Finite Element Analysis Research In Crack Detection Of Marine Diesel Engine Shafts

In the thesis, finite element analysis (FEA) software ANSYS was taken as basic analysis tool and marine diesel engine crankshaft with cracks was taken as research object. ANSYS Parametric Design Language (APDL) and MATLAB data visualization technology were used for crankshaft stress analysis revolved in crack detection by metal magnetic memory testing (MMMT) and harmonic electromagnetic field analysis around the sensor in eddy current testing. Therefore mechanism of crack development, magnetic memory testing, finite element analysis of crankshaft stress, eddy current testing and electromagnetic field numerical simulation were combined in the thesis for research of crack detection in marine diesel engine crankshaft using electromagnetic Non-Destructive Testing (NDT).In the first instance, three kinds of crankshaft crack in marine diesel engine were compared, and it was pointed out that fatigue crack was one of main causes of shaft rupture. Four methods of stress calculation of shaft were summarized. Two different methods of solving electromagnetic problem were compared and according to Maxwell's Equations, finite element method solution of electromagnetic problem was infer by introduction of magnetic vector A and scalarΦ.Secondly, based on standardization of crankshaft FEA model, APDL was used to write a program for parametric modeling of crankshaft and therefore the work efficiency of finite element analysis was improved. Cracks were developed from stress concentration zone. Loads and restrictions similar with practical operation were applied on the model, and stress distribution was calculated out which would be helpful for detecting cracks exactly by instructing collocation and testing of MMM sensor.Finally, based on impendence analysis method, testing model of cracks character and eddy current signal were built to find impendence change of testing coil. Planar FEA model was built by ANSYS to solve the distribution of eddy current electromagnetic field near surface and then voltage signal of sensor coil would be calculated out. Data result of FEA was sent to MATLAB for visualization to describe effect on electromagnetic signal by cracks. Compared with practical testing, calculation result was similar with signal of testing instrument. Therefore eddy current testing, with its advantages such as simple and quick operation, distinct signal and reliable result, was suitable for crack detection of marine diesel engine.