CN101793647A - Method for testing circumferential mechanical performance of thin-wall pipe - Google Patents

Abstract

The invention relates to a method for testing the circumferential mechanical performance of a thin-wall part .The circumferential mechanical performance of a thin-wall pipe is tested by adopting a valve type thin pipe circumferential mechanical performance testing device. The method comprises the steps of: determining a friction coefficient mu by using a calibrating test; obtaining the value sigmate of the pipe by using a tensile test to obtain the maximum loading pressure P required by the expansion of the thin-wall pipe, determining a loading device according to the maximum loading pressure P; extruding the expended pipe by a tapered press head through a material mechanical performance tester to make the pipe expand and split to obtain a relation curve of the circumferential stress of the pipe and time in the entire process of expansion and split; recording the relation curve of the circumferential stress of the pipe and time in the entire process of expansion and split with a strain gauge; obtaining a relation curve of the load and time in the process of extrusion by the material mechanical performance tester; converting the load to circumferential stress by a formula to obtain a relation curve of stress and time; and averaging test results to obtain the circumferential mechanical performance parameters of the thin-wall pipe.

Description

Test method for circumferential mechanical properties of thin-walled pipe fittings

technical field

The invention relates to the field of testing methods for mechanical properties of materials, in particular to a method for testing circumferential mechanical properties of thin-walled pipe fittings.

Background technique

The use of pipe fittings and sleeves is all involved in aviation, aerospace, automobile, mechanical equipment and other fields. Taking an aircraft as an example, the piping system is the lifeline of the aircraft, and its performance directly affects the overall performance of the aircraft. Therefore, it is very important to improve the technical level of the pipeline system to improve the performance of the aircraft. The hydraulic pipeline is the part with the highest working pressure and the strictest reliability requirements among all the pipelines of the aircraft. The level of aircraft pipeline system technology is concentrated in the hydraulic pipeline system. For the hydraulic system, under the same power conditions, the higher the working pressure, the smaller the required area of the cylinder and the piston bottom of the oil pump, and the smaller the flow rate of the pipeline, so the overall size of the hydraulic system will be reduced and the weight will be reduced. will be alleviated, and the lower medium flow rate also reduces the power loss flowing in the pipeline. Therefore, the technical research on the hydraulic system and its standard parts is an objective demand for the development of the aviation industry. Due to the increase of the working pressure of the hydraulic pipeline, many new problems will be brought to the design of the hydraulic system, mainly attributed to the two major problems of strength and sealing, which requires the study of the strength of the pipe fittings.

The traditional method is to cut the thin-walled pipe and roll it flat, and then test the circumferential mechanical properties of the pipe after preparing a tensile sample. However, re-deformation occurs during the flattening process, so the measured data cannot accurately represent the circumferential mechanical properties of the pipe fittings, not to mention that it is impossible to cut, flatten, and prepare samples for small-sized thin-walled pipe fittings.

Contents of the invention

In order to overcome the defect that it is difficult to accurately measure the circumferential mechanical properties of thin-walled pipe fittings in the prior art methods, the present invention proposes a method for testing the circumferential mechanical properties of thin-walled pipe fittings.

The present invention includes a group of tubular test pieces, characterized in that the method for testing the circumferential mechanical properties of thin-walled test pieces comprises the following steps:

Step 1. Determine the friction coefficient μ through the calibration test; place the valve mold in the tubular calibration specimen, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve; Thin-walled pipe fittings apply a load to the circumferential stress test device to obtain the stress value of the loaded load; substitute the loaded load P and the stress value σ of the loaded load into the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

Obtain the friction coefficient; where: H is the height of the pipe fitting; t is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; β is the half-cone angle of the conical indenter;

Step 2, tooling preparation; take a test piece, and paste strain gauges along the circumference on the outer circumference of the axially symmetrical plane of the test piece; connect the strain gauges and strain gauges through wires; place the valve mold on In the tested tube, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve;

Step 3, determine the pressure required for the expansion of the pipe fitting; obtain the σ value of the test piece through the tensile test; pass the following formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

Obtain the maximum loading pressure P required to expand and burst the thin-walled pipe fittings, and determine the loading device according to the maximum loading pressure P; where: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient ; β is the half-cone angle of the conical indenter;

Step 4. Load the pipe fittings; through the material mechanical performance testing machine, the conical pressure head presses the extruded pipe fittings until the pipe fittings burst; the pressing speed is 1-5mm/min;

Step 5. Obtain the relationship curve between the circumferential stress and time of the pipe fitting during the expansion process; record the relationship curve between the circumferential strain and time of the pipe fitting during the entire expansion process through the strain gauge; obtain the pressure during the extrusion process through the material mechanical performance testing machine Load vs. time curve; via the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

Convert the load into circumferential stress to obtain the relationship curve of circumferential stress and time; in the above formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient; β is the conical pressure The half-cone angle of the head; repeat steps 2 to 5, test each test piece one by one, and obtain the mechanical properties of each test piece;

Step 6. Obtaining the circumferential mechanical property parameters of the thin-walled pipe fittings; taking the average value of each test result to obtain the circumferential mechanical property parameters of the thin-walled pipe fittings.

The invention uses the special structure of the valve mold to change the force transmission direction in the extrusion process to obtain the circumferential stress-strain curve of the pipe fitting and the yield strength, tensile strength and elastic modulus parameters of the pipe fitting circumferential direction.

The test method of circumferential mechanical properties of thin-walled pipe fittings utilizes the tapered structure characteristics of the test device and the split structure characteristics of the valve mold to realize the mechanical and kinematic transformation and analysis method of axial loading and circumferential deformation of thin-walled pipe fittings. Based on this method, the circumferential mechanical properties of thin-walled pipes can be tested. Compared with the traditional method of cutting thin-walled pipes, rolling them flat, and preparing tensile samples to test the circumferential mechanical properties of pipes, This method does not need to cut the thin-walled pipe, so it can reduce the influence of the sample preparation process on the final test results. Based on this method, the circumferential mechanical properties of the pipe can be accurately obtained, and it is not necessary to destroy some large pipes. into tensile samples. Since the circumferential mechanical properties of thin-walled small-sized pipe fittings can be accurately obtained, it can provide technical support for the engineering design and application of thin-walled small-sized pipe fittings.

Description of drawings

Accompanying drawing 1 is the schematic diagram of testing device force;

Accompanying drawing 2 is the stress-strain graph that the present invention obtains;

Accompanying drawing 3 is the stress-strain graph that the present invention obtains;

Accompanying drawing 4 is flow chart of the present invention.

Detailed ways

Embodiment one

This embodiment is a test method for testing the circumferential mechanical properties of 7050 high-strength aluminum alloy pipe fittings.

20mm×1mm，高度为20mm。在材料力学性能试验机上的加载速度为1mm/min。In this embodiment, the circumferential mechanical properties of 7050 high-strength aluminum alloy pipes are tested by using a test device for circumferential mechanical properties of thin-walled pipes in a four-petal mode. The number of test pieces is eight, and their specific dimensions are

20mm×1mm, height is 20mm. The loading speed on the material mechanical performance testing machine is 1mm/min.

When using the test device of this embodiment to expand the pipe fittings, the conical indenter is driven by the material mechanical performance testing machine, and the conical indenter moves axially along the pipe fitting downwards, so that the conical indenter drives the valve mold radially outward. On, the specific test process includes the following steps:

Step 1. Determine the coefficient of friction μ through a calibration test;

The calibration test process in this embodiment: take a calibration test piece, attach strain gauges along the circumferential direction on the outer circumference of the test piece at the axially symmetrical plane; connect the strain gauges to the strain gauges through wires. Place the valve mold in the tested tube, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve. By applying a load of 16000N to the circumferential stress test device of thin-walled pipe fittings on the material performance testing machine. Multiply the strain value obtained by the strain gauge on the calibration pipe to be measured and the known elastic modulus of the calibration piece to obtain the stress value of the loaded load; substitute the loaded load P and the stress value σ of the loaded load into the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The coefficient of friction μ=0.16 was obtained. In the formula: H is the height of the pipe fitting; t is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; β is the half-cone angle of the conical indenter, β=8°.

The shape and size of the above-mentioned calibration pipe fittings are the same as the shape and size of the test pipe fittings; and the mechanical properties of the calibration pipe fittings are known.

Step 2, preparation of tooling; take a test piece, and paste strain gauges along the circumference on the outer circumference of the axially symmetrical plane of the test piece; connect the strain gauges and strain gauges through wires. Place the valve mold in the tested tube, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve.

Step 3, determine the pressure required for the expansion of the pipe fitting; the tensile strength of the high-strength aluminum alloy obtained according to the tensile test is 565MPa, according to the stress situation shown in Figure 1, through the following formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The maximum loading pressure required to burst the thin-walled pipe fittings is 22941N, and a 5-ton material mechanical performance testing machine is selected.

In the formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient, μ=0.16; β is the half cone angle of the conical indenter, β=8°.

Step 4. Load the pipe fittings; use the material mechanical properties testing machine to make the conical indenter squeeze the pipe fittings at a depressing speed of 1 mm/min until the pipe fittings burst.

Step 5. Obtain the relationship curve between the circumferential stress and time of the pipe fitting during the expansion process; record the circumferential strain change curve of the pipe fitting during the entire expansion process through the strain gauge, that is, the relationship curve between the circumferential strain and time; through the mechanical properties of the material The testing machine obtains the load change curve during the entire extrusion process, that is, the relationship curve between load and time; through the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The load is transformed into circumferential stress, and the relation curve of circumferential stress and time is obtained. In the above formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient, and the value of μ is 0.16; Repeat steps 2 to 5 to test the eight specimens one by one to obtain the mechanical properties of each specimen.

Step 6. Obtaining the circumferential mechanical property parameters of the thin-walled pipe fittings; taking the average value of eight test results to obtain the circumferential mechanical property parameters of the thin-walled pipe fittings.

As shown in Figure 2. This embodiment utilizes the consistency of stress and strain and time to synthesize the relationship curve of circumferential strain and time with the relationship curve of circumferential stress and time to obtain the circumferential stress-strain curve of the pipe fitting and the circumferential yield of the pipe fitting The strength σ _s is 480.57MPa, the tensile strength σ _b is 543.05MPa, and the elastic modulus E is 56.79GPa.

In this embodiment, in the calibration test, the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;Ht\&sigma;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

It is determined according to the frictional force shown in Figure 1 and the reaction force Q of the conical indenter on the mold flap; the balance equation after each mold flap is stressed is:

$\left\{\begin{array}{cc}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; h</span>}\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\end{array}\right.$

Equation (1) is the balance equation in the vertical direction of the mold lobe

Equation (2) is the balance equation in the horizontal direction of the mold lobe

Combining the above two equations and substituting n=2π/a, p'=(2t/D)σ, the axial pressure required for the bulging of the thin-walled pipe is obtained. In the above formula: n is the number of petals of the petal mold; a is the radian of the mold petal, p' is the bulging force, D is the outer diameter of the thin-walled pipe, H is the height of the pipe; t is the wall thickness of the pipe; σ is the circumference of the pipe Axial stress; β is the half-cone angle of the conical indenter, and u is the friction coefficient.

Embodiment two

This embodiment is a test method for testing the circumferential mechanical properties of 69111 high-strength steel pipe fittings.

22mm×1mm，高度为20mm。在材料力学性能试验机上的加载速度为3mm/min。In this example, a test device for circumferential mechanical properties of thin-walled pipe fittings in a five-petal mode is used to test the circumferential mechanical properties of 69111 high-strength steel pipe fittings. The number of test pieces is ten, and its specific size is

22mm×1mm, height 20mm. The loading speed on the material mechanical performance testing machine is 3mm/min.

When using the test device of this embodiment to expand the pipe fittings, the conical indenter is driven by the material mechanical performance testing machine, and the conical indenter moves axially along the pipe fitting downwards, so that the conical indenter drives the valve mold radially outward. On, the specific test process includes the following steps:

Step 1. Determine the coefficient of friction μ through a calibration test;

The calibration test process in this embodiment: take a calibration test piece, attach strain gauges along the circumferential direction on the outer circumference of the test piece at the axially symmetrical plane; connect the strain gauges to the strain gauges through wires. Place the valve mold in the tube to be tested, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve. By applying a load of 30000N to the thin-walled pipe circumferential stress test device on the material performance testing machine. Multiply the strain value obtained by the strain gauge on the calibration pipe to be measured and the known elastic modulus of the calibration piece to obtain the stress value of the loaded load; substitute the loaded load P and the stress value σ of the loaded load into the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}<span\; class="notranslate">\; ,</span>$

A nominal friction μ = 0.16 was obtained. In the formula: H is the height of the pipe fitting; t is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; β is the half cone angle of the conical indenter, β=10°.

The shape and size of the above-mentioned calibration pipe fittings are the same as the shape and size of the test pipe fittings; and the mechanical properties of the calibration pipe fittings are known.

Step 2, preparation of tooling; take a test piece, and paste strain gauges along the circumference on the outer circumference of the axially symmetrical plane of the test piece; connect the strain gauges and strain gauges through wires. Place the valve mold in the tested tube, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve.

Step 3. Determine the pressure required for the expanded pipe fitting; the tensile strength of the high-strength aluminum alloy obtained according to the tensile test is 1660MPa, and according to the stress situation shown in Figure 1, pass the following formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The maximum loading pressure required to burst the thin-walled pipe fittings is 76365N, and a 10-ton material mechanical performance testing machine is selected.

In the formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient, μ=0.16; β is the half cone angle of the conical indenter, β=10°.

Step 4. Load the pipe fittings; use the material mechanical properties testing machine to make the conical indenter squeeze the pipe fittings at a depressing speed of 3 mm/min until the pipe fittings burst.

Step 5. Obtain the relationship curve between the circumferential stress and time of the pipe fitting during the expansion process; record the circumferential strain change curve of the pipe fitting during the entire expansion process through the strain gauge, that is, the relationship curve between the circumferential strain and time; through the mechanical properties of the material The testing machine obtains the load change curve during the entire extrusion process, that is, the relationship curve between load and time; through the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The load is transformed into circumferential stress, and the relation curve of circumferential stress and time is obtained. In the above formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient, and the value of μ is 0.16; Repeat steps 2 to 5 to test the ten specimens one by one to obtain the mechanical properties of each specimen.

Step 6. Obtaining the circumferential mechanical property parameters of the thin-walled pipe fittings; taking the average value of ten test results to obtain the circumferential mechanical property parameters of the thin-walled pipe fittings.

As shown in Figure 3. This embodiment utilizes the consistency of stress and strain and time to synthesize the relationship curve of circumferential strain and time with the relationship curve of circumferential stress and time to obtain the circumferential stress-strain curve of the pipe fitting and the circumferential yield of the pipe fitting The strength σ _s is 976.09MPa, the tensile strength σ _b is 1228.19MPa, and the elastic modulus E is 198.16GPa.

In this embodiment, in the calibration test, the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;Ht\&sigma;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

It is determined according to the frictional force shown in Figure 1 and the reaction force Q of the conical indenter on the mold flap; the balance equation after each mold flap is stressed is:

$\left\{\begin{array}{cc}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; h</span>}\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\end{array}\right.$

Equation (1) is the balance equation in the vertical direction of the mold lobe

Equation (2) is the balance equation in the horizontal direction of the mold lobe

Combining the above two equations and substituting n=2π/a, p'=(2t/D)σ, the axial pressure required for the bulging of the thin-walled pipe is obtained. In the above formula: n is the number of petals of the petal mold; a is the radian of the mold petal, p' is the bulging force, D is the outer diameter of the thin-walled pipe, H is the height of the pipe; t is the wall thickness of the pipe; σ is the circumference of the pipe Axial stress; β is the half-cone angle of the conical indenter, and u is the friction coefficient.

Embodiment three

This embodiment is a test method for testing the circumferential mechanical properties of 7050 high-strength aluminum alloy pipe fittings.

24mm×1mm，高度为20mm。在材料力学性能试验机上的加载速度为5mm/min。In this embodiment, the circumferential mechanical properties of 7050 high-strength aluminum alloy pipes are tested by using a test device for circumferential mechanical properties of thin-walled pipes in a four-petal mode. The number of test pieces is twelve, and its specific size is

24mm×1mm, height 20mm. The loading speed on the material mechanical performance testing machine is 5mm/min.

When using the test device of this embodiment to expand the pipe fittings, the conical indenter is driven by the material mechanical performance testing machine, and the conical indenter moves axially along the pipe fitting downwards, so that the conical indenter drives the valve mold radially outward. On, the specific test process includes the following steps:

Step 1. Determine the coefficient of friction μ through a calibration test;

The calibration test process in this embodiment: take a calibration test piece, attach strain gauges along the circumferential direction on the outer circumference of the test piece at the axially symmetrical plane; connect the strain gauges to the strain gauges through wires. Place the valve mold in the tested tube, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve. By applying a load of 16000N to the circumferential stress test device of thin-walled pipe fittings on the material performance testing machine. Multiply the strain value obtained by the strain gauge on the calibration pipe to be measured and the known elastic modulus of the calibration piece to obtain the stress value of the loaded load; substitute the loaded load P and the stress value σ of the loaded load into the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The coefficient of friction μ=0.16 was obtained. In the formula: H is the height of the pipe fitting; t is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; β is the half-cone angle of the conical indenter, β=8°.

The shape and size of the above-mentioned calibration pipe fittings are the same as the shape and size of the test pipe fittings; and the mechanical properties of the calibration pipe fittings are known.

Step 2, preparation of tooling; take a test piece, and paste strain gauges along the circumference on the outer circumference of the axially symmetrical plane of the test piece; connect the strain gauges and strain gauges through wires. Place the valve mold in the tested tube, insert the conical indenter into the valve mold; place the valve mold with the conical indenter in the protective sleeve.

Step 3, determine the pressure required for the expansion of the pipe fitting; the tensile strength of the high-strength aluminum alloy obtained according to the tensile test is 565MPa, according to the stress situation shown in Figure 1, through the following formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The maximum loading pressure required to burst the thin-walled pipe fittings is 22941N, and a 5-ton material mechanical performance testing machine is selected.

In the formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient, μ=0.16; β is the half cone angle of the conical indenter, β=8°.

Step 4. Load the pipe fittings; use the material mechanical properties testing machine to make the conical indenter squeeze the pipe fittings at a depressing speed of 5 mm/min until the pipe fittings burst.

Step 5. Obtain the relationship curve between the circumferential stress and time of the pipe fitting during the expansion process; record the circumferential strain change curve of the pipe fitting during the entire expansion process through the strain gauge, that is, the relationship curve between the circumferential strain and time; through the mechanical properties of the material The testing machine obtains the load change curve during the entire extrusion process, that is, the relationship curve between load and time; through the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; \&sigma;</span>}\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;tH</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

The load is transformed into circumferential stress, and the relation curve of circumferential stress and time is obtained. In the above formula: H is the height of the pipe fitting; T is the wall thickness of the pipe fitting; σ is the circumferential stress of the pipe fitting; μ is the friction coefficient, and the value of μ is 0.16; Repeat steps 2 to 5 to test the twelve specimens one by one to obtain the mechanical properties of each specimen.

Step 6. Obtaining the circumferential mechanical property parameters of the thin-walled pipe fittings; taking the average value of twelve test results to obtain the circumferential mechanical property parameters of the thin-walled pipe fittings.

As shown in Figure 2. This embodiment utilizes the consistency of stress and strain and time to synthesize the relationship curve of circumferential strain and time with the relationship curve of circumferential stress and time to obtain the circumferential stress-strain curve of the pipe fitting and the circumferential yield of the pipe fitting The strength σ _s is 480.57MPa, the tensile strength σ _b is 543.05MPa, and the elastic modulus E is 56.79GPa.

In this embodiment, in the calibration test, the formula

$\mathrm{<span\; class="notranslate">\; P</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&pi;Ht\&sigma;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&mu;</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; \&mu;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; the\; tan</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}}$

It is determined according to the frictional force shown in Figure 1 and the reaction force Q of the conical indenter on the mold flap; the balance equation after each mold flap is stressed is:

$\left\{\begin{array}{cc}<span\; class="notranslate">\; -</span>\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>\\ <span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\frac{\mathrm{<span\; class="notranslate">\; P</span>}}{\mathrm{<span\; class="notranslate">\; no</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; \&mu;</span>}\mathrm{<span\; class="notranslate">\; Q</span>}\mathrm{<span\; class="notranslate">\; sin</span>}\mathrm{<span\; class="notranslate">\; \&beta;</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; p</span>}}^{<span\; class="notranslate">\; \&prime;</span>}\mathrm{<span\; class="notranslate">\; h</span>}\frac{\mathrm{<span\; class="notranslate">\; D.</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}\mathrm{<span\; class="notranslate">\; a</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}& <span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>\end{array}\right.$

Equation (1) is the balance equation in the vertical direction of the mold lobe

Equation (2) is the balance equation in the horizontal direction of the mold lobe

Combining the above two equations and substituting n=2π/a, p'=(2t/D)σ, the axial pressure required for the bulging of the thin-walled pipe is obtained. In the above formula: n is the number of petals of the petal mold; a is the radian of the mold petal, p' is the bulging force, D is the outer diameter of the thin-walled pipe, H is the height of the pipe; t is the wall thickness of the pipe; σ is the circumference of the pipe Axial stress; β is the half-cone angle of the conical indenter, and u is the friction coefficient.

Claims (1)

1. a thin-walled test specimen method for testing circumferential mechanical performance is characterized in that, described thin-walled test specimen method for testing circumferential mechanical performance may further comprise the steps:

Step 1, determine coefficientoffriction by rating test; The lobe mould is positioned in the tubular demarcation test specimen, conical indenter is inserted in the lobe mould; The lobe mould that conical indenter is housed is placed in the protective sleeve; To thin-wall pipe circumferential stress proving installation imposed load, obtain the stress value of loaded load; Stress value σ substitution formula with loaded load P and loaded load

$P=\mathrm{\&sigma;}\frac{2\mathrm{\&pi;tH}(\tan \mathrm{\&beta;}+\mathrm{\&mu;})}{1-{\mathrm{\&mu;}}^2-2\mathrm{\&mu;}\tan \mathrm{\&beta;}}$

Obtain coefficientoffriction=0.16; In the formula: H is the pipe fitting height; T is a tube wall thickness; σ is the pipe fitting circumferential stress; β is the semi-cone angle of conical indenter;

Step 2, frock are prepared; Get a test specimen, on the excircle at the axial plane of symmetry place of this test specimen, along circumferentially sticking foil gauge; By lead foil gauge and strainmeter are coupled together; The lobe mould is positioned in the tested pipe fitting, conical indenter is inserted in the lobe mould; The lobe mould that conical indenter is housed is placed in the protective sleeve;

Step 3, determine the pressure that the spalling pipe fitting is required; Obtain the σ value of test specimen by tension test; Pass through following formula

$P=\mathrm{\&sigma;}\frac{2\mathrm{\&pi;tH}(\tan \mathrm{\&beta;}+\mathrm{\&mu;})}{1-{\mathrm{\&mu;}}^2-2\mathrm{\&mu;}\tan \mathrm{\&beta;}}$

Obtain the needed maximum load pressure P of thin-wall pipe spalling, and determine charger according to the maximum load pressure P;

In the formula: H is the pipe fitting height; T is a tube wall thickness; σ is the pipe fitting circumferential stress; μ is a friction factor, μ=0.16; β is the semi-cone angle of conical indenter;

Step 4, pipe fitting is loaded; By the material mechanical performance testing machine, conical indenter is depressed squeezed expand tube spare to the pipe fitting spalling; The speed of depressing is 1～5mm/min;

Pipe fitting circumferential stress and time relation curve in the process of expanding squeezed in step 5, acquisition; Note whole pipe fitting circumferential strain and the time relation curve in the process of expanding that squeeze by strainmeter; Obtain load and time relation curve in the extrusion process by the material mechanical performance testing machine; Pass through formula

$P=\mathrm{\&sigma;}\frac{2\mathrm{\&pi;tH}(\tan \mathrm{\&beta;}+\mathrm{\&mu;})}{1-{\mathrm{\&mu;}}^2-2\mathrm{\&mu;}\tan \mathrm{\&beta;}}$

Load is changed into circumferential stress, obtain circumferential stress and time relation curve; In the following formula: H is the pipe fitting height; T is a tube wall thickness; σ is the pipe fitting circumferential stress; μ is a friction factor, and the value of μ is 0.16; β is the semi-cone angle of conical indenter; Repeating step 2 is tested each test specimen one by one to step 5, obtains the mechanical property of each test specimen respectively;

Step 6, acquisition thin-wall pipe circumferential mechanical performance parameter; The mean value of getting each test result obtains thin-wall pipe circumferential mechanical performance parameter.

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