CN107941609B - Method and device for establishing forming limit diagram of thin-wall pipe - Google Patents
Method and device for establishing forming limit diagram of thin-wall pipe Download PDFInfo
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- 238000010586 diagram Methods 0.000 title claims abstract description 41
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- 238000012545 processing Methods 0.000 claims description 9
- 238000005520 cutting process Methods 0.000 claims description 6
- 229910000838 Al alloy Inorganic materials 0.000 claims description 2
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 claims description 2
- 229910000881 Cu alloy Inorganic materials 0.000 claims description 2
- 229910000861 Mg alloy Inorganic materials 0.000 claims description 2
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 claims description 2
- 229910052782 aluminium Inorganic materials 0.000 claims description 2
- 239000010949 copper Substances 0.000 claims description 2
- 229910052802 copper Inorganic materials 0.000 claims description 2
- 238000001125 extrusion Methods 0.000 claims description 2
- 238000012360 testing method Methods 0.000 abstract description 6
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- 230000002457 bidirectional effect Effects 0.000 description 14
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- 238000002347 injection Methods 0.000 description 3
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- 229910000831 Steel Inorganic materials 0.000 description 1
- 238000004364 calculation method Methods 0.000 description 1
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- 238000007796 conventional method Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 238000006073 displacement reaction Methods 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000004088 simulation Methods 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 238000010998 test method Methods 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 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
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- G01N3/06—Special adaptations of indicating or recording means
- G01N3/068—Special adaptations of indicating or recording means with optical indicating or recording means
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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
- G01N3/10—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces generated by pneumatic or hydraulic pressure
- G01N3/12—Pressure testing
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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
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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
- G01N2203/003—Generation of the force
- G01N2203/0042—Pneumatic or hydraulic means
- G01N2203/0048—Hydraulic means
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- 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
- G01N2203/0274—Tubular or ring-shaped specimens
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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
- G01N2203/06—Indicating or recording means; Sensing means
- G01N2203/0641—Indicating or recording means; Sensing means using optical, X-ray, ultraviolet, infrared or similar detectors
- G01N2203/0647—Image analysis
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Abstract
The invention discloses a method and a device for establishing a forming limit diagram of a thin-wall pipe, wherein symmetrical holes are formed on the surface of a target pipe, bulging is simultaneously generated under the action of hydraulic pressure in an inner-layer pressure-bearing pipe, and the forming limit of the target pipe in all stress states from one-way stretching to two-way equal-stretching ranges can be obtained by changing the shape, size and position of the holes; under the action of hydraulic pressure inside the inner layer pressure-bearing pipe, the target pipe and the inner layer pressure-bearing pipe synchronously expand, the friction between the two pipes is small, and the target pipe cannot cause result misalignment due to the influence of friction; compared with a method for applying pressure or tension in the axial direction, the testing method is simpler, does not need closed-loop servo control of internal pressure and axial force, and can be realized by only reasonably designing the shape, size and position of the hole and selecting a proper inner layer pressure-bearing pipe as a support.
Description
Technical Field
The invention relates to the field of tube hydroforming, in particular to a method and a device for establishing a forming limit diagram of a thin-wall tube.
Background
the forming limit of the panel represents the maximum deformation that can be achieved without plastic instability, the main modes of instability of the panel being necking, breaking and wrinkling. For many years, Forming Limit Diagrams (FLD) have been widely used to describe the formability of sheet materials, and there are several different experimental methods for establishing the Forming Limit diagrams of flat sheet materials. By uniaxially stretching the sheet material, the forming limit of the tension-compression strain region (left side of the FLD) can be studied, and when the width of the stretched specimen is wide, deformation in a plane strain state is possible, so that the uniaxial stretching is applicable only to the measurement of the forming limit of the left side region of the FLD. The forming limit of the pull-pull strain region (right side of FLD) can be obtained in two ways: firstly, obtaining a forming limit in a bidirectional equal-tension stress state by utilizing hydraulic bulging of a circular die, wherein the forming limit in a bidirectional equal-tension range from plane strain is obtained by changing the shape of a sample in steel die stretching; secondly, the forming limit under the condition of bidirectional equal tensile stress is obtained by hydraulic bulging of a circular die, but the forming limit of plane strain in the range of bidirectional equal tensile stress is realized by a method of hydraulic bulging on an elliptical die, and different strain states of a pull-pull area can be realized by changing the proportion of the long axis and the short axis of an elliptical die. The international IDDRG working group has established a standard building method for sheet forming limit diagrams (ISO 12004) according to the Nakazima and Marciniak test methods.
The thin-wall pipe mainly has two forms: one is to crimp the plate and then weld it into a tube, for this kind of tube, the original plate can be used to establish its forming limit diagram according to the above method to approximately replace the forming limit of the tube after the roll welding; another is a seamless tube, rolled, extruded or drawn, which, due to its special structure, cannot be used to establish its forming limit diagram using the above-mentioned method. At present, two methods are mainly used for establishing a pipe forming limit diagram in the field of pipe forming. One is to obtain different stress states by changing the length of the pipe bulging area, but this method can only establish the right side of the FLD, the pipe gradually changes from a plane strain mode to a bidirectional tensile stress mode from the beginning to the end of deformation, and for some pipes with lower plasticity, the strain path is broken when deviating from the plane strain state for a very small time, and the unidirectional tensile stress state needs to be obtained by unidirectional stretching of an axial sample, and actually should be obtained by unidirectional stretching of a circumferential sample. The second method is to apply hydraulic pressure inside the pipe and simultaneously apply axial pressure or tension on both ends of the pipe, however, such experimental devices are difficult to implement, and especially in the case of axial tension, the experimental devices are very complicated. In addition, axial loads can only be reflected by displacement and are difficult to control by force. Therefore, the experimental measurement of the forming limit diagram of the tube is not perfect so far, and no simple and effective method for obtaining the forming limit of the tube under all strain paths in the range from single-pulling to bidirectional equal-pulling exists.
Disclosure of Invention
The invention aims to avoid the defects of the prior art and provides a method and a device for establishing a forming limit diagram of a thin-wall pipe.
the aim of the invention can be realized by adopting the following technical measures, and the method for establishing the forming limit diagram of the thin-wall pipe is designed, and comprises the following steps: drawing a grid on the surface of a target pipe, cutting holes at a specified position according to the preset, and loading an inner layer pressure-bearing pipe inside the target pipe; the outer diameter of the inner layer pressure-bearing pipe is equal to the inner diameter of a target pipe, and the length of the inner layer pressure-bearing pipe is equal to the length of the target pipe; fixing and sealing two ends of the target pipe and the inner layer pressure-bearing pipe through a seal, and arranging a channel communicated with the interior of the inner layer pressure-bearing pipe on the seal at one end; injecting a high-pressure medium into the inner layer pressure-bearing pipe through the channel, and applying axial pressure to the seals at two ends to enable the inner layer pressure-bearing pipe to drive the target pipe to synchronously expand and deform until the target pipe is broken and unstable; measuring the limit strain of a region near a target pipe fracture and crack to obtain the forming limit strain of the target pipe in a stress state; and changing the position of the cut hole on the target pipe and the size and shape of the hole for multiple times, repeating the steps to obtain the forming limit strain of the target pipe in different stress states, and forming a forming limit diagram in a coordinate system taking the circumferential strain and the axial strain as coordinates.
The aim of the invention can be achieved by adopting the following technical measures, and the device for establishing the forming limit diagram of the pipe is designed, and comprises the following steps: the mould is used for fixing a combined pipe consisting of a target pipe and an inner layer pressure-bearing pipe; the closing mechanism is used for closing two ends of the combined pipe and providing a channel leading to the interior of the combined pipe; the injection mechanism is used for injecting high-pressure medium into the combined pipe through the channel; and the processing mechanism is used for analyzing and processing the forming limit strain of the target pipe in different stress states when the target pipe is subjected to fracture instability due to hydraulic action, and forming a forming limit diagram in a coordinate system taking the annular strain and the axial strain as coordinates.
different from the prior art, the method and the device for establishing the forming limit diagram of the thin-wall pipe are characterized in that symmetrical holes are formed in the surface of a target pipe, and the forming limit of the pipe in all stress states in the range from unidirectional stretching to bidirectional equal-stretching can be obtained by changing the shape, size and position of the holes; under the action of hydraulic pressure inside the inner layer pressure-bearing pipe, the target pipe and the inner layer pressure-bearing pipe synchronously expand, the friction between the two pipes is small, and the target pipe cannot cause result misalignment due to the influence of friction; compared with a method for applying pressure or tension in the axial direction, the testing method is simpler, does not need closed-loop servo control of internal pressure and axial force, and can be realized by only reasonably designing the shape, size and position of the hole and selecting a proper inner layer pressure-bearing pipe as a support.
Drawings
FIG. 1 is a schematic flow chart of a method for establishing a forming limit diagram of a thin-wall tube provided by the invention;
FIG. 2 is a schematic structural diagram of a first embodiment of the device for establishing a forming limit diagram of a thin-wall pipe provided by the invention;
FIG. 3 is a schematic diagram of a target pipe expanding along with an inner layer pressure-bearing pipe in another embodiment of the device for establishing a forming limit diagram of a thin-wall pipe provided by the invention;
Fig. 4 is a schematic diagram of a target pipe expanding along with an inner layer pressure-bearing pipe in the first embodiment of the device for establishing a thin-wall pipe forming limit diagram.
Detailed Description
The technical solution of the present invention will be further described in more detail with reference to the following embodiments. It is to be understood that the described embodiments are merely a few embodiments of the invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
Referring to fig. 1, fig. 1 is a schematic flow chart of a method for establishing a forming limit diagram of a thin-walled tube according to the present invention. The method comprises the following steps:
S110: drawing grids on the surface of the target pipe, cutting holes at the designated positions according to the preset conditions, and loading the inner-layer pressure-bearing pipe inside the target pipe.
And cutting holes in a designated area of the thin-wall target pipe to be measured according to a preset shape. If the hole is cut in the central area of the target pipe, the cut holes are arranged on two sides which take the central point of the target pipe as a symmetrical point, the shape and the size are kept consistent, circular or square grids are printed on the target pipe, then the inner layer pressure-bearing pipe is loaded into the target pipe, the outer diameter of the inner layer pressure-bearing pipe is kept equal to the inner diameter of the target pipe, and the inner layer pressure-bearing pipe can be just and smoothly placed into the target pipe.
the material or the wall thickness of the inner layer pressure-bearing pipe and the outer layer target pipe can be the same or different, but the rupture instability of the inner layer pressure-bearing pipe is ensured to be later than that of the outer layer target pipe, and the inner layer pressure-bearing pipe can be ruptured simultaneously or not ruptured when the target pipe is ruptured. Wherein the target pipe material is a seamless pipe obtained by extrusion and drawing. As in the background art, such pipes cannot be tested for forming limits by conventional methods of establishing a sheet forming limit diagram. Specifically, the target pipe material is one of aluminum, aluminum alloy, magnesium alloy, copper and copper alloy.
S120: the target pipe and the inner layer pressure-bearing pipe are fixedly sealed at two ends through a seal, and a channel communicated with the interior of the inner layer pressure-bearing pipe is arranged on the seal at one end.
After the target pipe and the inner layer pressure-bearing pipe are assembled, two ends of the target pipe and the inner layer pressure-bearing pipe are fixedly sealed through a sealing object. In the present invention, the closure on both sides is two punches, as shown in fig. 2. The two ends of the target pipe and the inner layer pressure-bearing pipe are fixedly sealed by applying opposite axial pressure to the punch. One of the two punches is provided with a channel communicated with the inside of the inner layer pressure-bearing pipe. In other embodiments, a fixed closure as shown in FIG. 3 may be used. In fig. 3, a mandrel is disposed inside the inner pressure containing pipe. The core rod is dumbbell-shaped, the diameters of the two end parts are equal to the inner diameter of the inner layer pressure-bearing pipe, and the diameter of the middle part is smaller than the inner diameter of the inner layer pressure-bearing pipe, so that a gap is formed between the core rod and the inner wall of the inner layer pressure-bearing pipe. A channel is arranged in the core rod, an inlet of the channel is arranged at any one end of two sides of the dumbbell-shaped core rod, the channel extends towards the inside of the core rod, an outlet of the channel is arranged in the middle of the core rod, and a gap between the core rod and the inner wall of the inner layer pressure-bearing pipe is communicated with the outside through the channel. Meanwhile, O-shaped sealing rings are respectively arranged at the positions where the two ends of the core rod are contacted with the inner layer pressure-bearing pipe, so that the sealing performance is ensured. Furthermore, the two ends of the target pipe are provided with the tensioning rings so as to realize the fixed sealing of the two ends of the target pipe. Compared with the technical scheme of fixing by using the punch, the fixing and sealing of the two ends of the target pipe and the inner layer pressure-bearing pipe are realized by clamping the tensioning rings, so that the problem of axial wrinkling and instability of the pipe in the axial direction easily caused in the flaring sealing process in the technical scheme of applying axial pressure by using the punch can be solved.
S130: high-pressure medium is injected into the inner layer pressure-bearing pipe through the channel, and meanwhile, axial pressure is applied to the seals at the two ends, so that the inner layer pressure-bearing pipe drives the target pipe to synchronously expand and deform until the target pipe is broken and unstable.
High-pressure media such as liquid water and the like are injected into the inner-layer pressure-bearing pipe through the channel. Along with the continuous injection of high-pressure medium, the internal pressure of the inner layer pressure-bearing pipe is also increased continuously, so that the inner layer pressure-bearing pipe gradually expands under the action of the internal pressure, and the outer layer target pipe is simultaneously expanded under the drive of the inner layer pressure-bearing pipe. Because the outer layer target pipe and the inner layer pressure-bearing pipe keep synchronous expansion deformation, the friction action between the outer layer target pipe and the inner layer pressure-bearing pipe is small, the deformation of the target pipe is less influenced by friction, and the pressure in the inner layer pressure-bearing pipe is increased by continuously injecting high-pressure medium until the target pipe is broken and unstable.
s140: and measuring the ultimate strain of the area near the target pipe fracture and crack to obtain the forming ultimate strain of the target pipe in a stress state, namely the annular and axial ultimate strains.
Since the hole cutting operation is performed on the target tubular product in step S110, the fracture position at which the target tubular product is fractured is generally in the vicinity of the hole cutting. And measuring the limit strain of the area near the target pipe crack by using an ASAME grid strain test system, so as to obtain the forming limit strain of the target pipe corresponding to the current stress state.
The strain of the target pipe at the fracture point in the deformation process can also be used for preparing a speckle image on the pipe in advance, real-time acquisition is carried out through a CCD (charge coupled device) camera, then a strain path of the area near the fracture point of the target pipe in the deformation process is obtained through an analysis experiment through a special three-dimensional digital speckle strain measurement and analysis system, and the forming limit strain under the current stress state is further calculated.
S150: and changing the position of the cut hole on the target pipe and the size and the shape of the hole for multiple times, repeating the steps to obtain the forming limit strain of the target pipe in different stress states, and forming a forming limit diagram in a coordinate system taking the circumferential strain and the axial strain as coordinates.
And repeating the operations of the steps S110 to S140 by changing the position of the cut hole on the target pipe and the size and the shape of the cut hole for multiple times to obtain the forming limit strain of the target pipe in different stress states. By changing the position, size and shape of the cut hole, any stress state in the range of tensile stress from unidirectional stretching to bidirectional stretching can be obtained, so that the forming limit under any strain path can be obtained, and the shape, position and size of the cut hole can be designed by a numerical simulation means, so that the strain path in the deformation process of the target pipe can also be obtained. By varying the length of the bulging zone for a given shape, size and location on the target pipe, a variety of different strain paths can be obtained. The stress state of the target pipe in the area between the holes can be changed by changing the shape, size and position of the holes, so that the stress state of the rupture point of the target pipe is changed from unidirectional stretching to bidirectional equal stretching, the strain path is close to a linear loading form, the holes are arranged on two sides of the pipe and are symmetrical, and the target pipe is kept balanced in the bulging process.
And (3) obtaining the forming limit strain of the target pipe under different stress states, and describing the limit strain under different stress states in a coordinate system taking the circumferential strain and the axial strain as coordinates to obtain a forming limit diagram of the target pipe. Generally, five experimental points are sufficient for the range from unidirectional stretching to bidirectional equal stretching.
Different from the prior art, the method for establishing the forming limit diagram of the thin-wall pipe is characterized in that symmetrical holes are formed in the surface of a target pipe, and the forming limit of the pipe in all stress states in the range from unidirectional stretching to bidirectional equal-stretching can be obtained by changing the shape, size and position of the holes; under the action of hydraulic pressure inside the inner layer pressure-bearing pipe, the target pipe and the inner layer pressure-bearing pipe synchronously expand, the friction between the two pipes is small, and the target pipe cannot cause result misalignment due to the influence of friction; compared with a method for applying pressure or tension in the axial direction, the testing method is simpler, does not need closed-loop servo control of internal pressure and axial force, and can be realized by only reasonably designing the shape, size and position of the hole and selecting a proper inner layer pressure-bearing pipe as a support.
In addition, the invention provides a device for establishing a forming limit diagram of the thin-wall pipe. The apparatus 200 comprises:
And the mould 3 is used for loading a combined pipe consisting of the target pipe 1 and the inner layer pressure-bearing pipe 2.
And the sealing mechanism is used for applying opposite axial pressure to the sealing object after the combined pipe formed by the target pipe 1 and the inner layer pressure-bearing pipe 2 is fixedly sealed by the sealing object. In one embodiment of the invention, the closing objects are punches 4 and 5 arranged at two ends of the combined pipe, and the fixed closing of the two ends of the combined pipe can be realized by applying axial pressure in opposite directions to the punches 4 and 5. Meanwhile, a passage 6 is arranged on the punch 4, and the passage 6 is communicated with the outside and the inside of the inner layer pressure-bearing pipe 2, as shown in figure 2. Fig. 4 is a schematic view of the target pipe 1 after bulging along with the inner pressure-bearing pipe 2 in the present embodiment. In another embodiment, the closure is a mandrel 7 disposed inside the inner layer pressure-bearing pipe 2, the mandrel 7 is dumbbell-shaped, the diameter of the two end portions is equal to the inner diameter of the inner layer pressure-bearing pipe 2, and the diameter of the middle portion is smaller than the inner diameter of the inner layer pressure-bearing pipe 2, so that a gap is formed between the inner wall of the inner layer pressure-bearing pipe 2. A channel 11 is arranged in the core rod 7, the inlet of the channel 11 is arranged at any one end of two sides of the dumbbell-shaped core rod 7, the channel 11 extends towards the inside of the core rod 7, the outlet is arranged in the middle of the core rod 7, and the channel 11 is used for communicating the gap between the core rod 7 and the inner wall of the inner layer pressure-bearing pipe 2 with the outside. O-shaped sealing rings 10 are respectively arranged at the positions where the two ends of the core rod 7 are contacted with the inner layer pressure-bearing pipe 2 so as to ensure the sealing property. Meanwhile, the tensioning rings 8 and 9 are arranged at the two ends of the target pipe 1, so that the two ends of the target pipe 1 are fixedly closed, as shown in fig. 3. Therefore, the problem that the axial wrinkling and instability of the pipe are easily caused in the flaring sealing process by the left punch 4 and the right punch 5 can be avoided.
The injection mechanism injects high-pressure medium into the inner layer pressure-bearing pipe 2 or into the gap between the inner layer pressure-bearing pipe 2 and the core rod 7 through the channel (6 or 11) until the target pipe 1 is broken and unstable.
And the processing mechanism 15 is used for analyzing and processing the forming limit strain of the target pipe 1 in different stress states when the target pipe 1 is subjected to fracture instability due to hydraulic action, and drawing a forming limit diagram in a coordinate system taking the annular strain and the axial strain as coordinates.
the processing mechanism 15 measures the limit strain of the target pipe 1 in the vicinity of the fracture and crack by using an ASAME grid strain test system, and obtains the forming limit strain of the target pipe in a corresponding stress state. The strain near the rupture point of the target pipe 1 in the deformation process can also be used for preparing a speckle image on the pipe in advance, real-time acquisition is carried out through a CCD (charge coupled device) camera, then a strain path of the area near the rupture point of the target pipe in the deformation process is obtained through an analysis experiment through a special three-dimensional digital speckle strain measurement and analysis system, and the forming limit strain under the current stress state is further calculated.
And obtaining the forming limit strain of the target pipe 1 in different stress states by changing the position of the cut hole on the target pipe 1 and the size and shape of the cut hole for many times. By changing the position, size and shape of the cut hole, an arbitrary stress state in a tensile stress range from unidirectional stretching to bidirectional stretching can be obtained, and the forming limit under an arbitrary strain path can be obtained. By varying the length of the bulging zone for a given shape, size and location on the target pipe, a variety of different strain paths can be obtained. As in the embodiment shown in fig. 3, the length of the expansion zone can be changed by changing the tension position of the tension rings 8 and 9 on the target tubing 1.
The processing mechanism 15 receives and processes the image acquired by the CCD camera in a wireless mode, and finally draws a forming limit diagram of the target pipe in combination with the calculation information.
The forming limit strain of the target pipe under different stress states is obtained, and the processing mechanism 15 draws the limit strain under different stress states in a coordinate system taking the circumferential strain and the axial strain as coordinates, so that a forming limit diagram of the target pipe can be obtained. Generally, five experimental points are sufficient for the range from unidirectional stretching to bidirectional equal stretching.
The device for establishing the forming limit diagram of the thin-wall pipe is different from the prior art in that symmetrical holes are formed in the surface of a target pipe, and the forming limit of the pipe in all stress states in the range from unidirectional stretching to bidirectional equal-stretching can be obtained by changing the shape, size and position of the holes; under the action of hydraulic pressure inside the inner layer pressure-bearing pipe, the target pipe and the inner layer pressure-bearing pipe synchronously expand, the friction between the two pipes is small, and the target pipe cannot cause result misalignment due to the influence of friction; compared with a method for applying pressure or tension in the axial direction, the testing method is simpler, does not need closed-loop servo control of internal pressure and axial force, and can be realized by only reasonably designing the shape, size and position of the hole and selecting a proper inner layer pressure-bearing pipe as a support.
The above description is only an embodiment of the present invention, and not intended to limit the scope of the present invention, and all modifications of equivalent structures and equivalent processes, which are made by using the contents of the present specification and the accompanying drawings, or directly or indirectly applied to other related technical fields, are included in the scope of the present invention.
Claims (6)
1. A method for establishing a forming limit diagram of a thin-wall pipe is characterized by comprising the following steps:
Drawing a grid on the surface of a target pipe, cutting holes at a specified position according to preset, and loading an inner layer pressure-bearing pipe inside the target pipe; the outer diameter of the inner layer pressure-bearing pipe is equal to the inner diameter of the target pipe, and the length of the inner layer pressure-bearing pipe is equal to the length of the target pipe;
Fixedly sealing two ends of the target pipe and the inner layer pressure-bearing pipe through a seal, and arranging a channel communicated with the interior of the inner layer pressure-bearing pipe on the seal at one end;
Injecting a high-pressure medium into the inner layer pressure-bearing pipe through the channel, and applying axial pressure to the seals at two ends simultaneously to enable the inner layer pressure-bearing pipe to drive the target pipe to synchronously expand and deform until the target pipe is broken and unstabilized;
Measuring the limit strain of the area near the target pipe fracture and crack to obtain the forming limit strain of the target pipe in a stress state;
And changing the position of the cut hole on the target pipe and the size and the shape of the hole for multiple times, repeating the steps to obtain the forming limit strain of the target pipe in different stress states, and forming a forming limit diagram in a coordinate system taking the circumferential strain and the axial strain as coordinates.
2. a method of establishing a forming limit diagram of a thin walled tube according to claim 1, wherein in the step of fixedly closing both ends of the target tube and the inner pressure-bearing tube by a closure, the closure is a punch, one of which is provided with a passage for a high pressure medium.
3. A method for establishing a forming limit diagram of a thin-walled tube according to claim 1, wherein in the step of fixedly closing both ends of the target tube and the inner layer pressure-bearing tube by means of closures, a mandrel is provided inside the inner layer pressure-bearing tube, the mandrel is dumbbell-shaped, the diameter of both end portions is equal to the inner diameter of the inner layer pressure-bearing tube, and the diameter of the middle portion is smaller than the inner diameter of the inner layer pressure-bearing tube.
4. a method for establishing a forming limit diagram of a thin-walled tube according to claim 3, wherein O-shaped sealing rings are respectively arranged at the contact positions of two ends of the core rod and the inner wall of the inner layer pressure-bearing tube to realize hydraulic sealing, and tensioning rings are arranged at two ends of the target tube to fixedly seal the two ends of the target tube.
5. The method for establishing a forming limit diagram of a thin-walled tube according to claim 1, wherein the target tube is a seamless tube obtained by extrusion and drawing; the target pipe is made of one of aluminum, aluminum alloy, magnesium alloy, copper and copper alloy.
6. The method for establishing the forming limit diagram of the thin-walled tube according to claim 1, wherein the strain of the region of the target tube at the fracture point can be acquired in real time through a CCD camera during the deformation process, and the strain path of the region of the target tube at the fracture point during the deformation process is obtained through experimental processing by an image processing system.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CN201711041052.3A CN107941609B (en) | 2017-10-31 | 2017-10-31 | Method and device for establishing forming limit diagram of thin-wall pipe |
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