Single-curve, multi-curve ceramic body armor plate debate

There are a lot of smart people out there.  I don't consider myself social media "saavy". I am a member of Generation X (not that we can't be good at computer stuff). But, when my brain was developed, the tracks in my record were grooved towards hands-on, outside music and things to do.  Of course, there were a couple of exceptions to that rule - like playing Atari, or Doom... even that green line tank game on Apple's first computer.

News outlets and social media create their own realities.  Sometimes, these micro-worlds can exist within themselves with no fact-checking.  Debate within these circles is often vicious, with an alternate point of view immediately shred to pieces.  The disintegrating lack of respect for people with competing points of view has been one of my most significant disappointments as I've entered my later years.

I sure wish I knew what I know now when I was in my twenties and thirties.  If I could do it all over again, I would listen more.  I would be a calmer person and understand that there is a lot of unseen truth out there that is not tied to screaming and hollering or associated with a sales strategy.  In the armor world, there are a lot of things that live in their own reality.  Some of these are resilient rumors and others are more verifiable.  A string of them: Steel plates are dangerous (they are), Chinese armor is junk (not all are), anything acquired outside the USA is garbage, monolithics are better than mosaic plates, multi-curve armor is better than single curve.  Well, to put it mildly - there is a lot to write about, video about and complain about in that short list above.

This blog post is specifically about single-curve and multi-curve plates.  Which is better?  It's an advanced topic but I want to focus on an issue that no one has really broached yet.  The idea of ballistic performance relative to the ceramic layout on these two designs.

I will surrender on some of the arguments to jump right to the points I want to make.  Multi-curve are more expensive (generally), and more comfortable.  Single-curve don't fit as well, especially at the top of the armor.  Single-curve are more adaptable to various body types. I get all of that and agree with most of these conclusions.  But here is what everyone is missing... it's all about the design and resultant ballistic performance.

Single-curved armor can be manufactured with lots of options to include the world's most ballistically effective tile: the 99% aluminum oxide 2" (50mm x 50mm).  In my years of building armor, the most effective ceramic armor plate is the 2" mosaic array with a 2-4mm crack arrestor and trauma reducing stiffener on the wear face.  Nothing else beats it - hands down.  

Other options for building the single-curve plates include hexagonal shapes and monolithic, single-piece tile.

Photo 1: the venerable 2' alumina mosaic tile array

Multi-curve plates have two options for assembly:

1. Hexagonal flat tile.

2. The monolithic ceramic plate.

The underlying issues with the multi-curve construction are related to weaknesses in the monolithic ceramic itself and the performance limitations of hex tile.

Hex tile works but the larger the better.  To get the ceramic to transverse the complex curves of multi-curve armor, the hex must be small enough to accommodate the changes in back plate shape without opening up a gap between the tiles themselves, mainly along the strike face seam line where the angle between the ceramic's flat back and mechanical angle at the strike face are most pronounced.  Usually, common ballistic hex tile are in the 30mm range.  When a projectile strikes hex that small, there really isn't a large area for the ceramic to work its magic and properly form the conoid crack that allows the ballistic energy to stomp you in the chest with a foot instead of a spear. With hex armor, you must have a very strong backing plate because while the projectile will be off center of thrust and yawing - it will still be moving at a high velocity and penetrating without the aid  of additional surface dissipation present in the larger mosaic arrays or monolithics. While hex tile can meet NIJ requirements for BFD, in general - it is the least effective system out of the three discussed here.

Monolithic tile are used in ceramic armor manufacturing because:

1. They are easy to assemble with less room for error during construction.

2. Their shape is conducive to autoclaving bonding techniques (mosaics can be autoclaved also with forming procedures... we are working on a system now).

3. They are an excellent choice for one-hit resistance for heavy calibers (think .30 M2 AP).

Monolithic plates are not necessarily a great choice for being fired at in unpredictable ways.  In other words, in real life, no one is going to be laying down the "NIJ approved shot pattern for testing as per the 0101.07 standard."  

Why do I believe this?  I have built and tested hundreds of plates and I usually dissect each one so that we can evaluate our systems, materials, adhesives, etc. It's what you can't see that's relative to poor multi-hit performance on a monolithic. 

If you were to shoot an RF3 monolithic plate with .30 M2AP and then peel the ceramic away from the polyethylene (or other material) backer, you would see something like the picture below. The monolithic is on the left.  Remember you are looking at the reverse side of the strike face - where the ceramic meets the backer.

This circle of ceramic that you see broken off surrounding the projectile entry point is what I refer to as the "spall circle".  The radius is generally 2-3".  The spall circle is an area where the conoid crack forms along the periphery. The positive thing is that this spall circle is what helped fragment and yaw the original projectile.  The negative thing is that the thickness inside of this spall circle is now significantly diminished - making it less resistant to additional projectiles.  What once was a 10mm thick alumina tile is now a 5mm, 6mm, 8mm tile unpredictably resistant and vulnerable to follow on shots, even to lower calibers.

This is why when you see shot testing videos on social media (especially paid performers barking for the product) the projectiles will be placed at least 4"-5" from one another.  Any monolithic plate has this vulnerability.  I am not saying that it's necessarily bad - it's just there.  It's part of why it works.  Besides, you get hit once with .30 M2 AP, it's probably going to be "enough."

Whether the monolithic is utilized in single-curve or multi-curve construction, the spall circle will exist as a significant vulnerability after shot one.  

Monolithic plates will also crack throughout when hit by a projectile.  These cracks can open unpredictably, especially when there is poor adhesive activation between the strike face and the backing plate.  I have seen instances (and seen it in other videos where the OP didn't understand what he was looking at) where T-Link adhesives had not reached proper activation temperatures during manufacturing and had reverted to their semi-original forms.  Errors like this open- up large cracks in the ceramic making those areas also vulnerable to follow-on shots.

Let's bring up the picture of the spall circle again - this time, with emphasis on the right-hand section of the image which shows a mosaic tile pattern.

Notice that the reverse side of the mosaic (2" tile) shows two shots of .30 M2 AP in the same geographical boundary as the monolithic.  However, the spalling area accommodates the boundaries between the ceramic tiles.  The result is that the ballistic energy moves along the adhesives between the tiles and transmits itself through the adhesive bed between the tile and the UHMWPE backing plate.  This disperses the energy over a wide area and causes less spalling damage.  This leaves proximate tile more undisturbed, ready to resist additional projectiles at full, original thicknesses.

This activity is enhanced through use of a crack arresting layer. Some call this a "laminate" but that label really misses the intent of the material.  A crack arresting layer 2-4mm across the strike face of a mosaic plate significantly increases its performance in the data over a long period of time.

Use of a monolithic tile in a multi-curved plate bypasses the ideal protection offered by the 2" mosaic tile array.  While it may be more comfortable and something to brag about owning... the best protection is offered by the single-curve mosaic tile alumina ceramic strike face with a 2-4mm crack arresting layer.

Monolithics can be very effective but they require assembly techniques rarely utilized in today’s race toward “lighter and thinner” armor. To be most effective, the monolithic tile must be sandwiched between a 2-4mm crack arresting layer and a wear face trauma reducer that limits actual deformation of the backing materials. This stiffening effect helps prevent deformities in the strike face while it is simultaneously protected by strike face arrestors. BFD will still be present in testing but not so much physically.  

Unfortunately, this system is rarely used on monolithics. Our edge-to-edge silicon carbide plate would (and could) be just over 6 pounds if we didn’t add the trauma reducer and crack arrestor. It sits at 7 pounds as built, but that extra pound makes it a higher performing armor due to the enhancements described. 

Unless you can locate a multi-curve monolithic with trauma stiffener and crack arrestor - you will get better performance from a single-curve, 2” x 2” alumina strike face. 

We will get into trauma stiffeners in a later blog post but stay tuned.  We will be applying to the NIJ's Compliance and Testing Program soon with a super design.  Looking forward to discussing it more later.

 

WG