CN115615779A - Fracture opening method for defects and damages of metal parts - Google Patents
Fracture opening method for defects and damages of metal parts Download PDFInfo
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- CN115615779A CN115615779A CN202211239181.4A CN202211239181A CN115615779A CN 115615779 A CN115615779 A CN 115615779A CN 202211239181 A CN202211239181 A CN 202211239181A CN 115615779 A CN115615779 A CN 115615779A
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/02—Devices for withdrawing samples
- G01N1/04—Devices for withdrawing samples in the solid state, e.g. by cutting
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
- G01N29/04—Analysing solids
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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
- G01N3/32—Investigating strength properties of solid materials by application of mechanical stress by applying repeated or pulsating forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N1/00—Sampling; Preparing specimens for investigation
- G01N1/28—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q
- G01N1/286—Preparing specimens for investigation including physical details of (bio-)chemical methods covered elsewhere, e.g. G01N33/50, C12Q involving mechanical work, e.g. chopping, disintegrating, compacting, homogenising
- G01N2001/2873—Cutting or cleaving
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2291/00—Indexing codes associated with group G01N29/00
- G01N2291/02—Indexing codes associated with the analysed material
- G01N2291/023—Solids
- G01N2291/0234—Metals, e.g. steel
Abstract
The invention provides a fracture opening method for defects and damages of metal parts, and belongs to the technical field of material failure analysis. The fracture opening method for the defects and the damages of the metal parts determines the positions of the defects and the damages of the metal parts by ultrasonic flaw detection; intercepting a sample of a damaged area; placing the sample on a three-point bending tester; carrying out a three-point bending fatigue test on the sample; with the continuous increase of the fatigue times, fatigue fractures of the defects and the damaged parts are initiated and increased until the fatigue fractures of the defects and the damaged parts form fractures penetrating through the defects and the damaged parts. The metal part with internal damage is accurately positioned and opened by the defect of the metal part and the fracture opening mode of the damage provided by the invention. Therefore, the damaged position is effectively and accurately opened, the fracture penetrates through the position of the crack source, and the crack source is found and analyzed.
Description
Technical Field
The invention belongs to the technical field of material failure analysis, and particularly relates to a fracture opening method for defects and damages of metal parts.
Background
With the development of railway industry in China, the total operating mileage of China railways exceeds 15 kilometers, and internal defects and damages of steel rails and welded joints become one of important damage types influencing the railway transportation safety. At present, the railway industry carries out regular ultrasonic flaw detection work on steel rails, welding joints and turnout parts which are in service on line, and is used for detecting whether internal defects and damages exist on metal parts. The field management department can replace the defective and damaged parts in time, and part of the parts need to be subjected to failure analysis work subsequently to find out the failure cause, thereby facilitating the definition of field safety responsibility and the improvement of the production process of the metal parts.
The internal defects of the steel rail refer to metallurgical defects, heat treatment defects and the like formed in the production process of the steel rail, such as white spots, coarse non-metallic inclusions, slag inclusions and the like. The internal defects of the steel rail welding joint refer to the defects of dust spot inclusion, looseness, air holes, slag inclusion and the like formed in the welding process of the steel rail. Such manufacturing defects are typically small in size (typically no more than 3mm in length), but can form crack origins and fatigue propagation under the alternating loads of train operation, resulting in fatigue damage.
The method is an important method for finding the cause of the damage by analyzing the crack source of the damaged steel rail piece and determining the type of the damage. Because the defects and the damages are small in size and are located inside the steel rail piece, how to effectively open the fracture at the position of the crack source is a difficult point faced at present. At present, the fracture at the defect position cannot be opened accurately by the conventional press-breaking method and the conventional knocking method, so that a crack source cannot be found, and the root cause of the damage cannot be determined finally.
The invention discloses a CN113155560 invention patent which discloses a metal workpiece crack opening method without damaging a fracture, belonging to the technical field of material failure analysis, wherein the process comprises the steps of cutting a crack-containing workpiece into blocks containing cracks, and keeping a set distance from the end face of each block to the tip of each crack; a clamp capable of enabling three points of a crack-containing block to be stressed is arranged on a testing machine with a compression function; placing the block containing the cracks between an upper clamp and a lower clamp of a testing machine; moving the clamp on the testing machine downwards, and applying a stable bending force until the clamp is in three-point contact with the block body containing the cracks; thereby realizing the opening of the crack of the metal workpiece.
The fracture opening mode of the prior art depends on observing the crack position on the surface of the metal part by naked eyes, and only the fracture that the crack propagates to the surface of the metal part can be opened. However, internal defects and damage to the components cannot be effectively opened. Particularly for internal defects and damages with small size, when the three-point bending and fracturing method in the prior art is adopted, the fracture crack is a rapid propagation process, and the fracture crack can not be guaranteed to just penetrate through the position of a crack source.
The invention patent CN106226171 discloses a piezoelectric semiconductor fracture failure experimental research method based on planned direction change, which aims at fracture damage and fracture toughness of a piezoelectric semiconductor based on polarization direction change in mechanical stress field, current field, high voltage field and coupling field loading environments thereof. And (3) placing the piezoelectric semiconductor standard sample on a three-point bending fixture of a testing machine with the crack facing downwards, and then loading mechanical stress on the top surface of the piezoelectric semiconductor standard sample to perform a fracture toughness test of the piezoelectric semiconductor standard sample. The piezoelectric semiconductor standard sample is placed on a three-point bending fixture of a testing machine, cracks face downwards, and the piezoelectric semiconductor standard sample is immersed in an experiment box filled with dimethyl silicone oil, wherein the three-point bending fixture is made of insulating materials and has strength and hardness which are correspondingly required; and then loading different current values and/or mechanical stress values on the piezoelectric semiconductor standard sample, and carrying out fracture toughness experiments on the piezoelectric semiconductor standard sample under the action of a current field and under the joint coupling action of the mechanical stress field and the current field.
The mechanism of the prior art is that a crack sample is prefabricated on a piezoelectric semiconductor by a notching method, the sample is placed on a three-point bending clamp of a testing machine, and a piezoelectric semiconductor fracture failure is obtained under the condition of simultaneously applying a mechanical stress field, a current field, a high voltage field and a coupling field thereof. The technical schemes of the two patents adopt a three-point bending method, and a test sample is directly crushed to be broken, so that a broken part can be broken due to the stress in a short time. Compared with the actual situation, the fracture condition generated by repeated reciprocating stress for a long time is completely different, the analysis result of fracture opening is influenced, and even the value of analysis research is lost.
Disclosure of Invention
The invention aims to provide a fracture opening mode for metal part defects and damages, which can effectively and accurately open the position of the damage, ensure that a fracture penetrates through the position of a crack source and is beneficial to finding the crack source and analyzing.
The invention also aims to provide a fracture opening method for metal part defects and damages, which realizes accurate fracture opening of the metal part with internal damages.
The invention also aims to provide a fracture opening mode for metal part defects and damages, which can ensure that the fracture opening condition is the same as that of the fracture generated by repeated reciprocating stress for a long time in the actual condition, and the analysis result of the fracture opening has analytical research value.
The purpose of the invention is realized as follows:
in order to achieve the purpose, the invention provides a fracture opening method for metal part defects and damage, which is characterized in that the metal part defects and damage positions are determined by ultrasonic flaw detection; intercepting a sample of a damaged area; placing the sample on a three-point bending tester; carrying out a three-point bending fatigue test on the sample; with the continuous increase of the fatigue times, fatigue fractures of the defects and the damaged parts are initiated and increased until the fatigue fractures of the defects and the damaged parts form fractures penetrating through the defects and the damaged parts.
The method for opening the defect or damaged fracture of the metal part comprises the following steps of.
The fracture opening method for metal part defects and damages described above is characterized in that the metal part defects and damages include internal defects and damages of the metal part.
The fracture opening method for defects and damages of metal parts as described above is characterized in that the internal defects and damages of metal parts include, but are not limited to, white spots in rails, coarse non-metallic inclusions, heat treatment defects, and fatigue microcracks.
The fracture opening method of the defects and the damages of the metal parts comprises the steps of but not limited to ash inclusion, porosity, pores and slag inclusion in the welded joints.
The fracture opening method for the metal part defects and the damages includes the external defects and the damages of the metal part.
The fracture opening method for the defects and the damages of the metal member as described above is a method in which the external defects and the damages of the metal member are fractures in which cracks have propagated to the surface of the metal member, and the positions of the cracks on the surface of the metal member are visually observed.
The fracture opening method for the metal part defect and the damage as described above, wherein the step of determining the position of the defect and the damage of the metal part includes locating the internal defect and the damage of the metal part by using ultrasonic waves, marking the projected positions of the internal defect and the damage on the surface of the metal part, and recording the depth of the defect and the damage from the surface to be inspected.
The fracture opening method for metal part defects and damages described above, wherein the cutting out the damaged area sample includes cutting out an elongated sample with the metal part defect and damage position as a center.
The method for opening the fracture of the defects and the damages of the metal parts is characterized in that the longest length of the strip-shaped test sample is not more than 200mm, and the shortest length of the strip-shaped test sample is not less than the minimum support distance of the three-point bending tool of the fatigue testing machine.
The fracture opening method for the defects and the damages of the metal parts as described above, wherein the width and the thickness of the elongated sample are determined according to the sizes of the defects and the damages of the metal parts and the sizes of the metal parts.
In the method for opening a fracture in a flaw or a damage of a metal part as described above, the flaw or the damage edge of the metal part obtained by flaw detection in the elongated sample has a depth of about 5mm from the cross-sectional surface of the sample.
In the fracture opening method for the defects and the damages of the metal member, any one side surface of the internal defects and the damaged samples of the metal member is designated as a damaged surface, and the edge of the damaged surface is chamfered at 45 degrees.
In the fracture opening method for the defects and the damages of the metal parts, in the long sample, the side surface where the defects and the damages are located is designated as the damaged surface, and the edge of the damaged surface is chamfered by 45 degrees.
The fracture opening method for the defects and the damages of the metal parts is characterized in that the sample is placed on a three-point bending tester, and the damaged surface is perpendicular to the longitudinal direction of the sample.
The fracture opening method for the defects and the damages of the metal parts is characterized in that the damaged surface is placed on a three-point bending tester in a downward mode.
In the three-point bending fatigue test, fatigue treatment is performed on the defect and damage sample of the metal component by setting the parameters of the fatigue testing machine and adopting a three-point bending fatigue loading mode, and the fracture is opened from the defect and damage.
The fracture opening method for the defects and the damages of the metal parts is characterized in that the parameters of a fatigue testing machine are set according to the size, the loading span and the mechanical property of the three-point bending test sample.
The method for opening a fracture of a defect or a flaw in a metal part as described above, wherein the defect or flaw specimen of the metal part is placed on a fatigue testing machine, and the flaw position is located directly below the indenter of the fatigue testing machine.
The fracture opening method for the defects and the damages of the metal parts is characterized in that the pressure head is positioned at the center of the span of the samples of the defects and the damages of the metal parts.
The method for opening a defect or damaged fracture in a metal part as defined above, wherein the fatigue testing machine parameters comprise: fatigue load, stress ratio, loading frequency, cycle number and loading waveform.
The method for opening the fracture of the defects and the damages of the metal parts, wherein the maximum fatigue load of the fatigue testing machine is calculated according to the following formula:
wherein:
f is the maximum fatigue load applied to the bending specimen in newtons (N);
σ max maximum fatigue stress in units of megapascals (MPa);
l is the span of the clamp in millimeters (mm);
b is the width of the bent specimen in millimeters (mm);
h is the height of the bent specimen in millimeters (mm).
The method for opening a fracture in which defects and damage occur in a metal part as described above, wherein the maximum fatigue stress σ is set max Is set near the yield strength of metal material and between 500MPa and 700 MPa.
The fracture opening method for the defects and the damages of the metal parts is characterized in that the stress ratio is selected from 0.1-0.3.
The fracture opening method for the defects and the damages of the metal parts is characterized in that the loading frequency is 10 Hz-40 Hz, and the loading mode adopts a sine wave.
The fracture opening method has the advantages that the internal defects and the damage of the metal part are obviously overcome, the internal damage of the metal is positioned in an ultrasonic positioning mode, and finally, the metal part with the internal damage is accurately positioned and opened in a three-point bending and fatigue loading experiment mode. Therefore, the damaged position is effectively and accurately opened, the fracture penetrates through the position of the crack source, and the crack source is found and analyzed.
The invention has another technical effect that the fracture of the metal piece with internal damage can be accurately opened.
According to the invention, through a fatigue loading experiment mode, the condition of the opened fracture is the same as that of the fracture generated by repeated reciprocating stress for a long time in an actual condition, and the analysis result of the opened fracture has analytical research value.
Drawings
The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. In addition, the shapes, the proportional sizes, and the like of the respective members in the drawings are merely schematic for facilitating the understanding of the present invention, and do not specifically limit the shapes, the proportional sizes, and the like of the respective members of the present invention. Those skilled in the art, having the benefit of the teachings of this invention, may choose from the various possible shapes and proportional sizes to implement the invention as a matter of case.
FIG. 1 is a first schematic view of a three-point bend test specimen with defects and damage on the interior of a metal part according to the present invention;
FIG. 2 is a second schematic view of a three-point bend test specimen with defects and damage in the metal part of the present invention;
FIG. 3 is a first schematic diagram of a three-point bending fatigue test of the invention for defects and damage of a metal part;
FIG. 4 is a second schematic diagram of a three-point bending fatigue test of the invention for defects and damages of metal parts.
FIG. 5 is a first schematic view of a three-point bend test specimen of the invention with defects and damage to the surface of a metal part;
FIG. 6 is a second schematic view of a three-point bend test specimen of the invention with defects and damage to the surface of the metal part;
FIG. 7 is a first schematic view of a three-point bending fatigue test of a metal part of the present invention on a surface for defects and damage;
FIG. 8 is a second schematic view of a three-point bending fatigue test of the invention for defects and damage to a metal part on a surface;
FIG. 9 is a schematic view of a fracture of a metal part of the present invention after the three-point bending fatigue test is completed for defects and damage.
Description of the figures:
1. a sample; 2. internal defects or damage; 3. a pressure head; 4. a support roller;
5. internal fatigue cracking; 6. surface defects or damage; 7. external fatigue cracking;
8. an internal defect location; 9. a fatigue extension zone; 10 momentary interruption zone.
Detailed Description
The details of the present invention can be more clearly understood in conjunction with the accompanying drawings and the description of the embodiments of the present invention. However, the specific embodiments of the present invention described herein are for the purpose of illustration only and are not to be construed as limiting the invention in any way. Any possible variations based on the present invention may be conceived by the skilled person in the light of the teachings of the present invention, and these should be considered to fall within the scope of the present invention.
As shown in fig. 1 to 9, the present invention provides a fracture opening method for defects and damages of a metal component, which determines the positions of the defects and the damages of the metal component by ultrasonic flaw detection on the metal component; cutting out a sample 1 in a damaged area; placing the three-point bending fatigue test sample 1 on a three-point bending testing machine; carrying out a three-point bending fatigue test on the sample 1; with the continuous increase of the fatigue times, fatigue fractures of the defects and the damaged parts are initiated and increased until the fatigue fractures of the defects and the damaged parts form fractures penetrating through the defects and the damaged parts.
According to the fracture opening method for the defects and the damages of the metal parts, the defects and the damaged positions of the metal parts are determined by ultrasonic flaw detection of the metal parts, and the damaged positions can be accurately positioned; and then accelerating the initiation and the enlargement of the fatigue fracture at the defect and the injury part by utilizing a three-point bending fatigue test, and further forming the fracture penetrating through the defect and the injury part, so that the fracture can necessarily penetrate through the position of the defect source, and the crack source can be found and analyzed.
The fracture opening method for metal part defects and injuries provided by the invention can effectively and accurately open the position of the injury, ensure that the fracture penetrates through the position of a crack source, and ensure that the fracture is opened to be the same as the fracture generated by repeated stress for a long time in the actual situation, so that the analysis result of the fracture opening has the value of analysis and research.
In the present invention, the metal parts include, but are not limited to, rails and welded joints, and metal parts other than rails and welded joints are also applicable to the technical solution of the present invention.
In an alternative embodiment of the present invention, the metal part defect and damage includes an internal defect and damage of the metal part, which is a condition that the metal part cannot be directly observed by naked eyes and the surface has no defect or damage. The internal defect defects of the metal parts are generally small in size (generally not greater than 3mm in length), and when the metal parts are steel rails, the internal defects and the internal defects can form crack sources and fatigue propagation under the action of alternating loads of train operation to form fatigue damage.
In an alternative example of this embodiment, internal defects and damage to the metal components include, but are not limited to, white spots in the rail, coarse non-metallic inclusions, heat treatment defects, fatigue microcracks. Such defects are metallurgical defects and heat treatment defects formed during the production of the rail.
In an alternative example of this embodiment, internal defects and damage to the metal parts include, but are not limited to, dust inclusions, porosity, slag inclusions in the weld joint. Such defects are formed during the welding process of the rail.
In another alternative embodiment of the invention, the metal part defects and damage are internal defects and damage as well as external defects and damage of the metal part.
In an alternative example of this embodiment, the external defect or damage to the metal part is a fracture in which a crack has propagated to the surface of the metal part, and the location of the crack on the surface of the metal part is visually observed.
In an alternative embodiment of the invention, the determining the positions of the defects and the damages of the metal component comprises positioning the internal defects and the damages of the metal component by using ultrasonic waves, marking the projection positions of the internal defects and the damages on the surface of the metal component, and recording the depth sizes of the defects and the damages from the flaw detection surface.
In an alternative example, the detailed positions and sizes of the internal defects and the damages of the metal part are found out through ultrasonic waves, the projection positions of the internal defects and the damages are marked on the surface of the metal part subjected to flaw detection, and in addition, the depth sizes of the internal defects and the damages from the flaw detection surface are manually recorded, so that the positions and the sizes of the three-point bending test sample 1 which is subsequently intercepted can be conveniently determined.
In an alternative example, the metal part surface is marked with a marker (or paint pen).
In an alternative embodiment of the present invention, cutting out the damaged area specimen 1 includes cutting out an elongated specimen 1 centering on the defective and damaged positions of the metal member.
Preferably, the long three-point bending test piece 1 is cut with the flaw position obtained by ultrasonic flaw detection as the center, and the flaw surface should be as perpendicular as possible to the longitudinal direction of the bending test piece 1.
In an alternative embodiment of the invention, the length dimension of the strip-shaped test sample 1 is theoretically as long as the test sample is longer, the longest test sample is not more than 200mm, and the shortest test sample is not less than the minimum support distance of the three-point bending tool of the fatigue testing machine.
In an alternative embodiment of the present invention, the width and thickness of the elongated sample 1 are determined according to the size of the defect and damage of the metal member and the size of the metal member.
In an alternative embodiment of the present invention, the depth of the elongated test piece 1, which is the flaw or damaged edge of the metal part obtained by flaw detection, from the cross-sectional surface of the test piece 1 is about 5 mm. On the premise of ensuring that the section size of the bending sample 1 is smaller, the damage caused by mistaken cutting in machining is prevented from being damaged.
In an alternative example of this embodiment, the three-point bending test specimen 1 is cut out by mainly using a sawing method or a wire cutting method.
In an alternative example of this embodiment, in the sample 1 of the internal defect and damage of the metal part, any side surface is designated as the damage surface, the edge of the damage surface is chamfered by 45 degrees, and the chamfered surface is placed downwards in the fatigue test in order to eliminate the stress concentration effect of the edge of the sample 1 and avoid fatigue cracks from being initiated from the edge of the sample 1 but not from being initiated at the internal damage.
In another alternative embodiment of the present invention, for the long sample 1 having defects and damage on the surface of the metal member, the side surface on which the defects and damage are located is designated as a damaged surface, the edge of the damaged surface is chamfered at 45 °, and the chamfered surface is placed downward in the fatigue test.
In an alternative embodiment of the present invention, the elongated test piece 1 is placed on a three-point bending tester, and the damaged surface is perpendicular to the longitudinal direction of the test piece 1.
In an alternative example, the damaged side should be placed face down on a three point bend tester.
In an alternative embodiment of the invention, in the three-point bending fatigue test, fatigue treatment is carried out on the sample 1 with defects and damage of the metal part by setting the parameters of a fatigue testing machine and adopting a three-point bending fatigue loading mode, and a fracture is opened from the defects and the damage.
Specifically, as shown in fig. 9, the three-point bending test specimen 1 is placed on a fatigue testing machine, and a three-point bending fatigue test is performed by setting a fatigue parameter; because the internal defect and the damage position have stress concentration effect, the sample has fatigue crack at the internal defect position 6 and continuously grows up; with the increase of fatigue times, the fatigue fracture of the fatigue crack at the internal defect position 6 is gradually increased and is expanded to form a fatigue expansion area 7, when the fatigue expansion area grows to a certain size, the fatigue expansion area is rapidly fractured after reaching a critical stress finally, and the fracture forms a transient fracture area 10.
In an alternative example, fatigue testing machine parameters are set according to the size of the test specimen 1, the loading span and the mechanical properties of the metal part.
In an alternative example, the test specimen 1 is placed on a fatigue tester with the damage location directly below the fatigue tester indenter 3.
In an alternative example, the indenter 3 should be centered on the span of the sample 1.
Specifically, the span and the pressure head 3 of the fatigue testing machine are adjusted, and the pressure head 3 is positioned at the center of the span; the sample 1 was placed on the back-up roll 4 of the fatigue testing machine with its 45 ° chamfered surface facing downward and the damage position located directly below the indenter 3.
In an alternative example, the fatigue tester parameters include: fatigue load, stress ratio, loading frequency, cycle number and loading waveform.
And selecting proper fatigue load, stress ratio, loading frequency, cycle frequency and loading waveform parameters to enable internal defects or damaged 2 positions (stress concentration areas) with small original sizes to generate fatigue cracks and grow continuously.
In an alternative example, the maximum fatigue load of the fatigue tester is calculated as follows:
wherein:
f is the maximum fatigue load applied to the bending specimen 1 in newtons (N);
σ max maximum fatigue stress in units of megapascals (MPa);
l is the span of the clamp in millimeters (mm);
b is the width of the bent specimen 1 in millimeters (mm);
h is the height of the bent specimen 1 in millimeters (mm).
It should be noted that the fatigue load of the fatigue testing machine can be neither too large nor too small. The excessive fatigue load can cause the three-point bending test sample 1 to be rapidly fractured, and the fracture cannot pass through a crack source region; too small fatigue load may cause that fatigue crack cannot be initiated at the damaged part of the sample 1 or the fatigue period is longer, and the test efficiency is not high.
In an alternative example, the maximum fatigue stress σ max The method is arranged near the yield strength of the metal material and is arranged between 500MPa and 700 MPa.
In the invention, the fatigue load of the test is mainly set according to the yield strength of the actual metal material, the yield strength of the common steel rail is between 500 and 700MPa, and the fatigue test is carried out near the yield strength, so that the fatigue crack can be rapidly initiated and expanded at the internal damage position.
In an alternative example, the stress ratio is selected to be between 0.1 and 0.3.
It should be noted that the stress ratio is the ratio of the minimum load to the maximum load, the smaller the value is, the larger the amplitude is, the faster the fatigue crack propagates, and the selection is preferably between 0.1 and 0.3.
In an optional example, the loading frequency is 10Hz to 40Hz, and the loading mode adopts a sine wave.
It should be noted that, the loading frequency is set according to the parameters of the actual fatigue testing machine, and theoretically, the faster the frequency is, the better the frequency is, so that the testing period is shorter.
The set fatigue parameters are adopted for carrying out fatigue tests, fatigue cracks are generated at the internal defect position along with the increase of the fatigue times, the subsequent fatigue fracture is gradually increased, and the rapid fracture is finally generated after the critical stress is reached. And taking down the fractured sample 1, and carrying out subsequent analysis work of the crack source.
It should be noted that the fatigue test is only a means for effectively opening the fracture, so that only the test parameter range is provided, and the specific numerical value of the test parameter can be determined by those skilled in the art according to the material of the analysis object.
The present invention is not limited to the above embodiments, and in particular, various features described in different embodiments can be arbitrarily combined with each other to form other embodiments, and the features are understood to be applicable to any embodiment except the explicitly opposite descriptions, and are not limited to the described embodiments.
Claims (25)
1. A fracture opening method for metal part defects and injuries comprises the steps of determining the positions of the defects and the injuries of the metal part through ultrasonic flaw detection; intercepting a sample in a damaged area; placing the sample on a three-point bending tester; carrying out a three-point bending fatigue test on the sample; with the continuous increase of the fatigue times, fatigue fractures of the defects and the damaged parts are initiated and increased until the fatigue fractures of the defects and the damaged parts form fractures penetrating through the defects and the damaged parts.
2. A method of opening a defect or damage fracture in a metal component as claimed in claim 1 wherein said metal component includes but is not limited to steel rails and welded joints.
3. A fracture opening method for metal parts defects and damage as claimed in claim 1, wherein said metal part defects and damage include internal defects and damage of metal parts.
4. A method of fracture opening of defects and damages of metal parts according to claim 3, characterized in that said internal defects and damages of metal parts include but are not limited to white spots in steel rails, coarse non-metallic inclusions, heat treatment defects, fatigue micro-cracks.
5. A method of opening a fracture of defects and damage in metal parts according to claim 3, wherein said internal defects and damage of metal parts include but are not limited to dust inclusions, porosity, slag inclusions in welded joints.
6. A method of opening a fracture of a metallic component defect or damage as recited in claim 1 wherein said metallic component defect or damage comprises an external defect or damage of a metallic component.
7. A fracture opening method for defects and damages of metal parts according to claim 6, wherein the external defects and damages of metal parts are fractures in which cracks have propagated to the surface of metal parts, and the positions of the cracks on the surface of metal parts are observed by naked eyes.
8. A method of opening a fracture of a flaw or damage in a metallic component as recited in claim 1, wherein determining the location of the flaw or damage in the metallic component comprises locating the internal flaw or damage in the metallic component using ultrasonic waves, marking the projected location of the internal flaw or damage on the surface of the metallic component, and recording the depth dimension of the flaw or damage from the inspection surface.
9. A method of opening a fracture in a metal part having defects and damage according to claim 1, wherein said sectioning a sample of the damaged area comprises sectioning an elongated sample of the metal part centered at the location of the defect and damage.
10. A method for opening a fracture of a metal part defect or damage according to claim 9, characterized in that the longest length of the strip-shaped test specimen is not more than 200mm, and the shortest length is not less than the minimum support distance of a three-point bending tool of a fatigue testing machine.
11. A fracture opening method for metal parts defects and damages according to claim 9, characterized in that the width and thickness of said elongated specimen are determined according to the size of the defects and damages of the metal parts and the size of the metal parts.
12. A method of opening a flaw or damage in a metal part according to claim 9, wherein the flaw or damage edge of the metal part obtained by flaw detection in the elongated specimen has a depth of about 5mm from the cross-sectional surface of the specimen.
13. A fracture opening method for defects and damages of metal parts according to claim 12, wherein said internal defect and damaged specimen of metal parts is subjected to 45 ° chamfering treatment for the edge of the damaged surface by designating any one side surface as the damaged surface.
14. A fracture opening method for defects and damages of metal parts according to claim 13, characterized in that in said elongated specimen, the side where the defect and the damage are located is designated as a damaged surface, and the edge of the damaged surface is chamfered at 45 °.
15. A method for opening a defect or damage in a metal part according to claim 1, wherein said test piece is placed on a three-point bending tester with the surface of the damage perpendicular to the longitudinal direction of the test piece.
16. A method of opening a defect or damage fracture in a metal part according to claim 15, wherein said surface of said damage is placed down on a three point bend tester.
17. A method for opening a defect or damage fracture in a metal part according to claim 1, wherein said three-point bending fatigue test is carried out by setting fatigue testing machine parameters and applying three-point bending fatigue loading to a sample of the defect or damage in the metal part to fatigue-treat the sample and open the fracture from the defect or damage.
18. A method of opening a defect or damage fracture in a metallic component as claimed in claim 17, wherein the dimensions of said three-point bending test specimen, the load span and the mechanical properties of the metallic component set the fatigue tester parameters.
19. A method of opening a flaw or damage in a metal part according to claim 17, wherein a flaw or damage specimen of the metal part is placed on a fatigue testing machine with the location of the flaw or damage directly below the head of the fatigue testing machine.
20. A fracture opening method for defects and damage in metallic components according to claim 19, wherein said indenter should be located at the center of the span of said test specimen of defects and damage in metallic components.
21. A method of opening a defect or damage fracture in a metallic component as defined in claim 17, wherein said fatigue testing machine parameters include: fatigue load, stress ratio, loading frequency, cycle number and loading waveform.
22. A fracture opening method for defects and damages of metal parts according to claim 22, wherein the maximum fatigue load of said fatigue testing machine is calculated according to the following formula:
wherein:
f is the maximum fatigue load applied to the bending specimen in newtons (N);
σ max maximum fatigue stress in units of megapascals (MPa);
l is the span of the clamp in millimeters (mm);
b is the width of the bent specimen in millimeters (mm);
h is the height of the bent specimen in millimeters (mm).
23. Method for opening a defect or damage fracture in a metallic component according to claim 22, characterized in that said maximum fatigue stress σ is max Is set near the yield strength of metal material and between 500MPa and 700 MPa.
24. A method of opening a fracture of a metal part having defects and damage according to claim 22, wherein said stress ratio is selected between 0.1 and 0.3.
25. A fracture opening method for defects and damages of metal parts according to claim 22, wherein the loading frequency is selected from 10Hz to 40Hz and the loading mode is sine wave.
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| CN202211239181.4A CN115615779A (en) | 2022-10-11 | 2022-10-11 | Fracture opening method for defects and damages of metal parts |
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