Improving Armour Performance by Drilling it Full of Holes

[Michael OLeary]

Holes give edge to new MoD armour

http://news.bbc.co.uk/2/hi/science/nature/7811567.stm

  By Paul Rincon
Science reporter, BBC News

Super-bainite armour (Peter Brown)
The armour has performed very well in ballistic testing

Scientists from the UK Ministry of Defence (MoD) have devised an ultra-hard vehicle armour to protect military personnel.

Details of the steel armour, called Super Bainite, were outlined during a seminar at the University of Cambridge.

Unexpectedly, the MoD team has given the armour a protective advantage by introducing an array of holes.

According to scientist Professor Peter Brown, these perforations help deflect incoming projectiles.

"I wouldn't like to have been the first person to have suggested that," said Professor Brown, from the Defence Science and Technology Laboratory (DSTL) at Porton Down in Wiltshire.

He explained: "You shouldn't think of them as holes, you should think of them as edges. When a bullet hits an edge, it gets deflected, and turns from a sharp projectile into a blunt fragment - which is much easier to stop. It doubles the ballistic performance and halves the weight."

More at link (above).

 

[geo]

Interesting... it even makes sense... but I'm not sure I'd be the 1st person into an APC that was drilled full of holes to take advantage of this concept....

Let's say, I'll catch the next ride

 

[RHFC_piper]

I know I'm going to sound like a total dork, but I find this article very interesting on a few levels;

It mentions the concept of these holes are to create edges to deflect the round and to fragment it;

"You shouldn't think of them as holes, you should think of them as edges. When a bullet hits an edge, it gets deflected, and turns from a sharp projectile into a blunt fragment - which is much easier to stop. It doubles the ballistic performance and halves the weight."

Very interesting concept.  Makes perfect sense; the round hits a sharp edge - a triangle shaped cross-section object, which would have a lot of material behind the point (to put it in a simple term) to help deflect the impact.  The impact from the round would most likely break, or bend the point or edge. This deformation or failure would help disperse the energy from the round, and, as the article stated, break up the round itself, turning it into lower velocity fragments which probably wouldn't penetrate the underlying armour.
And, as an added effect; hole reduce the amount of material and weight.


The other point I find interesting;

Certain heat treatments alter the fine-scale structure of steel, creating a "phase" known as bainite - which has been known about since the 1930s.

But the process, developed by DSTL scientists in collaboration with steelmaker Corus, allows the alloy to be produced quickly and cost effectively.

Super Bainite develops its exceptional strength through a new low-temperature process called "isothermal hardening".

The steel is heated to 1,000C, cooled to about 200C and then held at this temperature for a period of time before cooling to room temperature. Initially, the team held the steel at about 200C for just over two weeks to achieve the right ballistic protection.

However, this was too slow for the process to be commercialised. The researchers subsequently reduced the heat treatment time to eight hours by transforming the steel at 250C instead of 200C.

I find this very interesting since I just learned about all these Phase things in Engineering Materials class (Mechanical Engineer course).

I know Wikipedia isn't a great source, but this says just about the same thing as my Materials text book... But I'm not going to rewrite all of whats in the book.

Bainite is a phase that exists in steel microstructures after certain heat treatments. First described by Davenport E. S. and Edgar Bain, it is one of the decomposition products that may form when austenite (the face centered cubic crystal structure of iron) is cooled past a critical temperature of 723 °C (about 1333 °F). Davenport and Bain originally described the microstructure as being similar in appearance to tempered martensite.

A fine non-lamellar structure, bainite commonly consists of ferrite, carbide, and retained austenite. In these cases it is similar in constitution to pearlite, but with the ferrite forming by a displacive mechanism similar to martensite formation, usually followed by precipitation of carbides from the supersaturated ferrite or austenite.

The temperature range for transformation to bainite is between those for pearlite and martensite. When formed during continuous cooling, the cooling rate to form bainite is higher than that required to form pearlite, but lower than that to form martensite, in steel of the same composition.

The microstructures of martensite and bainite at first seem quite similar; this is a consequence of the two phases sharing many aspects of their transformation mechanisms. However, morphological differences do exist on the resolution level of the TEM and can be used in microstructural evaluation. Under a simple light microscope, the microstructure of bainite appears dark (i.e., it has low reflectivity).

Bainite is generally stronger but less ductile than pearlite.

Based on the description, Bainite is somewhere between Pearlite, a 2 phase structure, and martensite, a body centered tetragonal crystal structure... I know.. blah blah blah.
The technical deal on this is; Bainite has a similar structure to martensite, (body centered tetragonal crystal structure), which means less slip planes (improved toughness)... So, bainite is hard and tough... which would imply that; when hit by a round, will absorb the impact with little plastic deformation due to ductility, or failure due to brittleness... the perfect combination.

After learning about steel structures, phases and all that good stuff, I wondered what armour engineers would use... Good article... it answers a lot of questions.... but, adds some more (holes in armour).

Good find, Michael... thanks...



Now I'm going to be up all night reading about this stuff... thanks.

 

[Lance Wiebe]

Believe it or not, I saw a form of this being tested once upon a time.  Maybe 8 or 9 years ago.  The material certainly wasn't the same, but using a stand off armour with holes in it to deflect projectiles has been studied in the past.  The problem then was that any stand off armour strong enough to deflect projectiles was simply to heavy to bolt on to APC's and other light vehicles.  Nice to see that some people just wouldn't give up on the concept!

 

[geo]

If it doesn't work... give it a couple of years and try again.....
Repeat as required.

Let,s face it, this is just the continuation of development on sloped armour.  The minute you create bevels, nooks & cranies for projectiles to caroom off of, you reduce the likelyhood the projectile will follow it's original track into your back pocket.