I agree. I was curious what percentages of the ultimate strength it is. Well within. Nitinol is very strong, probably from all the nickel in it.
Note: The muscle force the 0.25 millimeter wire is capable of is, less than 35,000 because it has an area smaller than one inch.
ksi is per inch, MPa is per square meter.
Wire has an area of A=πr^2 or A=1/4πd^2. So the wire will have an area of 1/4π(0.25/25.4)^2 and a total force (TF) of area times 35,000. Or about 2.663 lbs force. Which is phenomenal in its own right.
TF=1/4π(0.25/25.4)^2 •35000 = about 2.663
To get 35000 pounds of lift out of it, the wire would need to be one inch by one inch, square. Then it would take a very large force to prebend it.
See if it gives you 2.663 pounds or 35000? Easy experiment to do.
Simple Nitinol heat engines
Re: Simple Nitinol heat engines
I'll take 2.66 lb for a wire as thick as fishing line.
Easy to bundle together if necessary.
Thicker stuff is available but extremely expensive and probably not suitable for this application. Thinner is better, more responsive, easier to work with.
Thanks for the input and doing the calculations.
I think for what I have in mind I only need a short piece for a kind of "elbow" joint. The rest of the connecting rods can be ordinary metal.
Easy to bundle together if necessary.
Thicker stuff is available but extremely expensive and probably not suitable for this application. Thinner is better, more responsive, easier to work with.
Thanks for the input and doing the calculations.
I think for what I have in mind I only need a short piece for a kind of "elbow" joint. The rest of the connecting rods can be ordinary metal.
Re: Simple Nitinol heat engines
Cool. Excellent. I'd love to play with nitinol.
Re: Simple Nitinol heat engines
I've been getting most of mine from Nexmetal:
https://nexmetal.com/collections/nitino ... 6787624516
The stuff that jumped out of the hot water and across the room was from there.
Most of the stuff on Amazon seems to be from there also, bought in bulk and resold most likely.
You want the shape memory not superelastic most likely, unless you are doing something low temperature.
NASA uses Nitinol "dynamite" to split asteroids
Interesting concept and demonstration.
A small cylinder of Nitinol used instead of dynamite or hydraulics to split rock.
https://youtu.be/GErWFSBlxDg
A small cylinder of Nitinol used instead of dynamite or hydraulics to split rock.
- Compress_20240702_001219_9881.jpg (12.85 KiB) Viewed 3119 times
Re: Simple Nitinol heat engines
I was doing some research to see if anything had been done previously to exploit Nitinols potential use as a heat exchanger material and came across this interesting article:
Nitinol refrigeration
I assume they are using the low temperature "superelastic" Nitinol for this application, which heats up when mechanically bent but cools down as it is released.
For a passive heat exchanger I think the higher temperature "shape memory" would be more appropriate as the phase change could be exploited without any mechanical work input.
During phase change, I assume it absorbs heat when heated and releases heat when cooled.
I don't see any reason why it should not work spectacularly well as regenerator material, if the transition temperature is between the hot and cold side temperatures of the Stirling engine.
Nitinol refrigeration
https://newatlas.com/shape-memory-alloy ... ing/58837/...cooled air at twice the efficiency of a heat pump or three times the efficiency of an air conditioner.
the heating or cooling power of the system is up to thirty times greater than the mechanical power required...
I assume they are using the low temperature "superelastic" Nitinol for this application, which heats up when mechanically bent but cools down as it is released.
For a passive heat exchanger I think the higher temperature "shape memory" would be more appropriate as the phase change could be exploited without any mechanical work input.
During phase change, I assume it absorbs heat when heated and releases heat when cooled.
I don't see any reason why it should not work spectacularly well as regenerator material, if the transition temperature is between the hot and cold side temperatures of the Stirling engine.
Re: Simple Nitinol heat engines
Just my thoughts on this....interesting material I had not seen before.
The tensile strength of this material does not seem relevant. All metals will exert a considerable force when heated if they are constrained and the metal will either yield if UTS is exceeded or the constraints will give way.
For your idea to work you need to know the force a bent piece of Nitinol will exert when heated and is trying to straighten which I would think you will only find by experiment. I suspect that force is quite low and similar to the force that was put into the metal to bend it in the first place (not a lot?). It is not clear to me why the wire straightens when heated. Is there stress in there from the initial bending which the heating releases? Or one side of the wire heated more when plunged into water so get same effect as Bi-metal strip??
The tensile strength is relevant if you use it as a muscle so a straight bit is connected to the crank and rotates the crank as it contracts/extends.
You will have the full force of the wire available which I think Fool calculated to about 2.5lbs. But according to the document you quote, a 25cm length will contract about 10mm which gives about a 4% contraction. So you will need to heat the whole 10" length to get a force of 2.5lbs acting on a 5mm radius on the crank from which you can then work out the torque potentially achieved. I think the trick here would be too find a way of coiling it or something so it occupies a smaller space, or 10 strands 1" long bundled over a heater and then amplifying that movement....ideas needed.
From the video clips and your description it seems quite violent but probably no more so than a small compressed spring being accidentally released (I do this all the time!) I think it is more the suddenness than the actual force created. I think the first clip shows more clearly what is occurring as it just lifts itself out of the jar as it straightens. Second clip more violent and the wire end obviously clouts the end of the jar as it straightens.
I think for me it's the speed of the reaction that is surprising rather than the force.
Hope this makes sense and helps.
The tensile strength of this material does not seem relevant. All metals will exert a considerable force when heated if they are constrained and the metal will either yield if UTS is exceeded or the constraints will give way.
For your idea to work you need to know the force a bent piece of Nitinol will exert when heated and is trying to straighten which I would think you will only find by experiment. I suspect that force is quite low and similar to the force that was put into the metal to bend it in the first place (not a lot?). It is not clear to me why the wire straightens when heated. Is there stress in there from the initial bending which the heating releases? Or one side of the wire heated more when plunged into water so get same effect as Bi-metal strip??
The tensile strength is relevant if you use it as a muscle so a straight bit is connected to the crank and rotates the crank as it contracts/extends.
You will have the full force of the wire available which I think Fool calculated to about 2.5lbs. But according to the document you quote, a 25cm length will contract about 10mm which gives about a 4% contraction. So you will need to heat the whole 10" length to get a force of 2.5lbs acting on a 5mm radius on the crank from which you can then work out the torque potentially achieved. I think the trick here would be too find a way of coiling it or something so it occupies a smaller space, or 10 strands 1" long bundled over a heater and then amplifying that movement....ideas needed.
From the video clips and your description it seems quite violent but probably no more so than a small compressed spring being accidentally released (I do this all the time!) I think it is more the suddenness than the actual force created. I think the first clip shows more clearly what is occurring as it just lifts itself out of the jar as it straightens. Second clip more violent and the wire end obviously clouts the end of the jar as it straightens.
I think for me it's the speed of the reaction that is surprising rather than the force.
Hope this makes sense and helps.
Re: Simple Nitinol heat engines
This thread might benefit from the following Wikipedia link.
https://en.m.wikipedia.org/wiki/Nickel_titanium
Cary on.
https://en.m.wikipedia.org/wiki/Nickel_titanium
Cary on.
Re: Simple Nitinol heat engines
Thanks Fool, helps if I am reading from same hymn sheet. Had to read a few times to start to understand some of that...
This is probably pertinent
"A great deal of pressure can be produced by preventing the reversion of deformed martensite to austenite—from 240 MPa (35,000 psi) to, in many cases, more than 690 MPa (100,000 psi). One of the reasons that nitinol works so hard to return to its original shape is that it is not just an ordinary metal alloy, but what is known as an intermetallic compound."
Apologies for jumping in half cocked.
This is probably pertinent
"A great deal of pressure can be produced by preventing the reversion of deformed martensite to austenite—from 240 MPa (35,000 psi) to, in many cases, more than 690 MPa (100,000 psi). One of the reasons that nitinol works so hard to return to its original shape is that it is not just an ordinary metal alloy, but what is known as an intermetallic compound."
Apologies for jumping in half cocked.
Re: Simple Nitinol heat engines
The declassified document is a bit of a "red Herring" as it only discusses force due to change in length
Re: Simple Nitinol heat engines
The 50 Tons (or whatever) per square inch is "the force a bent piece of Nitinol will exert when heated and is trying to straighten".
Nothing to do, really, with tensile strength.
Re: Simple Nitinol heat engines
I haven't really read that whole paper through in detail, but from the video,
https://youtu.be/vFAdkM5IZa4. (6:20)
they were experimenting with "stretching" the nitinol rather than bending. So when heated to its phase change temperature it would elongate (or shrink) lengthwise.
Re: Simple Nitinol heat engines
I haven't read this yet, just waiting for it to finish downloading now:
Proceedings of the NITINOL Heat Engine Conference, 26-27 September 1978, Silver Spring, Maryland
https://archive.org/details/DTIC_ADA108973/mode/1up
269 pages. Might contain something interesting. Or not.
Proceedings of the NITINOL Heat Engine Conference, 26-27 September 1978, Silver Spring, Maryland
https://archive.org/details/DTIC_ADA108973/mode/1up
269 pages. Might contain something interesting. Or not.
Re: Simple Nitinol heat engines
I've been thinking that the 90° driven oscillator advance probably applies to a Nitinol engine as well.
viewtopic.php?t=5683
At least the reciprocating type, such as illustrated in the introductory post.
viewtopic.php?t=5683
At least the reciprocating type, such as illustrated in the introductory post.
Re: Simple Nitinol heat engines
This might be useful. Just checking out uk suppliers . This one is on eBay but American and seems to give most information:
Nitinol Shape Memory Wire (SMA)
1.0 mm 40ºC Af, quantity = # of feet (single wire any length)
3-4 days delivery in USA; ships from California
a.k.a.: muscle wire, magic wire, shape memory alloy
Wire moves/straightens when heated to specific temperatures
Relaxes and becomes more pliable when cooled
Nitinol (an alloy of nickel and titanium), properly formulated and heat treated to react and change shape when heated.
All our wires are stocked on spools (not pre-cut) and we cut to the length of the order.
General Characteristics
The wire is very smooth with a lustrous dark coating on the outside. Light reflecting off of it sometimes appears in rainbow colors. Inside, wire is silver color. Cutting thicker diameter wire (1mm and especially 2mm) requires a good pair of cutting pliers. Nitinol is very abrasion resistant. It will slip and slide along itself. It will not react with most chemicals, will not corrode, and is non-allergenic.
The transition temperature indicated is the wire's As (austenite start) temp. The change in the crystal structure takes place over a gradient of approximately 10 degrees. The hotter the temperature that the wire is exposed to, the faster and more dramatic the effect. For example, dropping a coiled up piece of 60º 2mm wire into boiling (100ºC) water will make it jump out faster and with more force than dropping an 80º wire. However, at room temperature (25 - 35ºC if you're in a hot climate) the 80º wire will be much more flexible than 60º and especially 40º wire.
Varieties
This listing allows you to choose the transition temperature of the wire. There is a dramatic difference which alloy you use because they are sensitive to the surrounding temperatures. Click here for all available wires on one page.
NiTi (SMA) stock availability chart
15 ºC 30 ºC 40 ºC 50 ºC 60 ºC 70 ºC 80 ºC
0.5 mm x x x
1.0 mm x x x x
2.0 mm
x x x
15ºC wire: this is a difficult to use wire unless your application cycles to close to freezing temperatures. The wire is stiff and straight like spring steel at room temperatures. Place it in a fridge, and it will transform to a loose pliable wire that is easy to bend, like a cord. As you hold it in your hands outside of the fridge, it will return to its straight stiff shape as it warms up. Available in 1mm.
30ºC wire: excellent characteristics for applications in colder climates where the ambient temperatures are below 20ºC. It can be activated with very little heat, possibly even body heat for neat tricks. Available in 1mm.
40ºC wire: our most popular and recommended alloy. Recommended if you are new to nitinol for general experiments, demonstrations, etc. Available in 0.5mm (thin but strong), 1mm (very versatile), and 2mm (super strong, maybe could lift a car).
50ºC wire: an excellent choice for 0.5mm wire instead of the 40ºC if you are in a hot climate and want the wire to be more pliable before it's activated. Available in 0.5mm.
60ºC wire: an excellent all-around choice for 2mm wire, with a balance between fast activation at sub-boiling temperatures and flexibility at room temperature. Available in 2mm.
70ºC wire: This is the same as our 1mm 80ºC wire, however, due to its thinner diameter, it activates at a lower temperature, so it is referred to as the 70ºC.
80ºC wire: Our highest temperature alloys that remain the most pliable at room temperatures. Suitable for higher temperature activation (100ºC+). Available in 1mm and 2mm.
Memory v. Superelastic: This listing is for the "shape memory alloy" (SMA) type wire (which moves/changes crystal arrangement when heated/cooled). It is also known as muscle wire. There is another type, called "superelastic". Superelastic NiTi, sometimes called fishing line, is similar to activated memory wire (for example, the 15ºC wire at room temperatures), but it remains that way at most temperatures (except very cold, e.g., -10ºC and below). It can stretch like a rubber band substantially without plastic deformation. We also have superelastic in stock in 0.5mm, 0.8mm, 1mm, and 2mm under a separate listing.
Suggestions
Our most popular wire is the 1mm 40ºC wire. It remains pliable at typical room temperatures and will straighten out very quickly when heated, without requiring the need to use dangerously hot temperatures such as boiling water. For colder climates, if your ambient environment will not exceed 20ºC, we recommend the 30ºC 1mm wire instead for even better performance.
Lower temperature wires tend to exhibit more strength. For example, the 15ºC alloys will react with much more force when heated. However, they should be much colder before activation, ideally close to freezing. Otherwise, they will already be partially engaged and the effect will not be as dramatic.The 2mm wires are very stiff when fully austenite (activated). Our most popular 2mm wires are the 60ºC and the 80ºC. If you like the 1mm 40º wire, substitute with a 60º if using 2mm because the 40ºC 2mm will be too stiff, unless the temperature is below 30ºC.
At Cold&Colder, we specialize in environmental control systems. We use the materials we sell and have an in-depth knowledge of their characteristics. Any advice or consulting is always free and a click aw
Nitinol Shape Memory Wire (SMA)
1.0 mm 40ºC Af, quantity = # of feet (single wire any length)
3-4 days delivery in USA; ships from California
a.k.a.: muscle wire, magic wire, shape memory alloy
Wire moves/straightens when heated to specific temperatures
Relaxes and becomes more pliable when cooled
Nitinol (an alloy of nickel and titanium), properly formulated and heat treated to react and change shape when heated.
All our wires are stocked on spools (not pre-cut) and we cut to the length of the order.
General Characteristics
The wire is very smooth with a lustrous dark coating on the outside. Light reflecting off of it sometimes appears in rainbow colors. Inside, wire is silver color. Cutting thicker diameter wire (1mm and especially 2mm) requires a good pair of cutting pliers. Nitinol is very abrasion resistant. It will slip and slide along itself. It will not react with most chemicals, will not corrode, and is non-allergenic.
The transition temperature indicated is the wire's As (austenite start) temp. The change in the crystal structure takes place over a gradient of approximately 10 degrees. The hotter the temperature that the wire is exposed to, the faster and more dramatic the effect. For example, dropping a coiled up piece of 60º 2mm wire into boiling (100ºC) water will make it jump out faster and with more force than dropping an 80º wire. However, at room temperature (25 - 35ºC if you're in a hot climate) the 80º wire will be much more flexible than 60º and especially 40º wire.
Varieties
This listing allows you to choose the transition temperature of the wire. There is a dramatic difference which alloy you use because they are sensitive to the surrounding temperatures. Click here for all available wires on one page.
NiTi (SMA) stock availability chart
15 ºC 30 ºC 40 ºC 50 ºC 60 ºC 70 ºC 80 ºC
0.5 mm x x x
1.0 mm x x x x
2.0 mm
x x x
15ºC wire: this is a difficult to use wire unless your application cycles to close to freezing temperatures. The wire is stiff and straight like spring steel at room temperatures. Place it in a fridge, and it will transform to a loose pliable wire that is easy to bend, like a cord. As you hold it in your hands outside of the fridge, it will return to its straight stiff shape as it warms up. Available in 1mm.
30ºC wire: excellent characteristics for applications in colder climates where the ambient temperatures are below 20ºC. It can be activated with very little heat, possibly even body heat for neat tricks. Available in 1mm.
40ºC wire: our most popular and recommended alloy. Recommended if you are new to nitinol for general experiments, demonstrations, etc. Available in 0.5mm (thin but strong), 1mm (very versatile), and 2mm (super strong, maybe could lift a car).
50ºC wire: an excellent choice for 0.5mm wire instead of the 40ºC if you are in a hot climate and want the wire to be more pliable before it's activated. Available in 0.5mm.
60ºC wire: an excellent all-around choice for 2mm wire, with a balance between fast activation at sub-boiling temperatures and flexibility at room temperature. Available in 2mm.
70ºC wire: This is the same as our 1mm 80ºC wire, however, due to its thinner diameter, it activates at a lower temperature, so it is referred to as the 70ºC.
80ºC wire: Our highest temperature alloys that remain the most pliable at room temperatures. Suitable for higher temperature activation (100ºC+). Available in 1mm and 2mm.
Memory v. Superelastic: This listing is for the "shape memory alloy" (SMA) type wire (which moves/changes crystal arrangement when heated/cooled). It is also known as muscle wire. There is another type, called "superelastic". Superelastic NiTi, sometimes called fishing line, is similar to activated memory wire (for example, the 15ºC wire at room temperatures), but it remains that way at most temperatures (except very cold, e.g., -10ºC and below). It can stretch like a rubber band substantially without plastic deformation. We also have superelastic in stock in 0.5mm, 0.8mm, 1mm, and 2mm under a separate listing.
Suggestions
Our most popular wire is the 1mm 40ºC wire. It remains pliable at typical room temperatures and will straighten out very quickly when heated, without requiring the need to use dangerously hot temperatures such as boiling water. For colder climates, if your ambient environment will not exceed 20ºC, we recommend the 30ºC 1mm wire instead for even better performance.
Lower temperature wires tend to exhibit more strength. For example, the 15ºC alloys will react with much more force when heated. However, they should be much colder before activation, ideally close to freezing. Otherwise, they will already be partially engaged and the effect will not be as dramatic.The 2mm wires are very stiff when fully austenite (activated). Our most popular 2mm wires are the 60ºC and the 80ºC. If you like the 1mm 40º wire, substitute with a 60º if using 2mm because the 40ºC 2mm will be too stiff, unless the temperature is below 30ºC.
At Cold&Colder, we specialize in environmental control systems. We use the materials we sell and have an in-depth knowledge of their characteristics. Any advice or consulting is always free and a click aw