Frame Tension-Compression Fretting Fatigue Test Method

Abstract

The present invention provides a method for testing the tensile-compressive fretting fatigue of a vehicle frame, which relates to the field of vehicle frame fatigue testing. The method includes: obtaining a test sample body for simulating the service conditions of the vehicle frame; assembling a test bolt and a test nut on the test sample body to obtain a test specimen to be tested; applying tensile-compressive alternating loads to the test specimen to be tested respectively through a tensile-compressive fatigue testing machine according to a preset fatigue test standard until the test specimen to be tested has tensile-compressive fretting fatigue failure, so as to obtain the tensile-compressive fretting fatigue test data of the test specimen to be tested; sorting out the tensile-compressive fretting fatigue test data according to a preset data processing specification to obtain the fretting fatigue strength of the test sample body; and obtaining the fretting fatigue strength of the vehicle frame according to the fretting fatigue strength. By obtaining the fretting fatigue strength of the test sample body, the present invention obtains the fretting fatigue strength of the vehicle frame.

Description

Technical Field

[0001] The present invention relates to the field of frame fatigue tests, and particularly to a method for frame tensile-compressive fretting fatigue tests. Background Art

[0002] Automobile frames (especially frame side members) are generally formed by stamping sheets, and cross members, various assemblies and accessories of the automobile frame are connected to the frame by bolts. During actual operation, the failure analysis results of automobile frames show that fretting fatigue fracture failure of the frame bolt connection structure accounts for about 60%-70% of the frame failures.

[0003] During the process of an automobile running on a rough road surface, the torsional deformation of the frame generates tensile and compressive stresses on the wing surfaces of the frame side members. Therefore, fretting fatigue is likely to occur on the connection surfaces of the wing surfaces of the frame side members, and this fretting fatigue is also called tensile-compressive fretting fatigue.

[0004] The prior art usually uses bench tests and / or road tests to verify the failure problems of automobile frames. However, the above prior art solutions can only enable workers to determine whether the frame will fail due to fretting fatigue after the frame design and manufacturing are completed, and cannot obtain the fretting fatigue strength data of the frame under actual service conditions. As a result, workers cannot check the tensile-compressive fretting fatigue strength of the frame during the design stage, nor can they fully evaluate the influence of various structural factors, process factors and uncertain factors (real-time changes and uniformity of contact stress and friction force, loosening caused by fretting wear) under actual service conditions on the tensile-compressive fretting fatigue performance of the automobile frame. Summary of the Invention

[0005] The main purpose of the present invention is to provide a method for frame tensile-compressive fretting fatigue tests, aiming to solve the problem that the prior art cannot obtain the fretting fatigue strength data of the frame under actual service conditions.

[0006] In view of the above problems, the present invention provides a method for frame tensile-compressive fretting fatigue tests, which includes: obtaining a test sample body for simulating the service conditions of the frame; assembling a test bolt and a test nut on the test sample body to obtain a test specimen to be tested; applying tensile-compressive alternating loads to the test specimen to be tested respectively through a tensile-compressive fatigue testing machine according to a preset fatigue test standard until the test specimen to be tested has tensile-compressive fretting fatigue failure, so as to obtain the tensile-compressive fretting fatigue test data of the test specimen to be tested; sorting out the tensile-compressive fretting fatigue test data according to a preset data processing specification to obtain the fretting fatigue strength of the test sample body; and obtaining the fretting fatigue strength of the frame according to the fretting fatigue strength.

[0007] In some embodiments, after obtaining the test sample body for simulating the service conditions of the vehicle frame, before assembling the test bolt and the test nut on the test sample body to obtain the test specimen to be tested, the method further includes: performing surface treatment on the surface of the test sample body according to the surface treatment process of the vehicle frame in the actual production process.

[0008] In some embodiments, the test sample body includes an effective test area located in the middle of the test sample body and clamping areas located at both ends of the test sample body, and a central hole is provided in the middle of the effective test area.

[0009] In some embodiments, the diameter of the central hole is matched with the diameter of the vehicle frame bolt at the position where tensile-compressive fretting fatigue failure is likely to occur on the vehicle frame, and the thickness of the effective test area and the thickness of the clamping area are both the same as the thickness at the position where tensile-compressive fretting fatigue failure is likely to occur on the vehicle frame; the effective test width of the effective test area is not less than 6 times the diameter of the central hole, and the effective test length of the effective test area is not less than 12 times the diameter of the central hole; the total length of the test sample body is not less than the effective test length, and the total width of the test sample body is not less than the effective test width.

[0010] In some embodiments, the step of assembling the test bolt and the test nut on the test sample body to obtain the test specimen to be tested includes: determining the position of the part where tensile-compressive fretting fatigue failure is likely to occur on the vehicle frame, denoted as the fatigue-prone failure part; obtaining the actual specifications, structures, and surface states of the vehicle frame bolt and the vehicle frame nut at the fatigue-prone failure part, denoted as the specifications, structures, and surface states of the vehicle frame bolt and the vehicle frame nut; selecting the test bolt and the test nut according to the preset design specifications, and the specifications, structures, and surface states of the test bolt and the test nut are matched with the specifications, structures, and surface states of the vehicle frame bolt and the vehicle frame nut at the part where tensile-compressive fretting fatigue failure is likely to occur on the vehicle frame; assembling the test bolt and the test nut onto the test sample body to obtain the test specimen to be tested.

[0011] In some embodiments, the step of assembling the test bolt and the test nut on the test sample body to obtain the test specimen to be tested further includes: using different tightening processes to assemble the test bolt and the test nut on multiple test sample bodies respectively to obtain the test specimen to be tested.

[0012] In some embodiments, the step of assembling the test bolt and the test nut on the test sample body to obtain the test specimen to be tested further includes: assembling multiple groups of test bolts and test nuts with different structures on the test sample body respectively, and / or assembling multiple groups of test bolts and test nuts with different surface states on the test sample body respectively.

[0013] In some embodiments, obtaining the fretting fatigue strength of the vehicle frame according to the fretting fatigue strength includes: taking the tensile-compressive fretting fatigue strength of the test sample body as the allowable tensile-compressive fretting stress of the vehicle frame, and checking the tensile-compressive fretting fatigue strength of the vehicle frame, so as to obtain the fretting fatigue strength of the vehicle frame.

[0014] In some embodiments, after assembling the test bolt and the test nut on the test sample body to obtain the test sample to be tested, before installing the test sample to be tested on a preset tensile-compressive fatigue testing machine, it further includes: installing a test pad on the test sample to be tested, and the working state of the test pad is the same as that of the connecting piece of the vehicle frame.

[0015] In some embodiments, applying tensile-compressive alternating loads to the test sample to be tested respectively through a tensile-compressive fatigue testing machine according to a preset fatigue test standard until the test sample to be tested has tensile-compressive fretting fatigue failure to obtain the tensile-compressive fretting fatigue test data of the test sample to be tested, it further includes: calculating the test stress generated by the test sample to be tested according to the tensile-compressive alternating load according to the test stress calculation formula, and supplementing the test stress to the tensile-compressive test data; the test stress calculation formula is: σ = P / b / t, where σ is the test stress generated by the test sample to be tested, P is the tensile-compressive alternating load, b is the effective test width of the test sample body, and t is the thickness of the test sample body.

[0016] The present invention provides a method for testing the tensile-compressive fretting fatigue of a vehicle frame, including obtaining a test sample body for simulating the service conditions of the vehicle frame, assembling a test bolt and a test nut on the test sample body, obtaining the tensile-compressive fretting fatigue test data of the test sample to be tested, obtaining the fretting fatigue strength of the test sample body, and obtaining the fretting fatigue strength of the vehicle frame according to the fretting fatigue strength. The present invention can obtain the fretting fatigue strength data of the vehicle frame under actual service conditions, so that the staff can check the tensile-compressive fretting fatigue strength of the vehicle frame during the design stage, so that the staff can design the structure of the vehicle frame better, more conveniently and accurately. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic flow chart of the method for testing the tensile-compressive fretting fatigue of the vehicle frame according to the present invention;

[0018] Figure 2 It is a schematic structural diagram of the test sample body of the present invention when viewed from the top;

[0019] Figure 3 It is a schematic structural diagram of the test sample body of the present invention when viewed from the front;

[0020] Figure 4 It is a schematic structural diagram of the test sample body of the present invention when viewed from the top after assembling the bolt;

[0021] Figure 5 It is a physical diagram of the first group of test sample bodies when they are subjected to the tension-compression fretting fatigue test by using the frame tension-compression fretting fatigue test method of the present invention until the first group of test sample bodies fail;

[0022] Figure 6 It is a physical diagram of the second group of test sample bodies when they are subjected to the tension-compression fretting fatigue test by using the frame tension-compression fretting fatigue test method of the present invention until the second group of test sample bodies fail;

[0023] Figure 7 It is a physical diagram of the third group of test sample bodies when they are subjected to the tension-compression fretting fatigue test by using the frame tension-compression fretting fatigue test method of the present invention until the third group of test sample bodies fail.

[0024] The realization, functional characteristics and advantages of the object of the present invention will be further described with reference to the embodiments and the accompanying drawings. Specific embodiments

[0025] 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.

[0026] Fatigue refers to the phenomenon that materials or parts (components) suddenly fail or are damaged after operating under variable loads for a long number of stress cycles.

[0027] Fretting fatigue refers to the fretting damage phenomenon that occurs on the contact surface when two mutually contacting surfaces are under a certain normal load and there is a small relative movement between the contact surfaces. Fretting damage is manifested as surface adhesion, corrosion, wear, and accompanied by clustering cracks that reduce the fatigue strength of the material. The cracks expand into the component body, thus forming fatigue fracture.

[0028] In a bolt connection structure, there are generally at least two connected bodies. The bolts and nuts are in contact with the connected bodies, and the connected bodies are in contact with each other. The axial force generated by tightening the bolts provides a normal load for each contact surface of the bolt connection structure. At the same time, the connected parts often bear an external alternating stress and generate strain or deformation, thus generating a small relative movement between the contact surfaces. Therefore, fretting fatigue is a common cause of failure in bolt connection structures.

[0029] When the vehicle is driving on a rough road surface, the torsional deformation of the frame generates tensile and compressive stresses on the wing surfaces of the frame longitudinal beams. Therefore, the fretting fatigue that occurs on the connection surfaces of the frame longitudinal beam wing surfaces is tensile-compressive fretting fatigue. For this reason, when designing the frame, it is necessary to check the tensile-compressive fretting fatigue strength. Therefore, it is necessary to provide the tensile-compressive fretting fatigue strength data of the automotive frame material under actual service conditions for product design.

[0030] At present, the prior art generally uses a micro-motion bridge to simulate the micro-motion fatigue test to obtain the tensile-compressive micro-motion fatigue strength data of materials. However, the above prior art solutions cannot truly simulate the micro-motion fatigue conditions of the bolt connection structure under the actual service conditions of the vehicle frame longitudinal beam, nor can they simulate the effects of various structural factors (such as clamping of double-layer or multi-layer steel plates, taper angles of bolt and nut flange surfaces, diameters of bolt and nut flange surfaces, etc.), process factors (bolt assembly process), and the surface protection status of related structural parts (powder spraying or painting on the surface of the vehicle frame longitudinal beam and its accessories, zinc plating or phosphating on the bolt surface, etc.) on the micro-motion fatigue performance of the vehicle longitudinal beam.

[0031] Meanwhile, the tensile-compressive micro-motion fatigue strength data obtained through the above prior art solutions can only be used for qualitative analysis and reference, and cannot be used as the micro-motion fatigue strength data of materials for micro-motion fatigue strength verification during vehicle frame design.

[0032] Due to the lack of micro-motion fatigue strength data of the vehicle frame material under actual service conditions, it is impossible to conduct design verification of the tensile-compressive micro-motion fatigue strength during vehicle frame design. It completely relies on bench tests and road tests after design and manufacturing to verify, which is not only time-consuming and costly, but also unable to fully assess the effects of various structural factors, process factors, and uncertain factors under actual service conditions on the micro-motion fatigue performance of the vehicle longitudinal beam. Among them, the above uncertain factors include the real-time change and uniformity of contact stress and friction force, loosening caused by micro-motion wear, etc.

[0033] In view of the above problems, the present invention provides a method for tensile-compressive micro-motion fatigue test of a vehicle frame to solve the technical problem that the prior art cannot enable workers to obtain the tensile-compressive micro-motion fatigue strength of the vehicle frame and thus conduct verification of the tensile-compressive micro-motion fatigue strength of the vehicle frame in the design stage, and also provides a test means for fully assessing the effects of various structural factors, process factors, and uncertain factors (real-time change and uniformity of contact stress and friction force, loosening caused by micro-motion wear) under actual service conditions on the tensile-compressive micro-motion fatigue performance of the vehicle frame. It should be noted that if there are substantially the same results, the method of the present invention is not limited to Figure 1 the flow sequence shown. During actual work, the method for tensile-compressive micro-motion fatigue test of the vehicle frame includes:

[0034] S1. Obtain a test sample body for simulating the service conditions of the vehicle frame;

[0035] In this step, in order to simulate the micro-motion fatigue service conditions of the vehicle frame bolt connection structure, a waist-shaped or long-strip plate-shaped test sample body with a central hole is designed. During actual work, the present invention also includes the step of manufacturing a test sample body for simulating the service conditions of the vehicle frame, including: performing surface treatment on the surface of the test sample body according to the surface treatment process of the vehicle frame during actual production.

[0036] Among them, the parts of the test sample body that are surface-treated are two surfaces arranged along the thickness direction of the test sample body. In this way, after the test sample body undergoes the above-mentioned surface treatment (such as painting), the test sample body can more realistically simulate the actual service conditions of the vehicle frame, so that the tensile-compressive fretting fatigue strength data obtained by the present invention is more accurate, and the present invention can conveniently improve the structural strength of the parts of the above-mentioned vehicle frame that are prone to tensile-compressive fretting fatigue failure in subsequent production and processing, improve the structural strength of the vehicle frame, and further reduce the probability of vehicle frame failure and improve the service life of the vehicle frame.

[0037] The test sample body includes an effective test area located in the middle of the test sample body and clamping areas located at both ends of the test sample body. A central hole is provided in the middle of the effective test area. During actual operation, the clamping areas are mainly used to be clamped in a tensile-compressive fatigue testing machine to position the test sample body and apply a load to the test sample body. The effective test area is mainly used to conduct tensile-compressive fretting fatigue tests, so that the staff can obtain tensile-compressive fretting fatigue strength data. The central hole is used to assemble bolts and nuts to more realistically simulate the actual service conditions of the vehicle frame (assembling vehicle frame bolts and vehicle frame nuts on the vehicle frame), so that the tensile-compressive fretting fatigue strength data obtained by the present invention is more accurate.

[0038] Preferably, the diameter of the central hole matches the diameter of the vehicle frame bolt at the part of the vehicle frame that is prone to tensile-compressive fretting fatigue failure. The thickness of the effective test area and the thickness of the clamping area are the same as the thickness of the part of the vehicle frame that is prone to tensile-compressive fretting fatigue failure. The effective test width of the effective test area is not less than 6 times the diameter of the central hole, and the effective test length of the effective test area is not less than 12 times the diameter of the central hole. The total length of the test sample body is not less than the effective test length, and the total width of the test sample body is not less than the effective test width. In this way, the present invention can not only make the test sample body better simulate the actual service conditions of the vehicle frame, but also reduce the influence on the test sample body caused by improper setting of the central hole.

[0039] Furthermore, a transition area is provided between the effective test area and the clamping area. Even further, the above-mentioned transition area is an arc transition area, which can eliminate stress concentration and further reduce the influence of tensile-compressive alternating loads on the structure of the test sample body, so that failure occurs at the expected part.

[0040] During actual operation, the test sample body is made of the same material as the vehicle frame (the same type of sheet metal), and the test sample body is processed into a waist-shaped (such as Figure 2 ) or long-strip-shaped test sample body with an overall length of L, an overall width of B, a thickness of t, an effective test width of b, an effective test length of l, and a hole with a diameter of d in the center. The above main requirements and their functions are as follows:

[0041] a), Keep the thickness t of the test sample body unchanged as the original thickness of the frame longitudinal beam plate to ensure that the surface quality state of the test sample body material (such as surface decarburization, surface roughness, surface grain size, etc.) is the same as that of the raw material.

[0042] b), The diameter d of the central hole of the test sample body is determined according to the actual size of the hole at the position where tensile-compressive fretting fatigue failure is likely to occur on the longitudinal beam. The central hole of the test sample body is a reamed hole, and if necessary, the central hole is strengthened to ensure that the fatigue strength of the hole surface under the tensile-compressive load of the test sample body is higher than the fretting fatigue strength of the test sample body, and to avoid the initiation of fatigue cracks from the hole surface during the test.

[0043] c), The effective test width b of the test sample body is determined based on the effective load that the used fatigue testing machine can apply to ensure that the test can be carried out within the effective load range of the testing machine. However, the effective test width b of the test sample body is at least not less than 6 times the diameter d of the central hole of the test sample body (i.e., the central hole diameter d) to reduce the influence of the hole on the tensile-compressive stress distribution of the test sample body and ensure that the fretting fatigue crack initiates within the top fan-shaped range with an angle θ (90°) symmetric about the axis of the test sample body and with the center of the hole as the vertex ( Figure 4 ), so that the crack initiation position on the test sample body is the same as the crack initiation position during the tensile-compressive fretting fatigue failure in the actual use of the frame.

[0044] d), The effective test length l of the test sample body is not less than 12 times the diameter of the central hole of the test sample body (i.e., the central hole diameter) d, so that there is a sufficient stress uniform distribution area on the test sample body that is not affected by the clamping stress of the test sample body, and to ensure that the fretting fatigue crack initiates within the top fan-shaped range with an angle θ (90°) symmetric about the axis of the test sample body and with the center of the hole as the vertex ( Figure 4 ), so that the crack initiation position on the test sample body is the same as the crack initiation position during the tensile-compressive fretting fatigue failure in the actual use of the frame.

[0045] e), The total outer width B of the test sample body is determined according to the specific situation of the fatigue testing machine chuck (not greater than the chuck width) and is not less than the effective test width b of the test sample body to ensure that the fatigue crack of the test sample body during the fatigue test will not initiate from the clamping part of the test sample body due to excessive clamping stress. When the total outer width B of the test sample body is equal to the effective test width b of the test sample body, the test sample body is strip-shaped. When the total outer width B of the test sample body is greater than the effective test width (b) of the test sample body, the test sample body is waist-shaped ( Figure 2 ).

[0046] f) The total outer length L of the test sample body is determined according to the effective test space of the selected fatigue testing machine (not greater than the space length inside the fatigue testing machine to facilitate placement). While ensuring that the testing machine chuck has sufficient clamping length and the test sample body has sufficient effective test length l, it is ensured that the test sample body will not become unstable and fail due to excessive length.

[0047] g) Preferably, the two surfaces in the thickness direction of the test sample body are treated according to the surface treatment process in the actual production process of the vehicle frame to simulate the surface state under the actual service conditions of the vehicle frame longitudinal beam. When it is necessary to study the influence of different surface treatment processes on the fretting performance of the vehicle frame, different test sample bodies are treated according to different surface treatment processes specified in the test plan, so as to obtain the vehicle frame fretting fatigue simulation test sample bodies simulating different surface treatment processes.

[0048] S2. Assemble the test bolt and test nut on the test sample body to obtain the test specimen to be tested;

[0049] In this step, the above step S1 is mainly to simulate the actual service state of installing the vehicle frame bolt and vehicle frame nut on the vehicle frame, so that the staff can more clearly know the tensile and compressive fretting fatigue strength data at the installation positions of the vehicle frame bolt and vehicle frame nut on the vehicle frame.

[0050] During actual operation, the steps of assembling the test bolt and test nut include: S21. Determine the position of the part prone to tensile and compressive fretting fatigue failure on the vehicle frame, denoted as the fatigue prone failure part; S22. Obtain the actual specifications, structures and surface states of the vehicle frame bolt and vehicle frame nut on the fatigue prone failure part, denoted as the specifications, structures and surface states of the vehicle frame bolt and vehicle frame nut; S23. Select the test bolt and test nut according to the preset design specifications, and the specifications, structures and surface states of the test bolt and test nut match the specifications, structures and surface states of the vehicle frame bolt and vehicle frame nut at the part prone to tensile and compressive fretting fatigue failure on the vehicle frame; S24. Assemble the test bolt and test nut onto the test sample body to obtain the test specimen to be tested. In this way, the present invention also realizes the assembly of the test bolt and test nut on the test sample body, so that the test sample body more accurately simulates the actual service state of installing the vehicle frame bolt and vehicle frame nut on the vehicle frame.

[0051] Preferably, this step further includes: Assembling the test bolt and test nut on multiple test sample bodies respectively by using different tightening processes to obtain the test specimens to be tested. In this way, the present invention can assemble the test bolt and test nut by using different tightening processes, which is beneficial to studying the influence of different tightening processes on the fretting fatigue performance of the vehicle frame.

[0052] Preferably, this step further includes: respectively assembling multiple groups of test bolts and test nuts with different structures and / or respectively assembling multiple groups of test bolts and test nuts with different surface states on the test sample body to obtain a test specimen to be tested. The staff can use test bolts (test nuts) with different structures and surface states, which is conducive to studying the influence of different structures and surface states on the fretting fatigue performance of the vehicle frame. In this way, the structures and surface states of the test bolts (test nuts) are the same as those of the connecting bolts (vehicle frame bolts) at the parts of the vehicle frame prone to tensile and compressive fretting fatigue failure, so that the present invention realizes the simulation of the fretting fatigue service environment of the automotive vehicle frame under actual service conditions.

[0053] During actual assembly of the test bolts and test nuts, tighten the test bolts and test nuts according to the assembly (tightening) process of the bolts and nuts formulated during the actual production process of the automotive vehicle frame. The structures and surface states of the test bolts (test nuts) are the same as those of the vehicle frame bolts at the fatigue-prone failure parts, so that the present invention can simulate the fretting fatigue service environment of the automotive vehicle frame under actual service conditions.

[0054] During actual operation, according to the actual nominal dimension d1 (diameter of the vehicle frame bolt) of the connecting bolt (vehicle frame bolt) at the part of the vehicle frame prone to tensile and compressive fretting fatigue failure, insert a bolt and nut with a suitable specification, whose assembly hole diameter is d and thread nominal diameter is d1, into the central hole of the test sample body. Among them, the diameter d of the central hole and the diameter d1 of the test bolt need to meet the requirements of relevant design specifications. For example, when the hole diameter on the test sample body is φ11, it is appropriate to assemble test bolts and test nuts with a nominal size of M10.

[0055] During actual operation, if it is necessary to study the influence of different tightening processes and different structures and surface states acting together on the fretting fatigue strength of the vehicle frame, the present invention can first select suitable test bolts and test nuts according to different structures and surface states selected by the test plan, then install the test bolts and test nuts on different test sample bodies respectively, and tighten them according to different tightening processes formulated by the test plan. Finally, the staff can obtain the influence of different tightening processes and different structures and surface states acting together on the fretting fatigue strength of the vehicle frame through multiple groups of tests, so that the fretting fatigue strength data of the present invention are more accurate, and the present invention can conveniently improve the structural strength of the parts of the automotive vehicle frame prone to tensile and compressive fretting fatigue failure in subsequent production and processing, thereby improving the service life of the automotive vehicle frame.

[0056] S3. Apply tensile and compressive alternating loads to the test specimen to be tested respectively through a tensile and compressive fatigue testing machine according to a preset fatigue test standard until the test specimen to be tested undergoes tensile and compressive fretting fatigue failure, and obtain the tensile and compressive fretting fatigue test data of the test specimen to be tested;

[0057] During actual operation, the present invention further includes: installing a test pad on the test specimen to be tested, and the working state of the test pad is the same as that of the connecting member of the vehicle frame. The above test pad can also be referred to as a cushion block or gasket, and it is arranged on one or both sides of the test specimen body. In this step, the working state of the test pad mainly refers to factors such as the shape, size, and surface state of the test pad that affect the fretting fatigue performance of the vehicle frame. The working state of the test pad can be determined according to the actual situation of the connecting accessories on the vehicle frame, so as to simulate the fretting fatigue simulation test specimen body of the multi-layer connection structure of the vehicle frame.

[0058] In this step, install the test specimen to be tested on a preset tensile-compressive fatigue testing machine. According to the preset fatigue test standard, apply tensile-compressive alternating loads to a group of multiple test specimens to be tested through the tensile-compressive fatigue testing machine respectively, and generate tensile-compressive fretting fatigue failure on the test specimen body, so as to obtain the tensile-compressive fretting fatigue test data of this group of multiple specimens.

[0059] During actual operation, the tensile-compressive fatigue testing machine of the present invention can also be referred to as a fatigue testing machine. Its main function is to clamp the clamping parts at both ends of the assembled test specimen body on the selected tensile-compressive fatigue testing machine and apply an appropriate tensile-compressive alternating load P, so as to generate tensile-compressive alternating stress on the test specimen body. In this way, the present invention can obtain the test stress σ generated at the effective test part of the test specimen body without considering the influence of the opening of the test specimen body on the stress distribution of the effective test part on the test specimen body, and further obtain the allowable stress of the vehicle frame.

[0060] In this step, the steps of obtaining the tensile-compressive test data of this group further include: calculating the test stress generated by the test specimen to be tested according to the tensile-compressive alternating load according to the test stress calculation formula, and supplementing the test stress into the tensile-compressive test data; the test stress calculation formula is: σ = P / b / t, where σ is the test stress generated by the test specimen to be tested, P is the tensile-compressive alternating load, b is the effective test width of the test specimen body, and t is the thickness of the test specimen body.

[0061] S4. Sort out the tensile-compressive fretting fatigue test data according to the preset data processing specification to obtain the fretting fatigue strength of the test specimen body;

[0062] In this step, install the test specimen body to be tested on a preset tensile-compressive fatigue testing machine. According to the preset fatigue test standard, apply tensile-compressive alternating loads to a group of multiple test specimen bodies to be tested through the tensile-compressive fatigue testing machine respectively, and generate tensile-compressive fretting fatigue failure on the test specimen body, so as to obtain the tensile-compressive fretting fatigue test data of this group of multiple specimens.

[0063] In this step, the present invention mainly takes the tension-compression fretting fatigue strength of the test sample body as the allowable stress of the tension-compression fretting fatigue of the vehicle frame.

[0064] In this step, the above-mentioned preset fatigue test standard refers to the technical standard that the staff needs to use when conducting the tension-compression fretting fatigue test, such as GB / T 3075 "Fatigue test of metallic materials - Axial force control method"; at the same time, the preset data processing specification also refers to the data processing specification that the staff needs to use when conducting the tension-compression fretting fatigue test, such as GB / T 24176 "Statistical scheme and analysis method for fatigue test data of metallic materials"; sorting out the set of tension-compression test data means that the staff makes the tension-compression fretting fatigue strength data of the set of different test sample bodies under different tension-compression alternating loads through the set of tension-compression fretting fatigue strength data, so that the present invention can more truly simulate the actual service conditions of the vehicle.

[0065] During actual work, since the present invention can obtain the tension-compression fretting fatigue strength data of the vehicle frame through the test sample body, and thus accurately obtain the allowable stress of the vehicle frame, when designing the vehicle frame, the staff can conveniently conduct the fretting fatigue strength check for the tension-compression fretting fatigue, with low cost and short time consumption.

[0066] S5. Obtain the fretting fatigue strength of the vehicle frame according to the fretting fatigue strength;

[0067] In this step, the steps of obtaining the fretting fatigue strength of the vehicle frame include: taking the tension-compression fretting fatigue strength of the test sample body as the allowable stress of the tension-compression fretting fatigue of the vehicle frame, and conducting the tension-compression fretting fatigue strength check on the vehicle frame, so as to obtain the fretting fatigue strength of the vehicle frame.

[0068] During actual work, how to apply the tension-compression alternating load through the tension-compression fatigue testing machine, how to check the fretting fatigue strength according to the allowable stress, how to sort out the set of tension-compression test data to obtain the fretting fatigue strength of the test sample body, how to statistically analyze the influence of different tightening processes on the fretting fatigue strength of the vehicle frame, how to statistically analyze the influence of different structures and surface states on the fretting fatigue strength of the vehicle frame, and how to statistically analyze the influence of the combined action of different tightening processes and different structures and surface states on the fretting fatigue strength of the vehicle frame are all steps and conclusions that those skilled in the art can obtain according to the prior art without creative efforts, and will not be elaborated here.

[0069] During actual work, in order to make the technical solution of the present invention easier to understand, the present invention also takes how to obtain the tension-compression fretting fatigue strength data during the development process of a heavy-duty vehicle frame to determine the tension-compression fretting fatigue failure data as an example for illustration:

[0070] During the development of a heavy-duty vehicle frame, the tensile and compressive fretting fatigue strength of the frame under actual service conditions was detected, and the influence of the frame surface treatment process and the addition of large washers in the bolt connection structure on the tensile and compressive fretting fatigue performance of the frame was studied.

[0071] According to the frame design, the nominal size of the connecting bolts at the parts where the frame might undergo fretting fatigue failure was judged to be M10 by the staff. The fatigue test was planned to be carried out on an electromagnetic resonance high-frequency fatigue testing machine. Considering factors such as the clamping size of the testing machine chuck and the load of the testing machine, based on the aforementioned design principle of the test specimen body, Figure 2 the test specimen body shown in the figure was designed.

[0072] The thickness t of the test specimen body remained unchanged at 8 mm, which was the thickness of the frame longitudinal beam material. The maximum outer width B was 80 mm, which was the width of the two clamping parts at both ends, and the maximum outer length L was 240 mm. Since the nominal size of the connecting bolts used for installing accessories on the frame longitudinal beam was M10, the size of the bolt installation hole at the center of the test specimen body was taken as φ11. Therefore, the effective test width b of the test specimen body was designed to be 70 mm (greater than 6 times the hole diameter), and the effective test length l of the test specimen body was 140 (greater than 12 times the hole diameter). The effective test part of the test specimen body and the maximum width part were transitioned with an arc with a radius of 50 mm.

[0073] To improve the strength of the bolt installation hole at the center of the test specimen body, the surface roughness of the bolt installation hole was required to be Ra0.4, and strengthening treatment was carried out. The selected bolts and nuts were both flange surface galvanized bolts and flange surface galvanized nuts with a nominal size of M10.

[0074] The test specimen bodies were divided into three groups. The surface of the first group of test specimen bodies was treated with surface powder spraying technology that the automotive longitudinal beam was intended to adopt. The surface of the second group of test specimen bodies was kept in the original state of the longitudinal beam raw material without any treatment. The third group was installed with a large washer with a diameter of 50 mm on the basis of the aforementioned powder-sprayed test specimen bodies. The assembly process of the bolts on all test specimen bodies was tightened once with a torque of 130 Nm.

[0075] The test results showed that all the failed test specimen bodies of the frame were fretting fatigue failures, and the origin positions of the fretting fatigue cracks were all within Figure 4 the top fan-shaped range with an angle θ (90°) symmetric about the axis of the test specimen body and with the hole center as the vertex, as shown in Figure 5 、 Figure 6 、 Figure 7 shown. The above test results were consistent with the crack initiation positions during the tensile and compressive fretting fatigue failure in the actual use of the frame, achieving the expected effect.

[0076] To sum up, the present invention newly designed as shown in Figures 2 to 3The test sample body shown is used to simulate the actual service conditions of an automotive frame. This test sample body can relatively truly simulate the actual service conditions of the automotive frame, thereby making the tensile-compressive fretting fatigue strength data of the frame obtained by the present invention more accurate. As a result, the present invention can conveniently improve the structural strength of the parts prone to tensile-compressive fretting fatigue failure on the above-mentioned automotive frame during subsequent production and processing, enhance the structural strength of the automotive frame, and further reduce the probability of automotive frame failure and increase the service life of the automotive frame.

[0077] Meanwhile, the present invention avoids the initiation of fretting fatigue cracks in the stress non-uniform distribution areas on both sides of the central bolt mounting hole of the test sample body through the test sample body. Since the stress calculation formula of the present invention does not consider the influence of bolt holes on stress distribution, the present invention can more accurately obtain the tensile-compressive fretting fatigue strength data and allowable stress of the frame, thereby further increasing the service life of the automotive frame.

[0078] It should be noted that in this article, the terms "including", "comprising" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements not only includes those elements, but also includes other elements not explicitly listed, or also includes elements inherent to such a process, method, article or system. Without further limitations, an element defined by the statement "including one..." does not exclude the existence of additional identical elements in the process, method, article or system including that element.

[0079] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0080] Through the description of the above embodiments, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform. Of course, they can also be implemented by hardware, but in many cases the former is a better implementation method.

[0081] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural or equivalent process transformation made by using the specification and drawings of the present invention, or directly or indirectly applied to other related technical fields, shall be equally included in the patent protection scope of the present invention.

Claims

1. A method for testing the pull-compression fretting fatigue of a vehicle frame, characterized in that, It includes: Obtaining a test sample body for simulating the service conditions of the vehicle frame; Assembling a test bolt and a test nut on the test sample body to obtain a test specimen to be tested; According to a preset fatigue test standard, applying tensile and compressive alternating loads to the test specimen to be tested through a tensile-compressive fatigue testing machine until the test specimen to be tested undergoes tensile-compressive fretting fatigue failure, obtaining the tensile-compressive fretting fatigue test data of the test specimen to be tested, calculating the test stress generated by the test specimen to be tested according to the test stress calculation formula based on the tensile-compressive alternating load, and supplementing the test stress to the tensile-compressive test data, where the test stress calculation formula is: σ = P / b / t, σ is the test stress generated by the test specimen to be tested, P is the tensile-compressive alternating load, b is the effective test width of the test sample body, and t is the thickness of the test sample body; Sorting out the tensile-compressive fretting fatigue test data according to a preset data processing specification to obtain the fretting fatigue strength of the test sample body; Taking the tensile-compressive fretting fatigue strength of the test sample body as the allowable tensile-compressive fretting stress of the vehicle frame, and checking the tensile-compressive fretting fatigue strength of the vehicle frame, so as to obtain the fretting fatigue strength of the vehicle frame.

2. The method for the tensile and compressive fretting fatigue test of the vehicle frame according to claim 1, wherein After obtaining the test sample body for simulating the service conditions of the vehicle frame and before assembling the test bolt and the test nut on the test sample body to obtain a test specimen to be tested, it further includes: Performing surface treatment on the surface of the test sample body according to the surface treatment process of the vehicle frame in the actual production process.

3. The method for the pull-compression micro-motion fatigue test of the vehicle frame according to claim 1, wherein, The test sample body includes an effective test area in the middle of the test sample body and clamping areas at both ends of the test sample body, and a central hole is provided in the middle of the effective test area.

4. The method for testing the tensile-compressive fretting fatigue of a vehicle frame according to claim 3, wherein The diameter of the central hole matches the diameter of the vehicle frame bolt at the part of the vehicle frame prone to tensile-compressive fretting fatigue failure, and the thickness of the effective test area and the thickness of the clamping area are the same as the thickness of the part of the vehicle frame prone to tensile-compressive fretting fatigue failure; The effective test width of the effective test area is not less than 6 times the diameter of the central hole, and the effective test length of the effective test area is not less than 12 times the diameter of the central hole; The total length of the test sample body is not less than the effective test length, and the total width of the test sample body is not less than the effective test width.

5. The method for frame tensile and compressive fretting fatigue test according to claim 1 or 2 or 3 or 4, characterized in that, The assembling the test bolt and the test nut on the test sample body to obtain a test specimen to be tested includes: Determining the position of the part of the vehicle frame prone to tensile-compressive fretting fatigue failure on the vehicle frame, denoted as the fatigue-prone failure part; Obtaining the actual specifications, structures and surface states of the vehicle frame bolt and the vehicle frame nut at the fatigue-prone failure part, denoted as the specifications, structures and surface states of the vehicle frame bolt and the vehicle frame nut; Selecting the test bolt and the test nut according to a preset design specification, and the specifications, structures and surface states of the test bolt and the test nut match the specifications, structures and surface states of the vehicle frame bolt and the vehicle frame nut at the part of the vehicle frame prone to tensile-compressive fretting fatigue failure; Assembling the test bolt and the test nut onto the test sample body to obtain a test specimen to be tested.

6. The frame tension-compression fretting fatigue test method according to claim 5, wherein Assembling test bolts and test nuts on the test sample body to obtain a test specimen to be tested further includes: Using different tightening processes to assemble test bolts and test nuts on a plurality of the test sample bodies respectively to obtain the test specimen to be tested.

7. The method for the pull-compression micro-motion fatigue test of the vehicle frame according to claim 6, wherein, Assembling test bolts and test nuts on the test sample body to obtain a test specimen to be tested further includes: Assembling multiple groups of test bolts and test nuts with different structures and / or assembling multiple groups of test bolts and test nuts with different surface states on the test sample body respectively.

8. The frame tensile and compressive fretting fatigue test method according to claim 6, wherein After assembling test bolts and test nuts on the test sample body to obtain a test specimen to be tested and before installing the test specimen to be tested on a preset tensile-compressive fatigue testing machine, it further includes: Installing a test pad on the test specimen to be tested, and the working state of the test pad is consistent with the working state of the connecting member of the vehicle frame.

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