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CN-116337560-B - Loading method for testing pipe forming limit path and testing die thereof

CN116337560BCN 116337560 BCN116337560 BCN 116337560BCN-116337560-B

Abstract

The invention discloses a loading method for testing a pipe forming limit path, which comprises the steps of cutting a complete half pipe into a specified shape in a first part, always measuring the first main strain direction and the second main strain direction of the half pipe test piece under the stretching action of a hemispherical rigid male die to obtain a left half part of a strain forming limit, and changing the structure of the rigid male die in a second part, keeping the shape of the half pipe test piece to completely measure the first main strain direction and the second main strain direction of the half pipe test piece to be in the tension-stretching state, and obtaining a right half part of the strain forming limit. The method for acquiring the pipe strain forming limit diagram makes up the blank of the pipe rigid hemispherical rigid male die method for acquiring the complete forming limit diagram, is realized by replacing the semi-pipe test pieces with different shapes and sizes and the rigid male dies with different shapes and sizes, and has the advantages of convenience in operation, safety in test, few dies, high efficiency, low cost and the like.

Inventors

  • SUN ZHIYING
  • SHI ZHENGXIAN
  • Shen Mingting

Assignees

  • 江苏科技大学

Dates

Publication Date
20260512
Application Date
20230207

Claims (10)

  1. 1. The loading method for testing the pipe forming limit path is characterized by comprising the following steps of: firstly, taking a plurality of half pipes (6) to be tested, and cutting the half pipes into various shapes; Placing one half pipe (6) into a die, pressing the half pipe (6) between working parts of an upper die (1) and a lower die (2) of the die, enabling two side ends of the half pipe (6) to be flush with the groove boundary of the lower die, enabling the center of the half pipe (6) to be aligned with the groove center of the lower die, and connecting the upper die (1) with the lower die (2) through bolts so as to fix the half pipe (6) between the two; Step three, coaxially connecting a rigid male die (5) with a male die base (3) through a stud (4), and inserting the rigid male die (5) downwards from an upper die through hole through the male die base (3) until the rigid male die (5) contacts with the center of a half pipe (6); Step four, completing a strain forming limit test of the half pipe (6) in a downward drawing mode through a rigid male die (5); Step five, after the half pipe (6) is replaced in sequence, the half pipe is installed in a die again, and strain forming limit tests are carried out in sequence to measure the left part of the strain forming limit; taking a plurality of half pipes (6) to be tested with the same shape again, sequentially installing the half pipes in a die, removing the original rigid male dies (5), taking a plurality of rigid male dies (5) with various shapes, sequentially installing the rigid male dies on a male die base (3), carrying out strain forming limit test on the half pipes (6) to be tested with the same shape, and measuring the right part of the strain forming limit; And seventhly, acquiring all positive and negative parts of the second main strain under linear loading by measuring half pipes (6) with different shapes and sizes and rigid male dies (5) with different shapes and sizes, so as to acquire all complete pipe forming limit diagrams.
  2. 2. The method for loading a forming limit path of a test tube according to claim 1, wherein the test tube is made of aluminum, copper or steel and has a thickness of 0.5-5 mm.
  3. 3. The loading method for testing the pipe forming limit path according to claim 1, wherein when the left part of the strain forming limit is obtained, the shape of the half pipe (6) is variable, the middle part of the half pipe (6) is a testing area, two ends of the half pipe are non-testing areas, the center of the half pipe (6) takes various widths, the non-testing area is a hollow part, the corresponding rigid male mold (5) is hemispherical, and the testing area of the half pipe (6) is in a pull-press state.
  4. 4. The method for loading a test tube forming limit path according to claim 3, wherein when the left part of the strain forming limit is obtained, the diameter of the half tube (6) is 50-150 mm, the length of the half tube is 60-160 mm, the corresponding rigid male die (5) is hemispherical with the radius of 25-30 mm, and circular arc-shaped hollow parts are arranged on the outer peripheral surfaces of two ends of the half tube (6) along the circumferential direction.
  5. 5. A loading method for testing a pipe forming limit path according to claim 4, wherein the width of the testing area of the middle part of the half pipe (6) is 20mm,30mm,40mm,50mm and 60mm respectively, and the radius of the hollow part is 50mm, 50.278mm, 51.25mm, 53.214mm and 56.667mm respectively.
  6. 6. The loading method for testing the pipe forming limit path according to claim 1, wherein the shape of the rigid male die (5) is variable when the right part of the strain forming limit is obtained, the rigid male die (5) is ellipsoidal with various long and short axial ratios, and the half pipe (6) is complete in structure, so that the testing area of the half pipe (6) is in a pull-pull state.
  7. 7. A loading method for testing a pipe forming limit path according to claim 6, wherein when the right part of the strain forming limit is obtained, the long axis of the rigid male die (5) is 50mm, the short axis is 30mm, 35mm, 40mm, 45mm and 50mm respectively, and the width of the corresponding half pipe (6) is 120mm.
  8. 8. The loading method for testing the pipe forming limit path according to claim 1, wherein deformation of the half pipe (6) is monitored in real time by using a DIC three-dimensional full-field strain measurement analysis system when a strain forming limit test is carried out, and main strain and secondary strain at fracture positions of the half pipe (6) with different shapes and sizes are obtained.
  9. 9. A test die for a loading method for testing a pipe forming limit path according to any one of claims 1-8 is characterized by comprising an upper die (1), a lower die (2), a punch base (3), a stud (4) and a rigid punch (5), wherein a semicircular arc curved surface type upper die bump is arranged in the middle of the lower bottom surface of the upper die (1), a semicircular arc curved surface type lower die groove is arranged in the middle of the upper surface of the lower die (2), the upper die (1) is arranged on the lower die (2) and connected through a bolt, the upper die bump is matched with the lower die groove, a half pipe (6) is arranged between the upper die and the lower die, an upper die through hole penetrating through the upper die bump is formed in the middle of the upper die (1), a lower die through hole penetrating through the lower die groove is formed in the middle of the lower die (2), the upper die through hole is coaxially penetrated through the lower die through hole, the rigid punch (5) is coaxially connected with the bottom end of the punch base (3) through the stud (4), and the punch base (3) is inserted into the upper die through hole to enable the rigid punch (5) to be abutted against the half pipe (6).
  10. 10. The test die set of claim 8, wherein the upper die (1), the lower die (2) and the punch base (3) are made of die steel, the stud (4) is an M10 full-thread stud, and the punch base (3) and the rigid punch (5) are respectively provided with internal thread grooves of corresponding types.

Description

Loading method for testing pipe forming limit path and testing die thereof Technical Field The invention relates to a method for acquiring a pipe strain forming limit curve, in particular to a loading method for testing a pipe forming limit path and a testing die thereof. Background The test of the forming limit of the metal pipe is usually carried out by adopting a loading mode of pressurizing the inside of the pipe, the medium filled into the pipe is generally low-pressure medium (liquid or gas), the pipe is deformed to be necked or broken in a die cavity, and then the forming limit curve is obtained by measurement, wherein the method is a common method for measuring the forming limit of the metal pipe. However, since the filling medium is liquid or gas, the sealing performance in the test process is very strict, and in addition, the equipment requirement is high, so that the test cost is increased. The conventional hemispherical rigid male die method for testing the forming limit of the metal material generally requires that the test piece is a metal plate, and the test piece is loaded in the normal direction of the surface of the plate, so that the conventional hemispherical rigid male die method is the most common method for testing the forming limit of the metal material. For the forming limit of the pipe, many people directly test the forming limit of the material plate by using a hemispherical rigid male die method as a basis for judging the cracking instability, but the method cannot acquire a complete and accurate forming limit curve, namely cannot judge the forming limit of each part of the curved structural member. Disclosure of Invention Aiming at the problems, the invention aims to provide a loading method for testing a pipe forming limit path, optimize the shape of a test piece, simplify the processing, facilitate the test and installation operation, and obtain an accurate strain forming limit diagram. And provides a test mold thereof. The technical scheme is that the loading method for testing the pipe forming limit path comprises the following steps: step one, taking a plurality of half pipes to be tested, and cutting the half pipes into various shapes; Placing one half pipe into a die, pressing the half pipe between working parts of an upper die and a lower die of the die, wherein two side ends of the half pipe are flush with the groove boundary of the lower die, the center of the half pipe is aligned with the center of the groove of the lower die, and the upper die is connected with the lower die through a bolt, so that the half pipe is fixed between the upper die and the lower die; step three, coaxially connecting a rigid male die with a male die base through a stud, and inserting the rigid male die downwards from an upper die through hole through the male die base until the rigid male die contacts with the center of the half pipe; step four, completing a strain forming limit test of the half pipe in a mode of downward drawing of a rigid male die; Sequentially replacing the half pipes, then mounting the half pipes in the die in place again, and sequentially carrying out strain forming limit tests to obtain the left part of the strain forming limit; Step six, taking a plurality of half pipes to be tested with the same shape, sequentially installing the half pipes into a die, removing the original rigid male dies, taking a plurality of rigid male dies with various shapes, sequentially installing the rigid male dies on a male die base, carrying out strain forming limit test on the half pipes to be tested with the same shape, and measuring the right part of the strain forming limit; and seventhly, obtaining all positive and negative parts of the second main strain under linear loading by measuring half pipes with different shapes and sizes and rigid male dies with different shapes and sizes, thereby obtaining all complete pipe forming limit diagrams. In addition to metal tubing, the method is also applicable to the acquisition of sheet forming limits with curved features. Further, the measured pipe is made of aluminum, copper or steel, and the thickness of the measured pipe is 0.5-5 mm. Further, when the left part of the strain forming limit is obtained, the shape of the half pipe is variable, the middle part of the half pipe is a test area, two ends of the half pipe are non-test areas, the center of the half pipe is in various widths, the non-test area is a hollow part, and the corresponding rigid male die is hemispherical, so that the half pipe test area is in a pull-press state. Optimally, when the left part of the strain forming limit is obtained, the diameter of the half pipe is 50-150 mm, the length of the half pipe is 60-160 mm, the corresponding rigid male die is hemispherical with the radius of 25-30 mm, and the outer peripheral surfaces of the two ends of the half pipe are provided with circular arc-shaped hollow parts along the circumferential direction. Most preferably, the test