Assessment of unusual failure in crankshaft of heavy-duty truck engine

The unusual premature failure of a heavy-duty truck engine crankshaft has been the subject of a rigorous study, and this manuscript describes it in detail. The failure was happened to begin with the growth of the crack from the surface defects, in the form of the clusters of non-metallic inclusions, in the lubrication hole zone of the first main journal, which was the stress concentration zone. A series of experiments including chemical composition, microstructure, mechanical properties, hardness, toughness, and fractography were performed on the failed crankshaft. In addition, the stress analysis was performed on the crankshaft. Careful fractographic study with scanning electron microscopy equipped with energy dispersive spectroscopy revealed that failure with cluster inclusions MnS (r = S/Mn = 0.024 > 0.01) was more than the standard amount. Besides, stress analysis showed that the stress field in stress concentration zones with the lubricating hole is much less than the web-crankpin fillet but the presence of cluster impurities, low hardness (>600 HV0.1 proposed standard), downshifting has caused the growth of primary cracks. It is recommended to first increase the hardness by about 43% and then, decrease the size of non-metallic inclusions so that primary crack growth does not initiate from the worst clusters of inclusions.