain value ε is reached. N The corresponding stress relaxation process.
[0042] Step 4: Analyze the stress-time curve for each stress relaxation process to obtain the relaxation strain ε for each stress relaxation process. i The corresponding stress-plastic strain rate curve.
[0043] Step 5: From each relaxation strain ε i The stress-strain curves corresponding to each strain rate are obtained by analyzing the stress-plastic strain rate curves.
[0044] In this embodiment, the data recorded during the test process includes at least time, strain, and stress, and the data acquisition frequency is greater than or equal to 1Hz.
[0045] In this embodiment, the relaxation strain value sequence ε i The strain values are selected within the maximum force-to-total elongation range of the stress-strain relationship, and the number of values N is greater than or equal to 5; the relaxation strain value sequence ε i The distribution is selected at equal intervals or with increased relaxation strain density in a portion of the strain range.
[0046] In this embodiment, the maximum total elongation at force is the same as the maximum total elongation at force recorded in GB / T228-2002 Standard for Tensile Testing of Metallic Materials at Room Temperature.
[0047] In this embodiment, the stress relaxation time Δt is set according to the strain rate range, and the value range is greater than or equal to 10s.
[0048] In this embodiment, step 4 is specifically: for each relaxation strain value ε i The corresponding stress relaxation stress-time curve is taken, the differential is obtained to obtain the stress rate-time curve; further, the plastic strain rate-time curve is obtained by dividing the stress rate by the Young's modulus of the material multiplied by-1; based on the stress relaxation stress-time curve and the plastic strain rate-time curve, the stress and plastic strain rate data corresponding to the same time are obtained to obtain the relaxation strain value ε i The corresponding stress-plastic strain rate curve.
[0049] In this embodiment, step 5 is specifically: the stress-strain curve corresponding to each relaxation strain ε i The corresponding stress-plastic strain rate curve is obtained to obtain the stress value σ i corresponding to any plastic strain rate. i The curve fitting is performed on the (σ i , ε i ) data set to obtain the stress-strain curve corresponding to this plastic strain rate.
[0050] In an example, as shown in Figures 6-13 , taking a typical titanium alloy as an example:
[0051] The first step is to take a material sample to obtain a stress-strain curve by a quasi-static tensile test as shown in Figure 6 .
[0052] The second step is to analyze the maximum force total elongation strain according to the stress-strain curve of Figure 6 , which is about 0.08, and the relaxation strain value sequence ε i is selected in the range of (0, 0.08). The stress relaxation number N=10, and the corresponding ε i sequence is 0.004, 0.006, 0.008, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07. The single stress relaxation time is 2000s;
[0053] The third step is to take a second sample to perform a tensile test with a stress relaxation process according to the selected relaxation strain value sequence ε i , the engineering strain-time and engineering stress-time curves of the tensile process are shown in Figure 7 , and the corresponding engineering stress-engineering strain curve is shown in Figure 8 .
[0054] The fourth step is to take the true stress-time curve of each stress relaxation process, and calculate the corresponding plastic strain rate
[0055] (1)
[0056] here E is the true stress rate, and E is Young's modulus.
[0057] Relaxing strain For example, the true stress-time curve of its stress relaxation process is as follows: Figure 9 As shown, the true plastic strain rate-time curve calculated according to formula (1) is as follows: Figure 10 As shown, the obtained true stress-true plastic strain rate curve is as follows: Figure 11 As shown.
[0058] Analysis of all stress relaxation curves yielded a sequence of relaxation strain values ε. i The true stress-true plastic strain rate curves corresponding to the strains of each project are summarized as follows: Figure 12 As shown. In Figure 12 Within the range encompassed by the true plastic strain rate, any strain rate value can be taken. Both can obtain the relaxation strain sequence ε i Corresponding true stress sequence .
[0059] True stress sequence Converted into engineering stress sequence and to The strain rate can be obtained by curve fitting of the sequence data. The corresponding engineering stress-strain curves. The engineering stress-strain curves for different strain rates are summarized as follows: Figure 13 As shown.
[0060] It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes that element.
[0061] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural or procedural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the scope of patent protection of the present invention.
Claims
1. A method for measuring strain rate effect of a metallic material based on multiple stress relaxation, characterized by, The method comprises the following steps: Step 1: standard quasi-static tensile or compressive test is carried out on a material sample at a constant strain rate to obtain a stress-strain curve; Step 2: Determine the number of stress relaxation N to be carried out and the corresponding sequence of relaxation strain values ε based on the strain range from the stress-strain curve analysis i , i = 1...N; Step 3: Take a material sample to perform tensile or compressive test at the set strain rate, and then perform stress relaxation for the relaxation time Δt when the strain reaches each value in the sequence of strain values, and then perform tensile or compressive test at the set strain rate after each stress relaxation, until the Nth strain sequence value ε is completed N corresponding to the stress relaxation process of the relaxation time Δt, stop the tensile or compressive test; Step 4: Analysis of the stress-time curve for each stress relaxation process to obtain the relaxation strain ε i the corresponding stress-plastic strain rate curve; Step 5: Stress-Strain Curve from Each Relaxation Strain ε i The stress-strain curve corresponding to each strain rate is obtained from the analysis of the stress-plastic strain rate curves.
2. The method for measuring strain rate effect of metal material based on multiple stress relaxation according to claim 1, characterized in that, The data recorded in the test process at least include time, strain and stress, and the data acquisition frequency is greater than or equal to 1 Hz.
3. The method for measuring strain rate effect of metallic materials based on multiple stress relaxation according to claim 1, characterized in that, said sequence of relaxation strain values ε i selected in the maximum force total elongation strain range of the stress-strain of the material, greater than or equal to 5; said sequence of relaxation strain values ε i The distribution is selected at equal intervals or with increased density of selection of relaxation strain in parts of the strain range.
4. The method for measuring strain rate effect of metallic materials based on multiple stress relaxation according to claim 1, characterized in that, The stress relaxation time Δt is set according to the strain rate range, and the value range is greater than or equal to 10 s.
5. The method for measuring strain rate effect of metallic materials based on multiple stress relaxation according to claim 1, characterized in that, The step 4, in particular, is: for each relaxation strain value ε i The corresponding stress relaxation stress-time curve, taking the differential to obtain the stress rate-time curve; further by the stress rate divided by the Young's modulus of the material multiplied by -1 to obtain the plastic strain rate-time curve; Based on the stress relaxation stress-time curve and the plastic strain rate-time curve, the relaxation strain value ε is obtained by taking the stress and plastic strain rate data corresponding to the same time i The corresponding stress-plastic strain rate curve.
6. The method for measuring strain rate effect of metallic materials based on multiple stress relaxation according to claim 1, wherein, The step 5, specifically: by each relaxation strain ε i The corresponding stress-plastic strain rate curve, the stress value σ i corresponding to any plastic strain rate is obtained i ; Curve fitting is performed on the (σ i , ε i ) data set to obtain the stress-strain curve corresponding to this plastic strain rate.