Self organising steel balls explain metal heat treatment

TL;DW - Top video great, absolutely show in class...second video mathematical diversion, not efficient use of class time, good math...third video between the two - more mathy but more tightly edited and efficient and material-science-course tied)

I'm posting all three of these videos together because they're part of a series that Steve Mould made (with help on the lower two) exploring ball bearings and ball-pit balls as crystalline modeling tools.

In the above one, Mould makes a really fancy version of our ASM BB board (we use CD cases and airsoft pellets - he uses plexiglass and metal bb's, more akin to the Atomix toy of yesteryear). If you want to make something like his fancy version, here are a couple of links to check out.

Mould uses the BB board the same way we use it in class: to discuss grains, grain boundaries, heat treating etc in crystalline metals. He places the BB board on a shaker to model adding energy via heat (and there's a brilliant view of vacancy defects moving through the crystal at 2:27 and again at 2:35). Mould then discusses how the crystalline structure he's modeling affects the macroscopic properties (hardness, toughness, strength, etc) of the metal.

Honestly, it's a great explanation of about half a day of summer camp, even admitting that his model is limited in exactly how accurate it is compared to more complicated reality. He mentions a couple of videos that go further. I've already posted one and will look at the other.



The second video is Mould and Matt Parker going through to find the most efficient packing for spheres - using ball pit balls. They then shift from tetrahedral packing to a more square packing - which turns out to be exactly the same (check the below video to see that they're the same). 

I'll warn you that the second video is a lot less professionally laid out and more heavily math-leaning. (There's a slightly more organized video that shows about the same content.) But Mould and Parker do cut a whole bunch of oranges trying to calculate the percentage of space occupied in the face centered cubic packing. (It an IRL version of a computer animation that we use in class and that I'm STUNNED to see I haven't posted on the blog before - coming in two weeks now.) We include a mathematical version of the proof at 16:55 in our summer camp powerpoint (at least Becky and I do - check slides 85 & 86) and you can find the math laid out here, too.

The last video is back to Steve Mould's channel and shows - using ball pit balls and a cardboard box - hexagonal (and face centered cubic) packing. They use that to demonstrate stacking faults (maybe defects, maybe disolcations, maybe grain boundaries - I need to figure out which term is most correct there), brilliantly shown with the color-coded balls from about 6:00-8:00.

The idea that the face centered cubic lattice is really and A-B-C (repeat) hexagonal arrangement whereas hexagonal close packing is A-B (repeat) is kind of mind blowing and so brilliantly well shown with the ball arrangement. The ABC diagram is a little weird to me and very much a mathematical diagram, something I wouldn't get into in class.