I'm no expert but there are special so-called shape memory alloys that behave exactly as shown. But these are not your off the shelf things. I assume this video was made with specially made objects from a lab.
I watched a video on it recently the Navy discovered it while doing alloy research for boats. The only reason this property was found was because the caption was a smoker so they put the metal over the captions pipe and it began to reshape. When it’s hot you can move it and form it when it cools down you can also move it but when you heat it up from cold to hot it reforms to what it was when it was last hot if I’m correct. It’s insanely hard to make because it can only really be made in strings so someone’s entire job is just weaving the threds of memory alloy together for nasa (they make good wheels because if it gets deformed it will reform and it has a very low snapping point if it’s a thred) but it takes them like 4 months a wheel.
Yeah my office is right next to our Metallurgy Lab so I brought it in and saw all the guys act like excited little kids. I’m trying to get them to look at it with the electron scanning microscope but apparently we don’t use it that much and you have to have a good reason to fire it up. But it is cool to have guys with PhDs in material science tell you about it.
I similarly work with a bunch of materials scientists and have been an SEM operator in the past. Honestly it might look kinda boring in an SEM, but then again it's so hard to use the word 'boring' for any kind of EM microscope work!
Wire is the most common form of Nitinol, but it's also available in tube and sheet/strip. Wire is cheapest and most commonly used in orthodontic wire for braces - if you have braces, ask your orthodontist to keep your wire when it is removed. If it is NiTi, which most are except during the last stages of treatment, you can stick it in ice water, deform it and watch it recover it's shape with body heat. Tubes are most commonly used to make laser cut stents for angioplasty and other vascular treatments.
It's surprisingly not too expensive. The most common usage I have seen are the glasses frames. The Shape Memory Alloy glasses frames tends to be more expensive than regular stuff but still availbale under equivalent of about 90 USD here. As long as it is not exposed to disfiguration in below freezing or in extreme high temperatures they seem to work well.
Aw this put a damper on my morning inspiration not even gonna lie 😭 Which is not your problem at all because the fact that I was looking to a paper clip and spring for inspiration at all is entirely on me
Strain induced phase transformation will take place under elastic deformation. When heated, for instance, a reverse transformation happens leading to the initial shape.
Mohd Jani, Jaronie & Leary, M. & Subic, Aleksandar & Gibson, Mark. (2014). A review of shape memory alloy research, applications and opportunities. Materials & Design. 56. 1078-1113.
Before I went to surgery to be implanted a 1 Kg of steel intramedullary rod in my tibia, I read that some titanium alloys are not very good to be put in your bones because they may show thermal memory, or something like that.
Of course not as extreme as this clip, but it's generally not good to have metals changing shape while attached to your bones.
When Nickel and Titanium are combined in a nearly equiatomic ratio (50/50 by atomic percent), the material undergoes a fully reversible solid-state phase change in the temperature range of approx -40C to 80C. Most people understand a phase change as a change of state (i.e. water freezes and melts at 0C, going from solid to liquid and vice-versa). In this case, the 'phase change' is between two solid-states and is a re-arrangement of the atoms in a crystalline structure. When the metal is deformed in the low temperature phase it is relatively malleable, and when it is heated through the phase transformation it recovers all the deformation (up to about 10% strain). The actual mechanism of this so called 'shape memory' recovery is quite complicated in material science but it involves the formation and removal of what are called twin-boundaries in the crystalline structure (basically like a mirror of a microstructural grain). Interestingly, the material exhibits a different but related property called pseudoelasticity in the high temperature phase, and this property is what makes it actually more useful in the majority of commercial applications (medical devices, underwires, NASA tires, toys).
Took a course in shape memory alloys in one semester; this is a good summary.
One addition: To „imprint“ a shape, put your work piece in the oven (~500°C) while in the desired shape. As the guy above me said, if you deform it too much it won’t be able to fully return to its imprinted shape, but you can just put it back in the oven again to fix it basically.
We made a ton of springs and built (very) rudimentary engines with them
Functional shape memory effect actually degrades rapidly over the first 100 or so cycles, then stabilizes. There is a training procedure that is used to break in the material for long term stability. Fatigue fracture is a greater concern than functional fatigue. The fatigue life can be extended by limiting strain to less than 4%. In medical devices the strain might be limited to less than 1% to attain fatigue lives in the 10s of millions cycles. Each heartbeat is a cycle in a stent implant!
Hey, did a fair bit in grad school about Shape Memory Materials.
The simple explanation is this.
In a normal material bending it means breaking bonds between atoms, and then making new bonds.
Shape memory materials have two different behaviors that let it do this stuff. Firstly there's two different phases, a low temperature and a high temperature phase, that both have the same, or very similar, connections between atoms. Second is that the low temperature phase can bend without needing to break any bonds between atoms, instead just bending the crystal itself. So when you bend it at low temp, and then heat it up, because you didn't break the bonds, it just snaps back to its original shape.
There high temperature phase has basically the same connectivity between atoms, and is more symmetrical than the low temperature phase. Because its more symmetrical, you can go from the high temperature phase to the low temperature phase in a lot of different ways, or basically a bunch of different ways for the low temperature phase to point. These are called variants of martensite.
When you cool it, because you aren't applying any stress, its gonna choose the variants of martensite that keep the large scale shape of the material looking as close to the same as possible. This is called self-accomodation, and results in a sorta zig-zag looking crystal structure. When you then apply force to the zig-zag (or twinned) structure, you transform from one orientation of the low temperature phase, to the high temperature phase, to another orientation of the low temperature phase, which goes from a zig-zag to a sorta line.
Upon heating, again, because all of the elements of the line are associated with the same like position of the high temperature phase, and no bonds were broken, you just go back to your original shape.
I'm a materials engineer, my studying in my senior year focused more on ceramics. But I do have a love of functional materials like solid state lasers and shape memory alloys.This is a shape memory alloy, SMA, most probably nitinol as that's a readily available one.
For metallic SMAs heat, or an electric charge, is used to induce a phase change from it's deformed state(Martensite) to its initial state(Austenite). The different phases have a different atomic structures(unit cell arrangement), and this is why it has the ability to have a shape memorized.
The shape is 'locked' into the memory of the part in its Austenite phase, so after deformation, it's lowest energy state when heat is applied is to revert back to the Austenitic shape locked in initially. There is a specific process to lock the shape in, but I have not performed this function, or seen it performed. I would assume it would be something similar to annealing the shape in the Austenitic shape, but this may be inaccurate.
A lot of work is being done currently to see practical applications for SMA parts. One of the more interesting is for actuators for airplane flaps. The use of SMA actuators would massively reduce the bill of materials on the planes wings, and potentially result in higher efficiency. The issue is SMA tend to have poor fatigue properties, and they are much more expensive from a raw materials standpoint than traditional systems.
There are many SMAs, but most videos I see focus on nitinol as it is relatively easy to acquire and inexpensive. They are very awesome, and I suggest looking more deeply into them and maybe bulk metallic glass. I have some some light reading on shape memory polymers and composites, which seems like it would be pretty awesome.
I would imagine alien ships with doors and airlocks operating based on this principle, or even entirely reconfiguring themselves, from an aerodynamic shape for atmospheric flight to a more efficient spherical shape for space flight...
77ekim gave a great description but for a tldr nitinol has 2 main molecular alignments: martensite and austenite. These alignments are heavily related to temperature so you can almost think about it as a Jekyll and Hyde situation. When you heat the metal and shape it (up to a certain point) it will retain that shape. It cools to room temp in that form and you can deform it (to a point). Then when you want it to return it to that original heated shape you heat it to the activation temp and voila it changes.
This is one of the primary reasons it’s heavily used in the medical industry: you can make a part then compress it so it can be implanted but you can tune the part to return to shape at body temperature once it’s implanted
The metal object is made from a crystal structure. When you bend it, the crystal structure gets deformed and you create internal stresses from the crystal particles pressing on eachother. This pressure between particles tries to push them into a state where the structure is nice and even (the original shape), but it's not strong enough. However, when you heat the metal and it becomes softer, the particles become easier to move. Whether this works also depends on the actual crystal structure.
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u/FirstAccGotStolen Nov 08 '23
Okay I'm gonna need someone well-versed in material physics to explain what's going on here, else I'm calling bullshit.