Method for determining length of uniform temperature zone of high-temperature tensile sample

Abstract

The invention relates to the technical field of material testing, in particular to a method for determining the length of a uniform-temperature zone of a high-temperature tensile sample, which comprises the following steps of: determining the length of the uniform-temperature zone of the high-temperature tensile sample based on the characteristic that the outer surface of the sample presents a certain taper due to necking of the sample in a high-temperature tensile process; the surface is regarded as a curved surface formed by rotating a curve corresponding to a quadratic function around a symmetry axis of the curve, and the shape of the curved surface is closely related to the necking area of the sample and the radius of the original section of the sample, which corresponds to the continuous change of the diameter of the section of the necking area along with stretching in a high-temperature state of the sample; according to the rule that the volume of the part, participating in deformation, of the sample is not changed before and after deformation, the function relation between the tensile deformation amount and the uniform temperature zone is found, the uniform temperature zone of the sample in the high-temperature tensile state is accurately described, and a good foundation is laid for thermal simulation experiment operation and data analysis.

Description

Technical Field

[0001] This invention relates to the field of materials testing technology, and in particular to a method for determining the length of the uniform temperature zone of a high-temperature tensile specimen. Background Technology

[0002] High-temperature tensile testing can reflect the combined effects of external force and temperature on the properties of metallic materials. In scientific experiments or accident analysis, it is necessary to know the characteristic values ​​and curves of materials at various temperatures, such as maximum stress and true stress-true strain curves. However, generally, tests only provide force values ​​and engineering stress-strain curves at various temperatures, making it difficult to analyze the causes of material deformation and failure. For example, in the continuous casting process of steel, surface cracks often appear on the billet within certain specific temperature ranges. Analyzing the cause of these cracks requires understanding the strength of the billet within that temperature range and the true stress-true strain curve of the billet under tensile stress. This necessitates a corresponding transformation of the high-temperature tensile test results, the key to which lies in the deformation morphology of the specimen during the high-temperature tensile process. The deformation morphology of the specimen during high-temperature tensile testing is closely related to the internal temperature distribution of the specimen.

[0003] Currently, high-temperature tensile tests are mainly conducted using thermal simulation testing machines and material mechanics testing machines, and the high-temperature mechanical properties of materials are studied based on the data from these tests. The Gleeble series thermal simulation testing machine has been increasingly widely used in materials research. It consists of three main parts: a thermal system, a mechanical system, and a computer control system. The thermal system of the Gleeble series thermal simulation testing machine can accurately simulate the heating and cooling processes during material processing; therefore, it is suitable for testing the high-temperature mechanical properties and phase transformation characteristics of metallic materials. During the thermal simulation, the Gleeble series thermal simulation testing machine controls the heating rate of the sample by controlling the magnitude of the current in the sample; and uses clamps and a cooling system with good thermal conductivity to control the cooling rate. In reality, the temperature controlled in the thermal simulation test is the temperature at the thermocouple weld joint in the sample's cross-section, and the temperature distribution within the sample is highly uneven. The homogenized temperature zone near the thermocouple is a key area in the test analysis, and the size of this zone and its influencing factors are crucial for the operation and data analysis of the thermal simulation experiment. Therefore, accurate estimation of the homogenized temperature zone of the sample is necessary. Summary of the Invention

[0004] This invention provides a method for determining the length of the uniform temperature zone of a high-temperature tensile specimen, accurately identifying the uniform temperature zone of the specimen during high-temperature heating, thus laying the foundation for thermodynamic simulation experiments and data analysis.

[0005] To achieve the above objectives, the present invention employs the following technical solution: A method for determining the length of the uniform temperature zone of a high-temperature tensile specimen includes the following steps: S1. A rod-shaped tensile specimen with a circular cross-section is subjected to a high-temperature tensile test. The radius of the circular cross-section of the specimen is... , length is ; S2. Establish a rectangular coordinate system: Select one of the two specimens that broke during the high-temperature tensile test in step S1, and establish a rectangular coordinate system with the straight line containing the diameter of the fracture cross-section circle as the x-axis and the straight line containing the axis of the specimen as the y-axis. S3. Determination of feature length; The total length of the two specimens after the high-temperature tensile test is The total elongation of the sample at tensile fracture is ,but Half of it is ,Right now =2 One segment of the two fractured specimens is analyzed. The difference between the length of this segment and half the elongation of the specimen is the original length of this segment before deformation. The original length of this segment before deformation is half the length of the uniform temperature zone, denoted as... The length of the uniform temperature zone is 2. ; S4. Calculation of the length of the uniform temperature zone: The curve of the side of the fractured specimen in the established rectangular coordinate system, the curve rotated around its axis of symmetry to form a surface, and by utilizing the law that the volume of the deformed part of the specimen remains unchanged before and after deformation, a functional relationship between the tensile deformation and the uniform temperature zone is established: ; in, The radius of the cross-section circle at the fracture location of a section of the selected high-temperature tensile specimen after the test.

[0006] Furthermore, the high-temperature tensile test specifically includes: welding a thermocouple to the middle position of a circular rod-shaped tensile specimen, installing the specimen on a thermal simulation testing machine to conduct a high-temperature tensile test, heating the specimen to a set temperature, holding it at that temperature for a set time, and then stretching it at a set tensile rate at that temperature until the specimen breaks. During the experiment, the force value, the length of the specimen being stretched, and the temperature parameters are collected.

[0007] Furthermore, the curve of the side surface of the fractured specimen in the established rectangular coordinate system has the following equation: ; in, These are undetermined constants; The equation of the curve passes through two points with coordinates of ( , ( ) ,0), ( , + Then, substitute these two data points into the curve equation and solve for the undetermined constants. : ; .

[0008] Furthermore, the volume of the deformed portion of the sample remains unchanged before and after deformation as follows: ; In this equation, the left side is the formula for calculating the volume of half of the uniform temperature zone of the deformed specimen, and the right side is the formula for calculating the volume of this part of the specimen after deformation.

[0009] Compared with the prior art, the beneficial effects of the present invention are: The method described in this invention found the corresponding relationship between the continuous change of the cross-sectional diameter of the necking zone of the specimen under high temperature and the ongoing stretching. Furthermore, by observing the law that the volume of the deformed part of the specimen remains unchanged before and after deformation, a functional relationship between the amount of tensile deformation and the uniform temperature zone was found. This method accurately describes the uniform temperature zone of the specimen under high temperature stretching, laying a good foundation for thermodynamic simulation experiments and data analysis. Detailed Implementation

[0010] The specific embodiments of the present invention will be further described below: The present invention provides a method for determining the length of the uniform temperature zone of a high-temperature tensile specimen, comprising the following steps: S1, High-temperature tensile test; Take a rod-shaped tensile specimen with a circular cross-section, the radius of which is... , length is A thermocouple is welded to the middle of the specimen, and then the specimen is installed on a thermal simulation testing machine for a high-temperature tensile test. The specimen is heated to a temperature T and held for a time t. Then, it is stretched at a tensile rate v at this temperature until the specimen breaks. During the experiment, parameters such as force, the length of the specimen stretched, and temperature are collected.

[0011] S2. Establishment of a rectangular coordinate system; In step S1, the broken specimen is analyzed. One of the two broken specimen segments is selected. A rectangular coordinate system is established with the diameter of the fracture cross-section circle as the x-axis and the axis of the specimen as the y-axis. The side of the broken specimen segment will then show a curve in the established rectangular coordinate system.

[0012] S3. Determination of feature length; After step S1, the tensile specimen fractured into two segments under high temperature tensile stress, with a total length of [missing information]. When the sample breaks under tension, the total elongation is ,but Half of it is ,Right now =2 ; One segment of the two fractured specimens is analyzed. The length of the necking region along the specimen's axial direction represents the portion of the specimen that participates in deformation and is related to the specimen's elongation. The difference between this segment's length and half of the specimen's elongation is the original length of this segment before deformation. The original length of this segment before deformation is half the length of the uniform temperature zone, denoted as... The length of the uniform temperature zone is 2. .

[0013] S4. Calculation of the length of the uniform temperature zone; The diameter of the cross-sectional circle at the selected fracture location of the sample in step S2 is measured, and then the radius of the cross-sectional circle is calculated and denoted as . Next, according to step S2, a rectangular coordinate system is established with the straight line containing the diameter of the fracture cross-section circle as the x-axis and the straight line containing the axis of the specimen as the y-axis. The equation corresponding to the curve of this section of the fractured specimen side surface in the established rectangular coordinate system can be expressed by the following formula: (1) in, These are undetermined constants; The equation of the curve passes through two points with coordinates of ( , ( ) ,0), ( , + Substituting these two data points into formula (1) yields the following formula: (2) (3) By combining equations (2) and (3), the undetermined constants can be solved. : (4) (5) From formulas (4) and (5), it can be seen that the undetermined constants With elongation The length of the uniform temperature zone is 2 and the radius of the cross-section circle at the fracture end of the specimen. Closely related; Based on the principles of calculus, and considering the invariant volume of the tensile specimen before and after deformation in the deformed portion, the following formula applies: (6) The left side of formula (6) is the formula for calculating the volume of half of the uniform temperature zone of the deformed specimen, and the right side is the formula for calculating the volume of this part of the specimen after deformation. Combining formulas (4), (5), and (6), we get: (7) As can be seen from formula (7), the length of the uniform temperature zone of the high-temperature tensile specimen during the heating process is related to the original cross-sectional radius of the high-temperature tensile specimen, the cross-sectional radius of the specimen after fracture, and the elongation of the specimen at the time of fracture.

[0014] This invention is based on the characteristic that the necking of the specimen during high-temperature tensile testing causes the outer surface of the specimen to exhibit a certain taper. This part of the surface is regarded as a curved surface formed by rotating the curve corresponding to a quadratic function around its axis of symmetry. The shape of this curved surface is closely related to the necking region and the original cross-sectional radius of the specimen. This corresponds to the fact that the cross-sectional diameter of the necking region of the specimen changes continuously as the tensile test proceeds under high temperature conditions. Furthermore, by observing the law that the volume of the deformed part of the specimen remains unchanged before and after deformation, a functional relationship between the tensile deformation and the uniform temperature zone was found. This accurately describes the uniform temperature zone of the specimen under high-temperature tensile conditions, laying a good foundation for thermodynamic simulation experiments and data analysis.

[0015] The following embodiments are implemented based on the technical solution of the present invention, providing detailed implementation methods and specific operation processes. However, the scope of protection of the present invention is not limited to the following embodiments. Unless otherwise specified, the methods used in the following embodiments are conventional methods.

[0016] Example 1 The present invention provides a method for determining the length of the uniform temperature zone of a high-temperature tensile specimen, comprising the following steps: S1, High-temperature tensile test; Low-carbon microalloyed steel billets were selected and machined into circular bar-shaped tensile specimens with dimensions of Φ10×125mm. A thermocouple was welded to the center of the specimen. The specimen was then mounted on a thermal simulation testing machine for a high-temperature tensile test. The specimen was heated to 900℃ and held for 180s. Then, at this temperature, a 2×10⁻⁶ ohmmeter was applied. -3 s -1 The sample was stretched at a certain stretching rate until it broke. During the experiment, parameters such as force, the length of the stretched sample, and temperature were collected.

[0017] S2. Establishment of a rectangular coordinate system; In step S1, the broken specimen is analyzed. One of the two broken specimen segments is selected. A rectangular coordinate system is established with the diameter of the fracture cross-section circle as the x-axis and the axis of the specimen as the y-axis. The side of the broken specimen segment will then show a curve in the established rectangular coordinate system.

[0018] S3. Determination of feature length; After step S1, the tensile specimen fractured into two segments under high temperature tensile stress, with a total length of [missing information]. =130mm, when the specimen breaks under tension, the total elongation is =5mm, half of it =2.5mm; One segment of the two fractured specimens is analyzed. The length of the necking region along the specimen's axial direction represents the portion of the specimen that participates in deformation and is related to the specimen's elongation. The difference between this segment's length and half of the specimen's elongation is the original length of this segment before deformation. The original length of this segment before deformation is half the length of the uniform temperature zone, denoted as... The length of the uniform temperature zone is 2. .

[0019] S4. Calculation of the length of the uniform temperature zone; The diameter of the cross-sectional circle at the selected fracture location of the sample in step S2 is measured, and then the radius of that cross-sectional circle is calculated. =3.4mm; According to step S2, take the straight line where the diameter of the fracture section circle is located as the x-axis and the straight line where the axis of the sample is located as the y-axis, establish a rectangular coordinate system, then the equation corresponding to the curve of this fractured sample side in the established rectangular coordinate system can be expressed by formula (1). The equation of the curve passes through two points with coordinates (3.4, 0) and (5, 0). + Substituting these two data points into formula (1) yields the following formula: (8) (9) By combining equations (8) and (9), the undetermined constants can be solved. : (10) (11) From formulas (10) and (11), it can be seen that the undetermined constants In elongation and the radius of the cross-section circle at the end of the specimen fracture Under certain conditions, with a uniform temperature zone length of 2 Closely related; Based on the principles of calculus, and considering the volume invariance of the tensile specimen before and after deformation in the deformed part, we can... Substituting into formula (6), we get: (12) From formula (12), we can obtain mm, then the final calculated uniform temperature zone length is 2 mm.

[0020] Example 2 The present invention provides a method for determining the length of the uniform temperature zone of a high-temperature tensile specimen, comprising the following steps: S1, High-temperature tensile test; Low-carbon microalloyed steel billets were selected and machined into circular bar-shaped tensile specimens with dimensions of Φ10×125mm. A thermocouple was welded to the center of the specimen. The specimen was then mounted on a thermal simulation testing machine for a high-temperature tensile test. The specimen was heated to 1000℃ and held for 180s. Then, at this temperature, a 2×10⁻⁶ ohmmeter was applied. -3 s -1 The sample was stretched at a certain stretching rate until it broke. During the experiment, parameters such as force, the length of the stretched sample, and temperature were collected.

[0021] S2. Establishment of a rectangular coordinate system; In step S1, the broken specimen is analyzed. One of the two broken specimen segments is selected. A rectangular coordinate system is established with the diameter of the fracture cross-section circle as the x-axis and the axis of the specimen as the y-axis. The side of the broken specimen segment will then show a curve in the established rectangular coordinate system.

[0022] S3. Determination of feature length; After step 1, the tensile specimen fractured into two segments under high temperature tensile stress, with a total length of [missing information]. =132mm, the total elongation at tensile fracture of the specimen is =7mm, half of it =3.5mm; One segment of the two fractured specimens is analyzed. The length of the necking region along the specimen's axial direction represents the portion of the specimen that participates in deformation and is related to the specimen's elongation. The difference between this segment's length and half of the specimen's elongation is the original length of this segment before deformation. The original length of this segment before deformation is half the length of the uniform temperature zone, denoted as... The length of the uniform temperature zone is 2. .

[0023] S4. Calculation of the length of the uniform temperature zone; The diameter of the cross-sectional circle at the selected fracture location of the sample in step S2 is measured, and then the radius of that cross-sectional circle is calculated. =2.6mm, and according to step S2, take the straight line where the diameter of the fracture section circle is located as the x-axis and the straight line where the axis of the sample is located as the y-axis to establish a rectangular coordinate system. Then the equation corresponding to the curve of this fractured sample side in the established rectangular coordinate system can be expressed by formula (1). The equation of the curve passes through two points with coordinates (2.6, 0) and (5, 0). + Substituting these two data points into formula (1) yields the following formula: (13) (14) By combining equations (13) and (14), the undetermined constants can be solved. : (15) (16) From formulas (15) and (16), it can be seen that the undetermined constants are... In elongation and the radius of the cross-section circle at the end of the specimen fracture Under certain conditions, with a uniform temperature zone length of 2 Closely related; Based on the principles of calculus, and considering the volume invariance of the tensile specimen before and after deformation in the deformed part, we can... Substituting into formula (6), we get: (17) From formula (17), we can obtain mm, then the final calculated uniform temperature zone length is 2 mm.

Claims

1. A method for determining the length of the uniform temperature zone of a high-temperature tensile specimen, characterized in that, Includes the following steps: S1. A rod-shaped tensile specimen with a circular cross-section is subjected to a high-temperature tensile test until the specimen breaks. The radius of the circular cross-section of the specimen is... , length is ; S2. Establish a rectangular coordinate system: Select one of the two specimens that broke during the high-temperature tensile test in step S1, and establish a rectangular coordinate system with the straight line containing the diameter of the fracture cross-section circle as the x-axis and the straight line containing the axis of the specimen as the y-axis. S3. Determination of feature length; The total length of the two specimens after the high-temperature tensile test is The total elongation of the sample at tensile fracture is ,but Half of it is ,Right now =2 One segment of the two fractured specimens is analyzed. The difference between the length of this segment and half the elongation of the specimen is the original length of this segment before deformation. The original length of this segment before deformation is half the length of the uniform temperature zone, denoted as... The length of the uniform temperature zone is 2. ; S4. Calculation of the length of the uniform temperature zone: The curve of the side of the fractured specimen in the established rectangular coordinate system, the curve rotated around its axis of symmetry to form a surface, and by utilizing the law that the volume of the deformed part of the specimen remains unchanged before and after deformation, a functional relationship between the tensile deformation and the uniform temperature zone is established: ； in, The radius of the cross-section circle at the fracture location of a section of the selected high-temperature tensile specimen after the test.

2. The method for determining the length of the uniform temperature zone of a high-temperature tensile specimen according to claim 1, characterized in that, The high-temperature tensile test specifically includes: welding a thermocouple to the middle position of a circular rod-shaped tensile specimen, installing the specimen on a thermal simulation testing machine to conduct a high-temperature tensile test, heating the specimen to a set temperature, holding it at that temperature for a set time, and then stretching it at a set tensile rate at that temperature until the specimen breaks. During the test, the force value, the length of the specimen being stretched, and the temperature parameters are collected.

3. The method for determining the length of the uniform temperature zone of a high-temperature tensile specimen according to claim 1, characterized in that, The curve of the side surface of the fractured specimen in the established rectangular coordinate system has the following equation: ； in, These are undetermined constants; The equation of the curve passes through two points with coordinates of ( , ( ) ,0), ( , + Then, substitute these two data points into the curve equation and solve for the undetermined constants. : ； 。 4. The method for determining the length of the uniform temperature zone of a high-temperature tensile specimen according to claim 1, characterized in that, The principle that the volume of the deformed portion of the sample remains unchanged before and after deformation is as follows: ； In this equation, the left side is the formula for calculating the volume of half of the uniform temperature zone of the deformed specimen, and the right side is the formula for calculating the volume of this part of the specimen after deformation.

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