A Potential Mechanism for Defeat of Pure Polyethylene Plates by M-855 Projectiles

In more than a decade and a half of destructive testing of armor, to include both pure ultra-high molecular weight polyethylene (UHMWPE) and UHMWPE-backed rifle plates, it has been interesting to note that standard “Green Tip” (aka M-855) ammunition easily penetrates pure UHMWPE plates, and even causes problems for UHMWPE-backed hybrid/combination rifle armor.

Which lead to the working hypothesis that M-855 is able to defeat this material as a function of two factors:

A) Projectile heat, and

B) Non-deformable core

Regarding the first factor, independent testing by several disparate groups has demonstrated that 5.56 bullets can attain temperatures in excess of 500 degrees F upon leaving the muzzle, and retain those elevated temperatures out to several hundred meters. As readers of this site will recall, UHMWPE has impressive strength (tensile strength 15 times that of steel), but is extremely sensitive to elevated temperatures. Above 183 degrees F, it will experience “de-naturation,” and revert back to essentially the same material found in polymer milk-jugs. Hence, a projectile at three times this critical temperature would likely cause heat-denaturation (and outright melting @ 260-277 degrees F) of the fibers in the vicinity of the impact zone.

This would likely be far more noticeable in a pure polyethylene plate, but would also be a factor in ceramic and metal-faced hybrid plates (albeit much less of a factor due to projectile-fracture induced by these hard face materials causing a reduction in projectile thermal mass). M-855 projectiles, having a moderately hard (~45-50 RC) steel insert near the tip, would act as a “hot knife” system (which is how material such as UHMWPE is cut in the manufacturing process). The (ideal scenario) impressive tensile strength for UHMWPE material would be irrelevant due to heat-induced loss of strength.

Regarding the second factor, it offers a possible explanation as to why rounds such as M-193 and M-80 lead core ball are dealt with more easily by pure polyethylene plates. Even though their residual temperatures would be similar (~500 degrees F), their cores are easily de-formable (more so due to heat-softening of the core alloy). It is reasonable to conclude that though similar localized heat-denaturation is taking place, impact forces would cause enlargement of the frontal area of the projectile through deformation of the soft lead-alloy core of these threats, allowing engagement of a greater number of fibers, more rapid cooling, and commensurate increase in projectile-defeat efficiency of the plate.

Comparitively, UHMWPE is roughly 15 times stronger than steel on a per-weight basis. Aramid is roughly 7 times stronger than steel on a per-weight basis. However, UHMWPE loses 100% of its strength (de-naturation and melting) upon instantaneous exposure to temperatures above 277 degrees F. Whereas aramid fibers lose 10% of their strength -over the course of 500 hours continuous exposure- to temperatures above 320 degrees F, and 50% reduction -over the course of 70 hours continuous exposure- to temperatures of 500 degrees F.

So, in an apples to apples comparison, a bullet @ 500 degrees will reduce UHMWPE to essentially zero percent of its prior impressive tensile strength, while aramids will lose a small percentage (instantaneous vs. continuous exposure to 500 degrees F). Even assuming full strength loss similar to 70 hours continuous exposure, aramids will still be 3.5 times stronger than steel vs. UHMWPE (which functionally reverts to standard PE).

So, in an apples to apples comparison, a bullet @ 500 degrees will reduce UHMWPE to essentially zero percent of its prior impressive tensile strength within the impact zone, while a similar aramid matrix will lose a small percentage of its on-paper tensile strength (instantaneous vs. continuous exposure to 500 degrees F). Even assuming full strength loss similar to the worst-case 70 hours continuous exposure, aramid will still be 3.5 times stronger than steel vs. UHMWPE (which functionally reverts to standard PE structure).

It is therefore suggested that aramid unidirectional bias-ply materials be utilized in armors not containing a hardened strike face as a matter of course, specifically in the first third of the ballistic structure. Being far more tolerant of heat, aramid unidirectional fibers would serve to slow and cool the projectile before “hand-off” to the UHMWPE fibers making up the remainder of the plate. This suggestion also pertains to hybrid plates with a metallic or ceramic strike face. It is postulated that up to 50% of the total fiber mass of the pure fiber plate could be constructed with aramid, with a concurrent non-linear increase in functional efficiency.

Conclusions and suggestions for further research: It is reasonable to hypothesize that due to the unique characteristics of UHMWPE used in armor systems, projectiles that include a non-deformable core or sub-core (such as M-855, and the newer M-855A1 and M-80A1) will be more likely to defeat pure UHMWPE plates, and cause decreased real-world efficiency in plates utilizing this material as a backing matrix.

Further research is suggested, in particular post-impact measurement of the frontal cross section of both M-855 and M-193 prejectiles recovered from pure-UHMWPE plates. For more sophisticated labs, microscopic and mechanical evaluation of impact-adjacent UHMWPE fibers can be performed to evaluate potential temperature-induced loss of strength, and/or structural changes that would indicate compromised mechanical characteristics. Similar testing of unidirectional aramid used in rifle backing can also be performed to evaluate the amount of strength loss in each material. It is hypothesized that aramid will be found to lose far less strength as a percentage of its starting strength vis-a-vis UHMWPE.

It is reasonable to suggest that a pure aramid backing matrix for rifle plates would achieve similar or even superior performance vs. UHMWPE backing matrices when confronted by centerfire rifle projectiles due to the greater heat tolerance inherent in aramid. This in spite of aramid’s “on-paper” tensile strength difference compared to UHMWPE. It is further postulated that through optimization of the backing matrix (either with judicious combination of aramid with UHMWPE or use of a pure aramid backing matrix), existing designs might be incrementally improved in excess of what would be expected if simply looking at the “ideal scenario” mechanical strength numbers. Until such time as new materials (such as DuPont’s pending M5 fiber) are made widely available, it is suggested that aramid remains the “best practices” ballistic fiber for broad usage scenarios.

As always, it is my hope that this information will be used to improve the efficacy and safety of life-protecting products.

Copyright 2022, fair-use notice permitted with attribution.

An Introduction and Overview Of D-Rmor Gear FragTuf(TM) Technology

Over the past 15 years, we have been designing, building, innovating, and improving armor, tactical gear, and related equipment. Our philosophy has ever been, “there’s no such thing as over-engineering, merely proper engineering.” After wearing out, destroying, and dissecting more pieces of personal gear than we can recount, there were some themes that kept repeating: stitching geometry, materials, and design are all critical. It sounds like common sense, but after witnessing many gear failures, and tracing them to their causes, we saw that common sense is not so common.

We began to design gear that incorporated advanced materials. Materials normally only found in ballistic armor, such as Kevlar and Twaron. We sought out the best materials, and when they couldn’t be found, we had them custom milled to our specifications. And we realized that using ballistic-rated materials could enhance the overall protective capabilities of the entire system, meaning that pouches and load-bearing gear was no longer pure parasitic weight.

The results of that decade of design, planning, innovation and re-design are now available to you, a dividend that you can benefit from when you purchase any of our FragTuf(TM) gear.

When you see the FragTuf(TM) name, it means that the item is stronger, lighter, better. There are three levels of FragTuf(TM) construction:

FragTuf-A: Utilizes our signature dual-stitching, combining mil-spec Kevlar and Nylon. Can also include advanced HANK (High Abrasion Neoprene Kevlar) laminate.

FragTuf-B: Includes everything found in FragTuf-A, but goes a step further, and contains between one and three layers of fifth-generation woven ballistic aramid.

FragTuf-C The most rugged FragTuf gear includes everything A and B has, with the addition of our custom-milled SpallGuard aramid material, usually in places other makers would use mundane padding.

Our goal is to create a comprehensive line of gear, that is both universally compatible with everything we make, as well as interchangeable and compatible with as much extant gear (current, future, and legacy) as possible. To give you the absolute maximum number of possibilities in setting up your kit, with the absolute best quality and durability.

Body Armor: The Good, The Bad, and The Ugly, Part IV – The Zylon Debacle

With the push to create ever-thinner, ever-lighter concealable body armor, companies cast about for materials that had even better strength-to-weight ratios than UHMWPE. In the late 90’s, they believed they had found a miracle material.

Developed in the late 80’s by SRI International, and marketed by Toyobo a Japanese company, PBO Zylon [poly(p-phenylene-2,6-benzobisoxazole)] promised to be the holy grail of the armor industry. With nearly TWICE the strength and Young’s Modulus of Aramid, and over twice the decomposition temperature (1202 F), Zylon looked to be a champion. Armor companies immediately started producing high-end vests using the new material. Within a short time, laminates began to be used as well, with names such as Z-Shield and Z-Flex.

The armors produced were impressive, unbelievable even. Thinner, lighter, and more comfortable than anything produced up until that time. Nearly a quarter of a million vests were produced before the shine came off the rose.

Despite the impressive statistics put up by Zylon fiber, these were “ideal” numbers. After time in the environment (especially the harsh conditions body armor is subjected to), it was found that Zylon degraded at a horrifying rate. Light and humidity exposure caused as much as a 60% decrease in the effectiveness WITHIN AS LITTLE AS SIX MONTHS. Due to how the fiber was finished (a phosphoric acid scouring process), small amounts of water (such as the vapor found in human sweat) could react with trace quantities of phosphoric acid remaining on the fibers, and trigger those acids to break down the fibers. UV light accelerated the breakdown.

These dangerous properties were brought to light in 2000 by a researcher at a major University, and CONFIRMED by Toyobo in 2001 (who, to their credit, had never recommended this fiber for use in body armor). These findings were dismissed, and Zylon continued to be used in soft armor.

If not for the tireless efforts of individuals such as Kevin “Mad Dog” McClung and Dr. Gary Roberts, this dangerous material may still be used in vests. This in spite of at least 3 deaths directly attributed to Zylon breakdown, leading to vests failing during bullet impacts.

After these high profile failures, and do to the revelations of Zylon’s unsuitability, a rush for the door ensued. Zylon was pulled by numerous manufacturers, and it was decertified by the NIJ for use in armor. The trouble is, a lot of these vests still remain in circulation today, either because the wearer was not made aware of the issue, or unscrupulous sellers feel that making a quick buck selling, essentially, garbage, is more important than the wearer’s safety.

Zylon should never, EVER be used in armor. If you have a vest that contains ANY, it is not safe, even if it is only a small portion. Identification of this material is paramount, and I will be posting a tutorial in a future post to allow people to determine what their armor consists of.

So avoid Zylon, at all costs, and stay safe!

Next time: We look at hard armor. Same time, same channel!

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

And so it was that a great need was upon the land. With projectiles achieving higher velocities, and greater penetration, Nylon just was not cutting the mustard. Even though it excelled silk for use in soft armor, it still lacked the requisite tensile strength to stop modern copper jacketed handgun rounds in anything approaching wearable ADs.

In 1965, a Dupont chemist named Stephanie Kwolek stumbled upon a new material while searching for alternatives to steel in tire reinforcements. This new material had a tensile strength 5 times that of steel on an equal weight basis. The structure resembled natural silk, but what made Kevlar outstanding was the propensity for the fibers to form cross-linked hydrogen bonds at 90 degrees to the polymer chain. This gave the new fiber exceptional tenacity, making it ideally suited for use in ballistic armor.

This, combined with excellent heat and flame resistance (Aramid fibers do not burn, they char at around 700 F), lead to a resurgence in concealable personal body armor. Richard Davies, founder of Second Chance, immediately saw the potential of this fiber, and the modern “bulletproof vest” was born.

Kevlar is the trade name for aramid fiber developed by Dupont, but there are several different brands of aramid fiber, including Teijin’s Twaron. Though originally discovered by Dupont, Teijin, a Netherlands based company, perfected and patented an aramid fiber processing method that Dupont later licensed to use themselves. Whether we are talking about Kevlar aramid or Twaron aramid, the properties are very similar.

To this day, aramid is widely used in armor applications. During the 70’s and 80’s, the only form used was woven fabric, cut and layered up to 35 plies deep. In the 90’s, new iterations of bullet resistant composites were brought to market, including laminates.

Laminates were introduced in search of the ever moving goal post of thinner and lighter armor. Of course, as has been the case throughout history, heavy and cumbersome armor is not fun to wear. To get folks to wear their armor, thin and light make sense. However, as will be seen, laminates were not necessarily better, and could even be seen as a step backwards (at least the first and second generation iterations).

Laminates such as Goldflex and Gold Shield utilize polypropylene films (chemically similar to food preservative film) to sandwich unidirectional aramid fibers in alternating 0 degree and 90 degree layers. Admittedly, this results in a very good material for stopping bullets, including hits near the edge of a panel, and at acute angles to the panel.

Unfortunately, several drawbacks rear their ugly heads with aramid laminates. First off, they have the breatheability of plastic wrap. Which is zero, since similar materials are used as vapor barriers. Secondly, the plastic film has a nasty tendency to melt when the panel is subjected to the hot muzzle blast of contact shots (an event all-to common in the course of law enforcement). In contrast, woven aramid is extremely effective at resisting contact shots. Finally, armor made with first and second generation laminates experience accelerated wear, since the adhesion of the film is degraded by repeated exposure to flexing, heat, cold and moisture.

While an armor built with woven aramid could reasonably be expected to survive (and remain fully effective!) for over 25 years (and I have personally verified that they HAVE), a laminate constructed armor is usually toast after only two years of normal wear. The edges curl, the layers peel apart, and the ballistic effectiveness drops to unsafe levels. In much the same way that a chain is only as strong as its weakest link, first and second generation laminates are hobbled by their use of, essentially, plastic wrap in their construction.

Next episode, we will look at another laminate, one that has great numbers, but hidden dangers…

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

This will be the first part of an ongoing series providing an in-depth look at modern body armor, the materials used, and the pros/cons of these same materials. I will do my best to make it accessible, without pontificating too heavily. I will rely on my trusty readers to keep your humble author firmly grounded in reality, so if things get out of hand…let me know.

Without delving too far back into the history of protective gear (which, like a history of the martial arts, would involve sticks/rocks/major bones, and other guys wearing the skins of luckless beasts to prevent getting injured/killed by these sticks/rocks/major bones), it can be said that humans have always tried to give themselves an advantage in mortal contests. When the gun came on the scene, it shook things up a bit, but did not alter this fundamental reality. It just took a while for science to catch up.

The first verifiable shot-proof armors date back to the late 15th and early 16th century, appearing in both Europe and Asia. These were typically heavier versions of the standard plate armors (usually just the breast/thoracic plates), and while they did the job, the increased weight (never mind bulk), made these largely impractical in a combat setting.

And forget about concealment.

Armor smiths, lacking modern test methods, would use the expedient of shooting the finished article as a means of proofing it, and the dent was your guarantee that it would stop a round (as long as you shot it with the exact same combination of black powder, lead round-ball, barrel length, distance…). The first bench tested armor.

Most armor, by and large, fell out of favor after that, because carrying all that weight detracted from mobility (translation: on campaigns that lasted months or years, all the non-essential kit gets sold for beer/grog/mead/ale money and women of negotiable chastity).

With some notable exceptions (The ACW,The Franco-Prussian War, Ned Kelly’s gang, and the Great War), steel fell out of favor, at least for a time, as a personal armor material.

The first true “concealable” bullet resistant armor came about in the late 1800’s, and it is interesting to note that two inventors working (at first) separately, came up with very similar ideas A Ukrainian Catholic priest by the name of Casimir Zeglin developed a fabric-based armor that was successful at stopping the typically low-velocity, unjacketed projectiles of the times. He would start a tradition later used by Richard Davies of Second Chance, proving the efficacy of his armor by wearing it whilst being shot. The first successful demonstration was given in 1897, and over the next 30 years the concept was refined. A Polish inventor, Jan Szczepanik had also been developing silk-based body armor, and the two combined their talents to bring the vests to market in 1901 The vests consisted of silk, of a very tight weave. 4 layers was sufficient to stop most typical pocket pistols of the 1890’s-1900’s. The thickness was 1/8″ and the Areal Density (or AD, you will be seeing this abbreviation a lot) was .5 lb/ft sq.

Among the first notable “saves” attributed to his armor was the King of Spain, Alfonso VIII, who’s “uparmored carriage” protected him from an assassin’s bomb at his wedding in 1906. A notable “fail” (if only because the assassin chose an unprotected target area, the head) was Archduke Franz Ferdinand in 1914, who was wearing a silk-based vest.

Concealable silk body armor continued to increase, gaining modest popularity in the 20’s and 30’s, both with peace officers and their opposite number. During the Prohibition, the wearing of bullet-resistant vests became such an issue that the FBI developed the .38 Super for the 1911 in large part to enable penetration of soft armor and car bodies.

During World War II, body armor made some headway. Aside from some very Ned Kelly-esque steel armor suits worn by a few Russian troops for urban combat, they consisted of fabric. In the early years, bomber pilots would bring extra (silk) parachutes to place under them, which did a fair to underwhelming job at protecting from flak.

Development of the “wonder fiber” Nylon led to the manufacturing of the first “flak jackets,” heavy, bulky vests that gave the wearer modest protection against this very deadly threat. These jackets saw limited use, due to their encumbering nature. Similar armor was used in Korea and Vietnam, (the latter conflict which also saw the introduction of the first rifle-proof armor in years). Something better was needed, to get weight and bulk down. And something better was just around the corner.

Next In Part II: Kevlar Arrives on the Scene