Failure analysis of a dynamometer drive shaft coupled to an engine

A typical dynamometer drive shaft was damaged during its working condition. This failure was repeated in four cases. In the present article, a failure analysis of a dynamometer drive shaft has been performed. To analyze the failure, the material investigation was carried out by scanning electron microscopy (SEM) images. Additionally, the micro-structure of the failed coupling shaft was photographed, the hardness was measured and compared to properties of the original material. Besides, the fatigue lifetime was calculated based on the high cycle fatigue (HCF) regime and the fatigue endurance limit by simulating the misalignment in a finite element (FE) model. The possibility of torsional vibrations and the occurrence of the resonance condition were also studied. Finally, vibration-monitoring practices were done to compare the vibration amplitudes to an acceptable criterion. SEM images showed cleavage marks under fatigue loadings. These marks indicated the brittle behavior of the material. The micro-structure together with the hardness of the alloy was satisfied. Based on numerical results, the fatigue lifetime of the coupling was likely to terminate according to the misalignment increase, as a cause of the failure. The other cause could be the resonance and the shaft critical speed, which was calculated below the idle speed of engines.