An experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube

Abstract

The application provides an experimental method for directly measuring an in-plane anisotropy coefficient of a metal thin-walled tube, belongs to the field of plastic processing of metal tubes, and can solve the problem that the in-plane anisotropy coefficient of a non-main axis of a thin-walled tube cannot be directly measured through experiments. The method comprises the following steps: determining the shape and size of a hole experimental sample according to the size of a to-be-measured thin-walled tube; the maximum length of the experimental sample along the circumferential direction of the thin-walled tube should be less than half of the circumferential section length of the to-be-measured thin-walled tube; cutting the experimental sample from the to-be-measured thin-walled tube according to the shape and size of the experimental sample; determining the shape and size of a punch, a concave die and a blank holder required by the experiment according to the shape and size of the experimental sample, and designing an experimental die; completing deformation by using the punch of the experimental die to descend to the small hole of the experimental sample at a certain speed; obtaining characteristic parameters of the edge of the small hole; and determining the in-plane anisotropy coefficient of each direction of the thin-walled tube by using the obtained characteristic parameters of the edge of the small hole.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of plastic processing of metal pipes, in particular to an experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled pipe. BACKGROUND

[0002] A metal thin-walled pipe is a hollow structure, has a light weight, and has good mechanical properties and formability, and can be manufactured into various complex hollow variable cross-section integral components through plastic processing. Such components have good bending and torsion resistance, significant weight reduction effect, etc., and are widely used in the fields of aviation, aerospace, automobiles, etc. Common manufacturing processes of metal thin-walled pipes include rolling, extrusion and drawing, etc. During the manufacturing process, the material is subjected to large deformation in the same direction, and each grain will gradually rotate in the same direction to form a so-called preferred direction, resulting in that the manufactured thin-walled pipe has obvious in-plane anisotropy. Such anisotropy characteristics are generally characterized by an anisotropy coefficient, and the anisotropy coefficient is a key parameter for accurately constructing a plastic constitutive model of a metal thin-walled pipe.

[0003] The existing mechanical property testing methods of metal pipes mainly include: pipe axial single-pull experiment, pipe hoop tensile experiment, pipe free bulging experiment and pipe biaxial controllable loading experiment, etc. The pipe axial single-pull experiment can measure the anisotropy coefficient of the pipe in the axial direction, the pipe hoop tensile experiment can obtain the anisotropy coefficient of the pipe in the hoop direction, and the pipe free bulging experiment and the pipe biaxial controllable loading experiment can obtain the stress-strain curve under the biaxial stress state. However, the above methods cannot measure the anisotropy coefficient of the thin-walled pipe in the non-principal axis direction (non-axial, non-hoop direction). It is difficult to accurately obtain the anisotropy coefficient in the non-principal axis direction, which becomes a bottleneck problem for accurately constructing the plastic constitutive model of the in-plane anisotropic metal thin-walled pipe. Therefore, how to accurately obtain the anisotropy coefficient of the pipe in any direction in the plane is a technical problem to be solved in the field. SUMMARY

[0004] The purpose of the present application is to provide an experimental method for directly measuring the anisotropy coefficient of a metal thin-walled pipe in any direction in the plane, so as to solve the problems existing in the prior art. The experiment can directly reflect the plastic deformation of the metal thin-walled pipe in any direction in the plane, so as to directly measure the anisotropy coefficient of the metal thin-walled pipe in any direction in the plane.

[0005] In order to achieve the above-mentioned purpose, the present application provides an experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled pipe, comprising the following steps:

[0006] Step 1: According to the size of the thin-walled pipe to be measured, the shape and size of the experimental sample with holes are determined. The maximum length of the experimental sample along the hoop direction of the thin-walled pipe should be not greater than half of the circumferential length of the hoop cross-section of the thin-walled pipe to be measured;

[0007] Step two, according to the shape and size of the experimental sample determined in step one, cut the experimental sample from the thin-walled tube to be tested;

[0008] Step three, according to the shape and size of the experimental sample, determine the shape and size of the punch, the concave die and the blank holder required for the experiment, and design the experimental mold;

[0009] Step four, place the experimental sample on the top of the mold concave die, with the center of the small hole of the experimental sample coaxial with the center hole of the concave die, and the blank holder placed on the top of the experimental sample in the appropriate position, and the punch placed coaxially with the center hole of the concave die, and the punch is lowered at a certain speed to complete the deformation of the small hole of the experimental sample;

[0010] Step five, obtain the characteristic parameters of the edge of the small hole of the sample;

[0011] Step six, using the characteristic parameters of the edge of the small hole obtained in step five, determine the anisotropy coefficients of the thin-walled tube in each direction in the plane.

[0012] Preferably, in step one, the material of the thin-walled tube is metal, such as aluminum alloy, low carbon steel, magnesium alloy, high strength steel, and high temperature alloy;

[0013] Preferably, in step one, the shape of the experimental sample with a hole is determined as follows: according to the experimental requirements, the outer contour of the experimental sample after flattening is a specific shape, such as a circle, an ellipse, or a rectangle; the small hole on the experimental sample is a closed specific shape after flattening, such as a circle or an ellipse;

[0014] Preferably, in step two, the experimental sample can be cut according to the experimental conditions by selecting appropriate processing methods, such as wire electrical discharge machining, laser cutting, end milling, and water cutting;

[0015] Preferably, in step four, the size of the center hole of the mold concave die is larger than the size of the small hole of the experimental sample;

[0016] Preferably, in step four, when the edge of the small hole of the experimental sample is about to crack or the force of the punch suddenly decreases, the punch is stopped from descending, and the deformation of the small hole of the experimental sample is completed;

[0017] Preferably, in step five, the characteristic parameters of the edge of the small hole of the sample are strain, strain increment, wall thickness or length, which can be obtained by strain or wall thickness or length measuring equipment. If the characteristic parameter is strain, it can be hoop strain, thickness strain or radial strain; if the characteristic parameter is strain increment, it can be hoop strain increment, thickness strain increment or radial strain increment; if the characteristic parameter is wall thickness or length, it can be the thickness of the edge of the small hole, the hoop length or the radial length;

[0018] Preferably, in step five, the characteristic parameters of the edge of the small hole include those obtained during the experiment and after the experiment;

[0019] Preferably, in step six, based on the obtained orifice edge characteristic parameters, a suitable method for determining the anisotropy coefficients in various directions within the thin-walled tube surface is selected:

[0020] When step five yielded the angle between the edge of the sample aperture and the axial direction, it was found that... radial strain components in the direction and thickness strain components When, the angle with the axis is Anisotropy coefficient in direction It can be calculated as follows:

[0021]

[0022] When step five yielded the angle between the edge of the sample aperture and the axial direction, it was found that... Circumferential strain components in the direction and thickness strain components When, the angle with the axis is Anisotropy coefficient in direction It can be calculated as follows:

[0023]

[0024] When step five yielded the angle between the edge of the sample aperture and the axial direction, it was found that... Circumferential strain components in the direction and radial strain components When, the angle with the axis is Anisotropy coefficient in direction It can be calculated as follows:

[0025]

[0026] When step five yielded the angle between the edge of the sample aperture and the axial direction, it was found that... radial strain increment in the direction and thickness strain increment When, the angle with the axis is Anisotropy coefficient in direction It can be calculated as follows:

[0027]

[0028] When step five yielded the angle between the edge of the sample aperture and the axial direction, it was found that... Circumferential strain increment in the direction and thickness strain increment When, the angle with the axis is Anisotropy coefficient in direction It can be calculated as follows:

[0029]

[0030] When the step five obtains the angle between the edge of the sample hole and the axial direction is the increment of hoop strain in the direction of and the increment of radial strain in the direction of the anisotropy coefficient in the direction of the angle between the edge of the sample hole and the axial direction is can be calculated as follows:

[0031]

[0032] When the step five obtains the thickness or length characteristic parameters of the hole edge, the thickness or length change is calculated to obtain the thickness strain or hoop strain or radial strain, and then the anisotropy coefficient in each direction on the surface of the thin-walled tube is determined by the strain.

[0033] The present application has the following beneficial effects relative to the prior art:

[0034] (1) The anisotropy coefficient in the non-principal axis direction of the thin-walled tube can be directly obtained by experiment The problem that the anisotropy coefficient in the non-principal axis direction of the thin-walled tube cannot be directly determined by experiment is solved.

[0035] (2) The determination of the anisotropy coefficient in any direction on the surface of the thin-walled tube can be realized by one experiment, which provides important support for accurately establishing the plastic constitutive relationship of the thin-walled tube that can comprehensively reflect the anisotropic plastic flow characteristics on the surface of the thin-walled tube, and further lays a theoretical foundation for forming complex hollow variable cross-section integral components.

[0036] (3) The experimental method involved in the present method can reveal the anisotropy characteristics on the surface of various typical thin-walled tubes, including extruded thin-walled tubes, drawn thin-walled tubes, rolled thin-walled tubes, spun thin-walled tubes, and various thin-walled tubes subjected to diameter change treatment.

[0037] (4) The experimental principle involved in the present method is simple, and the experimental sample maintains the spatial curvature of the to-be-measured thin-walled tube, without introducing additional pre-strain to cause experimental errors.

[0038] (5) The experimental method involved in the present method is simple and does not require a complex control system, and is easy for operators to master.

[0039] (6) The experiment involved in the present method can be used to determine the in-plane anisotropy coefficients of thin-walled tubes made of various metal materials, such as aluminum alloy, titanium alloy, magnesium alloy, high-strength steel, etc., and has a wide range of applications.

[0040] (7) The experimental method involved in the method can be used to determine the in-plane anisotropy coefficient of the seamless metal thin-walled tube and the in-plane anisotropy coefficient of the jointed metal thin-walled tube. BRIEF DESCRIPTION OF DRAWINGS

[0041] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without any creative effort on the basis of these drawings.

[0042] Figure 1 The flowchart of the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application;

[0043] Figure 2 The schematic diagram of the thin-walled tube to be measured in the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application, and the axial line, the hoop direction and the angle between the axial line and the hoop direction of the tube are defined

[0044] Fig. 3(a) is a schematic diagram of the experimental sample cut from the thin-walled tube to be measured in the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application, and Fig. 3(b) is a circular flattened diagram of the experimental sample;

[0045] Fig. 4(a) is a schematic diagram of the experimental sample cut from the thin-walled tube to be measured in the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application, and Fig. 4(b) is an elliptical flattened diagram of the experimental sample;

[0046] Fig. 5(a) is a schematic diagram of the experimental sample cut from the thin-walled tube to be measured in the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application, and Fig. 5(b) is a rectangular flattened diagram of the experimental sample;

[0047] Fig. 6(a) is a schematic diagram of a circular small hole on the experimental sample in the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application, and Fig. 6(b) is a schematic diagram of an elliptical small hole on the experimental sample;

[0048] Figure 7 Fig. 7 is a schematic diagram of the experimental sample after the experiment is completed in the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application;

[0049] Figure 8 Fig. 8 is a schematic diagram of the in-plane anisotropy coefficient of the thin-walled tube to be measured in the embodiment of the experimental method for directly determining the in-plane anisotropy coefficient of the metal thin-walled tube of the present application.

[0050] Where H is the maximum length of the experimental specimen along the circumference after unfolding, Z is the maximum length of the experimental specimen along the axial direction after unfolding, and K is the minimum diameter of the small hole after unfolding. Detailed Implementation

[0051] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] The purpose of this invention is to solve the problem that the anisotropy coefficient in the non-principal axis direction (non-axial, non-circumferential) of the tube surface cannot be measured by this experimental method for determining the anisotropy coefficient in the surface of a thin-walled metal tube.

[0053] To make the objectives, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0054] The specific implementation steps of the experimental method for directly determining the in-plane anisotropy coefficient of thin-walled metal tubes proposed in this invention are as follows:

[0055] Step 1: Based on the thin-walled tube to be tested ( Figure 2 The dimensions are determined to establish the shape and size of the perforated test specimen. The maximum length H of the test specimen along the circumferential direction of the thin-walled tube should not exceed half the circumference of the circumferential section of the thin-walled tube to be tested. Assuming the initial outer diameter of the thin-walled tube to be tested is D0 and the initial wall thickness is t0, the diameter K of the small hole on the test specimen in Figures 3(a) and 3(b) should be greater than the initial wall thickness of the thin-walled tube. Therefore, H ≤ πD0 / 2 and K > t0.

[0056] Step 2: Cut the experimental sample from the thin-walled tube to be tested according to the experimental sample shape and size determined in Step 1.

[0057] Step 3: Based on the shape and size of the experimental sample, determine the shape and size of the punch, die, and blank holder required for the experiment, and design the experimental mold;

[0058] Step 4: Place the test specimen on the top of the die cavity, with the center of the small hole of the test specimen coaxial with the center hole of the die cavity. Place the pressure ring at the appropriate position on the top of the test specimen. Place the punch coaxial with the center hole of the die cavity. The punch descends to the small hole of the test specimen at a certain speed to complete the deformation.

[0059] Step 5: Obtain the characteristic parameters of the edge of the small hole in the sample;

[0060] Step Six: Using the orifice edge feature parameters obtained in Step Five, determine the anisotropy coefficients in each direction within the thin-walled tube surface. Figure 8 );

[0061] Preferably, in step one, the thin-walled tube is made of metal, such as aluminum alloy, low carbon steel, magnesium alloy, high strength steel, or high temperature alloy.

[0062] Preferably, in step one, the method for determining the shape of the perforated experimental specimen is as follows: according to experimental requirements, the outer contour of the experimental specimen after flattening is a specific shape, such as a circle (Figure 3(a), Figure 3(b)), an ellipse (Figure 4(a), Figure 4(b)), or a rectangle (Figure 5(a), Figure 5(b)); the small holes on the experimental specimen are closed specific shapes after flattening, such as a circle (Figure 6(a)) or an ellipse (Figure 6(b)).

[0063] Preferably, in step two, a suitable processing method can be selected to cut the experimental sample according to the experimental conditions, such as wire electrical discharge machining, laser cutting, end milling, or water jet cutting.

[0064] Preferably, in step four, the size of the center hole of the mold cavity is larger than the size of the small hole of the experimental sample;

[0065] Preferably, in step four, when the punch descends, the descent is stopped when it is observed that the edge of the small hole of the experimental sample is about to crack or the force of the punch suddenly decreases, thus completing the deformation of the small hole of the experimental sample.

[0066] Preferably, in step five, the characteristic parameters of the sample aperture edge are strain, strain increment, wall thickness, or length, which can be obtained by strain, wall thickness, or length measuring equipment. If the characteristic parameter is strain, it can be circumferential strain, thickness strain, or radial strain; if the characteristic parameter is strain increment, it can be circumferential strain increment, thickness strain increment, or radial strain increment; if the characteristic parameter is wall thickness or length, it can be aperture edge thickness, circumferential length, or radial length.

[0067] Preferably, obtaining the pinhole edge feature parameters in step five includes obtaining the pinhole edge feature parameters both during and after the experiment;

[0068] Preferably, in step six, based on the obtained orifice edge characteristic parameters, a suitable method for determining the anisotropy coefficients in various directions within the thin-walled tube surface is selected:

[0069] When step five yielded the angle between the edge of the sample aperture and the axial direction, it was found that... radial strain components in the direction and thickness strain components When, the angle with the axis is Anisotropy coefficient in direction It can be calculated as follows:

[0070]

[0071] When the hoop strain component in the direction of the angle between the edge of the hole in the test specimen and the axial direction is obtained in step five and the thickness strain component is obtained in step five then the anisotropy coefficient in the direction of the angle between the edge of the hole in the test specimen and the axial direction is calculated as follows:

[0072]

[0073] When the hoop strain component in the direction of the angle between the edge of the hole in the test specimen and the axial direction is obtained in step five and the radial strain component is obtained in step five then the anisotropy coefficient in the direction of the angle between the edge of the hole in the test specimen and the axial direction is calculated as follows:

[0074]

[0075] When the radial strain increment in the direction of the angle between the edge of the hole in the test specimen and the axial direction is obtained in step five and the thickness strain increment is obtained in step five then the anisotropy coefficient in the direction of the angle between the edge of the hole in the test specimen and the axial direction is calculated as follows:

[0076]

[0077] When the hoop strain increment in the direction of the angle between the edge of the hole in the test specimen and the axial direction is obtained in step five and the thickness strain increment is obtained in step five then the anisotropy coefficient in the direction of the angle between the edge of the hole in the test specimen and the axial direction is calculated as follows:

[0078]

[0079] When the hoop strain increment in the direction of the angle between the edge of the hole in the test specimen and the axial direction is obtained in step five and the radial strain increment is obtained in step five then the anisotropy coefficient in the direction of the angle between the edge of the hole in the test specimen and the axial direction is calculated as follows:

[0080] ​​​​​​​​​​​​​​​

[0081] When the small hole edge wall thickness or length characteristic parameter is obtained in step five, the thickness or length change is calculated to obtain the thickness strain or the hoop strain or the radial strain, and then the strain is used to determine the anisotropy coefficient of each direction on the thin-walled tube plane.

[0082] In embodiment two, the experiment can be completed by using uniform loading or pulse loading when the punch is descending in step four. The other steps are the same as those in embodiment one.

[0083] In embodiment three, the small hole edge strain or strain increment after deformation can be determined by using the digital image correlation method (DIC), a static strain measuring instrument or a strain gauge. The other steps are the same as those in embodiment one.

[0084] In embodiment four, the strain of the small hole edge of the sample can be measured in real time during the deformation of the small hole of the sample by using DIC in step five. The other steps are the same as those in embodiment one.

[0085] In embodiment five, the thickness of the small hole edge before and after deformation can be determined by using a micrometer or an ultrasonic thickness gauge. The other steps are the same as those in embodiment one.

[0086] In embodiment six, the length of the small hole edge before and after deformation can be determined by using a micrometer, a vernier caliper or DIC. The hoop length or the radial length of the small hole edge is obtained by length measurement. The other steps are the same as those in embodiment one.

[0087] In embodiment seven, the thickness strain of the small hole edge can be determined by using the initial wall thickness and the wall thickness after deformation of the small hole edge of the experimental sample, the hoop strain of the small hole edge can be determined by using the initial hoop length and the hoop length after deformation of the small hole edge of the experimental sample, and the radial strain can be further determined by using the volume invariance condition during plastic deformation. The other steps are the same as those in embodiment one.

[0088] The principles and embodiments of the present application are described in the embodiments, but these embodiments are only part of the embodiments of the present application, and are not all the embodiments of the present application, and therefore cannot be understood as limiting the scope of the present application. It should be pointed out that, for those skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, and these modifications and improvements all belong to the protection scope of the present application.

Claims

1. An experimental method for directly measuring the in-plane anisotropy coefficient of a thin-walled metal tube, characterized by, The method comprises the following steps: Step one: according to the size of the thin-walled pipe to be measured, the shape and size of the experimental sample with a hole are determined; the maximum length of the experimental sample along the circumferential direction of the thin-walled pipe should be less than half of the circumferential section length of the thin-walled pipe to be measured; Step two: according to the shape and size of the experimental sample determined in step one, the experimental sample is cut from the thin-walled pipe to be measured; Step three: according to the shape and size of the experimental sample, the shape and size of the punch, the concave die and the blank holder required for the experiment are determined, and the experimental mold is designed; Step four: the experimental sample is placed on the top of the mold concave die, the center of the small hole of the experimental sample is coaxial with the center hole of the concave die, the blank holder is placed on the top of the experimental sample at the appropriate position, the punch is coaxially placed with the center hole of the concave die, and the punch is lowered at a certain speed to complete the deformation of the small hole of the experimental sample; Step five: the characteristic parameters of the edge of the small hole of the sample are obtained; Step six: the anisotropy coefficients of the thin-walled pipe in each direction on the surface are determined by using the characteristic parameters of the edge of the small hole obtained in step five; According to the obtained characteristic parameters of the edge of the small hole, the appropriate determination method of the anisotropy coefficients of the thin-walled pipe in each direction on the surface is selected: When step five yields a sample hole edge to axial angle of the radial strain component in the direction and the thickwise strain component then the anisotropy coefficient in the direction of the hole edge to axial angle is calculated as follows: （1）； When the step five obtains the edge of the sample hole and the axial angle is the hoop strain component in the direction and the thick strain component then the anisotropy coefficient in the direction with the axial angle is calculated as follows: （2）； When the step five obtains the angle between the edge of the sample hole and the axial direction is the component of hoop strain in the direction and the component of radial strain then the anisotropy coefficient in the direction of the angle between the edge of the sample hole and the axial direction is calculated as follows: （3）； When the step five obtains the edge of the sample hole and the axial angle is the radial strain increment in the direction and the thickness strain increment is the anisotropy coefficient in the direction calculated as follows: （4）； When the step five obtains the edge of the sample hole and the axial angle is the circumferential strain increment in the direction and the thickness strain increment is the anisotropy coefficient in the direction calculated as follows: （5）； When the step five obtains the edge of the sample hole and the axial angle is the circumferential strain increment in the direction and the radial strain increment is the anisotropy coefficient in the direction calculated as follows: （6）； When the thickness or length characteristic parameters of the edge of the small hole are obtained in step five, the thickness or length change is calculated to obtain the thickness strain or circumferential strain or radial strain, and then the anisotropy coefficients of the thin-walled pipe in each direction on the surface are determined by the strain.

2. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step one, the metal thin-walled pipe is made of aluminum alloy, low-carbon steel, magnesium alloy, high-strength steel or high-temperature alloy.

3. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step one, the shape of the experimental sample with a hole is determined as follows: according to the experimental requirements, the outer contour of the experimental sample after flattening is circular, elliptical or rectangular; the small hole on the experimental sample is a closed circle or ellipse after flattening.

4. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step two, the experimental sample is cut by selecting the appropriate processing method according to the experimental conditions, and the processing method is wire electrical discharge machining, laser cutting, end milling or water cutting.

5. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step four, the size of the center hole of the mold concave die is larger than that of the small hole of the experimental sample.

6. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step four, when the edge of the small hole of the experimental sample is about to crack or the force of the punch suddenly decreases, the punch is stopped from descending, and the deformation of the small hole of the experimental sample is completed.

7. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step five, the characteristic parameters of the edge of the small hole of the sample are strain, strain increment, wall thickness or length, which are obtained by strain or wall thickness or length measuring equipment; if the characteristic parameters are strain, they are circumferential strain, thickness strain or radial strain; if the characteristic parameters are strain increment, they are circumferential strain increment, thickness strain increment or radial strain increment; if the characteristic parameters are wall thickness or length, they are the thickness of the edge of the small hole, the circumferential length or the radial length.

8. The experimental method for directly measuring the in-plane anisotropy coefficient of a metal thin-walled tube according to claim 1, characterized in that, In step five, the characteristic parameters of the edge of the small hole are obtained during the experiment and after the experiment.

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