Study On Propagation Mechanism For Surface Fatigue Crack On Automobile Gear

Gear is the key component to deliver sport and motive, the quality of which directly determines the quality and performance of mechanical products. Crack fatigue failure is one of the main failure modes of the gear, and the stress intensity factors(SIF) of the crack tip is a key factor of gear fatigue crack, fatigue crack propagation rate is an important index to evaluate fatigue crack propagation.Based on 3D model software Pro/E, adopting parametric modeling method, the spur gears geometric model is established. Then the geometric model is imported into finite element software ABAQUS, and the initial fatigue crack is simulated with an 3D elliptical cylinder, and then the fatigue crack analysis finite element model of the spur gears is established.Based on the established 3D fatigue crack analysis FE model of involute spur gears, this paper studies the influences of several parameters, such as torque, friction coefficient, crack initial depth, location and crack geometric size, on the mode ?, mode ?? and mode ??? SIFs of the crack tip. Results obtained show that: the distributions of mode ? and mode ?? SIFs of the crack tip are similarly parabolic, and the distribution of mode ??? SIF of the crack tip is similarly tangent curve. The SIF values of mode ? at the crack tip are larger than that of mode ?? and ???. This suggests that the open mode mainly dominates the fatigue crack propagation. With increasing the torque, the SIF values of mode ?, mode ?? and mode ??? of the crack tip increase, but the value of mode ??? SIF at the middle point of the crack tip keeps zero. With increasing friction coefficient, the SIF values of mode ?, mode ?? and mode ??? of the crack tip basically remain unchanged. With increasing crack initial depth, the SIF values of mode ?, mode ?? and mode ??? of the crack tip have obvious reduction, but the value of mode ??? SIF at the middle point of the crack tip keeps zero. With changing crack initial location, the SIF values of mode ?, mode ?? and mode ??? of the crack tip have a little change. With increasing the crack major size, the SIF values of mode ?, mode ?? and mode ??? of the crack tip increase, but the value of mode ??? SIF at the middle point of the crack tip keeps zero. With increasing the crack minor size, the SIFs values of mode ?, mode ?? and mode ??? of the crack tip reduce, but the value of mode ??? SIF at the middle point of the crack tip keeps zero.Based on the established 3D fatigue crack analysis FE model of spur gears, this paper studies the influences of several parameters, such as torque, friction coefficient, crack initial depth, location and crack size, on the crack propagation rate. Results obtained show that: With increasing the torque, the crack propagation rate increases. With increasing friction coefficient, the crack propagation rate increases. With increasing crack initial depth, the crack propagation rate reduces. With changing crack initial location, the crack propagation rate firstly reduces and then increases and finally reduces. With increasing the crack major size, the crack propagation rate firstly increases and then maintains stable. With increasing the crack minor size, the crack propagation rate reduces.The results of the study have some theoretical value and practical significance to develop the gear fatigue fracture theory and to improve the gear service performance.