U.S. Army Aberdeen Test Center

Tooth fracture is a major concern in the field of restorative dentistry. However, knowledge of the causes for tooth fracture has developed from contributions that are largely based within the field of mechanics. The present manuscript presents a technical review of advances in understanding the fracture of teeth and the fatigue and fracture behavior of their hard tissues (i.e., dentin and enamel). The importance of evaluating the fracture resistance of these materials, and the role of applied mechanics in developing this knowledge will be reviewed. In addition, the complex microstructures of tooth tissues, their roles in resisting tooth fracture, and the importance of hydration and aging on the fracture resistance of tooth tissues will be discussed. Studies in this area are essential for increasing the success of current treatments in dentistry, as well as in facilitating the development of novel bio-inspired restorative materials for the future.

First responders and military personnel are particularly susceptible to behind armor blunt thoracic trauma in occupational scenarios. The objective of this study was to develop an armored thorax injury risk criterion for short duration ballistic impacts. 9 cadavers and 2 anthropomorphic test dummies (AUSMAN and NIJ 0101.04 surrogate) were tested over a range of velocities encompassing low severity impacts, medium severity impacts, and high severity impacts based upon risk of sternal fracture. Thoracic injuries ranged from minor skin abrasions (abbreviated injury scale [AIS] 1) to severe sternal fractures (AIS 3+) and were well correlated with impact velocity and bone mineral density. 8 male cadavers were used in the injury risk criterion development. A 50% risk of AIS 3+ injury corresponded to a peak impact force of 24,900 +/- 1,400 N. The AUSMAN impact force correlated strongly with impact velocity. Recommendations to improve the biofidelity of the AUSMAN include implementing more realistic viscera and decreasing the skin thickness.

Abstract Numerous studies have attempted to address the land–precipitation coupling, but scientists’ understanding remains limited and discrepancies still exist from different studies. A new parameter Γ is proposed here to estimate the land–precipitation coupling strength based on the ratio of the covariance between monthly or seasonal precipitation and evaporation anomalies (from their climatological means) over the variance of precipitation anomalies. The Γ value is easy to compute and insensitive to the horizontal scales used; however, it does not provide causality. A relatively high Γ is a necessary—but not sufficient—condition for a relatively strong land–precipitation coupling. A computation of Γ values using two global reanalyses (ECMWF and NCEP), one regional reanalysis [North American Regional Reanalysis (NARR)], and observed precipitation along with Variable Infiltration Capacity (VIC)-derived evaporation data indicates that the land–precipitation coupling is stronger in summer and weaker in winter. The strongest coupling (i.e., hot spots) occurs over the western and central parts of North America, part of the Eurasia midlatitude, and Sahel in boreal summer and over most of Australia, Argentina, and South Africa in austral summer. The Community Climate System Model, version 3 (CCSM3) shows much higher Γ values, consistent with the strong coupling shown by its atmosphere–land coupled components in previous studies. Its overall spatial pattern of Γ values is not affected much over most regions by the doubling of CO2 in CCSM3. The Γ values from the Regional Atmospheric Modeling System (RAMS) are more realistic than those from CCSM3; however, they are still higher than those from observations over North America.

To reduce human casualties associated with explosive ordnance disposal, a wide range of protective wear has been designed to shield against the blast effects of improvised explosive devices and munitions. In this study, 4 commercially available bomb suits, representing a range of materials and armor masses, were evaluated against 0.227 and 0.567 kg of spherical C-4 explosives to determine the level of protection offered to the head, neck, and thorax. A Hybrid III dummy, an instrumented human surrogate [1], was tested with and without protection from the 4 commercially available bomb suits. 20 tests with the dummy torso mounted to simulate a kneeling position were performed to confirm repeatability and robustness of the dummies, as well as to evaluate the 4 suits. Correlations between injury risk assessments based on past human or animal injury model data and various parameters such as bomb suit mass, projected area, and dummy coverage area were drawn.

Modern ballistic helmets defeat penetrating bullets by energy transfer from the projectile to the helmet, producing helmet deformation. This deformation may cause severe injuries without completely perforating the helmet, termed "behind armor blunt trauma" (BABT). As helmets become lighter, the likelihood of larger helmet backface deformation under ballistic impact increases. To characterize the potential for BABT, seven postmortem human head/neck specimens wearing a ballistic protective helmet were exposed to nonperforating impact, using a 9 mm, full metal jacket, 124 grain bullet with velocities of 400-460 m/s. An increasing trend of injury severity was observed, ranging from simple linear fractures to combinations of linear and depressed fractures. Overall, the ability to identify skull fractures resulting from BABT can be used in forensic investigations. Our results demonstrate a high risk of skull fracture due to BABT and necessitate the prevention of BABT as a design factor in future generations of protective gear.

<div class="htmlview paragraph">As part of a multi-agency study concerning emissions and fuel consumption from heavy-duty diesel truck idling, Oak Ridge National Laboratory personnel measured CO, HC, NO<sub>x</sub>, CO<sub>2</sub>, O<sub>2</sub>, particulate matter (PM), aldehyde and ketone emissions from truck idle exhaust. Two methods of quantifying PM were employed: conventional filters and a Tapered Element Oscillating Microbalance (TEOM). A partial flow micro-dilution tunnel was used to dilute the sampled exhaust to make the PM and aldehyde measurements. The work was performed at the U.S. Army's Aberdeen Test Center's (ATC) climate controlled chamber. ATC performed 37 tests on five class-8 trucks (model years ranging from 1992 to 2001). One was equipped with an 11 hp diesel auxiliary power unit (APU), and another with a diesel direct-fired heater (DFH). The APU powers electrical accessories, heating, and air conditioning, whereas a DFH heats the cab in cold weather. Both devices offer an alternative to extended truck-engine idling. Exhaust emission measurements were also made for the APU and DFH. Trucks were idled at a high and low engine speed in the following environments: 32 °C (90 °F) with cabin air conditioning on, -18 °C (0 °F) with the cabin heater on, and 18 °C (65 °F) with no accessories on. ATC test technicians adjusted the air conditioning or heater to maintain a target cabin temperature of 21 °C (70 °F). Each test was run for approximately three hours.</div> <div class="htmlview paragraph">Comparison of the results from the APU to those from the idling trucks implies that use of an APU to replace truck idling gives fuel savings (and CO<sub>2</sub> reduction) on the order of 60-85%, 50-97% reductions in NO<sub>x</sub>, CO and HC, and PM reductions of -20% to 95%. PM emissions from the APU were higher than the “best” idling truck engine cases. The diesel-fired heater had significantly lower emissions and fuel consumption than the APU. The potential for fuel savings and environmental benefits are readily apparent.</div> <div class="htmlview paragraph">Results for PM emissions showed a wide range of emissions rates from <1 g/hr to over 20 g/hr, with the newest trucks in the 1-5 g/hr range. PM emissions generally decreased with an increase in ambient temperature and increased disproportionately with an increase in engine speed. Aldehyde mass emissions rate increased with both decreasing temperature and increasing engine speed. The mass emissions rate of regulated gaseous species generally increased with increasing engine speed. A comparison of PM measurements with the TEOM and the filter-based methods is presented.</div>

In this article, vehicle handling behavior of a nonlinear four-wheel vehicle system is studied. Bifurcations with respect to vehicle speed and roll moment distribution are examined for innate understeering and oversteering models. Lateral load transfer effects are investigated, and these effects are shown to alter the bifurcation locations for oversteering vehicles when the roll moment distribution is adjusted. When the roll moment distribution is used as a control parameter, transitions between bifurcation behavior characteristic of oversteering systems and bifurcation behavior characteristic of understeering systems are observed. This effort provides a framework for developing a complete vehicle handling assessment in terms of nonlinear regions of performance, transient behavior, and lateral load effects.

Road vibration tests were recently conducted on a series of shelters on dolly sets and on a series of prototype trucks at the U.S. Army Combat Systems Test Activity (USACSTA) at Aberdeen Proving Ground. Data from histogram or amplitude distribution tables were plotted in the normal probability domain to provide a graphic representation. When examining these probability plot data, a divergence of the actual distribution from the normal distribution at the tails was noticed. Of the 104 trials compared, the normal distribution was exceeded by 30 trials at the 90 percent level, 87 trials at the 99 percent level, and 88 trials at the 99.9 percent level. This indicates that the actual measured values at the extreme ends of the distribution (beyond the 90 percent occurrence levels) are larger in magnitude (acceleration) than would be predicted by the assumption of a normal distribution. This same trend was noticed during examination of the kurtosis values for the same data sets. The values generally exceeded a value of three, which is the expected value for a Gaussian distribution. Because the kurtosis is largely affected by data values far from the mean, a correlation between the normalized 99.9 percent values and the normalized kurtosis values was tried. A linear regression line was fit through the data, which produced a correlation of approximately 0.82. Although no formal effort has been put forth to catalog kurtosis measurements from military vehicles, it has generally been observed that the kurtosis values obtained from operation over our test courses is greater than three, indicating that the tails of a vibration distribution from operation over severe terrain are further from the mean (larger amplitude) than would be predicted from a normal distribution. If the kurtosis of the laboratory test distribution is less than that of the field distribution, the extreme values seen in the field environment will not be duplicated in the lab. The addition of conservatism during the schedule development process should be enough to overcome this difference; however, dome effort should be made to develop a "bi-domain" (frequency and time domain amplitude) control system so that the amplitude distribution of the lab test will more closely match that of the field data from which the schedule was derived.

<div class="htmlview paragraph">This paper describes the initial research and development of a novel parallel hybrid transmission that incorporates design features found in most production 3- and 4-speed automatic transmissions, except that the mechanism can transmit torque from two power sources to the drive wheels. The transmission functions with a heat engine and a single electric motor/ generator, and uses a Simpson gear set and four automatically controlled clutches.</div> <div class="htmlview paragraph">Thirteen modes of operation are possible, including one motor-only mode, three power modes, one CVT/charging mode, four engine-only modes, and four regenerative braking modes. Because the design is based on conventional automatic transmission components, the design is simple, compact, relatively efficient, and reliable.</div>

Roma Plastilina No. 1 (RP1), an artist modeling clay that has been used as a ballistic clay, is essential for evaluation and certification in standards-based ballistic resistance testing of body armor. It serves as a ballistic witness material (BWM) behind the armor, where the magnitude of the plastic deformation in the clay after a ballistic impact is the figure of merit (known as "backface signature"). RP1 is known to exhibit complex thermomechanical behavior that requires temperature conditioning and frequent performance-based evaluations to verify that its deformation response satisfies requirements. A less complex BWM formulation that allows for room-temperature storage and use as well as a more consistent thermomechanical behavior than RP1 is desired, but a validation based only on ballistic performance would be extensive and expensive to accommodate the different ballistic threats. A framework of lab-scale metrologies for measuring the effects of strain, strain rate, and temperature dependence on mechanical properties are needed to guide BWM development. The current work deals with rheological characterization of a candidate BWM, i.e., silicone composite backing material (SCBM), to understand the fundamental structure⁻property relationships in comparison to those of RP1. Small-amplitude oscillatory shear frequency sweep experiments were performed at temperatures that ranged from 20 °C to 50 °C to map elastic and damping contributions in the linear elastic regime. Large amplitude oscillatory shear (LAOS) experiments were conducted in the non-linear region and the material response was analyzed in the form of Lissajous curve representations with the values of perfect plastic dissipation ratio reported to identify the degree of plasticity. The results show that the SCBM exhibits dynamic properties that are similar in magnitude to those of temperature-conditioned RP1, but with minimal temperature sensitivity and weaker frequency dependence than RP1. Both SCBM and RP1 are identified as elastoviscoplastic materials, which is particularly important for accurate determination of backface signature in body armor evaluation. The mechanical properties of SCBM show some degree of aging and work history effects. The results from this work demonstrate that the rheological properties of SCBM, at small and large strains, are similar to RP1 with substantial improvements in BWM performance requirements in terms of temperature sensitivity and thixotropy.

An error identified in a 1993 textbook of military medicine led to an investigation of derivations of the Coburn-Forster-Kane equation (CFKE) for predicting carboxyhemoglobin (COHb) levels. Reviews of the scientific literature, military documents, and personal interviews revealed that errors were made in earlier derivations of the CFKE. One flawed derivation was used by the U.S. Army until 1985, and another is still used by the National Institute for Occupational Safety and Health (NIOSH). The original and later CFKE derivations are reviewed and errors in the equations are identified. The effect of the errors is discussed.

This paper describes a preliminary experimental investigation to convey acceleration measurements, made on-board an electromagnetic (EM) launched projectile, using microwave telemetry techniques. The focus of the investigation is to extend the Hardened Subminiature Telemetry and Sensor Systems (HSTSS) technology for use in EM launch environments. Many aspects of the HSTSS technology have already been successfully demonstrated in high-G, high-pressure launch environments in conventional gun systems. In addition, microwave transmission in stationary experiments, where the telemetry package was exposed to relatively high magnetic fields and EM transients in a railgun launcher, has been demonstrated. However, microwave telemetry during an EM launch has not been demonstrated until now. In this work, setback acceleration measurements obtained with an on-board accelerometer were processed by HSTSS electronics and transmitted simultaneously during launch via an antenna located in front of the EM launch package. While only the test conducted at 9-kG peak acceleration provided the most useful data, detailed analyses suggest that mechanical problems-rather than the microwave telemetry process itself-were probably responsible for difficulties experienced at higher accelerations. This paper reviews the experimental methodology and discusses the results of the investigation.

Tunable diode laser absorption spectroscopy (TDLAS) is used to measure the time evolution of hydrogen fluoride (HF) concentrations produced from a series of enclosed heptane/air pan fires extinguished by either FE-36, FM-200, FE-36 plus ammonium poly-phosphate (APP), or FM-200 plus APP. For the fires studied, the change in HF gas concentration with time is dependent upon the fire-fighting chemical used to extinguish the re. The presence of APP is observed to reduce HF concentrations in the re enclosure. Visible attenuation spectroscopy is also used to measure the amount of light attenuation (obscuration) that occurs as a hand-held re extinguisher containing powdered fire fighting agent is released in the crew space of a M1-Abrams land combat vehicle.

Several optical techniques (FT-IR emission and absorption spectroscopy, mid- and near-infrared tunable diode laser absorption spectroscopy) have been used to measure toxic gases produced during inhibition of flames by halogenated hydrocarbons (Halons). Fire types studied include low-pressure premixed flames, counterflow diffusion atmospheric-pressure flames, open-air JP-8 (turbine fuel) fires, and confined JP-8 fires. Spectra are presented and analyzed for these fires inhibited by CF 3 Br (Halon 1301) and C 3 F 7 H (FM-200). For low-pressure premixed flames, spectra are presented which show production of the CF 3 radical in methane/oxygen/Ar flames inhibited by CF 3 Br. For large-scale fire testing, it is shown that the type and amount of toxic gases produced during fire inhibition are highly dependent on fire conditions and temperatures and that some species not considered important (CF 2 O) are often produced in significant amounts. Finally, it is shown that HF production, during inhibition of vehicle fires using FM-200, is highly dependent on time to suppression.

INTRODUCTION: Personnel engaged in high-stakes occupations, such as military personnel, law enforcement, and emergency first responders, must sustain performance through a range of environmental stressors. To maximize the effectiveness of military personnel, an a priori understanding of traits can help predict their physical and cognitive performance under stress and adversity. This work developed and assessed a suite of measures that have the potential to predict performance during operational scenarios. These measures were designed to characterize four specific trait-based domains: cognitive, health, physical, and social-emotional. MATERIALS AND METHODS: One hundred and ninety-one active duty U.S. Army soldiers completed interleaved questionnaire-based, seated task-based, and physical task-based measures over a period of 3-5 days. Redundancy analysis, dimensionality reduction, and network analyses revealed several patterns of interest. RESULTS: First, unique variable analysis revealed a minimally redundant battery of instruments. Second, principal component analysis showed that metrics tended to cluster together in three to five components within each domain. Finally, analyses of cross-domain associations using network analysis illustrated that cognitive, health, physical, and social-emotional domains showed strong construct solidarity. CONCLUSIONS: The present battery of metrics presents a fieldable toolkit that may be used to predict operational performance that can be clustered into separate components or used independently. It will aid predictive algorithm development aimed to identify critical predictors of individual military personnel and small-unit performance outcomes.

The dynamic performance of a multi-wheeled combat vehicle model specially developed in multi-body dynamics code was validated against measured data obtained on the U.S. Army Aberdeen Test Center’s (ATC) test courses. The multi-wheeled combat vehicle variant that was tested was developed in the modeling software TruckSim from Mechanical Simulation Corporation. Prior to validating the model, the vehicle weights, dimensions, tires and suspension characteristics were measured and referenced in the specially developed computer simulation model. Non-linear measured tire and suspension look-up tables were used in the simulation. The predictions of the vehicle handling characteristics and transient response during lane change at different vehicle speeds were compared with field tests results. Measured and predicted results are compared on the basis of vehicle steering, yaw rates, accelerations and handling diagrams. Statistical methods such as power spectral density, root mean square, skewness, and kurtosis are applied to validate the model. Validation tolerances are defined for each set of statistical results based on ATC’s experience.

Vehicle manufacturers currently use dynamic modeling, finite element modeling, and durability analysis to incorporate reliability into their designs. Although these models are often used separately, there has been little effort toward integrating these analyses and performing an analysis from the "ground up" (i.e., using terrain data to determine dynamic stress and strain). This paper outlines the approach of an ongoing analysis of a US Army trailer, using an integrated process of dynamic modeling, finite element modeling, and durability analysis. This project outlines an approach to mechanical reliability analysis that can be used early in design.

Unexploded Ordnance (UXO) is military munitions that have been prepared for action, fired, dropped, or buried, and remain undetonated, posing a hazard to operations, personnel, or material The 1997 UXO Clearance Report to Congress estimates that millions of square meters (acres) throughout the United States, including 1,900 Formerly Used Defense Sites (FUDS) and 130 Base Realignment and Closure (BRAC) installations, potentially contain UXO Implementation of the Range Rule," which will identify the process for evaluating appropriate response actions on Closed, Transferred, and Transferring Military Ranges, will potentially add millions of additional acres to the Army's UXO cleanup liability.

ABSTRACT Wildlife–aircraft collisions (wildlife strikes) with civilian and military aircraft pose notable risks and economic losses. The 4 military services within the U.S. Department of Defense maintain records regarding wildlife strikes with military aircraft. Although rotary‐wing aircraft operations comprise important mission components within all 4 military services, no assessment of wildlife strikes to military rotary‐wing aircraft has been conducted. The objectives of this project were to 1) conduct a comprehensive analysis of data available from all military services regarding wildlife strikes with rotary‐wing aircraft, and 2) provide recommendations to reduce the frequency and negative impacts of these strikes. We acquired all available wildlife strike records and parsed our database to include only wildlife strikes to military rotary‐wing aircraft occurring within the contiguous United States, Alaska, Hawaii, or within near‐shore areas along the coasts. We assessed the effects of year, month, time of day, event location (i.e., on‐ or off‐airfield), and wildlife group involved on the frequency of wildlife strikes with rotary‐wing aircraft. The frequency of wildlife strikes was highest during autumn (Sept–Nov; 41.6% of all strikes) and lowest during winter (Dec–Feb; 10.4%). Wildlife strikes occurred most often when aircraft were traveling en route (38.3%) or were engaged in terrain flight (28.9%). Raptors and vultures were commonly associated with wildlife strikes that caused damage to aircraft. Wildlife strikes to military rotary‐wing aircraft during flight operations within the United States are both costly (averaging US$12,184–$337,281/strike event among the military services) and deadly (2 pilots were killed). Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

The Department of Defense strives to continuously develop and acquire systems that utilize novel technologies and methods for implementing new and complex mission requirements. One of the identified technologies with high impact and benefit to the Warfighter is the integration of Artificial Intelligence (AI) and Machine Learning (ML). Current AI models and methods have added layers of complexity to achieving a satisfactory level of verification and validation (V&V), possibly resulting in elevated risks with fewer mitigations. Regardless of the type of applications for AI technology within the DoD, the technology implementation must be verified, validated, and ultimately any residual risks accepted. This paper looks to introduce a V-model concept for Artificial Intelligence and Machine Learning, to include an outline of proposed activities that the development, assurance, and evaluation communities can follow. By following this proposed assessment, these organizations can increase their understanding and knowledge of the system, mitigating risk and helping to achieve justified confidence.