bluuebunny/crossref_metadata_2025_split huggingface dataset:
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 (&lt;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.
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.
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.
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.
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.
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.
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.
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.
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 &lt; m &lt; 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.
Predicting Fatigue Crack Retardation Under Single and Intermittent Overloading
Authors: Morman KN , Dubensky RG 
Published: March 2009

An expression which simulates both retardation and delayed retardation in crack propagation subsequent to tensile overloading is presented and related to test data for Man Ten, Hadfield, and AISI 1020 steels, and Ti-8Al-1Mo-IV titanium alloy.
The crack growth expression is then generalized to predict the crack growth life in specimens for a variety of intermittent overload conditions. Agreement between the predicted and test data values for the four materials is within 20 percent for approximately one half of the more than 80 overload conditions studied.
JIc Test Results From Two Steels
Authors: Underwood JH 
Published: March 2009

Fracture toughness tests were performed with 10 by 20-mm, deeply notched bend specimens of a mild steel and a nickel-chromiummolybdenum steel. Using the recently proposed J-integral test method, critical values of the energy line integral for Mode I crack growth, JIc, were determined for the two materials. The JIc results were discussed in relation to various specimen geometry criteria and critical crack growth criteria which have been proposed for a standardized JIc test procedure. The JIc results from the nickelchromium-molybdenum steel are found to be in excellent agreement with the known KIc value when the elastic deflection corresponding to the uncracked specimen is taken into account.
The JIc results from both steels are shown to be closely approximated by a one-specimen JIc test procedure, which is described and suggested for use as a fracture toughness screening test.
An analysis is presented of the error which arises in JIc determination when the effect of uncracked deflection in bend specimens is ignored. The error can be significant for materials with large values of yield strength relative to fracture toughness, even for deeply cracked specimens.
Influence of Configuration on R-Curve Shape and Gc When Plane Stress Conditions Prevail
Authors: Adams NJ 
Published: March 2009

Following a brief introduction, an examination is presented of the factors which define the fracture toughness, R-curve relationships, and the extent of stable crack extension. Use is made of the compliance calibrations for a center cracked sheet and a compact tension specimen to show how configuration influences the shape of the R-curve in specimens of equivalent width and identical thickness. The change in the shape of the R-curve is shown to affect stable crack extension and the G-curve tangency requirement to result in differing toughness levels in the different configurations.
In support of the analytical results, tests have been conducted on two high strength aluminium alloys to establish the variations in the shape of R-curves, using both compliance-indicated and measured absolute values of crack length. Various toughness values which highlight the influence of plastic deformation on toughness have been calculated.