Application of the hottest fatigue test in the lif

2022-08-09
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Application of fatigue test in life prediction of rubber vibration damping products

Abstract: rubber vibration damping products have the function of bearing and mitigating impact at the same time. Because of the advantages of small volume, light weight and maintenance free, they can replace the traditional metal springs and friction damping devices. The fatigue resistance of rubber shock absorber products seriously affects its service life. This paper summarizes the judgment criteria of fatigue failure of rubber shock absorber products and the application of fatigue test in service life prediction, as well as the research progress of life prediction of rubber shock absorber products at home and abroad

key words: rubber damping products; Fatigue failure; Life prediction

rubber damping products have the advantages of adjustable elastic parameters, attenuation and absorption of high-frequency vibration and noise, impact stiffness greater than dynamic and static stiffness, small volume, light weight, maintenance free, etc., so they can replace traditional metal springs and friction damping devices. Such products are widely used abroad, but they are still in the stage of introduction and imitation in China. Because rubber vibration damping products are usually used under periodic stress, the fatigue resistance of rubber vibration damping products is closely related to their service life. The most reliable method is to evaluate the real object under actual use conditions, but it requires a long test time and expensive cost. At present, the methods of predicting the fatigue life of rubber damping products include virtual analysis and fatigue test. Using software to simulate and calculate the service life of products can not replace fatigue test, and the fatigue reliability of products should be finally tested by fatigue test. Therefore, how to accurately predict the fatigue life of rubber damping products through fatigue test is of great significance to shorten the product development cycle, save money, and finally develop high-tech products with performance that meet the use requirements

1 criteria for fatigue failure of rubber vibration damping products

1.1 loss rate of static stiffness of products

rubber vibration damping products are the most widely used vibration and noise reduction devices at home and abroad, accounting for more than 90% of the total in rail transit (calculated by output value), mainly playing the role of load-bearing, suspension, traction, vibration isolation and cushioning, so stiffness is one of the key characteristics of rubber vibration damping products. The characteristic of the fatigue curve of rubber damping products is that after the number of cycles exceeds 107, the curve is not necessarily level. Therefore, the fatigue test does not require the products to stop the test until fatigue failure, that is, when the test is carried out for a certain number of times, the performance of the products is tested. If the requirements are met, the service life is considered to meet the design requirements. The elastic modulus of rubber materials will continue to decline in the process of use, and often its strength has been reduced to a level that is not enough to bear the rated load before failure. Therefore, the stiffness of products must be tested in the process of fatigue use to master the degree of failure. The formula for calculating the loss rate of static stiffness is:

Δ K=[(K2-K1)/K1] × 100%

where Δ K is the loss rate of static stiffness; K1 and K2 are the static stiffness values before and after fatigue respectively

1.2 deformation of products

creep is the characteristic of rubber products. Therefore, after a period of use, rubber products will have permanent deformation in the direction of force, thus changing part of the size of the product. If the creep of the product is too large, it will directly affect the running safety of the vehicle. Therefore, in order to ensure the balance and safety of the vehicle height, the free height detection after the fatigue test must be carried out on the rubber damping products. On the premise of not affecting the service performance of the product, any rubber product is allowed to continue to be used with a certain permanent deformation, but when the permanent deformation affects the connection between the product and other parts, measures should be taken to adjust it. For example, when the product creeps, the height of the product will drop. As the product is used for the primary suspension of locomotives and vehicles, the height of the car body and coupler will also decrease, thus affecting the connection between the front and rear vehicles. In this case, adjusting shims must be added to adjust the height of the product. When the adjusting shim is insufficient for adjustment, the product must be replaced

1.3 temperature rise of rubber materials

the fatigue resistance of rubber materials seriously affects the fatigue life of products, and too high temperature is an important factor for rubber damage. The temperature rise is related to load amplitude, vibration frequency, compound formula and heat dissipation conditions. Studies have shown that for rubber materials, when the surface temperature rise is greater than 20 ℃, the material begins to damage

rubber is a material with poor thermal conductivity. When the heat generated is higher than the heat emitted, the internal temperature will rise. This phenomenon becomes more serious with the increase of vibration frequency. Therefore, the frequency of fatigue test of most rubber materials is controlled at about 0.5Hz, but what value should be taken for the test frequency to save time and avoid excessive temperature rise? There is no specific provision in the test standard of rubber damping products, and it can be determined according to the use occasions, requirements and tests of rubber damping products

2 domestic research progress

in the field of life prediction research, the research on metal linear material products is relatively mature, while the research on rubber or rubber metal nonlinear products is still in its infancy

at present, the acceptance of vibration and noise reduction components for railway vehicles is determined by fatigue test under programmed load spectrum loading. Such as tb/t, tb/t, tb/t, gb/t and other standards. Sun Dagang of Taiyuan Institute of heavy machinery engineering studied the load spectrum of fatigue test program of rubber damper of sprocket of large crawler tractor [1]. The load of the program load spectrum is divided into 8 levels, and the test loads are arranged in the order of low high low. At the same time, the total program is divided into 20 subroutines for cycles, and the number of cycles of each subroutine is 105 (the total number of fatigue tests is 2 × 106)。 In order to speed up the test process, the test procedure is strengthened by increasing the test frequency and increasing the load amplitude. The vibration frequency under large load (≥ 53kn) is 0.5Hz, Under small load (5 times), the test time is greatly shortened.

Wu Yajun of Wuxi Zhongce studied the relationship between the fatigue life of rubber shock absorber and mold design [2] The reasons for the influence of the opening position of the rubber injection hole on the bonding and fatigue properties of the product are analyzed. It is considered that the opening of the injection hole should minimize the flow of the rubber in the cavity through the key parts, that is, minimize the loss of the adhesive in the key parts, and make each cavity full at the same time as much as possible

Mao Kunpeng of the Institute of metallurgy, Academy of Railway Sciences studied the rubber ball joint for DF11 locomotive [3]. Through the comprehensive study of the formula test of the rubber compound and the dynamic and static test of the product, it is found that the compression fatigue heat generation performance of the rubber compound directly affects the service life of the rubber ball joint, and good fatigue resistance can be obtained by adopting appropriate vulcanization system and reinforcement system. In addition, the gap between the three flaps of the rubber ball joint has a great impact on the static stiffness of the product. The test results of pressing the pin shaft directly onto the gap and a whole flap show that the static stiffness when pressing the joint is 2kn/mm smaller than that when not pressing the joint. The fatigue test shows that under the test conditions of sine wave, 18Hz, maximum and minimum loads of 42.5kn and 10kN respectively, the rubber ball joint with 2.1 million fatigue times can actually run 400000 kilometers, and the rubber ball joint with more than 6.2 million fatigue times can actually run 1million kilometers, which meets the use requirements of the Ministry of Railways in an overhaul period. Table 1 shows the fatigue test results of two ball joints. The service life of 2 # is 400000 km

Table 1 shows the results of two ball joint fatigue tests

fatigue times/10000 times 1# 2 #

38.47 normal normal

59.01 normal

135.88 normal

216 the outer ring is 3mm under the rubber at the normal pressure

286 the outer ring is 10mm under the rubber at the normal pressure

295.83 normal, the rubber temperature at the pressure is 36 ℃, the rubber temperature at the pressure is 39 ℃

352 normal,the, The rubber temperature at the pressure part is 36 ℃ and out of 25mm, the rubber temperature is 39 ℃

433 normal, the rubber temperature at the pressure part is 36 ℃ and out of 30mm, the rubber temperature is 39 ℃

495 normal, the rubber temperature at the pressure part is 36 ℃ and out of 32mm, the rubber temperature is 39 ℃

582 normal, the rubber temperature at the pressure part is 36 ℃ and out of 34mm, the rubber temperature is 39 ℃

624 and out of 2mm, the rubber temperature is 39 ℃ and out of 35mm, and the rubber temperature is 39 ℃

740 and out of 3mm, The rubber temperature is 39 ℃, 36mm, 39 ℃

799, 3mm, 38mm, 39 ℃

890, 4mm, 40mm, 39 ℃

946, 41mm, 39 ℃

1081, 43mm, 39 ℃

V-shaped rubber spring is installed between axle box and bogie frame, Each wheel set axle box uses two V-shaped rubber springs, which connect the bogie with the wheel set axle box and bear the guiding effect of the wheel set, which are used to transmit the traction and braking force of the wheel set; And provide elastic support for the vehicle body in the vertical direction; The function of providing flexible connection and limit in the longitudinal and transverse directions of the train is a supplement to the main shock absorption performance. The research on the fatigue life of rubber V-shaped spring shows that the frequency of test and the average value of alternating load are the main factors affecting its fatigue life [4]. Under the condition that the frequency of fatigue test is 2Hz and the average load is the rated working load of V-spring, the number of vibration is 2 × 106 is equivalent to actual operation 7 × 104 km, which can basically verify the fatigue resistance of V-shaped spring. At present, it is generally believed that the stiffness change rate of V-shaped spring is between -10% and 10%, which meets the use requirements

shiyanling of Tieling Rubber Industry Research Institute, etc. based on the empirical formula of rubber constant, which is mainly used in the welding strength experiment of large-scale and high-strength ship steel plate and other materials, and the relationship between the reaction rate constant and temperature in the process of chemical reaction obeys the Arrhenius equation, predict the service life of rubber damping block with the change law of constant compression permanent deformation of rubber damping block at different temperatures [5]. When the compression permanent deformation of NR rubber damping block is not greater than (6~7)% of the total height, although the stiffness increases, it can still work for a certain time. The working deformation of the damping block is 14.5mm, so when its compression permanent deformation is 30%, the deformation value is 4.35mm, which is 6.21% of the total height. That is, based on this calculation, at the equivalent temperature of 25 ℃, the time when the compression permanent deformation value is 4.35mm (working deformation 30%) is 3.2 years

foundation vibration isolation laminated rubber bearing is a new method for seismic protection of building structures. Its service life is required to be not less than the service life of the superstructure, that is, more than 50 years. Xu Bin et al. Studied the service life of rubber bearings by using the method of hot air aging [6]. The relationship between the service life of products and the time required for deterioration test at different temperatures is shown in Table 2. Table 2 service life and the time (hours) required for deterioration test at different temperatures

in addition, by comparing the influence of deterioration phenomenon at 80 ℃ on the horizontal stiffness of rubber bearing products and rubber test pieces, it is found that the service life of rubber is improved because the steel plate in the rubber bearing products isolates a large area of rubber from the air

in a word, the domestic means in the research and development of rubber damping products are still relatively backward, and still remain in the stage of empirical design and static strength design. Some products

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