bluuebunny/crossref_metadata_2025_split huggingface dataset:
A Composite Model of Microstructural Evolution in Austenitic Stainless Steel Under Fast Neutron Irradiation
Authors: Stoller RE , Odette GR 
Published: December 2008

A rate-theory-based model has been developed which includes the simultaneous evolution of the dislocation and cavity components of the microstructure of irradiated austenitic stainless steels. Previous work has generally focused on developing models for void swelling while neglecting the time dependence of the dislocation structure. These models have broadened our understanding of the physical processes that give rise to swelling, for example, the role of helium and void formation from critically-sized bubbles. That work has also demonstrated some predictive capability by successful calibration to fit the results of fast reactor swelling data. However, considerable uncertainty about the values of key parameters in these models limits their usefulness as predictive tools. Hence, the use of such models to extrapolate fission reactor swelling data to fusion reactor conditions is compromised.
The present work represents an effort to remove some of these uncertainties by self-consistently generating the time dependence of the dislocation structure, both faulted loops and network dislocations. The model's predictions reveal the closely coupled nature of the evolution of the various microstructural components and generally track the available fast reactor data in the temperature range of 350 to 700°C for doses up to 100 dpa. As the theoretical model has become more complex, parameter choices were constrained to a more limited range of values in order to obtain this agreement between theory and experiment. While the model remains approximate in many respects, it should ultimately provide a more useful tool for understanding microstructural evolution under irradiation and permit more confident predictions of void swelling in future fusion reactors.
The Effects of Applied Stress on the Irradiation Induced Microstructures of Dilute Nickel Alloys
Authors: Atkins T , McElroy RJ 
Published: December 2008

A detailed transmission electron microscopy (TEM) study has been performed on Ni-2.48% Si alloy specimens irradiated, in the stressed and unstressed condition, to a dose of 0.2 dpa at 623 K, with 3.5-MeV protons in the Proton Irradiation Creep Facility on the Harwell 6-MeV Van de Graaff accelerator. The objective of the work was to obtain detailed information on the size distributions of Frank loops, the primary irradiation produced microstructural feature in this material, which could be compared directly with the measured irradiation creep behavior. Low dose irradiations have been employed in order to minimize loop-loop interactions and maintain the microstructural record.
Because of specimen to specimen temperature variations the main body of the analysis was performed on eight grains from a single TEM disk, cut from a creep specimen irradiated at 50 MPa. The effect of applied stress on loop size and planar loop densities was assessed by comparing data from randomly oriented grains with a single grain, which had equal resolved normal stresses on each of the four {111} planes.
The Frank loop density is greatest on {111} planes with the highest normal stress. The applied stress influences the partitioning of loops between the different {111} planes but does not influence the overall loop density or the loop size. The present results support the stress-induced preferred nucleation (SIPN) or stress assisted rotation model of irradiation creep and no evidence has been found for either the stress-induced preferred absorption (SIPA) or stress-induced climb and glide (SICG) models. Frank loops account for less than 25% of the measured strain. The discrepancy probably arises from the unexpectedly high density and large size of unfaulted 110 loops. Additional information is required on vacancy loops and unfaulted loops in order to resolve the discrepancy between estimated and measured strains.
Radiation-Induced Segregation and Precipitation in Molybdenum-Rhenium Alloys
Authors: Erck RA , Wayman CM , Rehn LE 
Published: December 2008

Specimens of Mo-7 atomic % Re, Mo-27 atomic % Re, and Mo-30 atomic % Re were irradiated with 1.8-MeV 4He+ ions at elevated temperatures. Radiation-induced segregation of rhenium was measured during irradiation by in-situ Rutherford backscattering spectrometry (RBS). Segregation of the undersized rhenium atoms in the same direction as the defect fluxes, that is, toward the external surface, was observed. The amount of rhenium enrichment in the near-surface region was measured as a function of temperature and of dose at a calculated near-surface displacement rate near 1 × 10−4 dpa/s. Segregation was measured by RBS at temperatures from 800 to 1500°C in Mo-7Re, and from 850 to 1225°C in Mo-30Re.
Irradiated disks were examined by transmission electron microscopy. Chi phase precipitation was observed on grain boundaries, and at the irradiated surface in Mo-27Re and Mo-30Re after irradiation at temperatures from 750 to 1075°C. Chi precipitates formed with cube/cube and twin orientations with respect to the host matrix. No voids or loops were observed for ion doses up to 1.6 dpa.
Strength Development of Concrete Cured Under Arctic Sea Conditions
Authors: Aitcin P-C , Cheung MS , Shah VK 
Published: December 2008

Two sets of experiments simulating the curing conditions of concrete caisson constructions in the Arctic were carried out at Sherbrooke University, Province of Quebec, Canada, and at Nanisivik, in the extreme north of Baffin Island, Canada (73° north). More than 500 concrete specimens were tested for various ages and initial curing periods. After they were cast, the concrete specimens were initially cured at about 4°C (39°F) for 3 to 15 h and then immersed in seawater at 0°C (32°F) until testing. Their compressive strengths at different ages, up to one year, and Young's modulus at 28 days were compared with those of specimens of the same concrete and same age cured under room temperature.
These two sets of experiments have shown that if 9 h of initial curing at about 4°C (39°F) is allowed for the concrete before immersion in seawater at 0°C (32°F), the design compressive strength of the concrete can be achieved at 56 days. The rate of development of compressive strength during the first two weeks is slow because of the low temperature of the curing environment.
The temperature of the fresh concrete and its water/cement ratio are the two most important parameters that determine the early strength of the concrete.
Industrial Automation—The U.S. Government's Productivity and Standardization Initiatives
Authors: Newlin DB 
Published: December 2008

Industrial automation can be defined as the integration of computer technology with industrial machines, processes, and operations. It ranges from the industrial scanner that reads the bar codes on items purchased at the supermarket to the automated factories that utilize robots with artificial intelligence. The reasons for pursuing industrial automation range from reducing manufacturing cost and improving quality to the need for greater flexibility to change and the ability to respond to market demands. Industrial automation encompasses information processing, process control, inventory control, and sales forecasting. The results of industrial automation raise many questions concerning the use of technology to replace workers and the resulting social and economic impact. The government is addressing many of these issues and has a number of productivity and standardization initiatives that are directly related to industrial automation.
The initiatives that have been undertaken by the Department of Defense (DoD) that will have an impact on industrial automation include the Very High Speed Integrated Circuits (VHSIC) Program, the various interface standards that will play a key role as the integrator of machine and computer, the Industrial Modernization Incentives Program (IMIP), DoD Software Technology for Adaptable, Reliable Systems (STARS), Ada® Programming Language, and the Initial Graphics Exchange Specification (IGES).
An Examination of the IDEF0 Approach Used as a Potential Industry Standard for Production Control System Design
Authors: Mackulak GT 
Published: December 2008

Communication of a proposed or existing system design is an extremely important aspect of any system analysis. If the concept and intricacies of the design cannot be communicated to the evaluation personnel, analysis and improvement is quite likely to be impossible. The ability to communicate the design so as to be understandable by a group of analysts with widely ranging skills requires some type of standardization. The ICAM Definition (IDEF) languages have been proposed as just such a standardization methodology (ICAM = integrated computer-aided manufacturing).
The IDEF0 modeling capability was used to quantify a generic high level planning and control system for major airframe manufacture. The system designed was generic in nature; therefore it was not representative of any current existing system. This paper will discuss the IDEF methodology, applicability of IDEF0 as a system design standard, and results from IDEF0 application to the analysis of airframe manufacture.
Stress Distribution at the Tip of Cracks Originating from a Circular Hole under Biaxial Loads
Authors: Oladimeji MK 
Published: December 2008

The stress distribution at the tip of cracks originating from a circular hole under biaxial loads was examined. It was found that a numerical stress function can be developed, which when employed in the stress analysis of the neighborhood of the crack tip of this geometry, results in accurate evaluation of the crack-tip stress and displacement field. Some predictions of the fracture mechanical behavior of this geometry were then made based on these stress and displacement field representations.
The path-independent J-integral energy approach was used in examining the effect of the applied biaxial loads on this parameter. It was found that applied biaxial loads do affect the path independent J-integral taken around the crack tip. The direct relationship between the stress intensity factor and the J-integral which holds for line crack was found to be applicable to this geometry.
Critical Load Assessment Method for Stable Crack Growth Analysis
Authors: Rhee HC 
Published: December 2008

A new systematic procedure has been developed for analyzing stable crack growth. In this method, the crack instability point can be predicted from a single J-l record, which is developed from a given material Jr curve and the J-integral related solutions resulting from stress analysis of a flawed structure. Here l represents the physical load applied to the structure. The development of the J-l relation that satisfies the equilibrium state of crack growth is so simple that hand calculator analysis is possible for complex structural geometries with available J-related stress analysis results.
The advantage of the new method over existing ones, such as the failure assessment diagram approach or the tearing instability theory, is that it can predict the critical physical load level and the crack instability point at the same time without resorting to the use of a fixed diagram or evaluating tearing modulus. The validity of the procedure has been demonstrated by solving a center-cracked tensioned panel with various loading mechanisms (displacement-controlled, load-controlled, and mixed loading systems) and a pressure vessel geometry under internal pressure.
Fracture Toughness Testing of Ductile Cast Irons
Authors: Salzbrenner RJ , Van Den Avyle JA , Lutz TJ , Bradley WL 
Published: December 2008

The fracture toughness of ferritic, spheroidal graphite ductile cast iron has been measured by a single-specimen J-integral technique. The method used a servohydraulic test frame in the displacement control mode, with overall test control and data acquisition managed by a minicomputer. Digitized load and displacement values were combined to calculate incremental crack lengths based on measured crack length-compliance calibrations. Plots of J versus change in crack length were generated, and values of JIc (and equivalent KIc) were determined using ASTM Test for JIc, a Measure of Fracture Toughness (E 813). This technique thus provided a means of determining the plane-strain fracture toughness (KIc) using small samples (2.5 cm thick) at temperatures from −150 to +25°C. Previous attempts to measure KIc directly on similar materials had produced invalid results for all tests except those performed at very low temperatures (−60°C and below).
Two ductile cast irons were investigated that had similar volume fractions of graphite, graphite nodule sizes, and ferrite grain sizes, but one contained approximately 15% pearlite, while the other had less than 1% pearlite. The alloy with greater pearlite content exhibited higher strength and higher ductile-to-brittle transition temperature. Although cast irons are generally perceived as being low in toughness, the toughness values measured on fully ferritic nodular iron were quite high (KIc = 80 to 106 MPa√m [73 to 96 ksi√in.] on the upper shelf).
Strain-Rate Dependence of the Deformation at the Tip of a Stationary Crack
Authors: Hoff R , Rubin CA , Hahn GT 
Published: December 2008

A new analytical technique is presented whereby the Hutchinson-Rice-Rosengren singularity solutions can be used, in certain cases, to determine the stresses and strains near a crack tip for a dynamically loaded, strain rate-dependent material. This technique involves a simple modification of the constant, α, and the strain hardening exponent, n, in the power stress-strain law. Elastoplastic, dynamic finite element computations are in close agreement with this analytical technique.
Stresses and strains are generally higher in a dynamically loaded rate sensitive material than in a rate insensitive material. Also, J1c increases correspond to increases in the flow stress in rate-sensitive materials, provided that δc is rate-insensitive.
Fracture Mechanics Analysis of a Pressure Vessel with a Semi-Elliptical Surface Crack Using Elastic-Plastic Finite Element Calculations
Authors: Aurich D , Brocks W , Noack H-D , Veith H 
Published: December 2008

Elastic-plastic three-dimensional finite element (FE) calculations were performed on a semi-elliptical inner surface crack of a pressure vessel using the FE program ADINA. The pressure was increased until the ligament yielded entirely. The variations of the stress intensity factor K of the J-integral and of the crack tip opening displacement (CTOD) along the crack front are presented and discussed.
The stress intensity factors K1 calculated by extrapolation from stresses and displacements and by the energy release rate agree well within a tolerance of about 10%. As in linear elasticity, the plastic part of the J-integral can also be described by a power law of the applied load. The normal stresses in the crack opening direction in the ligament meet a power function (J/r) as the two-dimensional HRR (Hutchinson-Rice-Rosengren) field equations postulate. The exponent is not a material constant, however, but varies along the crack front. Therefore the distribution of the crack opening stress along the crack front at a fixed distance from the crack front cannot be characterized by the J-distribution along the crack front. Neither does the singular HRR field describe the redistribution of stresses due to crack tip blunting. For the considered pressure vessel the J-integral in the elastic-plastic range can be calculated from an elastic solution if small-scale yielding corrections for plane-stress conditions are performed.
A Critical Evaluation of Current Environment-Sensitive Fracture Test Methods
Authors: Parkins RN 
Published: December 2008

This paper does not attempt to review all aspects of environment-sensitive fracture testing, but rather is concerned specifically with continuing problems in relation to such tests and with relatively recent developments. The importance of conducting tests in environments related to possible service situations cannot be overemphasized, especially since, in relation to alloy selection, it is well established that alloy additions that provide good resistance in one environment may not do so in another. Similarly, in view of the importance of surface state in corrosion reactions, it is surprising how often laboratory tests involve surfaces that are not representative of those that may obtain in service, with the result that the free corrosion potentials in laboratory tests may differ markedly from those in service, with possibly serious consequences for cracking susceptibility. The problem is partially overcome by the use of potentiostatic control in laboratory tests, but in some, although not all, conditions of exposure composition and potential changes within precracks, crevices, or pits can influence results, and the crack tip potential may not equate to that which is measured at the surface where the crack emerges.
The importance of attempting to simulate service conditions in laboratory tests in relation to the chemistry of the environment and the potential is also the case in relation to stressing conditions, hence the significance of tests involving precracked specimens, the application of slow strain rates, and low-frequency cyclic loading. The last decade or so has seen the widespread introduction of these stressing modes, but there remain queries concerned with such tests, not least in relation to whether they are so demanding that materials which would behave satisfactorily in some service applications are disallowed. Also in the context of such tests there remains for rationalization methods for expressing results. The strain rate dependence of environment-sensitive fracture probably relates to the time dependence of corrosion-related reactions, and it may be worth considering that the parameters currently used for defining thresholds would be more realistically related to stressing rate or the rate of change of the threshold stress intensity factor.
Application of Laboratory Test Data to Engineering Design
Authors: Simenz RF , Pengra JJ , Langenbeck SL 
Published: December 2008

The use of currently available stress corrosion threshold data in design is discussed. Examples of service failures are detailed for parts which laboratory data have assisted in determining the cause of failure and resolution of the problem.
Stress corrosion test results of over 300 high-strength steel specimens are summarized. Specimens were tested by bend and axial tension loading and exposed to high humidity and alternate immersion in salt water. A comparison of 4340 and 300M alloys and the effect of product form, grain direction, part size, and stress concentration on the stress corrosion characteristics of these high-strength alloys are made. Methods for the use of these data and other published data are outlined. This use includes original design as well as analysis efforts to extend the service life of existing aircraft. Engineers' future needs for stress corrosion data point to the new-technology aluminum alloys and extended crack growth data under meaningful environments and loading conditions.
Utilizing Various Test Methods to Study the Stress Corrosion Behavior of Al-Li-Cu Alloys
Authors: Pizzo PP , Galvin RP , Nelson HG 
Published: December 2008

The stress corrosion (SC) behavior of two powder metallurgy (P/M) processed (Al-Li-Cu) alloys, with and without Mg addition, in aqueous 3.5% NaCl solution has been investigated. Three test techniques were employed in the investigation: (1) the alternate-immersion testing of tuning fork specimens, (2) slow crack growth tests using fracture-mechanics specimens, and (3) the slow-strain-rate testing of straining electrode specimens. The corrosion conditions investigated include cathodic and anodic potentiostatic control and free-corrosion under constant-immersion and alternate-immersion conditions. The heat treatment and the orientation of the alloys were varied to establish the more susceptible material conditions. Scanning electron microscopy and optical metallography were used to demonstrate the character of the interaction between the Al-Li-Cu alloys and the selected environment.
Both Al-Li-Cu alloys are susceptible to SC in an aqueous 3.5% NaCl solution under certain electrochemical and microstructural conditions. Each test method was found to yield important information on the character of the SC behavior. Under all conditions investigated, second-phase particle stringers along the extrusion direction in the alloys were rapidly attacked, and they played a principal role in the SC process. With time, larger pits developed from these rows of smaller pits, and under certain electrochemical conditions surface cracks initiated from the larger pits and contributed directly to the fracture process. Evidence to support slow crack growth was observed in both the slow-strain-rate tests and the sustained-immersion tests of precracked fracture-mechanics specimens. The possible role of H2 in the stress-corrosion cracking process is suggested.
Effect of Sequential Load or Potential Changes on Stress Corrosion Cracking Behavior of Steels
Authors: Fujii CT 
Published: December 2008

Experiences with stress corrosion cracking (SCC) test methods based on linear elastic fracture mechanics principles suggest that factors such as loading procedures, hold times, overloads during fatigue precracking, and electrochemical potential variances may substantially influence test results. However, the relative importance of each factor on SCC behavior has not been determined unequivocally and much remains to be explained.
Initial experiments to determine the baseline SCC properties (in terms of KIscc) of the two HY-130 steel plates used in these studies on the effect of cyclic load or potential changes on SCC behavior showed that a thickness-independent KIscc is obtainable from a specimen with a minimum 25 mm thickness for both the freely corroding (FC) and zinc-coupled (Zn) conditions. The step-loading procedure appears to be adequate for the determination of acceptable KIscc values. The KIscc values were used to guide the selection of load and potential in subsequent experiments.
Experiments on the effects of two types of cyclic loading, tension-compression and tension-zero, on SCC behavior of precracked specimens were conducted utilizing the cantilever test method. The period of load change was about 100 h and the waveform was approximately square. Cycling per se does not appear to influence the so-called incubation time for SCC initiation under tension-zero cycling; and for this loading mode a characteristic delay time of approximately 100 to 300 h elapsed prior to detecting the first indication of stable crack growth. In contrast, tension-compression load cycling caused a several-fold increase in the time required to initiate SCC on maintaining the load after several tension-compression cycles. The observations suggest that if the tension-compression cyclic loading pattern were sustained, initiation of crack growth could have been deferred for several thousand hours, if not indefinitely.
Studies on the kinetics of initiation or arrest of SCC show that these processes respond more rapidly to load changes than potential changes. The observed effects associated with changes in potential on crack growth response are suggestive of a hydrogen-influenced mechanism. These studies also showed that long hold times (10 000 h) will not initiate or reinitiate SCC if the applied KI is below the threshold (KIscc) for the material and environmental condition. No evidence of different threshold values associated with arrest and initiation of SCC was noted.