Bending fatigue testing device for metal pipe and testing method using bending fatigue testing device

Abstract

The invention relates to the technical field of metal conduit fatigue testing, and provides a bending fatigue testing device for a metal pipe and a testing method using the bending fatigue testing device. Comprising a headstock and a tailstock, and a test piece is connected between the headstock and the tailstock through a fixing assembly; a bending degree adjusting assembly is arranged in the headstock, one side of the bending degree adjusting assembly is connected with a rotation driving assembly, and the other side of the bending degree adjusting assembly is connected with a test piece fixing assembly; the top of the linear sliding table module is sequentially connected with an upper adjustable clamp and a lower adjustable clamp, and the upper adjustable clamp and the lower adjustable clamp are used for clamping a test piece; the joints of the upper adjustable clamp and the lower adjustable clamp with the test piece are far away from the joint of the test piece and the tailstock, and two groups of strain gauges are adhered to one sides of the joints of the upper adjustable clamp and the lower adjustable clamp with the test piece. The beneficial effects are that: aiming at the bending fatigue performance test of the pipe, joint determination of bending fatigue failure of the pipe and the pipe joint is avoided, and the test efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal pipe fatigue testing, and in particular to a bending fatigue testing device for a metal pipe and a testing method using the same. Background Art

[0002] Fatigue testing is an important means to ensure the reliability of materials during service. In 1964, the International Organization for Standardization formally proposed a standard descriptive definition of fatigue in the "General Principles of Metal Fatigue Testing", that is, the performance change of metal materials under the repeated action of stress or strain is called fatigue. The rotary bending fatigue test is the simplest and cheapest standard fatigue test method and one of the main methods for conducting high-cycle fatigue research. "HB6442-1990 Hydraulic Conduit and Connector Bending Fatigue Test" stipulates the bending fatigue test method and requirements for hydraulic metal conduits and their connectors, and assesses the fatigue performance of connectors and conduits. If one of the conduits or connectors fails due to fatigue during the test, it is determined to be a fatigue failure of the connector. Fatigue failure often occurs at the contact point between the conduit and the connector during the test, and it is difficult to determine whether it is a fatigue failure of the conduit.

[0003] In view of this, the present invention is proposed. Summary of the invention

[0004] The object of the present invention is to provide a bending fatigue testing device for a metal pipe and a testing method using the same, so as to solve the technical problems existing in the prior art.

[0005] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a bending fatigue test device for metal pipes, comprising: a headstock and a tailstock, wherein the headstock and the tailstock are connected to a test piece via a connecting piece; a curvature adjustment component is arranged in the headstock, one side of the curvature adjustment component is connected to a rotation drive component, the other side of the curvature adjustment component is connected to a test piece fixing component, and the outer surface of the test piece is in contact with a micrometer;

[0006] A linear slide module, the top of which is sequentially connected to an upper adjustable clamp and a lower adjustable clamp, and the upper adjustable clamp and the lower adjustable clamp clamp the test piece;

[0007] The connection between the upper adjustable clamp, the lower adjustable clamp and the test piece is far away from the connection between the test piece and the tailstock, and a plurality of sets of strain gauges are arranged on one side of the connection between the upper adjustable clamp, the lower adjustable clamp and the test piece;

[0008] The upper adjustable clamp and the lower adjustable clamp are adjustable in three directions: X, Y and Z.

[0009] In an optional embodiment, the curvature adjustment component is connected to the automatic centering bearing in the fixing component, and the automatic centering bearing is fixedly connected to the test piece via a connecting piece.

[0010] In an optional embodiment, the strain gauges are in two groups, and the two groups of strain gauges are pasted to the outer surface of the test piece at 90° in the circumferential direction, and the two groups of strain gauges are arranged to fit the left sides of the upper adjustable clamp and the lower adjustable clamp.

[0011] In an optional embodiment, a hydraulic source and a tailstock adjustment screw are provided inside the tailstock.

[0012] In an optional embodiment, the upper adjustable clamp and the lower adjustable clamp are symmetrical structures, and arc-shaped protective covers are provided in the upper adjustable clamp and the lower adjustable clamp, and the protective covers are in contact with the outer surface of the test piece.

[0013] In an optional embodiment, a pair of adjustment holes are provided on the upper adjustable clamp and the lower adjustable clamp, and the positions of the upper adjustable clamp and the lower adjustable clamp in the Y direction can be adjusted through the pair of adjustment holes.

[0014] In an optional embodiment, the linear slide module includes a screw and nut assembly, and the positions of the upper adjustable clamp and the lower adjustable clamp in the Z direction are adjusted by means of a screw, a nut, and a slide rail.

[0015] In an optional embodiment, the linear slide module can move as a whole along the axial direction of the test piece to adjust the positions of the upper adjustable fixture and the lower adjustable fixture in the X direction.

[0016] In an optional embodiment, the test piece is a metal pipe.

[0017] On the other hand, the present invention also provides a testing method of the bending fatigue testing device of the metal pipe as described above, comprising:

[0018] S1: Determine the length L of the test piece and install the test piece on the tailstock with one end of the test piece in a free state;

[0019] S2: Install the headstock, roughly align the self-centering bearing at the end of the headstock, connect the connector, and adjust the axis of the headstock, test piece, curvature adjustment assembly, connector, and tailstock to be roughly horizontal. Use the micrometer to fine-tune the test piece to make it level;

[0020] S3: Install the linear slide module and the upper and lower adjustable clamps on one side of the strain gauge, and adjust the upper and lower adjustable clamps in the X, Y, and Z directions to clamp the test piece and keep the axis of the test piece unchanged;

[0021] S4: The strain gauge measures the reading ε1 of the test piece in the free state;

[0022] S5: Remove the micrometer, determine the strain value ε2 according to the test purpose and the strain ε1, and adjust the curvature setting component to the target value ε2;

[0023] S6: applying a bending stress of ε2 to the test piece (1), setting the motor speed and starting the equipment to perform a rotational bending fatigue test;

[0024] S7: After the rotational bending fatigue test, record the number of rotations, draw the SN curve, and analyze the failure cause of the test piece.

[0025] The beneficial effects of the present invention are:

[0026] The test equipment adds an adjustable fixture, a protective sleeve, a bracket and a linear slide module to form a new bending fatigue test equipment. The equipment has a simple structure and a reasonable design. It is specifically designed for testing the bending fatigue performance of pipes. It avoids the HB6442-1990 method to jointly determine the bending fatigue failure of pipes and pipe joints. It can accurately determine whether it is pipe fatigue failure or connector fatigue failure, thereby improving test efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 The present invention is a schematic diagram of the overall structure of a bending fatigue testing device for conduits and connectors provided by the prior art.

[0029] Figure 2 A schematic diagram of the overall structure of a bending fatigue testing device for a metal pipe provided in one embodiment of the present invention.

[0030] Figure 3 It is a schematic structural diagram of an adjustable clamp provided in one embodiment of the present invention.

[0031] Figure 4 It is a schematic structural diagram of a linear slide module provided in one embodiment of the present invention.

[0032] Among them, the figure markings are: 1-test piece; 2-upper adjustable fixture; 3-lower adjustable fixture; 4-protective cover; 5-bracket; 6-linear slide module; 7-curvature adjustment component; 8-automatic centering bearing; 9-headstock; 10-connecting piece; 11-micrometer; 12-strain gauge; 13-tailstock; 14-hydraulic source; 15-tailstock adjustment screw; 16-adjustment hole; 17-screw; 18-nut; 19-guide rail. DETAILED DESCRIPTION

[0033] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0034] It should be noted that when a component is referred to as being "fixed to" or "affixed to" another component, it may be directly or indirectly located on the other component. When a component is referred to as being "connected to" another component, it may be directly or indirectly connected to the other component. The directions or positions indicated by the terms "upper", "lower", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the accompanying drawings and are only for the convenience of description and cannot be understood as limitations on the present technical solution. The terms "first" and "second" are only used for the convenience of description and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features. "Multiple" means two or more, and "several" means any number including one, unless otherwise clearly and specifically defined.

[0035] Embodiment 1

[0036] Please see attached Figure 1-4The purpose of this embodiment is to provide a bending fatigue test device for a metal pipe, comprising: a headstock 9 and a tailstock 13, wherein the headstock 9 and the tailstock 13 are connected to a test piece 1 via a connector 10; a curvature adjustment component 7 is provided in the headstock 9, one side of the curvature adjustment component 7 is connected to a rotation drive component, the other side of the curvature adjustment component 7 is connected to a fixed component of the test piece 1, and the outer surface of the test piece 1 is in contact with a micrometer 11; a linear slide module 6, wherein the top of the linear slide module 6 is sequentially connected to an upper adjustable clamp 2 and a lower adjustable clamp 3, wherein the upper adjustable clamp 2 and the lower adjustable clamp 3 clamp the test piece 1; the connection between the upper adjustable clamp 2, the lower adjustable clamp 3 and the test piece 1 is away from the connection between the test piece 1 and the tailstock 13, and two sets of strain gauges 12 are provided on one side of the connection between the upper adjustable clamp 2, the lower adjustable clamp 3 and the test piece 1; the upper adjustable clamp 2 and the lower adjustable clamp 3 are adjustable in three directions of X, Y and Z. The test piece 1 is a metal pipe fitting, and connectors 10 are provided at both ends of the metal pipe fitting. The connector 10 is an existing component, including a pipe joint and a transition joint.

[0037] In the prior art, as shown in the attached Figure 1 As shown in the figure, "HB6442-1990 Bending Fatigue Test for Hydraulic Pipes and Connectors" stipulates the bending fatigue test methods and requirements for hydraulic pipes and their connectors, and evaluates the fatigue performance of connectors and pipes. If one of the pipes or connectors fails due to fatigue during the test, it is determined to be a fatigue failure of the connector. In the test, fatigue failure often occurs at the contact point between the pipe and the connector. At this time, it is difficult to determine whether it is a fatigue failure of the pipe. Figure 1 The strain gauge of the equipment is fitted to the tailstock, that is, fitted to the conduit and the connector. It is impossible to accurately determine whether the fatigue performance failure measured here is the fatigue failure of the connector or the failure of the pipe.

[0038] The present invention forms a new bending fatigue testing device by adding an adjustable clamp, a protective sleeve, a bracket and a linear slide module. During the bending fatigue test of the new device, the above clamp has the same function as the tailstock. No connecting parts will appear on one side of the strain gauge. The strain gauge is attached to the pipe, and the bending fatigue strength of the pipe can be directly tested and directly judged. The bending fatigue failure of the pipe and the connecting parts will not be jointly judged, thereby improving the testing efficiency.

[0039] Specifically, the curvature adjustment component 7 is connected to the automatic centering bearing 8 in the fixing component, and the automatic centering bearing 8 is fixedly connected to the test piece 1 through the connecting piece 10. Two strain gauges 12 are pasted on the outer surface of the test piece 1 at 90° in the circumferential direction, and are away from the connecting piece 10 close to the tailstock 13 of the test piece 1. Specifically, the two groups of strain gauges 12 are arranged on the left side of the upper adjustable fixture 2 and the lower adjustable fixture 3, and are close to the bending fatigue test area (strain gauge 12 bonding area) with the support of the upper adjustable fixture 2 and the lower adjustable fixture 3, which can ensure the accurate performance of the bending fatigue test.

[0040] Furthermore, a hydraulic source 14 and a tailstock adjustment screw 15 are provided inside the tailstock 13 .

[0041] It should be pointed out that the upper adjustable clamp 2 and the lower adjustable clamp 3 are symmetrical structures, and arc-shaped protective covers 4 are provided in the upper adjustable clamp 2 and the lower adjustable clamp 3, and the protective covers 4 are in contact with the outer surface of the test piece 1. A pair of adjustment holes 16 are provided on the upper adjustable clamp 2 and the lower adjustable clamp 3, and the positions of the upper adjustable clamp 2 and the lower adjustable clamp 3 in the Y direction are adjusted through the pair of adjustment holes 16. The linear slide module 6 includes a screw nut assembly, and the positions of the upper adjustable clamp 2 and the lower adjustable clamp 3 in the Z direction are adjusted through the screw 17, the nut 18, and the slide rail 19. The linear slide module 6 can move as a whole along the axial direction of the test piece 1, adjust the positions of the upper adjustable clamp 2 and the lower adjustable clamp 3 in the X direction, and realize effective support for the test piece 1.

[0042] Embodiment 2

[0043] The purpose of this embodiment is to provide a testing method using the above-mentioned bending fatigue testing device for metal pipes, comprising:

[0044] S1: Determine the length L of the test piece 1, and install the test piece 1 on the tailstock 13, with one end of the test piece 1 in a free state;

[0045] S2: Install the headstock 9, roughly align the self-centering bearing 8 at the end of the headstock 9, connect the connector 10, adjust the axis of the headstock 9, the test piece 1, the curvature adjustment assembly 7, the connector 10, and the tailstock 13 to be roughly in a horizontal state, and fine-tune the test piece 1 through the micrometer 11 to make it level; S3: Install the linear slide module 6 and the upper adjustable clamp 2 and the lower adjustable clamp 3 on one side of the strain gauge 12, and adjust the upper adjustable clamp 2 and the lower adjustable clamp 3 in the three directions of X, Y, and Z to clamp the test piece 1 and keep the axis of the test piece 1 unchanged;

[0046] S4: the strain gauge 12 measures the reading ε1 of the test piece 1 in the free state;

[0047] S5: Remove the micrometer 11, determine the strain value ε2 according to the test purpose and the strain ε1, and adjust the curvature setting component 7 to the target value ε2; for example: the free state strain is ε1 = 60, and the test purpose is to set the curvature strain to 1200, then it needs to be adjusted to ε2 = 60 + 1200 = 1260;

[0048] S6: applying a bending stress of ε2 to the test piece (1), setting the motor speed and starting the equipment to perform a rotational bending fatigue test;

[0049] S7: After the rotation bending fatigue test is completed, the number of rotations is recorded, the SN curve is drawn, and the failure cause of the test piece (1) is analyzed.

[0050] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A bending fatigue testing device for a metal pipe, comprising: A headstock (9) and a tailstock (13), wherein the headstock (9) and the tailstock (13) are connected to a test piece (1) via a connecting piece (10); a curvature adjustment component (7) is provided inside the headstock (9), one side of the curvature adjustment component (7) is connected to a rotation drive component, and the other side of the curvature adjustment component (7) is connected to a test piece (1) fixing component, and the outer surface of the test piece (1) is in contact with a micrometer (11); The invention is characterized in that the linear slide module (6) has an upper adjustable clamp (2) and a lower adjustable clamp (3) connected in sequence to the top of the linear slide module (6), and the upper adjustable clamp (2) and the lower adjustable clamp (3) clamp the test piece (1); The connection between the upper adjustable clamp (2), the lower adjustable clamp (3) and the test piece (1) is far away from the connection between the test piece (1) and the tailstock (13), and a plurality of sets of strain gauges (12) are arranged on one side of the connection between the upper adjustable clamp (2), the lower adjustable clamp (3) and the test piece (1); The upper adjustable clamp (2) and the lower adjustable clamp (3) are adjustable in three directions: X, Y and Z.

2. The bending fatigue testing device for metal pipes according to claim 1, characterized in that: The curvature adjustment component (7) is connected to the automatic centering bearing (8) in the fixing component, and the automatic centering bearing (8) is fixedly connected to the test piece (1) via a connecting piece (10).

3. The bending fatigue testing device for metal pipes according to claim 1, characterized in that: The strain gauges (12) are in two groups, and the two groups of strain gauges (12) are pasted to the outer surface of the test piece (1) at 90 degrees in the circumferential direction, and the two groups of strain gauges (12) are arranged in contact with the left sides of the upper adjustable clamp (2) and the lower adjustable clamp (3).

4. The bending fatigue testing device for metal pipes according to claim 1, characterized in that: A hydraulic source (14) and a tailstock adjustment screw (15) are arranged inside the tailstock (13).

5. The bending fatigue testing device for metal pipes according to claim 1, characterized in that: The upper adjustable clamp (2) and the lower adjustable clamp (3) are symmetrical structures. An arc-shaped protective cover (4) is arranged inside the upper adjustable clamp (2) and the lower adjustable clamp (3). The protective cover (4) fits the outer surface of the test piece (1).

6. The bending fatigue testing device for metal pipes according to claim 5, characterized in that: The upper adjustable clamp (2) and the lower adjustable clamp (3) are both provided with a pair of adjustment holes (16), and the positions of the upper adjustable clamp (2) and the lower adjustable clamp (3) in the Y direction are adjusted through the pair of adjustment holes (16).

7. The bending fatigue testing device for metal pipes according to claim 6, characterized in that: The linear slide module (6) comprises a screw and nut assembly, and the positions of the upper adjustable clamp (2) and the lower adjustable clamp (3) in the Z direction are adjusted by means of a screw (17), a nut (18) and a slide rail (19).

8. The bending fatigue testing device for metal pipes according to claim 7, characterized in that: The linear slide module (6) can move as a whole along the axial direction of the test piece (1) to adjust the positions of the upper adjustable clamp (2) and the lower adjustable clamp (3) in the X direction.

9. The bending fatigue testing device for metal pipes according to claim 1, characterized in that: The test piece (1) is a metal pipe.

10. A testing method using the bending fatigue testing device for a metal pipe according to any one of claims 1 to 9, characterized in that: include: S1: Determine the length L of the test piece (1), and install the test piece (1) on the tailstock (13) with one end of the test piece (1) in a free state; S2: Install the headstock (9), roughly align the self-centering bearing (8) at the end of the headstock (9), connect the connecting piece (10), adjust so that the axis of the headstock (9), the test piece (1), the curvature adjustment assembly (7), the connecting piece (10), and the tailstock (13) are roughly in a horizontal state, and fine-tune the test piece (1) using the micrometer (11) to make it level; S3: Install a linear slide module (6) and an upper adjustable clamp (2) and a lower adjustable clamp (3) on one side of the strain gauge (12), and adjust the upper adjustable clamp (2) and the lower adjustable clamp (3) in three directions, namely, X, Y, and Z, to clamp the test piece (1) and keep the axis of the test piece (1) unchanged; S4: the strain gauge (12) measures the reading ε1 of the test piece (1) in the free state; S5: Remove the micrometer (11), determine the strain value ε2 according to the test purpose and the strain ε1, and adjust the curvature setting component (7) to the target value ε2; S6: applying a bending stress of ε2 to the test piece (1), setting the motor speed and starting the equipment to perform a rotational bending fatigue test; S7: After the rotation bending fatigue test is completed, the number of rotations is recorded, the SN curve is drawn, and the failure cause of the test piece (1) is analyzed.

Images