A novel 'non-cuttable' material.

Apologies if this has already been mentioned, but I stumbled across this article in Nature in which the authors report a novel material which is highly resistant to 'attack' by angle grinder discs or drills. The material consists of ceramic balls embedded in a matrix of foamed aluminium. The cunning thing (if I have understood the article correctly) is that the 'dynamic hardness' of the material is the result of resonances set up in the cutter when it encounters the hard ceramic suspended in the much more compliant aluminium matrix, rather than the static hardness of the ceramic.

Seems like clever materials science - informed by biological studies.

Robin.

That sounds clever and interesting and it lead to me thinking about something I was told as an apprentice in a large production factory and have always wondered if it was true or not. We used a large amount of replaceable tipped tooling, all the used tips had to be placed in a bin outside the stores. Asking what happened to the old tips I was told they went to safe manufacturers too be welded into the doors and walls to prevent drilling into them, the loose tips catching the drill stopping it dead.

Was this true or just one of the wind ups that our older colleages were so fond of inflicting on us gullible innocents? Sorry if I seem to have hijacked the thread but this set me thinking that if it were true about the tool tips this would be an interesting development.

I think my youthful gullibility level is dependent on the answers, I'm sure someone on this forum knows the answer.

Dave

Edited By Dave Wootton on 28/07/2020 06:37:30

I suppose if you make anything thick enough it will be hard to penatrate ,

The test shows that in 1min the 40mm thick test piece was only cut 15-20% of it's depth. So that's 8mm which would be a good depth to cut in 1min into steel so unless you are talking armor plate thickness I can't see it being a lot different. The also only used a 125mm grinder, the series would go at it with a Stlhl saw. They also show a disc for cutting steel, wonder what the result would have been using one for aluminium or even diamond which would have coped with the ceramic better.

Don't suppose it would resist attack by thermic lance... Or mercury. Or gallium. But it's still a nifty idea.

.

Dave,

True in spirit, if not in technical detail ^^^

Wikipedia gives a better description:

[quote]
All but the simplest safes are designed to protect against drilling attacks through the implementation of hardplate steel (extremely wear-resistant) or composite hardplate (a casting of metal such as cobalt-vanadium alloys with embedded tungsten carbide chips designed to shatter the cutting tips of a drill bit) within the safe, protecting the locking mechanism and other critical areas such as the locking bolts. The use of hardplate ensures that conventional drilling is not successful when used against the safe. Drilling through hardplate requires the use of special-purpose diamond or tungsten-carbide drill-bits. Even then, this can be a time-consuming and difficult process with safes equipped with modern composite hardplates.[/quote]

MichaelG.

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Ref. https://en.wikipedia.org/wiki/Safe-cracking

See also: https://alwayssecurity.com/products/safes/

Edited By Michael Gilligan on 28/07/2020 07:22:13

Edited By Michael Gilligan on 28/07/2020 07:26:17

.

Excellent find, Robin

I have downloaded the full paper to read after a caffeine boost

MichaelG.

Hi Dave Wootton, at my old job a hollow steel door was made in our workshop, which was filled with balls and rollers of different sizes from old bearings, the idea was the same as you say, that it stopped or a least took a long time to drill and you would need a whole heap of drill bits, because although you would be able to drill through the skin, the drill would skew off on one of the balls or rollers and break. This was a security door to a small room. I suspect all the old tips you mention would have the same effect. I will add that battery powered angle grinders didn't exist then, although there were 9" angle grinders, mini grinders were relatively new, but you didn't get thin or diamond cutting disc then.

Regards Nick.

Edited By Nicholas Farr on 28/07/2020 08:31:13

Not really that new an idea. If you look at the bolt of a quality high security door look, especially one for double doors it may be a "brass" alloy. So just slip a hacksaw blade between the doors and cut it? No, because if you look at the end of the bolt you can see that there is is typically two hardened rollers in the bolt. These spin under a cutting blade resisting cutting.
I've seen some work done on safes, While cobalt / carbide scrap may be cast in the metal, the ones I've seen had it (and other materials) as filler in th high strength "concrete" between the walls.
Another safe trick is a toughened glass plate covering the lock. Any attempt to drill or force the lock causes the plate to shatter releasing springloaded additional bolts or latches that lock the door even if you the key or combination. Even some fairly plain looking MOD steel storage cupboards used this additional protection. I saw a case years ago of a strong room which had the keys locked inside. The makers provided a local locksmith with a set of dimensions for holes to drill in the door and pns to insert in them to unlock the door. Story was that there were a number of plates with different hole patterns and if you got the drill in the wrong place you broke it. Obviously detals of the plates and what doors they were in is a security issue.

Robert G8RPI.

looking at the way the cutting disc has worn I would suggest that the grade of disc was wrong for the material but probably okay for the steel hence the difference in performance.

Many years ago I worked with metallurgists who had developed an aluminium reinforced with steel mesh, not so different in ethos to the material described in the article. The guys developing the aluminium/steel hybrid material thought it would be difficult to cut by the "thin grinding wheel" method and indeed it was with the DIY shop bought discs. The Norton rep soon came up with a disc that cut it successfully.

John

Some hardwood's have small crystals of calcium and other materials which play merry hell with saws.

regards Martin

only 15% steel density

I bet the tank and armoured car industry will have a peek at this approach

How do you machine it into useful shapes?

Reminds me of the evil genius "All I have to do is mix these two liquids to create the ultimate solvent - but what would I keep it in?"

Neil

3D print, cast?

That is why the "concrete" is more common. Just cast in place. the tick is stopping all the crbide fallig to the bottom before it sets.

I think they already have : -

**LINK**

I read about this in the paper and thought that if you had a padlock made of this material, what would happen if you used a blowlamp to melt the aluminium ?

Gras has tiny silica 'spicules' which do the same job on herbivores' teeth.

Nature has many more examples of 'smart materials' than the original article gives.

Neil

If I recall my geology text-books correctly, of the natural minerals silica is second in hardness to diamonds. It is most familiar to us as flint and chert (essentially the same), and quartz; the latter being a constituent of igneous rocks like granite and basalt, released by weathering to become grains of sand. It is also the material of sea-urchin spines.

I don't know how these two minerals compare with tool-tip ceramics, but I have often wondered if the Bronze Age metalworkers used flint / chert tools, especially for the finer, and often exquisite, detailing on the decorative work, and perhaps in shard form, as drills. They would no doubt have used silica for abrasive (stones and sand), and indeed understood how to polish the metal sufficiently for mirrors.

Not that I'd recommend trying flint as an insert material, for if it crumbles it would put what would then be grains of sand in the slideways!

Linking this to the OP, I am not sure what a masonry-bit does in concrete, because the aggregate is usually irregular flint pebbles, from ancient river deposits. The drill is helped by the hammer action, but must cut the pebbles too, and a core-drill certainly does, putting tungsten-carbide between silica and diamond for hardness.

+++

responding to Robert Atkinson:

My employer had a lot of security-cupboards with combination-locks, and it was not unknown for people to set the number but not leave that with the security-office, even when they were leaving the company. As a result, thanks to such measures as the sprung bolts you describe, it was sometimes necessary to destroy an expensive cupboard in order to retrieve the contents. Especially so after some middle-manager told the only staff-member with the training and tools to open high-grade lever and combination locks non-destructively, he no longer needed them!

The problem with the concrete you suggest may be mistaken. Concrete does not need very much water, and if the constituents are measured correctly the carbide fragments should no more sink to the bottom than the gravel does.