Wheel Axle Material

[JamesCH95]

Originally Posted by craigboez

Has anyone ever seen a snap ring/e-clip give way?

I haven't seen a snap ring give out directly, but there was a case last year where a team had a snap ring groove in a torque-loaded section of the drive shaft. That is a serious stress-riser and it caused the shaft to fail.

A few thoughts: While 7075 Al has a higher yield strength than 4140 steel, 66ksi vs 60ksi, 7075 has a lower ultimate strength than 4140, 78ksi vs 95ksi. That means that the steel shaft will start to permanently bend at a lower load, but the aluminum will actually break in half first in a bending-load situation.

Aluminum and steel do not have the same tensile-strength to shear-strength relation. A rule of thumb is that for steel, shear strength = 0.75*tensile strength, but for aluminum shear strength = 0.65*tensile strength. This means that 4140 has a slight strength advantage in shear strength, the strength required to resist torsion. 4140 has the option to be heat-treated by most small machine shops to be considerably stronger, easily twice the strength of 7075 T6 aluminum.

I would use 4140 steel for the reasons I discussed above, and because I'd have the option to weld features onto the shaft if I wanted to.