Method of material tensile testing

Abstract

The application provides a material tensile test method, comprising the following steps: S1, determining an upper limit value of working stress of a test piece; S2, performing a pre-tension unloading test on the test piece under a preset stress not higher than the upper limit value of working stress, and detecting and obtaining a residual strain of the test piece after unloading, and determining that the test piece is qualified when the residual strain is zero; S3, performing a static tensile test on the test piece qualified in the test to detect and obtain a plasticity index of the test piece; wherein the plasticity index at least includes tensile strength and elongation at break. That is, the material stability of the test piece is screened before the static tensile test through steps S1 and S2, that is, whether the test piece appears instability phenomenon is detected in advance, so that the test piece screened qualified enters the subsequent static tensile test, the material performance of the test piece is accurately evaluated, and the defect that the static tensile test is qualified but the working condition appears instability in actual operation is avoided.

Description

Technical Field

[0001] This application relates to the field of materials testing technology, and in particular to a method for tensile testing of materials. Background Technology

[0002] Turbo compressors are widely used in the field of gas compression. Their core structure consists of two main components: the rotor and the stator.

[0003] Currently, in actual industrial production, it has been found that under high-speed, high-pressure, and high-power conditions, and even at low-intensity speeds, some rotor materials lose stability during operation. These materials have often undergone static tensile testing as required, and their yield strength fully meets the usage requirements. This indicates that the rotor material instability occurs before the static tensile test, rendering conventional static tensile testing inadequate for comprehensively evaluating the rotor's material properties.

[0004] Therefore, how to determine whether the rotor material is unstable before the static tensile test and how to test the rotor material to meet the requirements of comprehensive performance evaluation are the problems that this application urgently needs to solve. Summary of the Invention

[0005] The purpose of this application is to provide a material tensile testing method, which aims to solve the problem of how to test the material of a rotor to meet the requirements of comprehensive performance evaluation.

[0006] This application provides a method for tensile testing of materials, including: Step S1: Determine the upper limit of the working stress of the test piece; Step S2: The test piece is subjected to a pre-tension unloading test under a preset stress not exceeding the upper limit of the working stress, and the residual strain of the test piece after unloading is detected and obtained. When the residual strain is zero, the test piece is deemed to be qualified. Step S3: Perform a static tensile test on the test piece that has passed the test to detect and obtain the plasticity index of the test piece; wherein, the plasticity index includes at least tensile strength and elongation after fracture.

[0007] In some embodiments, step S2 includes: A tensile load is applied to the test piece; When the tensile load reaches the preset stress, the test piece is held under the preset stress for a preset time. After the preset time is reached, the tensile load applied to the test piece is unloaded, and the residual strain of the test piece after the tensile load is unloaded to zero is detected. The test piece is deemed to be qualified when the residual strain is zero, and deemed to be unqualified when the residual strain is greater than zero.

[0008] In some embodiments, if the test piece is determined to be unqualified, the material tensile testing method further includes: The unqualified test specimens were subjected to repeated pre-tension unloading tests, and the residual strain of the test specimens was detected and obtained during each pre-tension unloading test. Once the residual strain remains constant, the pre-tension unloading test on the test specimen is stopped. The residual strain variation law of the unqualified test specimen was obtained based on multiple pre-stretch unloading tests.

[0009] In some embodiments, a method for performing a pre-tension unloading test on the test specimen under a preset stress not exceeding the upper limit of the working stress, and detecting and obtaining the residual strain of the test specimen after unloading includes: The test specimen is placed on the pre-tension unloading test device, and a tensile load is applied to the test specimen or the tensile load is unloaded through the pre-tension unloading test device. After the tensile load is unloaded, a strain measuring element is set on the test piece to detect and obtain the residual strain of the test piece.

[0010] In some embodiments, the measurement accuracy of the strain measuring element is not less than 10. -5 .

[0011] In some embodiments, step S3 includes: The test specimen that has passed the test is placed on a static tensile testing device, and static pressure is applied to the test specimen; The plasticity index of the test piece is obtained by measuring and calculating after the test piece is tensilely fractured.

[0012] In some embodiments, the method for placing the qualified test specimen on a static tensile testing device and applying static pressure to the test specimen until it fractures under tension, and then detecting and calculating the plasticity index of the test specimen, includes: The test specimen that has passed the test is placed on the static tensile testing equipment, and static pressure is applied to the test specimen in the elastic stage. The actual strain of the test specimen is obtained by the stress detection element of the static tensile testing equipment, and the elastic modulus is calculated based on the actual strain and the applied stress value. Continue applying pressure, and calculate the elastic strain based on the elastic modulus and the applied stress value. Calculate the plastic strain based on the elastic strain and the detected actual strain; wherein the difference between the actual strain and the elastic strain is the plastic strain. When the plastic strain reaches the preset strain value, the strain detection element is unloaded, and the tensile test piece continues to be stretched until it breaks. The tensile strength and elongation after fracture of the test piece are measured and calculated.

[0013] In some embodiments, the material tensile testing method further includes determining the nominal yield strength of the test piece based on the stress value corresponding to the nominal strain value when the plastic strain of the test piece reaches a nominal strain value lower than a preset strain value.

[0014] In some embodiments, the test specimen that has passed the test is placed on a static tensile testing device, and when static pressure is applied to the test specimen, the static tensile testing device uses a constant displacement speed control method to apply static pressure to the test specimen.

[0015] In some embodiments, the test specimen includes the rotor of a turbine compressor.

[0016] The beneficial effects of this invention are: This application provides a method for tensile testing of materials, including: step S1, determining the upper limit of the working stress of the test piece; step S2, subjecting the test piece to a pre-tension unloading test under a preset stress not exceeding the upper limit of the working stress, and detecting and obtaining the residual strain of the test piece after unloading, and determining that the test piece is qualified when the residual strain is zero; step S3, subjecting the qualified test piece to a static tensile test to detect and obtain the plasticity index of the test piece; wherein, the plasticity index includes at least tensile strength and elongation after fracture.

[0017] In other words, the material tensile testing method of this application screens the material stability of the test piece before the static tensile test through steps S1 and S2. That is, it detects and screens whether the test piece will show instability in advance, ensuring that the test piece that passes the screening enters the subsequent static tensile test for plasticity index testing. That is, it ensures that the test piece does not show instability before the static tensile test. Then, the static tensile test is carried out on the test piece that does not show instability, so as to achieve an accurate evaluation of the material properties of the test piece. This can effectively avoid the defect of related technologies where the static tensile test is qualified but the actual operation is unstable. Attached Figure Description

[0018] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0019] Figure 1 This is a schematic diagram of the process flow for the material tensile testing method shown in the embodiments of this application; Figure 2 This is a schematic diagram of the pre-tension unloading test apparatus used in the material tensile testing method shown in the embodiments of this application; Figure 3 A schematic diagram of the stress-strain curve of the impeller of Example 2 tested using the material tensile testing method shown in the embodiments of this application; Figure 4 This is a schematic diagram of the stress-strain curve of the impeller of Example 3 tested using the material tensile testing method shown in the embodiments of this application; Figure 5 This is a schematic diagram of a test specimen.

[0020] Figure label: 100. Pre-tension test unloading device; 110. Fixture; 200. Strain measuring element; 300. Test piece; 310. Impeller. Detailed Implementation

[0021] In the embodiments of this application, the terms "first," "second," "third," "fourth," "fifth," and "sixth" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined with "first," "second," "third," "fourth," "fifth," and "sixth" may explicitly or implicitly include one or more of that feature.

[0022] In embodiments of this application, 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. Without further limitation, 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.

[0023] Reference Figure 1 As shown in the embodiment of this application, a method for tensile testing of materials is provided, including: Step S1: Determine the upper limit of the working stress of the test specimen; Step S2: The test piece is subjected to a pre-tension unloading test under a preset stress not exceeding the upper limit of the working stress, and the residual strain of the test piece after unloading is detected and obtained. The test piece is deemed qualified when the residual strain is zero. Step S3: Perform a static tensile test on the test piece that has passed the test to detect and obtain the plasticity index of the test piece; wherein, the plasticity index includes at least tensile strength and elongation after fracture.

[0024] In practice, step S1 is a preparation step for the pre-tension unloading test. Specifically, it is used to determine the upper limit of the working stress based on the actual operating parameters of the test piece, ensuring that the upper limit of the working stress does not exceed the theoretical or estimated yield strength of the material itself.

[0025] In step S2, after determining the upper limit of the working stress, a preset stress not higher than the upper limit of the working stress is set to carry out a pre-tension unloading test on the test piece. That is, the test piece is first subjected to pressure tension according to the preset stress and then pressure unloading is performed to complete a pre-tension unloading test, so as to completely replicate the stress loading and unloading process of the test piece in actual work.

[0026] After the pre-tension unloading test, the residual strain of the test specimen is accurately measured, and the instability of the test specimen is determined based on the residual strain. The specific judgment logic is as follows: if the residual strain of the test specimen after unloading is zero, it means that the test specimen has no residual plastic deformation, no internal micro-slip, and no initial stress instability under working stress below the upper limit value. That is, the test specimen is stable before the static tensile test, and the test is deemed qualified. If residual strain exists, it proves that the test specimen already has hidden structural defects, micro-stress concentration, or initial instability problems before the static tensile test. Even if the performance of the subsequent static tensile test meets the standard, the test specimen cannot meet the working condition requirements. This allows for the early screening of unqualified test specimens.

[0027] Therefore, step S2 completely fills the detection blind spot of traditional static tensile test, thus avoiding the phenomenon that the static performance of the test piece meets the standard but the operation is unstable. In this way, it can effectively realize the accurate verification of the initial state of the test piece before the static tensile test.

[0028] It should be noted that since the material of the test specimen is designed in the initial stage to ensure that its upper limit of working stress is less than its theoretical upper limit of stress or estimated yield strength, and the preset stress during the pre-tension unloading test is also less than the upper limit of working stress, the deformation of the test specimen in the above pre-tension unloading test process is theoretically purely elastic. If obvious residual strain appears after unloading, it proves that there is instability in the internal structure of the test specimen. It is necessary to analyze the quality of the test specimen or the heat treatment process to find the cause and prevent the use of test specimens with unstable internal structures in actual operating conditions. If there is no residual strain in the above process, the test specimen can be considered to have passed the test, and the test specimen has always been in the elastic deformation stage, so it can be guaranteed that it will not affect the results of the next static tensile performance test.

[0029] In step S3, the preceding steps S1 and S2 address the initial instability screening of the test specimen. Step S3 then performs a static tensile test to quantitatively detect the macroscopic mechanical properties of the material. Through these steps, both hidden defects that traditional tests cannot identify and the standard mechanical property parameters of the material can be accurately obtained, ultimately achieving dual detection of initial stability and macroscopic performance compliance.

[0030] In summary, the material tensile testing method of this embodiment screens the material stability of the test piece before the static tensile test through steps S1 and S2. That is, it detects and screens whether the test piece will show instability in advance. This ensures that the test piece that passes the screening enters the subsequent static tensile test for plasticity index testing. In other words, it ensures that the test piece does not show instability before the static tensile test. Then, the static tensile test is carried out on the test piece that does not show instability. This ultimately achieves an accurate evaluation of the material properties of the test piece and avoids the defect in related technologies where the static tensile test is qualified but the actual operation is unstable.

[0031] It should be noted that the material tensile testing method in this embodiment can simply and efficiently determine the stability of the internal structure of the test piece, while ensuring that the measurement of mechanical properties such as material strength, elongation after fracture, and plasticity of the test piece is not affected under subsequent static tensile test conditions. When the test piece is the rotor of a turbo compressor, it can provide data support for a comprehensive safety assessment of the rotor operation of the turbo compressor. Furthermore, this method is only applicable to determining the stability of the material itself, including the heat treatment process, but instabilities caused by the rotor during manufacturing processes such as turning, milling, and assembly are not included in this method.

[0032] In some embodiments, step S2 includes: Apply a tensile load to the test specimen; When the tensile load reaches the preset stress, the test piece is held under the preset stress for a preset time. After the preset time is reached, the tensile load applied to the test specimen is unloaded, and the residual strain of the test specimen after the tensile load is unloaded to zero is detected. The test piece is deemed to be qualified when the residual strain is zero, and to be unqualified when the residual strain is greater than zero.

[0033] Specifically, when performing the pre-tension unloading test, firstly, apply a tensile load to the test piece smoothly, using a controllable loading rate to increase the pressure at a uniform speed, avoiding impact loads that could cause artificial damage to the internal structure of the test piece, and ensuring that the loading process conforms to the actual stress state of the equipment.

[0034] Secondly, the tensile load value is monitored in real time. When the tensile load accurately reaches the preset stress that is not higher than the upper limit of the rotor working stress, the load output is stabilized immediately, so that the test piece is kept under the preset stress state for a preset time, that is, pressure holding is performed.

[0035] For example, the test piece is, for instance, the rotor of a turbo compressor. This pressure holding process simulates the core operating condition of the turbo compressor rotor during long-term steady-state service, replicating the rotor's operating state under constant load during actual operation.

[0036] Then, after the preset time has completely ended, all tensile loads are unloaded smoothly and at a constant speed until the load is completely zero, thus eliminating external loading force interference. After the stress on the test specimen is completely released and the state is stable, the specific value of the residual strain of the test specimen is accurately detected and obtained. If the detected residual strain is zero, it proves that the test specimen has no trace plastic deformation and the internal structure is stable, and the test specimen is judged to be qualified; if the residual strain is greater than zero, it indicates that the test specimen has undergone irreversible plastic deformation under the action of working-level stress, and there is a hidden instability defect, and the test specimen is directly judged to be unqualified.

[0037] For example, the preset duration can be 3 to 5 minutes.

[0038] In some embodiments, if the test piece is determined to be unqualified, the material tensile testing method further includes: For unqualified test specimens, the pre-tension unloading test was repeated multiple times, and the residual strain of the test specimens was detected and obtained during each pre-tension unloading test. Once the residual strain remains constant, the pre-tension unloading test on the test specimen is stopped. The residual strain variation law of unqualified test specimens was obtained based on multiple pre-stretch unloading tests.

[0039] In this embodiment, when the test specimen fails the first pre-tension unloading test, it is not directly discarded. Instead, multiple pre-tension unloading tests are repeated, and the residual strain value is recorded after each round of pre-tension unloading test. The pre-tension unloading test is iterated until the residual strain value of multiple consecutive pre-tension unloading tests remains constant and no longer changes. Then the pre-tension unloading test is stopped. Finally, the data from multiple pre-tension unloading tests are integrated to summarize and extract the residual strain change law of the unqualified test specimen.

[0040] It should be noted that when the test specimen is a rotor, in actual industrial scenarios, the residual strain of some rotor materials is not a fixed value. Some materials exhibit stress hardening and gradual stabilization of their microstructure, and the residual strain will gradually decrease until it stabilizes after multiple pre-tension unloading tests. However, for materials with severe material defects or internal damage, the residual strain will remain constant and cannot be eliminated. A single test can only determine that the test specimen is unqualified; it cannot distinguish whether the material is repairably stress-instable or has permanent material defects, nor can it provide data support for material optimization and operating condition adaptation.

[0041] Therefore, this embodiment conducts multiple pre-stretch unloading tests on unqualified test pieces to determine whether the test pieces are repairable or irreparable, thereby providing data for material improvement and heat treatment process optimization, and also providing a reference for the classification and adaptation of rotor materials with different defect levels to working conditions.

[0042] For example, the number of repetitions can be 2-10 times.

[0043] Reference Figure 2 As shown, in some embodiments, the method for performing a pre-tension unloading test on the test specimen under a preset stress not exceeding the upper limit of the working stress, and detecting and obtaining the residual strain of the test specimen after unloading includes: The test specimen 300 is placed on the pre-tension unloading test device 100, and the pre-tension unloading test device 100 applies a tensile load to the test specimen 300 or unloads the tensile load. After the tensile load is unloaded, a strain measuring element 200 is set on the test specimen 300 to detect and obtain the residual strain of the test specimen.

[0044] In practice, the test specimen 300 is first reliably clamped and fixed on the dedicated pre-tension unloading test device 100. The pre-tension unloading test device 100 is used to accurately apply and completely unload the tensile load, ensuring the stability and controllability of the loading and unloading process. After the load is completely unloaded, strain measuring elements 200 are placed at the test points on the test specimen to accurately collect the residual strain data of the test specimen 300.

[0045] Specifically, refer to Figure 2 As shown, the pre-tension unloading test apparatus 100 may include two oppositely arranged clamps 110, with the test specimen 300 clamped between the two clamps 110. The strain measuring element 200 may be, for example, a strain gauge.

[0046] In some embodiments, the measurement accuracy of the strain measuring element is not less than 10. -5 This embodiment utilizes a high-precision strain measurement element to accurately capture minute residual plastic deformations generated in the test piece under working stress, thereby precisely identifying minor instability defects that conventional testing equipment cannot detect, ensuring the accuracy of defect screening from a hardware perspective.

[0047] In some embodiments, step S3 includes: Place the qualified test specimen on the static tensile testing equipment and apply static pressure to the test specimen; The plasticity index of the test piece is obtained by measuring and calculating after the test piece is tensilely fractured.

[0048] In practice, the test specimen that has passed the pre-tension unloading test screening and has no initial instability defects is stably clamped on the static tensile testing equipment, and static pressure loading is continuously applied to the test specimen. The loading continues until the test specimen is completely tensile and fractured. Test data is collected throughout the process, and the core plasticity indicators such as tensile strength and elongation after fracture of the test specimen are accurately calculated through data calculation and dimensional measurement.

[0049] In some embodiments, the method for placing a qualified test specimen on a static tensile testing device and applying static pressure to the specimen until it fractures under tension, and then detecting and calculating the plasticity index of the specimen, includes: The test specimen that has passed the test is placed on a static tensile testing device, and static pressure is applied to the test specimen in the elastic stage. The actual strain of the test specimen is obtained by detecting the stress detection element of the static tensile testing device. The elastic modulus is calculated based on the actual strain and the applied stress value. Continue applying pressure and calculate the elastic strain based on the elastic modulus and the applied stress value. Calculate the plastic strain based on the elastic strain and the actual strain detected. The difference between the actual strain and the elastic strain is the plastic strain. When the plastic strain reaches the preset strain value, the strain detection element is unloaded, and the tensile test piece continues to be stretched until it breaks. The tensile strength and elongation after fracture of the test piece are then measured and calculated.

[0050] In practice, firstly, the test specimens that have passed the pre-tension unloading test screening and have no initial residual instability defects are clamped and fixed, and the static tensile testing equipment is started to carry out static compression in the elastic stage. This static compression in the elastic stage refers to the stage in which the test specimen has not undergone plastic deformation. In this stage, it is necessary to strictly control the compression rate to ensure that the test specimen is always in the pure elastic deformation range and no irreversible plastic deformation occurs.

[0051] Then, using the high-precision stress detection element and strain detection element built into the static tensile testing equipment, the stress value under pressure and the actual strain of the test piece are collected in real time and synchronously. Combining Hooke's law, the true elastic modulus of the material of the test piece is accurately calculated by the ratio of the stress value to the actual strain, thus completing the calibration of the material's basic elastic parameters.

[0052] Next, after calibrating the elastic modulus, progressive pressure is continuously applied to the test specimen, gradually bringing it into the elastoplastic deformation stage. Based on the precisely calibrated elastic modulus and the real-time applied stress value, the theoretical elastic strain corresponding to the current stress value can be accurately calculated. Then, the actual strain of the test specimen is collected in real time using a static tensile testing device. The difference between the actual strain and the theoretical elastic strain is the current true plastic strain of the test specimen, achieving precise separation and independent calculation of elastic strain and plastic strain, effectively distinguishing between recoverable elastic deformation and irreversible plastic deformation of the material.

[0053] Then, when the plastic strain calculated by the test rises to the preset strain threshold, the strain detection element is unloaded and removed, terminating the fine strain monitoring process; subsequently, the static tensile testing equipment continues to maintain tensile loading and continues to perform tensile operations on the test piece until the test piece is completely tensile and fractures.

[0054] Finally, by accurately measuring and calculating the ultimate load at the moment of fracture, the original size of the test piece, and the dimensional changes after fracture, the core plasticity indicators of the test piece, namely tensile strength and elongation after fracture, are obtained, thus completing the entire set of static performance tests.

[0055] Specifically, tensile strength is the ratio of the ultimate maximum tensile load of the test specimen before fracture to the initial cross-sectional area of ​​the test specimen. Elongation after fracture is the percentage of the residual elongation of the test specimen after fracture to the original elongation.

[0056] For example, the preset strain threshold can be 0.0025 mm / mm.

[0057] In some embodiments, the material tensile testing method further includes determining the nominal yield strength of the test piece based on the stress value corresponding to the nominal strain value when the plastic strain of the test piece reaches a nominal strain value lower than a preset strain value.

[0058] Specifically, this embodiment adds a precise testing and calibration process for the nominal yield strength of the test specimen, based on the aforementioned testing process, to improve the evaluation dimension of material yield performance. The specific technical solution is as follows: During the static tensile test, the real-time plastic strain change of the test specimen is continuously monitored. When the plastic strain of the test specimen reaches the nominal strain value which is lower than the preset strain value, the real-time stress value corresponding to the nominal strain value is collected in real time, and the stress value is determined and recorded as the nominal yield strength of the material of the test specimen.

[0059] For example, the nominal strain value is 0.002 mm / mm.

[0060] In some embodiments, the qualified test specimen is placed on a static tensile testing device. When statically pressurizing the test specimen, the static tensile testing device adopts a constant displacement speed control method to statically pressurize the test specimen, keeping the loading rate stable, uniform, and controllable until the test specimen finally breaks. No sudden rate changes, impact loading, speed fluctuations, or other working conditions occur throughout the process, effectively eliminating the interference of the loading rate on the mechanical property test results of the test specimen.

[0061] In summary, the material tensile testing method of this embodiment has the following advantages: (1) The proposed method of measuring residual strain by multiple pre-tension unloading tests can effectively obtain material instability characteristic parameters caused by the combined influence of different factors, and can more comprehensively examine the comprehensive influence of the material in manufacturing and front-end processes.

[0062] (2) In this embodiment, the preset stress during the pre-tensioning test is less than the yield strength of the material, ensuring that the residual strain does not contain plastic strain components, which can more accurately reflect the influence of material instability, and does not affect the subsequent measurement of the material's yield strength, tensile strength, elongation after fracture and other performance indicators.

[0063] (3) The static tensile testing equipment involved in this embodiment is a conventional tensile performance testing equipment. It has strong versatility, simple testing process, low testing technical difficulty and cost, and is suitable for enterprise application.

[0064] Finally, refer to Figures 3 to 5 As shown, with the impeller 310 as the test piece, the material tensile testing method of this embodiment is explained below with reference to the specific examples: Example 1: The impeller 310 is made of 17-4PH steel, with a designed yield strength requirement of 686~827MPa and a preset stress of 640MPa. After a pre-tension unloading test to remove stress, the strain returns to its original point. Then, a static tensile test is performed, and the measured yield strength is 760MPa. In the over-rotation condition before the tensile test in this embodiment, the dimensional deviations of the impeller 310 before and after over-rotation are as follows: outer diameter D: 0.002%; mouth ring d: 0%; inner hole R: 0.003%, meeting the standard requirements.

[0065] Example 2: The impeller 310 is made of FV520B steel, with a design yield strength requirement of <1029MPa and a preset stress of 700MPa. After a pre-tension test, the material exhibits a yield strength of 1.8 MPa. 10⁻⁴ mm / mm, such as Figure 3 As shown, the material was then subjected to a pre-tension test again, with the pre-tension strength set at 700 MPa. After the stress was unloaded in the second pre-tension test, the strain returned to the original point. Then, a static tensile test was performed on the material, and the measured yield strength was 1078 MPa. Before the overspeed test, a 1 mm allowance was left in the inner hole of the impeller 310. The results of the first overspeed test were as follows: the dimensional deviations of the impeller 310 before and after overspeed were: outer diameter D deviation 0.02%; ring diameter d deviation 0.015%; inner hole diameter r deviation 0.0479%. The deviations of the ring diameter and inner hole diameter exceeded the standard requirements. The results of the second overspeed test were as follows: the dimensional deviations of the impeller 310 before and after overspeed were: outer diameter deviation 0%; ring diameter deviation 0%; inner hole diameter deviation 0.006%, which met the standard requirements and satisfied the rotor's operating conditions.

[0066] Example 3: The test plan is the same as Example 2, but the preset stress is set to 700 MPa, refer to... Figure 4 As shown, the material exhibits a strength of 2.8 after the pre-tension test and subsequent unloading. The strength was 10⁻⁴ mm / mm, and after the material underwent a second pre-tension test and unloading, the strength reached 3.2. The strength was 10⁻⁴ mm / mm, and then a third pre-tensile test was conducted on the material. After unloading, the strength was 3.47. 10⁻⁴ mm / mm, such as Figure 3As shown, a static tensile test was then conducted on the material, and the measured yield strength was 1100 MPa. Before the overspeed test, a 1 mm allowance was made for the inner hole of the impeller 310. The results of the first overspeed test were as follows: the outer diameter D of the impeller 310 before and after overspeed was 0.02%; the diameter d of the mouth ring was 0%; and the diameter R of the inner hole was 0.09%. The deviations of the mouth ring diameter and the inner hole diameter exceeded the standard requirements. The results of the second overspeed test were as follows: the outer diameter deviation of the impeller 310 before and after overspeed was 0.015%; the mouth ring diameter deviation was 0%; and the inner hole diameter deviation was 0.03%. It still failed to meet the standard requirements and did not meet the rotor's operating conditions.

[0067] In the description of the embodiments of this application, specific features, structures, materials or characteristics may be combined in any suitable manner in one or more embodiments or examples.

[0068] The above are merely specific embodiments of this application, but the scope of protection of this application is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application.

Claims

1. A method for tensile testing of materials, characterized in that, include: Step S1: Determine the upper limit of the working stress of the test piece; Step S2: The test piece is subjected to a pre-tension unloading test under a preset stress not exceeding the upper limit of the working stress, and the residual strain of the test piece after unloading is detected and obtained. When the residual strain is zero, the test piece is deemed to be qualified. Step S3: Perform a static tensile test on the test piece that has passed the test to detect and obtain the plasticity index of the test piece; wherein, the plasticity index includes at least tensile strength and elongation after fracture.

2. The material tensile testing method according to claim 1, characterized in that, Step S2 includes: A tensile load is applied to the test piece; When the tensile load reaches the preset stress, the test piece is held under the preset stress for a preset time. After the preset time is reached, the tensile load applied to the test piece is unloaded, and the residual strain of the test piece after the tensile load is unloaded to zero is detected. The test piece is deemed to be qualified when the residual strain is zero, and deemed to be unqualified when the residual strain is greater than zero.

3. The material tensile testing method according to claim 2, characterized in that, If the test piece is determined to be unqualified, the material tensile testing method further includes: The unqualified test specimens were subjected to pre-tension unloading tests multiple times, and the residual strain of the test specimens was detected and obtained during each pre-tension unloading test. Once the residual strain remains constant, the pre-tension unloading test on the test specimen is stopped. The residual strain variation law of the unqualified test specimen was obtained based on multiple pre-stretch unloading tests.

4. The material tensile testing method according to claim 1, characterized in that, The method for conducting a pre-tension unloading test on the test specimen under a preset stress not exceeding the upper limit of the working stress, and detecting and obtaining the residual strain of the test specimen after unloading includes: The test specimen is placed on the pre-tension unloading test device, and a tensile load is applied to the test specimen or the tensile load is unloaded through the pre-tension unloading test device. After the tensile load is unloaded, a strain measuring element is set on the test piece to detect and obtain the residual strain of the test piece.

5. The material tensile testing method according to claim 4, characterized in that, The measurement accuracy of the strain measuring element is not less than 10. -5 .

6. The material tensile testing method according to claim 1, characterized in that, Step S3 includes: The test specimen that has passed the test is placed on a static tensile testing device, and static pressure is applied to the test specimen; The plasticity index of the test piece is obtained by measuring and calculating after the test piece is tensilely fractured.

7. The material tensile testing method according to claim 6, characterized in that, The test specimen that has passed the test is placed on a static tensile testing device, and static pressure is applied to the test specimen; The method for detecting and calculating the plasticity index of the test specimen after it has been tensilely fractured includes: The test specimen that has passed the test is placed on the static tensile testing equipment, and static pressure is applied to the test specimen in the elastic stage. The actual strain of the test specimen is obtained by the stress detection element of the static tensile testing equipment, and the elastic modulus is calculated based on the actual strain and the applied stress value. Continue applying pressure, and calculate the elastic strain based on the elastic modulus and the applied stress value. Calculate the plastic strain based on the elastic strain and the detected actual strain; wherein the difference between the actual strain and the elastic strain is the plastic strain. When the plastic strain reaches the preset strain value, the strain detection element is unloaded, and the tensile test piece continues to be stretched until it breaks. The tensile strength and elongation after fracture of the test piece are measured and calculated.

8. The material tensile testing method according to claim 7, characterized in that, The material tensile testing method further includes determining the nominal yield strength of the test piece based on the stress value corresponding to the nominal strain value when the plastic strain of the test piece reaches a nominal strain value lower than a preset strain value.

9. The material tensile testing method according to claim 6, characterized in that, The test specimen that has passed the test is placed on a static tensile testing device. When static pressure is applied to the test specimen, the static tensile testing device uses a constant displacement speed control method to apply static pressure to the test specimen.

10. The method for tensile testing of materials according to any one of claims 1 to 9, characterized in that, The test specimen includes the rotor of a turbine compressor.

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