You got it! And a lot faster than most people get that point. It's kind of counter-intuitive.
There are several people here who are good at that sort of thing. You'll get some help.
Very close. As Carl said, the various alloys of steel are very close in terms of Young's modulus, which is the value you're dealing with.
You're quite welcome.
--sp
You can buy a 24" length of hardened steel as a "bell hanger" drill bit to experiment with and confirm that you are applying the formulas correctly.
-jsw
Straight from the horse's mouth.
AFAIK the physics behind it is that the Young's modulus is about how the atoms interact wherever they may be in the crystals, and the ultimate strength is about how readily the individual crystals (or perhaps planes within the crystals) can slip -- and carbon atoms tend to "pin" the crystals (or crystal planes -- see how little I know?) to one another.
(Everything everyone else said about material properties was accurate: I can't add to it)
I'm not sure what site you're posting through, but this is an unmoderated USENET newsgroup, so there's no administrator in the web forum sense. Moreover, if I'm correct your posts are now distributed around on multiple servers, so there's no way to unsay anything.
The lack of moderators is why you see so much political crap on this group, unless your site has really good spam filtering.
Thank you, Tim. That's a *big* help.
As for strength, yes, you're on the right track. The martensitic crystal phase creates a pre-strain between the crystals, and that keeps them from slipping as easily.
But I have no clue about stiffness. It's something going on deeper than any materials discussion I've read, or that I recall, anyway. I read a ton of this stuff when I was materials editor at American Machinist, but that was 34 years ago.
Well, I can't help thinking that what the OP really needs here is very high carbon steel - so high carbon it's not got any iron and is not, in fact, steel, but rather, carbon fiber, which is quite stiff, as materials we actually have available go.
And/or a much larger diameter rod, which may require a better design of whatever this is - certainly if going to 10 feet I don't think there's
*any* 3/8" rod that will even resemble "stiff" unless there's also a robust frame and the rod can be put under great tension.
Those bits also have a convenient hole from which to hang your test weights. But, are they really hardened for their full length? Most drill bits are not hard at the chuck end, so that the chuck jaws can get some bite.
A file will show the difference.
-jsw
Awesome clarification. Thank you.
Hi Carl!
Wow, great information -- I'm a biologist so this engineering is fascinating but elusive to me!
We have a similar problem, and I was wondering if you could lend your expertise:
We have a 1inch tube (25.4x3mm) at 3000mm length. It currently "sags" and we need to improve its rigidity. We can changer the diameter if needed, but I'm looking for a steer on what would be the best way to ensure high levels of rigidity over that distance, either tube or rod. any thoughts?
Many thanks in advance
Hi Carl!
Wow, great information -- I'm a biologist so this engineering is fascinating but elusive to me!
We have a similar problem, and I was wondering if you could lend your expertise:
We have a 1inch tube (25.4x3mm) at 3000mm length. It currently "sags" and we need to improve its rigidity. We can changer the diameter if needed, but I'm looking for a steer on what would be the best way to ensure high levels of rigidity over that distance, either tube or rod. any thoughts?
Many thanks in advance
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All types of steel regardless of hardness have the same elastic constant, so changing the material won't help. A thicker wall will increase stiffness somewhat, but the best simple answer is likely to be increasing the diameter. Since your length is more than 8' I suggest 1-1/2" or 2" by 10' EMT electrical conduit (from a big box hardware store) if you can tolerate the diameter. The trade size is a nominal value related to water pipe, actual dimensions are different. You can attach to it with hanger hardware or perforated pipe strap.
The Area Moment of Inertia is a measure of stiffness, to compare different geometries or calculate the sag from loads.
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Oh, you are in Britain. The same reasoning applies for whatever you have easily available for larger diameter steel tubing. In the USA electrical conduit and chain link fence posts are cheaper than water pipe of the same nominal size because they have thinner walls, and may be suitable for structural use. I'm not a mechanical engineer and can't figure the safe loading for you.
1 inch X5/16 wall DOM tubing would be one of the best solutions if you need to stay with one inch. 1 inch by 1/4 wall 4130 electric welded tubing will likely be about the same price - trading off mild steel for alloy vd the extra cost of mandrel drawn (which you don't need the bore accuracy of). - or if you can go larger go to 1 1/2 inch 4130 or 1 1/4 inch DOM. Tubing has better bens strength than bar stock and weighs a bit less - contributing less to the sag - - -
1 inch X5/16 wall DOM tubing would be one of the best solutions if you need to stay with one inch. 1 inch by 1/4 wall 4130 electric welded tubing will likely be about the same price - trading off mild steel for alloy vd the extra cost of mandrel drawn (which you don't need the bore accuracy of). - or if you can go larger go to 1 1/2 inch 4130 or 1 1/4 inch DOM. Tubing has better bens strength than bar stock and weighs a bit less - contributing less to the sag - - -
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That's another good approach depending on your size versus cost constraints. The thicker wall increases bending stiffness, the more expensive chrome-moly
4130 gives a higher overload safety factor though it bends the same as mild steel of the same dimensions.A possible problem with non-stocked, special-ordered material is that you may have to pay for an entire standard length plus a cutting fee or spend time searching for remnants. My stock of 1" 4142 solid rod was a specialty metal supplier's leftover remnant and the discounted price was still $100, about 10 years ago. It rusts readily in humid areas, which is why I suggested galvanized tubing.
Aluminized steel or stainless car exhaust pipe from a custom fabricator may be the quickest and easiest to find.
As Jim and others say: number-one approach - increase the diameter.
I'll add a complimentary comment. Does the section have to resist local buckling? This is a crucial issue in engineering. Sometimes with something like an aeroplane weight it crucial and you have to accept structures where if they buckle "that's it" - they are finished. For buildings and static steel structures you aften ensure that the sections will keep "distributed" bending and will never buckle.
You will have to look-up about this. For commercial steel sections it's the "Class" of a section.
As Jim and others say: number-one approach - increase the diameter.
I'll add a complimentary comment. Does the section have to resist local buckling? This is a crucial issue in engineering. Sometimes with something like an aeroplane weight it crucial and you have to accept structures where if they buckle "that's it" - they are finished. For buildings and static steel structures you aften ensure that the sections will keep "distributed" bending and will never buckle.
You will have to look-up about this. For commercial steel sections it's the "Class" of a section.
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That's a good point. As you increase the diameter and decrease the wall thickness of tube to increase stiffness without raising cost/weight too much the wall becomes vulnerable to indenting and buckling (sudden collapse) from concentrated stress of a load hanger, especially if it makes only point or line contact at the top. A strap reduces the concentration and a rigid pipe hanger that keeps the side walls from bulging is even better. The end supports are less of an issue because there's no bending stress there. The ends can even be flattened and drilled for a bolt.
Buckling failure is different from tension or compression failure where the metal's strength is exceeded. Buckling depends on its stiffness, resistance to bending, and becomes more likely as unsupported length increases. A wooden meter stick is easy to bend by hand though a short section of it isn't. A good example of the failure is a beer can that is very strong when filled because the internal pressure resists denting. When empty it's still fairly strong unless dented, then hand pressure can crush it flat.
Commercial tubes meant for structural strength, such as chain link fence posts, have a wall thickness around 1 to 1.5mm which resists accidental dents but allows intentional bending. I didn't mention fence posts because in the USA the commonly available ones are less than 3 meters long. Thin-walled electrical conduit is similar and sold in 10 foot lengths. Fence posts have the same outer diameter as water pipe, conduit the same inner diameter which means that their fittings and rigid hangers are different. Some combinations telescope together. Car exhaust tubing has similar walls and is sized in even fractions of an inch in the USA while water pipe, fence posts and conduit aren't, neither inch nor metric in the smaller sizes.
Yesterday I machined custom stainless flange repair fittings for exhaust tubing that measured 1.997", though it was original equipment on a vehicle made in Japan. The original (plain steel?) flange that connects the engine outlet to the converter had rusted completely off, leaving only the fillet weld which must have been stainless like the tube. I made a stainless two piece split flange that fit snugly upstream of the fillet and a solid flange to back up the graphite donut gasket below the fillet. Nuts on the spring bolts tightened the solid flange against the gasket and slightly opened the joint where the tubes contacted, allowing the springs to seal the gasket.
The exhaust leak past the unseated gasket had been very easy to find because it dripped and sprayed condensed water after a cold start. At first the gasket had appeared to seat from a tight fit on the tube but heat and pressure moved it until the tubes touched instead. I didn't know what to look for at first because I thought that area was all stainless and good for life. I had replaced the catcon only because its rear flange had rusted away enough to allow a leak.
In college while under-aged we "allowed" cider to ferment naturally.
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