Certainly a discovery, but a new one?<p>Ok, this is based on an article from Nature and I'm just a random dude from the Internet, so take this with a grain of salt:<p>What they claim is what I've learned in materials science class 20 years ago.<p>Metals fatigue under cyclic loading because of micro-cracks. This effect can be quantified by the Wöhler curve, which very simply put tells you how often you can bend a piece of metal until it breaks.<p>From what I remember, it is well known that this fatigue reverses by itself slowly and depending on the temperature and type of metal.<p>It is true that the effect is negligible for steel at room temperature, which admittedly is the most interesting case.<p>But for other metals this self healing effect can actually be exploited at room temperature. The example we learned in class was the leaden rulers everyone of us owned back then. These are rulers you can bend to draw nice curves in technical drawings. They are made out of pure lead. If you bend them very very often in one sitting they can eventually break. But if you stop before and you leave them alone over night they will be like new.<p>At least that is how I remember the story.
[Recycling a comment from an earlier submission yesterday]<p>Isn't this a bit like cold welding? [0] Unless something is in-between them or some force is pulling them apart, there's no big reason for two exactly-fitted pieces of the same crystalline metal to _not_ join together. It's not like the atoms "know" which side they belong to.<p>Actually... [tap tap tap] It looks like that's explicitly in the original Nature title: "Autonomous healing of fatigue cracks via cold welding." [1]<p>[0] <a href="https://en.wikipedia.org/wiki/Cold_welding" rel="nofollow noreferrer">https://en.wikipedia.org/wiki/Cold_welding</a><p>[1] <a href="https://www.nature.com/article" rel="nofollow noreferrer">https://www.nature.com/article</a>
Metals have been known to have a kind of memory. If you bend a cable out of shape, it will bend itself right back. I have to think that this self-healing is an instance of the same principle.
No preprint although government labs have direction to make their research openly available asap. Probably a paper written just for other researchers to cite and not for any generic interest.
Prof. Demkowic was a very good instructor at MIT.<p>Once I learned about the amazing world of dislocation growth/glide in materials, it helped me see physical objects in a whole new way.<p><a href="https://youtu.be/EXbiEopDJ_g" rel="nofollow noreferrer">https://youtu.be/EXbiEopDJ_g</a><p>The math describing these defect strings was also interesting and challenging :) I wondered if they could be used for one-way computation.
I thought reforming the bonds of microfractures was already well known as a differentiator between metalloids and true metals? So does this mean that metalloids just shouldn't be a group anymore, or that they instead have to be expanded to include more materials? And certain substitutional alloys can be argued to be self healing. In bronze the copper will replace any displaced tin and zinc bonds without heat, for example.
It's cool that they observed this, but I'm a little confused why this is seen as surprising. Unless there's oxidation at the fissure, metals seem like they should be able to glue back together pretty easily...