A method for measuring plastic strain ratio of medium manganese steel

Abstract

This invention provides a method for measuring the plastic strain ratio of medium-manganese steel, including a tensile testing machine, a heating furnace, and an extensometer measurement system. The tensile testing machine clamps the sheet material to be tested and stretches it according to preset parameters. The heating furnace is located outside the sheet material and provides the testing environment according to preset parameters. The extensometer measurement system is used to measure the state or parameters of the sheet material. The advantages of this invention are: a method for measuring the plastic strain ratio of medium-manganese steel using contact strain measurement, which can accurately record deformation data throughout the entire experimental process and avoids experimental errors caused by measuring the lateral displacement of the sheet material after cooling.

Description

Technical Field

[0001] This invention belongs to the field of warm forming process, and in particular relates to a method for measuring the plastic strain ratio of medium manganese steel. Background Technology

[0002] The plastic strain ratio (hereinafter referred to as R value) is the ratio of the true plastic strain in the width direction to the true plastic deformation in the thickness direction of a specimen under uniaxial tensile stress.

[0003]

[0004] In the formula ε a ε is the strain in the thickness direction. b Strain in the width direction;

[0005] Because the deformation along the length is easier to measure than the deformation of a square with a thickness, the plastic strain ratio can be obtained using the principle of constant volume:

[0006]

[0007] The r-value of sheet metal reflects the difference in its deformation capacity between the surface and thickness directions. Generally, when r = 1, the sheet metal is considered isotropic; when r < 1, the sheet metal is stretched, resulting in significant thinning in the thickness direction; and when r > 1, the sheet metal is stretched, with minimal thinning in the thickness direction. The r-value is closely related to stamping performance, especially when the sheet metal has a large r-value, which facilitates tangential shrinkage of the flange during stretch forming, improving the load-bearing capacity of the bottom of deep-drawn parts. For deep-drawn parts, the r-value can reach 1.5, and for ultra-deep-drawn parts, the r-value can reach 2.0.

[0008] Before actual production, accurate finite element simulation plays a crucial role in saving costs and improving development precision. Among them, Autoform, as a mainstream sheet metal stamping simulation software, is widely used in various industries. Its material card parameters include basic physical parameters, thermodynamic parameters, chemical composition, FLC forming limit curve, yield surface parameters, etc. The AF material card includes seven yield criteria such as BBC. The required measurement parameters involve parameters such as anisotropic yield stress, biaxial tension, shear, and plane strain. The r-value, as one of the important parameters, appears in many yield criteria and has a great influence on the yield curve trajectory (yield circle). The elastic region and plastic region of the material are distinguished by the yield circle, so the r-value is an important indicator characterizing the forming performance of the material.

[0009] Currently, the mainstream measurement methods include manual measurement, semi-automatic measurement, and DIC measurement.

[0010] 1. Manual measurement method

[0011] The manual measurement method involves manually measuring the four dimensional parameters b, b0, L, and L0 using measuring tools, and then directly calculating the r value using formula (2).

[0012] 2. Semi-automatic measurement method

[0013] The semi-automatic measurement method uses a longitudinal extensometer system (or device) to automatically measure the gauge length and its change in the length direction of the specimen, while other dimensional parameters are measured manually using measuring tools.

[0014] 3. DIC Measurement Method: The non-contact strain measurement method (DIC technology) is widely used in the mechanical property testing of metal sheets. DIC technology can not only obtain the accurate strain of metal sheets, but also record the strain development history during the deformation process of the sheet, thereby accurately measuring the anisotropy r value of the sheet under uniaxial tension.

[0015] Manual and semi-automatic measurement methods can only record values ​​after cooling, failing to capture the complete stretching process. Furthermore, the material undergoes thermal deformation under significant temperature differences, affecting the accuracy of transverse measurements. While DIC (Dielectric Injection Control) can record the entire experimental process, the hot airflow affects light refraction, impacting its accuracy. Unlike traditional thermoforming materials, medium manganese steel exhibits minimal decarburization during heating, eliminating the need for adding inert gas within the furnace. Its more open environment makes it more suitable for a contact-based, low-cost measurement method. Summary of the Invention

[0016] In view of this, the present invention aims to provide a method for measuring the plastic strain ratio of medium-manganese steel, so as to solve at least one of the problems in the background art.

[0017] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0018] A method for measuring the plastic strain ratio of medium-manganese steel includes a tensile testing machine, a heating furnace, and an extensometer measurement system;

[0019] The sheet material to be tested is held in the clamps of the tensile testing machine, and the sheet material is stretched using the tensile testing machine according to the preset parameters;

[0020] The heating furnace is set on the outside of the sheet material to be tested, and provides the testing environment according to preset parameters;

[0021] An extensometer measurement system is used to measure the condition or parameters of a sheet material.

[0022] Furthermore, the clamps of the tensile testing machine include an upper clamp and a lower clamp, and the upper and lower ends of the sheet metal to be tested are clamped by the upper clamp and the lower clamp, respectively.

[0023] The upper or lower clamp is connected to a power source.

[0024] Furthermore, the heating furnace has a built-in induction heating resistance wire, an inner refractory material layer, and heat insulation material;

[0025] The furnace body of the heating furnace has a split structure, with cross grooves arranged along the transverse and longitudinal directions of the furnace body, through which the extensometer passes.

[0026] Furthermore, a four-axis adjustment bracket is included, on which the furnace body of the heating furnace is mounted.

[0027] Furthermore, the extensometer measurement system includes a transverse extensometer and an axial extensometer, which use strain gauges to measure displacement signals.

[0028] Furthermore, it includes an extensometer support, comprising a first support, a second support, a third support, a first sliding plate, a second sliding plate, and a third sliding plate;

[0029] The third bracket is used to position the transverse extensometer. The first bracket is fixed on the longitudinal beam of the testing machine. The second bracket slides left and right on the first bracket. The first slide plate slides back and forth on the second bracket. The third bracket slides up and down on the first slide plate to complete the spatial positioning of the transverse extensometer.

[0030] The first support, second support, second slide plate, and third slide plate are used to position the axial extensometer. The first support is fixed on the longitudinal beam of the testing machine. The second support slides left and right on the first support. The second slide plate slides back and forth on the second support. The third slide plate slides up and down on the second slide plate, thereby completing the spatial positioning of the axial extensometer.

[0031] Furthermore, the test includes the following steps:

[0032] Start the tensile testing machine, adjust the clamps to the appropriate position and install the specimen, and set the operating parameters of the tensile testing machine;

[0033] Set the heating rate and heating temperature through the heating furnace temperature control system, adjust the heating furnace support so that the cross groove of the heating furnace is parallel to the insertion direction of the extensometer, start the heating furnace, and heat to the set temperature;

[0034] Turn on the heating furnace, adjust the extensometer bracket, position the extensometer in the appropriate position, adjust the transverse extensometer and the axial extensometer, clamp the transverse extensometer in the center width direction of the sample, and clamp the axial extensometer against the gauge length section of the sample, then turn off the heating furnace.

[0035] After the temperature stabilizes, start the tensile testing machine to complete a single test and output the transverse and longitudinal strain data throughout the entire process.

[0036] Furthermore, this solution discloses an electronic device, including a processor and a memory communicatively connected to the processor and used to store executable instructions of the processor, wherein the processor is used to execute a method for measuring the plastic strain ratio of medium manganese steel.

[0037] Furthermore, this solution discloses a server, including at least one processor and a memory communicatively connected to the processor, the memory storing instructions executable by the at least one processor, the instructions being executed by the processor to cause the at least one processor to perform a method for measuring the plastic strain ratio of medium manganese steel.

[0038] A computer-readable storage medium storing a computer program, which, when executed by a processor, implements a method for measuring the plastic strain ratio of medium-manganese steel.

[0039] Compared with existing technologies, the method for measuring the plastic strain ratio of medium-manganese steel described in this invention has the following advantages:

[0040] (1) The method for measuring the plastic strain ratio of medium manganese steel described in this invention uses contact strain measurement, which can accurately record the deformation data of the entire process during the experiment and avoid the experimental error caused by measuring the lateral displacement of the plate after cooling.

[0041] (2) The method for measuring the plastic strain ratio of medium manganese steel described in this invention outputs both transverse strain and longitudinal strain in a single experiment.

[0042] (3) The method for measuring the plastic strain ratio of medium manganese steel described in this invention, compared with the DIC optical strain measurement system, can reduce costs while meeting accuracy requirements. Attached Figure Description

[0043] 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:

[0044] Figure 1 This is a schematic diagram of the overall structure according to an embodiment of the present invention;

[0045] Figure 2 This is a schematic diagram of the heating furnace structure according to an embodiment of the present invention;

[0046] Figure 3 This is a top view schematic diagram of the overall structure according to an embodiment of the present invention;

[0047] Figure 4 This is a partial structural diagram of the heating furnace described in an embodiment of the present invention;

[0048] Figure 5 This is a schematic diagram of the extensometer support structure according to an embodiment of the present invention.

[0049] Explanation of reference numerals in the attached figures:

[0050] 1-Tensile testing machine; 2-Heating furnace; 201-Induction heating resistance wire; 202-Refractory material layer; 203-Insulation material; 204-Cross groove; 3-Heating furnace support; 301-Four-axis adjustment support; 4-Heating furnace temperature control system; 401-Transverse extensometer; 402-Axial extensometer; 403-Ceramic deformation transmission lever; 404-Signal transmission line; 5-Extensometer measurement system; 501-First support; 502-Second support; 503-First slide plate; 504-Third support; 505-Second slide plate; 506-Third slide plate; 6-Extensometer support. Detailed Implementation

[0051] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0052] The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0053] With increasing demands for lightweight design, hot forming has become the primary forming method for large deep-drawn parts. Medium-manganese steel, due to its unique material composition, exhibits lower austenitizing heating temperatures and lower stamping temperatures, making its warm forming process particularly promising. During the forming process of medium-manganese steel, the anisotropy decreases as the sheet temperature increases, but warm forming involves greater deformation and more stringent process parameter requirements. Accurate characterization of the r-value of the sheet at different temperatures is crucial for numerical simulation of sheet hot forming and optimization of sheet forming process parameters.

[0054] This solution provides a fully automatic system for measuring the plastic strain ratio of medium manganese steel, including a tensile testing machine 1, an electromagnetic induction heating furnace 2, a heating furnace support 3, a heating furnace 2 temperature control system, an extensometer measurement system 5, and an extensometer support 6;

[0055] 1. The tensile testing machine 1 used can accurately record force-displacement data during the tensile process, with a force measurement error of less than 1% and a tensile range of 200KN. The punch part of the tensile testing machine 1 can be connected to the dog bar-shaped sample with pins to ensure that the sample is only subjected to axial force during the experiment.

[0056] 2. The structure of the heating furnace 2 used is as follows: Figure 2As shown, the heating furnace 2 has a built-in induction heating resistance wire 201, an inner refractory material layer 202, and an outer heat insulation material 203. The maximum heating temperature is 1500℃. The furnace body adopts a split structure design, with cross-shaped grooves 204 for horizontal and vertical extensometers. The furnace body is mounted on a four-axis adjusting bracket 301, making sample loading and unloading more convenient. Figure 3 As shown, the four-axis adjustment bracket 301 can ensure that the cross groove 204 opened can be parallel to the extensometer direction when the furnace body is adjusted from any position, thus avoiding the phenomenon that the extensometer touches the furnace body and reduces the measurement accuracy.

[0057] The heating furnace 2 temperature control system uses frequency conversion regulation to control the furnace temperature. Temperature sensors are installed inside the furnace to monitor the temperature of various parts of the furnace cavity in real time. When the furnace temperature is much lower than the design temperature (less than 80%), the electromagnetic induction coil heats up normally. When the furnace temperature rises to 80% of the design temperature, the frequency conversion function in the temperature control system will reduce the current intensity, thereby reducing the heating rate inside the furnace and reducing the influence of heating inertia on the temperature.

[0058] 3. The extensometer measurement system 5 consists of a transverse extensometer 401 and an axial extensometer 402. The transverse extensometer 401 is small in size and can clamp the ceramic deformation transmission lever 403 in the width direction of the gauge length of the sample through the internal clamping spring. The axial extensometer 402 has a larger span and can straddle the transverse extensometer 401. The spring inside the extensometer can press the ceramic deformation transmission lever 403 against the sample surface. Both the axial extensometer 402 and the transverse extensometer 401 use strain gauges to measure the displacement signal. The deformation transmission lever causes the elastic element to generate strain, which is converted into a change in resistance by the strain gauge. Then, it is converted into a voltage signal by the measurement amplification circuit. The voltage signal is output through the signal transmission line 404 and the computer analyzes the voltage signal and converts it into a displacement signal.

[0059] 4. Since both the transverse extensometer 401 system and the axial extensometer 402 system are used to measure strain, the sliding support can meet the requirement of simultaneous three-dimensional spatial adjustment of both systems. The extensometer support 6 is composed of a first support 501, a second support 502, a first sliding plate 503, a third support 504, a second sliding plate 505, and a third sliding plate 506.

[0060] The combination of the first bracket 501, the second bracket 502, the first slide plate 503, and the third bracket 504 can position the transverse extensometer 401: the first bracket 501 is fixed on the longitudinal beam of the testing machine, the second bracket 502 can slide left and right on the first bracket 501, the first slide plate 503 can slide back and forth on the second bracket 502, and the third bracket 504 can slide up and down on the first slide plate 503, thereby completing the spatial positioning of the transverse extensometer 401;

[0061] The combination of the first bracket 501, the second bracket 502, the second slide plate 505, and the third slide plate 506 can position the axial extensometer 402: the first bracket 501 is fixed on the longitudinal beam of the testing machine, the second bracket 502 can slide left and right on the first bracket 501, the second slide plate 505 can slide back and forth on the second bracket 502, and the third slide plate 506 can slide up and down on the slide plate, thereby completing the spatial positioning of the axial extensometer 402.

[0062] To meet the need for accurate simulation of medium manganese steel in warm forming, a plastic strain ratio measurement system for medium manganese steel in warm forming was designed, which can measure the plastic strain ratio of medium manganese steel. The system includes a tensile testing machine 1, an electromagnetic induction heating furnace 2, a heating furnace support 3, a temperature control system for the heating furnace 2, an extensometer measurement system 5, and an extensometer support 6.

[0063] Start the tensile testing machine 1, adjust the clamps to the appropriate position and install the sample, and set parameters such as the tensile rate; set the heating rate and heating temperature through the temperature control system of the heating furnace 2, adjust the heating furnace support 3 so that the groove in the heating furnace 2 is parallel to the insertion direction of the extensometer, start the heating furnace 2, and heat to the set temperature; open the heating furnace 2, adjust the extensometer support 6 to position the extensometer in the appropriate position, adjust the transverse extensometer 401 and the axial extensometer 402, with the transverse extensometer 401 clamped in the center width direction of the sample and the axial extensometer 402 pressed against the gauge length section of the sample, and close the heating furnace 2; after the temperature stabilizes, start the tensile testing machine 1 to complete a single experiment and output the transverse and longitudinal strain data throughout the entire process.

[0064] Those skilled in the art will recognize that the units and method steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this invention.

[0065] In the several embodiments provided in this application, it should be understood that the disclosed methods and systems can be implemented in other ways. For example, the division of units described above is merely a logical functional division, and in actual implementation, there may be other division methods. For instance, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. The aforementioned units may or may not be physically separated. The components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of the embodiments of the present invention according to actual needs.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention, and they should all be covered within the scope of the claims and specification of the present invention.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for measuring the plastic strain ratio of medium-manganese steel, characterized in that: Includes a tensile testing machine (1), a heating furnace (2), and an extensometer measuring system (5); The sheet material to be tested is held in the clamp of the tensile testing machine (1), and the sheet material is stretched using the tensile testing machine (1) according to the preset parameters. The heating furnace (2) is set on the outside of the sheet material to be tested, and provides the test environment according to the preset parameters; The extensometer measurement system (5) is used to measure the state or parameters of the sheet material to be measured; the heating furnace (2) has a built-in induction heating resistance wire (201), an inner refractory material layer (202), and a heat insulation material (203); The furnace body of the heating furnace (2) is a split structure, and cross grooves (204) are provided along the transverse and longitudinal directions of the furnace body. The extensometer passes through the cross grooves (204). It also includes a four-axis adjustment bracket (301), on which the furnace body of the heating furnace (2) is mounted. The extensometer measurement system (5) includes a transverse extensometer (401) and an axial extensometer (402). The axial extensometer (402) and the transverse extensometer (401) use strain gauges to measure displacement signals. It also includes an extensometer support (6), comprising a first support (501), a second support (502), a third support (504), a first sliding plate (503), a second sliding plate (505), and a third sliding plate (506). The third bracket (504) is used to position the transverse extensometer (401). The first bracket (501) is fixed on the longitudinal beam of the testing machine. The second bracket (502) slides left and right on the first bracket (501). The first sliding plate (503) slides back and forth on the second bracket (502). The third bracket (504) slides up and down on the first sliding plate (503) to complete the spatial positioning of the transverse extensometer (401). The first bracket (501), the second bracket (502), the second slide plate (505), and the third slide plate (506) are used to position the axial extensometer (402). The first bracket (501) is fixed on the longitudinal beam of the testing machine. The second bracket (502) slides left and right on the first bracket (501). The second slide plate (505) slides back and forth on the second bracket (502). The third slide plate (506) slides up and down on the second slide plate (505), thereby completing the spatial positioning of the axial extensometer (402).

2. The method for measuring the plastic strain ratio of medium-manganese steel according to claim 1, characterized in that: The clamps of the tensile testing machine (1) include an upper clamp and a lower clamp, and the upper and lower ends of the sheet metal to be tested are clamped by the upper clamp and the lower clamp respectively; The upper or lower clamp is connected to a power source.

3. The method for measuring the plastic strain ratio of medium-manganese steel according to claim 1, characterized in that: The test includes the following steps: Start the tensile testing machine (1), adjust the clamp to the appropriate position and install the sample, and set the working parameters of the tensile testing machine (1); The heating rate and heating temperature are set by the temperature control system of the heating furnace (2). The heating furnace support (3) is adjusted so that the cross groove (204) of the heating furnace (2) is parallel to the insertion direction of the extensometer. The heating furnace (2) is started and heated to the set temperature. Turn on the heating furnace (2), adjust the extensometer bracket (6), position the extensometer in a suitable position, adjust the transverse extensometer (401) and the axial extensometer (402), the transverse extensometer (401) is clamped in the center width direction of the sample, and the axial extensometer (402) is pressed against the gauge length section of the sample, and turn off the heating furnace (2). After the temperature stabilizes, start the tensile testing machine (1) to complete a single experiment and output the transverse and longitudinal strain data throughout the process.

4. An electronic device, comprising a processor and a memory communicatively connected to the processor and used for storing processor-executable instructions, characterized in that: The processor is used to execute the method for measuring the plastic strain ratio of medium manganese steel as described in any one of claims 1-3.

5. A server, characterized in that: It includes at least one processor and a memory communicatively connected to the processor, the memory storing instructions executable by the at least one processor, the instructions being executed by the processor to cause the at least one processor to perform a method for measuring the plastic strain ratio of medium manganese steel as described in any one of claims 1-3.

6. A computer-readable storage medium storing a computer program, characterized in that: When the computer program is executed by the processor, it implements the method for measuring the plastic strain ratio of medium manganese steel as described in any one of claims 1-3.

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