Spiral Fracture of Hex shaft 1

[ewalk]

I have a 30mm hex shaft turning at 650 rpm. The torque varies from about 339 ft-lbs to 1357 ft-lbs. Normal running torque should be about 450.

The shaft fails at the lowest torque. The latest failure is continuous spiral with fractures about 1/4 inch apart.

The material is DIN 42CrMo4 or AISI (41400).

I do not believe there is any heat treat on the shaft as I can easily cut it with the bandsaw.

 

[JCJackson]

Corrosion will induce cracks that can significantly reduce endurance limit. Up to 7x has been recorded. Check out:

http://www.epi-eng.com/BAS-Fretting.htm

http://www.epi-eng.com/RW-ShaftFatigue.htm