Method for testing elastic modulus of metal material
By collecting stress and strain results in metal material testing in multiple directions and calculating the average of elastic modulus values at multiple locations, the impact of coaxiality and equipment accuracy on the test results in the prior art is solved, the test accuracy and stability are improved, and the cost is reduced.
Patent Information
- Application Number
- CN202510623140.2
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-05-15
- Publication Date
- 2025-07-25
AI Technical Summary
In the existing elastic modulus testing methods of metal materials, factors such as coaxiality and equipment accuracy lead to large differences in the test results, which affects the accuracy of the test.
The stress and strain results of the sample are collected in multiple directions, and by fixing the electronic extensometer at different positions in the parallel section of the sample, the average value of the elastic modulus at multiple positions is calculated to reduce the impact of the system coaxiality on the test results.
It improves the accuracy of elastic modulus testing of metal materials, reduces the differences in multiple measurement results of materials in the same batch, reduces the testing cost and simplifies the process.
Smart Images
Figure CN120369465A_ABST
Abstract
Description
Technical Field
[0001] The present invention belongs to the technical field of mechanical property testing methods for metal materials, and relates to a method for testing the elastic modulus of metal materials. Background Art
[0002] The elastic modulus of metal materials is one of the important mechanical property parameters of engineering materials. From a macroscopic perspective, it is a measure of the ability of metal materials to resist elastic deformation. From a microscopic perspective, the elastic modulus is a reflection of the interatomic bonding force of metal materials. In industrial production, material selection, and design, it is of great significance to master the elastic modulus of materials. For example, when manufacturing high-precision mechanical parts, materials with a high elastic modulus are required so that the parts can ensure small shape changes under external forces and the machine can operate accurately. In addition, engineering designers can estimate the response of materials under different stress conditions based on the elastic modulus of metal materials, so as to select suitable metal materials for specific engineering structures or products. With the rapid development of new processes and new materials, the characterization and evaluation of material mechanical properties are becoming increasingly important, and higher requirements are put forward for the accuracy of elastic modulus measurement.
[0003] Measuring the elastic modulus of metal materials by the static tension method has the advantages of convenient operation, data traceability, and a large number of existing devices. This method has been widely used in the engineering field. The current GB / T 22315-2008 "Test Methods for Elastic Modulus and Poisson's Ratio of Metal Materials" and GB / T 228.1-2021 "Tensile Testing of Metal Materials - Part 1: Room Temperature Test Methods" are the main methods for testing the elastic modulus of metal materials. GB / T 22315-2008 gives the method for calculating the elastic modulus of metal materials by static tension, and GB / T 228.1-2021 gives the test method for the elastic modulus of metal materials. However, in the actual testing process, affected by factors such as the coaxiality of the testing machine, jaws, specimen processing accuracy, specimen clamping method, tooling selection, testing scheme, and the operation habits of the testing personnel, there will be differences in the test results of the same batch of materials. The main reason is the influence of each testing link on the coaxiality of the testing system. In addition, affected by the structure and stiffness of the testing equipment, the lower the load of the testing machine, the lower the coaxiality of the equipment, and the greater the impact on the test results. Therefore, it is necessary to adopt a simple static tension test method to reduce the influence of system coaxiality on the test results of the elastic modulus. Summary of the Invention
[0004] The purpose of the present invention is to provide a method for testing the elastic modulus of metal materials, which improves the accuracy of the test results of the elastic modulus by collecting the stress and strain results of the specimen from multiple aspects.
[0005] The technical solution adopted by the present invention is a method for testing the elastic modulus of a metal material, which is specifically implemented according to the following steps: Step 1, test the specified plastic extension strength of the material to be tested R p0.2 or the upper yield strength R eH ; Step 2, process the material to be tested into a specimen and measure the diameter of the test section of the specimen; Step 3, zero the force value of the testing machine, clamp the specimen using the jaws, and apply a preload; Step 4, fix the electronic extensometer at the exact left position of the parallel section of the specimen; Step 5, set the test parameters of the testing machine; Step 6, select the stress-strain curve and conduct the first elastic modulus E 1 test; Step 7, measure the elastic modulus when the electronic extensometer is fixed at the exact right, exact front, and exact rear positions of the parallel section of the specimen according to Steps 3-6 E 2, E 3 and E 4, and obtain the E 1, E 2, E 3, E 4 average value, which is the elastic modulus of the metal material E 均 .
[0006] The characteristics of the present invention also lie in: In Step 3, the load accuracy of the testing machine is class 0.5.
[0007] In Step 4, the gauge length of the electronic extensometer is 25 mm or 50 mm, and the accuracy class of the electronic extensometer is class 0.5.
[0008] In Step 4, fix the electronic extensometer on the parallel section of the specimen using a steel clamp or a rubber band.
[0009] The control method in Step 5 is crosshead displacement + extensometer strain, specifically: First, adopt crosshead displacement control, where the rate is set to 1 mm / min, and the termination condition is not exceeding 5% of the load corresponding to the specified plastic extension strength or the upper yield strength of the material; After reaching the preload, conduct extensometer strain control, where the rate is set to: or ; the termination condition is: 50% of the material R p0.2 or 50% R eH corresponding load.
[0010] The data acquisition frequency in Step 5 is set to 20 Hz to 50 Hz.
[0011] Step 6 is specifically as follows: Conduct an elastic modulus test on the specimen according to the test parameters in Step 5, select the stress-strain curve, and end the detection when the stress to be tested reaches 50% R p0.2 or 50% R eH ; then, select two points A and B at the starting and terminal positions of the stress-strain curve to fit a straight line. Among them, point A is selected at a stress of 15% R p0.2 position, and point B is selected at a stress of 40% R p0.2 position, extract the stress and strain values of points A and B, calculate the first elastic modulus test value E 1, and retain 3 significant figures for the test result.
[0012] Step 7 is specifically as follows: Slowly return the test load to zero, keep the specimen jaws clamped, reapply the preload according to Step 3, then fix the electronic extensometer at the right front, right front, and right rear positions of the parallel section of the specimen respectively according to Step 4, and measure the elastic modulus under the three extensometer clamping positions respectively according to the test parameters in Step 5 E 2, E 3, and E 4. Finally, obtain the E 1, E 2, E 3, E 4 average value, which is the elastic modulus of the metal material E 均 .
[0013] The beneficial effects of the present invention are as follows: During the test process of the method of the present invention, in the elastic stage of the specimen, by collecting the stress and strain results of the specimen in multiple directions, the influences on the system coaxiality caused by factors such as equipment precision differences, specimen specifications, specimen clamping methods, tooling precision, and personnel operation habits are eliminated. Furthermore, the influence of coaxiality on the test results is reduced, making the multiple measurement results of the method of the present invention for materials of the same batch stable and with very small differences. Comparing the test results of the method of the present invention with the test results of the dynamic method, the detection results are close.
[0014] In addition, when using the method of the present invention for elastic modulus testing, only an electronic universal testing machine and an electronic extensometer that meet the conventional detection requirements are required, and it is not necessary to use the bilateral extensometer in GB / T 228.1-2021, which reduces the test cost and simplifies the test process. Description of the Drawings
[0015] Figure 1 It is a processing schematic diagram of a smooth specimen with a circular cross-section in the method of the present invention; Figure 2 It is a processing schematic diagram of a threaded specimen with a circular cross-section in the method of the present invention; Figure 3 It is the stress-strain curve of the specimen elastic modulus test in Example 1 of the present invention. Specific embodiments
[0016] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
[0017] The test method for the elastic modulus of the metal material of the present invention is specifically implemented according to the following steps: Step 1, test the specified plastic extension strength ( R p0.2 ) or the upper yield strength ( R eH ) of the material to be tested; Process the material to be tested into a conventional tensile specimen, which meets the relevant requirements for tensile specimens in GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature"; select 3 specimens, and test the specified plastic extension strength or the upper yield strength in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Method of test at room temperature", and take the average value of the test results of the 3 specimens.
[0018] Step 2, process the material to be tested into a specimen required for elastic modulus testing, and measure the diameter of the test section of the specimen; The sampling method of the elastic modulus specimen refers to GB / T 2975-2018. After sampling, process the material into a specimen required for elastic modulus testing, and then use a micrometer to measure the diameters at both ends and the center position of the test section of the specimen respectively. Calculate the original cross-sectional area at each position and take the average value for subsequent elastic modulus calculation. All measuring devices for determining the original cross-sectional area should be calibrated in accordance with relevant standards and traceable to the national measurement system.
[0019] In terms of the specimen structure, the material can be processed into a dumbbell-shaped smooth specimen with a circular cross-section or a threaded specimen with a circular cross-section according to the structure shown in Figure 1 or Figure 2 . Among them, the processing dimensions and requirements of the smooth specimen with a circular cross-section are shown in Table 1, and the processing dimensions and requirements of the threaded specimen with a circular cross-section are implemented according to Figure 2 . The processing of the elastic modulus specimen should be carried out in combination with the original material specifications, testing machine parameters, tooling and other conditions.
[0020] Table 1 Processing dimensions and requirements of smooth specimens with circular cross-sections
[0021] Step 3, start the elastic modulus test, first adjust the force value of the testing machine to zero, then use the jaws to clamp the sample and apply a preload: The test machine used in the test is an electronic universal testing machine with a precision of 0.5 level, which refers to the load precision. The full-scale load range (0.5-100%) is 0.5 level. The test machine must be within the effective measurement cycle, the equipment must meet the use requirements, and traceable to the national measurement system. The test machine is equipped with tooling that meets the test of the sample to be tested, and the test load is within the effective test range. The alloy with lower strength has a lower yield load, resulting in too little data collected in the elastic section. It is recommended to use a test machine with a small range, and the optimal use load is the full load of the test machine (20%-80%).
[0022] After adjusting the force value of the testing machine to zero, use wedge-shaped or threaded jaws to clamp the specimen. If a hydraulic clamp is used, select appropriate hydraulic pressure to avoid damage to the specimen due to excessive extrusion or tensile load, and return the load generated by the specimen during the clamping process to zero in time. For materials with lower hardness, scratches are easily formed at the clamping part. Threaded connections can be used, or the diameter or length of the specimen at the clamping end can be increased. In order to ensure that the specimen is aligned with the chuck and the jaws fit tightly with the specimen, a preload corresponding to no more than 2% of the specified strength is usually applied during the test.
[0023] Step 4: Clamp the sample with an extensometer: The gauge length of the electronic extensometer used in the test is approximately equal to the gauge length of the specimen, and an extensometer with a gauge length of 25mm or 50mm is preferred; the accuracy level of the electronic extensometer is 0.5, and it is measured regularly as required and traceable to the national measurement system; a steel clip or rubber ring is used to fix the electronic extensometer to the parallel section of the specimen, and it is fixed firmly to avoid slipping during the test.
[0024] According to the sample clamping requirements, when the sample is in a taut state, fix the electronic extensometer to the left of the parallel section of the sample, with the extensometer blade perpendicular to the length direction of the sample. After the extensometer is firmly fixed, remove the extensometer positioning pin and reset the indication to zero.
[0025] Step 5, set the test machine control mode, detection rate, termination condition and sampling frequency; Among them, the control method is beam displacement + extensometer strain, specifically: First, the crossbeam displacement control is adopted: rate: 1mm / min; termination condition: not exceeding 5% of the load corresponding to the specified plastic extension strength (or upper yield strength) of the material; Extensometer strain control after preload: Rate: or ; Termination condition: 50% of materialsR p0.2 (or 50% R eH ) corresponding load.
[0026] The data acquisition frequency is set to 20 Hz to 50 Hz.
[0027] Step 6, the first elastic modulus E 1 test: Conduct an elastic modulus test on the specimen according to the test parameters in Step 5. Select the stress-strain curve. When the stress to be tested reaches 50% R p0.2 (or 50% R eH ) end the detection. Then, select two points A and B at the starting and terminal positions of the stress-strain curve to fit a straight line, so that the fitted straight line coincides with the straight line segment of the test curve as much as possible. Among them, point A is selected at the stress of 15% R p0.2 position, and point B is selected at the stress of 40% R p0.2 position. Extract the stress and strain values of points A and B, and calculate the first elastic modulus test value E 1, and retain 3 significant figures for the test result.
[0028] Step 7, slowly return the test load to zero, keep the specimen jaws clamped, re-apply the pre-load according to Step 3, then fix the extensometers at the right front, right front, and right rear positions of the specimen parallel section respectively according to Step 4, and measure the elastic modulus E 2, E 3 and E 4 respectively under the three extensometer clamping positions according to the test parameters in Step 5. Finally, obtain E 1, E 2, E 3, E 4 average value, which is the elastic modulus of this metal material E 均 , that is: E 均 = (E1 + E2 + E3 + E4) / 4 Example 1: (1) Select a conventional grade Al-Si series cast aluminum alloy. After testing, the average value of the specified plastic extension strength ( R p0.2 ) of this material is 240 MPa.
[0029] (2) Select a dumbbell-shaped threaded specimen with a thread specification of M16. The total length of the specimen is 120 mm, the gauge section is Φ10 mm × 60 mm, and the roughness of the parallel section Ra < 0.8 μm.
[0030] (3) The testing machine selected is the MTS E45.305 electronic universal testing machine, with a maximum load of 300 kN for the equipment and a load accuracy class of 0.5 level.
[0031] (4) The MTS 634.25F-24 electronic extensometer is selected for strain control, with a gauge length of 50 mm and an accuracy class of 0.5 level.
[0032] (5) Testing scheme: The displacement + strain control method is adopted during the testing process. Among them, the displacement control rate is 1 mm / min. After reaching the preload of 0.9 kN, strain control is carried out, and the strain rate is 0.00007 s -1 , and the testing is ended when the stress reaches 120 MPa (50% R p0.2 ).
[0033] (6) The elastic modulus of the test bars is tested 4 times respectively. Among them, the clamping positions of the extensometer are at four positions, namely, the directly left side, directly right side, directly front side, and directly rear side of the parallel section of the test bar. The test results are shown in Table 2 and Figure 3 , Figure 3 The fitting line in is the fitting line of the 4th test.
[0034] Table 2 Test results of the elastic modulus of Al-Si series cast aluminum alloy (specimen 1) by the E45.305 testing machine
[0035] Example 2: Using the same method as in Example 1, another dumbbell-shaped threaded specimen of Al-Si series cast aluminum alloy is prepared, and its elastic modulus is tested using the same method as in Example 1. The results are shown in Table 3.
[0036] Table 3 Test results of the elastic modulus of Al-Si series cast aluminum alloy (specimen 2) by the E45.305 testing machine
[0037] Example 3: Using the same method as in Example 1, another dumbbell-shaped threaded specimen of Al-Si series cast aluminum alloy is prepared, and its elastic modulus is tested using the same method as in Example 1. The results are shown in Table 4.
[0038] Table 4 Test results of the elastic modulus of Al-Si series cast aluminum alloy (specimen 3) by the E45.305 testing machine
[0039] Example 4: Select materials from the same batch as in Example 1 and machine a smooth specimen with a circular cross-section according to the dimensions of Specimen No. 1 in Table 1. The testing machine used is INSTRON 68YM-30 with a maximum load of 30 kN, and the extensometer used is INSTRON 2620-601 manual clamping type extensometer with a gauge length of 25 mm. The displacement + strain control method is adopted, where the displacement control rate is 1 mm / min. After reaching the preload, strain control is carried out with a strain rate of 0.00025 s -1 , and the test is ended when the stress reaches 120 MPa (50% R p0.2 ). The extensometer is clamped at four positions on the left, right, front, and rear of the parallel section of the specimen to measure the elastic modulus of the material respectively. The test results are shown in Table 5.
[0040] Table 5 Test results of the elastic modulus of Al-Si series cast aluminum alloy by INSTRON 68YM-30 equipment
[0041] Example 5: Machine the 32Cr13Mo alloy into a tensile test bar according to the dimensions of Specimen No. 2 in Table 1. Select MTS E45.305 and MTS634.25F-24 extensometers with a gauge length of 50 mm. The displacement + strain control method is adopted during the test, where the displacement control rate is 1 mm / min. After reaching the preload, strain control is carried out with a strain rate of 0.00025 s -1 . The extensometer is clamped at four positions on the left, right, front, and rear of the parallel section of the specimen to measure the elastic modulus of the material. The test results are shown in Table 6.
[0042] Table 6 Test results of the elastic modulus of 32Cr13Mo alloy by E45.305 equipment
[0043] In addition, the elastic modulus of the specimen in this example is measured by the dynamic method, and the results are shown in Table 7.
[0044] Table 7 Test results of the dynamic method elastic modulus tester
[0045] Example 6: The Mg-RE alloy was processed into a tensile test bar according to the dimensions of Specimen No. 2 in Table 1. The TSE 305D testing machine was selected, with a load of 300 kN for the testing machine, and the Epsilon 3542-050M-05ST extensometer was selected, with a gauge length of 50 mm for the extensometer. During the testing process, the displacement + strain control method was adopted, where the displacement control rate was 1 mm / min. After reaching the preload, strain control was carried out, and the strain rate was 0.00007 s -1 . The extensometer was clamped at four positions on the left, right, front, and rear of the specimen respectively to test the elastic modulus of the material. The test results are shown in Table 8.
[0046] Table 8 Test results of the elastic modulus of Mg-RE alloy by TSE 305D equipment
[0047] From the test results of Examples 1-6, it can be seen that if the extensometer is only clamped on one side of the specimen for elastic modulus testing, the test results at each position may deviate greatly. As shown in Table 6 E 1 and E 4 have a difference as high as 6.6 GPa. If at this time E 1 or E 4 is taken as the final elastic modulus of the material, the test value may deviate greatly from the actual value. When using the method of the present invention for testing, the extensometer is clamped at the left, right, front, and rear positions of the parallel section of the specimen respectively for testing, and then the average value is taken, which greatly improves the accuracy of the test results. As shown in Tables 6 and 7 of Example 5, the test results of the method of the present invention and the dynamic method are very close.
Claims
1. A method for testing the elastic modulus of a metallic material, characterized in that, The implementation is specifically carried out according to the following steps: Step 1, test the specified plastic elongation strength of the material to be tested R p0.2 or the upper yield strength R eH ; Step 2: Process the material to be inspected into a specimen and measure the diameter of the test section of the specimen. Step 3: Zero the force value of the testing machine, clamp the specimen using the jaws, and apply a preload. Step 4: Fix the electronic extensometer at the exact left position of the parallel section of the specimen. Step 5: Set the test parameters of the testing machine. Step 6, select the stress-strain curve and conduct the first elastic modulus E 1 test; Step 7: Measure the elastic modulus of the extensometer fixed at the positions directly to the right, directly in front of, and directly behind the parallel section of the specimen according to Steps 3 - 6 E 2、 E 3 and E 4, and obtain E 1、 E 2、 E 3、 E the average value of 4, which is the elastic modulus of the metal material E 均 。 2. The test method for the elastic modulus of the metal material according to claim 1, wherein In Step 3, the load accuracy of the testing machine is Class 0.
5.
3. The method for testing the elastic modulus of a metallic material according to claim 1, wherein In Step 4, the gauge length of the electronic extensometer is 25 mm or 50 mm, and the accuracy class of the electronic extensometer is Class 0.
5.
4. The method for testing the elastic modulus of the metal material according to claim 1, wherein In Step 4, fix the electronic extensometer on the parallel section of the specimen using a steel clamp or a rubber band.
5. The method for testing the elastic modulus of the metal material according to claim 1, wherein The control mode in Step 5 is crosshead displacement + extensometer strain, specifically: First, use crosshead displacement control, where the rate is set to 1 mm / min, and the termination condition is not exceeding 5% of the load corresponding to the specified plastic extension strength or the upper yield strength of the material. After reaching the preload, extensometer strain control is carried out, and the rate is set as: or ; The termination condition is: 50% of the material R p0.2 or 50% R eH corresponding load.
6. The method for testing the elastic modulus of the metal material according to claim 5, characterized in that, The data acquisition frequency in Step 5 is set to 20 Hz to 50 Hz.
7. The method for testing the elastic modulus of the metal material according to claim 1, characterized in that, Step 6 is specifically: Test the elastic modulus of the specimen according to the test parameters in Step 5, select the stress-strain curve, and end the detection when the stress to be tested reaches 50% R p0.2 or 50% R eH ; then, select two points A and B at the starting and ending positions of the stress-strain curve to fit a straight line. Among them, point A is selected at the stress of 15% R p0.2 position, and point B is selected at the stress of 40% R p0.2 position, extract the stress and strain values of points A and B, and calculate the first elastic modulus test value E 1, and retain 3 significant figures for the test result.
8. The method for testing the elastic modulus of the metal material according to claim 1, characterized in that Step 7 is specifically: Slowly return the test load to zero, keep the specimen jaws clamped, reapply the preload according to Step 3, then fix the electronic extensometer at the positions directly to the right, directly in front of, and directly behind the parallel section of the specimen respectively according to Step 4, and measure the elastic modulus at the three extensometer clamping positions respectively according to the test parameters in Step 5 E 2、 E 3 and E 4, and finally obtain E 1、 E 2、 E 3、 E 4's average value, which is the elastic modulus of this metal material E 均 。