Minimum thickness required for contact area
Minimum thickness required for contact area
(OP)
Hi all. I have a triangular load distribution due to contact between a plate and a hinged fitting. I know load magnitude and contact area.
How do I go about determining minimum plate thickness required to prevent this thing being a can opener? It seems that if I consider the load magnitude as the volume of a wedge, I get an astronomically high running load along the edge I'm concerned about. Am I missing something here?
How do I go about determining minimum plate thickness required to prevent this thing being a can opener? It seems that if I consider the load magnitude as the volume of a wedge, I get an astronomically high running load along the edge I'm concerned about. Am I missing something here?





RE: Minimum thickness required for contact area
Are you FEAing this or is it a hand calc?
Cheers
Greg Locock
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RE: Minimum thickness required for contact area
Dan
RE: Minimum thickness required for contact area
The hinged fitting is radiused along all contact edges.
RE: Minimum thickness required for contact area
Show us a sketch, maybe it's easier to visualize.
RE: Minimum thickness required for contact area
RE: Minimum thickness required for contact area
This part will react against a piece of machined plate. I'd like to have an idea on how to determine the minimum plate thickness so that we don't end up punching thru the plate with the part.
RE: Minimum thickness required for contact area
Need a drawing of the structure that the part reacts against: plate and substructure. And need dimensions in the width direction (into the paper on your first sketch)
RE: Minimum thickness required for contact area
a triangular bearing load (as shown) is a reasonable assumption, so you know the peak load per unit thickness.
hint, about 24,000 lbs/in
divid by thickness to be less than the bearing allowable (or either side of the interface). hint, about 0.25" (assuming Al)
lick of paint ...
RE: Minimum thickness required for contact area
Timelord
RE: Minimum thickness required for contact area
the moment in the link is about 10,000 in.lbs,
at 0.25in thk the bending stress is something like 60,000/(1^2*0.25) = 240ksi ... better be steel
RE: Minimum thickness required for contact area
Thank you so much for your responses. I've been trying to clean up another inherited mess (another idiot who thought shearing stress due to bending is V/A).
rb -
I think we're on the same wavelength here. I guess my brain is vapor locked on this:
divid by thickness to be less than the bearing allowable (or either side of the interface). hint, about 0.25" (assuming Al)
Could you elaborate a little on this?
BTW - the link has two legs approx .6 wide each.
RE: Minimum thickness required for contact area
What if you check the link for bearing stress at the edge and the plate it bears upon as if the link was, indeed, a can opener. That is, check for shear in the plate along the edge of the link. (shear area = link width + 2x distance to (say) R2 x plate thickness.) If the link is radiused, this calculation will probably be very conservative and you will never have to worry.
RE: Minimum thickness required for contact area
triangular distributed load, peak = A, span = B
resultant = A*B/2 = R1
R1 = 12,000lbs
B = 1in (near enough)
A (peak contact load) = 12,000*2/1 = 24,000 lbs/in
bearing stress = peak load/thk = 24,000/0.25 = 96ksi
but look at bending through the pivot M = 10,000 in.lbs
stress, for 0.25" thk, = 6*M/(0.25*1^2) = 240ksi
of course if there are two links then this'd be the combined thickness. how are the links joined together ? how is the load applied to the combination (to has link ? to the middle of the spacer ??)
RE: Minimum thickness required for contact area
So what you did is figure out the thickness of the link required to bring it under Fbry, right?
My concern is the thickness of the material under the link, i.e. the machined base, not the link itself. I have the link pretty well figured out.
The link is loaded by contact along the vertical face. I've attached an old solid model of the part to give you an idea.
RE: Minimum thickness required for contact area
but it seems you're asking not about the link, but about the structure that link contacts. but that's a whole different thing. this it one thick flange ? does it have stiffeners ? aligned to the link axis or normal (so that only a small area is fully effective) ? on one level, how much area would have to shear for the links to break the supporting structure ? how does the supporting structure react to the link loads (bending ?) ??
RE: Minimum thickness required for contact area
RE: Minimum thickness required for contact area
so it's either ...
1) the panel is essentially rigid, what pressure does it take to crush the honeycomb; or
2) the panel is flexible (being "rigidly" supported somewhere else) and bends like a beam.