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This analysis methodology focused on fracture surface examination and finite element method
In this paper, we present a failure analysis methodology of a structural component using a conventional 14-step failure analysis approach. This failure analysis methodology focused on observation, information gathering, preliminary visual examination and record keeping, nondestructive testing, mechanical testing, selecting/preservation of fracture surfaces, macroscopic examinations, microscopic examinations, metallography, failure mechanism determination, chemical analysis, mechanical failure analysis, testing under simulated service conditions, and final analysis and report. The application of this methodology is demonstrated in the failure analysis of a mixer unit shaft made of AISI 304 stainless steel. Using this failure analysis approach, we pinpointed the primary mode of failure and developed a means of circumventing this type of failure in the future.
The results show that the steel shaft failed due to intergranular stress cracking (sensitization during welding) at the heat affected zones (weld plugs).Fracture failure analysis of an agitator shaft in a large vessel is investigated in the present work. This analysis methodology focused on fracture surface examination and finite element method (FEM) simulation using Abaqus software for stress analysis. The results show that the steel shaft failed due to inadequate fillet radius size and more importantly marking defects originated during machining on the shaft. In addition, after visual investigation of the fracture surface, it is concluded that fracture occurred due to torsional–bending fatigue during operation.A fractured in-service ship-propeller shaft (50.8 mm, i.e., 2-inches nominal diameter) was examined to determine the causes of failure and to recommend preventive measures to minimize the risk of recurrence.
The findings of the failure analysis investigation suggest strongly that the shaft failed due to rotating bending fatigue initiated from the surface and close to the keyway area. The origin is located on a surface flaw (recess or dent) of approximately 100 μm depth, which could have probably being caused either during installation, operation, or maintenance. In addition, scoring lines formed due to friction-related processes and found on the journal surface were considered as stress raisers acting as potential sites for fatigue crack initiation. Careful review of the shaft service conditions and the implementation of suitable inspection procedures adapted to the vessel planned maintenance are recommended as necessary corrective actions for failure prevention.