Shear Stress vs Bending
Shear Stress vs Bending
(OP)
When analyzing a clevis type connection...where the pin will be in double shear...at what point (distance between clevis supports) do you need to consider the bending stress in the pin?
For example...I have a typical application with a 3/4" pin seeing a load of 5.5 kips...the clevis supports are on a 1.34" center to center spacing (approx 1" inside to inside)
Area = 0.44 in^2
Sx = 0.041 in^3
Shear Stress = 1/2 x (5.5) / 0.44 = 6.25 ksi
but if I would analyze the bending here it would be...
M = PL/4 = 5.5*1.34/4 = 1.84 in*kips (if analyzed as simply supported)
M = PL/8 = 5.5*1.34/8 = 0.92 in*kips (if analyzed as fixed)
Bending Stress = M/S = M/0.041 = 44.8 ksi or 22 ksi
In either analysis(simply supported or fixed), the bending stress starts to get pretty high.
I usually analyze the bending stress, but is it necessary?
Thanks !
For example...I have a typical application with a 3/4" pin seeing a load of 5.5 kips...the clevis supports are on a 1.34" center to center spacing (approx 1" inside to inside)
Area = 0.44 in^2
Sx = 0.041 in^3
Shear Stress = 1/2 x (5.5) / 0.44 = 6.25 ksi
but if I would analyze the bending here it would be...
M = PL/4 = 5.5*1.34/4 = 1.84 in*kips (if analyzed as simply supported)
M = PL/8 = 5.5*1.34/8 = 0.92 in*kips (if analyzed as fixed)
Bending Stress = M/S = M/0.041 = 44.8 ksi or 22 ksi
In either analysis(simply supported or fixed), the bending stress starts to get pretty high.
I usually analyze the bending stress, but is it necessary?
Thanks !





RE: Shear Stress vs Bending
SIGMA' = (SIGMAa^2-SIGMAa*SIGMAb+SIGMAb^2)^(1/2)
where SIGMA' = von Mises stress
SIGMAa = principal bending stress
SIGMAb = principal shear stress
For better understanding of your problem, or if you discover you have a triaxial stress case, I recommend reviewing distortion-energy theory and other failure theories. See Chapter 6 of ME Design by Shigley/Mischke 5th edition 1989.
RE: Shear Stress vs Bending
Yes, I usually do combine stresses.
The reason I am asking about the bending in this case, is that I have seen calculations that don't even consider bending in this case. They assume that the clevis is a pure shear connection.
RE: Shear Stress vs Bending
Sometimes we engineers design to requirements that we make up in our own heads, which the customer could care less about and would rather not pay for. I've done it lots of times...
RE: Shear Stress vs Bending
so, I am aware what I need to check...was just curious if bending is really imposed in a clevis type arrangement. I assumed it was fixed in its support...I can even reduce the stress more by assuming a distributed load instead of a point load at the center.
Thanks.
RE: Shear Stress vs Bending
RE: Shear Stress vs Bending
V V
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If your pin is 'too' long then of course the bending stresses can be significant.
Cheers
Greg Locock
RE: Shear Stress vs Bending
Also .....I would not combine bending and shear stresses as max bending occurs at the outer fibers and shear is zero there; max shear occurs at the neutral axis and bending is zero there.
daveleo
RE: Shear Stress vs Bending
There are a variety of aerospace textbooks that deal with this topic. "Analysis and Design of Flight Vehicle Structures" by Bruhn is the "bible" and contains a conservative approach for computation of the bending in the pin.
The Bruhn approach is to compute the bending distance as tlug/4 + tclevis/2 + gap. (Where "gap" is the physical gap on each side between the lug and the clevis).
There are many less conservative methods found in company manuals and other texts.
As for when you need to check the bending, it's pretty much a function of how the various elements of the joint are designed. (e/D, thicknesses, gaps, pin diameter, hollow or solid pin, etc.)
Bending should definitely be checked whenever large tolerances allow significant fit-up gaps or when lug or clevis materials are soft relative to the hardness of the bolt. It's really not purely a function of distance between the clevis ears.
SuperStress
RE: Shear Stress vs Bending
AISC is a good reference that has acceptable criteria for all of these cases.
Happy New Year!
RE: Shear Stress vs Bending