An investigation of contact stresses and crack initiation in spur gears based on finite element dynamics analysis

• The surface and subsurface stresses of gear teeth are investigated using Hertzian theory and finite element method.
• Finite element dynamics analysis is used to obtain the realistic description of a stress cyclic loading of a material point in meshing gears.
• The effects of friction and speeds on stress cycles and fatigue lives of gears are studied.

Contact fatigue, one of the main failure modes of gear tooth flanks, is caused by repeated compression and shear stress cycles. In this study, the surface and subsurface stresses of gear teeth are investigated using Hertzian theory and the finite element method. The number of loading cycles required for fatigue crack initiation is predicted using the Smith–Watson–Topper method based on the multiaxial fatigue mechanism. The effects of friction and speed on stress cycles and fatigue life are studied. Friction is found to shift the distributions of von Mises stress, change the extreme values of the shear stress cycle, and results in low fatigue life. The stresses near the engagement and recess areas are also found to be greater than the static contact conditions and thus result in low fatigue life, particularly at high speeds. The tip relief of the teeth is introduced to decrease the stresses on these points and improve their initiation fatigue life.