Crack Propagation And Fault Diagnosis For Gears Using FEM

The monitoring and diagnosis of mechanical systems rose to the rank of major industrial concerns. The current trend is to look for tools that can reveal an early onset of dysfunction in order to gradually replace the systematic maintenance by preventive maintenance.Over the last two decades, problems arising from excessive wear and gear tooth damage in gear transmission systems have been of increasing concern for a variety of gear users. A large range of gear models have appeared in the literature either discussing about the effect of gear rim thickness on crack propagation path or simulating the dynamic behavior of gears in the presence of faults. In the former, they are mainly based on the fundamentals of fracture mechanics that involve tremendous variables and equations, and/or coupling different computer software packages to make crack propagation predictions possible. In the later, few literatures are manly focus in one hand on three dimensional crack fault simulation and in another hand, use analytical approach to study other defect cases. In the aim to improve the current generation of diagnostic techniques this present thesis firstly introduced a new appropriate methodology for gear tooth crack path prediction bases on an evolutionary structural optimization using a two dimensional analysis of a spur gear sector. Secondly to assess the severity of tooth damage on the vibration response, three dimensional spur gear-pair with defect tooth as crack and spall are simulated and analyzed by means of finite element method. The major woks of the thesis oriented on finite element static and dynamic analysis– 2D and 3D static and dynamic analysis are summarized as follows:①Based on ESO (Evolutionary Structural Optimization) tooth crack propagation was predicted. The major emphasis was to determine in which direction a crack will grow, either through the tooth foot or through the rim. Four undamaged two dimensional Finite Element Models with different backup ratio were analyzed.②Dynamic responses of a one stage spur gear meshing with faults were investigated using a three dimensional finite element model that offers significant advantages for dynamic gear analyses. To evaluate the default effects under identical loading condition on the vibration responses, two types of defects are incorporated in these 3D models for simulation: crack at the tooth foot with different depth and spalling at the tooth flank with various sizes. ③To further investigate the effect of the concerning defaults on the dynamic responses of the gear meshing; Finite element models were also developed for analyzing dynamic characteristic where stiffness evaluation and modal analysis has been conducted to evaluate the influence of crack and spalling on the magnitude changes in the gear-mesh stiffness and on the natural frequencies.For gear path prediction simulated results agree remarkably well with solutions, experimentally and analytically, proposed by previous rigorous procedures while in the next section, the processing simulation vibration results that reflect the dynamics performance of the overall gear system transmission meet as well our expectation. They provide a basic idea for dynamic researches and engineering application. The proposed method can be used for different types of gear for design optimization.