3 ms·
> This occurs, the researchers believe, because the weaker bonds are randomly distributed as junctions between otherwise strong strands throughout the material,
by nerpderp82 3y ago
> This occurs, the researchers believe, because the weaker bonds are randomly distributed as junctions between otherwise strong strands throughout the material, instead of being part of the ultimate strands themselves. When this material is stretched to the breaking point, any cracks propagating through the material try to avoid the stronger bonds and go through the weaker bonds instead. This means the crack has to break more bonds than it would if all of the bonds were the same strength.
> “Even though those bonds are weaker, more of them end up needing to be broken, because the crack takes a path through the weakest bonds, which ends up being a longer path,” Johnson says.
I believe it is similar. Braess's Paradox, Antifragility, Crystalline vs Plastic materials and smooth response profiles to stressors can all be related.
The weaker material here is a sacrificial substance that spreads the load over a larger amount of material. Extremely strong substances that are not also plastic fail catastrophically, counter intuitively strong things can increase the local force and cause cracks to propagate through a material. Everything fails via crack propagation.
If you over optimize your system, you do so by removing the portions that potentially make it resilient to stressors. Strength in one dimension is often at the detriment to strength and resilience in others.
- Arrath 3y agoThis discovery does make sense. I wonder how well it will scale to production, is it as simple as ensuring that this ~2% differing binder material is homogenized throughout the mix?
- Terr_ 3y agoJust playing around with metaphors and analogies, I'm imagining a sheet of paper hanging vertically, its bottom edge held down with a weight. When nicked on one side, that becomes a tear that causes it to separate in two. In contrast, there's another sheet of paper which has a bunch of small holes punched into it. Despite being "weaker" from having less material, it's more resistant to a particular failure mode, since when the advancing tear hits one of the holes there's a chance that it will stop. Eh, never mind, that's probably its own differently-named principle in materials-science durability.
- nerpderp82 3y agoThat is exactly how material scientists study the grain structure and crack propagation. If the crack joint is too small, it acts as a lever. This is why you fillet and chamfer a joint in a designed part, but the concept works down to the molecular level. The holes you are talking about are points of stress relief, without them, the crack can continue to travel through the material, amplifying the forces. Fiberglass isn't strong because the material is special, it is stronger because the imperfections in it have been removed due to surface tension self organizing the impurities away (that would form cracks) during the remelt. The polymer structure in the linked article is not unlike a fiberglass+epoxy composite.
- dmbche 3y agoWould you have any good primer on materials science to point me towards? I find this fascinating!
- nerpderp82 3y agoChatGPT can point you to many relevant texts. courses https://www.google.com/search?q=materials+science+crack+propagation+formation+syllabus++site%3Aedu https://www.google.com/search?q=materials+science+crack+prop... pdfs https://www.google.com/search?q=materials+science+crack+propagation+formation+site%3Aedu+filetype%3Apdf https://www.google.com/search?q=materials+science+crack+prop...
- alexmolas 3y agoThat's a very good metaphor indeed!
- eternityforest 3y agoFountain pens use a hole for exactly this reason. One of the coolest things in engineering IMHO, empty space making something more durable.