Method for testing uniaxial creep threshold value of metal material

Abstract

The invention relates to a method for testing a uniaxial creep threshold value of a metal material, which comprises the following steps of: 1, setting nominal stress, and performing a creep test on a metal material sample based on the nominal stress; step 2, if the creep strain within the preset time is determined to be greater than 1 / 10000, reducing the nominal stress and adopting a new sample to perform the creep test for the preset time again; the step 2 or the step 3 is executed again; 3, determining that the creep strain in the preset time is less than or equal to 1 / 10000, increasing the nominal stress, continuing the creep test in the same preset time, and stopping the test until the creep strain in the preset time is greater than 1 / 10000; and step 4, obtaining the creep threshold value of the sample. According to the invention, the uniaxial creep threshold of the metal material can be rapidly measured, and the test cost is saved.

Description

Technical Field

[0001] The present invention belongs to the technical field of material and component testing, and particularly relates to a method for testing the uniaxial creep threshold of metal materials. Background Art

[0002] Creep is an important phenomenon in material mechanics. Quickly and accurately determining the creep threshold of materials is crucial for the long-term service safety and design of materials and structures. The existing methods for determining the uniaxial creep threshold of metal materials are slow in determination speed and high in cost. Therefore, there is an urgent need to establish a fast and accurate method for testing the creep threshold of materials. Summary of the Invention

[0003] The present invention provides a method for testing the uniaxial creep threshold of metal materials to solve the problems of slow determination speed and high cost in determining the uniaxial creep threshold of metal materials in the prior art.

[0004] To achieve the above object, the present invention relates to a method for testing the uniaxial creep threshold of metal materials, including: Step 1: Set the nominal stress, where the nominal stress is 0.6 to 0.65 times the yield strength of the metal material, and perform a creep test on the metal material specimen based on the nominal stress; Step 2: If it is determined that the creep strain within the preset time is greater than 1 / 10000, reduce the nominal stress and re-perform the creep test for the preset time with a new specimen. The reduction of the nominal stress is to reduce the nominal stress by 0.1 times the yield strength; and then perform Step 2 or Step 3 again; Step 3: If it is determined that the creep strain within the preset time is less than or equal to 1 / 10000, increase the nominal stress by 0.02 times the yield strength, and continue the creep test for the same preset time until it is determined that the creep strain within the preset time is greater than 1 / 10000, then stop the test, where the preset time is not less than 10 h; Step 4: Take the nominal stress at the previous level of the lowest nominal stress with a creep strain greater than 1 / 10000 as the creep threshold of the specimen.

[0005] Preferably, the step of "until it is determined that the creep strain within the time is greater than 1 / 10000, then stop the test" further includes: If it is difficult to accurately judge whether the cumulative creep strain reaches greater than 1 / 10000 during the test, stop the test when the change in creep deformation with time is obvious; or if it is difficult to accurately judge whether the creep strain reaches greater than 1 / 10000 during the test, stop the test when the test stress is 0.86 times the yield strength.

[0006] Preferably, before the nominal stress of the previous stage with a cumulative creep strain greater than 1 / 10000 can be used as the creep threshold of the specimen after the test is stopped, it further includes obtaining the creep strain within the preset time of creep under different nominal stresses based on the obtained creep test data.

[0007] A uniaxial creep threshold testing method for metal materials according to the present invention has the following beneficial effects compared with the prior art: Through this method, the uniaxial creep threshold of metal materials under a given environment can be tested and estimated. The present invention is of great significance for quickly grasping the creep performance of metal materials. This invention patent can quickly determine the uniaxial creep threshold of metal materials, greatly saving the testing cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 It is a flow schematic diagram of a uniaxial creep threshold testing method for a metal material in an embodiment. Figure 1 .

[0009] Figure 2 It is the shape and size (unit: mm) of a tensile creep specimen of Ti80 titanium alloy in an embodiment.

[0010] Figure 3 It is the relationship between creep strain and time within 10 h of creep under different test stress levels in an embodiment. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0011] The present invention will be further described in detail below with reference to the drawings and embodiments. It can be understood that the specific embodiments described herein are only used to explain the present invention, rather than limiting the present invention. In addition, it should be noted that only parts related to the present invention rather than all structures are shown in the drawings for the sake of description.

[0012] Embodiment

[0013] A uniaxial creep threshold testing method for metal materials. Please refer to Figure 1 , As Figure 1 shown, a uniaxial creep threshold testing method for metal materials according to the present invention is used for testing the uniaxial creep threshold of metal materials and includes the following steps: S101 to S104.

[0014] S101 Set the nominal stress, where the nominal stress is 0.6 to 0.65 times the yield strength of the metal material, and conduct a creep test on the metal material specimen based on the nominal stress.

[0015] Conduct a creep test on the specimen of the metal material, specifically including: conducting a uniaxial creep threshold test on the metal material.

[0016] In some embodiments, the nominal stress is 0.65 times the yield strength of the metallic material.

[0017] S102 If it is determined that the creep strain within the preset time is greater than 1 / 10000, reduce the nominal stress and re-perform the creep test for the preset time with a new specimen. The reduction in the nominal stress is to reduce the nominal stress by 0.1 times the yield strength; and then perform step 2 or step 3 again.

[0018] S103 If it is determined that the creep strain within the preset time is less than or equal to 1 / 10000, increase the nominal stress by 0.02 times the yield strength and continue the creep test for the same preset time until it is determined that the creep strain within the preset time is greater than 1 / 10000, then stop the test, where the preset time is not less than 10 h.

[0019] S104 Take the nominal stress at the level before the lowest nominal stress with a creep strain greater than 1 / 10000 as the creep threshold of the specimen.

[0020] In this embodiment, until it is determined that the creep strain within this time is greater than 1 / 10000 and the test is stopped, it further includes: If it is difficult to accurately judge whether the cumulative creep strain is greater than 1 / 10000 during the test, stop the test when the change in the creep deformation amount with time is obvious; or if it is difficult to accurately judge whether the cumulative creep strain is greater than 1 / 10000 during the test, stop the test when the test stress is 0.86 times the yield strength. Stopping the experiment when the experimenter observes that the change in the creep deformation amount with time is obvious is beneficial to facilitating the experimental operation and reducing the calculation amount for judging the creep strain.

[0021] In this embodiment, S101 sets the nominal stress between 0.6 and 0.65 times the yield strength of the metallic material, and it further includes: S105 Obtain the yield strength of the metallic material by means of a uniaxial test.

[0022] In this embodiment, after S103 stops the test and before S104 can take the nominal stress at the level before the lowest nominal stress with a creep strain greater than 1 / 10000 as the creep threshold of the specimen, it further includes S106 Based on the obtained creep test data, obtain the creep strain within the creep preset time under different nominal stresses.

[0023] To better illustrate the solution of the present invention, the following takes the uniaxial tensile creep threshold test of a Ti80 titanium alloy specimen at room temperature as an example, as Figure 2 shown, including the following steps: First, the tensile yield strength σs of Ti80 titanium alloy was obtained as 811.66 ± 16.8 MPa through a uniaxial tensile test. The nominal stress was selected as 0.65 times the tensile yield strength, the creep time was selected as 10 h, and the nominal stress increment was selected as 0.02 times the yield strength.

[0024] Then, the uniaxial tensile creep threshold test of Ti80 titanium alloy specimens at room temperature was carried out. An electronic tensile testing machine RDL-100 was used for the creep test, and the specimens are as Figure 2 shown. During the test, an extensometer was used to record the creep deformation, and the change degree of the creep deformation amount with time increase under different test stresses was observed. When the nominal stress was 0.83σs, the creep deformation amount increased significantly with time, and the test was stopped. The obtained test data were processed to obtain the relationship between creep strain and time within 10 h of creep under different test stress levels, as Figure 3 shown.

[0025] From Figure 3 it can be seen that when the nominal stress was between 0.65σs and 0.73σs, the creep strain within 10 h of creep was less than 1 / 10000. When the nominal stress was 0.75σs, the creep strain within 10 h of creep was greater than 1 / 10000. Therefore, the creep threshold of this specimen was 0.73σs, that is, 592.5 MPa.

[0026] It should be noted that in this article, the term "including", "comprising" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements not only includes those elements, but also includes other elements not expressly listed, or also includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "including a..." does not exclude the existence of another identical element in the process, method, article or device including that element.

[0027] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structure or equivalent process transformation made by using the content of the specification and drawings of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A method for testing the uniaxial creep threshold of a metallic material, characterized in that, Including: Step 1: Set the nominal stress, which is 0.6 to 0.65 times the yield strength of the metal material, and conduct a creep test on the metal material specimen based on the nominal stress. Step 2: If it is determined that the creep strain within the preset time is greater than 1 / 10000, reduce the nominal stress and re-conduct the creep test for the preset time using a new specimen. The reduction of the nominal stress is to reduce the nominal stress by 0.1 times the yield strength; and then execute Step 2 or Step 3 again. Step 3: If it is determined that the creep strain within the preset time is less than or equal to 1 / 10000, increase the nominal stress by 0.02 times the yield strength and continue the creep test for the same preset time until it is determined that the creep strain within the preset time is greater than 1 / 10000, then stop the test, where the preset time is not less than 10 h. Step 4: Take the nominal stress at the previous level of the lowest nominal stress with a cumulative creep strain greater than 1 / 10000 as the creep threshold of the specimen.

2. The uniaxial creep threshold test method for a metal material according to claim 1, characterized in that The step of stopping the test when it is determined that the creep strain within the time is greater than 1 / 10000 further includes: If it is difficult to accurately judge whether the creep strain is greater than 1 / 10000 during the test, stop the test when the change in creep deformation with time is obvious, or if it is difficult to accurately judge whether the creep strain is greater than 1 / 10000 during the test, stop the test when the test stress is 0.86 times the yield strength.

3. A uniaxial creep threshold testing method for a metal material according to claim 2, characterized in that Before setting the nominal stress to be 0.6 to 0.65 times the yield strength of the metal material, it further includes: Obtain the yield strength of the metal material by using a uniaxial test.

4. According to the method for testing the uniaxial creep threshold of a metal material as claimed in claim 1, characterized in that After stopping the test, before taking the nominal stress at the previous level of the lowest nominal stress with a creep strain greater than 1 / 10000 as the creep threshold of the specimen, it further includes obtaining the creep strain within the preset time under different nominal stresses based on the obtained creep test data.

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