Showing papers by "Wright-Patterson Air Force Base published in 1981"

Fitting Models to Composite Materials Fatigue Data

Abstract: A new procedure for fitting fatigue models (consisting of a deterministic equation defining the shape of the S-N curve and a probabilistic description of the data scatter) is presented. The procedure consists of (1) transforming the fatigue data into equivalent static strength data by using the deterministic equation in the fatigue model with unknown parameters, (2) obtaining the maximum-likelihood estimates for the parameters of the (two-parameter Weibull) distribution describing the equivalent static strength data, and (3) repeating Steps 1 and 2 until the largest maximum-likelihood estimate of the shape parameter is obtained. The procedure can handle runouts and tab failures through progressive censoring. Finally, the procedure is well defined when small fatigue data samples are available.

Application of Conjoint Measurement to Workload Scale Development

Abstract: Practical considerations make subjective opinion one of the most widely used methods to assess mental workload. However, the value of the data obtained by subjective methods is often limited becaus...

Saturable metabolism and its relationship to toxicity

Abstract: Metabolism plays a central role in regulating the toxicity of a variety of chemicals. Relatively innocuous substances can be converted to highly toxic metabolites. Conversely, toxic substances can be biotransformed to less harmful metabolites or be excreted, thus limiting their duration of biological action. Virtually all metabolism and many excretory processes utilize specific binding proteins, i.e., enzymes and carrier proteins. These metabolic and carrier-mediated excretory clearance pathways are capacity-limited, becoming saturated at sufficiently high substrate concentrations. Saturable metabolic clearance processes lead to dose-dependent pharmacokinetics for many chemicals. When dose-dependent pharmacokinetics prevail, internally significant parameters, such as area under the curve for concentration of toxicant at active sites and the amount of metabolite formed during inhalation exposure, are not linearly related to externally significant parameters such as administered dose or inspired concentration. Dose-response curves should relate observed effects to some internally significant parameter. Toxic response should often be indexed to area under the curve relationships or total amount metabolized, instead of dose or inspired concentration. The former parameters are complexly related to the latter. The nature of the relationship depends on the kinetic constants for metabolic and excretory clearance. Pharmacokinetic analyses of dose-dependent clearance mechanisms provide an understanding of how one transforms externally significant parameters to internally significant parameters under various exposure conditions. Consideration of metabolic clearance at the organ level illuminates the importance of physiological factors, showing unequivocally that blood flow may be rate-limiting for metabolism under many exposure conditions. Recognition of the potential for this behavior is essential to the proper design and evaluation of certain toxicological experimentation. Development of comprehensive pharmacokinetic descriptions of the influence of saturable clearance on delivery of active chemical to target sites augurs well for improving both intraspecies and interspecies extrapolation of toxicity data. This is a critical area of contemporary toxicology. Dose selection for chronic studies could also be improved by knowledge of the dose-dependence of pharmacokinetic parameters in proposed test species. The field of toxicology reviewed here represents an interface between pharmacokinetic research and studies on basic mechanisms of toxic action. It entails utilization of quantitative concepts to better understand the physiological and biochemical controls which regulate the expression of the toxicity of various chemicals. Much work remains to be accomplished in this exciting area of toxicological research. Some of the predictions of the pharmacokinetic analyses are still tentative and require more definitive experimentation...

High/Low Modulus Si3N4‐BN Composite for Improved Electrical and Thermal Shock Behavior

Abstract: High-density Si3N4+6% CeO2 composites with 5 to 50% BN were fabricated by hot-pressing. BN remained as a discrete phase. Dielectric constants were 4 to 8 and loss tangents were 0.0008 to 0.06 for the room temperature to 1100°C range for compositions with 10 to 50% BN. Thermal-expansion values perpendicular to the hot-pressing direction were somewhat less than those of hot-pressed Si3N4+6% CeO2. Flexure strengths at room temperature were considerably lower than those of hot-pressed Si3N4+6% CeO2 but values at 1000°, 1250°, and 1400°C in air were only slightly lower. Young's modulus values were found to decrease with increasing BN content at all temperatures. Better thermal shock resistance was found than for commercial hot-pressed Si3N4.

Wind Tunnel Demonstration of Aeroelastic Tailoring Applied to Forward Swept Wings

Abstract: The principle of aeroelastic tailoring with advanced composite materials to increase the divergence speed of a forward swept wing has been demonstrated through low-speed wind tunnel tests The approach was to perform a low-cost, fairly simple wind tunnel test on a variable sweep cantilever wing model Available analytical methods were shown to accurately predict the divergence speed of both aluminum and composite plate structures in the subsonic speed range Methods were evaluated for predicting the onset of divergence using subcritical windtunnel data Results of the analyses and tests are presented in this report

Ion Scattering Spectrometry: A Versatile Technique for a Variety of Materials.

Abstract: : The extraordinary surface sensitivity of low energy ion scattering spectrometry may be applied to the characterization of a wide variety of materials. On the one hand, the surface chemistry may be determined using ion scattering spectrometry for engineering materials used in diverse technologies such as lubrication and adhesive bonding; such surface chemistry, perhaps involving only a few monoplayers, may govern the success or failure of a process. On the other hand, ion scattering spectrometry is also useful in investigating the chemistry and physical and electronic structure of single crystals. The presence of fine features in the spectra enable shadowing and selective neutralization effects to be observed. Striking spectral features are seen in III-V, II-VI, and I-VII compounds. Scattered ion yield curves show a potential for the use of ion scattering spectrometry to determine bonding and electronic structure in some elements. In addition, conventional scattering experiments may be used to determine subtle elemental changes on crystal faces having different orientations. Adsorption-desorption characteristics of different orientations may also be studied in conjunction with the complementary secondary ion mass spectrometry technique. (Author)

Living area contamination by chlordane used for termite treatment

Abstract: Over the past several years, the United States Air Force has experienced incidences of living quarters contamination with airborne chlordane. The first noted incident occurred in two houses at a southwestern Air Force base (CALLAHAN 1970). Chlordane was inadvertently introduced into heating ducts during subslab injection for termite control. When furnaces were activated, chlordane vaporized and was disseminated throughout the living area. A second incident occurred at a large midwestern air base in housing constructed with heating ducts in the slabs. Termite pretreatment had been performed using 2% chlordane as a soil drench on the pea gravel and fill beneath the slab. When the heat was first turned on in the fall, an odor was noticed. Subsequent air sampling detected chlordane (i, 2, 4, 5, 6, 7, 8, 8a-octochloro-2, 3, 3a, 4, 7, 7a-hexahydro-4, 7-methanoindene). Sampling showed chlordane contamination to be common in those newly constructed houses (unpublished data). The most recent incident of chlordane contamination was at a midwestern air base in October 1978. Two ground-floor apartments with subslab heating ducts were involved. One apartment was unoccupied at the time while the other was occupied. In late summer both apartments were treated by subslab injection with 2% chlordane for termite control. When the furnaces were first activated in October, a strong "organic" odor was noted in the occupied apartment. A similar odor but not as strong, was noted in the unoccupied apartment. Subsequent air sampling revealed airborne chlordane in both units. These findings precipitated a random sampling of ground floor apartments in the housing area. Based on the results of the random sampling, the decision was made to sample the air in all ground floor apartments at that air base. This report presents the results of the preliminary survey and the following complete sampling of all ground floor apartments.

Electron irradiation damage in TiC

Abstract: Electron irradiation experiments were carried out on (1 0 0) TiC0.93 thin foils inside an electron microscope operated at 100 kV at room temperature. Both graphite rings and extra diffraction spots were observed as irradiation continued. The extra diffraction spots correspond to an ordered cubic superstructure having a composition near TiC0.5, as determined by Goretzki. These extra spots were disrupted with continued irradiation. These results are discussed in the light of displacement damage in TiC.

Inhibition of Corrosion Fatigue in High Strength Aluminum Alloys

Abstract: The effects of environment upon the crack growth rate of several high strength aluminum alloys such as 7075-T6, 7075-T73, and 2024-T3 have been investigated. The environments studied were distilled water, tap water, aqueous sodium chloride, aqueous inhibitors with and without sodium chloride, and ambient air. Low cycle corrosion fatigue studies were conducted at 0.1 Hz and R=0.1 on compact-tension specimens. The highest crack growth rates were observed in salt solution and the lowest in ambient air and inhibited solutions. The borax-nitrite base inhibitor virtually eliminates accelerated crack growth by reducing the crack growth rates (in salt solutions by nearly an order of magnitude) to the ambient air value. The apparent threshold for corrosion fatigue, KICF, was not affected by the inorganic inhibitors. However, the results from tests conducted with an organic inhibitor, piperazine, showed nearly 60% increase in KICF. The effects of various environments are shown through microstructural obser...

Numerical simulation of wing-fuselage interference

Abstract: T wing-fuselage problem is investigated by means of the Navier-Stokes equations incorporated with an approximate turbulence model. The numerical solution yields a reasonable global agreement with experimental data in static and impact pressure distributions. However, in order to better describe the flowfield structure near the leading edge of the wing, an alternative choice of coordinate system is required.

Torsion impregnated cloth analysis (TICA): A forced torsion technique to study resins supported by inert substrate†

Abstract: Torsion Impregnated Cloth Analysis (TICA) uses fiber glass cloth as support for polymeric resins and measures the clothresin composite's in-phase and out-of-phase dynamic mechanical responses with a Rheometrics mechanical spectrometer. The TICA thermoscan results of a thermoplastic were compared with that of the neat material. A similar comparison was made between the isothermal curing results of a thermosetting resin and the corresponding parallel plate and TBA measurements. The peaks associated with the vitrification were verified to correspond to those in the glass transition region. Conventional thermoscans of partially cured specimens with known Tg were shown under certain conditions to give erroneous results about the glass transition temperatures. A reduced parameter (T-Tg) was introduced to describe the response of a specimen undergoing additional cure while being subjected to a thermoscan. Examples using this parameter to understand seemingly complex experimental results are given.

Comparative mutagenicity of hydrazine and 3 methylated derivatives in L5178Y mouse lymphoma cells.

Abstract: The mutagenicity of hydrazine, monomethylhydrazine (MMH), 1,1-dimethylhydrazine (UDMH) and 1,2-dimethylhydrazine (SDMH) in L5178Y mouselymphoma cells has been investigated. Hydrazine, UDMH and SDMH induced thymidine mutation, in the absence of extraneous metabolic activation. Dose—response curves were produced for these compounds. MMH did not induce thymidine mutation. All 4 compounds were negative in the ouabain, thioguanine and cytosine arabinoside selective systems. Induction of mutation by hydrazine and UDMH is correlated with toxicity. This is not the case for SDMH-induced mutation. Hydrazine, UDMH and SDMH produce different ratios of large and small thymidine-resistant clones. The compounds appear to have different modes of action in the cell.

Visual fatigue: The need for an integrated model

Abstract: Two experiments were conducted to examine possible decrements in performance over time on two visual tracking tasks. In Experiment 1, six subjects tracked a horizontal, sinusoidally moving target in the picture plane for 6.5 min. In Experiment 2, six subjects tracked a target sinusoidally changing focus in the depth plane between 0 and 4 D over 6.5 min. Results indicated a linearly decreasing amplitude of both pursuit eye movements (.29 deg of visual angle per minute) and accommodation (.11 D/min). These visual fatigue effects are discussed in the context of several competing explanations.

Determination of critical observed frequencies in chi square

Abstract: The chi-square goodness-of-fit test is viewed as restrictive in interpretation potentials. The concept, rationale, formulas, and limitations for a simple test of observed frequencies are offered. This test, respecting limitations, allows the determination of a critical observed frequency value for any cell that would yield a significant deviation from expectations. The test is statistically conservative and allows category- or condition-specific interpretation of chi-square data.

An experimental investigation of creep crack growth in IN100

Abstract: Sustained load crack growth in IN100 at 732°C (1350°F) is studied using two specimen geometries, a standard compact tension specimen, and a radially crack ring loaded in tension. The effects of specimen thickness on the growth rate are investigated covering a range from 5.6 mm to 18.3 mm (0.22 to 0.72 in.) in thickness. Only the thinnest specimens show a crack growth rate which is lower than that obtained from all of the other thickness specimens. Stress-intensity factor, net section stress, and the C*-integral were investigated as possible crack growth rate correlating parameters. The concept of an "effective" crack length determined from specimen compliance measurements is introduced as a measure of crack length for severely tunneled crack front geometries. Neither net section stress nor C* is found to be acceptable as a crack growth parameter based on data from both test geometries. Although K provides fair correlation, the phenomenology of creep crack growth prevents its description adequately with only a single parameter. In particular, the crack growth rate is observed to decrease from an initially higher value to a "steady state" rate for constant values for any of the correlating parameters investigated.

Design, analyses, and model tests of an aeroelastically tailored lifting surface

Abstract: Aeroelastic tailoring provides a measure of control over the interaction of aerodynamic loading and structural response during the design of composite lifting surfaces. A recent investigation involving the design, fabrication, and test of an aeroelastically tailored fighter wing was conducted to provide data for validating the design methodology. Three sets of composite wings with different design objectives were tested in addition to a set of rigid steel wings. The static aeroelastic tests featured the measurement of model forces, pressure distributions, and deflected shapes in the transonic regime. Test results are compared with analytical predictions and show significant aeroelastic benefits.

Anisotropy Effects in the Thermal Diffusivity of Si3N4-BN Composites

Abstract: The thermal diffusivity of silicon nitride-boron nitride composites is shown to exhibit considerable anisotropy with respect to the hot-pressing direction due to the preferred orientation of the boron nitride inclusions.

Synthesis and properties of conjugated enyne polysulfones

Abstract: High-molecular-weight polysulfones that contained 1,3-enyne linkages in the polymer backbone were prepared by the reaction of potassium salts of (E)-1,3-bis(3-hydroxyphenyl)-1-buten-3-yne and 4,4′-dihydroxybiphenyl with 4,4′-dihalodiphenylsulfones in DMSO-sulfolane solvent mixtures. The polymers were soluble in methylene chloride and exhibited intrinsic viscosities as high as 0.74 (in DMAC at 30°C) with glass transition temperatures ranging from 179 to 214°C. It was postulated that on heating the polymers would cure via a intramolecular cycloaddition reaction to from a 2-phenylnaphthalene fused ring system along the polymer backbone. Thermal analytical data studies on cured polymer films and investigations of the products obtained from the thermal reactions of model compounds indicated that the primary curing reaction was intermolecular rather than intramolecular in nature. Additional data from testing fabricated composites indicated that the enyne polysulfones have suitable properties for use as high-temperature thermoplastic composite materials.