A method for testing and evaluating the high-cycle fatigue failure life of a metal shock absorber

Abstract

The present invention discloses a method for testing and evaluating the high-cycle fatigue failure life of a metal shock absorber. According to the remaining pre-tightening amounts measured at the initial stage and at the end of the test, and in combination with the displacement amplitude-life evolution curve of the shock absorber, the remaining pre-tightening amount-life evolution curve of the metal shock absorber can be predicted; the number of cycles when the displacement amplitude of the metal shock absorber is equal to the remaining pre-tightening amount is taken as its fatigue failure life; by means of the peak-valley displacement-life curve and the remaining pre-tightening amount-life curve obtained by the metal shock absorber at different load levels, a fatigue failure assessment diagram is drawn. By measuring the remaining pre-tightening amount of the in-service metal shock absorber, the assessment of its remaining fatigue life can be realized; the present invention can conveniently test or predict the fatigue failure life of the metal shock absorber. In combination with the drawn fatigue failure assessment diagram, the prediction of the remaining fatigue life of the in-service metal shock absorber can also be realized. This invention is of great significance for the assessment of the structural safety and reliability of the metal shock absorber.

Description

Technical Field

[0001] The present invention relates to the technical field of fatigue failure life testing of metal shock absorber structures, and particularly to a high-cycle fatigue failure life testing and evaluation method for metal shock absorbers. Background Technique

[0002] Compared with traditional rubber shock absorbers, metal shock absorbers have the advantages of being resistant to high and low temperatures, not being easily aged, and having a designable stiffness. They can serve under various complex environmental conditions and are a new type of shock absorber device with broad application prospects. Since metal shock absorbers mainly bear alternating fatigue loads, accurately obtaining their fatigue failure life is of great significance for the reliability and safety assessment of shock absorber structures. Some scholars have also carried out research on the fatigue performance testing of metal shock absorbers, and tried to use the change ratio of the resonance frequency of the metal shock absorber as the failure criterion to obtain the fatigue failure life of the metal shock absorber with certain rules. However, this method requires a special resonance frequency test to obtain the real-time resonance frequency of the metal shock absorber, and the fatigue test must be interrupted multiple times. In addition, the resonance frequency test will also have a certain impact on the fatigue failure life of the metal shock absorber. Therefore, it is of great significance to develop a more convenient and practical new method for testing the fatigue life of metal shock absorbers.

[0003] It is necessary to develop a high-cycle fatigue failure life testing and evaluation method for metal shock absorbers to solve the above problems. Summary of the Invention

[0004] The purpose of the present invention is to design a high-cycle fatigue failure life testing and evaluation method for metal shock absorbers to solve the above problems.

[0005] The present invention realizes the above purpose through the following technical solutions:

[0006] A high-cycle fatigue failure life testing and evaluation method for metal shock absorbers,

[0007] S1. Measure the pre-tightening amount dimensions of each metal shock absorber before and after the test, and obtain the change value of the pre-tightening amount;

[0008] S2. Process the peak-valley displacement-life curves of each metal shock absorber to obtain the displacement amplitude-life curve of the specimen;

[0009] S3. According to the change amount of the displacement amplitude of each shock absorber compared with the initial value, predict the real-time pre-tightening amount at any amplitude by means of formula (1):

[0010]

[0011] In formula (1), δ is the remaining pre-tightening amount at any fatigue life, δ i is the initial measured pre-tightening amount of the metal shock absorber, δ fTo measure the remaining pre-tightening amount after fatigue tests for a specific number of cycles It represents the change in displacement amplitude Δh compared to the initial minimum value at the current fatigue life min That is Δh represents the displacement amplitude at any fatigue life It represents the change in displacement amplitude compared to Δh after fatigue life of a specific number of cycles min Of the change amount;

[0012] S4. Obtain the remaining pre-tightening amount-life evolution curves of each metal shock absorber through data processing according to Equation (1). Combining the displacement amplitude-life curves of each specimen, with the displacement amplitude equal to the remaining pre-tightening amount of the specimen as the failure criterion, the failure life of the metal shock absorber under the current fatigue load can be determined; for the metal shock absorber that has not failed after fatigue tests for a specific number of cycles, assuming that the decrease value of the pre-tightening amount and the increase value of the displacement amplitude of the metal shock absorber remain constant for each subsequent fatigue test with the same number of cycles, the failure life of the metal shock absorber under the current fatigue load can be predicted. Fitting the failure lives of the metal shock absorber at different load levels can obtain the fatigue failure life model;

[0013] S5. Plot the peak-valley displacement-life curves and remaining pre-tightening amount-life curves obtained for the metal shock absorber at different load levels into a fatigue failure assessment diagram; by measuring the remaining pre-tightening amount of the in-service metal shock absorber and combining it with the failure assessment diagram, its remaining fatigue life can be evaluated.

[0014] The beneficial effects of the present invention are as follows:

[0015] The physical meaning of the fatigue failure criterion proposed by the present invention is clear, and both the test operation and data processing are relatively simple. Scholars only need to master simple theories and basic test skills to easily obtain the fatigue failure life of the metal shock absorber through the present invention. Combining the drawn fatigue failure assessment diagram, the remaining fatigue life assessment of the in-service metal shock absorber can also be realized, which has high practical value. Brief Description of the Drawings

[0016] Figure 1 It is a schematic diagram of the high-cycle fatigue test loading device for the metal shock absorber.

[0017] Figure 2 It is the displacement amplitude-life curve of the metal shock absorber.

[0018] Figure 3 It is the remaining pre-tightening amount-life evolution curve of the metal shock absorber.

[0019] Figure 4 It is the critical failure load-displacement hysteresis curve when the fatigue load is 600N.

[0020] Figure 5It is a fatigue failure assessment diagram of a metal shock absorber.

[0021] In the figure: 1 upper fixture, 2 metal shock absorber, 3 hexagon socket head bolt, 4 lower fixture. Specific implementation manners

[0022] To make the objectives, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some but not all of the embodiments of the present invention. Components of the embodiments of the present invention usually described and illustrated in the accompanying drawings here can be arranged and designed in various different configurations.

[0023] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0024] It should be noted that: Similar reference numerals and letters denote similar items in the following drawings. Therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings.

[0025] In the description of the present invention, it should be understood that the orientation or positional relationship indicated by the terms "upper", "lower", "inner", "outer", "left", "right", etc. is based on the orientation or positional relationship shown in the drawings, or the orientation or positional relationship when the product of the present invention is normally placed, or the orientation or positional relationship commonly understood by those skilled in the art. It is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present invention.

[0026] In addition, the terms "first", "second", etc. are only used for distinguishing descriptions and cannot be understood as indicating or implying relative importance.

[0027] In the description of the present invention, it should also be noted that unless otherwise clearly defined and limited, terms such as "set", "connected" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0028] The specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings.

[0029] A method for testing and evaluating the high-cycle fatigue failure life of a metal shock absorber

[0030] S1. Measure the pre-tightening amount dimensions of each metal shock absorber before and after the test, and obtain the change value of the pre-tightening amount;

[0031] S2. Process the peak-valley displacement-life curves of each metal shock absorber to obtain the displacement amplitude-life curve of the specimen;

[0032] S3. According to the change amount of the displacement amplitude of each shock absorber compared with the initial value, use Equation (1) to predict the real-time pre-tightening amount at any amplitude:

[0033]

[0034] In Equation (1), δ is the remaining pre-tightening amount at any fatigue life, δ i is the initial measured pre-tightening amount of the metal shock absorber, δ f is the measured remaining pre-tightening amount after fatigue test at a specific number of cycles, represents the change amount of the displacement amplitude compared with the initial minimum value Δh min at the current fatigue life, that is Δh represents the displacement amplitude at any fatigue life, represents the change amount of the displacement amplitude compared with Δh min after fatigue life at a specific number of cycles;

[0035] S4. According to the data processing of Equation (1), obtain the remaining pre-tightening amount-life evolution curve of each metal shock absorber. Combine the displacement amplitude-life curve of each specimen, and use the displacement amplitude equal to the remaining pre-tightening amount of the specimen as the failure criterion to determine the failure life of the metal shock absorber under the current fatigue load; for the metal shock absorber that has not failed after fatigue test at a specific number of cycles, assume that the decrease value of the pre-tightening amount and the increase value of the displacement amplitude of the metal shock absorber remain constant for each subsequent fatigue test with the same number of cycles. Then, the failure life of the metal shock absorber under the current fatigue load can be predicted, and the fatigue failure life model can be obtained by fitting the failure life of the metal shock absorber at different load levels;

[0036] S5. Plot the peak-valley displacement-life curve and the remaining pre-tightening amount-life curve obtained by the metal shock absorber at different load levels into a fatigue failure assessment diagram; by measuring the remaining pre-tightening amount of the in-service metal shock absorber and combining the failure assessment diagram, its remaining fatigue life can be evaluated.

[0037] Note: The large number of cycles of fatigue test in the method can be 10 million times, 5 million times, 1 million times or other number of cycles.

[0038] The present invention can predict the residual preload-life evolution curve of the metal shock absorber based on the residual preload measured at the beginning and at the end of the test, combined with the shock absorber displacement amplitude-life evolution curve, and compare the displacement amplitude-life curve and the residual preload-life curve under the same fatigue load level. When the displacement amplitude exceeds the residual preload, the metal shock absorber is determined to be failed, and the number of cycles when the displacement amplitude of the metal shock absorber is equal to the residual preload is used as its fatigue failure life; for the metal shock absorber that has not failed under the specified number of cycles, it is assumed that the decrease value of the preload and the increase value of the displacement amplitude of the metal shock absorber are kept constant in each subsequent fatigue test with the same number of cycles, and the fatigue displacement amplitude is equal to the residual preload of the metal shock absorber as the failure criterion, thereby predicting the relatively safe failure life of the metal shock absorber under the current fatigue load.

[0039] Example:

[0040] First, design the fixture for high cycle fatigue test of metal shock absorber:

[0041] The high cycle fatigue failure life test of the metal vibration absorber was carried out. In order to connect the metal vibration absorber with the testing machine, the following design was made: Figure 1 The special high-cycle fatigue test fixture shown. In order to be closer to the actual service conditions of the metal shock absorber, the key dimensional parameters of the fatigue test special fixture are consistent with those in actual service. The upper metal shock absorber fixture adopts a hollow design, which is convenient for applying the specified preload force to the metal shock absorber 2 through the hexagonal wrench acting on the hexagonal bolt 3. The upper fixture 1 and the lower fixture 4 are fastened to the test machine through the drill chuck provided by the test machine.

[0042] Then carry out the high cycle fatigue loading test of the metal shock absorber:

[0043] Use Figure 1 The fatigue test fixture shown is used to carry out high-cycle fatigue test of metal shock absorber. The residual preload size of the metal shock absorber is accurately measured before the test. The test adopts load control method for loading. The real-time load, displacement data and peak-to-valley displacement data are collected through the load and displacement sensors provided by the testing machine. After the test, the residual preload size of the metal shock absorber is accurately measured again.

[0044] Finally, fatigue test data processing and analysis are carried out:

[0045] Data processing is carried out on the peak-valley displacement-life curve obtained from the test to obtain the displacement amplitude-life evolution curve; according to the remaining pre-tightening amount dimensions of the metal shock absorber measured before and after the test, and the displacement amplitude-life curve, the remaining pre-tightening amount-life curve of the metal shock absorber is analyzed and obtained. Taking the displacement amplitude of the metal shock absorber reaching the remaining pre-tightening amount as the fatigue failure criterion, the fatigue failure life of the metal shock absorber is obtained; if the metal shock absorber does not undergo fatigue failure after 10 million fatigue loadings, the fatigue failure life of the metal shock absorber can be extrapolated and predicted based on the change of the remaining pre-tightening amount and displacement amplitude of the metal shock absorber at 10 million times. According to the displacement amplitude-life curve and the remaining pre-tightening amount-life curve obtained by the metal shock absorber under different load levels, the fatigue failure assessment diagram of the metal shock absorber can be obtained.

[0046] In the technical solution of the present invention, according to the remaining pre-tightening amount dimensions of the metal shock absorber measured before and after the test, and the peak-valley displacement-life curve measured during the experiment, the failure life of the metal shock absorber under the specified fatigue load can be obtained, and the fatigue failure assessment diagram can be drawn.

[0047] In the technical solution of the present invention, based on the remaining pre-tightening amount of the metal shock absorber before and after the test and the peak-valley displacement-life curve obtained during the test, a new method for effectively testing or predicting the failure life of the metal shock absorber under different fatigue loads is proposed.

[0048] The high-cycle fatigue test of the metal shock absorber under different fatigue loads is carried out by using a high-frequency electromagnetic fatigue testing machine. The remaining pre-tightening amount of each specimen is measured before the test, and a high-cycle fatigue test fixture as shown in Figure 1 is designed. During the test, the real-time load, displacement data and peak-valley displacement data of the specimen are measured. After the test, the remaining pre-tightening amount of the specimen is measured. Data processing is carried out on the peak-valley displacement to obtain the displacement amplitude-life curve of each specimen, as shown in Figure 2 . By using formula (1) to calculate and obtain the real-time remaining pre-tightening amount of each specimen, the remaining pre-tightening amount-life curve is obtained, as shown in Figure 3 . By comparing the displacement amplitude-life curve and the remaining pre-tightening amount-life curve of each metal shock absorber, and taking the displacement amplitude equal to the remaining pre-tightening amount as the fatigue failure criterion, the failure life of the metal shock absorber under the current fatigue load can be obtained; Figure 4The load-displacement hysteresis curve at the moment of fracture of the metal shock absorber determined by this failure criterion when the maximum fatigue load is 600 N is shown. It can be seen from the figure that the fatigue hysteresis curve has become relatively flat, and the loading and unloading curves are relatively close near zero load, and fatigue loosening is likely to occur, indicating that the shock absorption function has been lost, which verifies the effectiveness of this criterion. For the metal shock absorber that has not failed after 10 million fatigue tests, the fatigue failure life of the metal shock absorber can be predicted by means of step S4 in the method. Table 1 shows the remaining pre-tightening amounts and the predicted fatigue failure lives of 5 metal shock absorber specimens before and after the test. It can be seen that there is a good pattern in obtaining the failure lives of metal shock absorbers under different fatigue loads by this method. The fatigue failure life model can be obtained by fitting the fatigue failure lives of metal shock absorbers under different loads with a power function. Based on the displacement amplitude-life curve and the remaining pre-tightening amount-life curve obtained for metal shock absorbers at different load levels, as well as the predicted displacement amplitude and remaining pre-tightening amount at longer lives, the fatigue failure assessment diagram of the metal shock absorber can be obtained, as shown in Figure 5 shown. For the in-service metal shock absorber, assuming that the service load level and the remaining pre-tightening amount are at the position of point “A” in Figure 5 , the corresponding in-service fatigue life is 2.3×10 7 , while the failure life of the fresh metal shock absorber at the current load level is the fatigue life corresponding to point “B” in Figure 5 , which is 3.06×10 7 . Therefore, the remaining fatigue life of this in-service metal shock absorber can be obtained as 7.6×10 6 . For other service load levels for which no tests have been carried out, the displacement amplitude-life curve and the remaining pre-tightening amount-life curve can be obtained by appropriate fitting and extrapolation of the existing test data, so as to evaluate its failure life.

[0049] Table 1:

[0050]

[0051] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art of this technology, without departing from the technical principle of the present invention, several improvements and refinements can be made, and these improvements and refinements should also be regarded as the protection scope of the present invention.

Claims

1. A method for testing and evaluating the high-cycle fatigue failure life of a metal shock absorber, characterized in that S1. Measure the pre-tightening amount dimensions of each metal shock absorber before and after the test to obtain the change value of the pre-tightening amount; S2. Process the peak-valley displacement-life curves of each metal shock absorber to obtain the displacement amplitude-life curve of the specimen; S3. According to the change amount of the displacement amplitude of each shock absorber compared with the initial value, use Equation (1) to predict the real-time pre-tightening amount at any amplitude: In formula (1), δ is the remaining pre-tightening amount at any fatigue life, δ i is the initial measured pre-tightening amount of the metal shock absorber, δ f is the measured remaining pre-tightening amount after the fatigue test of a specific number of cycles, represents the change in the displacement amplitude compared to the initial minimum value Δh at the current fatigue life min , that is Δh represents the displacement amplitude at any fatigue life, represents the change in the displacement amplitude compared to Δh after the fatigue life of a specific number of cycles min ; S4. Obtain the remaining pre-tightening amount-life evolution curve of each metal shock absorber through data processing of Equation (1). Combine the displacement amplitude-life curve of each specimen. Taking the displacement amplitude equal to the remaining pre-tightening amount of the specimen as the failure criterion, the failure life of the metal shock absorber under the current fatigue load can be determined; for the metal shock absorber that has not failed after a fatigue test with a specific number of cycles, assume that the decrease value of the pre-tightening amount and the increase value of the displacement amplitude of the metal shock absorber remain constant for each subsequent fatigue test with the same number of cycles. Furthermore, the failure life of the metal shock absorber under the current fatigue load can be predicted. Fitting the failure life of the metal shock absorber at different load levels can obtain the fatigue failure life model; S5. Plot the peak-valley displacement-life curve and the remaining pre-tightening amount-life curve obtained by the metal shock absorber at different load levels into a fatigue failure assessment diagram; by measuring the remaining pre-tightening amount of the in-service metal shock absorber and combining it with the failure assessment diagram, its remaining fatigue life can be evaluated.

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