bluuebunny/crossref_metadata_2025 huggingface dataset:
Fatigue Behavior of 5Ni-Cr-Mo-V Steel Weldments Containing Fabrication Discontinuities
Authors: Gill SJ , Hauser JA , Crooker TW , Kruse BJ , Menon R , Lundin CD
Published: February 2009

Fabrication discontinuities in weldments pose a serious engineering problem for structural applications involving cyclic loading. Often, the discovery of fabrication discontinuities through nondestructive inspection can pose a dilemma: if not repaired, failure can result from crack initiation and growth; however, if improperly repaired, post-repair discontinuities of even greater severity may result. Thus, rational decision-making criteria are needed to assess the mechanical severity of actual fabrication defects in weldments. This study was undertaken to explore the applicability of linear elastic fracture mechanics to characterize the fatigue behavior of high-strength steel weldments containing lack-of-penetration (LOP) and slag/lack-of-fusion (S/LOF) discontinuities. Full penetration, double-V butt welds with reinforcements removed were tested under zero-to-tension axial loading. Various filler metals and welding techniques were used. Both sound welds and welds containing discontinuities were cycled to failure. Whenever possible, cycles to crack initiation were estimated by strain gage measurements. The fracture mechanics approach was successful in correlating the fatigue lifetimes of specimens containing single LOP discontinuities of varying size. However, the fatigue behavior of specimens containing multiple S/LOF discontinuities proved to be much more complex and difficult to analyze.
The Properties of Laser Annealed Dielectric Films
Authors: Stewart AF , Guenther AH , Domann FE
Published: February 2009

The annealing of dielectric thin film coatings has been explored in an attempt to identify the potential benefits of this method of post deposition treatment. Single layer coatings fabricated using several different deposition techniques were annealed and subsequently characterized. All properties so determined evidenced substantial changes as a result of the annealing process. Film microstructure, optical absorption levels, and laser damage thresholds varied considerably with annealing power levels. Although oven annealing is known to improve the performance of certain types of multilayer films, significant improvements were seen only in certain films over a limited range of annealing conditions. As a consequence of this, there were changes in other important optical properties, which will be discussed as well.
An Update of the Total-Strain Version of Strainrange Partitioning
Authors: Saltsman JF , Halford GR
Published: February 2009

An updated procedure has been developed for characterizing an alloy and predicting cyclic life by using the total-strain-range version of strainrange partitioning (TS-SRP). The principal feature of the update is a new procedure for determining the intercept of time-dependent elastic-strain-range-versus-cyclic-life lines. The procedure is based on an established relation between failure and the cyclic stress-strain response. The stress-strain response is characterized by empirical equations presented in this report. These equations were determined with the aid of a cyclic constitutive model. The procedures presented herein reduce the testing required to characterize an alloy. Failure testing is done only in the high-strain, short-life regime; cyclic stress-strain response is determined from tests conducted in both the high- and low-strain regimes. These tests are carried out to stability of the stress-strain hysteresis loop but not to failure. Thus both the time and costs required to characterize an alloy are greatly reduced. This procedure was evaluated and verified for two nickel-base superalloys, AF2-1DA and Inconel 718. The analyst can now predict cyclic life in the low-strain, long-life regime without having to conduct expensive failure tests in this regime or resort to questionable larger extrapolations.
Low-Frequency, High-Temperature Low Cycle Fatigue of 60Sn-40Pb Solder
Authors: Solomon HD
Published: February 2009

Solder thermal fatigue is a critical problem for large surface mounted leadless chip carriers. This fatigue results from the thermal mismatch between the Al2O3 chip carrier and the circuit board. This study was aimed at this problem, particularly the influence of time-dependent effects.

Isothermal tests were run on 0.15 to 0.23 mm (0.006 to 0.009 in.) solder layers tested in simple shear. It has been found, as expected, that solder exhibits Coffin-Manson low-cycle fatigue (LCF) behavior. The present study details the influence of cycling frequency on the fatigue life. Results were obtained on 60Sn-40Pb tested at 35 and 150°C. In agreement with previous studies made on Pb, it is shown that, at both temperatures, the fatigue life decreases as the frequency decreases, especially below 10−3 Hz. The fatigue life can be described by Coffin's frequency modified LCF law; i.e., (Nfνκ−1)αΔγp=θ

The data were also analyzed by means of strain range partitioning (SRP). It was found that this approach does not describe the data. A time-modified SRP approach, i.e., the time to failure tf is given by 1tf=fcctcc+νfppNpp was found to describe the data. The primary difference between this and the standard SRP approach is that with the time-modified SRP we assume that at low frequencies the time to failure tcc is a constant, not the number of cycles to failure Ncc. The correlation between this approach and the frequency-modified fatigue law is discussed. There is also a characterization of the different types of fatigue fracture surfaces that are observed.
Creep-Fatigue Behavior of Ni-Co-Cr-Al-Y Coated PWA 1480 Superalloy Single Crystals
Authors: Miner RV , Gayda J , Hebsur MG
Published: February 2009

Single-crystal specimens of a Ni-base superalloy, PWA 1480, with a low pressure plasma sprayed Ni-Co-Cr-Al-Y coating, were tested in various 0.1 Hz fatigue and creep-fatigue cycles at 1015 and 1050°C. Creep-fatigue tests of the cp, pc, and cc types were conducted with various constant total strain ranges employing creep dwells at various constant stresses. Considerable cyclic softening occurred as was evidenced particularly by rapidly increasing creep rates in the creep-fatigue tests. The cycle time in the creep-fatigue tests typically decreased by more than 80% at 0.5 Nf.

Though cyclic life did correlate with Δεin, a better correlation existed with Δσ both the fatigue and creep-fatigue tests, and poor correlations were observed with either σmax or the average cycle time. A model containing both Δσ and Δεin, Nf = αΔεβinΔσγ, with best fit values of α for each cycle type but the same values of β and γ, was found to provide good correlations. Lifelines were not greatly different among the cycle types, differing by only a factor of about three. The cp cycle life line was lowest for both test temperatures; however, among the other three cycle types there was no consistent ranking. For all test types, failure occurred predominately by multiple internal cracking originating at porosity. The strong correlation of life with Δσ may reflect a significant crack growth period in the life of the specimens. The lack of improvement in the models when average cycle time was considered reflects both that there is no large effect of strain rate on the damage mechanisms in the single-crystal material nor any environmental effect due to the internal cracking mode of failure.
A Maximum Stress Modified Life Equation on the Basis of a Fatigue-Creep Interaction Map
Authors: Chen GL , He QF , Gao L , Zhang SH
Published: February 2009

The effects of maximum stress on crack initiation and propagation, the fracture life, and the dynamic creep rate have been studied on the basis of a fatigue-creep interaction fracture map. A number of maximum stress modified equations have been deduced to describe the complete interaction behavior of a large ESR-Cast-to-Shape superalloy disk under a wide range of fatigue and creep stress combinations at a constant temperature. All the observed fracture lives fall within a range of a factor of two of fracture lives predicted by these equations.
Bithermal Fatigue: A Link Between Isothermal and Thermomechanical Fatigue
Authors: Halford GR , McGaw MA , Bill RC , Fanti PD
Published: February 2009

Many technologically important elevated temperature service cycles are non-isothermal. Nevertheless, major design codes rely on the most severe—usually the highest—temperature of an operational cycle as being the pertinent temperature upon which to base a design. Consequently, most high-temperature fatigue data for design have been generated under isothermal conditions. There is a growing awareness of the potential inadequacy of such a simplistic approach since many thermomechanical fatigue results have been found to exhibit considerably lower fatigue lives than would be expected on the basis of isothermal results at the maximum cycle temperature. Yet, variable-temperature, low-cycle fatigue tests are difficult to conduct and to interpret. The considerable gap between isothermal and thermomechanical fatigue technology can be bridged by an approach which retains the simplicity and ease of interpretation of isothermal fatigue, but captures many of the first order effects of the greater complexities involved in thermomechanical fatigue. We have developed a procedure for conducting what has been designated as bithermal fatigue experiments. In this procedure, the tensile and compressive halves of the cycle are conducted isothermally at two significantly different temperatures. The higher temperature is chosen to be in the time-dependent creep and oxidation prone regime and the lower temperature in the regime wherein time dependencies are minimized due to lack of thermal activation.

Interestingly, bithermal fatigue tests prior to those performed for this paper have been conducted in conjunction with the evaluation of the isothermal Strainrange Partitioning characteristics of high-temperature alloys, not with thermomechanical behavior per se. Nevertheless, the bithermal fatigue test may well be used as an alternative to thermomechanical cycling. In this paper, we place emphasis on using the bithermal testing concept as a link between isothermal and thermomechanical testing. New bithermal fatigue data for the nickel-base superalloy B1900 + Hf are presented herein.
Microstructural Aspects of Crack Initiation and Propagation in Extremely Low Cycle Fatigue
Authors: Kunio T , Shimizu M , Ohtani N , Abe T
Published: February 2009

A study has been made of the crack initiation and propagation in a low cycle fatigue of annealed carbon steel including extremely short fatigue life (Nf < 100), with an emphasis on the establishment of the relation between the microfracture behavior and the damage accumulation process depending on the plastic strain range, Δεp, as well as the mean strain, εm.

It was found that at the small Δεp the surface damage due to the initiation and propagation of surface microcracks is predominant, while at the very large Δεp giving fatigue life less than Nf = 10, the internal cracking originated from the fracture of a pearlite becomes a primary source of the damage which results in the reduction of the residual ductility, εFR. The transition from the surface damage to the internal one takes place when Δεp becomes so large that the pearlite cracking may start inside the material at each level of εm.

Good correlation was obtained between the reduction of residual ductility and the cracked pearlite ratio newly defined as a parameter for the evaluation of the internal microfracture behavior.
Damage Development During Multiaxial Fatigue of Unnotched and Notched Specimens
Authors: JW Fash , NJ Hurd , CT Hua , DF Socie
Published: February 2009

Life prediction methodologies based on low-cycle fatigue concepts are well established for the evaluation of component fatigue behavior. A critical assumption made in applying these concepts is that the fatigue damage process in the critical region of the component is similar to that which occurs in the smooth specimen used to characterize the material fatigue behavior. This approach has been verified experimentally for uniaxial loading conditions but methods for applying these concepts to multiaxial fatigue problems are not yet established.

Multiaxial fatigue theories that relate to the physical damage processes have shown the most promise for reliable design criteria. Two test programs are reported and discussed to further the understanding of the physical damage processes. First, thin-wall tube specimens have been tested in combined tension-torsion strain controlled loading. Second, notched shaft specimens, designed to represent a typical component, have been tested in combined moment control torsion-bending. For both test series, the development and growth of fatigue damage from initiation to failure is reported.

The thin-wall tube geometry is considered the smooth specimen for multi-axial fatigue. Tests on this geometry establish the expected damage behavior for the normalized SAE 1045 steel used in this investigation. Damage initiates on planes of maximum shear strain. At long lives a single crack develops and eventually grows perpendicular to the maximum principal strain. At short lives extensive damage develops on shear planes and failure occurs rapidly by a crack linking process. For equivalent local strain states similar behavior is expected for the notched shaft. However, initiation and early damage development in the notched shaft occurs in the circumferential direction of the notch, rather than on maximum shear planes. At long lives crack growth resulting in failure occurs on planes perpendicular to the maximum principal strain. At short lives extensive damage occurs in the notch and failure results by crack linking perpendicular to the primary bending stress.

Specimen geometry and stress gradients have a significant influence on damage development during multiaxial loading of components. The damage processes in the notched shaft are not represented by the thin-wall tube tests. Increased understanding of the detailed micromechanisms of fatigue represents an important direction for future improvements in life prediction methods.
Computer-Based Prediction of Cyclic Deformation and Fatigue Behavior
Authors: A Conle , TR Oxland , TH Topper
Published: February 2009

The paper briefly reviews the history of rheological spring-slider based, stress-strain models, and the early computerized versions used to simulate cyclic deformation and predict fatigue life. A set of rules is introduced which allows cycle by cycle simulation of the local stress-strain behavior at the root of a notched component subjected to any variable amplitude load history; predicts the crack initiation life; and, with two modifications to the notch analysis and the fatigue damage summation routines, models the local stress-strain behavior at the crack tip and resulting crack propagation rates. Supporting software that has resulted in practical applications for automotive design is discussed.
The Joint NASA/Geosat Test Case Project
Authors: Henderson FB , Settle M ,   American Association of Petroleum Geologists
Published: February 2009

The following material has been taken from a report on the Joint NASA/Geosat Test Case Project presented by F. B. Henderson1 at the symposium on which this publication is based. This report presents the findings of an Executive Summary of the project, authored by Mark Settle2; the full report of the Joint NASA/Geosat Test Case Project has been published by the American Association of Petroleum Geologists and is available from them.3 Permission to include this information has been granted by the American Association of Petroleum Geologists.
The Correlation of Low-Velocity Impact Resistance of Graphite-Fiber-Reinforced Composites with Matrix Properties
Authors: Bowles KJ
Published: February 2009

This paper summarizes basic studies that were conducted to correlate the impact resistance of graphite-fiber-reinforced composites with polymer matrix properties. Three crosslinked epoxy resins and a linear polysulfone were selected as composite matrices. As a group, these resins possess a significantly large range of mechanical properties. The mechanical properties of the resins and their respective composites were measured. Neat resin specimens and unidirectional and crossply composite specimens were impact-tested with an instrumented drop-weight tester. Impact resistances of the specimens were assessed on the basis of loading capability, energy absorption, and extent of damage.
Interlaminar Fracture Processes in Resin Matrix Composites Under Static and Fatigue Loading
Authors: Reddy AD , Rehfield LW , Weinstein F , Armanios EA
Published: February 2009

Both static and fatigue test results on a double-cracked-lap-shear specimen are presented under tensile and compressive loading. The specimen is made of AS4/3501-6 graphite/epoxy material with (±45,0,90) quasi-isotropic balanced symmetric layups in the lap and strap. In order to suppress the Mode I contribution in this specimen which exhibits mixed mode behavior in tensile loading, a normal force is applied close to the delamination front. The response due to this force is estimated from a sublaminate theory which accounts for transverse shear strain and normal and axial displacements. The normal force application is effective only when the delamination growth is dictated by mixed mode behavior. On the basis of the limited experimental data generated thus far, it seems that the static and fatigue delamination growth thresholds are indistinguishable, though cyclic tensile loading induces larger delamination growth. Considerable improvement in fracture behavior was exhibited by Mode I suppression under both tensile and fatigue loading. This partially explains the effectiveness of stitching and wrapping free edges in practical structures.
Strength of Woven-Fabric Composites with Drilled and Molded Holes
Authors: Yau S-S , Chou T-W
Published: February 2009

Two woven-fabric reinforced composite systems, one with PEEK matrix and the other with epoxy matrix, have been studied for their open-hole tensile and compressive strengths. The feasibility of enhancing open-hole strength of these composites through the design of micro-structure (molded hole) has been evaluated. Specimens containing molded holes had higher failure strength than those with drilled holes. The results also indicated that PEEK composite performed better than epoxy in preventing the degradation of both tensile and compressive strengths caused by a small circular hole. From the relative performance (normalized strength) viewpoint, PEEK composites with small holes exhibited higher tensile and compressive strengths than epoxy composites. However, for epoxy composites with molded holes, both normalized tensile and compressive strengths increased with hole size.
Electrochemical Theory of Galvanic Corrosion
Authors: Oldfield JW
Published: February 2009

Galvanic corrosion can be defined simply as that corrosion that occurs as a result of one metal being in electrical contact with another in a conducting corrosive environment. The corrosion is stimulated by the potential difference that exists between the two metals, the more noble material acting as a cathode where some oxidizing species is reduced, the more active metal, which corrodes, acting as the anode. To fully understand this process it is first necessary to understand the basic thermodynamics and kinetics of electrochemical reactions. These are considered with particular reference to exchange current densities and the factors that control them, linear and Tafel kinetics, concentration and mass transfer effects, and mixed potential theory. The practical side of galvanic corrosion and its relationship to electrochemical parameters is considered with particular reference to the most important cathodic processes, that is, oxygen reduction and hydrogen evolution, as they occur on engineering materials, for example, steel, stainless steel, copper base alloys, and so forth and to the general form of the anodic processes that occur. Finally the use of galvanic series as a predictive tool is discussed. In addition methods used to model galvanic situations with the aim of predicting corrosion are briefly mentioned and their advantages and limitations outlined.
The Role of Carbides in Performance of High-Alloy Bearing Steels
Authors: Pearson PK , Dickinson TW
Published: February 2009

Larger carbides inherent in high-alloy steels can initiate surface peeling failures and cause other raceway distress which affects bearing performance under thin lubrication film operating conditions. They can also contribute to the microstructural alteration in conventional subsurface rolling contact fatigue. Carburizing low-carbon, high-alloy bearing steel produces fine carbides comparable to low-alloy steels.
Rolling Contact Fatigue Life of Various Kinds of High-Hardness Steels and Influence of Material Factors on Rolling Contact Fatigue Life
Authors: Tsushima N , Maeda K , Nakashima H
Published: February 2009

The influence of material factors, such as types of steels, steelmaking process, cleanliness, fiber orientation, forging ratio, subzero treatment upon rolling contact fatigue life, was investigated for rolling bearing steels produced recently. Rolling contact fatigue life of recent steels which have high cleanliness has increased remarkably, and the influence of fiber orientation or subzero treatment upon rolling contact fatigue life is negligible, contrary to previous steels. Rolling contact fatigue life levels of each type of steels tested under three different test conditions were described. Depending on test conditions, their rolling contact fatigue strengths relative to others differed significantly in some cases.
Relationship of Melting Practice, Inclusion Type, and Size with Fatigue Resistance of Bearing Steels
Authors: Monnot J , Heritier B , Cogne JY
Published: February 2009

The evaluation of numerous steelmaking practices and the consequences of process modifications have been assessed by both fatigue tests and analysis of the inclusions at the origin of fracture. Increasing the average size of oxides causes the fatigue properties to deteriorate; the harmful influence of large globular Al2O3-CaO inclusions was confirmed, and the role of other types such as titanium nitrides, alumina, and certain sulfides was clarified. General criteria of total oxygen or total titanium content are not related to the fatigue performance of steels manufactured by different steelmaking processes and practices; within an individual practice, however, they may serve as useful indicators of fatigue life. The poor correlation between standard cleanliness ratings and fatigue performances has been explained. The application of these results to qualification procedures and quality-control methods are discussed. Currently, the best quality assurance can be obtained through the qualification of the steelmaking practice by fatigue tests and a strict control over the reliability of the process by measurements of the critical parameters.
Ladle Refining: An Integral Part of Bearing Steel Manufacture
Authors: Davies IG , Clarke MA , Dulieu D
Published: February 2009

The entire bearing steel output of Stocksbridge Engineering Steels is produced through a ladle furnace route which encompasses the major process elements necessary for the achievement of high product-cleanliness levels. The equipment and process routes involved are described, together with the vacuum arc remelting capability and its associated, high-integrity ultrasonic inspection unit. Improvements in steel cleanliness achievable with these manufacturing facilities have been assessed in terms of lower oxygen levels, better microcleanliness, and higher fatigue lives.
Microbial Enzyme Activities: Potential Use for Monitoring Decomposition Processes
Authors: Lanza GR , Allen Burton G , Dougherty JM
Published: February 2009

Decomposition processes in subsurface soils and aquatic sediments have proven difficult to monitor because of their complex interactions. This research describes the use of indigenous microbial enzyme activities (MEA) and surrogate parameters to monitor decomposition in oligotrophic subsurface soils (76 to 168 cm below the surface) and in aquatic sediments from a eutrophic reservoir.

Measurements of total plate counts (TPC) of aerobic and anaerobic bacteria, alkaline phosphatase activity (APA), and total gas production in anaerobic subsurface soil microcosms are reported. Microcosms with titanium3+ citrate (TC) as a redox buffer appeared to have statistically higher numbers of anaerobes and to have uniform APA and gas production with and without sucrose (amendment (nested ANOVA, P < 0.001). These studies indicate that subsurface soil microcosms have considerable potential for monitoring decomposition in vadose-zone soils.

Aquatic sediment microcosm studies revealed dose-response patterns in APA and dehydrogenase activity (DHA) after 96 h of exposure to As5+, Cd2+, Se4+, and Cu2+. The relative APA toxicities based on the calculated median effective concentration (EC50) levels were As5+ > Cu2+ > Cd2+ > Se4+. The relative DHA toxicities were the reverse: Se4+ > Cd2+ > Cu2+ > As5+. As5+ produced a nonlinear dose-response pattern in DHA, which prevented calculation of the EC50 value. As5+ also produced decreased DHA activity at 10 mg/L and apparent stimulation of DHA at high levels, that is, at 500 and 1000 mg/L. The proteolysis activity was highly variable (coefficient of variation greater than 40%) with five-day activities (percentage of controls) of 71 and 36% at 50 and 500-mg/L doses of As5+, and 96 and 9% at the same doses of Cu2+. No clear relationship was noted between MEA and either microbial density, as TPC, or acridine orange direct counts (AODC) with reduction of 2-iodophenyl-3-phenyl-5-nitrophenyl tetrazolium chloride (INT).

MEA appear useful in monitoring decomposition by indigenous microflora with and without toxicants. The MEA method detects sublethal indications of toxicant stress and can be correlated with other parameters commonly used to monitor ecosystem function.
Pollution-Induced Community Tolerance—A New Ecotoxicological Tool
Authors: Blanck H , Wängberg S-Å , Molander S
Published: February 2009

The authors hypothesize that pollution-induced community tolerance (PICT) is direct evidence that a community is disturbed by a pollutant and, furthermore, that the agent or agents causing the effects can be identified, because induced tolerance will be observed only for those compounds that have exerted selection pressure on the community. A similar concept has been formulated for population tolerance, but we suggest that the concept is more useful when applied at the community level. Our examination of some crucial points behind PICT, using arsenate and periphyton communities, demonstrates that (1) the tolerance increase can be determined in short-term photosynthesis experiments, (2) PICT correctly indicates changes in species composition and net production, and (3) the selection pressure of arsenate is specific—that is, a tolerance increase for one compound is not followed by co-tolerance to other compounds unless they are closely related chemically or in their mode of action. These results support the idea of using PICT as an ecotoxicological tool. If further corroborated, PICT can be applied in both laboratory and field studies. PICT might be used retrospecitively in the field to detect minor disturbances and to identify the causing agent. In a laboratory test system, PICT can be used to estimate the no-effect concentration for the community under study. The authors argue that test systems based on PICT will be sensitive and yield ecologically relevant information.
Measuring the Protective Insulation of Fabrics in Hot Surface Contact
Authors: Barker RL , Stamper SK , Shalev I
Published: February 2009

This research demonstrates procedures useful in measuring the ability of fabrics to block heat transfer when in contact with a hot surface. Experiments show how the temperature of the contacting surface, contact pressure, and fabric moisture content affect protective insulation in conductive tests. Single-layer fabrics made with flame-resistant cotton, rayon, and wool; glass fabrics, ceramic fabrics; and fabrics from aramids, novoloids, modacrylic, and stabilized acrylic fibers are evaluated. Statistical methods show the correlation between measured fabric properties and insulative values. An analytical model is developed that predicts a burn protection index from simple measurement of fabric thickness.
Residual Stress Alterations via Cold Rolling and Stretching of an Aluminum Alloy
Authors: Nickola WE
Published: February 2009

A solution heart-treated, cold-water quenched experimental aluminum alloy was subjected to two sequential mechanical treatments: an 11.5% reduction by cold rolling followed by a 1.25% cold stretching. The layer-removal and hole-drilling strain-gage methods of residual stress analysis were used, independently, to quantify both the changes in residual stresses produced by cold rolling and the reduction of stress produced by cold stretching. The initial residual stress condition, surface compression with mid-plane tension, was reversed by the cold rolling mechanical treatment to a condition of tensile surface stresses with mid-plane compression. Cold stretching produced a marked reduction in the magnitudes of the cold-rolling-induced residual stress. The independent experimental results of the layer-removal and hole-drilling strain-gage methods corroborated the effectiveness of stretching as a method for reducing residual stresses.
Measurement of Vibration-Induced Stress Relief in the Heavy Fabrication Industry
Authors: Ohol RD , Nagendra Kumar BV , Noras RA
Published: February 2009

The use of mechanical vibrations to relieve residual stresses in engineering components is increasing in use. Several vibratory conditioning systems are commercially available. When the technique was considered for treatment of fabricated structures at Larsen and Toubro Limited, residual stress measurements were made to determine the effectiveness of the treatment. A bedplate structure was vibrated by means of a commercially available variable-frequency vibrator. Residual stresses were measured near a weld location in the structure before and after treatment. Stress relief of about 30 to 57 % was noted. During the vibratory treatment, surface strains were monitored; at resonance the applied surface strain amplitude was measured to be about 600 microstrains. Subsequent to machining, the bedplate showed good stability of dimensions. A stainless steel bowl assembly was fabricated with carbon steel cooling jackets. The bowl contained heavy weldments but could not be thermally stress relieved prior to machining. The bowl was treated by vibrations and the close tolerances on the machined dimensions were satisfied. Both the components described have been installed on site and have maintained dimensional stability.
Closure Behavior of Small Cracks Under High Strain Fatigue Histories
Authors: McClung RC , Sehitoglu H
Published: February 2009

Specimens of a Society of Automotive Engineers (SAE) 1026 steel are subjected to constant amplitude and block loading fatigue histories. Nominal strain amplitudes range from 0.001 to 0.007. The behavior of small cracks (0.1 to 1.5 mm) initiated at very small (50 μm) electro-discharge machined edge notches is studied using a two-step replication technique that enables identification of the load level at which the crack tip first opens or closes. Replicas of the crack tip region are examined in the scanning electron microscope at magnifications up to ×4500. The normalized crack opening level is observed to decrease with increasing strain amplitude for constant amplitude histories. Results compare favorably with the modified Dugdale analysis of Newman. Crack closing levels also decrease with strain amplitude, and closing levels are significantly lower than opening levels at high strains. Correlations of constant amplitude crack growth rates based on estimates of the change in the J integral (ΔJ) or crack-tip opening displacement (ΔCTOD) are more successful when effective stress ranges are considered. Large strain excursions in simple block histories are observed to have a major impact on crack opening behavior during the smaller strain cycles. Typically the crack tip remains entirely open during subcycles immediately following a major cycle, causing significant crack growth acceleration. A simple model is used to correlate these variable amplitude crack growth rates.
Analysis of Crack Closure Under Plane Strain Conditions
Authors: Fleck NA , Newman JC
Published: February 2009

An elastic-perfectly plastic finite-element analysis has been conducted of plasticity-induced crack closure under plane strain conditions. At a load ratio R ( = Kmin/Kmax) of zero, crack closure was observed in a center-cracked panel but not in a bend specimen. Crack closure in the center-cracked panel occurred for a transient period of growth as the crack evolved from the state of a stationary crack to the steady state of a growing fatigue crack. The influence of specimen geometry upon closure response was rationalized in terms of the “T-stress.” This stress is the nonsingular constant second term in the near tip series expansion of the normal stress parallel to the crack plane. No closure was observed in the center-cracked panel for R ≧ 0.3. The crack opening response and plastic zone distribution of a growing fatigue crack were compared with those of a cyclically loaded stationary crack and a statically loaded tearing crack. Some of the features of the solution for the growing fatigue crack were similar to the solution for a stationary crack, while other features bore more resemblance to those of a tearing crack.
An Analytical Investigation of Plasticity Induced Closure Involving Short Cracks
Authors: Nicholas T , Palazotto AN , Bednarz E
Published: February 2009

Plasticity induced crack closure and its effect on the fatigue growth of short cracks is investigated numerically. A plane stress finite-element analysis is used to simulate a nonpropagating crack of length 65 μm in a single-edge-cracked specimen under two stress levels and two values of stress ratio R. A comparison of results is then made with a propagating crack of an initial length of 25 μm, which is allowed to grow to a final length of 65 μm. R values of 0.1 and −1.0 with stress levels of 60 and 90% of the yield stress for the material are considered. The plastic zone size for each case studied is approximately equal to the initial crack length, which provides conditions characteristic of short cracks.

It is observed that the displacement profile behind the crack tip is unrealistic unless cumulative history is considered. Crack closure develops as the crack propagates because of formation of a wake of residual deformation behind the crack tip. Closure develops rapidly for fully reversed loading but requires longer propagation distances to develop under R = 0.1 loading. Closure load/maximum load appears to eventually achieve a steady state value, which decreases with increasing stress or decreasing R. Numerically determined load-displacement data demonstrate that closure, as determined from deviations from linearity in such a plot, is easier to determine using displacements measured near the crack tip than from far-field displacements.
Analytical and Experimental Study of Crack Closure Behavior Based on an S-Shaped Unloading Curve
Authors: Chen D , Nisitani H
Published: February 2009

Based on the S-shaped unloading hysteresis curve a new method for determining the crack closure has been developed in which the plastic deformation near the crack tip is taken into consideration. The crack growth rate can be expressed uniquely by the effective stress intensity range, ΔKeffop = Kmax − Kop or ΔKeffcl = Kmax − Kcl, which is independent of the stress ratio and the loading history. The tip of a nonpropagating crack does not open even under the maximum tensile load during one loading cycle. The measured values of the crack opening ratios Uop(ΔKeffop/Kmax) and Ucl(ΔKeffcl/Kmax) of a steadily propagating crack are mainly controlled by Kmax and the stress ratio R.
A Simple Crack Closure Model for Predicting Fatigue Crack Growth Under Flight Simulation Loading
Authors: Aliaga D , Davy A , Schaff H
Published: February 2009

This paper presents a new approach for calculating the crack growth under spectrum loading in various different industrial applications. The paper includes (1) An original model based on the crack closure concept. The model combines a cycle by cycle analysis with a conservative cycle counting method similar to the “rain flow” one. A rule that fixes the crack tip opening point at every cycle to take into account the R ratio effect and the retardation effects is developed. (2) A method used for the determination of parameters. The model requires only three parameters that can be obtained with two simple crack growth tests. These two tests give both the values of parameters and the K range where the model is valid. The three parameters depend on the material and the specimen thickness. (3) Some industrial applications—the results show a good correlation between tests and calculations for several different materials. Furthermore, calculation with standard fatigue spectra (TWIST, MINITWIST, FALSTAFF) are given for a range of parameters.
Inadequacy of Property Specifications in ASTM C 270
Authors: Robinson GC , Brown RH
Published: February 2009

Bond strength and water leakage were determined for Types M, S, and N mortars joined to six different brick types. The air content, water retention, and flow rate were varied for each mortar-brick combination. It was found that air content, water retention, and compressive strength were inadequate indices of bond strength and water leakage. Yet these are the only properties specified in ASTM Specification for Mortar for Unit Masonry (C 270-84). A plea is made to add a bond strength requirement to present property requirements. The initial rate of absorption (IRA) of brick was found to be significant in predicting water leakage. Low IRA brick provided the highest probability of zero leakage.
The Effectiveness of Waterproofing Coatings, Surface Grouting, and Tuckpointing on a Specific Project
Authors: Coney WB , Stockbridge JG
Published: February 2009

Water leakage in a building gave the authors an opportunity to try a variety of widely used procedures to improve the watertightness of masonry walls.

The water permeance of the masonry walls in their original condition ranged from 11 to 60 L/h. Three types of clear waterproofing coatings, two types of surface grout, and conventional tuck-pointing were tested. Each procedure was applied to two wall areas. Water permeance tests were performed on each sample area in accordance with a field-modified version of ASTM Test Method for Water Permeance of Masonry (E 514). Sample areas were tested prior to repair, after repair, and in some cases after weathering through one winter.

The tests relate to one type of brick and mortar on one specific building. It would be unwise to extrapolate our findings to other buildings, but the results are interesting, and we believe they contribute to a growing wealth of experience.
Flow Pump Applications in Triaxial Testing
Authors: Olsen HW , Morin RH , Nichols RW
Published: February 2009

New testing capabilities can be added to a conventional triaxial system by using a commercially available flow pump to control the rate and amount of pore fluid movement to or from the ends of a test specimen. These capabilities include measurements of equipment compliance, constant-rate-of-deformation consolidation, very-small-strain compressibility, permeability, coefficient of consolidation, and strain-path control with arbitrary combinations of vertical and volumetric strain rates. These capabilities are of interest not only in themselves; they facilitate a testing strategy that reduces the amount of equipment and the number of replicate specimens needed to define the permeability, compressibility, and strength of a soil.
State-of-the-Art Paper: Triaxial Testing Methods for Soils
Authors: Lacasse S , Berre T
Published: February 2009

The paper presents the 1986 practice at the Norwegian Geotechnical Institute (NGI) for triaxial testing of soils that are fully saturated in situ. The test procedures for specimen mounting, saturation, consolidation, and static and cyclic shearing are outlined. Sample disturbance, specimen height, end friction, and anisotropic consolidation are discussed at length. Simplified procedures for anisotropic consolidation according to soil types are proposed. Sources of error are mentioned. A new method to measure the initial shear modulus in triaxial soil specimens is described.
Triaxial Permeability and Strength Testing of Contaminated Soils
Authors: Evans JC , Fang H-Y
Published: February 2009

As a consequence of hazardous and toxic waste disposal in the subsurface environment, triaxial permeability and strength tests on contaminated soils or with hazardous pore fluids must be conducted for extended time periods. The determination of hydraulic conductivity and shear strength of contaminated soils (or of uncontaminated soils using contaminated permeants) requires equipment and procedures different from those required for conventional triaxial permeability and strength testing.

The application of a back pressure works well to maintain saturation for short-term testing but may be insufficient for long-term testing. Procedure and equipment modifications are required to maintain saturation. Reservoir modifications may be made to dissolve contaminants at the solubility limit. Frequent replacement of influent permeant may maintain saturation and influent equilibrium. Equipment modifications may be required due to the chemical nature of the permeant and its incompatibility with the equipment. Long-term testing variables also include gradient, effective stress, particle migration, differential consolidation, diffusion through the membrane, and changes in water chemistry. Due to the need to permeate the specimen with at least one pore volume of permeant, gradients higher than those typically encountered in the field are used. This results in high effective stresses and differential consolidation. The volatile nature of certain permeants may cause diffusion through the membrane and changes in influent chemistry throughout the test.
State-of-the-Art Paper: Triaxial Testing of Saturated Cohesive Soils
Authors: Germaine JT , Ladd CC
Published: February 2009

The paper first covers common problems with testing equipment and procedures that cause errors in the measured properties of the soil specimen, with emphasis on consolidated-undrained (CU) and consolidated-drained (CD) triaxial tests. These problems are divided into three categories: errors that can be handled via appropriate corrections; errors that must be avoided; and potential errors that must be evaluated when selecting test procedures or interpreting measured data, the most important being the nonuniform stresses and strains caused by frictional end caps. The paper then assesses the use of triaxial testing in practice to predict undrained stability and deformations for saturated cohesive deposits. Based on considerations of strain rate effects, soil anisotropy, disturbance from tube sampling, and results from case histories of failures, the authors make four recommendations. 1. UU compression tests should not be used as the principal means of estimating in situ undrained strengths because the values can be either significantly too high or too low. 2. CIU compression tests have little value because the measured undrained strength will be unsafe for stability analyses, and the stress-strain data do not simulate in situ behavior. 3. Therefore, more reliance should be placed on CKoU compression and extension tests, which would be aided by the availability of more reliable and less expensive automated “stress path” triaxial cells. 4. Oedometer tests should always be conducted to ascertain the stress history of the deposit.
Observational Approach to Membrane and Area Corrections in Triaxial Tests
Authors: La Rochelle P , Leroueil S , Trak B , Blais-Leroux L , Tavenas F
Published: February 2009

The corrections to account for the changes in the cross-sectional area and for the restraint of the membrane during a triaxial test may vary considerably depending on the actual behavior of the soil specimen. This paper shows how observations and measures can lead to a choice of corrections which are in good agreement with the true behavior of the soil-membrane system both for bulging failures and for failures along a shear plane. The data obtained by compression tests on rubber and rigid dummies offer a valuable basis for quantifying the required area and membrane corrections. An example illustrates the merits of the proposed corrections and shows that different interpretations of the membrane correction may have an important implication on the effective stress cohesion intercept.
Trends in Atomization and Consolidation of Powders for High-Temperature Aerospace Materials
Authors: Lawley A
Published: February 2009

The status and emerging trends in the science and technology of power atomization and consolidation are reviewed in the context of high temperature aerospace materials. Commercial and near-commercial methods of powder production by atomization are assessed with respect to product characteristics and properties. Subsequent hot consolidation of the particulates to full density is then considered. Included in this review are state-of-the-art particle metallurgy superalloys and intermetallics for gas turbine disks, and aluminum and titanium alloys for aerospace structural components. Rapid solidification is inherent to particle production by atomization with concomitant attributes of alloying flexibility, increased solid solubility limits, fine-scale microstructures, and chemical homogeneity. This particle metallurgy-rapid solidification interface is discussed with respect to the potential for alloy development in high temperature applications. A redirection in powder processing is discerned with the focus on real-time monitoring and control.
Microstructure and Property Relationships in Oxide Dispersion Strengthened Alloys
Authors: Benn RC
Published: February 2009

Control of the thermomechanical processing parameters and recrystallization response of oxide dispersion strengthened (ODS) alloys is required to obtain the very high temperature properties unique to these materials. Useful strength is retained up to a relatively high fraction of the melting point due to the presence of fine uniformly dispersed, stable oxide particles. In this paper the factors affecting the development of microstructures to meet desired property goals will be discussed. The effects of powder structure, pre-cursor grain size, directional recrystallization, grain aspect ratio, γ/γ' phase proportions, dispersoid content, and texture on properties will be reviewed. Long-term stress and creep rupture data will be discussed in terms of the corresponding microstructural changes. Such studies offer an insight into our understanding of the complex and unusual creep behavior in certain ODS alloys. These and other structure-property relationships will be addressed which offer significant practical applications.
Stress Analysis Concepts for Adhesive Bonding of Aircraft Primary Structure
Authors: Krieger RB
Published: February 2009

This paper is a summation of the author's work towards creating valid stress analysis of adhesively bonded structure. The context is airframe construction, specifically metal to metal bonds, and excluding sandwich structure. A model joint is presented as being a basic representation of the problem. A linear formula is given to calculate the maximum stress on the joint. This is seen to be stiffness driven, hence the adhesive shear stiffness is indispensable. Two extensometers are described as follows: KGR-1 for adhesive shear stress versus strain, and KGR-2 for maximum adhesive strain on the model joint. An actual design is discussed, including adhesive selection by strain properties and adhesive quality control by adhesive stress versus strain data.