Annual X-ray testing of monolithic ceramic plates

Tactical Gear Tactical Gear
1

Hi All

I am in the process of contacting manufacturers and “people in the know” to request information about the pass and fail criteria when it comes to X-raying privately-owned monolithic ceramic plates (body armour).

I am going to draw up a technical guide for the X-raying of these plates using high-end medical X-ray units (digital radiography).

I have conducted some preliminary tests with ceramic, glass and porcelain tiles and also with ceramic plates from used body armour.
I now know what sort of image quality I can get, but there are two pieces of information I need in order to set up the final protocol for these plates.

  1. When it comes to cracks, what is the maximum width permissible (say for a level III monolithic ceramic plate) before the plate is deemed unsuitable for use? This is not such a simple question, because there are very small cracks in the micrometre range and then there are the larger (but nonetheless very fine) cracks such as what we see in radiology of undisplaced fractures.

  2. When it comes to low density areas or indications of porosity, what is the maximum area permissible, before the plate is deemed unsuitable for use?

I suspect that for monolithic ceramic plates both questions may have different answers depending on the material from which the plate is made, the thickness of the plate and its advertised rating.

Without getting into how these plates are made or what the material is, I just need to be able to match or exceed whatever X-ray imaging the manufacturer would employ for an annual inspection. I am looking at strategies to index the images in serial examinations, much the same as we do for medical imaging on PACS (Picture Archiving and Communication System).

If anyone has any contacts who can help with this information, that would be much appreciated.
PMs are welcome if you want to check my background :cool:

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Radiographs are only one possible method for annual non-destructive inspection of hard armor plates…

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I’ve looked into it and there are several ways of doing it, yes.

For this thread I am only concerned with radiography. That’s partly why I need the answer to the two questions I posed. Those answers will determine whether the radiography is sufficient or not (and if it is sufficient, what the detection requirements are).

If radiography isn’t sufficient, then private owners of body armour need to know what exactly they need to be doing for their annual inspections.

4

There has never been a definitive answer on what is or isn’t an “acceptable” crack in a ceramic plate. Without going into detail, I’ve had God knows how many conversations about this with the folks running these programs and no one has a definitive answer and that’s when everyone is using the same manufacturer/model plates.

Remember that “cracks” vary in width, depth, length, and location. Some “cracking” is acceptable but beyond that it gets really, really murky.

Additionally, on certain military plates detailed testing is done re: intentionally shooting test rounds directly on cracks and the rounds must still be stopped but often with different percentages, etc.

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Hi David

That was my understanding when it comes to plates being fielded and inspected by the US Army. I found some interesting reading about Army Contract 0040 here:

http://tinyurl.com/ozpqxs7

That report is a bit dated now, but they do reference the shooting of plates where cracks have been found (see page 21 and 22):

PEO Soldier stated that the Army conducts multiple levels of continuous testing throughout the life cycle of the ballistic plates, including rigorous first article testing, lot acceptance testing, and surveillance testing. The lot acceptance testing is conducted at ambient conditions with the same test and scoring criteria as the first article tests, thereby increasing the statistical confidence that the plates accepted are of the highest quality and will meet the soldiers’ needs for protection.

PEO Soldier stated that the M3D2S2 design passed 15 of 17 lot acceptance tests, providing the Army high confidence that the plates met the performance requirements. Further, PEO Soldier stated that the plates are also undergoing surveillance testing, which requires the plates to be x-rayed in Kuwait. If cracks are found, the plates are sent to Aberdeen Test Center, Aberdeen Proving Ground for further testing.

PEO Soldier stated that, of the 1,750 plates sent to the Aberdeen Test Center, 533 have been live-fire tested. Testing results indicate that when tested against the most prevalent round found in theater and on the most vulnerable part of the plate (location of the crack), the plates have successfully stopped 180 of 180 shots (100 percent). In addition, in testing conducted with ammunition beyond what would be found in theater, the plates successfully stopped 212 of 278 shots (76.3 percent).

Note that the DoD Inspector General had reservations about the statistical validity of that testing (you can read about that on page 22).

In another document, PEO Soldier acknowledged that the exact technical requirements of their X-ray inspection system are not documented, but need to be. See this report:

http://tinyurl.com/pe2q6qt

From Page 17:

The Army has not determined whether x-raying ballistic plates with the Testing Equipment should be a published requirement and therefore, has not issued guidance regarding its limitations and capabilities.

From page 18:

The Testing Equipment Draft Acquisition Strategy states that the equipment inspects ballistic plates at a rate of at least 240 per hour with an accuracy rate of 95 percent. The inspection process starts with the material handlers sorting ballistic plates by size and
condition, and then inserting the ballistic plates onto the system’s conveyer belt. As the ballistic plates pass through the Testing Equipment, an x-ray is taken and compared to the manufacturer’s standard image to determine if there are differences. If there are cracks or other anomalies, the Testing Equipment rejects the plate and automatically offloads it into a discard bin.
The material handler then places a “Requires Further Testing” label on the plate (Figure 13). For ballistic plates that pass the testing, material handlers place a “Passed Inspection” label on the plate (Figure 14).
If the ballistic plates pass the testing, but have an external material failure, material handlers place an external material failure “For Training Purposes Only” label on the plate (Figure 15). An external material failure includes a rip or tear in the ESAPI outer covering.

PEO Soldier’s comment on page 26:

PEO Soldier agreed and stated that the Army continuously tests and evaluates the capabilities of the Testing Equipment and that PEO Soldier will make a recommendation to Headquarters, Department of the Army, to x-ray all serviceable ballistic plates with the Testing Equipment. PEO Solder also stated that if the Department of the Army decides that the use of the Testing Equipment should be a requirement, PEO Soldier will develop guidance including the equipments’ capabilities and limitations, and how often and which ballistic plates should be x-rayed.

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I find it interesting from the point of view that they were (are?) using an automated X-ray unit with Computer Aided Detection (CAD) for finding cracks.

Here is some further detail on the automated X-ray unit (the inventor is listed as Karl Masters, patent filed October 2007):

http://www.google.com/patents/US20120177177

Karl Masters is a well respected individual and I can find nothing in any of the reports that criticizes the X-ray equipment itself.

I question whether a private individual (or even a security firm) would have access to that technology to inspect their plates.

There is also the nagging question about the widths of the cracks vs the compromised integrity of the plate vs the ballistic testing of a cracked plate. How do you precisely aim at a crack on a plate which cannot be seen externally? I don’t know how they are doing it at the Aberdeen Proving Ground test center. It may very well turn out to be the case that a closed crack doesn’t change the ability of a plate to stop a first round. I would love to know the details on that…

Of course, being the skeptic that I am, I also question whether an automated system as described in the article can apply CAD to plates which are X-rayed in their outer carriers (any sort of grit in the fabric could affect the CAD although I conceded it will probably result in more false positives than false negatives). I also don’t know whether the system can detect density defects such as indications of porosity within the plate. I’ll see if I can get Karl Masters to comment here directly on that, as I don’t know the detail of his system.

Nonetheless it is a side issue.

I think the military inspection of these plates, the arguments about first article testing, the criticism about the Army’s storage and transport and maintenance of these plates is very interesting.

But…I also think it is a whole different “animal” compared to the testing and maintenance of privately-owned body armor. You have a huge amount of plates which means there are added pitfalls in the storage, transport and inspection of the items in bulk.
This is not what the private owner has to deal with.

I have been finding in some preliminary tests with porcelain, ceramic and glass that the appearance of cracks can vary (and even disappear) depending on how a plate is aligned to the X-ray beam. These tests so far have been with flat tiles. The likelihood of the effect is going to be increased with curved plates, because you have a diverging beam and therefore you can have foreshortening of any artefacts found.

The private person is going to be X-raying the plates on a system which relies on subjective interpretation of an image displayed on a screen. That in itself introduces a whole host of variables:

  1. Equipment differences (stationary anode vs rotating, etc)
  2. Image receptor differences (film, CR, DR)
  3. Differences in display algorithms (histograms and filters)
  4. Monitor differences (DICOM display vs others, megapixel ratings etc)
  5. Issues to do with consistency in serial examinations (the reason why I want to write a guide).
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I am going to bump this once and specify I am interested in civilian plates. Should we be X-raying them annually or not?