Presentation on theme: "General Testing Issues Issues Related to the Test Protocols and Procedures in the NIJ Standard."— Presentation transcript:
General Testing Issues Issues Related to the Test Protocols and Procedures in the NIJ Standard
Overview of Issues Blunt trauma test improvements. Sample armor size issues. Improved ballistic limit testing. Ballistic limit testing with multiple calibers. Standard threat rounds. Shot to edge distance. Contact shots. Multi-hit testing.
Current NIJ Standard Test For soft armors: »V 0 Tests (Penetration/Back Face Signature): Test 4 armors (8 panels). 48 Shots. 24 with 9 mm/24 with secondary threat. No penetrations allowed. BFS must be less than 44 mm. »V 50 Tests (Ballistic Limit): Test 1 armor (2 panels). Determine V 50 for each panel. No performance requirements. »All tests performed with clay backing material.
Blunt Trauma Test Improvements Need to prevent injury or death due force of impact. Current blunt trauma test requirements: »Test on calibrated clay. »Back face signature must be less than 44mm. »Advantages: Easy, Cheap. Proven to be reasonably effective. »Disadvantages: Poor science. –Current requirements based on limited tests on animals. Does not account for varying risks at different locations.
Blunt Trauma Test Improvements Requirements for an improved test: »Biofidelic solution. Should accurately predict injury potential. Should allow armor to be mounted as worn. Should respond similarly to the human body. »Consistent and repeatable. »Cost should not be excessive. Numerous ongoing research efforts. Extensive research still needs to be done.
Courtesy Biokinetics and Associates Ltd., Ottawa, Canada 2005 Complex Physical Models Test Device – Approx. Cost OriginMeasurementsValidation – Injury Criteria Objective - Usage AUSman $15,000 no instr. Defence Science and Technology Organisation (DSTO) - sternal force and acceleration - skin, visceral and lung pressure - spinal accel. and angular rate Limited PMHS (University of Virginia) Blunt: C, VC, accel Blast: Bowen curves Blast/ballistic protection research Tissue and sensor repairs difficult Human Surrogate Torso Model (HSTM) $24,000 no instr. Office of Naval Research Johns Hopkins University pressure sensor placed in heart, each lung, both sides of liver, stomach Not validatedBlast/ballistic protection research Bones frangible, sensor repairs difficult Gelman $ ? Naval Research Laboratory Spinal accel, pressure sensor at tissue interfaces (lung, heart, surfaces) Not validatedBlast/ballistic/ blunt protection research Limited lifespan of gelatin, sensor repairs difficult
Simple Physical Models Test Device – Approx. Cost OriginMeasurementsValidationObjective - Usage BABT Torso Rig $2,000 for membrane, no instr. DERA (Defense Logistics Organization) Chest wall deflection KeNLW pig, Firearm projectile pig Blunt: C, VC Ballistic system evaluation Replaceable and repairable Thoracic Impact Membrane (TIM) $1,500 for membrane, no instr. Defence R&D Canada Valcartier Chest wall deflection and acceleration KeNLW – PMHS Automotive - PHMS Blunt: C, VC, accel Ballistic/blunt impact system evaluation Replaceable and repairable Impact Measuring Device (IMD) $ ? U.S. Army Medical Research and Materiel Command Measured forces behind body armour Firearm projectile Pig Biofidelity? Ballistic system evaluation 3-Rib Chest Structure $ ? Wayne State University Chest wall deflection KeNLW - PMHSKeNLW research Courtesy Biokinetics and Associates Ltd., Ottawa, Canada 2005
Potential Advanced Blunt Trauma Performance Measurement System Thoracic Impact Membrane »Uses polymer membrane to reproduce the response of a chest wall. »Relatively low cost (expected to be similar to clay). »Ongoing research to correlate membrane deflection to injury. Just one of numerous possible future directions. rear view laser displacement transducer Instrumentation
Sample Armor Size Issues Larger armor panels may be slightly more penetrable. Smaller panels tend to exhibit larger BFS. Sizing templates used to limit size of NIJ standard test panels. »Templates approximate "large" size armor. Represent neither the largest not the smallest armors. »Extra large or small armors may not perform as expected.
Sample Armor Size Issues Two options for better evaluating performance: 1.Select two (or more) standard template sizes. One template for large or extra-large armors. One template for small or extra-small armors. P-BFS tests would be performed on both sizes. BL tests would be performed on the larger size. 2.(Stricter) Require testing of the largest and smallest panel sizes sold. Potentially more reliable. Retest required for armors outside the original test range. Small size variations allowed for special fitting requirements. Second option is useful for keeping large armors light. »Manufacturer might certify two models: a thinner one for larger armors, and a thicker one for smaller armors.
Overview of Ballistic Limit Test Data Analysis Ballistic Limit (V 50 ) is normally calculated as the average velocity of the “good” shots. »To be good the shots must: Have equal numbers of partial and complete penetrations. All must be within a predefined velocity range. Must include fastest partial and slowest complete. »Usually 8 or 10 shots used in calculation. There are other ways to calculate the V 50 and other ways to analyze the data.
Example Ballistic Limit Test
Example – Data Reformatted
Example – With Logistic Curve
Example – With Logistic Curve and Confidence Intervals
Example – With Data from Multiple Armors
Analysis of Ballistic Limit Other Considerations
Possible Changes and Improvements to Ballistic Limit Testing Increase the number of armors tested. Remove the 3 clause for identical construction. Improve the ballistic limit test and analysis procedures. Use an alternate backing material for ballistic limit tests.
Increase the Number of Armors Tested Research has shown ballistic limit testing is relatively inaccurate. Experiments by DuPont. Simulations by NIST. »Accuracy of V 50 will vary due to: Number of shots used. Accuracy of initial estimate of V 50. Typical V 50 results have 35 ft/s standard deviation. Example: »Test a single panel. »V 50 is determined to be 1700 ft/s. »Actual V 50 may be: as low as 1595 ft/s. as high as 1805 ft/s.
Increase the Number of Armors Tested Increasing the number of armors tested allows results to be averaged. »Average of multiple tests will be more accurate. Averaging results from 10 panels will decrease the standard deviation of the estimated V 50 to 11 ft/s. Repeating the example: »Test 10 panels. »Average V 50 is 1700 ft/s. »Model’s actual V 50 may be: as low as 1667 ft/s (instead of 1595 ft/s). as high as 1733 ft/s (instead of 1805 ft/s).
Remove the 3 clause for Identical Construction Currently, the NIJ standard uses the standard deviation of the shots during one V 50 test for assessing equivalency. »This standard deviation describes the variation in shot velocities during the test. A larger number of armors must be tested for determining equivalency of two sets of armor. »Average V50 and standard deviation should be based on 10 or more panels. »These results can be used to determine if an additional armor is reasonably similar to the original group.
Improvements to Test and Analysis Minor adjustments to the V 50 test procedures may minimize disparate results and improve accuracy. Possible changes include: »Require a zone of mixed results. »Tighter control of the allowable step sizes. »Tighter control of the allowable results range. »Require a larger number of shots in the test. »Fit test data to a logistic curve and determine confidence intervals. Provides estimate of goodness of the results. Allows improved estimation of armor model performance.
Use an Alternate Backing Material Current ballistic limit tests performed with clay backing material. »Somewhat time consuming and labor intensive. Some military BL tests performed with armor mounted in a rigid frame with no backing material. »Potentially faster tests. »Reduced testing costs. Other backing materials/mounting methods might be used. Impact of new backing material or mounting method on the accuracy needs to be determined. »Results with new backing material must: Be similar to those obtained on clay. Or, be correlated to results on clay (may require extensive study).
Ballistic Limit Tests with Both Calibers Current standard requires ballistic limit tests with only the 9mm Luger threat round. »Estimate of armor's performance vs. 9 mm FMJ. »Does not show on how armor will perform against other threats. Testing with both threat calibers will improve understanding of armor model’s performance. »May provide indication of limitations of some models. »Will require testing more armor samples. Tests with the heavier, "blunt trauma" threat round may be very important for level IIIA armors. »44 Magnum round is often more penetrative than the 9mm round.
Standard Threat Rounds Weapons and calibers in use are constantly changing. »Officers carry duty rounds that did not exist when some current standard threats were chosen NIJ standard rounds should represent the most dangerous, common threats. »Test rounds should have some additional velocity to create a safety margin. What are the appropriate test rounds for each armor level?
Standard Threat Rounds
LEO Killed by Year and Caliber
Standard Threat Rounds If new threats are defined, what should they be? »What calibers are most often carried by law enforcement? »What calibers are most often used against law enforcement? »What bullet types are a problem for body armor? »What are the street velocities of the chosen threats? »What additional velocity is necessary for safety? What manufacture should be used for standard bullets? »Should the standard bullets be tightly defined? e.g. the NATO M882 9 mm round. Should "optional" threats be added to the standard? »To provide guidance to manufacturers on what threats law enforcement would like to see tested?
Shot to Edge Distance Currently, fair shots must be 3 inches from nearest edge. »Reduces the chance armor will fail test due to impact near edge. »Decreases the area that can be relied upon for protection. For small armors, there is limited area with full protection. Early versions of the NIJ Standard required only 2 inches. Reducing the shot to edge distance: »Will increase the area that provides reliable protection. »May lead to heavier armor. Should distance be returned to 2 inches? »Decreased further to 1 inch? Should smaller edge distances be an optional rating?
Contact Shots Concern among some law enforcement. FBI LEOKA data shows: »Approximately 1/2 of LEO shootings are at 5 feet or less. »Does not differentiate between contact shots and greater distance. »No known case of fatality due to a contact shot through vest. Some armor designs may be susceptible. Should a standardized test be developed? »What threat rounds and velocities? »How much contact force? Should a contact shot test be optional?
Multi-hit testing Armor may need to stop multiple rounds, fired in quick succession. »Automatic weapon fire is a particular problem. »NIJ standard ignores rate of fire. »NIJ standard separates all shots by at least 2 in. Test method and fixture are being developed to perform a three shot test on armor. »Test would place three shots in a small area. »Shots would be fired at automatic weapon rates.
Multi-hit Test Apparatus
Multi-hit Testing Should a multi-hit test be required in the standard? Should the test be optional?