bluuebunny/crossref_metadata_2025 huggingface dataset:
Use of Cuprous Iodide as a Precipitation Matrix in the Radiochemical Determination of lodine-131 in Milk
Authors: McCurdy DE , Mellor RA , Lambdin RW , McLain ME
Published: March 2009

As a result of the implementation of the as low as reasonably achievable (ALARA) philosophy to the nuclear power industry, recent U.S. Nuclear Regulatory Commission (NRC) requirements have prompted high-sensitivity radiochemical analysis for the measurement of iodine-131 (I-131) in milk. The most recognized and commonly employed technique incorporates costly palladium iodide as the final precipitate in the radiochemical purification of the iodine chemical species. The procedure presented in this paper outlines the many advantages of using cuprous iodide (CuI) as the final precipitate. These include lower cost per analysis, consistent recoveries, better precipitate matrix, and good self-absorption characteristics. Typical lower-limit-of-detection values and operating characteristics obtained for high-sensitivity beta-gamma (β-γ) analyis are presented as well as gas proportional counting and a comparison of radiochemical and germanium (lithium) spectrometric results for environmental samples collected during the recent Chinese weapons fallout incident.
Confirmatory Measurements of Radionuclide Concentrations in Power Reactor Effluents
Authors: Gibson GT , Pagliaro JA
Published: March 2009

The U. S. Nuclear Regulatory Commission (NRC) conducts a radioactive waste system inspection program with nuclear power facility licensees. The confirmatory measurements portion of the program consists of a test of the licensee's measurements of radioactivity in actual or simulated plant effluent samples (liquid, off-gas, participate filter, and charcoal adsorber), comparing the licensee's measurements with those of the NRC reference laboratory.

The NRC has developed a computer data analysis system (CDAS) which performs comparisons of the analytical results of the licensee and NRC reference laboratory and which provides statistical analyses of licensee performance. Licensee ability to adequately identify and quantify radionuclides in plant effluents is thereby documented. Comparison of these analytical results is the basis for the NRC Confirmatory Measurement Inspection Program.
Migration of Radionuclides in Geologic Media—Laboratory and Field Studies
Authors: Wolfsberg K , Daniels WR , Hoffman DC , Erdal BR
Published: March 2009

Experimental results obtained from investigation of the radionuclide distribution in the environment around the 0.75-kiloton nuclear test Cambric, fired in alluvium at the Nevada Test Site, are presented and discussed. Laboratory measurements of distribution ratios for sorption-desorption between alluvium and ground-water and leaching rates from test debris are also presented and compared with field data.
Experience with an Analytical Quality-Control Program
Authors: Harley JH
Published: March 2009

Over the past few years there has been an increasing tendency to question the results of scientific work, including analytical measurements. There has always been some review by our scientific peers, but we are now finding that we must justify quality to the public as well. This is not unreasonable since they are usually paying for the work either as consumers or as taxpayers, and any analytical laboratory should be able to stand behind the quality of its work.

The Environmental Measurements Laboratory (formerly the Health and Safety Laboratory) has had a formal quality-control program since 1960. This has been used for both internal analyses and for measurements performed under contract to commercial laboratories. The program has consisted of submitting from 10 to 15 percent of the samples in the form of standards, blanks, or blind duplicates. In almost all cases, the analyst is not aware of which samples are the quality-control samples. The results of this program are published annually in our Environmental Quarterly so that those that use our data can recognize the quality of the analytical work.

The benefits of this program have been an increase in confidence by the data users and a sense of pride in the analyst for having produced useful measurements. In addition, problems of calibration drift, operator performance, and inadequacy of methods can be recognized at a reasonably early stage and the necessary corrective action taken.

The paper includes extensive data presentations covering-quality control samples, calibrations, and participation in intercomparisons.
The DOE-OES-EML Quality Assurance Program
Authors: Sanderson CG
Published: March 2009

Contractor laboratories handling radioactive materials for the U.S. Department of Energy (DOE) are required to monitor the environmental exposure and publish annual reports for the Division of Operational and Environmental Safety (OES). In order to determine the validity of the data contained in these reports the Environmental Measurements Laboratory (EML) was requested to develop, coordinate, and conduct an Environmental Quality Assurance Program (QAP).

There are four major phases to the DOE-OES-EML Quality Assurance Program: Sample collection and preparation, sample analyses at EML, quarterly sample distribution, and reporting the data returned by the participants.

This paper discusses the various phases of the QAP and briefly discusses the data reported during the first year of the program.
Minority Carrier Lifetime Characteristics in Semiconductor Silicon—An Overview
Authors: Vieweg-Gutberlet FG
Published: March 2009

For the characterization of the starting silicon material lifetime measurements were carried out very early in silicon technology. A wide variety of measurement techniques was developed, such as diffusion length measurement, the photocurrent method, and the widely used photoconductivity decay method (PCD).

As silicon technology developed, lifetime measurements for the characterization of the starting (ingot) material became less important because of the increase in the perfection and purity of the silicon. In turn, lifetime measurements for in-process control of the device fabrication became more and more important.

For the characterization of neutron transmutation doped (NTD) silicon, lifetime measurements on the ingot material have become important again because of the dependence of the lifetime on the thermal annealing process subsequent to the irradiation.
Minority Carrier Lifetime Degradation in Silicon Due to Thermally Generated Dislocations
Authors: Liang AY , Varker CJ
Published: March 2009

Minority carrier lifetime uniformity is examined in processed silicon wafers containing thermally induced dislocations. The experimental method, which utilizes transient and steady-state measurements, includes open-circuit voltage decay (OCVD), junction current recovery (JCR), forward voltage drop, VF, and current-voltage characteristics on small-area p+-n diode arrays. The observation is made that the minority carrier lifetime profiles correlate with the distribution of dislocations revealed by preferential chemical etching and that general agreement exists among these measurement methods regarding the spatial uniformity of carrier lifetime. The authors conclude that the processing-induced dislocations degrade the carrier lifetime and possibly reduce the carrier mobility. Moreover, it is clearly demonstrated that a simple direct-current measurement such as VF can be used as an indicator of the lifetime variations across the processed wafer, particularly when a correlation between the minority carrier lifetime, τ, and VF is established experimentally.
Study of Minority Carrier Lifetime Behavior in Czochralski-Grown Silicon Crystals
Authors: Wong DC , Wakefield GF
Published: March 2009

By using the surface photovoltage technique to measure minority carrier lifetime, it was found that grown-in defects of swirl in Czochralski-grown silicon crystals appear to be oxygen related and create recombination centers that degrade the lifetime more in the swirled areas. In addition, the degradation was also observed to be very sensitive to the previous thermal history of the starting material and to subsequent thermal treatments.
Influence of Crystal Defects on the Generation Lifetime of Minority Carriers in Silicon
Authors: Eder A , Werner C
Published: March 2009

Measurements of generation- lifetime inhomogeneities were performed on wafers containing crystal defects. The lateral resolution was 250 μm, so that the influence of single defects could be seen.

The authors show that both dislocations and oxidation-induced stacking faults may severely reduce lifetime in a very small region. Moreover, examples are presented where lifetime was improved in the vicinity of the defects because of some sort of gettering action. Finally, it is shown that lifetime inhomogeneities can be avoided by performing a preoxidational back-side gettering (POGO) procedure.
Minority Carrier Lifetime Profile Measurements by Use of the Photocurrent Technique
Authors: Reichl H , Ruge I , Eichinger P , Müller JL
Published: March 2009

Using the photocurrent technique, lifetime measurements on electron irradiated silicon were carried out. The electron energy was varied between 0.5 and 2.5 MeV. The doses were in the range of 5 × 1013 cm−2 to 1016 cm−2. The measured lifetime distribution over the wafer showed a decrease of lifetime from about 50 μs outside to less than 0.5 μs within the irradiated area for an electron energy of 0.5 MeV. For doses increasing from 5 × 1013 cm−2 to 1016 cm−2, a decrease in lifetime outside the irradiated area was also observed.

It was shown that the determination of lifetimes by use of the photocurrent method is restricted to layers thicker than 2.5 times the diffusion length. However, if light with a short penetration depth is used, the travel time of the minority carriers from the illuminated side of the specimen to the Schottky contact can be measured, and the measurement can be extended to thinner specimens. The influence of the absorption coefficient and the surface recombination velocity are discussed.

The measurements were carried out on a silicon wafer with a diffusion length comparable to the thickness of the specimen.
A Contactless Method of p-n Junction Leakage Testing and Comparison of Associated Data with Contact-Determined Leakage
Authors: Verkuil RL , Pak MS
Published: March 2009

A contactless p-n junction leakage measurement method is described, which uses specialized very-high-frequency oscillator circuitry. This circuitry utilizes the eddy current loading effect, via inductive coupling, in order to determine the leakage-dependent decay time of the photoinduced voltage across the diffused p-n junctions in a silicon wafer.

The contactless measurement is made under low forward bias conditions (≤ 10 mV), in such a way that this measurement and the contacting reverse leakage, measured at 100 mV, will both be functions of generation-recombination processes in the junction depletion region. Detectable signals were made possible by low-noise circuitry and by the increase in junction eddy currents from induced voltages across the diffused regions.

The following model was derived from basic circuit theory, which relates the contactless decay time measurement, τ, to the conventional contacting reverse leakage, J0 J0=CkT∕qτ

where

J0 = reverse leakage, A/cm2,

C = junction capacitance, F/cm2,

τ = decay time, s, and

kT/q = 26 mV at T = 300 K.

Good agreement was obtained between experiment and theory. The examined range was four orders of magnitude in leakage current.
Fundamental Mechanisms of the Erosive Wear of Ductile Metals by Solid Particles
Authors: Finnie I , Levy A , McFadden DH
Published: March 2009

A brief survey is presented of the mechanisms which have been proposed for the erosion of ductile metals by solid particles. After reviewing these and examining scanning electron microscope photographs, it is concluded that a ductile cutting mode applies when the velocity vector of the eroding particle makes an angle of less than about 45 deg with the surface. Above this angle the removal process appears to involve quite different mechanisms. An earlier analysis of the cutting mechanism is reexamined and shown to predict many features of the erosion process. In particular, the roles of particle velocity, elevated temperatures, and material properties are discussed. Some preliminary results are presented for erosion at higher angles, and possible mechanisms for material removal are discussed. Finally, some suggestions are made for future directions in erosion research in view of the current interest in coal-hydrogenation processes.
Multiple Water Drop Impact Damage in Layered Infrared Transparent Materials
Authors: Peterson TL
Published: March 2009

The influence of materials and construction variables on the rain erosion behavior of layered infrared window materials has been investigated at 210 m/s in the simulated rain environment (1.8 mm drop diameter, 2.5 cm/h rainfall rate) of the Air Force Materials Laboratory rotating-arm apparatus.

Outer-layer materials included chemical vapor deposited (CVD) zinc sulfide, hotpressed zinc sulfide, and CVD gallium arsenide. These materials were either deposited directly onto CVD zinc selenide substrates or adhesively bonded to the zinc selenide.

In general, damage mechanisms and relative rates of degradation were predictable from studies of the erosion behavior of homogeneous specimens. The effect of layer thickness on erosion behavior was determined for outer layers of CVD zinc sulfide. For outer layers thicker than approximately 1.0 mm, damage in the layered specimens was comparable to that in homogeneous CVD zinc sulfide specimens. The amount of multiple impact damage in layers thinner than 1.0 mm compared with that in thicker layers depended upon the technique of fabrication. Damage was more severe for thinner layers bonded to zinc selenide but was somewhat reduced for thinner layers deposited directly on zinc selenide.

The effect of grain size on erosion resistance was demonstrated by comparison of the behavior of layers of CVD gallium arsenide bonded to zinc selenide with that of gradient-freeze grown gallium arsenide. The CVD material was more resistant to impact damage because of its much smaller grain size.

Thin films deposited on zinc sulfide and gallium arsenide as antireflection coatings were susceptible to removal by drop impacts and the subsequent radial outward flow of water away from the impact site. However, more durable antireflection coatings on zinc sulfide have been developed.
High-Speed Liquid Jet and Drop Impact on Brittle Targets
Authors: Field JE , Gorham DA , Rickerby DG
Published: March 2009

Two methods are described for producing high-velocity liquid impacts. The first involves projecting a jet of liquid at a stationary target while in the second specimens are fired at suspended drops. An objective of the study was to place the jet method on a quantitative basis. Detailed studies of jets, using high-speed photography, allowed the conditions for producing stable and reproducible jets to be obtained for a range of jet velocities (up to ∼1000ms-1) and jet diameters (0.4 to 3.2 mm). The relation between jet impact and drop impact damage was achieved after experiments in which high-speed photography, pressure measuring techniques, and damage studies played important roles. The quantitative establishment of the jet method has practical implications since it has advantages in its ease of operation, its ability to simulate large drops, and in having the target stationary. Finally, a hydrostatic test apparatus for measuring the residual strength of brittle specimens following impact and examples of measurements on glasses and silicon nitride are described. Factors affecting the shape of residual strength curves are discussed.
A Study of Erosion by High-Pressure Cavitating and Noncavitating Waterjets
Authors: Vijay MM , Brierley WH
Published: March 2009

A study was made of erosion by high-pressure noncavitating and cavitating waterjets issuing from five different arrangements of nozzles, consisting of (A) jet in air, (B) submerged jet, (C) jet surrounded by another of lower velocity, (D) jet from long nozzles, and (E) jet from a nozzle containing a cylindrical body insert. The purpose was to evaluate the two methods of erosion for jet cutting applications.

Simple visual examination of the craters on specimens of copper showed distinct type (size, shape, depth, etc.) of erosion. However, microscopic examination did not reveal clearly any characteristics peculiar to cavitating or noncavitating jets.

Quantitative experimental results were obtained by measuring the mass loss of lead specimens as a function of time of exposure for the conditions where either the nozzle pressure or the standoff distance was held constant. By comparing the different arrangements on the basis of material loss, it is concluded that Arrangement B performed best for all periods of exposure and standoff distances followed by Arrangement C for short periods of exposure, smaller standoff distance, and for certain flow conditions.
Studies on Crack Initiation and Stable Crack Growth
Authors: Shih CF , deLorenzi HG , Andrews WR
Published: March 2009

Experimental results are presented which suggest that parameters based on the J-integral and the crack opening tip displacement δ are viable characterizations of crack initiation and stable crack growth. Observations based on some theoretical studies and finite-element investigations of the extending crack revealed that J and δ when appropriately employed do indeed characterize the near-field deformation. In particular, the analytical and experimental studies show that crack initiation is characterizable by the critical value of J or δ, and stable crack growth is characterizable in terms of the J or δ resistance curves. The crack opening angle, dδ/da, appears to be relatively constant over a significant range of crack growth. Thus, appropriate measures of the material toughness associated with initiation are JIc and δIc, and measures of material toughness associated with stable crack growth are given by the dimensionless parameters TJ [= (E/σo2)(dJ/da)] and Tδ [= (E/σo)(dδ/(da)]. The two-parameter characterization of fracture behavior by JIc and TJ or δIc and Tδ is analogous to the characterization of deformation behavior by the yield stress and strain hardening exponent.
A Finite-Element Analysis of Stable Crack Growth—I
Authors: Nakagaki M , Chen WH , Atluri SN
Published: March 2009

A finite-element methodology is developed to study the phenomenon of stable crack growth in two-dimensional problems involving ductile materials. Crack growth is simulated by (1) the translation in steps, of a core of sector elements, with embedded singularities of Hutchinson-Rice-Rosengran type by an arbitrary amount, Δa in each step, in the desired direction; (2) reinterpolation of the requisite data in the new finite-element mesh; and (3) incremental relaxation of tractions in order to create a new crack face of length Δa. Steps 1 and 2 were followed by corrective equilibrium-check iterations. A finite deformation analysis based on the incremental updated Lagrangian formulation of the hybrid-displacement finite-element method is used.

The present procedure is used to simulate available experimental data on stable crack growth, and thus to study the variation during crack growth of certain physical parameters that may govern the stability of such growth and the subsequent onset of rapid fracture. Attention is focused in this study on the following parameters: G*Δ, the energy release to the crack tip per unit crack growth, for growth in finite steps Δa, calculated from global energy balance considerations; GpzΔ the energy release to a finite “process zone” near the crack tip per unit crack growth, for growth in finite steps Δa, calculated again from global energy balance considerations; and the crack opening angles. However, the work reported here is limited to the first phase of our study, that is, to simulation of available experimental data.
A Comparison of Elastic-Plastic Fracture Parameters in Biaxial Stress States
Authors: Miller KJ , Kfouri AP
Published: March 2009

Parameters used in fracture predictions in elastic-plastic materials will differ from those used when the material is elastic. However, the first set of parameters may reduce to the latter in the limiting case of brittle behavior involving minimal plasticity. Analyses of the stress and plastic strain fields in the region of the crack tip and evaluations of energy release rates are therefore relevant to studies on fracture processes in engineering materials. It is becoming generally recognized that more than one parameter is needed in the formulation of a realistic fracture criterion applicable to elastic-plastic materials. In particular, such a criterion must take into account the possible biaxial nature of the applied stress.

This paper presents some of the results of extensive elastic-plastic finite-element analyses on a center-cracked plate. Information is provided, and comparisons made, on such features as crack-tip plastic zone sizes, intensities of plastic strain near the tip, the major principal stress in the crack-tip region, crack opening displacements, values of the J contour integral, and crack separation energy rates GΔ—all corresponding to different biaxial stress states.
Evaluation of Estimation Procedures Used in J-lntegral Testing
Authors: Landes JD , Walker H , Clarke GA
Published: March 2009

Estimation techniques for the calculation of J have enabled the development of simpler data reduction methods for multiple specimen J-integral tests and also prompted the development of single-specimen tests. This report describes an experimental program conducted to evaluate the accuracy of these estimation techniques. Comparisons between the values of J as calculated by the energy rate definition and those calculated by the estimation techniques for compact toughness, three-point bend, and center-cracked tension specimens are made.
An Evaluation of Elastic-Plastic Methods Applied to Crack Growth Resistance Measurements
Authors: McCabe DE , Landes JD
Published: March 2009

Information from tests on blunt notched specimens for J-integral calibration by conventional J = -1/B ∂U/∂a analysis is used to evaluate the significance of plastic zone adjustment to physical crack length in crack growth resistance, KR, calculations. Secants are drawn to load versus displacement test records to determine plastic zone adjusted crack lengths. Tests on three specimen geometries [compact specimen (CS), single-edge notched bend (SENB), and center-notched tension (CNT)] and on two materials (HY130 steel and 2024 aluminum) have shown that this procedure develops KR values that are equivalent to J. This demonstration opens possibilities that J can now be applied to cases where there is subcritical crack growth such as in R-curve work, KIscc, and possibly in creep cracking studies. Also, this provides a simplified method for computing J experimentally on complex geometries for which elastic KI solutions are available.

Alternative J computational procedures are compared. These include J by a Ramberg-Osgood work-hardening law fit to load-displacement records, and J by area approximation methods. The Ramberg-Osgood modeling appeared to work reasonably well in tests on compact specimens but was found to be unreliable on SENB and CNT specimens and therefore is not recommended. With no stable crack propagation, the area approximation procedures for J determination produce reasonably accurate estimates of J as might have been anticipated from past experience. Tests on the compact specimen geometry required a Merkle-Corten correction procedure which worked well on large crack aspect ratios, where a/w ⩾ 0.5, but tended to overcorrect for short cracks, giving nonconservative results.
Determination of Fracture Toughness with Linear-Elastic and Elastic-Plastic Methods
Authors: Berger C , Keller HP , Munz D
Published: March 2009

Fracture toughness was determined for two nickel-chromium-molybdenum steels with linear-elastic and elastic-plastic methods. From the evaluation of linear-elastic/ideal plastic load-displacement curves and from the experimental results it follows that the relation of Merkle and Corten should be applied for J-integral determination for compact specimens. The extrapolation method for the determination of a critical J-value implies some problems. As an alternative it is proposed to determine J at a fixed distance from the blunting line. A comparison between stress intensity factors calculated from J and with linear-elastic methods shows that linear-elastic fracture mechanics can be applied to much smaller specimens than given by the ASTM Test for Bane-Strain Fracture Toughness of Metallic Materials (E 399-74). The equivalent-energy method and measurement of crack tip opening displacement with different clip gages at different distances from the crack tip yield stress intensity factors in agreement with the J-integral method.
Computer Interactive JIc of Testing Navy Alloys
Authors: Joyce JA , Gudas JP
Published: March 2009

A computer interactive unloading compliance single-specimen JIc test procedure has been developed. This procedure utilizes an on-line minicomputer to analyze digitized load-displacement data during testing. Unique values of JI and crack length are determined from compliance measurement on short unloadings along the load displacement record. The test procedure is presented in detail and analysis procedures are discussed.

Three tasks which demonstrate the validity and utility of the computer interactive test method are discussed. Results for single-specimen and multiple-specimen tests are presented for HY 130, 10Ni steel, 17-4PH steel, Ti-7Al-2Cb-1Ta, and Ti-6Al-4V which show close correspondence between the two methods. Tests on 17-4PH steel compact tension specimens with various thicknesses and crack lengths are summarized and dimensional effects on JIc and the J-Δa resistance curve slopes are discussed. Finally, tests on HY 130 specimens with various notch root radii demonstrate effects of notch acuity on JIc.
The COD Approach and Its Application to Welded Structures
Authors: Harrison JD , Dawes MG , Archer GL , Kamath MS
Published: March 2009

The crack opening displacement (COD) approach has, since its inception as a fracture initiation parameter in yielding fracture mechanics, gained increasing acceptance both as a viable research tool and an engineering design concept. In the United Kingdom, The Welding Institute has pioneered the application of COD in the structural fabrication industry largely through the development of the COD design curve. This paper is a representation of the philosophy underlying design curve applications and illustrates the practical significance of COD by drawing on case studies from various welded structures.

Following a brief appraisal of the origins of the design curve, the paper outlines procedures for the use of COD in design, that is, either as a basis for material selection or in setting up acceptance levels for weld defects. The reliability of a small-scale test prediction from the design curve has been investigated on a statistical basis from a survey of more than 70 wide-plate tension test results in which the material had also been categorized by COD. Specific practical examples are then discussed covering the various types of application, material selection defect assessment, and failure investigation.

Structures included in these examples are offshore rigs, oil and gas pipelines, pressure vessels, etc., with special emphasis on the manner in which small-scale COD test results are translated to the structural situation.

Finally, the paper includes information on the considerable range of structures to which the concept has been applied during the past five years.
Random Load Analysis as a Link Between Operational Stress Measurement and Fatigue Life Assessment
Authors: Buxbaum O
Published: March 2009

All relevant methods for the description of measured stress-time histories in connection with fatigue life assessment are reviewed critically, that is, one- and two- parameter counting methods as well as analyses in the time and frequency domains.
Simulation of Service Fatigue Loads for Short-Span Highway Bridges
Authors: Albrecht P , Yamada K
Published: March 2009

A mean stress range histogram and corresponding frequency distribution function for single truck crossings over short-span highway bridges, derived from 106 published histograms, is proposed. A major portion of this load history was applied to a welded transverse stiffener detail in blocks varying from 100 cycles to 100 000 cycles. When the number of cycles in the block was 1000 cycles or less, the block size had no significant effect on the total number of cycles to failure. Block loading simulated then random loading, and the root-mean-cube stress range provided a reasonable transfer function between block loading and constant amplitude cycling.
Fatigue Mechanism—Key to the Solution of the Engineer's Second Fundamental Problem
Authors: Fong JT
Published: March 2009

The rationale for studying fatigue and fatigue mechanism is examined by considering two fundamental problems in engineering, namely, the problem of feasibility, by asking whether a product works, and the problem of fatigue, by asking whether a product lasts. It is shown that the first problem (feasibility) is easier than the second (fatigue) because the solution to the second requires experimental information of a time scale incompatible with that available to the engineer or the material scientist. To resolve this dilemma, it is proposed that advances in computer-aided quantitative microscopy, fracture mechanics, and many other allied disciplines, be incorporated in measuring microstructural changes due to fatigue at a time scale workable in a laboratory. It is concluded that such study in discovering fundamental mechanisms of fatigue holds the key to the solution of the second fundamental problem in engineering.
The Study of Fatigue Mechanisms with Electron Channeling
Authors: Davidson DL
Published: March 2009

The application of electron channeling techniques to the study of material response under cyclic loading conditions is providing some useful information on mechanisms from bulk specimens. Most of the effort thus far has been on examining the plastic zone parameters (size, shape, and strain distribution) but other useful information may be obtained as well (such as crystallographic interactions). Subcells may be observed directly in bulk specimens, and environmental effects may be studied. This paper reviews many of the details of the application of electron channeling to fatigue mechanism study, references results, and illustrates some of the concepts. A few of the possible future uses are also discussed.
Dynamic, Real-Time Fatigue Crack Propagation at High Resolution as Observed in the Scanning Electron Microscope
Authors: Davidson DL , Lankford J
Published: March 2009

A videotape of dynamic, high-resolution, real-time fatigue crack propagation, made from experiments with a special cyclic loading stage in the scanning electron microscope, was shown to the conference attendees. This paper briefly summarizes the video presentation and illustrates a few of the main points made by it.
Microstructural Aspects of the Threshold Condition for Nonpropagating Fatigue Cracks in Martensitic-Ferritic Structures
Authors: Kunio T , Yamada K
Published: March 2009

A study has been made of the critical condition for the growth of microscopic fatigue cracks at the endurance limit from metallurgical considerations. The specimens employed have a microstructure with a matrix of ferrite and the second phase of martensite, the volume fraction of which is about 50 percent. All the non-propagating cracks nucleated in the ferrite matrix are stopped by the second-phase martensite at the endurance limit stress. The threshold condition for microscopic nonpropagating cracks in the ferrite matrix was investigated by restressing to slightly above the endurance limit. Subsequently it was found that the critical condition for the fatal growth of microscopic cracks into the second-phase martensite from the ferrite matrix can be evaluated by the linear theory of fracture mechanics. It is also recognized from the experiments that all the microscopic cracks in the ferrite matrix remain as nonpropagating unless the stress intensity factor at the crack tip exceeds the magnitude of the crack growth resistance of the second phase martensite, Kthm. Furthermore, experimental results show that the Kthm of the second-phase martensite is about 7.7 MPam. In addition, quantitative metallographic observations show that the critical length of the nonpropagating cracks at the endurance limits does not depend on the mean spacing of the second phase.
Some Effects of Microstructure and Environment on Fatigue Crack Propagation
Authors: Scarlin RB
Published: March 2009

Fatigue crack growth rates have been determined in nickel-base alloys both after a normal heat treatment and after heating for a further 10 000 h. The latter treatment causes coarsening of the γ‵-particles so that they are no longer sheared by dislocations when the material is deformed. Differences in cracking rates at both ambient and elevated temperatures may be understood in terms of slip reversibility and oxide penetration when deformation occurs by shearing of precipitates.

A further result of the prolonged aging period is a considerable reduction in the cyclic fracture toughness of a cast alloy. This can be traced to a transition to intergranular cracking along regions of coarsened precipitation adjacent to the grain boundaries.

A comparison of cracking rates in air and vacuum shows that the presence of air can lead to an increase in growth rate and to a situation where no clear threshold is apparent. Crystallographic cracking (analogous to Stage I fatigue) is observed in both air and vacuum. One effect of oxygen in tests at high temperatures is to cause dissolution of the γ‵-particles in the region of the crack tip. Under high-temperature corrosive conditions (air/SC2/SO3 atmosphere) an increase in scatter and in average propagation rate can be correlated with the formation of liquid sulphide films at the crack tip.
Quantitative Analysis of Fatigue Process—Microcracks and Slip Lines Under Cyclic Strains
Authors: Kitagawa H , Takahashi S , Suh CM , Miyashita S
Published: March 2009

Quantitative observations have been made on the microcracks or small surface cracks and slip lines on the surfaces of steels under cyclic strains, for the purpose of unifying two approaches to the study of fatigue, namely, that based on fracture by crack growth (fracture mechanics concept) and that of cyclic strain accumulation (low-cycle fatigue concept). Important results are: (1) initiation of cracks at the early stage of fatigue life even on unnotched smooth specimens; (2) growth of the small surface cracks below ΔKTH level; (3) higher growth rate of small surface cracks than that of a large through crack; (4) dependence of ΔK versus da/dN relation on stress level for small surface cracks; and (5) a definite relation between λ, the ratio of the number of slipped grains to the number of total grains, and Δϵ, the cyclic strain range. From these results it is suggested that the growth rate of small surface fatigue cracks can be represented as either da/dN = C (ΔKεp)m or da/dN = C (ΔKεt)m, where ΔKεp is the plastic strain-intensity factor range given by Δεpπa⋅f (a), and ΔKεt is the total strain-intensity factor range given by Δεtπa⋅f (a).
Fatigue Fracture Micromechanisms in Engineering Plastics
Authors: Hertzberg RW , Skibo MD , Manson JA
Published: March 2009

This paper deals with an examination of fatigue micromechanisms present in polymers of various chemistry and microstructure. At low stress-intensity (ΔΚ) levels in several amorphous homopolymers, poly (methymethacrylate) (PMMA), polycarbonate (PC), poly (vinyl chloride) (PVC), polystyrene (PS), and polysulfone (PSF), each with viscosity-average molecular weight (M¯v) in the range 1 × 105 < Mv < 4 × 105, the macroscopic and microscopic appearances of the fracture surface were observed. Observations were also made in both rubber-modified amorphous polymers such as an acrylonitrile-butadiene-styrene (ABS) copolymer and a rubber-toughened PS-poly (phenylene oxide) blend, and the crystalline polyacetal (PA). Regardless of the degree of surface roughness, the crack front in all these materials advanced discontinuously in increments equal to the bandwidth after remaining stationary for as many as 105 fatigue cycles (in PA). In single-phase amorphous polymers, the discontinuous growth process was identified with the failure of a single craze ahead of the crack tip. At high ΔΚ levels the fracture surfaces of most polymers were striated, with one striation representing the increment of crack advance during one load excursion. It is concluded that large errors can be made in estimating the overall fatigue life of engineering plastics if the significance of the microscopic bands observed at low ΔΚ and the striations observed at high ΔΚ as fatigue fracture markings is misinterpreted.
Micromechanisms of Low-Cycle Fatigue in Nickel-Based Superalloys at Elevated Temperatures
Authors: Runkle JC , Pelloux RM
Published: March 2009

The micromechanisms of high-temperature fatigue crack initiation and crack propagation in solid-solution and precipitation-strengthened nickel-base super-alloys are reviewed. The marked decrease in fatigue strength of a given superalloy with increasing temperature cannot be solely correlated with the temperature dependence of the short-time mechanical properties. The interactions between oxidation rates and fatigue strengths are very complex. The air environment plays a large role in accelerating the initiation and propagation of fatigue cracks at elevated temperatures. Increasing temperature and decreasing frequency lead to a transition from transgranular to intergranular fracture path.

The influence of different microstructural factors on the high-temperature low-cycle fatigue (LCF) behavior of a typical superalloy, Astroloy, was investigated in detail. A combination of fine 500 Å matrix γ′ in conjunction with a wavy grain boundary produced by both coarse intergranular M23 C6 carbides and primary γ′ is found to offer the best LCF performance in the range of 0.2 to 0.7 Tm. The fine γ′ retards Stage I cracking, and the wavy grain boundaries retard intergranular cracking. The observations made with Astroloy can be extrapolated to different γ/γ′ nickel-base superalloys.
Cyclic Stress-Strain Response and Damage Mechanisms at High Temperature
Authors: Bhat SP , Laird C
Published: March 2009

The cyclic stress-strain response and damage of commercially pure nickel, thoria dispersed (TD) nickel, and Al-4Cu alloy aged to contain θ′ and θ″ are investigated as a function of test temperature. Up to 23 melting point, the slipband morphology, and hence the crack nucleation mechanism, does not change in nickel and TD-nickel when tested under vacuum using a symmetrical sawtooth waveform. The microstructure containing θ′, however, exhibits an increased tendency toward transgranular slip with increase in temperature. This is quite contrary to our intuition and is shown to be due to the plastic deformation of the θ′ precipitate and subsequent dissolution at high temperatures. The θ″ microstructure exhibits intense slipband deformation and cracking at all tested temperatures; this is surprising in view of the metastability of the microstructure and the fact that cyclic disordering of the crystal structure could be reordered at high temperatures. Both of these factors would be expected to homogenize the slip, but this was not observed.
A Critical Evaluation of Mathematical Equations for Fatigue Crack Growth with Special Reference to Ferrite Grain Size and Monotonic Yield Strength Dependence
Authors: Yokobori T
Published: March 2009

In order to select the correct mathematical equation among many. for fatigue crack growth or to develop a new criterion, some critical assessments are carried out by compiling the experimental data on the effect of ferrite grain diameter on fatigue crack growth rate for two low-carbon steels and a 3 weight percent silicon iron. The effect of monotonic yield strength is also studied. Emphasis is on fatigue crack growth in the second region of fatigue crack growth rate versus ΔK curve. Results suggest that, if fatigue crack growth rate is expressed as da/dN=B(ΔKsσc)′​′ where σc is some constant with the dimension of stress and s is an appropriate measure of length, then σc and B are practically independent of monotonic yield strength, but n has the trend of a slowly increasing function of the ferrite grain diameter and, thus, indirectly a decreasing function of the monotonic yield strength. Moreover, it is suggested that n is also affected with some other microstructural factor.
In-Vivo/In-Vitro Life Testing of Vascular Prostheses
Authors: Botzko K , Snyder R , Larkin J , Edwards WS
Published: March 2009

A real-time in-vitro life tester for vascular prostheses has been developed and demonstrated. The existing tester can be used for initial testing of new materials and structures for vascular prostheses, minimizing expensive and difficult long-term animal implants. The in-vivo/in-vitro data suggest that a mechanical fatigue mode of failure must be investigated for new types of vascular prostheses. The short-term data achieved to date indicate that the most commonly used vascular prostheses material, Dacron yarn, initially loses some strength but then appears to stabilize. Teflon yarn, in a textile structure, demonstrates a slight gain in strength. Long-term explant data confirm these observations.
Corrosion Fatigue of 316L Stainless Steel, Co-Cr-Mo Alloy, and ELI Ti-6Al-4V
Authors: Imam MA , Fraker AC , Gilmore CM
Published: March 2009

The purpose of this paper is to compare corrosion-fatigue properties of selected implant alloys and to discuss the corrosion fatigue-life in terms of the corrosion behavior and the metal microstructure. The tests were conducted in fully reversed torsion in flowing Hank's solution at a temperature of 37°C and a pH of 7.4. Specimens were subjected to fatigue at shear strains ranging from 0.006 to 0.018 and at a frequency of 1 Hz. Surfaces of the 0.5-cm-diameter specimens were prepared by mechanically polishing through a 0.05 alumina powder and following this with steam sterilization.

During the tests, the specimen electrode potentials versus time were monitored on a strip chart recorder. The potential-time curves for the metals studied show the establishment of a steady rest potential which does not change until the fatigue motion has been applied. The potential then goes in the negative direction. The rate of this decline in potential appears to-be related to the metal microstructure as well as to the alloy composition. This electronegativity of the potential-time curves indicated the formation of cracks in the oxide film. These curves were more electronegative with increased shear strain, and the curves were different for the different metals tested.

Fatigue results of these tests show that the ELI Ti-6Al-4V has the longest fatigue life under these conditions. The fatigue strength of the Ti-6Al-4V can be increased many times by changing the microstructure through heat treating and quenching. The Type 316L stainless steel had the next longest fatigue life. The cast Co-Cr-Mo alloy had the shortest fatigue life and also showed more scatter in the results. Other workers have shown that further heat treating and processing improves the fatigue resistance of this material too.
Corrosion-Fatigue Performance of Stainless Steel Hip Nails—Jewett Type
Authors: Sloter LE , Piekler HR
Published: March 2009

Criteria and standards for the corrosion-fatigue performance of orthopedic fixation devices are reviewed in general and with specific reference to hip nails. The development and application of a simulated, in-vitro, performance test for a fixation device are demonstrated for the Jewett combination nail plate. Corrosion-fatigue results obtained both in air and in Ringer's solution and failure modes are presented and discussed with regard to the Jewett device. The importance of fatigue crack initiation on the fatigue life of fixation devices is demonstrated, and the mechanisms and locations of fatigue crack initiation are documented in detail. This study has shown that initiation is dependent not only on the location of maximum stress but also on the environment and on the incidence of fretting or fretting corrosion. Minor surface scratches appear to have no effect on fatigue crack initiation.
Environmental Contaminant Studies by the Patuxent Wildlife Research Center
Authors: Heinz GH , Hill EF , Stickel WH , Stickel LF
Published: March 2009

Evaluation of the effects of environmental contaminants on wildlife is geared to interpreting events in the field, especially population effects, and both field and laboratory studies are planned for this purpose; procedures are adapted to specific problems and therefore do not include strict protocols or routine testing. Field evaluations include measurements of cholinesterase inhibition in brain or blood, search for dead or disabled animals, study of nesting success of birds, and general ecological observations. Residue analyses are used in evaluating organochlorine chemicals; samples may include whole bodies for determining level of exposure, brains for mortality diagnosis, whole blood for certain special studies, and eggs to help in evaluation of possible reproductive effects. Bird counts, singing-male census counts, small mammal trapping, and cage-in-field tests have proven to be ineffective or misleading and are not considered suitable for field evaluations under most circumstances. Usefulness of simulated field trials is limited to very special situations. Experimental studies that help predict and interpret field effects include determinations of lethal diagnostic levels, comparative lethal dietary toxicity tests, tests of secondary poisoning, measurement of residue loss rates, measurement of blood enzymes, tests of behavioral effects, and studies of reproductive effects.
Endrin Versus 12-Ketoendrin in Birds and Rodents
Authors: Stickel WH , Kaiser TE , Reichel WL
Published: March 2009

British workers showed that in rats the endrin metabolite, 12-ketoendrin, was five times as toxic as endrin, was probably the ultimate cause of death, and was the main form of endrin in the brain at death. In cows and rabbits, however, they detected little of this metabolite. They found none in hens. We found no 12-ketoendrin in birds of four orders that had been heavily exposed to or killed by endrin. We suggest that residue work with birds need not consider this compound unless birds have been eating endrin-killed rodents. White mice had much less 12-ketoendrin than rats, but had more endrin. In tests with spiked samples, 12-ketoendrin was successfully recovered from extracts by gel permeation chromatography, but not by florisil.