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Summary
In 2009, the Government Accountability Office (GAO) released the report
Warfighter Support: Independent Expert Assessment of Army Body Armor Test
Results and Procedures Needed Before Fielding, which commented on the
conduct of the test procedures governing acceptance of body armor vest-plate
inserts worn by military service members (GAO, 2009). This GAO report, as well
as other observations—for example, the Army Audit Agency report to the
Program Executive Officer Soldier on Body Armor Testing (AAA, 2009)—led
the Department of Defense (DoD) Director, Operational Test & Evaluation
(DOT&E) to request that the National Research Council (NRC) Division on
Engineering and Physical Sciences (DEPS) conduct an ad hoc study to investigate
issues related to the testing of body armor materials for use by the U.S. Army and
other military departments. Box S-1 contains the statement of task for the three-
phase study. Phases I and II resulted in two NRC letter reports: one in 2009 and
one in 2010.1 This is the Phase III report.
1
Findings and recommendations from the Phase I and Phase II reports are in Appendixes
K and L respectively.
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Box S-1 Statement of Task
The National Research Council will convene specialists in committee form to consi der the
technical issues relating to the testing of body armor. To do this the National Research Council
shall conduct a 3-phase study:
In Phase I a 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. The
Committee will also provide interim observations regarding the column drop performance test
described by the Army for assessing the part to part consiste ncy of a clay body used in testing
body armor. The committee will prepare a letter report documenting the findings from its Phase I
considerations. This is a six week effort beginning November 1 2009 and ending mid December
2009.
In Phase II a committee will consider in greater detail the validity of using the column drop
performance test described by the Army for assessing the part -to-part consistency of a clay body
within the level of precision that is identified by the Army test procedures. The committe e will
prepare a letter report documenting the findings from its Phase II considerations. This is a three
months effort beginning November 1 2009 and ending early February 2010.
In Phase III a committee will consider test materials, protocols and standard s that should be used
for future testing of personal armor by the Army. The committee will also consider any other
issues associated with body armor testing that the committee considers relevant, including issues
raised in the Government Accountability Office Report---Warfighter Support, Independent Expert
Assessment of Body Armor Test Results and Procedures Needed Before Fielding (GAO -10-
119).The committee will prepare a final report. This is a 14 -months effort beginning November 1
2009 and ending January 2011.
The final report will document the committee’s findings pertaining to the following issues that are
of particular immediate concern to DOT&E including the following:
The best methods for obtaining consistency of the clay, and of conditioning a nd calibrating the
clay backing used currently to test armor.
The best instrumentation (e.g., laser scanning system, digital caliper, etc.) and procedures to
use to measure the back face deformation (BFD) in the clay.
The appropriate use of statistical techniques (e.g., rounding numbers, choosing sample sizes, or
test designs) in gathering the data.
The appropriate criteria to apply to determine whether body armor plates can provide needed
protection to soldiers; this includes the proper prescription for determining whether a test results in
a partial or complete penetration of body armor, including, as appropriate, the soft armor
underlying hard armor.
The final report will also document the committee’s findings regarding any other issues re garding
body armor testing that the committee found relevant. The study team will have access to all data
with respect to body armor testing that the team needs for the conduct of the study.
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The last task for Phase III of the study was to document in its final report
any other issues regarding body armor testing that the committee found relevant.
In response, this report also addresses the following tasks:
Provide a road map to reduce the variability of clay processes and
show how to migrate from clay to future solutions.
Consider the use of statistics to permit a more scientific determination
of sample sizes to be used in body armor testing.
Develop ideas for revising or replacing the Prather study methodology.
Review and comment on methodologies and technical approaches to
military helmet testing.
Consider the possibility of combining various national body armor
testing standards.
The preponderance of body armor testing is conducted by the U.S. Army
Aberdeen Test Center (ATC) in support of the body armor acquisition authority,
which is the U.S. Army Program Executive Office Soldier (PEO Soldier). In
developing its report, the Phase III Committee on Testing of Body Armor
Materials for Use by the U.S. Army (the Phase III committee) built on the work of
the Phase I and Phase II committees, conducting data-gathering sessions at the
ATC in Maryland and visiting testing facilities of the Army and commercial
testers. Appendix B provides a list of committee briefings and activities.
The broad purposes of the study were to verify and validate current test
procedures for body armor plates, to investigate long-standing issues related to the
testing process, and to recommend approaches that will improve testing
methodologies and procedures in the future. Committee responses to specific
issues raised in the GAO Report are contained in Appendix F. This summary
includes the numbered recommendations from each chapter of the report with
principal findings of the study highlighted in italic typeface.
OVERVIEW OF BODY ARMOR TESTING
Ceramic materials have been used successfully in personal armor systems
to defeat small-arms threats in both Iraq and Afghanistan, and there have been no
known instances where a death resulting from small arms fire can be attributable
to a failure of issued ceramic body armor. Since hard body armor systems add a
significant weight to the burden on the soldier, the testing of body armor has an
implied goal of ensuring that survivability standards are met while allowing
sufficient soldier mobility and flexibility.
In 1977, a study was performed to correlate the depth that a 200-g, 80-mm
hemispherical missile impacting at approximately 55 m/sec penetrated live-animal
tissue and other media (Prather et al., 1977). The goal of the Prather study was to
develop a simple, readily available backing material for characterizing both the
penetration and deformation effects of ballistic impacts on body armor materials
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and to relate this information to the injury potential of nonpenetrating ballistic
impacts.
When there was no penetration of the armor, the researchers noticed that
dynamic ballistics forces caused an indent in the recording material behind the
point where the bullet struck the front side of the armor. This deformation in the
backing material was termed a “backface deformation” (BFD). The depth of the
deformation into various media, such as modeling clay or ballistics gelatin, as a
function of time was compared to the probability of lethality for an identical
degree of deformation inflicted on a live-animal model.
The Prather study observed strong correlations between lethality
probability and the deformation of ballistic gelatin2 and of a modeling clay, Roma
Plastilina #1 (RP #1). Ballistic gel required the use of high-speed photography to
record the BFDs because the gel was elastic and returned to its original shape
immediately after the projectile firing. To avoid the need to use high-speed
photography, which was expensive at that time, clay was selected as an alternative
and is used today as the medium for recording the BFDs in body armor testing.
RP #1 in its current formulation is the standard recording medium for
testing, even though there are imperfect correlations between existing medical
data and the BFD testing approach. In a nonpenetrating impact, kinetic energy
must be dissipated by the armor through deformation or fragmentation of the
armor, bullet, and underlying body wall. The transfer of energy to the body has
the potential to cause serious injury or death. Nonpenetrating impact injury is
termed “behind-armor blunt trauma” (BABT).
Numerous studies and experiments have been conducted and are ongoing
to better determine the relationships among blunt force trauma, human injury, and
the body armor testing processes. Since past research was based on smaller and
slower bullets, the committee recognized that the existing research raises
concerns regarding the correlation between damage measured in RP #1 and
bodily injury at the very high rates typical of BFDs caused by rifle rounds in hard
body armor.
CLAY AND BACKING MATERIALS
The committee assessed the use of clay in testing and described how the
variability inherent in the backing material might be incorrectly attributed to
variability in the armor. The study investigated the role of the backing material as
a recording medium, the properties and limitations of RP #1 clay in body armor
testing, and alternatives for future backing materials and systems for testing.
2
Ballistic gelatin is a clear or yellowish gelatin that is the standard medium for evaluating
what happens to bullets on impact with soft tissue.
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Clay as a Recording Medium
The qualitative assertion that RP #1 exhibits little recovery has been
interpreted to mean that the level of elastic recovery is small enough to be safely
neglected. This has led to an assumption that the shape of the resultant cavity
provides a record of the BFD. Since the relative degree of elastic and plastic
deformation will vary as a function of strain rate, the backing material must be
characterized under conditions that are relevant to those under which the tests will
be performed. The cavity that results from live-fire ballistic testing is indeed
related to the deformation on the back face of the armor, but it is not a true record
of maximum deflection. It remains unknown how the dimensions of the cavity
relate to the true BFD and how such a relationship may depend on the rate at
which the cavity is formed.
RP #1 was originally developed as a modeling clay for artists. Over time
its composition changed and the clay became stiffer to suit the ceramic arts
community’s needs. Consequently, testers recognized the need for a method for
calibrating the clay. The so-called column drop test was developed in response to
this need. Because the oil-based modeling clay is readily softened by heating,
ovens are now used on the firing range to warm the clay so that the newer
formulations respond in the same way as the older ones.
Experiments conducted by the ATC show that RP #1 exhibits highly
variable penetrations under nominally identical conditions. This unambiguously
indicates that RP #1 is an inherently imprecise recording medium.
The committee found that both the spatial and the temporal variations of
the modeling clay are significant. Experiments can be conducted to determine the
variation due to box geometry and location of the drop in relation to the side of
the box. Also, the scaling relationship between drop tests and ballistic tests
remains mostly unexplored.
Understanding the structure-property relationships of oil-based modeling
clay as they pertain to mechanical working, thermal processing, friction, and how
the various ingredients of the clay modify behavior could lead to alternative clay
systems with more favorable properties. A clay working group consisting of
interested government and civilian experts from the body armor testing
community is working to develop a near-term replacement clay that can meet the
calibration specification of the column drop test at ambient temperature and
whose properties are little affected by temperature.
Recommendation 4-1: The Office of the Director, Operational Test and
Evaluation, and the Army should continue to expedite the development of a
replacement for the current Roma Plastilina #1 oil-based modeling clay that can
be used at room temperature.
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Clay Conditioning and Handling
Interim opportunities for improvements in clay conditioning and handling were
recommended in Phase II of the study, because in the short term, testing will
continue to be conducted with available RP #1. As long as heating the clay is
necessary, cooling will take place, and a post-test calibration drop test, as
recommended in the Phase II Report (NRC, 2010), will continue to be an urgent
requirement for the Army test operating procedure (TOP).
There is also a continuing need for detailed and systematic
characterization of both the medium and the testing process. The comprehensive
thermomechanical characterization of RP #1 that was recommended in the Phase
II Report (NRC, 2010) will quantify the effect of shear history and thermal history
on the storage and dissipative components of mechanical deformation. Such a
characterization will also quantify the times associated with recovery of
properties as well as the thermal properties, including thermal expansion,
thermal conductivity, thermal diffusivity, heat capacity, and thermal arrests
associated with phase changes.
In the drop test, the strain rate experienced by the clay is qualitatively
lower than the rate experienced in the live-fire ballistic test of armor, and there is
little information on clay behavior in these two strain-rate domains. Further, the
volumes of cavities formed in the drop tests and the live-fire tests differ
significantly. The testing community would benefit greatly from devising an
alternative to the column drop test and certifying the validity of the current drop
tests for calibration.
Medium-Term and Long-Term Replacements for Modeling Clay
There are two broad classes of backing material replacements for
consideration in the medium and longer terms: (1) elastic materials that recover
their original shape after unloading and (2) plastic materials that preserve a
permanent cavity whose dimensions can be correlated to lethality probability.
There is no compelling rationale for expending resources to achieve an interim
solution using an elastic material such as ballistic gelatin. The committee also
found that for the foreseeable future, plastically deforming recording media
appear to be the proper choice of backing material for production testing of body
armor.
The committee assessed the potential of the anthropomorphic test module
(ATM) technology currently used by the Army for ballistics injury research. The
committee concluded that the use of the ATM represents a transition to a
challenging methodology with only limited ability to extend results to injury
prediction. Also, it is too costly to be used as a production testing alternative to
RP #1 at this time. The ATM is judged a research tool that is not practical or
appropriate for widespread deployment in ballistic testing ranges.
There are several other test devices that are potentially suitable for use in
the development of a test methodology for ballistic BABT, but they all need
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significant development and validation experimentation. Much depends on the
degree to which it is desirable to rank armor or predict injury probability, which
would have to be addressed. Overall, instrumented electronic sensor response
elements are in a primitive state for the evaluation and assessment by medical
researchers of ballistic BABT with rifle round threats. They also are too costly to
be used in high-volume production testing. More research and detailed validation
is necessary before electronic sensors can be considered as a practical medium-
or long-term alternative to the use of RP #1.
The report describes near-term actions, medium-term needs, and long-term
goals that are consistent with earlier recommendations of the Phase II study
(NRC, 2010).
Recommendation 4-2: The Office of the Director, Operational Test and
Evaluation, and the Army should provide resources and execute the road map
described in this chapter and graphically shown in Figure S-1 with the objective
of developing a standard ballistics backing material for testing body armor. The
properties and behaviors of the material should be well understood. It should
exhibit minimal variability due to temperature, working, and aging and require
simple calibration techniques and equipment, and it should enable reliable and
accurate recording of body armor test results.
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Medium-Term
FIGURE S-1 Road map showing suggested near-term actions, medium-term research
needs, and a long-term goal to develop a more consistent backing material and a more
reliable process for evaluating hard armor. The color coding shows “highest priority”
items in red text with “high priority” actions in orange.
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INSTRUMENTATION AND PROCEDURES FOR MEASURING AN
INDENT IN THE BACKING MATERIALS
The committee was tasked to determine the best instrumentation and
procedures for measuring BFD (see Box S-1). To do this, it reviewed technical
specifications, viewed demonstrations of the operation and use of current and
prospective systems, and evaluated factors such as human handling variability,
process transparency, and software variability judgment.
The committee found that given the current clay variation, a measurement
precision (standard deviation) of 0.5 mm is sufficient; instruments featuring
greater precision add little practical value to the testing process. Future
improvements in the inherent variability of the backing material will require
instruments that are correspondingly more precise. It is important that quantified
data from actual tests be obtained for all instruments and measurement scenarios
in order to make valid comparisons of instrumentation for different applications.
In evaluating the instrumentation methods, the committee noted that there
is unknown variability associated with the software smoothing algorithm used by
the Faro laser scanner system.
Recommendation 5-1: An organization such as the National Institute of
Standards and Technology should conduct a controlled study to determine the
most reasonable and consistent Faro smoothing settings to be used while
measuring backface deformations (BFDs) in body armor testing. Similarly, any
other software selections that could cause relevant changes to BFD measurements
should be studied. Corresponding values for the precision and accuracy of each
software setting will need to be quantified.
It is possible that a standard BFD cavity artifact could be used by testers to
help to ensure that all measuring devices provide standard measures of accuracy
and precision at different locations.
Recommendation 5-2: An organization such as the National Institute of
Standards and Technology should develop a standard backface deformation
artifact system and procedures to allow operators to ensure that different
measurement devices at different locations are able to meet specified levels of
accuracy and precision.
Finally, the committee derived criteria for a “best utility” measuring
instrument based on its assessment of the characteristics of instrumentation
systems presently used by military and commercial testers.
Recommendation 5-3: In anticipation of future test measurement requirements,
the Office of the Director, Operational Test and Evaluation, and/or the Army
should charter an organization such as the National Institute of Standards and
Technology to conduct an analysis of available candidate commercial instruments
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with inputs from vest users, manufacturers, testers, policy makers, and others. The
goal is to identify one or more devices meeting the characteristics of “best utility”
measuring instruments as defined in this study to the government, industry, and
private testing labs.
The list of best utility instruments should be shared with the National
Institute of Justice (NIJ), international allies, and others, as appropriate, to
promote measuring instrument standardization for body armor testing nationally
and internationally. A formal gauge or “artifact standard” repeatability and
reproducibility study is required to quantify accuracy and precision as inputs to
the best utility analysis.
STATISTICAL CONSIDERATIONS IN BODY ARMOR TESTING
The Phase II committee was asked to review a statistically based protocol
that had been developed by DOT&E with assistance from Army statisticians and
testers, and the Phase II report (NRC, 2010) provided initial insights on statistics-
related issues. The committee reviewed historical test protocols as well as the new
DOT&E first article testing (FAT) protocol and a proposed lot acceptance testing
(LAT) protocol with regard to the assumptions underlying the statistical methods
and design trade-offs.
The committee found that because of their differences, and as
demonstrated in the DoD Inspector General calculations, neither the historical
Army protocols nor the U.S. Special Operations Command (USSOCOM)
protocols met the key protocol design requirement as a common standard DoD-
wide. In addition, the historical Army protocol did not meet the key design
requirement as a statistically principled test.
During the course of the committee’s research and deliberations, the
DOT&E, Army, and USSOCOM have endeavored to establish statistically
principled test standards that are realistically achievable with the current body
armor designs. The committee found these collaborative efforts to be
commendable.
The new DOT&E protocol meets both key protocol design requirements; it
is statistically principled and it provides a minimum DoD-wide body armor test
standard. However, since the distribution for some combinations of vendor,
threat, and design may not be normally distributed, the tolerance-bound
calculation that is specified by the protocol may not be appropriate in all cases.
The committee found that use of the Clopper-Pearson method for
calculating the lower confidence limit is conservative, resulting in actual
confidence levels that are at least as great as, and often greater than, the
confidence level specified in the standard. The actual confidence level varies
substantially as a function of the probability of no penetration [Pr(nP)] of the
plates, and it can be quite different for small changes. For most lot sizes, and over
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the higher levels of Pr(nP), the S-4 inspection level3 results in a greater
probability that a lot will pass the LAT.
The committee concluded that using a statistically principled protocol
enables decision makers to explicitly address the necessary and inherently
unavoidable risk trade-offs that must be faced in testing. Furthermore, while
additional research and coordination may be necessary to finalize the protocol
design, and continuing review will likely be required as manufacturing conditions
and plate designs change over time, a statistically principled protocol ensures
that decision makers have sound information about body armor performance in
order to ensure the quality of a critical soldier safety item.
Recommendation 6-1: The Office of the Director, Operational Test and
Evaluation (DOT&E) should continue to conduct due diligence to carefully and
completely assess the effects, large and small, of its statistical protocol as it is
adopted across the body armor testing community. In particular, DOT&E should
continue to
Collaborate with the Army and the United States Special
Operations Command (USSOCOM ) to revise the test protocol
as necessary, based on the results of Army and USSOCOM
“for government reference” first article testing test results and
other empirical evidence, to ensure that currently acceptable
plate designs are not eliminated under the new protocol; and
Regularly assess the impact or impacts of the new protocol on
plate design, particularly plate weight, to ensure the test
protocol results in body armor that achieves the requisite soldier
safety while not negatively, inappropriately, or inadvertently
affecting plate design.
Recommendation 6-2: The Office of the Director, Operational Test and
Evaluation, should consider modifying the first article testing protocol to
Generalize the description of the backface deformation (BFD)
upper tolerance interval calculation to allow for nonnormal
BFD distributions;
Specify a confidence interval calculation methodology that has
better coverage properties, such as the Agresti-Coull interval
recommended by Brown et al. (2001) and described in detail in
Agresti and Coull (1998); and
Specify guidelines that will accommodate deviations in
environmental conditions and/or plate size from the current 60-
plate design matrix.
3
Sample sizes in the protocol are based on special inspection level S-4 of ANSI/ASQ
Z1.4-2008 (American Society for Quality, 2008).
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Recommendation 6-3: The Office of the Director, Operational Test and
Evaluation, and the Army should continue to consult and engage statisticians
throughout the process of assessing and revising protocols, comparing the
performance of the new and old protocols, assessing the effects of the new
protocols, and considering possible changes.
Testers and statisticians should continue to work together as a team to (1)
quantify in a statistically rigorous manner the amount of variation in BFD
attributable to the testing process and that attributable to the plates and (2) ensure
these results are appropriately reflected in an updated protocol. In particular, the
statisticians involved with developing and implementing the statistically
principled protocol should be involved with the clay experimentation discussed
and recommended in the study.
Over the course of the committee’s research and deliberations, the
DOT&E, the Army, and USSOCOM have endeavored to establish statistically
principled test standards that are realistically achievable with the current body
armor designs.
Recommendation 6-4: The Office of the Director, Operational Test and
Evaluation, the Army, and the United States Special Operations Command should
work together to arrive at an acceptable set of test standards for lot acceptance
testing that is both statistically principled and is realistically achievable with
current body armor designs.
HELMET TESTING
A specific tasking for Phase III of the study was to provide ideas for future
improvement of helmet testing. Helmet testing follows a methodology similar to
that for the testing of body armor plates. Head forms filled with the same RP #1
modeling clay are heated and subjected to drop tests to assure uniformity. The
helmet to be tested is placed over a head form and a test round is fired into the
front and side of the helmet. Ballistic forces from the bullet cause an indent in the
clay similar to the BFD behind the armor plate, and the indent must be within
specifications for it to pass the test.
The committee found that existing helmet test methodologies, including
the current Army test methodology, do not relate directly enough to human injury
to confidently assess injury risk from back-face trauma to the head. Improving the
link between test methodology and human injury is an urgent matter in light of the
newer helmet systems with lower areal densities and increased threat velocities.
Also, it is uncertain how clay response correlates with human head/skull/brain
response. Yet, clay response serves as the basis for current clay-based helmet
methodologies. From a broader systems perspective the same problem exists with
body armor plate methodologies. That is, it is uncertain how clay response is
correlated with human injury in the thorax.
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Recommendation 7-1: The Army should perform research to define the link
between human injury and the testing methodology for head behind-armor blunt
trauma.
Recommendation 7-2: The Aberdeen Test Center should ensure the following:
1. Dynamic mechanical strain/deformation response of the head surrogate
is similar for both types of loading at loading rates typical of behind-
helmet response;
2. Response of the head surrogate is similar to that of the human head;
3. Required head quality control calibration is either performed on the
head surrogate itself or is shown to be demonstrably represented by a
surrogate for the head itself (i.e., by a sample box filled with clay) in
controlled testing using a standard test procedure; and,
4. Response of the clay for the low-rate calibration tests is shown to be
similar or scalable to the high-rate backface deformation response of
the surrogate in controlled testing using a standard test procedure.
The Army Research Laboratory has developed what is referred to as the
“Peepsite” head form to deal with some of the shortcomings of existing test head
forms. The committee found that the Peepsite head form reduces or eliminates
several potential problems with the NIJ head form that is used in the current clay
test methodology.
A potentially important aspect of ballistic protective helmet design is the
suspension system that provides helmet stand-off from the head, an important
factor in ballistic protection. This complicates any analysis of injury risk due to
deformation of the helmet.
Recommendation 7-3: The Army should investigate use of the Peepsite
headform currently in development by the Army Research Laboratory with room-
temperature clay. This headform and procedure has potential as a near-term
alternative to testing using the National Institute of Justice clay head form tested
at elevated clay temperatures.
MEDICAL BASIS FOR FUTURE BODY ARMOR TESTING
Much is to be gained by applying medical knowledge to body armor
design and test processes. The committee reviewed applicable advances in
medicine and biomechanics since the Prather study and concluded that the
researchers at the time made good use of the data that were available (Prather et
al., 1977). However, advances in imaging and measurement technology since then
could facilitate a better understanding of the injury mechanisms, which will help
to identify different and more appropriate engineering tests for armor
qualification.
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Thoracic Ballistic Test Methodologies
As previously noted, injuries to the thorax due to deformation of the armor
are often termed BABT. Dynamic pressures transmitted to the thorax can cause
local and remote fractures, contusions, and hemorrhage, as has been demonstrated
in numerous animal studies. The committee found that carried mass, such as that
associated with body armor, may decrease a soldier’s mobility and lead to
fatigue. Further, body armor can prevent high-velocity bullets from penetrating
the body but may not protect personnel from the shock wave from the initial
projectile impact and the trauma induced by the BFD.
The committee found that the details surrounding the force that is
transmitted from the body armor to the person wearing the armor, including the
amount, the timing, and the immediate and long-term consequences of this force,
are unknown. Techniques are needed not only to identify and treat BABT injuries,
but also to assess the risk of BABT injury to those who wear the body armor. An
instrumented surrogate (dummy) has been used effectively in many fields of
injury biomechanics to evaluate the risk of injury from blunt trauma. Elements of
this technique include a biofidelic surrogate, an engineering measurement system,
an injury risk evaluation, and validation by physical injury model (such as by tests
on animals or cadavers). Development of a relationship between a robust
surrogate for injury and a validated injury model is crucial for success of this
approach.
The body armor plates were designed to resist penetration by threat projectiles
as detailed in the performance specifications. As a consequence, the plates are
tested primarily on their ability to defeat the threat projectiles. In combat, the
vests and plates also may provide warfighters with an unknown degree of
protection against other battle hazards, including blast effects. The design for
future body armor vests should consider blast effects as well as trade-offs between
bulk, weight, and protection. Discrepancies between published measurements of
changes in intrathoracic pressure for human subjects exposed to blasts from
explosives with and without vests need to be resolved.
Recommendation 8-1: The Army medical and scientific testing communities
should adequately fund and expedite the research necessary to experimentally and
epidemiologically quantify the physiologic and medical impact of blunt force
trauma on the body from both ballistic and blast threats to soldiers.
Cadaveric Experiments for Behind-Armor Blunt Trauma
Although there are several studies using animal and cadaveric
experiments to study BABT injuries for hard body armor, the committee found
that the current work does not allow the development of a thoracic BABT injury
criterion from existing studies. Additional animal and/or cadaveric
experimentation is necessary to develop a BABT injury criterion. Also, there is a
need for a robust and widely used ballistic trauma injury classification scale.
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Although there are a number of existing injury scales, including a widely used
scale for automobile injuries, the abbreviated injury scale promulgated by the
Association for the Advancement of Automotive Medicine, none is well suited to
ballistic trauma. Data on which to base a satisfactory injury scale will require the
collection of military epidemiological data on a large scale.
Models used by blunt trauma researchers do not reflect realistic battlefield
threats, and the fidelity of anatomical, physical, and mathematical finite-element
models simulating the human thorax, heart, lungs, liver, and kidneys, is limited at
the present time. Thus, damage from transmitted pressures associated with blunt
trauma to such organs as the intestines, spinal cord, brain, or vascular system
cannot be predicted.
Recommendation 8-2: The Army should perform high-speed ballistic tests using
human cadavers and large animal cadavers to provide responses to deforming
hard armor impacted by velocities likely to be encountered in combat. These tests
should be extensively instrumented to determine dynamic deformation
characteristics in the human and animal torsos to provide data that can be
correlated with clay response at the same rates (or with alternative media or other
test methodology) and with epidemiology and medical outcomes in the soldier.
The studies should ensure that velocity and backface deformation regimes
replicate those for current and future desired body armor testing protocols.
The observations and data needed for large animal studies are far more
extensive than data collected in the past. As described in Appendix J, studies will
require extensive use of pressure transducers, cineradiography, metabolic imaging
and neurochemical cerebral spinal fluid and blood assays.
Recommendation 8-3: The Army should perform live large-animal, live-fire tests
to simulate the behavior of current and proposed new body armor against
expected threats.
Instrumented Alternatives to Determine BABT
Technologies developed for research to evaluate injury effects, such as the
ATM and clay sensors, have been considered by the Army for use in developing
alternative testing methodologies. The committee found that instrumented
response elements are in a primitive state for the evaluation of ballistic BABT for
hard body armor against rifle round threats. Although several devices have
associated instrument response and injury criteria that have been validated
against a small range of loading conditions, there is no test device suitable for
use without further development and validation. Also, instrumented anatomical
surrogates are not detailed enough to assess ballistic BABT for hard body armor
with rifle round threats.
Recommendation 8-4: The Army should develop finite-element simulation
models of human and live-animal thoracic response to behind-armor blunt impact.
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The validation of this simulation should be hierarchical from the small scale to the
large scale. This includes the dynamic local response of constituent materials such
as skin, bone, muscle, lung, liver, and other tissues; the regional response of the
tissues under loading; and the global response of the whole torso. It should also
include deformations from soft and hard body armor impacted with appropriate
threats.
Recommendation 8-5: The Army medical community should enhance the
current trauma registries to provide a program of injury epidemiology for ballistic
impact, including behind-armor blunt trauma. This should include collection of
both injury and noninjury events and should be similar to the federal crash
databases used by the Department of Transportation—for example, the Fatality
Analysis Reporting System and the National Automotive Sampling System for
traffic injuries/fatalities, including injuries induced by both penetrations and
backface deformations.
Recommendation 8-6: Using experimentally determined links to injury,
response, and epidemiology, the Army should ensure that the clay or other
alternative test methodology for hard body armor has humanlike dynamic
response and is suitable for the development of behind-armor blunt trauma injury
criteria.
Recommendation 8-7: To achieve improvements in behind-armor blunt trauma
(BABT) research methodology in the medium term, the Army should develop
instrumented thoracic simulators as response elements (sensors). Necessary
preludes to this effort include the following:
Establishing BABT phenomenology and injury criteria using human
cadavers, animal models, and field injury epidemiology coupled with
well-validated finite-element simulations.
Establishing human BABT mechanical response for the range of design
conditions for personal protective body armor. This should include
impact on soft and hard body armor of anticipated threats.
Recommendation 8-8: In the long term, beyond simple clay torso surrogates and
one-layer torso simulants, the Army should use the road map in Figure S-2 to
investigate the use of detailed anatomical surrogates (such as cadavers,
instrumented models, etc.) as research devices to evaluate behind-armor blunt
trauma.
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FIGURE S-2 Road map showing suggested near-term and medium-term research needs,
and a long-term goal to provide the fundamental medical basis for injury risk assessment
behind helmets and hard body armor.
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FUTURE IMPROVEMENTS IN TESTING METHODOLOGY
In addition to the several recommendations that propose refinements to
improve or replace the standing methodology for body armor testing, the
committee reflected on ways that the existing national standards used to guide
body armor testing for military and police force applications might be better
synchronized in the future.
The committee found that the current body armor testing methodology
that has evolved from the early work of Prather and others should be retained and
improved on while investigating alternative methods. Recommended priorities for
near-term actions are illustrated in Figure S-1.
The committee discerned differences between production testers and
medical researchers relating to experimentation methods, objectives, and test
instruments. Most importantly, it found that recording medium data from medical
research and production testing need to be correlated using identical sensors
having the requisite time resolution. The results need to be shared among the
stakeholders.
Recommendation 9-1: The Director of Operational Testing and Evaluation
should take the lead in aligning the production testing, medical research, and body
armor/helmet technology development communities so that the data outputs from
their various processes can be easily correlated. This will lead to a better
understanding of the relationships among body armor testing performance,
human/animal survivability, and other trade-offs. Specifically, two policies should
be adopted and applied: (1) specify acceptable ranges for projectile weights and
velocities used to generate behind-armor dynamic forces during testing and
research and (2) investigate the use of standardized sensors behind armor to
measure the amount of dynamic force that is produced during testing and
research.
The overall need is for a coordinating committee to provide oversight and
facilitate the exchange of information between stakeholder groups. The committee
believes that the nationally recognized coordination committee recommended in
the Phase II report is needed to align and accelerate efforts of technologists,
production testers, and biomedical researchers in BABT/BFD-related research
for both body armor and helmets. As an important step in this process, the ad hoc
clay working group approach that was started by and is currently chaired by
DOT&E offers an organizational nucleus for a way ahead for DoD. The
committee agreed that the original ad hoc clay working group could be expanded
to form DoD’s portion of the national body armor testing standardization
committee recommended in the Phase II report.
The committee’s last recommendation is conceptually the same as
Recommendation 15 in the Phase II report (NRC, 2010) but has been expanded to
include helmet testing. Helmets and body armor plates have different
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requirements, and there will likely be different testing standards for them for the
foreseeable future.
Recommendation 9-2: The Office of the Director, Operational Test and
Evaluation and the National Institute of Justice (NIJ), in collaboration with the
military services, unified commands, government testing organizations, NIJ -
certified testing laboratories, medical researchers and governmental and
commercial material developers should convene a national body armor testing
standard committee to review all appropriate considerations and develop
recommendations that could lead to updated national body armor configurations
and testing standards for body armor and helmet testing.
REFERENCES
AAA (U.S. Army Audit Agency). 2009. Body Armor Testing. A-2009-0086-
ALA. Alexandria, Va.: U.S. Army Audit Agency.
Agresti, A., and B. Coull. 1998. Approximate Is Better Than “Exact” for Interval
Estimation of Binomial Proportions. The American Statistician 52(2):119-
126.
American Society for Quality. 2008. American National Standard Sampling
Procedures and Tables for Inspection by Attributes. ANSI/ASQ Z1.4-2008.
Milwaukee, W.I.: American Society for Quality.
Brown, L., T. Cai, and A. DasGupta. 2001. Interval Estimation for Binomial
Proportions. Statistical Science 16(2):101-117.
GAO (United States Government Accountability Office). 2009. Independent
Expert Assessment of Army Body Armor Test Results and Procedures Needed
Before Fielding. GAO-10-119. Washington, D.C.: Government
Accountability Office.
NRC (National Research Council). 2009. Phase I Report on Review of the Testing
of Body Armor Materials for Use by the U.S. Army: Letter Report.
Washington, D.C.: National Academies Press.
NRC. 2010. Phase II Report on Review of the Testing of Body Armor Materials
for Use by the U.S. Army. Washington, D.C.: National Academies Press.
Prather, R., C. Swann and C. Hawkins. 1977. Backface Signatures of Soft Body
Armors and the Associated Trauma Effects. ARCSL-TR-77055. Aberdeen
Proving Ground, MD: U.S. Army Armament Research and Development
Command Technology Center.
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