bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Crack Growth Behavior and Life Predictions for 2219-T851 Aluminum Subjected to Variable-Amplitude Loadings
Authors: Chang JB , Engle RM , Stolpestad J
Published: March 2009

Fatigue crack growth behavior of 2219-T851 aluminum is characterized for variable-amplitude loading conditions which include the single and periodic tensile or compressive overload, single tensile overload followed by a single compressive load, multiple tensile and compressive overloads, high-low or low-high block loading, and compression-compression loads followed by tension-tension loads. A load interaction model which accounts for the overload retardation and compressive load acceleration effects on fatigue crack growth lives is introduced. Fatigue crack growth analyses are performed on all test cases using a computer program which employs this load interaction model. Analytical predictions are correlated with the test data. Results show that this model adequately predicted fatigue crack growth behavior and fatigue crack lives for most of the test loading conditions to within ±30 percent.
A Simple Crack Closure Model for Prediction of Fatigue Crack Growth Rates Under Variable-Amplitude Loading
Authors: de Koning AU
Published: March 2009

A model for the prediction of growth rates of fatigue cracks in aluminium alloys is presented. The model is based on an approximate description of the crack closure behavior and can be used to predict effects of crack growth acceleration and retardation observed experimentally under variable-amplitude loading.

A computer program was developed for analysis of fatigue crack growth. It was used to analyze the effect of certain parameter variations in a flight simulation load spectrum on the crack growth rate. For 7075-T6 thin sheet material the results are compared with experimental data.
Some Problems in the Application of Fracture Mechanics
Authors: Clark WG
Published: March 2009

In addition to the widely recognized continuum mechanics restrictions associated with the use of fracture mechanics, there are a number of problems and areas of concern that even arise in the application of the technology to actual situations. These problems range from the development of adequate material properties data to the analytical and defect characterization aspects of the technology. Some of these problems are identified and discussed with regard to their potential impact on structural life predictions and quantitative risk analyses. Material characterization problems associated with data scatter, prior loading effects, and time-dependent behavior are included along with the consideration of the probability of flaw detection and the analysis of small defects and interacting flaws. Suggestions and recommendations for experimental work required to resolve these problems are included.
Effect of Cyclic Frequency on the Corrosion-Fatigue Crack-Initiation Behavior of ASTM A517 Grade F Steel
Authors: Taylor ME , Barsom JM
Published: March 2009

This study was conducted to investigate the effect of cyclic frequency on the corrosion-fatigue crack-initiation behavior in regions of stress concentration in ASTM A517 Grade F steel. The tests were conducted on notched compact tension specimens at a stress ratio of 0.1 in a room-temperature 3.5 percent solution of sodium chloride. The test results showed that the corrosion-fatigue crack-initiation life under full immersion conditions was significantly less than the fatigue-crack-initiation life in air. Moreover, the test results showed no effect of cyclic frequency in the range of 12 to 300 cpm on the corrosion-fatigue life. The data indicate the possible existence of a corrosion-fatigue crack-initiation limit, below which cracks did not initiate, at a ΔK/√ρ of about 172 MPa (25 ksi). This value of ΔK/√ρ corresponds to a maximum stress range, Δσmax, of about 207 MPa (30 ksi) and is one-fourth the value for the fatigue-crack-initiation limit in air.

Fatigue-crack-initiation tests results on precorroded notched specimens showed a 25 percent reduction in the fatigue-crack-initiation limit. This decrease was attributed to an increase in the stress concentration caused by corrosion pits on the surface of the notch radius.

Metallographic investigations showed that corrosion-fatigue cracks initiate at corrosion pits on the surface of the notch tip. These cracks initiate as microcracks that form by a sharpening of the corrosion-pit tip under the combined influence of the environment and cyclic loads. No relationship was found between microstructure and corrosion-pit sites.
Evaluation of Fly Ash Leachability Using Batch Leaching Procedures
Authors: Sack WA , Boomer BA , Tarantino JT , Keefer GB , Seals RK , Miller M
Published: March 2009

The leachability of two fly ashes was evaluated using two different proposed procedures environmental Protection Agency-Extraction Procedure (EPA-EP) and American Society for Testing and Materials method (ASTM). The EP test was also run to study the influence of contact time and the presence of dissolved oxygen. Finally, a modified EP was carried out with repeated extraction of the same ash with fresh leachate and repeated contact of the same leachate with fresh ash. Both acid and deionized water extractions were used.

The EP test was found to extract more material than the ASTM procedure on a milligrams per kilogram of ash basis, although the ASTM test gave higher concentrations. For the contact times studies (2 to 48 h), no one elution time could be chosen which would allow equilibrium for all parameters. Although certain elements evidenced sensitivity to the presence or absence of oxygen, no general pattern was found. Release during repeated extraction of the same ash with fresh leachate was found to be highly pH dependent. Most of the mobilization tended to occur in the first two extractions for the acid test, while release occurred more gradually for 5 to 7 elutions using deionized water.
Comparison of Three Solid Waste Batch Leach Testing Methods and a Column Leach Test Method
Authors: Jackson K , Benedik J , Jackson L
Published: March 2009

As a participant in the American Society for Testing and Materials (ASTM) program evaluating U.S. Environmental Protection Agency (EPA) and ASTM solid waste extraction procedures, the Laramie Energy Technology Center of the U.S. Department of Energy has been conducting a study comparing various aspects of batch versus column extraction techniques. This study evaluates three batch extraction methods and compares these results with results obtained from column leach tests.

A standard fly ash material was leached using three types of mixers, five liquid-to-solid ratios, and leach times ranging from 1 h to 96 h. The leachates were analyzed using an atomic absorption spectrophotometer equipped with a graphite furnace for the following metals: selenium, chromium, arsenic, lead, and cadmium. The pH was also determined on all the leachate samples.

The data show that the batch test can be improved by increasing the liquid-to-solid ratio. The data also indicate that the leaching time can be decreased. Comparison of the data from the batch and column leach tests indicates that a correlation may exist.
Comparison of Inductively Coupled Plasma and Atomic Absorption Spectroscopies for Determination of Twenty-five Elements in Fly Ash Leachate Solution
Authors: Drenski TL , Paxton CA , Varnes AW
Published: March 2009

Atomic absorption (AA) spectroscopy is the approved method for determining metallic and semimetallic elements in aqueous specimens. When many elements are required on a specimen, however, it is a tedious technique, because only one or two elements can be determined at a time. Inductively coupled plasma (ICP) emission speetroscopy, however, is capable of determining up to 50 elements in a single determination, printing out results in less than 2 min.

Data obtained in this study show that for compliance purposes, acceptable agreement is obtained between AA and ICP for 25 elements in fly ash leachate, a fairly complex matrix. Procedures are described for overcoming interference effects encountered in AA. An automated system for ICP is described briefly. Where significant differences were found between the techniques, possible causes and solutions are proposed.
Evaluation of Methodology for the Survey Analysis of Solid Wastes
Authors: Miller HC , James RH , Dickson WR , Neptune MD , Carter MH
Published: March 2009

This paper presents the results of an experimental program of evaluation of analytical methods for “total content” (survey analysis) of residual wastes. Candidate methods were first studied and modified, and then evaluated with the analysis of a variety of residual waste specimens and determination of a broad range of organic compounds and metals. The methods depend on extraction, gel permeation chromatography (GPC) cleanup, preconcentration, and gas chromatography/mass spectrometry (GC/MS) analysis for identification and quantitation of semivolatile organics; purge-and-trap and GC/MS for purgeable organics; and acid digestion combined with atomic absorption spectroscopy (AAS) or inductively coupled plasma emission spectroscopy (ICP) determinations for metals.

The results of the study are presented in terms of observed accuracy and precision and are based on statistical analysis of over 10 000 data points.
Testing of Materials for Use in the Lining of Waste Disposal Facilities
Authors: Haxo HE
Published: March 2009

The lining of waste disposal facilities with materials of low permeability is a feasible means of preventing potentially polluting constituents in wastes impounded on the land from seeping out of the impoundment and entering the groundwater. A great array of materials, including fine-grain soils and clays, asphaltic compositions, concretes, and polymeric membranes, are potential candidates for use as liners.

The use of materials for lining waste impoundments and disposal facilities is comparatively new, and experience in their field performance is limited. Considering the variety of lining materials that are available and the vast number of compositions of the waste streams that must be impounded, a body of test methods is needed to: (1) guide the selection of liners for specific applications, (2) assure that the quality of the liner that has been selected is placed on the site, and (3) monitor the condition of the liner during service.

This paper discusses the test methods that are currently available for use in liner technology, and describes an overall approach to the testing of liners, principally membrane liners. Emphasis is placed on tests needed for liner selection and impoundment design. Of particular interest are the descriptions of several tests designed to simulate the conditions of service of liners in actual waste impoundments. Data from two ongoing Environmental Protection Agency (EPA) liner research projects are presented to illustrate the tests that are described.
Preliminary Clinical Analysis of Mechanical Performance of the STH Titanium Alloy Total Hip Replacement
Authors: Zych G , Latta LL , Mnaymneh W
Published: March 2009

Total hip replacement has been performed with the STH titanium alloy femoral stem at the University of Miami School of Medicine consistently since 1976. During the period of 1976 through 1980, eight different staff surgeons and many residents operated on 154 patients and performed 178 total hip replacements utilizing this device. A retrospective analysis of hip replacements in 52 patients from this group who could be adequately followed is reported, utilizing subjective and objective measures of early results. The prosthesis was designed to prevent fracture of femoral component stems, decrease proximal lysis of the femur, decrease femoral component loosening, and provide a prosthesis that could be easily implantable while maintaining good reconstructive procedure about the hip. Since the implementation of the first prosthesis questions about the use of such a design have been raised regarding the vulnerability of titanium to wear and the vulnerability of the proximal cement around the titanium stem to premature failure. The short-term clinical and radiographic results were comparable to those of other series of more conventional total hip replacements. The mechanical reconstruction of the hip and cement failure were comparable, and lysis of the proximal bone was favorably comparable to early results of previous series. Concerns about abnormal wear cannot be supported by the in vivo data in this study.
Porous Titanium Alloy for Prosthesis Attachment
Authors: Wheeler KR , Karagianes MT , Sump KR
Published: March 2009

Void metal composite (VMC) is a porous metal developed to fix a prosthesis to bone by tissue ingrowth. The material is made by techniques which produce structures with controlled porosity, density, and physical properties. The ability to produce a range of structures creates opportunities to study the effects of pore size, shape, and density on bone-metal interface strength.

Ti-6Al-4V is the metal of choice for VMC. This titanium alloy was selected for its corrosion resistance, good mechanical properties, low density, and good tolerance by body tissue. Structures with spherical pore sizes ranging from 275 to 650 μm have been fabricated, with up to 80 percent theoretical densities. Cylindrical pores with controlled direction and arrangement were also produced. The optimum structure for attachment strength seems to be a pore size of 450 μm and 50 percent theoretical density.

Titanium alloy porous implants are well tolerated by body tissue. Intramedullary pins having up to 18 months' implant time and dental implants having 4 years' implant time show development of strong bonds to bone with no adverse tissue reaction.
On the Off-Axis and Angle-Ply Strength of Composites
Authors: Kim RY
Published: March 2009

This paper is concerned with the static strength of off-axis and angle-ply laminates under uniaxial tension and compression. The experimental data were compared with the tensor polynomial failure criterion, assuming the interaction term based on the Von Mises yield criterion for the isotropic materials. The curing residual stresses are also included in the strength analysis for the angle-ply laminate. The fracture surface was examined using a scanning electron microscope and the results are discussed in conjunction with the failure theory.
Buckling of Composite Cylinders Under Combined Compression and Torsion—Theoretical/Experimental Correlation
Authors: Herakovich CT , Johnson ER
Published: March 2009

Elastic buckling loads for laminated composite circular cylindrical shells subject to combined compression and torsion are determined experimentally. Test specimens include both boron/epoxy and graphite/epoxy laminates with symmetric layups of [∓45]s, [−452/452]s, and [0/±45/90]s, and with the unsymmetric layup of [−82.5/30/20/−82.5]. Results are presented on dimensionless buckling interaction diagrams on which the compression load ratios versus torsional load ratios at buckling are plotted. Theoretically predicted buckling loads for the test specimens obtained from a computer program based on Flügge's cylindrical shell buckling equations are also plotted on the interaction diagrams. Good comparison between experiment and theory is achieved when the results are plotted on the interaction diagrams.
Statistical Design and Analysis of an Interlaboratory Program on the Fatigue Properties of Welded Joints in Structural Steels
Authors: Haibach E , Olivier R , Rinaldi F
Published: March 2009

The constant-amplitude fatigue behavior of welded joints in two types of normalized structural high-strength steel has been studied in an interlaboratory program within the European community. The statistical design and analysis of a part of that program is described. This part was aimed at establishing complete S-N curves for three types of fillet welded joints with reference to a comprehensive statistical test plan. The test plan closely linked the activities of six laboratories involved in testing and three welding institutes fabricating the specimens under specified conditions, and it organized the repartition of the specimens to the stress levels to be applied and to the laboratories. Some restrictions, however, were imposed on the test plan due to limitations in test load capacity in some of the laboratories and to limitations in time and costs.

The results were evaluated according to the concept followed in planning, using various methods of analysis that were outlined and compared in treating the 753 test results available and in deducing characteristic figures of the fatigue strength at 2·106 cycles. The assumption of a “uniform” slope of S-N curves for welded joints in structural steel proved to be reasonable. Moreover, it was possible to analyze the additional variability of the results caused by sharing the tests at each stress level among several laboratories or caused by fabricating equal portions of the specimens in three welding institutes.
Distillate Fuels from Nonpetroleum Sources
Authors: White EW
Published: March 2009

Among the samples examined in a U.S. Navy investigation of alternative fuels for ship propulsion were 15 distillates derived from oil shale, coal, and tar sands. The chemical and physical properties of these distillates were similar in many respects to those required by specifications for gas turbine fuels. In this paper, the chemical and physical properties of the 15 distillates are compared with those required by the ASTM Specification for Gas Turbine Fuel Oils (D 2880-82) for Grades 1-GT, 2-GT, 3-GT, and 4-GT gas turbine fuels, as well as with military specification requirements and published commercial fuel properties. Differences have been noted in properties not controlled under ASTM Specification D 2880-82, and supplemental specification requirements for alternative fuels will probably be needed. The aromatics content, nitrogen content, and other property differences stemming from the raw material source affect the handling, storage, and combustion of the fuel. Low heats of combustion, low smoke points, and poor storage stability have been observed for some of the distillates, and these properties may be dependent on the degree of refining, particularly of hydrogenation, that the distillate undergoes in its manufacture. The author has concluded that fuels meeting the current requirements for the various grades of ASTM Specification D 2880-82 gas turbine fuels can be made from liquids derived from coal, oil shale, and tar sands. However, for the satisfactory performance of such liquids, the specification requirements will have to be augmented by limitations in the composition or in related properties, such as smoke point and stability.
Coal Gasification for Stationary Gas Turbine Applications
Authors: Goyal A , Fleming DK , Bair WG
Published: March 2009

Various types of coal gasification processes which are available commercially or in the developmental stage are reviewed. The properties of the gaseous fuels produced by different gasifiers are discussed. Gas cleanup systems that are adaptable for turbine applications are presented, and factors influencing process selection are outlined.
Measurement Techniques for Fuel Stability Characterization
Authors: Cummings AL , Pei P , Hsu SM
Published: March 2009

A measurement technique has been developed to characterize the oxidation stability of liquid fuels under various conditions. The technique is based on high-pressure differential scanning calorimetry (DSC). It is shown to be sensitive to the chemical compositions of some fuels, including shale-derived jet fuel and a marine diesel fuel. These fuels were subsequently fractionated according to molecular type using liquid chromatography. Using the procedure developed, the oxidation characteristics of the fuel fractions were examined. The results suggest that the different amounts of the various molecular types present in different fuels may affect the overall stability of the fuels.

The DSC technique offers many advantages in terms of precision and sample size requirement, as well as in the number of parameters measured.
Cytotoxicity Testing: Prediction of In Vivo Toxicity from In Vitro Tests
Authors: Genova TF , Bodnar S , Vaccarella M , Stafford C , Schady KM
Published: March 2009

Tissue culture laboratories can play key roles in the development and evaluation of products. Three broad categories of materials are evaluated: new product components (polymers, fabrics, and adhesives), candidate packaging materials (papers, plastics, coatings, and inks), and existing products undergoing stability studies. Material cytotoxicity is evaluated with mouse fibroblasts (L-929) using several standardized tests: agar overlay, elution assay, and direct growth assay. The severity of specimen testing is governed by the intended use of the material. Testing severity decreases in order of the following end use categories: implantations, limited patient contact, indirect patient contact, and no patient contact.

Sample cytotoxicity is compared with that of standard, calibrated controls. Controls are formulated such that they evoke minimal responses in United States Pharmacopeia toxicity tests. Each lot of control material is certified via in vivo analysis before being used in cell culture. Control responses in vitro are then used to predict in vivo toxicity. Since the control is known to evoke a minimal in vivo response, its cell-culture response may be assumed to be equivalent to that of minimal in vivo toxicity. It is assumed that any material having a cell-culture response greater than the control will be toxic when tested in vivo. Studies are underway to further refine the correlation between in vivo and in vitro test methods.
Cell-Culture Cytotoxicity Testing of Candidate Device Materials
Authors: Meyers SG , O'Connell MB , Korczynski MS
Published: March 2009

In vitro cytotoxicity evaluation of candidate materials for medical devices is described. Materials and material extracts are added to freshly seeded human embryonic lung fibroblast (IMR-90) cell cultures. Both negative control and positive control materials are included in each evaluation of test materials. The negative control material does not cause detectable cytotoxicity to the cell system, and the positive control material causes cytotoxic effects.

Controls are used to monitor the cell system over time and detect any changes in the system that would alter the testing results. Results are scored on the basis of degree of morphological deterioration of cells and time required to obtain maximum deterioration. Candidate materials are evaluated comparatively in terms of their relative lack of cytotoxic effects on cell culture. Final results are not interpreted on a pass/fail basis but in terms of which materials are most likely to demonstrate biocompatibility in vivo.

This paper also reviews the need to develop specific cell-culture cytotoxicity assays on the basis of the intended end use of the material being evaluated. Some historical information concerning endothelial cell-culture systems and the need to develop a standardized cytotoxicity assay for blood contact materials is reviewed.
In Vitro Toxicity Testing: A Quantitative Microassay
Authors: Ulreich JB , Chvapil M
Published: March 2009

In vitro methods for testing the toxicity of biomaterials have many advantages over in vivo tests. They are more sensitive, simpler, more reproducible, rapid, inexpensive, easily duplicated, adaptable, and conservative of test materials. The microassay in use in our laboratory has the additional advantages of being quantitative, not requiring extensive microscopic observation or the presence of materials that may themselves be toxic (for example, agar and dyes), measuring parameters of cellular activity other than cell death, and being suitable for screening of a large number of specimens. The material to be evaluated, or in the case of insoluble materials an extract of the material, is incubated on monolayers of fibroblasts in 24 well culture plates. The activity of the fibroblasts is ascertained by measuring the rate of incorporation of 3H-thymidine, 35SO4, or 3H-tryptophan. By proper choice of label, the effect of the biomaterial on cellular proliferation or production of macromolecules or both may be assessed. Materials that are cytotoxic cause inhibition of incorporation of radioactive label in the assay. Cell monolayers are also inspected microscopically for evidence of cytotoxicity. Examples are given to demonstrate use of the microassay.
Tests of the Enhancement of Avian Repellent Chemicals with Sensory Cues
Authors: Bullard RW , Schafer EW , Bruggers RL
Published: March 2009

Spray applications of nonlethal repellents are often effective means of protecting maturing agricultural crops from bird damage. Repellents are generally classified as either primary, in which case the animal reacts to the noxious effects of the chemical alone, or secondary, in which case conditioned aversion responses are induced. Secondary repellents more reliably resist high bird depredation of these crops over time. Unfortunately, most pest bird species are not able to detect some secondary repellents at levels which induce conditioned aversion. Thus, higher levels must be used than are actually needed for crop protection. One alternative to this dilemma has been the incorporation of an inexpensive sensory cue (for example, calcium carbonate) into the formulation to replace some of the repellent and reduce crop protection costs. Methiocarb [3,5-dimethyl-4-(methylthio)-phenol methylcarbamate (Mesurol)], currently the most effective avian repellent for field crops, has been the model chemical for testing the action of secondary repellents at the Denver Wildlife Research Center. This paper presents a general review of laboratory and semifield tests used to evaluate various methiocarb-cue (olfactory, tactile, and visual) formulations on both quelea (Quelea quelea), a destructive African pest, and red-winged blackbirds (Agelaius phoeniceus), a problem species in the United States. Single-choice and paired-preference test methods used on wheat, rice, millet, sorghum, and sunflower in individual cages and group enclosures and conducted under conditions of varying palatability in the alternate food are described. Appropriately designed tests to answer specific questions will lead to further advancements in effectively using chemical repellent-cue combinations for protecting crops from bird pests.
Estimating Bird Damage to Sprouting Rice
Authors: Otis DL , Holler NR , Lefebvre PW , Mott DF
Published: March 2009

Sampling procedures are described for assessing bird damage to sprouting rice. Optimum sampling schemes are derived for both large-scale surveys and controlled experimental research from data collected from a 1980 controlled experiment and a 1981 survey. A basic recommendation is that each field be sampled by using a stratified or systematic design, depending on the objective of the specific study. Sampling points consist of paired plots, one of which is protected from bird damage by a wire exclosure, that are located on transects placed randomly across the field. Methods are derived for calculating the number of plots per transect and the number of transects necessary to achieve a given level of precision or to maximize precision for a given cost. A stratified design is also proposed for conducting large-scale surveys, and recommendations are given concerning the required number of fields for a desired precision.
A Test Protocol for Assessment of Primary Poisoning Hazard to Ground-Feeding Birds from Broadcast Pelletized Rodenticides
Authors: Merson MH , Byers RE , Kaukeinen DE
Published: March 2009

A test protocol was developed after the large-pen field study guidelines suggested by the U.S. Environmental Protection Agency to assess potential primary poisoning hazard to birds from broadcast pelletized rodenticides used in orchards. The test employed six pen-reared ring-necked pheasants (Phasianus colchicus) confined in each of twelve stationary 0.0047-ha pens. The pens were erected over ground cover similar to that in an adjacent orchard. The bait material was broadcast in the pens at zero (control), one, two, or ten times a base rate. The pheasants were maintained on a grain and seed mixture, which was broadcast into the pens. The advantages of the test protocol and the rationale for some of its features are discussed.
A Method for Inferring the Taste Qualities of Rodenticides to Rodents
Authors: Stewart CN , Reidinger RF , Mason JR
Published: March 2009

A method recently developed for the study of animal psychophysics was adapted for use in inferring the taste characteristics of rodenticides, as perceived by rodents. The method is based on generalization of learned food aversions to other materials having similar tastes. The potential of the method was illustrated in two experiments. In Experiment 1, five specimens of Rattus norvegicus (Sprague-Dawley) were conditioned to avoid the taste of strychnine (alkaloid) by pairing brief exposures to the strychnine with intraperitoneal injections of lithium chloride (LiCl). In subsequent 15-min drinking tests, the rats avoided mainly quinine sulfate and sucrose octaacetate [but not sodium chloride (NaCl) or hydrochloric acid (HCl), and sucrose only slightly] when compared with control rats. These results were confirmed in Experiment 2, and results from this experiment also indicated that sodium bicarbonate was not an effective agent for masking the taste of strychnine (that is, four rats conditioned with strychnine containing sodium bicarbonate still avoided quinine sulfate, compared with control rats in subsequent drinking tests, and four rats conditioned with only strychnine avoided quinine sulfate containing sodium bicarbonate in subsequent drinking tests). We suggest that the method has potential for use in assessing taste characteristics of rodenticides, as well as such bait additives as taste enhancers and masking agents, to rodents.
Fatigue Crack Initiation by Cyclic Slip Irreversibilities in High-Cycle Fatigue
Authors: Mughrabi H , Wang R , Differt K , Essmann U
Published: March 2009

Dislocation mechanisms of fatigue crack initiation in high-cycle fatigue are formulated, with special consideration given to those material properties which determine the cyclic slip mode. The models developed are related to pertinent experimental observations, referring mainly to copper mono- and polycrystals fatigued at room temperature. In particular, the following topics are considered: (1) the origin of cyclic slip irreversibilities in the bulk and near the surface, (2) computer simulations of surface roughening by random irreversible slip processes in planar- and wavy-slip materials, and (3) fatigue crack initiation by cyclic strain localization in persistent slip bands (PSBs) in mono- and polycrystalline wavy-slip materials. The evolution of the surface profile at emerging PSBs is described by a new semiquantitative model which is compared with other models. The model distinguishes between the rather rapid formation of extrusions and the more gradual development of surface roughness. It is shown that specific predictions regarding differences between PSB surface-profiles in mono- and polycrystals are borne out fully by the observations. In the case of copper polycrystals, the experiments show that PSBs are not only responsible for slip-band cracking in PSBs but also induce intergranular cracks. A model is proposed according to which cracks initiate as a result of the piling-up of PSB-matrix interface dislocations against the grain boundaries. Furthermore, the supporting role of environmental interaction and/or deformation-induced diffusion and grain boundary sliding is discussed.
Effect of Microstructure on Fatigue Crack Propagation: A Review of Existing Models and Suggestions for Further Research
Authors: Baïlon J-P , Antolovich SD
Published: March 2009

Systematic improvements in the fatigue crack propagation (FCP) properties of metal alloys through combinations of heat treatment, processing, and composition control depend on identifying the basic processes and parameters that are involved. Towards that end, numerous models have been developed. These models generally fall into three classes: (1) macroscopic, in which bulk properties are used to fit a modified Paris equation; (2) microscopic, in which dislocation deformation processes are incorporated into a criterion for crack advance; and (3) low-cycle fatigue (LCF) based, in which crack propagation is assumed to result from failure of a microscopic LCF ligament defining a process zone directly ahead of the propagating crack. This paper reviews the basic assumptions underlying these models. Their implications are discussed and compared with experimental data, both numerical and microstructural. Various experimental procedures are reviewed and some suggestions are made for research that could be used to verify the validity of these models.
Fatigue Crack Tip Strains in 7075-T6 Aluminum Alloy by Stereoimaging and Their Use in Crack Growth Models
Authors: Davidson DL , Lankford J
Published: March 2009

Detailed quantitative measurements of crack tip strains have been made for near-threshold fatigue cracks in 7075-T6 aluminum specimens grown in a vacuum environment. In addition, crack tip opening displacements and crack growth rates have been measured. These data are used in three related models which examine cumulative and critical strain and critical energy dissipation as criteria for crack advance. These models are then examined in light of observed crack growth patterns.
Crack Tip Geometry for Fatigue Cracks Grown in Air and Vacuum
Authors: Bowles CQ , Schijve J
Published: March 2009

Plastic castings of fatigue cracks were produced by a process of vacuum infiltration and subsequently examined in a scanning electron microscope. Study of the castings revealed that the crack tip geometry in the 2024-T3 and 7075-T6 alloys was essentially the same. Crack advance in air is initially “brittle” in both alloys, with the crack tip subsequently blunting to an elliptical geometry at maximum load. Brittle crack extension presumably results from tensile rupture due to the presence of water vapor. At minimum load the crack tip has been resharpened but remains generally elliptical and singly notched.

In contrast, crack advance in vacuum appears to result solely from slip activity in the absence of any active species to promote failure by tensile rupture. Crack branching is believed to be a significant means of accommodating plastic flow near the maximum of the load cycle. The crack front itself appears to be highly disorganized due to crack propagation at different levels and on different slip systems in adjacent grains of the polycrystalline materials.

Castings of air fatigued specimens also shed some new light on plasticity just behind the crack tip and on contact between the two fracture surfaces during crack closure at a larger distance behind the crack tip.
Comparison of Fatigue Damage in Stable and Unstable Stainless Steels
Authors: Schuster G , Altstetter C
Published: March 2009

As a result of the stress-induced martensitic transformation of certain austenitic stainless steels their fatigue behavior is modified. A number of experimental techniques have been applied in order to understand why this occurs. The methods used include metallography of various types, electron diffraction, magnetic permeability, and local mechanical property determination. The advantages and disadvantages of the various techniques are discussed, and by a combination of techniques various hypotheses to explain the fatigue phenomena are examined and reinforced or rejected. It is concluded that the volume expansion resulting from the phase transformation causes a favorable residual stress state at the crack tip.
Analysis of Silvered Glass Reflectors Exposed to Controlled Environments
Authors: Masterson KD , Lind MA
Published: March 2009

This paper describes a matrix approach to testing mirrors (MATM) for solar concentrator applications. Specimens are exposed to elevated temperatures, high humidity, ultraviolet light, thermal cycling, atmospheric pollutants, and mechanical stresses at levels greater than those encountered in natural weathering but low enough that the degradation modes are expected to be similar to those observed in naturally weathered mirrors. The degradation of mirror performance is characterized by its reflectance. Microphotography and light-scattering measurements reveal defects in the silver layer.

In the initial phase of the research, specimens of commercially available wet chemical processed silver/glass mirrors were exposed for up to eight weeks at 80°C and 80 percent relative humidity (RH) and at 80 percent RH with a temperature cycle of 20 to 80 °C. A degradation in hemispherical reflectance of 15 percent and a tenfold increase in light scattering were observed for the least durable mirror types tested. The growth of defects causing light scattering is evident in the dark-field microphotography.

Removing the specimens, characterizing them optically, and returning them to the chambers did not alter their degradation rates in comparison with those of the specimens left undisturbed for equivalent exposure. Specimens subjected to temperature cycling between 20 and 80 °C showed less drop in reflectance than specimens left at high temperatures for equivalent exposure periods. However, temperature cycling caused severe edge corrosion in some mirror types. The differences in degradation rates between the specimen sets enabled a rank ordering of performance to be made. The precision of all the optical measurements was much greater than the specimen-to-specimen variation in the degradation rates. Hemispherical and diffuse reflectance measurements, especially at wavelengths less than 500 nm, provide a good means for assessing the degradation of silver/glass mirrors.
Package Development from the Pesticide Industry Viewpoint
Authors: McGreevy JP
Published: March 2009

An outline of the general activities and concerns associated with package development for agricultural chemicals is given: Storage stability studies are initiated at accelerated and normal warehouse conditions, with the prospective product packaged in various candidate containers. Subsequent chemical and physical evaluations are conducted. Compatibility with materials of construction of application equipment is examined. Various pieces of laboratory test equipment, used in package development and later for quality control, are discussed. The impact of future performance-oriented package specifications, instead of current U.S. Department of Transportation detailed construction requirements, is considered. The use of the laboratory transportation simulator is outlined. Palletization and various packaging regulations are important aspects of package development. The end result of various tests and considerations is a satisfactory specification and package.
Pesticide Packaging Container Standards—Sizes and Fittings
Authors: Giammanco J
Published: March 2009

The purpose of this paper is to present the current standards and practices for steel shipping containers and their interfacing with closed system application equipment for liquid pesticides. The paper highlights existing standards and regulations which currently govern steel shipping containers. In addition, there is a summarization of a study done for the U.S. Environmental Protection Agency (EPA) which deals with the impact on chemical manufacturers and formulators of containers and closure standardization for Category I (highly toxic) liquid agricultural pesticides. Additional factors that affect pesticide packaging containers and their compatibility with existing closed system equipment are also discussed in light of the conclusions presented by the EPA study.
Determination of the Presence of Antistripping Agents in Asphalt Cement by High-Performance Liquid Chromatography
Authors: Gilmore DW , Weisman MR , Dalter RS , Kugele TG
Published: March 2009

Chemical agents are often introduced into asphalt for the purpose of influencing the performance of bituminous concrete. The presence of these added chemicals can serve to complicate already difficult methods for asphalt compositional analysis. A description of high performance liquid chromatography (HPLC) techniques that aid in identifying antistripping additives in asphalt is presented. The method is sensitive to both the additive and the asphalt. The utility of HPLC as a probe in investigating the effects of thermal conditioning on asphalt/additive combinations is demonstrated.
Normalized Characterization Model of Pavement Materials
Authors: Baladi GY , Vallejo LE , Goiton T
Published: March 2009

The principal objective of any pavement design procedure is to provide a structural system that will be suitable in a specific regional area and be able to sustain the anticipated traffic loading and frequency. The accomplishment of this objective and the utilization of the design procedure is highly dependent on its ability to predict future pavement performance. The success of such prediction is a function of the pavement model used and the relevancy and accuracy of its input parameters.

This paper presents and discusses the results of extensive laboratory investigations and an analytical study of permanent deformation model of several unbound materials. The developed model screens and normalizes the effects of several specimen and test variables. The model was found to be unique for each class of soil and independent of compaction, density, water content, and stress level. A significant finding of this study is that the permanent strain of any class material subjected to cyclic loading could be calculated, with high confidence level, using the developed predictive normalized model.
Determination of Resilient Properties of Unbound Materials with Diametral and Cyclic Triaxial Test Systems
Authors: Hsu S-Y , Vinson TS , Hicks RG
Published: March 2009

Repeated load diametral test systems are experiencing increased use to determine resilient properties of asphalt concrete and admixture stabilized materials. For these materials, the resilient properties obtained with the diametral test systems compare favorably to properties determined with conventional repeated load triaxial test systems. To date, repeated load diametral test systems have not been used extensively to determine the resilient properties of unbound materials. This is due, in part, to the fact that comparative studies between the properties obtained with the diametral test systems and the repeated load triaxial test systems have not been made. In response to the need to establish a correlative data base between resilient properties determined with repeated load diametral and triaxial test systems, a laboratory test program was conducted. Specifically, resilient properties of two base-course and two cohesionless-subgrade soils were determined using both repeated load triaxial and diametral test systems. The resilient properties of duplicate specimens (with respect to water content, dry density, and method of compaction) were compared over a range of stress conditions. The resilient properties determined with either the repeated load diametral or triaxial test systems were approximately equivalent. The maximum differences between resilient moduli for comparable states of stress were ±80%. Correlations between resilient moduli can be only made for a specific material at a given water content, dry density, and method of compaction. It was not possible with the data set developed in the study to establish general correlation factors between resilient properties determined with diametral or triaxial test systems.
Design of Desert Sand-Sulfur-Bitumen Mixes
Authors: Singh G , Al-Ausi MJ
Published: March 2009

Results of the first stage of a continuing research into design and characterization of dune type sand-sulfur-bitumen mixes are presented. The work is designed to complement and supplement efforts by other researchers in this field so as to produce recommendations for design of pavements. Rheological properties of binders with a wide range of sulfur to bitumen ratios have been measured for 60–70 penetration and 85–100 penetration bitumen. The mixes were made up of poorly graded fine sand with binder contents of 5.5 to 8.0% by weight. Compactibility of these mixes was studied using the Gyratory Testing Machine, and the cured specimens were tested for Marshall stability and flow values.
Design and Structural Condition Evaluation of a Cold Recycled Pavement
Authors: Bandyopadhyay SS
Published: March 2009

A section of highway K-96 in western Kansas, 0.8 km long, was cold recycled in August 1979. Three different rejuvenating agents were mixed in different proportions with the reclaimed material and the physical and structural properties of the cold mix were evaluated. From the test results, a concentration of about 18% ARA-1, based on asphalt content of the reclaimed material, was found to be optimum. Asphalt properties of the mix before, during, and after construction are presented. The construction method used for the in-place cold recycling process is described. A 305-m conventional hot-mix overlay section and a 152.5-m cold recycled section with no additive were included in the project for comparative evaluation purposes. Dynaflect deflection measurements were periodically obtained to evaluate the performance of the test sections. Preliminary analyses indicate that structural performance of the section with no rejuvenating agent is slightly superior to the conventional overlay section and a cold recycled section with ARA-1. Savings in energy and cost favor in-place cold recycling over hot recycling processes or conventional hot mix overlay procedures.
Characterization of Flexible Pavement: A Case Study
Authors: Baladi GY
Published: March 2009

The degradation and the damage state of a flexible pavement section may be attributed to several factors. These include environmental factors, traffic loading factors, and material interaction and variability factors. The collective conditions of a pavement section in a particular damage state may be called pavement damage index (PDI). Such a damage index is related to the pavement deflection output.

This paper discusses the characteristic parameters of the pavement time-dependent deflection response and their relationship to the damage done to the flexible pavement section in question. Further, a case study is presented where a full-depth asphaltic highway pavement section was tested after construction and before it was subjected to any traffic loading. The calculated characteristic parameters of the time-dependent deflection response indicated, at the time, that a severe damage in the form of permanent deformations (rut depth) should be expected when the pavement section is opened to traffic. The highway section in this case study experienced a rut depth of up to 25.4 mm (1 in.) after only six months of mixed traffic (trucks and cars).