1,815 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
Hydraulic Performance of Xbloc+ Armor Unit
No full textIn recent years, the use of Xbloc units has increased exponentially. However, the placement of this unit is not always done as randomly as it should be and consequently, the stability of the armor is affected. In order to overcome this problem, Delta Marine Consultants is developing a new armor unit called Xbloc+ that has a regular placement. In this research, the hydraulic performance of version 1 and 2 of this block are analyzed. Small scale tests were performed in a 2D wave flume in order to analyze the damage, rocking and the (partially and fully) displacement of units. In total, 1 series of tests were performed with Xbloc+v1 and 6 series with Xbloc+v2. To analyze the influence of the wave steepness and the slope angle, three wave steepness were tested (Sop = 2%, 4% and 6%) and tests were conducted in two different slope angles (1:2 and 3:4). Each series is formed by several sub tests conducted with increasing wave heights (and wave period in order to maintain a constant wave steepness). Tests were carried out until the failure of the armor slope was reached in order to completely define the failure mechanism. Furthermore, tests after failure where also executed to further investigate the stability of the armor after the damage has started.Results obtained from the laboratory tests provided an overall understanding of how the Xbloc+ performs under certain conditions. It was perceived that the permeability of the armor layer is low as it happens often with single layer units. Thus, the pressure gradient between the underlayer and armor layer is significantly high creating an uplift pressure that leads to a revetment-like failure mechanism.Although the failure mechanism can be related to both slopes used during the laboratory tests, (3:4 and 1:2), the behavior of the armor layer differed completely between slopes. On a steeper slope, the armor layer remained undamaged for wave heights significantly higher than the design wave. However, once one unit was fully displaced, the damage was quite destructive.In contrast, on a milder slope, failure occurred much faster but the damage was not as aggressive. Moreover, after the failure was reached, the structure gained a new level of stability in which remained to provide shelter without reflecting significant damage.Furthermore, the wave height variation did not have much influence as the wave steepness. There was a noticeable difference between the performance of the structure during swell and wind waves. During swell waves, it could be seen that not only failure was achieved faster but it caused much more damage to the structure, while during wind waves the structure had a higher stability.Coastal and Marine Engineering and Management (CoMEM
Armor breakup and reformation in a degradational laboratory experiment
No full textArmor breakup and reformation was studied in a laboratory experiment using a
trimodal mixture composed of a 1 mm sand fraction and two gravel fractions
(6 and 10 mm). The initial bed was characterized by a stepwise downstream
fining pattern (trimodal reach) and a downstream sand reach, and the
experiment was conducted under conditions without sediment supply. In the
initial stage of the experiment an armor formed over the trimodal reach. The
formation of the armor under partial transport conditions led to an abrupt
spatial transition in the bed slope and in the mean grain size of the bed
surface, as such showing similar results to a previous laboratory experiment
conducted with a bimodal mixture. The focus of the current analysis is to
study the mechanisms of armor breakup. After an increase in flow rate the
armor broke up and a new coarser armor quickly formed. The breakup initially
induced a bed surface fining due to the exposure of the finer substrate,
which was accompanied by a sudden increase in the sediment transport rate,
followed by the formation of an armor that was coarser than the initial one.
The reformation of the armor was enabled by the supply of coarse material
from the upstream degrading reach and the presence of gravel in the original
substrate sediment. Here armor breakup and reformation enabled slope
adjustment such that the new steady state was closer to normal flow
conditions
Armor & ornament
No full textIs This Not a Strange Life to Which I Call You -- A Flaming Sword -- The Storm on the Lake -- Holy Water in a Dry-House -- The Dynamited Mass -- Cain the Earthmover -- To Rain -- My Scallop-Shell of Quiet -- The Burden of the Valley of Vision -- Burn Pit -- The House of the Forest -- A Procession in the Cave -- The Spell of the Covenant -- Holy Convocations -- Scandalized People, Meaning All of Us -- The Riches of Darkness -- To Serve Those Who Do Not Serve -- Bell-Sound -- The Thin Harvest -- Sworn to Secrecy the Morning He Performed the Sacrament -- Apron of Leaves -- The Supernumerary Persons Being Enrichers of His Inheritance -- Holy Convocations -- The Exasperated Spirit -- Spun Wisdom -- The Blood Forsakes My Face -- The Stench of Cursed Ground -- Holy Convocations -- Our Days All Pass Awaiting Its Return -- He Houghed Their Horses, and Burnt Their Chariots with Fire -- They Held to Sanity So Hard They Were Insane -- The Burden of the Valley of Vision -- The Morning Light -- Dawn's Careful Seal -- Air Craft -- Bodies into Hills, Hills into Homes -- Thinking Is Weeping Entering Eternity -- On Ester Mountain -- An Orgy of Absence -- To Take Corporeal Shape -- The Morning Light -- Dining at the Core of an Old Silence -- The Soul's Chiasmus -- A Crown of Thistles -- A Detail of Devotion -- A Cipher for the Symbol of Zero -- Choke the Word -- Under What Shadow -- The Grooves along Which the Cranes Glide -- Ornamental Armor -- Armor & Ornament -- The Armor of Light
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
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