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How to obtain Allowable Shear Stress 
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#1
Jun509, 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?? http://www.matweb.com/search/DataShe...b66bb80&ckck=1 


#2
Jun509, 06:23 AM

P: 35



#3
Jun509, 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.



#4
Jun509, 07:34 AM

Sci Advisor
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 DistortionEnergy theory: Ssy=.577Sy 


#5
Jun709, 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 SAE4340/ any steel. for example Quenching. What's the multiply factor on Yield and ultimate strength? 


#6
Jun709, 08:12 PM

Sci Advisor
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 473474. 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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