bluuebunny/crossref_metadata_2025 huggingface dataset:
Subsized Bend and Charpy V-Notch Specimens for Irradiated Testing
Authors: Lucas GE , Odette GR , Sheckherd JW , McConnell P , Perrin J
Published: December 2008

Characterization of the fracture resistance of structural materials from specimens small in volume is an essential element of fission and fusion reactor design and alloy development. In this study ⅓-sized Charpy V-notch specimens and small bend bars ranging in thickness down to 2.5 mm have been investigated. Techniques have been developed for fabricating these specimens and testing them over a temperature range of 170 to 590 K under static and dynamic conditions. Tests have been performed to extract fracture mechanics parameters (KIc, JIc) and fundamental material parameters (e.g., micro-cleavage fracture stress σ*f) and to examine behavior anticipated in thin wall ferritic structures at temperatures corresponding to the lower shelf.
Specimen-Size Considerations in Crack-Arrest Testing of Irradiated RPV Steels
Authors: Marschall CW , Rosenfield AR , Landow MP
Published: December 2008

Few crack-arrest data are available for irradiated reactor pressure vessel steels, in part because the specimens commonly used to investigate crack-arrest behavior are relatively large (200 mm square by 50 mm thick). This paper addresses the question of specimen-size requirements for crack-arrest testing of irradiated RPV steels and offers several recommendations with regard to specimen size, specimen design, and testing procedures for efficient utilization of the limited space available in irradiation capsules.
The Need for Rapidly Solidified Powder Metallurgy Aluminum Alloys for Aerospace Applications
Authors: Quist WE , Lewis RE
Published: December 2008

A need exists within the aerospace industry for the engineering properties promised by aluminum alloys produced by rapid solidification technology (RST). The extent to which these alloys will achieve technical and commercial success depends, however, upon (1) achievement of the engineering property goals, (2) the degree of success in the development of competitive materials, including other aluminum products, and (3) the economics of using such alloys for any given application, including the total production, fabrication, and life cycle costs for the material. Useful applications of the new RST aluminum alloys are envisioned for each of the three primary groups of aerospace vehicles: aircraft, missiles, and space vehicles. Each of these groups has a different general set of material property and cost objectives. The current powder metallurgy (PM) aluminum alloy development efforts for aerospace applications can be divided conveniently into three categories or classes of alloys: (1) high-strength, corrosion-resistant alloys; (2) low-density, high-modulus alloys; and (3) elevated-temperature, creep-resistant alloys. The development objectives for each of these alloy categories depend on the specific needs of the aerospace market for that category. The current status of progress in the development of the RST aluminum alloys indicates that some technical and economic success will be achieved in each category. The extent of this success is yet to be established. An assessment of various factors that affect the future course of development for these materials is presented.
Microstructural Scaling Laws for Dendritically Solidified Aluminum Alloys
Authors: Glicksman ME , Singh NB
Published: December 2008

Studies have been conducted on the kinetics and morphology of dendrite formation in model systems over a range of supercoolings. The evolution of microstructure from the nascent dendritic state can be quantified through a series of scaling laws based on such fundamental considerations as heat and solute transport and interfacial dynamics. A brief review is presented of the salient ideas that explain dendrite formation as an interfacial stability. The influence of parameters of the materials on the microstructures of aluminum alloys versus those of the experimentally studied model systems will be discussed, along with the effects of certain processing parameters such as supercooling, supersaturation, or cooling rate. The key requirements for suitable organic models of aluminum solidifcation are that they possess cubic centrosymmetry (face-centered cubic or body-centered cubic), relatively low surface energy anisotropy, and molecularly rough solid/liquid interfaces to avoid facet formation and large departures from local equilibrium. The major microstructural relationships developed from our studies show that the initial branching, which eventually establishes the scale of microsegregation, is simply a multiple of the dendrite tip radius, which, in turn, depends on the local cooling rate and on certain groupings of the thermophysical constants.
Stereological Characterization of Porous Microstructures
Authors: DeHoff RT
Published: December 2008

The evolution of microstructure during powder consolidation consists of the disintegration of a connected network of porosity into separate parts, which ultimately disappear, and the integration of a grain boundary network from initially separated fragments into a connected network, which coarsens. The path by which these two processes develop depends upon the initial powder and its stack, the processing sequence, and the competition of various transport processes that produce microstructural changes. The properties of the material depend upon its final structure, which is the end point of the evolutionary path.

Stereology provides the means for characterizing the geometric properties of microstructures along the paths of evolution of the pore and grain boundary networks.

This paper reviews both the levels of description of the microstructural state and the principles involved in describing the evolution of the microstructural state during processing. These principles are illustrated with applications to evolving porous structures.
Hardening Mechanism in Rapidly Solidified Al-8Fe Alloy
Authors: Dermarkar S
Published: December 2008

Increased microhardness in rapidly solidified Al-Fe alloys is usually interpreted by means of extended solubility of iron atoms in the aluminum matrix and solid solution hardening. Transmission electron microscopy observations, however, frequently reveal the presence of aggregates of an intermetallic microcrystalline phase in the as-solidified specimens. Depending on the segregation scale of the phase, Jones identified higher microhardness areas (A type) and lower microhardness areas (B type). This paper provides a more detailed description of melt-spun and air-atomized microstructures of Al-8(weight percent)Fe alloys by optical and analytical electron microscopy. Significant increases in A-type microhardness result from decreased size in the phase aggregates. The hardening mechanism is consistent with an Orowan model of dislocation looping around incoherent and nonshearable precipitates. From a grain morphology standpoint, a columnar and an equiaxed zone can be distinguished. The metastable solidification paths leading to their formation are briefly discussed.
Rapid Solidification and Subsequent Analysis of Some Hypereutectic Aluminum-Based Alloys
Authors: Zindel JW , Stanley JT , Field RD , Fraser HL
Published: December 2008

A number of hypereutectic aluminum-based alloys have been prepared using rapid solidification processing. Two types of studies have been made, each involving a different set of alloy compositions. The first experiment was concerned with determination of the change in microstructural morphology of rapidly solidified Al-Ni alloys as a function of solute concentration. The results obtained for both laser surface melting and melt spinning were essentially identical in that there is a marked variation in microstructure for nickel concentrations in the range of 4.5 to 8.0% (atomic percent). The occurrence of these various microstructural morphologies has been interpreted on the basis of local interface undercooling and an asymmetrically disposed region of coupled growth. The second experimental approach involved a comparison of the responses of Al-4.1Fe-0.6X (indicated in atomic percent), where X was either molybdenum or cerium. The microstructure of the rapidly solidified molybdenum-containing alloy was found to be identical to that of the binary Al-4.7Fe and consisted of a cellular morphology with randomly distributed refined intercellular particles. The cerium-containing alloy also exhibited a cellular morphology, but the intercellular regions seemed to contain two phases, the first being the same as that found in the binary and molybdenum-containing alloys and the second tentatively identified as an oxide based on cerium. The microstructural changes and hardness variations have been determined as a function of aging at temperatures up to 773 K.
Ultralow-Density, High-Modulus, and High-Strength RSP Al-Li-Be Alloys
Authors: Vidoz AE , Crooks DD , Lewis RE , Palmer IG , Wadsworth J
Published: December 2008

Aluminum-lithium-beryllium alloys have been prepared by melt spinning, using prealloyed arc-melted buttons. The alloy ribbon was comminuted and cold compacted to 30 to 50% density, vacuum hot pressed to 100% density, and extruded. The bar product was subsequently solution heat treated, quenched, and aged. The microstructure of the alloys consists of a relatively featureless matrix containing a homogeneous dispersion of fine beryllium particles, mostly 50 to 500 nm in size. The results of heat treatment show that the alloys respond to age hardening in a manner similar to that of binary Al-Li alloys. Preliminary results on the mechanical properties and their relationships with microstructural features are presented for the Al-Li-Be alloys, as well as their potential for weight savings. The authors estimate that these monolithic aluminum alloys may exhibit specific strength and elastic modulus values comparable to those of the best whisker or particulate metal-matrix composites, while showing concomitant high weight savings.
Microstructure/Mechanical Property Relationships for Various Thermal Treatments of Al-Cu-Mg-X PM Aluminum Alloys
Authors: Blackburn LB
Published: December 2008

The thermal response and aging behavior of three 2XXX-series powder metallurgy aluminum alloys have been investigated, using Rockwell B hardness measurements, optical and electron microscopy, and energy-dispersive chemical analysis, in order to correlate microstructure with measured mechanical properties. Results of the thermal response study indicated that an increased solution heat treatment temperature was effective in resolutionizing large primary constituents in the alloy bearing more copper but had no apparent effect on the microconstituents of the other two. Aging studies conducted at room temperature and at 120, 150, and 180°C for times ranging up to 60 days indicated that classic aging response curves, as determined by hardness measurements, occurred at lower aging temperatures than were previously studied for these alloys, as well as at lower aging temperatures than are commonly used for ingot metallurgy alloys of similar compositions. Microstructural examination and fracture surface analysis of peak-aged tension specimens indicated that the highest tensile strengths are associated with extremely fine and homogeneous distributions of θ′ or S′ phases combined with low levels of both large constituent particles and dispersoids. Examination of the results suggest that refined solution heat treatments and lower aging temperatures may be necessary to achieve optimum mechanical properties for these 2XXX series alloys.
Characterization of Al-Fe-Ce Alloys
Authors: Langenbeck SL , Cox JM , Simenz RF
Published: December 2008

Characterization of Al-Fe-Ce alloys has been conducted in the areas of static and fatigue mechanical property behavior, corrosion behavior, and joining and fabrication methods. Evaluation of the elevated-temperature powder metallurgy materials, which were fabricated by the Aluminum Company of America (Alcoa) under Air Force Contract No. F33615-81-C-5096, was performed on both extruded and sheet products. The constant-amplitude fatigue and crack growth properties of these alloys are similar to those of 7091-T7E69 aluminum; however, no effect of R-ratio on fatigue crack growth was observed in the Al-Fe-Ce alloys. The corrosion resistance of the Al-Fe-Ce alloys is superior to that of other aluminum alloys, such as Alloys 7075, 2024, and 6061, under all conditions evaluated to date. Adhesive bonding, ultrasonic weldbonding, and spot welding have been demonstrated to be viable joining techniques. This research has helped to establish an initial data base on the Al-Fe-Ce alloys. Continuation of these studies will lead to application of these alloys, primarily as replacements for titanium.
Rationale for Data Collection and Interpretation in the Northern Lakes Long-Term Ecological Research Program
Authors: Kratz TK , Magnuson JJ , Bowser CB , Frost TM
Published: December 2008

The Northern Lakes Long-Term Ecological Research Program has three general goals: (1) to detect long-term changes in physical, chemical, and biotic features of lakes, (2) to understand linkages among water and sediment chemistry, hydrology, climate, and biology, and (3) to detect lake features associated with stability and resilience to natural and human disturbance. To accomplish these goals we selected eight northern Wisconsin lakes for semi-intensive study. These lakes lie in the same local groundwater flow system and include oligotrophic, mesotrophic, and dystrophic types. To meet the first goal we have established an ongoing sampling program to provide seasonal or annual estimates of important physical (including light penetration and heat budgets), chemical (including nutrients, pH, alkalinity, and major cations and anions), and biotic (including phytoplankton, zooplankton, macroinvertebrates, and fish) parameters. Frequency and timing of measurements are designed to allow comparisons among lakes, seasons, or years. In addition, we are making long-term comparisons of recent data with those collected from the same lakes by Birge and Juday in the 1930's. To accomplish the second goal we have instituted a series of shorter term, process-oriented studies designed to describe mechanisms of interaction among system parts and to help us refine our sampling protocol. To meet the third goal we are involved in a whole-lake acidification experiment and in ecological studies of invading fish and crayfish.
Sampling Effort Required to Find Rare Species of Freshwater Mussels
Authors: Kovalak WP , Dennis SD , Bates JM
Published: December 2008

Several approaches for determining the sampling effort required to find rare species of freshwater mussels were examined. Methods based on the relationship between number of species and number of individuals collected may provide a basis for estimating sampling effort, but more research is required to verify their applicability. Collections of dead shells (from lake shores or river banks) cannot be used because dead shells do not accumulate in proportion to the occurrence of five specimens in adjacent waters. Methods based on quantitative sampling are most promising. However, several methodological problems must be overcome to make quantitative sampling cost-effective.

A tentative protocol for searching for rare species is presented. A preliminary survey using qualitative methods is used to determine the distribution of mussels in a habitat. These data are used to stratify the habitat for quantitative sampling, preferably using quadrats. The number of samples taken depends on the scope of the study. Sample number may be set by some predetermined target density that must be detected or by funding.
Characterizing the Influence of Natural Variables During Environmental Impact Analysis
Authors: Brown RT , Dycus DL
Published: December 2008

Biological field sampling can be expensive, time consuming, and the results highly variable. A major goal of ecological data collection should be to obtain maximum information from each series of biological samples. Major factors regulating sampled populations must be identified if impacts are to be discriminated from effects of natural environmental variations.

There are often meteorological, hydrological, and water quality (physical-chemical) data available from nearby locations which can be used to describe the aquatic conditions between sample dates. This paper describes a methodology for using environmental data to better understand changes in biological populations by characterizing variations in natural factors.

Environmental factors which influence sampled organisms are examined to determine naturally occurring spatial gradients throughout the study region and temporal changes during the period of study. These environmental data are used to examine observed differences in sampled populations relative to natural environmental fluctuations. The methodology is demonstrated with environmental data used in the interpretation of phytoplankton samples. Recommendations are made for improving ecological data collection programs to allow analyses of impacts relative to natural environmental variations.
Developing a Sampling Strategy
Authors: Cairns J , Pratt JR
Published: December 2008

Sampling decisions must emphasize not only data collection and analysis, but also data use in decisions made for protection and management of aquatic ecosystems. Although data gathering is often the main focus of an investigation, it only provides the opportunity for generating information. The quality of this information is dependent upon the method of data acquisition and analysis, and the effectiveness of the decision made depends on the entire process—not only sampling. The basic problem with analyzing aquatic ecosystems is their complexity which may not be adequately displayed if the sampling program is not carefully designed. Furthermore, even the most effectively designed program may not achieve the desired objectives if the sampling program design does not recognize the way the information will be used. This paper discusses the limitation of common experimental designs and sampling methods including the use of structural and functional measures, the sampling of natural and artificial substrates, and use of appropriate statistical tests. Certain sampling regimes, including sampling over a single annual cycle, may underestimate ecosystem variability. The use of artificial substrates for collections may be misleading if the behavior of the substrate over time is not understood. Nevertheless, artificial substrates may show greater replicability and reliability than collections from naturally heterogeneous substrates. Generators of information should understand the uses that will be made of the data and that the limitations of the data should be understood by those who must make decisions with it. A simple checklist is provided for use of investigators to ensure adequate preparation of hypotheses, selection of sampling methods, and use of statistical tests.
History of Vascular Graft Development
Authors: Callow AD
Published: December 2008

Synthetic vascular grafts developed beginning in the 1950s as a consequence of observations of Voorhees in the late 1940s and early 1950s that a synthetic fabric made from Vinyon “N” became coated with a smooth, relatively nonthrombogenic surface when implanted in the dog's aorta. Earlier efforts to modify human and other mammalian aortas — denaturation, freeze drying, and the like, were unsuccessful because of gradual breakdown and aneurysm formation. Desirable qualities of a graft included that it was bloodtight after interstitial clotting, would have an adequate pore size to permit fibroblast reorganization, be conformable to the tissues around it, and would be biologically inert. Great success was achieved with such grafts in large diameter arteries with high flow rates and low resistance, but satisfactory grafts for smaller vessels have been disappointing because of incomplete healing in the human. All synthetic grafts and modified grafts of biologic origin fail to develop an endothelial lining. Anastomotic hyperplasia, chiefly of smooth muscle cells, gradually reduces flow, leading to retrograde thrombosis and failure. For better grafts to be developed, a greater understanding of the cellular, humoral, and enzymatic aspects involved in graft/host healing mechanisms in the circulating blood/graft interface is necessary.
Endothelial Cell Seeded Synthetic Vascular Grafts
Authors: Stanley JC , Graham LM , Burkel WE
Published: December 2008

Seeding of synthetic vascular grafts with enzymatically derived autologous endothelial cells in canine and baboon experimental models results in early development of an antithrombogenic lining. Investigators from ten different institutions have published results of research on graft endothelialization. Linings of seeded grafts have been proven to be endothelium by electron microscopy as well as immunofluorescent microscopy using factor VIII-related antigen. The endothelial surface produces prostacyclin. Endothelial cell-seeded grafts, in contrast to unseeded grafts, have less affinity for platelet attachment, as demonstrated by lesser graft imaging using In111 labeled platelets, longer platelet survival times, reduced thrombogenicity at low flow rates, and improved patencies. The efficacy of this technology in clinical settings has not been defined.
Lower Extremity Revascularization with the Glutaraldehyde Stabilized Human Umbilical Cord Vein Graft
Authors: Dardik H
Published: December 2008

The introduction of new graft materials for vascular reconstruction has rekindled interest in patency rates and the long-term morphologic changes that occur after implantation. Our experience with glutaraldehyde stabilized umbilical vein grafts has provided an opportunity to examine some long-term clinical implants and derive information based upon prior laboratory evaluations and current clinical experiences. Glutaraldehyde stabilization of the preimplant graft results in retention of the original architecture, including the inner elastic lamina that is responsible for the thromboresistance of the deendothelialized flow surface. Results of surface energy studies showed that the umbilical vein maintains values in the biocompatible zone, 2.5 ± 0.5 MN · m (25 ± 5 dynes · cm), even after chemical processing and implantation. Internal reflection spectroscopy confirms that lipid deposition occurs but is quantitatively related to systemic progression or stability of the atherosclerotic process. Angiography up to four-years postimplantation shows no significant degree of biodegradation, but in some instances, irregularity of the surface is present, perhaps being related to graft lengthening. Aneurysmal deterioration is uncommon. Other changes that occur, such as lipid imbibition, probably reflect the metabolic status of the host more so than the graft itself. Cumulative graft patency and limb salvage rates additionally confirm the value of the glutaraldehyde stabilized umbilical vein graft as an alternative to the saphenous vein. Compromise of morphologic and biophysical durability reflects host metabolic factors, surgical technique, and inadequacy or reversal of aldehyde cross-links.
Small Caliber Vascular Grafts—Alternatives
Authors: Wright CB , White RA , Hiratzka LF , Morin RP , Mitts DL
Published: December 2008

This paper reviews the authors' work with experimental silicone rubber and polyurethane replamineform small caliber vascular grafts. Description of the method of preparation of prostheses and in vivo implantation results is presented.
Properties and Characteristics of Bioprosthetic Grafts
Authors: Baier RE
Published: December 2008

Bioprosthetic grafts are combinations of synthetic and natural materials intended to serve as high-integrity blood conduits when the ideal natural arterial substitute is not available. This article focuses on those combinations of tissue and synthetic materials, usually stabilized with some cross-linking reagent, that are meant to function from the instant of implantation as thromboresistant conduits inciting minimal reactions on their blood flow surfaces while also fostering integration with the surrounding host tissue. Several major problems associated with bioprosthetic grafts are discussed, as well as their advantages.
Porosity Testing of Polyester Vascular Grafts
Authors: Botzko KM
Published: December 2008

Water porosity testing of vascular prostheses is used by the manufacturer as a measure of quality control. It is also used by the surgeon to indicate ease of preparation and preclotting of the prostheses. The test was initially derived as a modification of the air porosity testing which is commonly done by textile manufacturers. Although porosity testing has been common for about 20 years, the equipment is not fully standardized and varying results are quoted by different laboratories. The results of a round robin test are presented as well as a series of experimental studies in which test parameters were deliberately varied. The effects of pretensioning prosthesis specimens while mounting, presoaking specimens, as well as the effect of orifice size and the duration of flow were studied. These studies revealed that pretensioning of the specimens had the largest effect on the porosity results. The second most significant factor was the time elapsed between the initiation of flow and the measurement of porosity. The significance of these variations in porosity in the clinical setting are also discussed.
Studies on the Healing of Human Vascular Grafts: Quantitative Analysis of Collagen and Collagen Types
Authors: Anderson JM , Hering TH , Suzuki Y
Published: December 2008

Tissue encapsulating Dacron® vascular prostheses recovered from humans were extracted and analyzed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis to determine the distribution of genetically distinct collagen types. Type V collagen was in maximal concentration in extracts of tissues nearest to the prosthesis lumen. The pattern of distribution of collagen types across the prosthesis wall may be due to the influence of modulating factors originating in the blood flowing through the prosthesis, and factors produced by inflammatory cells chronically present at the tissue-biomaterial interface. We postulate that the macrophage may play a key role in determining the composition and organization of the pseudointima of human vascular grafts and the neointima in vascular grafts in animals. We suggest that the increased proportion of Type V collagen at or near the lumen contributes to the relatively nonthrombogenic properties of human pseudointima.
Biochemistry of Seeded Endothelial Cells
Authors: Sharp WV , Schmidt SP , Hunter TJ
Published: December 2008

The beneficial effect of seeding endothelial cells on synthetic vascular conduits has been well established by Herring, Graham, Schmidt, and others. This report discusses the biochemical production and interaction of the prostaglandins, prostacyclin (PGI2) and thromboxane (TXA2). A series of animal implantations was carried out with seeded and nonseeded grafts. Animals were medicated with cyclooxygenase inhibitors and TXA2 synthase inhibitors. Analysis was performed of PGI2 and TXA2 production on seeded and nonseeded grafts. Results of this analysis indicate: (1) seeded endothelial cells in Dacron® velour grafts can synthesize PGI2, (2) the levels of PGI2 from seeded endothelial cells are far less than the adjacent carotid artery, (3) the biochemistry of PGI2 production can be modulated by various antiplatelet agents, and (4) TXA2 synthase inhibitors improve thromboresistance of seeded grafts without significant effect on PGI2 production.
Aspects of Biodegradable Vascular Prostheses
Authors: Greisler HP , Kim DU
Published: December 2008

The clinical efficacy of vascular prostheses depends largely on the histologic and functional characteristics of its induced tissue reactions. Various woven and knitted absorbable and partially absorbable compound polymeric prostheses were implanted into rabbit aortas to evaluate the effect of the prostheses on the regenerative and functional capabilities of repopulating endothelial and smooth muscle-like cells. Specimens harvested to one year were evaluated grossly and by light and scanning and transmission electron microscopy, compliance studies, and 6-keto prostaglandin F1α (PGF1α) assays. Results suggest that certain polymers may activate macrophages to induce a transinterstitial migration and proliferation of primitive mesenchymal cells which differentiate into cells with ultrastructural and functional characteristics of smooth muscle-like myofibroblasts and endothelial-like cells. Dacron® appears to inhibit these regenerative activities actively. Following total prosthetic reabsorption, conduits regenerated over polyglactin 910 or polydioxanone prostheses produced 6-keto PGF1α and demonstrated strengths and compliances resembling normal aortic tissue. Clarification of factors controlling arterial regeneration should provide insights into the development of nonefficacious vascular prostheses and into the process of artherogenesis and myointimal hyperplasia.
Acellular Vascular Matrix as a Small Diameter Vascular Graft
Authors: Brendel K , Duhamel RC , Malone JM , Reinert RL
Published: December 2008

Extraction of soft tissues with detergents yield histoarchitecturally intact extracellular matrix frameworks of the original tissue. When applied to dog carotid arteries, this procedure results in acellular vascular matrix (AVM) tubes that retain the physical properties of the original artery. This material is less thrombogenic than a number of other graft materials. The internal diameter of greyhound AVM averages 3.0 mm under physiological pressure. Carotid interposition grafts of 10 cm of noncross-linked AVM exhibit an overall patency of 75% at 150 days. Cross-carotid grafts of 15 cm of noncross-linked AVM implanted for 18 months were fully endothelialized as shown by histology, scanning electron microscopy (SEM), and factor VIII staining.
Vascular Prostheses: Innovative Properties
Authors: Sawyer PN , Sophie Z , O'Shaughnessy A
Published: December 2008

Findings resulting from electro-chemical and biophysical studies of the vascular tree are correlated with the development of modern vascular prostheses, many of biologic origin. Multiple studies indicate that thrombosis in the vascular tree of mammalia obeys fundamental electrochemical laws. Experiments further reveal that electron giving and taking at 0 mV with respect to the normal hydrogen electrode via intermediate metabolism relates directly to platelet depositing and the incitement of thrombosis. This information permits a logical approach to the development of modern prosthetic grafts. The resulting vascular grafts—umbilical vein, modified mature collagen, and others—are described. The functional results following long-term implantation are summarized.
Report on Consolidation Behavior
Authors: Peters JF
Published: December 2008

The papers of the session discussed here deal primarily with the traditional role of consolidation theory in soil mechanics, that of controlling and predicting the volume change of fine-grained soils. Reclamation of soft ground, performance of soil-drain systems, behavior of man-made fill materials and industrial wastes, and problems in characterization of behavior of special soil types are addressed. With one exception, behavior as determined by laboratory-scale investigations is emphasized. This report is organized into three major themes: Compression Behavior, Performance of Drains, and Special Problems. The report concludes with a selection of topics for general discussion.
General Theory of Consolidation for Clays
Authors: Juárez-Badillo E
Published: December 2008

A general nonlinear differential equation for the one-dimensional consolidation of saturated plastic soils is presented. The variations of compressibility, of permeability, and of the coefficient of consolidation are taken into account. Application of the theory to the oedometer test, neglecting the submerged unit weight of the soil and assuming the change in thickness to be small, is made. The consolidation curves are found to depend on the ratio of the final to the initial thicknesses H2/H1 and on the ratio of the parameters λ/γ. Here λ = 1 − γκ, where γ and κ are the nonlinear coefficient of compressibility and the coefficient of permeachange, respectively. For the special case that the coefficient of consolidation is constant, λ = 0, the consolidation curves move somewhat (to the left for compression and to the right for swelling), more as the values of H2/H1 are smaller for compression or higher for swelling compared to unity, respectively. The effective stresses at any time and depth are smaller than those predicted by the linear Terzaghi's theory. The significance of the degree of consolidation given by Terzaghi's theory, for the case Cv = constant, is given introducing a nonlinear concept for U. For the general case that the coefficient of consolidation is not constant, λ ≠ 0, the corresponding consolidation curves are the subject of a companion paper.
Unsaturated Soil Consolidation Theory and Laboratory Experimental Data
Authors: Fredlund DG , Rahardjo H
Published: December 2008

The volume change process of an unsaturated soil was considered as a transient flow problem with water and air flowing simultaneously under an applied stress gradient. laboratory experiments were performed to study the volume change behavior of unsaturated soils. Several compacted kaolin specimens were tested using modified Anteus oedometers and triaxial cells. Theoretical analyses were also made to best-fit the results from laboratory experiments. The fitting was accomplished by approximating the compressibility coefficients and adjusting the coefficients of permeability. The comparisons of the results obtained from the theory and the laboratory yield to a similar behavior of volume changes with respect to time.
Compressibility and Settlement of Compacted Fills
Authors: Nwabuokei SO , Lovell CW
Published: December 2008

Settlement predictions are necessary for compacted fills under a variety of circumstances (e.g., when fills are high, where major structural loads are to be supported, and when the fill materials are clays or weak rocks). As a result of an extensive testing program on both laboratory- and field-compacted materials, a systematic approach to this prediction has been developed. The recommended procedure involves one-dimensional compression testing in three parts.

The initial vertical strains experienced by the compacted fill are those due to self-weight. The magnitudes of these are highly dependent upon the values of prestress established by the compaction process; however, they occur as rapidly as the fill can be built. The major vertical strains will probably occur as the fill becomes wetter and “softens” in service. The timing of this settlement is uncertain, because it depends upon climatic variables at the site. Materials in the upper portion of the fill will often swell under the low confinement, and the net movement is an appropriate summing of these events with the compressions that occur deeper in the fill. Assuming that the fill becomes essentially saturated in service, further settlements can be produced by loading of the saturated material. The latter response is conventional in nature.

By testing a series of specimens, with a range of confinements which match those which will be imposed by the prototype fill, representative vertical strains are defined. Integration of these strains over the fill height produces the prediction of movement for the upper surface of the fill. The total testing and prediction technique is illustrated in the paper by example.
Desktop Computer Application for Consolidation Testing and Analysis
Authors: von Fay KF , Byers JG , Kunzer BA
Published: December 2008

The use of desktop microcomputers for automatic data acquisition of consolidation test data and data analyses is discussed. The various electrical sensing devices used to measure several test parameters are briefly described. In addition to using the desktop computer for automatic data acquisition, a program was written to analyze the data using several classical empirical procedures. The Casagrande logarithm of time fitting method and the Cour inflection point method for computing Cv are used to analyze the time-dependent data. The Casagrande and Schmertmann construction techniques are used to analyze the time-independent data. Additionally, the density, water content, and degree of saturation of the specimen are determined throughout the test.
Influence of a Critical Gradient on the Consolidation of Clays
Authors: Dubin B , Moulin G
Published: December 2008

Several studies in the laboratory have shown the existence of a permeability law which is different from Darcy's law and which defines the flow of the pore water in certain natural clays.

Consolidation tests in the laboratory, including the measurement of permeability at different stages of loading, that were carried out on Saint Herblain clay at the E.N.S.M. Soil Mechanics Laboratory prove the existence of major critical gradients (12 < i0 < 20). According to this observation, a consolidation model worked out with a non-Darcian permeability law has been produced by means of a finite-difference computer program.

On the one hand, this model is compared with Terzaghi's consolidation model and, on the other hand, the law that has been established is tested next to the laboratory tests.
Conventional Consolidation Tests on Two Soils
Authors: Chakrabarti S , Horvath RG
Published: December 2008

The consolidation behavior of laboratory prepared “young” specimens of two clay soils, kaolin and Dundas soil, was examined using conventional consolidation tests. The specimens were prepared under either isotropic or K0 stress conditions. A fixed-ring type consolidometer was used for the tests. A 24-h loading time increment with a load increment ratio of 1.0 was used.

Test results indicate that the consolidation behavior of both soils was influenced by the past loading history and the test loading conditions. The soils were able to remember the past maximum stress.

Based on the test results, normalized e-σ‵v relationships are suggested for the two soils.
Lateral Strain Measurement by an Ultrasonic Method
Authors: Barański T , Wolski W
Published: December 2008

An ultrasonic method for the measurement of lateral strain of a soil specimen in triaxial tests has been developed. The measuring device combined with a triaxial cell consists of an ultrasonic detector and three ultrasonic heads which transform sound waves into electronic impulses. The ultrasonic wave, which penetrates into the triaxial cell, is reflected from the contour of the specimen, and comes back to the ultrasonic head. The measured values of lateral strains can be used not only for the evaluation of Poisson's ratio, but also for other parameters or functions required for different constitutive equations.
Determination of Consolidation Parameters by Selfweight Consolidation Test in Centrifuge
Authors: Takada N , Mikasa M
Published: December 2008

Consolidation parameters such as volume compressibility, mv, and permeability, k, of very soft slurry clay are difficult to obtain from a conventional oedometer test. A selfweight consolidation test in a centrifuge is available as an alternative test. The mv value is calculated from the f-log p relationship which is obtained from a correlation between volume ratio f and effective overburden pressure along the specimen depth after self-weight consolidation, and k is obtained from the initial settlement rate of a singly drained selfweight consolidation test. Some examples of determination of these parameters are shown for four highly plastic clays. The effect of particle segregation on these parameters in a high centrifugal acceleration field is also discussed.
Centrifugal Evaluation of a Time-Dependent Numerical Model for Soft Clay Deformations
Authors: Mitchell JK , Liang RYK
Published: December 2008

A series of centrifuge tests on embankment-type soil structures founded on soft clay is being conducted to evaluate a time-dependent constitutive model that incorporates the combined effects of creep and hydrodynamic consolidation. Because final coding of this new constitutive model has not yet been completed, a two-dimensional consolidation program (CON2D, developed by Chang and Duncan) is being used for preliminary analysis of test results. This paper describes the building, testing, and monitoring of the centrifuge models. The results of the centrifuge tests are interpreted and shown to compare well with predictions made using the CON2D computer program.

Centrifuge testing is a valuable method for investigating the accuracy and usefulness of new soil behavior models, particularly in the absence of or as a supplement to detailed field records. The testing limitations imposed by centrifugal environment—the radical acceleration field and “curved” stress distribution—are examined. Stress histories and stress paths experienced by the centrifuged model are shown accountable in the numerical analyses. Data generated in this testing program can provide a reference for evaluating other constitutive relations or numerical models, thus assisting further development of predictive analytical techniques.
Centrifuge Consolidation Study for Purposes of Plasticity Theory Validation
Authors: Shen CK , Sohn J , Mish K , Kaliakin VN , Herrmann LR
Published: December 2008

The experimental phase of the research described in the paper involves a centrifuge model study of consolidation and surface settlement of a storage tank located on a soft soil foundation during a filling-storage-emptying cycle. The tank is placed on a thin layer of sandfill over a weak and compressible deposit of clay soil. The clay deposit is formed by consolidating a kaolin slurry in a 40.6-cm-diameter circular mold which is subsequently moved to the centrifuge for further consolidation and “field stress” initiation. The combined processes of consolidation cause the clay deposit to form an overconsolidated layer in the upper portion and a normally consolidated layer below. This situation simulates conditions often encountered in nature. Pore water pressure transducers are embedded in the clay deposit to monitor the rise and dissipation of water pressure as a result of loading and unloading. Furthermore, the surface settlement profile of the tank bottom is measured using a number of optical-electrical displacement transducers.

The second phase of the study involved a comparison of finite-element predictions with the experimentally measured quantities. These comparisons are part of a validation study for the recently developed bounding surface plasticity model for cohesive soils. The model is calibrated using the results of standard laboratory triaxial tests for the soil in question. A system of Fortran subroutines to numerically evaluate the model has been developed and incorporated into 2-D and 3-D finite-element consolidation programs. In this study the 2-D program is used to predict the soil response for comparison with experimental results. The predicted pore water pressures and surface displacements are presented and compared with the measured values. The agreement between the pore pressure values is very good while for the displacement it is adequate.
Effectiveness of Prefabricated Drains on Laboratory Consolidation of Remolded Soils
Authors: David Suits L , Gemme RL , Masi JJ
Published: December 2008

The Soil Mechanics Bureau of the New York State Department of Transportation has carried out an extensive testing program over the past two years to determine the relative effectiveness of several types of prefabricated “wick” drains in the laboratory and field environments. The test program and results, along with discussions, and the relationship of the test results to theoretical field performance are presented in this paper.
Bolted Composite Repairs Subjected to Biaxial or Shear Loads
Authors: Bohlmann RE , Renieri GD , Riley BL
Published: December 2008

The methodology to analyze bolted composite repairs subjected to biaxial or shear loads was developed. The methodology was incorporated into an existing McDonnell Aircraft Company (MCAIR) interactive computer program, BREPAIR, which was initially developed for uniaxial loading. The analysis determines bolt loads while accounting for hole clearances and determines patch and laminate strains for doubly symmetric finite regions where the damage is represented as a circular cutout. The analysis was verified by comparing predicted results to industry-recognized solutions for laminates containing circular holes (unrepaired), and to test results of an unrepaired and repaired shear panel. Results of this investigation verified that the methodology developed was a viable analytical tool for determining bolted repair designs for damaged laminates subjected to biaxial or shear loads.
Modified Mircodebonding Test for Direct In Situ Fiber/Matrix Bond Strength Determination in Fiber Composites
Authors: Mandell JF , Grande DH , Tsiang T-H , McGarry FJ
Published: December 2008

This paper describes a test method for determining the in situ fiber/matrix bond strength of composites. In a sequence of steps, a compressive load is applied to individual fibers oriented normal to a polished surface, and the interface is observed microscopically between loading steps, until debonding occurs. The direct result of a test is the force to produce debonding of a particular fiber. The data are reduced to a nominal interfacial shear strength through a finite-element analysis using a simplified model of the fiber, surrounding matrix, and uniform composite properties beyond the matrix. Bond strength results for a variety of composites range from 23 MPa for E-glass/polyester to 86 MPa for T300/5208 graphite/epoxy. The results are consistent with data available from other test methods.
Bond Thickness Effect in Adhesive Joints and Its Significance for Mode I Interlaminar Fracture of Composites
Authors: Chai H
Published: December 2008

The effect of constraining the crack-tip damage zone on the Mode I fracture of a toughened epoxy resin (BP-907) was studied systematically using the double-cantilever-beam (DCB) adhesive joint specimen and scanning electron microscopy (SEM). While a broad bond thickness range was employed (5 < t < 875 µm), particular attention was given to the lower bond spectrum and to the applicability of the results to interlaminar fracture of toughened composites.

Depending on t, interesting fracture characteristics were found including continuous, unstable, and a combination of both types of growth. For t > 33 µm the fracture energy exhibited dramatic variations with t that were shown to follow from the variations in size of a certain dimple-like morphological feature. In constrast, the arrest energy was fixed, in consistency with the unchanging morphology. The fracture behavior for t < 33 µm was equally interesting, now though because GIC was fixed while GICa varied with t. These changes in failure conditions were accompanied by morphological changes; as t decreased from 33 µm, the failure locus shifted from the bond center to the metal/matrix interface, and the failure itself occurred by shear yielding.

Similarities were found in the failure conditions of butt joint and DCB adhesive specimens, on the one hand, and in that of the latter and composite interlaminar fracture, on the other hand, which suggest an interrelationship among these three failure phenomena.