bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Extreme Aircraft Storage and Flight Environments on Graphite/Epoxy
Authors: Shyprykevich P , Wolter W
Published: March 2009

The ability of graphite/epoxy composites to absorb moisture from the environment and the consequent degradation of resin-dependent strength properties is well understood under conditions of constant temperature and humidity. However, if the environment consists of high humidity exposure with intermittent high temperature excursions, anomalous diffusion behavior occurs accompanied by further reductions in strength. This paper reports the results obtained from a test program in which graphite/epoxy specimens were exposed to a tropical environment representative of extreme aircraft runway storage and frequent 127°C temperature excursions of long duration representative of supersonic flights.

The tests were conducted in a specially developed apparatus which held specimens in chains of five each with accompanying travelers while exposing the specimens to prescribed daily environmental conditions. The duration of the real-time simulation test was 15 months. After various intervals of exposure, weight data were gathered using accompanying travelers, and residual static tests were performed at room temperature and 127°C. The test results for the extreme environment are compared to test results obtained for specimens exposed to the same flight profile, but temperate runway storage. The results indicate that the moisture gains of the extreme environment specimens are much greater than what is thought possible to be held by the resin. Since the static compressive strength is reduced with increases in moisture content, the degradation in compressive strength is greater than what was expected.

A semiempirical transport model based on Fickian diffusion and hygrothermal history dependent material properties was developed to account for changes in absorptivity characteristics as a function of glass transition temperature (Tg) exceedances. The test data for model development were obtained from an accelerated environment test which attempted to find economic alternatives to real-time exposure tests. The moisture predictions with the new model gave reasonable correlation with real-time test observations.
Influence of Quality Control Variables on Failure of Graphite/Epoxy Under Extreme Moisture Conditions
Authors: Clements LL , Lee PR
Published: March 2009

Tension tests on (0°)g T300/5208 graphite/epoxy composites were performed to determine the influence of various quality control variables on failure strength as a function of moisture and moderate temperatures. The extremely high- and low-moisture contents investigated were found to have less effect upon properties than did temperature or the quality control variables of specimen flaws and prepreg batch-to-batch variations. In particular, specimen flaws were found to reduce drastically the predicted strength of the composite, whereas specimens from different batches of prepreg displayed differences in strength as a function of temperature and extreme moisture exposure. The findings illustrate the need for careful specimen preparation, studies of flaw sensitivity, and careful quality control in any study of composite materials.
Dry Sliding Wear Studies of Nickel-Phosphorus and Chromium Coatings on 0–2 Tool Steel
Authors: Ruff AW , Lashmore DS
Published: March 2009

An investigation of dry sliding wear of electrodeposited nickel-phosphorus and chromium coatings on 0–2 tool steel against 52100 steel has been carried out. Wear and friction measurements were made in an argon atmosphere under dry sliding conditions at 0.2 m/s sliding speed and a load of 10 N. Among the materials studied, significant differences in wear rates were found that depended upon the nature of the coating. This work has determined the wear rates and has examined factors involved in the wear process for nickel-alloy coatings produced using electroless, direct-current, and pulsed-current plating, and chromium coatings. Thermal treatments after plating affected wear performance and indentation hardness. In all the nickel-alloy coatings, a laminar morphology was found that varied with the deposition method and was affected by thermal treatment. The wear test system used in this research was designed to examine flat specimens using a rotating 52100 steel ring as the counterface. The system was computer-interfaced and controlled, which permitted real-time measurements of wear and friction coefficient. These features made the system particularly suitable for studying the wear of thin metal coatings.
Effect of Fiber Systems on Stiffness Properties of Chopped Fiber Reinforced Sheet Molding Compound Composites
Authors: Chang DC
Published: March 2009

The effect of such fiber characteristics as weight content, modulus, and density on the stiffness properties of a chopped fiber reinforced sheet molding compound (SMC) composite are analytically evaluated. Comparisons are made among SMC composites reinforced by four commercially available fiber systems, glass, Kevlar, carbon, and high-modulus carbon.
Static and Fatigue Strength of Glass Chopped Strand Mat/Polyester Resin Laminates
Authors: Owen MJ
Published: March 2009

Chopped strand mat/polyester resin laminates are regarded as plane isotropic. However, under load the aligned fibers provide reinforcement, whereas the transverse fibers initiate progressive damage by filament debonding and resin cracking. This transverse damage rapidly involves the aligned fibers, particularly under repeated loading. Static and fatigue strength data have been developed for recognizable states of damage as well as final separation of the specimens. The effect of mean load on stress amplitude has been studied, together with cumulative damage and the effect of stress concentrators. Failure theories for biaxial stress conditions have been examined using thin-walled tubes. The biaxial tensile condition is particularly damaging.

There appear to be three main difficulties in applying conventional data to design. The S-N curves appear to be straight lines and there is difficulty in extrapolating to long lives; there is a marked adverse size effect on strength; and designing to avoid incipient damage at stress concentrators gives very uncompetitive designs. Fracture toughness and macroscopic crack growth studies appear to offer an alternative approach to the prediction of strength.
An Investigation of Stress-Dependent, Temperature-Dependent, and Time-Dependent Strains in Randomly Oriented Fiber Reinforced Composites
Authors: Caulfield EM
Published: March 2009

The effect on modulus change due to temperature on the stress-strain response of a glass fiber reinforced composite is discussed. Operationally simple constitutive equations for stress and strain computation while material temperature is transient are presented; these equations employ stress, internal specimen time, coefficient of thermal expansion, and measured material constants to determine the stress-strain response of fiberglass composites. Formulation of generalized constitutive equations to particular stress temperature histories is adduced and experimentally verified.
Mechanical Behavior of Three Sheet Molding Compounds
Authors: Walrath DE , Adams DF , Riegner DA , Sanders BA
Published: March 2009

A test program was conducted to measure various mechanical properties of three sheet molding compounds, SMC-R25, SMC-R30, and SMC-R65. Static tension tests were conducted in ambient and elevated temperature environments on both dry and moisture preconditioned specimens. Compression, shear, flexure, and impact tests were also conducted; these were performed at ambient temperatures on dry specimens.
Viscoelastic Characterization of a Random Fiber Composite Material Employing Micromechanics
Authors: Jerina KL , Schapery RA , Tung RW , Sanders BA
Published: March 2009

The mechanical creep and recovery behavior for uniaxial loading of a short glass-fiber reinforced polyester composite, SMC-R50, with random fiber orientation was investigated experimentally and theoretically. The strain at different stress levels and temperatures was measured during isothermal tests involving several loading-unloading cycles; each cycle consisted of a period of constant load and zero load. Repeatable creep and recovery response was observed only after several cycles; an accelerated mechanical conditioning method was used, in which the duration of each cycle was progressively increased. It is shown that the thermally complex, linear viscoelastic response of SMC-R50 in the mechanically conditioned state can be described by the time-dependent and temperature-dependent behavior of the matrix system and micromechanics calculations of the effective properties of the composite. The data analysis methods for parameters of the model are discussed and illustrated. Master curves for the matrix and for the in situ matrix, the matrix in the composite, were obtained and found to be virtually the same. In order to achieve this agreement it was necessary to use a micromechanics analysis in which the reinforcement is properly modeled as viscoelastic, orthotropic ribbons rather than isotropic, elastic fibers.
An Evaluation of Fretting at Small Slip Amplitudes
Authors: Kennedy P , Peterson MB , Stallings L
Published: March 2009

Fretting wear, produced by the twisting motion of a flat steel specimen against a fixed 12.7-mm steel ball, has been investigated in the limited microslip region ranging from 0.05 to 5.0 μm. The construction of the test rig and the type of fretting wear associated with this particular specimen configuration and motion are discussed. This discussion is exemplified by data obtained either with SAE 52100 steel or Hastelloy B alloy ball specimens in combination with SAE 1018 steel flat specimens. The first indication of metal oxidation normally associated with the onset of fretting occurred at a slip amplitude of about 0.075 μm. Severe damage was noted at 2.5 μm.
An Electrochemical Method for Investigating Corrosion in Rubbing Surfaces
Authors: Agarwala VS , Kim KY , Bhattacharyya S
Published: March 2009

An electrochemical polarization cell has been designed in which the test electrode is a rotating disk with a pin for the load contact to simulate a rubbing surface and a chamber for the electrolyte to create a diverse corrosive environment. Polarization measurements are performed on several bearing alloys with various corrosion properties (both the active and the passive type). The effects of the load, the speed, and the nature of the environment are studied to establish a correlation between corrosion, wear, and the nature of protective films formed on rubbing surfaces.
Thermodynamics of Corrosion for Geothermal Systems
Authors: Macdonald DD
Published: March 2009

Potential-pH diagrams, which summarize the thermodynamic properties of a system, are extensively used for interpreting the corrosion behavior of metals in condensed media. In this paper, E-pH diagrams are presented for iron and nickel in sulfide-containing high-salinity geothermal brine at 25°C and 250°C. The diagrams have been constructed on the assumption of a constant total sulfide constraint which leads to nonlinearity of the equilibrium relationships in potential-pH space. The application of these diagrams in the interpretation of chemical and corrosion processes in geothermal systems is briefly discussed.
Application of Linear Polarization Techniques to the Measurement of Corrosion Rates in Simulated Geothermal Brines
Authors: Danielson MJ
Published: March 2009

The linear polarization or polarization resistance (PR) technique was investigated in high and low salinity geothermal brine at 150 and 250°C on a lowcarbon steel (A53B) and a ferritic stainless steel (E-Brite 26-1) with and without the presence of oxygen in the brine. There was good agreement between the weight loss data and the linear polarization data. Oxygen generally accelerates the corrosion rate, and in the presence of oxygen the usual form of the polarization resistance equation must be replaced by the mass transfer equation to predict the correct corrosion rates. The results were compared with the corrosion rate determined by commercial PR instrumentation, and it was concluded that this instrumentation is adequate for field investigations in which oxygen is absent. However, when oxygen is present, the commercial instruments may underestimate the actual corrosion rate by a considerable amount.
Corrosion of Structural Steels in High-Salinity Geothermal Brine
Authors: Lee WT , Kramer D
Published: March 2009

In support of geothermal power plant development, Rockwell International's Energy Systems Group (ESG) has conducted extensive studies and tests on the behavior of materials in geothermal environments. The materials tested include both metallic and nonmetallic materials. This paper presents Rockwell's recent stress corrosion test data on structural steels and their weldments under uniaxial loading (stress, 80 percent of yield strength) in static Sinclair 4 geothermal brine at 204°C for 1700 h (10 weeks). The alloys tested were 26Cr-1Mo, 18Cr-2Mo, 9Cr-1Mo, and Type 316 stainless steel and their weldments. Under these test conditions, the following results were obtained: 1. In testing without air contamination: (a) Alloys 26Cr-1Mo, 18Cr-2Mo, and 9Cr-1Mo and their weldments were resistant to stress corrosion cracking; and (b) the average corrosion rates for the welded specimens made of 26Cr-1Mo, 18Cr-2Mo, and 9Cr-1Mo were 7.7 μm/year, 7.4 μm/year, and 18.2 μm/year, respectively. 2. In testing with air contamination: (a) the 18Cr-2Mo and 9Cr-1Mo ferritic steels were found to be resistant to stress corrosion cracking in air-contaminated brine; (b) Alloy 26Cr-1Mo and Type 316 stainless steel exhibited cracking typical of stress corrosion; and (c) the average corrosion rates were much higher than those obtained for the alloys without air contamination.

Results of the posttest mechanical properties testing and metallographic analysis are also presented.
Degradation of Elastomers in Geothermal Environments
Authors: Arnold C , Bieg KW , Coquat JA
Published: March 2009

The thermochemical degradation and sealing capability of various commercial O-rings in geothermal brine was evaluated at elevated temperatures and pressures to facilitate the selection of suitable elastomeric seals for the cable heads of geothermal logging tools. The extent of degradation was determined by measuring the change in tensile properties and glass transition temperatures that occurred as a result of exposure to brine at 548 K (275°C) and 34 MPa (5000 psi). The sealing capabilities of the O-rings in brine under these conditions were evaluated, using O-ring fixtures that simulated the cable head of a commercial logging tool. All of the elastomers became degraded to some extent. The elastomers that retained some measure of elasticity and also were not breached by brine in seal tests were the perfluoroelastomers, ethylenepropylene rubbers, and a peroxide-cured fluoroelastomer. Data obtained on the properties of aged specimens of these elastomers suggest that the most likely mode of degradation was chain scission. Nitrile rubber, silicone, and the peroxide-cured fluoroelastomer suffered a complete loss of elasticity and failed as seals. Data obtained on the properties of these elastomers indicate that extensive cross-linking took place. Polychloro-p-xylylene coatings were found to inhibit the rate of degradation in both brine and steam/sour gas environments.
Treatment Methods for Geothermal Brines
Authors: Phillips SL , Mathur AK , Garrison W
Published: March 2009

A survey is made of commercially available methods currently in use, as well as those which might be used, to prevent scaling and corrosion in geothermal brines. More emphasis is placed on scaling than on corrosion. Treatments are classified as inhibitors, alterants, and coagulants and are applied to control scaling and corrosion in fresh and waste geothermal brines. Recommendations for research in brine treatment are described.
Capabilities and Limitations of the Human Being as a Sensor
Authors: Leibowitz HW , Post RB
Published: March 2009

For many complex sensory and perceptual judgments, the human is indispensable. However, awareness of sources of human error is necessary in order to take advantage of the unique capabilities of human beings in sensory evaluation. In this context, the literature in experimental psychology which treats complex discriminations, illusions, expectancy, and response bias is discussed. Judicial and human engineering examples are presented, and literature sources are suggested.
Thermal Comfort in an Era of Energy Shortage
Authors: Goldman RF
Published: March 2009

Human thermal comfort rests upon the interaction between six key factors, four from the environment and two regulated by the individual and his job. The ambient environmental factors include air temperature, air motion, vapor pressure, and the mean radiant temperature of the surroundings, while the heat production and clothing of the human are the individual factors. A body of studies, largely encouraged by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers over the past decade, has led to the recognition of such trade-offs as that changing air motion by 0.18 m/s (35 ft/m) roughly corresponds to a change of 1°C (1.8°F) in comfort temperature; a change of 36 percent relative humidity similarly corresponds to a 1°C (1.8°F) change, as does a change of 1°C (1.8°F) in mean radiant temperature. These trade-offs only operate within finite limits. Greater potentials for enhancement of thermal comfort and energy conservation are associated with regulation of the two key factors controlled by the occupant of the space. Increasingly since the 1940s, we have been substituting machines for manual labor and are less active, yet a heat production increase of 50 W by the individual allows comfort temperature to drop by 3°C (5.4°F). The clothing worn by the individual has also been decreasing from the 1940s, when the average office business clothing provided 1.0 clo unit of thermal insulation; today, the average office wear provides less than 0.6 clo of insulation. The 0.4 clo difference in clothing insulation represents a change in the comfort temperature of about 2.2°C (4°F); that is from the 20°C (68°F) average acceptable low thermostat setting of our childhood to the 22.2°C (72°F) low accepted today (pre-OPEC). Looking to the future, economics alone forecasts a return to the heavier clothing of our grandparents (with 1.0 kg of clothing providing about 2.0 clo) as the most feasible offset to diminishing energy sources and their increasing costs.
Nondestructive and Semidestructive Methods for Residual Stress Measurement
Authors: Ruud CO
Published: March 2009

The effect of residual stresses on the fatigue life in metallic components has long been recognized. However, the most commonly employed methods for its measurement are destructive or at least partially so. This has led to an active interest in nondestructive methods for residual stress measurement. A review and evaluation has recently been published that describes the essence of the principles of nearly all the applied and proposed methods for nondestructive and semidestructive residual stress measurement. This review is summarized herein.
Effects of Residual Stress on Fatigue Crack Propagation
Authors: Nelson DV
Published: March 2009

Experimental results on the effects of compressive and tensile residual stresses on Mode I fatigue crack growth are briefly reviewed. Prediction methods that attempt to account for the observed effects are compared. Current limitations of the methods and their relative advantages and drawbacks for use in design analysis are discussed. The possible role of residual stress re-equilibration on growth behavior, caused by crack extension itself, is also discussed.
An Autoclave Expansion Test Method for Type N Hydrated Lime Intended for Use in Masonry Mortar
Authors: Davison JI
Published: March 2009

This paper reviews the attempts of ASTM Committee C-7 on Lime to develop an acceptable method of assessing the expansive potential of unhydrated MgO in Type N hydrated lime in masonry mortar. Autoclave expansion tests on bars of mortar containing hydrated lime, portland cement, and aggregate are rejected because of variable results. A new test method has been developed in which autoclave expansion values for pressed tablets are more consistent and are considered more realistic in terms of field performance.
Properties of Ready-Mixed Mortar
Authors: Hatzinikolas M , Longworth J , Warwaruk J
Published: March 2009

The introduction into North America of a chemical specifically designed to retard setting of cement and lime mortars has led the way to the introduction of ready-mixed mortars for the masonry industry. Such mortar is delivered to the job site ready for use in containers; it can be kept up to 48 h and used at any time during this period. Once the mortar is placed between masonry units, it sets like an ordinary mortar. In this paper, the properties of Type S ready-mixed mortar are experimentally evaluated. The effect of elapsed time from production to use on compressive strength and tensile and shear bond are studied. Tensile and shear bond are established by using a centrifugal force testing apparatus developed by the authors.
Grout for Reinforced Masonry
Authors: Isberner AW
Published: March 2009

Grout for reinforced masonry is reviewed through national product specifications and national masonry standards and codes. The role of grout and the factors affecting grout performance lead into a review of ASTM Specification for Mortar and Grout for Reinforced Masonry (C 476-71). A critical review of the specification shows that provisions for grout design, materials, and testing are deficient or nonexistent.

Past and present research on grout for reinforced masonry was reviewed and found deficient. Early research allowed measuring the bond of grout to reinforcing steel. Material changes warrant further testing. Recent grouted masonry testing shows grout compressive strength per se is a poor indicator of the interaction of grout in masonry. Research areas deemed essential include grout mix design, grout placement, and grout physical properties of equal or greater significance than compressive strength.
Effect of Strain Gradient on Tensile Strength of Concrete Blocks
Authors: Hamid AA , Drysdale RG
Published: March 2009

The tensile strength of the masonry unit is an important characteristic affecting the capacity of concrete block masonry under various loading conditions. Therefore it is necessary to have some measure of the tensile strength of the block that is both reliable and representative of its strength in the stress field associated with the loading conditions. The tensile strength was observed to vary considerably depending on the stress field created. From tests of concrete blocks under concentric axial tension, eccentric axial load, flexural tension, and splitting tension, it was shown that the tensile strength is significantly affected by the strain gradient. A linear relationship between the tensile strength and the strain gradient was proposed based on experimental data. It is suggested that this relationship could be used in the analysis of masonry assemblages where tension is the governing failure mode.
Shear Capacity of Reinforced Concrete Masonry Beams
Authors: Suter GT , Keller H
Published: March 2009

Extensive research is under way in many parts of the world to move masonry design from an allowable stress approach to a more consistent ultimate strength approach based on limit states criteria. At Carleton University over the past three years work towards limit states design has concentrated on concrete masonry flexural members such as lintel beams or slender shear walls. This paper deals with the ultimate strength and behavior of flexural members subjected to high shear forces. The experimental investigation, comprising over 70 concrete masonry beams, studied the effect of a number of key parameters on shear capacity. These parameters were the ratio of shear span to effective depth, joint spacing, type and slump of fill, effective depth, coursing of beams, and percentage of reinforcement. The results show that ultimate beam shear capacity of reinforced concrete masonry falls between the shear strengths of reinforced concrete and reinforced brick masonry. The results also show that the ratio of shear span to effective depth has the most pronounced effect on shear capacity and that, in general, composite behavior exists up to ultimate failure. No serviceability problem exists for deflections at working load levels.
Shelf Angle Component Considerations in Cavity Wall Construction
Authors: Parise CJ
Published: March 2009

An evaluation is made of the key features of shelf angle support and its related components with suggested alignment tolerances; shimming methods; flashing treatment to avoid corrosion, movement restricting mortar placement, and water permeance to the interior; and sealing of the joint between the flashing and masonry below.
Masonry Failure Investigations
Authors: Grimm CT
Published: March 2009

Masonry failure is inadequate performance of masonry. The purposes of a masonry failure investigation are to avoid greater failure, provide a basis for recommended remedial action, and settle a claim by negotiation, arbitration, administrative hearing, or litigation. Causes of failures, twelve aspects of investigation, and qualifications of the investigator are described. Initial problem definition, three types of site visits, inspection equipment needs, laboratory and field testing, interviews with construction craftsmen, document discovery, literature search, and research are discussed. Attributes of an expert witness are enumerated.
Lifetime Predictions and Cumulative Damage under High-Temperature Conditions
Authors: Chaboche JL
Published: March 2009

Lifetime of a structure is considered as the time needed to initiate some macroscopic crack, propagation of which is then calculated with the help of Fracture Mechanics concepts. The paper gives a brief discussion of the possibilities of lifetime parametric relations, based on strain variables, in the high-temperature range. Alternative approaches based on Continuous Damage Mechanics are then developed and discussed; they introduce internal damage variables, describing the progressive deterioration of the material before macroscopic crack initiation. A particular definition of damage, based on the effective stress concept, gives a macroscopic measure, which constitutes a guideline to the development of differential damage equations. Some examples show the possibilities of these approaches and deal with nonlinear cumulative effects (or sequence effects) and creep-fatigue interaction.
An Evaluation of Four Creep-Fatigue Models for a Nickel-Base Superalloy
Authors: Bernstein HL
Published: March 2009

Four models for the creep-fatigue interaction were evaluated for their ability to predict fatigue behavior at 650°C (1200°F) of thermomechanically processed René 95, a nickel-base superalloy used for turbine disks. These models are the Strain-range-Partitioning Model, the Frequency-Separation Model, the Frequency-Modified Damage Function, and the Damage-Rate Model. The data base was divided into baseline and verification tests. The correlations of the baseline tests, having the smallest standard deviation of 0.18, were by the Frequency-Separation Model and the Frequency-Modified Damage Function. The other two models had standard deviations greater than 0.22. These standard deviations correspond to worst correlations of 3.6 and over 5.0 times the observed life. The ratios of the observed to the predicted life of the verification tests ranged from 5.2 by the Frequency-Modified Damage Function to 18 by the Frequency-Separation Model. Each of the models consistently overpredicted or underpredicted the lives of certain types of tests in the data base. The models did not account for the mean stresses observed in the fatigue tests. A method based upon the stress versus minimum creep rate and the cyclic stress-strain curves is suggested to indicate whether an environmental-fatigue interaction or a creep-environmental-fatigue interaction is present. For René 95, this method indicates an environmental-fatigue interaction.
Cumulation of High-Temperature Low-Cycle Fatigue Damage in Two-Temperature Tests
Authors: Reuchet J , Réger M. , Rezai-Aria F , Rémy L
Published: March 2009

The cumulation of damage in high-temperature low-cycle fatigue is investigated for a cast cobalt-base superalloy MarM509, by using two-temperature testing. The two temperature levels [600 and 900°C (873 and 1173 K)] are taken as representative of low and high temperature behavior. At low temperatures crack initiation is crystallographic, while at high temperatures MC carbides are preferentially oxidized, giving rise to early initiation. Testing is conducted at a constant plastic strain range (Δεp/2 = 0.2 percent), and the remaining fatigue life is determined at one temperature after cycling at the other temperature for a definite amount of the expected life. The fatigue lives so obtained exhibit a large deviation from Miner's rule, particularly when the first cycling is carried out at the higher temperature. A detailed metallographic study using a replication technique shows that this deviation was related to the differences in the microcracking process at each temperature. More quantitatively, an estimate of the life to initiation is defined using a potential drop technique, which has shown that conservative predictions can be made from the application of Miner's rule to the initiation period.
Effect of Discontinuities on Low-Cycle Fatigue Behavior of NiMoV Rotor Forging Steel
Authors: Miller GA , Shih T-T , Reemsnyder HS , Swenson CE
Published: March 2009

An assessment of the effects of discontinuities and a gaseous environment on the low-cycle fatigue behavior of NiMoV generator rotor forging steel is presented. Discontinuities were positioned near the notch root in blunt-notch compact tension specimens machined from trepanned core bars. These specimens were subjected to cyclic loading with two maximum stress/yield stress ratios, 0.95 and 1.37. For tests conducted in air, discontinuities reduced the average crack initiation and propagation cycles by factors of as much as 6 and 1.5, respectively. The discontinuity influence was greater at the low cyclic load. Hydrogen reduced the cycles for crack propagation in discontinuity-free specimens by as much as a factor of 2 but had less influence on initiation. In specimens containing discontinuities, the crack propagation interval was shorter in hydrogen than in air, thus indicating the existence of a discontinuity-environment interaction. The variability in cycles to crack initiation from specimen to specimen was reduced by taking into account the initiation criterion as well as the discontinuity size and location with respect to the notch. The relation between discontinuities, cracks, and the service performance of generator rotors is discussed.
Prediction of Fatigue Life of Smooth Specimens of SG Iron by Using a Fracture Mechanics Approach
Authors: Starkey MS , Irving PE
Published: March 2009

Studies have been made of factors influencing fatigue life of smooth specimens of SG iron. It is shown that nodule size does not influence fatigue life, whereas pore size exerts a strong influence. Microcrack growth commenced from the pores within a few percent of the life of the specimen, for lives up to 105 reversals. Using an experimentally determined expression for microcrack growth, and approximating the defects to small cracks, fatigue lives for a variety of starting defect shapes and sizes have been calculated. Calculated lives agree with the experimentally determined lives within a factor of four. It is shown that fatigue life is predominantly controlled by pores (owing to their larger size and more rapid crack initiation) rather than by nodules. The variation in observed fatigue lives can be related to the variation in pore size within the iron.
Fatigue Behavior of Carbon Steel Components in High-Temperature Water Environments
Authors: Ranganath S , Kass JN , Heald JD
Published: March 2009

This paper describes the results of a combined experimental/analytical program on the fatigue initiation behavior of carbon steel components. Based on this study, several improvements in the fatigue analysis procedures are suggested: (1) a notch factor for local strains, (2) a mean stress factor, (3) improved fatigue strength reduction factor for butt welds, and (4) an environmental correction factor. It is shown that with the suggested fatigue analysis procedures, the fatigue design margins of the ASME Code will be maintained even with unusually severe local strain and mean stress.
Two Decades of Progress in the Assessment of Multiaxial Low-Cycle Fatigue Life
Authors: Brown MW , Miller KJ
Published: March 2009

A number of studies of the influence of multiaxial stresses and strains on low-cycle fatigue life have been published during the past 20 years. Development of correlations is reviewed and comparisons are made with high-cycle fatigue theories. It is recommended that the more advanced criteria should be incorporated in design procedures to replace the octahedral equivalent strain approach currently used.
Multiaxial Nonproportional Cyclic Deformation
Authors: McDowell DL , Socie DF , Lamba HS
Published: March 2009

A model employing a modified Mroz kinematic hardening rule with a Tresca yield surface is derived for a state of plane stress, combining together successful attributes of previous nonproportional incremental plasticity theories. Results from several nonproportional tests on oxygen-free high-conductivity copper are compared with computer predictions. Solution sensitivity to the particular cyclic stress-stain curve used, its piecewise linearization for the Mroz-type hardening rule, and the magnitude of the effective strain increment in the analysis is studied. A trade-off between the number of surfaces used in the Mroz-type rule and the effective strain increment size is observed for optimum solution with respect to convergence and speed.
Low-Cycle Fatigue under Biaxial Strain
Authors: Moguerou A , Vassal R , Vessiere G , Bahuaud J
Published: March 2009

The present work aims to obtain some information about the crack initiation criterion under biaxial low-cycle fatigue strain in phase or 180 deg out of phase. The investigation was carried out on A 316 stainless steel.

A servohydraulic experimental rig was developed for application of biaxial high-strain reversed cycles. The strains were controlled and the axes of principal strain were fixed during these tests. The test specimens are thin-walled tube on which we apply axial tension-compression and internal-external pressure difference by using two hydraulic servosystems. The results obtained for three different strain ratios are plotted as a function of half of the equivalent Tresca strain.

The Tresca criterion has been shown to be nonconservative for cases where the axes of principal strain rotate continuously, but in our tests we observe that torsion is less damaging than plane strain, which is less severe than tension. In other words the Tresca criterion is conservative, which is in agreement with the ASME code.

Finally, the fatigue crack growth is studied by a scanning electron microscope, and a propagation law is proposed.
Fatigue Life Evaluation of the A-7E Arresting Gear Hook Shank
Authors: White DJ , Ellis JR , Dumesnil CE , Gray TD
Published: March 2009

This paper describes a program conducted to develop criteria, based on test results, to safely extend the service life of the A-7E arresting gear hook shank. Fracture mechanics techniques provided a method for assessing the significance of proof testing and correlating proof loads with remaining life under operating loads. Additional tests were performed to validate the proof-test criteria.

The proof load developed in this program defined the maximum possible flaw size that could exist in the structure and provided data for establishing remaining life under operating loads. In addition, local yielding resulted in residual stresses that maximized crack growth retardation. As a result, an increase in fatigue life was produced by periodically inserting the proof load into the operating load spectrum. The primary impact of this program was to demonstrate that the proof test interval for the hook shank could be extended from 100 to 550 arrested landing cycles, and that the total service life could be extended from 500 to an indeterminate number of arrestments.
Materials-Data Needs for Fatigue Design of Pressure Vessel Systems
Authors: Jaske CE
Published: March 2009

Materials data are essential to the proper formulation of fatigue-design guidelines for pressure-vessel systems. These data are needed for two main reasons: (1) to develop and evaluate prediction methods used in fatigue-damage analysis and (2) to quantify the fatigue behavior of various alloys from which pressure vessels are fabricated. The former reason involves verification of models of the fatigue-damage process and must include both deformation and life prediction as well as demonstrating that the reference damage basis and damage rules are relevant to actual hardware. The latter reason relates to the establishment of an adequate data base and must incorporate material variability, environmental effects, and temperature effects.

In the above context, this paper addresses the data needs within the framework of the American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code. Low-temperature (negligible creep) and high-temperature (significant creep) regimes and crack-initiation and crack-propagation damage criteria are addressed. The background for existing fatigue-design guidelines of the ASME Code is briefly reviewed. Areas where fatigue-damage criteria need to be improved are creep/fatigue/environmental interaction at low strain ranges and long times, thermal-mechanical fatigue, multiaxial fatigue, and long-life fatigue. Existing guidelines for crack initiation are based mainly on strain cycling of uniaxially loaded specimens. There are some crack-initiation data on notch effects at low temperature, but more information is needed for high temperatures and welded components. Additionally, crack-initiation data are needed for multiaxial conditions, especially nonproportional loading, for thermal-mechanical cycling, and for high-cycle fatigue. To apply fatigue crack growth methodology, data on the size, shape, and distribution of initial flaws, methods of dealing with small cracks, and techniques for treating cracks in inelastic strain fields are required. With these requirements in mind, guidelines for the development of fatigue data are discussed, and recommended guidelines for data development are outlined.
Sea Dredged Sand for Concrete
Authors: Ramaswamy SD , Aziz MA , Murthy CK
Published: March 2009

A study was conducted by the authors to assess the possibility of using sea dredged sand from Singapore in concrete construction. Various combinations comprising normal sand, washed and unwashed sea dredged sand, potable water and seawater for mixing were considered. The properties of concrete made with washed and unwashed sea dredged sand by using potable and seawater for mixing were evaluated and compared with those determined for concrete made by using normal sand and potable water. The study has shown very encouraging results. The authors report the details of this study and offer arguments based on their research in favor of using sea dredged sand as aggregate in making concrete.
Corrosion Aggressivity of Atmospheres (Derivation and Classification)
Authors: Knotková-Čermáková D , Bartoň K
Published: March 2009

Corrosivity classification of the atmosphere is important for selecting optimal protective systems. This classification should be based on an understanding of the corrosion process together with reasonable engineering principles. By a critical analysis of the factors providing limits to the classification problem, several heretofore unresolved questions have been answered. These questions involve design factors, effects of different types of sheltering, fabrication effects, and the transformation of measured values to information which can be utilized technically. The Czechoslovakian system of standards covering this field is described and complemented by examples of specialized specifications for different industries. Questions for further research are proposed in order to further the classification efforts.
Advantages and Disadvantages of Using Invertebrates in Toxicity Testing
Authors: Maciorowski HD , Clarke RMV
Published: March 2009

Aquatic invertebrates should be included in toxicity tests to assess the hazards of toxicants because of their ecological and economic importance and their morphological, physiological, and ecological diversity. The practical advantages to the use of aquatic invertebrates in toxicity tests are the small size and short life cycles of most species, and the fact that it is possible to produce genetically uniform cultures of certain species and to standardize stocks of other species. Considerations in designing toxicity tests with aquatic invertebrates include the lack of culture methods for many species, the variation in sensitivity of aquatic invertebrates throughout the life cycle and with previous exposure to toxicants, and the difficulty in ascertaining death.

Most laboratory toxicity tests are measures of acute lethality obtained under controlled and constant conditions; the data are available for relatively few species and usually have been obtained using single species. Since such data do not reflect environmental conditions and the complexity of aquatic ecosystems, they are often of limited use in predicting effects of toxicants on aquatic ecosystems or on aquatic organisms valued by man. The utility of laboratory toxicity tests can be increased by the use of protocols that emphasize the most sensitive procedures, such as life-cycle studies or tests with model ecosystems, and such tests should include several aquatic invertebrates from different levels in the food chain, exhibiting different responses to toxicants, plus other aquatic organisms. Laboratory test conditions should reflect, as far as possible, the test organism's ecological requirements and should not constrain the test organism's natural behavior. Additional studies also are required to describe the effect of toxicants on natural aquatic ecosystems to ensure that toxicity tests do predict the actual effects of toxicants on aquatic ecosystems.
Daphnia Toxicity Tests
Authors: Buikema AL , Geiger JG , Lee DR
Published: March 2009

The purpose of this paper is to review the literature and to discuss the use of Daphnia in toxicity tests in the context of what we understand about its biology. For example, the effects of nutrition and starvation on the toxicant sensitivity of daphnids and on the test design were evaluated. Furthermore, the variation in data from chronic studies may be an artifact resulting from poor food quality, competition between the female and the offspring for food, testing a hard-water species in soft water, and other environmental parameters that have not been considered in the experimental design. Based on this review, research needs are briefly discussed. These include research on: foods, trace elements, and vitamins and their effects on reproduction; the development of culture health indexes; procedures for culture synchronization in order to produce large numbers of organisms of similar age or size; the stability of culture biomass; and temperature-light interactions on toxicant sensitivity. User groups have not been given the guidance they need in conducting toxicity tests, and one alternative guideline is suggested.
Toxicity of Chlorine-Produced Oxidants to Estuarine Copepods
Authors: Heinle DR , Beaven MS
Published: March 2009

The toxicity of chlorine to one estuarine copepod, Acartia tonsa, appeared to be a simple dose response, that is, doubling the times of exposure had the same effect on mortalities as doubling the concentration of the toxicant. Chlorine toxicity to at least one of the other species tested, Eurytemora affinis, did not follow a simple dose response; changing the times of exposure affected mortalities differently, depending on the dose concentration and the temperature. The relative toxicity of chlorine to the four species tested varied with time and temperature.
Formulating Acceptable Levels of Fire Risk
Authors: Cohn BM
Published: March 2009

Building codes and standards traditionally have set levels of performance based on the experienced judgment of the code writer. Occasionally, a certain level of safety is envisioned, but the objective tends to be expressed in imprecise terms, such as the “minimum” or “reasonable” level of safety. There is a need to set goals for fire safety in terms which can be measured so that they can be specified in building codes and standards. With such quantification, systematic fire safety analyses will be more meaningful.

A probabilistic approach can be used to set fire safety goals. Sufficient statistics are available today to set realistic goals, and the state of the art in fire safety systems analysis is sufficiently advanced to develop the methodology needed to calculate the failure probabilities for specific events. Such a methodology is described. It assigns probabilities to events associated with fire development in a building and allows these probabilities for a specific set of conditions to be related to the risk being evaluated (loss of life, property damage, business interruption, and so on). Statistics of industry experience help to relate the relative safety levels to the actual loss forecasts. Similar statistical analysis can be used to establish goals for fire safety in building codes, regulations, and standards.
Stresses in Piles
Authors: Davisson MT
Published: March 2009

Factors controlling the static, long-term, and dynamic structural strength of pile sections are delineated and discussed for timber, concrete, and steel piles. It is shown that current design stresses for steel and concrete are reasonable, but that timber design stresses equal or exceed long-term constant load ultimate stresses. Reasonable limits to dynamic driving stresses are recommended. Other sources of load and stress in piles are discussed along with pile strength reducing factors; many of these factors are not now considered in design. It is concluded that the normal current pile-to-soil factor of safety of 2.0 is reasonable, and that pile structural factors of safety should always exceed the pile-to-soil factor of safety. It is also concluded that normal factors of safety should not be lowered until the profession attains a higher level of competence in inspection of pile installation.
Special Requirements for Testing Auger-Placed Grout Piles
Authors: Lamb GE
Published: March 2009

Experience in testing auger-placed grout piles using ASTM Testing Piles Under Axial Compressive Load (D 1143) indicates that modification of the testing methods for this type of pile can improve interpretation of test data and provide greater confidence in the test results. Much of the load testing specified for auger-placed piles is intended to evaluate soil-pile interaction as with driven piles. Other load testing is often specified for auger-placed piles mainly to ensure continuity of the piles. This paper compares pile test procedures and results in a number of auger-placed pile installations and recommends modifications to the testing methods to take the special nature of these piles into account.