bluuebunny/crossref_metadata_2025 huggingface dataset:
A CTOD-Based Mixed-Mode Fracture Criterion
Authors: Ma F , Deng X , Sutton MA , Newman JC
Published: March 2009

This paper presents a mixed-mode fracture criterion that uses the crack-tip opening displacement (CTOD) at a fixed distance behind the crack tip as the fracture parameter. This criterion is developed based on a detailed analysis of crack kinking in arbitrary directions. In essence, the proposed criterion states that crack growth occurs when the current CTOD reaches a critical value and the direction of crack growth is the direction that causes either the opening or the shearing CTOD component at the new crack tip to be the absolute maximum. Under linearly elastic conditions, it is shown that this criterion is equivalent to several commonly accepted mixed-mode criteria and predicts that crack growth will occur in a locally Mode I manner. Under elastic-plastic conditions, the mixed-mode CTOD criterion predicts that crack growth will be along either a local Mode I or a local Mode II direction. The prediction of the abrupt transition from Mode I-dominated crack growth to Mode II-dominated crack is in good agreement with the observation of the mixed-mode fracture test results from the Arcan specimens. Alternative forms or extensions of this criterion are also discussed.
Metallurgy, Microstructure, Chemistry and Mechanical Properties of a New Grade of Cobalt-Chromium Alloy Before and After Porous-Coating
Authors: Mishra AK , Hamby MA , Kaiser WB
Published: March 2009

Titanium alloy (Ti-6Al-4V) and cast cobalt-chromium-molybdenum alloy (CoCr) have a long history of successful clinical use. However, a higher strength material would be useful to manufacture certain implants, such as smaller hip-stems, with more extensive porous-coating to facilitate improved fixation. A new grade [high carbon (C), proposed grade 2] of CoCr, within the ASTM specification for wrought cobalt - 28 chromium - 6 molybdenum alloy for surgical implants (F 1537), has been developed to meet this objective. One producer's version of this new material was compared with cast CoCr. The typical C content of this material is similar to that of cast CoCr. In the mock-sintered condition, the tensile and yield strength of bar and forgings of this new CoCr were similar to each other and greater than that of cast CoCr, and all three materials had similar ductility. In both porous-coated and mock-sintered conditions, the average grain size of bar and forgings of this new CoCr was 63±19 to 145±12 μm, while that of two commercially available porous-coated cast CoCr hip-stems from two manufacturers was 2540±395 and 3394±876 μm respectively. Metallography revealed that the cast CoCr implants contain the eutectic phase [face centered cubic (fcc) Co, the intermetallic sigma (σ) phase, and metal carbides (M23C6 and M7C3)] in the interdendritic regions. The 10 million cycle fatigue strength was 207 MPa for cast CoCr and 241 MPa for the new CoCr bar in the porous-coated condition, and 345 MPa for cast CoCr and at least 448 MPa for the new CoCr bar in the mock-sintered condition. Fatigue testing was performed only on bar since the tensile properties and microstructure of bar and forgings were very similar, both in the porous-coated and the mock-sintered condition. Thus, the new grade of wrought CoCr exhibited higher fatigue strength than cast CoCr in both porous-coated and mock-sintered conditions. This may be attributed to the finer grain size of this material.
Metal-on-Metal Wear Testing of Co-Cr Alloys
Authors: Wang KK , Wang A , Gustavson LJ
Published: March 2009

The wear characteristics of various Co-Cr alloy combinations were studied using a reciprocating wear machine. Wear test specimens were made from three Co-Cr alloys, cast Co-Cr, low carbon wrought Co-Cr and high carbon wrought Co-Cr alloys. The cast Co-Cr alloy was evaluated in both the as-cast and the solution-treated conditions. All specimens were polished with a surface roughness in the range of 0.01–0.02 μm. The clearance in diameter between the convex and the concave specimens was 100 or 300 μm. The same test conditions were applied to all specimens. Results showed that the best alloy couple was as-cast Co-Cr on as-cast Co-Cr alloy and this couple was found to be superior to the high carbon wrought on the high carbon wrought couple. This finding is also supported by using a hip simulator wear test machine.
A Rapid Method for Generation of a Haigh Diagram for High Cycle Fatigue
Authors: Maxwell DC , Nicholas T
Published: March 2009

A rapid test method is described for generating data points for a Haigh diagram for Ti-6A1-4V at a constant life of 107 cycles at room temperature. It involves subjecting specimens to loading blocks of 107 fatigue cycles and progressively increasing the load until failure occurs. An equivalent stress is obtained for each test specimen for plotting on the Haigh diagram. The method is applied to tests conducted at stress ratios (ratio of minimum to maximum stress) from R=-l to R=0.9. The validity of the method is confirmed by comparing data with those obtained using the conventional S-N interpolation approach at values of R=0.1, 0.5, and 0.8. The rapid testing technique is then extended to the generation of a Haigh diagram for the same material subjected to prior low cycle fatigue (LCF) for ten percent of its LCF life. No degradation of the fatigue limit is observed from subsequent HCF testing using the rapid testing technique.
An Evaluation of the Adjusted Compliance Ratio Technique for Determining the Effective Stress Intensity Factor
Authors: Donald JK , Bray GH , Bush RW
Published: March 2009

In a common interpretation of crack closure, the crack is visualized as “peeling” open as stress is applied. This interpretation has led to the assumption that the driving force for crack propagation, ΔKeff, exists only when the crack tip is fully open (above K-opening). The current opening load method of closure measurement in accordance with ASTM Standard Test Method for Measurement of Fatigue Crack Growth Rates, Appendix X2 (E 647) is based on this concept. However, based on a comparison with “closure free” data, evidence of significant crack-tip cyclic strain below K-opening will be presented to show that the exclusion of this additional driving force can give misleading values of ΔKeff. This is so particularly in the near-threshold regime where opening loads are typically high. The new analysis technique for estimating ΔKeff is referred to as the adjusted compliance ratio (ACR) method and is based on an interpretation of crack closure as a stress redistribution (or load transfer) on a relatively compliant crack wake. The ACR method is evaluated using the results of fatigue crack growth tests on 6013-T651, 2324-T39 and 7055-T7751 aluminum alloys using both compact tension C(T) and middle crack tension M(T) specimen geometries. The results of this study indicate that ΔKeff obtained by the ACR method is relatively independent of measurement location, crack length and specimen geometry. Comparison of ΔKeff data obtained by both methods with “closure free” crack growth data obtained at high stress ratios indicates that the ACR method is superior to the ASTM opening load method in the near-threshold regime for estimating the “true” driving force for crack propagation.
Residual Strength Predictions for Multiple Site Damage Cracking Using a Three-Dimensional Finite Element Analysis and a CTOA Criterion
Authors: Dawicke DS , Newman JC
Published: March 2009

Fracture tests were conducted on 2.3 mm thick 2024-T3 aluminum alloy middle crack tension, M(T), compact tension, C(T), and multiple-site damage (MSD) specimens covering a wide range in specimen widths (30 to 610 mm). Three-dimensional, elastic-plastic finite element analyses were conducted for each experiment. A critical CTOA value of 5.25° was determined from a 152.4 mm wide C(T) fracture test and was then used to predict the fracture behavior of the other tests. The critical angle was within the scatter in the experimental surface CTOA measurements. All of the predicted failure stresses for the single crack specimens, except for the smallest C(T) and M(T) specimens, were within 5% of the experimental failure stresses. The CTOA criterion predicted stable tearing, link-up stresses, and maximum stresses to within 7% of the experimental measurements.
Effect of Collection and Handling Practices on Concentrations of Volatile Organic Compounds Detected in Soil Subsamples
Authors: Hewitt AD
Published: March 2009

The losses of trichloroethylene from soil samples transferred to and from a storage bottle were evaluated by comparing values obtained using standard techniques with values obtained using a method that limits sample disruption, exposure, and volatilization losses from a subsample after a single transfer step. Results strongly suggest that volatile organic compounds (VOCs) are readily lost from contaminated soils when care is not taken to limit surface area exposure and ensure subsample isolation. For this site investigation and others using similar sample-handling protocols, VOC losses are most abundant during field collection and storage.
Sorption Capacity of Ground Tires for Vapor-Phase Volatile Organic Compounds
Authors: Kim JY , Park JK , Edil TB , Jhung JK
Published: March 2009

Batch sorption tests were conducted to determine the partition coefficient of volatile organic compounds (VOCs) by ground tires. The partition coefficient in the vapor phase was estimated by dividing the partition coefficient in the aqueous phase by Henry's law constant. Under a diluted condition (<0.6 mM), VOCs are sorbed onto ground tires noncompetitively regardless of the existence of other VOCs. Polar compounds such as methylene chloride were less sorbed onto ground tires than nonpolar compounds. The vapor-phase partition coefficient was found to have a logarithmic relationship with the saturation vapor concentration. VOCs emitted from waste-water treatment facilities can be effectively retarded by the ground tires.
Determination and Comparisons of the Pore Structure of Nonwoven Geotextiles
Authors: Elsharief AM , Lovell CW
Published: March 2009

Microstructural properties of 14 nonwoven geotextiles obtained from 4 manufacturers were measured using mercury intrusion porosimetry (MIP) and image analysis. Different testing techniques were attempted and evaluated for the two methods. The controlled volume MIP option was found to suit geotextiles more than the pressure table option. For image analysis a one dimensional model was used to measure the pore size distribution from enlarged photographic prints of thin sections. The results from the two methods indicated similar pore size distribution for geotextiles from the same manufacturer with thickness being the major difference. However, significant differences in porosity and specific surface area between different geotextile manufacturers were obtained. The O95values obtained from image analysis and MIP were found to be much higher than the apparent opening size (AOS) and the filtration opening size (FOS) for the same geotextile.
An Empirical Approach to Filtration Criteria for Non-Woven Geotextiles
Authors: Chin YM , Nikraz HR
Published: March 2009

Many filter design criteria have been produced by various researchers. However, none of these criteria have been universally accepted to be the standard design method. In order to develop a reliable design criteria, an empirical design method was produced. The methodology adopted for this study consisted of the filtration test (long-term gradient ratio test), the hydrodynamic sieving test, and the image analysis test. In the filtration test, eight different soil gradings were tested with six sizes of non-woven needled-punched geotextiles to determine the compatibility of each soil/geotextile combination system. From the hydrodynamic sieving test and the image analysis test, the opening size distribution (OSD) was determined, including the influencing factor of a geotextile's compressibility. As soil characteristics can be determined from standard soil tests and knowing the geotextile's characteristics (OSD) together with the soil/geotextile compatibility, an empirical design method could be developed.
Metallic Contamination from Wafer Handling
Authors: Beaudoin F , Simard-Normandin M , Meunier M
Published: March 2009

The surface photovoltage (SPV) method is used to characterize metallic contamination introduced by wafer handling. It is shown that particles from handling equipment introduce significant levels of metallic contamination. In most cases the correlation between particle contamination and metallic contamination is excellent. We also find that metallic contamination can be introduced during handling in areas where no particles are detected. However, in order to take manufacturing decisions based on surface photovoltage data, one must understand the strengths and limitations of the technique and avoid its pitfalls.
Determination of Long-Lived Beta Emitters in Nuclear Waste by Inductively Coupled Plasma-Mass Spectrometry
Authors: Bienvenu PG , Brochard EA , Excoffier EA
Published: March 2009

Inductively Coupled Plasma-Mass Spectrometry (ICP-MS) constitutes a very attractive alternative to radiochemical techniques for the determination of long-lived radionuclides considered critical for the safety of nuclear waste repositories. By measuring isotopic abundance instead of ionizing radiation, it is shown that ICP-MS should exhibit lower detection limits than liquid scintillation counting for the measurement of β emitters with half-lives longer than ∼104 years. However, a specific preparative chemistry is generally required prior to measurement in order to separate the analyte from major radioactive contaminants and potentially interfering isotopes. Original methods we have recently developed for the determination of three long-lived β emitters: 93Zr, 107Pd and 135Cs in radioactive waste are described in this paper. The procedures involve various separative and measurement strategies, such as liquid-liquid extraction, Chromatographic separation as well as electrothermal vaporization coupled with ICP-MS. The performances are discussed in terms of selectivity and detection capabilities.
High-Precision Determination of 234U/238U Activity Ratios in Natural Waters and Carbonates by ICPMS
Authors: Ketterer ME , Khourey CJ
Published: March 2009

A method has been developed for precise measurement of 234U/238U activity ratios in natural waters and carbonates using quadrupole inductively coupled plasma mass spectrometry. A recovery of 80–85% of seawater U is achieved by Fe(III) coprecipitation followed by extraction chromatography with a supported dipentyl pentane phosphonate material; 90–95% of U is recovered from carbonates, which are are dissolved in HNO3 and subjected to the same extraction Chromatographic preparation. Isotopic measurements are made via recirculating pneumatic nebulization of small volumes of solutions containing 0.5–5 mg/L U. 234U/235U measured as a proxy for determination of 234U/238U; iridium is added to sample solutions and the ion ratio 191Ir40Ar+/193Ir40Ar+is measured for internal mass discrimination correction. 234U/238U activity ratios in the range 1.143–1.154 are observed for 13 seawater and contemporary corals, in agreement with the established marine 234U/238U activity ratio. For sample sizes of 5–25 μg U, ICPMS uncertainties of +/- 0.2–0.5 % relative, 2σ standard error, approach those obtained for < 0.1 μg U by thermal ionization mass spectrometry. Measurements of 234U/238U activity ratios in bottled waters, Lake Erie surface waters, mollusk fossils, and fertilizers are also demonstrated.
An Evaluation of Plasticity-Induced Crack Closure Concept and Measurement Methods
Authors: Newman JC
Published: March 2009

An assessment of the plasticity-induced crack closure concept is made, in light of some of the questions that have been raised on the validity of the concept, and the assumptions that have been made concerning crack-tip damage below the crack-opening stress. The impact of using other crack-tip parameters, such as the cyclic crack-tip displacement or cyclic crack-tip hysteresis energy, to model crack-growth rate behavior was studied. Crack-growth simulations using the modified Dugdale crack closure model showed a close relation between traditional ΔKeff and the cyclic crack-tip displacement (Δδeff) for an aluminum alloy and a steel over a wide range in stress ratios. Evaluations of the cyclic hysteresis energy demonstrated that the cyclic plastic damage below the crack-opening stress was negligible in the Paris crack-growth regime. Some of the standard and newly proposed remote measurement methods to determine crack-opening stresses and the “effective” crack-tip driving parameter were evaluated from crack-growth simulations made on middle-crack tension specimens. Here, analyses were conducted under both constant-amplitude and single-spike-overload conditions. A potential source of the Kmax effect on crack-growth rates was studied at high stress ratios and at high stress levels for an aluminum alloy. Results showed that the ratio of Kmaxto Kc had a strong effect on crack-growth rates at high stress ratios and at low stress ratios for very high stress levels. The crack-closure concept and the traditional crack-growth rate equations were able to correlate and predict crack-growth rates under these extreme conditions.
Local Crack Closure Measurements: Development of a Measurement System Using Computer Vision and a Far-Field Microscope
Authors: Sutton MA , Zhao W , McNeill SR , Helm JD , Piascik RS , Riddell WT
Published: March 2009

An accurate and relatively simple methodology for estimating crack closure loads has been developed. Using this method, measurements may be taken at a user-specified position behind the crack tip during the entire fatigue crack growth process. The methodology has three distinct components: (a) an imaging system having adequate magnification with minimal distortion, (b) a simple, Windows-based procedure for image acquisition and image analysis, and (c) techniques for applying a random, high contrast pattern on the specimen's surface.

To meet the imaging requirements, a far-field microscope objective capable of high magnifications was employed to image small regions on the order of 0.5 mm by 0.5 mm. The regions were near the crack tip. To meet the requirements of a user-friendly system, a Windows-based data-acquisition interface was developed to run the system on a common PC. Using the interface, images are acquired automatically during a loading/unloading cycle and stored digitally. Image analysis is performed on the saved images to rapidly obtain the crack opening displacement as a function of load; these data are used to estimate the crack closure load. Finally, two methodologies for applying a random, high-contrast pattern with average sizes of 4 to 20 μm were developed. The first method uses 11 μm filter paper and a low-pressure compressed air supply to apply small particles of photocopier toner powder to the surface of the specimen. The second method uses contact lithography to achieve a random pattern with smaller feature sizes, on the order of 2 to 8 μm.

Baseline tests of the overall system have demonstrated that it is both easy to use and accurate. Specifically, (a) the PC interface has demonstrated that images can be acquired automatically while the loading frame is cycling at 0.01 Hz, and (b) the crack tip opening displacement data have been shown to have errors on the order of 0.05 pixels for the toner powder patterns, corresponding to 27 nm for the magnification used.
Role of Fatigue Crack Closure Stresses in Hydrogen-Assisted Cracking
Authors: Toribio J , Kharin V
Published: March 2009

Crack closure effects on hydrogen-assisted cracking (HAC) were studied in terms of the influence of residual stresses produced by load removals at fatigue cycling on stress-assisted hydrogen diffusion towards rupture sites in the crack tip zone. The finite element procedure was applied to cyclic load elastoplastic large-deformation analysis combined with stress-assisted diffusion. Small-scale yielding near the crack tip was addressed and characterized in terms of the stress intensity factor (SIF). The elastoplastic situation near the tip of a blunting-closing crack revealed the cyclically stable stress evolution established after a couple of loading cycles (but this was not attained for strains). Crack closure effects were negligible for sustained-load HAC at SIF above the maximum value at precracking. The test duration for reliable evaluation of the threshold SIF for HAC was estimated. Crack closure affects near-tip hydrogen diffusion, and consequently HAC, at dynamic rising loading after precracking. Modeling was performed for the range of SIF increase rates. It showed that a premature fulfillment of the local fracture criterion in terms of critical combination of the hydrogen concentration and stress-strain parameters can occur at slow dynamic loading if compared with the sustained-load case. The dominating factor—stress or strain—and the “scale” of the local rupture event are of decisive importance for this. The performed simulations provide more insight into the items of conservatism of HAC testing data and the sources of their uncertainty.
A Proposed Standard for Evaluating Structural Integrity of Reinforced Concrete Beams by Acoustic Emission
Authors: Yuyama S , Okamoto T , Shigeishi M , Ohtsu M , Kishi T
Published: March 2009

A series of studies has been performed to evaluate the structural integrity of reinforced concrete (RC) beams by acoustic emission (AE). Cyclic loadings were applied to RC beams with a single reinforcing bar, large repaired beams, beams deteriorated due to corrosion of reinforcement, and two beams with different damage levels in an aging dock. The test results demonstrated that the Kaiser effect starts to break down when shear cracking starts to play a primary role. It has been also shown that high AE activity is observed during unloadings after serious damage (slips between the concrete and the reinforcement or those between the original concrete and the repaired part) has occurred. A standard for evaluating structural integrity of RC beams by AE is proposed, based on these results.
Calibration of Acoustic Emission Transducers by a Reciprocity Method
Authors: Hatano H
Published: March 2009

The paper reviews and discusses the background, methodology and application fields of absolute calibration of acoustic emission transducers by means of the reciprocity method. For characterizing and calibrating acoustic emission transducers, a number of methods utilizing various mechanical sound sources appear in the literature. Reciprocity calibration of acoustic emission transducers was proposed some time ago, and has since been employed by transducer manufacturers and laboratories. An outstanding advantage of the reciprocity method is that absolute sensitivity, including frequency characteristics and impulse responses, both to Rayleigh wave and longitudinal wave, can be determined by means of purely electrical measurements without the use of mechanical sound sources or reference transducers. The procedure for calibration was standardized as NDIS 2109 by the Japanese Society for Non-Destructive Inspection.
Characterization of Micro and Macro Cracks in Rocks by Acoustic Emission
Authors: Nagaraja Rao GM , Murthy CRL , Raju NM
Published: March 2009

Rock is a natural brittle material, and under compressive stresses fracture and failure occur by initiation, growth and interaction of microcracks forming macroscopic cracks and finally leading to a fault. As stress vs. volumetric strain curve can give only qualitative results, both for understanding the phenomenon of fault formation in terms of microcracking stages quantitatively and also for accurate prediction of impeding failure it becomes essential to identify the stages of the stress vs. volumetric strain curve by a suitable technique. Thus, in this respect the advantages of acoustic emission, a real-time on-line monitoring technique, is investigated. Conventionally, plots based on cumulative events, event rate and amplitude distribution are used to understand crack growth. while these parametric plots give the trends in terms of their AE activity, the exact characteristics of events in relation to the phenomena at different stress levels of micro and macro crack progression to failure are not easily discernible. So, in the present work based on the recorded wave form parameters, events are classified into four groups as α, β, γ and δ and are characterized as micro and macro crack phases which correlate with ultrasonically imaged data. Classification of events into micro and macro crack phases gives a better understanding of fault formation in rock materials and also the effect of stress, temperature, macrostructure, mineralogy, etc.
Physical-Chemical Changes in Silicone Elastomers Used for Building Sealants
Authors: Tock RW , Keshavaraj R
Published: March 2009

The modulus of a silicone sealant elastomer is one of the most fundamental properties of these materials that can be measured on a routine basis. It is also a very complex function of several variables. These variables include the chemistry of the silicone polymer and the type of filler compounded into the product. Moreover, once the sealant is placed into service, additional variables such as loading and displacement history, time-temperature cycles, and weathering exposure become significant. Several approaches have been developed to monitor and characterize changes observed in three specific commercial silicone sealants. While silicone polymerization chemistry determines the broad characteristics of these sealants, it was observed that filler type, particulate bulk and cohesive material performance, and weathering can also contribute long term effects. These effects on some of the engineering properties pertaining to silicone elastomers used in building sealant application is the subject of this paper. Elastomers exhibit compressive moduli that can be several times that of the tensile moduli. In addition, acid and base pH levels from exposure to precipitation can accelerate residual cross-linking and ultimately lead to sealant degradation. The net result produced by such experiments has been a better understanding of sealant properties.
Overview of Surface Engineering and Wear
Authors: Budinski KG
Published: March 2009

Surface engineering is a multidiscipline activity aimed at tailoring the properties or surfaces of engineering materials to improve their function or service life. As applied to metals, surface engineering includes processes such as plating, diffusion treatment, physical and chemical vapor deposition, ion implantation, thermal spray coatings, selective hardening, hardfacing, and a variety of less-used and proprietary processes. These processes will be described briefly and it will be shown that each process has a niche where it works better or is more cost effective than competing surface engineering treatments or bulk materials. This paper will review the various forms of wear that occur in industrial environments. Techniques will be described to match available surface engineering processes with wear situations. The goal is to present selection guidelines for machine designers and industrial operating personnel on the use of surface engineering to solve wear problems.
Geostatistics for Environmental and Geotechnical Applications: A Technology Transferred
Authors: Cromer MV
Published: March 2009

Although successfully applied during the past few decades for predicting the spatial occurrences of properties that are cloaked from direct observation, geostatistical methods remain somewhat of a mystery to practitioners in the environmental and geotechnical fields. The techniques are powerful analytical tools that integrate numerical and statistical methods with scientific intuition and professional judgment to resolve conflicts between conceptual interpretation and direct measurement. This paper examines the practicality of these techniques within the entitles field of study and concludes by introducing a practical case study in which the geostatistical approach is thoroughly executed.
Describing Spatial Variability Using Geostatistical Analysis
Authors: Srivastava RM
Published: March 2009

The description, analysis and interpretation of spatial variability is one of the cornerstones of a geostatistical study. When analyzed and interpreted properly, the pattern of spatial variability can be used to plan further sampling programs, to improve estimates and to build geologically realistic models of rock, soil and fluid properties. This paper discusses the tools that geostatisticians use to study spatial variability. It focuses on two of the most common measures of spatial variability, the variogram and the correlogram, describes their appropriate uses, their strengths and their weaknesses. The interpretation and modelling of experimental measures of spatial variability are discussed and demonstrated with examples based on a hypothetical data set consisting of lead and arsenic measurements collected from a contaminated soil site.
Modeling Spatial Variability Using Geostatistical Simulation
Authors: Desbarats AJ
Published: March 2009

This paper, the last in a four part introduction to geostatistics, describes the application of simulation to site investigation problems. Geostatistical simulation is a method for generating digital representations or “maps” of a variable that are consistent with its values at sampled locations and with its in situ spatial variability, as characterized by histogram and variogram models. Continuing the synthetic case study of the three previous papers, the reader is lead through the steps of a geostatistical simulation. The simulated fields are then compared with the exhaustive data sets describing the synthetic site. Finally, it is shown how simulated fields can be used to answer questions concerning alternative site remediation strategies.
Geostatistical Site Characterization of Hydraulic Head and Uranium Concentration in Groundwater
Authors: Buxton BE , Wells DE , Pate AD
Published: March 2009

The first case study presented in this paper describes an assessment of the spatial distribution and temporal changes in hydraulic head pressure in the groundwater beneath a retired federal government uranium processing facility. Analysis of the hydraulic heads involved ordinary kriging which was found to be a better mapping method than such alternatives as inverse-distance weighting, mainly because kriging provides measures of estimation uncertainty. The objective of this kriging was to provide estimated steady-state head values for use in calibrating a groundwater flow model for the site. In the second case study, the spatial distribution of potential uranium contamination in the aquifer was assessed with lognormal kriging. Uranium measurements for this analysis were available at roughly three-month intervals across a four-year time period. The objective of the analysis was to assess where the uranium concentrations were highest. A second objective, not addressed in this paper, was to determine if the concentrations were changing significantly during the four-year time period.
Effective Use of Field Screening Techniques in Environmental Investigations: A Multivariate Geostatistical Approach
Authors: Wild MR , Rouhani S
Published: March 2009

Environmental investigations typically entail broad data gathering efforts which include field screening surveys and laboratory analyses. Although usually collected extensively, data from field screening surveys are rarely used in the actual delineation of media contamination. On the other hand, laboratory analyses, which are used in the delineation, are minimized to avoid potentially high cost. Multivariate geostatistical techniques, such as indicator cokriging, were employed to incorporate volatile organic screening and laboratory data in order to better estimate soil contamination concentrations at a underground storage tank site. In this work, the direct and cross variographies are based on a multi-scale approach. The results indicate that soil gas measurements show good correlations with laboratory data at large scales. These correlations, however, can be masked by poor correlations at micro-scale distances. Consequently, a classical direct correlation analysis between the two measured values is very likely to fail. In contrast, the presented multi-scale co-estimation procedure provides tools for a cost-effective and reliable assessment of soil contamination based on a combined use of laboratory and field screening data.
Evaluation of a Soil Contaminated Site and Clean-Up Criteria: A Geostatistical Approach
Authors: Leonte D , Schofield N
Published: March 2009

A case study of soil contamination assessment and clean-up in a site proposed for residential development is presented in this paper. The contamination consists mainly of heavy metals of which lead is the most important contaminant. The site has been sampled on an approximately 25 × 25 square meter grid to between 1 and 3 meters depth to evaluate the extent of the contamination. Three hotspots were identified based on eyeballing the lead sample values and a crude contouring. A geostatistical approach is proposed to map the lead contamination and provide an alternate evaluation. The results suggest a significantly different evaluation of the area for clean-up based on the probability of the lead concentration exceeding allowable levels.
Solid Waste Disposal Site Characterization Using Non-Intrusive Electromagnetic Survey Techniques and Geostatistics
Authors: Kuhn GN , Woldt WE , Jones DD , Schulte DD
Published: March 2009

Prior to the research reported in this paper, a site-specific hydrogeologic investigation was developed for a closed solid waste facility in Eastern Nebraska using phased subsurface characterizations. Based on the findings of this prior investigation, a surface based geoelectric survey using electromagnetic induction to measure subsurface conductivity was implemented to delineate the vertical and horizontal extent of buried waste and subsurface contamination. This technique proved to be a key non-intrusive, cost-effective element in the refinement of the second phase of the hydrogeologic investigation.

Three-dimensional ordinary kriging was used to estimate conductivity values at unsampled locations. These estimates were utilized to prepare a contaminant plume map and a cross section depicting interpreted subsurface features. Pertinent subsurface features were identified by associating a unique range of conductivity values to that of solid waste, saturated and unsaturated soils and possible leachate migrating from the identified disposal areas.
Enhanced Subsurface Characterization for Prediction of Contaminant Transport Using Co-Kriging
Authors: Benson CH , Rashad SM
Published: March 2009

Groundwater flow and advective transport were simulated in a heterogeneous synthetic aquifer. These simulations were conducted when the aquifer was fully defined and when it was characterized using a limited amount of hard and soft data (hydraulic conductivity data and soil classifications). Co-kriging was used to combine the data types when estimating the hydraulic conductivity field throughout the aquifer. Results of the flow and transport simulations showed that soil classifications were useful in characterizing the hydraulic conductivity field and reducing errors in statistics describing the plume.
A Study of Naturally Initiating Notch Root Fatigue Cracks Under Spectrum Loading
Authors: Prakash RV , Sunder R , Mitchenko EI
Published: March 2009

The kinetics of short cracks at notches were studied in 2014-T6511 Al-Cu alloy extruded bar stock under modified versions of FALSTAFF and TWIST load spectra. Experiments were conducted on test coupons of different thickness and at different stress levels. The effects of these and other parameters on the density and growth rate patterns of multiple cracks were investigated. The quality of fractographic crack growth rate measurements was found to be superior to surface replica technique. It was also observed that artificially initiated fatigue cracks grow slower than naturally initiated ones. Interaction of naturally initiating multiple cracks was quantified.
Performance Degradation, Polymer Encapsulant Degradation, and Estimating Lifetimes for Photovoltaic Modules from Accelerated Testing
Authors: Czanderna AW , Pern FJ
Published: March 2009

The purposes of this paper are to provide background information about encapsulants for photovoltaic (PV) modules and to evaluate estimates of the durability of different materials used in PV modules. We summarize field-deployed module degradation in performance, the established degradation mechanisms of ethylene vinyl acetate (EVA) copolymer, and potential degradation mechanisms in other module components and at materials interfaces. Most of the emphasis is on estimates for the commercially used EVA formulations A9918 and 15295. These formulations have degraded in field-deployed modules to produce acetic acid and a yellow to brown color from polyenes and the module efficiencies have been reduced by 10% to 70% in 4 to 12 years. Yet, projections were made by several different research groups in the 1980s that the EVA lifetime could range from 20 to 100 years, the production of acetic acid would only be 0.006% in 20 years, and that silver metallization would survive attack from acetic acid for 300 years at 55°C. Those authors did not use appropriate variables or specimen configurations that simulate reality, and based their projections using the generalization that chemical reaction rates double for every 10°C increase in T. We review the inherent errors in their assumptions about the Arrhenius relation. We also show how degradation in efficiency (from current-voltage data) comparable to field experience is obtained using minimodules with a construction that simulates reality and by using appropriate variables in accelerated testing, i.e., UV, T, and RH. A test protocol is outlined that simulates reality and permits making suitable service lifetime projections.
Microstructure of Oxides on Zircaloy-4, 1.0Nb Zircaloy-4, and Zircaloy-2 Formed in 10.3-MPa Steam at 673 K
Authors: Anada H , Takeda K
Published: March 2009

The microstructure of ZrO2 formed on sheet materials of Zircaloy-2 (Zr2), Zircaloy-4 (Zr4), and an alloy of 1.0% Nb added to Zircaloy-4 (1Nb-Zr4) was analyzed using HRTEM (high-resolution transmission electron microscopy). The relationship between the corrosion behavior of the alloys and the microstructure is discussed. Stress-relieved sheet specimens of the three alloys were prepared and corrosion tested under static conditions in steam at 673 K and 10.3 MPa for a total of 220 days. The order of corrosion resistance in 673-K steam was Zr2, 1Nb-Zr4, and Zr4. Several transitions were observed in the corrosion kinetic curve of 1Nb-Zr4 and Zr2. However, only the first transition was observed in the curve of Zr4. Oxide structure in the pre-transition region on Zr4 was analyzed to be in the following order from the outside surface: columnar m-ZrO2, t-ZrO2 layer, substoichiometric Zr oxide layer, and α-Zr matrix. The t-ZrO2 layer was approximately 50 to 80 nm thick, and the substoichiometric Zr oxide layer was approximately 100 to 200 nm. These layers were absent in the microstructure of the oxide in the post-transition region. The substoichiometric Zr oxide layer consisted of m-ZrO2 grains that were less than 10 nm in diameter and some as yet unidentified grains that had lattice parameters similar to distorted and significantly oriented α-Zr. However, the t-ZrO2 layered structure and the substoichiometric Zr oxide layer structure were observed in the post-transition oxides on Zr2 and 1Nb-Zr4. It was also observed that transformation of columnar grains to fine equiaxed grains had occurred near the lateral cracks and the incorporated intermetallic precipitates in post-transition oxides. It is implied from these results that the t-ZrO2 layer and the substoichiometric Zr oxide layer structures play an important role as a barrier layer in controlling the occurrence of kinetic transitions.
Microstructure Evolutions and Iron Redistribution in Zircaloy Oxide Layers: Comparative Effects of Neutron Irradiation Flux and Irradiation Damages
Authors: Iltis X , Lefebvre F , Lemaignan C
Published: March 2009

To understand the acceleration of the Zircaloy corrosion kinetics in PWR conditions, TEM microstructural characterizations of oxide layers grown in an autoclave or directly in-reactor have been performed. To separate the influence on the oxidation process of the irradiation damage in the alloy from the dynamic effect of neutron flux, oxide layers have also been grown in an autoclave on previously neutron-irradiated cladding. The comparative characterization of these oxide layers leads to the following results: the nucleation and growth process are observed to be similar on oxides formed in-autoclave and significantly different on oxides grown directly in-reactor, indicating that this process is essentially affected by neutron irradiation or, more generally, parameters specific to the reactor environment. Concerning grain growth phenomena, it appears that the high microstructural instability noticed in oxides formed in-reactor is also the consequence of parameters specific to the reactor environment such as neutron irradiation or the lithium concentration gradient. Finally, the iron distribution in the oxide is almost the direct image of the iron distribution in the metal.

The impact of each experimental statement on the oxidation kinetics is discussed. The role of neutron irradiation on the structure of the oxide layer appears to be the most determining.
Effect of In-PWR Irradiation on Size, Structure, and Composition of Intermetallic Precipitates of Zr Alloys
Authors: Garzarolli F , Goll W , Seibold A , Ray I
Published: March 2009

The corrosion behavior of Zr alloys depends on the kind, size, and distribution of the intermetallic second-phase particles. TEM examinations of Zr-Sn-Fe-Cr alloys irradiated in PWRs at temperatures between 300 and 370°C and fast fluences in the range of 5E21 to 1.3E22 cm-2 have been performed to study the irradiation-induced effects on the precipitates. The alloys contained different types of second-phase particles such as Zr(Fe,Cr)2, Zr2(Fe,Si), and Zr3Fe before irradiation. The influence of irradiation was found to depend on temperature and type of second-phase particles.

At temperatures below 310°C, the Laves phase Zr(Fe,Cr)2, which normally is the most frequent precipitate in Zry-4, depletes in Fe, becomes amorphous, and dissolves completely at higher fluences. With increasing temperature, the rate of Fe depletion and dissolution decreases and new Zr-Fe phases are formed. At temperatures above 370°C, the Laves phase remains stable or even grows under irradiation.

In Fe-containing Zr alloys with little or no Cr, rather large Zr3Fe precipitates are the most frequent particles. These particles are not dissolved by irradiation even at low temperatures. This was confirmed by annealing after irradiation.

As a hypothesis, it was assumed that the different behavior of the various precipitates can be related to their melting or decomposition temperatures by using the homologous temperature (i.e., the temperature under consideration in K normalized to the melting or decomposition temperature in K). This interrelationship has been found to apply for irradiation-induced amorphization. The empirical approach to describe the thermal ripening behavior of second-phase particles before irradiation and to describe the transition from irradiation-induced dissolution to irradiation-induced growth by a normalized (homologous) temperature led to reasonable results.
Evolution of Microstructure in Zirconium Alloys During Irradiation
Authors: Griffiths M , Mecke JF , Winegar JE
Published: March 2009

X-ray diffraction (XRD) and transmission electron microscopy (TEM) have been used to characterize microstructural and microchemical changes produced by neutron irradiation in zirconium and zirconium alloys. Zircaloy-2, Zircaloy-4, and Zr-2.5Nb alloys with differing metallurgical states have been analyzed after irradiation for neutron fluences up to 25 × 1025 n.m-2 (E > 1 MeV) for a range of temperatures between 330 and 580 K.

Irradiation modifies the dislocation structure through nucleation and growth of dislocation loops and, for cold-worked materials in particular, climb of existing network dislocations. In general, the a-type dislocation structure tends to saturate at low fluences (< 1 × 1025 n.m-2). The c-component dislocation structure, however, may evolve over long periods of irradiation (for fluences >10 × 1025 n.m-2 in some cases).

The phase structure is also modified by irradiation. The common alloying/impurity elements, Fe, Cr, and Ni, are relatively insoluble in the α-phase but are dispersed into the α-phase during irradiation irrespective of the state of the phase initially containing these elements, i.e., metastable β-phase or stable intermetallic precipitate. The stable intermetallic particles may undergo structural changes dependent on their composition and the temperature. For the metastable dual-phase α/β-alloys (Zr-2.5Nb alloy), the β-phase structure is modified during irradiation, but the change is complex, being a combination of thermal decomposition and radiation-induced mixing.
Non-Linear Irradiation Growth of Cold-Worked Zircaloy-2
Authors: Holt RA , Causey AR , Christodoulou N , Griffiths M , Ho ETC , Woo CH
Published: March 2009

Accelerating irradiation growth has been reported for several zirconium alloys with a range of metallurgical states during high-temperature tests in fast-breeder reactors (673 to 723 K) for annealed Zircaloys in thermal test reactors at power reactor temperatures (523 to 623 K) and in power reactor core components fabricated from annealed or recrystallized Zircaloy. In the latter case, there was a transition from low to high irradiation growth rates at moderate fluences (about 3 × 1025 n/m2, E > 1 MeV, at 580 K) related to the nucleation and growth of basal plane c-component loops.

It was recently reported that the elongation rate of cold-worked Zircaloy-2 pressure tubes also accelerates with increased fluence at about 550 K. This gradual acceleration coincides with a gradual increase in the density of c-component dislocations as a result of the helical climb of those dislocation segments with a predominantly screw character.

New data showing the acceleration of growth of cold-worked Zircaloy-2 at 550 K are presented, and a model is presented for the irradiation growth behavior of cold-worked Zircaloy-2 based on the evolution of the sink strengths of c-component dislocations (net vacancy sinks) and a-type dislocations (net interstitial sinks) as a function of fast fluence. According to the model, the growth rate reaches a maximum when the sink strength of c-component dislocations is approximately equal to that of the a-type dislocations, and hence the growth rate tends to saturate with increasing fluence.