bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of DNA Strand Damage (Comet Assay) and Embryo Hatching Effects to Assess Contaminant Exposure in Blue Crab (Callinectes sapidus) Embryos
Authors: Lee RF , Steinert SA , Nakayama K , Oshima Y
Published: March 2009

After fertilization, blue crab eggs are embedded in a “sponge” which is attached to the female abdomen during embryo development. Embryos after 9 stages in the egg sac hatch into a swimming zoea stage (stage 10). We have developed a bioassay where embryo development is monitored in culture plates with and without toxicants in the water. Toxicant effects are based on determining the percentage of embryos which hatch to zoea. Hatching EC50 (toxicant concentration at which 50% of the embryos fail to hatch) for a number of pesticides, organometallics and metals were determined. The test takes from 2 to 6 days depending on the embryo stage selected for the study. In addition to embryo development effects the prevalence of DNA single-strand breaks in individual embryo cells were determined using the single cell gel electrophoresis method (Comet assay). A good correlation between DNA strand breakage and embryo defects was found after exposure to genotoxic contaminants. Thus, the bioassay linking DNA damage to embryo hatching effects is rapid, sensitive and mechanistically relevant.
An Evaluation of the Use of Toxic Equivalency Factors to Assess Reproductive Hazards of PCBs to Wildlife
Authors: Smith JS
Published: March 2009

Toxic equivalency factor (TEF) approaches have been used to evaluate the reproductive hazards of polychlorinated biphenyls (PCBs) to wildlife. These approaches are based primarily on the relative potency of individual PCB congeners for 2,3,7,8-tetrachlorodibenzo-p-dioxin-like induction of ethoxyresorufin-O-deethylase (EROD) enzyme activity. One of the primary concerns in this practice is the fact that induction of EROD activity has not been mechanistically linked to the occurrence of any adverse effect. Other PCB-induced enzyme activities are more plausibly linked to mechanisms of potential reproductive toxicity. For example: some PCB-induced enzymes are responsible for altered metabolism of androgens and estrogens. Induction of these enzymes by dioxin typically requires much greater doses than does EROD. Consequently, an EROD-based TEF approach is likely to over-estimate potential reproductive health risks to wildlife, perhaps by as much as several orders of magnitude.
Impact of Soil Heterogeneity on Measuring the Attainment of PCB Clean-Up Standards
Authors: Phillips IM , Ghirardi JK , Morin JO
Published: March 2009

The sources of variance in the results of samples collected during a pilot-scale remediation treatability testing for PCBs were evaluated using basic statistical methods. The relative contributions of soil heterogeneity and chemical testing methods were estimated. The sources of variance were estimated using both inter- and intralaboratory testing and the determination of the total variance of each sample set.

It was found that 67 to 94 percent of the variance in the results was contributed by the sample heterogeneity which can not be readily controlled. The results of treated samples from the pilot-scale treatability testing showed a mean concentration of PCBs of 13.6 ppm with a standard deviation of 10.1. The range of the distribution of concentrations was 1.3 to 35 ppm.

Based on these findings, it is inappropriate to use an “absolute” clean-up standard to evaluate whether the clean-up has been achieved. The use of the mean is more appropriate as it takes into account the variance in the results caused by sample heterogeneity.
Failure of EPA's IEUBK Model to Identify Children at Risk from Lead Exposure
Authors: Coomes RM
Published: March 2009

Modeled blood lead concentrations derived from EPA's Integrated Exposure Uptake Biokinetic Model LEAD99 (Model) were compared to measured blood lead concentrations for two populations of children living in Colorado mining communities. The study areas were Clear Creek and California Gulch. Both studies presented paired blood lead level measurements and environmental media lead concentrations. The data for this paper were obtained from the Colorado Department of Health and publicly-available submissions made to EPA Region VIII. There was little agreement between model blood lead levels and measured blood lead values. Nine children in the Clear Creek Study were identified as having blood lead levels greater than 10 micrograms per deciliter (μg/dl) by Model or measurement. However, only one individual child was identified as having a blood lead level greater than 10 μg/dl by modelling and measurement. Eight children (89 percent of the children at risk measured) were not identified by the Model. The California Gulch Superfund study included 312 children 294 of which had paired environmental data. The Model estimated that 117 children would have blood lead levels greater than 10 μg/dl. However, the Model only identified 17 of the 26 children that had measured blood lead values greater than 10 μg/dl. The Model failed to identify more than 3 percent of the total population that was at measured risk. The Model did not identify 34.6 percent of the children at measured risk. When the California Gulch populations were grouped by neighborhood, age of housing, and other demographic parameters, the Model predicted lower blood lead concentrations (average of the individual Model runs) than were obtained by measurement. Significant changes have been incorporated into the Model compared to previous versions (Lead 6). The potential impacts of the changes are discussed.
Effect of Electrostatic Charging on the Dose Transfer of Water-Based Pesticide Mixtures
Authors: Wolf TM , Downer RA , Hall FR , Wagner OB , Kuhn P
Published: March 2009

In an attempt to implement safe and reliable electrostatic charging of agricultural sprays, a conductive charging system based on conventional hydraulic spray booms and existing pesticide formulations is being developed. Atomization measurements showed that in general, the drop size distributions of hydraulic nozzles remained unchanged when voltage was applied to the spray solution. Applying voltage did, however, increase the velocity of droplets in the spray cloud. Deposit quantity on weeds increased up to 4 fold with voltage on. This effect was most pronounced at a fast travel speed and wide nozzle spacing. The benefit of electrostatic charging was reduced, but still significant, in the presence of a wheat stubble or soybean plant canopy. Spray coverage on the under-side of single leaves of exposed soybean plants was negligible without voltage, but increased to a maximum of 15% of the upper-side leaf coverage with applied voltage (25 kV). Spray penetration to the lower half of the plants also increased with voltage. At least a two fold rate reduction with glyphosate could be demonstrated with voltage on. Application of voltage to a bifenthrin spray dramatically increased control of aphids, mites and thrips on the under-side of cotton leaves.
FSCBG Predictions Coupled to GPS/GIS Aircraft Tracking
Authors: Teske ME , Barry JW , Thistle HW
Published: March 2009

One of the most exciting areas of current aerial application technology is the use of global positioning (in particular, differential GPS) to provide a real-time image of the position of a spray aircraft during spray operation. Current hardware range from simple systems that keep track of the aircraft flight path (for later playback), to more sophisticated aircraft navigational systems that provide a means for the pilot to correct the aircraft flight path while spraying (continuous feedback). One addition expected to these systems is access to a very fast version of the USDA Forest Service aerial application prediction model FSCBG (Forest Service Cramer-Barry-Grim). This version of the model (FSCBG/RT) will run in real time on the on-board computer, and will access application rate, meteorological parameters, release height, and aircraft direction, to predict the effects of aircraft speed, flight profile, pump pressure changes, flow rate, and other data, on the spray plume. This prediction will be returned to the navigation and monitoring system for possible corrective action. The end product will be a system that will track the aircraft, display the spray swath width, and visualize the pesticide spray deposition and movement, all in real time. This paper reviews the need for a GPS/GIS tracking system in the aerial application of pesticides, highlights the field evaluation of these devices by the USDA Forest Service, summarizes the development of the FSCBG/RT model, visualizes how the model will interact with real-time data, and anticipates its potential for decision-making, environmental monitoring and accounting, tracking, and documentation.
Staining Potential of Sealants In/On Exterior Wall Substrates
Authors: Chin IR , Gorrell TA , Scheffler MJ
Published: March 2009

The investigation of dozens of exterior walls on buildings by the authors have revealed that certain sealants used to seal joints in exterior walls have caused the following conditions: 1. Local staining and discoloration of masonry wall substrates due to penetration of sealant into substrates. 2. Local change in absorption of masonry wall substrates due to penetration of sealant into the substrates which results in local discoloration of wall substrates after rains. 3. Surface discoloration of sealant due to dirt accumulation on sealant. 4. Stains in the form of streaks of dirt on masonry and on metal wall substrates due to transfer by rain water of some of the dirt on the sealant surface onto the adjacent surface of the substrate.

Laboratory and field testing of the major commercially available sealants by the authors to date have revealed that silicone sealants have the propensity to stain certain exterior wall substrates while polyurethane sealants do not; that silicone sealants in service discolor more significantly and faster due to dirt accumulation than polyurethane sealants; that sealant that has penetrated into masonry substrates cannot be entirely removed from the substrate by cleaning; and that preconstruction testing of sealants and proper material selection can help to avoid staining of sealant.
Laboratory Testing of Sealants with a Marble Substrate
Authors: Farmer MC , Cechner RA
Published: March 2009

Polyurethane and silicone sealants are widely specified for installations with porous substrates such as some stones. However, when a sealant is used against such surfaces, there is a potential for a lack of adequate adhesion, or staining of the stone by misapplication or migration of the liquid components of the sealant system, such as primers or plasticizers in the formulation. Some varieties of marble in particular have been reported to be susceptible to staining and discoloration over time from sealants. Application of new sealant over existing sealants is also of great concern for remedial applications. Determining the level of substrate preparation necessary to achieve adequate bond is critical to the success of the remedial construction project.

This paper discusses the development and results of a test program conducted to determine the relative performance of sealants installed on a white marble substrate. The tests performed included wet adhesion tests, accelerated weathering studies, and staining due to plasticizer migration.
Performance-based Adhesion Testing of Structural Sealants
Authors: Cerra AP , Gutowski VS
Published: March 2009

Existing accelerated laboratory procedures for the assessment of the adhesion of silicone sealants fail to consider the fact that the sealant/substrate interface in a building facade is continuously subjected to a combination of both mechanical and environmental stress. As a result of this, standardised test protocols lack the discrimination necessary to assess relative adhesive behaviour. A novel test procedure is offered which enables improved discrimination of the adhesive strength of the sealant/substrate system. The method is based on the simultaneous application of both mechanical and hydrothermal stress, in order to promote adhesive failure at loads below the cohesive strength of the bulk sealant.

A simpler version of the novel procedure allows for the screening of sealant/substrate combinations that represent potential long-term durability risks. This is achieved by the combination of hydrothermal and mechanical stress at a level close to the structural silicone design stress (0.138 MPa) applied through imposing a 12.5% strain (equal to the normal design strain in silicone sealants) together with immersion of the joint in hot water.
Evaluation of Various Generic Types of Building Sealants Against ASTM C-920, Standard Specification for Elastomeric Joint Sealants
Authors: Fiorillo AR
Published: March 2009

A number of sealant manufacturers suggest that although they supply primers for their sealants, in many cases the primers may not be necessary. They usually suggest running a test on the substrates the sealants are to be used with to determine if the primers are needed. This paper will discuss the results of testing several commercially available polysulfide, silicone and polyurethane sealants against ASTM C-920, Standard Specification For Elastomeric Joint Sealants. Mortar, plate glass and anodized aluminum were used as the substrates. Where manufacturers supplied primers, the sealant was tested with and without their primer. Where the manufacturer did not recommend primers, testing was only done without a primer.
Friction and Wear of Self-Lubricating TiN-MoS2 Coatings Produced by Chemical Vapor Deposition
Authors: Blau PJ , Yust CS , Bae YW , Besmann TM , Lee WY
Published: March 2009

The purpose of the work reported here was to develop special chemical vapor deposition (CVD) methods to produce self-lubricating ceramic coatings in which the lubricating and structural phases were co-deposited on Ti-6Al-4V alloy substrates. These novel composite coatings are based on a system containing titanium nitride and molybdenum disulfide. The method for producing these coatings and their sliding behavior against silicon nitride counterfaces, in the temperature range of 20 to 700°C in air, are described. The initial sliding friction coefficients for the composite coatings at room temperature were 0.07 to 0.30, but longer-term transitions to higher friction occurred, and specimen-to-specimen test variations suggested that further developments of the deposition process are required to assure repeatable friction and wear results. Friction and wear tests at 300 and 700°C produced encouraging results, but tests run at an intermediate temperature of 400°C exhibited friction coefficients of 1.0 or more. Oxidation and a change in the nature of the debris layers formed during sliding are believed to be responsible for this behavior.
Laser Surface Melting of Carbide Coatings and Their Tribological Behavior
Authors: Bahadur S , Yang C-N
Published: March 2009

The effect of laser surface-melting on the friction and wear of detonation gunsprayed (W, Ti)C-Ni (tungsten and titanium carbide-nickel) and WC-Co (tungsten carbide-co-balt) ceramic coatings on AISI 1044 steel and Ti-6Al-4V substrates was studied. The coated surfaces were melted using a 1.5 kW CO2 laser with a power setting of 1.4 kW and travel speed of 0.01 m/s. The changes in microstructure and microhardness due to the laser treatment were examined. The melted layers were found to be full of dispersed pores that started 65 to 70 μm below the surface. The surface hardness of (W, Ti)C-Ni coated specimens either decreased or remained constant after surface melting; however, the hardness of WC-Co coated specimens increased. Dry sliding friction and wear tests were conducted in a block-on-ring wear tester, with the coated specimens as block specimens and hardened tool steel as the ring specimen. The width of both the ring and the block was 6.35 mm. The test conditions were 4 m/s sliding speed and 4.9 N load. It was found that as a result of laser treatment the wear resistance of WC-Co coating increased, but that of (W, Ti)C-Ni coating decreased. Scanning electron microscopy of the wear surfaces showed that the micromechanisms of wear were cracking and material disintegration from the edges of the cracks and holes.
Coating-Substrate Interface Stress Management in Wear Protection of Light Alloy Components
Authors: Ramalingam S , Zheng L
Published: March 2009

Hard coating light alloys for wear protection presents an interface stress problem due to mismatch in elastic constants across the film-substrate interface. The displacement formulation method is used in this work to calculate interface stresses as a function of contact parameters, coating/substrate properties, and coating thickness. Quantitative results obtained suggests that interface stresses can be managed with a judicious choice of coating materials, film thickness, contact parameters, and film deposition conditions.
Geostatistical Estimation: Kriging
Authors: Rouhani S
Published: March 2009

Geostatistics offers a variety of spatial estimation procedures which are known as kriging. These techniques are commonly used for interpolation of point values at unsampled locations and estimation of average block values. Kriging techniques provide a measure of accuracy in the form of an estimation variance. These estimates are dependent on the model of spatial variability and the relative geometry of measured and estimated locations. Ordinary kriging is a linear minimum-variance interpolator that assumes a constant, but unknown global mean. Other forms of linear kriging includes simple and universal kriging, as well as co-kriging. If measured data display non-Gaussian tendencies, more accurate interpolation may be obtained through non-linear kriging techniques, such as lognormal and indicator kriging.
Integrating Geophysical Data for Mapping the Contamination of Industrial Sites by Polycyclic Aromatic Hydrocarbons: A Geostatistical Approach
Authors: Colin P , Froidevaux R , Garcia M , Nicoletis S
Published: March 2009

A case study is presented of building a map showing the probability that the concentration in polycyclic aromatic hydrocarbon (PAH) exceeds a critical threshold. This assessment is based on existing PAH sample data (direct information) and on an electrical resistivity survey (indirect information). Simulated annealing is used to build a model of the range of possible values for PAH concentrations and of the bivariate relationship between PAH concentrations and electrical resistivity. The geostatistical technique of simple indicator kriging is then used, together with the probabilistic model, to infer, at each node of a grid, the range of possible values which the PAH concentration can take. The risk map is then extracted for this characterization of the local uncertainty. The difference between this risk map and a traditional iso-concentration map is then discussed in terms of decision-making.
A Bayesian/Geostatistical Approach to the Design of Adaptive Sampling Programs
Authors: Johnson RL
Published: March 2009

Traditional approaches to the delineation of subsurface contamination extent are costly and time consuming. Recent advances in field screening technologies present the possibility for adaptive sampling programs---programs that adapt or change to reflect sample results generated in the field. A coupled Bayesian/geostatistical methodology can be used to guide adaptive sampling programs. A Bayesian approach quantitatively combines “soft” information regarding contaminant location with “hard” sampling results. Soft information can include historical information, non-intrusive geophysical survey data, preliminary transport modeling results, past experience with similar sites, etc. Soft information is used to build an initial conceptual image of where contamination is likely to be. As samples are collected and analyzed, indicator kriging is used to update the initial conceptual image. New sampling locations are selected to minimize the uncertainty associated with contaminant extent. An example is provided that illustrates the methodology.
Fatigue Crack Propagation in IN-718 Material under Biaxial Stress Bending
Authors: Zamrik SY , Ryan RE
Published: March 2009

The effect of biaxial stress cycling on the crack growth process in IN-718 plate specimens was investigated using a semielliptical surface flaw as a crack starter. The method of anticlastic bending was used to generate the biaxial stress field. This bending method generates two bending stresses: a tensile stress normal to the crack surface and a compressive stress transverse to the tensile stress at the tip of the crack. In a biaxial stress field, the linear elastic fracture mechanics (LEFM) theory predicts that the stress parallel to the crack direction has no effect on crack growth rate. However, in the past two decades, experimental studies have shown that a stress parallel (transverse) to the crack tip influences crack growth rate. In this investigation, the effect of biaxial stress ratio (β = − σ2/σ1) of − 1 on fatigue crack growth is presented. At a constant cyclic load, a crack growth transition from Mode I to Mode II was observed to take place when ΔK reached the value of 17.5 ksi √in. (19.2 MPa √m). Also, an acceleration in the fatigue crack growth rate was observed due to the compressive transverse stress.
The Impact of Microstructural Interactions, Closure, and Temperature on Crack Propagation Based Lifing Criteria
Authors: Evans WJ , Nicholas PJ , Spence SH
Published: March 2009

This paper addresses the problem of predicting crack development at a stress concentration feature from simple laboratory crack growth data. It uses a specifically designed double edge notch geometry as a test vehicle and growth rates generated on standard corner crack and compact tension specimens. A coarse-grained, near-alpha titanium alloy is employed to emphasize any microstructural interaction effects. The bulk of the work is at ambient temperature with a small amount of data obtained at 300°C. It is shown that at low stress (350 MPa), conventional fracture mechanics, without an allowance for crack closure, can correctly predict both crack shape development and cyclic life. The only significant errors occur when the crack front is retarded by prior beta or alpha colony boundaries. These tend to lead to pessimistic predictions. At 550 MPa, however, there is significant notch root plasticity that induces crack closure. An allowance for notch closure in the numerical procedures permits a more accurate prediction of crack shape and cyclic life at this stress level. To support the computer models, a detailed assessment of closure is made using potential difference (PD), strain gage, and replica techniques.
Structural Life Analysis Methods Used on the B-2 Bomber
Authors: Bunch JO , Trammell RT , Tanouye PA
Published: March 2009

The methods used to predict crack initiation life (durability) and crack growth life (damage tolerance) of the United States Air Force/Northrop Grumman B-2 Bomber are discussed. The test matrix used to verify the methodologies is presented, followed by a discussion of each method and the results of the verification tests.

Durability analysis on the B-2 is based on a notch strain analysis method. The method uses the cyclic stress-strain properties of a material combined with the Neuber equation for strain concentration at a notch to predict crack initiation lifetimes. The method results in a design-allowable curve for durability.

Damage tolerance analyses must account for the effects of crack retardation due to overload cycles in a flight spectrum. The methods used for crack growth analysis rely on empirical parameters that are dependent on material; however, they are also often dependent on the type of spectrum. If the spectrum changes drastically, it is often necessary to recalibrate the crack growth model. A model based on phenomenon of crack closure has been developed that overcomes the need to recalibrate the model for each new spectrum. The model, referred to as the “constant closure model,” was used for crack growth life prediction of metallic components in the B-2. In the constant closure model, the closure factor (CF) is the only empirical parameter. The other parameters needed to use the constant closure model are obtained from the load spectrum.
Further Refinement of a Methodology for Fatigue Life Estimation in Resistance Spot Weld Connections
Authors: Sheppard SD
Published: March 2009

The overall objective of this research is to develop a general model of fatigue crack propagation in resistance spot-welded joints. An important feature of this development is that the model and accompanying methodology should be accessible to designers evaluating fatigue response of structures containing multiple welds. This objective is achieved by examining the stress state around a resistance spot weld. A general expression for the structural stress around the weld is formulated that is dependent only on the loading immediately surrounding the weld; as such, it is specimen independent.

In previous work [1] it was found that structural stress could be successfully used to estimate life for crack initiation and growth to a length of 0.01 in. (0.254 mm) in resistance spot welds, and that this period represents less than 30% of the total life in as-welded joints. It is important to note that estimation of this period is highly dependent on fatigue-related material properties. In Ref 2 it was shown that structural stress can be related to crack propagation life through linear elastic fracture mechanics. Using the resulting relationship between structural stress and life, life estimations were made for a variety of HSLA steel specimens (e.g., tensile-shear, coach peel) in a number of conditions (e.g., as-welded, prestressed) and were compared with experimentally measured lives. Life estimations were within a factor of 3 of measured lives.

In the current work, the methodology developed in Ref 2 for estimating propagation life is extended by explicitly considering the effects of axial loading and of load ratio on life estimates. In addition, issues related to creating an appropriate finite element model are addressed, and a number of modeling guidelines are established. Total life estimations are made and compare favorably with experimentally measured lives of welds in mild steels in a variety of specimen configurations.
Factors Influencing the Reliability of Results in Accelerated Weathering Tests
Authors: Kockott D
Published: March 2009

The influence of both radiation and temperature on the ageing of polymers is discussed. With the purpose of improving the reliability of test results gained in accelerated weathering devices, it is recommended to measure the effective irradiance Eeff = ∫Eλ s(λ) dλ (Eλ: spectral irradiance, s(λ): spectral sensitivity of the material) and the effective radiant exposure Heff =∫Eeff dt. The temperature of the irradiated sample, among others, depends on both the spectral distribution Eλ of solar radiation and on the absorptance ε(λ) of the material as well as on the longwave infrared radiation of the environment. These influencing factors have to be observed when simulating environmental factors in laboratory devices. As an example, the testing of big component parts and entire vehicles is discussed.
Effects of Filter and Burner Aging on the Spectral Power Distribution of Xenon Arc Lamps
Authors: Ketola WD , Skogland TS , Fischer RM
Published: March 2009

Solarization caused by aging of the borosilicate glass filters used for xenon arc lamps has a very large effect on the short wavelength ultraviolet radiation emitted by the lamps, even with strict control of irradiance. If irradiance is precisely controlled at a constant mid UV wavelength, filter aging causes significant reductions in short wavelength UV and increases in long wavelength UV and visible light intensities. If irradiance is controlled in a broad band which includes long wavelength UV, filter aging will cause changes in short wavelength UV, even when the broad band irradiance is kept constant. Differences in short wavelength UV transmission between different lots of the same type of filter can cause very large changes in short wavelength UV emission of the lamp when aged filters are replaced. The differences in UV transmission between different lots of glass persist even after aging. Changes in the spectral power distribution of the xenon lamp caused by filter aging can have a significant effect on the rate of polymer or product degradation and may be a major cause of the variability in results between different devices running identical test cycles. Changes in xenon lamp spectral irradiance caused by aging of the xenon burner are much smaller than the changes caused by filter aging. Xenon burners used in high irradiance cycles may show larger losses of short wavelength UV emmissions than burners used in cycles controlled to produce lower irradiance.
Man Versus Machine: A Comparison of Visual Evaluation and Computerized Image Analysis for the Measurement of Weather-Induced Surface Cracking
Authors: Jacques LFE , Lee FH
Published: March 2009

Many of the types of weathering-induced degradation are not measured in an accurate quantitative manner. The cracking of a coating is a good example of such a parameter. Visual scales are used that can be either a photograph or a representative drawing of the degradation. Visual evaluation of cracking is particularly susceptible to operator bias and may not produce a repeatable or precise result. It is desirable to make a more exact measurement to discriminate more easily between coatings of different performances. It is also desirable to measure quantitatively the initial stages of cracking since these give the ability to shorten test times and develop more effective pass/fail criteria.

Technology is now available to measure cracking in a precise and repeatable way using digitized photographs or other images of the coatings and image analysis software techniques. A set of cracked coatings were measured using both image analysis and multiple visual inspectors, and the results were compared. The coatings used exhibited a wide range of colours and different levels and sizes of cracking defects. The specimens were evaluated by a team of professional coatings inspectors and were rated according to several industry standard scales, such as ASTM, and TNO(Toegepast Natuuwetenschappelyk Onderzok) of Delft, Netherlands. Items of interest were precision of measurement, reduction of operator-induced bias, and the speed of repetitive measurement. The data were analyzed statistically and the results presented.
Durability Studies of Solar Reflector Materials Exposed to Environmental Stresses
Authors: Jorgensen GJ , Kim H-M , Wendelin TJ
Published: March 2009

Methods that allow accurate prediction of service lifetimes need to be developed and demonstrated to spur the commercialization of solar reflector materials and systems. Without confident knowledge of service lifetimes, uncertainties in life cycle cost and warranty projections will significantly limit the economic viability of solar concentrators. To assure general and robust usefulness, methods should be based on correlations between accelerated, laboratory-controlled environmental stress factors and actual deployment conditions for a variety of applicable geographical locations. Accelerated experiments have identified the key stress factors of UV radiation, temperature, and relative humidity, and their effect on loss of performance, for a particular class of reflector materials. A model is proposed that allows prediction of the time dependent degradation of such materials as an analytic function of combined applied stresses. The model is shown to provide excellent agreement with measured performance data and provides a strong basis for future comparisons with data collected in field tests.
Comparison of Outdoor Behind Glass Weathering Exposure Standard Practices in Arizona and Florida
Authors: Putman WJ , McGreer M
Published: March 2009

Behind glass outdoor exposure testing is widely used within the automotive industry for the qualification of interior materials. This paper presents color change data for fourteen materials that underwent behind glass exposure testing, both in Arizona and south Florida. Six separate behind glass exposure methods were used for the Arizona testing and three for the Florida testing. All of the under glass exposures in this experiment are test methods that are either being used or accepted by major automotive companies. Color change test data is compared for all of the behind glass exposure methods and the resultant differences in test results and their causes are discussed.
Report on Joint SSPC/ASTM Round Robin
Authors: Boocock SK
Published: March 2009

ASTM Task Group D 01.27.31, (Corrosion Tests — Non-Automotive), is responsible for an ambitious Round Robin testing program to evaluate the capabilities of cyclic accelerated corrosion tests for coated products. This paper provides a report on the genesis of this program and provides preliminary analysis of typical results.
Development of a Methodology for Service Lifetime Prediction of Renewable Energy Devices
Authors: Kim H-M , Jorgensen GJ , King DE , Czanderna AW
Published: March 2009

Emerging advanced multilayer renewable energy devices, such as reflector materials and photovoltaic modules, are expected to exhibit significantly increased service lifetimes compared to existing devices. Such devices must be capable of 20 to 30 years of operation under harsh outdoor weathering conditions. Industrial manufacturers cannot afford to wait extended periods of time to determine whether such lifetimes are realistic. Consequently, a flexible, robust, and accurate method for predicting the service lifetime of such devices is essential. Two requirements for developing such a method are first, to correlate the accelerated lifetime test methods with anticipated life under real-world operating environments; and second, to establish statistical models for predicting service lifetimes based on environmental stress factors.

The relative significance of the weathering stress factors ultraviolet light (UV), temperature (T), and relative humidity (RH) was ascertained. Optical properties of new reflector materials were measured and their loss of performance with exposure time was modelled as a function of an appropriate combination of stress factors. Then, the functional relationship between performance measurements and time in accelerated lifetime tests was investigated. The basic framework of this approach is SPt analysis because it intends to explain the bridge functions from Stresses (S) to Performance (P) and from Performance to lifetime (t) of the materials. The results show that the cumulative dosage of ultraviolet radiation between 290–320 nm (UV-B) with synergistic effects of T and RH is a very critical factor in inducing performance loss. Finally, the SPt model developed for accelerated laboratory data was verified for data obtained from outdoor sites, and excellent agreement was found.
The Use of Ranked Versus Rated Data in the Evaluation of Weathered Specimens or Material
Authors: Asher LB
Published: March 2009

The evaluation of specimens after weathering (in natural outdoor exposures or accelerated cycles) can be handled by a number of approaches; two of these are ranking and rating. This paper will center on these two approaches and will demonstrate how ranking is often superior. Rating requires one to compare the specimens against a scale (ie. 1 through 10 with 1 being “excellent”, 5 being “good” and 10 being “poor”, etc.). Ranking on the other hand requires the direct comparison of the specimens against each other.

Since people typically do not like to be overly critical or overly generous, the rating approach of ten leads to the specimens being rated in the middle of the scale (with ratings of 4 to 7 out of a scale of 1 to 10). The specimens differentiation or discrimination is therefore greatly reduced. The ranking approach forces people to rank the specimens from best to worst. It is highly recommended that ties not be allowed; this forces the evaluators to clearly state their preferences.

Since ranking involves a direct comparison, all the specimens must be available at the same time. If this is not possible, the rating approach would be the logical choice. The use of visual examples or standards (that visually demonstrate three ratings,ie. 1,5 & 10) is strongly recommended in these situations.

The ranked and rated data from a visual comparison of six reflective sheetings for whiteness will be used to demonstrate the effectiveness of each approach. The statistical evaluation of the ranked data will be discussed. This will include both simplified and more comprehensive analysis approaches. The averages and ranges of ranked data will represent the simplified methods. Thurstone Scaling and Analysis of Variance (ANOVA) represent the more comprehensive methods.
Mechanisms of LiOH Degradation and H3BO3Repair of ZrO2 Films
Authors: Cox B , Ungurelu M , Wong Y-M , Wu C
Published: March 2009

During a program to elucidate the mechanisms by which LiOH accelerates the corrosion of zirconium alloys and boric acid inhibits this effect, specimens were exposed to 0.01, 0.1, and 1.0 M LiOH solutions at 300°C (573 K) or 360°C (673 K) with and without the addition of boric acid. Results showed that local dissolution of the ZrO2 films formed pores whose depth was a function of the LiOH concentration and probably also of the temperature, alloy composition, and structure. Below a critical LiOH concentration, only superficial porosity was developed in short experiments. Above this critical concentration (which lies between 0.1 and 1.0 M LiOH for Zircaloy-2 at 300°C) porosity develops throughout the initially impervious oxide and no pretransition corrosion kinetics are observed. Below this critical concentration, no effect of LiOH is observed on the pretransition oxidation kinetics until pores and cracks start to develop in the oxide prior to the oxidation rate transition. At this point (1.5 to 1.8 μm) LiOH can concentrate in the freshly developed pores by chemical extraction of water from the solution in the pores to form new ZrO2. Once the critical LiOH concentration is reached in the pores, enlargement or extension of the pores can occur by dissolution. This process should occur beneath the relatively untouched pretransition oxide when the bulk solution is not concentrated enough to attack the oxide surface. Hydrothermal redeposition of much of the dissolved ZrO2 occurs on specimen surfaces or within the porous oxide. Boric acid has no effect on ZrO2 dissolution by LiOH. It is considered that in concentrated solutions the solubility product of some complex lithium zirconate borate can be exceeded and this can plug the pores. In dilute solutions, therefore, boric acid can only operate inside the porous oxide film, where the chemical concentration mechanism should be equally effective for both LiOH and H2BO3. Any Li or B found subsequently in the film will be there as a consequence and not a cause of the corrosion process. It would be expected to occur in at least two forms, Li or B within pores or adsorbed on pore walls, and Li or B that is incorporated in hydrothermally deposited oxide. These two forms of doping would be “leachable” and “non-leachable,” respectively.
The Effect of the Trace Impurity Uranium on PWR Aqueous Corrosion of Zircaloy-4
Authors: Peters HR , Harlow JL
Published: March 2009

Commercial Zircaloy-4 specifications control natural uranium to <3.5 ppm by weight. Long-term in-pile corrosion tests were conducted on Zircaloy-4 coupons containing 0.1, 2.1, 10.6, and 24.1 ppm by weight of natural uranium. The objective of this testing was to determine the effect of the trace impurity uranium on the in-pile corrosion of Zircaloy-4. The tests were conducted in the advanced test reactor in Idaho at test temperatures of 355, 332, 310, and 274°C and at fast-neutron (>1 MeV) fluxes of > 1.0 × 1014 n/cm2-s. Limited testing was also conducted at lower fluxes.

The pre-transition corrosion rates were observed to increase with increasing uranium content and flux level. The transition times were doubled at 2.1 ppm and quadrupled at 10.6 and 24.1 ppm uranium compared to the 0.1 ppm control ingot. Transition time differences were observed to diminish with decreasing fast-neutron flux. Post-transition corrosion rates also increased with uranium levels. The net effect on long-term corrosion is a reduction (X2 to X5) in corrosion film thickness for Zircaloy-4 containing uranium levels at the specification limit (3.5 ppm) compared to the 0.1 ppm control ingot. Based on the data presented, significant differences in PWR corrosion will develop as a result of varying natural uranium levels in ingots.
Properties of an Irradiated Heat-Treated Zr-2.5Nb Pressure Tube Removed From the NPD Reactor
Authors: Chow CK , Coleman CE , Koike MH , Causey AR , Ells CE , Hosbons RR , Sagat S , Urbanic VF , Rodgers DK
Published: March 2009

Some pressure tubes in reactors moderated by heavy water have been made from heat-treated (HT) Zr-2.5Nb. One such tube was removed from the NPD nuclear reactor after 20 years of operation. An extensive program was carried out jointly by AECL and PNC to evaluate the condition and properties of this pressure tube. The investigations include irradiation creep, tensile, corrosion, delayed hydride cracking (DHC), fatigue, and fracture properties.

Results show that: (1) the in-reactor elongation rate is much lower and the transverse strain rates are slightly larger than in cold-worked (CW) Zr-2.5Nb tubes; (2) the tensile properties, hydrogen pickup, threshold stress intensity factor for DHC initiation, DHC velocity, and fatigue crack growth rates were similar to those of the CW Zr-2.5Nb material; (3) the fracture toughness of this tube, as measured by curved compact toughness specimens and burst tests, is slightly higher than the CW tubes. The results were also compared with other heat-treated Zr-2.5Nb materials irradiated in the Fugen reactor.

The tube was in excellent condition when removed from the reactor and would have been satisfactory for further service.
Effects of Microstructure on Ductility and Fracture Resistance of Zr-1.2Sn-1 Nb-0.4Fe Alloy
Authors: Nikulin SA , Goncharov VI , Markelov VA , Shishov VN
Published: March 2009

The effect of microstructure on the ductility and fracture resistance of Zr-1.2Sn-1Nb-(0.2–0.5)Fe alloy has been studied. Different structural states of the alloy were attained by varying the iron content and working/heat treatment schedules, which comprised quenching, cold work, and anneal. The results of the tests for uniaxial tension, impact toughness, and static crack resistance as well as the electron microscope analysis of the microstructure revealed that the main structural factors governing the level of the as-recrystallized alloy ductility and fracture resistance are the sizes and uniformity of distribution of intermetallic particles of different types in the matrix. The highest ductility and impact toughness are reached when fine intermetallic particles from 0.03 to 0.20 μm are distributed uniformly within the structure. The impact toughness and critical crack opening grow linearly with an increase of particle distribution density and a decrease in interparticle spacing. Changes in the alloy microstructure and mechanical properties were investigated upon its anneal after β-quenching. It is demonstrated that the highest values of ductility and impact toughness are reached with the formation of a polygonized matrix structure without intermetallic particle precipitation.
Influence of Processing Variables and Alloy Chemistry on the Corrosion Behavior of ZIRLO Nuclear Fuel Cladding
Authors: Comstock RJ , Schoenberger G , Sabol GP
Published: March 2009

Variations in the thermal heat treatments used during the fabrication of ZIRLO (Zr-1Nb-1Sn-0.1Fe) fuel clad tubing and in ZIRLO alloy chemistry were explored to develop a further understanding of the relationship between processing, microstructure, and cladding corrosion performance. Heat treatment variables included intermediate tube annealing temperatures as well as a beta-phase heat treatment during the latter stages of the tube reduction schedule. Chemistry variables included deviations in niobium and tin content from the nominal composition. The effects of both heat treatment and chemistry on corrosion behavior were assessed by autoclave tests in both pure and lithiated water and high-temperature steam. Analytical electron microscopy demonstrated that the best out-reactor corrosion performance is obtained for microstructures containing a fine distribution of beta-niobium and Zr-Nb-Fe particles. Deviations from this microstructure, such as the presence of beta-zirconium phase, tend to degrade corrosion resistance.

ZIRLO fuel cladding was irradiated in four commercial reactors. In all cases, the microstructure in the cladding included beta-niobium and Zr-Nb-Fe particles. ZIRLO fuel cladding processed with a late-stage beta heat treatment to further refine the second-phase particle size exhibited inreactor corrosion behavior that was similar to reference ZIRLO cladding. Variations of the inreactor corrosion behavior of ZIRLO were correlated to tin content, with higher oxide thickness observed in the ZIRLO cladding containing higher tin. The results of these studies indicate that optimum corrosion performance of ZIRLO is achieved by maintaining a uniform distribution of fine second-phase particles and controlled levels of tin.
Embrittlement of Reactor Core Materials
Authors: Kreyns PH , Bourgeois WF , White CJ , Charpentier PL , Kammenzind BF , Franklin DG
Published: March 2009

Over a core lifetime, the reactor materials Zircaloy-2, Zircaloy-4, and hafnium may become embrittled due to the absorption of corrosion-generated hydrogen and neutron irradiation damage. Results are presented on the effects of fast fluence on the fracture toughness of: (1) wrought Zircaloy-2, Zircaloy-4, and hafnium; (2) Zircaloy-4 to hafnium butt welds; and (3) hydrogen-precharged beta-treated and weld-metal Zircaloy-4 for fluences up to a maximum of approximately 150 × 1024 n/m2 (>1 MeV). While Zircaloy-4 did not exhibit a decrement in KIC due to irradiation, hafnium and butt welds between hafnium and Zircaloy-4 are susceptible to embrittlement with irradiation. The embrittlement can be attributed to irradiation strengthening, which promotes void formation in the high-strain crack-tip region, and, in part, to the lower chemical potential of hydrogen in Zircaloy-4 compared to hafnium, which causes hydrogen to drift over time from the hafnium end toward the Zircaloy-4 end and to precipitate at the interface between the weld and base-metal interface. Neutron radiation apparently affects the fracture toughness of Zircaloy-2, Zircaloy-4, and hafnium in different ways. Possible explanations for these differences are suggested. It was found that Zircaloy-4 is preferred over Zircaloy-2 in hafnium-to-Zircaloy butt-weld applications due to absence of a radiation-induced reduction in KIC plus its lower hydrogen absorption characteristics compared with Zircaloy-2.