Development of fatigue life evaluation technology for multi-layer bellows exhaust pipe

Abstract

In the hydraulic excavator, the bellows exhaust pipe connects the engine and the exhaust gas post-processing device and is exposed to thumping vibration from the engine and the body. In order to ensure the reliability of the pipe under such harsh conditions, we developed a technology for evaluating the fatigue life of the bellows. First, in order to get the appropriate fatigue life curve of the bellows, the fatigue tests of bellows were conducted. In the fatigue tests, we judged that a fracture had occurred when a crack was detected in either the outer layer or the inner layer of the bellows. The cracks in the outer layer were detected by the change of strain measured with axial strain gauges installed on the outer layer, and the cracks in the inner layer were detected by the change of the internal pressure of the bellows. A fatigue life curve was derived from the fatigue test results by using the method of least squares. Next, the resonance endurance test (repeat cycles: 107) of the bellows exhaust pipe was carried out with the actual machine, and the derived fatigue life curve was verified using the endurance test results. In order to verify the fatigue life curve, the endurance test results were plotted on the stress limit diagram obtained from the derived fatigue life curve. In the stress limit diagram, failure and non-failure of the bellows were mixed at the boundary of the proposed curve. From this result, it became clear that the derived stress limit diagram can evaluate the fatigue life of bellows.

Keywords

• bellows
• multilayer
• fatigue test
• fatigue life evaluation
• initial stress
• endurance test