1. The utility model provides a sheet metal material high temperature FLC testing arrangement under frictionless condition which characterized in that: the clamping mechanism is used for clamping and fixing the plate and dividing the cavity into an upper section and a lower section;

the temperature adjusting mechanism is arranged in a cavity below the plate and used for heating and/or cooling the plate;

the image acquisition mechanism is arranged above the clamping mechanism and used for photographing the plate;

and the pressurizing mechanism is communicated with the opening at the lower end of the cavity and is used for injecting gas into the cavity and enabling the plate to deform and break through the pressure difference between the upper part and the lower part of the plate.

2. The test device of claim 1, wherein: the clamping mechanism comprises an upper module and a lower module, through holes are formed in the upper module and the lower module, and the plate is arranged between the upper module and the lower module.

3. The test device of claim 1, wherein: the temperature adjusting mechanism comprises a heating coil and an air cooling assembly, the heating coil is arranged in the cavity and used for heating the plate, an air outlet of the air cooling assembly faces the plate, and the air cooling assembly is used for cooling the plate.

4. The test device of claim 1, wherein: still include temperature sensor, temperature sensor locates the fixture top, temperature sensor and temperature regulation mechanism electric connection.

5. The test device of claim 1, wherein: the opening at the upper end of the cavity is detachably and hermetically connected with a transparent cover plate.

6. A high-temperature FLC testing method for a metal plate material under a friction-free condition is characterized by comprising the following steps:

(1) etching the plate to form an initial grid;

(2) clamping and fixing the plate by a clamping mechanism;

(3) heating, cooling or insulating the plate by a temperature adjusting mechanism;

(4) the pressurizing mechanism injects gas into the cavity in the clamping mechanism, and the plate is deformed to be broken through the air pressure difference;

(5) the image acquisition mechanism takes pictures of the plate.

7. The test method of claim 6, wherein: and (5) keeping the plate materials under the protection of inert gas all the time in the processes of the steps (3) to (5).

8. The test method according to claim 6, wherein the step (3) is embodied as follows: firstly heating to a certain temperature and preserving heat, and then cooling to a certain temperature and preserving heat.

9. The test method of claim 6, wherein: in the step (4), the air pressure applied by the pressurizing mechanism is 0-20MPa, and the time from the beginning of gas injection of the pressurizing mechanism to the fracture of the plate is less than or equal to 2 s.

10. The test method of claim 6, wherein: the frequency of the pictures shot in the step (5) is more than or equal to 20 frames/s.

Background

The forming limit diagram is an important basis for judging and evaluating the sheet material stamping forming performance, and the material is mainly under the action of tensile stress in the stamping forming process, is thinned and can crack under severe conditions; the localized areas may become compressed, which in severe conditions may lead to wrinkling.

The forming limit curve of the metal sheet material in a room temperature state is tested by the national standard GB/T15825.8-2008 'guide for forming performance and test method of metal sheet-Forming Limit Diagram (FLD) determination': cutting the plate into 10 (at least 3) material slices with different sizes and then carrying out grid printing by an electrochemical method; forming through a standard die until cracking; and processing the grid data strain so as to obtain primary and secondary strains under different strain paths and further obtain a forming limit curve of the plate. However, this method cannot achieve the Forming Limit Curve (FLC) of the slab under high temperature conditions.

Patent publication No. CN 106053259A discloses a thin plate high-temperature forming limit test device, wherein the temperature rise process of the plate material in the device depends on a built-in heating rod in a mould, and the mould is heated to transfer heat to the plate material; however, the heating mode cannot realize the measurement of the forming limit under the conditions that the temperature is firstly increased and then reduced to different temperatures in the hot forming process; and complete austenitizing (about 900 ℃) is needed for heating the 22MnB5 type hot forming steel plate; the mold material and the heating rod are difficult to withstand such high temperatures. The deformation of the plate is realized by drawing the plate by a die, the friction coefficient between the plate and the die is large (the friction coefficient is 0.4-0.6 under the condition of hot forming of a steel plate), the fracture position is not in the middle (the plate at the middle position does not flow), and the corresponding fracture path of the material is changed.

Disclosure of Invention

In view of this, the invention aims to provide a method for testing a high-temperature FLC (flash cycle) of a material under a friction-free condition of a metal plate, so as to avoid the influence of friction on a fracture path of the material and improve the accuracy of a measurement result.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a high-temperature FLC testing device for a metal plate under a friction-free condition comprises a clamping mechanism, wherein a through cavity is arranged in the clamping mechanism, the clamping mechanism is used for clamping and fixing the plate, and the plate divides the cavity into an upper section and a lower section;

the temperature adjusting mechanism is arranged in a cavity below the plate and used for heating and/or cooling the plate;

the image acquisition mechanism is arranged above the clamping mechanism and used for photographing the plate;

and the pressurizing mechanism is communicated with the opening at the lower end of the cavity and is used for injecting gas into the cavity and enabling the plate to deform and break through the pressure difference between the upper part and the lower part of the plate.

The clamping mechanism comprises an upper module and a lower module, the upper module and the lower module are both provided with through holes, and the plate is arranged between the upper module and the lower module; preferably, heat insulation pads are arranged between the plate and the upper module and between the plate and the lower module.

Specifically, temperature regulation mechanism is including locating heating coil and the air-cooled subassembly in the cavity, heating coil is used for heating the sheet material, the air outlet of air-cooled subassembly sets up towards the sheet material, and the air-cooled subassembly is used for making the sheet material cooling.

Specifically, still include temperature sensor, temperature sensor locates the fixture top, temperature sensor and temperature adjustment mechanism electric connection.

Specifically, an opening at the upper end of the cavity is detachably and hermetically connected with a transparent cover plate; preferably, the transparent cover plate is made of glass.

A high-temperature FLC testing method for a metal plate material under a friction-free condition comprises the following steps:

(1) etching the plate to form an initial grid, preferably, mechanically processing and thinning the plate before etching to form a test area, etching the test area of the plate to form the initial grid, and further preferably, the depth of the initial grid is 0.001-0.01 mm;

(2) clamping and fixing the plate by a clamping mechanism;

(3) heating, cooling or insulating the plate by a temperature adjusting mechanism;

(4) the pressurizing mechanism injects gas into the cavity in the clamping mechanism, the plate is deformed to be broken through air pressure difference, preferably, the broken position of the plate is the middle part of the plate and only has one strain peak;

(5) the image acquisition mechanism takes pictures of the plate.

Specifically, the plate is always under the protection of inert gas in the processes of the steps (3) to (5); preferably, the gases blown out by the pressurizing mechanism and the temperature adjusting mechanism are inert gases; further preferably, the inert gas is argon.

Specifically, the step (3) is implemented as follows: firstly heating to a certain temperature and preserving heat, and then cooling to a certain temperature and preserving heat; preferably, the power supply current of the heating coil is 100-1000A, and the power supply frequency is 20-120 KHz.

Specifically, the air pressure applied by the pressurizing mechanism in the step (4) is 0-20MPa, and the time from the beginning of gas injection of the pressurizing mechanism to the fracture of the plate is less than or equal to 2 s.

Specifically, the frequency of the pictures taken in the step (5) is more than or equal to 20 frames/s.

Compared with the prior art, the high-temperature FLC testing method for the metal plate material under the friction-free condition has the following advantages:

(1) compared with the existing high-temperature FLC testing technology, the testing method provided by the invention has the advantages that the plate is deformed until being broken through air pressure driving, and the impact head is not in direct contact with the plate, so that the influence of friction on a material fracture path can be eliminated, and the testing data result is more accurate;

(2) the testing method provided by the invention changes the shape and size of the testing area by processing the plate, controls the strain state before fracture, and is easy to control the temperature and deformation of the plate through the temperature adjusting mechanism, and simple and convenient to operate.

Drawings

The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate an embodiment of the invention and, together with the description, serve to explain the invention and not to limit the invention. In the drawings:

FIG. 1 is a schematic cross-sectional view of a testing apparatus according to an embodiment of the present invention;

fig. 2 is a schematic view of a connection structure between a clamping mechanism and a plate according to an embodiment of the present invention;

FIG. 3 is a schematic diagram of a forming limit curve generated by the testing method according to the embodiment of the present invention.

Description of reference numerals:

1. a plate material; 2. an upper module; 3. a lower module; 4. an air-cooled assembly; 5. a heating coil; 6. a temperature sensor; 7. an image acquisition mechanism; 8. a transparent cover plate; 9. a test zone.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

In the description of the present invention, it is to be understood that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like, indicate orientations or positional relationships based on those shown in the drawings, and are used only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus, are not to be construed as limiting the present invention. Furthermore, the terms "first", "second", etc. are used for descriptive purposes only and are not to be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defined as "first," "second," etc. may explicitly or implicitly include one or more of that feature. In the description of the present invention, "a plurality" means two or more unless otherwise specified.

In the description of the present invention, it should be noted that, unless otherwise explicitly specified or limited, the terms "mounted," "connected," and "connected" are to be construed broadly, e.g., as meaning either a fixed connection, a removable connection, or an integral connection; can be mechanically or electrically connected; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art through specific situations.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

The testing method of the invention is that the testing area 9 of the plate 1 is mechanically processed and thinned; etching the grid by laser; mounting the clamping mechanism into a clamping mechanism for fixing; heating coils 5 and an air cooling assembly 4 are respectively adopted to heat up, rapidly cool down and preserve heat of the plate 1 in the testing area 9; introducing gas into the testing device, and gradually increasing the pressure until the plate 1 is broken; the whole process from deformation to fracture of the plate 1 is shot by an image acquisition mechanism 7 on the outer side of the plate 1; and analyzing the strain state of the plate 1 before fracture to obtain the maximum strain and the minimum strain. According to the method, the deformation of the plate 1 is driven by gas pressure, the clamping mechanism is not in direct contact with the testing area 9 of the plate 1 (forming limit curve, FLC under a friction-free condition), and the strain state before fracture is controlled by changing the shape of the testing area 9 of the plate 1; the temperature and the deformation of the plate 1 are easy to control, and the operation is simple and convenient.

The testing device used in the testing method is shown in fig. 1-2, and comprises a clamping mechanism, wherein a through cavity is arranged in the clamping mechanism, the clamping mechanism is used for clamping and fixing a plate 1, the plate 1 divides the cavity into an upper section and a lower section, the clamping mechanism comprises an upper module 2 and a lower module 3, the upper module 2 and the lower module 3 are both provided with through holes, the plate 1 is arranged between the upper module 2 and the lower module 3, heat insulation pads are arranged between the plate 1 and the upper module 2 as well as between the plate 1 and the lower module 3, an opening at the upper end of the cavity is detachably and hermetically connected with a transparent cover plate 8, and the transparent cover plate 8 is made of glass in the embodiment;

the temperature adjusting mechanism is arranged in a cavity below the plate 1 and used for heating and/or cooling the plate 1, the temperature adjusting mechanism comprises a heating coil 5 and an air cooling assembly 4 which are arranged in the cavity, the heating coil 5 is used for heating the plate 1, an air outlet of the air cooling assembly 4 is arranged towards the plate 1, the air cooling assembly 4 is used for cooling the plate 1, the temperature adjusting mechanism also comprises a temperature sensor 6, the temperature sensor 6 is arranged above the clamping mechanism, and the temperature sensor 6 is electrically connected with the temperature adjusting mechanism;

the image acquisition mechanism 7 is arranged above the clamping mechanism and used for photographing the plate 1;

and the pressurizing mechanism is communicated with the opening at the lower end of the cavity and is used for injecting gas into the cavity and enabling the plate 1 to deform and break through the pressure difference between the upper part and the lower part of the plate 1.

In this example, isothermal FLC curves at 600 ℃, 700 ℃ and 800 ℃ were tested according to the hot forming conditions of 1.5GPa hot formed steel, and a forming performance criterion was provided for the analysis of the hot formed steel stamping process.

Example 1

A, machining and thinning a plate material 1 to be tested with the thickness of 2.0mm to form a test area 9, wherein the test area 9 can be designed into different shapes according to the required strain state, the number of the strain states is not less than 7, at least 3 points of a left quadrant area (the main strain Major strain is greater than 0, and the secondary strain Minr strain is less than 0) and a right quadrant area ((the main strain Major strain is greater than 0, and the secondary strain Minr strain is greater than 0)) are ensured, the thickness of the test area 9 in the embodiment is 1.5mm, and the strain states are 8;

b: carrying out laser etching on a test area 9 of a plate 1 to be tested to obtain an initial grid, and recording size data of the initial grid, wherein the depth of the laser etching grid is 0.001-0.010 mm, and the depth of the grid in the embodiment is 0.005 mm;

c, a plate material 1 to be tested is installed in the clamping mechanism to be fixed and pressed tightly, and heat insulation pads are arranged between the plate material 1 to be tested and the upper module 2 and the lower module 3 of the clamping mechanism; inert gas (argon, helium and the like) is firstly introduced into a cavity between the plate material 1 to be tested and the transparent cover plate 8 and a cavity in the lower module 3 to replace the original air, argon is used in the embodiment, and the argon is always flushed for protection before the test is finished, so that the plate material 1 is prevented from being seriously oxidized in subsequent heating and forming;

d: adopt heating coil 5 and air-cooled subassembly 4 respectively to heat up, rapid cooling and heat preservation to test zone 9 sheet material 1, use in this embodiment for dull and stereotyped induction heating coil 5, it is connected with heating power supply and makes it generate heat for its power supply, heating power supply's supply current is 100 and supplyes 1000A, the power supply frequency range: 20-120 KHZ; the temperature sensor 6 senses the temperature of the test area 9 in real time and sends the temperature to the processor, the processor compares the received temperature data with the set temperature, if the temperature data exceeds the set temperature range, the heating coil 5 or the air cooling assembly 4 is controlled to adjust the temperature, in the embodiment, the temperature is increased to 930 ℃ through the heating coil 5 at the speed of 10 ℃/s, and the temperature is kept for 3 min. Then reducing the temperature to 800 ℃ at a cooling rate of more than 30 ℃/s, and preserving the temperature for 3 s;

e: starting a pressurizing mechanism, introducing gas into a cavity of the lower module 3, gradually increasing the gas pressure P1 in the cavity, and enabling the plate 1 to deform until the plate 1 is broken because the gas pressure difference between the upper surface and the lower surface of the plate 1 is gradually increased, wherein the pressure range of P1 is 0-20MPa, the gas pressure rising speed is 10MPa/S, the deformation of the plate 1 is completed within 2S until the plate 1 is broken, and then closing the pressurizing mechanism and quickly relieving pressure;

f: the image acquisition mechanism 7 at the outer side of the plate 1 shoots the whole process from deformation to fracture of the plate 1, and the shooting frequency is not lower than 20 frames/s;

g: and identifying the size change of the grid before the sheet 1 is broken according to the picture, analyzing the strain state to obtain the maximum strain and the minimum strain, repeating the experiment for 3 times, wherein the breakage position only occurs at the central position of the sheet 1, namely only one strain peak is existed, and if the breakage position is not at the central position of the test area 9 of the sheet 1 or a plurality of strain peaks appear, the test is invalid, and the group of data needs to be removed.

Example 2

The difference from example 1 is that the temperature in step D is reduced to 700 ℃, and the other operation steps are the same as example 1.

Example 3

The difference from example 1 is that the temperature in step D is reduced to 600 ℃, and the other operation steps are the same as example 1.

The FLC curves for the hot formed steels under frictionless conditions measured for examples 1-3 are shown in FIG. 3.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.