bluuebunny/crossref_metadata_2025 huggingface dataset:
The Optical Excitation Effect in Transition Metal Doped CZ Silicon Wafers Revealed by the Microwave Photoconductive Decay Lifetime Measurement
Authors: Kurita K , Shingyouji T
Published: March 2009

The prospect of identifying metallic impurities in p-type silicon has been studied by using the microwave photoconductive decay lifetime measurement method at various high injection levels. Samples intentionally doped with transition metals during crystal growth were prepared. It was found that point defects associated with Fe-B, Cr-B, and Ti, in decreasing order of effectiveness, degrade recombination lifetime in p-type Si.The effects of Fe-B pairs and Fe-B pair dissociation on recombination lifetime were also compared by various high injection levels.
Contactless Frequency Resolved Photoconductance (FR-PC) Measurement of Iron Contaminated P-Type Silicon
Authors: Romanowski A , Buczkowski A , Karoui A , Rozgonyi GA
Published: March 2009

The temperature dependence of the minority carrier lifetime and the surface recombination velocity have been measured in p-type Si wafers containing 1011cm−3 Fe, using Frequency Resolved Photoconductance (FR-PC) method. The recombination trapping centers have been identified from the microwave signals drawn as Nyquist plots. Changing the temperature and dc injection level enables one to characterize the traps with the nonlinear simplex fitting procedure. Under moderate dc injection level the Nyquist plots exhibit a large arc over the temperature range 24°C to 240°C. For low dc injection, and at temperatures below 100°C, the principal arc is deformed giving rise to second arc. However, this deformation and the second arc disappear above 180°C. Optimum fitting procedures show that the principal arc is associated with carrier recombination due to interstitial Fei, while the arc deformation is attributed to electron trapping at this level. The second arc can not be fitted by the above models; however, the Lorentzian amplitude and peak dependence on dc injection level leads us to believe that another level, donor Fe-B, is involved in electron trapping. Observed discrepancy at the room temperature between the effective lifetime and the frequency resolved lifetime is attributed to this level. Above 180°C both lifetimes correlate perfectly.
Lifetime Measured by Low Injection Level μ-PCD Technique
Authors: Swiatkowski C
Published: March 2009

The non-contact, non-destructive microwave photoconductivity decay (μ-PCD) technique is well established for the determination of effective carrier lifetimes in silicon material and a useful tool in monitoring different production steps. The measured lifetime is influenced by bulk and surface effects, whereby the bulk lifetime is a characteristic parameter of the material. We show that the Corona charge method in combination with μ-PCD gives an excellent, easy to use technique to suppress the surface effects and to determine bulk lifetime on oxidized samples. Using Corona charging it is possible to reduce the effective surface recombination velocity down to the 1 cm/s region. Furthermore the influences of injection level in conjunction with bias light on the measured lifetimes will be presented. This point is very important in the interpretation and comparison of effective lifetime measurements for defect and impurity identification.
Effects of Sample Inhomogeneity and Geometry on Photoconductivity Decay
Authors: Wang T , Ciszek TF
Published: March 2009

Excess minority carrier decay is simulated by a finite element method in cylindrical, rectangular (including epitaxial structures), and wafer samples with consideration of limited absorption of excitation light and spatial variation of lifetime in multicrystalline materials. It is found that, as long as a lifetime is derived from a later part of a phtoconductivity decay where a single-exponential signal is obtained, (1) the ASTM correction factors are valid for large bulk samples without the need to roughen the surfaces; (2) the 1-D asymptotic solution commonly used for lifetime measurements on wafers does not agree with the simulation for intermediate (102~104 cm/sec) surface recombination velocities and thin wafers (<0.1 cm); (3) for multicrystalline samples, the final decay represents overall quality of the material; and (4) when grain sizes are much less than the effective carrier diffusion length, carrier injection is uniform, and no surface nor grain boundary recombination is present, the effective lifetime of a multicrystalline material is the inverse of the volume-weighted inverse sum of local lifetimes.
Optimization and Control of Elymat Lifetime Measurement for Use in a Manufacturing Setting
Authors: Keefe GA , Hughes WM
Published: March 2009

In order for the Elymat minority carrier diffusion length imaging technique to become a useful and robust manufacturing tool for characterization of silicon wafers, optimum machine settings must be developed and tight control of the measurement process must be maintained to achieve maximum lifetimes and repeatable results. This paper describes a method for determining optimum injection currents to compensate for resistivity characteristics of the sample. Test results, obtained on wafers with resistivity ranging from 0.9 to 20 ohm-cm subjected to 60 measurements each using various combinations of wavelength and photo injection currents, are discussed. This paper also presents test results for the Injection Level Search (ILS) option designed to set the optimum injection level for each individual sample. Finally, the authors make recommendations concerning methods for control of the measurement process (i.e., control charting, troubleshooting, etc.).
Monitoring of Surface Minority Carrier Lifetime Using Modulated Photocurrent
Authors: Liberman S
Published: March 2009

Effective minority carrier recombination lifetime may vary substantially depending on measurement techniques and sample parameters not directly related to the recombination process. This makes it difficult to measure the bulk recombination lifetime and the surface recombination velocity - the fundamental parameters affecting the recombination of minority carriers in the semiconductor. At the same time, effective lifetime can be used as an efficient monitor of contamination, particularly when combined with statistical process control (SPC). Effective lifetime as measured by the Surface Charge Analyzer SCA-2500 is strongly affected by the surface conditions of the sample and thus is particularly sensitive to surface contamination. No sample preparation is required for the measurements. These features have proven the usefulness of SCA-2500 as an in-line contamination monitor in the production environment.
Canalysis of Photoconductance Decay and Surface Photovoltage Techniques: Theoretical Perspective and Experimental Evidence
Authors: Buczkowski A
Published: March 2009

Theoretical basis of Photoconductance Decay and Surface Photovoltage Techniques is presented. Impact of typical measurement set-ups and sample preparation procedures on the differences observed in experimental results which include diffusion length, recombination lifetime, and bulk iron concentration is emphasized. Measurement accuracy and evaluation repeatability for both techniques is simulated. Relevant experimental evidence is presented based on a variety of samples with different intentionally introduced metal contamination, oxygen levels, and surface electrical properties.
Application and Comparison of SPV and μPCD for Iron Measurement in Silicon Wafer Manufacturing
Authors: Pan Y
Published: March 2009

Minority carrier lifetime tools μ-PCD and SPV diffusion length are used in process monitoring in silicon wafer manufacturing for metal contamination control. In p-type silicon, both lifetime tools had been correlated with DLTS so as to be able to measure [Fe] concentration. In comparison of these two methods, a good correlation was obtained in a large range with extrapolation to the upper 1e10/cm3 level using Czochralski (CZ) silicon samples. In general, SPV resulted in a higher [Fe] than μ-PCD methods. At lower 1e10/cm3 level, the boron and oxygen concentrations significantly limit the [Fe] detection capability of μ-PCD, but less significantly on that of SPV.
Recombination Lifetime Variations and Defect Introduction by Rapid Thermal Processing
Authors: Karoui A , Zhang Q , Romanowski A , Rozgonyi GA , Rushbrook P , Daviet JF
Published: March 2009

Extended defects generated during RTP processing at the quartz wafer support and contact fingers of the wafer transfer robot have been examined by minority carrier recombination lifetime, τr, and X-Ray Topography. Silicon CZ wafers of 8”dia have been mapped laterally, and the defects imaged as a function of depth. Various RTP chamber cleaning and annealing experiments were carried out to control the reduced lifetime/pin defect formation process. A τr reduction of up to two orders of magnitude can occur at the contact points. The low lifetime has been profiled in-depth by Laser Microwave Photoconductance Decay following sequential sample thinning to yield 3D lifetime maps. HF-passivation was used to lower the impact of surface recombination. A two exponential model was used to separate the surface and bulk components of lifetime, which were resolved by the Nelder-Mead non-linear fitting method. The range of lifetime degradation at the RTP induced defects varies with the level of contamination which occurs during pin/wafer contact. Fortunately, the extended defects, i.e. slip dislocations, are confined to the wafer backside, where they getter the contaminants.
Influence of Iron and Copper on Minority Carrier Recombination Lifetime in Silicon
Authors: Kempf A , Blöchl P , Huber A , Fabry F , Meinecke L
Published: March 2009

A contamination experiment was carried to prove the possibility of a quantitative determination of the Fe-concentration in the high injection level region for p-type silicon. Calculation factors for two formulas were obtained, one assuming only FeB as life-time killer and another general one. A comparison between DLTS-, SPV- and μ-PCD-results showed a very good correlation of all instruments. Copper was proved to have also a strong influence on lifetime measurement, especially in n-type Silicon. Cu is suspected to affect the efficiency of Oxide passivation. Nitrogen also seemed to have a considerable influence at least in connection with a Cu contamination.
Characteristics and Evaluation Methods of Carrier Recombination Lifetimes in High-quality Silicon Wafers
Authors: Kitagawara Y , Yoshida T , Koide T , Hayamizu Y
Published: March 2009

Lifetime quality and the evaluation methods are discussed for (i) high-quality bulk Czochralski-grown crystals, (ii) polished wafers, and (iii) epitaxial layers in p/p+ wafers, (i) To determine the bulk lifetime value accurately for high-quality Si, it is important to measure a bulk sample 1–2cm-thick by a photoconductive decay method based on JIS: H0604-1995 or ASTM: F28-75. This high-sensitivity measurement reveals a new phenomenon of oxygen-related recombination-enhanced lifetime shift. (ii) For wafer analyses using an iodine-ethanol chemical passivation technique, the surface recombination velocities are determined precisely, (iii) To evaluate epi-layer lifetime qualities of p/p+ wafers, “Short-Wavelength Laser-Excited Photoluminescence (PL) Technique” is useful. Applying this technique to a heavy-metal gettering study, it is found that, even in p/p+ wafers with excellent Fe gettering capability, optimization of the substrate oxygen precipitation and the stability of the gettering sites are important.
Influence of Metal Impurities on Lifetime
Authors: Morimasa M
Published: March 2009

Influence of Fe, Ni and Cu contamination on lifetime in Si wafers was studied by microwave photoconductive decay (μ -PCD), surface photovoltage (SPV) and MOS C-t methods. Lifetime degradation was determined by measurement of bulk trap density using deep level transient spectroscopy (DLTS) and observation of surface defects after selective etching by optical microscope. As Fe concentration in the bulk increased, recombination lifetime measured by μ -PCD and SPV method decreased but generation lifetime measured by MOS C-t method depended on the type of contamination. Fe-B pairs in p-type samples and interstitial Fe in n-type samples seem to shorten the recombination lifetime. Surface defects induced by Ni contamination shortened lifetime measured by μ -PCD method, but when measured by SPV method, which measure deeper into the bulk, this lifetime did not change. Also, in the Ni contaminated samples, lifetime measured by MOS C-t method was shortened. MOS C-t method therefore, seems to be sensitive to bulk state near interface of Si/SiO2. As Cu concentration was increased, both the recombination lifetimes measured in n-type samples shortened and those in p-type samples did not change. It is postulated that Cu-related impurities in n-type samples are electrically active and those in p-type samples are inactive. No surface defects induced by Cu were observed in either case. The defects were, however visible after removal of Al electrode and gate oxide layer of MOS capacitors. The defects caused by Cu contamination as well as those caused by Ni contamination remarkably shorten lifetime measured by MOS C-t.
Oxygen Precipitation Characterization Using the Elymat Technique
Authors: Obermeier G , Hage J , Huber D
Published: March 2009

In processed wafers the depth of the precipitate-free zone and the density of bulk microdefects are of great importance. In this case the constant diffusion length is no longer valid. A two region model (defect-free / precipitated region) was assumed with two different diffusion lengths LD in a depth t. Solving the set of differential equations a three-dimensional picture of denuded zone depth and diffusion length in the precipitated bulk of the wafer is obtained. Investigating precipitated wafers using the Electrolytical Metal Tracer technique a correlation between the bulk microdefects and the measured minority carrier diffusion length was found. An empirical expression was determined to estimate Bulk Micro Defect density in the range from 8 × 104 to 2 × 107 cm−2. This means for practical application to receive more information on the oxygen precipitation behavio r of the whole wafer using an improved Electrolytical Metal Tracer technique.
Measurement of Minority Carrier Recombination Lifetime in Silicon Wafers by Measurement of Photoconductivity Decay by Microwave Reflectance: Result of Round Robin Test
Authors: Miyazaki M , Kawai K , Ichimura M
Published: March 2009

The round robin test was conducted, in order to check the deviation of lifetime errors by microwave photoconductive decay (µ -PCD) method. The samples were CZ thermally oxidized wafers of p- and n-type. Two resistivity values were set between 3 Ω cm and 47 Ω cm and three lifetime levels between 2 µ s and 1500 µ s, and total 12 kinds of wafers were characterized in the round robin test. 19 organizations joined the test. The center value of the standard deviation of primary mode lifetime errors was 11.8% for an injected photon density of 5×1013 photons/cm2.
Results of the Lifetime Round Robins Done in the Framework of the Semi M6 Solar Silicon Standardization Task Force
Authors: Schönecker AG , Koch W
Published: March 2009

In the framework SEMI standardization activities the SEMI M6-85 “Specification for Silicon Wafers for Use in Photovoltaic Solar Cells” is revised by an European task force. After more than four decades of silicon solar cell development there is still no reliable and strong correlation between the achievable cell efficiency and the electronic bulk material of unprocessed silicon wafers. The minority carrier lifetime of unprocessed bulk material is considered to have the potential to deliver this correlation. Therefore, similar to solar cell efficiency measurements, an easily applicable, instrument independent measurement for minority carrier lifetime under realistic photovoltaic conditions is desirable.

Four lifetime round robins were finished until now and a fifth one is going on at the moment. Many lessons, like how to perform these round robins, what are the sample characteristics, what is the influence of measurement conditions and surface passivation, were learned. But although there is a steady progress in defining more accurate measurement and sample preparation conditions, there is still no general carrier lifetime measurement procedure available that could be used in the above mentioned standard.
A Study of Isotopic Homogeneity in “Blended Uranium” Using ICP-MS
Authors: Crain JS
Published: March 2009

A 20 kg uranium metal ingot was prepared from two isotopically distinct feedstocks, and drillings from various ingot sections were dissolved in a mixture of HCl, HNO3, and HF. Uranium isotope ratios in each solution were determined by inductively coupled plasma-mass spectrometry (ICP-MS); total dissolved solid content was 20 μg/L for determination of 238U/235U, and 2 mg/L for determination of 236U/235U and 234U/235U. Between-sample coefficients of variation (n=35) for 238U/235U, 236U/235U, and 234U/235U were 0.70%, 0.90%, and 1.4%, respectively. Linear regression indicated that 236U/235U versus 238U/235U and 234 234 234U/235U versus 238U/235U were significantly correlated at the 90% confidence interval; 234U/235U versus 236U/235U was significantly correlated at the 98% confidence interval. These data show that the samples were not isotopically homogeneous, and demonstrate that ICP-MS can be used to assess isotopic homogeneity, even in cases where aggregate variations in isotopic composition are on the order of 1%.
Isotope Ratios of Uranium Using High Resolution Inductively Coupled Plasma—Mass Spectrometry (ICP-MS)
Authors: Hearn R , Wildner H
Published: March 2009

Actinide element isotope ratios have been determined in environmental samples using high resolution ICP-MS with ultrasonic nebulisation. Precisions as low as 0.1% RSD have been achieved using various methods of acquisition. The methodology has been used for environmental monitoring of uranium isotope ratios as an indicator of nuclear activity. Also, it has been applied to calcite dating studies as a measure of past geochemical disturbances.
Machining Conditions and the Wear of TiC-Coated Carbide Tools
Authors: Lim CYH , Lim S-C , Lee K-S
Published: March 2009

This paper examines the wear behavior of TiC-coated cemented carbide tools in turning. Experimental data from dry turning tests, together with similar data from the open literature, are used to construct wear maps depicting the flank and crater wear characteristics of these tools over a wide range of machining conditions. The maps show that both flank and crater wear rates vary according to the cutting speeds and feed rates used. An overall wear-damage map for this class of coated tools is also presented for the first time. The presence of the safety zone and the least-wear regime, within which the overall wear damage to the tools is low, suggests the possibility of selecting the machining conditions to achieve a compromise between the rates of material removal and tool wear.
Evaluation of Coatings and Materials for Rotating Slitter Knives
Authors: Schlatter M
Published: March 2009

Magnetic tapes are manufactured in broad webs of large length. The single tapes are cut from this with rotating slitter knives. Because of the extremely high quality requirements to the tape edges, the endurance of the slitter knives is limited. Among other things, experiments were carried out with knives made from ceramics and cermets, with coatings of PVD-TiN, TiAlN and DLC and with ion implantation on cemented carbide knives. Most experiments were not successful, only a plasma enhanced CVD titanium nitride coating brought a technical, if not economic success.
Tribology in Secondary Wood Machining
Authors: Ko PL , Hawthorne HM , Andiappan J
Published: March 2009

Secondary wood manufacturing covers a wide range of products from furniture, cabinets, doors and windows, to musical instruments. Many of these are now mass produced in sophisticated, high speed numerical controlled machines. The performance and the reliability of the tools are key to an efficient and economical manufacturing process as well as to the quality of the finished products. A program concerned with three aspects of tribology of wood machining, namely, tool wear, tool-wood friction characteristics and wood surface quality characterization, was set up in the Integrated Manufacturing Technologies Institute (IMTI) of the National Research Council of Canada. The studies include friction and wear mechanism identification and modelling, wear performance of surface-engineered tool materials, friction-induced vibration and cutting efficiency, and the influence of wear and friction on finished products. This research program underlines the importance of tribology in secondary wood manufacturing and at the same time adds new challenges to tribology research since wood is a complex, heterogeneous, material and its behaviour during machining is highly sensitive to the surrounding environments and to the moisture content in the work piece.
Chaotic Behavior on In-Phase Vibratory Conveyors
Authors: Raski JZ
Published: March 2009

One of the basic building blocks of IBM's computer technology is the thin-film interstitial metallized ceramic (IMC) substrate. The packaging of these substrates employs small input/output (IO) pins to provide both mechanical and electrical connection to the printed circuit board. In the automated manufacturing of the substrate, the input and output pins are individually conveyed by in-line vibratory conveyors. However, a non-periodic motion of these pins is observed at certain angles of conveyor table tilt that cannot be explained by classical models of friction. This paper models the motion of a single I/O pin on an in-phase, linearly oscillating conveyor using the classical model of friction and compares that result with experimental observations. It is shown here, analytically and experimentally, that when the vibratory conveyor table amplitude and the coefficient of friction between the pin and the table are sufficiently large, the pin is conveyed forward with some velocity. If the conveyor table's angle of tilt is sufficiently large and the coefficient of friction is sufficiently low, the pin may slip backwards just as fast as the conveyor table drives it forward, resulting in a net pin velocity of zero. Surrounding the condition at which the net velocity of the pin is zero is a chaotic basin of attraction in which the pin motion is non-periodic. This basin of attraction was experimentally determined to be bracketed within a range of values of the coefficient of friction. The implications of these theoretical and experimental results are discussed in terms of the practical application of in-phase vibratory conveyors in manufacturing.
Erosion and Corrosion Mechanisms in Pneumatic Conveying of Direct Reduced Iron Pellets
Authors: Pérez-Unzueta AJ , Martínez D , Flores MA , Arroyave R , Velasco A , Viramontes R
Published: March 2009

Samples of steel pipe segments and hard coatings were separately tested for hot gas corrosion resistance and hot erosion resistance by multiple impacts of direct reduced iron (DRI) pellets in a hot erosion testing device and in a pilot plant. Material loss and microscopic observations were used to evaluate both the corrosion and erosion mechanisms. This will help to evaluate the main mechanisms of pipe damage as the conditions for high temperature pneumatic transport of direct reduced iron pellets become more stringent. Corrosion tests were performed in a laboratory reactor with atmospheres composed of hydrogen and carbon monoxide mixtures in order to simulate conditions at the pilot plant. Results from the corrosion tests provided an indication of the suitability of these materials to be used as pipes. Laboratory tests provide useful information on the behavior of different materials at different temperatures ranging from room temperature up to 600 °C, and at different impact angles.
Separating the Influence of Kmax from Closure-Related Stress Ratio Effects Using the Adjusted Compliance Ratio Technique
Authors: Bray GH , Donald JK
Published: March 2009

In a common interpretation of crack closure, the crack is visualized as “peeling” open as stress is applied. This interpretation, while useful, has led to the assumption that the driving force for crack propagation, ΔKeff, exists only when the crack tip is fully open (above K-opening). However, evidence of significant crack-tip cyclic strain below the K-opening will be presented. The exclusion of this additional driving force can yield misleading values of ΔKeff. This is particularly so in the near-threshold regime where opening loads are typically high. The new analysis technique for estimating ΔKeff is referred to as the adjusted compliance ratio (ACR) method and is based on an interpretation of crack closure as a stress redistribution (or load transfer) on a relatively compliant crack wake. The ACR method is evaluated using the results of fatigue crack growth tests on 6013-T651, 2324-T39 and 7055-T7751 aluminum alloys using the center crack tension M(T) specimen geometry and stress ratios ranging from -1.0 to above 0.96. The experimental results of this study indicate that the fatigue crack growth rate is not determined solely by ΔKeff but also depends on Kmax. It was observed that this Kmax dependence takes the form of a power law with the magnitude of the exponent being a measure of Kmax sensitivity. As a result, ΔKeff curves from all test conditions could be collapsed to a unique intrinsic FCGR curve using a simple modification to the Paris Law. It is expected that continued research in this area will lead to improvements in fatigue life prediction methodology.
Description of Load Interaction Effects by the ΔKeff Concept
Authors: Lang M
Published: March 2009

An experimental study of load interaction effects in Al 7475-T7351 is presented. The crack propagation stress intensity factor, KPR, was determined after different overload sequences, also involving subsequent compression loading. The results of these experiments demonstrate that the single overload can be described by a single function, which describes the unloading process after the overload. One main conclusion is that load interaction effects are governed by residual compressive stresses in front of the crack tip, while crack closure plays a minor role.
Role of Crack Closure Mechanisms on Fatigue Crack Growth of Ti-62222 Under Constant-Amplitude and Transient Loading at —54, 25, and 175°C
Authors: Stephens RR , Stephens RI , Lemm DE , Berge SG , Liknes HO , Cousins CJ
Published: March 2009

Fatigue crack growth behavior of Ti-62222 in sheet form was investigated at three temperatures under various load histories with a specific emphasis on crack opening measurements and mechanisms. Constant-amplitude R = 0.1 near-threshold results showed that based upon applied ΔK, fatigue crack growth rates were lower at the two temperature extremes in comparison with those at room temperature. Based upon ΔKeff, a moderate temperature effect was observed. The various shifts in the ΔKeff curves were a result of different controlling crack closure mechanisms at each temperature. Single tensile overloads at 2.5 × Kmax produced a delay in fatigue crack growth and was most significant at -54°C. Remote crack opening measurements showed no appreciable change during the delay period due to the small region along the crack front that experienced crack closure. Near crack tip opening measured for various combinations of overloads, underloads, and constant ΔK at 25°C revealed a general trend for higher near tip opening following a tensile overload. However, a sufficient number of measurements were inconsistent and thus only minimal confidence could be placed with the method. Scanning electron microscopy was used to evaluate surface fatigue crack growth profiles and fatigue crack growth fracture surface morphology.
Effect of Load Excursions and Specimen Thickness on Crack Closure Measurements
Authors: McMaster FJ , Smith DJ
Published: March 2009

The effects of simple load excursions on fatigue crack growth and crack closure measurements in aluminum alloy 2024-T351 are presented. The crack closure loads were measured local to the crack tip in 6-mm and 14-mm-thick specimens, using an Elbert-type gage for measuring crack-tip opening displacement (CTOD). All specimens were manufactured from a single lot of 15.7-mm-thick plate. Preliminary tests to establish the level of crack closure for a given level of remote constant-am- plitude loading were also undertaken, with consistently different levels of crack opening and closing loads observed. Crack opening and closing stresses obtained from the Elber-type (CTOD) gage, when compared with those from a (global) clip gage, showed identical results for opening stresses, but crack closing stresses were approximately 15% to 20% higher in the CTOD measurements. The results apparently contradict many analytical closure models, which have crack closing stresses lower than crack opening stresses.

Simple overload, underload and over/underload cycles were performed. Differences in the number of post-overload retardation cycles for the two thicknesses, in the single overload test, were obtained. It was found that the 6-mm-thick specimen's fatigue life was two times larger than for the 14-mm-thick specimen. The measured opening stresses were found to be in general agreement with the trends obtained for the fatigue crack growth results. Greater fatigue lives were obtained in the overload tests, with subsequent higher crack opening stresses measured. After a certain number of cycles following an overload, constant-amplitude crack growth rates were restored. However, the crack opening stresses did not return to the preoverload constant-amplitude values, but increased relative to the preoverload constantamplitude crack opening stresses.
Fatigue Crack Growth and Crack Closure Behavior of Ti-6Al-4V Alloy Under Variable-Amplitude Loadings
Authors: Jono M , Sugeta A , Uematsu Y
Published: March 2009

Fatigue crack growth tests under constant-amplitude and repeated two-step loadings were carried out on a (α + β) Ti-6Al-4V alloy which has duplex structure made up of equiaxed primary α-phase grains with a discontinuous fine β-phase dispersed in the boundaries. It was found that fatigue crack grew along α-phase grain boundaries and that the fracture surface was very rough in the low stress intensity region under constant-amplitude loading. On the other hand, in the high region, transgranular crack growth was observed and the fracture surface was relatively smooth. The crack opening point, Kop, was affected by the amplitude of low-level load, ΔKL, under repeated two-step loadings where the high-level load amplitude was kept constant. Kop was found to be higher than that predicted by Kop — Kmax relationship under constant-amplitude loading and the fracture surface was rougher in comparison with that under constant-amplitude loading which has the identical stress intensity range. It was concluded that the crack opening point was controlled by both plasticity-induced crack closure in terms ofKmax and roughness-induced crack closure resulted from rougher surface in ΔKL.
Effects of Thickness on Plasticity-Induced Fatigue Crack Closure: Analysis and Experiment
Authors: Hsu C , Chan KK , Yu J
Published: March 2009

The crack-opening stress was measured using a strain gage technique on 7050 aluminum alloy, under constant amplitude and repeated overload. The behavior of crack-opening stress predicted by Newman's FASTRAN-II is consistent with the experimental results for repeated overload. It is also found that the FASTRAN-II program is capable of predicting crack growth on the 7050-T76 aluminum plate and 7050-T7452 aluminum hand forging under complex simulated flight loading which contains a significant number of compression cycles.
Effect of Periodic Compressive Overstrain Excursions on Crack Closure and Crack Growth Rates of Short Fatigue Cracks—Measurements and Modeling
Authors: Varvani-Farahani A , Topper TH
Published: March 2009

A comparison of the growth of fatigue cracks under constant-amplitude straining and under strain histories having periodic compressive overstrains revealed that the fracture surface near the crack tip and the crack growth rate changed dramatically with the application of compressive overstrains. When the magnitude of compressive overstrains was increased, the height of the fracture surface irregularities was reduced as the increasing overstrain progressively flattened fracture surface asperities near the crack tip. The reduced asperity height was accompanied by a lower crack closure stress and a higher crack growth rate.

The fatigue strength was reduced by a factor that ranged from 1.24 at short lives (104 cycles) to 3.37 at long lives (107 cycles) when periodic compressive overstrains of near yield point magnitude were applied in uniaxial tests. The corresponding reductions in the fatigue strength for shear tests varied from 1.40 to 1.70.

A model of the plastic deformation of the fracture surface asperities at the crack tip (under periodic compressive overstrains) was developed to relate the crushing of the asperities to crack closure and crack growth rate. The model correlates the magnitude of the periodic compressive overstrain, the fracture surface asperity height, and the plastically flattened area to the fully effective strain intensity factor range (ΔKeff) and its ratio to the range of strain intensity factor (ΔK(ε)) obtained from constant-amplitude straining, U =ΔKeff/ΔK(ε).

For both uniaxial and shear fatigue straining, the strain range at a fatigue life of 107 cycles for constant-amplitude straining (Δεfl) and the effective strain range, (Δεeff.fl) at 107 cycles in the strain-equivalent life curve, obtained from strain histories containing periodic compressive overstrains, were used to calculate the U ratio (U= Δεeff.fl /Δεfl). These values were close to those obtained from the model.
Simulation of Fatigue Crack Closure Behavior Under Variable-Amplitude Loading by a 2D Finite Element Analysis Based on the Most Appropriate Mesh Size Concept
Authors: Park S-J , Song J-H
Published: March 2009

A two-dimensional elastic-plastic finite element analysis is performed for plane stress conditions with 4-node isoparametric elements to investigate the closure behavior under various variable-amplitude loading, i.e., single overloading, Hi-Lo block loading, and narrow- and wide-band random loading. The closure behavior under single overloading and Hi-Lo block loading can be well simulated by applying the concept of the most appropriate mesh size that will provide numerical results consistent with experimental data under constant-amplitude loading. It is found that the crack opening load under random loading may be predicted approximately by replacing the complicated random load history with the appropriate equivalent, simplified variable load history.
Synergetic Effects of Fatigue Crack Closure Mechanisms
Authors: Zuidema J , van Soest TM , Janssen M
Published: March 2009

Results are presented relating to the relative effect of two closure mechanisms. Two different crack closure mechanisms, closure due to surface roughness induced by shear lips and conventional plasticity-induced closure, are investigated and compared by performing fatigue crack growth tests on aluminum 2024 and technically pure aluminum. Constant ΔK tests using a sudden change in ΔK are used in order to measure both closure effects separately and also the combined effects of both mechanisms. It is found that in the case of a combined application of closure mechanisms the retardation result after a load transition is sometimes greater than the sum of the retardations of the separate mechanisms. Under the test conditions used the combined effect may be 2.4 times greater than the sum of the separate effects.
Evaluating The Influence of Plasticity-Induced Closure on Surface Flaw Shape Evolution Under Cyclic Loading Using a Modified Strip-Yield Model
Authors: Daniewicz SR
Published: March 2009

A slice synthesis methodology is used to construct a modified strip-yield model for the part-through semi-elliptical surface flaw, enabling prediction of plasticity-induced closure along the crack front and subsequent fatigue crack growth. Predictions of flaw shape evolution under cyclic loading are compared with experimental data for steel specimens under constant-amplitude cyclic bending. Model predictions are shown to correlate well with experimental data. The influence of stress level and mean stress on surface flaw shape evolution is evaluated.
A Displacement-Based Method for Predicting Plasticity-Induced Fatigue Crack Closure
Authors: Pawlik ME , Saff CR
Published: March 2009

A numerical method for predicting closure and its effects on thermomechanical crack growth has been developed. A finite element model, using linear-elastic fracture mechanics shape functions, is employed to predict crack tip displacements. The effective changes in stress intensity, and therefore crack growth, are obtained from the minimum and maximum crack tip displacement predictions. When a flaw is loaded in Mode I, a ligament of material ahead of the flaw yields, and a maximum crack tip displacement is computed. Upon unloading, plastically deformed material from prior plastic zones acts to limit the minimum displacements of the crack tip. The material is modeled as elastic-perfectly plastic. The yield strength of the material is varied based on the degree of constraint. The upper limit of constraint is a plane strain condition while the lowest constraint is a plane stress condition. The level of constraint is predicted by relating the stress intensity to the thickness of the component. Temperatures also affect yield strength, along with stiffness, and can cause the plastic zone to expand due to creep. During variable-amplitude loadings, and/or temperature changes, the irregular shape of the wake can be accommodated with this numerical procedure. The method has proven to accurately account for load interaction effects such as delayed retardation, crack arrest, initial accelerations following overloads, and the transient growth and stabilization of closure level with number of overloads. This method has been verified against data obtained in the literature, and data collected under the program in which the method was developed, NASA's High Speed Research [1].
The Development of Acoustic Emission for Leak Detection and Location in Liquid-Filled, Buried Pipelines
Authors: Miller RK , Pollock AA , Finkel P , Watts DJ , Carlyle JM , Tafuri AN , Yezzi JJ
Published: March 2009

Acoustic Emission leak detection and location for liquid-filled, buried pipelines was studied using various leak sources and laboratory reference standards.These standards provided significant data that have contributed to the development of test procedures for generating two-phase flow and a better understanding of the leak mechanism. Results are discussed for leak signal enhancement due to two-phase flow, leak orientation and the presence of backfill surrounding the pipe.

Field studies were performed on buried pipes to demonstrate that small leaks (less than 0.1 gallons/hour or 0.1 mL/second) can be detected under the right test conditions and that the location of these small leaks can be determined using a variety of location methods. Among the different location methods examined was a location technique referred to as “tuned” linear location. In addition, a modification to the conventional Signal Difference location technique is discussed.
Acoustic Emission Applied to Detect Workpiece Burn During Grinding
Authors: de Aguiar PR , Willett P , Webster J
Published: March 2009

Overly-aggressive or otherwise inappropriate grinding of metals can produce an undesirable change in metallurgical properties of the material being processed; usually this is referred to as workpiece “burn”. In this experimental paper the acoustic signature of grinding is collected, and compared to the processed workpiece condition, for thirteen data sets including both relatively hard (Inconel) and soft (52100 bearing steel) metals. This work is distinguished by its use of a high sampling rate (2.56 MHz) in data acquisition and in its processing of the raw, rather than RMS/filtered, data samples. Signs of burn are seen in the frequency domain, and in the correlation between wheel rotations.
Identification of AE Sources by Using SiGMA-2D Moment Tensor Analysis
Authors: Shigeishi M , Ohtsu M
Published: March 2009

Acoustic Emission (AE) is a phenomenon caused by the emission and propagation of elastic waves generated from micro-cracking. A procedure named “SiGMA” (simplified Green's function for moment tensor analysis) to identify the crack kinematics from AE waveforms has been developed recently. Using this procedure, the crack location, crack orientation and crack type can be determined. Computer software for the SiGMA procedure has been developed and applied in practice. To apply the SiGMA procedure for AE source inversion in a thin plate and other two-dimensional (2D) models, the SiGMA-2D procedure is proposed in this paper. The most distinctive feature of this procedure is projection of 3D moment tensor components onto a plane. For confirmation of SiGMA-2D solutions in practical AE waveforms, the in-plane uniaxial compression tests of plates, which are made by mortar having an internal through-thickness slit, are carried out. The results confirm the applicability of the SiGMA-2D procedure for elucidating the crack mechanisms in 2D models. Further, estimation of crack volume is proposed. For this purpose, the AE sensors are quantitatively calibrated using the Davies-bar technique. A laser opto-interferometer is used to measure the oscillation at the bar end. These results are applied to determination of micro-crack volume.
Practical AE Methodology for Use on Aircraft
Authors: Carlyle JM , Bodine HL , Henley SS , Dawes RL , Demeski R , Hill EvK
Published: March 2009

The first production use of practical acoustic emission (AE) on aircraft was on the F-111, where more than 240 U.S. and Australian aircraft have been successfully monitored during cold proof testing since 1987. A key factor was the design of an instrument which automatically configured itself at power-on, so that aircraft testing could take place in a highly efficient and reliable manner. The second production use of AE on aircraft was on the VC-10, where an entire fleet of 22 aircraft was monitored 40 times during pneumatic proof pressurization. The monitoring of this large transport required anywhere from 282 to 313 narrowband AE sensors per aircraft. In both aircraft types, numerous significant defects were discovered through AE-based nondestructive testing. Finally, we present on-going in-flight AE research. This new research uses digital waveform processing of wideband AE signals and offers the potential of adding new and complementary capabilities to classical, narrowband AE.
Periodic AE Re-Tests of Seamless Steel Gas Cylinders
Authors: Blackburn PR
Published: March 2009

Sometimes industrial gas distribution involves hauling pressurized gas over the highways in seamless, forged, steel cylinders which are mounted on truck trailers. To ensure public safety, Federal regulations require periodic cylinder examinations. In 1983 the U.S. Department of Transportation (DOT) began to allow use of acoustic emission (AE) examinations in lieu of hydrostatic tests for this purpose. AE data are recorded in the linear location mode while cylinders are filled with gas. Examples and explanation of excellent location accuracy are provided. Significant AE sources are subjected to secondary inspection and flaw depth is determined. If flaw depth exceeds a prescribed limit the cylinder is removed from service. Study of emission from specific flaws over two and three subsequent periodic re-tests shows that, generally, flaws are benign.
Biomarkers of Endocrine Disruption at the mRNA Level
Authors: Denslow ND , Bowman CJ , Robinson G , Lee HS , Ferguson RJ , Hemmer MJ , Folmar LC
Published: March 2009

A large number of estrogen-mimicking, anthropogenic chemicals capable of disrupting normal reproductive function have been identified. The ubiquitous distribution of these compounds, many as components of complex industrial or municipal waste, has spurred an effort to develop methods to screen for chemicals which disrupt normal endocrine regulation of reproduction. We have developed assays that both allow exposure of animals in vivo and measure the response at the level of gene activation. We have developed a probe for measuring the induction of vitellogenin mRNA by Northern Blot in livers of sheepshead minnows treated with 17-β-estradiol. We have also developed a strategy for using Differential Display Polymerase Chain Reaction for determining gene induction profiles following exposure to estradiol. These methods should be adaptable to a variety of structurally diverse estrogen mimics.
Assays for Endocrine-Disrupting Chemicals: Beyond Environmental Estrogens
Authors: Folmar LC
Published: March 2009

Recent popular and scientific articles have reported the presence of estrogenic and other hormone mimicking chemicals in the environment and their potential for causing reproductive dysfunction in humans and wildlife. The purpose of this session was to present the best available, if not standard, analytical methods to assay for the effects of xenobiotic chemicals on a broad range of endocrine-mediated events, including reproduction, growth, development and stress responses in aquatic vertebrate and invertebrate animals.
Appropriate Uses of Physiological Techniques for Endocrine Studies
Authors: Munkittrick KR , Van Der Kraak G
Published: March 2009

The recent explosion of interest in the potential of chemicals to disrupt endocrine processes at very low exposure levels has led to the increased use of physiological tools in field studies. Physiological studies have not been fully developed for ecotoxicological applications and are underappreciated or poorly utilized. In ecotoxicological studies, physiological tools have historically been focused on direct impacts of specific chemicals, and usually on general indicators of health or exposure. The result has been that most surveillance programs have only used physiological tools for the assessment of exposure. An increasing need to link responses in wild fish with the underlying ecological mechanisms means that physiological studies have to play a key role in the assessment of impact. However, the use of physiological studies in endocrine assessments requires a level of detail not previously warranted in ecotoxicological studies. This overview will discuss the limitations of physiological indicators, as well as critical areas requiring further study and the requirements for the future development of physiological indicators of endocrine disruption.