CN115165562B - Testing method for limiting strain at edge of metal sheet - Google Patents
Testing method for limiting strain at edge of metal sheet Download PDFInfo
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- CN115165562B CN115165562B CN202210751278.7A CN202210751278A CN115165562B CN 115165562 B CN115165562 B CN 115165562B CN 202210751278 A CN202210751278 A CN 202210751278A CN 115165562 B CN115165562 B CN 115165562B
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- 238000012360 testing method Methods 0.000 title claims abstract description 30
- 239000002184 metal Substances 0.000 title claims abstract description 19
- 238000005452 bending Methods 0.000 claims abstract description 91
- 238000005336 cracking Methods 0.000 claims abstract description 27
- 239000000463 material Substances 0.000 claims abstract description 23
- 238000000034 method Methods 0.000 claims abstract description 17
- 230000000717 retained effect Effects 0.000 claims 1
- 238000004088 simulation Methods 0.000 abstract description 4
- 230000007704 transition Effects 0.000 abstract 1
- 238000013461 design Methods 0.000 description 6
- 229910000831 Steel Inorganic materials 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 238000005259 measurement Methods 0.000 description 4
- 238000010586 diagram Methods 0.000 description 3
- 238000010998 test method Methods 0.000 description 3
- 238000001514 detection method Methods 0.000 description 2
- 238000012986 modification Methods 0.000 description 2
- 230000004048 modification Effects 0.000 description 2
- 230000007306 turnover Effects 0.000 description 2
- 229910001209 Low-carbon steel Inorganic materials 0.000 description 1
- 230000009286 beneficial effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
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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
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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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
- G01N3/04—Chucks
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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
- G01N2203/0001—Type of application of the stress
- G01N2203/0003—Steady
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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
- G01N2203/0016—Tensile or compressive
- G01N2203/0017—Tensile
-
- 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
- G01N2203/0058—Kind of property studied
- G01N2203/006—Crack, flaws, fracture or rupture
- G01N2203/0062—Crack or flaws
- G01N2203/0064—Initiation of crack
-
- 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
- G01N2203/0058—Kind of property studied
- G01N2203/0069—Fatigue, creep, strain-stress relations or elastic constants
- G01N2203/0075—Strain-stress relations or elastic constants
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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
- G01N2203/026—Specifications of the specimen
- G01N2203/0262—Shape of the specimen
- G01N2203/0278—Thin specimens
- G01N2203/0282—Two dimensional, e.g. tapes, webs, sheets, strips, disks or membranes
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- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Chemical & Material Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Strength Of Materials By Application Of Mechanical Stress (AREA)
Abstract
本发明公开了一种金属薄板边部极限应变测试方法，选长条金属薄板为试样，试样的一端窄、另一端宽、中间为过渡的等腰梯形，将试样两长边垂直弯折形成U形槽；用外弯芯抵在U形槽的底壁外侧并对两侧壁外侧限位、用内弯芯抵在U形槽的底壁内侧并对两侧壁内侧限位，使U形槽贴绕外弯芯弯曲一定角度；用拉伸夹头夹住U形槽侧壁矮的一端，让外弯芯和内弯芯对夹固定U形槽远离拉伸夹头的切点位置，再通过拉伸夹头连续拉伸U形槽，在拉伸过程中观察弯曲部分的侧壁，当侧壁出现初始裂纹时停止，测量开裂位置的侧壁高度；计算临界应变。本方法能准确快速的获得材料开始出现边部起裂的极限应变，可直接作为零件成形仿真分析中边部开裂的判据。
The invention discloses a method for testing the edge limit strain of a metal sheet. A long metal sheet is selected as a sample. One end of the sample is narrow, the other end is wide, and the middle is an isosceles trapezoid of transition. The two long sides of the sample are vertically bent to form a U-shaped groove. An outer bending core is used to press against the outer side of the bottom wall of the U-shaped groove and limit the outer side of the two side walls. An inner bending core is used to press against the inner side of the bottom wall of the U-shaped groove and limit the inner side of the two side walls, so that the U-shaped groove is bent around the outer bending core at a certain angle. A stretching chuck is used to clamp the short end of the side wall of the U-shaped groove, and the outer bending core and the inner bending core are clamped to fix the U-shaped groove away from the tangent point position of the stretching chuck. Then the U-shaped groove is continuously stretched by the stretching chuck. The side wall of the bent part is observed during the stretching process. When the initial crack appears on the side wall, the side wall height at the cracking position is measured. The critical strain is calculated. The method can accurately and quickly obtain the limit strain at which the material begins to crack at the edge, and can be directly used as a criterion for edge cracking in part forming simulation analysis.
Description
Technical Field
The invention belongs to the field of detection of mechanical properties of materials, and particularly relates to a limit strain test method for edges of a metal sheet.
Background
The criterion of advanced high-strength steel edge cracking is not a mature and reliable test method at present:
For unidirectional tensile tests-due to the effects of original gauge length and non-uniform neck deformation-have proven unsuitable for the measurement of ultimate strain at break.
For the reaming test, the principle of the reaming test is shown in the following figure 1, a conical punch is adopted to ream and turn over a standard diameter round hole metal sheet sample, the test is stopped when a through crack appears at the edge, the size of the bore after reaming is measured, and the reaming and turn-over performance of the material is measured through the change of the bore. The diameter and the edge quality of the round hole of the sample, the thickness of the material, the compressive stress of the hole edge and the determination time of the through crack all affect the measurement result of the hole expansion rate, and the actual flanging performance of the material often cannot reach the hole expansion performance, so that the hole expansion test is used for evaluating the transverse performance of the material without problems, but the measurement result of the hole expansion rate is difficult to be directly used for the design of a die or the selection of the material. The reaming ratio of common mild steel is over 60%, but the high-strength steel is less than 50%, the reaming ratio of many high-strength and ultra-high-strength steels is between 15 and 30%, and because the limit reaming ratio of the high-strength steel is smaller, the interference of test conditions, material performance fluctuation and human factors in the test process is larger, the fluctuation of the detection data is also larger and can reach over 5%, so that the reaming ratio is also unsuitable for serving as the limit cracking strain of the edge part of the high-strength steel. In addition, the structural change of the actual part after flanging deformation is larger, the structural change is inconsistent with the structure of the reaming flange made of the material, and the reaming ratio is difficult to directly use in the design of the part and the selection of the material.
Disclosure of Invention
The invention aims to provide a limit strain test method for the edge of a metal sheet, which can accurately and rapidly obtain the limit strain of the edge cracking of a material, can be directly used as a criterion of the edge cracking in part forming simulation analysis, and has more practical value.
The technical scheme adopted by the invention is as follows:
A method for testing limit strain of edge of metal sheet includes selecting strip metal sheet as specimen, bending two long sides of specimen to form U-shaped slot, using external bending core to prop against outside of bottom wall of U-shaped slot and limit outside of two side walls of U-shaped slot, using internal bending core to prop against inside of bottom wall of U-shaped slot and limit inside of two side walls of U-shaped slot, bending U-shaped slot by internal bending core to make U-shaped slot stick around external bending core to bend it by a certain angle, clamping short end of side wall of U-shaped slot by stretching chuck, fixing U-shaped slot by external bending core and internal bending core to be far from tangent point of stretching chuck, continuously stretching U-shaped slot by stretching chuck, observing side wall of bending part in stretching process, stopping when initial crack appears on side wall, measuring side wall height of cracking position, calculating critical strain by side wall height of cracking position, thickness of specimen and radius of external bending core, namely limit strain that material starts to crack at edge.
Further, the dimensions of the test pieces are set according to the predicted limit strain range of edge cracking of the material to ensure that an initial crack is obtained.
Further, when the two long sides of the sample are vertically bent to form a U-shaped groove, the bending fillet radius r= (0.1-0.5) t, the width b= (30-70) t of the bottom wall of the U-shaped groove, and t is the thickness of the sample.
Further, both the outside sweep core and the inside sweep core are free to rotate.
Further, the widths of the outer bending core and the inner bending core are finely adjusted through the gasket so as to ensure the limit of the U-shaped groove.
Further, when the U-shaped groove is bent in a mode that one outer bending core is matched with two inner bending cores, the U-shaped groove is fixed by the outer bending core and one inner bending core in a butt-clamping mode, and when the U-shaped groove is stretched by the other inner bending core around the outer bending core bending U-shaped groove, the inner bending core at the position far away from the tangent point of the stretching chuck is reserved, and the inner bending core at the position close to the tangent point of the stretching chuck is removed.
Further, critical strainIs calculated as
Wherein h is the height of the side wall at the cracking position, t is the thickness of the sample, and R is the radius of the outer bending core.
Further, the test is performed multiple times to obtain a critical strain average value as a final value.
The beneficial effects of the invention are as follows:
The method can accurately and rapidly obtain the limit strain of the starting edge cracking of the material, the parameter can be directly used as the criterion of the edge cracking in the part forming simulation analysis, and compared with the limit hole expansion rate obtained by methods such as a hole expansion test, the limit design of the outer bending core and the inner bending core has more practical use value in the judgment of the edge cracking of the material, the limit design of the outer bending core and the inner bending core can prevent the U-shaped groove from expanding and collapsing in the stretching bending process, the test is ensured to be accurate, the isosceles trapezoid in the middle of the sample can enable the bending part of the U-shaped groove to form gradually heightened side walls, and the measurement can be carried out after the initial cracking occurs, thereby being convenient and rapid.
Drawings
Fig. 1 is a schematic diagram of a reaming test.
Fig. 2 is a top view of a test piece in an embodiment of the present invention.
FIG. 3 is a cross-sectional view of one end of a short U-shaped channel sidewall in accordance with an embodiment of the present invention.
Fig. 4 is a cross-sectional view of one end of a U-shaped channel with a high sidewall in an embodiment of the invention.
Fig. 5 is a schematic view of an embodiment of the invention before starting to bend the U-shaped groove.
Fig. 6 is a schematic diagram of an embodiment of the invention prior to the start of stretching the U-shaped groove.
Fig. 7 is a schematic diagram of a U-shaped groove stretched in an embodiment of the invention.
FIG. 8 is a schematic representation of the occurrence of an initial crack in an embodiment of the present invention.
In the figure, 1-sample, 2-bending line, 3-U-shaped groove, 4-outer bending core, 5-inner bending core, 6-stretching chuck and 7-initial crack.
Detailed Description
The invention is further described below with reference to the drawings and examples.
A limit strain testing method for the edge of a metal sheet comprises the following steps:
1. The strip metal sheet is selected as a sample 1, one end of the sample 1 is narrow, the other end is wide, the middle is in a transitional isosceles trapezoid, the size of the sample 1 is set according to the predicted limit strain range of edge cracking of the material to ensure that an initial crack 7 can be obtained, the material is 1mm thick, the predicted limit strain of edge cracking is 15-30%, the size is shown in figure 2, two long sides of the sample 1 are vertically bent to form a U-shaped groove 3, bending lines 2 on two sides are parallel and symmetrical with respect to a central line, and in the embodiment, when the two long sides of the sample 1 are vertically bent to form the U-shaped groove 3, the bending fillet radius r= (0.1-0.5) t, the width b= (30-70) t of the bottom wall of the U-shaped groove is the thickness of the sample 1, and the size of the U-shaped groove 3 is shown in figures 3 and 4.
2. As shown in fig. 5 and 6, the outer bending core 4 is abutted against the outer side of the bottom wall of the U-shaped groove 3 and limits the outer sides of two side walls of the U-shaped groove 3, the inner bending core 5 is abutted against the inner side of the bottom wall of the U-shaped groove 3 and limits the inner sides of two side walls of the U-shaped groove 3, the U-shaped groove 3 is bent by the inner bending core 5 to enable the U-shaped groove 3 to be attached around the outer bending core 4 by a certain angle, in the embodiment, the outer bending core 4 and the inner bending core 5 can freely rotate, the resistance in bending and subsequent stretching processes is effectively reduced, in the embodiment, the widths of the outer bending core 4 and the inner bending core 5 are finely adjusted through gaskets to ensure the limits of the U-shaped groove 3, and in the embodiment, the diameter of the outer bending core 4 is 100mm, the width of flanges at two sides is not calculated, and the diameter of the inner bending core 5 is 35mm, and the width is 70mm.
3. As shown in fig. 6 to 8, the short end of the side wall of the U-shaped groove 3 is clamped by the stretching clamp 6, the U-shaped groove 3 is clamped and fixed by the outer bending core 4 and the inner bending core 5 at the position far away from the tangent point of the stretching clamp 6, the U-shaped groove 3 is continuously stretched by the stretching clamp 6, the side wall of the bending part is observed in the stretching process, when the initial crack 7 of the side wall appears, the side wall height of the cracking position is measured, in the embodiment, when the U-shaped groove is bent by adopting the mode that one outer bending core 4 is matched with two inner bending cores 5, the U-shaped groove 3 is clamped by the outer bending core 4 and one inner bending core 5, and when the U-shaped groove 3 is stretched by the other inner bending core 5 around the outer bending core 4, the inner bending core 5 at the position far away from the tangent point of the stretching clamp 6 is reserved, and the inner bending core 5 near the tangent point of the stretching clamp 6 is removed.
4. Calculating critical strain by the side wall height of the cracking position, the thickness of the sample 1 and the radius of the outer bending core 4, namely, the limit strain of the edge cracking of the material starts to appear, wherein the critical strain is calculated by the side wall height of the cracking positionIs calculated as
Wherein h is the height of the side wall at the cracking position, t is the thickness of the sample 1, and R is the radius of the outer bending core 4.
5. The test was repeated to obtain a critical strain average value as a final value, and the results of the test of 5 samples 1 in this example are shown in the following table
From the test results in the above table, the ultimate strain of the material at the edge crack was found to be 0.136 and the engineering ultimate strain was found to be 14.6%.
The method can accurately and rapidly obtain the limit strain of the starting edge cracking of the material, the parameter can be directly used as a criterion of the edge cracking in the part forming simulation analysis, and compared with the limit hole expansion rate obtained by methods such as a hole expansion test, the limit design of the outer bending core 4 and the inner bending core 5 has more practical use value in the judgment of the edge cracking of the material, the limit design of the outer bending core 4 and the inner bending core 5 can prevent the U-shaped groove 3 from expanding and collapsing in the stretching bending process, the test is accurate, the isosceles trapezoid in the middle of the sample 1 can enable the bending part of the U-shaped groove 3 to form gradually-increased side walls, and the initial crack 7 can be measured after the occurrence.
It will be understood that modifications and variations will be apparent to those skilled in the art from the foregoing description, and it is intended that all such modifications and variations be included within the scope of the following claims.
Claims (7)
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| CN202210751278.7A CN115165562B (en) | 2022-06-28 | 2022-06-28 | Testing method for limiting strain at edge of metal sheet |
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| CN202210751278.7A CN115165562B (en) | 2022-06-28 | 2022-06-28 | Testing method for limiting strain at edge of metal sheet |
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| CN115165562A CN115165562A (en) | 2022-10-11 |
| CN115165562B true CN115165562B (en) | 2025-02-25 |
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Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102341196A (en) * | 2009-03-04 | 2012-02-01 | 新日本制铁株式会社 | Metal plate processing device and processing method |
| CN111633121A (en) * | 2020-06-05 | 2020-09-08 | 湖南大学 | A mold structure and test method capable of measuring the limit value of sheet metal flanging |
Family Cites Families (4)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP5381606B2 (en) * | 2009-10-19 | 2014-01-08 | 新日鐵住金株式会社 | Flange crack analysis method |
| JP6875285B2 (en) * | 2015-03-13 | 2021-05-19 | コーニング インコーポレイテッド | Edge strength test method and equipment |
| WO2020184712A1 (en) * | 2019-03-14 | 2020-09-17 | Ｊｆｅスチール株式会社 | Stretch flange crack evaluation method, metal sheet selection method, press die design method, component shape design method, and pressed component manufacturing method |
| CN112547555B (en) * | 2020-11-19 | 2022-03-08 | 无锡普天铁心股份有限公司 | Silicon steel hot rolling limit portion breach detection device |
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- 2022-06-28 CN CN202210751278.7A patent/CN115165562B/en active Active
Patent Citations (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN102341196A (en) * | 2009-03-04 | 2012-02-01 | 新日本制铁株式会社 | Metal plate processing device and processing method |
| CN111633121A (en) * | 2020-06-05 | 2020-09-08 | 湖南大学 | A mold structure and test method capable of measuring the limit value of sheet metal flanging |
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| CN115165562A (en) | 2022-10-11 |
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