Thesis (M.S. in Operations Research)--Naval Postgraduate School, 2005. / Title from title screen (viewed Jan. 31, 2006). "June 2005." Includes bibliographical references (p. 89-90). Also issued in paper format.

Thesis (M.S. in Operations Research)--Naval Postgraduate School, June 2005. / Thesis Advisor(s): Thomas W. Lucas, Richard Spainhour. Includes bibliographical references (p. 89-90). Also available online.

abstract: Ultra-concealable multi-threat body armor used by law-enforcement is a multi-purpose armor that protects against attacks from knife, spikes, and small caliber rounds. The design of this type of armor involves fiber-resin composite materials that are flexible, light, are not unduly affected by environmental conditions, and perform as required. The National Institute of Justice (NIJ) characterizes this type of armor as low-level protection armor. NIJ also specifies the geometry of the knife and spike as well as the strike energy levels required for this level of protection. The biggest challenges are to design a thin, lightweight and ultra-concealable armor that can be worn under street clothes. In this study, several fundamental tasks involved in the design of such armor are addressed. First, the roles of design of experiments and regression analysis in experimental testing and finite element analysis are presented. Second, off-the-shelf materials available from international material manufacturers are characterized via laboratory experiments. Third, the calibration process required for a constitutive model is explained through the use of experimental data and computer software. Various material models in LS-DYNA for use in the finite element model are discussed. Numerical results are generated via finite element simulations and are compared against experimental data thus establishing the foundation for optimizing the design. / Dissertation/Thesis / M.S. Civil and Environmental Engineering 2012

Shear thickening fluids have the potential to improve the effectiveness of fabric materials in body armor applications as they have shown to increase the puncture and ballistic resistance of Kevlar fabrics. However, the effect of using STFs with natural fabrics such as flax has never been studied. The rheology of STFs at varying concentrations of nanosilica dispersed in polyethylene glycol PEG was studied at different temperatures and it was found that the STFs behave as a non-Newtonian fluid in response to changes in shear rate. In this study the effectiveness on the puncture and ballistic resistance of impregnating flax fabric with STF of nanosilica in PEG were investigated. The effect of hybridization of flax and Kevlar was also investigated. The puncture and ballistic resistance of the samples treated with STFs was found to increase significantly and can be controlled by STF concentration.

Sintering parameter effects on the microstructure of boron carbide and boron carbide/titanium diboride composites are investigated. The resulting microstructure and composition are characterized by scanning electron microscopy (SEM), x-ray microscopy (XRM) and x-ray diffraction (XRD). Starting powder size distribution effects on microstructure are present and effect the mechanical properties. Reactive spark plasma sintering introduces boron nitride (BN) intergranular films (IGF's) and their effects on fracture toughness, hardness and flexural strength are shown. Mechanical testing of Vickers hardness, 3-point bend and Chevron notch was done and the microstructural effects on the resulting mechanical properties are investigated.

How does body armor and posture affect Soldier marksmanship? The Interceptor Body Armor (IBA) has significantly improved Soldier combat survivability, but in what ways does it change rifleman lethality? Moreover, can we model these effects so as to develop better tactics and operational plans? This study quantifies the effects of Soldier equipment on lethality through multi-factor logistic regression using data from range experiments with the 1st Brigade, 1st Infantry Division (Mechanized), at Fort Riley, Kansas. The designed experiment of this study estimates the probability of a qualified US rifleman hitting a human target. It uses the rifleman's equipment, posture, Military Occupational Specialty (MOS), and experience along with the target's distance, time exposure and silhouette presentation as input factors. The resulting family of mathematical models provides a Probability of Hit prediction tailored to a shooter-target scenario. The study shows that for targets closer than 150 meters, Soldiers shot better while wearing body armor than they did without. Body armor had a negative effect for targets farther than 200 meters, and this could significantly impact the employment of the Squad Designated Marksman. The study also shows that the kneeling posture is an effective technique and recommends standardized training on this method of firing.

Low velocity impacts to the back are known to cause severe injury to crucial components such as the spine and kidneys. Researchers at Natick Soldier Center want to develop a solution that incorporates protection against low velocity impacts with the ballistic body armor (vest and plate) that is used today. The current ballistic body armor was developed to provide ballistic protection. Ballistic protection is designed to stop the penetration of bullets at velocities exceeding 300 m/s. Techniques to provide low velocity impact protection include reducing transmitted force by elongating collision time. In order to develop back protection for the soldier against low velocity impacts the performance of the ballistic body armor and impact protecting foams was evaluated. Low velocity impact tests were performed based on European standards for back protectors for horse riders (EN 13158) and motorcyclists (EN 1621-2). Performance requirements outlined by the standards and published literature established peak forces of 4 kN and 9 kN transmitted through materials under impact as minimum levels of safety before significant injury occurs. Experiments were conducted at an energy level of 4 J to compare the performance of different materials. Energy levels were then increased until maximum acceptable force transmissions were reached. At 4 J the ballistic materials showed peak transmitted forces between 11.0-16.2 kN. This indicated that the ballistic materials were not an adequate method to provide sufficient back protection. The addition of polyurethane foams to ballistic materials reduced peak force values by a factor of 15. Energy levels of 25 J and 40 J were reached with peak forces of 3.5 kN and 6.6 kN. This research provided a basis for the future development of protective equipment that provides both ballistic and low velocity impact protection.

In this dissertation, the rate of the BFD during body armor impact is characterized with fiber Bragg gratings for the first time ever. The depth rate is characterized using a single fiber optic sensor, while the entire shape rate can be characterized using multiple fiber optic sensors. This is done with a final depth accuracy of less than 10% and a timing accuracy of 15% for BFDs as deep as 50 mm and impact event of less than 1 millisecond. The shape sensing method introduced in this dissertation is different from traditional fiber optic sensor shape reconstruction methods in the fact that strain from the kinetic friction regime is used rather than the static friction regime. In other words, information from the fiber optic sensors slipping is used to reconstruct the shape in this work, whereas strain from the fiber optic sensor remaining fixed to a reference is used for typical fiber optic shape sensing purposes.

Current body armor technologies need further improvements in their design to help reduce combat injuries of military and law enforcement personnel. Kevlar-based body armor systems have good ballistic resistance up to a certain ballistic threat level due to limitations such as decreased mobility and increased weight [1,2]. Kevlar fibers have been modified in this work using a nano-scale boron carbide coating and a marked increase in the puncture resistance has been experimentally observed. It is hypothesized that this improvement is due to the enhancement of the mechanical properties of the individual Kevlar fibers due to the nano-scale coatings. This study presents a comprehensive experimental investigation of individual Kevlar fibers based on nanoindentation to quantify the cause of the enhanced puncture resistance. The experimental setup was validated using copper wires with a diameter size in the same order of magnitude as Kevlar fibers. Results from nanoindentation did not show significant changes in the modulus or hardness of the Kevlar fibers. Scanning Electron Microscopy revealed that the coated fibers had a marked change in their surface morphology. The main finding of this work is that the boron carbide coating did not affect the properties of the individual fibers due to poor adhesion and non-uniformity. This implies that the observed enhancement in puncture resistance originates from the interaction between fibers due to the increase in roughness. The results are important in identifying further ways to enhance Kevlar puncture resistance by modifying the surface properties of fibers.

In this work, the development of theoretically-dense, clean grain boundary, high hardness solid-state sintered silicon carbide (SiC) armor was pursued. Boron carbide and graphite (added as phenolic resin to ensure the carbon is finely dispersed throughout the microstructure) were used as sintering aids. SiC batches between 0.25-4.00 wt.% carbon were mixed and spray dried. Cylindrical pellets were pressed at 13.7 MPa, cold-isostatically pressed (CIP) at 344 MPa, sintered under varying sintering soaking temperatures and heating rates, and varying post hot-isostatic pressing (HIP) parameters. Carbon additive amounts between 2.0-2.5 wt.% (based on the resin source), a 0.36 wt.% B4C addition, and a 2050°C sintering soak yielded parts with high sintering densities (~95.5-96.5%) and a fine, equiaxed microstructure (d50 = 2.525 µm). A slow ramp rate (10°C/min) prevented any occurrence of abnormal grain growth. Post-HIPing at 1900°C removed the remaining closed porosity to yield a theoretically-dense part (3.175 g/cm3, according to rule of mixtures). These parts exhibited higher density and finer microstructure than a commercially-available sintered SiC from Saint-Gobain (Hexoloy Enhanced, 3.153 g/cm3 and d50 = 4.837 µm). Due to the optimized microstructure, Verco SiC parts exhibited the highest Vickers (2628.30 ± 44.13 kg/mm2) and Knoop (2098.50 ± 24.8 kg/mm2) hardness values of any SiC ceramic, and values equal to those of the "gold standard" hot-pressed boron carbide (PAD-B4C). While the fracture toughness of hot-pressed SiC materials (~4.5 MPa m1/2) are almost double that of Verco SiC (2.4 MPa m1/2), Verco SiC is a better performing ballistic product, implying that the higher hardness of the theoretically-dense, clean-grain boundary, fine-grained SiC is the defining mechanical property for optimization of ballistic behavior.