CN117347188A - Low-temperature fracture toughness test method for metal material - Google Patents
Low-temperature fracture toughness test method for metal material Download PDFInfo
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- 239000007769 metal material Substances 0.000 title claims abstract description 31
- 238000007656 fracture toughness test Methods 0.000 title abstract description 27
- 238000012360 testing method Methods 0.000 claims abstract description 203
- 239000007788 liquid Substances 0.000 claims abstract description 134
- 239000002826 coolant Substances 0.000 claims abstract description 108
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- 229910052757 nitrogen Inorganic materials 0.000 claims description 29
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical group CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 claims description 16
- 150000001335 aliphatic alkanes Chemical class 0.000 claims description 12
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/20—Investigating strength properties of solid materials by application of mechanical stress by applying steady bending forces
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F25—REFRIGERATION OR COOLING; COMBINED HEATING AND REFRIGERATION SYSTEMS; HEAT PUMP SYSTEMS; MANUFACTURE OR STORAGE OF ICE; LIQUEFACTION SOLIDIFICATION OF GASES
- F25D—REFRIGERATORS; COLD ROOMS; ICE-BOXES; COOLING OR FREEZING APPARATUS NOT OTHERWISE PROVIDED FOR
- F25D3/00—Devices using other cold materials; Devices using cold-storage bodies
- F25D3/10—Devices using other cold materials; Devices using cold-storage bodies using liquefied gases, e.g. liquid air
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/02—Details
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0023—Bending
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/02—Details not specific for a particular testing method
- G01N2203/022—Environment of the test
- G01N2203/0222—Temperature
- G01N2203/0228—Low temperature; Cooling means
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The utility model relates to the technical field of low-temperature fracture toughness tests of metal materials, in particular to a low-temperature fracture toughness test method of a metal material. A low-temperature fracture toughness test method for a metal material comprises the following steps: s100, preparing a liquid cooling medium, and injecting the liquid cooling medium into a low-temperature tank; s200, placing the test piece into a low-temperature tank for heat preservation; s300, loading a test piece, and recording and storing the load and change data of a COD gauge; s400, unloading and taking out the test piece. The low-temperature fracture toughness test method for the metal material has the advantages that the liquid cooling medium cools the test piece uniformly, the heat conductivity is high, the cooling time is saved, the compression roller meets the relevant standard, and the test between-196 ℃ and-100 ℃ is effectively realized.
Description
Technical Field
The utility model relates to the technical field of low-temperature fracture toughness tests of metal materials, in particular to a low-temperature fracture toughness test method of a metal material.
Background
Liquefied natural gas (Liquefied Natural Gas, LNG) is a cryogenic liquid formed by compressing natural gas, cooling to a condensation point temperature, re-vaporizing when in use, and the same mass of liquefied natural gas has a volume of about 1/625 of the volume of gaseous natural gas, so LNG is a highly efficient, clean fossil energy source and has wide use worldwide. LNG is generally stored and transported by a storage tank at the temperature of-162 ℃ and the pressure of 0.1MPa, the contact material of the inner layer of the storage tank is usually 9 percent Ni steel or high manganese austenitic steel (high manganese steel), and the steel for low temperature has strict requirements on mechanical property, fatigue property and fracture property. Fracture toughness reflects the ability of a crack-containing material to resist crack propagation when loaded, and defects (e.g., inclusions, weld defects, cracks, etc.) that inevitably occur in the material during production, processing, service, are approximated to cracks in the material, and therefore the fracture toughness of the load-bearing material must be tested and evaluated. The fracture toughness of the material is generally considered to be reduced along with the reduction of the temperature, and the fracture toughness of the material under the low-temperature condition is tested and researched for the material for low temperature, so that the material has very important engineering significance for the safe service of the material.
According to the existing fracture toughness testing standards (GB/T21143-2014, ISO 12135:2021, ASTM E1820-23), the three-point bending test sample and the compact tensile test sample can be used for testing the fracture toughness of materials, wherein the three-point bending test sample has the characteristics of simple loading, strong device universality and the like, and can be widely applied to the fracture toughness testing in the fields of ships, petroleum pipelines, pressure vessels and the like. The test standard indicates that for the ambient temperature test, the test should be performed in a low temperature medium, and the temperature deviation should be controlled within + -2 ℃. There are many methods and apparatuses for low temperature fracture toughness test of metallic materials, for example, chinese patent publication No. CN 202720153U uses an apparatus similar to a low temperature environment test box, and application of low temperature environment (No. 100 c) is achieved by introducing liquid nitrogen into the box, then vaporizing and cooling and mixing air. The scheme uses an air medium, the temperature uniformity and the fluctuation degree can be affected by the air flow to a certain extent, and the heat conduction efficiency of the air medium is lower than that of a liquid medium, so that the air medium needs longer cooling time. Chinese utility model patent publication No. CN 217212005U uses a water tank to Cheng Fangdi a temperature medium, and the low temperature medium used is alcohol or liquid nitrogen. When the test temperature approaches the melting point of alcohol (-115 ℃ to-100 ℃), the alcohol becomes viscous and is not easy to flow; below the melting point (-115 ℃) of alcohol, alcohol solidifies; the temperature of the pure liquid nitrogen is-196 ℃, so that the method is suitable for the low-temperature fracture toughness test with the test temperature of-196 ℃ and-100 ℃ to room temperature. The device in the method does not consider the problem of cooling medium flow, uneven temperature distribution is easy to occur, and the compression roller in the method is embedded and installed and does not meet the requirements of fracture toughness test standard GB/T21143-2014 and other related standards. In other scientific research papers, most of the low-temperature fracture toughness tests are carried out in liquid nitrogen at a low temperature higher than-100 ℃ or at-196 ℃, and few test results are about the temperature between-196 ℃ and-100 ℃ and no low-temperature environment application method is described.
Disclosure of Invention
In view of the above, the present utility model aims to provide a low-temperature fracture toughness test method for metal materials, which is characterized in that a temperature sensor is provided to monitor the temperature of a liquid cooling medium, a load is applied to a test piece through a loading device and a lower clamping piece through a tester, two loading components of the loading device apply loads to the test piece, opposite loads are applied to the lower clamping piece, the change states of cracks are recorded through a COD gauge, and liquid cooling mediums with different temperature ranges are prepared through absolute alcohol, alkane liquid, alkene liquid and liquid nitrogen, so that the problems that the temperature uniformity and fluctuation degree of the air medium are affected by air flow to a certain extent, the heat conduction efficiency of the air medium is lower than that of the liquid medium, long cooling time is required, the temperature distribution of the cooling medium is uneven, and a compression roller does not meet the requirements of fracture toughness test standard GB/T21143-2014 and other related standards, and the test method is not recorded between-196 ℃ to-100 ℃ are solved.
In order to solve the above problems, the present utility model provides a method for testing low-temperature fracture toughness of a metal material, comprising:
s100, injecting liquid cooling medium into the low-temperature tank, wherein the liquid cooling medium comprises a first cooling medium, a second cooling medium and a third cooling medium;
the temperature range of the first cooling medium is a first low temperature range T 1 ；
The second cooling medium is formed by adding liquid nitrogen into the first liquid material, and the temperature range of the second cooling medium is a second low temperature range T 2 ；
The third cooling medium is formed by adding a second liquid substance into the second cooling medium, and the temperature range of the third cooling medium is a third temperature range T 3 ；
Wherein T is 1 ＞T 2 ＞T 3 ；
Selecting the liquid cooling medium according to test requirements;
s200, placing a test piece into a liquid cooling medium, continuously adding liquid nitrogen in the heat preservation process, and monitoring the temperature of the liquid cooling medium until reaching a preset test temperature required by a test, and preserving the heat of the test piece to ensure that the thickness of the test piece per millimeter is at least preserved for 30S;
s300, supporting the lower part of the test piece through a lower supporting part, applying acting force on two positions of the test piece in the length direction through a loading device above the test piece, wherein the two positions of the applied acting force are symmetrical relative to the supporting position, arranging a COD gauge on the upper part of the test piece, applying relative load to the lower supporting and loading device through a testing machine, and recording and storing load and change data of the COD gauge through the testing machine;
s400, unloading the load applied by the testing machine when the load reaches the maximum value or the sample breaks, and taking out the test piece.
Further, in step S100, the method includes:
the first cooling medium is absolute alcohol, so that the temperature range T of the first cooling medium 1 ≥-100℃；
The method for preparing the second cooling medium comprises the following steps: liquid nitrogen is added into alkane liquid to ensure that the temperature range of the liquid cooling medium is-100 ℃ to be more than T 2 ≥-160℃；
The method for preparing the third cooling medium comprises the following steps:
adding liquid nitrogen to the alkane liquid, adding the alkene liquid when the temperature drops to-50 ℃, and continuing to add liquid nitrogen to a temperature T 3 ＜-160℃。
Further, in preparing the second cooling medium and the third cooling medium, stirring was continued by a stirrer.
Further, in step S200, the method includes:
when the test piece is placed in the liquid cooling medium, the surface of the test piece protrudes from the liquid level of the liquid cooling medium, and the protruding part height H is 0mm < H < 8mm.
Further, in step S200, the method includes:
during the incubation, stirring was continued by the stirrer.
Further, in step S200, the method includes:
at the temperature T of the liquid cooling medium m With a test preset temperature T t Gradually reducing the injection amount of liquid nitrogen when the temperature difference delta T between the two is less than 5 ℃ until the injection amount meets the requirement＜2℃。
Further, in step S200, the method includes:
the whole heat preservation time of the test piece is ensured to be not less than 15min.
Further, the test method according to any one of the above performs a low-temperature fracture toughness test of a metal material on a test apparatus comprising:
a low temperature tank into which a liquid cooling medium is injected;
the lower clamping piece is connected with the bottom of the low-temperature groove;
the loading device is provided with two loading components, and the distance between the two loading components is adjustable;
the lower clamping piece and the loading device are connected with the testing machine;
the temperature sensor is arranged at a position 0-5mm away from the crack tip of the test piece;
the COD gauge is arranged at the position of the crack notch;
and the stirrer is arranged in the low-temperature tank.
Further, the loading device further includes:
the upper clamping piece is connected with the testing machine, and a chute is arranged on one side of the upper clamping piece, which is opposite to the testing machine;
the loading assembly includes:
the sliding block is connected with the sliding groove in a sliding manner;
and the compression roller is connected with the sliding block through a spring, the two springs extend in the deviating direction, and the load loaded by the testing machine acts on the test piece through the two compression rollers.
Further, the low-temperature fracture toughness test method of the metal material further comprises the following steps:
the lower support piece is fixed at the bottom in the low-temperature groove, and the upper end part of the lower support piece is arc-shaped;
the bearing piece comprises a body and a handle connected with the body.
Compared with the prior art, the low-temperature fracture toughness test method for the metal material has the following advantages:
the technical scheme has the advantages that the temperature of the liquid cooling medium is monitored by the temperature sensor, the load is applied to the test piece through the loading device and the lower clamping piece by the test machine, the load is applied to the test piece through the two loading components of the loading device, the opposite load is applied to the lower clamping piece, the change state of cracks is recorded through the COD gauge, the liquid cooling medium in different temperature ranges is prepared through absolute ethyl alcohol, alkane liquid, alkene liquid and liquid nitrogen, the cooling of the liquid cooling medium to the test piece is uniform, the heat conductivity is high, the cooling time is saved, the compression roller accords with related standards, and the test between-196 ℃ to-100 ℃ is effectively realized.
Drawings
FIG. 1 is a flow chart of a method of testing the low temperature fracture toughness of a metallic material according to an embodiment of the present utility model;
FIG. 2 is a schematic diagram of a low temperature fracture toughness testing apparatus for metallic materials according to an embodiment of the present utility model;
FIG. 3 is a dimensional view of a low temperature fracture toughness test piece of a metallic material according to an embodiment of the present utility model;
FIG. 4 is a graph showing load-notch displacement curves of test pieces 1-3 at room temperature according to an embodiment of the present utility model;
FIG. 5 is a graph showing load-notched displacement curves at-165℃for test pieces 4-6 according to an embodiment of the present utility model.
Reference numerals illustrate:
10-low temperature groove, 20-loading device, 21-upper clamping piece, 211-chute, 22-slide block, 23-compression roller, 24-spring, 30-supporting device, 31-lower supporting piece, 32-lower clamping piece, 40-liquid cooling medium, 50-temperature sensor, 60-COD gauge, 70-bearing piece, 80-stirrer and 90-test piece.
Detailed Description
In order that the above objects, features and advantages of the utility model will be readily understood, a more particular description of the utility model will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings.
The description of "first," "second," "upper," "lower," etc. in this disclosure is for descriptive purposes only and is not to be construed as indicating or implying a relative importance or the number of technical features indicated. Thus, a feature defining "first", "second", "upper", "lower" may include at least one such feature, either explicitly or implicitly. In addition, the technical solutions of the embodiments may be combined with each other, but it is necessary to be based on the fact that those skilled in the art can implement the combination between the embodiments, and all the technical solutions are within the scope of protection claimed by the present utility model.
The utility model will be described in detail below with reference to the drawings in connection with embodiments.
As shown in fig. 1, a method for testing low-temperature fracture toughness of a metal material includes:
s100, injecting liquid cooling medium into the low-temperature tank, wherein the liquid cooling medium comprises a first cooling medium, a second cooling medium and a third cooling medium;
the temperature range of the first cooling medium is a first low temperature range T 1 ；
The second cooling medium is formed by adding liquid nitrogen into the first liquid material, and the temperature range of the second cooling medium is a second low temperature range T 2 ；
The third cooling medium is formed by adding a second liquid substance into the second cooling medium, and the temperature range of the third cooling medium is a third temperature range T 3 ；
Wherein T is 1 ＞T 2 ＞T 3 ；
Selecting the liquid cooling medium according to test requirements;
s200, placing a test piece into a liquid cooling medium, continuously adding liquid nitrogen in the heat preservation process, and monitoring the temperature of the liquid cooling medium until reaching a preset test temperature required by a test, and preserving the heat of the test piece to ensure that the thickness of the test piece per millimeter is at least preserved for 30S;
s300, supporting the lower part of the test piece through a lower supporting part, applying acting force on two positions of the test piece in the length direction through a loading device above the test piece, wherein the two positions of the applied acting force are symmetrical relative to the supporting position, arranging a COD gauge on the upper part of the test piece, applying relative load to the lower supporting and loading device through a testing machine, and recording and storing load and change data of the COD gauge through the testing machine;
s400, unloading the load applied by the testing machine when the load reaches the maximum value or the sample breaks, and taking out the test piece.
Preferably T 1 ≥-100℃，-100℃＞T 2 ≥-160℃，T 3 And (3) selecting the temperature range according to the low-temperature environment temperature required by the test requirement, selecting different liquid cooling media and preparation methods according to the temperature range, and injecting the prepared liquid cooling media into the low-temperature tank. The test piece is insulated in the low-temperature tank, liquid nitrogen is injected into the low-temperature tank according to the monitored temperature of the liquid cooling medium, so that the liquid cooling medium is cooled, and when the temperature of the liquid cooling medium reaches the cooling temperature required by the test, the test piece is insulated for at least 30s per millimeter of thickness of the test piece. After the test piece is subjected to low-temperature heat preservation, a fracture toughness test is started. The testing machine loads the test piece through the lower supporting part and the loading device, specifically, the lower supporting part acts on the middle part below the test piece, the two sides of the lower supporting part are symmetrically loaded above the test piece through the loading device respectively, three-point loading is achieved, and meanwhile, the change of cracks is recorded through the COD gauge. When loading, the loading curve is from low to high until reaching the highest point, at this time, along with the expansion of the crack, the load acting on the test piece becomes smaller, so that the loading curve starts to descend, and the loading is finished until the moment, or the test piece breaks in the process of ascending the loading curve, and the loading is finished. And unloading the load by the testing machine, taking out the test piece, ending the test, and outputting a test result.
According to the method, the liquid cooling medium with different temperature ranges is prepared, so that the test requirement is met, the liquid cooling medium cools the test piece uniformly, the heat conductivity is high, the cooling time is saved, the compression roller meets the relevant standard, and the test at-196 ℃ to-100 ℃ is effectively realized.
Specifically, in step S100, the method includes:
the first cooling medium is absolute alcohol, so that the temperature range T of the first cooling medium 1 ≥-100℃。
The method for preparing the second cooling medium comprises the following steps: adding liquid nitrogen to an alkane liquid to provide a liquidThe temperature range of the cooling medium is-100 ℃ to be more than T 2 ≥-160℃。
The method for preparing the third cooling medium comprises the following steps:
adding liquid nitrogen to the alkane liquid, adding the alkene liquid when the temperature drops to-50 ℃, and continuing to add liquid nitrogen to a temperature T 3 ＜-160℃。
The method is mainly aimed at a low-temperature fracture toughness test below minus 100 ℃, and absolute alcohol can be selected as a liquid cooling medium for a low-temperature environment above minus 100 ℃. When the test temperature is lower than-100 ℃, the liquid in the method is selected as the cooling medium. The liquid cooling medium is prepared according to the following principle:
when the test temperature is between-160 ℃ and-100 ℃, alkane liquid C is selected 5 H 12 Alkane liquid C as cooling medium 5 H 12 The melting point of (C) is about-160℃and the boiling point is about 28 ℃.
When the test temperature is below-160 ℃, alkane liquid C is selected 5 H 12 With olefin liquid C 4 H 8 The mixed liquid of (C) as a cooling medium, olefin liquid C 4 H 8 The melting point of the mixture is about-185 ℃ and the boiling point is about-6 ℃, and the preparation steps of the mixture are as follows:
first, C is poured into a low-temperature tank 5 H 12 A liquid; then, liquid nitrogen is mixed into the low-temperature tank and stirred, so that the temperature of the solution is reduced to about-50 ℃; then, C is poured into a low-temperature tank 4 H 8 The two liquids are mutually dissolved and then are stable after being stirred, and the temperature of the mixed liquid is lower than C 4 H 8 Can be used as a cryogenic liquid cooling medium; finally, liquid nitrogen is continuously mixed into the mixed liquid to enable the mixed liquid to reach the test temperature. The mixed liquor can still keep the liquid state at-175 ℃ after verification, if C is increased in the mixed liquor 4 H 8 The ratio of (c) can keep the mixed liquid in a liquid state at a lower temperature.
Further, in step S200, the method includes:
when the test piece is placed in the liquid cooling medium, the surface of the test piece slightly protrudes from the liquid level of the liquid cooling medium, and the protruding part height H is 0mm < H < 8mm.
The total amount of the liquid cooling medium is such that the upper edge of the liquid level is close to the surface of the sample, so that the whole thermal insulation effect on the crack tip and the sample can be achieved during loading, and damage to the COD gauge due to contact of a large amount of low-temperature liquid can be avoided. Preferably, the height H of the protruding part is more than 0mm and less than 3mm, and the whole test piece is immersed into the liquid cooling medium as much as possible on the basis that the liquid level is ensured not to exceed the upper surface of the test piece.
Further, in step S200, the method includes: during the incubation, stirring was continued by the stirrer.
So that the liquid cooling medium is uniformly mixed and cooled.
Further, in step S200, the method includes: at the temperature T of the liquid cooling medium m With a test preset temperature T t Temperature difference betweenGradually decreasing the liquid nitrogen injection amount at < 5 ℃ until +.>＜2℃。
The difference between the temperature of the liquid cooling medium and the preset temperature of the experiment is strictly ensured to be within +/-2 ℃, and accurate test data can be obtained.
Further, in step S200, the method includes: the whole heat preservation time of the test piece is ensured to be not less than 15min.
On the basis of ensuring the heat preservation of the test piece with the thickness of each millimeter for at least 30 seconds, the whole heat preservation time of the test piece is required to be ensured to be not less than 15 minutes. So that the temperature of the whole test piece is in the temperature range required by the test.
The low-temperature fracture toughness test of the metal material at-175 ℃ to-100 ℃ is completed through the steps. After one test piece is taken out for testing, the next test piece is put in, and the test is continued from step S200. The samples may be incubated centrally using a liquid cooling medium and then transferred one by one to a loading and cryogenic device for loading, but it should be ensured that the temperature inside the test piece after transfer remains within 2 ℃ of the test temperature. It is recommended that the transfer be as fast as possible and continue to keep warm for a period of time after transfer to the loading and cryogenic device.
The liquid cooling medium in the method has the characteristics of inflammability and slight toxicity, and measures such as fire prevention, static electricity prevention, ventilation enhancement and the like are adopted in the test, and the skin is prevented from contacting the liquid cooling medium.
Further, the test method according to any one of the above is performed on a test apparatus comprising: the low temperature tank 10, the lower clamp 32, the loading device 20, the testing machine (not shown), the temperature sensor 50, the COD gauge 60 and the stirrer 80. A liquid cooling medium 40 is injected into the low temperature tank 10. A lower clamp 32 is connected to the bottom of the cryogenic tank 10. The loading device 20 is provided with two loading assemblies, the distance between which is adjustable. The lower clamp 32 and the loading device 20 are connected to the testing machine. The temperature sensor 50 is disposed at a position 0-5mm from the crack tip of the test piece 90. The COD gauge 60 is disposed at the position of the crack gap. An agitator 80 is provided in the cryogenic tank 10.
Through the preparation method of the liquid cooling medium 40, the proper liquid cooling medium 40 is selected according to the temperature range required by the test and is injected into the low-temperature tank 10, the test piece 90 is placed into the low-temperature tank 10, after heat preservation, a test machine is started to load the test piece through the lower clamping piece 32 and the loading device 20, the temperature change of the liquid cooling medium 40 is monitored through the temperature sensor 50, and when the temperature is close to the temperature required by the test @At < 5 ℃, the liquid nitrogen injection amount is reduced so that the temperature slowly reaches the test requirement temperature (T) t 2 deg.c) and the liquid cooling medium 40 is stirred by the stirrer 80 during the injection of the liquid nitrogen, so that the temperature change of the liquid cooling medium 40 is uniform and the mixed liquid is uniformly mixed. In the loading process, the load curve is recorded by the COD gauge 60, and when the load curve reaches the highest point or the test piece breaks, the loading is finished.
Further, the loading device 20 further includes: the upper clamping piece 21 is connected with the testing machine, and a sliding groove 211 is formed in one side of the upper clamping piece 21 opposite to the testing machine.
The loading assembly includes: a slider 22 and a press roller 23. The slide 22 is slidably connected to the slide slot 211. The press roller 23 is connected to the slide 22 by a spring 24, and the two springs 24 extend in a direction away from each other, so that the load applied by the testing machine is applied to the test piece 90 by the two press rollers 23.
As shown in fig. 2, the slider is L-shaped and includes a slider and a shutter connected to each other, the slider slides along the slide slot 211, the distance between two loading positions is adjusted by the sliding of the two sliders, and the slider is fixed in the slide slot 211 after the adjustment. The baffle is used for limiting the movement of the press rolls 23, after the tester is loaded, a load is applied to the test piece 90 through the two press rolls 23, the test piece 90 is bent along with the increase of the load, and the press rolls 23 can only move in the directions deviating from each other under the action of the baffle. In addition, when not loaded, the pressing roller 23 can be prevented from being separated from the sliding block 22 by the spring 24, so that the connection of the spring 24 and the pressing roller forms a certain angle with the vertical direction, and the angle ranges from 0 DEG to 90 deg. Preferably, one end of the spring is connected to the center of the pressing roller 23, and the other end is connected to the corner of the L-shaped slider 22, and the pressing roller 23 contacts the test piece 90, and the spring forms an angle of 45 ° with the horizontal direction when the force is 0. Preferably, the sliding groove 211 is a T-shaped groove, and the sliding plate is correspondingly T-shaped and matched with the sliding groove 211.
Further, the low-temperature fracture toughness test method of the metal material further comprises the following steps: a lower support 31 and a carrier 70. The lower support 31 is fixed to the bottom inside the low temperature tank 10, and the upper end is arc-shaped. The carrier 70 includes a body and a handle connected to the body.
Preferably, the lower support 31 is formed by extending the shape shown in fig. 2 in the direction of the test piece 90. Before the test piece 90 is placed in the low-temperature tank 10, the test piece 90 is supported by the lower support piece 31 and the bearing piece 70, after the heat preservation is finished, the bearing piece 70 is taken out by the handle, and the test piece 90 is subjected to three-point loading by the lower clamping piece 32 and the two pressing rollers 23. The setting of the handle can avoid operator frostbite.
As an example, the cryogenic tank 10 may be welded to the bottom of the lower support 31. The lower clamp 32 is screwed with the lower support 31. When loaded, the tester applies a load to the bottom of test piece 90 through lower support 31 by lower clamp 32.
The method is characterized in that a fracture toughness test (CTOD test) of a high manganese steel parent metal at room temperature and a low temperature of-165 ℃ is taken as an example, and the test process meets the standard requirement by comparing and analyzing the test results of 2 groups of CTOD tests at room temperature and-165 ℃ and stably maintaining the test piece in a low-temperature environment of-165 ℃ in the process of heat preservation and loading. The CTOD value of the high manganese steel parent metal is not obviously reduced in a low-temperature environment of-165 ℃, and the high manganese steel parent metal has better low-temperature fracture toughness.
1) Test materials: high manganese steel base material
2) Ambient temperature: 26-29 ℃, and the relative humidity of the environment: 30-44%
3) The test piece type was a three-point bending test piece, the shape and size of which are shown in fig. 3, and the unit is mm.
4) Test item: CTOD test.
5) The test process comprises the following steps:
CTOD test was performed according to the requirements of standard ISO 12135:2021.
(1) Prefabricating fatigue cracks of a three-point bending test piece and carrying out maximum fatigue load F in the final stage fmax The stress ratio R was 0.1, the waveform was a sine wave, and the frequency f was 20kN, 8 Hz.
(2) According to the method, a loading and low-temperature device is arranged on a fatigue testing machine, CTOD test is carried out at room temperature, and loading test is directly carried out without heat preservation. For the CTOD test at-165 ℃ a mixed liquid of an alkane liquid and an alkene liquid was used as a cooling medium. The test piece is symmetrically placed between an upper press roller and a lower support, the loading span S is adjusted to 216mm, the test piece is loaded after being insulated for 15min at the temperature of-165 ℃, the loading rate is 1.5 mm/min, and the change of the load F and the notch opening displacement V is recorded by a testing machine.
(3) When the loading load reaches the maximum value and descends, the loading process is finished, the test piece is taken out after being unloaded, and the next test piece is kept warm and loaded.
(4) The loaded test piece is crushed by adopting a three-point bending mode, and the initial crack length a is measured by a nine-point method in the standard 0 The CTOD value of the material is calculated according to the formula in the standard by combining the load F-notch opening displacement V curve.
(5) CTOD test of 3 parallel test pieces was performed on the high manganese steel base material at room temperature and-165℃respectively. The test temperature of the test pieces 1-3 is room temperature, and the test temperature of the test pieces 4-6 is-165 ℃.
6) Test results:
(1) F-V curves of the high manganese steel base material at the temperature of-165 ℃ are shown in figures 4 and 5. And (3) calculating the CTOD value by the load when the gap opening displacement V reaches the full range of 5mm because the load is not reduced in the loading process.
(2) The results of the CTOD test of the high manganese steel base material are shown in Table 1.
TABLE 1
According to the low-temperature fracture toughness test method in the patent, CTOD test of the three-point bending test piece at the temperature of-165 ℃ is completed by means of a set of loading and low-temperature device by means of the liquid cooling medium, the heat preservation and loading processes of the test meet the requirements of fracture toughness test standards, the accuracy and consistency of the test results of the low-temperature fracture toughness test are ensured, and the fracture toughness test of the metal material in the low-temperature (less than or equal to-100 ℃) environment can be effectively performed according to the method.
Although the present utility model is disclosed above, the present utility model is not limited thereto. Various changes and modifications may be made by one skilled in the art without departing from the spirit and scope of the utility model, and the scope of the utility model should be assessed accordingly to that of the appended claims.
Claims (10)
1. A method for testing the low-temperature fracture toughness of a metal material, comprising:
s100, injecting liquid cooling medium into the low-temperature tank, wherein the liquid cooling medium comprises a first cooling medium, a second cooling medium and a third cooling medium;
the temperature range of the first cooling medium is a first low temperature range T 1 ；
The second cooling medium is formed by adding liquid nitrogen into the first liquid material, and the temperature range of the second cooling medium is a second low temperature range T 2 ；
The third cooling medium is formed by adding a second liquid substance into the second cooling medium, and the temperature range of the third cooling medium is a third temperature range T 3 ；
Wherein T is 1 ＞T 2 ＞T 3 ；
Selecting the liquid cooling medium according to test requirements;
s200, placing a test piece into a liquid cooling medium, continuously adding liquid nitrogen in the heat preservation process, and monitoring the temperature of the liquid cooling medium until reaching a preset test temperature required by a test, and preserving the heat of the test piece to ensure that the thickness of the test piece per millimeter is at least preserved for 30S;
s300, supporting the lower part of the test piece through a lower supporting part, applying acting force on two positions of the test piece in the length direction through a loading device above the test piece, wherein the two positions of the applied acting force are symmetrical relative to the supporting position, arranging a COD gauge on the upper part of the test piece, applying relative load to the lower supporting and loading device through a testing machine, and recording and storing load and change data of the COD gauge through the testing machine;
s400, unloading the load applied by the testing machine when the load reaches the maximum value or the sample breaks, and taking out the test piece.
2. The method for testing the low-temperature fracture toughness of a metallic material according to claim 1,
in step S100, it includes:
the first cooling medium is absolute alcohol, so that the temperature range T of the first cooling medium 1 ≥-100℃；
The method for preparing the second cooling medium comprises the following steps: liquid nitrogen is added into alkane liquid to ensure that the temperature range of the liquid cooling medium is-100 ℃ to be more than T 2 ≥-160℃；
The method for preparing the third cooling medium comprises the following steps:
adding liquid nitrogen to the alkane liquid, adding the alkene liquid when the temperature drops to-50 ℃, and continuing to add liquid nitrogen to a temperature T 3 ＜-160℃。
3. A method for testing the low-temperature fracture toughness of a metallic material according to claim 2,
in preparing the second cooling medium and the third cooling medium, stirring was continued by a stirrer.
4. The method for testing the low-temperature fracture toughness of a metallic material according to claim 1,
in step S200, it includes:
when the test piece is placed in the liquid cooling medium, the surface of the test piece protrudes from the liquid level of the liquid cooling medium, and the protruding part height H is 0mm < H < 8mm.
5. The method for testing the low-temperature fracture toughness of a metallic material according to claim 1,
in step S200, it includes:
during the incubation, stirring was continued by the stirrer.
6. The method for testing the low-temperature fracture toughness of a metallic material according to claim 1,
in step S200, it includes:
at the temperature T of the liquid cooling medium m With a test preset temperature T t The temperature difference delta T between the two is less than 5 ℃ graduallyReducing the liquid nitrogen injection amount until meeting＜2℃。
7. The method for testing the low-temperature fracture toughness of a metallic material according to claim 1,
in step S200, it includes:
the whole heat preservation time of the test piece is ensured to be not less than 15min.
8. A method for testing the low-temperature fracture toughness of a metal material according to any one of claims 1 to 7, wherein the method is performed on a test apparatus,
the test apparatus comprises:
a low temperature tank (10), wherein a liquid cooling medium (40) is injected into the low temperature tank (10);
a lower clamping member (32) connected to the bottom of the low-temperature tank (10);
the loading device (20) is provided with two loading components, and the distance between the two loading components is adjustable;
the lower clamping piece (32) and the loading device (20) are connected with the testing machine;
a temperature sensor (50) disposed at a position 0-5mm from the crack tip of the test piece (90);
a COD gauge (60) arranged at the position of the crack gap;
and a stirrer (80) provided in the low-temperature tank (10).
9. The method of low temperature fracture toughness testing of a metallic material according to claim 8, wherein the loading apparatus (20) further comprises:
an upper clamping piece (21) connected with the testing machine, wherein a chute (211) is arranged on one side of the upper clamping piece (21) opposite to the testing machine;
the loading assembly includes:
a slider (22) slidably connected to the chute (211);
the press rollers (23) are connected with the sliding blocks (22) through springs (24), and the two springs (24) extend in the deviating direction, so that the load applied by the testing machine acts on the test piece (90) through the two press rollers (23).
10. The method for testing the low-temperature fracture toughness of a metallic material according to claim 8, further comprising:
a lower support (31) fixed at the bottom in the low-temperature tank (10) and having an arc-shaped upper end;
a carrier (70) comprising a body and a handle connected to the body.
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