Abstract
Abstract A six-cylinder crankshaft in a 12L diesel engine was locked after testing for about 840 hours in the bench test. The fractography investigation indicates that fatigue is the dominant failure mechanism of the crankshaft. It is found that the fatigue crack mainly initiated at the fillet of the crankweb between the 6th main journal and 6th crankpin. The fatigue crack initiation area lies outside the induction surface hardened zone. From detailed metallographic inspection, abnormal microstructure containing Widmannstatten was found in the fatigue crack initiation area and the 5th main journal, while that was not found at the severely deformed crankweb. Since the region containing Widmannstatten has lower hardness, the root cause of the failure may be that the abnormal microstructure lowered the fatigue strength at the stress concentrated fillet. The crankshaft prematurely fractured under the complex stress condition in the bench test.
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