Porous, 3D forms of graphene can be 10 times as strong as steel but much lighter | Hacker News Reader

Porous, 3D forms of graphene can be 10 times as strong as steel but much lighter

news.mit.edu

78 pointsmattiemass26 comments

So this is just saying that the shape of a material determines its strength? From what I gathered from the video, they didn't actually use graphene in these objects.

I was reading a introductory book on metallurgy over the holidays and realized that I had no idea what "stretching" was. I still hardly have any idea, but from what I was able to gather from the book, in steel at least, when stretched, there are these molecular "fault-lines" that can shift and still stay stable without actually breaking. Apparently, steel can be put under stress to fall to this final state to avoid further shifting during use in machines and whatnot.

Maybe I'm completely missing the point and the plastic is somehow stronger than steel, but the quote

>"You can replace the material itself with anything," MIT's head of Civil and Environmental Engineering said. "The geometry is the dominant factor."

makes me think that this is the case?

Ironically, they could replace the graphene with steel and end up with steel being ten times stronger than steel.

What they are likely referring to here is strength to weight ratio. By more intelligently distributing material in space, one can get a higher strength to weight ratio than using solid material.

Of course geometry does in fact influence material strength. One way geometry can influence material strength is by making crack propagation more difficult. In a simple plane sheet, a small crack at one end can easily propagate to the other end of the sheet resulting in failure. However, if we put a number of holes in our sheet, it becomes more difficult for the crack to propagate. A new crack has to be made each time the crack crosses one of the holes.

Now this result of an additively gyroid structure having a high strength is a bit comical. One of the first 3d printing artists produced a sculpture of the gyroid a while back[0] and in fact the files for said sculpture are well known[1] and have been used to test 3d printers. It's sort of funny no one thought to crush one till now!

[0]https://www.bathsheba.com/math/gyroid/ [1]https://www.bathsheba.com/downloads/

But the article says:

> In its two-dimensional form, graphene is thought to be the strongest of all known materials

Doesn't this imply it is stronger than steel in 2 dimensions?

I think this implies that GRAPHENE is stronger than steel, but this 3d printed thermoplastic is definitely not stronger than steel given the same shape.

What I mean is "in 2 dimensions" may be relevant, since the shape seems to be a 2D sheet folded into 3D space.

The original journal article is open access [0], and I think it's pretty well-written and accessible.

This is a really great example of theory-driven materials design.

[0]: http://advances.sciencemag.org/content/3/1/e1601536.full

(ten times stronger than mild steel, at 2.7 GPa tensile yield.) Nobody is deciding between mild steel and graphene. Comparing to PAN carbon fiber (which can achieve 7.0 GPa yield with careful manufacture) would be more useful.

> MIT says that this is because the thinner walls allow the structure to deform gradually while the thicker one stores the deformation energy, which releases all at once

I'm not sure that's the failure mode I want load-bearing things to have...

It's a perfectly fine failure mode in applications where failure of any type is automatically catastrophic anyway - for instance, a submarine's pressure hull.

I don't know much about submarines, but I assume that you mean once the pressure hull is penetrated, the resulting pressure difference will quickly make short work of the hull.

My point was that, if I could choose the failure mode, I wouldn't pick fail-all-at-once, if I could avoid it (for most things that bear load). If I could design/create a pressure hull that somehow didn't fail all at once, I think everyone would be happy?

If it was torpedoed a moderate diffence in hole size is not going to matter. A larger issue would be how flammable this stuff is.

Is it just me or are prestigious institutions such as MIT frittering away their respectability with press briefs such as this?

You should compare the actual university press release [0] to the article written by an external organization above.

[0] http://news.mit.edu/2017/3-d-graphene-strongest-lightest-mat...

As long as the PR departments meet their assigned goals and earn their bonus, what's a bit of tarnish on the escutcheon?

Yes, yes, graphene is awesome, we know. Can you make cheap sheets of it?

Imagine the burj al arab ten times higher.

I don't know if the writer really understood what's going on there. Those models are just plastic. Understanding how to make strong shapes is useful for eventually building real structures with graphene in the future, but nothing about that research used graphene.

I think they're saying that if that plastic model was graphene then it would be 5% as dense and 10x as strong as steel...but no such thing was actually created. The title here is pretty click baity.

Title is very click-bait. The MIT News article it links to is much more informative: http://news.mit.edu/2017/3-d-graphene-strongest-lightest-mat...

So they show that a graphene gyroid structure could be quite strong compressively. Now, the challenge is actually make such a structure. Making a template for graphene to grow on like this is bound to be quite challenging, minimizing the amount of defects in such structure even more so!

They have a pretty plausible-sounding (I am not an aerogels expert) synthesis route based on cyclic annealing of graphene flakes, and they have molecular dynamics calculations to back it up. In the open access research paper [0] there's some discussion of the defects that form in the MD simulations, so that's baked into the mechanical property calculations to some extent...

I agree that actually synthesizing this stuff still remains a big challenge, but at this point I think it's just engineering.

[0] http://advances.sciencemag.org/content/3/1/e1601536.full

Yes that was what I got out of it, and at the same time I am totally updating the Slicer infill pattern on my 3D printer to make stronger structures :-)

While this is worth trying for the sheer coolness of it, I'm a bit skeptical about how it will perform. For FDM things are much weaker in the Z-direction than they are in the x-y plane.

Exactly correct, the Z direction is a challenge in FDM printing. I built some "strength tester" forms (basically thinks I could crush or pull apart or bend) to understand what sort of structural stability could be expected out of a given filament and the process in general.

So https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_t... https://en.wikipedia.org/wiki/I-beam I think this is essentially MIT finding that the structure of graphene in 3d is also an extremely efficient beam/plane regardless of material. Which is a very cool empirical discovery even if it doesn't mean much for graphene as a building material.

I think it's very cool especially because it applies to things other than graphene. With all the issues producing graphene inexpensively, if we can get some great strength and durability increases in low-density constructions with other materials that could be a real boon.

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