Duplicate of https://news.ycombinator.com/item?id=23901635

There's a great YouTube video, probably from defcon, where someone talks all about safes and the many decades of materials science that have gone into them. When hard-to-cut materials were tried, thieves ended up crushing safes or trying to shear them in half.

See also Tim Hunkin: https://www.timhunkin.com/94_illegal_engineering.htm

Please share the link if you can find it, it sounds very interesting.

...not that I have any safes I'd like to crack, incidentally.

Seems similar in concept to composite tank armor

https://en.wikipedia.org/wiki/Chobham_armour

Could we finally get closer to safety gloves that work for table saws? As much as I would love to use own, that thing just scares the shit out of me. And yes, I know about the saw stop.

If you looked at any of the pictures or watch the demo video you will see that the material is very stiff and thick. I wouldn't saw it is suitable for gloves.

But the general consensus is always not to wear gloves at all. The risk of it getting caught in the machine amplifies the risk much greater than just cutting yourself or losing a finger.

You don't use gloves around spinning motors because it will suck the glove up. Even if the gloves survive tearing, your fingers don't survive mushing.

You might be interested in this. https://www.sawstop.com/

I am in the 9 finger club and I do not believe that gloves would help. Or as the doctor said when I was 16: "You can no longer sew on mush." and dropped my "what was previous known as my finger" into the garbadge bin. I was wearing gloves. Big, hard ones.

The gloves you want don't exist yet but there is a safe table saw https://www.sawstop.com/why-sawstop/the-technology/

Go look up "degloving" to see why gloves are bad idea around spinning tools.

Might want to mention that's NSFL.

Would chainmail armour be practical here ?

What did they use to cut it for the cross-section picture?

It's a CT scan, they did not cut it for that.

Ahhh and of course it says exactly that in the caption I did not read!

Looks like it's non-cuttable in the same vein as unlimited data plans.

"These cause it to become even harder the faster you grind or drill "due to interatomic forces between the ceramic grains," and "the force and energy of the disc or the drill is turned back on itself, and it is weakened and destroyed by its own attack."

So what happens if you cut or drill at low speed?

Same damage done on the upper layer to the cutting device. Just takes much longer to wear down - the only way you make any slight cut into it is with high speeds

pour some liquid nitrogen on it and hit it with a sledgehammer?

No mention of plasma cutters. I think a big enough plasma cutter will make the plasma go around the ceramic to reach the conductive metal and the ceramic will fall out.

If bike thieves have plasma cutters, we’re definitely in trouble.

> No mention of plasma cutters. I think a big enough plasma cutter will make the plasma go around the ceramic to reach the conductive metal and the ceramic will fall out.

Any method that lets you attack the aluminum and avoid the ceramic will be extremely effective.

I suspect the simplest effective attack is to just apply a shearing force - something like cable cutters although ideally with less of an edge so they're less vulnerable to deformation. As long as the tool doesn't rely on a cutting edge to work, it should be able to ignore the ceramic component of the composite material.

Based on my read of the article seems like this would fall apart under evenly applied force. Like a bolt cutter. Odd that the article doesn't mention bolt cutters.

And in the first paragraph they even mention that this might have applications for bike locks. If that was an intended application, surely testing against bolt cutters which are so frequently used would be something they'd have done.

Maybe they are using the technical definitions of sheering and cutting?

Yep, bolt cutter would go through that aluminum like butter; or use a car jack or long lever to bend it in half.

A layer of this on top of steel bar would help guard against power tools. My bike lock already has a rubberized coating; embed ceramic balls in that.

>cellular aluminum structure

Seems like this could be easily degraded through chemical means. The analogy of Jello filled with chicken nuggets made me think of just eating the Jello part.

I think folks are getting hung up on "non-cuttable". That just means you can't remove material in a typical way with a cutting tool that shears off chips of material (a saw, grinder, drill bit, etc). They're not claiming it's indestructible-- just useful for certain scenarios.

Gallium comes to mind

Of course gallium is very expensive (a few thousand $ per kilogram).

Aluminum is much less susceptible to most acids than steel. Usually it calls for hydrofluoric acid, which is very nasty stuff.

Let’s see it resist oxy acetylene torches and plasma cutters.

And liquid nitrogen. Extreme heat and cold are usually the easy ways around these materials. I wonder how the ceramic would hold up.

But isn't the video of them cutting it? Or is the uncuttable material underneath the bit that got cut by the angle grinder? I can't know if that's the material stopping at an arbitrary point, or something heavy underneath.

The paper describes the construction in some detail. It's an aluminum foam with ceramic spheres embedded in it. They then welded into a thin steel box to give it a uniform surface. If you watch the video, you can see that the grinder gets through the steel box very easily, but the deeper it goes into the aluminum, the faster it is worn away. The grinding wheel is destroyed in just a few seconds, which is pretty impressive. On the other hand I doubt that this will be useful for smaller objects like locks.

It says it right in the text of the article

"An angle grinder or drill bit will cut through the outer layer of a Proteus plate, but once it reaches the embedded ceramic spheres, the fun begins with vibrations that blunt the tool's sharp edges, and then fine particles of ceramic dust begin filling up gaps in the matrix-like structure of the metal."

Ah, ok. Looking at the composition on the side seems to indicate that it's two separate metals entirely. Which I guess is the case?

If you don't want to wait for someone to answer, the short article has answers for all the questions you put forth so far.

I did read the article, but I don't see anywhere it states that there will clearly be one material on the outside and then a block of proteus underneath. What they are grinding is clearly two different materials, and it stops when it gets to the second one. The x-rays and the example don't seem to have a metal outside welded on, which is my confusion - it looks like someone welded a plate onto the miracle material, when in that little image in the corner of the x-ray it looks entirely homogeneous.

Because we can't directly see the miracle material, the video feels disingenuous.

It's not clear to me either when exactly does the "cutting" start, but note that when he finally gives up the grinder wheel is an inch smaller.

Thank you - I was having a hard time understanding why the video was a successful demonstration. Re-watching with the diameter of the cutting wheel in mind was illuminating.

Looks like it was a 3mm thick plate.

Given that this stuff is half as dense as Aluminum, it's pretty impressive that the grinder behaves like it's cutting the most nasty steel (steel is ~3x the density of aluminum and much tougher).

If the plate had been aluminum, the grinder would have cut through like it was playdough.