CN113624602B - Experimental device and construction method for right area curve of pipe forming limit diagram - Google Patents
Experimental device and construction method for right area curve of pipe forming limit diagram Download PDFInfo
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Abstract
The invention provides an experimental device and a construction method for a curve of a right area of a pipe forming limit diagram, wherein the experimental device comprises a first positioning die and a second positioning die which are used for respectively forming positioning on two ends of the length of a test pipe, the first positioning die and the second positioning die are arranged at intervals, the experimental device also comprises a strain path limiting cylinder group, the strain path limiting cylinder group comprises a plurality of elliptical hole path limiting cylinders with elliptical holes of different sizes, and any one of the elliptical hole path limiting cylinders can be alternatively sleeved on the outer peripheral wall of the test pipe between the first positioning die and the second positioning die. According to the invention, the forming limit measurement of the test pipe in a large-range double-tensile-strain state is realized, the linearity of a loading path of the test pipe can be ensured, the fracture position of the test pipe in the double-tensile-strain state can be controlled by changing the position of the elliptical hole path limiting cylinder, and the deformation capability analysis of local defect areas such as welding seams and the like can be performed in a targeted manner.
Description
Technical Field
The invention belongs to the technical field of metal pipe forming performance evaluation, and particularly relates to an experimental device and a construction method for a curve of a right area of a pipe forming limit diagram.
Background
The tube hydroforming technology is an advanced integral forming technology for tube parts, and products of the tube hydroforming technology can be applied to the fields of aerospace, nuclear engineering, automobile engineering and the like, and make important contribution to light weight and manufacturing upgrade. The hydroforming process of the tube is generally as follows: firstly, a tube blank is placed into a mould, a certain mould closing force is applied to the mould to keep an internal cavity of the mould fixed, and after the tube blank is filled with liquid, the required part with a complex shape is formed by reasonably controlling the internal pressure and the axial material supplement amount. The parts formed by the technology have the advantages of few welding lines, small number of parts, high precision and the like, but the shapes of the parts are more and more complex along with the requirement of process upgrading, and the accurate pipe forming limit diagram is more and more important for part design and process development.
Unlike sheet materials, achieving an ideal linear loading path is more difficult due to the difficulty in obtaining forming limit test results in the range of the complete strain ratio β as a result of the shape constraints of the tubing. The existing forming limit construction method and device mainly have the problems that the strain ratio beta range of an experimentally obtained forming limit diagram is not complete enough, and particularly the obtained forming limit diagram is not forming limit data under an ideal linear path. The influence of the strain path on the forming limit cannot be ignored, so that the guidance of the result obtained by the existing pipe forming limit construction method on the analysis of the actual pipe forming process has limitation.
Disclosure of Invention
Therefore, the invention provides an experimental device and a construction method for a curve of a right area of a pipe forming limit diagram, which realize forming limit measurement of a test pipe in a large-range double-tensile-strain state through a series of elliptical hole path limiting cylinders with elliptical holes of different elliptical hole sizes, can ensure the linearity of a loading path of the test pipe, can control the fracture position of the test pipe in the double-tensile-strain state by changing the position of the elliptical hole path limiting cylinders, and can perform deformation capability analysis on local defect areas such as welding seams and the like in a targeted manner.
In order to solve the above problems, the present invention provides an experimental apparatus for a curve of a right area of a pipe forming limit diagram, comprising a first positioning mold and a second positioning mold for respectively positioning two ends of a length of a test pipe, wherein the first positioning mold and the second positioning mold are arranged at an interval, and further comprising a strain path defining cylinder set, the strain path defining cylinder set comprises a plurality of elliptical hole path defining cylinders with elliptical holes of different sizes, and any one of the elliptical hole path defining cylinders can be alternatively sleeved on an outer circumferential wall of the test pipe between the first positioning mold and the second positioning mold.
Preferably, a plurality of the elliptical hole paths define elliptical holes respectively having equal major axes and unequal minor axes.
Preferably, the strain path defining cylinder group further includes a circular hole path defining cylinder having a circular hole, the circular hole path defining cylinder being replaceably fitted to the outer peripheral wall of the test tube between the first positioning die and the second positioning die; and/or the ratio of the long axis to the short axis of the elliptical hole on each elliptical hole path limiting cylinder is 1: 1-5: 1.
Preferably, the elliptical hole has a chamfer or radius near the opening of the test tube.
Preferably, the elliptical holes respectively have a short axis and a radius of the circular hole which are sequentially in an increasing equal difference series; and/or the long axis is in the circumferential direction of the test tubing and the short axis is in the axial direction of the test tubing.
Preferably, the oval hole path defining cylinder comprises a first non-hole part and a first hole part which are mutually buckled into a whole circle, and the equal round hole path defining cylinder comprises a second non-hole part and a second hole part which are mutually buckled into a whole circle; and/or the device also comprises a mould positioning structure used for fixing the distance between the first positioning mould and the second positioning mould.
Preferably, the experimental apparatus further comprises a defining cylinder support supported at the bottom of the strain path defining cylinder group; and/or the first positioning mould comprises a first upper half mould and a first lower half mould, and the first upper half mould and the first lower half mould are buckled through a first concave-convex structure; and/or the second positioning mold comprises a second upper mold half and a second lower mold half, and the second upper mold half and the second lower mold half are buckled through a second concave-convex structure.
Preferably, the experimental device further comprises a first push rod arranged corresponding to the first end opening of the test tube, the tail end of the first push rod is provided with a first sealing head, and the first sealing head can extend into the first end opening to form a seal for the first end opening; and/or the test tube further comprises a second push rod arranged corresponding to the second end opening of the test tube, the tail end of the second push rod is provided with a second sealing head, and the second sealing head can extend into the second end opening to form closure on the second end opening.
Preferably, the first sealing head is detachably connected to the end of the first push rod, and the second sealing head is detachably connected to the end of the second push rod; and/or the axial sections of the first sealing head and the second sealing head are isosceles trapezoids.
The invention also provides a construction method of the curve of the right area of the pipe forming limit diagram, which is carried out by adopting the experimental device of the curve of the right area of the pipe forming limit diagram and comprises the following steps:
a strain path limiting step, namely selecting a round hole path limiting cylinder in the strain path limiting cylinder group to be sleeved on the test pipe, and adjusting a round hole in the round hole path limiting cylinder to be positioned in a target test area of the test pipe;
a positioning step, fixing the test pipe between the first positioning die and the second positioning die;
a loading test step, namely, after openings at two ends of the test pipe are sealed, injecting pressure fluid into the test pipe until the test pipe deforms and breaks, and testing and recording main strain data and secondary strain data of the target test area;
replacing the test tube, sequentially selecting a round hole path limiting cylinder or an elliptical hole path limiting cylinder before replacing the elliptical hole path limiting cylinder from the strain path limiting cylinder group according to the sequence that the minor axes of elliptical holes respectively arranged on the elliptical hole path limiting cylinders are from long to short, sleeving the round hole path limiting cylinder or the elliptical hole path limiting cylinder on the replaced test tube, and repeating the positioning step and the loading test step;
and drawing a curve of the right area of the pipe forming limit diagram, confirming a limit primary strain value and a limit secondary strain value under each strain path, and drawing a curve of the right area of the pipe forming limit diagram according to the limit primary strain value and the limit secondary strain value under each strain path.
According to the experimental device and the construction method for the curve of the right area of the pipe forming limit diagram, the forming limit measurement of a tested pipe in a large-range double-tensile-strain state is realized through a series of elliptical hole path limiting cylinders with elliptical holes of different sizes, the linearity of a loading path of the tested pipe can be ensured, the fracture position of the tested pipe in the double-tensile-strain state can be controlled by changing the positions of the elliptical hole path limiting cylinders, the deformation capacity of a local defect area such as a welding seam and the like can be analyzed in a targeted manner, and the experimental device and the construction method have the characteristics of simple shape, low implementation cost, good measurement effect and the like.
Drawings
FIG. 1 is a schematic structural diagram (section) of an experimental apparatus for a right area curve of a pipe forming limit diagram according to an embodiment of the present invention;
fig. 2 is a specific example of elliptical holes and circular holes that each of the limiting cylinders in the strain path defining cylinder group has;
FIG. 3 is a schematic perspective view of an experimental apparatus for the right area curve of the limit diagram for forming a pipe according to an embodiment of the present invention;
FIG. 4 is a right-side area curve of a pipe forming limit diagram constructed using the construction method of the present invention, in which the primary strain corresponds to the hoop strain at the target test area of the test pipe, and the secondary strain corresponds to the axial strain at the target test area of the test pipe.
The reference numerals are represented as:
1. a first positioning die; 2. a second positioning mold; 31. an elliptical hole path defining cylinder; 41. an elliptical hole; 42. a circular hole; 51. a first push rod; 52. a first sealing head; 61. a second push rod; 62. a second sealing head; 7. a mold positioning structure; 8. defining a cartridge support; 100. and (6) testing the pipe.
Detailed Description
Referring to fig. 1 to 4 in combination, according to an embodiment of the present invention, there is provided an experimental apparatus for a curve of a right area (also referred to as a first quadrant) of a pipe forming limit diagram, including a first positioning mold 1 and a second positioning mold 2 for positioning two ends of a length of a test pipe 100, in particular, the first positioning mold 1 has a first positioning hole (not shown) matched with the test pipe 100, the second positioning mold 2 has a second positioning hole (not shown) matched with the test pipe 100, the first positioning mold 1 and the second positioning mold 2 are arranged at an interval and position the test pipe 100 through the first positioning hole and the second positioning hole, respectively, and further including a strain path defining barrel set, the strain path defining barrel set includes a plurality of elliptical hole path defining barrels 31 having elliptical holes 41 with different sizes, any one of the plurality of elliptical hole path defining cylinders 31 may alternatively be sleeved on the outer circumferential wall of the test tubular 100 between the first and second positioning dies 1 and 2, each elliptical hole path defining cylinder 31 being rotatable in a circumferential direction (i.e., a circumferential direction) of the test tubular 100 to adjust a position of the elliptical hole 41 relative to the test tubular 100, for example, to avoid a position of a weld of the test tubular 100, and to enable the elliptical hole 41 to face a position of a corresponding strain measuring device to be provided. According to the technical scheme, the forming limit measurement of the test pipe in a large-range double-pulling-strain state is realized through a series of elliptical hole path limiting cylinders with elliptical holes of different sizes, the linearity of a loading path of the test pipe can be guaranteed, the breaking position of the test pipe in the double-pulling-strain state can be controlled by changing the positions of the elliptical hole path limiting cylinders, the deformation capacity of local defect areas such as welding seams is analyzed in a targeted manner, and the method has the advantages of being simple in shape, low in implementation cost, good in measurement effect and the like. Specifically, a plurality of elliptical hole path limiting cylinders with elliptical holes of different sizes are sleeved on the periphery of a tested pipe in a replacement mode, controllable limiting of a path of pipe deformation is achieved, control from deformation to breakage of the pipe at different target positions is achieved, the strain path is more ideal and linear, forming limit data under different strain paths can be obtained by matching with corresponding strain detection devices, and then construction of a right area curve of a pipe forming limit diagram is achieved.
It should be noted that the experimental apparatus is generally used in cooperation with a hydraulic expanding machine in the industry during use, and specifically, the hydraulic expanding machine has a working platform, the experimental apparatus is integrally mounted on the working platform, the first positioning mold 1 includes a first upper mold half and a first lower mold half, the second positioning mold 2 includes a second upper mold half and a second lower mold half, wherein the first lower mold half and the second lower mold half can be respectively and fixedly connected with the working platform to realize reliable and stable spacing therebetween, the first upper mold half and the second upper mold half are respectively and fixedly connected to an upper beam plate of the hydraulic expanding machine, so that the hydraulic expanding machine can control (specifically, facilitate movement of a master cylinder of the hydraulic expanding machine) closing and opening of the first upper mold half and the first lower mold half and closing and opening of the second upper mold half and the second lower mold half, thereby enabling the removal and insertion of different test tubes 100.
Preferably, the first upper half mold and the first lower half mold are fastened through a first concave-convex structure, the second upper half mold and the second lower half mold are fastened through a second concave-convex structure, for example, two matched half molds are made into a female-male type, so that the upper half mold and the lower half mold are kept relatively fixed in the horizontal direction after mold closing, and dislocation under the action of side pushing is avoided.
In some embodiments, a plurality of the elliptical hole path defining cylinders 31 respectively have elliptical holes 41 with equal major axes and unequal minor axes, so as to ensure the linearity of the deformation path; in one embodiment, the elliptical hole path defining cylinders 31 have elliptical holes 41 with a ratio of the major axis to the minor axis of 1:1 to 5:1, so as to cover the equal double-tensile strain state. As shown in fig. 4, when the ratio of the major axis to the minor axis of the elliptical hole 41 on the elliptical hole path defining cylinder 31 is 3:1 (i.e. elliptical holes with 10mm minor axis and 30mm major axis), the strain ratio is 1, and thus the equal double-tensile strain state is obtained. In a conventional pipe fitting double-pulling strain test experiment, two ends of a pipe are constrained to expand the pipe, and the strain characteristic hoop strain of the pipe is obviously greater than the axial strain, so that the strain ratio is far less than 1, and the strain paths are all nonlinear due to the large deformation area. According to the technical scheme, the deformation of the pipe is limited in a smaller area through the arrangement of the elliptical holes, so that the linearity of a strain path is effectively improved; by gradually reducing the length of the minor axis of the elliptical hole, the axial strain of the tube is promoted to increase, and the strain ratio is gradually brought closer to 1.
In the experimental apparatus of the present invention, the strain path defining cylinder set further includes a circular hole path defining cylinder (not shown, not referenced) having a circular hole 42, which is replaceably fitted to the outer circumferential wall of the test tube 100 between the first and second positioning dies 1 and 2.
In some embodiments, the major axis of the elliptical hole 41 is equal to the diameter of the circular hole 42; further, the elliptical holes 41 respectively have a short axis and a radius of the circular hole 42 in an equal difference sequence which is gradually increased; the major axis is in the hoop direction of the test tubing 100 and the minor axis is in the axial direction of the test tubing 100. Specifically, as shown in fig. 2, the elliptical hole path defining cylinders 31 have 4, each of which is configured with an elliptical hole, the major axes of the elliptical hole path defining cylinders are 30mm, but the minor axes of the elliptical hole path defining cylinders are 10mm, 15mm, 20mm and 25mm, respectively, in a specific test construction process, the circular hole path defining cylinders are firstly sleeved and then the elliptical hole path defining cylinders are sequentially sleeved, and the minor axes of the elliptical holes 41 are replaced with shorter and shorter ones (25mm to 10mm) each time until a result that the strain ratio is 1 is obtained through a test, so that construction of a forming limit diagram of a linear strain path in which the strain ratio β is 0-1 can be facilitated.
Preferably, the elliptical hole 41 has a chamfer or a radius near the opening of the test tube 100, and the circular hole 42 has a chamfer or a radius near the opening of the test tube 100, so that the stress concentration of the test tube 100 at the opening of the elliptical hole 41 or the circular hole 42 can be effectively prevented, and the influence of the cutting-off during the deformation process on the accuracy of the strain test result can be prevented.
As a specific implementation manner of the elliptical hole path defining cylinder 31 or the equal circular hole path defining cylinder, the elliptical hole path defining cylinder 31 includes a first non-hole portion (not referenced in the figure) and a first hole portion (not referenced in the figure) that are mutually fastened to form a complete circle, and the equal circular hole path defining cylinder includes a second non-hole portion (not referenced in the figure) and a second hole portion (not referenced in the figure) that are mutually fastened to form a complete circle, that is, the elliptical hole path defining cylinder 31 or the equal circular hole path defining cylinder is respectively a detachably assembled component, so that replacement of each defining cylinder in the whole test construction process can be facilitated, and the test construction efficiency is improved.
In some embodiments, the experimental apparatus further includes a mold positioning structure 7 for fixing a distance between the first positioning mold 1 and the second positioning mold 2, which may be, for example, some pressing plates, pressing strips, etc. having locking through holes in a specific implementation form, and may be fixedly connected to the working platform by bolts.
In some embodiments, the experimental apparatus further comprises a limiting cylinder support 8 supported at the bottom of the strain path limiting cylinder group, and particularly configured with a shape matching the cylinder outer wall of the elliptical hole path limiting cylinder 31 and the circular hole path limiting cylinder, for example, when the cylinder outer wall is circular, a semicircular cavity is configured on the limiting cylinder support 8 to ensure the position stability of the elliptical hole path limiting cylinder or the circular hole path limiting cylinder during the pressurization deformation. Preferably, two sets of the limiting cylinder supporting pieces 8 are arranged, and are respectively arranged corresponding to the positions of the first positioning die 1 and the second positioning die 2, so as to form balanced supports for the two axial ends of the elliptical hole path limiting cylinder 31 and the circular hole path limiting cylinder.
In some embodiments, the experimental apparatus further includes a first push rod 51 disposed corresponding to the first end opening of the test tubing 100, a first sealing head 52 is disposed at a distal end of the first push rod 51, the first sealing head 52 can extend into the first end opening to form a closure to the first end opening, and a second push rod 61 disposed corresponding to the second end opening of the test tubing 100, a second sealing head 62 is disposed at a distal end of the second push rod 61, and the second sealing head 62 can extend into the second end opening to form a closure to the second end opening, so that the inner cavity of the test tubing 100 forms a sealed cavity, and pressurization after filling with an external pressure fluid (e.g., water, hydraulic oil, etc.) is facilitated. Preferably, the first sealing head 52 is detachably connected to the end of the first push rod 51, and the second sealing head 62 is detachably connected to the end of the second push rod 61, so that the first sealing head 52 or the second sealing head 62 can be replaced by a corresponding force application component under some tension and compression working conditions, thereby further enriching the function of the experimental device of the present invention. In some embodiments, the axial cross section of the first sealing head 52 and the second sealing head 62 is an isosceles trapezoid, that is, the first sealing head 52 and the second sealing head 62 are in a truncated cone structure, which can form a reliable seal with the inner hole wall of the test tube 100 by using its own formation. The first push rod 51 and the second push rod 61 can be controlled by the hydraulic expander to move toward or away from the test pipe 100 along the axial direction of the test pipe 100.
According to an embodiment of the present invention, there is also provided a method for constructing a curve in a right area of a tube forming limit diagram, which is performed by using the above experimental apparatus for a curve in a right area of a tube forming limit diagram, and includes the following steps:
the method comprises the steps of preparing, determining the length Ld of a pipe deformation area, adjusting the distance between a first positioning die 1 and a second positioning die 2 according to the Ld, fixing the distance, sampling the test pipe 100, and printing speckles or grids on the outer surface of the test pipe;
a strain path defining step of selecting a circular hole path defining cylinder in the strain path defining cylinder group to be sleeved on the test pipe 100 and adjusting a circular hole 42 of the circular hole path defining cylinder to be in a target test area of the test pipe 100;
a positioning step, fixing the test pipe 100 between the first positioning die 1 and the second positioning die 2;
a loading test step, namely after openings at two ends of the test pipe 100 are sealed, injecting pressure fluid into the test pipe 100 until the test pipe 100 deforms and breaks, and testing and recording main strain data and secondary strain data of the target test area;
a replacement testing step, namely replacing the test pipe 100, sequentially selecting a round hole path limiting cylinder or an elliptical hole path limiting cylinder 31 before replacing the elliptical hole path limiting cylinder 31 from the strain path limiting cylinder group according to the sequence from long to short of the short axis of the elliptical hole 41 respectively arranged on the elliptical hole path limiting cylinder 31, sleeving the round hole path limiting cylinder or the elliptical hole path limiting cylinder 31 on the replaced test pipe 100, and repeating the positioning step and the loading testing step;
and drawing a curve of the right area of the pipe forming limit diagram, confirming a limit primary strain value and a limit secondary strain value under each strain path, and drawing a curve of the right area of the pipe forming limit diagram according to the limit primary strain value and the limit secondary strain value under each strain path.
The above process of the present invention is further illustrated below with reference to a specific example.
The experimental object tests that the pipe material is SAPH400, the wall thickness is 2.0mm, the diameter phi of the pipe material is 65mm, and the pipe material is a straight welded pipe.
Step 1: the length Ld of the deformation zone is selected to be 60mm with reference to the pipe diameter. As shown in fig. 1, after the dies (i.e. the first positioning die 1 and the second positioning die 2) are assembled, the dies are connected to a hydroforming device (e.g. the aforesaid hydraulic bulging machine), the distance between the first positioning die 1 and the second positioning die is adjusted to 60mm, and the dies are fixed by a die positioning structure 7;
and 2, step: cutting a pipe (namely the test pipe 100) with the length of 300mm according to the length Ld of the deformation zone, and printing speckles on the surface of the pipe;
and 3, step 3: placing the pipe into the circular hole path limiting cylinder, adjusting the position of the welding seam of the pipe to avoid the area of the circular hole 42, then integrally placing the pipe on the lower half dies respectively arranged on the first positioning die 1 and the second positioning die 2, supporting and fixing the pipe by using a limiting cylinder supporting piece 8, and adjusting the position of the elliptical hole to face the strain measuring device;
and 4, step 4: controlling a main cylinder of the hydraulic bulging machine to move downwards to enable upper half dies of the first positioning die 1 and the second positioning die 2 to be respectively matched with lower half dies, and simultaneously controlling a first push rod 51 and a second push rod 61 to seal two axial ends of the pipe;
and 5: injecting liquid into the pipe, controlling the pressure of the liquid to enable the pipe to deform until the pipe breaks, and measuring primary and secondary strain data of the deformation process of the elliptical hole area by using a strain measuring device;
and 6: according to the illustration in fig. 2, replacing the elliptical hole path defining cylinder 31 with different hole sizes (replacing the elliptical hole path defining cylinder with the minor axis of 25mm first, then performing iterative replacement with 20mm, 15mm and 10mm in sequence), repeating the above processes to realize the strain states under different strain paths, and respectively measuring the primary and secondary strain data of the deformation process of the elliptical hole area;
and 7: analyzing each group of measured data, confirming strain paths and limit primary and secondary strain values, and finally drawing the limit primary and secondary strain values under each strain path into a graph to obtain a right area curve of the pipe forming limit graph, wherein the right area curve is shown in fig. 4.
The embodiment not only overcomes the problem that a linear strain path is difficult to realize in a double-pulling strain area, but also expands the strain ratio beta range to 1, realizes the double-pulling strain state of the pipe and the like, can control the bursting position and realizes the real-time monitoring of the strain path of the pipe in the test process.
It is readily understood by a person skilled in the art that the advantageous ways described above can be freely combined, superimposed without conflict.
The present invention is not limited to the above preferred embodiments, and any modifications, equivalent substitutions and improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention. The above is only a preferred embodiment of the present invention, and it should be noted that, for those skilled in the art, several improvements and modifications can be made without departing from the technical principle of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.
Claims (8)
1. An experimental device for a curve of a right area of a pipe forming limit diagram is characterized by comprising a first positioning die (1) and a second positioning die (2) which are used for respectively forming and positioning two ends of the length of a test pipe (100), wherein the first positioning die (1) and the second positioning die (2) are arranged at intervals, and a strain path limiting cylinder group is further included, the strain path limiting cylinder group comprises a plurality of elliptical hole path limiting cylinders (31) with elliptical holes (41) of different sizes, and any one of the elliptical hole path limiting cylinders (31) can be alternatively sleeved on the outer peripheral wall of the test pipe (100) between the first positioning die (1) and the second positioning die (2); the elliptical hole path defining cylinders (31) respectively have elliptical holes (41) having equal major axes and unequal minor axes; the major axis is in the circumferential direction of the test tubular (100) and the minor axis is in the axial direction of the test tubular (100); the ratio of the major axis to the minor axis of the elliptical holes (41) respectively arranged on the elliptical hole path defining cylinders (31) is 3: 1-5: 1, so that the equal-double-tensile-strain state can be guaranteed; the elliptical holes (41) respectively have a short axis and a radius of the circular hole (42) in an equal difference number sequence which is gradually increased.
2. The laboratory apparatus according to claim 1, wherein said strain path defining cylinder set further comprises a circular hole path defining cylinder having a circular hole (42), said circular hole path defining cylinder being alternatively fitted on the outer circumferential wall of said test tube (100) between said first positioning die (1) and said second positioning die (2).
3. The laboratory device according to claim 2, characterized in that the major axis of said oblong holes (41) is equal to the diameter of said circular holes (42); and/or the elliptical hole (41) has a chamfer or a radius close to the opening of the test tubing (100), and the circular hole (42) has a chamfer or a radius close to the opening of the test tubing (100).
4. The testing device according to claim 2, wherein the elliptical hole path defining cylinder (31) comprises a first non-porous portion and a first porous portion which are mutually engaged to form a complete circle, and the circular hole path defining cylinder comprises a second non-porous portion and a second porous portion which are mutually engaged to form a complete circle; and/or the mould positioning structure (7) is used for fixing the distance between the first positioning mould (1) and the second positioning mould (2).
5. The laboratory device according to claim 2, further comprising a defining cartridge support (8) supported at a bottom of said strain path defining cartridge group; and/or the first positioning mould (1) comprises a first upper half mould and a first lower half mould, and the first upper half mould and the first lower half mould are buckled through a first concave-convex structure; and/or the second positioning mould (2) comprises a second upper mould half and a second lower mould half, and the second upper mould half and the second lower mould half are buckled through a second concave-convex structure.
6. The experimental device according to claim 2, further comprising a first push rod (51) disposed corresponding to the first end opening of the test tube (100), wherein the first push rod (51) has a first sealing head (52) at a terminal end thereof, and the first sealing head (52) can extend into the first end opening pair to form a closure of the first end opening; and/or the test tube further comprises a second push rod (61) arranged corresponding to the second end opening of the test tube (100), wherein the tail end of the second push rod (61) is provided with a second sealing head (62), and the second sealing head (62) can extend into the second end opening to form a closure of the second end opening.
7. Laboratory apparatus according to claim 6, characterized in that said first sealing head (52) is removably connected to the end of said first push rod (51) and said second sealing head (62) is removably connected to the end of said second push rod (61); and/or the axial sections of the first sealing head (52) and the second sealing head (62) are isosceles trapezoid.
8. A method for constructing a curve of a right area of a pipe forming limit diagram, which is carried out by adopting the experimental device of the curve of the right area of the pipe forming limit diagram in any one of claims 2 to 7, and comprises the following steps:
a strain path defining step of selecting a circular hole path defining cylinder in the strain path defining cylinder group to be sleeved on the test pipe (100) and adjusting a circular hole (42) of the circular hole path defining cylinder to be in a target test area of the test pipe (100);
a positioning step, namely fixing a test pipe (100) between the first positioning mould (1) and the second positioning mould (2);
a loading test step, namely sealing openings at two ends of the test pipe (100), injecting pressure fluid into the test pipe (100) until the test pipe (100) deforms and breaks, and testing and recording main strain data and secondary strain data of the target test area;
a replacement testing step, namely replacing the test pipe (100), sequentially selecting a round hole path limiting cylinder or an elliptical hole path limiting cylinder (31) before replacing the elliptical hole path limiting cylinder (31) from the strain path limiting cylinder group according to the sequence from long to short of the short axis of the elliptical hole (41) respectively arranged on the elliptical hole path limiting cylinder (31), sleeving the round hole path limiting cylinder or the elliptical hole path limiting cylinder (31) on the replaced test pipe (100), and repeating the positioning step and the loading testing step;
and drawing a curve of the right area of the pipe forming limit diagram, confirming a limit primary strain value and a limit secondary strain value under each strain path, and drawing a curve of the right area of the pipe forming limit diagram according to the limit primary strain value and the limit secondary strain value under each strain path.
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