Appendix D


Test Range Description and the Ballistic Testing Process

The combat helmet test range at Aberdeen Test Center (ATC) is shown in Figures D-1a and D-1b. The ATC firing range uses a rifle-like test barrel to fire a projectile against a helmet. Electronic instrumentation is used to measure projectile velocity before impact. Tested helmets are affixed to headforms that are packed with modeling clay, where the clay serves as a recording medium.

Per the Director of Operational Test and Evaluation (DOT&E) test protocol, the test range is set up in accordance with a variety of ATC Test Operating Procedures; see Table 1 in the DOT&E FAT and LAT protocols (DOT&E, 2010, 2012). The test ranges are environmentally controlled at 68 ±10°F and a relative humidity of 50 ±20 percent (ATC, 2013).

Per ATC (2013), in the range set-up, the test barrels are mounted in a universal receiver, and the weapon is fired using a solenoid. A double base configuration of light screens is used to measure projectile velocity, and drag is applied to calculate strike velocity. A yaw card is used in conjunction with a go/no-go gauge to check the striking yaw of the projectile.

image

FIGURE D-1a The helmet test range at the U.S. Army Aberdeen Test Center. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013.

image

FIGURE D-1b Typical test range at set-up for helmet V0 testing. SOURCE: ATC (2012).

In general, the test is conducted in accordance with National Institute of Justice (NIJ) Standard 0106.01 with the following four exceptions (NRC, 2012):

•   Test items may be conditioned as required.

•   Test distances may be altered.

•   The ATC headform is modified from the NIJ head-form with slots in both the coronal and midsagittal directions.

•   Striking velocities are calculated according to the U.S. Army Test and Evaluation Command International Test Operating Procedure 4-2-805 in order to determine if a shot is fair (DOT&E, 2010).

Ballistic testing of combat helmets involves both the evaluation of resistance to penetration (RTP) and helmet backface deformation (BFD) as recorded in clay. With the exception of V50 testing, RTP and BFD are measured on a metal headform (Figure D-2) packed with Roma Plastilina #1



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Appendix D Test Range Description and the Ballistic Testing Process The combat helmet test range at Aberdeen Test Center (ATC) is shown in Figures D-1a and D-1b. The ATC firing range uses a rifle-like test barrel to fire a projectile against a helmet. Electronic instrumentation is used to measure projectile velocity before impact. Tested helmets are affixed to headforms that are packed with modeling clay, where the clay serves as a recording medium. Per the Director of Operational Test and Evaluation (DOT&E) test protocol, the test range is set up in accordance with a variety of ATC Test Operating Procedures; see Table 1 in the DOT&E FAT and LAT protocols (DOT&E, 2010, FIGURE D-1b Typical test range at set-up for helmet V0 testing. 2012). The test ranges are environmentally controlled at SOURCE: ATC (2012). Figure E-1b fixed 68 ±10°F and a relative humidity of 50 ±20 percent (ATC, 2013). Per ATC (2013), in the range set-up, the test barrels are used to measure projectile velocity, and drag is applied to cal- mounted in a universal receiver, and the weapon is fired using culate strike velocity. A yaw card is used in conjunction with a solenoid. A double base configuration of light screens is a go/no-go gauge to check the striking yaw of the projectile. In general, the test is conducted in accordance with National Institute of Justice (NIJ) Standard 0106.01 with the following four exceptions (NRC, 2012): • Test items may be conditioned as required. • Test distances may be altered. • The ATC headform is modified from the NIJ head- form with slots in both the coronal and midsagittal directions. • Striking velocities are calculated according to the U.S. Army Test and Evaluation Command Interna- tional Test Operating Procedure 4-2-805 in order to determine if a shot is fair (DOT&E, 2010). Ballistic testing of combat helmets involves both the evaluation of resistance to penetration (RTP) and helmet FIGURE D-1a The helmet test range at the U.S. Army Aberdeen backface deformation (BFD) as recorded in clay. With the Test Center. SOURCE: Kyle Markwardt, Test Officer, Aberdeen exception of V50 testing, RTP and BFD are measured on a Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Proto- metal headform (Figure D-2) packed with Roma Plastilina #1 Figure E-1a fixed cols Committee,” presentation to the committee on March 22, 2013. 124

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APPENDIX D 125 1997) . (See Chapter 6 for further discussion of the V50 cal- culation methodology.) Appendix A of the DOT&E FAT protocol (DOT&E, 2010) specifies the distribution of helmet sizes and impact location order for V0, V50, and hardware testing. See Chapter 5 for additional discussion. The DOT&E LAT protocol does not specify helmet sizes, but impact location order for V0 test- ing is contained in Appendix B. See Chapter 7 for additional discussion. TEST ITEM CONFIGURATION AND IMPACT LOCATIONS To allow positioning the headform in the required posi- tions, the headform used is mounted on a test fixture capable of being rigidly fixed with six degrees of freedom. Prior to mounting, the helmet is marked to show the impact locations and the helmet pads are put into a standard configuration, as illustrated in Figure D-6. For V0 testing, the helmet is mounted on the headform in accordance with IOP PED-003 using the helmet’s suspen- sion/retention system to hold it on the headform (Figure D-7). Per IOP PED-003, “The finished helmet will be FIGURE D-2 U.S. Army Aberdeen Test Center headform. mounted on the headform such that it has the standoffs given SOURCE: NRC (2012). in table from the inside of the crown shell to the top of the clay (as illustrated in Figure D-3), which ultimately results in crown clay” (ATC, 2013). a completed test headform such as that shown in Figure D-4. The headform is mounted on the test frame shown in Per the test methodology, a helmet is placed over the Figure D-8. The helmet is aligned to ensure the target loca- clay-filled headform. RTP (or V0 testing) is then conducted tion achieves the required obliquity. During the test, the as a sequence of five ballistic impacts, one each to the front, velocity of the projectile is measured using Oehler Model rear, left, and right sides of the helmet, and the helmet crown 57 Ballistic Screens to verify that it was within the desired (Figure D-5). Internal Operating Procedure IOP PED-003 range (NRC, 2010). A fair hit is recorded if the shot location, specifies the precise requirements for the five impact loca- obliquity, yaw, and shot velocity are within required limits as tions for V0 9-mm RTP/BFD testing. In addition, the ballistic specified in the DOT&E protocol (and associated reference forces from the bullet cause an indent in the clay from which documents). BFD is measured. Current protocol also tests the V50 ballistic limit using a series of 6 to 14 shots to the five regions of the helmet at varying velocities per MIL-STD-622F (DoD, FIGURE D-3 Packing the headform with clay and shaping the clay. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013.

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126 REVIEW OF DEPARTMENT OF DEFENSE TEST PROTOCOLS FOR COMBAT HELMETS FIGURE D-5 Test impact locations. SOURCE: NRC (2012). Figure E-5, fixed FIGURE D-4 U.S. Army Aberdeen Test Center headform with clay. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Commit- tee,” presentation to the committee on March 22, 2013. Figuer E-4 FIGURE D-6 Pad Configuration for V0 resistance to penetration testing for full cut style helmet (top) or the tactical cut style helmet (bottom). SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013. Figure E-6

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APPENDIX D 127 Measuring Resistance to Penetration In V0 testing, resistance to penetration is measured by visual presence of either (1) the projectile or pieces or frag- ments of the projectile in the clay of the headform (Figure D-9) or (2) by a hole that passes thru the helmet shell. For hardware and V50 testing, penetration is recorded via a wit- ness plate inserted in the headform. See Figure D-10 for hardware testing and Figure D-11 for V50 testing witness plates. V0 testing is conducted with the helmet retention and pad systems in place, while V50 testing is conducted without the retention and pad systems. Measuring Backface Deformation Helmet BFD, defined as the maximum depth in clay as measured from the original clay surface at the intended impact location, is assessed using the nonperforating bal- listic impacts from RTP testing. It is measured as follows. After mounting the headform in the test fixture and mount- ing the helmet on the headform, the helmet is removed from the headform, and the clay surface is scanned with a Faro® Quantum Laser Scan Arm laser. The helmet is then reat- tached to the headform, and the shot taken. The helmet is again removed from the headform and inspected for penetra- tion and perforation. The clay is rescanned with the FARO laser to calculate BFD. Figure D-12 is an illustrative BFD indentation in the clay. ATC IOP-002 revision E describes the BFD measure- ment process using a Faro scanning laser instrument scan FIGURE D-7 Helmet mounted on a headform. SOURCE: ATC (2013). Figure E-7 FIGURE D-8 Test frame and fixture. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013. Figure E-8

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128 REVIEW OF DEPARTMENT OF DEFENSE TEST PROTOCOLS FOR COMBAT HELMETS arm (Figure D-13) and associated software. As described in Testing of Body Armor Materials: Phase III: Laser profilometry, as used by the Faro scanning laser instru- ment, employs the commonly used principle of optical triangulation. A laser generates a collimated beam, which is then focused and projected onto a target surface. A lens reimages the laser spot formed on the surface of the target onto a charge-coupled device, which generates a signal that is indicative of the spot’s position on the detector. As the height of the target surface changes, the image of the laser spot shifts owing to parallax. To generate a three- dimensional image of the specimen’s surface, the sensor scans in two dimensions, generating a set of noncontact measurements that represent the surface topography of the specimen under inspection. The data are then used to compute the three-dimensional geometrical profile of the surface, with readings essentially continuous over the scanned region. Thus, the laser scanner produces a series of measurements over the whole surface of the clay, as opposed to the single reading obtained with the digital caliper (NRC, 2010, pp. 97-98). Clay Calibration FIGURE D-9 Example of headform showing a penetration as As described in the Phase II and Phase III body armor evidenced by the presence of projectile fragments in the clay. reports (NRC, 2010, 2012), the Roma Plastilina #1 clay Figure E-9 SOURCE: ATC (2013). currently being used to test helmets and body armor must be heated to achieve rheological properties consistent with past FIGURE D-10 Witness plate headforms for hardware testing. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013. Figure E-10

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APPENDIX D 129 FIGURE D-11 V50 helmet test mount (left) and associated witness plate (right). SOURCE: ATC (2013). Figure E-11 FIGURE D-12 Headform showing indent in the clay as a result of helmet backface deformation. SOURCE: Janice Hester, Research Figure E-12 Staff Member, Institute for Defense Analysis, “DOT&E Helmet Test Protocols Overview: Statistical Considerations and Concerns,” FIGURE D-13 Faro® scanning laser instrument laser scan arm. presentation to the committee on January 25, 2013. SOURCE: NRC (2012). Figure E-13

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130 REVIEW OF DEPARTMENT OF DEFENSE TEST PROTOCOLS FOR COMBAT HELMETS FIGURE D-14 Headform clay conditioning by analogy. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED- 003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013. Figure E-14 tests. This occurs because the manufacturer has changed the Roma Plastilina #1 clay composition over time for commer- cial reasons unrelated to armor and helmet testing. For helmet testing, the clay in the headform is calibrated by analogy to a reference 12 inch × 12 inch × 4 inch ply- wood-backed box of clay.1 Up to eight headforms may be conditioned with each box as long as the clay in the box and in the headforms come from the same lot and the headforms are conditioned within 12 inches of the box (Figure D-14). Once conditioned, calibration of the box is performed via drop test in which 2.2-lb, 1.75-in.-diameter steel cylinders are dropped three times from a height of 78.7±0.8 in. into the clay box. The test rig is shown in Figure D-15. The clay is considered to be within calibration if the indentations made by the steel cylinders are all within 1.0±0.1 in. as measured by a digital caliper (NRC, 2012). The first clay headform removed from the oven with the clay box may be used for up to 45 minutes after the third drop. The remaining headforms may be used for up to 4 hours from the time of the third drop and for up to 45 minutes after being removed from the oven (NRC, 2012). 1Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to FIGURE D-15 Clay calibration test rig. SOURCE: ATC (2013). the committee on March 22, 2013. Figure E-15

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APPENDIX D 131 FIGURE D-16 Examples of helmet conditioning. SOURCE: Kyle Markwardt, Test Officer, Aberdeen Test Center, “Helmet IOP PED-003 Briefing to NRC Helmet Protocols Committee,” presentation to the committee on March 22, 2013. Helmet Conditioning REFERENCES First article testing requires ballistic testing after the fol- ATC (Aberdeen Test Center). 2012. Helmet Ballistic Testing Procedures. lowing conditioning: Internal Operating Procedure PED-003. Aberdeen, Md. March 7. ATC. 2013. “Helmet Testing Procedures.” Presentation to the Committee on Review of Test Protocols Used by the DoD to Test Combat Hel- • Ambient: conditioned at 68 ±10°F and a relative humid- mets on January 25, 2013. Available from National Research Council, ity of 50 ±20 percent; Washington, D.C. • High temperature: conditioned at 160 ±10°F for mini- DoD (Department of Defense). 1997. Department of Defense Test Method mum of 24 hours; Standard: V50 Ballistic Test for Armor. MIL-STD-662F. U.S. Army Research Laboratory, Aberdeen Proving Ground, Md. • Low temperature: conditioned at −60 ±10°F for mini- DOT&E (Director of Operational Test and Evaluation). 2011. Standardiza- mum of 24 hours; tion of Combat Helmet Testing. Memorandum from J. Michael Gilm- • Seawater soak: fully submersed in 3 ft. seawater for ore, Director. September 20, 2011. Office of the Secretary of Defense, minimum of 3 hours; Washington, D.C. [reprinted in Appendix B] • Accelerated aging: 30-lb weight on the apex of the DOT&E. 2012. Standard for Lot Acceptance Ballistic Testing of Military Combat Helmets. Memorandum from J. Michael Gilmore, Director. shell, conditioned for 4 hours at a temperature of 104 ±2˚F May 4, 2012. Office of the Secretary of Defense, Washington, D.C. followed by conditioning at a minimum ozone level of 50 +5 [reprinted in Appendix B] mPa partial ozone pressure for 72 hours; and NRC (National Research Council). 2010. Testing of Body Armor Materi- • Weather resistance: exposed to 100 kJ/m2 of energy. als for Use by the U.S. Army—Phase II: Letter Report. The National Academies Press, Washington, D.C. NRC. 2012. Testing of Body Armor Materials: Phase III. The National See Figure D-16 (ATC, 2013, slide 17; Marqwardt, 2013, Academies Press, Washington, D.C. slides 23-26) for examples of helmet conditioning. For additional details and information about the testing process, see ATC (2013), the documents listed in Table 1 of the DOT&E FAT and LAT protocols (DOT&E, 2010, 2012), and particularly MIL-STD-3027 [Department of Defense Test Method for Performance Requirements and Testing of Body Armor (DoD, 1997)], ATC-IOP-PED-003 (Helmet Testing Procedures), ATC-MMTB-IOP-002 Rev. E (Measurement of Backface Deformation (BFD) Using FARO Quantum Laser Scan Arm and Geomagic Qualify for Helmets), and ATC-MMTB-IOP-004 (Ball Bar Laser Scan- ning, Rev. A).