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

摘要

The presence of cracks in any type of structure is undesirable as they often lead toudfracture or failure of the structure. Marine propeller shaft is a key component in marineudpropulsion systems; moreover due to the strenuous working conditions, to which it isudsubjected during its marine operation, it is prone to develop crack(s). The presentlyudavailable crack detection methods, either require disassembly of the shaft substructure forudvisual inspection or require external excitation of the relevant portion of the shaft forudsubsequent dynamic analyses; consequently these methods are quite complex and timeudconsuming.udIn this study a simpler crack detection method is proposed for crack detection in rotatingudmarine propeller shafts. The crack detection method is based on simple strain anduddisplacement measurements at identified locations and hence easy to execute. The studyudwas carried out using Finite Element Analysis through ABAQUS, a well-knownudcommercial finite element package. The analysis was carried out both for the existence ofudsingle bending crack and single circumferential crack, on the body of the rotating shaftudcomponent, and the proposed method was able to identify both types of cracks at quiteudearly stages of their growth and development. It was found that if measured at the properudlocations, the percentage changes and slopes of percentage changes for these parametersud(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 beuddirectly related to crack location and size. Based on the computed and analyzedudnumerical results, a simple but effective crack detection method has been proposed whichudwould eliminate the complexities present in the currently available crack detectionudmethods for such structures.