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How to obtain Allowable Shear Stress

by Su Solberg
Tags: allowable, obtain, shear, stress
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Su Solberg
Jun5-09, 01:47 AM
P: 79
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??
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Jun5-09, 06:23 AM
P: 35

Have a look at this table.

Jun5-09, 07:22 AM
Sci Advisor
P: 1,498
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.

Jun5-09, 07:34 AM
Sci Advisor
FredGarvin's Avatar
P: 5,095
How to obtain Allowable Shear Stress

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
Jun7-09, 11:30 AM
P: 79
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?
Jun7-09, 08:12 PM
Sci Advisor
FredGarvin's Avatar
P: 5,095
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.

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