A Study Of The Prediction Method Of Equipment Fatigue Life Based On Vibration Energy

With the rapid development of science and technology, more and more mechanical equipment is applied in engineering practice. The mechanical parts or engineering components in the complex and changeable working environment are easily to be fatigue failure, so the research on the prediction of fatigue life is becoming extremely urgent. The traditional methods of fatigue life prediction are based on the static theories of fatigue analysis of the materials’ stress or average stress amplitude, ignoring the dynamic change in the process of the system’ fatigue damage. So its calculation tends to have a certain degree of error. This paper in the perspective of both theory and experiment studies the change rules of vibration features of single degree of freedom system under the harmonic excitation force and the prediction methods of fatigue life; based on the experimental results it combining with traditional theories which are mainly based on energy rules puts forward the prediction model of fatigue life based on vibration energy. The main research tasks and results of this paper are as follows:1. The forced vibration of the single degree of freedom system under the harmonic excitation force is well studied in the thesis and it also deduces the calculation formula of vibration energy and cumulative vibration energy. The results indicate that when the operating time of the system becomes comparatively longer, the vibration energy and cumulative vibration energy of the system and the time show an approximate linear relation. From the calculation formula, it can be seen that both of them are proportional to the vibration amplitude’s square and the varying frequency of harmonic variable is twice as much as the vibration frequency of the system.2. To simulate the fatigue vibration process of the simply-supported beam’s lateral bending with the software ANSYS, this thesis studies the relationship between cumulative vibration energy and fatigue life. The results indicate that both the cumulative vibration energy and the fatigue life of the system are in relation to the displacement amplification factor and the cumulative vibration energy is negatively correlated with the fatigue so it can be deemed as a valid feature to measure the fatigue life of the system.3. To simulate the process of the simply-supported beam’s vibration fatigue with ZK-4VIC vibration and control test bed this thesis analyzes the influence that the exciting frequencies and amplitude have upon the vibration characteristics and fatigue life. The results indicate that when the exciting frequency loaded harmonic excitation force is higher than the natural frequency; the amplitude will decrease slowly with the expansion of the crack and tend to be steady; when it is lower than the natural frequency, with the difference of the proximity degree between the exciting force frequency and the natural frequency, the amplitude variation shows a different trend; After the crack is formed, the influence that crack has on the stiff system is larger than that on the flexible system, therefore the fatigue life is shorter; It is easier to find the existence of crack faults from the vibration change of the stiff system than from that of the flexible system.4. Combined with traditional method of fatigue life prediction based on energy rules, this paper applying the concept of cumulative vibration energy into the prediction of the fatigue life deduced the prediction model of fatigue life with a single harmonic excitation force, double harmonic excitation forces and multiple harmonic excitation forces. The results indicate that after taking respectively the log of cumulative vibration energy and vibration fatigue life of the simply-supported beam both basically show a linear relation; calculating the vibration fatigue life of the beam with the method based on cumulative vibration energy is simple and more accurate.