A jelly-like material that acts like hard, shatterproof glass when compressed | Hacker News Reader

A jelly-like material that acts like hard, shatterproof glass when compressed

cam.ac.uk

63 pointsrustoo40 comments

Impressive, but I feel like they cheated a bit by sandwiching it between sheets of plastic before running it over. How would it perform in the real world without the plastic, and all the sharp stones and grit found on a normal road surface?

The objective is use in medical devices, not as a road surface.

I’ve seen demonstrations for pothole fillings with non-Newtonian fluids where it’s kept in a tough kevlar like bag, which seems like closer to real world.

Seems like it could be cool, but too little information; I reallywant to know several more things to start.

How does its shape actually behave under pressure? They say "acts like an ultra-hard, shatterproof glass when compressed", so is it really changing state that hard? - I'm not seeing an crisp edge imprint of the rectangle in the top metal sheet that I'd expect from the same setup running a car over something like a wood/metal block of the same shape. If it really stays hard and firm as glass under a certain amount of pressure, that could be actually bad as a cartilage replacement. OTOH, if it just squishes and regains it's form, seems like a lot of other plastics.

How much energy does it absorb? If it really absorbs and redistributes a lot of energy both spatially and temporally, it could be really good shock protection. But I can't tell from this announcement.

What is the real stress level it can handle? They talk about an elephant, but the reality is that it is about 300kg (25% of a 1200kg car assuming roughly wheel weight allocation) over a aprox 3"x3" piece, which amounts to less than 75psi, or about 5x atmospheric pressure. As it turns out, if they are talking about the actual pressure under an elephant's step, it is in the same ballpark [1]. However, the way it is phrased is the entire weight of an elephant, which would be 3000kg on that square, which would be 730+psi.

All in all, disappointingly vague announcement from a crew that should have some expertise readily available in physics and mechanics...

> All in all, disappointingly vague announcement from a crew that should have some expertise readily available in physics and mechanics...

It's a press release that should be somewhat understandable for non-scientists.

I fully expect that a press release would be fully understandable by non-scientsts.

I'm not asking for a scientific paper, just to reduce the huge ambiguities. They could have answered all three of my questions more clearly with no scientific jargon whatsoever. E.g. (assuming these examples are true for the sake of discussion):

Instead of "acts like an ultra-hard, shatterproof glass when compressed", "with a bit more pressure than a soup can sitting on it becomes like an ultra hard shatterproof glass and retains it's shape"

Instead of "withstand the equivalent of an elephant standing on it", how about "can support the weight of a full elephant across a 3" square" or "can support the weight of an elephant stepping on it". Both are very different, use no jargon, and at least if we can assume that the author was intentionally accurate will let us know the properties within a half an order of magnitude, instead of being so uncertain that we really have no clue as to it's actual utility.

The link to the article is in the press release

https://www.nature.com/articles/s41563-021-01124-x

however, it's paywalled (you could pay $9 to maybe answer your questions).

I'm pretty sure my $5 silicone place mats can do the same thing.

I don't see any of this as novel. This is just a non-Newtonian fluid where the suspension is made up of flexible polymers, just like many others. They talk about specifically selecting guest molecules and altering them to change the properties of the material, but the exact same functionality can be accomplished with any NN fluid by adjusting the ratio of water to particulates or polymers. That has been known for a long time.

I think describing anything as non-Newtonian makes puts it into out of the novel level.

Not sure what you are trying to say here, but non-Newtonian (non linear shear stress vs viscosity) fluids are common and studied.

Ketchup is non-Newtonian (shear thinning) as is corn starch suspension (shear thickening).

Non-Newtonian liquids aren't rare. In fact, if we consider pure water to be a Newtonian fluid just about every fluid in nature is non-Newtonian.

I know it's typically not interesting to talk about the website rather than the content, but this website has the biggest cookie banner I've ever seen. It has a form with check boxes, descriptive prose, and links to more info. Took up my entire screen. It's pretty wild.

I wonder how it would fare if bullets were fired at it.

At GaTech there was a professor whose research included a suspension that could stop bullets. The idea was to make flexible body armor.

It worked in the lab, but there was a problem keeping the suspension mixed

It's interesting it made a dent in the metal it was covered with.

Someone should sell protective clothing made of this material.

Only thing it'll be protecting is itself

Precisely what I was thinking, wouldn't using non-newtonian type physics in such a situation just increase the impact force on the body?

No because it would couple the impact’s energy over a (much) larger area.

There is something similar called D30. It's in motorcycle gear

1200kg for the car divided by 4 points of surface contact („wheels“) equals 300kg. Wikipedia says an Elephant is 5.2-6.9t. So.. well.. seems a bit off.

Yep, also known as "corner weight" w.r.t. cars. Strange how they missed it. I wonder if it's a common misconception?

Plus if it was back of the car, it is more ligtweight.

Moreover, that tire surface is much bigger and by part rests outside of material bounds.

Isn't an elephant's weight also distributed on 4 points of surface contact ("feet")?

That's what I thought, then I realised they took into account walking.

The forelimbs also take more weight (60%)

Foot pressure distributions during walking in African elephants

https://royalsocietypublishing.org/doi/10.1098/rsos.160203

Unlike a horse they never have all feet off the ground.

Typical car tires are inflated to 35 PSI or so. There is a surprisingly large "footprint" from a tire supporting a car.

I think the PSI in their test is fairly small. While I'm sure finding an elephant is difficult, a simply hydraulic press in the lab could deliver hundreds of PSI.

I would be generous and assume this is a demo of something that is more relatable to normal people experiences, and they did actually test this with a hydraulic press in reality.

It's a press release aimed at making the news, not a scholarly article, and those can be pretty.. misleading.

how does the inflation of the tire affect the mass load on the sample? are you saying if they changed the PSI of the car's tires they'd get different results (ignoring uninteresting details like how the PSI changed the tire geometry slightly?)

The pressure to which the tire is inflated affects how much it spreads against the surface it sits on, changing the applied pressure.

There are lots of things that can be run over by a car. Grass for instance. Sand. And so on. The property 'able to survive being run over by a car' only starts to have value when it is coupled with other desirable properties. Jelly doesn't normally have many of those. There must be a better way to describe material properties besides being able to be run over by a car. It's a bit like picking something that sounds impressive but without context it is next to meaningless.

The article goes into some more detail that describes the material properties a lot better than this, and I think the article would improve if the title claim would be left out of it. It is just a click bait thing that doesn't convey any useful information.

I think the more specific (and more interesting) claim is that it retains its shape after being run over by a car. Grass gets flattened. Sand doesn't really have a shape to begin with.

It's interesting that they place a cover over the jelly first. Makes me think it's not nearly as good at surviving shear forces.

> Makes me think it's not nearly as good at surviving shear forces.

It would definitely tear extremely easily due to the polymer scaffolding being entirely exposed, which makes it useless for most applications. By contrast, non-Newtonian fluids already being used in protective applications are encapsulated in materials far more resistant to scratching and shearing, which also allows the fluid to retain shape without the need for any specialized polymers inside the suspended fluid itself.

One of the useful applications is D3O (brand name) which is a non-newtonian fluid that is soft/rubber like until it takes an impact and then solidifies pretty much instantly - it's used in higher end motorcycle gear.

https://www.youtube.com/watch?v=MzJowUKgxNU

The fluid in D3O is encapsulated in plastics, which is how it maintains its scratch and tear resistance. Whereas the entire structure of the hydrogel in the article is bare, which means the friction of a rotating tire would easily rip it to shreds -- which is why they sandwiched the gel between two sheets of something in the video.

The point here was to create a hydrogel, which many useful properties missing from random non Newtonian fluids.

https://en.m.wikipedia.org/wiki/Hydrogel

My foot was once run over by a car. It wasn't too bad and the foot still works.

It was a small car though.

And a Big Foot

Another "jelly/fluid" that can be ran over by cars and trucks and remains its shape (mostly) is asphalt. It has been in use especially for being ran over by cars for as long as cars existed and has been in use (edit: for other things) since the fifth millennium BC.

I too probably miss context, because it hardly impresses me.

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