A method of determining the elastic limit of a corrosion-resistant titanium alloy material
By performing stress-relief annealing on titanium alloy materials and accurately measuring the stress-strain curves, the tangent modulus-strain relationship is calculated, and the elastic limit of titanium alloy materials is determined. This solves the problem of large calculation errors in existing technologies and ensures the safety and accuracy of titanium alloy structural components.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA SHIPBUILDING INDUSTRY CORPORATION NO725 RESEARCH INSTITUTE
- Filing Date
- 2026-04-14
- Publication Date
- 2026-06-05
Smart Images
Figure CN122149999A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of mechanical property testing technology for metallic materials, and more specifically, to a method for determining the elastic limit of corrosion-resistant titanium alloy materials. Background Technology
[0002] Titanium alloys possess advantages such as low density, high specific strength, non-magnetic properties, and corrosion resistance, making them widely used in the manufacture of various precision structural components. In practical engineering applications, the complex and variable service environment can lead to overload in components within a short period, causing localized plastic deformation. This plastic deformation can result in compression between adjacent precision components, creating an interference fit. Furthermore, titanium alloys are highly sensitive to stress; plastic deformation can lead to residual stress within the component, altering its mechanical properties and corrosion resistance, thus affecting the safe operation of the component. Therefore, accurately determining the critical point between elastic and plastic deformation in titanium alloys remains a significant challenge in current engineering applications.
[0003] GB / T 228 specifies that the stress value corresponding to the stress axis when the tangent of the angle between the tangent on the stress-strain curve and the stress axis increases by 50% compared to the tangent of the angle between the straight portion of the stress-strain curve and the stress axis is the specified proportional limit of the material. In engineering, this value is usually used as the critical point between the elastic deformation and plastic deformation of the material. However, in practical applications, this method is greatly affected by the skill level of the testers, the accuracy of the measuring equipment, and the material properties, and the test results vary greatly.
[0004] Kang Yaming (Kang Yaming, Jia Yan, Niu Sheng, et al. Correlation between peak value of secant modulus and elastic limit of metallic materials [J]. Journal of Shenyang University of Technology, 2019, 41(1):42-46.) found that there is a certain correlation between the secant modulus and elastic limit of carbon steel during the tensile process, and the elastic limit is numerically close to the upper yield strength of the material. The peak value in the secant modulus-strain curve was used as the elastic limit point. The study found that this method is only applicable to materials with obvious yield and obvious peak value of secant modulus. For titanium alloy materials without obvious yield or without peak value of secant modulus, this method is not applicable.
[0005] Although there are existing studies on the elastic limit of metallic materials, these studies have large errors and are applicable to a limited range of materials, making them unsuitable for effectively calculating the elastic limit of titanium alloys. Therefore, establishing a test method for the elastic limit of titanium alloys is of great significance for ensuring the safe service of titanium alloy structural components. Summary of the Invention
[0006] In view of this, the present invention aims to propose a method for determining the elastic limit of corrosion-resistant titanium alloy materials, in order to solve the problem that the calculation results of the elastic limit of metallic materials, especially titanium alloy materials, in the prior art have large errors and are applicable to a limited number of materials, and cannot be used to effectively calculate the elastic limit of titanium alloy materials.
[0007] To achieve the above objectives, the technical solution of the present invention is implemented as follows:
[0008] A method for determining the elastic limit of corrosion-resistant titanium alloy materials includes the following steps:
[0009] Step 1: Process the titanium alloy material to be tested into a standard tensile specimen and perform stress-relief annealing.
[0010] Step 2: Perform tensile property tests on the standard tensile specimens after stress-relief annealing and obtain the corresponding test results;
[0011] Step 3: Calculate the tangent modulus based on the test results to obtain the tangent modulus under different strain conditions;
[0012] Step 4: Determine the strain point corresponding to the elastic limit based on the test results and the tangent modulus;
[0013] Step 5: Determine the elastic limit value in the stress-strain curve based on the strain point corresponding to the elastic limit.
[0014] Furthermore, in step one, a titanium alloy material with uniform composition is selected for testing.
[0015] Furthermore, in step one, the processed standard tensile specimen is placed in a high-temperature furnace for stress-relief annealing, wherein the stress-relief annealing conditions are 500~700℃ for 2~3 hours.
[0016] Furthermore, in step two, a tensile testing machine with an accuracy of not less than 0.5 is used to test the tensile properties of the stress-relieved annealed standard tensile specimen at a constant strain rate, and an extensometer with an accuracy of not less than 0.5 is used to measure the stress-strain curve of the standard tensile specimen throughout the tensile process.
[0017] Furthermore, in step two, the test results shall at least include the stress-strain curve and the stress R at a plastic elongation of 0.2%. p0.2 , elastic modulus.
[0018] Furthermore, in step three, the formula for calculating the tangent modulus is shown in equation (1):
[0019] ,
[0020] Among them, E iLet σ be the tangent modulus at point i on the stress-strain curve, i=1……n; （1） The stress point at the initial moment of the stress-strain curve; ε （1） The strain point at the initial moment of the stress-strain curve; σ （i+1） ε represents the (i+1)th stress point on the stress-strain curve; （i+1） Let be the (i+1)th strain point on the stress-strain curve.
[0021] Furthermore, in step four, based on the test results and the tangent modulus, a relationship curve between the tangent modulus and strain is plotted to obtain the tangent modulus-strain curve. An elastic modulus line is then plotted on the tangent modulus-strain curve. The strain corresponding to the intersection of the elastic modulus line and the tangent modulus-strain curve is the strain point of the elastic limit.
[0022] Furthermore, in step five, based on the strain point corresponding to the elastic limit determined in step four, an iso-strain line is drawn on the stress-strain curve in step two. The stress corresponding to the intersection of the iso-strain line and the stress-strain curve is the elastic limit of the titanium alloy material.
[0023] Compared with existing technologies, the method for determining the elastic limit of corrosion-resistant titanium alloy materials described in this invention has the following advantages:
[0024] (1) By using the experimental method established in this invention, the elastic limit of titanium alloy materials with no obvious yield phenomenon can be calculated, providing theoretical support for ensuring the design and safe service of titanium alloy precision structural parts.
[0025] (2) The obtained elastic limit has high accuracy and small error. Attached Figure Description
[0026] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:
[0027] Figure 1 The engineering stress-strain curves of specimens 1 and 2 of this invention are shown below.
[0028] Figure 2 This shows the intersection of the isoelastic modulus line and the tangent modulus-strain curve of sample 1 of the present invention.
[0029] Figure 3 This shows the intersection of the isoelastic modulus line and the tangent modulus-strain curve of sample 2 of the present invention.
[0030] Figure 4 This shows the intersection of the iso-strain line and the stress-strain curve of specimen 1 of the present invention.
[0031] Figure 5 This shows the intersection of the iso-strain line and the stress-strain curve of sample 2 of the present invention. Detailed Implementation
[0032] The present invention will be further described below with reference to specific embodiments. First, it should be noted that the data in the following experimental examples were obtained by the inventors through numerous experiments. Due to space limitations, only a portion of these data is shown in the specification, and those skilled in the art can understand and implement the present invention based on this data. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the contents of this invention, those skilled in the art can make various modifications or alterations to the invention, and these modifications or alterations also fall within the scope of protection of this application.
[0033] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.
[0034] This invention proposes a method for determining the elastic limit of corrosion-resistant titanium alloy materials, comprising the following steps:
[0035] Step 1: Process the titanium alloy material to be tested into a standard tensile specimen and perform stress-relief annealing.
[0036] Step 2: Perform tensile property tests on the standard tensile specimens after stress-relief annealing and obtain the corresponding test results;
[0037] Step 3: Calculate the tangent modulus based on the test results to obtain the tangent modulus under different strain conditions;
[0038] Step 4: Determine the strain point corresponding to the elastic limit based on the test results and the tangent modulus;
[0039] Step 5: Determine the elastic limit value in the stress-strain curve based on the strain point corresponding to the elastic limit.
[0040] Specifically, in step one, a titanium alloy material with uniform composition is preferred to improve the accuracy of the test. The alloy material to be tested is processed into standard tensile specimens according to the relevant requirements in GB / T 228.1, and the processed standard tensile specimens are placed in a high-temperature furnace for stress-relief annealing to eliminate the influence of work hardening on the stress-strain curve. The stress-relief annealing conditions are 500~700℃ for 2~3 hours.
[0041] In step two, a tensile testing machine with an accuracy of at least 0.5 is used to test the tensile properties of the stress-relieved annealed standard tensile specimens at a constant strain rate. An extensometer with an accuracy of at least 0.5 is used to measure the stress-strain curve of the standard tensile specimens throughout the tensile process. The test results include at least the stress-strain curve and the stress R at a plastic elongation of 0.2%. p0.2 , elastic modulus.
[0042] The strain rate during tensile property testing is determined based on the operator's experience and the dimensions of the standard tensile specimen.
[0043] In step three, the formula for calculating the tangent modulus is shown in equation (1):
[0044]
[0045] Among them, E i Let σ be the tangent modulus at point i on the stress-strain curve, i=1……n; （1） The stress point at the initial moment of the stress-strain curve; ε （1） The strain point at the initial moment of the stress-strain curve; σ （i+1） ε represents the (i+1)th stress point on the stress-strain curve; （i+1） Let be the (i+1)th strain point on the stress-strain curve.
[0046] In step four, based on the test results and the tangent modulus, a relationship curve between the tangent modulus and strain is plotted to obtain the tangent modulus-strain curve. An elastic modulus line is then plotted on the tangent modulus-strain curve. The strain corresponding to the intersection of the elastic modulus line and the tangent modulus-strain curve is the strain point of the elastic limit.
[0047] In step five, based on the strain point corresponding to the elastic limit determined in step four, an iso-strain line is drawn on the stress-strain curve in step two. The stress corresponding to the intersection of the iso-strain line and the stress-strain curve is the elastic limit of the titanium alloy material.
[0048] This invention obtains stress-strain data and related mechanical parameters by conducting tensile property tests on titanium alloy materials with uniform composition. Based on the measured data, the tangent modulus of the stress-strain curve is calculated to obtain the tangent modulus-strain curve. The elastic modulus strain point and elastic limit value are then determined based on the measured elastic modulus and the tangent modulus-strain curve. This invention has wide applicability and can even calculate the elastic limit of titanium alloy materials with insignificant yielding phenomena. Furthermore, the method used to calculate the elastic limit of titanium alloy materials has high accuracy, providing theoretical support for ensuring the safe service of precision titanium alloy structural components. Testing has shown that this invention has been applied to the elastic limit testing of various titanium alloy materials with good results.
[0049] Example 1
[0050] Two homogeneous TC4 materials were selected as the titanium alloy materials to be tested, and were designated as Sample 1 (1#) and Sample 2 (2#) respectively.
[0051] Step 1: Samples 1 and 2 are processed into standard circular tensile specimens with a parallel section diameter of 5 mm according to the relevant requirements in GB / T 228.1. The surface quality of the standard circular tensile specimens is then inspected to ensure that the processing quality meets the standard requirements. Subsequently, the qualified specimens are placed in a high-temperature furnace and held at 600℃ for 2 hours for stress-relief annealing to eliminate the influence of work hardening on the stress-strain curve test.
[0052] Step 2: Using an electronic universal testing machine with an accuracy of not less than 0.5, apply a 0.00025s pressure to the stress-relieved annealed standard round tensile specimen. -1 Tensile properties were tested at the strain rate, and the stress-strain curves of the specimens throughout the tensile process were measured using an extensometer with an accuracy of 0.5. The results are as follows: Figure 1 As shown, the R of the material is determined based on the measured stress-strain curve. p0.2 Parameters such as elastic modulus.
[0053] Step 3: Calculate the tangent modulus of the measured stress-strain curve according to formula (1) to obtain the tangent modulus of TC4 material under different strain conditions during the tensile process.
[0054] Step 4: Plot the relationship curve between the tangent modulus and strain, and draw an isoelastic modulus line on the tangent modulus-strain curve. The strain corresponding to the intersection of the isoelastic modulus line and the tangent modulus-strain curve is the strain point of the elastic limit. The intersection of the isoelastic modulus line and the tangent modulus-strain curve of sample 1 is as follows. Figure 2 As shown, the intersection points of the isoelastic modulus line and the tangent modulus-strain curve of sample 2 are as follows: Figure 3 As shown.
[0055] Step 5: Based on the strain point corresponding to the determined elastic limit, draw an isostrain line on the measured stress-strain curve. The stress corresponding to the intersection of the isostrain line and the stress-strain curve is the elastic limit of the material. The intersection of the isostrain line and the stress-strain curve for sample 1 is shown below. Figure 4 As shown, the intersection points of the iso-strain lines and the stress-strain curve of specimen 2 are as follows: Figure 5 As shown.
[0056] The tensile properties of specimens 1 and 2 are shown in Table 1.
[0057] Table 1
[0058]
[0059] To verify the accuracy of the elastic limits of specimens 1 and 2 determined by the method of this invention, the stress-relieved annealed specimens 1 and 2 obtained in step one were subjected to tensile deformation at 90%, 100%, and 110% of the elastic limit strain determined in step four, respectively. Electron backscattering (EBSD) was used to observe the specimens after tensile deformation under different strain conditions. The EBSD observation results show that after tensile deformation at 90% of the elastic limit strain, there was no obvious plastic deformation inside specimens 1 and 2, indicating that they were in the elastic deformation stage. After tensile deformation at 100% of the elastic limit strain, there was a small amount of plastic deformation inside specimens 1 and 2, indicating that the two specimens began to transition from elastic deformation to plastic deformation. After tensile deformation at 110% of the elastic limit strain, there was a large amount of plastic deformation inside the two specimens, indicating that the two specimens had entered the plastic deformation stage during the tensile process.
[0060] Therefore, the elastic limit of TC4 material determined by the method of the present invention is effective, and the method established by the present invention can be used to determine the elastic limit of titanium alloy materials.
[0061] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.
Claims
1. A method for determining the elastic limit of corrosion-resistant titanium alloy materials, characterized in that, Includes the following steps: Step 1: Process the titanium alloy material to be tested into a standard tensile specimen and perform stress-relief annealing. Step 2: Perform tensile property tests on the standard tensile specimens after stress-relief annealing and obtain the corresponding test results; Step 3: Calculate the tangent modulus based on the test results to obtain the tangent modulus under different strain conditions; Step 4: Determine the strain point corresponding to the elastic limit based on the test results and the tangent modulus; Step 5: Determine the elastic limit value in the stress-strain curve based on the strain point corresponding to the elastic limit.
2. The method according to claim 1, characterized in that, In step one, a titanium alloy material with uniform composition is selected for the experiment.
3. The method according to claim 1, characterized in that, In step one, the processed standard tensile specimen is placed in a high-temperature furnace for stress-relief annealing. The stress-relief annealing conditions are 500~700℃ for 2~3 hours.
4. The method according to claim 1, characterized in that, In step two, a tensile testing machine with an accuracy of not less than 0.5 is used to test the tensile properties of the stress-relieved annealed standard tensile specimen at a constant strain rate, and an extensometer with an accuracy of not less than 0.5 is used to measure the stress-strain curve of the standard tensile specimen throughout the tensile process.
5. The method according to claim 1, characterized in that, In step two, the test results shall include at least the stress-strain curve and the stress R when the plastic elongation is 0.2%. p0.2 , elastic modulus.
6. The method according to claim 1, characterized in that, In step three, the formula for calculating the tangent modulus is shown in equation (1): ， Among them, E i Let σ be the tangent modulus at point i on the stress-strain curve, i=1……n; （1） The stress point at the initial moment of the stress-strain curve; ε （1） The strain point at the initial moment of the stress-strain curve; σ （i+1） ε represents the (i+1)th stress point on the stress-strain curve; （i+1） Let be the (i+1)th strain point on the stress-strain curve.
7. The method according to claim 1, characterized in that, In step four, based on the test results and the tangent modulus, a relationship curve between the tangent modulus and strain is plotted to obtain the tangent modulus-strain curve. An elastic modulus line is then plotted on the tangent modulus-strain curve. The strain corresponding to the intersection of the elastic modulus line and the tangent modulus-strain curve is the strain point of the elastic limit.
8. The method according to claim 1, characterized in that, In step five, based on the strain point corresponding to the elastic limit determined in step four, an iso-strain line is drawn on the stress-strain curve in step two. The stress corresponding to the intersection of the iso-strain line and the stress-strain curve is the elastic limit of the titanium alloy material.