bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling the Behavior of Short Fatigue Cracks in a Near-α Titanium Alloy
Authors: Hardy MC
Published: March 2009

Low-cycle fatigue is the greatest potential cause of failure in critical aeroengine components. To prevent premature failure, the fatigue life of these components needs to be predicted accurately. This requires knowledge of crack nucleation and growth under fatigue loading. Initial crack propagation is not continuous as a result of obstacles such as grain boundaries. Laboratory observation has shown that cracks decelerate rapidly as they approach these boundaries. Further growth may be impeded for a considerable number of cycles if there is a significant difference in orientation between the cracked and adjacent grains. This behavior effectively disappears at longer crack sizes. A detailed quantitative appraisal of crack growth rates is vital for component life predictions based on fracture mechanics. Cracks that nucleate during engine operation experience very high stresses that may exceed the material yield stress. Established linear elastic fracture mechanics may not be applicable due to loss of similitude caused by violation of the small-scale yielding criterion. These concepts are also based on continuum fracture mechanics and therefore cannot describe the early stages of crack growth. This paper considers an empirical model for short crack growth in a β heat-treated near-α titanium alloy at room temperature. Crack growth rate equations are expressed in terms of crack length and effective stress range and were derived from experimental crack length versus cycles data. These data were generated at constant peak stress and various stress ratios. The expressions are shown to give an excellent representation of experimental crack growth rate versus crack length data. In producing the model, procedures have been established to determine crack opening loads and critical crack sizes above which continuum fracture mechanics apply.
A Study of Fatigue Crack Growth in Lugs Under Spectrum Loading
Authors: Sunder R , Prakash RV
Published: March 2009

Optical fractography and special load sequencing were used to characterize the growth of naturally initiating fatigue cracks under FALSTAFF spectrum loading in lugs with bushes fitted to varying degrees of interference. The same technique was used to obtain a stress intensity calibration under constant amplitude loading. This calibration, combined with crack growth analysis using the hysteretic closure concept and the rainflow cycle count, correlated well with experimental observations of growth rate down to a crack depth of 400 µm. Available analytical stress intensity solutions do not appear to explain observed high crack growth rates, particularly as crack size diminishes to part-through dimensions.
Prestraining and its Influence on Subsequent Fatigue Life
Authors: Kalluri S , Halford GR , McGaw MA
Published: March 2009

An experimental program was conducted to study the damaging effects of tensile and compressive prestrains on the fatigue life of nickel-base, Inconel 718 superalloy at room temperature. To establish baseline fatigue behavior, virgin specimens with a solid uniform gage section were fatigued to failure under fully reversed strain control. Additional specimens were prestrained to 2, 5, and 10% (engineering strains) in the tensile direction and to 2% (engineering strain) in the compressive direction under stroke control and were subsequently fatigued to failure under fully reversed strain control. Experimental results are compared with estimates of remaining fatigue lives (after prestraining) using three life prediction approaches: (1) the linear damage rule (LDR), (2) the linear strain and life fraction rule (LSLFR), and (3) the nonlinear damage curve approach (DCA). The Smith-Watson-Topper parameter was used to estimate fatigue lives in the presence of mean stresses. Among the cumulative damage rules investigated, the best remaining fatigue life predictions were obtained with the nonlinear damage curve approach.
The Impact of Recent Research on the Development and Modification of ASTM Weathering Standards
Authors: Fischer RM , Ketola WD
Published: March 2009

Research conducted in the past ten years under the auspices of ASTM G-3 has been pointed at evaluating the quality of test information that is obtained when following the G-3 weathering standards. The results of these studies indicated that gloss data obtained from replicate specimens using identical equipment, following identical standard practices, had poor (lab-to-lab) reproducibility. Many material specifications used by both government and industry rely on weathering tests having “good” reproducibility so that exposure results from different laboratories can be compared. The primary purpose of this paper is to demonstrate a recommended weathering experiment and subsequent data treatment. Emphasis is placed on the use of analysis of variance to determine statistically significant performance differences for materials exposed in weathering tests. When analysis of variance is used in conjuction with an appropriate reference material, weathering specification tests can be established that have excellent reproducibility and are in compliance with the precision and bias recommendations of ASTM G-3 weathering standards.
Parametric Control of a Fresnel Reflecting Concentrator Outdoor Accelerated Weathering Device
Authors: Putman WJ , McGreer M , Pekara D
Published: March 2009

Outdoor accelerated weathering testing of materials using fresnel reflecting concentrators was pioneered by DSET in 1960. This type of testing is described in “Practice for Performing Accelerated Outdoor Weathering of Nonmetallic Materials Using Concentrated Natural Sunlight” (ASTM G90) and “Accelerated Exposure of Automotive Exterior Materials Using a Solar Fresnel Reflective Apparatus” (SAE J1961). The advantage of this form of accelerated weathering is that the sun's natural solar energy spectrum is used to irradiate the specimens under test. Since this is an outdoor method, variations in test conditions occur due to the natural seasonal weather differences. These seasonal variations mimic what occurs in the real world and correlation between real time weathering and outdoor accelerated weathering can be obtained for most materials with the traditional test cycles. However, advances in paint technology may require test cycles different than those specified by current test standards. The characteristics of modern, stabilized coatings indicate that they are now more resistant to the effects of both real time and accelerated weathering. Still, some failures occur in the real world that are not predicted by accelerated weathering tests. This paper will discuss the temperature and moisture control methodologies evolved over the last three years for a type of fresnel reflecting concentrator designated as “EMMAQUA®+”, an outdoor accelerated weathering test device, and the development of new test cycles for this device. This test device can simultaneously control black and white panel temperatures and provide several different moisture delivery methods. Data will be presented that will compare the results obtained with the new test cycles to the traditional cycles and to real time exposures.
Predicting Water Spot and Acid Etch Resistance of Clearcoats by Artificial Weathering: Acid Dew and Fog Test
Authors: Schulz U , Trubiroha P
Published: March 2009

The formation of water spots and acid etches at the surfaces of modern automotive basecoat/clearcoat systems occurs sporadically. This is caused by acid depositions and acid chemical attack during outdoor exposures. Currently used outdoor exposure tests in locations having a high incidence of acid rain, dew or fog, show often contradicting data of coating weatherability. This is because they depend on a large number of randomly occuring conditions like frequency, combination and acidity of the actual atmospheric precipitations. Current artificial weathering standardized test methods do not incorporate conditions such as controlled, introduced variables like acid depositions. The objective of our investigations was the development of an artificial weathering test for automotive finishes which includes the action of acid depositions, that will provide reproducibility and repeatability of test results. The conditions that result in environmental etch are examined and an improved artificial weathering test proposed.
Learning from History: A Case Study in Nuclear Fuel
Authors: Robertson JAL
Published: March 2009

The award of the 1993 W. J. Kroll Zirconium Medal recognized the value of cooperative, multidisciplinary, applied research in tackling practical problems. This paper suggests that several other lessons relevant to the current debate on science-and-technology (S&T) policy can be drawn from our experience a quarter of a century ago. It outlines how close cooperation among those involved with the fuel for the Canadian CANDU heavy-water reactors identified a problem, then proceeded to solve it expeditiously. This capability for a rapid response to an unforeseen problem was no accident, but arose out of the conditions that existed at the Chalk River Laboratory of Atomic Energy of Canada Limited (AECL) and a deliberate policy to maintain this capability even when the utility's power reactors were demonstrating excellent performance.
Behavior and Properties of Zircaloys in Power Reactors: A Short Review of Pertinent Aspects in LWR Fuel
Authors: Garzarolli F , Stehle H , Steinberg E
Published: March 2009

Zircaloy-2 and -4, developed mainly in the United States, have been used in Germany for fuel rod claddings and in-core structural components from the beginning of reactor technology. Extensive studies of the material properties of the Zircaloys have been performed in Siemens laboratories since 1957. Irradiation testing was done in several test reactors. However, the combined effects of irradiation and real environmental conditions were determined through many experimental irradiations in existing power reactors. Elaborate examinations in the reactor pools of such experimental materials and of many standard fuel rods and assemblies after intermediate, full, and intentionally extended exposures were the main source of information and hard data. These programs were supported by several utilities and in certain areas carried out in cooperation with others.

Zircaloy-2 and -4 turned out to be very reliable materials that fulfilled all requirements for normal operation and likewise the requirements for postulated accidental conditions and for intermediate storage for many years. Optimization of Zircaloy-2 and -4 during recent years includes both optimization of microstructure and of chemical composition. BWRs and PWRs need differently optimized materials. Today's more demanding operation conditions and discharge burnups required a further optimization of the Zircaloys and for “hot” PWRs even the development of more corrosion-resistant Zr alloys. A significant improvement of PWR corrosion behavior can be achieved with Zr alloys using the alloying elements of Zircaloy with somewhat modified concentrations. Sn should be below or at least in the lower range of the ASTM specification range for Zircaloy-4, Fe and Cr should be somewhat higher, and Si should be specified as an alloying element rather than as an impurity.
The Importance of Oxide Morphology for the Oxidation Rate of Zirconium Alloys
Authors: Wikmark G , Rudling P , Lehtinen B , Hutchinson B , Oscarsson A , Ahlberg E
Published: March 2009

The oxide growth rate of zirconium alloys, e.g., Zircaloy-2 and Zircaloy-4, has been proposed to be controlled mainly by the transformation of the zirconium oxide from tetragonal to monoclinic structure at some distance from the metal-oxide interface, leading to cracking. This oxide growth rate model is inconsistent with our results. Zirconium alloys of varying chemical composition but with identical manufacturing process had markedly different oxide growth and hydriding properties in autoclave testing (400°C steam). The materials were characterized by several methods, e.g., electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical impedance (EIS). The SEM and some of the XRD investigations of the oxide were performed on the metal-oxide interface after dissolution of the metal. The oxide growth developed through three different stages with an altered oxide morphology at the metaloxide interface at each stage. The developments of the stages were correlated with the oxide growth rate. Impedance measurements suggested that the oxide film had three layers, the outermost being extensively porous. Relaxation of the oxide film stress showed that the compressive stress in the oxide was not essential for retention of a significant amount of the tetragonal phase.
Effect of Annealing Temperature on Corrosion Behavior and ZrO2 Microstructure of Zircaloy-4 Cladding Tube
Authors: Anada H , Herb BJ , Nomoto K , Hagi S , Graham RA , Kuroda T
Published: March 2009

This paper describes the corrosion behavior and the ZrO2 microstructure of Zircaloy-4 (Zry-4) cladding tubes that were intermediate annealed at various temperatures. The corrosion behavior of the cladding tubes was studied by autoclave tests performed under 633 K water condition and 673 K steam condition. A TEM examination shows that the microstructure of ZrO2 formed on the Zry-4 matrix consisted of both the columnar structure and the equiaxed grain. The grain size of the columnar grain was approximately 30 by 200 nm, while that of the equiaxed grain was less than 20 nm. The equiaxed grain was dominantly observed near lateral cracks and around intermetallic compounds that were incorporated into the ZrO2 film. An analysis of the HR-SEM images indicated that the equiaxed grain to columnar grain volume ratio increased with increasing weight gain, especially after the first transition. The equiaxed grain to the columnar grain volume fraction decreased with increasing annealing temperature, which corresponded to decreasing weight gain. It was suggested that grain boundary diffusion of oxygen ions was accelerated by grain-size change of the oxide owing to the ZrO2 microstructure transformation from the large columnar grains to the fine equiaxed grains. The ZrO2 microstructure transformation might be caused dominantly by the oxidation of the intermetallic precipitates. The intermetallic precipitates were fine and uniformly distributed in the low-temperature TREX annealed Zry-4. This resulted in high-temperature TREX annealing being beneficial for improving corrosion resistance of the Zry-4 tube in PWR environments.
Correlation Between Electrochemical Properties and Corrosion Resistance of Zirconium Alloys
Authors: Ito Y , Furuya T
Published: March 2009

The electrochemical behavior of some zirconium alloys including Zry-2 with various ΣAi from 2.5 × 10-20 to 1.2 × 10-17 (h), modified Zry-2 with iron contents of 0.15, 0.25, and 0.5%, and standard Zry-4 was studied by measuring anodic polarization curves in sulfuric acid solution. The results of these electrochemical tests were compared with those of steam autoclave tests.

In Zry-2, the current peak was observed at 1250 mV (versus SCE) on the anodic polarization curve, and this peak area increased with ΣAi and with the size of secondary precipitates. Also, this peak was closely correlated with nodular corrosion resistance as expected from the above results. As iron contents in modified Zry-2 increased, the current peak at 1250 mV decreased and a new peak at 1900 mV appeared. The former peak disappeared and the latter peak increased further at 0.5% iron. In Zry-4, the current peak was observed at 1900 mV, but not at 1250 mV, and this behavior was the same as that of modified Zry-2 of 0.5% iron.

AEM observation of secondary precipitates in these zirconium alloys indicated that the peak at 1250 mV appeared when the Fe/Cr ratio of Zr(Fe,Cr)2 was below 1.0 and the peak at 1900 mV appeared when the ratio was above 1.5. In order to clarify the mechanism of these peak behaviors, the anodic polarization properties of intermetallic compounds that precipitated in zirconium alloys were studied. The results suggest that the peak at 1250 mV is related to the reaction Cr3+ → Cr6+ (soluble in solution) and the peak at 1900 mV is related to the reaction Fe3+ → Fe6+ (soluble in solution) and oxygen generation on iron-rich precipitates.
Long-Term In Situ Corrosion Investigation of Zr Alloys in Simulated PWR Environment by Electrochemical Measurements
Authors: Göhr H , Schaller J , Ruhmann H , Garzarolli F
Published: March 2009

The corrosion behavior of Zircaloy-type alloys with different tin contents of 1.55, 0.70, and 0.55 wt% was studied at 350°C and 17 MPa in an environment similar to PWR primary water. For this non-interrupted test, a special autoclave system was used that was equipped with electrical feed that allowed followup on the growth of oxide layers by impedance spectroscopy and corrosion potential measurement at high temperature and pressure. As a reference electrode, a platinum wire was used that works as a hydrogen electrode according to the hydrogenated environment established during the start-up procedure. The test ran without interruption for 471 days.

Impedance spectra were taken at time intervals and evaluated for thickness and morphology of the oxide layer as well as for its electrical resistance. The tests without any temperature and pressure cycling showed similar oxidation behavior with repeated transitions as in discontinuously performed standard autoclave tests. Early in the pre-transition range, a dense oxide layer is formed, and fast changes of corrosion potential and electrical resistance are observed. The dense layer increases in thickness and homogeneity up to the transition, where a sudden breakdown occurs. Abrupt changes of the corrosion potential and electrical resistance were observed also at those points. After transition, a new dense layer is built up.

The corrosion potential changes are caused by a decrease of the electrical corrosion current with increasing oxide layer thickness, by the formation of a potential drop over the high-resistance dense oxide layer, and by structural changes at the transition points.

In general, alloys with different tin contents show similar behavior. However, they show differences in the times to transition, the kinetic constants deduced from their impedance spectra, and in the ionic and electronic resistance of the dense inner layer controlling corrosion.
Anodic Protection Provided by Precipitates in Aqueous Corrosion of Zircaloy
Authors: Isobe T , Murai T , Mae Y
Published: March 2009

Alloying elements such as Fe and Cr are generally considered to be effective even in small quantities for corrosion resistance of Zircaloy-4. The maximum total solubility of Fe + Cr in a Zr-Sn matrix has been reported to be very low [1]. Therefore, most of these elements are observed in the form of ternary Zr-Fe-Cr-type precipitates.

To clarify the effects of precipitates on corrosion property, Zr-1.3 Sn-(Fe,Cr) alloys containing Fe + Cr from 45 up to 180 ppm (the Fe to Cr ratio is about 2) were melted from pure zirconium (X-bar Zr and EB-Zr) and pure alloying elements. They were subjected to corrosion testing in 633 K water and microstructural analysis. It was found that precipitate-free materials showed much larger weight gains than precipitate-containing materials even at the same alloy compositions.

Subsequently, a corrosion test on the precipitate-free material galvanically coupled with a noble intermetallic compound of Zr(Fe0.66Cr0.33)2 was performed. It was found that the precipitate-free material, having very poor corrosion resistance in itself, was covered with thin and adherent black film under galvanically coupled conditions. In addition, its oxide grain structure was almost the same as that of the precipitate-containing material Zircaloy. From these results, it was concluded that the good corrosion resistance of Zircaloy-4 is attributed to the anodic protection provided by precipitates in the alloy.
Detrimental Role of Hydrogen on the Corrosion Rate of Zirconium Alloys
Authors: Blat M , Noel D
Published: March 2009

Recent studies have suggested that hydride precipitation at the metal/oxide interface could play a detrimental role on the waterside corrosion rate. Nevertheless, the mechanism of that detrimental role is not completely understood, and two hypotheses were investigated to understand the mechanism that controls the role of the hydrides. The first hypothesis is based on a mechanical effect: the hydrides precipitate at the metal/oxide interface and destroy the physical integrity of the “barrier” oxide layer. The second hypothesis is a modification of the transport properties of the oxide grown on the hydrided metal.

The detrimental role of hydrides on the corrosion rate was studied by charging unirradiated Zircaloy-4 cladding material with hydrogen to a level higher than the limit of solubility at 400°C. Both gaseous and cathodic charging techniques were used. Static corrosion tests were carried out in autoclave with steam at 400°C on an as-received and hydrided sample. The detrimental role of hydrides is confirmed for the post-transition corrosion rate, and that effect is more significant for high cathodic charging.

The results of the metallurgical examinations are discussed to provide an understanding of the mechanism. No relationship between hydrides, physical defects in the oxide, and local corrosion rate enhancement was found. Therefore, our results do not support the hypothesis of a mechanical effect at the scale of the performed examinations, but more detailed work is required to confirm this.
Hydrogen Pickup and Redistribution in Alpha-Annealed Zircaloy-4
Authors: Kammenzind BF , Franklin DG , Peters HR , Duffin WJ
Published: March 2009

Zircaloy-4, which is used widely as a core structural material in pressurized water reactors (PWR), picks up hydrogen during service. Hydrogen solubility in Zircaloy-4 is low, and hydrides precipitate after the Zircaloy-4 matrix becomes supersaturated with hydrogen. These hydrides embrittle the Zircaloy-4. To study hydrogen pickup and concentration, a post-irradiation nondestructive radiographic technique for measuring hydrogen concentration was developed and qualified. Experiments on hydrogen pickup were conducted in the advanced test reactor (ATR). Ex-reactor tests were conducted to determine the conditions in which hydrogen would dissolve, migrate, and precipitate. Finally, a phenomenological model for hydrogen diffusion was indexed to the data. This presentation describes the equipment and the model, presents the results of experiments, and compares the model predictions to experimental results.
A Unified Model to Describe the Anisotropic Viscoplastic Behavior of Zircaloy-4 Cladding Tubes
Authors: Delobelle P , Robinet P , Bouffioux P , Geyer P , Le Pichon I
Published: March 2009

This paper presents the constitutive equations of a unified viscoplastic model and its validation with experimental data. The mechanical tests were carried out in a temperature range of 20 to 400°C on both cold-worked stress-relieved and fully annealed Zircaloy-4 tubes. Although their geometry (14.3 by 1.2 mm) is different, the crystallographic texture was close to that expected in the cladding tubes. To characterize the anisotropy, mechanical tests were performed under both monotonic and cyclic uni- and bi-directional loadings, i.e., tension-compression, tension-torsion, and tension-internal pressure tests. The results obtained at ambient temperatures and the independence of the ratio Rp = εp θθ/εp zz. with respect to temperature would seem to indicate that the set of anisotropy coefficients does not depend on temperature. Zircaloy-4 material also has a slight supplementary hardening during out-of-phase cyclic loading.

We propose to extend the formulation of a unified viscoplastic model, developed and identified elsewhere for other initially isotropic materials, to the case of Zircaloy-4. Generally speaking, anisotropy is introduced through fourth order tensors affecting the flow directions, the linear kinematical hardening components, as well as the dynamic and static recoveries of the forementioned hardening variables. The ability of the model to describe all the mechanical properties of the material is shown. The application of the model to simulate mechanical tests (tension, creep, and relaxation) performed on true CWSR Zircaloy-4 cladding tubes with low tin content is also presented.
Effects of Hydride Precipitate Localization and Neutron Fluence on the Ductility of Irradiated Zircaloy-4
Authors: Garde AM , Smith GP , Pirek RC
Published: March 2009

The ductility of highly irradiated Zircaloy-4 material was evaluated by conducting tube burst, tube tensile, and ring tensile tests on fuel cladding and guide tubes irradiated in two PWRs. The specimen fluence ranged between 9 and 12.3 × 1021 n/cm2 (E > 1 MeV), and test temperatures ranged from 313 to 673 K. The average thickness of the waterside oxide layer on the specimens ranged from 12 to 114 μm. Specimens with an oxide thickness greater than about 100μm contained regions of spalling oxide and local areas of oxide significantly thicker than the specimen average. The corresponding average hydrogen contents ranged from 40 to 674 ppm for specimens without spalling oxide and estimated to be greater than 950 ppm with spalling. Non-uniform hydride distributions were observed in the specimens due to temperature gradients during operation.

The residual ductility for these high-fluence specimens is on the order of 1% uniform plastic strain for all the specimens except for two specimens with average concentration of hydrogen greater than 700 ppm and spalled oxide. The reduction in the material ductility due to radiation damage appears to be synergistically affected by localized hydride distributions and the orientation of hydride precipitates relative to the loading direction. The extent of ductility reduction due to hydride precipitates appears to be the most for the burst tests among the three tests investigated. The tensile specimens showed different fracture modes depending on deformation temperature, hydrogen concentration, local hydride volume fraction, and hydride orientation.

Neckdown and spiral fractures were observed. Examination of fracture surfaces indicated ductile failure in the metallic ligaments separating the hydride precipitates that appeared to have failed in a brittle fashion. The ductility data are analyzed by treating the material as a composite of relatively ductile metal phase separated by more brittle hydride platelets. Localization of hydride phase with a reduced presence of metallic ligaments in the composite results in reduction of ductility. A local hydride volume fraction greater than a critical value is needed to initiate and propagate fracture across the specimen cross section to thereby reduce the ductility below a set value. A model is proposed to suggest a possible ductility minima at intermediate fluences and the effect of hydride precipitates on ductility.
Fracture Toughness of Zircaloy Cladding Tubes
Authors: Grigoriev V , Josefsson B , Rosborg B
Published: March 2009

The fracture toughness of Zircaloy-2 cladding has been estimated by means of the recently developed pin-loading (PL) tension test. Axially notched ring specimens, cut directly from different cladding (annealed, cold-worked, hydrided, and irradiated), have been tested in a way similar to that used for compact tension specimens.

The results of the PL tension tests, performed at temperatures of 293 and 573 K, revealed for actual cladding all main phenomena observed earlier for Zircaloy materials. A threshold hydrogen content of 600 to 700 wtppm, above which only brittle fracture occurred at ambient temperature, was observed for unirradiated cladding. Existence of a continuous hydride network in the cladding facilitated brittle fracture. There was no obvious influence of the hydrogen content of about 900 wtppm on the fracture toughness at 573 K. The irradiation changed the fracture toughness in accordance with its known influence on the ductility and strength of the cladding. Intensive load serrations occurred for both irradiated and unirradiated cladding during plastic deformation of the notched ring specimens at 573 K.

A maximum-load fracture toughness of about Jmax ≈ 100 kN/m, obtained for irradiated cladding at 573 K, is comparable with fracture toughness of the cold-worked unirradiated cladding and reasonably agrees with published results for pressure tube materials.

The PL tension test was shown to be an effective method for evaluating the fracture toughness of actual cladding after hydriding or irradiation.
Link Between Results of Small- and Large-Scale Toughness Tests on Irradiated Zr-2.5Nb Pressure Tube Material
Authors: Davies PH , Shewfelt RSW
Published: March 2009

The link between the results of small- (curved compact) and large-scale (burst) toughness tests on irradiated Zr-2.5Nb pressure tube material was investigated using material from tubes of different toughness values. Comparison between the crack growth resistance (deformation J-R) curves from the small- and large-scale specimens reveals the material dependence of geometry effects and shows that the crack-tip constraint in the compact specimen is generally higher than that in the burst specimen. For higher toughness material, the crack-extension region over which there is good correspondence between the J-R curves from the small- and large-scale specimens is in agreement with current knowledge of validity requirements for J-controlled crack growth of bend-type specimens. Fractographic studies were conducted and the results shown to be consistent with the observed geometry effects, a larger proportion of highly constrained, flat fracture being produced with the small bend-type specimens than with the burst tests. The results are discussed using a volume-controlled fracture model for bend-type specimens in which it is assumed that the toughness is governed by the development of the plastic zone associated with an intermediate-constraint, transition region between the central, flat-fracture zone and surfaceshear or slant-fracture zone. Applying scaling factors from the volume-controlled fracture model, good agreement is obtained between scaled values of the maximum pressure/load toughness from the small- and large-scale tests over a range of normalized plastic zone size of 0.4 to 1.
Influence of Neutron Irradiation on Dislocation Structure and Phase Composition of Zr-Base Alloys
Authors: Shishov VN , Nikulina AV , Markelov VA , Peregud MM , Kozlov AV , Averin SA , Kolbenkov SA , Novoselov AE
Published: March 2009

Studied were evolution of dislocation structure, phase, and element composition of binary alloys Zr-1Nb and Zr-2.5Nb and multicomponent alloys Zr-1Nb-1.2Sn-0.4Fe and Zr-1.2Sn-0.4Fe under neutron irradiation. The investigations were carried out using cladding and pressure tubes before and after irradiation to a fluence of ∼1026 n/m2 (E ≥ 0.1 MeV) in experimental and commercial reactors at 300 to 350°C using TEM, EDX, and XRD. In most cases, irradiation-induced defects are in the form of dislocation loops with Burgers vector 1/3 ⟨1120⟩. The density of dislocations with a ⟨c⟩ component is less than 2 × 1014 m-2. A higher fluence or the presence of strain results in the ordering of the dislocation structure of ⟨c⟩ component and ⟨a⟩-type dislocation loops. Before irradiation, the multicomponent alloys contain fine precipitates of Zr-Nb-Fe composition, and the matrix is depleted in Fe. Under irradiation, recrystallization proceeds intensively (as distinct from Zr-Nb alloys), changes take place in size, distribution, and composition of precipitates (with a relative decrease of Fe content compared to Nb), and the Fecontent of α-Zr matrix is increased. None of the materials studied showed any significant evidence of secondary phase particle amorphization. The density of dislocations with ⟨a⟩ and ⟨c⟩ components and irradiation-induced defects, their mean size, the extent of ordering, and the planes of their occurrence were determined. A comparison was made between irradiation-induced evolutions of microstructures of the different alloys.
Effects of Thermomechanical Processing on In-Reactor Corrosion and Post-Irradiation Mechanical Properties of Zircaloy-2
Authors: Huang PY , Mahmood ST , Adamson RB
Published: March 2009

Interest continues to be high in the effects of irradiation on the microstructure and microchemistry of Zircaloy and on the resultant effects on performance of Zircaloy components in-reactor. In this study, we have investigated the behavior of material prepared to have excellent resistance to nodular corrosion in a BWR. Coupon specimens of Zircaloy-2 were prepared having a range of critical microstructural parameters (precipitate size and distribution) by varying the thermomechanical processing history (quench rate and cumulative annealing parameter). Irradiation was conducted in a BWR at 561 K to fluences between 1.3 and 8.5 × 1025 n/m2 (E > 1 MeV).

As expected, nodular corrosion was absent in these materials, and, at low fluence, corrosion and hydriding of all materials was very low. At the highest fluences, patch-type uniform corrosion developed, with oxide thickness increasing with decreasing initial precipitate size. Detailed STEM investigation revealed that precipitates dissolved and decreased in size continuously until at the highest fluence no precipitates remained for material having the smallest initial precipitate size. Post-irradiation mechanical property tests showed strength somewhat higher than expected.

The results indicate that corrosion resistance and mechanical properties change as the microstructure evolves during irradiation. However, at the highest fluence tested, strength, ductility, and corrosion resistance ensure excellent performance of BWR components.
Development of New Zirconium Alloys for a BWR
Authors: Etoh Y , Shimada S , Yasuda T , Ikeda T , Adamson RB , Chen J-SF , Ishii Y , Takei K
Published: March 2009

Specimens for irradiation testing in a commercial BWR were prepared from 24 kinds of Zr alloys. The corrosion performance of these specimens was investigated after irradiation for up to four cycles. Two cycles of irradiation were not always sufficient to identify the lowest corrosion alloys. Marked acceleration of corrosion occurred for many alloys between one and four cycles. The onset of mildly accelerated oxidation was observed for standard Zircaloy-2 at four cycles of irradiation. On the other hand, for Zircaloy-like alloys, increasing Fe and Ni contents or decreasing the Sn content promoted a saturation oxidation between two and four cycles of irradiation. The effects of alloying elements on corrosion behavior were evaluated by both in-pile and out-of-pile corrosion tests. The alloying elements Fe, Cr, and Ni, which have smaller valences than Zr, improved the in-pile corrosion resistance of Zr alloys, while the alloying elements Nb, Mo, and Te, which have larger valences than Zr, were responsible for increased weight gain during the irradiation test in the BWR.
Testing Facilities for Multiaxial Loading of Tubular Specimens
Authors: Ellyin F , Wolodko JD
Published: March 2009

The development of a new multiaxial testing machine is presented. The testing machine is capable of applying axial load, differential pressure, and torsion to a tubular specimen under independent servohydraulic control. Relative merits of various loading configurations are described. Stress/strain controlled, monotonic/cyclic, and in-phase/out-of-phase (nonproportional) tests under ambient temperature conditions can be performed with this system. The associated computer control hardware and software allows for a number of complex user-defined loading and acquisition schemes. Monotonic and cyclic tests on tubular specimens made of glassfiber-reinforced epoxy with fiber orientations of ±45° and 0°, are presented. Details of the experimental apparatus and representative test results are discussed in this paper.
Experimental Determination of Yield and Flow Surfaces Under Axial-Torsional Loading
Authors: Lissenden CJ , Lerch BA , Ellis JR , Robinson DN
Published: March 2009

The concept of a yield surface is central to the mathematical formulation of classical plasticity theories. However, at elevated temperatures, material response can be highly rate-dependent, which is beyond the realm of classical plasticity. Viscoplastic theories have been developed for just these conditions. In viscoplastic theories, the flow law is given in terms of inelastic strain rate rather than the inelastic strain increment used in rate-independent plasticity and in unified viscoplastic theories no yield criterion is used. Thus, surfaces of constant inelastic strain rate or flow surfaces, which describe hardening behavior, are considered to be more useful than yield surfaces.

Experimental procedures to determine yield surfaces in axial-torsional stress space are well established. The use of small-offset definitions of yield minimizes the change of material state and allows multiple loadings to be applied to a single specimen. Flow surfaces are determined using the same procedures with the exception that inelastic strain rates are used rather than total inelastic strains. The key to these experiments is precise, decoupled measurement of axial and torsional strain. With this requirement in mind, the performance of a high-temperature multiaxial extensometer was evaluated through comparison with strain gage results at room temperature. Yield surfaces (both initial and subsequent) were found to be nearly identical when determined for Type 316 stainless steel using the extensometer and strain gages. The extensometer was then used successfully to determine flow surfaces for Type 316 stainless steel at 650°C.
Notch-Tip Stresses and Strains Under Nonproportional Loading
Authors: Singh MNK , Glinka G , Dubey RN
Published: March 2009

An analytical method for estimating notch-root elastic-plastic strains and stresses in isotropic bodies subjected to multiaxial nonproportional loading sequences is presented. Two models are proposed based on the analysis of strain energy density in the notch-tip region. Each model consists of a set of seven relationships that can be solved easily for elastic-plastic strain and stress increments knowing the fictitious notch-tip elastic stress history and the material stress-strain curve. Results of the validation show that the proposed methods compare well with finite element data and that each solution set forms the limits of a band within which actual notch-tip strains can be found.
Fretting Fatigue Strength of Specimens Subjected to Combined Axial and Transversal Loading
Authors: Switek W
Published: March 2009

The theoretical and experimental considerations presented in this paper refer to flat specimens, with a special bridge clamped to their surfaces, subjected to axial cyclic loading, transversal clamping load, and a friction force appearing on contacting surfaces. The theoretical analysis shows that the highest tensile stress exists at the edge of the bridge along with the maximum level of an elastic strain energy.

The fatigue experiments and the metallographic examinations of the specimens proved the theoretical assumption that the fatigue crack propagates in such a direction, that the total strain energy decrease, caused by the crack growth, is maximum. The main crack, which is responsible for the final fracture of the specimen, originates from the edge of the bridge, propagates initially at a 45° angle to the surface and, while growing, gradually becomes perpendicular to the surface.

The paper also presents a theoretical approach to the conditions of development of short fatigue cracks remaining in the area of residual stresses appearing as the result of clamping pressure. The linear theory of fracture mechanics has been applied to calculate the range of the stress intensity factor in the specimen and the fretting fatigue limit of the junction. The result of the experiments conducted with carbon steel are generally in good agreement with the calculations.
Life Prediction: A Case for Multidisciplinary Research
Authors: Wei RP
Published: March 2009

Concerns with aging infrastructure worldwide and with the life-cycle costs and management of engineered systems have placed increased emphasis on the development of methods for life prediction. To be effective as “true predictors” of future performance (i.e., to provide accurate estimates beyond the range employed in the development of supporting data), such methods must be built upon mechanistic models that capture the functional dependence on all of the key external and internal variables. The development of these methods argues strongly for multidisciplinary research that integrates mechanistic understanding with probability analysis. In this paper, a mechanistically based probability approach to life prediction (versus the more traditional statistically based parametric approach) and the processes for model development are outlined to provide a framework for discussion. The use of a coordinated, multidisciplinary approach to develop mechanistic understanding and to model material response is illustrated through examples on crack growth in a high-strength steel. The need for multidisciplinary research that broadens the perspective from testing to testing and materials is discussed.
A Practical Methodology for Elastic-Plastic Fatigue Crack Growth
Authors: McClung RC , Chell GG , Russell DA , Orient GE
Published: March 2009

A practical methodology is being developed to characterize elastic-plastic fatigue crack growth (EPFCG) behavior. The methodology will be implemented in engineering software for crack growth analysis and life prediction of advanced reusable aerospace propulsion systems. The correlating parameter upon which the methodology is based is the range of the J-integral, ΔJ. Existing J solutions are summarized, and robust methods for developing new J solutions under various loading configurations are introduced and validated. Some practical crack growth algorithms required to translate a J calculation into a quantitative prediction of EPFCG life are highlighted. Crack closure plays a significant role in the engineering characterization of EPFCG rates, and simple algorithms to estimate closure stresses are described. Other algorithms address the tearing-fatigue interaction near final instability and the estimation of required material properties. Early results from experimental verification tests are reported.
The Analysis of Underclad Cracks in Large-Scale Tests Using the Local Approach to Cleavage Fracture
Authors: Moinereau D , Rousselier G
Published: March 2009

Electricité de France has conducted a large program including experiments on large-size cladded specimens and their interpretations to evaluate different methods of fracture analysis used in French safety studies regarding the risk of fast fracture in reactor pressure vessels. Four specimens made of ferritic steel A508 C13 with stainless steel cladding, containing small artificial underclad defects, have been tested in four-point bending. Experiments have been conducted at very low temperature, and crack instability by cleavage fracture without crack arrest was obtained in base metal.

The tests have been interpreted using the local approach to cleavage fracture (Weibull model) by two-dimensional finite element computations. The Weibull model parameters have been determined using axisymmetrical notched specimens. The probability of failure has been evaluated in each test using finite element analyses with varying mesh sizes. The results show an important effect of the size of the elements at the crack tip on the calculated probability of failure. Those effects are confirmed using the model of a CT specimen. Also discussed is the shallow flaw effect with the Weibull model.
Boundary Element/Dislocation Density Methodology for Analysis of Cracks in Anisotropic Solids
Authors: Heim D , Xiao L , Mear ME
Published: March 2009

A boundary element method is presented for the stress analysis of cracks in two-dimensional, linearly elastic anisotropic solids. The technique is an extension of that by Chang and Mear [5] for isotropic solids and involves the use of a special “regularization” for certain integrals associated with the crack line. The resulting integral equations consist of the conventional ordinary boundary terms as well as two additional terms that correspond to a distribution of concentrated forces and a distribution of dislocations along the crack line. In the numerical implementation of the formulation, the ordinary boundary integrals are treated with standard boundary element techniques, while a special numerical procedure is used to treat the crack line integrals. The resulting procedure is applied to several example problems to demonstrate the accuracy and efficiency of the method.
Standardization Activities for Testing of Fire Resistant Fluids
Authors: Reichel J
Published: March 2009

The use of mineral oil as a hydraulic fluid in industrial plants, installations and equipment may create a problem, if exposure of the fluid to sources of iginition are possible. Many industrial processes require the use of hydraulic fluids that afford better fire safety than achievable with mineral oils. In proposals to the governments of the member states of the European Union (EU) fire-resistant fluids intended for use in underground mines must conform the “Requirements and Tests Applicable to Fire Resistant Hydraulic Fluids used for Power Transmission” (7th Luxembourg Report, adopted by the Safety and Health Commission, March 3rd 1994). The immediate stimulus for this work, which spans a period of 35 years, was the disastrous fire which occurred in 1956 at the Bois du Cazier mine at Marcinelle in Belgium, resulting in 267 fatalities.

The general classifications of hydraulic fluids are given in ISO 6743/4 (Lubricants, Industrial Oils and Related Products — Class L — Classification, Part 4: Family H, Hydraulic Systems), guidelines for use have been developed in ISO 7745 (Hydraulic Fluid Power — Fire Resistant (FR) Fluid — Guidlines for Use), but no formal standards are available to interrelate fluid classification with the relative fire risk. Two fundamental parameters are considered when selecting tests for standardisation: 1. spray ignition tests and 2. flame propagation or wick tests. This paper discusses the use of testing methods to characterize the performance of conventional fire resistant hydraulic fluids.
Fire Resistant Hydraulic Fluids and Fire Resistance Test Methods Used by the Air Force
Authors: Snyder CE , Gschwender LJ
Published: March 2009

The concern about the fire resistance of hydraulic fluids by the Air Force and the rest of the Department of Defense (DoD) dates back to the introduction of the mineral oil based hydraulic fluid, MIL-H-5606 [1], into aircraft hydraulic systems. This concern has led to the development of two fire resistant hydraulic fluids that can be directly substituted into aircraft hydraulic systems that were designed to use MIL-H-5606, i.e., MIL-H-83282 [2] and MIL-H-87257 [3], and a nonflammable hydraulic fluid, MTL-H-53119 [4], that can be used only in hydraulic systems that were designed for that fluid or in subsystems originally designed for MIL-H-5606, MIL-H-83282 or MIL-H-87257, for which re-design of the components and retrofit of the system with compatible seals, if required, would be cost effective. Another fire resistant hydraulic fluid was developed for use in commercial aircraft hydraulic systems, a phosphate ester based hydraulic fluid described by Society of Automotive Engineers document AS1241, Fire Resistant Phosphate Ester Hydraulic Fluid for Aircraft The fire resistant properties of these fire resistant and nonflammable hydraulic fluids are discussed and the flammability test methods are presented.