bluuebunny/crossref_metadata_2025_split huggingface dataset:
The COD Approach and Its Application to Welded Structures
Authors: Harrison JD , Dawes MG , Archer GL , Kamath MS 
Published: March 2009

The crack opening displacement (COD) approach has, since its inception as a fracture initiation parameter in yielding fracture mechanics, gained increasing acceptance both as a viable research tool and an engineering design concept. In the United Kingdom, The Welding Institute has pioneered the application of COD in the structural fabrication industry largely through the development of the COD design curve. This paper is a representation of the philosophy underlying design curve applications and illustrates the practical significance of COD by drawing on case studies from various welded structures.
Following a brief appraisal of the origins of the design curve, the paper outlines procedures for the use of COD in design, that is, either as a basis for material selection or in setting up acceptance levels for weld defects. The reliability of a small-scale test prediction from the design curve has been investigated on a statistical basis from a survey of more than 70 wide-plate tension test results in which the material had also been categorized by COD. Specific practical examples are then discussed covering the various types of application, material selection defect assessment, and failure investigation.
Structures included in these examples are offshore rigs, oil and gas pipelines, pressure vessels, etc., with special emphasis on the manner in which small-scale COD test results are translated to the structural situation.
Finally, the paper includes information on the considerable range of structures to which the concept has been applied during the past five years.
Some Effects of Microstructure and Environment on Fatigue Crack Propagation
Authors: Scarlin RB 
Published: March 2009

Fatigue crack growth rates have been determined in nickel-base alloys both after a normal heat treatment and after heating for a further 10 000 h. The latter treatment causes coarsening of the γ‵-particles so that they are no longer sheared by dislocations when the material is deformed. Differences in cracking rates at both ambient and elevated temperatures may be understood in terms of slip reversibility and oxide penetration when deformation occurs by shearing of precipitates.
A further result of the prolonged aging period is a considerable reduction in the cyclic fracture toughness of a cast alloy. This can be traced to a transition to intergranular cracking along regions of coarsened precipitation adjacent to the grain boundaries.
A comparison of cracking rates in air and vacuum shows that the presence of air can lead to an increase in growth rate and to a situation where no clear threshold is apparent. Crystallographic cracking (analogous to Stage I fatigue) is observed in both air and vacuum. One effect of oxygen in tests at high temperatures is to cause dissolution of the γ‵-particles in the region of the crack tip. Under high-temperature corrosive conditions (air/SC2/SO3 atmosphere) an increase in scatter and in average propagation rate can be correlated with the formation of liquid sulphide films at the crack tip.
Micromechanisms of Low-Cycle Fatigue in Nickel-Based Superalloys at Elevated Temperatures
Authors: Runkle JC , Pelloux RM 
Published: March 2009

The micromechanisms of high-temperature fatigue crack initiation and crack propagation in solid-solution and precipitation-strengthened nickel-base super-alloys are reviewed. The marked decrease in fatigue strength of a given superalloy with increasing temperature cannot be solely correlated with the temperature dependence of the short-time mechanical properties. The interactions between oxidation rates and fatigue strengths are very complex. The air environment plays a large role in accelerating the initiation and propagation of fatigue cracks at elevated temperatures. Increasing temperature and decreasing frequency lead to a transition from transgranular to intergranular fracture path.
The influence of different microstructural factors on the high-temperature low-cycle fatigue (LCF) behavior of a typical superalloy, Astroloy, was investigated in detail. A combination of fine 500 Å matrix γ′ in conjunction with a wavy grain boundary produced by both coarse intergranular M23 C6 carbides and primary γ′ is found to offer the best LCF performance in the range of 0.2 to 0.7 Tm. The fine γ′ retards Stage I cracking, and the wavy grain boundaries retard intergranular cracking. The observations made with Astroloy can be extrapolated to different γ/γ′ nickel-base superalloys.
Corrosion Fatigue of 316L Stainless Steel, Co-Cr-Mo Alloy, and ELI Ti-6Al-4V
Authors: Imam MA , Fraker AC , Gilmore CM 
Published: March 2009

The purpose of this paper is to compare corrosion-fatigue properties of selected implant alloys and to discuss the corrosion fatigue-life in terms of the corrosion behavior and the metal microstructure. The tests were conducted in fully reversed torsion in flowing Hank's solution at a temperature of 37°C and a pH of 7.4. Specimens were subjected to fatigue at shear strains ranging from 0.006 to 0.018 and at a frequency of 1 Hz. Surfaces of the 0.5-cm-diameter specimens were prepared by mechanically polishing through a 0.05 alumina powder and following this with steam sterilization.
During the tests, the specimen electrode potentials versus time were monitored on a strip chart recorder. The potential-time curves for the metals studied show the establishment of a steady rest potential which does not change until the fatigue motion has been applied. The potential then goes in the negative direction. The rate of this decline in potential appears to-be related to the metal microstructure as well as to the alloy composition. This electronegativity of the potential-time curves indicated the formation of cracks in the oxide film. These curves were more electronegative with increased shear strain, and the curves were different for the different metals tested.
Fatigue results of these tests show that the ELI Ti-6Al-4V has the longest fatigue life under these conditions. The fatigue strength of the Ti-6Al-4V can be increased many times by changing the microstructure through heat treating and quenching. The Type 316L stainless steel had the next longest fatigue life. The cast Co-Cr-Mo alloy had the shortest fatigue life and also showed more scatter in the results. Other workers have shown that further heat treating and processing improves the fatigue resistance of this material too.
Impact Damage Effects on the Strength of Advanced Composites
Authors: Labor JD 
Published: March 2009

This paper discusses the effect of flaws created by impact damage on the strength of graphite/epoxy panels that were tested as sandwich beams and as skin panels on box beams. A majority of the panels were exposed to random spectrum fatigue loads prior to failing them under static loading conditions. The maximum loads in the fatigue spectrum were scaled to provide a strain equal to the B-basis matrix failure strain for the resin system used. Box beam skin panels were designed to fail by compressive panel buckling in order to evaluate the effect of the impact damage on the buckling strength of the panels. All testing was conducted at room temperature on panels with no moisture conditioning.
Marginally visible damage was found to cause a strength loss up to 35 percent in compression but less in tension. Acoustic C-scan inspections showed that none of the impact damage sizes grew during spectrum loading. Panel stability was unaffected by localized impact damage. The most severe impact damage caused strength losses comparable to drilled fastener holes.
Moisture-Induced Surface Damage in T300/5208 Graphite/Epoxy Laminates
Authors: Shirrell CD , Leisler WH , Sandow FA 
Published: March 2009

A microscopic examination of hygrothermally expsoed T300/5208 cross-ply laminates is described. Moisture-induced surface and edge microcracks were observed in specimens exposed at 82° and 9, 20, 37, 74, and 91 percent relative humidity or water immersion. Specimens exposed at similar relative humidities but at lower temperatures (21, 43, and 63°C) generally did not form microcracks.
The severity and frequency of the microcracking at 82°C increased with relative humidity. The majority of the microcracks were observed to be oriented parallel to the graphite fibers in the surface laminae. Specimens with extensive microcracks were also observed to exhibit non-Fickian diffusion phenomena during their hygrothermal exposure.
Evaluation of Powder-Processed Metals for Turbine Engine Ball Bearings
Authors: Brown PF , Bogardus GA , Dayton RD , Schulze DR 
Published: March 2009

Two different types of rolling element fatigue testers and a full-scale bearing tester were used in a program aimed at developing a highly fatigue-resistant powder-processed material (P/M) for use in turbine engine bearings. The testers were the single-ball machine evaluating 0.0238-m (15/16-in.)-diameter balls, a rolling contact fatigue machine evaluating 0.00953-m (⅜ in.) rods, and a full-scale bearing rig evaluating 140-mm-bore, 0.0238-m (15/16 in.)-diameter ball, angular contact thrust bearings.
The two-element testers, used to screen three different P/M alloys and the baseline vacuum induction melted-vacuum arc remelted (VIMVAR) M-50 alloy, each produced essentially the same ranking for these materials. The best results, about twice the life of the baseline VIMVAR M-50, were achieved with P/M CRB-7, a 14 percent chrome corrosion-resistant alloy. P/M M-50 produced lives equivalent to VIMVAR M-50. P/M T-15, a 4 percent chrome alloy, exhibited lives ranging from that realized with the baseline material down to one third of that level. Based on these tests, CRB-7 was selected as the material out of which the balls and races for 20 full-scale 140-mm bearings were subsequently fabricated and tested. The tests were conducted at a thrust load of 34 872 N (7 840 lb) and at a speed of 12 500 rpm. A wear problem encountered in these tests was circumvented by nickel plating the cage guiding surfaces of the inner ring lands. The B10 rolling contact fatigue life realized with these bearings was equivalent to that expected for these same bearings had they been made of conventional VIMVAR M-50 material. These results were quite encouraging considering the fact that this was the first attempt at applying powder processing to the manufacture of aircraft-quality rolling element bearings.
Microstructural Control in Microalloyed Steels
Authors: Cohen M , Hansen SS 
Published: March 2009

High-strength low-alloy (HSLA) steels constitute a classic metallurgical development in which alloying additions and thermomechanical processing have been brought together effectively to attain desired combinations of engineering properties through microstructural control. Moreover, the microstructural control is relatively inexpensive because the alloying elements are used only in small concentrations as carbide-formers, and the associated thermomechanical processing is introduced merely as a modification of the final hot-rolling operation. A key feature of the resulting microstructure is the small ferritic grain size that provides a favorable balance of strength and toughness in the as-rolled steel.
Here, we examine the interactions in columbium-treated HSLA steels among austenite chemistry, plastic deformation, strain-induced carbonitride precipitation, recrystallization characteristics, and the subsequent transformation of the thermomechanically-processed or conditioned austenite to the final ferrite-based structures. The latter transformations are studied in order to relate the ferrite nucleation and growth as well as its ultimate morphology to the state of the prior austenite.
An Evaluation of Double-Torsion Testing—Analysis
Authors: Fuller ER 
Published: March 2009

The double-torsion test configuration has many advantages over conventional fracture mechanics configurations for the evaluation of subcritical crack growth parameters and fracture toughness. These advantages—such as crack-length independence, four-point loading, simple specimen geometry, and ease of precracking—have been responsible for the increased use of the double-torsion configuration in recent years. However, before double-torsion testing can be adopted as a standard configuration, a number of unresolved questions need to be answered about the double-torsion specimen and about the experimental techniques involved in its use.
The purpose of this paper is to address some of these questions and to indicate where further effort is needed to establish the validity of double-torsion testing. Assumptions of a compliance analysis for the double-torsion configuration are examined with particular attention given to the influence on experimental results that the violation of any of these assumptions may have. An analytical expression is derived for the compliance of a finite-thickness beam in torsion and is compared to the empirical compliance. Again the emphasis is on the assumptions of the derivation and how some of these restrictions might be relaxed.
Ductility of Zircaloy Canning Tubes in Relation to Stress Ratio in Biaxial Testing
Authors: Andersson T , Wilson A 
Published: March 2009

A biaxial-burst testing machine has been designed in which biaxial plane stress tests can be carried out on tubular material with any stress ratio in the range σθ:σz 4:5 to 2:1, where 2:1 implies the closed-end burst test. Unirradiated Zircaloy tubes cold worked 80 percent, recrystallized at 575°C, and characterized by a texture having a basal pole tilt angle of 33 deg were tested at room temperature with various stress ratios, namely, 4:5, 1:1, 5:4, 3:2, and 2:1. In addition, tension and open-end burst tests were carried out in conventional machines.
The uniform ductility measured as uniform effective strain displays a minimum at the stress ratio 3:2. It has been found experimentally that the stress ratio for minimum uniform ductility corresponds to deformation under a plane strain loading condition, that is, the stress ratio which gives no change in the tube length. The fracture ductility defined as the effective strain at fracture exhibits a minimum at the stress ratio 5:4. When bulging begins, the applied stress ratio cannot be kept constant, but the stress ratio decreases due to an increased axial stress. This behavior probably explains the observed shift in minimum ductility from the uniform value 3:2 to the fracture value 5:4.
Performance of Irradiated Copper and Zirconium Barrier-Modified Zircaloy Cladding Under Simulated Pellet-Cladding Interaction Conditions
Authors: Tomalin DS , Adamson RB , Gangloff&gt; RP 
Published: March 2009

Expanding mandrel laboratory simulations of the pellet-clad interaction (PCI) mechanism (including argon, iodine, and cadmium environments) were employed to evaluate copper barriers and zirconium-lined tubing performance. Zircaloy-2 and copper-plated and zirconium-lined barrier tube specimens were tested in the unirradiated (cold-worked) and in the irradiated (recrystallized) conditions at about 600 K. Tubing was irradiated at 620 K to a fast (E &gt; 1 MeV) fluence near 2 × 1025 n/m2.
Brittle PCI-type failures were produced in unirradiated Zircaloy-2 tubing by expanding mandrel loading with iodine and cadmium. Failure strains were further reduced for irradiated Zircaloy-2 tested in each embrittling environment. Fractographic analyses revealed brittle fracture surface features similar to those reported for failed fuel rods. In contrast, high-strain ductile ruptures were produced in both unirradiated and irradiated tube samples tested in argon. These findings support the PCI description for fuel rod fractures. Zirconium-lined Zircaloy was not embrittled by cadmium even after neutron irradiation. High average failure strains and ductile fracture surface features were observed for the zirconium-lined tubing tested with cadmium, analogous to Zircaloy-2 tested in an inert environment. Similar experiments with low-pressure (4 to 40 Pa) gaseous iodine produced brittle cracking in the zirconium liner and in the underlying Zircaloy, both before and after irradiation, but at average strains well in excess of those required for brittle failure of Zircaloy tubing. Copper-electroplated Zircaloy tubing also exhibited excellent resistance to simulated PCI failure for both irradiated and unirradiated conditions when exposed to iodine or cadmium. Average failure strains and fractographic features were similar to results obtained for Zircaloy-2 tested in an inert environment. Mechanisms for the performance of copper zirconium barrier tubing were discussed. It was concluded that, based on laboratory testing, both copper plated and zirconium-lined cladding systems offer significant potential for improved PCI resistance. Reactor evaluations are required to confirm this conclusion.
Analysis of Irradiation Growth and Multiaxial Deformation Behavior of Nuclear Fuel Cladding
Authors: Clevinger GS , Adams BL , Murty KL 
Published: March 2009

Postirradiation analysis of the multiaxial strain behavior of nuclear fuel cladding requires a comprehensive evaluation of the various mechanisms contributing to the total observed principal strains. Measurements are usually taken for diametral change, which accrues as a result of irradiation-enhanced multiaxial creep, and of changes in axial length, which is predominantly caused by irradiation-induced growth. In this context, it is important to note that under multiaxial loading, the generalized strain vector produced by creep deformation is not coincident with the hoop direction of the cladding except under special conditions and, similarly, that the expected direction of the irradiation growth component derived from texture considerations is not coincident with the axial direction of the tubing. Rather, both mechanisms usually produce component strains in each of the principal directions of the cladding. It is generally observed, in fact, that the total strain vector determined from postirradiation measurements is well displayed from that which would be predicted for either creep deformation or the irradiation growth mechanism and is obviously the resultant strain produced by the combined effects of irradiation growth and multiaxial creep deformation.
Thus, it becomes important in efforts to model and predict this behavior from baseline laboratory test results and material anisotropy constants to appropriately separate the strain components that result from irradiation growth from those produced by multiaxial creep behavior. This paper describes a procedure that leads to an expected direction of the creep vector based on multiaxial flow equations for an anisotropic material and a predicted irradiation growth vector based on crystallographic texture analyses and stress-free irradiation growth data. The observations discussed here support the hypothesis that irradiation growth is essentially stress independent in Zircaloy and suggest that anisotropic multiaxial strain ratios due to creep or plastic deformation are unaffected by the presence of a neutron flux.
The mechanistic aspects of irradiation growth are discussed, particularly as they relate to cold-worked material, and the ideas of Northwood are extended to hypothetically account for observed variations in irradiation damage rate and loss of ductility in materials having varying degrees of cold work and recrystallization.
Predicting High-Temperature Transient Deformation from Microstructural Models
Authors: Sills HE , Holt RA 
Published: March 2009

We have developed a multicomponent model to describe the transient plastic deformation of Zircaloy fuel sheathing during postulated loss-of-coolant accidents (LOCA). From deformation maps, we identify three creep mechanisms, which in principle, occur in all three phase fields of Zircaloy-4 (α, α + β, β): diffusional creep, dislocation creep and athermal strain. Diffusional creep (phase boundary or grain boundary sliding) is modeled in the α and α + β phase fields. Dislocation creep is modeled in all three phase fields and controlled by a work-hardening/recovery expression. Athermal strain has practical significance only at lower temperatures (&lt; 900 K). The sum of the strain rates of the three deformation mechanisms is the total plastic strain rate. At a particular point in the stress-temperature field, one mechanism usually dominates.
Microstructural changes that affect deformation are also taken into account; these are changes in grain structure, recrystallization, and the α ⇌ (α + β ) ⇌ β phase transformation. When two components are present (α + β or recrystallized and unrecrystallized), they are assumed to deform with equal rates according to the appropriate single-phase model.
The individual components of the model give excellent agreement with the isothermal data on which they are based, and the entire model gives very good agreement with transient data over a range of temperatures from 700 to 1600 K, a range of heating rates from 0 to 100 K/s, and a range of strain rates from 10-5 to 10-1 s-1. Several applications of the model in evaluating the history dependence of deformation are given.
Influence of Iodine on the Strain and Rupture Behavior of Zircaloy-4 Cladding Tubes at High Temperatures
Authors: Hofmann P 
Published: March 2009

The stress corrosion cracking (SCC) behavior of short tubular Zircaloy-4 specimens by the action of iodine (initial iodine concentration: 0.1 to 10 mg/cm3) was investigated out-of-pile between 600 and 1100°C under inert gas conditions. The Zircaloy cladding tube was used as-received and with an inner preliminary oxidation. Moreover, the influence of the uranium oxide (UO2) oxygen potential on the SCC behavior was studied.
The burst and creep-rupture tests (time-to-rupture ≤ 15 min) clearly show that the deformation behavior of Zircaloy cladding tubes below 850°C is heavily influenced by the presence of iodine. A failure of Zircaloy tubes takes place that is characterized by little deformation as compared to reference specimens without iodine. With decreasing temperature, the burst strain is greatly reduced. Moreover, in the isothermal, isobaric experiments, the time-to-failure of the iodine containing specimens is markedly shorter as compared to the iodine-free reference specimens. Internal preoxidation of the cladding tube or UO2 in the specimens exert an additional influence on the mechanical properties of Zircaloy.
Scanning electron microscope examinations of the rupture surfaces of the cladding tubes show that in the presence of iodine and at burst temperatures below 850°C the cracks in the cladding material are mainly intergranular followed by ductile residual rupture. By contrast, iodine-free specimens are exclusively subject to ductile failure.
Studies on Zircaloy Fuel Clad Ballooning in a Loss-of-Coolant Accident—Results of Burst Tests with Indirectly Heated Fuel Rod Simulators
Authors: Erbacher F , Neitzel HJ , Wiehr K 
Published: March 2009

Burst tests with indirectly heated fuel rod simulators were performed under cooling and temperature conditions postulated for a loss-of-coolant accident (LOCA) of a pressurized water reactor (PWR). The tests were designed to investigate the ballooning behavior of Zircaloy fuel rod claddings and to determine the resulting coolant channel blockage in a rod bundle.
The deformation behavior of the Zircaloy cladding tubes was found to be influenced mainly by local effects due to nonuniform temperature distributions. Single rod and bundle tests exhibited large azimuthal and axial temperature differences. This resulted in relatively small and axially limited strains of the Zircaloy cladding tubes and a tolerable coolant channel blockage in the rod bundle.