Abstract: As the key component of the EMU vehicle, the bogie is taking on the tasks such as carrying, running, and transferring different forms of dynamic forces, therefore, it is very necessary to study its fatigue problems. In this research, the bogie frames of a certain intercity EMU motor car and trailer car are chosen as the research object. Based on the measurement of the bogie frame on the high-speed line, the dynamic stress of the key point on the frame is acquired. Combining with the signals such as speed, heading angle and some line parameters, the working condition such as straight lines, curves with different radius, traction process, hybrid braking process and passing stations with a low speed are differentiated, and the dynamic stress referring to these working conditions are extracted. Then the fatigue characteristics of each measuring point under different working conditions are analyzed and compared. Through time-frequency transform, the amplitude-frequency characteristics of dynamic stress at the main measuring points of the motor car and trailer under different speeds are obtained, and then the system natural frequency and the external excitation frequency corresponding to the peak frequency of the dynamic stress at each measuring point are analyzed. Furthermore, the contribution of the dynamic stress with different frequency component to the damage of each measuring point are discussed. The results show that with the same speed and curve radius, the equivalent stress at most key point of motor car is greater than that of the trailer. When the speed is closing to zero, there will be a large-magnitude cycle of the dynamic stress at the hunger of anti-hunting damper and the connection of lateral beam and side beam, which is associated to the action from the inertial force of the car body to the anti-hunting damper. When crossing a turnout at a low speed, the range of dynamic stress at each measuring point is increased to a certain level, the most obvious change is at the hanger of anti-hunting damper and the connection of lateral beam and side beam, and relatively smaller change can be seen at other key points. With the same speed, when the equal damage ratio approaching, the frequency band of the dynamic stress at most key points of the motor car's bogie frames is wider than that of the trailer car.

Key words: bogie frame, working conditions, frequency domain characteristics, dynamic stress, fatigue