Showing papers by "Wright-Patterson Air Force Base published in 1986"
TL;DR: Aeroelastic tailoring technology is reviewed with reference to the historical background, underlying theory, current trends, and specific applications as mentioned in this paper, and the future of aero-linear tailoring and the development of an automated strength-aero-elastic design tool under the Automated Strength-AeroELastic Design program are examined.
Abstract: Aeroelastic tailoring technology is reviewed with reference to the historical background, the underlying theory, current trends, and specific applications. The specific application discussed include the Transonic Aircraft Technology program, an Advanced Design Composite Aircraft, the Wing/Inlet Advanced Development program, and the forward-swept wing. Finally, the future of aeroelastic tailoring and the development of an aeroelastic tailoring analysis and design tool under the Automated Strength-Aeroelastic Design program are examined.
364 citations
TL;DR: In this paper, the modification of alpha lamellar phase in Ti-6A1-4V by hot working was investigated with the aim of controlling morphology (aspect ratio) and final grain size.
Abstract: The modification of lamellar alpha phase in Ti-6A1-4V by hot working was investigated with the aim of controlling morphology (aspect ratio) and final grain size. The effect of strain was studied using forging at 955 °C (1750 °F), followed by annealing at 925 °C (1700 °F) to allow the alpha morphology to adjust. Increasing the deformation from 6.5 pct to 80 pct reduction caused the lamellar alpha morphology to become progressively more equiaxed upon annealing. TEM observations showed that annealing of material deformed to 6.5 pct resulted in recovery of the alpha, without a noticeable change in the morphology, while higher deformation resulted in plate shearing and beta cusp formation. It was found that material with an initial thin alpha plate structure (thickness — 3.4 ώm) breaks up at a lower critical strain than a material with a thicker plate morphology (thickness ≃ 6 μm). The material with thin alpha plates more rapidly forms equiaxed alpha grains separated by beta phase, while the material with a thicker plate structure exhibits more alpha/alpha boundaries after deformation and annealing. The morphology change from alpha lamellae into lower aspect ratio grains was identified to be by a break-up of the alpha lamellae, essentially by a two-step process: a formation of low and high angle alpha/alpha boundaries or shear bands across the alpha plates followed by penetration of beta phase to complete the separation. This break-up takes place during hot deformation and subsequent annealing.
307 citations
TL;DR: The simulation approach for analyzing gas uptake data distinguishes between single and multiple metabolic pathways and provides kinetic constants that can be used in predictive toxicokinetic models for describing constant concentration inhalation exposure as well as exposures by other routes of administration.
179 citations
01 Jan 1986
168 citations
TL;DR: Drawing-board manikins are used with computer-aided design systems to estimate the best work location for a given task to control repetitive trauma disorders of the upper extremity.
Abstract: Repetitive trauma disorders of the upper extremity are a major cause of lost work in many hand-intensive industries. Reported risk factors include repetitive and forceful exertions, certain posture...
157 citations
TL;DR: Dihalomethanes are metabolized by two major pathways: an oxidative, cytochrome P-450-mediated pathway that has been previously thought to yield only CO, and a glutathione (GSH)-dependent one that yields CO2.
152 citations
TL;DR: In this article, the morphology of poly(aryl-ether-etherketone) (PEEK) has been studied using optical microscopy (at room temperature and at elevated temperatures), small-angle light scattering (H v and V v ), transmission electron microscopy(bright field, dark field, and selected area electron diffraction), and wide and smallangle X-ray scattering.
108 citations
TL;DR: In this article, the major parameters of a colloidal array optical filter have been investigated theoretically, and the results compared to published experimental data, showing that extremely high absorbance values are achievable with relatively thin filters.
Abstract: The major parameters of a crystalline colloidal array optical filter have been investigated theoretically, and the results compared to published experimental data. This filter consists of an aqueous suspension of polystyrene spheres in a lattice which produces Bragg diffraction of incident light. The development of expressions for the filter bandwidth and attenuation utilized both dynamical x-ray diffraction theory and light scattering theory. The theoretical attenuation function indicates that extremely high absorbance values are achievable with relatively thin filters.
78 citations
TL;DR: The most striking histopathological change was seen in the liver with a uniform persistent cellular swelling at all times, and separation of the lipids by thin layer chromatography indicated that NDFDA was present in the most polar fraction.
66 citations
TL;DR: In this paper, the crystal structure of oriented fibres of poly(ether-ether-ketone) (PEEK) has been analyzed by X-ray diffraction and refined by the linked-atom least squares procedure.
TL;DR: In this article, a method of vibration control of large space structures by simultaneously integrating the structure and control design to reduce the structural response from a disturbance is presented. But the structural modifications are achieved by using a nonlinear mathematical optimization technique.
Abstract: This study provides a method of vibration control of large space structures by simultaneously integrating the structure and control design to reduce the structural response from a disturbance. The formulation of the design scheme is obtained by the structural modification of some nominal finite element model, which is controlled in an optimal fashion by a linear regulator, to increase the active modal damping factor beyond that of the nominal structure. The structural modifications are achieved by using a nonlinear mathematical optimization technique. The objective function is the weight of the structure with a constraint on the damping parameter of the closedloop system. The application of the algorithm is illustrated by designing an ACOSS-FOUR model with different constraint values.
TL;DR: The structure and morphology of homopolymers and blends of rigid-rod poly(p-phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide-angle x-ray diffraction and scanning and transmission electron microscopy as discussed by the authors.
Abstract: The structure and morphology of homopolymers and blends of rigid-rod poly(p-phenylene benzobisthiazole) (PBT) and semiflexible coil poly[2,5(6)benzimidazole] (ABPBI) were examined by wide-angle x-ray diffraction and scanning and transmission electron microscopy. When samples were processed from a solution where the total polymer concentration of 30% PBT/70% ABPBI blend was greater than a critical concentration, large-scale phase separation occurred and 0.1–4 μm ellipsoidal particles were present in a ductile matrix. The ellipsoids were chiefly composed of aggregates of well-oriented 10-nm PBT crystallites, while the matrix material was chiefly ABPBI. When the concentration was less than a critical concentration, the solution was optically homogeneous. In processing of fiber and film samples from the homogeneous solution, large-scale phase separation was inhibited by rapid coagulation in a water bath. After heat treatment, these samples were found to contain crystallites of both PBT and ABPBI with lateral dimensions of ordered regions no larger than 3 nm. The PBT homopolymer was dispersed in the matrix at the molecular level in ordered regions at a scale no larger than 3 nm, resulting in a rigid-rod molecular composite. In the rigid-rod molecular composite fiber both the molecular-level dispersion and high orientation contributed to higher values of strength and modulus compared to the properties of a phase-separated fiber. The strength and modulus of highly oriented fiber were only 25% higher than those of planar isotropically oriented film, suggesting that the level of dispersion of rod molecules is more important than orientation of the reinforcing phase in rigid-rod molecular composites.
TL;DR: In this paper, the effect of constraining the crack-tip damage zone on the Mode I fracture of a toughened epoxy resin (BP-907) was studied systematically using the double-cantilever-beam (DCB) adhesive joint specimen and scanning electron microscopy (SEM).
Abstract: The effect of constraining the crack-tip damage zone on the Mode I fracture of a toughened epoxy resin (BP-907) was studied systematically using the double-cantilever-beam (DCB) adhesive joint specimen and scanning electron microscopy (SEM). While a broad bond thickness range was employed (5 33 μm the fracture energy exhibited dramatic variations with t that were shown to follow from the variations in size of a certain dimple-like morphological feature. In constrast, the arrest energy was fixed, in consistency with the unchanging morphology. The fracture behavior for t < 33 μm was equally interesting, now though because Gic was fixed while G 1 C a varied with t. These changes in failure conditions were accompanied by morphological changes; as t decreased from 33 μm, the failure locus shifted from the bond center to the metal/matrix interface, and the failure itself occurred by shear yielding. Similarities were found in the failure conditions of butt joint and DCB adhesive specimens, on the one hand, and in that of the latter and composite interlaminar fracture, on the other hand, which suggest an interrelationship among these three failure phenomena.
TL;DR: In this article, the Navier-Stokes equations for subsonic, sonic, and supersonic leading-edge flow were derived for a thin delta wing at angle of attack in a free-stream.
Abstract: Steady flowfields describing respectively the distinguished structure for subsonic, sonic, and supersonic leading-edge flow about a thin delta wing at angle of attack in a supersonic freestream are calculated numerically. Solutions of the steady three-dimensional compressible laminar Navier-Stokes equations are obtained by time integration. Details of these solutions demonstrate that the essential physical behavior of such flows, including both primary and secondary vortex motions, has been simulated. For purposes of comparison, a corresponding inviscid numerical solution was generated for the case of a subsonic leading edge. It is shown that, although the secondary features are absent, the gross dominant characteristics of the flowfield have been reproduced by the Euler equations. Effects of turbulence are assessed by incorporating a simple closure model in the viscous computation. Comparison between the numerical solutions and experimental data is provided for all flow regimes.
TL;DR: Previous variational calculations of the ground and 2p-like excited states of a shallow donor in a quantum well are extended to include the effects of an applied magnetic field and arbitrary donor position, suggesting that some experimental samples may possess thin donor-impurity layers at the interfaces between semiconductors.
Abstract: Previous variational calculations of the ground and 2p-like excited states of a shallow donor in a quantum well are extended to include the effects of an applied magnetic field and arbitrary donor position. The extended wave functions are then used in a theory for the absorption profiles of shallow donor transitions in quantum wells. Absorption profiles for several donor-impurity distributions are calculated and compared with recent far-infrared absorption experiments. The comparison with experiment is somewhat ambiguous, but the theory does suggest that some experimental samples may possess thin donor-impurity layers at the interfaces between semiconductors.
TL;DR: The study examined the relative numerical performance of various optimization methods as candidates for a hybrid algorithm using optimality criteria and mathematical programming methods to determine what techniques are reliable and efficient for optimization of a complex design problem.
Abstract: Automated design of large aerospace structures requires efficient optimization algorithms because of a large number of design variables and design constraints. Most of the difficulties associated with large structural design are solution convergence and computer resources requirements. Practical aerospace structures generally involve limitations on gage sizes, displacements, stresses, and frequencies. The objective of this study was to determine what techniques are reliable and efficient for optimization of a complex design problem. The study examined the relative numerical performance of various optimization methods as candidates for a hybrid algorithm using optimality criteria and mathematical programming methods. Several optimization programs were used to design trussand wing-type structures, and the iteration history for each technique is presented. The computer programs using the method of feasible directions and a modified Newton's method of unconstrained minimization were the most reliable mathematical programming methods.
TL;DR: Utilisation des equations de plaques a grande deflexion de von Karman, de la methode de Galerkin and de la technique de linearisation equivalente as discussed by the authors.
Abstract: Utilisation des equations de plaques a grande deflexion de von Karman, de la methode de Galerkin et de la technique de linearisation equivalente
TL;DR: However, even the results of well-designed quality circle evaluation studies may be misleading if relevant organizational circumstances are not given due consideration when a change agent selects quality circles from his or her repertoire of organizational development (OD) interventions as discussed by the authors.
Abstract: The unprecedented rapidity with which quality circle principles and techniques have caught on in U.S. and European industry belies the fact that a dearth of evaluation research exists documenting quality circle program outcomes. A review of the available studies constituting this literature revealed that this research has frequently been susceptible to a common set of methodological deficiencies. However, even the results of well-designed quality circle evaluation studies may be misleading if relevant organizational circumstances are not given due consideration when a change agent selects quality circles from his or her repertoire of organizational development (OD) interventions. The effectiveness of quality circles, and for that matter organizational intervention procedures in general, depends upon the compatibility of the intervention and attributes of the organization's situation, the demand placed upon tangible and intangible resources, and the type of response desired from participants.
TL;DR: Reactions of dimercapto compounds with lipophilic TBT aggregates may depend on their relative lipid solubilities, and conversion of the weak Lewis acid, TBT, from a four to a five or six‐coordinate tin adduct by the dimarcapto Lewis bases used could also be a factor slowing hemolysis rates.
Abstract: Hydrophobic tributylin (TBT) compounds at concentrations greater than 10 μM used hemolysis of human erythrocytes and formed structures in plasma membranes. The mercapto compounds, β-mercaptoethanol (β MER), 2,3-dimercaptopropanol (BAL), 2,3-dimercapto-1-propane sulfonate (DMPS), DL-dithiothreitol (DTT), and meso-2,3-dimercaptosuccinic acid (DMSA) were examined for their ability to inhibit TBT mediated hemolysis. The relative order of effectiveness for inhibition of TBT mediated hemolysis was BAL>DTT>DMSA>DMPS>β MER. A four-fold excess of BAL over TBT prevented hemolysis for 4 hrs and addition of BAL 0.5 hr after TBT reduced the rate of hemolysis. The number of membrane associated TBT aggregates observed per cell profile decreased as the BAL concentration increased from 0 to 100 μM. However, the mean diameter of TBT aggregates nearly doubled in erythrocyte suspensions at 100 μM BAL. Reactions of dimercapto compounds with lipophilic TBT aggregates may depend on their relative lipid solubilities. Also, conversion of the weak Lewis acid, TBT, from a four to a five or six-coordinate tin adduct by the dimercapto Lewis bases used could also be a factor slowing hemolysis rates.
TL;DR: In this paper, the double cantilever beam (DCB) test was used as a convenient method for evaluating and ranking the Mode I delamination resistance of these construction concepts since the interlaminar crack growth region of the test coupon could easily be altered and characterized as to its influence on Mode I deformation behavior.
Abstract: Delamination is the most prevalent life-limiting failure mode in advanced composite structures and is a fundamental issue in their evaluation for both durability and damage tolerance. Consequently, the attainment of improved delamination resistance and, in turn, more damage tolerant composite structures has been a major goal of a significant number of materials development activities. One approach to more delamination resistant composites is a laminate construction concept in which materials are utilized in a composite construction that is tailored for maximum resistance to interlaminar forces. The double cantilever beam (DCB) test was used as a convenient method for evaluating and ranking the Mode I delamination resistance of these construction concepts since the interlaminar crack growth region of the test coupon could easily be altered and characterized as to its influence on Mode I delamination behavior. Hercules' ASI/3502 graphite/epoxy was chosen as a baseline material and the construction of the interlaminar crack growth region in the mid-plane of the laminate was varied using inner-layer materials that have previously demonstrated the potential for resisting matrix crack growth-a rubber toughened epoxy adhesive, organic fiber mats, and glass fiber mat and scrim. Resultant laminates were characterized as to their Mode I behavior using the DCB test and were also subjected to compression testing. Fractured surfaces were examined with a scanning electron microscope (SEM). Results show that significant improvements in delamination resistance can be achieved by specifically tailoring the construction of the laminate.
TL;DR: In this article, a 3D model of the mixing, chemical reaction, and flowfield development in a typical ducted rocket configuration is presented, where the governing partial differential equations are numerically solved by an iterative finite-difference solution procedure.
Abstract: Calculations have been made of the three-dimensional mixing, chemical reaction, and flowfield development in a typical ducted rocket configuration. The governing partial differential equations are numerically solved by an iterative finite-difference solution procedure. The physical models include the A; ~ e turbulence model, onestep reaction, and mixing controlled chemical reaction rate. Radiation is neglected. The mean flow structure, fuel dispersal patterns, and temperature field are presented in detail for a base configuration with a 0.058 m dome height, 45-deg side-arm inclination, and with gaseous ethylene injected from the dome plate at an eccentric location. In addition, the influences of the geometrical parameters, such as dome height, inclination of the side arms, and location of the fuel injector, are studied.
TL;DR: In this paper, the role of computer simulations in understanding the growth and fabrication of heterostructure interfaces grown by molecular beam epitaxy (MBE) is discussed and the ingredients of a computer simulation model are described.
TL;DR: In this paper, a study experimentale du mouvement de la cage d'un roulement a billes a contact angulaire and a vitesse elevee en fonction du balourd donne, jusqu'a des vitesses de FONctionnement correspondant a trois millions de DN.
Abstract: Etude experimentale du mouvement de la cage d'un roulement a billes a contact angulaire et a vitesse elevee en fonction du balourd donne, jusqu'a des vitesses de fonctionnement correspondant a trois millions de DN. Comparaison des donnees experimentales obtenues avec les previsions d'un modele d'ordinateur recemment mis au point, ADORE et constatation d'un tres bon accord, dans le domaine tout entier des conditions de balourd et de fonctionnement du palier
TL;DR: A different way of looking at the pilot's role in the intelligent cockpit is developed, and knowledge concerning human cognition is meshed with the capabilities and limitations of artificial intelligence.
Abstract: A human factors perspective for creating intelligent cockpits is described and explained. A conceptualized interface among the pilots, mental models, and human information technologies is proposed wherein knowledge concerning human cognition is meshed with the capabilities and limitations of artificial intelligence (AI). Necessarily, a different way of looking at the pilot's role in the intelligent cockpit is developed.
TL;DR: In this article, the effect of isothermal hot forging on microstructure, pore closure, and tensile and fatigue properties of Ti-6A1-4V blended elemental cold pressed and sintered powder compacts was investigated.
Abstract: The effect of isothermal hot forging (IHF) on microstructure, pore closure, and tensile and fatigue properties of Ti-6A1-4V blended elemental cold pressed and sintered powder compacts was investigated. Two types of sponge fines were used: (a) high chloride produced by the Hunter sodium reduction process (HP) and (b) low chloride produced by the electrolytic process (EP). The as-sintered HP compacts were 99 pct dense while the EP compacts were only 92 pct dense. All sintered preforms were isothermally hot forged below the beta transus temperature and reached almost full density. The microstructure of the HP forged compacts consisted of fine equiaxed alpha, while the EP forged compacts exhibited a coarse lenticular alpha structure after 30 pct reduction and a partially recrystallized structure after 68 pct reduction. It was found that EP compacts forged to a 30 pct reduction exhibited a low fatigue limit of 172 MPa (25 ksi), since the lenticular alpha morphology and the residual porosity resulted in premature fatigue crack initiation. On the other hand, a higher fatigue strength of 485 MPa (70 ksi) was obtained for EP compacts forged to a 78 pct reduction due to the mixed equiaxed/lenticular alpha morphology as well as removal of stress concentration features such as interparticle pore interfaces.
TL;DR: In this paper, a differential scanning calorimeter (DSC) investigation (heating rate 10 K/min) is presented on the multiple transition (relaxation) spectra of PMMA: Tβ Tg; and Tlρ > Tll, as a function of tacticity.
Abstract: A differential scanning calorimeter (DSC) investigation (heating rate 10 K/min) is presented on the multiple transition (relaxation) spectra of PMMA: Tβ Tg; and Tlρ > Tll, as a function of tacticity. Specimens are characterized by fractional triad content: isotactic (it-), Xii; syndiotactic (st-), Xss; and atactic (at-), Xis. Values for the seven specimens are it-, 1.0;, at-, 0.495 to 0.750; st-, 0.958. Results on Tβ were inconclusive. Our Tg results clarify some discrepancies in the prior literature. Linear least squares regression analyses give: Tg (°C) = 56.6 + 76.6 Xss (our data) Tg (°C) = 49.1 + 87.3 Xss (our data plus selected literature data) Extrapolated Tg 's for Xss = 1 are 133.2°C and 136.1°C, respectively, in contrast to Thompson's extrapolated value of 160°C. Similarly Tg(°C) = 99.5 + 71.6 (1−Xii) for our DSC data. The extrapolated Tll for Xss = 1 is 171.1°C. The intensity of Tll is high for st-and it-, with a broad minimum over the at-region. A second liquid state pr...
TL;DR: In this paper, slow strain rate tensile tests were performed at room temperature on Monel 400 specimens of grain sizes 35 to 500 μm, in the environments of air, mercury, and electrolytically generated hydrogen.
Abstract: Slow strain rate tensile tests were performed at room temperature on Monel 400 specimens of grain sizes 35 to 500 μm, in the environments of air, mercury, and electrolytically generated hydrogen. Specimens of grain size 250 μm were tested at a range of strain rates in the three environments. It was found that cracks initiated easiest in hydrogen but propagated easiest in mercury; consequently the embrittlement was usually more severe in mercury. The embrittlement decreased with increasing strain rate, and with increasing grain size in hydrogen. Embrittlement in mercury was a maximum at intermediate grain sizes. A fracture sequence of intergranular to transgranular to microvoid coalescence was common. The intergranular and transgranular fractures are interpreted in terms of the reduced cohesive stress and enhanced shear models of embrittlement, respectively.