bluuebunny/crossref_metadata_2025 huggingface dataset:
Variability of Irradiation Growth in Zr-2.5Nb Pressure Tubes
Authors: Fleck RG , Elder JE , Causey AR , Holt RA
Published: March 2009

Pressure tubes in CANDU reactors are manufactured by extrusion and cold work from the Zr-2.5Nb alloy. Historically, the details of the pre-extrusion production of the tubes have changed since the first tubes were produced (1969) for Ontario Hydro's Pickering A station. The pressure tubes exhibit variations in elongation rate during service that may partially result from these changes. Irradiation growth is a component of the elongation. This paper describes the longitudinal irradiation growth of specimens prepared from pressure tubes with a range of iron contents and in which billets were extruded either in the as-forged condition or after β-quenching.

The irradiations are performed in the Osiris reactor at Saclay, France, in two inserts with nominal operating temperatures of 280°C (Trillium 2) and 310°C (Trillium 3). Results are reported for fast fluences up to 4.3 × 1025 n/m2, E > 1 MeV. Throughout the irradiation, the temperature of each tier of six specimens is recorded and this shows that the actual range of temperatures is 262 to 309°C. In agreement with previous studies, the temperature dependence of growth is negative, that is, an increase in temperature decreases the growth rate.

When this experimental variable is taken into account, there is still considerable variation among specimens from different pressure tubes. There is no effect of β-quenching. However, an increase in iron in the range 367 to 1060 ppm (by weight used exclusively in this paper) reduces the growth rate by about 2 × 10-29 m2/n, E > 1 MeV at both 280 and 310°C. If this difference extends to high fluences, it accounts for about half of the variability in elongation rates observed in pressure tubes in-service.
Change of Mechanical Properties by Irradiation and Evaluation of the Heat-Treated Zr-2.5Nb Pressure Tube
Authors: Koike MH , Akiyama T , Nagamatsu K , Shibahara I
Published: March 2009

The prototype advanced thermal reactor, Fugen (165MWe), is a heavy-water-moderated, boiling-light-water-cooled, pressure tube type reactor. A Zr-2.5 Nb alloy, in the heat-treated condition to improve its high-temperature strength, is used for the pressure tubes in the Fugen. Pressure tube surveillance specimens were assembled in the inside of the special fuel assemblies from the initial stage of the operation and were exposed to irradiation. The post-irradiation examinations of the first and second surveillance specimens were performed. The tensile strength increased by 30% when fast neutron fluence was >2 × 1025 n/m2. The decreasing rate of the fracture toughness was large over the initial period of the irradiation and became smaller when fast neutron fluence was >2 × 1025 n/m2. The corrosion rate was measured as -1 μm/year and the hydrogen pickup rate was measured as 1 ppm/year. Based on the results, a predictive capability for each respective property for 30 years was established, which demonstrated the integrity of the pressure tube for 30 years.
Corrosion Behavior of Zircaloy-4 Sheets Produced Under Various Hot-Rolling and Annealing Conditions
Authors: Anada H , Nomoto K , Shida Y
Published: March 2009

The uniform corrosion resistance of Zircaloy-4 sheets produced under various hot-rolling and annealing conditions was investigated. The uniform corrosion resistance in static steam at 673 K improved with an increasing cumulative annealing parameter (ΣA). However, to clarify the physical meaning of the annealing parameter and the different combinations of various heating stages, the effects of individual manufacturing conditions that influence the corrosion behavior and ripening behavior of the precipitates were investigated. As a result, the annealing temperature after hot-rolling influenced the uniform corrosion more significantly than the intermediate annealing and the final annealing temperatures. Size distributions of the intermetallic compound precipitates that were observed by means of a scanning electron microscope (SEM) with an image analyzer were examined for a correlation with weight gain. The percentage of small precipitates below 100 nm in size was important in determining corrosion resistance and had a good correlation with the annealing parameter; that is, if the percentage was lower than 30%, the corrosion resistance was satisfactory. Also, the frequency of precipitates under 100 nm in size decreased sharply with increasing annealing temperature after hot-rolling. The intermetallic compounds that were incorporated into the ZrOst oxide scale and the scale/metal interface were observed by a transmission electron microscope (TEM). The incorporated intermetallic precipitates were observed to have changed their composition; that is, the iron content decreased and the iron/chromium (Fe/Cr) ratio for the zirconium-chromiumiron intermetallic precipitate was approximately 1 compared to approximately 2 in the Zircaloy matrix. During oxidation, iron from the intermetallic compound precipitates scattered more into the oxide than chromium. These results suggest that the iron that diffused into the oxide from the incorporated intermetallic precipitates may play an important role in the corrosion process. It was observed that a stress-relieved microstructure of the Zircaloy-4 just beneath the growing front of the oxide was transformed into a recrystallized microstructure. This was especially clear in a high ΣA material compared to a low ΣA material. This seems to be one of the reasons that a higher ΣA Zircaloy-4 is more corrosion resistant under uniform corrosion conditions.
Optimization of PWR Behavior of Stress-Relieved Zircaloy-4 Cladding Tubes by Improving the Manufacturing and Inspection Process
Authors: Mardon J-P , Charquet D , Senevat J
Published: March 2009

With the aim of optimizing the basic properties of stress-relieved Zircaloy-4 cladding tubes, particularly those that make it possible to push back the initial technological limits that may be encountered, and of reducing the scatter of those properties and enhancing tube quality, the role of the main parameters involved in manufacturing the ingot, Trex, and cladding tube has been evaluated on an industrial scale. A series of large-sized tube lots were produced under controlled manufacturing conditions, then characterized by out-of-pile test results (short-and long-term corrosion, stress corrosion cracking (SCC), creep, mechanical, and structural properties) on finished tubes. For the investigated parameters (chemical composition, number of melt, quench rate, accumulated annealing parameter, the ΣA factor, surface condition (outside and inside diameters), and finished tube quality), this role is indeed important but complex due to the highly interactive nature of the variables investigated.

Adjustment of the chemical composition within ASTM limits enables generalized corrosion resistance to be enhanced and irradiation growth to be minimized. A significant decrease of the observed scatter in corrosion and mechanical properties is obtained by optimization of the ΣA range, the quenching rate, and the final heat treatment. The optimum seems to be reached for a final treatment at the highest possible temperature compatible with the stress-relieved state, corresponding to an average precipitate size and ΣA. Moreover, by adding anneals upstream in the process, a further increase in this ΣA no longer seems to have a significant effect on generalized corrosion.

Finally, extensive efforts have been employed in the pilgering, surface preparation (outside diameter polishing, flush-pickling), and examination method (UT, EC) leading to a sizable improvement in SCC resistance and to a reduction in scatter for finished tubes.

The result of these optimizations has been implemented in the current AFA-2G, that shows that under irradiation a 30% corrosion gain is reached after three cycles, without degrading creep strength or growth. The intrinsic effect of tin on generalized corrosion resistance under irradiation was also confirmed on this occasion.
Experimental and Theoretical Studies of Parameters that Influence Corrosion of Zircaloy-4
Authors: Billot P , Robin J-C , Giordano A , Peybernès J , Thomazet J , Amanrich H
Published: March 2009

Waterside corrosion of Zircaloy cladding in pressurized water reactors (PWRs) is largely dependent upon the operating parameters and microstructure of the zirconium alloys. The impact of these parameters on the corrosion kinetics of Zircaloys is investigated on the basis of empirical data and experiences that can be interpreted using existing corrosion models.

The influence of thermo-hydraulic data, heat flux, local boiling conditions, and of the growing oxide films has been studied from corrosion tests performed in static autoclaves or in out-of-pile loops. These parametric investigations are described as well as the models that were developed.

The impact of microstructure is studied from the comparison of the corrosion behavior of different Zircaloy-4 specimens corroded in out-of-pile tests. In particular, a poor corrosion resistance of an experimental Zircaloy-4 material is analyzed as a function of the microstructure close to the metal/oxide interface.

The impact of the alloy composition and primary coolant chemistry on the corrosion kinetics of Zircaloy-4 is modeled empirically or uses a mechanistic approach that proposes a series of chemical equations with a mathematical representation of the kinetics.

These proposed models are then used to investigate the corrosion behavior of Zircaloy-4 cladding in 17 by 17 plants for rods irradiated at high burnups. Higher PWR operating cycles, core average coolant temperature, power, and elevated primary coolant lithium concentrations (3.5 to 4 ppm) are then simulated and discussed in terms of Zircaloy corrosion resistance considerations.
Prediction of Creep Anisotropy in Zircaloy Cladding
Authors: Perkins RA , Shann S-H
Published: March 2009

Due to the hexagonal crystal structure of zirconium and the radial orientation of the basal poles in Zircaloy cladding, the deformation of light water reactor Zircaloy fuel cladding is anisotropic. Plastic deformation of this cladding can be defined by the R and P factors that are the circumferential/radial and axial/radial contractile strain ratios under uniaxial deformation along the axial and circumferential direction, respectively. The in-reactor deformation performance of the cladding can be modeled with good accuracy if the R and P values of the irradiation-induced creep are known.

In a boiling water reactor (BWR) fuel assembly, most fuel rods have a hoop stress to axial stress ratio of about 2:1. The assembly also contains several fuel rods (tie rods) that connect the upper and lower tie plates. The tie rods have an additional stress component in the axial direction. BWR assemblies can, furthermore, contain water rods that are free of stress, and therefore, provide a measure of stress-free irradiation growth. Post-irradiation deformation measurements of these three types of rods are used to derive the R and P factors for BWR cladding during irradiation.

Laboratory tensile and creep tests at several temperatures have been performed on five types of cladding to determine if a short-term test could be used to obtain R values representative of the in-reactor values. For standard Zircaloy-2 cladding that was examined in-reactor, a good correlation with the in-reactor R value was obtained from both tensile and creep tests performed at 382°C. For another type of Zircaloy-2 cladding (late beta-quenched (LBQ) cladding), inreactor deformation performance correlates better with the tensile test results than the creep test results. The other three types of cladding (Zircaloy-4) with differing textures and processing histories have exhibited significant differences in the R values in the laboratory tests.
Microstructure and Properties of Corrosion-Resistant Zirconium-Tin-lron-Chromium-Nickel Alloys
Authors: Bradley ER , Nyström A-L
Published: March 2009

Long-term autoclave tests in steam at 673 K and mechanical property (tensile and creep) tests have been conducted to evaluate the effects of chromium (0 to 0.3%) and nickel (0 to 0.08%) additions on the corrosion and mechanical properties of dilute zirconium-tin-iron alloys. The base alloys contain 0.4% iron and either 0.5% or 1.0% tin.

Multiple regression analysis showed tin concentration to have a statistically significant effect on corrosion, hydrogen pickup, creep, and tensile strength. The corrosion resistance of the alloys increased significantly when the tin concentration decreased from 1.0 to 0.5%. An additional improvement in corrosion resistance was observed with increasing chromium content. Nickel additions had no apparent effect on corrosion for the alloy compositions examined. Lower hydrogen pickup fractions were measured for alloys containing 0.5% tin compared to alloys containing 1.0% tin. No significant effects of chromium or nickel additions to hydrogen pickup were observed.

Creep rate decreased with increasing tin concentration and to a lesser extent with increasing chromium content. Nickel additions produced a large increase in creep rate for some alloys but not others. This suggests a possible interaction between nickel and the other alloy additions in determining creep strength.

Intermetallic particle type and size distribution varied with alloy composition. Chromium additions tended to decrease the particle size distribution of Zr(Fe,Cr)2 intermetallic particles. Conversely, nickel additions produced large particles of the Zr2(Fe,Ni) type intermetallic. Changes in the intermetallic particle distributions and matrix compositions are discussed with regard to the observed changes in corrosion and mechanical properties of the alloys.
Effect of Irradiation on the Microstructure of Zircaloy-4
Authors: Gilbon D , Simonot C
Published: March 2009

This paper deals with the irradiation growth and the radiation-induced changes in the microstructure of Zircaloy-type materials. The experimental irradiations that were conducted at 400°C in Siloé (metallurgical test reactor) and Phénix (fast breeder reactor) show that the growth of both alpha-recrystallized and beta-quenched Zy-4FORT (high tin and oxygen contents) is accelerated after a dose of about 4 dpa (displacements per atom). In correlation with this acceleration, a high density of basal-plane c-component dislocations is revealed by transmission electron microscope (TEM) examinations. At this temperature, the structure of precipitates remains fully crystalline, but radiation-induced dissolution occurs and allows the formation of Zr5Sn3 particles evenly dispersed throughout the matrix. To allow comparisons with the microstructural evolutions produced in pressurized water reactor (PWR) conditions, TEM examinations were also performed on standard Zircaloy-4 irradiated as recrystallized guide tube and stress-relieved cladding. In recrystallized Zircaloy-4 irradiated to 10 × 1021 n/cm2 (T ͌ 320°C), a high density of basal-plane c-component dislocations is also observed, the Zr(Fe,Cr)2 Laves phases undergo a partial crystalline-to-amorphous transformation, and their outer rim is severely depleted in iron. In stress-relieved Zircaloy-4 irradiated to the same neutron fluence. irradiation does not produce any significant recovery of the initial dislocation network. Although the Laves phases undergo an amorphous transformation only in the lower part (T ͌ 335°C), a marked dissolution is observed all along the cladding (335 to 380°C).
On the Initial Corrosion Mechanism of Zirconium Alloy: Interaction of Oxygen and Water with Zircaloy at Room Temperature and 450°C Evaluated by X-Ray Absorption Spectroscopy and Photoelectron Spectroscopy
Authors: Döbler U , Knop A , Ruhmann H , Beie H-J
Published: March 2009

The initial stages of zirconium oxide formation on Zircaloy after water (H2O) and oxygen (O2) exposures have been investigated in situ using photoelectron spectroscopy and X-ray-absorption spectroscopy. The reactivity of the zirconium alloy with O2 at room temperature is about 1000 times higher than for H2O. Up to 100 L (1 L = 1 Langmuir unit = 1 ∙ 10-6 mbar ∙ s) H2O exposure, the reactivity of the zirconium alloy at 450°C is comparable to the room temperature reaction. At higher H2O exposure, a sharp increase in the reaction rate for the high-temperature oxidation is observed. From the energy position of the Zr 3d photo emission line and their oxygen-induced chemical shifts, one can directly follow the formation of the oxide films. Two different substoichiometric oxides were found during reaction with water. Suboxide (1) is located at the zirconium/zirconium-oxide interface. Subsequently, a Suboxide (2) is concluded from the chemical shift of the zirconium photoelectrons. After an oxide thickness of 2 nm, the stoichiometric ZrO2 phase is not yet developed.
How the Tetragonal Zirconia is Stabilized in the Oxide Scale that is Formed on a Zirconium Alloy Corroded at 400°C in Steam
Authors: Godlewski J
Published: March 2009

Zircaloy-4, in three different metallurgical forms (stress relieved, recrystallized, and β-quenched), was oxidized at 400°C, in steam, up to 95 days. For each sample, the fraction of tetragonal zirconia was measured by X-ray diffraction and Raman spectroscopy. These two techniques show the presence of several zones containing tetragonal zirconia: a zone rich in the oxide near the metal-oxide interface and an other zones with lower concentrations in the rest of the pre-transition layers. For the post-transition samples, the external sublayer contains only a small amount of tetragonal zirconia.

Measurements of residual stresses by X-ray diffraction in the metal underlying the oxide show that the metal is under tensile stress state and that the stress values vary with oxidation duration. The level of the stress depends on the metallurgical form of the initial metal. The low penetration of X-rays in the material also made it possible to show the presence of a very high stress gradient near the metal-oxide interface that can explain the high proportion of tetragonal zirconia near the interface.

The study of the incorporation of intermetallic precipitates in the oxide and their chemical changes was carried out by electron microprobe analysis on taper cross sections of the oxide. This technique makes it possible to perform a large number of point analyses that yield satisfactory statistics for the variation in the iron/chromium (Fe/Cr) atom ratio of the precipitates in the oxide.

The intermetallic precipitates are incorporated into the oxide layer and then undergo a chemical change starting at a particular distance from the metal/oxide interface. The characteristic values of the Fe/Cr ratio before oxidation (1.6 for stress relieved and recrystallized conditions and 0.8 for β-quenched samples) are progressively spread out during oxidation. This change could correspond to an oxidation of intermetallic precipitates with segregations of iron at the precipitate-oxide interface, as shown in the literature.

The oxidation of the precipitates is accompanied by a volume change that should lead to the formation of a stress field around the precipitates and could stabilize the neighboring tetragonal phase. When the precipitates are completely oxidized, the stress field disappears and there is a transformation of the tetragonal phase to a monoclinic form, leading to the kinetic transition. Stress relaxation is shown by a decrease of the tensile stresses in the metal underlying the oxide that is undergoing kinetic transition.
Phenomenological Study of In-Reactor Corrosion of Zircaloy-4 in Pressurized Water Reactors
Authors: Kim YS , Rheem KS , Min DK
Published: March 2009

Uniform in-reactor corrosion has been examined on pressurized water reactor (PWR) Zircaloy-4 fuel claddings that were irradiated up to four cycles in the KORI Unit 1. The oxide layer that was formed on the Zircaloy-4 fuel claddings changes from a uniform black oxide into the nonuniform white granular oxides when the oxide layer reaches about 5 to 10 μm. With irradiation exposure, enough of the white granular oxides have nucleated above the black oxide layer to entirely cover the fuel cladding, resulting in a gray or white cladding surface. The change in the oxide layer growth pattern from the uniform black oxide layer into the nonuniform granular oxides resulted in the formation of macro-pores or cracks in the oxide layer, causing the corrosion rate to change into a linear rate from the cubic rate, especially at the beginning of fuel rod life. Consequently, the nucleation of white granular oxides is a phenomenological indicator of the transition of the in-reactor corrosion rate.

To explain the effect of hydride precipitates on the in-reactor corrosion, the corrosion behavior for a defective fuel rod with a through-hole and an intact fuel rod adjacent to it (both were irradiated for two cycles in the KORI Unit 1) has been investigated. Even though both of them were found to have almost identical operating power histories, their corrosion behavior was quite different: the maximum oxide layer thickness for the intact fuel rod was less than 10 μm, while the defective fuel rod had an abnormally thick oxide of 50 μm, especially at an elevation where a large extent of hydrides (corresponding to 1295 to 1520 ppm hydrogen) were precipitated at the cladding outer surface. Therefore, the hydrides that were locally precipitated on the cladding outer surface initiated the in-reactor corrosion enhancement to a degree that was dependent upon the extent of the hydrides. Furthermore, the corrosion enhancement by hydrides is likely to effectively occur late in the fuel life time or after more than three or four cycles of irradiation, thus leading to the enhanced post-transition corrosion rate.
Effects of Pressurized Water Reactor (PWR) Coolant Chemistry on Zircaloy Corrosion Behavior
Authors: Karlsen T , Vitanza C
Published: March 2009

A number of the test programs currently in progress at the Halden Project are aimed at evaluating Zircaloy cladding performance in terms of corrosion behavior, particularly at high burnup.

A pressurized water reactor (PWR) facility has been used to determine the effects of high (4 to 4.5 ppm) lithium on the corrosion behavior of Zircaloy-4 cladding material exposed to nucleate boiling (1% void) and to one-phase cooling conditions. The test employed four fuel rod segments, base-irradiated to an average burnup of 28.5 MWd/kg UO2 in a commercial power plant, and with average initial oxide layers of either 10, 20, or 40 μm, respectively. Four sets of oxide layer thickness measurements were performed on the four rods during the course of the investigation. Pre-test eddy current measurements were performed on the as-received segments and two interim sets of measurements were made after 80 and 245 full power days of irradiation. Final oxide measurements were made after 425 full power days, when maximum rod burnup was 45 MWd/kg UO2.

Average oxide layer increases of 30 and 55 μm were observed for the rods exposed to one-phase cooling and nucleate boiling conditions, respectively. Although maximum oxide thickness exceeded 95 μm, no evidence of spalling was apparent. The measured oxide layer thicknesses compared favorably with predicted values based on model calculations derived from power plant data, with little evidence of enhanced corrosion rates in the presence of increased lithium concentrations.
Terrorism and Sabotage in Civil Aviation: The European View
Authors: Loos J
Published: March 2009

This paper will review the actual existing situation of terrorism committed against civil aviation. The effectiveness of current countermeasures will be analyzed, and new, possibly, less expensive ways to overcome the threat situation in civil air transportation will be demonstrated.
Integrated Screening Systems in the 1990s
Authors: Guthrie SC
Published: March 2009

More integrated detection systems using various combinations of imaging, explosive detection, weapons detection, and access control technologies will be employed in security screening in the 1990s. These systems use more than one technology to perform specific screening functions to increase the probability of detection and improve discrimination between target items and innocent items. This paper presents some of the existing and possible configurations of these integrated systems and introduces some of the issues and problems associated with their use.
Designing Modern Walk-Through Metal Detectors
Authors: Jarvi A , Leinonen E , Thompson M , Valkonen K
Published: March 2009

Metor walk-through metal detectors, produced by Outokumpu Electronics, have been on the market since the security application first started more than 20 years ago. But because of increased terrorist activity, rapid handgun development, and increased electromagnetic “pollution,” the performance requirements of metal detectors today are much more complex than 20 years ago, requiring solutions that are extremely research intensive.
Operating Airport Weapons Detectors in the 1990s
Authors: Jaquet JR
Published: March 2009

More stringent regulation on walk-through gun detectors for airports are imminent. The expected increase in alarms from innocent objects, their underlying causes, and typical examples are examined from an operator's viewpoint. The changes in passenger habits, security stations, and improved detectors that can minimize the increase in alarms are discussed from a historical perspective.
Perimeter Radiation Monitors for the Control and Physical Security of Special Nuclear Materials
Authors: Fehlau PE
Published: March 2009

Perimeter radiation monitors are gamma-ray and neutron measurement systems that can provide timely notice of theft or diversion of special nuclear material (SNM). The monitors may be hand-held instruments operated by security inspectors or automatic pedestrian or vehicle monitors located in exit pathways. A monitor's performance depends on its design, the characteristics of SNM and the operating environment, and proper monitor calibration and maintenance. Goals of ASTM Subcommittee C26.12 are to describe monitoring technology, how to apply it, and how to test its performance.
Portal Metal Detectors at the U.S. Department of Energy Hanford Site
Authors: Swank RG , Riedeman GW
Published: March 2009

The U.S. Department of Energy's Hanford Site has devoted considerable attention to improving the operation of and confidence in the commercially available metal detectors installed at the site. A set of testing and calibration specifications was prepared and applied that yielded appreciable improvements.

These specifications were based on a set of tests developed to measure portal zone sensitivity and to derive the probability of detection and nuisance alarm statistics. A pragmatic approach to test article selection was also developed. This paper desribes these specifications, their underlying philosophy and methodology, and the results of their application.
The TNA™ Experience
Authors: Bar-Nir IM , Cole RL , Bozorgmanesh H
Published: March 2009

Thermal neutron analysis (TNA™) explosive detection systems (EDS) have been in operation in John F. Kennedy International Airport in New York (from September 1989) and in Miami International Airport (from January 1990). Based on the experience gained from these real-life examples, it is clear that TNA technology is suitable for full-scale deployment in airports.
A Review of DOD Wear and Friction Tests for Rubber Products
Authors: Wood FW , Taylor JW
Published: March 2009

Some Department of Defense (DOD) specifications for rubber products contain requirements for wear testing. The wear testing aspects of two of these specifications and a friction test included in one of them will be reviewed. In addition, at least one ASTM standard for rubber wear testing has DOD acceptance. It and another ASTM standard that is closely related will be reviewed.
The Role of System Dynamics on the Behavior of Elastomeric Friction
Authors: De Togni RS , Eiss NS , Rorrer RAL
Published: March 2009

Friction induced vibration of an epoxy coated shaft rotating in an elastomer bushing is investigated. Three factional regimes were observed. System stiffness and load were varied to observe changes in the critical velocities bounding each regime. The load, velocity, and support stiffness interact to influence the vibration amplitude, the vibration frequency, and the frequency content of the friction torque.
Measurement of Frictional Stick-Slip Transitions for Various Elastomeric Materials Sliding against Hard Counterfaces
Authors: Rorrer RAL , Eiss NS , De Togni RS
Published: March 2009

The focus of this research was to determine the conditions under which friction induced vibration occurred in elastomeric sliding. Various elastomers were tested against chromium oxide and glass in an elastomeric hemisphere-on-flat configuration. Four regimes of oscillatory sliding were identified: 1. Steady state sliding were the sliding friction is constant; 2. A low frequency self-excited oscillation due to the natural frequency of the elastomer; 3. A high frequency self-excited oscillation due to the natural frequency of the test apparatus independent of the elastomer natural frequency; 4. Stick-slip motion of the elastomer. It was found that the friction-velocity curves reached a plateau in the coefficient of friction in the same decade of velocity (v= 100- 101 mm/s). Previous theories and experimental results predict that the friction will go through a maximum at a velocity related to the glass transition temperatures or the loss modulus.
Friction and Wear Characterization of UHMWPE in Reciprocating Sliding Contact with Co-Cr, Ti-6Al-4V, and Zirconia Implant Bearing Surfaces
Authors: Poggie RA , Wert JJ , Mishra AK , Davidson JA
Published: March 2009

A tribometer, especially designed to simulate the high contact stresses, reciprocating sliding, and plowing conditions observed for the non-conformal mating wear couple of a total knee prosthesis is described. This tribometer was used to evaluate the tribological behavior of Co-Cr, Ti-6Al-4V, yttria-stabilized tetragonal zirconia, and monoclinic zirconia-coated zirconium alloy pins in cyclic sliding contact with UHMWPE.

The tribometer described employs a right cylinder on flat geometry. The metallic and ceramic pins were in the form of cylinders which were 9 mm in diameter and 19 mm long. The cylinders were wear tested in reciprocating sliding contact (15 mm stroke length, 2.1 Hz) with 12.7 mm wide UHMWPE strips. The wear tests were conducted in deionized water for two million cycles. The wear of the UHMWPE strips and cylinders was characterized using an appropriate combination of weight and thickness change measurements, optical stereomicroscopy, scanning electron microscopy (SEM), and measurement of UHMWPE debris and metal ion concentrations in the deionized water solutions.

The lowest friction coefficients (0.02 – 0.04) occurred during the run-in period for all materials tested. The observed increases in COF values coincided with the formation of UHMWPE transfer layers and abrasion of the cylinder surface. Transfer layer formation and an increase in the COF, as well as cylinder abrasion and the resultant increase in surface roughness, correlated with an increase in wear of the UHMWPE strips and an increase in the concentration of UHMWPE wear debris and metal ion levels in the deionized water solutions. The results of this series of wear tests show that this tribometer is capable of obtaining reliable and accurate dynamic friction data and that measured changes in the COF correlate well with observed changes in surface roughness and chemistry of the contact surfaces.
Adherence, Friction and Wear of Rubber-Like Materials
Authors: Barquins M
Published: March 2009

The underlying mechanisms of the adherence and of the sliding and rolling friction of rubber-like materials are studied at a microscale level, by scrutinizing phenomena occuring inside both static and rolling or sliding contact areas between a single hard transparent spherical or cylindrical asperity and the smooth and flat surface of a soft elastomer sample. Various mechanisms have been studied such as equilibrium conditions and kinetics of adherence of different rigid punches, contact geometry and rolling friction force of a rigid cylinder, static friction, deformation and interfacial phenomena in sliding friction of a spherical asperity, influence of the radius of curvature of a blunt rigid asperity in sliding contact, stages of formation of re-attachment folds, conditions for the appearance of detachment waves, friction of silica filled compounds and the onset of wear.
Tribological Approaches for Elastomer Applications in Computer Peripherals
Authors: Bayer RG
Published: March 2009

In computer peripheral equipment, such as printers and check sorters, elastomers are frequently used as dampers to control impact and as rollers to stop and feed paper and ribbon. To address such applications tests and models were developed to evaluate materials and predict performance. In this paper, the models and tests used to address both impact and feed roll applications are described, along with examples of their applications. In both applications the tests are used to compare materials and to provide values of empirical parameters required for application of the models.

The test techniques and apparatii used to evaluate materials for these applications are described. Further a model developed for impact wear of elastomers and its application to several wear points in an electro-magnet unit of a high speed printer will be presented. Also an abrasive wear model used for feed roll applications will be discussed. Its use will be illustrated by two examples. One is taken from a check sorter; the other, from a ribbon stuffing box application. In both feed roll applications additional friction tests were required. The methods used to determine the coefficient of friction will also be presented.

In these applications predictions of the models were compared with actual performance. The agreement between these predictions and actual performance, which is generally good, will also be discussed.

Additionally, various aspects of another application of elastomers in high speed printing, i.e., as push rod tips, will be discussed. In this application cracking at stress concentration locations is a concern, as well as surface wear. The experimental and analytical approaches used to understand and characterize behavior in this application will be presented.
Modeling Crack Growth Resistance in Ceramics and Ceramic-Matrix Composites
Authors: LLorca J , Elices M
Published: March 2009

Crack growth resistance in ceramics and ceramic-matrix composites at ambient temperature is provided mainly by the interaction between the crack surfaces in the crack wake. A cohesive crack model is presented to study the fracture behavior of these materials. The constitutive equation for the cohesive crack is obtained through micromechanical considerations and experimental observations in the crack wake. The model predictions show good agreement with experimental results in one monolithic ceramic (alumina) and two fibeoreinforced ceramic-matrix composites. The applications and limitations of the model are discussed.
Fatigue Characteristics of Heavily Cold-Rolled Cu-20Nb
Authors: Biner SB , Spitzig WA
Published: March 2009

Initiation and growth of fatigue cracks emanating from four different notches ranging in stress concentration factors from 2.0 to 9.6 were investigated. Results obtained for Cu-20Nb were compared with the results obtained for pure copper that was cold rolled the same amount as the Cu-20Nb. The Cu-20Nb exhibited superior fatigue characteristics in comparison to pure copper. Finite element method simulations indicated that this improvement is associated with the plasticity-induced crack closure resulting from nonhomogeneous deformation ahead of the crack tip due to the presence of the niobium filaments.
Effect of Tensile Mean Stress on Fatigue Behavior of Single-Crystal and Directionally Solidified Superalloys
Authors: Kalluri S , McGaw MA
Published: March 2009

Two nickel-base superalloys, single-crystal PWA 1480 and directionally solidified MAR-M 246+Hf, were studied in view of the potential usage of the former and usage of the latter, respectively, as blade materials in the turbomachinery of the space shuttle main engine. The baseline zero-mean-stress fatigue life behavior of these superalloys was established, and then the effect of tensile mean stress on their fatigue life behavior was characterized. At room temperature, these superalloys have lower ductilities and higher strengths than most polycrystalline engineering alloys. The cyclic stress-strain response was thus nominally elastic in most of the fatigue tests. Therefore, a stress range based fatigue life prediction approach was used to characterize both the zero- and tensile-mean-stress fatigue data. In the past, several researchers, namely, Goodman, Gerber, Soderberg, Smith, and Morrow, have developed methods to account for the detrimental effect of tensile mean stress on the fatigue life for polycrystalline engineering alloys. Applicability of these methods to single-crystal and directionally solidified superalloys has not been established. In this study, these methods were applied to characterize the tensile-mean-stress fatigue data of single-crystal PWA 1480 and directionally solidified MAR-M 246+Hf and were found to be unsatisfactory. Therefore, a method of accounting for the tensile-mean-stress effect on fatigue life that is based on atechnique proposed by Heidmann and Manson was developed to characterize the tensilemean-stress fatigue data of these superalloys. Details of this method and its relationship to the conventionally used mean stress methods in fatigue life prediction are discussed.
Crack Resistance, Fracture Toughness, and Instability in Damage-Tolerant Aluminum-Lithium Alloys
Authors: Wanhill RJH , Schra L , 't Hart WGJ
Published: March 2009

A comparison is made of the crack resistance (R-curve), fracture toughness, and instability behavior of candidate damage-tolerant aluminum-lithium (Al-Li) alloys, 2091 and 8090, and the widely used conventional 2024-T3 alloy. The 2091 alloy was in three heat treatment conditions, T8X, TX, and TY, all artificially aged. The 8090 alloy was in the T81 condition. The crack resistances and fracture toughnesses of 2091-T8X and 8091-T81 were similar to those of 2024-T3, but at a 50 MPa lower strength level. The crack resistances and fracture toughnesses of 2091-TX and 2091-TY were much inferior.

In all cases, stable (slow) crack growth was ductile, but unstable crack growth in 2091-TX and 2091-TY was 100% intergranular and macroscopically brittle. Unstable crack growth in 2091-T8X was 50% intergranular and macroscopically ductile. Fractographic analysis indicated the 2091-TX and 2091-TY alloys to be sensitive to dynamic effects, such that the dynamic fracture toughness could be significantly lower than the quasi-static fracture toughness. This may also be true of 2091-T8X. In view of these results, fail-safe crack arrest tests should be included in any evaluation of damage-tolerant Al-Li sheet alloys for aircraft structures.
Ultrasonic Wave Technique to Assess Cyclic-Load Fatigue Damage in Silicon-Carbide Whisker Reinforced 2124 Aluminum Alloy Composites
Authors: Achenbach JD , Fine ME , Komsky I , McGuire S
Published: March 2009

Composites composed of a precipitation-hardened 2124 aluminum (Al) alloy matrix reinforced by silicon-carbide (SiC) whiskers, which are fabricated by powder metallurgy, are susceptible to fatigue damage due to microcracking along SiC-Al interfaces, especially at the external surfaces of a body. The microcracks that are produced in the crack initiation process are generally too small to be detected and characterized by conventional ultrasonic techniques. Since they may link up to produce macrocracks and rapid final fracture, a simple experimental technique is required to assess the extent of the microcracking. This paper reports on an ultrasonic surface wave technique that was developed for that purpose. In this technique, the integrated effect of the damage is established by careful measurements of the changes of the phase velocity and the coefficient of attenuation as the number of cycles of fatigue loading increases.

The specimens, 6.6 mm thick, 13 mm wide, and 105 mm long in the gage section, were fatigued in pull-pull under load control. Surface waves were generated at 5 MHz with conventional surface wave transducers. A special self-calibrating ultrasonic bridge was employed to measure surface wave motion by means of two dry contact point pickups separated by a known distance along the direction of surface wave propagation. Wave speed measurements were obtained by the use of a variation of the overlap technique. To measure the attenuation, the data were deconvolved from the response functions of the point contacts by the use of data for surface wave generation in two opposite directions.
Acoustic Emission Monitoring of Fatigue in Titanium Aluminide XD Composite
Authors: Lee EU , Granata DM , Scott WR
Published: March 2009

The feasibility of acoustic emission (AE) monitoring of fatigue crack growth in titanium aluminide XD composites was investigated. Under tension-tension and compression-compression loading, the total accumulated number of AE events corresponds closely to the fatigue crack growth. The majority of the AE occurs near the maximum load during uploading. In the tension fatigue test, the AE is controlled by the stress intensity factor, and its relationship is given by the equations An=(1.1×10−3)·(Kmax)6.3 An=(1.1×10−3)·(ΔK)6.3 where An is the total number of AE events, Kmax the maximum stress intensity factor, and ΔK the range of stress intensity factor.
The Nature of the Glass Transition and its Determination by Thermal Analysis
Authors: Wunderlich B
Published: March 2009

In this paper operational definitions of the glass transition and the pertinent condensed phases are given. This is followed by a description of the basic observations of glass transitions via thermal analysis using calorimetry, dilatometry, as well as theromechanical, dielectric, and dynamic mechanical analysis. The time dependence of the glass transition causes hysteresis phenomena and physical aging. Strain effects on the observation of the glass transition are identified. Complications resulting in symmetric and asymmetric broadening of the glass transition are linked to nanometer and micrometer scale phase separations. Finally, a rigid amorphous phase is identified in some semicrystalline polymers.
Phenomenology of the Structural Relaxation Process and the Glass Transition
Authors: Moynihan CT
Published: March 2009

The glass transition is a kinetic phenomenon caused by the inability of the liquid structure to equilibrate on an experimental timescale at sufficiently low temperatures. This results in changes during heating or cooling in the temperature dependence of macroscopic properties such as volume, enthalpy, dielectric constant and loss, etc., over a narrow range in temperature generally referred to as the “glass transition region.” During the past 25 years, fairly straightforward semi-empirical models have been developed for the behavior of liquids and glasses in the glass transition region. These models are able to describe both qualitatively and, if the system is not too far from equilibrium, quantitatively the time and temperature dependence of properties during cooling, heating, and annealing. In addition, analysis of the structural relaxation process using irreversible thermodynamics has shown that different properties, e.g., volume and enthalpy, are expected to exhibit different time dependencies in the glass transition region. The relevance of these models and theories to a meaningful assignment of a “glass transition temperature” is discussed.
Glass Transition Measurements by DSC
Authors: Bair HE
Published: March 2009

This is a review of glass transition temperature (Tg) measurements of materials by differential scanning calorimetry (DSC). Tg is noted in DSC derived heat capacity (Cp) plots against temperature as the jump in Cp or (∆Cp) that occurs usually over a temperature interval of a few tens of degrees (°C). Under conditions which are normal for DSC experiments it was found that the temperature gradient across and from top to bottom of a 0.6-mm-thick molded disk of polycarbonate (17 mg) was no greater than 0.6°C when heated at 15°C/min. Under these conditions a glassy polymer can be scanned for its Tg as defined by its half-vitrification temperature (½ ∆Cp) as well as the beginning and end of the transition to within 1°C. DSC Tg measurements are reviewed to show how the location, shape, and magnitude of the transition can be used to characterize the composition and behavior of a wide variety of polymeric materials ranging from homopolymers, blocks, grafts, and blends to networks. Also the effect of molecular weight, plasticizers, aging, crystals, and stress on the Tg of several polymers is re-examined.
Assignment of Glass Transition Temperatures Using Thermomechanical Analysis
Authors: Earnest CM
Published: March 2009

The use of thermomechanical analysis (TMA) as a tool for assignment of glass transition temperatures, Tg, is discussed in this paper. An attempt to address the minimum requirements of TMA instrumentation necessary for Tg assignments is included. The subject of temperature calibration of the TMA instrument, which is a prerequisite for any temperature of transition assignment, is discussed. Methodology is offered for using the TMA nstrument in the expansion mode for Tg assignments. In addition, TMA methodology mploying a flat-tipped penetration probe for the assignment of the softening temperature, Ts, is also given here. For most amorphous materials, Ts is very close to the Tg value assigned by expansion TMA or differential scanning calorimetry (DSC).
Glass Transition in Polymers: Comparison of Results from DSC, TMA, and TOA Measurements
Authors: Wiedemann HG , Widmann G , Bayer G
Published: March 2009

The determination of the glass transition temperature, Tg, of polymers by differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) is sometimes problematic and rather subjective. This was shown previously in the ICTA certificate (distributed by NBS as GM-754) for the certified reference material polystyrene (PS). The not very good reproducibility of the measured value of the onset is due to a variety of instrumental and experimental parameters. This is true also for the determination of the glass transition by TMA measurements. The main reasons are temperature gradients caused by the relatively high sample mass required for DSC and by the limited heat transfer in TMA, respectively. Our own experiments which were carried out with polystyrene and with [poly(ethyleneterephthalate)] (PET) proved that a combination of DSC with TOA (thermo-optical analysis or hot stage microscopy under polarized light) can solve some of these problems. TOA is a nonsubjective method since the changes in birefringence and light transmittance during the glass transition which are visible under the microscope are measured with a photocell. TOA allows Tgmeasurements of small samples (fraction of milligrams).