Body Armor Guide

Soft armor panels are extremely simple to care for.  There’s one rule:  Don’t expose them to heat in excess of 160°F.  For if they contain UHMWPE, even if only a few layers, exposure to extreme ambient heat will degrade them.  But that’s it; that’s the only rule.  If you need to clean your soft armor panel, a wet rag will usually suffice to remove dirt and grime.  Follow the instructions on the label.

There are a couple more rules for plates, but they’re still simple to care for:  

• Don’t drop them. 
• Don’t expose them to heat in excess of 160°F.
• Try not to submerge them in salt water.

Ceramic armor is highly effective, but the ceramic layer can be damaged if dropped or handled carelessly.  

There’s not much data on how cracks affect the performance of ceramic armor systems, but there’s enough to confirm that cracks decrease ballistic performance.  In “The Effect of Through-Thickness Cracks on the Ballistic Performance of Ceramic Armour Systems,” published in 1995 by Horsfall et al., a cracked system performed worse than an intact ceramic system by 3%.  

“[T}he introduction of a full width, through-thickness, pre-crack reduces the V50 ballistic limit velocity from 764 m/s to 740 m/s, a drop of 3% … The Students t-test was then used to determine the significance of the difference in the [V50s] of the standard and pre-crack samples. This difference was determined to be statistically significant to a level of better than 1%. Therefore it is possible to conclude that the pre-crack does significantly reduce the V50 ballistic limit.”

In 2010, Horsfall revisited the subject in a paper titled “Ballistic and physical properties of highly fractured alumina,” where intact undamaged alumina, explosively shattered alumina, and pressed Al2O3 powder were compared in ballistic experiments.  The ballistic performance of the shattered alumina was roughly 30% worse than that of the intact alumina.  The pressed powder was >40% worse.  (To such an extent that it really had very little ballistic resistance at all.)  

So it appears that through-thickness cracks can decrease performance by as little as 3% to as much as 30%, or perhaps even more than that, depending on the threat and the extent of the damage.  In any case, it is clear that the ballistic performance of damaged ceramics is degraded.  So non-destructive methods of ceramic plate evaluation are critically important.  

The first to see widespread use was the “torque test” described by Haynes et al. in the 2009 paper “Automated Non-Destructive Evaluation System for Hard Armor Inserts of Body Armor,” which could hardly be any simpler.  To quote:

“[The torque test] is a process which an individual grabs opposing corners of a plate and tries to twist the plate listening for crunching or cracking. When this test works, adjoining surfaces of a crack rub and create the sound that reveals the crack.”

Though the torque test has a high false-positive and false-negative rate, it can easily be done in any quiet location, at any time, without any equipment whatsoever.  It has become quite popular, and should be employed whenever ceramic armor needs to be inspected.  

There is, however, an important exception: If a ceramic armor plate is mosaic-style, the torque test will not work and should not be performed.  It’s far more likely to lead to a false positive than a valid result, and it may even damage the armor plate.  If you do not know whether your ceramic armor plate is monolithic or mosaic-style in construction, contact the plate’s manufacturer.  

Similar to the torque test is the “tap test,” which was developed by the US military and is used to evaluate whether or not certain types of ceramic plate have had their ceramic components delaminate from their backers.  As a general rule, the tap test is only useful in the evaluation of military SAPI/ESAPI and SPEAR armor plates.   The test is performed by holding a ceramic plate on the fingertips of one’s non-dominant hand, and then striking the edge of the ceramic strike-face with a metal implement like a bolt or folding knife.  If the plate rings or chimes, much like a bell, then it’s good to go.  If the plate makes a dull thudding sound, delamination should be suspected.  

The tap test won’t work at all on modern armor plates built to comply with the NIJ .06 and forthcoming .07 standards, because those plates generally have thick foam layers on their surfaces.  But if you have, or are issued, SAPI or ESAPI plates — or if you have ceramic armor plates with a minimal foam layer or no foam layer at all (such as the Hesco 4800LV and many older plates built to the NIJ .04 specification) — the tap test should be performed whenever your plate requires inspection.

Ceramic plates can, of course, also be tested via more sophisticated non-destructive means.  Methods proposed in the scientific literature include digital X-ray evaluation, ultrasound, X-ray computed tomography (XCT), microwave interference scanning, and infrared thermography.  Of the lot, XCT is the most established and well-validated method.  XCT requires dedicated and sensitive instrumentation and cannot be performed in the field or individually by end users.  The primary advantage of XCT is that it provides 3-dimensional structural information, which makes results very easy to interpret and fast to read.  Furthermore, XCT images are digital, so the test results can be enhanced, superimposed over digital data from other test sources, and rapidly transmitted to the end-users.  Large police departments and certain military units may find it worthwhile to run XCT analyses of in-service armor plates on a regular, though necessarily infrequent, basis.