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Old 11-04-2020, 10:24 PM
staybusy staybusy is offline
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Default Strength of 1" plate vs 2x 0.5"?

I need to know if the structural integrity of steel drops off a lot if I use multiple small plates instead of 1 thick one.

See attached image for example. Assume plates are bolted in and can't shift and have the same force applied on both by a hydraulic press.

Would they both take the same pressure? I assume yes but just need to confirm for safety reasons.
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Old 11-05-2020, 06:08 AM
bunkclimber bunkclimber is offline
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Default plate strength

you're better off with the 1"thick section. Even tho the two 1/2"thick pieces are bolted together, they will still shift under pressure. When you ask about 'structural integrity'-what KIND of integrity loss are you asking about?
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Old 11-05-2020, 06:23 AM
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Non degreed engineer here. If you were to weld completely around the plates, and drill and plug weld several spots in the center, then the 2 -1/2” plates might be the same or stronger. There are times when laminated plates are stronger, but they have to be pinned, bolted or welded together for the extra strength. My $0.02.




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Old 11-05-2020, 07:17 AM
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Granted the joint between the (2) 1/2" plates is the neutral axis (for this bending example) ....there is still stress there.
Shear stress's travel at a 45 degree angle from top to bottom.

and you allowing that force to slip.
Are we doing your homework assignment ?

Last edited by digger doug; 11-05-2020 at 07:45 AM.
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Old 11-05-2020, 11:42 AM
bunkclimber bunkclimber is offline
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Default strength of 1"plate

ok,so get on Youtube and ask the fella over at 'Hydraulic Press Channel' to do a realtime evaluation for you..he has something like 150tons at his disposal.
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Old 11-05-2020, 12:17 PM
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Quote:
Originally Posted by bunkclimber View Post
ok,so get on Youtube and ask the fella over at 'Hydraulic Press Channel' to do a realtime evaluation for you..he has something like 150tons at his disposal.
I like bunk's idea. I watch that channel on occasion...

My THEORY (or 2 cents) is that the 1" will be stronger and that the 1/2" will act like TWO separate pieces. This is assuming they are NOT completely bolted/welded together--only at the press attachment points. The bottom half will bend on a smaller arc than the top half once friction between the two halves is overcome. Both pieces will become "stretched" on top and "compressed" on the bottom as pressure is applied and they bend. The bottom of the top piece will try to follow the top of the bottom piece which has now increased in length so the top piece will have to stretch even more to follow the arc of bottom piece. I would say the top half would crack at the top in the middle. The 1" came out of the mill as one piece and is more homogeneous in grain and structure.

Now if you were welding/bolting the 2 halves in strategic areas, you might create a piece that is as close in strength as the 1", but drilling/welding can add their own stresses and weaknesses to the metal.

PS: the hydraulic guy will test stuff that people send in, but if you go to his Patreon channel and ask him this question, he might have the resources to do it for you. Otherwise you will have to ship your experiment to Finland...
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Old 11-05-2020, 05:47 PM
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The old Lincoln handbook of arc welding procedures has some interesting stuff about strength of plates. Not doubled but with various thicknesses with reinforcing straps underneath. Very informative and not what one would expect. Thinner can be better.

I bought a copy of that book for 50 cents. Great bedside read.
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Old 11-05-2020, 08:29 PM
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Resistance to bending moment is a simple formula, (B * H^3)/12 for a given length. You can double the resistant moment by doubling B, or you can increase by 8 fold (2^3) by doubling H. In your case, you are getting 1/8 (1/2^3) the resistance by halving H. Since you have two pieces 1/2 as thick, you are netting 1/4 the resistance of a single piece that is full thickness. There are many other factors at play, so this is just a simplification.

A pack of leaf springs comes to mind. Adding leaves increases resistance, making each leaf thicker really ups the ante. Also, a stack of leaves are designed to slip against each other.

In your diagram, the shear strength of the bolts would have to be calculated in since, as Doug pointed out, the neutral axis is where your parting line is if full thickness. Now you have two neutral axis and compressive forces are adjacent to tensile forces at the parting line.
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Last edited by arizonian; 11-05-2020 at 08:39 PM.
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Old 11-05-2020, 11:24 PM
staybusy staybusy is offline
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I'm building my own 100 ton hydraulic press. I'm trying to understand some basic structural safety principles to make sure everything is built to a respectable standard. I'll build the press in a software then share it so you guys can critique it before I move forward with the build. I just downloaded FreeCAD.. hopefully the learning curve isn't too steep.

The reason I was curious if I can use multiple plates is just a way to save money. 1/4" steel is easy for me to come by, while 1" thick plate is expensive as hell and I only have a very limited amount that I'm saving for other projects. If I can stack 4x - 1/4" plates, bolt them together and weld them that's great news!
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Old 11-06-2020, 07:34 AM
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Quote:
Originally Posted by staybusy View Post
I'm building my own 100 ton hydraulic press. I'm trying to understand some basic structural safety principles to make sure everything is built to a respectable standard. I'll build the press in a software then share it so you guys can critique it before I move forward with the build. I just downloaded FreeCAD.. hopefully the learning curve isn't too steep.

The reason I was curious if I can use multiple plates is just a way to save money. 1/4" steel is easy for me to come by, while 1" thick plate is expensive as hell and I only have a very limited amount that I'm saving for other projects. If I can stack 4x - 1/4" plates, bolt them together and weld them that's great news!
Your lack of knowledge & understanding our explanations show you really should not be attempting a 100 ton press build.
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