Method for calculating elongation of high-temperature tensile sample

Abstract

The invention relates to the technical field of high-temperature tensile experiments, in particular to a method for calculating the elongation of a high-temperature tensile sample, which comprises the following steps of: calculating the elongation of the high-temperature tensile sample on the basis of 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 length before deformation is found out, the characteristic length of the sample before and after high-temperature tensile deformation is accurately found out, and therefore the elongation is accurately calculated, 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 high-temperature tensile testing technology, and in particular to a method for calculating the elongation 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 characteristic curves of materials at various temperatures, such as maximum stress, reduction of area, elongation, and true stress-true strain curves.

[0003] According to the continuous casting process of billets, a thermodynamic simulation testing machine is commonly used. The sample is heated to a high temperature range, held at that temperature for a period of time, then cooled to a certain temperature, and finally subjected to high-temperature stretching at a specific rate until the sample breaks. The cross-sectional area of ​​the broken sample is analyzed to obtain the reduction of area, thus studying the plasticity of the billet during continuous casting. However, in addition to the reduction of area, another parameter reflecting plasticity is the elongation after fracture. Measurements of elongation are generally focused on room temperature tensile tests. Because materials have a certain fluidity at high temperatures, and the temperature distribution of the sample has a certain gradient when heated in a thermodynamic simulation testing machine, not the entire sample participates in the tensile deformation. This is more pronounced in resistance thermodynamic simulation testing machines. If the original length of the entire sample is used when calculating the elongation, a significant error will inevitably occur.

[0004] Patent application number 201110081820.4, entitled "Clamping Device for Measuring Elongation and Reduction of Area of ​​Columnar Tensile Specimens," designs a device to center and fasten the fractured specimens together, and then uses vernier calipers for relevant measurements. This patent addresses the issue of centering and fastening the specimens for subsequent measurements, but it does not consider the problems of temperature and uneven deformation along the length of the specimen. Patents CN200620045221.1, entitled "Rapid Measurement Device for Elongation and Reduction of Area of ​​Circular Specimens," and CN200820020540.6, entitled "Auxiliary Clamping Device for Measuring Specimen Elongation and Reduction of Area," also limit their elongation calculations to room temperature tensile specimens, similarly using the original length of the specimen in the calculation. This will inevitably cause significant deviations when calculating the elongation of high-temperature tensile specimens.

[0005] Therefore, there is currently no effective method for calculating the elongation of high-temperature tensile specimens. Because high-temperature tensile specimens exhibit uneven temperature and deformation at high temperatures, it is not possible to simply calculate the elongation by dividing the difference between the fractured length and the original length by the original length. A more effective and accurate method is needed to determine the elongation of high-temperature tensile specimens. Summary of the Invention

[0006] This invention provides a method for calculating the elongation of a high-temperature tensile specimen. This method can quickly and accurately identify the characteristic length of the specimen before and after high-temperature tensile deformation, thereby accurately calculating the elongation and laying the foundation for the analysis of high-temperature tensile data of materials.

[0007] To achieve the above objectives, the present invention employs the following technical solution: A method for calculating the elongation 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 original length of the entire specimen before deformation. Let's call this segment... The original length of the entire sample before deformation is 2. ; S4. Calculation of elongation: The curve of the side of the fractured specimen in the established rectangular coordinate system, the curve is rotated around its axis of symmetry to form a curved surface. By taking into account the law that the volume of the part of the specimen that participates in the deformation remains unchanged before and after deformation, the formula for calculating the elongation of the specimen is as follows. ; 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.

[0008] 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 and the length of the specimen being stretched are collected.

[0009] 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. : ; .

[0010] 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.

[0011] Based on the characteristic of necking during high-temperature tensile testing, which causes a certain taper on the outer surface of the specimen, this surface is considered as a surface formed by rotating the curve corresponding to a quadratic function around its axis of symmetry. The shape of this surface is closely related to the necking region and the original cross-sectional radius of the specimen. This corresponds to the continuous change in the cross-sectional diameter of the necking region as tensile testing progresses at high temperatures. Furthermore, by observing the constant volume of the deformed portion of the specimen before and after deformation, a functional relationship between the tensile deformation and the original length was found. This accurately identifies the characteristic length of the specimen before and after high-temperature tensile deformation, thereby accurately calculating the elongation. This lays a solid foundation for thermodynamic simulation experiments and data analysis. Compared with the prior art, the beneficial effects of the present invention are: This invention addresses the characteristics of high-temperature tensile specimens, such as uneven temperature and deformation at high temperatures. It enables the rapid and accurate identification of the characteristic lengths of the specimens before and after high-temperature tensile deformation, thereby accurately calculating the elongation and laying the foundation for high-temperature tensile data analysis. Detailed Implementation

[0012] The specific embodiments of the present invention will be further described below: This invention provides a method for calculating the elongation 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.

[0013] 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.

[0014] 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 of the original length of the entire specimen before deformation. Let's assume... The original length of the entire sample before deformation is 2. .

[0015] S4. Calculation of elongation; 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 . Following step S2, a rectangular coordinate system is established with the line containing the diameter of the fracture cross-section circle as the x-axis and the line containing the axis of the specimen as the y-axis. The equation corresponding to the curve of this section of the fractured specimen's side surface within 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 Original sample length 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 constant volume of the tensile specimen before and after deformation, the following formula applies: (6) The left side of formula (6) is the original volume calculation formula for the part of the specimen that participates in deformation, and the right side is the volume calculation formula for the part of the specimen after deformation. Combining formulas (4), (5), and (6), we get: (7) As can be seen from formula (7), the original length of the part of the specimen involved in deformation and the total elongation of the specimen during high-temperature tensile process are determined by the original radius of the specimen and the radius of the fracture cross-section after the specimen breaks. The formula for calculating elongation is derived from formula (7): (8) 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 A method for calculating the elongation of a high-temperature tensile specimen includes 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 of the original length of the entire specimen before deformation. Let's assume... The original length of the entire sample before deformation is 2. .

[0019] S4. Calculation of elongation; 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: (9) (10) By combining equations (9) and (10), the undetermined constants can be solved. : (11) (12) From formulas (11) and (12), it can be seen that the undetermined constants 2 with the original length of the sample 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: (13) The elongation is then calculated using formula (8) as follows: (14).

[0020] Example 2 A method for calculating the elongation of a high-temperature tensile specimen includes 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. The force value and the length of the stretching were collected during the experiment.

[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 S1, 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 of the original length of the entire specimen before deformation. Let's assume... The original length of the entire sample before deformation is 2. .

[0023] S4. Calculation of elongation; 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; 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 (2.6, 0) and (5, 0). + Substituting these two data points into formula (1) yields the following formula: (15) (16) By combining equations (15) and (16), the undetermined constants can be solved. : (17) (18) From formulas (17) and (18), it can be seen that the undetermined constants are... 2 with the original length of the sample 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: (19) The elongation is then calculated using formula (8) as follows: (20).

Claims

1. A method for calculating the elongation 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. 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 original length of the entire specimen before deformation. Let's call this segment... The original length of the entire sample before deformation is 2. ; S4. Calculation of elongation: The curve of the side of the fractured specimen in the established rectangular coordinate system, the curve is rotated around its axis of symmetry to form a curved surface. By taking into account the law that the volume of the part of the specimen that participates in the deformation remains unchanged before and after deformation, the formula for calculating the elongation of the specimen is as follows. ； 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 calculating the elongation 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 experiment, the force value and the length of the specimen being stretched are collected.

3. The method for calculating the elongation 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 calculating the elongation 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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