Shoot Test: Contact Shots vs. UHMWPE Soft Armor

In several of my posts, I mention that while UHMWPE UD armor is an excellent choice for certain applications, and has material advantages over woven or laminate Aramid ballistic fabrics (higher potential V50, positive buoyancy, UV resistant, waterproof), it suffers from several glaring weaknesses (degrades to complete ineffectiveness above 170F, no breathability, delaminates/curls, and is WEAK AGAINST CONTACT SHOTS).

It is important to reiterate that last weakness: a large number (if not the majority) of self-defense and duty scenarios take place at 0-5 feet, where contact shots are a high likelihood. Woven Kevlar soft armor has shown to provide EXTREMELY good protection against contact shots (defined as the muzzle of the weapon being in physical contact with the vest or armor panel). The point at which Kevlar chars is around 500F, and it will retain its strength below this temperature.

The failure mechanism for UHMWPE in contact shots is the high temperature propellant gases that exit the muzzle microseconds after the bullet. These gases heat the area surrounding the muzzle and bullet path, and cause the laminate to melt/denature. This allows the bullet to penetrate much further than would normally be possible. In the case of large caliber revolvers (with a large muzzle blast footprint), this can allow the round to completely defeat the vest.

Test Round

For the sake of the test, the round chosen was the .357 Magnum, rather than a .44 Magnum, as I wanted to see if the (relatively!) more modest caliber would still defeat the level II ballistic panel. The panel consisted of 15 layers of Dyneema SB-38. Round chosen was Hornady Custom 158 gr. XTP @ 1250 fps muzzle velocity, from 6″ barrel. The level II panel is specced to stop an equivalent round.

Test Panel

Backing

The panel was placed against a backing material consisting of 8 layers of bubble wrap, covered in a dish towel. In retrospect, this was probably a bit too “springy,” giving the panel an advantage by permitting it to move away from the hot muzzle blast faster than if the armor was being worn.

Test Panel Ready To Shoot

The test panel and backing were placed upon the ground, and the muzzle pressed firmly (but not forcefully) against the surface. The round was discharged into the center of the panel.

First shot

First shot, through the backing

First shot, rear of panel…

The panel was defeated, showing that the muzzle blast had melted a moderately large area around the point of contact. The round penetrated the backing and buried itself into the dirt (as shown).

To verify, a second round was fired into the lower left area of the panel (away from the heat affected zone of the first round). The second round performed identically, burying itself into the dirt beneath the panel.

Second Contact Shot

Second Round, showing penetration

Second shot, layers peeled back

Second shot, showing exit into backing…

…And into the dirt

Conclusions:

The results of the test shows that UD UHMWPE laminates are at risk vs. contact shots. Heat from the muzzle gases (especially medium to large caliber revolvers) “blazes a trail” so to speak, for the round to penetrate further than it normally would.

Body Armor: The Good, The Bad, and The Ugly, Part III

In the late 80’s and early 90’s a relatively new material was making an appearance in concealable body armor. Based on the Ultra High Molecular Weight Polyethylene molecule, this material offered tensile strength 8-15 times that of steel on a weight-to-weight basis. This was up to 40% higher than Aramid fiber. Developed by DSM, this material became known by two different trade names, Dyneema (DSM) and Spectra (Honeywell). Initially, this material was utilized as both a woven panel (which had immediate problems, as will be discussed below), and later in a laminate form (called Shield technology, similar to Gold Shield aramid laminate).

In the same way that aramid laminates utilized a poly-film matrix, so too did Dyneema and Spectra laminates. The UHMWPE fibers in laminate armor materials are unidirectional (all running in the same direction) and offset by 90 degrees in each successive layer. While this material, which is still widely used in soft armor, has impressive performance (much lower AD than aramid based armors, no UV susceptibility, positive buoyancy), there are fatal flaws that an end-user must be made aware of.

In addition to having the drawbacks of aramid laminates (de-lamination/peeling, extremely poor breateability), UHMWPE laminates also suffer from heat sensitivity. The UHMWPE molecule is chemically similar to garden-variety Polyethylene (the same material used in plastic milk jugs). When Spectra or Dyneema is exposed to temperatures above 170 Degrees F, it permanently and irreversibly denatures/reverts to the same milk-jug plastic (which has absolutely NO ballistic properties at all).

Because armor is often exposed to a wide range of temperatures (for example, in many parts of the country, a car trunk/interior can easily reach 180-190 F), this is a major concern. Furthermore, since there is no visible change to the material, there is no way for the end user to know if their armor is still viable, or merely layers of coffee can lid. Originally, woven UHMWPE armors were produced (called Spectraflex), but since the higher surface area of the woven fibers made the armor even more prone to heat degradation (a hot cup of coffee, for instance, would have a greater effect on a woven UHMWPE vest compared to a laminate, due to the vapor/moisture barrier properties of the laminate), they were quickly withdrawn from the market.

In addition, Spectra/Dyneema based armors fare poorly in situations where they may be subjected to contact shots- the hot muzzle blast gasses can melt the armor around the impact area, allowing the bullet to penetrate more layers (sometimes even the entire vest) than would have been possible with a woven aramid based vest. All laminates suffer poor contact shot resistance, but UHMWPE is especially susceptible. I will be dedicating a post on contact shots in the coming months.

What does all this mean for you, the end user? First of all, it is vital to identify armor containing UHMWPE, and to a similar extent, first and second generation laminates (I will be posting a tutorial on armor material identification in the coming months). If you are able to assess your needs prior to purchasing armor, ask yourself if you will be operating in environments that expose the weaknesses of UHMWPE or laminates (potential for elevated temperatures, likelihood of contact shots, requirement for high exertion/perspiration). If none of these circumstances are likely to be encountered, the dangers of UHMWPE/Laminates will be minimized. But if one or more apply, it is strongly recommended you find an armor system consisting of 100% WOVEN ARAMID.

It is important to note that this applies only to soft armor. UHMWPE/Spectra/Dyneema/Aramid Laminates find extensive use in hard/rigid armors (both as a pure defense and as backing material for the strike face. This will be discussed in a later post, but for now, please note that evidence strongly suggests in a rigid configuration, UHMWPE/Laminates do not exhibit the same dangers/weaknesses as when utilized in soft armor.

Next: The most dangerous (to the wearer) soft armor material. Stay tuned.