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Showing papers by "Wright-Patterson Air Force Base published in 1979"


Journal ArticleDOI
TL;DR: This paper presents a comparison of frequently used optimization algorithms based on optimality criteria to design a minimum weight structure, and presents a new iterative scheme, similar to Newton-Raphson, that can be obtained with a smaller number of analyses of the structure than with previously proposed methods.
Abstract: This paper presents a comparison of frequently used optimization algorithms based on optimality criteria to design a minimum weight structure. After summarizing the different methods, the relationship between the various algorithms is shown. They differ only in the degree of approximations made in formulating the recurrence relations to modify the design variables and to evaluate the Lagrange multipliers. A new iterative scheme, similar to Newton-Raphson, is also presented, with the equations written in such a form that it is not necessary to select the initial design vector of the unknown Lagrange multipliers. It is shown that with this scheme a minimum weight design can be obtained with a smaller number of analyses of the structure than with previously proposed methods.

104 citations


Journal ArticleDOI
TL;DR: In this paper, the authors evaluated the validity of using the load at the point of linearity on the displacement load curve, as suggested by Elber, as an experimental measure of the crack-tip-opening Displacement-load behavior was investigated for a fatigue-cracked modified compact specimen of a nickel-base superalloy.
Abstract: The work presented here evaluates the validity of using the load at the point of linearity on the displacement load curve, as suggested by Elber, as an experimental measure of the crack-tip-opening Displacement-load behavior was investigated for a fatigue-cracked modified compact specimen of a nickel-base superalloy. Displacements were determined at the notch mouth using a standard clip-on gage, along the crack sufrace using a laser-interferometric displacement gage and, in the plastic zone ahead of the crack, using an optical- interferometry technique. Acoustic-emission monitoring was employed as a means to detect potential crack extension during measurement-load cycles and to detect physical- crack closure. The magnitude of the crack-tip-opening as determined from these measurements, is dependent on the distance from the crack tip at which the measurement is made. As an additional means of evaluating the crack-tip-opening load, crack-surface profiles are constructed from the displacement- load measurements made behind the crack tip. A discussion is given concerning the significance of these results in evaluating the validity of using the toad at the point of linearity as a para- meter to quantify crack closure.

74 citations


Book ChapterDOI
TL;DR: In this paper, a power law representation of the S-N curve and a two-parameter Weibull distribution for time-to-failure at a specific stress level are discussed.
Abstract: : A procedure is outlined which allows the generation of an S-N curve with some statistical value without resorting to an extremely large data base. The procedure is based on a power law representation of the S-N curve and a two- parameter Weibull Distribution for time-to-failure at a specific stress level. A data pooling scheme is also discussed which allows the determination of a fatigue shape parameter which is independent of stress level.

67 citations


Journal ArticleDOI
TL;DR: In this article, an experimental technique of detecting the first ply-failure in laminated composites using a combination of long strain gages and acoustic emission measurement is described, and the material sy...
Abstract: This paper describes an experimental technique of detecting the first ply-failure in laminated composites using a combination of long strain gages and acoustic emission measurement. The material sy...

65 citations



Journal ArticleDOI
TL;DR: In this article, microstructural characterization and electron diffraction crystal structure determinations have been carried out on the tool steel M2 using optical microscopy and thin-film and replica transmission electron microscopy.
Abstract: Microstructural characterization and electron diffraction crystal structure determinations have been carried out on the tool steel M2. Detailed examination using optical microscopy and thin-film and replica transmission electron microscopy substantiate preliminary findings.2,3 Namely, that laser melted material has a two-phase σ-ferrite/austenite matrix containing a dispersion of fine M2C carbides together with a smaller amount of M23C6 carbides. Subsequent heat treatment at 560 and 1230°C increases the hardness (to a maximum value of ∼1100 VHN) by carbide precipitation. In material heat treated at 560°C there is a preponderance of M23C6 carbides together with a small amount of M2C carbides. In contrast, the effect of heat treatment at 1230°C is to produce material containing only MC1-x type carbides with diameters in the range from 20 nm to ∼1 µm.

55 citations


Journal ArticleDOI
TL;DR: In this article, the numerical solution of a 3D laminar-transitional-turbulent flow along a symmetric corner was obtained for the Navier-Stokes equations using a modified Gessner's turbulence model.
Abstract: The numerical solution of a three-dimensional laminar-transitional-turbulent flow along a symmetric corner was obtained for the Navier-Stokes equations using a modified Gessner's turbulence model. The specific case examined was the symmetric corner formed by the intersection of two wedges with identical wedge angles of 9.48 deg at a Mach number of 3, with the Reynolds number spanning a range from 0.4 x 10 to 1.1 X 10 for which experimental data existed. The numerical results duplicated all of the essential experimental observations. The present investigation seems to indicate that careful application of a turbulent eddy-viscosity concept is not limited to mere two-dimensional thin shear-layer flows. Finally, the present procedure appears to offer promise for practical engineering applications.

50 citations


Journal ArticleDOI
01 Oct 1979
TL;DR: Redundant color-coding was found to significantly reduce both response time and error rate in pilot flight performance and threat recognition performance using two coding conditions for a threat display.
Abstract: The effectiveness of redundant color-coding for displays used by highly-loaded operators performing a series of complex tasks has never been clearly demonstrated. Pilot flight performance and threat recognition performance using two coding conditions for a threat display were compared in a simulated mission. One coding condition consisted of shape-coded symbols, the other of symbols that were both color- and shape-coded. Redundant color-coding was found to significantly reduce both response time and error rate. Language: en

49 citations


Journal ArticleDOI
TL;DR: A direct correspondence was found between the time of exposure required to kill rats and the time calculated to produce a constant amount of metabolite(s) at concentrations between 200–1000 ppm.

47 citations


Journal ArticleDOI
TL;DR: In this paper, single crystals of titanium carbide were deformed in compression over a wide range of temperature, and the operative slip systems were determined by etch-pitting and electron microscopy.
Abstract: Single crystals of titanium carbide were deformed in compression over a wide range of temperature, and the operative slip systems were determined by etch-pitting and electron microscopy. Around the brittle-ductile transition temperature, the slip system undergoes a gradual change from {1 1 0} 〈1 ¯1 O〉 to {1 1 1} 〈1 ¯1 0〉; this is interpreted to be the mechanism governing the brittle-ductile transition in titanium carbide.

43 citations



Journal ArticleDOI
TL;DR: The existence of monoclinic compounds between Si3N4-CeO2 and Si 3N4Ce2O3 for firing temperatures of 1600° to 1700°C was investigated in this paper.
Abstract: The existence of compounds between Si3N4-CeO2 and Si3N4-Ce2O3 was investigated for firing temperatures of 1600° to 1700°C. The two new monoclinic compounds found were Ce2O3·2Si3N4 with lattice parameters a= 16.288, b= 4.848, and c=7.853 A and β=91.54° and Ce4Si2O7N2 with lattice parameters a= 10.360, b= 10.865, and c=3.974 A and β=90.33°. Cerium orthosilicate (Ce4.67(SiO4)3O) is present during firing as a glassy intermediate phase which promotes sintering and densification and then reacts with silicon nitride to form cerium silicon oxynitrde (CeSiO2N).



Journal ArticleDOI
TL;DR: In this paper, boundary-fitted curvilinear coordinate systems are optimized for viscous flows about arbitrary airfoils at angles of attack such that boundary-layer-dependent grid systems for high Reynolds numbers are generated efficiently.
Abstract: Boundary-fitted curvilinear coordinate systems are optimized for viscous flows about arbitrary airfoils at angles of attack such that boundary-layer-dependent grid systems for high Reynolds numbers are generated efficiently. The grid systems are utilized in implicit finite-difference solutions. Solution of a one-dimensional model equation is compared with the theoretical solution. The unsteady Navier-Stokes equations are solved for the incompressible flow around a cylinder and around NACA airfoils approaching stall. The predicted flows around a NACA 6412 airfoil near stall at Reynolds numbers of 4x 10 and 2x 10 are compared with the experimental observations obtained in a smoke tunnel.

Journal ArticleDOI
TL;DR: In this paper, the importance of radiation on the temperature distribution in a semi-transparent solid is reported and the first-order differential approximation of radiation is combined with conduction analysis to investigate the temperature profiles in a plane slab and a rectangular region.
Abstract: The importance of radiation on the temperature distribution in a semi-transparent solid is reported. The first-order differential approximation of radiation is combined with conduction analysis to investigate the temperature profiles in a plane slab and a rectangular region. The coupled nonlinear partial differential equations are solved numerically by either a standard implicit or an implicit alternating direction method. Results obtained for opaque boundaries are in good agreement with exact formulations found in the literature. An extension to partially transparent boundaries is made and results presented

Journal ArticleDOI
TL;DR: In this article, a general physical model is presented for predicting the stiffness and thermal expansion coefficient of low and high density polyethylene having quenched, slowcooled, and annealed thermal histories.
Abstract: Among the increased structural demands now being made on both unfilled and reinforced plastics is that of dimensional stability under various performance environments. Crystalline polymers are heterogeneous materials consisting of two distinct phases and, as such, can be treated as molecular versions of engineering composites. This paper first outlines the general physical model whereby a crystalline polymer is considered to be a multi-ply laminate of unidirectionally reinforced plies. The calculational format is then detailed for the prediction of the stiffness and thermal expansion coefficient of an isotropic sheet of crystalline polymer and a sample calculation is given for quenched high density polyethylene. A data base is presented for the stiffness and thermal expansion coefficient of low and high density polyethylene having quenched, slowcooled, and annealed thermal histories. Comparison between experimental and predicted results yields good agreement in all cases to better than 25 percent. Implications and limitations of the predictive technique are discussed.

Journal ArticleDOI
TL;DR: In this article, a study was carried out to determine the optimum placement and volume of a reinforcing frame around a cutout in an axially loaded stringer and ring and stringer stiffened cylindrical shell.
Abstract: A study was carried out to determine the optimum placement and volume of a reinforcing frame around a cutout in an axially loaded stringer and ring and stringer stiffened cylindrical shell. The problem was analyzed using the linear bifurcation portion of STAGS (Structural Analysis of General Shells). Four parameters were varied; stringers vs rings and stringers, cutout size, ratio of frame volume to cutout volume, and frame position. It appeared that the frame's position next to the cutout edge was the most effective, which is simply a con- firmation of a well-known fact concerning reinforcement of shell cutouts. However, there was a relative maximum in the frame distance vs critical load curves for a frame positioned away from the cutout edge at a low ratio of frame to cutout volume. Nomenclature Asf,bsf,hsf =area, width, and depth of reinforcing frame a = hole radius or half-width of space cutout d = distance of frame from the centerline of the cutout E = modulus of elasticity G = shear modulus h = shell thickness Ixory Iz = moment of inertia of reinforcing frame L = length of the shell Previous research into the presence of cutouts in cylindrical shell structures can be traced to work performed by Starnes,' who investigated the buckling of a thin unstiffened cylindrical shell with a single cutout, both experimentally and theoretically. He conducted two series of experiments, one on shells made of Dupont's Mylar with a lap seam; and the other series of tests on seamless electroformed copper shells. The parameters ranged between 400

Book ChapterDOI
TL;DR: In this article, a microscopic examination of hygrothermally exposed T300/5208 cross-ply laminates is described, and surface and edge microcracks are observed in specimens exposed at 82° and 9, 20, 37, 74, and 91 percent relative humidity or water immersion.
Abstract: A microscopic examination of hygrothermally exposed T300/5208 cross-ply laminates is described. Moisture-induced surface and edge microcracks were observed in specimens exposed at 82° and 9, 20, 37, 74, and 91 percent relative humidity or water immersion. Specimens exposed at similar relative humidities but at lower temperatures (21, 43, and 63°C) generally did not form microcracks. The severity and frequency of the microcracking at 82°C increased with relative humidity. The majority of the microcracks were observed to be oriented parallel to the graphite fibers in the surface laminae. Specimens with extensive microcracks were also observed to exhibit non-Fickian diffusion phenomena during their hygrothermal exposure.

Journal ArticleDOI
TL;DR: In this article, the Ritz method with simple polynomials and the extended Kantorovich method were used to solve the title problem, and the natural boundary conditions along the free edge were not satisfied in the first case, while they were complied with approximately in the second case.

Journal ArticleDOI
TL;DR: In this article, the Grignard compounds react very slowly with the secondary acid halides (RfCF(CF3C(O)F) whereby competing reactions cause undesirable by-products and reduction of ketone yields.

Journal ArticleDOI
TL;DR: A wind tunnel test program was conducted to demonstrate the active wing/store flutter suppression systems on a lightweight fighter aircraft as mentioned in this paper, which included the design, analysis, fabrication, and testing of a scale model.
Abstract: A wind tunnel test program was conducted to demonstrate the active wing/store flutter suppression systems on a lightweight fighter aircraft. The program, completed in mid-1978, included the design, analysis, fabrication, and testing of a scale model. The tests were conducted at the NASA Langley 16-ft Transonic Dynamics Tunnel. Three store configurations were selected for testing. Two of these configurations were deliberately designed to exhibit low flutter speeds with rapid reductions in damping at the incipient flutter condition. After initial tunnel entries, which showed the need for certain improvements in the model and the control system design, substantial increases in the flutter speeds were achieved using both leading- and trailing-edge control surfaces, separately. For the most critical configuration, a demonstrated improvement of 18% and a projected improvement of 29% in the dynamic pressure were achieved.

Journal ArticleDOI
TL;DR: In this paper, the progress of recrystallization and subsequent grain growth has been systematically investigated in a metastable beta titanium alloy (Ti-11.5 Mo-6 Zr-4.5 Sn).
Abstract: The progress of recrystallization and subsequent grain growth has been systematically investigated in a metastable beta titanium alloy (Ti-11.5 Mo-6 Zr-4.5 Sn). Quantitative evaluation of the kinetics of these processes over a wide range of temperature, deformation, and initial grain sizes has been performed. For a given deformation, the average grain boundary velocity, decreasing with the reciprocal of annealing time, suggests the occurrences of recovery with second order kinetics concurrent with the recrystallization. The amount of deformation, varying from 20 to 80 pct cold reduction and proportional to the stored energy of deformation in the alloy, increases the average grain boundary migration rate during recrystallization by three orders of magnitude. The temperature dependence of the recrystallization rate, however, remains unaffected by the amount of deformation at 83 kcal/mole (347 kJ/mole). The isothermal grain growth kinetics follow the power law such that the time exponent of the process remains at a value of 0.35 at most annealing temperatures. The excellent agreement between the driving force exponent of recrystallization and the time exponent of grain growth based on a model which relates the driving force dependence of the rates of both processes, clearly suggests that the kinetics of these processes are controlled by a single mechanism,i.e. impurity dependent boundary migration.

Journal ArticleDOI
TL;DR: A series of new acetylene-terminated phenylquinoxaline oligomers and diacetylene compounds have been prepared utilizing 4-(3-ethynylphenoxy)benzil as discussed by the authors.
Abstract: A series of new acetylene-terminated phenylquinoxaline oligomers and diacetylene compounds have been prepared utilizing 4-(3-ethynylphenoxy)benzil. The amorphous materials with molecular weights from 500 to 1460 exhibited softening in the 25–160°C range with a strong polymerization exotherm reaching a maximum at 270–290°C. The addition nonvolatile cure provides materials which show excellent thermoxidative stability and processability for high-temperature matrix and adhesive resins.

Journal ArticleDOI
TL;DR: In this paper, the effect of temperature on the fatigue crack growth retardation behavior of IN-100, a nickel base superalloy, when subjected to a single peak tensile overload cycle was examined.


Journal ArticleDOI
TL;DR: In this article, a grain boundary alpha fusion and near heat-affected zone microstructures in heat-treated Ti-6A1-6V-2Sn weldments fractured predominantly transgranularly despite the presence of an extremely large prior-beta grain size and a nearly continuous grain boundary α morphology.


Journal ArticleDOI
TL;DR: In this article, the influence of strain-rate on the stress-corrosion cracking properties of wholly austenitic Type 304 base metal and duplex austeno-ferritic Type 304 weld metal in boiling MgCl2 was investigated using constant extension rate tensile testing techniques.
Abstract: The influence of strain-rate on the stress-corrosion cracking properties of wholly austenitic Type 304 base metal and duplex austeno-ferritic Type 304 weld metal in boiling MgCl2 was investigated using constant extension rate tensile testing techniques. Transgranular SCC in both base and weld metals is preferred at low strain-rates, while intergranular cracking in the base metal and interphase cracking along the austenite-ferrite interface in the weld metal are preferred at higher strain-rates. Promotion of the intergranular stress-corrosion cracking in the base metal and “interphase-interface” stresscorrosion cracking in the weld metal with increases in strain-rate may be mechanistically analogous. Stress-induced alterations in the grain or interphase boundary defect structure may make these regions preferentially susceptible to dissolution.

Journal ArticleDOI
TL;DR: In this article, the Huygens-Fresnel principle is used to investigate the field properties in the Fraunhofer region for two cases: the first case is N beams superimposed with optical axes coincident.
Abstract: The coherent combination of several single-mode lasers can produce a field similar to that of a mode-locked laser but with more flexibility. The field for a quasi-monochromatic wave is considered a complex coherence-separable random process. The ensemble mean and covariance are determined for the case of a temporally stabilized amplitude and a temporal phase that, with appropriate assumptions, is a stationary, Gaussian random process. Mean fields are used throughout as the signals of interest. The Huygens-Fresnel principle is used to investigate the field properties in the Fraunhofer region for two cases. The first case is N beams superimposed with optical axes coincident. Range measurement precision is found to be proportional to 1/(N3Δf)1/2, where Δf is the frequency difference between adjacent lasers. Velocity measurement precision is found to be proportional to (NΔf3)1/2. The second case is N beams in a linear array. The far-field result is a scanning beam that in certain cases can be steered. An array of about 1000 lasers is needed for reasonably low sidelobes.