CN105806709B

CN105806709B - Method and equipment for testing performance of pipe

Info

Publication number: CN105806709B
Application number: CN201610134351.0A
Authority: CN
Inventors: 郎利辉; 阮尚文; 孔德帅; 吴磊; 葛宇龙; 张弛
Original assignee: Beihang University
Current assignee: Beihang University
Priority date: 2016-03-10
Filing date: 2016-03-10
Publication date: 2021-04-27
Anticipated expiration: 2036-03-10
Also published as: CN105806709A

Abstract

A method and equipment for testing the performance of a pipe material. In the test, the displacement and the thrust of two ends of the pipe are controlled, and liquid pressure is applied to the inside of the pipe. In the bulging process, the strain state of the pipe is monitored in real time by using a digital speckle measurement technology, and the thrust or displacement is adjusted. The test was stopped when the equivalent strain reached a certain value or the pipe broke. And recording the pressure of liquid filled in the pipe and the bulging height around the highest bulging point of the pipe in the test process, and calculating a stress-strain curve and a forming limit of the pipe by combining real-time strain measurement data. The tubular product test piece uses the mode dress card and sealed of triangle chuck plus bush, has realized convenient test piece installation.

Description

Method and equipment for testing performance of pipe

Technical Field

The invention belongs to the technical field of material performance test, and particularly relates to a test method and equipment for testing the performance of a pipe material.

Background

The pipe parts are widely applied to industries such as aerospace, automobile manufacturing and the like due to the characteristics of high material utilization rate and low production cost. With the development of process technology, the traditional tensile test method cannot meet the requirement of complex forming process analysis. Aiming at the defects of the method for testing the material performance of the pipe, the invention provides a method and equipment for measuring the material parameters and the forming limit based on the combination of the liquid filling bulging of the pipe and the digital speckle real-time strain measurement. According to the method, different loading paths can be designed, and a Forming Limit Diagram (FLD) and a stress forming line diagram (FLSD) can be drawn for material parameters through verification.

Disclosure of Invention

The invention aims to provide a method and equipment for testing the performance of a pipe material based on the combination of liquid-filled bulging of the pipe and digital speckle real-time strain measurement, so as to obtain reliable parameters, stress-strain curves, forming limit diagrams and the like of the pipe material and provide a reliable reference basis for process design.

The invention provides a method and equipment for testing a pipe material, which are characterized in that: the tube is expanded and deformed by using a liquid filling expansion method. And in the deformation process, the strain condition in the pipe bulging process is measured in real time by using a three-dimensional digital speckle measurement technology. Meanwhile, the deformation at the highest point of the expansion is subjected to auxiliary measurement by using a three-foot displacement ruler, and deformation information is fed back. The pressure sensor records the pressure change process in the liquid filling and bulging process of the pipe. And the control system adjusts the bulging pressure and the feeding amount of the two sides according to the stress or strain index of the experimental design through the real-time measurement result of the deformation process. And the stress-strain relationship, the forming limit diagram and the forming stress limit diagram of the pipe material are drawn, and the deformation process is analyzed. The performance of the pipe material is described more completely.

Drawings

FIG. 1 clamping part

1-switching disk, 2-tripod chuck, 3-supporting axle center, 4-guide groove

FIG. 2 side thrust cylinder assembly

5-oil cylinder push rod, 6-oil discharge port, 7-displacement sensor and 8-oil cylinder body

Figure 3 three-foot displacement ruler

9-displacement ruler, 10-inner sleeve, 11-outer sleeve, 12-mounting bolt

FIG. 4 three-dimensional Strain measurement component

13-camera, 14-LED light source, 15-tripod.

FIG. 5 bulging Process

t-peak thickness, rho z-axial outer wall radius of curvature, rho theta-circumferential outer wall radius of curvature, rho 0-initial inner wall radius of curvature

FIG. 6 highest point stress state

Sigma z-axial stress, sigma theta-circumferential stress

FIG. 7 flexural expansion Performance test

16-guide rail rotation axis and 17-angle positioning hole

FIG. 8 highest point strain state

Epsilon z-axial strain, epsilon theta-circumferential strain, epsilon t-thickness strain

Detailed description of the preferred embodiments

The invention can complete the performance test of the basic material of the pipe and can test the bulging performance of the bent pipe.

The performance test of the base material was completed using a straight tube bulging experiment. The pipe is first pretreated. And sequentially spraying white and black paints to the middle area of the pipe test piece to manufacture an artificial speckle field for global three-dimensional speckle strain measurement.

And adjusting the testing machine and clamping the test piece. The side-push oil cylinder is connected with the clamping part through the adapter plate and is installed on the guide plate through the guide rail, and the push force collineation at the two ends of the pipe is guaranteed. One end of the pipe test piece is installed and clamped tightly through a triangular chuck in the clamping part. And controlling the side-push oil cylinder at the other side by control software to approach the test piece, pressing the pipe end into the support mandrel and clamping. And synchronously adjusting the side-push oil cylinders on the two sides to enable the center of the pipe test piece to be positioned below the middle ruler of the three-foot displacement ruler. And adjusting the height of the displacement ruler, and resetting the data of the displacement ruler after the displacement ruler is contacted with the test piece.

And installing a three-dimensional speckle strain measurement system. And ensuring that the horizontal line of the measuring system is approximately parallel to the central line of the test piece. And placing the calibration plate near the test piece, and carrying out three-dimensional calibration on the camera of the measurement system.

And obtaining a stress-strain relation curve of the pipe material. As shown in fig. 8, the circumferential strain at the highest point of the test piece bulge can be expressed as:

the axial strain may be expressed as:

according to the principle that the plastic deformation volume is constant, the equivalent strain can be expressed as:

meanwhile, the thickness of the highest point may be expressed as:

the highest point axial stress can therefore be obtained from the axial equilibrium equation:

in the test, the servo control system ensured that p · s-F is 0. From fig. 6, the circumferential stress can be found:

according to the thin-wall theory, the normal stress of the test piece can be ignored, so the Mises stress can be obtained:

in the deformation process, stress and strain are monitored in real time, and a stress and strain relation curve of the pipe material can be established by a plurality of groups of stress-strain pairs and selecting a proper material model. Meanwhile, a corresponding equivalent strain obtained by the three-dimensional speckle strain measurement system can verify the strain change process in the deformation process. The three-dimensional speckle strain measurement system has the advantages that multi-directional strain in the deformation process can be stably measured in a full field, and errors caused by impact in mechanical measurement are avoided.

The forming limit diagram is an index for determining the maximum fracture limit of a material, using in-plane principal strains ε 1 and ε 2 as the vertical and horizontal axes. The invention provides a method for establishing a forming limit diagram at multiple points. According to the outer diameter d of the pipe, the ratio of the length l to the length d of the deformation area of the test piece is set to be 8: 1, 6: 1, 5: 1, 4: 1 and 3: 1 respectively, the bulging test of the two fixing sections is carried out, and as the ratio of the axial strain of the highest point of the bulging test of the fixing end to the circumferential strain is approximately unchanged, 5 forming limit points are obtained, so that a forming limit diagram is drawn.

Studies have found that forming limit maps are not accurate for crack prediction of nonlinear strain paths and methods of forming stress limit maps have been developed. The invention provides a method for testing a forming stress limit. Since the axial stress is directly determined by the side thrust force F, the bidirectional stress change process in the forming process is drawn and the stress forming limit is determined by adjusting the ratio of F to p.s to be 0.8, 0.9, 1.0, 1.1 and 1.2.

The invention also provides a method for limiting the bulging of a bent pipe fitting. In an attempt 7, the angle of the test machine rail was adjusted to the same angle as the bent test piece. And bending the three groups of pipe test pieces through a numerical control pipe bending machine to enable the welding seams to be respectively positioned on the outer side of the bending, the inner side of the bending and the vertical plane. And (4) keeping the clamping parts at the two ends of the pipe fixed, and carrying out free bulging test on the three groups of test pieces. And (3) measuring the deformation process of the test piece in real time by using a three-dimensional speckle strain measurement system, and analyzing the influence of the welding seam and the bending on the bulging.

Claims

1. The equipment for testing the performance of the liquid-filled bulging material of the pipe is characterized in that: the equipment comprises a real-time bulging height measuring device for testing the straight pipe performance, and the pipe is used for adapting to the adjustable guide pipe device for testing the bending angle of a test piece and further comprises:

the end part clamping part consists of a connecting plate, a tripod chuck, a supporting core rod and a guide rail groove, the connecting plate is connected with the side pushing device, the tripod chuck and the supporting core rod clamp the pipe test piece together, and the guide rail is connected with the guide rail platform and slides on the guide rail;

the hydraulic control equipment and the side thrust device are composed of a servo valve, a hydraulic cylinder, a hydraulic push rod and a control system, two control modes, namely a force control mode and a speed control mode, are provided, and the hydraulic system provides the same or different side thrusts in the force control mode; in the speed control mode, the hydraulic system provides the same or different lateral pushing speeds at two sides as required;

the three-foot displacement ruler is connected with the guide rail platform, adjusts the height and is used for recording the height of the periphery of the highest point during the deformation period of the linear pipe test piece;

the three-dimensional speckle strain testing device consists of a three-dimensional speckle deformation process recording camera and special analysis software, wherein the two cameras are fixed on a movable triangular foot or a portal frame;

and the guide rail platform is provided with a positioning hole so as to determine the position of the components, and the installation angle of the side pushing device is adjusted according to the angle of the test piece.

2. The method for testing the performance of the liquid-filled bulging material of the pipe is characterized by comprising the following steps of:

adjusting three-dimensional speckle strain test equipment, clamping a test piece, connecting a side-push oil cylinder with a clamping part through an adapter plate, installing the side-push oil cylinder on a guide plate through a guide rail to ensure that the thrust at two ends of the pipe is collinear, installing and clamping one end of the pipe test piece through a triangular chuck in the clamping part, controlling the side-push oil cylinder at the other side through control software, pressing and clamping the pipe end into a supporting mandrel, synchronously adjusting the side-push oil cylinders at two sides to ensure that the center of the pipe test piece is positioned below a middle ruler of a three-foot displacement ruler, adjusting the height of the displacement ruler to ensure that the displacement ruler is reset after being contacted with the test piece,

loading a test piece by adopting a displacement control or side thrust control method according to the experimental requirements, recording measurement data, and calculating a stress-strain curve and a forming limit according to a calculation formula;

the circumferential strain at the highest point of the test piece bulge is expressed as:

the axial strain is expressed as:

according to the principle that the plastic deformation volume is constant, the equivalent strain is expressed as:

meanwhile, the thickness of the highest point is expressed as:

the highest point axial stress is thus obtained according to the equilibrium equation in the axial direction:

in the test, the servo control system ensures that p.s-F is 0; and (3) solving the circumferential stress:

according to the thin-wall theory, the normal stress of the test piece is neglected, so that the Mises stress is obtained:

setting the ratio of the length l to the length d of the deformation area of the test piece to be 8: 1, 6: 1, 5: 1, 4: 1 and 3: 1 respectively according to the outer diameter d of the pipe, and performing bulging tests on two fixed ends, wherein 5 forming limit points are obtained because the ratio of the axial strain to the circumferential strain of the highest point of the bulging test at the fixed end is approximately unchanged, so that a forming limit diagram is drawn; because the axial stress is directly determined by the side thrust F, the bidirectional stress change process in the forming process is drawn and the stress forming limit is determined by adjusting the proportion of F to p.s to be 0.8, 0.9, 1.0, 1.1 and 1.2 groups of tests; the angle of the guide rail of the adjusting testing machine is the same as that of the bent test piece, the three groups of pipe test pieces are bent through the numerical control pipe bending machine, welding seams are respectively positioned on the outer side of the bending, the inner side of the bending and a plane perpendicular to the bending axis, clamping parts at two ends of the pipe are kept fixed, free bulging tests are carried out on the three groups of test pieces, a three-dimensional speckle strain measurement system is used for measuring the deformation process of the test pieces in real time, and the influence of the welding seams and the bending on the bulging is.