Elucidation of damage mechanism of multi-layer bellows exhaust pipe installed in actual machine

Abstract

In this report, we have clarified the cause of damage to the bellows exhaust pipe installed in the hydraulic excavator, and the influence of the seam welded part of the bellows on the damage to ensure the strength reliability of the bellows. First, the fracture surface of the damaged bellows was observed which was installed in the prototype machine of the hydraulic excavator, and it was clarified that the damage cause was the fatigue fracture starting from the seam welded part. Next, the natural frequencies of the engine exhaust system with bellows were derived by eigenvalue analysis, and the main stress frequencies were obtained by the frequency analysis of the stress time waveform measured in the actual machine test. By comparing the natural frequencies and the main stress frequencies, it was confirmed that the repeated shear deformation of the bellows due to the 2nd vibration mode was the main cause of the bellows breakage. Finally, a fatigue test simulating the shear deformation of the bellows was carried out, and it was confirmed that the damage of bellows could be reproduced by the fatigue test and that both inner and outer layers were fatigue-fractured at the seam welded parts. From the above, it can be judged that the seam welded part is the weakest part of the bellows, and the strength reliability can be improved by removing the seam welded part from the high stress part of the bellows.