bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Conductivity of Evacuated Glass Beads: Line Source Measurements in a Large Volume Bead Bed Between 225 and 300 K
Authors: Langseth MG , Ruccia FE , Wechsler AE
Published: March 2009

Line source measurements of thermal conductivity have been made in a large tank of evacuated glass beads that were used as a thermal simulator for the Lunar Heat Flow Experiment. Measurements were made with two 3/16 inch diameter probes 87 inches long that contained five (5) evenly spaced thermocouples and a double filament heater wire. The probes were inserted vertically from the top into the bead bed, which allowed ten (10) measurements of conductivity to be made over an interval of depth of 55 inches in tank. Power densities used ranged from 1.2 to 2.2 MW/cm. The bead tank is 21 inches in diameter by 86.75 inches in depth with temperature control at the outer walls. This tank was contained in a vacuum chamber that could be evacuated to gas pressure 10−5 to 10−4 Torr. Measurements were made at various bead bed temperatures between 225 and 300 K.

Measurements at 225 K gave a range of conductivity values from 1.0 to 4.0 × 10−4 watt/cm ∙ K. The conductivity increased uniformity over the interval of depth measured. Extrapolation of the values to the surface of the bead tank indicates an average conductivity of 0.7 × 10−4 wattcm K. Measurements using the Lunar Heat Flow Experiment probes at 225 K yield values in good agreement, ± 10%, with the line source data. All of the probe qualification tests were made at 225 K. These comparisons demonstrate that valid conductivity measurements can be made with the heat flow probe.

The increase in conductivity with depth is due to an increase in compressive stress. However, the observed increase at 225 K is much greater than would be expected from “hydrostatic” loading alone. Measurements at higher bead bed temperatures, 246 K and 258 K, yield lower values of conductivity. If the increase of conductivity with depth is due to “hydrostatic” loading alone, an increase of conductivity with increasing temperature would be expected. The opposite observed effect suggests that compressive stresses from thermal contraction of the bead jacket are important.
High Performance Thermal Insulation for an Implantable Artificial Heart
Authors: Stoner DR , Svedberg RC , Chi JWH , Vojnovich T
Published: March 2009

The practicability of an implantable artificial heart is strongly dependent on the availability of a high performance, compact, and lightweight thermal insulation system to contain the radioisotope energy source. The insulation system must limit heat losses to less than 0.024 W/cm2 to maintain an acceptable thermal efficiency with the Stirling engine heat source at 870°C (1600°F). On the basis of the overall system requirements, vacuum metal foil insulation is the only acceptable choice. Concentric nickel foil cups were utilized in place of the standard spiral-wrapped foil design with mitered corners, thereby eliminating a serious heat leak and the structural problems generally associated with the corners. Initial total system thermal performance tests have been very encouraging and predict that a system heat loss of 2 W can be met with about 35 to 40 foil cup layers. Since the implantable system is to be designed for a sealed ten-year lifetime under static vacuum, measurements are also being made to determine the long-time performance and outgassing characteristics of the nickel packages.
Study of Thermophysical Properties of Constructional Materials in a Temperature Range from 10 to 400 K
Authors: Luikov AV , Shashkov AG , Vasiliev LL , Tanaeva SA , Bolshakov YP , Domorod LS
Published: March 2009

A brief description is given of an experimental apparatus for determining thermal conductivity, thermal diffusivity and heat capacity in the range of 10 to 400 K. The results on thermal properties of some constructional polymers are tabulated.
Threeui-Dimensional Solution for a Through-Thickness Crack with Crack Tip Damage in a Cross-Plied Laminate
Authors: Wang SS , Mandell JF , McGarry FJ
Published: March 2009

A three-dimensional finite-element solution is given for the stress field of a 0/90 laminate containing a sharp through-thickness edge crack with crack tip damage consisting of subcracks parallel to the fibers of each ply. The solution is compared to that for a sharp crack with no subcracks given in an associated paper, and the introduction of the subcracks is shown to significantly alter the stress field. Outside of a core zone at the main crack tip, the two stress distributions are nearly identical. Inside of the core zone, the subcracks serve to relax the in-plane stresses in a manner similar to the action of a plastic zone in a metal; the mechanisms of stress transfer around the subcracks are identified. The results also indicate that the fundamental fracture mechanics concept of a zone of relaxed stresses near the main crack tip, surrounded by an undisturbed singular stress field, is preserved, and that the subcracks cause no shift in the singular stress field which would require a crack length correction.
A Finite-Element Program for Fracture Mechanics Analysis of Composite Material
Authors: Atluri SN , Kobayashi AS , Nakagaki M
Published: March 2009

An assumed displacement hybrid finite-element procedure developed for treating a general class of problems involving mixed-mode behavior of cracks is used to solve some two-dimensional, fracture mechanics problems involving rectilinear-anisotropic materials. This finite-element program uses four “singular” elements which surround the crack tip and “regular” elements which occupy the remaining region. The singular element has a built-in displacement field of the √r type with the two modes of stress intensity factors, KI and KII, as unknowns. Displacement compatibility between singular and regular elements is also maintained. Isoparametric transformations are used to derive the stiffness matrix of quadrilateral curved elements. Rectilinear anisotropic, nonhomogeneous, but linear elastic, material properties are considered. The program was checked out by analyzing a bimaterial tension plate with an eccentric crack and a centrally-cracked orthotropic tension plate. The results thus obtained agreed well with those by Erdogan and Biricikoglu, and Bowie and Freese, respectively. The program was then used to analyze two fracture test specimens for which analytical solutions do not exist. The first specimen was the doubly edge-notched tension plate with material principal directions oriented 0°–90° or ±45° to the geometric axes of symmetry and with varying crack length. The second specimen was the three-point bend specimen with material principal directions oriented 0°–90° to the geometric axes of symmetry. Finally, an orthotropic tension plate with an oblique center crack was analyzed. Finite-element solutions of most of these problems do not seem to have appeared in prior literature.
Rate and Time Dependent Failure of Structural Adhesives
Authors: Brinson HF , Renieri MP , Herakovich CT
Published: March 2009

Studies on two adhesives (Metlbond 1113 and 1113-2) identified as having important applications in the bonding of composite materials are presented. A testing program to ascertain stress-strain, strain-rate, time, yield, and/or failure behavior of these materials in bulk form using uniaxial tensile constant strain-rate, creep, and relaxation tests is described. The stress-strain behavior of each material is shown to be significantly rate dependent. Further, it is shown that a rate dependent stress whitening (crazing) phenomenon occurs prior to either yield or fracture. A region of linear elasticity, a region of viscoelasticity, and the onset of yielding are identified in the stress-strain behavior. The linear elastic limit and the yield point are shown to be rate dependent and agree well with an empirical equation proposed by Ludwik. A creep to failure phenomenon is shown to exist and is correlated with a delayed yield equation proposed by Crochet. Analytical predictions based on a modified Bingham model are shown to agree well with experimental stress-strain strain-rate data. Analytical predictions based on a modified Ramberg-Osgood equation are also shown for comparison purposes. Information regarding rate and time dependent Poisson's ratios is also presented.
A Study of the Significance of Lubricant Viscosity in Blow-By Control
Authors: Neveu C
Published: March 2009

An engine test procedure was developed to measure blowby rates with a modified European diesel test engine. With monograde oils, the rate correlates with viscosity. The higher the engine blowby level the less the engine sensitivity to lubricant viscosity. The differences in blowby control observed with multigraded oils appear to correlate with their viscosities at temperatures well above 210°F (98.9°C). Other factors such as temporary shear loss may play a part as indicated by qualitative observations. The same general trends were also confirmed in an unmodified multicylinder gasoline engine.
The Use of Simulant Devices to Evaluate the Wear Performance of Multigraded Engine Oils
Authors: Goldblatt IL
Published: March 2009

Conditions for the laboratory simulation of engine ring and cam-and-tappet wear performance have been established. By using these test conditions, the wear performance of twelve oils of known viscometric properties has been determined. The results suggest that viscosity under either high or low shear conditions is not related to the wear performance under these thin film simulated engine conditions. Wear performance for these oils does appear to be related to the degree of polymer degradation experienced under the conditions of thin film or elastohydrodynamic lubrication.
Epidemiological Consideration in the Application of Indicator Bacteria in North America
Authors: McCabe LJ
Published: March 2009

The microbiological needs of the epidemiologist for the investigation of waterborne disease outbreaks are reviewed. The density of indicators needs to be determined during outbreaks, but the isolation of pathogens from the water provides more definitive data. It is suggested that the measurement of chlorine residual is more useful than bacteriological monitoring of drinking water supplies.
Concept of a Bacterial Species: Importance to Writers of Microbiological Standards for Water
Authors: Farmer JJ , Brenner DJ
Published: March 2009

A bacterial species is operationally difficult to define. There is considerable phenotypic variation in some species, such as Escherichia coli; thus, the limits of the species are difficult to determine. Other species such as Edwardsiella tarda and Serratia marcescens are “tighter” because the strains which comprise these species show little phenotypic variation. The latter species are easier to define biochemically.

Newer taxonomic techniques have been helpful in defining bacterial species. Often, the results have agreed with those obtained by conventional methods. However, species such as Enterobacter agglomerans have been shown by DNA-DNA hybridization to be composed of over twelve different hybridization groups which could be considered “new species.”

Many different bacterial species are washed from the soil into water. Some of these are soil bacteria; others make up the gut flora of insects, invertebrates, and lower vertebrates. Often, these environmental species are closely related to species known to be pathogenic for man. Sometimes environmental isolates can be differentiated from the human pathogens by simple tests; S. liquefaciens and S. rubidaea are phenotypically different from the human pathogen S. marcescens and can be recognized easily. Environmental strains of Klebsiella, for which the taxonomy has not been completely defined, cannot yet be differentiated from the human pathogens. Similarly, in Enterobacter, Citrobacter, Proteus, Vibrio, Pseudomonas, Aeromonas, and other groups, there are taxonomic gaps where species lines are not completely clear. Many isolates that have been classified in these genera may not be pathogenic for man. Consequently, to ensure that standards will have relevance in public health, writers of microbiological standards for water should proceed very carefully in their treatment of indicator organisms. Many species in water are probably not pathogenic for humans but are closely related to species which are pathogenic. Even with a complete battery of biochemical and serological tests, isolates cannot always be assigned to their correct species. We see many isolates which probably belong to new species which have not been defined.
Total Coliform Bacteria
Authors: Mack WN
Published: March 2009

Although the total coliform bacterial count has its shortcomings, it is our best indicator of the health hazards associated with drinking water that we have today. Some of these defects can be corrected by additional bacterial tests to determine interference or identify nonconliform lactose fermenting organisms. Occasionally drinking water samples containing viruses have given negative tests for coliform bacteria when tested by the standard methods. Concentration methods used to recover viruses in water samples have shown that the coliform organisms were present but in an insufficient number to be indicated by the routine standard methods.

Suggestions are given for the search for a better method to detect bacterial pollution in drinking water.
Clostridium perfringens as a Water Quality Indicator
Authors: Cabelli VJ
Published: March 2009

Clostridium perfringens and the more general group to which it belongs, “sulfite-reducing, spore forming anaerobes,” are considered with regard to their use as health effects, water quality indicators. The groups are examined with regard to their identification, their importance, the characteristics which impinge on their use as indicators, monitoring applications, available evaluation data, and enumeration methods. C. perfringens has specific and limited applications as a water quality indicator. It appears to be the fecal indicator of choice for measuring remote or intermittent pollution and in situations where resistance to disinfectants and environmental stress is at a premium.
Vibrio Species as Bacterial Indicators of Potential Health Hazards Associated With Water
Authors: Colwell RR , Kaper J
Published: March 2009

Vibrio species have been suggested as indicators of water quality. Methods for the isolation, identification, and enumeration of V. cholerae and V. parahaemolyticus (Biotype 1, parahaemolyticus, and Biotype 2, alginolyticus) have been developed and successfully applied in analyses of water. Recent isolations of V. cholerae from a harbor in the United States suggest that greater attention should be paid to the Vibrio species as waterborne pathogens. The identification and classification of V. cholerae and the two biotypes of V. parahaemolyticus have been greatly advanced. Other related Vibrio species remain to be described, and practical methods for their enumeration are not yet available. Because Vibrio species occur throughout the world in bays, estuaries, and marine waters, it is imperative that the ecology of this bacterial group be elucidated.
Coagulase Positive Staphylococci as Indicators of Potential Health Hazards From Water
Authors: Evans JB
Published: March 2009

Coagulase-positive staphylococci are synonymous with the species Staphylococcus aureus. They are normal inhabitants of the nose, skin, and intestinal tract of healthy individuals as well as a cause of purulent infections of the skin, eyes, and ears. They are a major component of the bacterial flora of swimming pools and recreational waters that have a high density of swimmers and are potentially a good index of the health hazard associated with bathing in such waters. The major obstacle to their use as an indicator organism is the lack of a medium and method that is sufficiently selective and reliable for the quantitative recovery of these bacteria from aquatic habitats.
Spread and Significance of Salmonellae in Surface Waters in The Netherlands
Authors: Kampelmacher EH
Published: March 2009

The spread of salmonellae in surface water in The Netherlands was studied during recent years. Epidemiological studies revealed that infection cycles exist probably in the following way: food of animal origin, humans, sick persons, discharge of contaminated feces into the sewage system, contamination of surface water, carry-over via insects, rodents, and birds, into stables, and on feed or directly on food. Data are given in order to substantiate this hypothesis. Salmonella contamination to surface water is discussed with regard to the significance in Salmonella epidemiology. Also the effect of the chlorination of effluents in order to break possible contamination infection cycles is summarized. Moreover, attention is given to the fact that also other infectious diseases may be maintained by infection cycles in the environment.
Bacterial Water Quality and Standards: The Role of the World Health Organization
Authors: Suess MJ
Published: March 2009

One of the tasks of the World Health Organization (WHO) is the development of environmental health criteria. In this connection, it has been concerned with some problems related to the concept of indicator bacteria and the rapid and reliable identification of pathogenic ones. WHO requires the absence of any organisms of fecal origin in drinking water and refers to Escherichia coli, fecal streptococci, and Clostridium perfringens as the most representative of fecal pollution. Potable water supplies for aviation and shipping have to be of similar quality. To assist in the control of surface water pollution, a manual, which includes a chapter on bacteriological examination, has been prepared to encourage the use of approved analytical methods. Attention has also been given to the survey and examination of recreational and shellfish-bed waters.
Bacterial Indicators and Potential Health Hazard of Aquatic Viruses
Authors: Kraus MP
Published: March 2009

A fundamental difference exists between bacterial (living) and viral (nonliving) organisms in that a virus is a parasite depending on living host cells for material and energy to replicate viral entities. Therefore, an “indicator organism” for virus hazards must take into account the fact that a virus must be able to travel among hosts in order to remain virulent. In this paper, the author modifies the usual connotation of indicator organism to include an “indicator system” which consists of virus and the host on which it is assayed. The state of the art on virus hazards is examined in the light of the advanced technology useful to engineers in the solution of virus problems in water reuse. It is generally accepted that a virus is the most suitable “indicator organism” for a virus. The research use of various virus indicators is here briefly reviewed and requirements for a timely and realistic indicator system is set forth. A system containing multiple hosts is suggested, and data are given as to its effectiveness in monitoring virus quality in reuse water, sludges, and soil.
Indicators of Recreational Water Quality
Authors: Cabelli VJ
Published: March 2009

Water quality indicators, in general, and a number of potential health effects, water quality indicators, specifically, are examined with regard to their use in predicting the health hazards associated with the use of recreational waters. The factors considered are the requisite characteristics, constraints upon their use and the data obtained thereby, and their evaluation, especially as regards available epidemiological data. Based upon existing information, two indicator systems, Escherichia coli and enterococci, are tentatively recommended as the indicators of choice for this specific application.
Fecal Streptococci: Indicators of Pollution
Authors: Clausen EM , Green BL , Litsky W
Published: March 2009

The significance of fecal streptococci as indicators of fecal pollution is reviewed. Consideration is given to the classification and definition of these streptococci, methods and media suitable for their enumeration, and the incidence and persistence of fecal streptococci in clean and polluted enviornments.
Bacterial Indicators and Standards of Water Quality in Britain
Authors: Barrow GI
Published: March 2009

Health hazards vary greatly with different waters and their uses as well as with geography, climate, populations and their living standards. Only by defining practicable water quality objectives and priorities in the light of current knowledge and likely cost benefit can the risks of actual and potential disease be reduced to acceptable levels. These, however, will still vary in different parts of the world. Universal standards, in contrast to objectives, are still a long way ahead. In this paper, the British approach to the choice and use of bacterial indicator organisms in relation to potential health hazards and water quality criteria is reviewed briefly. Although no mandatory standards have ever been imposed, drinking water supplies in Britain are among the best in the world in quality and safety, even though about two thirds of them are derived directly from sewage polluted surface waters. However polluted these may be, in principle, they can be adequately treated, and British philosophy has always relied on this rather than on the more elusive targets of disinfecting sewage effluents and purifying water sources. For almost 50 years, coliform organisms and Escherichia coli have been used as the main indicators of fecal pollution, and, in this way, the efficiency of treatment and thus the safety of drinking water supplies have been effectively monitored. Despite increased water usage and recycling, there is no valid reason to change this view. Although viruses can be isolated readily from sewage effluents, there is no epidemiological evidence of transmission to man by the water route, and the current position is one of surveillance and research. Similarly, despite intensive investigation, there is no authenticated evidence of significant disease attributed to sewage polluted bathing beaches or efficiently maintained swimming pools. Aesthetic values, however, are now playing a greater role in environmental pollution control. In addition, compliance with microbiological and other standards for water for abstraction as well as for bathing recently accepted by the European Economic Community will be necessary in the future.
Indicators of Quality for Shellfish Waters
Authors: Hunt DA
Published: March 2009

A chronological review of the history of significant research contributing to the development of current bacteriological criteria and standards for shellfish waters is described beginning with Prescott, Winslow, and Eijkman in 1904 and culminating in a proposal for a fecal coliform standard in 1974. Coliform and fecal coliform standards are defined, and the significance of the presence of these organisms in shellfish waters is discussed. The National Shellfish Sanitation Program presumes that both coliform and fecal coliform standards represent equivalent degrees of pollution and resultant health hazard when measuring levels of diluted sewage related to point sources of pollution in shellfish growing area waters. These two indicator groups are used in conjunction with sanitary surveys for the classification of shellfish growing areas and interpreted according to the limitations of the groups.
Intergranular Corrosion in Nuclear Systems
Authors: Taboada A , Frank L
Published: March 2009

The occurrences of intergranular stress-corrosion cracking in nuclear power plant components made of austenitic alloys are discussed. Cracks of this type have occurred in sensitized Types 304 and 316 austenitic stainless steels in a variety of components at various stages of fabrication. Historically, cracking in early reactors occurred in heavily sensitized material or were related to the presence of chlorides or caustic ions. More recently, a rash of cracks were found in boiling water reactor piping adjacent to welds. This problem is evaluated.

Wastage and intergranular cracking of Inconel 600 alloy tubing of steam generators has occurred in the secondary side in plants that have used either sodium phosphate or all volatile water treatment. Design and environmental factors have had a pronounced influence on the tube degradation. The significance of these conditions is discussed, as is action taken by the Nuclear Regulatory Commission relating to this problem.
Detecting Susceptibility to Intergranular Corrosion of Stainless Steel Weld Heat-Affected Zones
Authors: Vyas B , Isaacs HS
Published: March 2009

A scanning reference electrode technique has been developed to study intergranular corrosion of austenitic stainless steels. The potential variations produced in the electrolyte due to the intergranular corrosion of the sensitized grain boundaries have been measured by scanning a microtip reference electrode across the heat-affected zone adjacent to a weld. The development of a test based on the scanning reference electrode technique for determining the degree of sensitization of stainless steels has been explored. The technique is particularly useful in determining the degree of sensitization and the location of the sensitized grain boundaries adjacent to welds. The effect of material and welding variables on the location and degree of sensitization has been studied. The results have been compared with conventional tests for detecting susceptibility to intergranular corrosion.
Detection of Susceptibility of Alloy 26-1S to Intergranular Attack
Authors: Sweet AJ
Published: March 2009

Alloy 26-1S, a titanium-stabilized ferritic stainless steel, is of commercial interest because of its good as-welded properties, its resistance to chloride stress-corrosion cracking (SCC), and its low cost relative to other alloys having these characteristics. It has been found that understabilization of 26-1S can lead to sensitization and susceptibility to intergranular attack (IGA) in typical chemical industry solutions and to SCC in hot, chloride-bearing water. To ensure that a given batch of Alloy 26-1S is stabilized properly and resistant to sensitization, specimens from each batch should be tested by appropriate acceptance tests. Two suitable acceptance tests were identified (an etch test and an acid corrosion test), and pass/fail criteria were determined.
Some Anomalies Associated with Moisture Diffusion in Epoxy Matrix Composite Materials
Authors: Whitney JM , Browning CE
Published: March 2009

Diffusion of moisture into graphite/epoxy composites was investigated and some anomalies observed. In particular, data are presented which indicate a departure from classical Fickian behavior. An apparent two-stage diffusion process is observed in both the neat epoxy resin and derived graphite/epoxy composites. Evidence is presented which suggests time-dependent matrix cracking as the mechanism associated with the two-stage diffusion process. Comparison of laminate diffusion data with unidirectional data suggests that the diffusion coefficient is stress dependent.
Fundamental and Operational Glass Transition Temperatures of Composite Resins and Adhesives
Authors: Carter HG , Kibler KG , Reynolds JD
Published: March 2009

Data are presented on the thermomechanical response and electrical conductivity of two commonly used epoxy materials, Narmco 5208 resin and RB 398 adhesive, as a function of increasing temperature. The overall conformity of the results shows that the second-order Ehrenfest-type glass transition temperature, designated as T2, governs the onset and evolution of changes in viscoelastic and electrical response as well as thermal expansion. The general features of this behavior are described with a five-element spring-and-dashpot model. The values of T2, and two other Williams-Landel-Ferry (WLF)-type parameters for the description of viscoelastic response above T2, can thus be derived from a single thermomechanical or electrical conductivity experiment conducted at constant heating rate.
Swelling of Composite Laminates
Authors: Hahn HT , Kim RY
Published: March 2009

The swelling behavior of a graphite/epoxy (AS/3501-5) is shown to be described by a model which is based on the assumption that the swelling is negligible until the moisture concentration reaches a threshold value and then increases linearly thereafter. The model also provides a means of measuring the volume fraction of voids. The analytical results, which take into account the curing stresses, are compared with the experimental data for the transverse and thickness strains of symmetric laminates as well as for the warpage of unsymmetric laminates. The initial absorption in virgin specimens facilitates the subsequent diffusion, and the residual stresses appear to be responsible for the absorption being slower than the desorption during the early stage of moisture conditioning. Warpage of unsymmetric laminates is discussed in light of the cracks found in constituent plies. Finally derived is a temperature-relative humidity relationship which renders the graphite/epoxy composite laminates free of residual stresses.
Inelastic Micromechanical Analysis of Graphite/Epoxy Composites Subjected to Hygrothermal Cycling
Authors: Miller AK , Adams DF
Published: March 2009

Results are presented of an inelastic finite-element analysis of the residual microstress state in a unidirectional graphite/epoxy composite subjected to temperature cycling from room temperature (294 K) to 405 K or a combined cycle of changing matrix moisture content from a saturated condition (5.6 percent water by weight) to 2.0 percent moisture content with a simultaneous temperature change from room temperature to 339 K. In the analysis, the graphite fibers are modeled as being transversely isotropic, and assumed temperature- and moisture-dependent properties of modulus and strength for epoxy are utilized.

The results indicate that relatively large residual microstresses result from the cooldown of the composite from the curing temperature (450 K) to room temperature, and that in portions of the matrix material the residual stresses nearly exceed the yield strength of the material for a 60 percent volume composite. It is shown that moisture saturation of the matrix causes matrix yielding in both 40 and 60 percent fiber volume composites. It is noted that subsequent thermal cycling, or hygrothermal cycling, promotes definite changes in these microstress states which cause dimensional instability of the composite.
Influence of Two-Dimensional Hygrotheramal Gradients on Interlaminar Stresses Near Free Edges
Authors: Faryley GL , Herakovich CT
Published: March 2009

Interlaminar stresses are determined for mechanical loading, uniform hygrothermal loading, and gradient moisture loading through implementation of a finite-element computer code. Nonuniform two-dimensional hygroscopic gradients are obtained from a finite-difference solution of the diffusion equation. It is shown that hygroscopic-induced stresses can be larger than those resulting from mechanical and thermal loading, and that the distribution of the interlaminar normal stress may be changed significantly in the presence of a two-dimensional moisture gradient in the boundary layer of a composite laminate.
Integrated Theory for Predicting the Hygrothermomechanical Response of Advanced Composite Structural Components
Authors: Chamis CC , Lark RF , Sinclair JH
Published: March 2009

An integrated theory is developed for predicting the hygrothermomechanical (HGTM) response of fiber composite components. This integrated theory is based on a combined theoretical and experimental investigation. In addition to predicting the HGTM response of components, the theory is structured to assess the combined hygrothermal effects on the mechanical properties of unidirectional composites loaded along the material axis and off-axis, and those of angle-plied laminates. The theory predicts values in good agreement with measured data at the micromechanics, macromechanics, laminate analysis, and structural analysis levels.
Attached, Filamentous Algal Communities
Authors: Trotter DM , Hendricks AC
Published: March 2009

The discussion of attached, filamentous algae is limited to those forms with a holdfast system and filaments that flow out into the water. These macroscopic assemblages are rarely studied, in comparison with the many studies of other types of benthic or planktonic algae. Techniques used to describe and quantify these algal communities are reviewed. Guidelines are set for the quantitative study of a wide variety of situations where attached filamentous algae occur. A continuous-flow algal bioassay system that employs a filamentous alga attached to a removable substrate is presented.
Analysis of the Flexure Test for Laminated Composite Materials
Authors: Whitney JM , Browning CE , Mair A
Published: March 2009

Equations applicable to a general class of symmetrically laminated beams are derived by considering a beam as a special case of a laminated plate. The beam bending stiffness thus becomes a function of all the bending stiffness coefficients of a laminated plate. The validity of this approach is verified by comparing theoretical results to flexure data on graphite/epoxy angle-ply and quasi-isotropic laminates. In addition, it is shown that flex strength on general composite laminates is extremely difficult to interpret, even though the stresses can be calculated from the modified beam theory. Discontinuities in the in-plane stresses at layer interfaces lead to a state of stress which is difficult to compare to standard laminate tensile coupons.
Debonding of Rigid Inclusions in Plane Elastostatic
Authors: Sendenckyj GP
Published: March 2009

The problem of an arc crack lying within the interface between a rigid elliptic inclusion and an unbounded matrix is considered under the assumption of plane deformation, and a general solution method, valid for other inclusion geometries, is presented. The particular example of a single arc crack debonding one end of the inclusion under uniaxial and equal biaxial loading at infinity is considered in detail. It is shown that, unless the matrix is incompressible in the plane of deformation, there is an oscillating square-root stress singularity at the crack tips. The strength of this singularity, referred to as the crack tip stress intensity factor, is analyzed for different ellipse shapes and applied loads. In particular, it is shown that (i) a crack debonding a slender inclusion will arrest when load is applied parallel to the inclusion, and (ii) the crack tip stress intensity factors become unbounded as the crack tip reaches a sharp geometrical discontinuity. This is shown to be a consequence of the change in the nature of the crack tip stress singularity in this case. Finally, the results are applied to a discussion of the debonding phenomenon observed in composite materials.
Evaluation of Experimental Methods for Determining Dynamic Stiffness and Damping of Composite Materials
Authors: Bert CW , Clary RR
Published: March 2009

Various methods potentially usable for determining dynamic stiffness and damping of composite materials are reviewed. Of these, the following most widely used techniques are singled out for more detailed discussion: free vibration, pulse propagation, and forced vibration response. To illustrate the usefulness and validity of dynamic property data, their application in dynamic analyses and comparison with measured structural response are described for the following composite-material structures: free-free sandwich beam with glass-epoxy facings, clamped-edge sandwich plate with similar facings, free-end sandwich conical shell with similar facings, and boron-epoxy free plate with layers arranged at various orientations.
Crack-Tip Deformation Measurements Accompanying Fracture in Fibrous and Laminar Composites
Authors: Underwood JH
Published: March 2009

Experimental measurements are described of various types and stages of crack-tip deformation which accompanies crack growth in boron-aluminum sheet and in laminar steel plate. Optical interference and oblique-light photography are used to show the interaction of a crack with individual fibers and layers in the two systems for various tensile loads and specimen configurations. A fracture mechanics analysis is used to categorize the fracture behavior of boron-aluminum specimens of different fiber orientation. The crack-tip deformation in laminar steel plate under fatigue load is related to the interlayer bond strength and to the subsequent fracture behavior of the plate.
Uniaxial, Biaxial, and Fatigue Properties of Polyester Fiber Glass
Authors: Irwin LH , Dunlap WA , Compton PV
Published: March 2009

Uniaxial flexure and tension tests and biaxial flexure tests were performed on two systems of fiber glass-reinforced polyester (FRP) and also on an FRP-polyurethane foam composite to evaluate their suitability for possible use as expedient paving materials. The principal parameters studied were ultimate strength, elastic modulus, and fatigue behavior.

Results of the uniaxial tests were found to compare favorably with the results of the biaxial tests. A method of stress analysis for the biaxial tests was developed to accommodate a center loaded, clamped, circular plate subjected to large deflections and having radial forces on the boundary.

From the results of the research it was found that factors affecting the volume proportions of resin, glass, and air, and factors affecting the properties of the resin could have an influence on the properties of the FRP, in accordance with the “rule of mixtures” [11]. Both the ultimate-strength test results and the fatigue tests results indicated that Materials Systems A was superior to Materials System B.
Mechanical and Physical Properties of Advanced Composites
Authors: Freeman WT , Kuebeler GC
Published: March 2009

The mechanical and physical properties of graphite, glass, PRD-49, and boron epoxy composites are compared with today's commonly used industrial materials to illustrate the many unique design alternatives available with advanced composite materials. Mechanical properties and the fatigue, creep, impact, thermal expansion, thermal conductivity, specific heat, electrical properties, wear, and friction characteristics of the materials are summarized. The purpose of each comparison is to show where performance improvements can be achieved by replacing present materials with advanced composite materials.

Cost advantages in the use of these materials are briefly discussed. Increased performance, increased productivity, longer service life, and less component maintenance should outweigh today's higher material costs of advanced composites.
Wear of Glass Fiber Reinforced Composite Material
Authors: Ward AL
Published: March 2009

Fiber-oriented glass-filled epoxy composite material was tested to determine the effect of fiber orientation on the wear rate. Three different fiber orientations were tested under constant load with wear occurring on both machined and nonmachined surfaces. In general, both the initial and steady-state friction and wear are lower when sliding occurs on nonmachined surfaces. Also, the variation of friction and wear with fiber orientation is not as marked as it is when sliding against a machined surface. The worst steady-state wear rate was exhibited by samples where the fibers were oriented perpendicular to the wear interface.
Reinforcement of Metals with Advanced Filamentary Composites
Authors: Herakovich CT , Davis JG , Dexter HB
Published: March 2009

This paper reviews some recent applications of the concept of reinforcing metal structures with advanced filamentary composites, and presents some results of an experimental investigation of the tensile behavior of aluminum and titanium reinforced with unidirectional boron/epoxy. Results are given for tubular and flat specimens, bonded at either room temperature or elevated temperature. The composite reinforced metals showed increased stiffness over the all-metal counterpart, as predicted by the rule of mixtures, and the results were independent of specimen geometry.

The tensile strength of the boron/epoxy reinforced metals is shown to be a function of the geometry of the test specimen and the method of bonding the composite to the metal. The ultimate strength of the tubular specimens and a flat modified dogbone specimen, both bonded at elevated temperature, and a flat coupon specimen bonded at room temperature showed good agreement with predicted values, which are well above the metal counterpart. Flat coupon specimens bonded at an elevated temperature exhibited early failures, which were as much as 40 percent below predicted values.
Plastic Deformation Processing and Compressive Failure Mechanism in Aluminum Composite Materials
Authors: Chang M , Scala E
Published: March 2009

Analytical models are presented for: (1) monolayer composite fabrication, (2) consolidation of monolayer composites into plates, and (3) composite deformation under transverse compression. Upper-bound solutions of the models are developed by using the limit analysis of plastic theory. These solutions depend on (1) the flow stress of the matrix material, and (2) frictional coefficients for the fiber-matrix and for the matrix-die interfaces. They were determined experimentally from compression ring tests.

The analytical predictions of the average consolidation pressure are in good agreement with experimental results for an aluminum matrix from room temperature to 750°F (399°C). Transverse compression deformations were examined by several methods including scanning electron microscopy for aluminum-steel wire, aluminum-Borsic, and aluminum-nickel unidirectionally solidified composites. The analytical predictions for flow line directions from a proposed strip compression model agree with the experimentally determined angles.
Experimental Stress Intensity Factor Measurements in Orthotropic Composites
Authors: Tirosh J , Berg CA
Published: March 2009

A new experimental technique is presented for studying the toughness of anisotropic plane bodies. The technique is based upon the Path Independent Integral concept (Rice, 1968) where a strain energy distribution is line-integrated (via a string of strain gages) along a convenient path which yields the singular behavior of the cracked body. The use of this technique is demonstrated for an isotropic (aluminum) plate and an orthotropic (fiber glass/epoxy) composite with favorable agreement with the analytical and numerical (finite elements) counterpart solutions.
Path Dependence of the J-Integral and the Role of J as a Parameter Characterizing the Near-Tip Field
Authors: McMeeking RM
Published: March 2009

The J-integral has significant path dependence immediately adjacent to a blunted crack tip under small-scale yielding conditions in an elastic-plastic material subject to mode I loads and plane-strain conditions. Since the J-integral, evaluated on a contour remote from the crack tip, can be used as the one fracture-mechanics parameter required to represent the intensity of the load when small-scale yielding conditions exist, J retains its role as a parameter characterizing the crack-tip stress fields, at least for materials modelled by the von Mises flow theory. Some results obtained using both the finite-element method and the slip-line theory are suggestive of a situation in which an outer field parameterized by a path-independent value of J controls the deformation in an inner or crack-tip field in which J is path dependent. The outer field is basically the solution to the crack problem when large deformation effects involved in the blunting are ignored. Thus, the conventional small-strain approaches in which the crack-tip deformation is represented by a singularity have been successful in characterizing such features as the crack-tip opening displacement in terms of a value of the J-integral on a remote contour. An interesting deduction concerns a nonlinear elastic material with characteristics in monotonic stressing similar to an elastic-plastic material. Since J is path independent everywhere in such a material, the stress and strain fields near the crack tip in such a material must differ greatly from those arising in the elastic-plastic materials studied so far. This result is of significance because it is believed that such nonlinear elastic constitutive laws can represent the limited strain-path independence suggested by models for plastic flow of polycrystalline aggregates based on crystalline slip within grains.
Fracture Analysis Under Large-Scale Plastic Yielding: A Finite Deformation, Embedded Singularity, Elastoplastic Incremental Finite-Element Solution
Authors: Atluri SN , Nakagaki M , Chen W-H
Published: March 2009

The potential of the well-known J-integral as a fracture initiation criterion has been demonstrated in recent experiments by Begley and Landes and others. This paper deals with a numerical procedure for the estimation of J-integral and for arbitrary strain-hardening materials, in general situations of ductile fracture under large-scale yielding conditions. A finite-deformation analysis is employed to study the effects of crack-tip blunting. An incremental “tangent modulus” finite-element method has been used to account for both the geometric nonlinearity and the elastoplastic strain-hardening material behavior. A kinematic hardening law was used to describe the incremental plastic flow. Strain and stress singularities, corresponding to the material model, have been embedded in finite elements near the crack tip. Displacement and traction continuities between these near-tip elements and the surrounding elements have been enforced through the hybrid-displacement, finite-element model. This numerical procedure has been used to solve the case of a three-point bend specimen of Ni-Cr-Mo-V steel for which experimental results are also available. Excellent correlation between the present results and available experimental results has been established for the J versus δ (load-point displacement) relatinships. To characterize the effect of crack-tip blunting, the present example also has been solved using a small-deformation theory, and solutions are compared with those from the present finite-deformation analysis. The implication of the results in predicting crack-growth initiation and its stability in ductile materials is discussed. By using the modified definition of J-integral as valid for finite deformation, it has been found that approximate path independence of J is maintained, accurately, even for a contour closest to the crack tip.
Correlation Between the Fatigue-Crack Initiation at the Root of a Notch and Low-Cycle Fatigue Data
Authors: Baus A , Lieurade HP , Sanz G , Truchon M
Published: March 2009

Fatigue-crack initiation was investigated by testing high-strength steels (AFNOR 35 NCD 16 and 35 CD 4) with 0.6-in. (15-mm) thick ASTM compact specimens having various notch-root radii between 0.003 in. (0.07 mm) and 0.04 in. (1 mm).

Measuring devices were used to detect flaws with a surface area of only a few square millimetres in their propagation planes.

In order to calculate the number of cycles required to initiate a crack, notch root behavior was investigated through several parameters. − ΔK/ √ρ, from linear-elastic fracture mechanics, which concentrate results when the initiation time is large; − KfEP, an experimental parameter derived from low-cycle fatigue data when Ni<105 cycles. In this case, the ratio between theoretical and experimental values of the initiation time is between one and two for a given nominal stress.
Stress-Corrosion Crack Initiation in High-Strength Type 4340 Steel
Authors: Clark WG
Published: March 2009

The stress-corrosion, crack-initiation properties of two high-strength (180 ksi, 1240 MPa and 215 ksi, 1480 MPa yield strength) American Iron and Steel Institute type 4340 steels were evaluated with blunt-notch test specimens exposed to hydrogen sulfide (H2S) gas (that is, an accelerated test environment). Results show that the initiation of a stress-corrosion crack from a blunt notch depends primarily upon the notch-tip strain which, in turn, can be related to the elasticity calculated maximum notch-tip stress and the notch-tip radius. A test method and analytical procedure is proposed which can be used to predict the critical strain required to develop stress-corrosion cracking at a blunt notch.