bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of Crack Growth Behavior in a Residual Stress Field Using the Modified Strip-Yield Model
Authors: Hou C-Y , Charng J-J
Published: March 2009

In a previous study, Newman's modified strip-yield model which estimates the plasticity-induced crack closure was modified to estimate the crack growth behavior in a residual stress field. The results showed that the model gave good predictions when compared with experimental data reported in literature. However, it was also found that the model failed to predict Glinka's experimental data. In the current study, this difficulty was explained by the unusual crack growth behavior in Glinka's specimens which were made of 18G2AV steel, that is, the crack closure concept cannot be used to explain the crack growth behavior in 18G2AV steel at various load ratios. Hence, it was assured that the modified strip-yield model can be used for the residual stress problems. In addition, it was found that the crack growth behavior in an overload or a notch plastic zone can be solved by treating the crack growth in a way that the crack propagates in the residual stress field caused by the overload or the notch plasticity. This approach successfully captured the crack growth behavior in these pre-existing plastic zones, and the phenomenon that the measured overload affected distance in thin plates being much larger than the overload plastic zone size could be possibly explained by the residual stresses induced by the overload plasticity.
Influence of Bauschinger Effect on Residual Stress and Fatigue Lifetimes in Autofrettaged Thick-Walled Cylinders
Authors: Parker AP , Underwood JH
Published: March 2009

This work addresses the influence of Bauschinger effect upon residual stresses and associated fatigue lifetimes for pressurized, autofrettaged thick cylinders.The model employed allows for the variation with radius of Bauschinger Effect Factor (BEF) thoughout the autofrettaged tube since the percentage plastic strain, which determines BEF, will vary from a maximum value at the bore to zero at the elastic-plastic interface.

Accounting for BEF variability it is demonstrated that the residual compressive hoop stress at the inner radius of the tube reaches a maximum value at the percentage overstrain level below which reversed yielding does not occur. Existing experimental residual stress measurements from a variety of sources are shown to support this thesis. This value of overstrain may serve to maximize crack initiation lifetime in autofrettaged thick cylinders.

For a tube with significant heat-checking and associated initial crack-like defects it is necessary to consider fatigue crack growth rates governed by a crack growth law such as Paris' Law. For a tube of radius ratio 2.0 and at a value of approximately 40% overstrain, slightly in excess of that for the onset of reversed yielding, the fatigue lifetime exhibits a maximum value. In general fatigue lifetimes achieve a maximum value at overstrain levels in which yielding reaches 1.4 times bore radius and are almost constant thereafter. Furthermore such extended overstrain leads to a small increase in residual stress at the outside diameter (OD), thus increasing R ratio at that location and reducing fatigue lifetime for crack growth originating at the OD. Existing experimental lifetime measurements are shown to require the inclusion of BEF to properly account for these observed lifetimes.
Fracture Analysis of Ductile Crack Growth in Weld Material from a Full-Thickness Clad RPV Shell Segment
Authors: Keeney JA , Williams PT
Published: March 2009

Recent studies indicate that the onset of stable ductile tearing leads to crack-tip fields ahead of the growing crack and crack-tip profiles that differ from those of a stationary crack. Stable ductile tearing exposes additional volumes of material to elevated stresses as the crack advances, which alters the sampling of potential cleavage initiation sites on the microstructural level. Also, measured cleavage fracture toughness values for these specimens will be influenced by changes in crack-tip constraint conditions that occur with prior stable crack growth. Fracture analysis techniques for inclusion of ductile crack growth in finite-element analyses were evaluated through applications to a full-thickness clad beam specimen containing a shallow crack in material for which metallurgical conditions are prototypic of those found in reactor pressure vessels (RPVs) at beginning of life. The beam specimen, which experienced a significant amount of precleavage stable ductile tearing, was fabricated from a section of an RPV wall (removed from a canceled nuclear plant) that includes weld, plate, and clad material. Effects of precleavage tearing on estimates of fracture toughness were investigated using continuum damage models.
A DNAPL Emergency Remedial Action Program in a Developing Country
Authors: Daus AD , Nobre MM
Published: March 2009

A chlorinated hydrocarbon (CHC) manufacturing facility in northeastern Brazil inadvertently released chlorinated hydrocarbons to the subsurface. The underlying ground water lies 60 to 70 m below the ground surface and is part of a large drinking water aquifer (Barreiras aquifer). Downgradient potential receptors include local inhabitants who draw their potable water from hand-dug wells (cacimbas), wetlands, and a large estuary.

The Barreiras aquifer is alluvial in origin and consists of interbedded clays, silts, sands, and gravels. A linear geologic structure was identified at the base of the Barreiras aquifer that resembles a paleo-channel. This channel appears to correlate with the zone of highest CHC contamination.

CHCs were subsequently detected in nearby production wells 500 m downgradient. An accelerated ground-water investigation and interim remedial action plan were implemented to contain the highest CHC concentrations and provide hydraulic control downgradient of the CHC source. Ground-water production wells were installed along the paleo-channel in the alluvial sediments. Ground-water level and quality monitoring suggest that the program has been successful although additional monitoring is required to confirm the initial results. Between April 1992 and December 1993, over 1.2 billion gallons of ground water have been pumped and over 52 tons of dissolved solvents have been removed. Future plans for the project include evaluation and optimization of the ground-water capture system and evaluation of dense nonaqueous phase liquid (DNAPL) recovery.
STERDI: An Innovation to Accelerate Remedial Investigations and Engineering
Authors: Waslenchuk D , Man V
Published: March 2009

The purpose of this paper is to introduce a procedure for remedial investigations and for beginning cleanup more quickly than by traditional approaches. Simultaneous Testing, Exploration, Remedial Design, and Installation (STERDI) speeds the early and mid-phases of the remediation process, eliminates some traditional repetitive steps, and thereby results in lower project costs. The procedure involves the installation of in-ground components of an appropriate remedial system during the same exploration program that delineates the contaminant distribution. The method is built upon two capabilities: (1) planning for the multiple possible contaminant distributions, and (2) conducting “real-time” quantitative chemical analyses of soils during explorations in the vicinity of a release.

To implement STERDI, one has to recognize the various contaminant distributions which may have resulted from the release, prior to conducting subsurface explorations. Several spill “conceptual models” are developed, based on knowledge of the contaminant's geochemical behavior and on local geological characteristics. For each model, a “presumptive remedial design” (involving borehole-installed equipment) is prepared. An exploration program, incorporating in-field chemical analysis, is planned with sequencing which would allow early identification of which set of modeled conditions actually occurs. Once actual conditions are identified, the exploratory boreholes are completed by immediately installing remediation system components, guided by the in-field chemical testing results, according to the presumptive design which was developed for that model prior to the fieldwork.

At a gasoline release, the contaminant distribution was discovered and the in-ground portions of a vapor extraction system, including monitoring wells, were installed, all in a single three-day field effort. At a tetrachloroethylene spill, contamination was found through the unsaturated zone, and within the upper 20 ft (6.1 m) of the 50-ft-deep (15 m) overburden aquifer; a bubbler was installed in an exploratory borehole for remediation, accurately placed just beneath the contaminated interval, all in a two-day effort.
A Comparison of Generic Human Health Risk-Based Soil Remediation Criteria in Canada and the U.S.: Two Case Studies
Authors: Kangas MJ , Scott PK , Finley BL , Paustenbach DJ
Published: March 2009

The Canadian government and the U.S. Environmental Protection Agency (U.S. EPA) are currently developing generic soil quality criteria that would be considered applicable to all sites, either as levels for screening analysis or, under some circumstances, as ultimate remediation goals. The draft Canadian criteria, currently under revision, are based on protection of both human and ecological health, while the draft U.S. EPA values are intended to be protective of residential exposures. In this analysis, we compare and contrast the technical basis for the generic criteria developed by both governments, with emphasis on cadmium and pentachlorophenol. Soil criteria for cadmium and pentachlorophenol are expected to be more conservative in Canada than in the U.S. if groundwater protection is not a concern. The pattern is reversed if groundwater is a concern. Therefore, the cost of achieving approximately the same level of health protection could be dramatically different in the two countries for remediating soil containing cadmium or pentachlorophenol.
Measures of Fish Behavior as Indicators of Sublethal Toxicosis During Standard Toxicity Tests
Authors: Little EE , DeLonay AJ
Published: March 2009

Behavioral functions essential for growth and survival can be dramatically altered by sublethal exposure to toxicants. Measures of these behavioral responses are effective in detecting adverse effects of sublethal contaminant exposure. Behavioral responses of fishes can be qualitatively and quantitatively evaluated during routine toxicity tests. At selected intervals of exposure, qualitative evaluations are accomplished through direct observations, whereas video recordings are used for quantitative evaluations. Standardized procedures for behavioral evaluation are readily applicable to different fish species and provide rapid, sensitive, and ecologically relevant assessments of sublethal exposure. The methods are readily applied to standardized test protocols.
Evaluating Geotextile Pore Structure
Authors: Fischer GR , Holtz RD , Christopher BR
Published: March 2009

There are many test methods available to determine the pore sizes of geotextile filters. Often overlooked is the fact that each method provides a different interpretation of a geotextile's pore structure. A survey of the available test methods, indicates that four categories of pores can be measured. Pore characteristics are identified by one of the following methodologies: sieving, theoretical, volumetric, and numerical. A critical review of the data produced by these methods shows that the actual pore structure as related to flow-through behavior can only be determined by the bubble point method, which provides a volumetric pore size. This test identifies the constriction size of each pore channel in a geotextile, where retention and clogging are most critical. The bubble point test method is advantageous because it provides for the complete pore size distribution of the geotextile, can be performed more efficiently than sieving methods, and provides an accurate estimate of the permeability of the geotextile.
Determination of Water Penetration Resistance of Geotextiles
Authors: Dierickx W
Published: March 2009

Some woven and nonwoven geotextiles exhibit a resistance to water penetration at initial wetting. This phenomenon is known as ‘Water Head Support’. Tests have been carried out to investigate whether the wetting problem is only an initial problem and whether geotextiles behave in the same way in contact with soil. Therefore drain tubes were wrapped with geotextiles and installed in a sand model. Tests were carried out under various soil conditions (dry and wet) and geotextile conditions (dry and wet).

This resistance to water penetration influences the performance of the geotextile and is disadvantageous compared with geotextiles which do not possess this resistance.

The apparatus described to evaluate the initial resistance to water penetration applies a water head to the geotextile. Tests were carried out for a number of geotextiles. The results revealed that, for some geotextiles, substantially high water heads are reached before the water starts to flow through the geotextile.
A Modified Gradient Ratio Test Device
Authors: Fannin RJ , Vaid YP , Palmeira EM , Shi YC
Published: March 2009

The gradient ratio test is used to assess soil-geotextile compatibility in filtration applications. Experience gained in performing the test is summarized for ten soils and four non-woven geotextiles, and the potential for application of the test method is demonstrated. Details of a new, modified test device are then presented which address a perceived limitation of the existing configuration of the test device. Results of a preliminary series of tests, performed to commission the modified gradient ratio test device, suggest the filtration behaviour of the geotextile is essentially independent of normal stress.
Geotextile Filter Design Critique
Authors: Wilson-Fahmy RF , Koerner GR , Koerner RM
Published: March 2009

The current status of design of geotextile filters in highway drainage applications is challenged in this paper by virtue of having the actual performance behavior of 91 exhumed field sites. The drainage systems investigated involved mainly highway edge drains in addition to some selected cases of retaining wall drains and erosion control systems. Considering the field data as “ground truth” information, they are compared with the existing permeability, soil retention and excessive-clogging criteria that have been proposed in the literature for design purposes. The current Federal Highway Administration (FHwA) guidelines are shown to be very suitable and perform well against the results of the field exhumed sites. It is suggested, however, that the gradient ratio test recommended by FHwA be replaced by the long term flow test or the hydraulic conductivity ratio test in evaluating the possibility of excessive clogging.
Field Performance of Geosynthetic Highway Drainage Systems
Authors: Koerner GR , Koerner RM , Wilson-Fahmy RF
Published: March 2009

This paper presents field results from a three year study focused on the performance of geosynthetic materials in transportation related drainage applications. The application areas of interest were mainly highway edge drains, although selected retaining wall drains and erosion control systems were also involved. Included in the study are geotextile filters, geocomposite edge drains, geocomposite sheet drains and, to a limited extent, plastic pipe. In many instances, the geotextile was observed to be the key element in the overall success or failure of the system. Thus the geotextile, serving in a primary function as a filter was the major focal point of the investigation.

The paper presents the results of exhuming ninety-one (91) field sites in seventeen (17) states throughout the United States. The results give a clear assessment of geosynthetic drainage systems from a long-term field perspective. Furthermore, it allows for specific recommendations to be made to avoid those situations where problems occurred. In a subsequent paper in these Proceedings the results will ultimately be used to challenge the necessary design formulas currently available for geotextile filters in highway drainage applications.
Evaluation of Pre-1994 Ontario Highway Edge Drain Practice
Authors: Raymond GP , Bathurst RJ , Hajek J
Published: March 2009

Presented are results from excavations made to evaluate the performance of various types of edge drains at selected locations on Ontario highways. The pavements are founded on both clay and sand subgrades. The edge drains excavated include Geocomposite Edge Drains, Geotextile Sock-Wrapped Pipe Edge Drains and Geotextile-Wrapped Aggregate Edge Drains. Installation techniques included: Ploughed-in-Place, Trench Excavation, and Mechanical Trencher and Boot. All edge drains were installed after the highway was completed (i.e. retrofit construction). In each case the backfill used was the excavated or displaced shoulder Granular ‘A’ material (typically similar to ASTM D-2940). The observations and resulting test data obtained show differences between the installation concepts and asbuilt construction. Drains that were installed adjacent to and in contact with the pavement edge were found to be separated from the pavement edge by eroded/pumped fine soil particles. This seriously compromised drainage, particularly from any open-graded drainage layer. Tests showed that the granular backfills were up to 1000 times less permeable than the geotextiles used for the edge drains. Recommendations are made for the installation of retrofitted edge drains.
Aspects of Silicon Contamination Control by Lifetime Measurements
Authors: Zoth G
Published: March 2009

In Si device fabrication lifetime measurements are frequently used for the routine control of heavy metal contamination induced by wafer processing. Today commercial, cleanroom-compatible tools are available for a number of lifetime measurement techniques, namely the Photoconductive Decay (PCD) method, the Surface Photovoltage (SPV) method, and the Elymat technique. All three methods are well suited for routine measurements in a manufacturing line. We present a number of correlation results between the different methods and show up some possible pitfalls connected with lifetime measurements. These pitfalls are often connected with the injection level, i.e. the ratio of the minority and majority carrier concentration during the measurement. The role of the injection level is discussed in the context with charge carrier trapping, Fe impurities and oxygen precipitates. Because of its practical relevance the properties of Fe in silicon are discussed in detail including comparisons between the bulk-sensitive lifetime methods and surface-sensitive techniques like Total Reflection X-Ray Fluorescence (TXRF). Furthermore, some results are given about the segregation of Fe in bulk Si and Si oxide after oxidation processes. Finally typical examples are presented for the application of the Elymat and SPV technique including the routine monitoring of furnace processes and the characterization of handling-induced backside contamination.
Carrier Lifetime Measurements by Microwave Photoconductivity Decay Method
Authors: Hashizume H , Sumie S , Nakai Y
Published: March 2009

The recombination lifetimes of silicon wafers were studied using microwave photo-conductivity decay(μ PCD) method with variable photo-injection function. For samples with surface inversion layers, the lifetimes increased as the injected carrier concentration decreased, and converged toward the value determined by the SiO2/Si interface trap density. It was found that the bulk recombination lifetimes could be measured in middle-high injection. Any clear dependence was not observed in the samples with surface accumulation layers. The recombination lifetimes of light-irradiated p-type silicon with iron contamination revealed strong dependence on injected carrier concentration due to breaking up iron-boron pairs. Molybdenum contamination of the epitaxial layers in p/p+ and p/p− wafers were also investigated using the differential μPCD technique.
Present Status of the Surface Photovoltage Method (SPV) for Measuring Minority Carrier Diffusion Length and Related Parameters
Authors: Lagowski J , Edelman P , Faifer V
Published: March 2009

We present an overview of the physics and practical issues related to surface photovoltage measurement of the minority carrier diffusion length and its application to monitoring recombination center defects in silicon. A tutorial description is given of the role of pertinent processes like injection, recombination and trapping. The evolution of the SPV method is presented followed by a description of most recent refinements addressing the measurement of long diffusion lengths in silicon wafers with emphasis on accuracy, measuring speed, tool-to-tool reproducibility and, practically the most important question of monitoring, iron concentration.
Silicon Lifetime Degradation as a Function of Wet Chemical Cleans and Chemical Purity
Authors: Linn J , Rouse G , Wereb W , Leggett R , Slasor S , Lowry R , Cameron R , Canfield R
Published: March 2009

Diffusion length data from silicon wafers exposed to various standard semiconductor process cleans and wet cleaning process tools will be presented. Data collected with an ElectroLYtic Metal Analysis Tool, or ELYMAT, will show the effects on silicon lifetimes of SC1, SC2 and SC1+SC2 combined cleans, as well as the cumulative effects which result from multiple cleaning cycles. Results from a variety of tools widely used for wafer cleaning will be presented. Data indicate that SC1 cleaning alone prior to thermal treatment can lead to extensive lifetime degradation. The data also suggest that lifetimes decrease as the number of SC1 + SC2 cleaning cycles increases. Along with the effects on silicon lifetimes of the standard wet cleans, number of clean cycles and specific tools will be data comparing different purity grades of chemicals. Higher purity grades of process chemicals are shown to favorably affect lifetimes in many but not all cleaning chemistries. ELYMAT analysis can be used to help determine which chemical grades are best suited for specific device processing requirements and to justify the added costs of ultra pure chemicals for processing certain product types which benefit from high silicon lifetimes.
Application of Recombination Lifetime Measurements in Silicon Wafer Manufacturing
Authors: Seacrist MR
Published: March 2009

Increasingly stringent demands are being placed on the surface and bulk metal contamination levels of silicon wafer starting material in order to meet ULSI device requirements. Recombination lifetime measurements are applied in silicon wafer manufacturing to monitor metal contamination from various processes including crystal growth, thermal treatments, cleaning processes, epitaxial growth, and to check final product quality. Applications of recombination lifetime measurements in silicon wafer manufacturing are reviewed. Comparisons of recombination lifetime data are made between measurement techniques.
High Precisin and High Accuracy Isotopic Measurement of Uranium Using Lead and Thorium Calibration Solutions by Inductively Coupled Plasma-Multiple Collector-Mass Spectrometry
Authors: Bowen I , Walder AJ , Hodgson T , Parrish RR
Published: March 2009

A novel method for the high accuracy and high precision measurement of uranium isotopic composition by Inductively Coupled Plasma-Multiple Collector-Mass Spectrometry is discussed. Uranium isotopic samples are spiked with either thorium or lead for use as internal calibration reference materials. This method eliminates the necessity to periodically measure uranium standards to correct for changing mass bias when samples are measured over long time periods. This technique has generated among the highest levels of analytical precision on both the major and minor isotopes of uranium. Sample throughput has also been demonstrated to exceed Thermal Ionization Mass Spectrometry by a factor of four to five.
99Tc Bioassay: A Direct Comparison of Liquid Scintillation Radiation Detection and ICP-MS Mass Detection of the 99Tc Isotope
Authors: Lewis LA , Schweitzer GK
Published: March 2009

A means of analyzing 99Tc in urine by inductively coupled plasma mass spectrometry (ICP-MS) has been developed. Historically, 99Tc analysis was based on the radiometric detection of the 293 keV Emax. beta decay product by liquid scintillation or gas flow proportional counting. A separation scheme for 99Tc detection by ICP-MS is given and is proven to be a sensitive and robust analytical alternative. A comparison of methods using radiometric and mass quantitation of 99Tc has been conducted in water, artificial urine, and real urine matrices at activity levels between 700 and 2200 dpm/L. Liquid scintillation results based on an external standard manual quench correction and an automatic quench curve correction method are compared with results obtained by ICP-MS. Each method produced accurate results; however, the precision of the ICP-MS results is superior to that of liquid scintillation results.
Wear Mechanisms of Milling Inserts: Dry and Wet Cutting
Authors: Gu J , Tung SC , Barber GC
Published: March 2009

There is less literature on wear of milling tools than on wear of turning tools because milling is one of the most complicated machining operations. The intermittent milling action creates mechanical and thermal surges that distinguish milling from single-point machining. A systematic tool life study for face milling inserts was conducted with and without coolant. Workpieces made of 4140 steel were cut by C5 grade carbide inserts under various cutting conditions. The comparison between dry and wet cutting shows that caution should be taken when applying a coolant for milling operations. Special tests should be carried out in evaluating potential coolant candidates. It is not always true that coolant enhances tool life for milling. Wear mechanisms are presented by means of wear maps. Identified wear mechanisms are: micro-attrition, micro-abrasion, mechanical fatigue, thermal fatigue, thermal pitting, and edge chipping.
On the ΔKeff Concept: An Investigation by Means of a Discrete Dislocation Model
Authors: Riemelmoser FO , Pippan R
Published: March 2009

Some results of discrete dislocation mechanics concerning fatigue crack growth are discussed in two parts. The first part deals with the plasticity-induced crack closure under plane strain conditions. The equations describing the deformation of crack flanks induced by edge dislocations are derived. These equations predict crack face contact for an edge dislocation in the wake of a sharp crack. The principle of superposition then immediately shows that the crack flanks even may contact at blunted cracks. This is visualized first by a suitable choice of the dislocation arrangement and afterwards also by the results of simulations of the dislocation motion at a growing fatigue crack.

In the second part these simulations are investigated more closely. During the initial period of a constant-amplitude test the crack growth increment per loading cycle and the closure stress intensity are monitored. By applying Elber's ΔKeff concept a conceptual crack growth rate is calculated and is compared with the real crack growth increment per loading cycle.
Analysis of Fatigue Crack Growth in Terms of Crack Closure and Energy
Authors: Ranganathan N
Published: March 2009

The fatigue crack growth behavior of the aluminum alloy 2024 is analyzed using the crack closure and an energy-based concept. The different test conditions studied include load ratio and environmental effects, crack growth retardation following a single overload, and crack propagation under block load tests. Crack opening loads using the compliance technique permit the effect of load ratio to be taken into account. After an overload, in the deceleration phase, the evolution of the crack opening load is not compatible with that of the crack growth rate. The measured crack opening levels under constant-amplitude loading conditions are comparable to those predicted under plane strain conditions for moderate ΔK levels. It is shown that most of the effects usually attributed to closure can be successfully explained using energy concepts. In particular, it is shown that there exists a linear relationship between the crack growth rate and the energy dissipated per cycle at high growth rates, which is valid for both the environments studied, and it corresponds to a crack growth mechanism characterized by striation formation during each cycle. For lower growth rates a power law relationship can be proposed between these two parameters. The above-mentioned linear relationship holds also for the block loading conditions based on total energy dissipated per block. Certain experimental facts bring out the effect of closure on the energy dissipated. It is further shown that the possible existence of a mixed (Mode I and Mode II) mode crack opening at the crack tip has to be taken into account to correctly evaluate the energy dissipated near the crack tip.
Measurability of Crack Closure
Authors: Pippan R , Riemelmoser FO , Bichler C
Published: March 2009

Crack closure can be measured either with compliance techniques or by means of crack propagation methods.

Each of these methods has its own specific limitation. We have performed simulations to show that the results of the measurements with compliance technique near the tip depend strongly on the position of the displacement gages and that the compliance curves of the remote clip gages are often too insensitive to detect the near-crack-tip closure.

Apart from the sensitivity of the various methods for measuring near-tip closure there are also problems in determining the effective stress intensity ranges from the load-displacement curves. The different procedures proposed in the literature are discussed, too. It will be shown that the measured stress intensity where the crack physically opens is the parameter which determines the effective stress intensity range. Only in the case of a minute number of contacts with a width very small in relation to the distance to the crack tip does the stress intensity factor, where the contacts open, underestimate the real acting effective stress intensity range at the tip.
Near-Tip and Remote Characterization of Plasticity-Induced Fatigue Crack Closure
Authors: McClung RC , Davidson DL
Published: March 2009

An elastic-plastic finite element model and high resolution experimental measurements of growing fatigue cracks are employed in partnership to investigate the relationship between crack closure, near-tip deformation behavior, and remote load-displacement measurements. The model focuses on plasticity-induced closure effects for fatigue cracks in the Paris regime, while the experiments study fatigue cracks in the Paris and near-threshold regimes in a variety of materials. The suitability of the ASTM compliance offset method and the recently-proposed adjusted compliance ratio (ACR) method to characterize near-tip closure effects is evaluated. The experiments and analyses both show that crack-tip strains below the crack-opening stress, Sop, are a relatively small fraction of the total crack-tip strain range for cracks in the Paris regime, and therefore may be insignificant for crack-tip deformation and damage and crack growth. The experiments further indicate that crack-tip strains below Sop are a relatively larger fraction of the total crack-tip strain at lower ΔK values, nearer the threshold, where Sop values are higher. The current ASTM compliance offset procedure for determining the crack opening load is shown to provide accurate information about true crack-tip opening loads in theory. However, due to the limited sensitivity of the method in practice, and the corresponding need to employ a non-zero compliance offset, the method gives underestimates of opening and closing loads that may be considerably in error relative to the true crack-tip values. The current ACR technique does not appear to do a good job of characterizing the near-tip deformation response for cracks in the Paris regime, because remote displacement measurements do not appear to be adequately sensitive to near-tip strains.
Determining Fatigue Crack Opening Loads from Near-Crack-Tip Displacement Measurements
Authors: Riddell WT , Piascik RS , Sutton MA , Zhao W , McNeill SR , Helm JD
Published: March 2009

The aim of this research was to develop a near-crack-tip measurement method that quantifies crack closure levels in the near-threshold fatigue crack growth regime—a regime where crack closure is not well characterized by remote compliance methods. Further understanding of crack closure mechanics was gained by performing novel crack growth experiments in conjunction with numerical simulations of three-dimensional crack-front propagation. Steady-state (i.e., constant growth rate) fatigue crack growth rates were characterized by performing constant cyclic stress intensity range (ΔK) experiments over a wide range of stress ratios (R). Near-crack-tip (less than 0.3 mm behind) load-versus-displacement measurements were conducted on the specimen surface using a novel noncontact experimental technique (Digital Imaging Displacement System—DIDS).

The experiments and simulations revealed that the three-dimensional aspects of fatigue crack closure must be considered to determine correct opening load levels from near-crack-tip load-versus-displacement data. It was shown that near-crack-front opening levels are nearly constant along the interior portion (greater than 90%) of the crack front, but increase near the free surface. The interior opening load was found to collapse closure-affected data to intrinsic rates, and thus shown to relate to the true crack-front driving force parameter. Surface opening load DIDS measurements made at an optimal distance behind the crack tip were used to correlate da/dN with ΔKeff. Opening load determinations made less than the optimal distance behind the crack tip were shown to be too high to correlate fatigue crack growth rates.
Direct Observation of the Residual Plastic Deformation Caused by a Single Tensile Overload
Authors: Bichler C , Pippan R
Published: March 2009

The fatigue crack growth behavior following single tensile overloads at high stress intensity ranges in a cold-rolled austenitic steel has been studied experimentally. After tensile overloads, fatigue cracks initially accelerate, followed by significant retardation, before the growth rates return to their baseline level. The initial acceleration was attributed to an immediate reduction in near-tip closure. Scanning electron micrography and stereophotogrammetric reconstruction of the fracture surface were applied to study the residual plastic deformation caused by a single tensile overload in the mid-thickness of the specimen. The measured residual opening displacement of the crack as a function of the overload is presented and compared with simple estimations. Also, free specimen surface observations of the residual plastic deformation and crack growth rate were performed. In the midsection of the specimens the striation spacing-length, i.e., the microscopic growth rates, were measured before and after the applied overload. It will be shown that the measured plasticity-induced wedges from the single overload and the observed propagation behavior support the significance of the concept of crack closure.
A Unified Elastic-Plastic Model for Fatigue Crack Growth at Notches Including Crack Closure Effects
Authors: Dankert M , Greuling S , Seeger T
Published: March 2009

The reasons for fatigue failure of many components and subassemblies are internal defects in the material or cracks and the subsequent propagation. Cracks normally originate in areas of stress concentration, e.g., at notches.

It is known that a major factor governing the service life of notched components under cyclic loading is fatigue crack growth in notches. A uniform elastic-plastic crack growth model, based on the J-integral, was developed which especially considers the crack opening and closure behavior for the determination of crack initiation and propagation lives for cracks at elliptical notches under constant or variable-amplitude loading.

For this model, an algorithm for the description of the crack opening and closure behavior and approximation formulas were developed for the determination of the stress intensity factor K and the J-integral for surface, corner and through-thickness cracks at elliptical internal and external notches. The crack growth model will be introduced and its individual modules, as well as the complete concept, were verified by experiments and two- and three-dimensional elastic and elastic-plastic finite-element analyses. Experiments, finite-element analyses, and calculations show excellent correspondence in all aspects.
Description of Crack Growth Using the Strip-Yield Model for Computation of Crack Opening Loads, Crack Tip Stretch, and Strain Rates
Authors: de Koning AU , ten Hoeve HJ , Henriksen TK
Published: March 2009

Nowadays, application of the strip-yield model for computation of crack opening load levels is well known. In this paper the incremental formulation of a fatigue crack growth law is used to demonstrate the role of the crack opening load level in time-independent fatigue crack growth. Less known is the ability of the strip-yield model to define the strain rate at the crack tip. A threshold level εth of this strain rate is introduced and used to formulate a criterion for initiation of time-dependent accelerated fatigue crack growth. This process is called corrosion fatigue. To account for effects of environment and frequency on the crack growth rate a time-dependent part is added to the incremental fatigue crack growth law. The resulting incremental crack growth equation is integrated to obtain the crack growth rate for a load cycle.

The model discussed in this paper is a mechanical model. Physical aspects other than strain rate, loading frequency and load wave shape are not modeled in an explicit way. Hence, the model is valid for specific environment/base metal combinations. However, in consideration of the effects of small variations of environment, temperature, and other variables on the crack growth rates, it can be used as a reference solution.

The fatigue crack growth model has been implemented in the NASGRO (ESACRACK) software. The time-dependent part is still subject to further evaluation.
AE Evaluation of Fatigue Damage in Traffic Signal Poles
Authors: Hamilton HR , Fowler TJ , Puckett JA
Published: March 2009

Two traffic signal structures recently collapsed in Wyoming. The collapse was a result of brittle fracture of the connection between the cantilever signal light support arm (mast arm) and the vertical pole (post) caused by wind-induced, largeamplitude vibrations of the mast arm. This paper presents the problem, the proposed test program, the results of initial development tests, and the effort to develop a viable AE testing technique along with evaluation criteria that can be used to screen in-service traffic signal poles.
Acoustic Emission and Ultrasonic Testing for Mechanical Integrity
Authors: Ternowchek SJ , Gandy TJ , Calva MV , Patterson TS
Published: March 2009

Today's owner/operator of process equipment is required to implement “good engineering tests” to ensure the mechanical reliability of his equipment. There are several ways this can be accomplished. One or more nondestructive testing (NDT) techniques, such as Acoustic Emission, Ultrasonics, Radiography, Magnetic Particle, Visual and others can be used. Most of these require the equipment be taken off line before the inspections can be performed. In some cases, when internal inspections are used, the cost of the inspection increases significantly. This paper describes an inspection program which uses Acoustic Emission (AE) as the primary technique for performing a global evaluation of the equipment's mechanical integrity. When the AE results indicate potential problems, a second NDT method, Ultrasonics (UT) shear wave analysis or thickness gauge, is utilized to determine the source mechanism, its characteristics and its boundaries. The two techniques complement each other quite well. This approach to equipment reliability offers several advantages: 1) the test, in many cases, can be performed on-line with product; 2) the equipment is evaluated under its normal operating conditions; 3) different damage mechanisms such as cracking, corrosion and embrittlement may be detected with a single test; 4) the cost savings can be substantial over other methods. In addition to describing the AE technique utilized, its advantages and disadvantages and an improved analysis method, there are examples of results produced on several recent tests, a 60 ft. diameter sphere, a 50 ft. diameter storage tank and a jacketed process vessel.
Prediction of Slope Failure Based on AE Activity
Authors: Shiotani T , Ohtsu M
Published: March 2009

Slope failure occurs transiently due to the brittle nature of failure, of which mechanisms are dependent greatly on the ground properties. Because the failure often produces large-scale damage, techniques for predicting slope failure are in urgent demand. In the present paper, the applicability of AE to the prediction of slope failure is discussed. Firstly, characteristics of AE wave attenuation in the ground are examined. Efficient wave-guide materials, which enable us to detect AE waves generated in the ground with good sensitivity, are studied. Secondly, in order to estimate the failure process inside the ground, a new procedure is proposed to determine the b-value in real-time from the peak-amplitude distribution of acquired AE waveforms. Finally, curve fitting techniques such as graphical analysis and the rate process analysis are applied to AE activity to predict the slope-failure time.
Field Data on Testing of Natural Gas Vehicle (NGV) Containers Using Proposed ASTM Standard Test Method for Examination of Gas-Filled Filament-Wound Pressure Vessels Using Acoustic Emission (ASTM E070403-95/1)
Authors: Fultineer RD , Mitchell JR
Published: March 2009

There are many composite wrapped pressure vessels in service. These containers are most widely used for gas storage in natural gas vehicles (NGV). A standard has been developed for the testing of these vessels by the subcommittee ASTM E07.04.03 Acoustic Emission (AE) applications. The AE test method is supported by both field test data and laboratory destructive testing. The test method describes a global volumetric testing technique which is offered as an alternative to the current practice of visual inspection.
Acoustic Emission Testing of Steel-Lined FRP Hoop-Wrapped NGV Cylinders
Authors: Akhtar A , Kung D
Published: March 2009

Acoustic emissions (AE) were examined from ten steel-lined cylinders, hoop-wrapped with continuous glass fiber reinforced plastic (FRP), after 4 years in natural gas vehicle (NGV) service. A test pressure of 27.6 MPa (4000 psi) was used which is 7% above the standard specified factor of 1.25 of the nominal service pressure. Hydraulic pressure cycling was applied in the range of 2.4–24.1 MPa (350–3500 psi) to simulate refueling in the laboratory. Burst pressure was measured for vessels containing no detectable flaw, with flaws in the FRP and cracks in the metallic liner. It was found that visual examination has shortcomings for the inspection of hoop-wrapped cylinders. AE data obtained through incremental pressurization to 27.6 MPa (4000 psi), holding pressure for 5 minutes, and unloading, do not provide useful information on structural integrity. Relative emission during two consecutive pressurization cycles holds promise for the nondestructive evaluation of metal lined FRP hoop-wrapped cylinders.
In Vitro Endocrine Disruptor Screening
Authors: Soto AM , Michaelson CL , Prechtl NV , Weill BC , Sonnenschein C
Published: March 2009

Environmental contaminants have been found to produce estrogen-like and androgen-antagonistic effects. It has been hypothesized that environmental estrogens may be playing a role in the decrease of the quantity and quality of human semen, and in the increased incidence of cryptorchidism, and testicular and breast cancer in humans. This hypothesis will require the solution of a series of technical problems before it can be explored. In vitro assays are crucial to accomplish this objective.

The MCF7 cell proliferation assay (E-SCREEN) is the most widely used of the estrogen screens. It is the most sensitive, as it discriminates among agonists and antagonists, and so far, neither false positives nor false negatives have been found among the chemicals screened. Yeast assays do not discriminate among agonists and antagonists. In addition, false negatives have been reported.

The androgen screen (A-SCREEN) assay measures cell proliferation. Alternative assays based on the expression of stable transfected reporter genes are being developed. The only limitation of in vitro/in culture assays is that they cannot detect most prohormones. In order to overcome this limitation, an activation step needs to be developed.
Deiodination as an Index of Chemical Disruption of Thyroid Hormone Homeostasis and Thyroidal Status in Fish
Authors: Eales JG , Brown SB , Cyr DG , Adams BA , Finnson KR
Published: March 2009

Commonly used indices of fish thyroidal status are based on thyroxine (T4) secretion by thyroid tissue under control of the central brain-pituitary-thyroid axis. However, much of the control of the fish thyroid system also occurs in peripheral tissues, such as liver, by regulating T4 prohormone conversion to biologically active 3,5,3'- triiodothyronine (T3) or to biologically inactive 3,3',5'-triiodothyronine and by regulating T3 conversion to inactive 3,3'-diiodothyronine. These extrathyroidal conversions depend on a family of independently-regulated selenocysteine-containing microsomal deiodinases. We describe deiodination assays and evaluate their potential as biomarkers for exposure to chemicals that directly or indirectly disrupt thyroid hormone homeostasis or thyroidal status. We conclude that deiodination be included in a minimum suite of assays to detect xenobiotic effects on the fish thyroid system.
Effect of Test Conditions on the Toxicity of Copper to Juvenile Unionid Mussels
Authors: Keller AE , Ruessler DS , Kernaghan NJ
Published: March 2009

During the past twnety years, unionid mussels have declined in both abundance and diversity throughout the eastern United States. As a result, there has been an increased call to evaluate the toxicity of various pollutants to unionids in an attempt to separate habitat-caused losses from those precipitated by aquatic contaminants. Few toxicity data for unionids were available until recently because unionids are not easily cultured and no test method had been developed for these animals. Therefore, water quality criteria developed by the USEPA in the 1970s and 1980s were derived from data lacking any information on unionid mussel sensitivities.

The Tennessee Valley Authority (TVA) has advocated the use of a 9-day toxicity test method its scientists developed in the late 1980s. This method, which requires the use of silt, an algal mixture for food and daily changes of water, is not only more labor intensive, it also introduces sources of variation with the use of silt and algae, as well as being substantially different from the standard 96-h fathead minnow or Zooplankton tests. The evaluation of TVA's suggested test conditions (24 h darkness, 800 mg/L silt and algal food) indicated that the use of a 16L:8D light regime, with or without silt or algae did not result in a change in the toxicity of dissolved copper to juvenile Utterbackia imbecillis mussels compared to that recorded using TVA's test conditions.