Abstract: Dynamic stress-time curves of gearbox is obtained by arranging strain sensors at key parts of gearbox of standard EMU. Combined with GPS signal, variation law of dynamic stress of gearbox under high and low speed running on straight line, traction state change and torque fluctuation conditions are analyzed. Dynamic stress amplitude of gearbox is calculated by rain flow counting method, and fitting analysis is carried out by kernel density estimation function and Weibull distribution function. On this basis, a combined distribution function is proposed to infer the maximum dynamic stress, and dynamic stress expansion spectrum is compiled. Finally, according to Miner linear cumulative damage theory, contribution of different stress levels to fatigue damage of gearbox is obtained. The results show that train speed and motor output torque have different effects on dynamic stress amplitude of gearbox. According to the proposed combined distribution function based on kernel density function and Weibull distribution function, maximum dynamic stress at the end of gearbox is 25.43 MPa. Based on dynamic stress expansion spectrum of gearbox prepared by the combined distribution probability density function, fatigue damage caused by stress at the end of gearbox at 9-17 MPa accounts for about 71.3% of total damage. Therefore, in fatigue damage assessment of gearbox, attention should be paid to stress amplitude with high frequency of action in structure to avoid early fatigue failure of gearbox structure.

Key words: EMU, gearbox, dynamic stress, cumulative damage, combination distribution