187,639 research outputs found
Body Armor, Performance, and Physiology During Repeated High-Intensity Work Tasks.
No full textThis study examined the effect of body armor during repeated, intermittent high-intensity simulated military work. Twelve males performed 11 repetitions of a military style circuit, wearing no armor on one occasion and full armor (~17 kg) on another. Performance was measured by the time to complete individual work tasks plus overall circuit time to completion. Heart rate, intestinal temperature, and rating of perceived exertion were recorded after each circuit. Participants’ circuit time to completion was 7.3 ± 1.0 seconds slower (p <0.01) when wearing armor. Shooting, vaulting, and crawling were also slower (0.8 ± 0.2, 0.4 ± 0.2, and 1.0 ± 0.4 seconds, respectively; all p ≤ 0.05). No differences were observed for box lifting. Higher core temperatures were reported for the armor condition for circuit’s 7 to 11 (p = 0.01–0.05). Rating of perceived exertion was higher (1 ± 0; p = 0.03) when wearing armor. No differences were observed for heart rate. Wearing armor impairs repeated high-intensity military task performance. In the relatively short work time utilized, this decrement did not accrue over time. The impairment may, then, be related to the armor load, rather than accumulating fatigue
John Armor
No full textMarietta High School students; studio portrait, names written in reverse. John Armor (Orian, v. 21, 1939, p. 48)
Riprap Stability Model Tests
No full textI. Introduction and Background 11. Test Setup and Conditions 111. Presentation of Data IV. Results V. Conclusions Appendices 1. Definition of Terms 2. Photographs of Model Dike Section 3. Model Riprap Stone Analysis 4. Tables of Expected Percent Damage for Armor Stone with Unit WeightsKWP-collectio
Baseline UT measurements for armor inspection
No full textSome prototype armor panels are fabricated from several layers of dissimilar material bonded together. These may include ceramics, graphite composites, fiberglass composites and rubber. The ultrasonic properties of these layers influence inspections for armor defects. In this paper we describe measurements of ultrasonic velocity, attenuation, sound beam distortion and signal fluctuations for the individual layers comprising one armor prototype. We then discuss how knowledge of these properties can be used when choosing an optimum frequency for an ultrasonic pitch∕catch immersion inspection. In our case an effective inspection frequency near 1.5 MHz affords: (1) adequate strength of through‐transmitted signals in unflawed armor; (2) adequate lateral resolution for detecting small disbonds at interfaces; and (3) low levels of UT signal fluctuations due to the natural inhomogeneity of certain armor layers. The utility of this approach is demonstrated using armor panels containing artificial disbonds at selected interfaces.Copyright 2010 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.
This article appeared in AIP Conference Proceedings 1211 (2010): 1217–1224 and may be found at http://dx.doi.org/10.1063/1.3362196.</p
Fish armor
No full textThesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from PDF version of thesis.Includes bibliographical references (p. 261-282).Biological materials have developed hierarchical and heterogeneous material nanostructures and microstructures to provide protection against various environmental threats that, in turn, provide bioinspired clues to man-made, protective material designs. In particular, designs of dermal fish armor are a tradeoff between protection and mobility. A comprehensive knowledge base of the materials and mechanical design principles of fish armor has broad applicability to the development of synthetic engineered protective/flexible materials. In this thesis, two fish armor model systems have been investigated by means of structure-property-function relationships, ultimately answering how the armor systems have been designed in response to their environmental threats. The first model system, Polypterus senegalus are descendants of ancient fish and their body is covered by a natural armor consisting of small bony scales. The quadlayered armor scales are composed of ganoine, dentin, isopedine and bone, to protect against predatory biting attacks. First of all, multilayer design principles of P. senegalus scales were understood with respect to penetration resistance by the multiscale experimental and computational study. The quad-layered scales exhibit mechanical gradient within and between material layers and have geometrically corrugated junctions with an undetectable gradation; all of which lead to effective penetration resistance including load-dependent effective material properties, circumferential surface cracking, plastic dissipation in the underlying dentin layer, stress redistribution around the interfaces with suppression of interfacial failure. Secondly, since the outmost ganoine is structurally anisotropic, the roles of anisotropy of ganoine in the entire system have been investigated by combining orientation-dependant indentation and mechanical modeling. The elastic-plastic anisotropy of the ganoine layer enhances the load-dependent penetration resistance of the multilayered armor compared with the isotropic ganoine layer mainly by (i) enhancing the transmission of stress and dissipation to the underlying dentin layer, (ii) lowering the ganoine/dentin interfacial stresses and hence reducing any propensity toward delamination, and (iii) providing discrete structural pathways for cracks to propagate normal to the surface for easy arrest by the underlying dentin layer. Inspired by P. senegalus scales, threat-protection interaction and structurefunction relationships among various layered armor systems have been investigated using parametric studies with finite element (FE) models. Geometry, microstructure and mechanical properties of a threat system significantly influence its ability to effectively penetrate into the armor system or to be defeated by the armor. Simultaneously, three structure parameters of multilayered armor designs are mainly considered: (i) the thickness of the outmost layer; (ii) the quad-layered vs. bilayer structure; and (iii) the sequence of the outer two layers. The role of the armor microstructure in defeating threats as well as providing avenues of energy dissipation to withstand biting attacks is identified. Microstructural length scale and material property matching between the threat and armor is clearly observed. Bilayered and quadlayred models are mechanically comparable, but the quad-layer model achieves a weight reduction. Studies of predatorprey threat-protection interactions may lead to insights into tunability in mechanical functionality of each system in conjunction with adaptive phenotypic plasticity of the tooth and scale microstructure and geometry, "adaptive stalemates," and the so-called evolutionary "arms race." The second model system, Gasterosteus aculeatus, is well-known for light-weight and morphologically varied armor structure among different G. aculeatus populations. Marine and freshwater G. aculeatus armor structures have been assessed quantitatively by micro-computed tomography ([mu]CT) technique. The convolution of plate geometry in conjunction with plate-to-plate overlap allows a relatively constant armor thickness to be maintained throughout the assembly, promoting spatially homogeneous protection and thereby avoiding weakness at the armor unit interconnections. Plate-to-plate junctures act to register and join the plates while permitting compliance in sliding and rotation in selected directions. SEM and [mu]CT revealed a porous, sandwich-like cross-section of lateral plates beneficial for bending stiffness and strength at minimum weight. Moreover, the structural parameters of the pelvic assemblies were also quantified via pCT, which include the spatial dependence of the suture amplitude and frequency, the suture plate inclination angle, and the suture gap. Significant differences in these structural parameters were observed between the different G. aculeatus populations. Composite analytical and finite element computational models were developed and used in conjunction with the pCT data to simulate the mechanical behavior of the pelvic assembly, to predict the effective suture stiffness and to understand the conformational change of the pelvic assembly from the "rest" to "offensive" states. This study elucidates the structural and functional differences between different divergent populations of G. aculeatus and serves as a model for other systems of interest in evolutionary biology.by Juha Song.Ph.D
Body armor configuration characteristics.
No full text<p>Body armor configuration characteristics.</p
Measuring the strength of brittle materials by depth-of-penetration testing
No full textBased on an energy conservation model, the strength offered by a number of brittle materials has been calculated from depth-of-penetration (DOP) test results. Each material was completely penetrated by a tungsten carbide cored projectile of known kinetic energy and the residual penetration into a ductile aluminium alloy backing material was measured. The energy transferred to the tile by the projectile has been calculated and has been shown to vary linearly with the tile thickness. From the energy transferred to the armour tile, the mean resisting stress that was offered to the penetrator was calculated and for the materials tested, scaled with the material hardness. This work shows that for DOP testing, where the projectile remains intact, the measured DOP is merely a facet of the ceramic’s hardness and not its true ballistic performance. The possibility of using this method to measure the strength of damaged ceramic is also discussed
Optimizing the stacking sequence in dual-purpose body armors
No full textMany police body armor systems are dual purpose, offering both ballistic and knife resistanceby combining a flexible ballistic textile pack with a stiffer knife resistant layer.The two types of protection differ in materials and mechanisms such that each individualcomponent may help or interfere with the function of the other. This paper investigatesthe effect on knife and ballistic penetration resistance when a single thin metal plate wasplaced at various different positions within an aramid textile armor pack. Two metalliclayers were used: aluminum 7075 and commercial purity titanium; these had similarareal densities and were positioned in the front, middle, and back of a 20 layer pack ofwoven KevlarVR 49. An instrumented drop weight machine was used to deliver a repeatableknife blade impact at comparable energy levels to those specified in the UK HomeOffice test standards for knife resistance. Ballistic tests were used to determine the V50ballistic limit velocity against typical 9mm and 0.357 Magnum handgun threats. Againsta stabbing threat, it was found that positioning the metal plate in the middle of the packprovided the greatest resistance to knife penetration by a factor of almost two, while aplate at the front of the pack provided less resistance and plates positioned at the rear ofthe pack provided the least resistance to penetration. Against the ballistic threat, the penetrationresistance of the textile pack can be significantly improved when a metal plate isat the front of the pack, while for all other positions the effect is negligible. However, thiseffect is sensitive to both the ammunition type and the metal plate composition. When themetal plate is positioned at the rear of the pack there is a significant decrease in theback-face deformation of the armor pack although, again, this effect is only present forcertain ammunition and metal combinations. The overall effect of combining soft andhard elements was that specific performance parameters could be substantially increasedby the correct combination. There were no significant negative effects, however, in anumber of cases, the combined systems performance was no greater than that of a singleelement type, despite the added weight
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