Abstract: As the load bearing structure, the equipment cabin frames connecting the bottom plates and apron plates are acted on the aerodynamic load and vibration load, which appear the fatigue cracks in service. The crack macro analysis of the frame fracture section and the life mileage statistics of the frames are demonstrated. On the basis of the online pressure test of the equipment cabin on the passenger dedicated railway lines, the inside and outside aerodynamic pressure and differential pressure of the equipment cabin bottom plates and apron plates are executed and analyzed under the conditions of trains running or passing each other in the open air or in the tunnel. The equivalent stress and the first-order frequency of the crack position are gained by the on track dynamic stress test. The first-order modal frequency in the vertical and horizontal direction of the frames is tested using the pulse excitation method. The results show that the exciting frequency from the bottom plate or apron plate aerodynamic differential pressure is mixed with the frame natural frequency and the resonance of the frame happens, which induces the high dynamic stress amplitude. This idea is helpful to improve the equipment cabin frame design and ensure the high speed train running in safety.

Key words: aerodynamic pressure, dynamic stress, equipment cabin frame, model, vibration fatigue