Fracture failure of automobile gear teeth

The teeth of automobile gears are equivalent to cantilever beams. The force between two meshing teeth acts along the common normal of the two wheel profiles. When loaded, the bending stress at the tooth root is the largest. In addition, the section mutation of the transition part of the tooth root and the stress concentration caused by machining knife marks, the metal material is more sensitive to the tensile force, and the tooth fracture mainly occurs on the side of the tensile stress of the dangerous profile of the tooth root.

According to different loading properties, gear tooth fracture can be divided into fatigue fracture and overload fracture.

Bending fatigue fracture:

In working engineering, when the gear teeth are subjected to cyclic alternating load, fatigue cracks will appear on the dangerous profile of the tooth root and gradually expand, resulting in bending and fatigue fracture of the gear teeth.

Overload breaking:

When the gear teeth are subjected to short-time overload or impact load, or the gear teeth become thinner due to serious wear, overload fracture will occur.

According to the location of failure, tooth fracture can be divided into full tooth fracture and local fracture. For spur gears with small tooth width, the root crack generally extends along the tooth direction from the root and breaks the whole tooth. In helical cylindrical gear transmission, the contact line on the working tooth surface of the tooth is a diagonal line, and the tooth will break locally after being loaded.

The measures to avoid tooth fracture and improve the anti fracture ability of tooth are: increasing the fillet diameter of tooth root transition and reducing the surface roughness to reduce the stress concentration of tooth root; Shot peening, rolling and other processes are used to strengthen the tooth root.

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