bluuebunny/crossref_metadata_2025 huggingface dataset:
Compositional Redistribution in Fe-Ni-Cr Alloys Under Proton Irradiation
Authors: Kimoto T , Shiraishi H
Published: December 2008

The compositional redistribution in the direction of depth in austenitic Fe-Ni-Cr-Si-C alloys under 200-keV proton irradiation was examined experimentally using the cross-section technique. After the solution-annealed Fe-25.5Ni-14.7Cr-0.97Si-0.026C and Fe-25.7Ni-14.5Cr-2.85Si-0.026C alloys were irradiated at 873 K by 200-keV protons to the dose of 175 dpa at the peak-damage position for the different irradiation times of 0.1 and 1.37 Ms, the depth profile of composition was measured with an energy dispersive X-ray microanalyzer. Significant depletion of nickel and enrichment of chromium were observed in the peak-damage region ranging from about 0.85 to 1.05 μm in depth, similarly in both the short-time (0.1 Ms) and long-time (1.37 Ms) irradiations. Slight enrichment of iron and slight depletion of silicon were also observed in the peak-damage region. The observed compositional changes in the peak-damage region is in good qualitative agreement with theoretical prediction, although some quantitative discrepancies between them remain.
Comparison of Plastic Deformation and Charged Particle Irradiation Influence on Phase Transformations in Stainless Steel
Authors: Zhetbaev A , Ibragimov SS , Vereshchak MF , Zhantikin TM
Published: December 2008

Transmission and post-nuclear-reaction emission Mössbauer spectroscopy were used for investigating radiation and deformation effects on Cr18Ni9Ti steel. The rolled foil was annealed for 2 h at 870 K and was irradiated with 30-MeV protons and 50-MeV alpha-particles up to doses of 5 × 1021 m−2 on a liquid nitrogen cooled target. All transmission spectra are identical. In the case of proton irradiation the emission spectrum is analogous to the spectrum of the plastically deformed specimen. But after alpha-particle irradiation there is no magnetic splitting in the spectra. It is concluded that with plastic deformation and proton irradiation the same processes change the neighborhood of the resonant atoms.
Point Defect Dynamics in Nonhomogenous Alloys Under Irradiation
Authors: Abromeit C , Martin G
Published: December 2008

With the aid of a simple reaction model for point defects in a nonhomogenous alloy, we show that large-scale point defect fluxes are to be expected under irradiation. The model is solved analytically in the limit of low-amplitude concentration fluctuations of sinusoïdal shape, under steady state conditions. We give expressions for the defect fluxes as a function of the irradiation intensity, the amplitude and wavelength of the composition fluctuation. It is shown that from the difference of the interstitial and vacancy fluxes a bias for defect elimination results, which is modulated at the scale of the chemical inhomogeneity. The latter bias, as estimated here, depends on the irradiation flux extremely weakly. Orders of magnitude of the defect fluxes and redistribution are given for the FeNiCr system. It is shown qualitatively that the implied processes have the proper direction to sustain the composition inhomogeneities, which have been reported in such alloys after irradiation.
Separation of Alloy Components in the Vicinity of a Collision Cascade
Authors: Ibragimov SS , Kirsanov VV , Melinkhov VD
Published: December 2008

The production of solute enriched (or depleted) regions has been observed in Fe3Al, Cu5Zn8, and Ni5Zn21 subject to neutron irradiation. The formation of those regions is due to the separation of the alloy components in the path of the atomic collision cascade, at the thermal stage of its development. A mechanism of formation of a region of different concentration in the collision cascade is proposed. Analyses of the kinetics of recovery of the in-cascade induced defect distribution show that the annealing of that damage can lead to the redistribution of the alloy components. Enrichment of one atomic species results in the depleted zone. The preferential flux of an atomic species toward the depleted zone is determined by the difference in the atomic mobilities and the characteristics of the interstitial configurations and migration mechanisms. A computer simulation of the separation confirmed the possibility of precipitation of a new phase at a sink, such as a depleted zone, which exists for a very short period of time.
The Influence of Microstructural Variability upon the Scatter in Mechanical Properties of R25 Sheet Molding Compound
Authors: Shirrell CD
Published: December 2008

The large scatter in the static strengths of R25 sheet molding compounds was observed to be related to the variability in the complex microstructure of this material. This microstructure consists of a subsurface veil of individual glass fibers and an internal core of intact fiber glass bundles.
Axial Fatigue of SMC-R65 Sheet Molding Compound in Liquid Environments
Authors: Ngo A-D , Hoa SV , Sankar TS
Published: December 2008

The fatigue behavior of an SMC-R65 sheet molding compound under axial fatigue loading and in the presence of water and iso octane is investigated. There is about a decade decrease in fatigue lives for specimens tested in water as compared to those tested in air. The fatigue lives of specimens tested in iso octane range from those in air to those in water. SMC-R65 specimens immersed in water show clear absorption boundaries.
Hygrothermal Degradation of Sheet Molding Compounds
Authors: Hosangadi AB , Hahn HT
Published: December 2008

Environmental variables such as moisture and temperature degrade fiber-reinforced polymer composites to various levels. This paper characterizes the hygrothermal degradation of a sheet molding compound (SMC) containing 65% by weight of E-glass fibers. Six different environments were chosen for the study: room temperature (RT)/65% relative humidity (RH), RT/98% RH, RT/water, 75°C/65% RH, 75°C/65% RH, 75°C/98% RH, and 75°C/water. The extent of degradation was evaluated using visual, microscopic, and chemical analysis techniques. From this study, distinct color changes and blistering on the specimen surfaces were evident. Degradation was manifested in the ultrasonic attenuation and in the reduction of short beam strength and stiffness.
Viscoelastic Response of SMC-R50 Under Different Thermomechanical Conditions
Authors: Yen S-C , Hiel C , Morris DH
Published: December 2008

The creep and creep recovery behavior of a random fiber composite (SMC-R50) was investigated. Time-dependent behavior at various stress and temperature levels was experimentally determined. Findley's equation was used to model the viscoelastic behavior of short-term tests. The Findley equation was also used to predict the time-dependent behavior of the random fiber composite for a multiple step loading. Excellent agreement between experimental results and the Findley equation was obtained. Since repeatable results were obtained only for mechanically conditioned specimens, the test results were compared to experimental data obtained from unconditioned specimens. Experimental results of the conditioned specimens fell within the scatter band of the data for the unconditioned specimens.
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.
Static and Cyclic Behavior of Structural Lightweight Concrete at Cryogenic Temperatures
Authors: Berner D , Gerwick BC , Polivka M
Published: December 2008

The mechanical behavior of a high-strength, lightweight concrete made with expanded-shale aggregate was determined in the temperature range from 23°C (73°F) to −196°C (−320°F). High-strength, lightweight concrete is of particular interest for use in offshore cryogenic containment structures in which the concrete may be subjected to low temperatures and high-intensity cyclic loading simulating 20-year stormwave action. Values of compressive strength, tensile strength, and elastic modulus were determined, with moisture content and cyclic loading serving as key parameters. An evaluation was also made of the behavior of embedded strain gages at cryogenic temperatures. The results indicate that the lightweight concrete performed favorably under the test conditions, with the mechanical properties generally increasing at low temperatures with greater gains for higher moisture contents. Cyclic loading induced relatively minor fatigue damage in the concrete and should not affect the structural performance of an offshore containment structure.
Effect of Hot Weather Conditions on the Strength Performance of Set-Retarded Field Concrete
Authors: Mittelacher M
Published: December 2008

Field test reports from seven major projects representing 1336 individual tests were evaluated for the effect of hot weather conditions, including the effects of placing temperatures of up to 37°C (99°F) on the 28-day compressive strength of set retarded concrete. The information was based on reports from independent agencies the concrete in behalf of the owner of the project. For the majority of the projects, the test specimens had been left exposed to ambient conditions during the initial curing period at the site. The concrete was supplied by different producers to power plant, high rise, mass transit, or highway projects in Florida and Atlanta, Georgia. The data were analyzed for temperature-strength relationships and for significant differences in average strength and standard deviation between data groups of concrete placed at temperatures below and above 32°C (90°F). The statistical analysis revealed the absence of a significant correlation between the placing temperatures and the strengths and of significant differences in the average strength and standard deviation of concrete of lower and higher placing temperature. Exceptions to these observations showed a more favorable performance in concrete of higher placing temperature.
The Willow Island Collapse: A Maturity Case Study
Authors: Halvorsen GT , Farahmandnia A
Published: December 2008

The Willow Island cooling tower collapse of April 1978 is reviewed with respect to the development of concrete maturity during construction. The tower shell was constructed during the fall and spring prior to the collapse. Fall and spring weather conditions were similar with regard to the potential for concrete strength development. However, an increased pace of construction in the spring effectively decreased the maturity of the concrete at the time it was subjected to construction loads. More than half of the concrete lifts placed during the spring construction of the cooling tower shell were supported by concrete with a maturity similar to that of the concrete in Lift 28, which failed during the placement of Lift 29. The collapse might have occurred sooner if several days of rainy weather had not apparently delayed the construction.
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).
Manufacturing Process Control Specification with Functional Programming
Authors: Walter C
Published: December 2008

This paper presents and explores the analogy between manufacturing and data processing from the point of view of the Functional Programming concept proposed by Backus. If the data file is replaced by a set of objects, a data processor becomes a manufacturing machine, and a factory is regarded as an object-flow interpreter. This suggests a manufacturing process description formalism, which in turn leads to a controller specification methodology. Although it can be extended to continuous processes, the analogy applies especially to discrete processes (i.e., processes whose evolution corresponds to sequences of easily identifiable and relatively few steps).
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.
Practical Problems in the Application of Industrial Robots
Authors: Dwivedi SN , Satyanarayana MS
Published: December 2008

Problems in robot application depend on the particular operation the robot has to perform and the environment in which it has to work. Though robots are becoming an essential and familiar feature in many manufacturing processes, they suffer from certain drawbacks. In this paper, an attempt has been made to pinpoint these problems and to indicate some possible solutions.
Wide-Range Displacement Expressions for Standard Fracture Mechanics Specimens
Authors: Kapp JA , Leger GS , Gross B
Published: December 2008

Wide-range algebraic expressions for the displacement of cracked fracture mechanics specimens are developed. For each specimen two equations are given: one for the displacement as a function of crack length, the other for crack length as a function of displacement. All the specimens that appear in ASTM Test for Plane-Strain Fracture Toughness of Metallic Materials (E 399) are represented in addition to the crack mouth displacement for a pure bending specimen. For the compact tension sample and the disk-shaped compact tension sample, the displacement at the crack mouth and at the load line are both considered. Only the crack mouth displacements for the arc-shaped tension samples are presented. The agreement between the displacements or crack lengths predicted by the various equations and the corresponding numerical data from which they were developed are nominally about 3% or better. These expressions should be useful in all types of fracture testing including JIc, KR, and fatigue crack growth.
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.
Analysis of an Externally Radially Cracked Ring Segment Subject to Three-Point Radial Loading
Authors: Gross B , Srawley JE , Shannon JL
Published: December 2008

The boundary collocation method was used to generate Mode I stress intensity and crack mouth opening displacement coefficients for externally radially (through-the-thickness) cracked ring segments subjected to three-point radial loading. Numerical results were obtained for ring segment outer-to-inner radius ratios (Ro/Ri) ranging from 1.10 to 2.50 and crack length to segment width ratios (a/W) ranging from 0.1 to 0.8. Stress intensity and crack mouth displacement coefficients were found to depend on the ratios Ro/Ri and a/W as well as the included angle between the directions of the reaction forces.
The Dugdale Model for Compact Specimen
Authors: Mall S , Newman JC
Published: December 2008

The purpose of this paper is to develop the Dugdale model for compact specimen. In particular, plastic-zone size and crack-tip-opening displacement (CTOD) equations are developed. Boundary-collocation analyses are used to analyze the compact specimen subjected to various loading conditions (pin loads, concentrated forces, and uniform pressure acting on the crack surface). Stress intensity factor and crack surface displacement equations for some of these loadings are developed and used to obtain the Dugdale model. The results from the equations for plastic-zone size and CTOD agreed well with numerical values calculated by Terada for crack-length-to-width ratios greater than 0.4.
Effect of Hydrogen on Crack Initiation and Growth in 18Mn-4Cr Steel
Authors: Kim Y-J , Mukherjee B , Carpenter DW
Published: December 2008

Hydrogen-assisted cracking in generator rotor end rings is a major concern of the utility industry. To assess the susceptibility of an austenitic 18Mn-4Cr end ring steel to a hydrogen environment, an experimental program was carried out to determine crack initiation and fatigue crack growth properties in hydrogen gas and air. In this program, a peak read detection circuit was designed to determine accurately crack initiation and early crack growth. Test results show that a hydrogen environment does not significantly influence the crack growth rate; however, it reduces the crack initiation life at a low notch root stress range.
A Model for Creep/Fatigue Interactions in Alloy 718
Authors: Nicholas T , Weerasooriya T , Ashbaugh NE
Published: December 2008

An experimental investigation was conducted to evaluate the crack growth rates in Inconel 718 at 649°C under symmetric and unsymmetric triangular waveshapes and triangular waves with hold times at maximum load. Data are presented as crack growth rate per cycle as a function of total cycle time. An analytical model is developed which predicts crack growth rate from an integration of the sustained load crack growth rates over the cycle when time-dependent behavior is dominant. The data show that the loading portion of a cycle is the major contributor to the time-dependent crack growth behavior. At low unloading frequencies or high load ratios, however, the unloading portion of the cycle is found to become increasingly important. The model utilizes minimum baseline data and is proposed for predictions of crack growth rate over a variety of loading cycle types.
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.
Analysis of Fracture Parameters for Bending-Type Specimens
Authors: Aizawa T , Yagawa G
Published: December 2008

The nonlinear crack analysis of bending-type specimens has been needed to evaluate the J integral values or T-modulus of the flawed structure made of ductile materials. In the present paper, the eigenmodes of Hutchinson-Rice-Rosengren (HRR) singularity at the nonlinear crack tip are obtained numerically by finite element eigenfunction analysis of the stress function model. Superposing the singularity functions thus obtained on the finite element displacement, several nonlinear fracture parameters are calculated taking into account the validity of uniform reduced integration in the bending-type problems. For the numerical examples, we use the single-edge-cracked panel and the compact tension specimen. Comparisons are made between the present study and other relevant results.
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).
Effects of Load Gradient on Applicability of a Fatigue Crack Growth Rate-Cyclic J Relation
Authors: Jolles M
Published: December 2008

The use of a cyclic J to characterize fatigue crack growth rates for conditions where the assumptions of linear elastic fracture mechanics are violated is addressed. In particular, the effects of the load gradient on the applicability of a cyclic J are examined. Experiments were conducted to quantify fatigue crack growth rates and cyclic J on modified compact tension specimens of A533B steel. Fatigue cycling at constant load amplitude where the cyclic J increases as the crack extends and constant displacement amplitude where the cyclic J decreases as the crack extends were performed. It is found that prior cyclic crack tip history affects the fatigue crack growth rate only as a consequence of influencing the extent of crack closure. Accounting for crack closure by requiring J equal to zero at the crack opening load results in excellent correlation between the fatigue crack growth rate and cyclic J for a wide range of loading conditions.
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.
Dynamic Crack Propagation Through Welded HY-80 Plates under Blast Loading
Authors: Barnes CR , Ahmad J , Kanninen MF
Published: December 2008

A systematic approach involving experiments and dynamic elastic-plastic finite element analyses was used to investigate the problem of crack initiation, propagation, and arrest in weldments under rapidly applied loading. The aim was to develop a predictive capability that can be used to assess the risk of fracture in welded structures subjected to blast loading. The experimental effort included residual stress measurements on welded HY-80 steel specimens together with a series of explosive loading experiments performed after precracking these specimens. Measurements were made of the time of crack growth initiation and the extent of crack growth at arrest. Elastic-thermoplastic finite element computations were made to obtain the weld-induced residual stresses. With these as initial conditions, dynamic elastic-plastic computations were then performed to predict crack initiation and growth behavior under the measured explosive loading history. These computations used estimates of the running fracture toughness based on fracture toughness data for HY-80 weldments available in the literature. Reasonably good agreement was obtained with the observed results. Of possible greater significance for subsequent fracture mechanics analyses of weld defect problems, it was found that the presence of weld-induced residual stresses strongly affects the prediction of the crack length at arrest.
Some Three-Dimensional Aspects of Subcritical Flaw Growth as Measured in a Transparent Polymeric Material
Authors: Smith CW , Epstein JS
Published: December 2008

After briefly reviewing an experimental optical technique for estimating crack shapes and corresponding stress intensity factor distributions in three-dimensional cracked body problems, this paper lists some basic observations on the three-dimensional aspects of subcritical flaw growth and supports them by citing results from application of the experimental method. Restrictions of the method are listed. It is concluded that, within the restrictions, the method is useful in supporting numerical analysis.
On the Three-Dimensional Implications of LEFM: Finite Element Analysis of Straight and Curved Through-Cracks in a Plate
Authors: Solecki JS , Swedlow JL
Published: December 2008

A linear elastic plate containing a central through-thickness crack is investigated using three-dimensional finite element analysis. The crack front profile is initially assumed to be straight, and the distributions of the energy release rate are calculated over a range of Poisson's ratios. Using the results from the straight crack problem, curved crack profiles are generated that are attuned to a uniform distribution of the energy release rate. Also, some attention is directed to the computation of the singular behavior in the vicinity of the vertex (i.e., where the crack front meets the free surface).
Fracture Behavior of a Uranium or Tungsten Alloy Notched Component with Inertia Loading
Authors: Underwood JH , Scavullo MA
Published: December 2008

A failure of a prototype long rod penetrator is described, including the stress and fracture analyses, the materials and service simulation testing performed, and the fracture toughness and nondestructive inspection requirements that were implemented. Results of a subsequent study are described, which involve the producibility of the long rod penetrator, particularly in relation to the complex fracture toughness testing methods that are required for use with this component.
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.
Loading Mode (Mode I/Mode III) Testing for Stress Corrosion Cracking
Authors: Thompson AW , Bernstein IM
Published: December 2008

The use of loading mode variation (Modes I and III) to identify the mechanisms of stress corrosion cracking is reviewed and evaluated, and some recent results on 7075 and 7090 aluminum are presented. It is concluded that the conventional interpretation (that anodic dissolution dominates when results in Modes I and III are similar, and hydrogen embrittlement dominates when the Mode III response is essentially zero) is likely correct. This separation of processes can serve as one means to verify that accelerated laboratory tests do in fact simulate service conditions and service failures.
A Fracture Mechanics Model for Iodine Stress Corrosion Crack Propagation in Zircaloy Tubing
Authors: Crescimanno PJ , Campbell WR , Goldberg I
Published: December 2008

A fracture mechanics model is presented for iodine-induced stress corrosion cracking in Zircaloy tubing. The model utilizes a power law to relate crack extension velocity to stress intensity factor, a hyperbolic tangent function for the influence of iodine concentration, and an exponential function for the influence of temperature and material strength. Comparisons of predicted to measured failure times show that predicted times are within a factor of two of the measured times for a majority of the specimens considered.
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.
Slow-Strain-Rate Stress Corrosion Testing of Aluminum Alloys
Authors: Holrody NJH , Scamans GM
Published: December 2008

An extensive program of slow-strain-rate stress corrosion testing of aluminum alloys in a wide variety of susceptibility conditions and environments produced results fully consistent with the expected behavior from service experience and the results of other established test methods. Tests were conducted both on laboratory alloys in sheet form and on commercial alloys in wire, sheet, and plate forms; the systems studied included Al-Zn-Mg, Al-Zn-Mg-Cu, Al-Cu-Mg, and Al-Mg. Suitable strain rate regimes for testing, standard environments, and optimum stress corrosion susceptibility parameters were established. In general, a rate of 10−6/s was found to be appropriate for 2000 and 7000 series alloys and 10−4/s for 5000 series alloys. The most effective test environment was found to be 3% NaCl + 0.3% H2O2 for all alloys tested, and in general either relative elongation or reduction in area was the most meaningful susceptibility assessment parameter.
Evaluating the Intergranular SCC Resistance of Sensitized Type 304 Stainless Steel in Low-Temperature Water Environments
Authors: Bruemmer SM , Jones RH , Divine JR , Johnson AB
Published: December 2008

The resistance of sensitized AISI Type 304 stainless steel to intergranular stress corrosion cracking (IGSCC) in 32°C water environments has been investigated by using constant axial load (CAL), constant extension rate (CER), U-bend, and crevice corrosion tests. Constant load tests were found to give a better simulation of a service failure and produced IGSCC under a wider range of conditions than CER or U-bend tests. Intergranular SCC of welded and furnace-sensitized Type 304 specimens was observed in CAL experiments in both deionized and borated water with ppm level chloride additions. Constant extension rate tests also produced IGSCC, but only in welded pipe specimens with the original ground and welded surfaces intact. If the original inner diameter and outer diameter surfaces were removed, fracture surfaces showed ductile, microvoid coalescence appearances. No evidence of SCC or significant corrosive attack was found in U-bend or crevice corrosion tests after more than six months in dilute chloride environments at temperatures of 30 or 50°C. However, intergranular cracking was observed in furnacesensitized, high-carbon Type 304 U-bend specimens at 80°C.
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.
Use of a Constant ΔK Test Method in the Investigation of Fatigue Crack Growth in 288°C Water Environments
Authors: Van Der Sluys WA , DeMiglio DS
Published: December 2008

To characterize environmental fatigue crack growth properties of reactor pressure vessel steels, experiments were conducted by a computer-controlled constant alternating stress intensity factor (ΔK) test technique over a wide range of R-ratios and loading frequencies in 288°C water environments. Compact fracture specimens of two nuclear pressure vessel steels were tested over a range of ΔK-values from 16 to 55 MPa √m. Loading frequencies ranged from 0.0017 to 10 Hz, and R-ratios from 0.16 to 0.72.

As many as 22 separate experiments were conducted on a single specimen. The constant ΔK test method permitted crack growth rate measurements to be made with a high degree of confidence over long intervals of crack extension.

A simulated pressurized water reactor (PWR) environment plays only a minor role in the enhancement of fatigue crack growth rates. The applied ΔK was the primary rate-controlling variable, while R-ratio and loading frequency were secondary.

In high-purity deoxygenated water, the environment had a very significant effect on crack growth rates. The loading frequency was a primary rate-controlling variable at low loading frequencies. At high loading frequencies crack growth rates were ΔK-dependent.
A Low-Cost Microcomputer Data Acquisition System for Fatigue Crack Growth Testing
Authors: Tipton DG
Published: December 2008

A data acquisition system has been designed and assembled to allow automated, unattended fatigue crack growth testing. The system employs a low-cost micro-computer and analog-to-digital converter interfaced to a standard MTS servohydraulic fatigue machine. The system is designed to comply with ASTM Test for Constant-Load-Amplitude Fatigue Crack Growth Rates Above 10−8 m/Cycle (E 647). High-performance data are obtained by the crack-opening displacement method.
Effect of Water Vapor on Fatigue Crack Growth in 7475-T651 Aluminum Alloy Plate
Authors: Dicus DL
Published: December 2008

An investigation was performed to assess the effects of water vapor on fatigue crack growth in 7475-T651 aluminum alloy plate at frequencies of 1 and 10 Hz. Twenty-five mm thick compact specimens were subjected to constant amplitude fatigue testing at a load ratio of 0.2. Fatigue crack growth rates were calculated from effective crack lengths determined by using a compliance method. Tests were conducted in hard vacuum and at water vapor partial pressures ranging from 94 Pa to 3.8 kPa.

Fatigue crack growth rates were frequency-insensitive under all environmental conditions tested. For constant stress intensity factor ranges, crack growth rate transitions occurred at low and high water vapor pressures. Crack growth rates at intermediate pressures were relatively constant and showed reasonable agreement with published data for two Al-Cu-Mg alloys. The existence of two crack growth rate transitions suggests either a change in rate-controlling kinetics or a change in corrosion fatigue mechanism as a function of water vapor pressure. Reduced residual deformation and transverse cracking on specimens tested in water vapor versus vacuum may be evidence of embrittlement within the plastic zone due to environmental interaction.
New Process for Zirconium and Hafnium Separation
Authors: Moulin L , Thouvenin P , Brun P
Published: December 2008

The separation of hafnium and zirconium, required for nuclear use of zirconium, is generally performed by liquid-liquid extraction in organic solvents. The paper describes a new process based on extractive distillation of zirconium chloride (ZrCl4) and hafnium chloride (HfCl4) in a solvent made of molten potassium chloride-aluminum chloride (KCl-AlCl3) mixture above 350°C at atmospheric pressure. The corresponding process is now in full-scale industrial production.