bluuebunny/crossref_metadata_2025_split huggingface dataset:
Translaminar Fracture Toughness Test Methods and Results from Interlaboratory Tests of Carbon/Epoxy Laminates
Authors: Underwood JH , Kortschot MT , Lloyd WR , Eidinoff HL , Wilson DA , Ashbaugh N 
Published: March 2009

Fracture tests were performed with carbon/polymer laminates and analyzed for the purpose of developing translaminar fracture toughness test and analysis procedures. Notched specimens were tested of two types of symmetrical layups — quasi-isotropic [0/45/90] and [0/90]; two carbon fiber/epoxy materials — a relatively brittle T300 fiber/976 epoxy and a tougher AS4 fiber/977-2 epoxy; two laminate thicknesses — 2 mm and 4 mm; and three specimen configurations — the standard three-point bend and compact configurations, and an extended compact specimen with arm-height to specimen-width ratio of 1.9. Stress and displacement expressions were obtained for the extended compact specimen, including those for stress intensity factor, K, and crack mouth opening displacement, V, in terms of relative notch length, a/W, and for a/W in terms of V. Relationships for the bending stresses that control self-similar and off-axis cracking for the extended compact specimen were derived.
Damage was characterized in the tests, including that associated with arm breakage in the standard compact specimen and load-point damage in the bend specimen. Two types of notch-tip damage were characterized using radiography, that which extends perpendicular to the notch in predominantly 0‡ fiber layups, and that which occurs ahead of the notch in quasi-isotropic and 90‡ fiber layups.
The applied K at maximum load, Kmax, determined in a way that took account of the effective crack growth up to the maximum load point, was used as a measure of fracture toughness. For deviations from the linear P-V plot corresponding to Δa/W ≤ 0.04, Kmax gave consistent measurements of fracture toughness. This criterion also excluded tests with damage of the type that violates the basic concept of fracture toughness measurement. Plots of Kmax vs δa/W showed increasing resistance to crack growth for quasi-isotropic layups and constant resistance to crack growth for predominantly 90‡ fiber layups.
Strain Rate and Inertial Effects on Impact Loaded Single-Edge Notch Bend Specimens
Authors: Vargas PM , Dodds RH 
Published: March 2009

Many significant problems in fracture mechanics of ductile metals involve surface breaking defects (cracks) located in structures subjected to short-duration loading caused by impact or blast. When the severity of impact loads is sufficient to produce large inelastic deformations, the assessment of crack-tip conditions must include the effects of plasticity, strain rate and inertia. This work examines the interaction of impact loading, inelastic material deformation and rate sensitivity with the goal of improving the interpretation of ductile fracture toughness values measured under dynamic loading. We focus on shallow and deeply notched bend test specimens, SE(B)s, employed routinely to measure the static fracture toughness of a material. A thorough understanding of the test specimen's dynamic behavior is a prerequisite to the application of measured fracture properties in structural applications.
Three-dimensional, nonlinear dynamic analyses are performed for SE(B) fracture specimens (a/W= 0.5, 0.15, 0.0725) subjected to impact loading. Loading rates obtained in conventional drop tower tests (impact load-line velocities of = 6 m/sec) are applied in the analyses. An explicit time integration procedure coupled with an efficient (one-point) element integration scheme is employed to compute the dynamic response of the specimen. Strain-rate sensitivity is introduced via a new, efficient implementation of the Bodner-Partom viscoplastic constitutive model. Material properties for A533B steel (a medium strength pressure vessel steel) are used in the analyses. Static analyses of the SE(B) specimens provide baseline responses for assessment of inertial effects. Similarly, dy namic analyses using a strain-rate insensitive material provide reference responses for the assess ment of strain rate effects. Strains at key locations on the specimens and the support reactions (ap plied load) are extracted from the analyses to assess the accuracy of static formulas commonly used to estimate applied J values. Inertial effects on the applied J are quantified by examining the accelera tion component of J evaluated through a domain integral procedure
The Seal Configuration Tester, a New Approach to the Evaluation of Elastomeric Materials for Oxygen Service
Authors: Haselmaier LH , Powell BA 
Published: March 2009

A new approach for evaluating elastomeric materials for use in high pressure oxygen has been developed. Because this approach replicates the dynamic forces that occur in pressure systems and subjects a specimen to progressive wear, it allows the user to compare wearability and oxygen sensitivity. This method determines if a candidate material ignites before it mechanically fails and provides a relative wearability ranking for that material.
Existing mechanical impact test methods produce data which is useful in screening various materials for oxygen sensitivity. The pass/fail data produced from these tests do not easily translate into a suitable material selection for a particular oxygen application. This new evaluation technique produces both mechanical wear data in combination with sensitivity data which can easily be applied when selecting elastomeric materials for a particular oxygen application.
An explanation of the process as well as sample data are presented.
Design of the LOX and GOX Systems for the Stennis Space Center High Heat Flux Facility
Authors: Yentzen MJ 
Published: March 2009

The High Heat Flux Facility (HHFF) was designed to test the high temperature performance of materials for the National Aerospace Plane (NASP) by directing the exhaust of several gas generators at actively cooled panels of the test materials. To accomplish this, a supply of high pressure gaseous oxygen (GOX) is required to feed the gas generators. In addition, a low pressure liquid oxygen (LOX) loading, storage, and supply system is required. The low pressure LOX system was designed for a maximum operating pressure of 722 KPa (90 psig) for the loading area and 1 135 KPa (150 psig) for the storage portion. A pump increases the operating pressure of the LOX from approximately 1 135 KPa (150 psig) to a maximum of 31.13 MPa (4 500 psig). An ambient air vaporizer converts the high pressure LOX to GOX. The high pressure GOX system was also designed for a maximum operating pressure of 31.13 MPa (4 500 psig).
This paper discusses the approach used for designing and constructing the LOX and GOX systems for the HHFF. Stennis Space Center and NASA requirements for the use of materials in oxygen systems are discussed. Particular emphasis is placed on the materials of construction and the selection of materials for the high pressure GOX components, piping, and other hardware. Several examples of actual components modified for use in oxygen are illustrated and the rationale used for selecting piece part materials for these components are provided. The system design philosophy is discussed and several general oxygen system design principles are mentioned. Specific portions of the design intended to reduce the likelihood of ignition are also addressed. Drawings of the systems and components are included to provide more specific information that could be used as a model for the design of similar systems.
Flammability of Metals in Fluorine and Nitrogen Trifluoride
Authors: Gugliemini CJ , Kadri SH , Martrich RL , Slusser JW , Vora J , Werley BL , Woytek AJ 
Published: March 2009

Fluorine and many of its compounds are more aggressive oxidizers than oxygen. Flammability test results for metals in fluorine and nitrogen trifluoride patterned after Air Products' tests of metals in oxygen are reported. Although, combustion in fluorine is distinctly different than combustion in oxygen, several of the thermodynamic properties and parameters used to understand metal flammability in oxygen in ASTM G 94 are presented for the fluorine-chemicals case. They suggest substantially different metal rank orders and combustion behaviors should be found for combustion in fluorine-containing oxidants. The data appear to support this prediction.
Despite the strong oxidizing nature of fluorine, nitrogen dilution levels at various pressures were identified at which test specimens did not propagate combustion in the configuration studied. Carbon steel rods 0.25-in (0.64-cm) diameter burned in atmospheric pressure fluorine but did not propagate upwards in fluorine/nitrogen mixtures of (%F2): 35% at 115 psig (0.89 MPa), 30% at 565 psig (4.00 MPa), 25% at 1065 psig (7.44 MPa) or 20% at 2015 psia (14.00 MPa).
The nitrogen trifluoride molecule contains atomic nitrogen equivalent to a 25% nitrogen/fluorine mixture, but it absorbs energy upon dissociation. Ignition of 0.25-in. (0.64-cm.) diameter rods at various pressures was attempted for the metals: 304L and 316 stainless steel, nickel alloys C22 and C276, Nickel 200, copper, nickel alloys 600 and 625, Monel®2 400, Chrome-Moly 4130X, and aluminum. Interestingly, aluminum, as well as nickel 200, Monel® 400, and copper, appeared to have the highest thresholds, above 750–1250 psig (5.3–8.72 MPa), and 304L and 4130X each experienced sustained combustion at atmospheric pressure. Stainless steel 316 appears to have a threshold at or below 225 psig (1.65 MPa). Nickel alloys 600, 625, C276 and C22 burned at 1000 psig (7 MPa) but were not tested at lower pressures.
An Evaluation of Polymers as Ignition Sources During Particle Impact in Oxygen
Authors: Dees J , Forsyth E , Gunaji MV , Stoltzfus JM 
Published: March 2009

When contaminant particles are present in oxygen systems they can be entrained in the flowing oxygen and collide with system components causing ignition and burning. This particle impact ignition mechanism has been the cause of many fires in oxygen systems and has been systematically studied in the laboratory. For the laboratory studies, materials for particles and targets are generally classified into three groups: metals, oxides (inert), and polymers. Of the three groups, metallic particles and targets have been tested most frequently. Oxide (inert) particles and targets have been studied occasionally. Polymers, however, have not been systematically studied either as particles or as targets.
In this work, four polymer materials commonly used in oxygen systems, Teflon (PTFE), Vespel SP-21, Kel-F 81, and Viton A, were evaluated as particles which were impacted against 316 stainless steel targets. Small particles, with major dimensions of approximately 250 micrometers (μm), were tested in quantities of one and five at subsonic and supersonic velocities. Single larger particles, with major dimensions of approximately 1000 and 2000 micrometers, were tested at subsonic and supersonic velocities. The oxygen pressure was maintained at 27.6 MPa (4000 psia) and the temperature was varied between 21 and 93 ‡C (20 and 200 ‡F). No ignitions of the target material occurred in any of the test series, which indicates that at least for these polymer materials and test sample configurations, particle impact ignition is unlikely. The limitations and applications of these tests results to actual oxygen systems is discussed.
Clay-Oil Flocculation and its Role in Natural Cleansing in Prince William Sound Following the Exxon Valdez Oil Spill
Authors: Bragg JR , Yang SH 
Published: March 2009

Natural interactions of fine mineral particles with residue oil and seawater, in a process called clay-oil flocculation, were found to create solids-stabilized oil-in-water emulsions on shoreline sediments at numerous locations in Prince William Sound following the Exxon Valdez spill. In laboratory tests using oiled sediment samples from Prince William Sound, these emulsions were shown to facilitate natural cleansing and dispersion of oil from sediments by moving water.
Microscopic examination showed that the emulsions consisted of complex and varied floe aggregates of about 1–100 microns in diameter. Fluorescence under ultraviolet light revealed that the interior of these particles consisted of numerous spheres of oil surrounded by mineral fines and seawater. X-ray diffraction and scanning electron microscope studies showed the minerals to consist of clays, quartz, and feldspar-typical components of glacial flour. Chemical analyses of the oil revealed a correlation between the fraction of polar hydrocarbons present and the amount of mineral fines bound with the oil. These factors were also related to the ease by which the oil could be removed from substrate sediments by hydrodynamic forces.
To investigate the effect of flocculation on natural cleansing, studies were conducted to determine the hydrodynamic energy needed for seawater to remove flocculated oil residues from sediments sampled from shorelines. Water was pumped at different velocities through a column packed with oiled sediment, and the amount and composition of oil removed from the sediment were measured as functions of water velocity and sediment movement. In separate tests, oil removal was observed in a wave tank that generated wave heights less than and greater than needed to move sediments. These tests demonstrated that, with clay-oil flocculation, substantial amounts of the oil could be removed at wave energies less than those needed to cause sediment movement and abrasion, which helps to explain observed removal of oil from the subsurface and from low energy shorelines where waves were not large enough to move sediments. Further, the large hydraulic cross section and nearly neutral buoyancy of floc particles removed from the sediment help to explain their efficient dispersal. The flocculation process also significantly increases the oil-water interfacial area, enhancing access to the oil by bacteria for biodegradation.
Clay-oil flocculation was found to be a beneficial process that we believe accelerated the removal of oil from shoreline sediments following the Exxon Valdez spill. The physical properties of the floc should have facilitated dispersion of the oil over large distances, thus helping to reduce buildup of hydrocarbons in subtidal sediments. Clay-oil flocculation, therefore, is another natural cleansing process that must be considered when studying the fate of oil spilled on shorelines.
Evaluation of the Toxic Properties of Naturally Weathered EXXON VALDEZ Crude Oil to Surrogate Wildlife Species
Authors: Stubblefield WA , Hancock GA , Ford WH , Prince HH , Ringer RK 
Published: March 2009

The toxic properties of naturally weathered Exxon Valdez crude oil (WEVC) to avian and mammalian wildlife species were evaluated using the surrogate species, mallard duck, Anas platyrhynchos, and European ferret, Mustela putorius. This study was conducted to evaluate the potential for toxic (rather than physical) injury to wildlife species that may have been exposed to WEVC, either through external contact or through dietary uptake. Previous studies have assessed the toxicity of unweathered crude oils, including Alaskan North Slope Crude, but little information exists regarding the toxicity of a naturally weathered crude oil, typical of that encountered following a spill.
A battery of laboratory toxicity tests was conducted, in compliance with standard and published test procedures, to evaluate acute and subchronic toxicity of WEVC. These included tests of food avoidance, reproductive effects, and direct eggshell application toxicity. Naturally weathered EVC, recovered postspill from Prince William Sound, was used as the test material. No treatment-related mortalities or gross signs of toxicity were noted in ducks at oral doses of 5 000 mg/kg body weight or at dietary concentrations up to 100 000 ppm (mg WEVC/kg diet), or in ferrets at oral doses up to 5 000 mg/kg body weight. Test animals did not avoid oil-contaminated food. No significant adverse effects were noted in birds fed diets containing up to 2 000 mg WEVC/kg diet in the reproductive toxicity test. However, significant reductions in mean eggshell thickness and strength were observed in birds fed 20 000 mg WEVC/kg diets. Applications of up to 92 mg/egg of WEVC to developing eggs produced no toxic effects.
Feeding weathered EVC to ducks and ferrets at oral doses or dietary concentrations exceeding those representing maximum likely field exposures from heavily affected spill areas did not significantly affect survival, growth, or reproduction. These results suggest that naturally weathered EVC posed little toxic risk to wildlife consuming oil or oiled food items following the Exxon Valdez spill, particularly considering the environmental exposure conditions that existed in the spill-affected area after 1989.
Surveys of Murre Colony Attendance in the Northern Gulf of Alaska Following the Exxon Valdez Oil Spill
Authors: Erikson DE 
Published: March 2009

Field surveys were conducted in July and August 1991 on 32 of the 36 murre (Uria spp.) colonies in the northern Gulf of Alaska to assess colony attendance (number of birds present at a colony) two years after the Exxon Valdez oil spill. The surveys focused on murre colonies because murres represented 74% of the recovered seabird carcasses and because it had been claimed that there was large-scale mortality of murres, leading to 60% to 70% decreases at some large colonies and population recovery periods of 20 to 70 years.
Murres were present at all 32 colonies, and colony attendance estimates were generally similar to those from historical (prespill) surveys, particularly for those colonies in the direct path of the spill, i.e., the Barren Islands and Chiswell Islands. Colony attendance levels in 1991 do not support the contention that murre colony attendance in the study area was drastically lower than historical levels. When colonies were grouped according to risk of oil exposure, the mean changes in attendance between 1991 and historical murre surveys did not differ significantly among the groups. Factors that could account for the observed similarity of 1991 and historical murre counts despite the high estimated mortality are (1) overestimation of mortality or (2) replacement of lost breeders through either recruitment of formerly nonbreeding individuals into the breeding population at spill-affected colonies or immigration of murres from nonaffected colonies. The findings of this study suggest that impacts of the Exxon Valdez oil spill on murre colony attendance in the northern Gulf of Alaska were relatively short-term.
Trace Water‐Promoted Oxidation of Benzylic Alcohols with Molecular Oxygen Catalyzed by Vanadyl Sulfate and Sodium Nitrite under Mild Conditions
Authors: Du Zhongtian , Miao Hong , Ma Hong , Sun Zhiqiang , Ma Jiping , Xu Jie 
Published: March 2009

Abstractmagnified imageAn inexpensive catalytic system consisting of vanadyl sulfate and sodium nitrite was developed for the oxidation of benzylic alcohols with molecular oxygen under mild conditions. Benzyl alcohols with various substitutions were efficiently converted to their corresponding aldehydes with high conversion and selectivity under 80 °C (e.g., 4‐nitrobenzyl alcohol was smoothly oxidized to 4‐nitrobenzyl aldehyde with 94% yield under 0.5 MPa of molecular oxygen). Halogen, noble metals, extra base or complicated ligands were avoided. Addition of a trace of water to this system before the reaction was crucial for the high efficiency.
Assessment of Relevant Factors Influencing Lipolytic Enzyme Production by Thermus thermophilus HB27 in Laboratory‐Scale Bioreactors
Authors: Deive F. J. , Carvalho E. , Pastrana L. , Rúa M. L. , Longo M. A. , Sanroman M. A. 
Published: March 2009

AbstractNowadays, there is not much information on the large‐scale production of thermostable lipolytic enzymes by thermophilic organisms. Therefore, in this study the lipolytic enzyme production by Thermus thermophilus HB27 in laboratory‐scale bioreactors was undertaken. In order to determine the most suitable bioreactor, two configurations were investigated: stirred‐tank and airlift bioreactor. It was demonstrated that the stirred‐tank configuration led to the highest lipolytic extracellular activities, about 2.3‐fold higher than those found in the corresponding cultivation in the airlift bioreactor. On the other hand, the influence of several factors such as culture nutrients concentration, aeration, and agitation rate on the production of thermophilic lipolytic enzymes in a 5‐L stirred‐tank bioreactor was assayed. At reduced nutrients concentration (50 % with respect to the basal medium), a higher product/biomass yield was attained, without any operational problems. From the relationship between mass transfer coefficient (KLa), aeration, and agitation rates it was concluded that there is a lesser dependence on the aeration than the agitation rate. In addition, the mechanical stirring of the bioreactor could tear the membranes that contain the rotund bodies often found in cultures of thermophilic microorganisms, thus increasing the extracellular enzyme production.
The Intramolecular Edge‐to‐Face Interactions of an Aryl CH Bond and of a Pyridine Nitrogen Lone‐Pair with Aromatic and Fluoroaromatic Systems in Some [3,3]Metaparacyclophanes: A Combined Computational and NMR Study
Authors: Annunziata Rita , Benaglia Maurizio , Cozzi Franco , Mazzanti Andrea 
Published: March 2009

AbstractHaving the edge on aromatic–aromatic interactions: Model systems containing aromatic, fluoroaromatic, and heteroaromatic residues arranged in an edge‐to‐face disposition have been synthesized (see figure). Investigation of their structures and stereodynamic behavior shows a favorable interaction between an “edge” ring featuring a pyridine nitrogen lone pair and a perfluorinated “face” ring.magnified imageSimple model systems based on the [3,3]metaparacyclophane skeleton have been designed to study the effect of fluorination of the “face” ring on the edge‐to–face (EtF) interactions with the CArH bond of a phenyl ring or the nitrogen lone‐pair of pyridine. Calculations established that in their more stable conformation the model systems adopt a tilted EtF disposition with the rim of the meta‐substituted ring pointing towards the face of the para‐substituted ring. Topomerization occurs by flipping of the meta‐substituted ring, a process that involves the formation of an intermediate featuring an orthogonal EtF disposition of the arenes, which is less stable than the tilted arrangement. The energy barriers to the isomerization were determined by variable‐temperature NMR spectroscopy and were well reproduced by DFT calculations. The variation in the energy barrier as a function of the substitution of the para‐substituted ring could be rationalized well by a polar interpretation of the EtF interaction in the cases of model systems presenting the PyN̈⋅⋅⋅π interaction but not in the cases of models featuring the CArH⋅⋅⋅π interaction.