Modeling of Spur Gear Meshing Characteristics under Various Crack Size

This report focused on the study of gear defect based on the gear meshing stiffness variation. The main objective of this study is to investigate the gear defect by modeling the gear based on the gear material and gear parameter. The main failure that occurs to gear is crack defect due to concentration of stress at the root of gear tooth. The crack cannot be detected because gear located at the middle of the system and the size of crack is too small to be seen with naked eyes. The crack also will affect the total gear meshing stiffness, which causes it to reduce drastically. The work focused on modeling the gear using different type of materials, which are mild steel and Aluminum S6061 to study the different characteristic of gear meshing stiffness. It also includes the modeling of the gear with various crack size to compare thetrend of the gear meshing stiffness.
The research methodology adopted involves modeling the healthy gear which is gear without defect for baseline data. The total meshing stiffness is the summation of the Hertzian contact, shear, bending and axial contact stiffnesses. The meshing period is calculated to differentiate between single and double meshing tooth. All the calculation is done using MATLAB software which is very handy in solving complex equations. The method adopted in this project was originally developed by Tian and it is also known as the Tian’s method. The vibration characteristic for the healthy gear resulted from the simulation is validated with the experimental data afterwhich the work proceeded to modeling the gear with various crack size ranging from 0.0014mm to 0.005mm. The gear with broken tooth is also modeled to review the characteristic of missing tooth gear stiffness.
It can be concluded that the crack would cause the reduction of gear meshing stiffness. The initiation of crack propagation will cause the changes in shear and bending stiffness thus changes the overall total gear meshing stiffness. Materials such as steel and Aluminum has different value of Young Modulus and it causes the different of total gear meshing stiffness. The size of crack also affects the meshing stiffness. If the crack size is bigger, the total gear meshing stiffness will be smaller.