Shaft Sizing: Calculating σmax from 1045 UTS/YTS

[DADDYJ]

Attempting to use the formula:
D = 1.72 (Tmax/σmax)^1/3

In my case I do not know σmax or at least how to calculate it from material properties.
Material is 1045
UTS 84800
YTS 74300
Tmax = 591.55 in-lbs

D = 1.72 (Tmax/σmax)^1/3

Any help would be appreciated.

Regards

 

[FredGarvin]

As a very rough pass, you can use your yield strength as $$\sigma_{max}$$. Your equation is essentially assuming a set relationship for ductile materials and the relationship between shear stresses and normal stresses. This is for static, pure shear only.