Phase I Report on Review of the Testing of Body Armor Materials for Use by the U.S. Army Letter Report (2009) / Chapter Skim
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, namely: • In Phase I, the committee will comment on the validity of using laser profilometry/laser interferometry techniques to determine the contours of an indent made by a ballistic test in a non-transparent clay material at the level of precision established in the Army's procedures for testing personal body armor. If laser profilometry/laser interferometry is not a valid method, the committee will consider whether a digital caliper can be used instead to collect valid data.
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During the site visit, the committee members engaged in direct observations of how A TC staff performs body armor testing using laser scanning 1 and digital caliper methodologies. The committee also witnessed the entire procedure for assessing the part-to-part consistency of the clay used in body armor testing.
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Larry G Lehowicz, Chair Committee to Review the Testing of Body Armor Materials for Use by the U.S.
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Armor testing therefore has implicit goals of ensuring that body armor meets survivability standards at an acceptable weight while allowing sufficient soldier mobility. Ceramic materials have been used successfully in personal armor systems to defeat small-arms threats.
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The deepest impression left in the clay is measured and analyzed as an indication of the survivability of a soldier, subjected to a similar shot, protected by a 5 similar plate in a protective vest. COMMENTS ON THE V ALIDITY OF USING LASER PROFILOMETRY/LASER INTERFEROMETRY FOR TESTING BODY ARMOR The Historical Measurement Approach Used in Testing Body Armor Historically, the digital caliper has been the measurement tool of choice for the testing of body armor.
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The shoot pack is then removed, and the laser scanning system is used to scan the surface of the appliqué in order to provide a reference surface relative to which subsequent deformations caused by the firing of the projectiles can be compared. Prior to the scanning of the surface of the appliqué, three reference points along the top and side of the aluminum frame around the clay box are used for calibration of the laser scanner's spatial location on thex-y, x-z, and y-z planes.
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001: ® Measurement of Backface Deformation [BFD] using Faro Quantum Laser Scan Arm and Geomagic® Qualify® for Hard and Soft Body Armor" (Aberdeen Proving Ground, Md.: Aberdeen Test Center, September 1, 2009)
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The measurement error of the laser scanning system and the digital caliper has been documented by the Army in several publications, including the following: • The U.S. Army Aberdeen Test Center (A TC)
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TABLE 1 Error Budget Measured for Etched Metal Gage Block Measurement Using Faro® Laser Scanner and Digital Caliper Components of Uncertainty Per Instrument, (mm) Faro ® Laser Scanner T ype Component Digital Caliper A Operator and session 0.0147 0.0074 variability B Inter-instrument variability 0.0323 0.0073 a,b,d Combined standard uncertaintyc 0.0355 0.0104 Expanded uncertainty d 0.0710 0.0208 Mean length e 50.7957 50.8015 a Instrument uncertainty obtained from Faro ® manufacturer's documentation was judged by the committee to be sufficiently like that in current use.
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Faro® Laser Scanner T ype Component Digital Caliper A Operator 0.0410 0.4715 random error 0.0817 0.3600 0.0325 a 0.0073 b Instrument specification B Correction factorc NA 0.570 d Combined standard uncertainty 0.0970 0.823 e 0.1939 Expanded uncertainty 1.645 a Instrumen t uncertainty obtained from FARO manufacturer's documentation was judged by the committee to be sufficiently like that in current use. b Digital Caliper uncertainty estimate obtained from manufacturer's document was judged by the committee to be sufficiently like that in current use.
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, Live Fire Test and Evaluation, and Tracy Sheppard, Executive Officer and Staff Specialist, OSD DOT&E Live Fire Test and Evaluation, "DoD in Brief to the National Research Council Study Team," presentation to the committee, Aberdeen, Maryland, November 30, 2009. As the committee examined its statement of task, it decided that it was necessary to determine first whether the laser scanning system is valid at the level of precision established in the Army's procedures.
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The first approach was to compare the laser's precision with that of the digital caliper's when used to make BFD measurements. The second approach was to compare the laser's precision to the total measurement variation.
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, if used in accordance with the Army's procedures, is a valid approach for determining the contours of an indent in a nontransparent clay material at a level of precision adequate for the Army's current ballistic testing of body armor. INTERIM OBSERV ATIONS ON COLUMN-DROP PERFORMANCE TESTS TO ENSURE THE CONSISTENCY OF CLAY USED IN BODY ARMOR TESTS In the testing of body armor, the medium used to record the backface deformation of a ceramic armor system experiencing ballistic impact is a multicomponent modelingclay body (also referred to as "clay")
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Roma Plastilina #1 has been adopted as a recording medium used to assess the likelihood of injury or death from ballistics, and its use has been extended from originally assessing soft armor (e.g., Kevlar™ vests) to use in assessing hard armor plates, knife wounds, industrial injuries to a drop-forge operator, and nonlethal projectiles (Lyon, 1997; Karahan, 2008; V aughan, 2001; O'Callaghan et al., 2001; Chadwick et al., 1999)
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This indicates an understanding by Army personnel that there are effects on the behavior of the clay from both the thermal history and the shear history of the clay. Based on reports that have been reviewed by the committee and on what it observed at Aberdeen Proving Ground, the Army employs the following procedures to ensure a common history to the modeling clay used as a backing material in the testing of body armor: 1.
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One implication of this assessment is that the Army procedure of allowing a second calibration, run after the rebuilding of the surface of the clay box and thermal re-equilibration, does not invalidate the use of that box in an armor test. Interim Committee Assessment of the Column-Drop Performance Test Method It is the assessment of the committee that Army personnel demonstrated an awareness of the combined influence of thermal and shear history on the behavior of a modeling-clay body.
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is a valid method for assessing the part-to-part consistency of clay boxes used in body armor testing. In its Phase II task, the committee will further analyze the data provided by the Army, conduct an open-literature search for studies and analyses that bear on oil-based modeling clay (which is widely used as a model material in deformation studies in fields as disparate as metalworking and earthquake simulation in addition to ballistic studies)
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10-2-210 Ballistic Testing of Hard Body Armor Using Clay Backing. Aberdeen Proving Ground, Md.: Aberdeen Test Center.
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2008. Summary Report of Laser Scanning Method Certification Study for Body Armor Backface Deformation Measurements.
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