How to obtain Allowable Shear Stress

[Su Solberg]

Hi every one,
I am going to find the maximum allowable torque of a 4340 shaft, 30Dia.
However I think that the maximum allowable shear stress is still missing.

Can i use the tensile strength instead??

http://www.matweb.com/search/DataSheet.aspx?MatGUID=4a3cfc1e1cfd451091e67d3f3b66bb80&ckck=1

 

[Claws]

http://www.roymech.co.uk/Useful_Tables/Matter/shear_tensile.htm

Have a look at this table.

/C

 

[minger]

If not specified directly by your materials reference, a general rule of thumb is that the theoretical ratio between shear and tensile stress for a homogeneous, isotropic material is 0.577.

 

[FredGarvin]

you are looking in terms of yield strength, the max shear stress theory and max distortion energy theory help.

Max shear stress: Ssy=.5Sy
Distortion-Energy theory: Ssy=.577Sy

 

[Su Solberg]

Thanks everyone.
I get the answers 0.5X, right ^_^.

Btw, I wonder what's the effect of Heat Treament on SAE-4340/ any steel. for example Quenching.

What's the multiply factor on Yield and ultimate strength?

 

[FredGarvin]

If you look in Machinery's Handbook, there is a nice section relating steel hardness to a relatively accurate form of estimating tensile properties. When you heat treat something, usually a Rockwell or some other hardness is mentioned as a requirement.

In my latest copy (26th edition) it starts on page 473-474.

My company did some internal testing quite some time ago with a lot of different alloys and found a relatively good relationship between the two parameters. The Machinery's section is pretty good.