Shear Strength

[dbh06]

Does anyone recall the criteria for specifying shear strength? I have found in Machinery Hndbk where the shear strength for steel is 0.75*Su. I also have peers who swear by the criteria of 0.6*St. My old texts lean towards the 0.6*St for failure analysis, but I cannot get an additional reference that proves this. There is a big variation between using the ultimate strength as opposed to tensile strength. In particular I am looking for a reference I can quote as the authority.

 

[profengmen]

dbh06,
There was some discussion about this a bit back, here is the thread, hopefully it will help a little.

thread404-37622

 

[Maui]

One well defined experiement is worth a thousand unapplied abstractions. Why don't you measure it? Run a simple test.


Maui

 

[israelkk]

Neasuring can give faulse results. You have to know the actual tensile strength of the bolt and compare it to the minimum the spec states. If the ultimate strength of the bolt is say 10% higher than the minimum the spec states, than you have to deduct 10% from your test results to be on the safe side, in case the next batch of bolts will have the minimum tensile strength available.

 

[liberty]

Shear strength for ductile metals can be determined a few different ways.

The maximum-shear-stress theory predicts Ssy = Sy/2.
The distortion-energy theory says Ssy = Sy/(3^-1).
Some design codes use Ssy = 0.60Sy.

BTW, if there is a combination of bending (SIGMAx) and torsion (TAUxy), here is an equation for Von Mises stress (SIGMA'):

SIGMA' = (SIGMAx^2 + 3*TAUxy^2)^(1/2)

source: Shigley-Mischke pp 246-251, 1989

 

[CoryPad]

liberty,

Maximum shear stress and distortion energy theories relate to yield behavior. Shear strength is the term used for the shear stress at fracture. There is no fundamental equation for this value; for many alloys, it is ~ 0.6 times the ultimate tensile strength.

Regards,

Cory

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[RPstress]

"Official" practice for airframe (as taught on the Cranfield, UK "Introduction to Stress Analysis" course) is to use 0.5 * ft (ultimate tensile strength).

Circular bars will have higher allowables, but the above is conservative in (almost?) all cases. In reality ult shear will rarely be less than 0.6 * ft.

RP.

 

[liberty]

dbh06,

You were originally looking for an authority to refer to when backing up your calculation of shear strength. I also suggest "Engineering Materials" by Joseph Marin, Prentice-Hall, Englewood Cliffs, N.J., 1952.

That sure would beat a bunch of guys on the internet telling you "oh, it's about ~.6*Sut."

Best regards!