It would be made from spring steel, say coat-hanger diameter, in s specific shape. Key to its use would be it could be bent in one way to deploy it, but it would revert to its original shape.
What controls how much it can be bent without altering the final shape?
How is such made? I assume it's a combination of steel formulation and post-manufacture heat treating; true?
The modulous of elasticity for most grades of steel is the same (29x10^6) What varies is the amount it can be bent before it takes a permanent set in the new shape. So you are looking for a steel with high yield strength.
I'd suggest heading to the local hobby shop or well stocked hardware store, ask for 'music wire'. It comes in 36" lengths, can be bent to take a shape, is about as springy as you can get without special alloys or special heat treating. Make the shape you are looking for, see it the music wire will do the job for you.
If so, your local wireform place can make them by the milli> I'm envisioning a gadget I can see a use for....
The simple answer is that the amount it can be sprung is a function of its yield strength.
Springs like you're describing fail in one of two ways: they exceed their elastic limit, which is another way of saying yield strength, and then take a permanent bend that doesn't fully recover. Or they break.
Yes, your assumptions about steel grade and heat treatment are correct. If you're pushing your spring pretty hard, finding the right material and treatment can be a real challenge. If you're well within the elastic limit of ordinary carbon steel that's hard-drawn, such as music wire, you'll find the task to be an easy one. And everything in between, etc.
Any spring should return to its original shape if you don't exceed that limit. Some will break before you bend them far enough. Some will eventually get weaker and lose some of their ability to spring back. How many millions of cycles are you thinking of? And if not millions, what?
You could experiment with Music Wire, or study Statics to learn the mathematical principles of deformation. Music wire can be bent to shape cold but not necessarily annealed and then heat-treated back to the original condition. Spring tempering is a tricky art if you don't have the right expensive equipment.
As Ed mentioned the modulus of elasticity is pretty much the same for all steels. What makes a difference to how far you can bend something before it yields is the ratio of the modulus of elasticity and the yield strength of the material.
Heat treatment and high carbons increase the yield strength, until eventually the material snaps instead of permanently bending. But they don't significantly change the modulus of elasticity.
Y'know, I could envision some things (a basket-shaped stent, for instance) that could be done just with the right temper of material. But at some point, yes, you need shape memory alloy.
I want to get some sometime, just to play. Small parts carries shape memory wire, and I think it's really cool that you can make a part at one temperature, wad it up into a ball at another temperature, then cool it down and have it spring out in the original shape.
Ahh, thank you. I didn't think "yield strength" when bending up a coat hanger in the shape I needed.
Dozens, I guess. It would be a seldom-used hand tool, to reach in and "give a hand" somewhere no hand [save Thing, I guess..] could be.
But you'd have to bend it a different way to get it in there and out, later. Hence my query re: original shape. Something with the flexibility of a Slinky might do the job.
OK, so the long-term ability of the material to hold up is not an issue. You can use practically any steel that has the required strength.
I'm not visualizing this, but if you're saying you have to bend a round bar one way and then the other way, the material will bend to the same degree either way. If you're trying to trigger a return to a specific shape, you'll note the references to shape-memory alloys. They're triggered by specific temperatures, and they don't sound to me like what you're looking for.
Why don't you go down to your local hobby shop and buy a few pieces of music wire, and try them out? It's a cheap way to see what you're dealing with. You can bend it without breaking, but the material has pretty good spring properties. Standard music wire is available in diameters up to 1/8". There are some suppliers who make it in larger diameters but the larger the diameter, the weaker the steel.
That's because it's very high-carbon steel that's work-hardened by drawing, not by heat-treating. Strength of music wire is inversely related to its diameter. But its strength is pretty high. It's a nice, simple material from which to make medium-performance springs.
Metals work-harden when bent or stretched beyond their elastic limit. That's why you can bend but not completely straighten a paper clip with your fingers. Each new bend will be in a different place. Coat- hanger-sized music wire may be too difficult to bend accurately by hand. Try gas welding rod, which is similar in initial strength to a coat hanger but readily available in 3' lengths. You still won't be able to bend and straighten it again very well, or more than a few times. Soft black iron wire, like baling wire, might last longest. It isn't nearly as stiff as the welding rod or a coathanger.
I just tried bending 1/16" welding rod and soft black iron wire 90 degrees and back in a vise. I'm not going to sacrifice an irreplaceable old coathanger for you. The welding rod snapped off at the 4th bend. The soft wire started to weaken at 10 and cracked at 16. These were very sharp bends around the vise jaw. Your mileage (and the properties of the particular batch of steel you buy) may vary.
I can not find the small parts catalog atm. How pricey is that stuff?
Wes
-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
-- "Additionally as a security officer, I carry a gun to protect government officials but my life isn't worth protecting at home in their eyes." Dick Anthony Heller
No, I need it to be one shape, say, oh, a S-curve 2 inches wide, and 4 tall. But the access hole is ~0.75" dia. so you have to straighten it to fit inside. Then it reverts to S. You do your magic. You pull it out again, and it again is S shaped. You store it.
And no, this is no Slim-Jim. I own one somewhere, however.
Oh, then that's either a shape-memory alloy, or something you hold into one shape and then let it spring into another. For example, sliding the S-shaped spring into a 5/8" tube to get it into the entry hole, and then sliding the tube back out when the spring is inside.
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