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Bob Cramblitt

Metrology

A Ballet with Live Ammo

3-D laser scanning adds measure of confidence to U.S. Army’s body armor tests

Published: Thursday, January 20, 2011 - 04:30

The term “a measure of confidence” has always been considered a nebulous thing. But it becomes very real when applied to body armor testing at the U.S. Army’s Aberdeen Test Center (ATC) in Maryland. Using a FaroArm Quantum scanner and Geomagic Qualify 3-D inspection software, the Army has decreased the uncertainty of its body-armor test results by as much as tenfold over its former caliper-based process. That translates directly into confidence, according to Craig Miser, chief of the Applied Science Test Division.

“Our accuracy is significantly better now,” says Miser. “We have taken human decision out of the process. Our current process has removed sources of uncertainty and is now defendable and repeatable.”

Accuracy is no small matter when you are dealing with products that are used to protect U.S. soldiers facing armed attacks. It’s also critical to ensuring that customers are getting the maximum benefits out of testing.

“We need to make certain vendors have the best test results to ensure success,” says Miser. “But most important, we want to save the lives of our troops in the battlefield.”

A choreographed test

Testing body armor is like an elaborate ballet involving live ammunition. The highly choreographed action takes place within a 30- to 45-minute window of time. The deadline is governed largely by the conditioned clay used as a stand-in for the human torso. If the clay is exposed to the elements too long, it loses the elasticity needed for accurate back-face deformation measurement.

The process starts with frames containing clay heated to 103°F. The clay is used to display similar impact characteristics as the human torso. An appliqué is applied to the clay so that it curves to fit the contours of the body armor placed over it.

Before the body armor plate is strapped to the clay, a prescan is done with the FaroArm Quantum to serve as reference data (figure 1). This is a 3-D laser scanner mounted on an articulated arm. It can capture the clay surface in minutes with an accuracy of 0.018 mm (one-fifth the width of a human hair).

Figure 1: A FaroArm Quantum 3-D scanner is used to establish reference data for body armor testing at the U.S. Army’s Aberdeen Test Center.

Data from the FaroArm are captured on a laptop and transmitted to a workstation outside of the firing range for immediate processing in Geomagic Qualify software. Geomagic Qualify is used worldwide to save time and increase accuracy for first-article inspection, in-line or shop-floor inspection, trend analysis, 2-D and 3-D dimensioning, and automated reporting.

While prescan data are being saved, the body armor is placed on the clay form, the scanning equipment moved out of the way, and the first shot fired. The body armor comes off, the scanner springs into action to capture the key back-face deformation measurements, and the post-scan is sent to Geomagic Qualify for processing and comparison to the prescan data (figure 2).

Figure 2: A second scan after ammunition has been fired collects data on the back-face deformation of the clay.

Automation accelerates process

Geomagic Qualify automates critical procedures such as registering and merging multiple scans, removing scanning noise, smoothing data, filling holes, and transforming point-cloud data into highly accurate 3-D surface models (figure 3). Further accelerating the process are macros written by ATC’s Jeff Huber that work within Geomagic Qualify to streamline tasks specific to body armor testing.

Figure 3: Point-cloud data of the back-face deformation from the bullet is processed by Geomagic Qualify software.

It only takes about three to five minutes to scan and then about one minute to process the results of each shot, according to Huber (figure 4).

Figure 4: Geomagic Qualify generates a nearly instant analysis of back-face deformation, the key measurement in determining effectiveness of body armor against incoming ammunition.

Testing is done for both soft (vests) and hard (plates) armor at the Aberdeen facility. Hard armor plates are normally tested with a few shots; several shots are fired for soft armor testing, with two of them used for official measurement.

Both soft and hard armor generally go through two types of testing: One is a first-article inspection for a product scheduled for manufacturing, and the other verifies the effectiveness of materials and properties for products under development.

In the case of first-article inspection, testing could stop after the first shot if the results show that the back-face deformation exceeds performance specifications.

Game-changing accuracy

The speed of the ATC process is certainly impressive, but it’s the accuracy that is the game-changer for the Army.

“The old method of using the depth rod of a vernier caliper captured only one point,” says Huber. “Now we can characterize the entire surface and archive the digitized file for further analysis at any time.”

According to ATC lab tests, the uncertainty threshold of test results has been improved tenfold—from 2 mm with the caliper process to 0.2 mm using 3-D scanning and processing (figure 5).

Figure 5: 3-D surface models created in Geomagic Qualify software have decreased uncertainty by tenfold over previous measurement methods.

The 3-D comparisons between pre- and post-scans are generated in an automated report program within Geomagic Qualify and sent on to the Army Project Management Office for further analysis. The results are combined with other research that leads to a better understanding of the effects of ammunition impact on the human body and improved ways of protecting soldiers’ bodies from that impact.

“We have greatly increased confidence in the accuracy of our critical back-face deformation measurements that correlate to human tissue damage,” says Miser. “That benefits our contractors in developing better products, and most of all protects our soldiers who are putting their lives on the line.”

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About The Author

Bob Cramblitt’s picture

Bob Cramblitt

Bob Cramblitt is a writer and communications professional specializing in computer graphics, CAD/CAM, performance benchmarking and IT issues. He’s based in Cary, North Carolina.