| The fan of auxiliary converter is one of the core components of the main auxiliary system of high-speed train.Its excellent performance determines whether the indexes of train power supply system can meet the standard.Therefore,studying the fatigue characteristics of fan of auxiliary converter and exploring the external factors affecting its fatigue life under long-term operation conditions are of great significance to improve its fatigue reliability,reduce vibration and noise and ensure the safety of train operation.In this paper,the fan of a high-speed train auxiliary converter is selected as the research object.Through finite element simulation,material test,bench test and dynamic stress test under operating conditions,the material properties of the fan structure are systematically studied and its fatigue strength is evaluated.The main research contents are as follows:（1）The fatigue performance test of aluminum alloy was carried out.According to the requirements of test tooling,small aluminum alloy samples are designed.Based on the basic theory of material fatigue performance test,the mathematical formula of S-N curve is given.According to two general S-N curve test methods:lifting method and group method,the statistical parameters characterizing the fatigue properties of material are obtained.The statistical law and probability distribution of fatigue life are studied,and the drawing method of p-S-N under the specified survival probability is given.Based on the test results,the S-N curve and p-S-N curve of aluminum alloy are obtained.（2）Based on the modal analysis theory,the first 10 modes of the fan are calculated,and the modal frequencies and modal shapes of each mode are obtained.According to the loading conditions specified in international standard,the finite element method is used to calculate the stress distribution of the fan structure under different loading conditions,and the finite element vibration fatigue strength and impact strength analysis are completed.The results show that the maximum damage value is 9.4×10-2under the condition of 5 hours of vibration excited by three-dimensional acceleration,less than 1,no fatigue failure occurs,meets the fatigue design requirements,and the structural strength of the fan meets the requirements.（3）Based on the measured acceleration of the line,the vibration fatigue test of fan structure is carried out.The actual random acceleration excitation of the fan structure is converted into constant amplitude excitation suitable for bench test.At the same time,the strain sensor is arranged to measure the strain response and calculate the fatigue damage.The finite time damage result is extended to the whole life cycle of the fan,and the fatigue strength in the whole life cycle is evaluated.The results show that the maximum damage of the measuring point is 3.89×10-3when the stress cycle reaches107times,far less than the damage critical value 1,and the fatigue strength of the fan structure meets the requirements.（4）Based on the field was dynamic stress test,the fatigue strength evaluation of the fan was studied.Referring to the finite element simulation and vibration test points,strain sensors ware arranged at the weak posits of the structure for line test.The time-frequency characteristics of dynamic stress data ware analyzed,the results show that the maximum equivalent stress at the measuring point is 59.4MPa,and the equivalent stress at the measuring point is far lower than fatigue limit of the corresponding materials used in the fan.The fatigue strength of fan structure can meet the design life requirements. |
