clamping 1

[xd76]

I am trying to calculate the stresses developed in a lug which is CLAMPED, on one side, to another bar (not the classic fork-knife way). My problem is that without introducing the clamping into the calculation I am being too conservative, and the stresses I calculate due to the moments (since it is a single side clamp) are extreemly high. I know that what I get is actually not true or physical but I have no knowladge of how to introduce the clamping into the calculation.
Anyone can hint me?
Thanks

xd

 

[ABCENGINEER]

Can or do you have access to FEA or have someone that knows how to model the problem in FEA. This constrainment is ideal for such a calculation and your right that the stress calculated from a problem set-up like Maybe one that you might find in Roark's formulas for Stress and Strain is too conservative.

 

[rb1957]

i understand that you are clamping two lugs together (as you say, not clamping a clevis which is very bad) ...

are you loading the lug along the axis of the bolt, which would mean transferring load via friction, or across the lugs so you want both lugs to react the applied bending moment together ?

assuming its the latter, you're probably right in that visualising the stress field, it's probably way conservative to have the two lugs reacting the moment independently ... and visualising the stress field it looks very odd (you'd have have compression on one lug adjacent to tension on the other). if the lugs are clamped together then i think it's reasonable that they work together (bending across the combined thicknesses of the lugs). try and draw a free body diagram of the lugs ... what sort of "heel-and-toe" forces would be required ? are the implied tension forces reasonable compared with the preload on the bolt ? probably it makes sense to assume the neutral axis is on the parting plane (between the two lugs) ?

good luck

 

[vonlueke]

xd76: Friction is typically neglected in this scenario. If your applied load is static, and both lugs have the same width, thickness, and modulus of elasticity, then at ultimate load, the lug bearing stress is approximated by sigma = 3*P/(D*t), where P = tensile force applied to single-shear lug, D = pin diameter, and t = plate thickness of either lug plate.

 

[vonlueke]

Also, under all of the conditions stated in my previous post, at ultimate load, the nominal value of the outer fiber tensile stress in the single-shear lug net section is approximated by sigma = 3*P/[(w-D)t], where w = lug width.

 

[xd76]

In my case the load is suspected to be an impact. If I understand the physics well I'd say that the friction cannot be neglected. Please correct me if I am wrong.

 

[vonlueke]

Friction might become even less reliable under impact. The theoretical, factored pin shear force would be P*FS - n*mu*Pi, where FS = project factor of safety, n = number of shear planes, mu = kinetic coefficient of friction, and Pi = minimum bolt preload.

 

[arto]

How about curved beam analysis [i.e. Budynas ""Advanced Strenths & Applied Stress Analysis"}