From the analysis results of a large number of measured vibration data, the vibration in transportation is basically a narrow-band random vibration (relative to the vibration caused by aerodynamic noise), and its amplitude domain distribution does not satisfy the Rayleigh distribution, and it also deviates from the Gaussian distribution, but It is close to the Gaussian distribution in a small amplitude range.
It can be seen that most of the vibration energy is concentrated in the low frequency range, and the energy above 200 Hz is rather weak. Approximately 70% of the energy is concentrated at 150 Hz, especially in the 120 Hz range.
The main factors that cause the low-frequency vibration environment are: main suspension system, tire runout, engine drive shaft drive, body natural frequency, harmonics and local vibration.
Simulated transportation test conditions Because the vibration environment of the vehicle on the test piece during transportation is a complicated process, subject to various random factors, the theoretical response to the response of the product to this loading mode has not been developed satisfactorily. Methods. Therefore, experimental studies are still widely used to evaluate the dynamic behavior and wear resistance of the tested products. However, field trials under real and representative conditions are very expensive and time consuming, and only the overall vehicle can be tested. Therefore, most tests are required to be performed on the vibration equipment in the test chamber. This method requires the control system to correctly simulate the external field excitation.
According to the requirements of the development task book, the cumulative transportation distance of the product usually requires thousands of kilometers. If the 11-hour simulation is used indoors, it takes a long time. Therefore, indoor simulations use intensive test conditions to reduce time. The national military standard GJB150 (the environmental test method for military equipment), the US military standard MIL-STD-810E (environmental test method and engineering guidelines), the basic road transport regulations are, according to the test conditions given, the test represents 1600 km every 60 minutes. .
Since transportation is a random vibration, it is necessary to use the method of probability theory and mathematical statistics. Based on the assumption of linear fatigue cumulative damage, the product failure probability is consistent as the equivalent criterion for accelerated simulation, which is the basis for formulating experimental conditions.
As the original basis for the time history of the random vibration response of each point measured, there are theoretically two ways to accelerate the fatigue damage process. One method is to keep the vibration characteristics constant while changing the frequency characteristics of the random vibration. Whether the product is damaged by random alternating stress causes damage to the state of the failure surface. The failure surface is a spatial surface composed of a coordinate axis, a vibration frequency, and a number of cycles, and a curved surface indicates whether the product breaks under the action of alternating stress. The failure surface is a function of the vibration frequency. Changing the frequency characteristics will cause the actual damaged product not to be destroyed during the test, and the damaged product will not be destroyed in the test. Therefore, the method of changing the frequency characteristics cannot achieve the purpose of accelerating the transportation simulation equivalent. Another method is to increase the amount of vibration, which does not change the state of the failure surface. This method is feasible. However, excessively increasing the amount of vibration may cause a change in the mechanism of failure. Therefore, the increase in the amount of vibration must be controlled within a certain range.
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