$JHG %RG\ $UPRXU 7HVWLQJ )XUWKHU 5HVXOWV

Transcription

1 $JHG %RG\ $UPRXU 7HVWLQJ )XUWKHU 5HVXOWV Authors: D. Bourget (DRDC Valcartier, WEP Section C. Withnall, Biokinetics and Associates S. Palmer, DRDC Center for Security Science K. Rice, NIJ/OLES/NIST S. Swann, Combating Terrorism Technical Support Office Presented at the CTTSO PPE Conference 2012 Hollywood, Florida, USA 29 November 2012

2 Background 2 Police forces across Canada and USA do not follow any common guidelines on the safe life expectancy of personal body armour No such guidelines exist Some automatically replace armour at the expiry of the manufacturer s fiveyear warranty Others extend service life to ten years and beyond. The Canadian Association of Chiefs of Police (CACP) and the Ontario Association of Chiefs of Police (OACP) asked the Canadian Police Research Centre (CPRC) to investigate this issue Intent to develop an Aged Armour Replacement Protocol. Interest from NIJ: Body Armour standards Work co-sponsored by DRDC, NIJ and TSWG All tests done at Biokinetics and Associates ballistic lab.

3 Objectives and Approach Objectives Assess if there is degradation of armour performance due to aging using Vproof tests and ballistic limit tests (V50) Investigate if there is failures of NIJ compliant armours with age Approach Three (3) phases of Vproof tests, 150 naturally aged armour per phases One (1) series of V50 testing on naturally aged armour One (1) series of V50 tests (50 armour each) with naturally aged, artificially aged (conditioned) and new armour 3

4 Some definitions: Armour performance measures V proof V 50 Capacity of armour to stop projectile Trauma behind the armour Multi-hit capability 4

5 5 Test method Vproof tests Triangular shot pattern as described in the NIJ , and NIJ 2005 standards for NIJ level II body armour was used All 6 shots were done perpendicular to the body armour (within ± 5 ) and Shot spacing was 75 mm from any edges and 50 mm minimum from previous shots. All armours were backed with calibrated Roma Plastilina, as per NIJ standard Measurements included impact velocity and backface signature (BFS) All shots were done at ambient temperature. Fair velocity ranges for NIJ Level II body armour vs.357 Magnum JSP were: Street velocity: 376 m/s NIJ : between 425 and 440 m/s NIJ and 05: between 427 and 445 m/s NIJ : New armours: between 427 and 445 m/s Environmentally degraded: 399 and 417 m/s

6 Test method Ballistic limit (V50) Followed methodology defined by MIL-STD 662F Up-and-down method The V50 was calculated using the arithmetic mean based on six shots (3 highest partial and 3 lowest complete impact within a velocity spread of 45 m/s. In some cases up to ten shots were necessary to achieve this criterion. Backing material used was Minicel instead of Plastilina to facilitate testing. Shot spacing was 76 mm from any edge and a minimum of 64 mm between shots (Figure 1). All shots done at ambient temperature and perpendicular to the armour (within ± 5 ) 6

7 Armour samples Vproof tests Twenty two police forces across Canada donated soft body armour removed from service. All compliance to either NIJ , NIJ and the NIJ 2005 Interim Standard All armour were rated NIJ level II. All armours were made from 18 to 35 layers of Aramid. Not feasible to obtain complete information on the service history of each garment Total: 450 panels tested, 2415 shots fired 7

8 Panel perforation rate within or below fair speed Vproof tests Phase I Phase II Phase III Overall Below fair speed 4.4% 1.7% 3.2% 2.7% Fair speed 6.1% 3.0% 6.6% 5.0% 8

9 9 Rate of panel perforation with age Vproof tests

10 10 V50 tests on naturally aged armour Executed V50 tests on the back panel of Phase I 150 armours Total number of armour tested: 120 panels Tests done on Minicel rather than on Clay Fair velocity ranges for the.357 Magnum are: NIJ : between 425 and 440 m/s NIJ and 05: between 427 and 445 m/s NIJ environmentally degraded: between 399 & 417 m/s No correlation with age observed

11 Discussion No correlation between Age and test failure Age and V50 Possible explanation: variation in make, manufacturer and police force requirements are quite large, although they all claim certification to some version of NIJ Level II Attempt to refine the process by selecting data applicable to a single manufacturer or for one particular police force did not show any trends. 11

12 Discussion Failures: Possible explanation Safety margins seem quite low Process to approve armours (number of shot done) resulted in low confidence level that observed sample actually represents reality High perforation rate among the small sample of panels 17 years and older does suggest that it would be unwise to extend life expectancy to this length of time. 12

13 Way ahead: Series of V50 Tests for Naturally, Conditioned and New Armours Study a batch of 7 years old armours from one manufacturer and from the same police force (naturally aged armours). Acquire 100 new armours made from the same manufacturer with the same material Execute V50 tests on the 50 naturally aged armours and compare to V50 tests on 50 new armours and 50 new armours environmentally degraded as specified in NIJ standard 10 shots V50 with Mag JSP 13

14 Discussion Naturally aged armour V50 New armour V50: 7 m/s difference observed. There is a slight aging affect Conditioned armour V50 Naturally Aged armour V50: Conditioning tests does not represent actual aging Conditioning process is effective to expose weakness in PBO armour (degradation with humidity), but not necessarily other materials such as Aramid 14

15 Conclusions and way ahead Conclusions Could not see a correlation between armour performance with age There seems to be a slight decrease of ballistic performance for 7 years old Aramid armours Indications that very old (17 to 19 years old) armours significantly degraded NIJ environmental conditioning does not simulate actual armour aging Way Ahead Establish a protocol to monitor armour aging that will most probably include: Testing of brand new armours (sample size = X) per lot: Baseline performance Armour sampling program throughout the years to verify degradation (sample size = Y): Sampling point at 5 and 7-9 years Follow-up of armour use (assign armour to officer) 15

16