Identification of size and location of a single crack in marine propeller shaft using strain and displacement

Hossain, Ridwan (2014) Identification of size and location of a single crack in marine propeller shaft using strain and displacement. Masters thesis, Memorial University of Newfoundland.

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Abstract

The presence of cracks in any type of structure is undesirable as they often lead to fracture or failure of the structure. Marine propeller shaft is a key component in marine propulsion systems; moreover due to the strenuous working conditions, to which it is subjected during its marine operation, it is prone to develop crack(s). The presently available crack detection methods, either require disassembly of the shaft substructure for visual inspection or require external excitation of the relevant portion of the shaft for subsequent dynamic analyses; consequently these methods are quite complex and time consuming. In this study a simpler crack detection method is proposed for crack detection in rotating marine propeller shafts. The crack detection method is based on simple strain and displacement measurements at identified locations and hence easy to execute. The study was carried out using Finite Element Analysis through ABAQUS, a well-known commercial finite element package. The analysis was carried out both for the existence of single bending crack and single circumferential crack, on the body of the rotating shaft component, and the proposed method was able to identify both types of cracks at quite early stages of their growth and development. It was found that if measured at the proper locations, the percentage changes and slopes of percentage changes for these parameters (strain and displacement) changed more rapidly than frequencies, due to the presence of a crack. Only two measurements were required to get such identification which could be directly related to crack location and size. Based on the computed and analyzed numerical results, a simple but effective crack detection method has been proposed which would eliminate the complexities present in the currently available crack detection methods for such structures.

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