bluuebunny/crossref_metadata_2025 huggingface dataset:
Methanogenesis: A Measure of Chemoorganotrophic (Heterotrophic) Activity in Anaerobic Lake Sediments
Authors: Kelly CA , Chynoweth DP
Published: March 2009

Particulate organic matter, in varying amounts, falls to the sediment in lakes, where it undergoes decomposition via a mixed chemoorganotrophic bacterial population. This paper proposes the use of methanogenesis as a means of measuring this chemoorganotrophic activity in strict anaerobic environments typical of eutrophic lake sediments. The theory, a review of methods, applications, and examples of data are presented for both in vitro and in situ methods of measuring rates of methane production in sediments. Data are presented from the literature and the author's laboratory demonstrating a direct relationship between sedimentation rates of organic matter and rates of methanogenesis
Determining Fracture Directions and Fracture Origins on Failed Graphite/Epoxy Surfaces
Authors: Morris GE
Published: March 2009

During this investigation, methods were developed for determining the fracture directions of failed graphite fiber/epoxy resin composite test specimens and structures. Notched test specimens with 90-deg unidirectional fiber orientations were failed in tension by delamination. The resulting fracture surface features consisted of the graphite fiber and epoxy components. Epoxy fracture surface topographic features were identified with a scanning electron microscope (SEM). These features, designated as “hackles,” were correlated with the fracture direction. The direction of hackle overlap or tilt reversed when the fracture direction changed. This characteristic can be used to isolate fracture origins on failed test specimens or structures.

Test specimens having cracks with known fracture directions were sectioned, mounted, and polished using standard laboratory techniques and were examined with an optical microscope. A crack tip was detected which provided evidence to support a proposed theory for delamination crack initiation and propagation in graphite/epoxy structures.

Finally, graphite/epoxy test specimens and structural test articles that had been tested to failure in tension and fatigue were examined, and the hackle features were correlated with the fracture directions and origin locations within the specimens.
Nondestructive Testing Methods for Graphite/Aluminum Composites
Authors: Sullivan PG , Davis LW
Published: March 2009

Development of the C-scan method for nondestructively inspecting graphite/aluminum metal matrix composites is discussed. Specific test results are shown and mechanical properties are correlated with anomalous regions which were detected by the C-scan technique.
Materials Evaluation by Flat Washer Testing
Authors: Hampshire JM , Nash JV , Hollox GE
Published: March 2009

A flat washer test for assessing the rolling contact fatigue performance of bearing materials is described in detail. Measurements of the life of commercial bearing quality SAE 52100 steel has established the baseline against which the relative performance of different steels or developments in heat treatment and bearing manufacturing can be judged. The life of carburized SAE 8720 steel has been shown to be inferior to that of SAE 52100 because of the lower level of cleanness of carburizing steels. Electroslag remelting of SAE 52100 produces an improvement in life. Heat treatment to produce lower bainite in SAE 52100 is advantageous, particularly under conditions of water-contaminated lubrication or where the use of fire-resistant fluids is required. Sinter forging is a viable production route for SAE 52100 bearings when the powder oxygen content is controlled.
Influence of Wear Debris on Rolling Contact Fatigue
Authors: Sayles RS , Macpherson PB
Published: March 2009

Results are presented on the influence of internally generated wear debris on the failure characteristics of rolling element bearings. The effects of lubricant filtration are studied, and by means of Weibull failure distributions the gains in fatigue life are shown to be as high as sevenfold if the filtration level is set correctly. Metallurgical results are presented which show that, when lubricant contamination is present, early failures, and particularly those which strongly influence L10 lives, are mostly surface initiated, and not subsurface in origin, as was previously believed to be the case with rolling contact.
Rolling Contact Fatigue Evaluation of Advanced Bearing Steels
Authors: Popgoshev D , Valori R
Published: March 2009

A series of rolling contact fatigue tests were performed on nine advanced rolling element bearing materials and processes in combination with three lubricants (an unformulated ester base stock, a qualified MIL-L-23699, and an advanced MIL-L-23699-type lubricant) in order to determine their rolling contact fatigue performance. The performance of each material was compared with the performance of a baseline AMS-6490 (AISI M-50) steel. The results indicate that (1) all of the test materials and processes perform at least as well as AMS-6490, (2) the best performing materials were a powder-processed CRB-7 and an AMS-5749, and (3) the performance of one material (CBS-1000M) improved with the use of fully formulated lubricants.
Design of High Hardness, Tough Steels for Energy-Related Applications
Authors: Zackay VF
Published: March 2009

The need for improved wear and abrasion resistant steels for components in advanced fossil energy conversion systems is described. Desirable combinations of mechanical properties for these components are enumerated. A critical component, coal feeders, in coal gasification plants requires adequate room temperature toughness and high strength at both room and moderately elevated temperatures. Through modification of both composition and heat treatment, it has been shown that commercial secondary hardening matrix steels are promising candidates for this application. It is further shown that improvements can be achieved by the synthesis of new secondary hardening steels. A key feature of the design of these steels is the suppression, by composition control, of solid-state tempering reactions that (in commercial secondary hardening steels) lead to inadequate toughness. In other components for advanced coal technology, hot strength is not required but hardness and impact strength are. Modified medium-alloy, ultra-high-strength steels are described with combinations of strength and toughness achievable only in the high-alloy (and expensive) maraging steels.
Use of Indentation Fracture to Determine Fracture Toughness
Authors: Marion RH
Published: March 2009

In recent studies on indentation fracture in brittle materials, use of the cracks which form beneath a pointed indenter and grow stably with load has been suggested as a simple technique for the determination of fracture toughness (Kc). The applicability of this technique has been assessed by performing tests on a number of polycrystalline ceramics, glass-ceramics, and glasses which span a range of fracture toughness from 0.7 to 4.5 MN−3/2. Various sharp indenter geometries were tested and it was concluded that cracks produced with the Vickers indenter were the easiest to measure. The existing theories for calculating Kc from experimental measurements (crack length, load, etc.) have been evaluated and their applicability has been determined. The results demonstrate the usefulness of a Vickers pyramid in obtaining a qualitative ranking of Kc for a wide range of brittle materials. A number of practical problems associated with this technique are discussed.
Determination of Fracture Mechanics Parameters Through Fractographic Analysis of Ceramics
Authors: Mecholsky JJ , Freiman SW
Published: March 2009

Fracture surface analysis of brittle materials can be used as a quantitative tool to determine not only the size of the fracture initiating flaw but also the stress at failure and the critical fracture toughness of the material. The techniques for standardizing these fracture surface measurements and the influence of factors such as microstructure, internal stress, and loading rate are described. The sizes and geometries of fracture initiating flaws are correlated with the KIc of the material local to the flaw periphery and these are compared to the KIc obtained from fracture surface analysis. Failure under combined KI and KII loading is shown to become more amenable to analysis through the use of fractography. Static fatigue failures can be analyzed through the fracture surface features they generate. Not only the stress causing failure but also the time under stress can be determined quantitatively through measurement of flaw and “fracture mirror” sizes.
Fracture Toughness Testing of Alumina
Authors: Buresch FE
Published: March 2009

It is recognized that the plane strain brittle fracture of ceramics can be described in terms of a critical stress criterion of failure. Provided that fracture is induced by thermal or mechanical mismatch between anisotropic grains of equal or different phases, slip, or twinning, the microcracks propagate in an unstable manner when the local tensile stress ahead of a stress concentrator exceeds a critical value (σmc). If fracture loads are well below stresses leading to “intense microcracking,” nonlinearity is confined to the vicinity of the notch. The σmc-concept establishes a local criterion for unstable cleavage fracture which is related to microstructural features using the model of the critical elastic energy density within the process zone proposed by the author. Similar to the case of metals, the stress state of specimen shape also has a strong influence on measured KI-value of ceramics. For plane strain, the process zone is an autonomous region. The overall size depends on the grain/microcrack size distribution and the elastic interaction of the microcracks. For plane stress, the process zone is strongly related to the specimen thickness, hence, the grain size dependence also will change with specimen thickness.
Zircaloy Performance in Light-Water Reactors
Authors: Roberts JTA , Gelhaus FE
Published: March 2009

The Zircaloys-2 and -4 are the principal metallic components of light-water reactor (LWR) fuel assemblies. This paper reviews progress in our understanding of Zircaloy behavior in the LWR environment. A significant body of data has been obtained on the characteristics of stress corrosion cracking pellet-cladding interaction (PCI) failures and on the mechanical stability of both fuel rod and assembly. All indications are that the mechanical performance of Zircaloy components is well understood and that cladding and assembly distortions can be controlled to avoid problems with operation, handling, or licensing. However, uncertainties still exist in our understanding of the resistance of Zircaloy to chemical attack from both the fission product environment and the coolant. Therefore, future emphasis will be on demonstrating improved resistance to PCI of various fuel rod design/material modifications and on establishing Zircaloy waterside corrosion limits for the new, higher-temperature, pressurized water reactor (PWR) cores that might be required to operate to higher exposures.
A Stress Corrosion Cracking Model for Pellet-Cladding Interaction Failures in Light-Water Reactor Fuel Rods
Authors: Roberts JTA , Jones RL , Cubicciotti D , Miller AK , Wachob HF , Smith E , Yaggee FL
Published: March 2009

A model for pellet-cladding interaction (PCI) fracture of light-water reactor (LWR) fuel rods is presented, the basis of which is that Zircaloy cladding fails by iodine stress corrosion cracking (SCC). Laboratory data on iodine SCC of irradiated Zircaloy provide the primary input to the model, but unirradiated Zircaloy SCC data and theoretical analyses are utilized to broaden the regime of validity to encompass the various power reactor observations.

The PCI model postulates a threshold stress below which cladding cracks are unable to form. The cladding hoop stress must exceed this threshold for a finite time at any particular fission product iodine availability for the crack(s) to form. Crack formation is the controlling event in cladding failure due to SCC, and therefore, “remedies” must address the situation at the cladding inner surface.
Effect of β-Phase Heat Treatment on the Subsequent α-Phase Ballooning Behavior of Zircaloy-4 Fuel Sheaths
Authors: Hunt CEL , Newell WG
Published: March 2009

During certain postulated transients, a fuel sheath could experience a thermal spike into the β-phase followed by a prolonged period under stress in the α-phase temperature region. This thermal cycle would alter the metallurgical structure and the mechanical behavior. Ballooning tests were done on β heat-treated tubes to compare with previous work on as-received fuel sheaths. Comparisons were made at fixed internal pressures. Two heating rates were used—0.5 and 25°Cs-1—and the temperature range covered was 600 to 900°C. For both heating rates, in the α-phase temperature region the β heat-treated tubes strained less than as-received material at the same temperature and pressure. At temperatures in the (α + β)-phase region, there was no difference between the behavior of the two material conditions.
A Proposed Criterion for the Oxygen Embrittlement of Zircaloy-4 Fuel Cladding
Authors: Sawatzky A
Published: March 2009

Under the condition postulated for a loss-of-coolant accident (LOCA), Zircaloy-4 fuel cladding may experience a temperature transient during which it absorbs an appreciable amount of oxygen from the coolant. Theoretical models for predicting cladding behavior during loss-of-coolant (LOC) are being developed, but until the failure mechanisms can be clearly established, an empirical criterion must be employed.

Since, under LOCA conditions, the fuel cladding would be predominantly exposed to tensile hoop stresses, the effects of oxygen on the tensile properties of Zircaloy-4 were investigated. It was found that, from room temperature to 800°C, the tensile properties were essentially independent of maximum cladding temperature and cooling rate, but were dependent on the oxygen distribution through the cladding wall.

On the basis of the present work, but also consistent with other published work, an interim oxygen embrittlement criterion is proposed, which states: “the oxygen concentration must be less than 0.7 weight percent over at least half the cladding thickness.”

Since the proposed criterion requires a prediction of the oxygen distribution for a given temperature transient, the available computer models are briefly described and compared with experiment. Preliminary results suggest that the prediction of OXWEX, SIMTRAN 1, and PRECIP 1 are in reasonable agreement with experiment.
Evaluation Models of Zircaloy Oxidation in Light of Recent Experiments
Authors: Ocken H , Biederman RR , Hann CR , Westerman RE
Published: March 2009

Measurements of Zircaloy-steam oxidation kinetics on as-received and preoxidized cladding are reported, as are measurements of the inside to outside diameter oxygen ratio following rupture of simulated fuel rods. The kinetics data confirm the conservative nature of the Baker-Just equation and suggest that preoxidation effects would provide an additional element of conservatism in regard to the amount of oxidation that would be expected if a fuel rod were subjected to a pressurized water reactor (PWR)-type temperature transient. Although a great deal of scatter was found in the measured inside-outside diameter oxygen ratios, the average value even at the rupture position was less than unity. The strongest trends showed a decreasing inside-outside diameter oxygen ratio with decreasing test time and increasing distance from the rupture site.

It was found that differences in values of published oxidation kinetics parameters can be reconciled if the procedure used to heat the test specimens is taken into account. A regression analysis of data reported from seven recent investigations showed that the activation energy for the oxidation process was about 7.6 kcal/mole less in experiments using internally heated specimens than in experiments using externally heated specimens. Similar effects are also seen in inside-outside diameter oxygen ratio data; values from externally heated specimens are larger than those from internally heated specimens.
Development of an Oxygen Embrittlement Criterion for Zircaloy Cladding Applicable to Loss-of-Coolant Accident Conditions in Light-Water Reactors
Authors: Chung HM , Garde AM , Kassner TF
Published: March 2009

To establish the mechanical response of Zircaloy cladding under thermal shock conditions typical of hypothetical loss-of-coolant accident (LOCA) situations in light-water reactors (LWRs), cladding specimens were ruptured in steam during transient heating (10 K/s), oxidized at maximum temperatures between 1140 and 1770 K for various times, and cooled from the isothermal oxidation temperature to ∼1100 K at a rate of 5 K/s, and rapidly quenched by bottom flooding with water at a rate of ∼0.05 m/s. Failure “maps” for fracture of the cladding by thermal shock were developed relative to the maximum oxidation temperature and various time-dependent oxidation parameters. In situ pendulum-load impact tests were conducted at room temperature on tubes that survived the thermal quench. Information on the total absorbed energy from these tests was correlated with more extensive results from instrumented drop-weight impact tests. The thermal shock results indicate that the present Zircaloy embrittlement criterion (that is, a total oxidation limit of 17 percent of the wall thickness and a maximum cladding temperature of 1477 K) is conservative and that a more quantitative criterion, based upon the mechanical behavior of the oxidized material, can be formulated with a specified degree of conservatism consistent with the mechanical loads imposed on the cladding during reflood and the maximum amount of oxidation set by the margin of performance of emergency core-cooling systems in LWRs.
A Monitoring Technique for Assessing Effects of Pollutants on Fish Activity
Authors: Fisher JW , Harrah CB , D'Allessandris R , Collins GT , Muhic LA , Umina JF , Blanchard RE , Klosterman EL
Published: March 2009

This study describes a method for monitoring the activity of aquatic organisms and reports preliminary results using hydrazine as the pollutant. Activity was detected using strain gages attached to immersed stainless steel paddles. Fish changing position or maintaining their position in the water column created water disturbances, and the relative amount of the water disturbance was used as an index of activity. Analog outputs from the gages were conditioned, amplified, recorded on frequency modulation (FM) magnetic tape, and processed off-line by computer. A computer program was developed that calculated mean absolute voltage levels of combined signals over 1-min intervals.

Preliminary information was obtained in four trials. Fish activity was monitored from 7 a.m. to 2 p.m. with three or four fish per trial. The activity of the control fish and that of the fish exposed to sublethal concentrations of hydrazine were compared by visual inspection of plots of mean 5-min voltage levels. The activity of the exposed fish was inconsistent between trials, variable, and usually not readily distinguishable from the corresponding control fish activity. Nevertheless, this strain gage-paddle apparatus detects fish activity and offers a new technique that has potential as a biological monitor of water and effluent quality.
Comparison of the Toxicities of Biphenyl, Monochlorobiphenyl, and 2,2′,4,4′-Tetrachlorobiphenyl to Fish and Daphnids
Authors: Dill DC , Mayes MA , Mendoza CG , Boggs GU , Emmitte JA
Published: March 2009

The static acute toxicities of biphenyl, 2-,3-, and 4-monochlorobiphenyl, and 2,2′,4,4′-tetrachlorobiphenyl(2,2′,4,4′-TCB) were determined for three freshwater fish species—bluegill (Lepomis macrochirus Rafinesque), rainbow trout (Salmo gairdneri Richardson) and fathead minnow (Pimephales promelas Rafinesque); one salt-water fish species—sheepshead minnow (Cyprinodon variegatus Lacepede); and one freshwater invertebrate—Daphnia magna Straus. The flow-through toxicities of 2-monochlorobiphenyl (2-MCB) and 2,2′,4,4′-TCB were determined for fathead minnows exposed for up to 32 days.

The static acute test data showed that the toxicities of the monochlorobiphenyls were intermediate between those of biphenyl and 2,2′,4,4′-TCB. There were only slight differences in the static acute median lethal concentrations (LC50S) among the individual monochlorobiphenyl isomers for any one particular species. Daphnids and rainbow trout (Salmo gairdneri) were more sensitive to all the tested compounds than the other species.

The flow-through 30-day LC50 values were 0.82 mg/litre (95 percent confidence interval, 0.73 to 0.94) for 2-MCB, and 0.029 mg/litre (95 percent confidence interval, 0.026 to 0.033) for 2,2′,4,4′-TCB, differing by a factor of 29-fold. In flow-through tests, exposure to both 2-MCB and 2,2′,4,4′-TCB resulted in observable toxic effects within 3 days of exposure. Melanization (body darkening) and loss of equilibrium (swimming disorientation) were the most consistently observed sublethal effects. The Day 3 median effective concentration (EC50) values for melanization were 1.36 mg/litre (95 percent confidence interval, 1.2 to 1.5) and 0.034 mg/litre (95 percent confidence interval, 0.03 to 0.039) for 2-MCB and 2,2′,4,4′-TCB, respectively. The Day 3 EC50 values for loss of equilibrium were 2.11 mg/litre (95 percent confidence interval, 1.93 to 2.37) and 0.054 mg/litre (95 percent confidence interval, 0.045 to 0.065) for 2-MCB and 2,2′,4,4′-TCB, respectively.

A no-observed-effect concentration (the highest concentration of test chemical that killed or affected no greater percentage of test organisms than did the control treatment) was not observed for 2,2′,4,4′-TCB within the range of concentrations set in this test. After 30 days, the fish exposed to the lowest concentration of 2,2′4,4′-TCB (0.014 mg/litre) had stopped feeding, were melanized, and the majority had lost their equilibrium. The two lowest exposure concentrations (0.30 and 0.38 mg/litre) of 2-MCB did not cause mortality or morbidity greater than in the controls. These data indicate that the no-observed-effect concentration for 2-MCB is less than 0.55 mg/litre (the third lowest concentration) and equal to or greater than 0.38 mg/litre.
Effects of Composition and Gage on the Microstructure of A533-B Steels
Authors: Smith RP , Swift RA
Published: March 2009

The effects of composition and gage on the microstructure of quenched and tempered A533-B steel were studied. The tests were performed on experimental heats of varying carbon contents. To fully assess the effects of minor variations in composition, the carbon equivalent was calculated and used in the data analysis. Controlled cooling was used to approximate gage effects, and the makeup of microstructure was studied by lineal analysis. Equations were generated from the experimental data to predict the microstructure as a function of carbon equivalent and cooling rate. These predictions are verified by comparing them with the microstructures of commercial heats.
Application of Superalloys in Internal Combustion Engine Exhaust Valves
Authors: Larson JM , Jenkins LF
Published: March 2009

The high-temperature and pressure conditions in some spark-ignited and heavy-duty diesel engines have necessitated the application of superalloy exhaust valve materials to meet long-term durability requirements. This penetration of superalloys is because of their excellent tensile, creep, and fatigue strengths, in combination with adequate oxidation resistance and forgeability. These attributes of the superalloys are discussed in conjunction with problems associated with manufacturing and alloy limitations. A strong emphasis is placed on field requirements versus material capabilities.
Steel Cord: Analysis of Used Truck Tires and Simulation of the Found Phenomena in Laboratory Experiments
Authors: de Jong CCJ
Published: March 2009

Analysis of used tires shows rust formation in the belt by penetration of water, deterioration of the adhesion of steel cord to rubber in the carcass, and also a loss of cord tenacity in the carcass. As a model for the belt, vulcanized T-test adhesion blocks with open cord ends were immersed in warm, salt water (90° C; 5 percent sodium chloride), after which the residual adhesion and rubber coverage were measured. The conclusion is that for a belt material, a good rubber penetration should be sought.

In the carcass the loss of adhesion seems to be the major problem. Thermal aging tests under different aging conditions have been carried out, and a rather large difference between the various products can be observed. Loss of cord tenacity, fretting, apparently is determined by the cord construction. As we have no reliable laboratory testing method available, fleet tests will be decisive in this respect.
Adhesive and Processing Concepts for Tire Reinforcing Materials
Authors: Bhakuni RS , Rye GW , Domchick SJ
Published: March 2009

A tire can be considered to be a composite of a reinforcing structure material and rubber compound. The reinforcing materials play a major role in tire performance. Several important contributing characteristics of the reinforcing materials are tensile, modulus, dimensional stability, fatigue, and adhesion under tire operating conditions. For optimum tire performance, adequate adhesion between the reinforcing material and the rubber compound is essential.

Choice of adhesive system(s) is dependent upon the nature of the substrates (fiber and rubber) to be bonded, as well as adhesive properties. Conventional resorcinol-formaldehyde-latex adhesion systems provide required adhesion for rayon, nylon, and fiberglass. Polyester and aramid require the use of reactive chemicals.

Time, temperature, and tension variables are required for processing organic fibers to tailor the fiber properties to a specific end use. Fabric properties such as modulus, shrinkage, and fatigue can be modified by varying processing conditions. Heat setting of the adhesive is also obtained during processing. Therefore, it is imperative that processing conditions be selected to achieve optimum fabric properties as well as adequate adhesion.

Processing and adhesive concepts used for organic fibers are reviewed. Effect of energy and environmental factors on the design and operation of the processing units is also discussed.
Study of Fiber Fracture and Interfacial Chemistry Using the Scanning Electron Microscope
Authors: Causa AG
Published: March 2009

The fracture surfaces of various tire cords (bare or embedded in rubber) were examined using scanning electron microscopy, to identify fractographic features characteristic of certain load history, testing mode, or fiber microstructure.

Axial splitting and fibrillation are the predominant morphological features in the fracture of aramid tire cord under either tensile or cyclic loading. Some additional topographic characteristics are also observed, for example, kink bands under MTS cyclic loading testing and a V-shaped fracture starting at the convex side of the bent fiber in the dynamic flex test.

Under severe dynamic loading, conventional polyester, namely, poly (ethylene terephthalate), shows some splintering, but the splits are much shorter than those noticed in aramid fiber. Under similar testing conditions, an experimental polyester, namely, poly (ethylene-2, 6-naphthalene dicarboxylate) can develop microstructural changes leading to an unusual conchoidal fracture.

The tensile fracture morphology of an experimental P-20 nylon monofil changed with changes in its tensile stress-strain behavior.

Energy dispersive electron microprobe analysis of nylon monofil-rubber interface suggests that sulfur, in the form of a sulfur-zinc complex, has diffused from the rubber phase to the fiber-rubber interface, to react with the adhesive dip.
Bias Passenger Tires: Effect of Construction on the Cord Deformation and Temperature Rise During Rolling
Authors: Prevorsek DC , Beringer CW , Kwon YD , Sharma RK
Published: March 2009

The effect of carcass construction on the cord deformation and temperature rise in tire during rolling is poorly understood. In order to establish the effects of changes in ply construction, number of plies, crown angle, and cord construction, we analyzed the cord deformation and temperature rise in a set of tires where these carcass construction characteristics were systematically varied. Other tire design variables were maintained constant including the polyethylene terephthalate yarn from which the cords were constructed. Four tires of each type were subjected to (a) an increasing speed-constant load test, and (b) an increasing load-constant speed test which were carried out on a laboratory testing wheel.

By means of an analytical procedure described in detail, we determined the temperature profiles in the tire cross section, the maximum temperature in tire, and the deformation amplitudes of the tire cords. The results of increasing speed and increasing load tests show that the tire which runs coolest at high speeds does not necessarily do so under high loads and vice versa. Cord deformation analysis showed that at high load the cords are subjected to significant compression which is detrimental because the fatigue resistance of polymeric cords in compression is very low. The cords removed from failed section of the tire (sidewall) show distinct kink bands which confirm the results of the deformation analysis.
Evaluation of C* for the Characterization of Creep-Crack-Growth Behavior in 304 Stainless Steel
Authors: Saxena A
Published: March 2009

An experimental program to characterize the creep-crack-growth behavior of 304 stainless steel at several temperatures was conducted. Crack growth rates, da/dt, obtained from center crack tension and compact type specimens were correlated by the energy rate line integral, C*. Experimental data indicate that minor differences in chemistry and microstructure do not significantly influence da/dt versus C* relationship. Also, in the range of 538 to 705°C (1000 to 1300°F), the da/dt versus C* relationship is not significantly affected by temperature. Simple analytical methods of estimating C* are also evaluated.
Stress Intensity Factor Due to Parallel Impact Loading of the Faces of a Crack
Authors: Abou-Sayed IS , Burgers P , Freund LB
Published: March 2009

The plane-strain response of an unbounded elastic body containing a semi-infinite crack subjected to a pair of concentrated forces suddenly applied to the crack faces at some distance from the crack tip is determined. The forces act on opposite faces of the crack, in the plane of the crack, and in the same direction. An exact solution is obtained within the framework of linear elastodynamics using a fundamental solution obtained from dynamic elastic dislocation theory. If the loading is quasi-statically applied, then the stress intensity factor is zero. However, if the loads are suddenly applied, the stress intensity factor varies with time, and, for a short time, it takes on very large values. As time becomes large compared to the transit time of a Rayleigh wave from the load point to the crack tip, the stress intensity factor decays to zero. The same procedure may be applied for growing cracks subjected to the same type of loading.
The Ubiquitous η Factor
Authors: Turner CE
Published: March 2009

The η factor relates G or J to elastic or plastic work per unit ligament area rather than to the differential of work per unit crack advance. In principle this adds nothing to the understanding of fracture, but in practice it provides convenient relationships for the analysis of several fracture problems. The η factor can be expressed in terms of compliance, load or displacement, instead of work, and can be determined experimentally or analytically. Expressions are given for a selection of elastic, nonlinear, and plastic cases in some of which deep and shallow notch behavior differs markedly.

Application to elastic and plastic test analyses, a J based design curve including an approximate treatment of residual stresses, and both elastic and plastic instability problems are outlined.
Fully Plastic Crack Solutions, Estimation Scheme, and Stability Analyses for the Compact Specimen
Authors: Kumar V , Shih CF
Published: March 2009

This paper presents the fully plastic solutions for the compact specimen and an estimation scheme that exploits these solutions to generate crack driving force diagrams under contained and large-scale plasticity conditions.

Plane-strain and plane-stress fully plastic solutions for compact specimens are obtained for a wide range of crack length to width ratios and for hardening exponent n of up to 20. The calculations are based on deformation plasticity theory and use the finite element method for incompressible deformation developed by Needleman and Shih. Relevant crack parameters like the J-integral, crack opening displacement, mouth opening displacement, and load-line displacement are appropriately normalized and tabulated. Simple formulas are given for estimating the relevant crack parameters from contained yielding to fully plastic situations using the elastic and the tabulated fully plastic solutions. The results thus obtained are compared with accurate finite element solutions for stationary and extending cracks based on flow theory of plasticity.

Crack driving forces in terms of the J-integral and crack opening displacement are computed for A533B compact specimens using the above estimation scheme. Assuming that the conditions for J-controlled growth are satisfied, the load-displacement behavior, stable crack extension, and the point of instability can be determined from the crack driving force diagrams if the material J-resistance curve is known. Comparisons of the predictions with actual test measurements for several different sized compact specimens show good agreement.
Mode I Crack Surface Displacements and Stress Intensity Factors for a Round Compact Specimen Subject to a Couple and Force
Authors: Gross B
Published: March 2009

Mode I displacement coefficients along the crack surface and stress intensity coefficients are presented for a radially cracked round compact specimen, treated as a plane elastostatic problem, subjected to two types of loading; a uniform tensile stress and a nominal bending stress distribution across the net section. By superposition the resultant displacement coefficient or the corresponding stress intensity coefficient can be obtained for any practical load location. Load line displacements and stress intensity coefficients are presented for A/D ratios ranging from 0.40 to 0.95, where A is the crack length measured from the crack mouth to the crack tip and D is the specimen diameter. Through a linear extrapolation procedure, crack mouth displacements are also obtained. Experimental evidence and comparisons with other investigators shows that the results of this study are valid over the range of A/D ratios analyzed for a practical pin loaded round compact specimen.
Development of Some Analytical Fracture Mechanics Models for Pipeline Girth Welds
Authors: de Wit R , Smith JH
Published: March 2009

Analytical models based on fracture mechanics technology are developed to establish predicted critical defect sizes for sharp, circumferential defects in pressurized pipe. These models are only intended to provide a theoretical basis for establishing predicted critical defect sizes. The general problem considered here is that of a surface-defect in a plate; that is, the flat plate analogy is used here for a pipeline. Failure is considered to occur when the ligament ruptures and provides a leakage path. The fracture mechanics model used, called the collapsed ligament model, is based on the work of Erdogan and Bakioglu, which is in turn based on the Dugdale model. The collapsed ligament model assumes plastic collapse in the depth direction but any fracture mechanics model in the length direction. To illustrate the use of these theoretical models for defects in pressurized pipes, curves are derived that show the predicted critical defect sizes. In these curves, the defect depth is plotted versus the defect length for a given set of material properties and applied stress. Defects having sizes that fall below this curve are not expected to extend. On the other hand, it is assumed that defects with sizes which fall above the curve will extend.
A Review of Texture and Texture Formation in Zircaloy Tubing
Authors: Tenckhoff E
Published: March 2009

In hexagonal close-packed metals, the development of a strong deformation texture is caused by the reduced availability of slip systems, their nonsymmetrical distribution, and the fact that twinning obeys strict, crystallographic orientation relationships. This in turn occurs characteristically according to the metal-specific structure parameters. In zirconium and Zircaloy, the development of the strong deformation texture is caused by the complicated interaction between slip and twinning. The factor governing the texture formation is the material flow, which for tube reductions is determined not only by the reduction in cross-section, but in addition by the reductions in wall thickness and diameter, and more specifically by the relative ratio of wall to diameter reduction. The knowledge gained from the tube reduction process can be used to explain the texture formation during sheet rolling and wire drawing. By knowing the relationship between texture formation and reduction parameters, it is possible to tailor the texture in Zircaloy tubing within the given limits, according to in-service requirements.
Burst Criterion of Zircaloy Fuel Claddings in a Loss-of-Coolant Accident
Authors: Erbacher FJ , Neitzel HJ , Rosinger H , Schmidt H , Wiehr K
Published: March 2009

A burst criterion model has been developed to calculate the burst data of Zircaloy claddings of a pressurized water reactor in a loss-of-coolant accident. It is assumed by this model that the time of burst is reached when the local stress equals the limiting burst stress. The burst stress is assumed to depend on the temperature and oxygen concentration of the Zircaloy.

With the histories of temperature and pressure known, the strain, stress, and oxygen content can be calculated by integration of the creep equation and correlation of the oxidation kinetics. Once the time of burst has been calculated, all burst data, that is, strain, stress, temperature, pressure, and oxygen content, are determined.

To verify the burst criterion model, single-rod transient burst tests in steam were performed using fuel rod simulators with indirect electric heating. The test parameters covered the following ranges: internal overpressure—10 to 140 bar, heating rate—1 to 30 K/s.

The burst temperatures and burst strains predicted by the burst criterion model are in good agreement with the test data.
Lifetime and Failure Strain Prediction for Material Subjected to Non-stationary Tensile Loading Conditions; Applications to Zircaloy-4
Authors: Boček M
Published: March 2009

The life fraction rule (LFR) is used to calculate the lifetime of materials subjected to stress and temperature ramp loading. The solutions for the individual nonstationary temperature and stress loading conditions can be applied to predict also the lifetime of structures loaded by superimposed ramps solely on the basis of normal “iso”-stress rupture data. The concept is applied to tensional stress and temperature cycling as well. Without any fitting procedure, the results of calculations are compared with those delivered by experiments performed on Zircaloy tension specimens. A variety of results from burst tests on Zircaloy cladding tubes conducted at different laboratories is compared as well. The agreement between calculations and experiments is in general surprisingly good. A modified Monkman-Grant relationship was applied to predict the failure strain of Zircaloy-4 subjected to tensile rupture test at load as well as at temperature ramp conditions, respectively. As compared with the peculiarities of the problem, the agreement between experiments and calculations is encouraging.
Flow Stress of Oxygen-Enriched Zircaloy-2 Between 1023 and 1873 K
Authors: Choubey R , Jonas JJ , Holt RA , Ells CE
Published: March 2009

The solute strengthening effect of oxygen in commercial-purity Zircaloy-2 was investigated over the temperature range 1023 to 1873 K, strain rate range 10−4 to 10−1s−1, and oxygen concentration range 1260 to 12 360 ppm. The flow parameters were determined in the fully α and fully β as well as (α + β) phase domains. In the two-phase region, the flow curves were characterized by significant yield drops as long as the β volume fraction was over about 50 percent. This effect is ascribed to the enrichment of the β-phase in the substitutional solutes iron and possibly chromium. The flow curves were otherwise normal. For the single-phase α and β structures, the yield and steady-state stresses obeyed the general relation σ = σ0 exp (kc), where σ0 and k are constants, and c represents the oxygen concentration (weight percent). The average values of kα and kβ were determined to be 0.57 ± 0.06 and 0.34 ± 0.10, respectively. The strain rate sensitivities fell in the following ranges, depending on the phases present: 0.15 to 0.20, 0.27 to 0.32, and 0.22 to 0.25 for the α, β, and (α + β) materials, respectively. The experimental activation energies decreased with stress in the ranges 450 to 330 kJ/mol (50 to 150 MPa) and 150 to 120 kJ/mol (1 to 5 MPa) for the α- and β-Zircaloy-2, respectively. The extrapolated zero stress values of Q were 530 and 170 kJ/mol, and are associated with the dominant dynamic recovery mechanism in each phase. The observed steady-state as well as yield stresses correspond closely to the rule-of-mixtures predictions but lie considerably above the values interpolated from the fully α-phase and fully β-phase. This is ascribed to the very powerful strengthening effect of oxygen on the α-phase when it is enriched during the formation of two phases from either single-phase region.
A Phenomenology of Room-Temperature Stress Relaxation in Cold-Rolled Copper Alloys
Authors: Parikh P , Shapiro E
Published: March 2009

Room-temperature tension stress relaxation tests on two copper alloys—CDA 510 and CDA 638—were conducted to determine if structural changes accompany stress relaxation. Changes in relaxation rate and in the shape of the tensile stress-strain curves as a result of stress relaxation were analyzed. The results indicate that structural changes during stress relaxation are brought about by a dislocation rearrangement process akin to recovery. Mobile dislocation density was found to change during testing, and work hardening did not contribute in decreasing the relaxation rate.
Stress Relaxation in Bending of AISI 301 Type Corrosion-Resistant Steel Strip
Authors: Fox A
Published: March 2009

Bending stress relaxation experiments were made on AISI 301 type corrosion-resistant steel strip. Test data obtained on standard, tapered cantilever beam test specimens at temperatures ranging from 23 to 93°C (73 to 200°F)2 over a time period of 20 000 h (2 years, 4 months) are compared with force relaxation data obtained on two complex clamp spring designs made from this material. Good correlation is obtained between the two sets of data. The effects of stress relief heat treatment and anisotropy on stress relaxation were also studied. Finally, the stress relaxation behavior of 301 type corrosion-resistant steel strip is compared to that of CA762 (12 percent nickel-silver). Both materials, if properly heat treated, retain better than 98 percent of the initial stress value after 20 000 h at 93°C (200°F) in the “elastic” range.
Stress Relaxation of Residual Metalworking Stresses
Authors: Geyling FT , Key PL
Published: March 2009

The stress relaxation behavior of 1010 and 1020 steels was evaluated for an application involving the relaxation of mandrel-drawn, roller-straightened tubes. The distortions observed in full-sized tubes after annealing at 260 and 482°C are reported, as well as measurements of the actual residual stress levels in such tubes. Bending stress relaxation experiments were performed on strip specimens removed from full-sized tubes at temperatures of 23, 149, and 260°C for up to 2000 h. The relaxation of metalworking stresses was modeled using small beams plastically deformed in four-point bending. The curvature relaxation of the beams after annealing at 260 and 482°C was measured. The results of this work indicate that less than 10 percent of the initial stresses due to metal forming should relax in tubes in service at room temperature.
Cyclic Relaxation Response Under Creep-Fatigue Conditions
Authors: Laflen JH , Jaske CE
Published: March 2009

The path and history dependence of elevated-temperature, time-dependent deformation response is investigated for three alloy steels—2¼Cr-1Mo steel, Type 304 stainless steel, and Type 316 stainless steel. The scope is limited to uniaxial loading under isothermal conditions. Relaxation data are evaluated for several prior cyclic (fatigue) loading histories. Results of these evaluations are compared with creep data for the same histories. To analyze stress relaxation data, creep equations are chosen and integrated using the time-hardening rule to develop closed-form expressions for relaxation response. Coefficients for these relaxation expressions are obtained using nonlinear least squares techniques. The appropriateness of using linearized transformations compared with direct nonlinear approaches is treated. For tensile hold-time creep-fatigue tests, the dependence of the coefficients on initial stress level is evaluated. Finally, the dramatic effects of both loading sequence and strain (both monotonic and cyclic) are discussed for one particular experimental case.
Stress Corrosion Cracking Test with Slow Strain Rate and Constant Current
Authors: Ondrejcin RS
Published: March 2009

A rapid electrochemical tension test was developed for evaluating stress corrosion crack initiation in carbon steel. Constant anodic current was imposed on smooth-bar tension specimens as the specimens were slowly strained to fracture at 1.3 × 10-6/s. Equivalent results were obtained for the following ductility properties measured: uniform elongation, total elongation, and reduction of area. Total elongation was chosen as the index for stress corrosion crack initiation. An equation was developed that allowed calculation of total elongation of specimens in electrolytes (test solutions) with composition ranges of 1.5 to 5.5 M nitrate, 0 to 3.5 M nitrite, and 0 to 5.0 M hydroxide, and a temperature range of 50 to 100°C. A minimum of 13 percent total elongation was selected to indicate the possible initiation of cracking in A 285-B steel alloy.

The test was used to evaluate relative aggressiveness of synthetic nuclear wastes on A 285-B carbon steel and the relative resistances of several steels to given solution compositions. Test results formed one of the bases for setting temperature and concentration limits for several ions in nuclear wastes that are stored in carbon steel tanks at the Savannah River Plant.
Slow Strain-Rate Stress Corrosion Testing of Aluminum Alloys
Authors: Ugiansky GM , Johnson CE , Thompson DS , Gillespie EH
Published: March 2009

The use of the slow strain-rate stress corrosion technique for testing aluminum alloys is discussed. This technique is compared to the more frequently used statically loaded, alternate immersion test technique used for evaluating the susceptibility of aluminum alloys to stress corrosion cracking (SCC). Aluminum alloys (2124 and 7075), each in three conditions with differing susceptibilities to SCC, were tested by both the statically loaded alternate immersion test and the slow strain-rate technique. The results of these tests are compared and the slow strain-rate test is shown to be a viable, rapid technique for determining the SCC susceptibility of aluminum alloys.