Why steel helmets, and why now?
The steel helmet and the aramid/UHMWPE helmet are products of two entirely different engineering traditions.
There’s a science fiction story by Harry Turtledove called “The Road Not Taken,” which has two core plot devices: (1) That faster-than-light and antigravity technologies are simple and obvious, but that humanity had somehow missed them — and, (2), that as soon as any nascent technological culture discovers those technologies, they obsess over them, and scientific progress in all other directions stagnates. It’s a good story. To excerpt a little bit from its sequel, which summarizes it:
Solving a mystery: Why is M193 better at penetrating steel armor plate than M855?
Ask an expert why M193 at full velocity will reliably perforate a steel armor plate, and you’ll hear “speed kills” or a variation of that refrain. In other words, it’s commonly assumed that M193 penetrates better simply because it is faster.
This is untrue.
A Short History of the Ballistic Steel Helmet
Although the first steel helmet is lost to history, it was the Romans who were first to make wide use of steel helmets in battle, and they were certainly the first to make those steel helmets iconic. Roman helmets, which were used alongside bronze helmets of similar design, were of sophisticated metallurgical composition — their helmets were generally either carburized or made of a reasonably high-quality medium-carbon steel alloy, though not necessarily quenched.
But to write the history of the steel helmet itself from the Roman era would fill an entire book. The history of the ballistic steel helmet is a much shorter story.
Modeling and Simulation in Ballistics (LS-DYNA)
Most of the people who work in armor and munitions design are die-hard experimentalists, and for good reason: The best way to test an armor system is to hit it with live rounds and see what happens.
But, true though that may still be, modeling software has become increasingly useful — even quite shockingly useful — and it is beginning to change the way we design products.
Numerical and hydrocode ballistic impact models aren’t new — they have been in regular use since the 1960s, when they were first applied to ceramic armor systems by the pioneering LLNL team led by Mark Wilkins. Initially, these early efforts attained good accuracy in modeling ballistic impacts onto monolithic aluminum armor systems.
Why fibers and fiber composites are strong, and why bulk materials usually aren’t.
One may wonder why soft armor materials — and other materials for defense and aerospace applications that exhibit a very high strength-to-weight ratio — all happen to be fiber composites. Why aren’t they bulk materials? Why is graphitic fiber so much stronger than graphite, why is fiberglass so much stronger and tougher than bulk glass, and why is it that basalt fibers are now heralded as a new-age superfiber, whereas basalt itself is almost completely useless? The below account of the origins of fiberglass may prove both interesting and enlightening. It is taken from the excellent “The New Science of Strong Materials,” by James Edward Gordon, one of the founders of materials science as a science:
New Ceramic Armor Materials – From Boron Suboxide to Diamond
At the present time, the only commonly-encountered ceramic armor materials are alumina, boron carbide, and silicon carbide. All of these materials were introduced in the 1960s and saw service in Vietnam-era armor plates. They haven’t changed since. The current state of the art — the monolithic, multi-curved boron carbide armor ceramic tile — was developed by scientists at the US Army Natick Research and Development Laboratories and Picatinny Arsenal in 1965. If there has been any innovation in the many years since, it has been to manufacturing processes; these innovations have brought boron carbide tile production costs down and have facilitated high-volume production, but, pointedly, they have not improved performance. (And, indeed, in many cases these innovations have actually reduced performance — e.g. in reaction-bonded boron carbide — RBB4C — that is softer, denser, and ultimately just less protective than the 1965 product.)
On Graphene Armor
A lot of ink has been spilled on the subject of graphene armor. For example:
https://www.newscientist.com/article/dn26626-bulletproof-graphene-makes-ultra-strong-body-armour/
Such articles show little understanding of the facts. A deeper reading should indicate that graphene will probably never make for an armor material.
Soft Body Armor Statistics — Level IIIa vs. Level II, Body Armor Cuts, and Rifle Plate Selection
The FBI keeps statistics on police officers murdered or assaulted in the line of duty, and they’ve recently released a number of reports which cover the past ten years, from the beginning of 2008, through the end of 2017.
The Ballistic Event
The Ballistic Event
When an hard projectile impacts a ceramic-faced armor plate at 400-2000 meters per second, there two factors that need to be taken into consideration: The behavior of the penetrator, and the behavior of the ceramic armor plate in a local zone.
The first phase of penetration: Dwell.
(When an AP bullet with a hard core impacts a ceramic armor target, it is stopped for a moment, on the order of microseconds. This is called “dwell.”)
– The Projectile: The nose of the AP core starts to break or erode as it comes into contact with the ceramic plate, which is always harder than the projectile, and which has a very high compressive strength. The penetrator, momentarily arrested, begins lose velocity. Temperatures begin to rise steeply in the area of impact. Thus the kinetic energy of the penetrator is reduced due to the mass loss of its tip, the deceleration of its back part, and the conversion of some of that kinetic energy to heat.
– The Armor: Fractures immediately begin appearing in the ceramic plate. They form in a characteristic inverted cone pattern, which has aptly been named the “fracture conoid.” This conoid typically has a base diameter of approximately two to three projectile diameters from the center of impact, and a semi-angle of 60-70°. (68° is often used for modeling purposes.)
Amorphous metals and bulk metallic glasses for armor applications
Steel has many merits as a body armor material, foremost of which are its durability and its ability to be used in very thin sections. Sadly, we’re all familiar with its drawbacks, too — its high density and its near-total uselessness against armor piercing rounds — and not just those made with tungsten carbide cores, but also those rounds with cores of hardened tool steel. But what if steel’s merits could be enhanced, and its drawbacks reduced or eliminated? Recent advances in amorphous metal alloys, also known as bulk metallic glasses, might be just the thing.
