CN114486513A

CN114486513A - Circumferential tensile test method and test device

Info

Publication number: CN114486513A
Application number: CN202011145295.3A
Authority: CN
Inventors: 李铭; 黄平; 李怀龙; 曹克强; 祝贺; 张蒙
Original assignee: SKF China Co Ltd China; SKF AB
Current assignee: SKF China Co Ltd China; SKF AB
Priority date: 2020-10-23
Filing date: 2020-10-23
Publication date: 2022-05-13

Abstract

A circumferential tensile test method is characterized in that a diameter-variable expansion mechanism (10) is utilized to apply extrusion from inside to outside in the radial direction to a roughly annular test sample (S) to be tested, so that the test sample (S) is forced to deform in the circumferential direction due to stretching, and therefore a tensile curve of the test sample (S) is recorded and generated. By adopting the test method, the annular test sample formed under the combination of various materials, structures and processes can be subjected to a circumferential tensile test, so that the test method is simple and convenient to operate, reliable in conclusion and cost-advantageous. On the basis of the test method, the invention also provides a circumferential tensile test device which comprises the reducing expansion mechanism (10) and can directly stretch the annular part, so that the necessity of implementing the traditional tensile test is avoided, and the test result which is closer to the real state of the product can be obtained by directly testing the finished sample.

Description

Circumferential tensile test method and test device

Technical Field

The present invention relates to a circumferential tensile test method for a ring-shaped test piece, and a test apparatus for performing circumferential tensile test according to the test method.

Background

The tensile test is a test method for measuring material properties under an axial tensile load, and is performed only for a standard specimen (specimen) in many cases to examine the material properties such as yield strength, elastic limit, plastic limit, and the like of a material. The tensile curve obtained on the basis of the tensile test may also be used for making preliminary evaluations of other properties of the material, such as toughness and structural fatigue properties, so as to avoid the necessity of further carrying out Charpy impact tests (Charpy impact tests) and/or various fatigue tests in more cases.

The standard sample is mostly a columnar standard part, a plate standard part and the like, and the influence of other shapes, structures and production processes on the performance of a finished product is not considered. Taking the bearing ring as an example, the bearing ring is annular on the whole, and the specific designs of the roller path, the flange and the like and the processes of forging, cutting, heat treatment and the like have obvious influence on the mechanical property of the bearing ring. Therefore, conventional tensile tests conducted only on standard test specimens often do not reflect the true performance of the finished part. Although some tests, such as the full bearing durability test, are designed for the finished test specimen, they are not suitable for guiding the selection of materials at the initial stage of development. There is a need for a test method and test apparatus that can apply tension to various annular components, including bearing rings.

Disclosure of Invention

In order to solve the technical problems, the invention provides a circumferential tensile test method, which utilizes a variable-diameter expansion mechanism to press a roughly annular sample to be tested from inside to outside in the radial direction, so that the sample is forced to deform in the circumferential direction due to being stretched, and accordingly, a tensile curve of the sample is recorded and generated.

By adopting the test method, the annular test sample formed under the combination of various materials, structures and processes can be subjected to a circumferential tensile test, so that the test method is simple and convenient to operate, reliable in conclusion and cost-advantageous.

On the basis of the test method, the invention also provides a circumferential tensile test device which comprises the reducing expansion mechanism and can directly stretch the annular part, so that the necessity of implementing the traditional tensile test is avoided, and the test result which is closer to the real state of a product can be obtained by directly testing the finished sample.

The following detailed description of the present invention and the accompanying drawings are provided to illustrate the embodiments and advantageous effects thereof.

Drawings

FIG. 1 is a perspective view of a test device according to the present invention;

FIG. 2 is a top view of the test device of the present invention.

Detailed Description

In the following description, directional terms such as "axial," "radial," and "circumferential" refer to the axial, radial, and circumferential directions of an annular test piece (e.g., a bearing ring), unless otherwise defined or stated.

FIG. 1 is a perspective view of a test device according to the present invention. The device 1 comprises a reducing expansion mechanism 10 capable of radially pressing the annular sample S from inside to outside, and is used for forcing the annular sample S to deform in the circumferential direction due to being stretched.

In the embodiment shown in fig. 1, the reducing expansion mechanism 10 is mainly composed of a conical member 11 and at least one squeeze pad 13 distributed circumferentially around the conical member 11. An equi-taper fit is formed between the conical member 11 and the crash pad 13 (the ratio of the difference between the diameters of the large and small ends of the cone to the height of the cone is defined as the taper, also referred to as the "taper ratio"), i.e. a taper fit is formed between the radially outer surface of the conical member 11 and the radially inner surface of the crash pad 13 with the same taper, so that the axial advancement of the conical member 11 towards the ring-shaped test specimen S forces the crash pad 13 radially outwards.

Taking the case where only one squeeze pad 13 is present as an example, radial squeezing of the annular test piece S can be achieved by additionally providing a fixed pad (not shown) on the test platform 21 (described later) and symmetrically distributed on both sides of the conical member with the one squeeze pad 13 to cooperate with the squeeze pads. As long as extrusion cushion and fixed cushion shape are reasonable, the radial expansion effect that both formed can produce even squeezing action to annular sample, just can realize being tested the sample by the experimental effect of uniform tension on the circumferencial direction.

In the above-described embodiment, the reducing expansion mechanism 10 is formed by combining the tapered member 11 and the dummy block 13. However, at least theoretically, without providing the pressing pad 13, the conical member 11 may directly drive the annular sample S to expand outward, although in this case, the direction in which the annular sample S undergoes expansion does not completely coincide with the radial direction, easily causing it to undergo radial pressing at an edge position on one side in the axial direction. It can be seen that the ram 13 not only transmits the expansion load, but also adjusts the transmission direction of the expansion load, thereby playing an important role in the variable diameter expansion mechanism 10.

In the load-elongation curve as a result of the test, the applied load exerted by the conical part and its stroke in the axial direction can be used directly as a coordinate variable for characterizing the tensile properties of the test specimen. Alternatively, the load and the stroke can be replaced (converted) into the radial stress and the circumferential deformation of the test sample respectively, so as to form a stress-strain curve of the tested test sample. The tensile curve developed under either index system can be used to evaluate the final properties of the loop specimen developed based on various material, structure and process combinations.

In the embodiment shown in fig. 1, the conical part 11 is a conical part. As a preferred embodiment, the conical part 11 may also be a pyramidal part. In the latter case, a matching pyramid fit is formed between the pyramid part 11 and the squeeze pads 13, and each squeeze pad 13 "rides" on an edge of the pyramid part 11, so that any axial thrust of the pyramid part 11 will not cause a mismatch with the squeeze pads 13.

During the test, friction between the parts, such as the conical part 11 and the squeeze pad 13, may adversely affect the test results, so that good lubrication is a prerequisite to ensure that the test results are sufficiently accurate. In addition, the part has a sufficiently high hardness to help avoid material deformation adversely affecting the test results. For this reason, as an embodiment, the tapered member 11 and the press pad 13 may be hardened to increase the hardness of both.

On the basis of the measures, the taper of the fit surface between the conical part 11 and the extrusion cushion block 13 is reduced, so that the test accuracy is further improved. For example, the taper ratio of the fit surface between the tapered member 11 and the ram 13 may be set to 1:30 to 1: 100. A larger taper ratio, such as 1:200, results in an excessively long length and travel of the tapered member 11. This results in the conical part 11 being easily broken due to the reduced stability, and on the other hand, it greatly increases the test time, which is not good for improving the working efficiency. Or, as another option, in order to adapt to the range of the stroke provided by the existing stretching equipment, the taper ratio of the fit surface between the tapered part 11 and the extrusion cushion block 13 can be selected to be between 1:10 and 1:30, so that the implementation cost of the invention can be reduced by adopting the existing stretching equipment.

In the embodiment shown in fig. 1, the test apparatus 1 further comprises a cylindrical housing 20 for accommodating a portion of the conical member 11 which is pushed in the axial direction on the one hand, and an upper end face 21 thereof is provided as a test platform 21 for supporting the expansion mechanism 10 and for carrying the sample S to be tested on the other hand.

Fig. 2 is a top view of the test device 1 shown in fig. 1, showing the conical member 11, the squeeze pad 12 and the annular test specimen S centered radially from the inside to the outside on the platform 21. In a preferred embodiment, the platform 21 is provided with a series of concentric circle scale markings sized to cover the normal caliber of the sample S to be tested for guiding the sample S to be tested to be centered on the platform. As a further preferred embodiment, at least in the radial range of the concentric circle scale distribution, the platform 23 is formed with a few depressions for storing lubricating oil, thereby reducing the friction between the press pad 12 and the annular test piece S and the platform 23, so as to minimize the adverse effect of the friction on the test result.

As can be seen from the above description, the linear stroke is vertically transferred from the tapered member 11 to the squeeze pad 13 through the iso-taper mating surface. Essentially, an iso-taper fit is a special form of the drive action transmitted by the two wedge members through the iso-taper ramp. In this sense, any two wedge-shaped elements which are matched through the inclined planes with equal slope can realize the vertical transmission of linear drive, namely the drive stroke of one wedge-shaped element in the axial direction is converted into the driven stroke of the other wedge-shaped element (or a group of wedge-shaped elements) in the radial direction, thereby realizing the aim of the invention of extruding the annular sample in the radial direction to cause the annular sample to be stretched and deformed.

Furthermore, the reducing expansion mechanism is not limited to be constituted by a wedge member that transmits a stroke by being engaged with an inclined surface, and any other type of radial expansion mechanism, for example, a curved cam expansion mechanism (curved cam expansion mechanism), a hydraulic reducing expansion tool (hydraulic expansion tools), or the like, can radially press the annular sample. They function exactly as the variable diameter expansion mechanism composed of wedge-shaped elements in the present invention, and therefore, they can be used for the purpose of the present invention.

The circumferential tensile test of the invention is not only more suitable for evaluating the tensile properties of annular test samples than the Charpy impact test and the rotating bending test, but also suitable for detecting the tensile properties of finished test samples formed under various material, structure and process combinations. In addition, compared with a rotating bending test and a full-bearing durability test, the circular tensile test is more convenient and time-saving to detect the annular sample, and the cost is low. When the device is used for detecting a finished product sample, the test result is more accurate and reliable because the finished product part is closer to the final shape of the product.

The circumferential tensile test can be widely used for detecting the tensile property of various annular samples including bearing rings. On the basis of the above-mentioned test method, the test device disclosed in the present invention is not limited by the specific embodiments, and the more general technical solution will be subject to the limitations in the appended claims. Any variations and modifications of the present invention, as long as they comply with the definitions of the following claims, are within the protection scope of the present invention.

Claims

1. A circumferential tensile test method is characterized in that a diameter-variable expansion mechanism (10) is utilized to apply extrusion from inside to outside in the radial direction to a roughly annular test sample (S) to be tested, so that the test sample (S) is forced to deform in the circumferential direction due to stretching, and therefore a tensile curve of the test sample (S) is recorded and generated.

2. The method of claim 1, wherein: the reducing expansion mechanism (10) comprises a first wedge-shaped part (11) and a second wedge-shaped part (13) which are matched through equal-inclination-angle inclined planes, the first wedge-shaped part (11) approaches to the sample (S) in the axial direction, the second wedge-shaped part (13) can be forced to move outwards in the radial direction by the pushing of the sample (S), and therefore the second wedge-shaped part (13) can extrude the sample (S) from inside to outside in the radial direction.

3. The method of claim 2, wherein: the first wedge-shaped part (11) is a conical part (11), the second wedge-shaped part (13) is at least one extrusion cushion block (13) arranged around the first wedge-shaped part (11) in the circumferential direction, and the equal-inclination-angle inclined plane is an equal-taper fit plane formed between the conical part (11) and the at least one cushion block (13).

4. A method as claimed in claim 3, characterized in that: the conical part (11) is a conical part or a pyramidal part.

5. A method as claimed in claim 3, characterized in that: the taper ratio of the equal-taper fitting surfaces is between 1: 10-1: 100, respectively.

6. The method according to any one of claims 1 to 5, characterized in that: in the tensile curve, the stroke of the first wedge-shaped part (11) is used for representing the tensile deformation of the tested sample (S), and the acting load applied by the first wedge-shaped part (11) is used for representing the acting load born by the tested sample (S).

7. The method according to any one of claims 1 to 5, characterized in that: the sample to be tested is a bearing ring sample.

8. A circumferential tensile test device (1) comprising the variable diameter expansion mechanism (10) according to any one of claims 1 to 7.

9. A circumferential tensile test apparatus (1) comprising the variable diameter expansion mechanism (10) according to any one of claims 2 to 7, wherein: further comprising a housing (20) accommodating the axially advanced portion of the first wedge member (11), the housing (20) having an end face (21) on which a test platform is formed for supporting the expansion mechanism (10) and for carrying the test specimen (S).

10. The testing device (1) according to claim 9, characterized in that: the platform (21) is provided with annular scale marks for guiding the sample (S) to be tested to be placed in the center of the platform (21).