bluuebunny/crossref_metadata_2025 huggingface dataset:
Welding of Railroad Rails—A Literature and Industry Survey
Authors: Hauser D
Published: March 2009

Literature and industrial sources relating to methods for welding of railroad rails are surveyed. The welding processes included are thermite, flash, gas-pressure, and arc welding. Process and procedural descriptions, weldment properties, service performance in track, fabrication costs, and production rates are reviewed.
Development of High-Strength Alloyed Rail Steels Suitable for Heavy Duty Applications
Authors: Marich S , Curcio P
Published: March 2009

In the first section of the paper, a summary will be given of the various defects which can develop in rails subjected to high axle loads, such as corrugations, gross plastic deformation and abrasive wear of the railhead, checking and spalling, shelling and transverse defects.

The second section of the paper will cover in detail the developmental work on high-strength alloyed rail steels conducted at Broken Hill Proprietary Co. Ltd. Melbourne Research Laboratories. An essential part of the work has been the development of techniques for laboratory simulation of industrial rail production and on-site welding procedures. Various other material properties have also been used in assessing material types.

The major emphasis of the work has been directed to optimizing the mechanical properties of three rail steel types, namely: chromium-columbium-vanadium steels, chromium-vanadium steels, and chromium-molybdenum steels. Fully pearlitic steels exhibiting yield strengths greater than 900 MPa have been developed without adversely influencing other mechanical properties. The steels can be flash butt welded using modified procedures.
United Kingdom Development of Rails Rolled from Continuously Cast Blooms
Authors: Young JD
Published: March 2009

The development of rails rolled from continuously cast blooms in the United Kingdom is described. Results of pilot (seven tonne) trials which were begun in 1962 are discussed. These trials evolved into larger scale experiments and eventually into routine processing routes and rail evaluations.

Production experience, mechanical test data, and the results of metallurgical evaluations of rails from the new continuously cast steel process route in various steel grades totalling over 300 000 tonnes are given. Because of the new nature of the process, special testing of the rails was undertaken. These tests included fracture toughness testing and wear tests which compared rails from continuously cast blooms with conventional rails. A program to survey hydrogen content and the development of retarded bloom cooling for shatter crack prevention is reviewed.
The Effect of Grain Boundary Ferrite on Fatigue Crack Propagation in Pearlitic Rail Steels
Authors: Fowler GJ , Tetelman AS
Published: March 2009

Fatigue crack growth has been examined in pearlitic rail steels to determine the effect of grain boundary ferrite and nonmetallic inclusions on the rates of crack propagation under Mode I loading at ambient temperature. The influence of alternating and maximum stress intensity on fatigue crack propagation in these materials has also been evaluated. The data were obtained using single-edge notch specimens machined from the head of rails and the web of wheels. Cyclic loading was performed on a hydraulic test machine at various R ratios.

As the maximum stress intensity, Kmax approaches the fracture toughness, KIc, increasing amounts of cleavage bursts occur and the crack growth rates increase. In steels containing ferrite at the prior austenite grain boundary, the amount of cleavage is reduced at a given K level and the growth rates are reduced by an order of magnitude. The results show that traces of grain boundary ferrite (∼2 to 4 percent by volume) can reduce crack growth rates by a factor of two at intermediate and low growth rates (<5 × 10-4 mm/cycle).

Increasing R ratio is shown to increase significantly the fatigue crack growth rate near KIc, due to the increase in percent cleavage, while little effect of R ratio is observed at intermediate growth rates. Stable fatigue growth is observed above KIc and is explained in terms of a pop-in model.

Inclusions were observed occasionally at the initiation site of a stable cleavage burst that occurred during fatigue. However, nonmetallic inclusions do not significantly affect the fatigue crack growth rates in rail steels within the range of inclusion content from 0.097 to 0.318 percent by area.
Elastodynamic Effects on Crack Arrest
Authors: Achenbach JD , Tolikas PK
Published: March 2009

The first part of the paper is concerned with the elastodynamic stress field in the vicinity of a rapidly propagating crack tip. Elastodynamic stress intensity factors and their role in the fracture criterion of the balance of rates of energies are discussed. The remainder of the paper deals with the near-tip stress field for a sudden discontinuous change of the speed of a rapidly propagating crack tip, including the case that the crack tip is suddenly arrested. Analytical expressions are derived for the elastodynamic stress intensity factor, for the case that the crack-tip speed instantaneously changes from c1 to 2, where c2 < c1. Arrest, or continued propagation of a crack tip at a reduced speed are investigated on the basis of the fracture criterion of the balance of rates of energies.
A Suddenly Stopping Crack in an Infinite Strip Under Tearing Action
Authors: Nilsson F
Published: March 2009

A problem for a clamped infinite strip, with a semi-infinite running crack under antiplane strain is considered. It is assumed that the crack initially moves steadily and then suddenly stops. By appropriate superpositioning of certain elementary problems, the stress intensity factor after the arrest is determined. This is achieved by application of the Wiener-Hopf method, and the result is given in Laplace transformed form. The inversion is done by numerical methods. For the short-time behavior explicit relations are derived. These are also applicable to other problems. The nature of the solution is discussed, and a criterion for momentaneous arrest is given.
A Crack Arrest Measuring Procedure for KIm, KID, and KIa Properties
Authors: Hoagland RG , Rosenfield AR , Gehlen PC , Hahn GT
Published: March 2009

New developments are described which offer a flexible procedure for measuring the fracture resistance values, KIm, KID, and KIa which characterize the crack arrest behavior of materials. The procedure relies on a dynamically stiff, wedge-loading which limits dynamic energy exchanges between the test specimen and the testing machine. This makes it possible to interpret both small and large crack jumps without recourse to crack velocity measurements. The procedure is general and can be applied to ordinary and duplex rectangular and contoured double-cantilever-beam (DCB) specimens, and to compact and single-edge-notched (SEN) specimens when dynamic analyses for these shapes become available. The paper examines the virtues of the different specimen configurations, size and thickness requirements, possible upper and lower bounds on the size of the crack jump, and the problem of branching and side grooves. Measurements of specimen machine interactions are described. Results obtained for A533B steel with a series of rectangular DCB specimens illustrate the dependence of KIa on the size of the crack jump as well as the previously proposed relations between KIa and KIm or KID. The results confirm that the KIm (or KID) values obtained with the new procedure from static measurements of load point displacement and the crack length at arrest agree with values derived from crack velocity measurements. The experiments also illustrate that duplex DCB specimens with modest dimensions (400 by 140 by 50 mm) have the capacity for measuring KIm and KID values in excess of 150 MPa·m½.
Characteristics of a Run-Arrest Segment of Crack Extension
Authors: Crosley PB , Ripling EJ
Published: March 2009

During a run-arrest segment of crack extension, the crack attains a high velocity shortly after initiating, and then decelerates in a continuous fashion to arrest.

Strain measurements made during the event show that over the early portion of the jump when the crack velocity is high, the specimen behavior requires a dynamic analysis. During the later portions of the jump, when the velocity is low, the specimen behavior is described adequately by an analysis that assumes a condition of static equilibrium. Hence, if the dependence of a on K for the test material is described by a gamma (Γ) shaped curve, the crack arrest toughness, KIa, is an adequate description of KIm, the minimum toughness for stable crack extension.
Relation Between Crack Velocity and the Stress Intensity Factor in Birefringent Polymers
Authors: Kobayashi T , Dally JW
Published: March 2009

An experimental investigation of the dynamic behavior of crack propagation in two birefringent polymers, Homalite-100 and KTE epoxy, is described. Photoelastic isochromatic fringe patterns associated with cracks propagating in center-pin-loaded, eccentric-pin-loaded, and crack-line-loaded single-edged-notched (SEN) specimens were recorded with a high-speed multiple spark camera. Experimental data were obtained in several tests for each polymer to cover cracks propagating from arrest to terminal velocity.

The size and shape of the isochromatic fringe loops were used to determine the instantaneous values of the stress intensity function K by matching analytical and experimental results. Analytical results for the fringe loop were obtained by employing a Westergaard stress function of the form Z(z)=K2πz[1+β′(z∕a)] together with a superimposed σox=α′∕2πa. Approximately 14 000 computer generated fringe loops were compared to the experimentally generated results, and values of the fitting parameters K, α′, and β′ were obtained.

Results obtained for ˙a versus K show an inverted L relationship for both polymers. Crack propagation behavior with respect to the shape of ˙a versus K curve is discussed.
An Investigation of Axisymmetric Crack Propagation
Authors: Bergkvist H
Published: March 2009

The strain energy released per unit of axisymmetric crack surface created statically can be expressed in terms of a J-integral related quantity. However, as soon as the crack starts to move only part of this energy will actually flow to the dissipative regions close to the crack tip and the rest will be distributed as kinetic and potential energy in the structure.

An energy balance at the crack tip requires that the flow of energy to the tip must be equal to the fracture energy, which for a given material is supposed to be a specific function of the crack-tip velocity. The energy flow is assumed to be expressible as the static strain energy release rate, times a dynamic screening function, which depends on the instantaneous crack-tip velocity only.

By using numerically calculated values for the strain energy release rate, an analytic expression for the dynamic screening function, and experimentally found data for the velocity dependence of the fracture energy, it has been possible to predict the motion of a penny-shaped crack in a bar of polymethylmethacrylate under uniaxial tension. The agreement with a small series of simple experiments is good.
Flight Simulation Testing Equipment for Composite Material Systems
Authors: Haskins JF , Wilkins DJ , Stein BA
Published: March 2009

In this work, an attempt has been made to establish the time-temperature-stress characteristics and capabilities for several classes of high-temperature composite materials to determine their suitability for supersonic cruise aircraft applications. Five advanced composite materials are being evaluated: Rigidite 5505 boron epoxy, B/P105AC boron polyimide, Type A-S/3501 graphite epoxy, Type HT-S/710 graphite polyimide, and diffusion-bonded boron aluminum. The flight test simulator is capable of long-time automatic testing using random loading and realistic flight temperature profiles. Both load level and maximum temperature were adjusted to suit the particular capabilities of each composite system.

The design, construction, and checkout of the flight simulator is discussed. The test fixture consists of 10 load frames, 10 whiffletree assemblies, attachment hardware for 100 specimens, 100 removable specimen stiffener assemblies, 20 lamp rack assemblies, and lateral support hardware. A digital load programmer (MTS) and 10 Servac load magnitude controllers program and control the fatigue loading spectrum and synchronize the heating and cooling cycles. The load and temperature programming systems have a number of self-checking safety features which will automatically stop all test operations when preset levels are exceeded. The hydraulic pumping system, the heating and cooling systems, control console, and data recording system also are discussed.

Short-term tests were done at constant temperatures and accelerated load rates to establish the load ranges that are being used for the 50 000-h simulated flight testing. Typical results for the accelerated load-rate tests (short-term tests) are presented using a random load spectrum and wearout model. The long-term tests are underway, and 2500 h of simulated flight testing have been completed.
Effects of Thermal Cycling Environment on Graphite/Epoxy Composites
Authors: Camahort JL , Rennhack EH , Coons WC
Published: March 2009

Graphite/epoxy (Gr/E) composites have attractive properties—low density, high stiffness, and a low coefficient of thermal expansion (CTE)—that make them prime candidates for many spacecraft applications. The effects of a thermal cycling environment on the dimensional stability and microstructural integrity of Gr/E composites were evaluated. Severe microcracking was found in several high-modulus fiber (HMS)-reinforced 350°F-cure epoxy resin systems after exposure to 25 thermal cycles between the temperature of liquid nitrogen (−320°F) and that of boiling water (+212°F). A hybrid system combining Thornel-300 (T-300) fabric and HMS tape exhibited fewer microcracks, with the fabric acting as a crack stopper. Of the material systems investigated, a 250°F-cure system, HMS/CE 339, was found to be the most resistant to microcracking. The effects of thermal cycling on the microyield strength (MYS) and CTE of several near-zero expansion Gr/E composites were also studied.
Effect of Natural Weathering on the Mechanical Properties of Graphite/Epoxy Composite Materials
Authors: Trabocco RE , Stander M
Published: March 2009

Natural weathering of selected graphite/epoxy composite materials has been studied primarily by measuring specific mechanical properties. Commercially available composite prepregs were fabricated into panels and exposed at Warminster, Pa., and Canal Zone, Panama. Principal mechanical property determinations used to assess degradation were tension, compression, and short-beam shear tests.

The T400/2544 panels were severely degraded after 18 months of exposure in Panama. Pronounced warping, loose fibers, and loss of resin were very much evident with this material.

Shear data taken from Panama exposures showed that the use of a coating system on the panels was extremely beneficial.

To data, the Modulite 5208 composite system has shown the least variability in measured mechanical properties with increasing exposure time.
A New Cold-Process Roofing System: Description and Performance
Authors: Davis DA , Krenick MP
Published: March 2009

A new cold-process built-up roofing system is described and evaluated. The basic system consists of asphalt-saturated and coated membranes bonded together with fibrated asphalt cutback and surfaced with mineral granules. The adhesive is applied with mechanized spray equipment which improves labor productivity. Finished roof weight is 266 lb/100 ft2 (13.0 kg/m2). Performance is evaluated in terms of field experience over a five-year period and laboratory test procedures. Field data show resistance to blistering, slippage, shrinkage, and splitting. Laboratory data show tensile strength increases and flexibility decreases with age, as the adhesive cures. Level of volatiles after several years' exposure is significant, and it is concluded that they provide a long-term plasticizing effect.
Development of Asphalt-Polymer Waterproofing Systems
Authors: Edwards RM
Published: March 2009

For some years, the need for improved waterproofing materials and systems for flat-roof weatherproofing has been appreciated worldwide. Modern building requirements place very exacting demands on weatherproof coverings, and these demands are frequently beyond the limitations of the traditional materials used in the various countries. Two main areas of demand are in the plaza deck waterproofing and road bridge deck waterproofing. Both are areas of very heavy construction work where damage to the waterproofing membrane during building construction work is a major problem.

A new type of waterproofing material, which is virtually an asphalt-modified rubber sheet, has been developed, together with a range of different weatherproofing systems (both protected and unprotected systems) to meet the demands of plaza decks, bridge decks, and roof decks where high insulation and light-weight construction are major factors. The major factors concerned with the development of this asphalt-modified polymer sheeting are covered.
Thermal Warp—A Hypothesis for Built-Up Roofing Splitting Failures
Authors: Cash CG
Published: March 2009

A hypothesis is advanced to explain the splitting failure of bituminous built-up roofing membranes applied to roof insulation which is inadequately attached to the structural deck. A mathematical model is used to explore the relative splitting potential of membranes composed of organic and asbestos felts, and of coal tar pitch and asphalt bitumens, applied over five common types of roof insulation. The analyses show that splitting is probable in roofing systems composed of weak membranes over insulations with a high modulus of elasticity, and membranes applied to insulation above a critical thickness.
Fracture Toughness Concept
Authors: Sih GC
Published: March 2009

Fracture toughness is an indication of the resistance of a material to physical separation by a process of unstable macrocrack propagation. Conceptually, it is an intrinsic material parameter that should not vary with changes in specimen size, speed of loading, temperature, etc.

The brittle-ductile transition size effect of metal specimens is discussed using the strain energy density theory. By assuming that the critical strain energy factor, Scr, is a material constant, predictions on the fracture behavior of metals can be made. The following remarks are helpful toward defining a fracture toughness parameter associated with instability of the macrocrack:

1. The dominant or continuum crack travels in the elastic portion of the material always skirting around or bypassing the yield material and hence releases only elastic energy. 2. Stable macrocrack growth in metals is the result of necking or constraint from specimen boundary. 3. The last ligament of macrofracture will terminate in a plane inclined to the free surface or boundary of the specimen.
Microstructure and Toughness of High-Strength Aluminum Alloys
Authors: Staley JT
Published: March 2009

The toughness of wrought, high-strength aluminum alloys is related to the amount, type, and morphology of coarse (larger than about 1 μm) constituent particles, intermediate size (about 0.02 to 0.5 µm) dispersoids, and fine (down to about 0.001 µm) precipitates. High toughness can be attained by minimizing the size and volume fraction of constituent particles, increasing the interdispersoid distance, refining the intragranular precipitate in 2XXX alloys, and controlling the intergranular precipitate in 7XXX alloys. For highest toughness in 7XXX alloy products where low residual stress is desired, rapid quenching followed by the minimum amount of cold work required for mechanical stress relief is recommended.
Keynote Address—Reflections on Pickle-Jar Ecology
Authors: Doudoroff P
Published: March 2009

Biological tests of effluent toxicity and appropriate formulas for application of toxicity bioassay results should be relied upon in regulating discharges of toxic effluents whenever reliance on chemical tests and chemical criteria or standards of water quality cannot be shown to be more reasonable. Some recent, pertinent recommendations made by biologists (committees) are ambiguous if not entirely inconsistent with this rule. They provide no clear guidelines for equitable regulatory action to be taken, or choice of requirements to be enforced, when recommended chemical criteria of water quality can be shown by biological tests or observations to be inappropriate to particular mixtures of chemicals being discharged, characteristics of the receiving waters, or other local circumstances. A need for reconsideration and clarification of these recommendations is indicated, and if reliance on biological, rather than chemical, tests and criteria is to be emphasized and promoted, a major redirection of research in aquatic toxicology should be considered. Formulas for application of the results of short-term toxicity bioassays of whole effluents then should be more fully developed and tested, largely through admittedly difficult and costly experiments whereby these results can be related to the harmful effects of the tested toxicants on aquatic life and fish production under conditions closely resembling natural conditions.
An Industrial View of Biological Monitoring
Authors: Ladd EC
Published: March 2009

Biological monitoring is required, along with chemical and physical measurements, for complete assessment of the nature of industrial wastewaters and their impact on the quality of receiving waters. Various approaches to biological monitoring are discussed along with several examples of specific concerns of industry. The need and opportunities for industrial participation in development of biological methods are emphasized.
Automated Measurement of River Productivity for Eutrophication Prediction
Authors: Kelly MG , Hornberger GM , Cosby BJ
Published: March 2009

A method for monitoring net and gross community oxygen productivity, community respiration, photosynthetic efficiency, and reaeration coefficient has been tested in five contrasting rivers. The technique uses relatively inexpensive digital data collection and processing, and allows detection of incipient eutrophication due to nutrient input and excess oxygen demand from organic waste input. Oxygen concentration, temperature, and solar radiation are recorded over a 24-h period and are the data used to calculate the parameters necessary for water quality monitoring. A few weeks data, taken during summer low-flow conditions, are then used to discriminate water quality.
Packaging Requirements for New Drug Applications
Authors: Kumkumian CS
Published: March 2009

The regulatory responsibilities of the Food and Drug Administration and the Consumer Product Safety Commission, under the Federal Food, Drug, and Cosmetic Act and the Poison Prevention Packaging Act of 1970, as they pertain to safety packaging, are reviewed. Details are given on container information required in a new drug application. The importance of the requirement for adequate stability testing of drug products in their containers is stressed. Sources of various public standards pertaining to testing of drug packaging and component parts are listed.
Description of a Computerized Method for Predicting Thermal Fatigue Life of Metals
Authors: Spera DA , Cox EC
Published: March 2009

A computer program called TFLIFE which can be used to predict the thermal fatigue life of metals and structural components from conventional metal properties is described. This program is used as a subroutine with a main program supplied by the user. The main program calculates input cycles of temperature and total strain for TFLIFE which then calculates a stress cycle, creep and plastic strain damage, and cyclic life. A unique feature of TFLIFE is that it calculates lives according to several different failure criteria for the same input data. These criteria are surface crack initiation, interior crack initiation, and complete fracture of both unnotched and notched fatigue specimens. Sample output tables are shown, together with results for two typical problems: (a) thermal-mechanical fatigue of bar specimens of the tantalum alloy T-111 and (b) thermal-stress fatigue of wedge specimens of the nickel alloy B-1900. Thermal fatigue lives calculated using TFLIFE have been verified by comparison with a variety of laboratory test data on different types of alloys. The computer program is now ready for more extensive evaluation on structural components as well as additional laboratory specimens.
A Study of Thermal Fatigue Mechanisms
Authors: Howes MAH
Published: March 2009

The thermal fatigue resistance of materials has been evaluated in a series of investigations using the fluidized bed method of thermal cycling. The factors that influence thermal cracking were studied for many materials and definite patterns of behavior observed. Particular attention was paid to H13 tool steel and an 18Ni maraging alloy as these represent materials with distinctly different mechanisms of heat treatment response.
Effect of Microstructure on the Thermal Fatigue Resistance of a Cast Cobalt-Base Alloy, Mar-M509
Authors: Beck CG , Santhanam AT
Published: March 2009

A study was undertaken to determine whether the thermal fatigue response of the cast cobalt-base alloy, Mar-M509, could be modified by changing the casting parameters. Single-edge wedge-type specimens were tested in a fluidized bed using a thermal cycle of 1915/525°F with a cycle time of 6 min divided equally between heating and cooling. The results revealed that the thermal fatigue life of Mar-M509, from the point of view of both crack initiation and propagation, could be significantly improved by changing the casting variables. Cracking was found to be predominantly transgranular and often initiated at interdendritic carbides. A good correlation was obtained between the secondary dendrite arm spacing and the number of cycles for crack initiation, as well as the crack propagation rates. Small dendrite spacings reduced the thermal fatigue life by accelerating both the crack initiation and propagation. Precipitation of MC and M23C6 carbide occurred during the thermal cycling and affected the crack propagation rate. Based on these results, a model for thermal fatigue cracking in Mar-M509 is presented.
Low-Cycle Thermal Mechanical Fatigue Testing
Authors: Hopkins SW
Published: March 2009

A test method is described for performing uniaxial low-cycle thermal mechanical fatigue tests at elevated temperatures on nickel-base superalloys. Both smooth specimen crack initiation and notched specimen crack propagation testing is discussed. Standard closed loop servohydraulic testing machines with closed loop electric induction heaters are utilized. The temperature and mechanical strain are independently controlled, allowing for a wide range of relationships between temperature and mechanical strain.

Tubular specimens are directly inductively heated in air and cooled with compressed air. The temperature is measured with a radiation pyrometer which eliminates thermocouples and premature failures caused by welded thermocouples. Axial strain in the specimen is measured from machined internal ridges on the specimen utilizing a linear variable differential transformer and a quartz internal extensometer.

An electronic system compensates for the thermal expansion component of strain for both the control loop and the recorders. This system permits direct recording of the load-induced mechanical strain. Load-strain hysteresis loops and strain-temperature plots can simply be recorded during the test.
Thermal-Mechanical, Low-Cycle Fatigue of AISI 1010 Steel
Authors: Jaske CE
Published: March 2009

This study was undertaken to develop an understanding of the fatigue resistance of AISI 1010 steel under conditions of combined thermal and mechanical strain cycling in air. Comparative evaluations were made with existing thermal-mechanical fatigue data on carbon steels and with results of a comprehensive, companion study of the fatigue behavior of this same steel under isothermal conditions.

Thermal-mechanical fatigue behavior was investigated for constant-amplitude, fully reversed, strain cycling of uniaxially loaded specimens at three ranges of temperature: (a) 93 to 316°C (200 to 600°F), (b) 93 to 427°C (200 to 800°F), and (c) 93 to 538°C (200 to 1000°F). Experiments were conducted both with maximum strain in phase with maximum temperature and out of phase with maximum temperature. Considering differences in experimental techniques and the difficulties associated with conducting these types of experiments, the present data agreed with similar data from the literature in limited instances where comparisons could be made. Thus, these results were considered to be representative of this type of steel, and they provided a significant extension of existing knowledge on the thermal-mechanical fatigue resistance of low-carbon steel.

Dynamic strain aging was observed to cause more cyclic hardening in these experiments than in isothermal fatigue experiments. In terms of total or plastic strainrange, out-of-phase cycling was more deleterious than in-phase cycling, and thermal-mechanical fatigue life was much less than isothermal fatigue life. However, on the basis of stable stress amplitude, there was little difference in fatigue life between in-phase and out-of-phase cycling, and the fatigue life was reasonably well correlated with isothermal fatigue results.
Life Prediction of Thermal-Mechanical Fatigue Using Strainrange Partitioning
Authors: Halford GR , Manson SS
Published: March 2009

This paper describes the features of the method of strainrange partitioning that make it applicable to the life prediction of thermal-mechanical strain-cycling fatigue. An in-phase (230 to 760°C) test on Type 316 stainless steel is analyzed as an illustrative example. The method utilizes the recently proposed step-stress procedure of experimental partitioning, the interaction damage rule, and the life relationships determined at an isothermal temperature of 705°C. Implications of the present study are discussed relative to the general thermal fatigue problem.
Accelerating Random-Sequence Fatigue Tests by Response Compensation and Cycle Deletion
Authors: Sherratt F , Davall PW
Published: March 2009

A way of applying on-line compensation for system dynamic response has been used on servohydraulic and electromagnetic single-input loading devices. While continuously measuring rig response by fast Fourier transform methods, a computer monitors the demand signal and applies to the rig a version of this, modified by the inverse transfer function. Signals generated by conventional white-noise filtering, by a digital technique which allows power spectrum and amplitude probability distribution to be chosen independently, and by random selection from joint peak-trough probability distributions have been handled by the process. A by-product of the system is the detection of changes in specimen response which may coincide with the start of macrocrack growth. Acceleration of tests by deleting small amplitude cycles from the demand history is shown to have weaknesses if elements in the joint peak-trough probability matrix are simply put to zero, and an alternative way using variable width dead zones in an off-line simulation is proposed.
Performance Criteria of Gasket Materials
Authors: Gordon AL
Published: March 2009

Many physical and functional properties of gasket materials may be involved in determining their performance under specific sets of conditions. The selection of gasket materials is complex and based upon the interpretation of numerous interrelated factors which may affect performance. Certain guidelines may be employed to facilitate the selection process in a systematic manner with a good level of reliability.
Corrosion of Reinforcing Steel in Concrete—A General Overview of the Problem
Authors: Cady PD
Published: March 2009

Corrosion of reinforcing steel in concrete has produced a problem of catastrophic proportions in the highway field. Bridge decks in the snow belt areas of the country, subject to heavy application of deicer salts in response to the public's demand for year-round bare pavements, frequently start to show signs of severe deterioration after only a few years of service. A wide variety of techniques for retarding or preventing corrosion of reinforcing steel and subsequent potholes in bridge decks have been tried, with varying degrees of success. It appears that the time is ripe for a synthesis and evaluation of these methods in order to properly assess the current status of ameliorative actions and to indicate those areas requiring further investigative effort.

Corrosion of reinforcing steel in concrete is not limited to bridge decks. Examples of reinforcement corrosion in a marine atmospheric environment are cited.
Iowa Method of Partial-Depth Portland Cement Resurfacing of Bridge Decks
Authors: O'Connor EJ
Published: March 2009

Low-slump, high-quality concrete is used in Iowa for partial-depth patching and resurfacing of bridge decks. All unsound concrete is removed, as well as a minimum of ¼ in. (0.054 m) of the remaining sound concrete surface. Sand cement grout is scrubbed onto dry, prepared deck immediately prior to compacting low-slump concrete into place using vibrating screeds.
Improvement of Fatigue Life of Boron/Epoxy Laminates by Heat Treatment Under Load
Authors: Sun CT , Roderick GL
Published: March 2009

A heat-treatment procedure was used to produce compressive residual stresses in the matrix of notched [902/02]s and [02/902]s boron/epoxy laminated composites. The residual stress was obtained by using the creep behavior of epoxy under high temperatures. A simple expression for the creep strain was derived from measured creep properties of epoxy. Using this expression a simple creep analysis showed that the residual stress induced by creep of matrix was of the same order of magnitude as the curing stress. Static strength and fatigue tests were conducted on both treated and untreated specimens. The results indicate that the heat treatment has the potential to increase significantly the fatigue life without reducing the static strength of the laminates.
Effect of Temperature on Fatigue Response of Surface-Notched [(0/ ± 45/0)s]3 Graphite/Epoxy Laminate
Authors: Sendeckyj GP , Stalnaker HD , Kleismit RA
Published: March 2009

The fatigue behavior of surface-notched [(0/± 45/0)s]3 T300/5208 graphite-epoxy specimens was studied over the temperature range from room temperature to 421 °F (216 °C). The specimens, after being subjected to two lifetimes of a 135 000-cycle tension-dominated flight-by-flight spectrum, were nondestructively inspected (using tetrabromoethane-enhanced X-ray radiography and C-scanning) and then tested at room temperature to determine their residual strengths. The test results show that both the extent of matrix damage and residual strengths increase with fatigue test temperature. If the fatigue-induced matrix damage region (FIMDR) is the same size or smaller than the delamination region observed prior to static failure, then the residual and static strengths are equal. If the FIMDR is larger than the delamination prior to static failure, then the residual strength is higher than the static strength. Finally, the residual strength is less than the net section strength.
Fatigue Behavior of Composites Under Different Loading Modes
Authors: Sims DF , Brogdon VH
Published: March 2009

The fatigue characteristics of S-glass/epoxy (Scoth-ply SP-250-SF1) and graphite/epoxy (Rigidite 5209-T300) laminates were studied for tension and shear loading. Emphasis was placed on fiber orientations where the matrix contribution to fatigue strength is significant. A general regression curve was used for data analysis, and a two-parameter Weibull model was used for reliability studies. An existing plane-stress macroscopic failure theory for static strength was extended to predict fatigue strength. It was found that the fatigue failure theory provides a conservative approach to first-ply failure which should be useful for preliminary design of composite structures.
Finite-Element Analysis of Crack Growth Under Monotonic and Cyclic Loading
Authors: Newman JC
Published: March 2009

An elastic-plastic (incremental) finite-element analysis, in conjunction with a crack-growth criterion, was used to study crack-growth behavior under monotonic and cyclic loading. The crack-growth criterion was based on crack-tip strain. Whenever the crack-tip strain equals or exceeds a critical strain value, the crack grows. The effects of element-mesh size, critical strain, strain hardening, and specimen type (tension or bending) on crack growth under monotonic loading were investigated. Crack growth under cyclic loading (constant amplitude and simple variable amplitude) were also studied. A combined hardening theory, which incorporates features of both isotropic and kinematic hardening under cyclic loading, was also developed for smooth yield surfaces and was used in the analysis.
Crack Growth During Low-Cycle Fatigue of Smooth Axial Specimens
Authors: Dowling NE
Published: March 2009

Crack growth data are reported for small axially loaded smooth specimens of A533B steel subjected to strain cycling fatigue at large plastic strains. Surface crack lengths were monitored using cellulose acetate replicas, and occasional specimens were broken open to determine crack depth. Experimental crack growth rates for different strain levels are correlated in fracture mechanics fashion by the J integral concept, with J values being estimated from stress-strain hysteresis loops. The crack growth rate data of this investigation are compared with previous data for the same material obtained from linear elastic fracture mechanics tests. It is suggested that research on the behavior of small cracks is fundamental to a better understanding of the fatigue process.
A Fatigue Crack Growth Analysis Method Based on a Simple Representation of Crack-Tip Plasticity
Authors: Kanninen MF , Atkinson C , Feddersen CE
Published: March 2009

A new approach to fatigue crack propagation is described. The key element in the analysis is the inclined strip-yield superdislocation representation of crack-tip plasticity. The basis of the model is given and its potential application in a cycle-by-cycle analysis of fatigue crack growth under arbitrary cycle-by-cycle loads indicated. It is shown that, to perform a fatigue crack growth computation for a given load sequence, only the material's shear modulus, tensile yield strength, and Poisson's ratio need to be specified. In the process, some account is taken of crack closure during the load cycle. Illustrative calculations for uniform cyclic loading are described and comparisons with experimental results made.
Fatigue Crack Growth and Life Predictions in Man-Ten Steel Subjected to Single and Intermittent Tensile Overloads
Authors: Stephens RI , Sheets EC , Njus GO
Published: March 2009

Fatigue crack growth behavior was investigated in Man-Ten steel under conditions of constant load amplitude, single tensile overloads followed by constant load amplitude and intermittent single tensile overloads. Constant-amplitude ratios, Rl = Plmin / Plmax, were + 1/2, 0, −1/2, −1 and −2. The single overload test program excluded Rl = +1/2, and the intermittent overload program was for Rl = 0 only. A new simplified mathematical model was introduced which assumes that fatigue crack growth retardation is primarily a function of the overload ratio and the load ratio. The model predicted intermittent tensile overload life within 57 to 112 percent of the experimental life. The average prediction was 77 percent of experimental life. For Man-Ten steel, constant-amplitude crack growth rate versus positive ▵К fell within a reasonable scatter band for Rl = 1/2 to −1. However, substantial decrease in life occurred with Rl = −2. Negative values of Rl following a single tensile overload substantially reduced retardation life. Thus compressive stress, either large or small, cannot be neglected in spectrum loading fatigue crack growth life predictions.
Critical Remarks on the Validity of Fatigue Life Evaluation Methods Based on Local Stress-Strain Behavior
Authors: Schutz D , Gerharz JJ
Published: March 2009

The conventional fatigue analysis using nominal stresses and Miner's rule is known to give inaccurate life predictions. It has been speculated that the major deficiencies can be overcome if local stresses and strains in the immediate vicinity of a stress raiser, instead of nominal stresses, are considered in the estimation of fatigue life. At present, there are a number of proposals which consider local stress-strain concepts, some of which are already developed to a state of practical applicability. In this paper, the best-known concepts are reviewed. It was found that all methods involving the determination of the stress-strain behavior at the notch root retained the conventional methods for computing damage accumulation. The question which arises is: What improvement in life prediction can be expected eventually when the correct local stress-strain history is known, but the damage due to local stress-strain cycles is linearly accumulated?

Open-hole specimens of the aluminum alloys 2024-T3 and 7075-T6 were subjected to a flight-by-flight load program. The corresponding local strain and stress histories were determined by local strain measurements and the companion specimen method, respectively. Fatigue life was estimated by three different methods using: (a) the local stress cycles and unnotched specimen applied stress-cycles to failure (S-N) data, (b) the nominal stress cycles and S-N data from prestressed open-hole specimens, and (c) for comparison, the nominal stress cycles and S-N data from the open-hole specimen. In each case the damage was linearly accumulated.

For the flight-by-flight testing sequences, the companion specimen method indicated that the residual stresses at the notch root stabilized asymptotically to a limiting value at between 5 and 20 percent of the life-to-crack initiation. Virgin open-hole specimens were also prestressed to develop, at the hole, the stress-strain status of the stabilized residual stresses determined previously during flight-by-flight loading. The prestressed specimens were subjected to constant amplitude loading and the resulting lives used for the damage calculation in Method B.

The ratios of test life to estimated life obtained using the three methods were compared and the following conclusions drawn: with increasing accuracy of the incorporation of local stress-strain behavior in future analysis methods (and using linear damage accumulation), the predicted life may still differ from the actual life. The estimated lives may be both conservative and unconservative, so that a scatter of life estimates of 1:3.0 is possible. This is, however, smaller than that of the life estimates using the conventional nominal stress concept which was found to be 1:6.0.
Multi-Parameter Yield Zone Model for Predicting Spectrum Crack Growth
Authors: Johnson WS
Published: March 2009

A systematic technique is presented for modeling crack growth load interaction effects due to spectrum loading. The Multi-Parameter Yield Zone (MPYZ) model accounts for crack growth retardation, acceleration, and underload effects. The load interactions are attributed to the residual stress intensity due to the plastic deformation at the crack tip. As part of an ASTM Task Group E24.06.01 round-robin effort, fatigue crack growth was predicted and compared with test data for a variety of spectrum loadings.
Geometry Effects and the J-Integral Approach to Elastic-Plastic Fatigue Crack Growth
Authors: Dowling NE
Published: March 2009

Fatigue crack growth rate data are obtained for center cracked specimens of A533B steel subjected to elastic-plastic cyclic loading. Cyclic J-integral values estimated from load versus deflection hysteresis loops are correlated with these growth rate data. The relationship obtained is in agreement with previous elastic-plastic data on compact specimens and also with linear elastic data on large size compact specimens. These experimental data suggest that the fracture mechanics approach to fatigue crack growth may be extended by the use of the J-integral concept, so that large scale plasticity effects are included.
Assessment of Strength-Probability-Time Relationships in Ceramics
Authors: Lenoe EM , Neal DM
Published: March 2009

In the past few years a number of test procedures have evolved as a result of attempts to observe stable crack growth in ceramics under constant stress conditions. The experimental procedures have included double cantilever, double torsion, in-plane moment, and controlled flaws in beam bending tests. These procedures are briefly reviewed. Available slow crack growth data for hot pressed silicon nitride, which has been presented in the literature, is utilized to estimate survival times for various stress levels. The computations are completed in several ways: (a) use of strength data obtained at various loading rates; (b) deterministic integration of the equations; and (c) in a Monte Carlo sense, wherein the controlling parameters are assumed to possess realistic variability. The end product of each set of computations is a design stress-survival time relationship, and the purpose of this paper is to compare these life estimates and comment on the adequacy of each method.

Additional motivations were to assess the status of properties information, and to establish, if possible, reasonable bounds on the accuracy of these probability-based life estimates. Examination of the data and application of the two probability techniques led to the conclusion that the procedures are appropriate for order of magnitude estimates, which are generally but not necessarily conservative. It was evident that additional data, improved experimental procedures, and further analysis of specimens were required.

Since the exponents of the crack velocity-stress intensity functions in a power law form are large and typically cover a wide range for ceramics of interest, that is, 4 < m < 50, difficulties were encountered in use of numerical simulation procedures. With m ⩽ 10, for example, the resulting life functions were widely distributed. Furthermore, the mean value estimates were highly unstable and for large m did not appear amenable to economical digital simulation. Accordingly, a number of different trial functions, including logarithmic, exponential, and polynomial approximations were employed to represent subcritical crack behavior. The final function selected was of the form F = A0exp(mK1), where F = KI/V.

This form seemed appropriate since log F versus KI resulted in reasonable requirements on number of simulations. The m values were appreciably lower than the power law representation. Application of the Monte Carlo method to lifetime estimates of ceramics provided an error tolerance for KI and allowed calculation of the probability density function.
Ductile Fracture of Cylindrical Vessels Containing a Large Flaw
Authors: Erdogan F , Irwin GR , Ratwani M
Published: March 2009

The fracture process in pressurized cylindrical vessels containing a relatively large flaw is considered. The flaw is assumed to be a part-through or through meridional crack. The flaw geometry, the yield behavior of the material, and the internal pressure are assumed to be such that in the neighborhood of the flaw the cylinder wall undergoes large-scale plastic deformations. Thus, the problem falls outside the range of applicability of conventional brittle fracture theories. To study the problem, plasticity considerations are introduced into the shell theory through the assumptions of fully-yielded net ligaments using a plastic strip model. Then a ductile fracture criterion is developed which is based on the concept of net ligament plastic instability. A limited verification is attempted by comparing the theoretical predictions with some existing experimental results.