CN110926940B - Method for testing ultimate contact strength of material surface - Google Patents
Method for testing ultimate contact strength of material surface Download PDFInfo
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- CN110926940B CN110926940B CN201811102095.2A CN201811102095A CN110926940B CN 110926940 B CN110926940 B CN 110926940B CN 201811102095 A CN201811102095 A CN 201811102095A CN 110926940 B CN110926940 B CN 110926940B
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N3/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N3/08—Investigating strength properties of solid materials by application of mechanical stress by applying steady tensile or compressive forces
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N2203/00—Investigating strength properties of solid materials by application of mechanical stress
- G01N2203/0014—Type of force applied
- G01N2203/0016—Tensile or compressive
- G01N2203/0017—Tensile
Abstract
The invention provides a method for testing the ultimate contact strength of a material surface, which comprises the following steps: step S 1 Installing a piece to be tested and connecting a data acquisition system to debug a testing device and the piece to be tested; step S 2 Tong (Chinese character of 'Tong')Applying a downward load force to the test piece to be tested through the testing device; step S 3 Increasing the load of the test piece to be tested in a grading way, wherein each grade is 5-10 KN, and the loading rate is 100-500N/s; step S 4 Obtaining the ultimate contact pressure P of the piece to be tested by measurement and calculation G . The method for testing the ultimate contact strength of the surface of the material can accurately measure the ultimate contact strength of the surface of the material by researching the test on the ultimate contact strength of the surface of the material, and the method is more consistent with the actual situation through continuous verification.
Description
Technical Field
The invention relates to the field of material performance testing, in particular to a method for testing the ultimate contact strength of a material surface.
Background
In the automotive field, fastener designs must meet automotive joint design performance and functionality requirements while reducing weight with the least safe fastener possible to improve automotive safety and driving comfort. In the design of the fastener installation process, the problem that the fastener connection fails due to the loss of tightening torque caused by the surface of the connected member being crushed by the fastening material during the tightening process of the fastener must be considered. This is also a key part of many connection failures, but how to correctly obtain the ultimate contact strength of the material surface, so far no professional institution or college has studied the material property in China.
The ultimate contact strength of the surface of a material is a physical quantity of the material and is also a very important performance parameter. However, this amount is very small in material application, and therefore, the research on this amount by steel mills and colleges has not been made. While there are some parameters of the surface contact strength of materials in the fastener design standards, the data in the standards have not been able to meet practical needs for the current continued use of high strength steels and lightweight aluminum alloys, magnesium alloys, and composites.
At present, theoretical design is usually performed in a mode of performing equal proportion conversion on the same type of materials in the standard in the design, but in an actual loading test or a test in a laboratory, the fact that the mode that the clamping force fails due to the fact that the surface crushing is considered according to the existing method is greatly different often results in the phenomenon that the design process parameters are inconsistent with the actual situation.
In view of the above, there is a need in the art for a test method that improves the ultimate contact strength of a material surface.
Disclosure of Invention
The invention aims to overcome the defect that parameters of the ultimate contact strength of the surface of a material in the prior art cannot meet actual requirements, and provides a method for testing the ultimate contact strength of the surface of the material.
The invention solves the technical problems through the following technical scheme:
a method for testing the ultimate contact strength of a material surface is characterized by comprising the following steps:
step S 1 Installing a piece to be tested and connecting a data acquisition system to carry out debugging work on the testing device and the piece to be tested;
step S 2 Applying a downward load force to the test piece to be tested by the testing device;
step S 3 Increasing the load of the test piece to be tested in a grading way, wherein each grade is 5-10 KN, and the loading rate is 100-500N/s;
step S 4 Obtaining the surface limit contact strength P of the piece to be tested through measurement and calculation G 。
According to one embodiment of the invention, the testing device adopted by the testing method comprises a dial indicator, a tensile bolt and a ring type pressure sensor, wherein the to-be-tested piece is placed on the ring type pressure sensor, and the applied external load is measured through the ring type pressure sensor;
the tensile bolt penetrates through the piece to be tested and the ring type pressure sensor, and the dial indicator is arranged on the upper portion of the tensile bolt and used for measuring displacement of the tensile bolt in the loading process.
According to an embodiment of the invention, said step S 2 The method also comprises the following steps: the tensile bolt applies downward load force to the piece to be tested, the downward load force is continuously increased from zero until the dial indicator starts to detect the displacement of the tensile bolt, the piece to be tested reaches the yield limit and is in a pre-tightening state, and the annular pressure sensor records F vmax Value, F vmax Is the maximum pre-tightening force.
According to an embodiment of the invention, said step S 3 The method also comprises the following steps: and the tensile bolt is loaded to a preset load for 15-120 s, and the dial indicator measures the displacement of the tensile bolt.
According to an embodiment of the invention, said step S 3 The method also comprises the following steps: when the plastic deformation of 2um-2.5um occurs in the holding time of 15s-120s or the pressure depth of 100um-150um is accumulated, the tension bolt is considered to have obvious short-term relaxation effect, the corresponding contact pressure is the limit contact pressure, and F is recorded by the ring-type pressure sensor SAmax Value, F SAmax Is the maximum additional tightening force.
According to an embodiment of the invention, said step S 4 The method also comprises the following steps: measuring and calculating the minimum projection area A of the piece to be tested and the stretching bolt pmin Value, A pmin Is the minimum projected area.
According to one embodiment of the invention, the test method is a material test at ambient temperature, so Δ F vth A value of 0,. DELTA.F vth Is a pre-load force under thermal load.
According to one embodiment of the invention, F vmax Value, F SAmax Value Δ F vth And A pmin Substitution into the formula:
According to one embodiment of the invention, the safety factor of the test method is verified as follows:
according to one embodiment of the invention, the tension bolt comprises a bolt and a screw.
The positive progress effects of the invention are as follows:
the method for testing the ultimate contact strength of the surface of the material can accurately measure the ultimate contact strength of the surface of the material by researching the test on the ultimate contact strength of the surface of the material, and the method is more consistent with the actual situation through continuous verification.
Drawings
The above and other features, properties and advantages of the present invention will become more apparent from the following description of the embodiments with reference to the accompanying drawings in which like reference numerals denote like features throughout the several views, wherein:
FIG. 1 is a schematic structural diagram of a testing device adopted in the testing method for the ultimate contact strength of the surface of the material.
Fig. 2 is an enlarged view of a portion a in fig. 1.
FIG. 3 is a front view of a tensile bolt in a testing device used in the testing method of the ultimate contact strength of the surface of the material according to the present invention.
Fig. 4 is a left side view of a tensile bolt in a test apparatus used in the test method for ultimate contact strength of a material surface according to the present invention.
FIG. 5 is a front view of a test piece to be tested in a test apparatus used in the method for testing the ultimate contact strength of the surface of a material according to the present invention.
FIG. 6 is a top view of a test piece in a test apparatus used in the method for testing the ultimate contact strength of the surface of a material according to the present invention.
[ reference numerals ]
Ring type pressure sensor 30
Bolt 21
Screw 22
Detailed Description
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers will be used throughout the drawings to refer to the same or like parts.
Further, although the terms used in the present invention are selected from publicly known and used terms, some of the terms mentioned in the description of the present invention may be selected by the applicant at his or her discretion, the detailed meanings of which are described in relevant parts of the description herein.
Furthermore, it is required that the present invention is understood, not simply by the actual terms used but by the meaning of each term lying within.
FIG. 1 is a schematic structural diagram of a testing device adopted in the testing method for the ultimate contact strength of the surface of the material. Fig. 2 is an enlarged view of a portion a in fig. 1. FIG. 3 is a front view of a tensile bolt in a testing device used in the testing method of the ultimate contact strength of the surface of the material according to the present invention. Fig. 4 is a left side view of a tensile bolt in a test apparatus used in the test method for the ultimate contact strength of the surface of a material according to the present invention. FIG. 5 is a front view of a test piece to be tested in a test apparatus used in the method for testing the ultimate contact strength of the surface of a material according to the present invention. FIG. 6 is a top view of a test piece in a test apparatus used in the method for testing the ultimate contact strength of the surface of a material according to the present invention.
As shown in fig. 1 to 6, the invention discloses a method for testing the ultimate contact strength of a material surface, which finds the ultimate contact strength of a bearing surface capable of ensuring the pre-tightening force precision through gradual loading. Below the yield strength of the connected piece, plastic deformation usually does not occur, and the short-term relaxation effect has little influence on the pre-tightening force precision. The connected piece is therefore continuously loaded step by step starting from the yield strength in the present application.
The testing device adopted by the testing method comprises a dial indicator 10, a stretching bolt 20 and a ring type pressure sensor 30, a piece to be tested 40 is placed on the ring type pressure sensor 30, and the applied external load is measured through the ring type pressure sensor 30. The tensile bolt 20 penetrates through the piece to be tested 40 and the ring type pressure sensor 30, and the dial indicator 10 is arranged on the upper portion of the tensile bolt 20 and used for measuring the displacement of the tensile bolt 20 in the loading process.
The tension bolt 20 preferably includes a bolt 21 and a threaded rod 22. The screw rod 22 sequentially penetrates through central holes of the piece to be tested 40 and the ring type pressure sensor 30, the screw rod 22 exerts tensile force downwards, the ring type pressure sensor 30 is used for measuring applied external load, the dial indicator 10 is arranged right above the end of the bolt 21, and displacement of the bolt 21 in the loading process is measured. Wherein, when a tensile force is applied on the screw 22, the upper surface of the to-be-tested piece 40 and the end surface of the bolt 21 are in sufficient contact and a certain pressure is generated on the to-be-tested piece 40. At this time, the testing object 40 is compressed by a certain displacement amount with the increasing of the load, the dial indicator 10 records the displacement amount generated by the compression of the testing object 40 under the pressure, and the annular pressure sensor 30 placed under the testing object 40 records the force value applied by the screw rod 22.
The method for testing the ultimate contact strength of the surface of the material specifically comprises the following steps:
step S 1 And installing the piece to be tested 40 and connecting a data acquisition system to debug the testing device and the piece to be tested 40.
Step S 2 A downward load force is applied to the test piece 40 by the test apparatus.
The tensile bolt 20 applies downward load force to the test piece 40, and the downward load force continuously increases from zero until the test piece 40 reaches the yield limit and is in the pre-determined range when the dial indicator 10 starts to detect the displacement of the tensile bolt 20Tight condition, recorded F by ring pressure sensor 30 vmax Value, F vmax Is the maximum pre-tightening force.
Step S 3 And increasing the load to the test piece 40 to be tested in a grading manner, wherein each grade is 5-10 KN, and the loading rate is 100-500N/s.
The tension bolt 20 is loaded to a preset load for a holding time of 15s-120s, and the dial gauge 10 measures the displacement of the tension bolt 20. When the plastic deformation of 2um-2.5um occurred within the holding time of 15s-120s or the accumulated pressing depth of 100um-150um has occurred, it is considered that the tension bolt 20 has a significant short-term relaxation effect, and the corresponding contact pressure is the ultimate contact pressure, and the ring-type pressure sensor 30 records F SAmax Value, F SAmax Is the maximum additional tightening force.
Step S 4 Obtaining the surface limit contact strength P of the test piece 40 by measurement and calculation G 。
By measuring and calculating the minimum projected area A of the test piece 40 and the tension bolt 20 pmin Value, A pmin Is the minimum projected area. The test method is a material test at normal temperature, so Δ F vth A value of 0,. DELTA.F vth Is a pre-load force under thermal load.
F is to be vmax Value, F SAmax Value Δ F vth And A pmin Substituting equation (1):
Preferably, the safety factor verification of the test method satisfies formula (2):
according to the above description, the principle of the method for testing the ultimate contact strength of the surface of the material of the invention is as follows: during the tightening of the bolt, a tightening effect is formed by the mutual contact action due to the swiveling movement as well as the circumferential movement of the fastening element. The loading mode in the invention does not consider the friction factor between the bolt head and the combined surface of the connected piece, and the pre-tightening is completed by stretching the screw rod part.
When the pretensioning is completed, the bearing surface is subjected to a contact pressure by the pretensioning force, which increases in magnitude with decreasing contact area and generally reaches the yield limit of the connected component, but rarely reaches the bolt yield limit. After the tensile yield limit is exceeded, the connected component is plastically deformed, since the plastic deformation occurs more slowly. Therefore, after the pre-tightening is completed, the connected part may have large plastic deformation, which is the loss of the pre-tightening force at the connection part and short-term relaxation effect.
An increase in the additional tightening force acting in extreme cases will lead to failure of the connection. Therefore, when designing the bolt tightening process, it is necessary to check that the surface pressure of the bolt under external load cannot exceed the requirement of the ultimate contact strength of the surface of the material to be joined.
The stresses occurring in the actual operating situation can be determined by the magnitude of the pretension, the additional tightening force and the thermal load. The first two factors play a major role in threaded connections, while the third heat load factor plays a major role in threaded connections with lightweight metal alloys (differing in thermal conductivity) and bolts. Many of the materials in the prior art documents have not been experimented with new materials, resulting in many new materials (e.g., cast materials of vermicular graphite) being unable to be used.
Regardless of the material properties of the connected parts, the most basic requirements of the formula (1) above must be met in the fastener design, the safety factor must reach the minimum requirement of the formula (2) above in the design, otherwise the reliability of the joint performance cannot be guaranteed by the design of the clamping force of the fastener.
The test of the method for testing the ultimate contact strength of the surface of the material is as follows, which is only an example and is not limited by the specific test:
test one:
in the method for testing the ultimate contact strength of the surface of the material, the material Q235B is taken as an example for testing, and a M10 multiplied by 10-12.9-grade hexagonal-head high-strength screw is taken as a tensile bolt 20 for testing.
In the test, the tested piece is selected to be a high gasket with the diameter of 40/10.5 multiplied by 20mm, and the gasket is not chamfered and only burrs are removed. After pre-tensioning the test piece 40, the load was increased in stages, 5KN per stage, held at each loading stage for 120s, and the traces of plastic deformation were measured.
The test is considered to be ended when a single trace of the plastic deformation exceeds 2um or the total depth of indentation exceeds 100um during the load holding time. At the moment, the connected part is judged to have obvious short-term relaxation effect, and the corresponding contact strength is the limit contact strength. The ultimate contact strength at this time is the ratio of the ultimate contact pressure to the effective contact area. Table 1 herein reports the test data for the above test at different loading rates of 100N/s and 500N/s.
Table 1: ultimate contact pressure of the same material under different loading rates
This test data was compared to Q235 in the International general high-strength bolting System calculation Standard VDI2230, and the data is shown in Table 2 below:
| data source | Yield strength MPa | Tensile strength MPa | Ultimate contact pressure MPa |
| VDI2230 | 230 | 340 | 490 |
| Results of the experiment | 252 | 330 | 433 |
Compared with the test data in the VDI2230 standard, the measured data and the comparative data have certain deviation, the deviation is caused by certain difference between foreign materials and domestic materials and the surface state of the connected piece, but the data difference is about 10%, which shows the effectiveness of the test method in measuring the ultimate contact strength.
And (2) test II:
the top support (mount) for the shock absorber, the upper and lower pieces of material, SAPH370/SAPH440/SPHC, had properties that could only be scaled (linear interpolation) to the contact pressure values of the S235 JRG1 material in the VDI2230 standard without the test method, and the results are shown in Table 3 below:
| material | Tensile limit MPa | Ultimate contact pressure MPa |
| S235 JRG1 | 340 | 490 |
| SAPH370 | 370 | 533 |
| SAPH440 | 440 | 634 |
| SPHC | 270 | 389 |
The whole damper hinge has the following functions: the upper end is fixedly connected with the auxiliary frame or the vehicle, and the lower end is fixedly connected with the car or the vehicle. It mainly has the following tasks and performances: 1. compensating for manufacturing tolerances of the axle; 2. universal angle flexibility can be provided, so that the reaction force distance is as small as possible; 3. elastic kinematic performance is provided in the overall axle kinematic range; 4. noise with frequencies greater than 30Hz can be isolated.
When the shock absorber designed according to the numerical value is subjected to bench tests and road tests, the shock absorber is found to have abnormal sound when 20% -80% of the service life of the bench test is finished or 20% -80% of kilometers of the road test is run out. The reason is analyzed and is basically caused by bolt torque attenuation. Such a verification of the bolt torque by the material surface ultimate contact strength obtained by the equal proportion conversion (linear interpolation method) does not theoretically cause the collapse to attenuate the torque, but in an actual test, there is a problem that the abnormal response is caused by the attenuation of the torque, and the collapse of the surface collapse should not occur, and such a theoretical calculation is not feasible.
The test method is adopted to test the upper and lower sheet materials of the shock absorber mount, and the test data are as follows
Shown in Table 4:
| material | Ultimate contact pressure N | Ultimate contact pressure MPa |
| SAPH370 | 33050.80 | 403.11 |
| SAPH440 | 38423.90 | 470.46 |
| SPHC | 32938.20 | 402.58 |
The data in the original design are exchanged by the test data, and the fact that the original design does not have surface collapse is found, namely PG is not more than PBmax, and the test method and the road test keep consistent, so that the data obtained by the test are more consistent with the actual working conditions of the actual bench test and the actual road test.
In conclusion, the method for testing the ultimate contact strength of the surface of the material can more correctly determine the ultimate contact strength of the surface of the material by researching the test on the ultimate contact strength of the surface of the material, and the method is more in line with the actual situation through continuous verification.
While specific embodiments of the invention have been described above, it will be appreciated by those skilled in the art that these are by way of example only, and that the scope of the invention is defined by the appended claims. Various changes and modifications to these embodiments may be made by those skilled in the art without departing from the spirit and scope of the invention, and these changes and modifications are within the scope of the invention.
Claims (3)
1. A method for testing the ultimate contact strength of a material surface, which is characterized by comprising the following steps:
step S 1 Installing a piece to be tested and connecting a data acquisition system to debug a testing device and the piece to be tested;
step S 2 Applying a downward load force to the test piece to be tested by the testing device;
step S 3 Increasing the load of the test piece to be tested in a grading way, wherein each grade is 5-10 KN, and the loading rate is 100-500N/s;
step S 4 Obtaining the surface limit contact strength P of the piece to be tested through measurement and calculation G ；
The testing device adopted by the testing method comprises a dial indicator, a stretching bolt and a ring-type pressure sensor, wherein the to-be-tested piece is placed on the ring-type pressure sensor, and the applied external load is measured through the ring-type pressure sensor;
the tensile bolt penetrates through the piece to be tested and the ring type pressure sensor, and the dial indicator is arranged at the upper part of the tensile bolt and used for measuring the displacement of the tensile bolt in the loading process;
said step S 2 The method also comprises the following steps: the tensile bolt applies downward load force to the piece to be tested, the downward load force is continuously increased from zero until the dial indicator starts to detect the displacement of the tensile bolt, the piece to be tested reaches the yield limit and is in a pre-tightening state, and the annular pressure sensor records F vmax Value, F vmax The maximum pre-tightening force is obtained;
said step S 3 The method also comprises the following steps: the tensile bolt is loaded to a preset load for 15-120 s, and the dial indicator measures the displacement of the tensile bolt;
said step S 3 The method also comprises the following steps: when the plastic deformation of 2um-2.5um occurred in the retention time of 15s-120s or the accumulated depth of 100um-150um has occurred, the tension bolt is considered to have obvious short-term relaxation effect, the corresponding contact pressure is the surface limit contact strength, and F is recorded by the ring-type pressure sensor SAmax Value, F SAmax The maximum additional tightening force is obtained;
said step S 4 The method also comprises the following steps: measuring and calculating the minimum projection area A of the piece to be tested and the stretching bolt pmin Value, A pmin Is the minimum projected area;
the test method is a material test at normal temperature, so Δ F vth A value of 0,. DELTA.F vth Pre-tightening force under thermal load;
f is to be vmax Value, F SAmax Value Δ F vth And A pmin Substitution into the formula:
2. The method for testing the ultimate contact strength of the surface of the material according to claim 1, wherein the safety factor of the test method is verified as follows:
3. the method for testing the ultimate contact strength of the surface of a material according to any one of claims 1 or 2, wherein the tensile bolt comprises a bolt and a screw.
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| CN113820112A (en) * | 2021-09-16 | 2021-12-21 | 常州格林电力机械制造有限公司 | Performance test method of valve pin type bolt stretching leveling device |
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| CH378069A (en) * | 1960-11-25 | 1964-05-31 | Centre Nat Rech Metall | Method for measuring the relaxation of metals at high temperature and device for implementing this method |
| CN201622207U (en) * | 2010-01-09 | 2010-11-03 | 湖南吉利汽车部件有限公司 | Bolt tensile strength test clamp |
| CN104833572B (en) * | 2015-05-21 | 2017-11-10 | 河南航天精工制造有限公司 | Bolt tension test tool and the tensile test apparatus using the test tool |
| CN106248488A (en) * | 2016-07-20 | 2016-12-21 | 哈尔滨电气动力装备有限公司 | Kingbolt stretching and measurement technique |
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| CN107179060B (en) * | 2017-06-14 | 2019-04-09 | 陕西科技大学 | A kind of bolt joint surface real contact area measuring device and method |
| CN107607398A (en) * | 2017-08-11 | 2018-01-19 | 北京工业大学 | A kind of measuring method of residual stress to bolt fastening structure clamping force influence of fading |
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