The gear contact stress is very difficult to calculate and test owing to complexity of gear pairs contact condition by manufacturing error

assembly error

support conditions

deformation of loaded gear pairs

etc.The gear contact can be constituted of line contact and point contact in non-loaded condition

and will be change to surface contact in loaded condition.When the load is applied

the area of the contact is rectangular and ellipse respectively in line contact and point contact.The theory of line contact is perfect using Hertz contact to calculate two cylinders contact.However the theory of point contact is more complicated considering contact ellipse and other nonlinear factors

etc.The calculation examples of involute gear and the same parameter gear with modification are analyzed by finite element method.It shows that the simulation result of gear line contact is consistent with calculation result of Hertz contact theory without considering assembly error

and contact stress of line contact is less than the one of point contact.The contact stress of line contact and point contact will both rise if considering assembly error

but contact stress of line contact and point contact will rise rapidly to 57 times and less than twice respectively comparing with no assembly error.It shows that contact sensitivity of line contact is more sensitively than one of point contact

and it is reason that line contact gear will easily cause gear pitting destruction.