Weapons and Protective Systems

Goals

To conduct a comprehensive testing program to address concerns with the ongoing ballistic-resistant performance of ZYLON-based body armor in response to the Department of Justice's Body Armor Safety Initiative, announced by Attorney General Ashcroft on November 18, 2003. This initiative came in response to concerns raised by the public safety community and members of Congress regarding the performance of ZYLON-based armor. ZYLON is the trade name for a high strength ballistic fiber known as poly (p-phenylenebenzoxazole) (PBO).

Customer Needs

Neither the NIJ Standard–0101.04, "Ballistic Resistance of Personal Body Armor," nor the current Body Armor Compliance Testing Program were originally intended to address the ongoing performance of used ballistic-resistant body armor. Ensuring ongoing ballistic-resistant performance has always been the responsibility of the body armor manufacturer. The ZYLON-based body armor concern has heightened an industry-wide awareness that ongoing ballistic performance must be satisfactorily addressed. Determinations and findings of this testing program are expected to highlight significant problems with some samples of body armor, lead to improved body armor performance standards, and very likely produce fundamental changes in the Compliance Testing Program, ultimately benefiting the users of body armor. The primary benefit anticipated will be the implementation of ongoing conformity assessment methods that will give criminal justice and public safety officers greater confidence in the performance of body armor.

Technical Strategy

The Body Armor Safety Initiative directs NIJ to conduct an immediate review of both new and used ZYLON-based bullet resistant vests to ensure that they are effective, and to include in this testing effort the upgrade kits provided by manufacturers to retrofit ZYLON-based armor. To address the requirements, multiple test efforts comprise this project: 1) Forest Hills Vest Study, 2) ZYLON-containing body armor Ballistic Performance Tests, and 3) Upgrade Kit Tests. Over the past two years, these projects have been described in prior program plans, details of the testing activities were presented in separate documents, and results of those activities were published in three reports to the Attorney General and several other technical reports. These activities also developed information that led to NIJ's establishment of the 2005 Interim Requirements. A brief summary of the status of each study follows:

Goals

To: (1) identify the exposure variables, acting individually or in combination, that initiate performance degradation in soft body armor, (2) identify chemical and physical degradation mechanisms in soft body armor and (3) initiate the development of standardized test protocols for accelerating, predicting, and monitoring the service lives of ballistic fibers and body armor.

Over the last couple of years, research focused on the identification of chemical indicators of PBO fiber tensile strength loss; systematic characterization of PBO fibers; procurement of needed equipment; and development of an experimental design for additional proposed research. Materials analyzed included yarns extracted from: 1) the back panel of the Forest Hills vest that failed in-service, 2) new vests, and 3) virgin spool yarn. In addition to identifying chemical and physical differences between the specimens, this work helped determine which analytical techniques were the most sensitive in detecting chemical changes that reflect subsequent losses in mechanical strength. In particular, Fourier transform infrared (FTIR) spectroscopy was particularly useful in elucidating chemical changes that occurred in the fibers. Evidence of benzamide breakdown, a product of benzoxazole ring-opening, was detected via detailed analysis of the FTIR spectra.

Beginning in 2004 and continuing into 2005, research focused on temperature and moisture aging of PBO ballistic panels in a humidity chamber. Fibers were extracted from the panels at biweekly intervals and tested in tensile mode and analyzed by FTIR. Over the course of the 25 week study, tensile strengths of the extracted yarns decreased ~ 30 % relative to the unaged material, and evidence of significant benzoxazole ring breakage was detected by the FTIR analysis.

A question that arose at the completion of this study was whether residual moisture in the fibers was sufficient to initiate degradation even if the fibers were shielded from external moisture. To help answer this question, a study was conducted in which PBO fibers were hermetically sealed in an inert argon environment in glass tubes and then subjected to the same temperatures as the PBO panels in the previous study. Tensile strengths of the glass-enclosed fibers decreased only a few percent relative to the unaged material.

The remainder of 2005 was focused on the combined effects of temperature, humidity and ultraviolet (UV) exposure on PBO yarns properties. Virgin yarn was placed in specially-designed specimen holders and subjected to a short-term high intensity UV-visible radiation on NIST's Simulated Photodegradation by High Energy Radiant Exposure (SPHERE) system, which is an integrating sphere-based weathering device. Severe degradation (> 50% decrease) of yarn tensile strength was observed. Preliminary chemical analysis results indicate similar changes in chemistry as observed with the moisture-conditioned specimens; more detailed testing and analyses are in progress.

Customer Needs

Identification and understanding of the phenomena responsible for the loss of mechanical strength in PBO and other ballistic fibers will lead to improvements in the selection of durable and reliable fibers used in body armor. The development of a scientifically- based protocol for screening, testing, and comparing the long-term performance of new and existing fibers for use in ballistic applications will have long term benefits in identifying fi bers having improved long-term ballistic performance.

Recent failures of body armor manufactured from PBO fibers have underscored the need to study the service life of these ballistic fibers under a variety of environmental and operating conditions. Manufacturer-supplied data, as well as tests conducted by other commercial research laboratories and governmental labs, have indicated that PBO fiber (which is relatively new in the ballistic armor arena) undergoes degradation in tensile strength following exposure to temperature, moisture and light. Degradation on this level has not yet been observed with more established materials such as Kevlar or Spectra fiber. An extensive and ongoing review of the scientific literature has revealed that neither systematically controlled experiments involving relevant environmental factors, nor detailed chemical analysis of the mechanisms and kinetics of fiber degradation, have yet been carried out. The proposed research will address these issues.

Technical Strategy

Development of scientifically-based accelerated aging and life monitoring protocols for ballistic materials is of vital importance to the body armor industry. Before such development can be undertaken, it is critical that the following issues are addressed:

• The key functional yarn/fiber properties that affect ballistic performance of body armor must be identified, and relevant performance metrics/ indices established.
• Key factors in the service environment must be accurately characterized, so that the appropriate test conditions, e.g., temperature, moisture (vapor and condensed), stress amplitude, number of cycles, etc., can be selected and rationally justified.
• A fundamental understanding of the effects of these key factors on degradation mechanisms and kinetics in ballistic fibers/yarns must be obtained.
• Input from key industry players: A NIST workshop is planned to bring key industry players (fiber manufacturers, weavers, vest manufacturers, law enforcement) and members of the NIJ technical working group on body armor together to discuss technical issues associated with accelerated test-ing/service life prediction including expected vest service life and warranty periods, expected conditions of use, selection of study materials, among others. It is also expected that the workshop will also provide NIST with pertinent information on fiber, fabric, and body armor manufacturing.

Deliverables

• Report on chemical analysis of failed and new vests.
• Research reports.

Goals

To reduce failures of personal body armor by developing tests and standards of assessment for reliability of the active polymeric materials that comprise them. Utilizing the test methods developed in phase I, the research program will be expanded to evaluate the property/performance relationships of other ballistic fibers, such as Kevlar and M5 and the impact of residual processing aids on long-term durability of ballistic fibers. Through the preparation of model fiber systems, the program will be expanded to quantify the link between molecular structure, ballistic performance, and durability. This endeavor will provide a much-needed database of design parameters to facilitate the development of new and more effective ballistic fibers.

Customer Needs

By developing test methodologies that assist in the certification process of protective equipment, the most important outcome of this research will be to save lives.

Technical Strategy

From Phase I of this research project conducted over the last several years it is now known that chemical activity (hydrolytic and UV exposures) and mechanical folding promotes ballistic fiber degradation. Furthermore, new ballistic technologies suggest that ballistic fiber performance and durability are linked to the molecular structure of the polymer. Outputs from Phase I include: (a) A moderately invasive test for evaluating the in service properties of soft body armor. (b) A new device for mechanically degrading yarns, woven fabric, and sections of ballistic armor, and (c) A new methodology for detecting the presence of residual acid.

In Phase I, an armor ballistic performance parameter called U*, which scales with the V50 velocity of an armor system, was shown to be related to the physical properties of the ballistic fi ber [see following equation]. Utilizing this concept, a test methodology was developed that monitors the in service properties of the ballistic fiber by testing fibers from a single strand of yarn. This method still compromises the integrity of the armor panel covering, but only minimally disturbs the ballistic panel structure. The new test methodology has been termed the modified-single fiber test (m-SFT). A journal publication describing the details, reproducibility, and sensitivity of this procedure to mechanical degradation is being prepared.

where

σ_uts   =   fiber ultimate axial tensile strength
ε_f   =   fiber ultimate tensile strain
ρ   =   fiber density
E   =   fiber modulus (assumed to be linear elastic)

[from P. M. Cunniff and M. A. Auerbach, "23rd Army Science Conference," Assistant Secretary of the Army (Acquisition, Logistics, and Technology), Orlando, FL, (December 2002)]

After determining the reproducibility of the procedure, a detailed investigation was initiated using the m-SFT to quantify the degree of degradation of aged and worn vests relative to un-aged vests. The testing is ongoing since the study involves over 1000 samples.

Mechanical Folding Device attached to MTS testing platform being loaded with a piece of woven ballistic fabric.

To address the issue of mechanical durability a single 180-degree fold was made in single fiber PBO specimens and evaluated using the m-SFT. The strain-to-failure and ultimate tensile strength of the fibers (i.e., key parameters that quantify the U* parameter) were degraded by approximately 10%. A device was then designed and built for the repeated folding of ballistic yarns, woven fabric, and sections of ballistic armor (see photo). Initial results from a fatigued woven yarn indicate that a 20% drop in the properties of the PBO ballistic fiber may occur within 7 months of wear. A fatigue test is ongoing to simulate longer wear times. Since this is a new testing methodology, a standard folding protocol must be determined.

To determine and quantify the morphological changes that occur during the mechanical folding of ballistic fibers, a special attachment was purchased for the critical dimension – small angle X-ray scattering (CD-SAXS) instrument. Data on virgin fibers shows that the ordered structure of the ballistic fibers can be observed by this approach. Analysis algorithms are currently being written to illuminate morphological changes that occur in damaged ballistic fibers.

Chemistry of preparation and structure of poly(p-phenylenebenzoxazole) [PBO] fibers. Fibers made from the reaction of 1,3-diamino-4,6-dihydroxyben-zene [DADHB] dihydrochloride with terephthalic acid [TA] with poly(phosphoric acid) [PPA] as a catalyst.

PBO and many ballistic fibers are precipitated from concentrated acid solutions (see figure). Many attempts have been made to unambiguously detect the presence of residual acid and determine the impact of these acids on the hydrolytic degradation of PBO fibers. Complicating this process in PBO is the presence of phosphorus containing processing aids. A test methodology was devised involving the water extraction of acid species coupled with a methylation procedure to facilitate detection. Interestingly, initial results indicate that the water extraction process removed only 25 % of the phosphorus from the fibers, presumably the phosphorus containing processing aids. The fibers are now being manually damaged to facilitate the ingress of moisture into the fibers during the extraction procedure.

The acid research is part of an overall effort to link the chemical degradation mechanisms to changes in the molecular structure of ballistic fibers. The MALDI (matrix assisted laser desorption ionization) technique is being used to detect and quantify these changes in model PBO compounds since ballistic fibers are insoluble in most mediums. In addition, a grinding methodology is being explored to facilitate the detection of insoluble ballistic fibers.

We proposed to complete the degree of aging study currently underway on worn, aged, and un-aged PBO vest and extend the study to include other ballistic fibers. To increase the throughput of this analysis procedure, we will evaluate the feasibly of modifying the Favimat automatic tensile testing device, which is currently being used throughout the fiber industry, to profile the diameter of the tested fiber and measure the fiber displacement.

Utilizing the newly developed mechanical folding device, we propose to standardize on a folding procedure and test all relevant ballistic fibers. The m-SFT will be used to quantify the properties of the tested fibers, since the m-SFT is the best method for quantifying fiber degradation. Therefore, automation of this technique utilizing the Favimat will be critical. The folded fiber region will also be analyzed using the CD-SAXS to quantify morphological changes in the fiber. The mechanical degradation research will be extended to include all ballistic fibers.

Proposed model compounds (shown in boxes) and their relevancy to the primary structure of PBO fibers

In addition to completing the residual acid study, we propose to perform the controlled hydrolytic and UV exposures on PBO model compounds (see figure for PBO model compounds shown in boxes) and PBO fibers. Initially, MALDI and related preparation procedures will be used to identify and quantify the degradation pathways. The key technical challenge is this research area is the insolubility of the ballistic fiber. As before, this research will be extended to include all relevant ballistic fibers.

The continued research into M5, which has been shown to be hydrolytically and UV stable, by Dupont, who also owns Kevlar fibers, and the similarity of the M5 polymer structure to PBO indicates that understanding the impact of molecular structure is the key to developing high performance and environmentally stable ballistic fibers. To predict the performance and durability of these new classes of ballistic fibers, we propose to quantify the impact that molecular modifications have on ballistic fiber performance by having model ballistic fibers prepared that gradually morph the structure of PBO to the environmentally stable M5 polymer. This type of data should facilitate the development of more effi cient ballistic fibers while showing the impact of structural modifications on ballistic performance. In addition, understanding the correlation between structure and performance will admit more efficient screening of new fibers targeted for ballistic applications.

Deliverables

• A detailed investigation using the m-SFT of how the physical material properties of worn PBO vests compare with un-aged and laboratory aged vests.
• Initiate and complete similar studies with Kevlar, M5 and other ballistic fibers.
• Automate the m-SFT through the use of the fiber industry standard Favimat automated testing system. Thereby delivering a protocol that has potential for adoption by industry.
• Assess using PBO ballistic fibers the impact of mechanical folding on ballistic performance through the testing of woven fabric, yarns, and/or sections of ballistic material.
• Extend this testing protocol to other ballistic fibers.
• Use CD-SAXS to quantify morphological changes in ballistic fibers due to mechanical folding.
• Write recommended practice guidelines for the m-SFT testing procedure and the mechanical folding device.
• Determine if phosphoric acid is extractable from PBO fibers and quantify its impact on PBO degradation.
• Establish the Hydrolysis and UV-photolysis degradation mechanisms through the use of MALDI, model compounds, chemical modification techniques, and relevant analytical techniques.
• Establish a database that quantifies the impact of molecular structural changes on ballistic performance. Morphing the structure of PBO to the M5 ballistic fiber will do this.

Goals

To improve the implementation of the conventional V50 ballistic limit test so that it can be relied upon as an estimator of armor performance.

Customer Needs

Recent studies of used body armor performance have indicated the need for improved ballistic test methods. Ballistic limit (V50) and penetrationbackface signature (P-BFS) testing is currently used to estimate the performance of body armor, but both methods have limitations. P-BFS tests can reliably determine if armor exhibits a certain level of ballistic resistance, but they cannot show if the performance of the body armor has changed, unless the performance has shifted dramatically to unacceptable levels that produce penetrations. V50 ballistic limit tests are more likely to identify modest shifts in performance; however, as the tests are currently performed they can only provide a rough estimate of the ballistic limit and they generally cannot determine how well the armor will perform at the real threat velocities. Furthermore, the uncertainty associated with the estimated V50 value has never been satisfactorily addressed. Improvements in the V50 test and data analysis methods can be incorporated into the NIJ body armor standard and adopted by the armor industry.

Technical Strategy

In 2004 and 2005, research involved analyzing the V50 ballistic limit tests from all NIJ Standard-0101.04 models tested under the NIJ compliance testing program up until that time and fi tting the data to a logistic model. The fitted data and certain other characteristics of each data series (experimentally determined V50, low complete velocity, zone of mixed results, NIJ reference velocity, etc.) were examined to identify weaknesses and inconsistencies in the current methods. Follow-on studies involved the development of computer simulations to mirror the test protocols employed by test laboratories when they conduct V50 tests. Decision making is guided by the prior ballistic test results, and the armor performance (penetration probability vs. velocity) was modeled as an idealized logistic function. Comparisons were made between the V50 values determined via simulation and the known V50 values used to define the idealized armor performance function.

In 2006, the approach was extended and Monte Carlo methods were used to explore a wide range of armor performance functions and variations in V50 test methods, and improved data analysis methods were implemented. A spreadsheet tool that employs the data analysis methods was also developed for ease of use. The Monte Carlo methods are important because they provide insight that cannot be determined experimentally because other factors interfere with isolating effects of certain key variables. Generally it is recognized that more ballistic testing can lead to a better characterization of the armor, but in the case of V50 testing, understanding how much testing is necessary to achieve reasonable levels of confidence in the results is critical. These simulations have produced estimates of bias and uncertainty associated with the V50 test method, and have proven invaluable in terms of providing evidence to support recommended changes in the amount of testing, in how the data are analyzed, and in how the tests should be performed.

Further studies are planned to determine if the "lower tail" of the armor performance curve can be estimated better using various test strategies. The more favorable strategies will be experimentally demonstrated by testing armor panels or shoot packs.

Deliverables

• Test methodology recommendations.
• Report summarizing research.
• Report of ballistic limit tests demonstrating preferred methods.

Goals

To improve the program whereby body armor is tested and certified as "compliant" to the NIJ standard. This effort provides technical support to develop a lab accreditation guide, involvement from the National Voluntary Laboratory Accreditation Program (NVLAP), and expertise from NIST's Technology Services group specializing in Conformity Assessment.

Customer Needs

The ballistic resistance issue that was discovered with used ZYLON-containing body armor has highlighted the importance in improving the process whereby body armor is certified. With the envisioned improvements, there would be greater confidence that future production lots of body armor also complied with the requirements of the standard and that used body armor was still performing as intended.

Technical Strategy

The performance of body armor is presently assessed against the applicable requirements of either:

• Ballistic Resistance of Personal Body Armor (NIJ Standard.0101.04)
• Stab Resistance of Personal Body Armor (NIJ Standard.0115.00)

A key gap inherent in the standards exists because armor is "certified" based on a test of manufacturer-provided samples that are intended to represent production units without any surveillance to provide confidence that production units meet the same minimum performance requirements as the tested samples. Ensuring that future production units comply with these requirements is not addressed by the standard; instead it is the responsibility of the body armor manufacturer to prove, and the purchasing authority to require, that new production units of body armor comply with certain performance requirements. There is much confusion about these issues among vest users and procurement officials.

An initial assessment of the standards and testing program has been made, and an outline for the "Body Armor Certification Program" has been developed. Potential revisions to the current certification program include enhancing the accreditation requirements, audits and assessments of the type-testing laboratories and developing a factory surveillance program to provide confidence that production units continue to meet the performance requirements. The surveillance program will enable the suspension and/or withdrawal of certification of models when continued compliance is in doubt or no longer demonstrated. Audit and assessment of manufacturers' production facilities, quality management system, and inspection of production units are surveillance tools that could be employed in the certification process. NIST intends to work with NIJ to define an improved conformity assessment program and then work with NIJ's certification authority to develop the necessary program documents.

Goals

The project goals are to:

• Use previous research into the chemical and physical degradation of ballistic fibers to develop an interim protocol for artificial aging, suitable for incorporation into the revisions to NIJ Standard - 0101.04
• Validate this interim artificial aging protocol by running new ZYLON, Kevlar, and Dyneema vests through it, and then comparing their condition to the condition of used vests.
• Adjust the artificial aging protocol based on the results to allow it to better approximate field aging.

Customer Needs

To comply with the recently modified NIJ requirements for soft body armor (2005 Interim Requirements that became effective September 26, 2005), manufacturers are required to provide evidence that their product(s) will maintain ballistic performance through a declared warranty period. There are significant technical challenges in demonstrating this. As an alternative, the introduction of a consistently applied artificial aging, or "armor pre-conditioning," protocol would provide an objective method for exposing armor to potential damage-causing mechanisms, and successful post-exposure ballistic test results would provide assurance that the armor will maintain acceptable ballistic performance levels under real field conditions. Body armor users and the industry will benefit from this approach because the exposure conditions can be applied consistently and it results in a demonstration that long-term performance requirements are met.

Technical Strategy

In 2003, field failures of body armor manufactured from poly(phenylenebenzobisoxazole) (PBO) fibers brought to national attention the need to study the service life of ballistic fibers under a variety of environmental and operational conditions. The current NIJ standard does not consider environmental factors in vest performance or provide test methods to predict the lifetime of the armor. In order to make an effort to assess the service life of body armor, the first step is to develop a basic artificial aging protocol which will give an approximate idea of body armor performance after exposure to aggressive, but reasonable, use and storage conditions. Then the protocol will be validated by comparison with field return (used) vests.

In early 2006, interactions with industry researchers led to a description of a proposed artificial aging protocol that incorporated elevated temperature, humidity, and mechanical damage as stressing factors. This protocol is based on an engineering assessment of the fundamental conditions influencing armor performance degradation. The protocol continues to be refined and is currently being drafted as a part of the revision to NIJ Standard - 0101.04.

Research is planned to perform simple validation tests on the protocol and to allow for adjustments to the test method to better approximate wear in the field. New equipment, including a temperature and humidity chamber and a tumbler, has been set up and the project is awaiting delivery of armor samples. Development of this interim accelerated aging protocol is of vital importance to the body armor industry. The following are crucial components that are being addressed by this research:

• The effect of tumbling/mechanical damage on vests will be investigated and guidelines for using tumbling to cause mechanical damage will be developed.
• The effect of the proposed protocol on new vests will be established through chemical, physical, and ballistic tests involving vests made from common materials such as Kevlar, ZYLON, and Dyneema. Later, this research will be extended to hybrid armor models.
• Comparisons must continue to be made between artificially aged vests and used field return vests to ensure that the damage induced in the artificial aging protocol is reasonable.
• Input from key industry players: Collaborations must be established between users, industry, and NIJ/NIST-OLES to acquire materials for these studies.

Deliverables

• Report summarizing the results of validation tests.
• Peer reviewed journal paper on damage effects.
• Final report describing protocol recommended for incorporation into standard.

Goals

To conduct a review of the body armor program and further strengthen the NIJ body armor standard and associated Compliance Testing Program.

Customer Needs

A critical review of the incident in Forest Hills and subsequent discussions with the criminal justice and public safety communities have clearly shown the need for more oversight of ongoing body armor performance and for changes to provide confidence that all body armor produced satisfies certain ballistic performance requirements. To address this, revisions to the ballistic-resistant body armor standard and related compliance testing program are necessary.

Technical Strategy

Consideration was given to input received from public safety agencies, organizations, and associations; manufacturers; and standards and testing organizations. This input coupled with research initiatives underway have led to recommendations to strengthen the ballistic-resistant body armor standard in the following areas: change shot-to-edge distances, revise threat levels, change V50 testing protocols, introduce artificial aging protocols, and test various sizes of body armor. These changes in concert with a more robust conformity assessment program are expected to strengthen the body armor standards and testing program to address the concerns expressed by the criminal justice and public safety communities.

Other efforts planned for the future will investigate additional improvements that could be incorporated into future versions of the standard, such as the development of an improved torso surrogate, introduction of electronic measurements of impact conditions, establishment of requirements of multiple shot resistance, development of contact shot methodologies, and establishment of coverage area requirements.

Deliverables

• Briefings to law enforcement, corrections, public safety, and industry personnel on proposed changes to the NIJ standard and testing program.
• Draft revised body armor standard for comment and review.

Goals

To develop a robust test methodology for evaluating the injury potential from Behind Armor Blunt Trauma (BABT) based on biomechanical studies.

Customer Needs

An area identified in the current NIJ standard requiring further attention is related to test fixturing and the backface deformation performance requirement that is often associated with the threat due to BABT. Deformation of body armor during the ballistic impact event may lead to injuries behind the armor. Though the NIJ standard has been successful in defining a test methodology and performance requirements that led to effective body armor systems, the biomechanical basis for using clay deformation to characterize BABT is uncertain. Unlike the clay, the human thorax is generally viscoelastic, so it is unlikely the response of clay is appropriate for widely varying rates or ranges of deformation. The current test methodology was validated using goat experiments performed over 30 years ago. In addition, the standard does not account for the "penciling effect." This impact does not penetrate the skin, but results in deep deformation over a small area.

Optimization of soft body armor systems requires a more biofidelic coupling of the body armor and the fixture on which it is mounted for testing. Thoracic deformations having the same deformation depths, but different cavity volumes may have significantly different risks of serious injury, and the standard does not address this possibility. In addition, deficiencies identified with the clay system argue for the development of a robust technique for BABT injury assessment. Beyond the existing NIJ standard, there exists no generally accepted injury criterion for thoracic BABT.

Technical Strategy

Two separate efforts have been initiated to address the needs identified. Biokinetics and Associates Ltd. was awarded a contract to develop a torso impact membrane that reproduces the human response for BABT assessment. Development of the enhanced technique for evaluating body armor will involve:

• Engineering of the membrane structure to produce a robust and repeatable physical response that responds in a human-like manner.
• Identification of a relevant engineering measurement, such as force, acceleration, etc. that may be used to quantify the physical response of the torso. The instrumentation is intended to indicate the severity of the ballistic impact.
• Establishment of an injury risk evaluation, which is accomplished by correlating the engineering measurement and an injury model. The injury risk evaluation is expected to be based on mid-thoracic injury tolerance levels. In the NIJ standard, the injury risk evaluation is based on a maximum clay deformation of 44 mm. Under this program, the injury risk evaluation will be based on other quantities obtained from biomechanics research.
• Validation of the injury model, which is accomplished by correlating the injury risk evaluation to a physical model of injury. A meaningful injury risk model must be validated using: 1) epidemiology or physical reconstruction of actual injury events, 2) an animal injury model, or 3) a cadaveric human injury model. Development of a relationship between a robust torso surrogate and a validated injury model is crucial to the success of this approach. The injury model for the NIJ standard includes animal tests that were scaled to human values. Under this program, the injury model will be based on epidemiology and existing injury models established by other biomechanics research programs.

With the development of an instrumented torso surrogate, a two-step process for evaluating body armor will be considered. The potential for bullet penetration would be assessed first on a surrogate with minimal cost risk (i.e., should a penetration occur, valuable instrumentation would not be lost). Following the penetration assessment, further tests on an instrumented surrogate would assess the potential for BABT impact injuries for those body armor systems that pass the penetration tests.

The second research effort supporting this project will provide epidemiological data. This research is being conducted by Wayne State University, which was awarded a contract to study the types of injuries sustained by officers wearing body armor. Study candidates will be identified from the IACP/DuPont Survivors' Club database, and after obtaining approvals, the medical details will be assessed by subject matter experts.

Deliverables

• Torso impact membrane design and test methodology recommendations.
• Report describing epidemiological findings.

Goals

To provide quantitative measurements of the deformation behavior of commercial bullets that threaten wearers of body armor to improve the ballistic threat assessments used in the NIJ Ballistic-Resistant Body Armor standard.

Customer Needs

An effective body armor standard depends on the ability to accurately characterize the ballistic threats facing officers. The NIJ standard currently specifies bullet velocity, mass, and basic construction (collectively constituting a "threat level"), but it does not address how the material properties of the various bullets, such as strength, ductility and strain rate sensitivity affect their ability to penetrate body armor. These properties can vary among bullets classified in a single threat level category due to different fabrication methods or different alloy compositions used by the various bullet manufacturers. Currently there is no test or means to evaluate the effect of these variations in bullet properties on the performance of body armor.

The customers of this project are those developing and using the NIJ ballistic-resistant body armor standard. This includes modelers who use constitutive models for bullet materials to simulate ballistic impacts on body armor, and government and industry researchers evaluating new threats. Ultimately, the beneficiaries of this work include all who employ body armor for personal protection in the line of duty.

Technical Strategy

Finite element analysis of a bullet deforming in a Kolsky Bar test. One quarter of the bullet is modeled.

Originally this effort began because of concerns over the threat posed by some types of frangible ammunition to soft body armor. "Frangible ammunition" is ammunition loaded with a bullet that is designed to shatter into small pieces upon impact with hard surfaces. Generally this type of ammunition is free of lead, and because of its tendency to shatter upon impact, thereby minimizing the potential for ricochets and collateral damage, it has gained widespread acceptance for use on shooting ranges, training exercises, and in some cases, certain tactical situations. Frangible ammunition is currently used by several government agencies, state and local law enforcement agencies, and other public safety agencies.

Work from various agencies and other groups was reviewed and construction details were researched to better understand differences between various types of frangible bullets. Ballistic tests using different types of frangible ammunition were also conducted against conventional soft body armor. Results suggested that some types of ammunition posed potentially serious problems that were not reflected in the NIJ ballistic-resistant body armor standard. To study this further, efforts were initiated to evaluate the influence of bullet material properties and construction on the penetration ability of the bullet against soft body armor using finite element modeling. However, the high-strain rate mechanical properties necessary for modeling are generally not available. To address this, we began development of a dynamic material properties database for bullet and armor materials, including high rate and heating effects.

Simply measuring the complete set of attributes for every material used in commercially available bullets is prohibitively time consuming and costly. Instead, a simple mechanical test was proposed to quickly evaluate and compare the overall deformation behavior of all commercially-available bullets. This technique was demonstrated on high strain rate mechanical testing of frangible bullets using the NIST Kolsky Bar. A similar approach has been taken to study high-strain rate mechanical properties of individual polymer fibers used in ballistics applications at Purdue University. Results from those mechanical properties tests have supported modeling work on frangible bullet deformation and fracture behavior.

The bullet characterization test subjects bullets to a precise impact load in the NIST Kolsky Bar facility. High speed video cameras capture the deformation of the bullet, and strain gage measurements record the applied force during deformation. The results can then be used to assess whether bullets of a given threat category produced by different manufacturers deform similarly or not. Then detailed metallurgical analyses will be performed on bullets that exhibit unusual deformations, including microstructure, yield stress and strain rate sensitivity measurements. The property data will then be used to predict the deformation observed in the Kolsky Bar tests using finite element analysis. The predictions will reveal the underlying causes of the varied deformation, whether they are due to geometry effects or property differences. The results of this work will enable an improved assessment of the current ballistic threat classification used in the body armor standard and, if necessary, to serve as a basis for developing a new, more useful classification system that would provide a better threat assessment for the next body armor standard.

The Technical Support Working Group is also sponsoring a related effort to examine the ballistic penetration performance of a wide variety of ammunition of interest to law enforcement. That information will become part of a projectile database, and when coupled with constitutive data from this project, will support advanced model development efforts.

Deliverables

Year 1:

• A data set of whole-bullet Kolsky Bar tests, including load vs. time during bullet deformation and video record of bullet deformation for at least 40 bullets from various threat categories and manufacturers.
• Evaluation of data set for consistency of deformation behavior within the existing categories identified in NIJ Standard 0101.04 and identification of possible outliers.

Years 2 and 3:

• Forensic metallurgical analysis of outlier and representative bullets from the same NIJ 0101.04 category.
• Finite element model of deformation of outlier and representative bullet using existing constitutive models of bullet materials as needed to identify possible structural influences on deformation behavior.
• Improved constitutive models for bullet materials based on in-house test data, as needed.
• Final analysis of the deformation behavior of outlier and normal bullets and conclusions as to the primary structural or material behaviors leading to unusual deformation behavior.
• Suggestions for revised categories of ballistic threats and recommended test methods/characteristic data needed to classify bullets into these new categories for next generation Body Armor Standards.

Protective Equipment Program

A number of projects are underway to revise other protective equipment performance standards. Similar to the body armor program, the public safety community depends on these standards to assist them in making informed purchasing decisions about important life safety equipment.

Goals

The objective of this project is to revise the NIJ "Ballistic Helmets" standard and establish new performance levels and test methods based on ballistic impact biomechanics research.

Customer Needs

The new standard will lead to improved helmet designs that will increase the probability of user survivability. It will also provide a standard in which the user community has confidence. Customers will also find that more test laboratories will be able to perform this testing because of changes to the equipment required for testing.

The current NIJ helmet standard is more than twenty years old, was not regularly updated, and was not based on ballistic impact biomechanical principles. Research conducted in the "Study of Head Injuries During Ballistic Loading of Helmets" by the University of Virginia Impact Biomechanics Center (under contract to the U.S. Army Soldier and Biological Chemical Command's Natick Soldier Center (NSC)) indicated that requirements in the existing standard may not ensure adequate protection for individuals wearing ballistic protective helmets meeting the standard. Additionally, relatively few helmets are certified to the existing standard due to a number of reasons: NIJ does not administer a formal Compliance Testing Program for ballistic helmets; the test equipment is difficult to obtain; and the performance levels are outdated and have not kept pace with those defined in the ballistic-resistant body armor standard. The new standard will reduce the risk of serious injury due to ballistic impacts, as well as standardize testing and performance requirements based on modern ballistic impact biomechanical principles.

Technical Strategy

Work will continue under a contract to Biokinetics and Associates Ltd. Numerous issues will be addressed: 1) the current revision only addresses threats up to level II, while existing helmet technologies can readily provide higher levels of protection; 2) the threat definitions in the current revision are different from those in the recently updated ballistic-resistant body armor standard; 3) instrumentation for assessing helmet performance has improved dramatically; and 4) head trauma research has led to a better understanding of injury mechanisms and injury risk criteria. A recently developed ballistic helmet test rig with a load cell module to measure impact loadings will be used to validate the improved test method against a number of commercial and experimental helmet designs. A draft revised standard will be written and sent out for comment and review.

Deliverables

• Report describing validation tests conducted under contract.
• Test equipment and instrumentation.
• Draft revised standard.

Goals

The objective of this project is to revise the NIJ standard that establishes minimum performance requirements and methods of test for ballistic resistant protective materials.

Customer Needs

Law enforcement agencies rely on the NIJ Standard–0108.01 to ensure the quality and reliability of ballistic resistant materials used for personal protection purposes. These materials are of many types, and can be found in shields, ballistic resistant plates, and vehicle armor.

The current revision of the standard, NIJ Standard– 0108.01 was released in September 1985. It added ballistic threat level IIIA and established threat level classifications that were consistent with other NIJ standards for ballistic protection. Since that time, an extensive amount of work was done that led to the NIJ ballistic-resistant body armor standard (NIJ Standard–0101.04), and more recently, the next version of the standard, which is still in draft form. The current NIJ Standard–0108.01 does not reflect any of the improvements that have been introduced into the ballistic resistant body armor standard, and harmonizing the test methods and threat levels of the two ballistic standards is important.

Technical Strategy

Several improvements that have been recommended for the NIJ ballistic-resistant body armor standard will be incorporated into the draft revision of the Ballistic Resistant Materials standard. Improvements include introduction of a V50 ballistic limit test methodology and updating of the ballistic threats. Further clarifications of the scope of the standard are also necessary, and a determination will be made whether to include testing of transparent materials in the revised standard or to develop a separate performance standard for those materials. Additional work is planned to evaluate alternative sample mounting methods, and experimental validation tests of the recommended methods will be conducted.

Deliverables

• Revised draft standard.
• Summary report of validation tests.

Goals

The objective of this project is to revise NIJ Standard–0104.02.

Customer Needs

NIJ Standard–0104.02, "Riot Helmets and Face Shields," was last reviewed in October 1984. Since that time, technological improvements incorporated into helmets and face shields offer better protection, and research has led to a better understanding of head and neck injuries. An improved performance standard that incorporates these considerations into it will allow law enforcement and corrections personnel to specify and procure improved equipment that offers higher levels of protection.

Technical Strategy

Other national standards dealing with helmets were reviewed and comments from practitioners were considered to develop a solicitation seeking a technical contractor to conduct further research leading to a revised draft of the standard. In 2006 a contract was awarded to Biokinetics and Associates Ltd. to conduct research leading to the establishment of a draft standard. Improvements envisioned include revising the threat levels to be consistent with current injury threshold research, requiring the use of ISO headforms, adopting flammability resistance test methods, and giving consideration to the performance of the "tails" protecting the nape. Validation tests are also anticipated to confirm that the test methods can be applied to a fair selection of commercially available riot helmets on the market. The contract duration is 18 months. After delivery of the draft standard, it will be circulated for review and comment by interested parties and then submitted to NIJ for final review and publication.

Deliverables

• Revised draft standard for comment and review.
• Validation test report.
• Finalized revised standard.