In this thesis the lifetime of the main gearbox of the leveler of corrective line I of Mobarakeh steel company has been defined. In this work two kinds of common failures in gears, fatigue fracture at tooth root and pitting on tooth flank have been investigated.These two kinds of failure are classified as fatigue fracture. There are several different approaches to study the fatigue phenomenon, in this thesis the fracture mechanics approach has been used. Fatigue failure is considered as a linear elastic fracture mechanics (LEFM) problem. In this project Paris equation has been used to evaluate fatigue life. Paris equation relates the fatigue crack growth rate to stress intensity factor range. Maximum circumferential stress theory has been used to determine the crack growth direction in each step of crack growth. In this project, first kinematic and force analysis has been done on leveler device and its power transmission set which consists of seven gearboxes and critical gear and the torque applied to it have been defined. Then by a contact analysis the exact load distribution on critical gear teeth has been calculated. In this thesis the extended finite element method has been used for simulation of 3D crack growth in gears. The extended finite element method has alleviated many limitations of conventional finite element method in modeling fracture mechanics problems.In the conventional finite element method it is needed to use very fine mesh in the vicinity of crack front to model the singular stress field. Also the mesh should conform to the discontinuity geometry and as a result after each step of crack growth the mesh should be updated. These two factors increase the modeling and computation time considerably. In the extended finite element method crack is not modeled explicitly, but is introduced to the finite element approximation by using some extra degrees of freedom. This procedure is called enrichment. In this project modeling and computation time has reduced considerably compared to previous works. Present study is one of the few works done on the 3D crack growth in gears. Most of the previous works have been limited to 2D cases. In this project ABAQUS software has been used to simulate fatigue crack growth. At the present time, ABAQUS does not have the ability to model fatigue crack growth by extended finite element method. Therefore a code has been written using the ABAQUS scripting abilities to provide a tool for simulating 3D crack growth by extended finite element method. Two above mentioned failures in gears are modeled using ABAQUS and provided code and the lifetime of the main gearbox of leveler device has been defined. Final configuration and crack growth shape also have been identified. . Key Words: Fatigue, gears, fracture Mechanics, extended finite element method.
