Calculating compression forces for a material

Technical Technical Discussion
#1

So a disclaimer, I’m not an engineer by any means… which is why I’m asking :smiley:

Trying to figure out what kind of material to use for a structural piece. For example, if I was planning on 1,000 lbs of weight as tension on aluminum square tube. From what I’ve seen, 6060 aluminum has a tensile strength of about 32,000 psi. I get force/area will give you psi, but how do you calculate the area for the tube? For a square tube, do you just use the area of the material? So the area of the diameter, subtracted from the area of the inner diameter? Or is it more complicated than that? And when it comes to tensile strength, does round/square tubing make a difference? Square is going to give more material in a given width, but how much does the shape come in to play?
Thanks!

#2

For straight tension and compression it is force/area of material. It gets complicated quickly though. You also want to use yield strength with a safety factor and not tensile. Exceed tensile it quickly become broken. Yield strength is where the material will not return to the original shape when the load is removed. (IE bent.)

#3

I’ll leave the actual calculations to someone else (I took a class in this…once…6 years ago…), but as far as the question that I CAN answer:

No. Strength is a property of the material’s composition/forming/production/heat treatment/etc and is independent of shape. I made a post last year with some basic explanations of material properties, that you can check out if you’re interested in it.

Also, compression and tension are different - you have “compression” in your thread title but it sounds like you’re actually talking about tension.

#4

Actually we will be dealing with compression, not tension… thanks for the link, I’ll have to check that out :slight_smile:

#5

Keep in mind that bending loads are what we usually design to, for structural parts. most parts are not loaded strictly in tension or compression (except for things like cables, bolts, etc)

If you give us a little bit more info about what you’re doing, we can probably be more helpful.

But if indeed your part is strictly in compression, then it’s pretty easy…just divide the load by the cross sectional area and that’s the stress. Except that it’s probably applied in a way that does not distribute it evenly, as you probably have fasteners connecting the tube to whatever is pushing on it…so yeah, it is always more complicated than it looks.

#6

The other thing is once something becomes a column it will buckle well below the yield. Then section modulus (shape) becomes important.

#7

Does shape come in to play at that point then? For example, a square tube would be less likely to buckle then a round tube? Or does it again not matter?

#8