Spline Bearing Stress

[DownHillHero]

I am looking at designing a straight spline for the end of a torsion bar.

The equation states that the torque capacity is based on the limit of 1000 psi bearing stress.

Is the bearing stress mentioned the stress that is placed on the internal spline?
The spline on the torsion bar and the mating internal spline are made from different materials and the materials both can resist a bearing stress greater than 1000 psi however I am unsure of which material should be used to design the spline. My intuition tells me to use the softer of the two materials.

 

[tbuelna]

DownHillHero,

The spline flank bearing stress limit of 1000 psi is probably based on a simple P/A calculation. The load (P) is the tangential force at the pitch line, and the area (A) is the external spline major diameter minus the internal spine minor diameter times the contact face width times the number of teeth.

The bearing stress limit of 1000 psi might seem quite modest for even very soft metals, but this number is for unlimited fatigue life in consideration of fretting. The combination of metals with somewhat differing hardness is actually good for minimizing fretting in a spline joint. And your intuition is correct, base your calculations on the softer of the two materials.

Good luck.
Terry