Why are metals so stretchy? (2^13 sub special)

this piece of metal that's you know all bowed out and whatnot started as a flat sheet and it was literally stretched into this shape and if you sort of think hard about it stretching a solid object is weird especially a crystalline object like a metal like where are all of the atoms going in a piece of metal when you stretch on it and force it into a new shape it's actually pretty incredible and it's given me the excuses if i needed one to do one of my all-time favorite material science demonstrations that i've never actually done or seen in person and it dates back no joke to 1952. [Music] years ago i set a ridiculous arbitrary task of making a new youtube play button out of a different material using a different fabrication technique every time that the channel subscriber count doubled and now very suddenly it's time for 2 to the 13. and i have that right here this play button is made out of embossed copper foil that i stretched out into the compound curve that is the youtube play button shape copper like this roll of foil is a very soft metal it's known for its malleability the ability to deform when compressed and its ductility the ability to deform under tension i first heard of copper embossing as an artistic technique like back in grade school art class and basically you just get a thin sheet of copper place it on a moderately soft surface like a stack of paper and slowly push designs into the metal with a blunt wooden or plastic object using this technique you can build up some really intricate designs which are awesome but it's not just leaving marks on the metal surface it's actually permanently deforming the foil making the sheet thinner to allow for the extra surface area and if you're pushing the copper into a surface you can actually squeeze the metal out from under the tip of what you're pushing with but if the copper is suspended in the air like this most of the deformation happens under tension if you're pushing on the copper here you're actually pulling on it here and here stretching it out and making it thinner this leads to an interesting question how can metals stretch metals have very well defined crystal lattices that means that all of the atoms that make up a metal need to be in really specific places how are those atoms moving such that they're maintaining this pattern inside the material but the shape of the material is changing despite the fact that humans have been using metals for thousands of years how they actually bend was a question that was still perplexing scientists less than a hundred years ago they were imagining that if you have some big ordered array of atoms and you try to shear that array of atoms that you basically need to lift half of the crystal and then move it and then set it back down and that lifting of the crystal takes so much energy they thought that it was basically never gonna happen they were calculating that metals should have been like a thousand times stronger than they actually were like metals are soft and all the math said metal should be really really hard in 1934 there were actually three separate scientists working on this problem that independently hit upon the idea of a dislocation which basically was what if instead of shifting the whole plane the crystal just sort of rippled so this was an actual physical shape a defect inside of a crystal that was invented to make the math work out properly and it wasn't until 1956 when somebody decided to put a chunk of metal into a transmission electron microscope and saw a dislocation it's a huge gap between we think this thing might explain the math and oh yes we see it imagine if you're trying to deform a cube and you need to shear the top of that cube with respect to the bottom if you drag the whole surface at once it's a lot of energy that's like and bear with me for a minute trying to drag a carpet across concrete there's just too much friction and it requires a lot of effort to drag that around but if you can add a ripple to the carpet that ripple can move very easily and when it reaches the far edge you'll notice that the whole carpet has actually shifted just a little bit and if you send a lot of ripples you could imagine that you could get the carpet to just keep moving along the sidewalk but you never actually have to drag the carpet along the sidewalk it's just rippling alright so we're almost there this is about to be the fun demo time this demo is from sir william lawrence bragg who can i would think accurately be described as the father of x-ray crystallography he earned a nobel prize when he was 25 feeling inadequate and apparently he likes to play with bubbles so here i have prepared a bath of soapy water and i've got a bike pump with a water bottle that is providing a constant downforce and at the end of the pump i have a glob of hot glue and pla that is forcing all of the air to come out of one extremely tiny hole this setup makes tiny bubbles but most importantly and this was sort of a pain to get right tiny bubbles that are all exactly the same size when these bubbles stick together the awesome thing is that they just naturally order themselves into this beautiful hexagonal lattice a material scientist would call this 2d hcp for two-dimensional hexagonal close pack i could talk about crystal symmetry for hours but right now just know that there are loads of materials that make structures like this in the real world and this lattice can play host to all sorts of real crystal defects including dislocations it's honestly just a lot of fun to play with this this thing right here is a vacancy and i can poke it with a needle and i can get the vacancy to move by sliding new bubbles into the spot where the vacancy used to be but what we really want to know is what happens to the atoms when you stretch a metal when you stretch a crystal an object so here i've got these two chunks of packaging foam and like a fork that i can use to sort of smoosh the bubble raft this is really technical stuff or wait let's be a little more technical put the bubble raft under compressive or tensile stress so when we push on a malleable material it sort of compresses without breaking and without losing its crystallinity and if we push on the bubble raft we can see that the whole shape of the raft the outline of the bubble raft is actually changing but if you zoom in they're all still hexagons it's still a crystal and if you look very closely you can see little dark lines zipping back and forth through the structure at really specific angles those are dislocations those are little carpet ripples propagating through this raft of ordered bubbles so let's take a closer look this is a dislocation and i have been describing the dislocation as basically a ripple which would make it sort of look like this but what's more common in the material science world is to describe a dislocation based on where there are too many atoms we say that this is the extra half plane because there's basically a bonus row of atoms here that doesn't fit anywhere when the carpet ripple reached the edge of the carpet the whole carpet had sort of moved just a little bit like one ripple length and every time that a dislocation reaches the edge of the bubble raft the entire raft has sheared by one bubble's width if we zoom out and look at the whole bubble raft you can see that these dislocations are absolutely everywhere there's oodles of them zipping back and forth through the crystal you know all doing their own thing just trying to move one atom so every dislocation only makes a tiny change but there are so many defects in any given crystal that the sum of their motion can actually produce really dramatic changes in shape all without sacrificing the crystallinity of the material the atoms or here bubbles always remain ordered into this little hexagonal grid so i only actually saw this demo a couple years ago in a grad lecture and my jaw kind of hit the floor because you can imagine that in an actual metal i mean this is what's happening this bubble raft demo is so good and so accurate that they were using it to study dislocation behavior before anybody had ever actually seen a dislocation instead of you know 10 dislocations in a bubble raft if you take a chunk of metal and you bend it there's going to be billions or trillions of dislocations that are zipping back and forth each of them only moving the metal by one atom but there are so many and the force that you exert on the metal causes all of those dislocations to work together to literally bend the metal to your will these zillions of tiny dislocations are diligently trudging through the crystal carrying with them a tiny little bit of plastic deformation so how do we make use of this well i need a new play button and i want to make it out of an extremely malleable and ductile metal copper because i'm not the best at freehand metal embossing i cheated and i printed out some forms that i could use that already had the perimeter of the play button pre-dimensioned for me and i literally bolted a chunk of foil into this frame that i printed out and then very slowly so that i didn't rip through the metal i used this sort of plastic pencil that i had also printed to push the metal out and every pass of the tool stretched the metal and made it bow just a little bit farther i was actually able to push this a lot farther than i anticipated i thought it was just going to rip pretty quickly after i started doing this but it was over a large enough area and i was looking for a smooth enough deformation that i was actually able to stretch it really far to make a little triangle in the middle i cheated again i used a different form that i'd printed out basically just so that i had something to push against while i was trying to draw this triangle on the surface so with the button bowed out and the little triangle logo pushed in i had the shape of a youtube play button but now i had a very very thin fragile piece of copper so i needed to reinforce this structure once i'd made it and for better and worse i decided that the best way to accomplish this was by filling the entire button with hot glue the really interesting thing about this is that because the button is made of copper and copper is a great thermal conductor basically all of the glue that i poured into the button was able to remain molten and formed a contiguous pool so it actually looks really nice and neat the bad news is that i was using the glue gun on its hottest setting and also dripped some straight out of the gun onto my leg but in the end it worked so we're going to ignore that part and fast forward to cutting out that button that has been newly reinforced using a little bit of super glue to attach a 3d printed border that i could use to stick the button to a back plate and then actually cutting that back plate out on a laser cutter at the santa barbara hackerspace giving it a couple coats of polyurethane and then assembling all of the pieces together so this is going to replace the old play button but it's right now it's still not glued together and it smells like polyurethane so i'll take some close-ups of it tomorrow but basically making a new play button is just that easy i need to extend an entire thank you to steve mold who after i talked to last week gave me a shout out in his recent video about peltier coolers i am working on a video that involves peltier coolers what i want to try to do is grow really large single crystals of water and try to get faceted off edges so you're actually growing big hexagons but i'm not sure that that's going to work for a couple of different physics e reasons if i do get it to work it'll be great if i don't get it to work i will at least make a video and explain to you why it's really hard and i would also like to thank all of my subscribers who have been watching my videos over the last couple years and providing great feedback and motivation and a welcome to all of the new subscribers that have just joined in the last couple days i really hope you enjoy it here i have a lot of fun making videos and it's wonderful like reading all the comments that have come in in the last couple days is just so energizing and making me want to work on the channel more and it's lovely so thank you since it may end up being a little sooner than i was originally planning i am now accepting suggestions for how to make the 2 to the 14 play button if anybody has ideas i would be all ears [Music] you

Channel: AlphaPhoenix

Views: 437,382

Keywords: Alpha, Phoenix, Alpha phoenix, Alphaphoenix, Materials science, crystallography, physics, chemistry, science, investigation, Crystals, defects, vacancy, interstitial, substitutional, dislocation, Plastic, elastic, deformation, bending, stretching, ductility, malleability, compression, tension, Bragg, xray, Bubble, raft, demonstration, DIY, atoms, atomic defect, Soap bubble, Education, teaching, grad school, university, high school

Id: sn1Y6zIS91g

Length: 13min 49sec (829 seconds)

Published: Mon Aug 17 2020

Reddit Comments

[u/Alpha-Phoenix]

Hey r/physics! I'm a materials science PhD student, and over the weekend I got to set up my favorite materials science demo, that I'd only ever seen before as a grainy black and white movie from the 50s. Before scientists could see atoms in microscopes, they used models like this raft of bubbles to understand how defects called dislocations wander through crystals to produce plastic deformation and bend the material. I hope you think it's as cool as I do!

[u/chewbacchanalia]

Literally studying this right now for my Material Science final tomorrow!

[u/Hostilis_]

This was really awesome dude, great work

[u/InAFakeBritishAccent]

Would be amazing to have a 5-10k particle simulation widget that allows you to play with this and drop in different size spheres.

I'm not sure if anyone is familiar with Falstad but he seems like a person who would do this.

I think processing can handle a simplified energy calculation for each particle now, no? I could be wrong.

[u/birdiesnbritts]

Subscriber! Your videos are amazing! Your passion and enthusiasm always make my day.

[u/Tar_AS]

If there were lectures on solid-state physics like this in my University, I would visit them definitely.

[u/-Alchem1st-]

Your channel is underrated. I hope you get to millions. Keep the good work up.

[u/MistyThree941]

Thanks! This was really awesome, great job

[u/CwColdwell]

I subscribed after the Steve Mould shoutout and watched this last night!