bluuebunny/crossref_metadata_2025 huggingface dataset:
A Model for Fatigue Crack Growth Delay Under Two-Level Block Loads
Authors: Adetifa OA , Gowda CVB , Topper TH
Published: March 2009

After reviewing previous attempts to quantify delay, a composite stress intensity parameter, (Kℓmax/Khmax) ∙ ΔKℓ; proposed to correlate the number of delay cycles in simple two-level variable-load amplitude tests for various combinations of stress levels. Its application is restricted in the present investigation to room temperature tests in an air environment. Delay (cycles) is defined herein as the period of apparent zero crack growth after the overload, and the stress intensity factors, Kℓmax and Khmax refer to the stress intensities accompanying the lower and higher load levels, respectively. It is hypothesized on the basis of experimental observations that material under different two-level block loading sequences, but having equal values of the parameter, will experience the same delay.

Good correlations for data on aluminum alloys, titanium alloys, and carbon steel taken from the work of several investigators are obtained using the parameter. An empirical model relating the delay to a power function of the parameter is suggested. Limitations of the model are pointed out and discussed. The engineering significances of the parameter with respect to the determination of crack propagation life and crack arrest conditions are discussed.
Experimental Results and a Hypothesis for Fatigue Crack Propagation Under Variable-Amplitude Loading
Authors: Jacoby GH , Nowack H , van Lipzig HTM
Published: March 2009

Many as yet inadequately-understood phenomena contribute to the sequence effects observed during fatigue crack propagation under variable-amplitude loading. In order to get an insight in the sequence effects, an extensive test program with 2024-T3 aluminum and Ti-6Al-4V sheet specimens with systematic variations in the loading conditions was performed, where special emphasis was placed on the accurate measurement of the crack propagation just after changes in the loading conditions. A hypothesis is proposed which explains the observed behavior. The hypothesis is based on deformation considerations within the plastic zones caused by the propagating crack.
Effect of Spectrum Type on Fatigue Crack Growth Life
Authors: Reiman JA , Landy MA , Kaplan MP
Published: March 2009

An ever-present problem in airplane design has been the accurate prediction of fatigue crack growth rate in new (never flown) aircraft. This problem has become even more critical in light of the new U. S. Air Force Damage Tolerance Requirements (MIL-A-83444). Briefly, the purpose of this specification is to protect flight structures from potentially deleterious defects which can be introduced into the structure during processing, manufacturing, etc. One of the most important things to consider when performing a damage tolerance analysis is the type of fatigue loading spectrum to be used. The purpose of this paper is to present a method of deriving a randomized flight-by-flight loading spectrum which can be used in preliminary design, and to show the effect on crack growth life of varying certain important parameters.

The random spectrum is derived using mission profiles, MIL-A-008866A or flight recorder exceedance data, design loads, and stress data. The mission mix and actual load sequence is determined randomly. The spectrum is then analyzed using a conventional crack growth computer program which calculates crack growth (a versus N) curves, and critical crack length.

The sensitivity of fatigue crack growth life to the variation in a number of parameters was investigated. These parameters include different random sequences and cycle counting methods. Random sequence effects include randomizing the loads on a mission segment or on a flight-by-flight basis. The results of this study are compared to the results obtained when the basic exceedance data was combined into a conventional block loading sequence.
Stress Spectrums for Short-Span Steel Bridges
Authors: Klippstein KH , Schilling CG
Published: March 2009

U. S. Steel's Research Laboratory is currently completing research on Project 12-12, sponsored by the National Cooperative Highway Research Program of the National Academy of Sciences, and entitled “Welded Steel Bridge Members Under Variable-Cycle Fatigue Loadings.” The main objectives of the program are to develop fatigue data on welded bridge members under variable-amplitude random-sequence stress cycles representative of stress spectrums such as occur in actual bridges and to develop an analytical method of predicting the fatigue behavior under variable-amplitude stress spectrums from constant-amplitude fatigue data.

This paper summarizes available field measurements of stresses in short-span bridges under traffic, and describes the stress spectrums that were developed from these measurements for use in the testing program. The available field data show that the passage of a vehicle over a bridge produces a single major stress cycle and superimposed vibrational stress cycles. In most types of bridges, the vibrational stresses are small enough to be neglected; however, the described method of deriving a simple equation for the stress spectrum is applicable to field data with or without vibrational stresses. The frequency of occurrence of stress cycles can be defined by a family of skewed Rayleigh probability-density curves; a particular curve from the family is defined by the modal value, Srm, and the dispersion, Srd. The major stress cycles (or stress ranges) are added to the dead-load stress, Smin, which remains essentially constant during the life of the bridge. In general, the stress cycles are arranged in random sequence. The stress spectrums used in the main test program, therefore, are defined by three parameters: Srm, Srd, and Smin. The fatigue-test control tapes corresponding to these spectrums record 500 individual loads that satisfy one of the family of Rayleigh probability-density curves and are arranged in a random sequence. The tape is continuously cycled throughout a fatigue test.
Fatigue Crack Growth Under Variable-Amplitude Loading in Various Bridge Steels
Authors: Barsom JM
Published: March 2009

Well-conceived procedures used to study the safety and reliability of structures recognize that the performance of a structure or a structural component is governed not only by material properties but also by the design, fabrication, inspection, erection, and use of the structure. These parameters govern the initiation of subcritical cracks and their propagation to critical dimensions, and therefore, determine the useful fatigue life of structural components subjected to load fluctuations.

This paper presents the results of the first phase of an investigation sponsored by the National Cooperative Highway Research Program, Project 12-14, to study “Subcritical Crack Growth in Steel Bridge Members.”

The paper describes the fatigue-crack-growth behavior of various bridge steels (A36, A588-A, A588-B, A514-B, A514-E, and A514-F) under variable-amplitude random-sequence stress spectra such as occur in actual bridges. The fatigue crack growth-rate data were obtained by using wedge-opening-loading specimens tested under variable-amplitude random-sequence load spectra that are represented by a Rayleigh distribution function.

The data obtained for these steels showed that the average fatigue crack growth rates, da/dN, under variable-amplitude random-sequence load fluctuation and under constant-amplitude load fluctuation agreed closely when da/dN was plotted as a function of the root-mean-square stress intensity factor range, ΔKrms. Thus, within the limits of the present investigation, the average fatigue crack-growth rates, da/dN, of various bridge steels subjected to variable-amplitude random-sequence load fluctuations, such as occur in actual bridges and to constant-amplitude load fluctuations, can be represented by the equation dadN=A(ΔKrms)n where ΔKrms is the root-mean-square stress intensity factor fluctuation, and A and n are material constants.
Equivalent Constant-Amplitude Concept for Crack Growth Under Spectrum Loading
Authors: Elber W
Published: March 2009

A concept based on the crack-closure phenomenon has been developed to replace random-load spectra with constant-amplitude loading in both analysis and tests. The maximum load and the crack-opening load in the constant-amplitude loading are chosen to be equal to those for the spectrum, so that both crack-growth mode and the crack length at failure are equivalent to those under the random-load spectra. The number of cycles of constant-amplitude loading is chosen so that the amount of crack growth is equal to that due to a given sequence or block of the random spectrum loading. The concept was tested experimentally after predicting the equivalent number of constant-amplitude cycles for six different random-load sequences. The agreement between predictions and test results was good.
Crack Growth in Ti-8Al-1Mo-1V with Real-Time and Accelerated Flight-by-Flight Loading
Authors: Imig LA
Published: March 2009

Crack growth in Ti-8Al-1Mo-1V was measured and calculated for real-time and accelerated simulations of supersonic airplane loading and heating. Crack-growth rates calculated on the assumption that an entire flight could be represented by a single cycle predicted the experimental rates poorly. Calculated crack-growth rates were slower than the experimental rates for all tests with flight-by-flight loading. For room-temperature accelerated tests, the calculated rates agreed well with the experimental rates; but the calculations became progressively less accurate for progressively more complex test conditions (tests that included elevated temperature). Calculations of crack growth using the crack-closure concept can probably be improved through study of crack-opening stresses using finite-element models that account for variable-amplitude loading, residual stresses, and temperature effects. The calculations of crack growth could also be improved through detailed studies of material properties and interactions among stress, temperature, and time as appropriate for the real-time operating conditions of a supersonic transport airplane.
Development and Application of Fatigue Data for Structural Steel Weldments
Authors: Reemsnyder HS
Published: March 2009

Traditionally, designs of and design specifications for welded joints have been based on test data. This paper describes axially loaded specimens containing butt and fillet welds, welded beams with typical beam details, and tubular welded-joint specimens, as well as the characteristics of the fatigue testing systems. Parameters affecting the fatigue resistance of structural steel weldments, for example, notches, residual stresses, and tensile strength, are reviewed in the light of test results. Fatigue design criteria for weldments are also discussed. Recent applications of linear elastic fracture mechanics and the concepts of strain-cycled fatigue to quantify the initiation and propagation of fatigue cracks in weldments are presented. Continued and refined application of these analytical techniques, quantification of environmental effects and of acceptance levels of internal discontinuities, and the application of load spectra to the design of weldments are recognized as research goals for the future.
Investigations of the Short Transverse Monotonic and Fatigue Strengths of Various Ship-Quality Steels
Authors: Pascoe KJ , Christopher PR
Published: March 2009

This paper summarizes a cooperative research program undertaken by the Naval Construction Research Establishment and the Department of Engineering of Cambridge University. It gives a tentative generalized picture of the monotonic and zero-to-tension low cycle fatigue (up to about 5000 cycles) behavior of cruciform welded ship quality plates in range 25 to 76 mm thick. The test results given were obtained over the past few years in a special rig capable of applying loads of 2 MN repeatedly. The rig was designed to accommodate short transverse specimens welded to loading ends so as to apply tension, combined tension and shear, or shear loading, the object being to develop short transverse failures (that is, failures associated with inclusions rolled into the plate). The results indicate the dependence of the short transverse properties on the method of loading, the strength of the steel, and the cleanness of the material. Although there were several forms of failure ranging from deep short transverse tears to failure in attachment welds, which occurred in some of the cleaner steels, it has been possible to rationalize the plots of stress range-logarithm of life to failure in the form of straight lines. This was particularly the case for the tension tests where there was less scatter than for the other two types of test.
Evaluation of Possible Life Improvement Methods for Aluminum-Zinc-Magnesium Fillet-Welded Details
Authors: Webber Don
Published: March 2009

Fillet welds have a low fatigue resistance compared with other types of weld detail, and it is difficult to design structures without using them. Results are presented of screening tests on methods of life improvement that have been applied successfully to fillet welds in steels under fluctuating tensile loading and are applicable to heat-treatable aluminum alloys. The welding method or shielding gas used did not affect fatigue life: (a) improvement of the weld profile during or after welding resulted in slightly increased lives; (b) local peening treatments had to be sufficiently intense to produce compressive residual stresses some depth below the surface to cause a worthwhile increase in life; and (c) specimen overloading treatments applied both initially and periodically generally were effective but the results for exclusion of the atmosphere by a conventional paint system were inconsistent. Results of tests on as-welded specimens, at various stress ratios which include compression in the loading cycle, corresponded with the results of treatments which include compressive residual stresses. The number of tests of each method was small, and further investigation of the more promising methods is recommended before they can be applied generally without qualifying tests.
Effect of Tungsten Inert Gas Dressing on Fatigue Performance and Hardness of Steel Weldments
Authors: Haagensen PJ
Published: March 2009

The fatigue performance of steel weldments can be improved significantly by remelting the toe region using standard tungsten inert gas (TIG) equipment. While the cost of TIG dressing is much lower than for comparable methods, the TIG process causes an increase in maximum hardness in the base metal adjacent to the remelted material. This may preclude the use of the TIG method for some applications. The hardness distribution in TIG dressed T- joints of St 52.3N and NVE 36 steel plates with thickness ranging from 20 to 38 mm was studied. A modified TIG dressing technique involving a second (tempering) run was developed, and a substantial reduction in maximum hardness as compared with conventional TIG dressing was obtained. Fatigue tests were performed on specimens with load carrying fillet welds in the as-welded and TIG-dressed conditions. The material was a quenched and tempered steel with a yield strength of 880 MN/mm2 (128 ksi). The increase in fatigue strength at the endurance limit due to TIG dressing amounted to approximately 65 percent.
Influence of Residual Stresses on Fatigue Crack Propagation in Electroslag Welds
Authors: Kapadia BM
Published: March 2009

An investigation of fatigue crack propagation behavior in air of as-deposited electroslag welds in two hot-rolled structural steels, prepared according to ASTM Specification for Structural Steel (A 36) and ASTM Specification for High-Strength Low-Alloy Structural Steel with 50 000 psi Minimum Yield Point to 4 in. Thick (Grade A) (A 588), has shown that the crack-growth rates (da/dN) in the welds were similar to or up to five times slower than the rate in the base steels. The retardation in crack-growth rate was observed to be substantially greater for crack propagation in the coarse-grained heat-affected-zone (HAZ) and bond-line regions than in the weld metal, but this was not consistently observed. Moreover, marked variations in the microstructure of the weld metal and HAZ did not significantly influence crack propagation. These crack-growth data for the weldments, described in an earlier paper, have been analyzed in the present paper in terms of residual stresses causing the observed retardation in crack-growth rate. In the present work, quantitative comparisons of the crack-growth behavior of the welds were based on a cyclic-life parameter (N1), which was defined as the number of cycles required for precracking the IT wedge-opening-loading (WOL) specimens to a total crack length of 2.54 cm (1 in.). This parameter gave results that were consistent with those based on incremental crack-growth (da/dN) data in the earlier paper. The observed retardation in crack-growth rate in the welds is attributed to compressive residual stresses introduced by welding. This effect was analyzed in the present paper in terms of a stress-intensity-range suppression concept, whereby the applied stress-intensity-factor range is decreased to some lower effective value. The results showed that the beneficial effect of compressive residual stresses on crack propagation appears to be of a variable nature and would diminish following a stress-relief heat treatment.
Conserve or Perish
Authors: Morgan JD
Published: March 2009

Mining and agriculture are the fundamental industries that convert natural resources into useable forms. The output of our mining, minerals, metal, mineral reclamation, and energy industries was valued at more than $175 billion in 1973. Over 4 billion tons—40 000 lb per person—of new mineral supplies are needed annually in our economy. Our use of energy is equivalent to 300 persons working around-the-clock for each one of our citizens. As we assess our current minerals posture we must keep in mind that our population is but 6 percent of the world's, and our land area but 6 percent of the world's. The other 94 percent of the people on earth also want significantly improved living standards, and world-wide demand for energy and minerals is rising rapidly. Despite our vast natural resources, we find increasing evidence that development of domestic resources is not keeping pace with domestic demand. Also, in the past 3 years our annual deficit in the mineral balance of trade has increased from only $6 billion in 1972 to $24 biilion in 1974. If this trend is not reversed it will approach $100 billion by the year 2000. We must begin now to conserve our natural resources or we may very well perish.
Demonstration of Systems for the Recovery of Materials and Energy from Solid Wastes
Authors: Skinner JH
Published: March 2009

This paper reviews the U.S. Environmental Protection Agency program to demonstrate new and innovative systems to recover materials and energy from municipal solid waste. The following resource recovery projects are described: (a) the use of shredded solid waste as a coal substitute, (b) the wet pulping of solid waste for materials recovery, (c) the pyrolysis of solid waste to produce a fuel oil, (d) the pyrolysis of solid waste for steam generation, (e) recovery of materials from incinerator residue, and (f) the use of shredded solid waste as a fuel in an oil-fired boiler.

The extent to which this program has been successful in promoting the implementation of resource recovery systems by state and local governments and by the private sector is discussed.
Deterrents to the Recycling of Ferrous Scrap from Urban Refuse
Authors: Kaplan RS
Published: March 2009

Although predictions indicate that the demand for ferrous scrap will shortly exceed supplies, resistance exits to the use of the ferrous fraction of urban refuse. Reasons for this resistance include lack of reliable supplies and the deleterious effects of contaminants, such as aluminum, copper, and tin. Aluminum can cause slag foaming in the BOF and pinholes in cast iron, while copper and tin promote a pearlitic structure thereby increasing ferrous alloy strength while decreasing ductility. With proper processing these problems can be overcome. Detinning of unburned cans removes the tin and aluminum (because they have not been incinerated they do not contain copper). Densification of the detinned steel produces a premium furnace feed. Alternatively, the unprocessed scrap can be used in amounts ranging up to 10 percent of the cast iron or steel produced.
Use of Aluminum Recovered from Municipal Solid Waste
Authors: Abbate ST
Published: March 2009

Recycling of aluminum from municipal refuse makes economic good sense and will be increasingly so due to the need to utilize resources and energy to the fullest.

The currect work of building a broad base of specifications, utilizing sample evaluations from many sources, will provide the municipal refuse processors with the technical criteria necessary to produce a product that is marketable.

Continued growth of the aluminum industry is contingent on metal supply from both primary and reclamation sources.

The durability of aluminum in its various produce forms, coupled with the growth factor, point to a strong demand on all of the suppliers of this metal. The reclamation industry, with its lower capital requirements per annual ton of output, relative to virgin aluminum, is a vital segment in the maintenance of an adequate supply of aluminum to the market. Two of the fastest growing aluminum markets today, containers and consumer products, can readily use the aluminum now being recovered and can potentially keep ahead of the supply. This helps assure market stability, and all that it means to the new industry of municipal refuse processing.
Problems and Potentials in Paper Recycling
Authors: Graminski EL
Published: March 2009

The U.S. consumed more than 60 million tons of paper and paperboard in 1973, about 20 percent of which was recycled. Steel is the only product that is consumed in larger quantities than paper. The principal disincentives for paper recycling are: (1) the ready availability of virgin wood fibers, (2) lack of research on recycling of paper, (3) economics favor the use of virgin fibers, and (4) contaminants in wastepaper present major problems in recycling. In spite of the large amount of wastepaper that is available, a wastepaper shortage occurred in 1973 and has continued into 1974 because of problems in collection, fluctuation of the wastepaper market, and lack of manufacturing capacity. It is anticipated that about 32 million tons of paper and paperboard are available for recycling. About 130 pulp mills with a capacity of 600 tons per day would be needed to recycle this amount of wastepaper, which would produce about 24 million tons of recycled paper. The capital for building these mills is not available, and if a large number of secondary fiber mills were built immediately, it would create chaos in the virgin fiber industry. It is suggested that market pulp mills, located in or near large municipalities, be erected as needed to provide the need for more market pulp. This secondary pulp would be available to many mills that now are not equipped to process wastepaper.
Report on the Ferrous Metals Workshop
Authors: Interrante CG
Published: March 2009

This paper reports the nontechnical and technical findings of the workshop on ferrous metals. Discussions include the technology for the use of municipal ferrous scrap, the economic outlook, and potential markets for ferrous waste. Eight recommendations are suggested for improved recovery of ferrous waste.
Report on the Nonferrous Metals Workshop
Authors: Newsome JW , Blayden LC
Published: March 2009

Three methods of separating nonferrous metals (principally aluminum) from municipal refuse were discussed and ranked with respect to several characteristics. There is no clearly “best” method today; much development is necessary. Seven action areas were defined to assist recycling of nonferrous metals.
Report on the Plastics Workshop
Authors: Ingle GW
Published: March 2009

The history of reclamation practices for plastics, textiles, and rubber is reviewed, with emphasis on more recent trends toward reduced levels of recovery. The causative factors are described—reduced selling prices for plastics (prior to 1974), technical problems arising from their very great variety of different materials (frequently incompatible), and the gradual disappearance of market systems for returning containers for consumer goods. A series of recommendations was developed to increase recovery. These include the creation of “return distribution” systems; provision for identifying—as by a simple code—the general compositions of polymeric materials to facilitate their separation where required; and the development of standards to identify reworkable combinations of plastics, textiles, and rubber recovered materials.
Neutron Radiography—An Overview
Authors: Barton JP
Published: March 2009

Neutron radiography is a nondestructive testing technique similar to X-radiography that can have important advantages in many specific situations. Large thicknesses of some dense metals can be penetrated; high sensitivity can be obtained for small details containing hydrogen and certain other light elements; materials of similar density can be contrasted: and highly radioactive objects can be neutron radiographed without interference from the gamma radiation. During the decade 1965 to 1975, industrial application of neutron radiography has grown rapidly due to (1) availability of suitable neutron sources, (2) advancements of the techniques, and (3) widening appreciation of the capabilities. Over 100 centers are now performing neutron radiography. Most use neutron beams of predominantly thermal energy from a nuclear reactor source, but there are examples of different techniques, some using different neutron energies, and some using accelerator or isotopic neutron sources.
Detection Systems for Neutron Radiography
Authors: Berger H
Published: March 2009

Image detection methods for neutron radiography are described and capabilities of the methods in terms of exposure requirements, spatial resolution, and contrast are given. Neutron energy ranges cold, thermal, epithermal, and fast are included, but emphasis is on detectors for thermal neutron images. Image methods include photographic film, real-time, track-etch, gas-cell, and thermoluminescent; major emphasis is on film techniques, both direct exposure and transfer.
Personnel Training and Certification
Authors: Whittemore WL
Published: March 2009

In order to make the full benefits of neutron radiography available in the nondestructive test (NDT) field, it has been necessary to formalize its application. A group under the Penetrating Radiation Committee of the American Society for Nondestructive Testing (ASNT) was organized to prepare a recommended practice for neutron radiography. The recommended practices require the establishment of an appropriate certification program. The requirements on the employer to establish and maintain a qualification and certification program are outlined. To conduct a program of nondestructive testing using neutron radiography requires the usual three levels of qualified and certified personnel. The program is administered by a Level III person. Routine exposure, reviews, and reporting of test results are the responsibilities of Level I and Level II personnel. The amount of training and nature of the required practical examination are also specified. The recommended practices document assures users that NDT work in the field of neutron radiography is performed by qualified personnel. Although no training courses are available to provide experience in the depth required by the recommended practices document, SNT-TC-1A, short courses are provided at a number of locations to familarize user's representatives with the interpretation of neutron radiographs and capabilities and limitations of the technique.
Use of a Low-Energy Van de Graaff Accelerator in Neutron Radiography of Encased Explosives
Authors: Cassidy JP
Published: March 2009

A neutron radiographic capability has been established at the Pantex ERDA Plant, Amarillo, Tex. A 3 MeV Van de Graaff generator has been installed and initial neutron radiographs have been made. The instrument has been employed to observe discontinuties of explosives encased in aluminum, lead, steel, Adiprene (a polyurethane), and combinations of these materials. These data demonstrate that the instrument possesses the capability of producing satisfactory neutron radiographs of many explosive-loaded components fabricated at Pantex Plant. Additional work will be performed to fully determine the capabilities of the 3 MeV Van de Graaff generator.
Neutron Radiography as an “In-Line” Product Acceptance Tool
Authors: Johnson PL
Published: March 2009

The background, advantages, and limitations of conventional X-ray or gamma-ray radiography in the acceptance inspection of electro-explosive components is examined. The development and application of neutron radiography proceeds and demonstrates the unique contribution of this technique toward higher product reliability when used as an “in-line” product acceptance tool.
Neutron Radiography to Detect Residual Core in Investment Cast Turbine Airfoils
Authors: Edenborough NB
Published: March 2009

Turbine engine blades and vanes for high-temperature applications are generally cooled by internal passages formed by the investment casting process. The cooling efficiency of the airfoil greatly depends on the removal of the ceramic core used to form the cooling passages. The detection of residual core in blades and vanes for operations above 2000 °F is difficult with standard visual and X-ray techniques because of the complexity of the cooling passages.

A technique using neutron radiography for improved residual core detection has been developed. The contrast is enhanced by “salting” the ceramic core base material with a 3 percent concentration of gadolinium oxide. Commercial reactors on the west coast are used for this production inspection. Turnaround time is approximately four days. Special fixtures were designed for both shipping and inspection.

Neutron radiography is now a standard production technique for high-temperature engines at Detroit Diesel Allison. Recently this inspection has been made a part of the vendor requirements.
Neutron Radiography of Nuclear Fuels at the Battelle Research Reactor
Authors: Kok KD
Published: March 2009

The development and use of neutron radiography at the Battelle Research Reactor (BRR) are described. Neutron radiography was conducted in the reactor pool and in a facility located outside the reactor pool. Neutron radiographs were obtained by both the direct and transfer techniques. In general, indium conversion screens were perferred. The handling techniques included still and scanning methods. The problems encountered while working in water are also described.

The uses of neutron radiographs of nuclear fuel materials include determination of the physical condition of the material, dimensional data, enrichment, and burn-up. Neutron radiographs were used to determine the location of PuO2 particles, less than 50 μm in size, in a UO2-PuO2 fuel material. Dimensions were determined to ± 50 μ when measurements were made. Neutron radiography was a useful tool in nuclear fuel development work at the BRR.
Detecting Cladding Leaks in Irradiated Fuel Elements by Neutron Radiography
Authors: Ross AM
Published: March 2009

At Chalk River, performance limits for advanced fuels are established by irradiating multi-element assemblies until one or more elements develop a cladding leak. Post-irradiation identification of leaky elements is assisted by thermal neutron radiography, because marked changes in radiographic appearance occur due to the effects of light water coolant entering during operation. Radiographs illustrating these changes are given for zirconium alloy-clad UO2 and uranium alloy fuel elements that had been irradiated in pressurized water to burnups up to 144 MWh/kg uranium.
Neutron Radiation in the Study of Soil and Rock
Authors: Lewis JT , Krinitzsky EL
Published: March 2009

X-radiography has been used at the Waterways Experiment Station for several years to study the internal characteristics of soils. These characteristics include density, secondary mineralizations, fracture planes, bedding, physical changes in the materials, and other features. Recently, a californium-252 facility was developed in order to complement the X-ray units through neutron radiation capabilities for scanning inhomogenieties in moisture and density. The neutron techniques include radiography, with detailed examination and quantification of film images, and neutron counting and monitoring through a tracking system. The gamma radiation from the californium-252 also will be utilized. These applications, and others which are under development, provide enhanced nondestructive laboratory assessments of earth materials for their engineering properties.
Measurement of Consistency of Pulpwood-Water Slurry Based on Neutron Slowing-Down and Diffusion
Authors: Hewitt JS , Slobodian VM
Published: March 2009

An analysis based on Fermi age approximation is used to explore the feasibility of using neutron migration phenomena to monitor the consistency, and possibly also the fiber density, in pulpwood-water slurries of the type processed in the pulp and paper industry. The results of preliminary experimental work are also presented. A significant experimental result is that the consistency of a 3 percent mixture of sulfite pulp in water may be monitored with a relative precision of ± 3 percent (or ±0.09 percentage points) in a sampling time of 1 s.
Miscellaneous Neutron Techniques
Authors: Iddings FA
Published: March 2009

Attention is brought to the less often uses of neutrons in the areas of neutron radiography, well logging, and neutron gaging. Emphasis on neutron radiography points toward the isotopic sensitivity of the method versus the classical bulk applications. Also recognized is the ability of neutron radiography to produce image changes that correspond to thickness and density changes obtained in photon radiography. Similarly, neutron gaging applications center on the measurement of water, oil, or plastics in industrial samples. Well logging extends the neutron gaging to encompass many neutron properties and reactions besides thermalization and capture. Neutron gaging also gives information on organic structure and concentrations of a variety of elements or specific compounds in selected matrices.
Application of the J-Integral to the Initiation of Crack Extension in a Titanium 6Al-4V Alloy
Authors: Yoder GR , Griffis CA
Published: March 2009

Tests were conducted to determine JIc from resistance curves of J versus crack extension, obtained from fatigue-precracked specimens of a titanium 6Al-4V alloy. Specimens of various geometries were employed, all in three-point bending. Crack extensions were delineated by heat tinting.

Results obtained with J computed from the equation, J = 2A/Bb, are compared to those obtained with the compliance technique, using the plane-stress solutions of Bucci et al. JIc results are compared with a valid KIc value for this material.

The range of ratios of crack length to specimen width (a/W) is explored over which the equation J = 2A/Bb applies. The decrease in crack extension at experimental limit load (Δapmax →Δac) is examined as the ratio of specimen thickness to uncracked ligament (B/b) is increased. Variation in JIc from specimens cut from different positions through the plate thickness is also examined.
Creep Cracking in 2219-T851 Plate at Elevated Temperatures
Authors: Kaufman JG , Bogardus KO , Mauney DA , Malcolm RC
Published: March 2009

The susceptibility of 2219 to time-dependent (creep) crack growth under sustained load has been evaluated, and, while no crack growth was observed at room temperature, it was observed at elevated temperatures at stress intensities (KIcc) well below KIc. It appears that creep cracking will take place at stress intensities down to a threshold, designated KIcct, about 40 percent of KIc at 300°F, and preliminary check tests suggest that similar behavior would be in evidence at 212 and 350°F in both the L-T and T-L orientations, though much work remains to be done in defining the extent of the temperature dependence. The rate of crack growth is controlled primarily by the instantaneous stress intensity factor and can be described by the following relationship: log da/dt = 0.085K - 4.14.
Effect of Specimen Size on Fracture Toughness of a Titanium Alloy
Authors: Munz D , Galda KH , Link F
Published: March 2009

This paper describes the effect of specimen size on slow crack growth and fracture toughness of the titanium alloy Ti-6A1-4V. The load versus crack opening displacement curve rises steeply after reaching the end of the linear part. Stable crack extension starts within the linear part of the P-v-curve. The crack growth resistance curve is independent of thickness B until KQ in the range 2 < B < 20 mm, leading to the conclusion that slow crack growth can occur in plane strain.

The secant method, leading to KQ at 2 percent crack extension, yields a specimen geometry dependent fracture toughness. KQ increases with width, W and is only slightly dependent on thickness, B.

The consequences of this behavior for fracture toughness determination in connection with the ASTM recommendation are discussed.
Running Ductile Fracture in a Pressurized Line Pipe
Authors: Freund LB , Parks DM , Rice JR
Published: March 2009

A model is developed for steady state propagation of a ductile crack in an initially pressurized line pipe. The analysis is directed toward the high toughness range of material behavior, for which extensive yielding occurs in the pipeline walls, and the material is represented as rigid-ideal plastic. Further, to obtain a tractable model, kinematical assumptions are made so that the deformation of the shell is expressed in terms of a single unknown function of position along the shell axis, which is determined in accordance with a variational statement of the equations of motion. Separation of material is represented by a Dugdale zone of localized yielding, in which a critical opening displacement is attained for fracture. With these approximations, the required decay length of the pressure distribution necessary to drive the crack, for a given exit plane pressure and decay shape, and the profile of the opened fracture, are estimated. Inertial effects due to the shell walls and backfill and crack arrest by branching are discussed, although it is pointed up that a complete analysis must await further progress on the fluid dynamics of gas escape through the fracture opening.
A Preliminary Study of Fatigue Crack Retardation Using Laser Interferometry to Measure Crack Surface Displacements
Authors: Sharpe WN , Grandt AF
Published: March 2009

A laser interferometry technique is described which is capable of resolving crack surface displacements to about 0.2 μm. The method provides continuous measurements of the free surface crack profile in metal specimens without being limited by rigid body displacements. Using the laser interferometry procedure to determine fatigue crack profiles in 2024-T851 aluminum specimens, it was possible to measure the load at which the crack faces completely separate. These opening loads were correlated with peak tensile overloads and subsequent crack retardation. These results are discussed in terms of the Elber concept of fatigue crack closure.
Cyclic Crack Growth Analysis for Notched Structures at Elevated Temperatures
Authors: Gamble RM , Paris PC
Published: March 2009

Linear elastic fracture mechanics analysis in conjunction with the appropriate experimental crack growth data were used to predict allowable thermal fatigue crack growth rates in gas turbine disks. The crack growth predictions made for the turbine disks compared favorably with subsequent service data.

Further studies were undertaken to determine the effect of geometric stress concentration on crack initiation and crack propagation. A general method of analysis was developed to provide simple approximations of the crack growth rates for cracks initiating at notches. The crack growth rates predicted by this method are in good agreement with both experimental laboratory specimen data and field service turbine disk data.
Application of Fracture Mechanics to the Calculation of Deflections in Stepped Structural Elements
Authors: Bluhm JI
Published: March 2009

Deflections of structural elements are determined frequently by using simple engineering strength of materials approaches. However, when geometric discontinuties are present, such approaches may lead to excessive errors in the predicted deflection. The present paper suggests a simple technique for refining these deflection predictions using available fracture mechanics data. Use of such techniques leads to predictions which do not differ significantly from “exact” solutions.
Water Vapor Diffusion and Frost in Porous Materials
Authors: Auracher H
Published: March 2009

It is well known that in porous materials moisture condensation occurs under certain physical conditions as a result of water vapor diffusion. In the temperature range below 0°C, ice crystals grow in the pores of the material generating a frost structure.

In pores of variable cross-sectional areas, frost growth is nonuniform. Therefore, a graphical procedure is developed with which the mass and location of frost growth in pores with any cross-sectional function can be determined. By this graphical procedure it is also possible to develop some general statements about the frost density distribution in pores at greater frost contents. It is shown, assuming a time-constant temperature function, that at the beginning of frost growth the diffusion flux in any cross section of the pore has a maximum value, and that it decreases continuously with increasing frost growth.

The results developed by means of the graphical procedure are confirmed by measurements made on capillaries with alternating cross-sectional areas. Afterwards, the diffusion and frost growth in pore-models of ordered sphere-packings are then investigated theoretically by the use of the same graphical procedure. It is shown, above all, that normally the frost growth does not begin at the smallest cross-sectional areas of the pores.

Finally, employing the graphical results, a method is developed through which the diffusion resistance factor of a porous material can be approximately calculated as a function of frost density.
Suitable Steady-State Methods for Measurement of Effective Thermal Conductivity in Rigid Insulations
Authors: Engelke WT
Published: March 2009

The ASTM Test for Thermal Conductivity of Materials by Means of the Guarded Hot Plate (C 177-63) is a recognized technique for measurement of thermal conductance of insulations. This method may not be the optimum choice due to temperature range, material availability, and other factors. This paper describes three other steady-state techniques that may be used. Two are modifications of the basic comparative rod apparatus, and the third is a modification of the radial inflow apparatus. The two modifications of the comparative rod apparatus are designed to minimize or monitor or both the axial heat bypass and radial heat interchange effects. The modification to the radial inflow apparatus converts a cylindrical specimen to obtain heat flows through a plane surface. These modifications represent an improvement in the state of the art.

The advantages of these procedures over the ASTM C 177-63 apparatus are smaller specimen size and wider temperature range. The disadvantages are that the precision and accuracy are not as good as that for the ASTM C 177-63 apparatus; however, an acceptable level for most engineering data may be obtained (< ±12 percent).

Data on various candidates for the reusable surface insulation of the shuttle were measured by these methods and are reported.
New Development in Design of Equipment for Measuring Thermal Conductivity and Heat Flow
Authors: Brendeng E , Frivik PE
Published: March 2009

Thermal conductivity of materials and heat transmission through complex structures have been studied for many years at the Refrigeration Division of the Trondheim University. This paper describes some of the recent developments in test equipment design and operation.

One fully-automatic guarded hot plate apparatus of the unidirectional type for high accuracy has been put in operation. It is capable of measuring at cold plate temperatures between 80 and 330 K at a typical difference of 10 K. A special method of accelerated balancing was introduced, and is used successfully for a number of different measuring purposes. A description of the control system is given.

The study of convection influence in full-size insulations is continued. A part of this work is done using a large-scale hot box apparatus with a special edge design. Further, a large guarded hot plate equipment with a measuring area of 2 by 3 m2 for the same purpose is under construction. The temperature range for this equipment has been extended to 90 K on the cold side with a view to the testing of liquid natural gas tank insulations.

Another important project concerns the heat transmission in natural ground freezing and the use of insulation for frost protection. Three guarded hot plate apparatus of special design are built to measure thermal conductivity of soils and building materials. These apparatus operate at cold plate temperatures between 200 and 320 K.

Some work on the development of transient methods for heat conductivity measurement is also recorded.
Some Recent Experimental Data on Glass Fiber Insulating Materials and Their Use for a Reliable Design of Insulations at Low Temperatures
Authors: Fournier D , Klarsfeld S
Published: March 2009

Reliable values of apparent thermal conductivity have been obtained under steady-state conditions and at low temperatures (between liquid nitrogen and room temperatures) together with air flow permeability (defined according to the Darcy law) of glass fiber materials. Both sets of data were used simultaneously to calculate actual conditions of heat transfer in porous media from recent theoretical analysis. It is shown by computation of filtration Rayleigh Number from these results that it is possible to design insulating structures to minimize convective heat transfer.