Naval Air Systems Command

Abstract Abstract Tensile strength, modulus of rupture, and impact resistance were found for different layer orientations of ABS rapid prototype solid models. The samples were fabricated by a Stratasys rapid prototyping machine in five different layer orientations. The 0° orientation where layers were deposited along the length of the samples displayed superior strength and impact resistance over all the other orientations. The anisotropic properties were probably caused by weak interlayer bonding and interlayer porosity.

Additive manufacturing (AM) has provided an opportunity for fabricating complex parts. Fabricating these parts without defects is currently a challenge. Therefore, understanding AM defects is fundamental to the structural integrity of load carrying components, failure analysis, and defect-based modeling of mechanical performance. This work investigates defect content of metal AM specimens and correlations between defect characteristics (size, sphericity/circularity, aspect ratio) using 2D and 3D defect characterization techniques. Distributions of defect characteristics based on location throughout AM specimens were analyzed and the variabilities of defect characteristics within these specimens were studied. Laser-Based Power Bed Fusion (L-PBF) specimens manufactured with different metals, different AM machines and built directions, different surface conditions, and different thicknesses were evaluated. Significant variability in defect characteristics based on location, especially in as-built surface specimens was observed. Well-optimized process parameters and post-processing reduced the overall volume fraction of defects, and the specified variabilities, and resulted in a more random dispersion of defects around the specimens. 2D and 3D defect analysis showed similar trends regarding correlations between defect characteristics and provided complementary information about the actual defect content based on their resolution. Keywords: Additive manufacturing, Defect characterization, Computed tomography, Defect variability, Ti-6Al-4V, 17-4 PH stainless steel

Abstract OVERVIEW: The development of innovative methods to efficiently convert biomass to fuels and industrial chemicals is one of the grand challenges of the current age. n ‐Butanol is a versatile and sustainable platform chemical that can be produced from a variety of waste biomass sources. The emergence of new technologies for the production of fuels and chemicals from butanol will allow it to be a significant component of a necessarily dynamic and multifaceted solution to the current global energy crisis. IMPACT: The production of butanol from biomass and its utilization as a precursor to a diverse set of fuel products has the potential to reduce petroleum use worldwide. In concert with other emerging renewable technologies, significant reductions in greenhouse gas emissions may be realized. The rapid incorporation of renewables into the world fuel supply may also help to offset predicted increases in transportation fuel prices as the supply of oil declines. APPLICATIONS: Recent work has shown that butanol is a potential gasoline replacement that can also be blended in significant quantities with conventional diesel fuel. These efforts have transitioned to research focused on the development of viable methods for the production of an array of oxygenated and fully saturated jet and diesel fuels from butanol. The technologies discussed in this paper will help drive the commercialization and utilization of a spectrum of butanol based sustainable fuels that can supplement and partially displace conventional petroleum derived fuels. Published 2010 by John Wiley and Sons, Ltd.

Using a transmission-spectrum-based method, the refractive index of a 50 μm thick sample of poly(methyl methacrylate) (PMMA) was measured as a function of wavelength. To mitigate the effects of nonplane-parallel surfaces, the sample was measured at 16 different locations. The technique resulted in the measurement of index at several thousand independent wavelengths from 0.42 to 1.62 μm, with a relative RMS accuracy <0.5×10(-4) and absolute accuracy <2×10(-4).

Description The Symposium on Effects of Environment and Complex Load History on Fatigue Life was presented at the Fall Meeting of ASTM held in Atlanta, Ga., 29 September–4 October, 1968. Committee E09 on Fatigue sponsored the symposium. M. S. Rosenfeld, U.S. Naval Air Engineering Center, was responsible for the session on Cumulative Damage and Life Estimation. S. R. Swanson, MTS Systems, was responsible for the session on Fatigue Under Random Loads. D. W. Hoeppner, Battelle Memorial Institute and R. I. Stephens, University of Iowa, were responsible for the two sessions on Influence of Environment on Fatigue.

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Optical links are currently being considered for high-bandwidth underwater communications at short ranges (<formula formulatype="inline"><tex Notation="TeX">${≪}$</tex> </formula>100 m). To predict the performance of these links, a firm understanding of how the inherent optical properties of water affect the encoded optical signal is needed. Of particular interest is the impact of scattering due to particulates. Typically, the link loss is computed using the beam attenuation coefficient, which describes the attenuation of nonscattered light due to absorption and scattering. This approach is insufficient, as it neglects the contribution of scattered light to the total received signal. Given the dynamic nature of underwater platforms, as well as the dynamic nature of the environment itself, knowledge of the angular dependence of forward-scattered light is imperative for determining pointing and tracking requirements as well as overall signal to noise. In this work, the theory necessary to describe spatial spreading of an optical beam in the presence of scattering agents underwater is reviewed. This theory is then applied to a performance prediction model that is validated via laboratory experiments. Finally, the model is used to study the impact of spatial spreading on an underwater optical link. </para>

OBJECTIVE: This article presents a model for predicting complex collaborative processes as they arise in one-of-a-kind problem-solving situations to predict performance outcomes. The goal is to outline a set of key processes and their interrelationship and to describe how these can be used to predict collaboration processes embedded within problem-solving contexts. BACKGROUND: Teams are increasingly called upon to address complex problem-solving tasks in novel situations. This represents a domain of performance that to date has been underrepresented in the research literature. METHOD: Multidisciplinary theoretical and empirical literature relating to knowledge work in teams is synthesized. RESULTS: A set of propositions developed to guide research into how teams externalize cognition and build knowledge in service of problem solving is presented. First, a brief overview of macrocognition in teams is provided to distinguish the present work from other views of team cognition. Second, a description of the foundational theoretical concepts driving the theory of macrocognition in teams presented here is provided. Third, a set of propositions described within the context of a model of macrocognition in teams is forwarded. CONCLUSION: The theoretical framework described in this article provides a set of empirically testable propositions that can ultimately guide practitioners in efforts to support macrocognition in teams. APPLICATION: A theory of macrocognition in teams can provide guidance for the development of training interventions and the design of collaborative tools to facilitate knowledge-based performance in teams.

A method is described for local heating or cooling of regions of the hypothalamus of the intact unanesthetized dog. Needle thermodes carrying warm or cold water are inserted through metal guides fixed permanently in the skull and placed symetrically across the mid-line thus permitting the controlled raising or lowering of the hypothalamic temperature. Insertion of the thermodes is painless and causes no hyperpyrexia or other reaction. The thermodes are withdrawn at the end of an experimental period and the animal can be used repeatedly without ill effects. The following observations were made: a) mild cooling causes vasoconstriction and shivering. There is a marked rise in internal temperature and in temperature of skin over trunk as the result of increased heat production. There is also a large drop in skin temperature of extremities as the result of vasoconstriction. b) With continued cooling, shivering weakens and finally ceases; vasoconstriction continues but rise in body temperature slows. c) Rapidly alternating heating and cooling permits the simultaneous stimulation of panting and shivering responses. These observations suggest that in the hypothalamus there are areas sensitive to cooling, which have thermoregulatory responses. As a result of continued cooling of these regions, inhibitory responses are also evoked which are probably associated with warmth stimulation due to elevated skin and internal body temperature outside of the hypothalamus.

, well beneath the forward error correction (FEC) threshold.

Additive manufacturing (AM) of metallic parts provides engineers with unprecedented design freedom. This enables designers to consolidate assemblies, lightweight designs, create intricate internal geometries for enhanced fluid flow or heat transfer performance, and fabricate complex components that previously could not be manufactured. While these design benefits may come “free” in many cases, it necessitates an understanding of the limitations and capabilities of the specific AM process used for production, the system-level design intent, and the postprocessing and inspection/qualification implications. Unfortunately, design for additive manufacturing (DfAM) guidelines for metal AM processes are nascent given the rapid advancements in metal AM technology recently. In this paper, we present a case study to provide insight into the challenges that engineers face when redesigning a multicomponent assembly into a single component fabricated using laser-based powder bed fusion for metal AM. In this case, part consolidation is used to reduce the weight by 60% and height by 53% of a multipart assembly while improving performance and minimizing leak points. Fabrication, postprocessing, and inspection issues are also discussed along with the implications on design. A generalized design approach for consolidating parts is presented to help designers realize the freedoms that metal AM provides, and numerous areas for investigation to improve DfAM are also highlighted and illustrated throughout the case study.

Kapton polyimde is extensively used in solar arrays, spacecraft thermal blankets, and space inflatable structures. Upon exposure to atomic oxygen in low Earth orbit (LEO), Kapton is severely eroded. An effective approach to prevent this erosion is to incorporate polyhedral oligomeric silsesquioxane (POSS) into the polyimide matrix by copolymerizing POSS monomers with the polyimide precursor. The copolymerization of POSS provides Si and O in the polymer matrix on the nano level. During exposure of POSS polyimide to atomic oxygen, organic material is degraded, and a silica passivation layer is formed. This silica layer protects the underlying polymer from further degradation. Laboratory and space-flight experiments have shown that POSS polyimides are highly resistant to atomic-oxygen attack, with erosion yields that may be as little as 1% those of Kapton. The results of all the studies indicate that POSS polyimide would be a space-survivable replacement for Kapton on spacecraft that operate in the LEO environment.

We realize beam splitters and mirrors for atom waves by employing a sequence of light pulses rather than individual ones. In this way we can tailor atom interferometers with improved sensitivity and accuracy. We demonstrate our method of composite pulses by creating a symmetric matter-wave interferometer which combines the advantages of conventional Bragg- and Raman-type concepts. This feature leads to an interferometer with a high immunity to technical noise allowing us to devise a large-area Sagnac gyroscope yielding a phase shift of 6.5 rad due to the Earth's rotation. With this device we achieve a rotation rate precision of 120 nrad s(-1) Hz(-1/2) and determine the Earth's rotation rate with a relative uncertainty of 1.2%.

Abstract Although additive manufacturing (AM) has gained significant attention due to the advantages it offers and is currently a focus of much research, design of critical load carrying components utilizing such processes is still at its infancy. This is due to the fact that most of the load carrying components made by AM processes are subjected to cyclic loads, and fatigue behaviour of AM metals is far less understood as compared with those made by conventional methods, such as wrought and cast metals. To better understand the fatigue behaviour of AM metals, a wide range of issues that affect the behaviour in a synergistic manner must be considered. These include the effects of defects, residual stresses, surface finish, geometry and size, layer orientation, and heat treatment. Additionally, due to the multiaxial nature of the loading and/or complex geometries typically manufactured by AM processes, the stress state is often multiaxial including both normal and shear stresses. In this paper, the aforementioned effects influencing the fatigue resistance of AM parts, including torsion and multiaxial fatigue behaviour, are briefly discussed using some recently generated experimental data on Ti‐6Al‐4V by the authors.

Intelligent Control and Health Management technology for aircraft propulsion systems is much more developed in the laboratory than in practice. With a renewed emphasis on reducing engine life cycle costs, improving fuel efficiency, increasing durability and life, etc., driven by various government programs, there is a strong push to move these technologies out of the laboratory and onto the engine. This paper describes the existing state of engine control and on-board health management, and surveys some specific technologies under development that will enable an aircraft propulsion system to operate in an intelligent way-defined as self-diagnostic, self-prognostic, self-optimizing, and mission adaptable. These technologies offer the potential for creating extremely safe, highly reliable systems. The technologies will help to enable a level of performance that far exceeds that of today's propulsion systems in terms of reduction of harmful emissions, maximization of fuel efficiency, and minimization of noise, while improving system affordability and safety. Technologies that are discussed include various aspects of propulsion control, diagnostics, prognostics, and their integration. The paper focuses on the improvements that can be achieved through innovative software and algorithms. It concentrates on those areas that do not require significant advances in sensors and actuators to make them achievable, while acknowledging the additional benefit that can be realized when those technologies become available. The paper also discusses issues associated with the introduction of some of the technologies.

The surface roughnesses of pure titanium implants were compared with scaling in vitro with curettes of dissimilar composition. Each of 10 transmucosal implant extensions (TIEs) was divided into three experimental surfaces and an untreated control surface. The three experimental surfaces were instrumented with either a titanium-alloy tipped curette, a curette of stainless steel, or a plastic curette. All experimental surfaces received 30 strokes with the designated curette within a 2 mm wide area. Alteration of the surfaces due to instrumentation was evaluated by a helium neon (HeNe) laser and reported as relative specular reflectance (RSR). Scanning electron microscopy (SEM) conformed the quantitative HeNe laser results. A significant decrease in mean RSR (greater roughness) was observed for surfaces treated by metal curettes compared to either untreated control surfaces (P less than 0.01) or surfaces treated by the plastic curette (P less than 0.01). No statistically significant difference was noted between untreated surfaces and those treated by the plastic curette. The titanium-alloy curette produced a significantly lower mean RSR (greater roughness) compared to those surfaces treated by the stainless steel curette (P less than 0.05). In summary, plastic instruments produced an insignificant alteration of the titanium implant surface following instrumentation, while metal instruments significantly altered the titanium surface.

Flight simulators are examples of virtual environment (VE) systems that often give rise to a form of discomfort resembling classical motion sickness. The major difference between simulator sickness and other forms of motion sickness is that the former exhibits more oculomotor-related symptoms and far less actual vomiting. VEs of the future are likely to include more compellingly realistic visual display systems, and these systems can also be expected to produce adverse symptoms. The implications of simulator sickness for future uses of VEs include adverse consequences for users' safety and health, user acceptance, training effectiveness, and overall system performance. Based on data from a factor analysis of over 1000 Navy and Marine Corps pilot simulation exposures, a new scoring procedure for simulator sickness has recently been developed (Lane &amp; Kennedy, 1988; Kennedy, Lane, Berbaum, &amp; Lilienthal, 1992). The factor analytic scoring key provides subscales for oculomotor stress (eyestrain), nausea, and disorientation. Simulators are being examined in terms of these factor profiles to identify causes of simulator sickness. This approach could also be used in evaluating motion sickness-like symptomatology that occurs in connection with the use of VEs. This paper describes the use of the multifactor scoring of the Simulator Sickness Questionnaire (SSQ) in diagnosing sources of simulator sickness in individual simulators. Reanalysis by this new methodology was employed to standardize existing simulator sickness survey data and to determine whether relationships existed that were missed by the more traditional scoring approaches.

Nanometer-sized aluminum powder was synthesized by thermal decomposition of an alane solution in the presence of a titanium catalyst under an inert atmosphere. The resulting material, formally devoid of an oxide layer, was used to reduce complexes of gold, nickel, palladium, and silver. The reduction process yielded materials that contained the transition metal at a level between 1 and 3 atom % on a metals basis, as determined by inductively coupled plasma atomic emission spectroscopy and energy dispersive spectroscopy. After exposure to air at ambient conditions, the transition metal treated aluminum materials were found to contain less aluminum oxide than an aluminum sample that was not treated with a transition metal. The nickel treated sample contained as much or more metallic aluminum as the untreated aluminum sample, indicating that the passivating layer in the nickel treated aluminum was highly efficient at protecting the underlying aluminum.

Abstract Lateral stirring is a basic oceanographic phenomenon affecting the distribution of physical, chemical, and biological fields. Eddy stirring at scales on the order of 100 km (the mesoscale) is fairly well understood and explicitly represented in modern eddy-resolving numerical models of global ocean circulation. The same cannot be said for smaller-scale stirring processes. Here, the authors describe a major oceanographic field experiment aimed at observing and understanding the processes responsible for stirring at scales of 0.1–10 km. Stirring processes of varying intensity were studied in the Sargasso Sea eddy field approximately 250 km southeast of Cape Hatteras. Lateral variability of water-mass properties, the distribution of microscale turbulence, and the evolution of several patches of inert dye were studied with an array of shipboard, autonomous, and airborne instruments. Observations were made at two sites, characterized by weak and moderate background mesoscale straining, to contrast different regimes of lateral stirring. Analyses to date suggest that, in both cases, the lateral dispersion of natural and deliberately released tracers was O(1) m2 s–1 as found elsewhere, which is faster than might be expected from traditional shear dispersion by persistent mesoscale flow and linear internal waves. These findings point to the possible importance of kilometer-scale stirring by submesoscale eddies and nonlinear internal-wave processes or the need to modify the traditional shear-dispersion paradigm to include higher-order effects. A unique aspect of the Scalable Lateral Mixing and Coherent Turbulence (LatMix) field experiment is the combination of direct measurements of dye dispersion with the concurrent multiscale hydrographic and turbulence observations, enabling evaluation of the underlying mechanisms responsible for the observed dispersion at a new level.

This article presents a historical overview of research in reconfigurable flight control. For the purpose of this article, the term ‘reconfigurable flight control’ is used to refer to software algorithms designed specifically to compensate for failures or damage of flight control effectors or lifting surfaces, using the remaining effectors to generate compensating forces and moments. This article will discuss initial research and flight testing of approaches based on explicit fault detection, isolation, and estimation, as well as later approaches based on continuously adaptive and intelligent control algorithms. In addition, approaches for trajectory reshaping of an impaired aircraft with reconfigurable inner loop control laws will be briefly discussed. Finally, there will be some discussion on current implementations of reconfigurable control to improve safety on production and flight test aircraft and remaining challenges to enable broader use of the technology, such as the difficulties of flight certification of these types of approaches.

A study was conducted to compare the relative comprehensibility of pictorial information and printed words in instructions. Six picture-word formats were examined using 24 procedural problems on three types of tasks. The formats were print-only, pictorial-only, pictorial-related print, print-related pictorial, pictorial-redundant print, and print-redundant pictorial. The results showed pictorial information important for speed but print information necessary for accuracy. Comprehension of instructions on all three tasks was most efficient with the pictorial-related print and pictorial-redundant print formats but could not be shown to be simply a function of number of visual information channels used or the degree of redundancy between channels. The type of information displayed in the visual channels was found to be important.