bluuebunny/crossref_metadata_2025 huggingface dataset:
Rain and Sand Erosion, Phenomena of Material Destruction Caused by Repeated Loads
Authors: Hoff G , Herbert W , Rieger H
Published: March 2009

A rotating arm for maximum peripheral speeds of 1000 m/s has been developed at Dornier-System for testing the material behavior of multiple impact of solids. The test equipment will be discussed.

Fundamental tests concerning the relationship between fatigue behavior and erosion and cavitation strength for various materials have been performed in a rain erosion test rig M = 1.4 and on a magnetostrictive oscillator of 20 kHz. The influence of various treatments on the erosion resistance has been investigated on the stellites which are important for the construction of steam turbines.

By altering the test temperature of high polymers the dependence of erosion resistance to the relaxation characteristics has been determined.

To detect the influence of the altitude on the rain erosion of aircrafts, measurements have been performed to investigate the rain erosion as a function of the atmospheric pressure.
Analogy Between Erosion Damage and Pitting of Machine Component Surfaces
Authors: Kozirev SP
Published: March 2009

Contact damage to the surfaces of gear teeth, of balls in antifriction bearings, of cams in distributing devices, etc. occurs, as a rule, only in the presence of a liquid libricant. The breakout by pitting in this case is similar in character to the surface damage by erosion. The main feature common to these two processes is the fatigue nature of surface damage involving a liquid. These processes have identical kinetics of development with time. In either case the damage rate is affected strongly by unit loading. Both pitting and erosion also depend heavily on viscosity and temperature of the liquid.
Cavitation Damage Resistance and Adhesion of Polymeric Overlay Materials
Authors: Lichtman JZ
Published: March 2009

This study is concerned with the general problem of cavitation erosion; in particular, with coatings which can provide protection of marine and other structures against cavitation erosion and which can remain adhered when exposed to severe hydrodynamic environments. Cavitation erosion studies were conducted on 25 coatings, comprising both neoprene and polyurethane formulations; the Naval Applied Science Laboratory (NASL) magnetostriction apparatus was used as the principal test device. The most erosion resistant of the coatings tested were found to be polyurethane formulations. Adhesion tests on the more erosion resistant coatings showed no effect of cavitation exposure on strength of adhesion. Comparison of magnetostriction data with data obtained on the NASL rotating disk apparatus showed that cavitation intensity of the magnetostriction test (under presently maintained operational parameters) exceeded the most severe intensity developed by the rotating disk apparatus.
ASTM Methods for the Surface Area Analysis of Portland Cement
Authors: Hime WG
Published: March 2009

The ASTM methods for the determination of surface area of portland cement are reviewed. The Blaine air-permeability method is rapid and probably relatively accurate, but does not provide particle size distribution data. The Wagner turbidimetric method does provide such data, but the data for the finer size ranges are erroneous. Procedures for the improvement of the Wagner data are outlined, and it is suggested that the analyses by the Wagner, or any other method, need not be very accurate. Overestimation of certain size fractions and underestimation of others may actually provide data of increased specification value.
Precision of Air-Permeability, Turbidimeter, and No. 325 Sieve Fineness Data
Authors: Arni HT
Published: March 2009

Data on air-permeability and turbidimeter fineness from an interlaboratory test program involving eight different portland cements and from about 80 to 150 laboratories over a period of a year and a half are presented and analyzed from the standpoint of between-laboratory and within-laboratory precision. Scatter diagrams for the four pairs of samples are presented and used as an aid in the analysis. For six of the cements, results of determinations of fineness by the No. 325 sieve are also analyzed and scatter diagrams shown. The effect on the calculated standard deviation of the elimination of some outlying results is assessed. A method of determining within-laboratory or single-laboratory precision without the use of duplicate determinations is presented. Laboratory bias was found to be significantly larger than the random error for all three tests. There was no indication of any significant difference in precision or in laboratory bias between the Type I and Type IA cements for any of the tests.
Comparison of the Air-Jet Sieve Method for Determining the Fineness of Cement with Some ASTM Standard Methods
Authors: Malhotra VM , Zoldners NG
Published: March 2009

This investigation is concerned with the fineness determination of cement, comparing the air-jet sieve method with ASTM standard test methods such as hand-sieving on the No. 200 sieve, wet-sieving on the No. 325 sieve, and the specific surface by the Blaine air-permeability method. The test results indicate that: 1. The air-jet sieve method for fineness by the No. 200 sieve gives more reproducible results than the hand-sieving method, coefficients of variation for the test results of the two test methods being 2.57 and 7.93 percent, respectively. 2. The air-jet sieve method for fineness using the No. 325 sieve gives results of poorer reproducibility than those obtained by the wet-sieving method. Coefficients of variation for the test results of the two methods were 8.46 and 4.17 percent, respectively. It is suspected that the poorer reproducibility of results by air-jet sieving is due to balling of fine dry cement. There was more clogging in the wet-sieving operation even though its results were more reproducible. 3. The method of fineness determination in terms of specific surface is superior to the air-jet sieving method using the No. 200 sieve, the coefficients of variation being 0.58 and 1.98 percent, respectively. But these methods cannot be related directly because they do not measure the same parameters.
Constant Amplitude and Cumulative Damage Fatigue Tests on Bailey Bridges
Authors: Webber D
Published: March 2009

In constant amplitude tests, main girder-bridge panels drawn from Ordnance store had slightly longer lives than newly made panels. Preloading and the improvement of a weld detail doubled lives, but shot peening was not effective. Tests below the Charpy transition temperature showed no change in life. Some Ordnance panels had significantly reduced lives due to prior fatigue damage. Block program tests gave cumulative cycle ratios of approximately 2, increasing with decrease in maximum stress and severity of the program. There was evidence of stresses below the endurance limit being beneficial to fatigue life. The manufacturing method for transoms or cross girders was shown to have an important bearing on fatigue life. Modes of failure are discussed together with the application of fatigue gages to give prior warning of fatigue failure.
Effects of Mean Stress and Prestrain on Fatigue-Damage Summation
Authors: Topper TH , Sandor BI
Published: March 2009

A cumulative damage procedure based on smooth-specimen tests of 2024-T4 aluminum alloy and aircraft quality SAE 4340 steel is formulated in which the effects of prestrain and mean stress on fatigue life are investigated separately. It is assumed that life reductions due to prestrain or mean stress at a given strain level may be separately incorporated into a simple cycle-ratio damage summation.

Small plastic prestrains are shown to cause considerable life reductions. Larger prestrains appear to have little additional adverse effect. It was found possible adequately to correlate results with and without mean stress by a parametric representation of mean stress and strain amplitude.

Analysis of arbitrary stress-strain sequences indicates that the proposed damage-summation procedure gives adequate life predictions. Cycle-ratio summations were close to unity for both stress-controlled and strain-controlled tests in which sequence, number of blocks, fraction of life at mean stress, and the life fraction at which plastic straining occurred were all varied.
Peak-Distribution Effects in Random-Load Fatigue
Authors: Broch JT
Published: March 2009

This paper reports the effects of the stress-peak distribution upon the fatigue life of a certain type of test specimen excited to bending by Gaussian random vibrations. Approximately 200 specimens were tested using two different peak-distribution functions. The peak-distribution functions were produced by means of single- and two-degrees-of-freedom systems, respectively, excited by bands of random noise.

The root-mean-square (RMS) level of the strain and the average number of zero crossings were kept constant and equal in both tests. Statistical and physical interpretations of the test results are presented and discussed.
Effects of Block Size, Stress Level, and Loading Sequence on Fatigue Characteristics of Aluminum-Alloy Box Beams
Authors: Breyan W
Published: March 2009

A fatigue investigation was performed for constant- and variable-load amplitudes using a box beam fabricated from 7075-T6 aluminum elements. This structure was tested as a simply supported beam under unidirectional bending. The primary objectives were to determine the relative cumulative fatigue damage resulting from the imposition of four flight-loads test spectra and to determine the effects of stress level, block size, and load sequence on life. A full factorial experiment with two replications was used to perform both fixed- and random-sequence tests for the parameters of load spectrum, static margin of safety, and block size.

The beam exhibited fatigue characteristics that correlated well with those of full-scale structures, the beam-fatigue lives appearing as the upper bound of the lives of full-scale structures. When subjected to fixed sequence loading, a significant increase in life was found for an 11 percent increase in static margin of safety and for increases in test-block size. These results were explained on the basis of the compressive residual stresses produced around the fastener holes. The results support the use of the smallest feasible block size for the fatigue tests of full-scale structures. Comparisons between fixed- and random-sequence experimental data showed that, in general, the smallest fixed-sequence block size most closely simulated random loading within a block and that the fatigue life under random loading was less than that for fixed-sequence loading.
Fatigue Life of 2024-T3 Aluminum Alloy Under Narrow- and Broad-Band Random Loading
Authors: Hillberry BM
Published: March 2009

Narrow- and broad-band random fatigue tests were conducted on small cantilever specimens of 2024-T3 aluminum alloy. A slightly longer fatigue life was found with the broad-band loading. Both the Palmgren-Miner and Corten-Dolan theories were found to overestimate the fatigue life. A proposed equivalent-crack-length theory shows good agreement with the test results. Also, a means for comparing the fatigue life under different types of random loading is illustrated. In this work fatigue life is based on the number of peaks to failure.
Tensile and Shear-Mode Cracking of Titanium Sheet in Air and in Salt Water
Authors: Walker K , Pendleberry S , McElwee R
Published: March 2009

Crack-propagation tests were conducted using titanium alloy (Ti-6A1-4V) sheet to study the relationship between changes in salt-water cracking behavior and rotation of the crack from a tensile to a shear mode of cracking. Analysis of stress intensity versus cracking rate and examination of electron fractographs for four 16-in. wide panels of Ti-6A1-4V cycled at two stress levels showed a definite change in salt-water cracking behavior occurring at a cracking rate of approximately 260 μ in. per cycle and between the stress-intensity range of 12 ksi √in. and 17.6 ksi √in. The cracking rates in salt water and in air were found to be the same after the crack front had rotated from a tensile to a shear mode of cracking in ten specimens examined including both Ti-6A1-4V and Ti-8Al-Mo-1V.
Evaluation of Methods to Alleviate Corrosion Fatigue in Type 135 Drill-Pipe Steel for Offshore-Drilling Applications
Authors: Pettit DE , Hoeppner DW , Hyler WS
Published: March 2009

Various methods of modifying the drilling environment and changing the response of the material to the environment were examined as potential methods of alleviating corrosion fatigue in Type 135 drill-pipe steel for use in offshore-drilling applications. The fatigue behavior of Type 135 steel specimens in seawater and in air was compared to the results obtained in deaerated seawater, freshwater and seawater drilling mud, inhibited drilling mud, and drilling mud with an elevated pH. No improvement in fatigue life resulted for any of the modified environments examined, several actually proving detrimental. Cathodic-protection studies were then conducted on specimens subjected to various applied current densities during fatigue cycling in seawater and a range of current densities that improved the fatigue behavior determined. The half-cell potential was determined for the steel in seawater and zinc selected as the sacrificial metal coating. Zinc-electroplated specimens fatigue tested in seawater showed a marked increase in fatigue life compared to that of uncoated specimens in seawater. Bare regions up to ⅜ in. wide were tolerated with no loss of protection and regions as large as ¾ in. wide still resulted in an improved fatigue-corrosion behavior.

Thus, zinc electroplating of Type 135 drill-pipe steel resulted in a substantial improvement in fatigue behavior in a seawater environment. Alteration of the chemical environment resulted in no improvement of the fatigue behavior of uncoated specimens over that obtained in plain seawater.
Predicting Low-Cycle Fatigue Data for Low-Alloy Cast Steels
Authors: Schmieder AK
Published: March 2009

Low-cycle fatigue tests were made on low-alloy cast steel in three conditions, as well as a few tests on wrought specimens. Specimens 1 in. in diameter with a ground surface were tested by reversed, push-pull, strain-controlled mode at room temperature. True stress-true strain, tension tests were also made on the materials.

The strain-hardening exponent for a single hysteresis loop agrees closely with that at certain portions of the tensile curve. Whether these materials will cyclic-strain harden or soften at a specified strain range could also be determined from the tension test data. Using these observations, and the work of Martin, Manson and Morrow and their colleagues, a formula was synthesized which predicted fatigue lives of all durations from tensile data and the fatigue limit of the material. When the fatigue limit was adjusted for the specimen conditions the cyclic lives were predicted with useful accuracy. For example, micro-shrink in one casting was found to reduce the cyclic life sharply without much loss in tensile fracture ductility. Use of the notched specimen fatigue limit in the formula gave a reasonably accurate prediction of cyclic life for this casting. The formula is also used to calculate cyclic life under conditions of variable stress and to calculate the reduction of fatigue limit due to cyclic pre-stressing at stresses higher than the fatigue limit.
Effect of Tempering Temperature on Fatigue-Crack Propagation in 4340 Steel
Authors: Anctil AA , Kula EB
Published: March 2009

The fatigue-crack propagation behavior of heat-treated 4340 steel has been studied as a function of tempering temperature from 400 to 800 F and at +80 and -50 F test temperatures. The Griffith-Irwin fracture-mechanics analysis of the data was used for through-thickness cracks in center-notched sheet specimens. Special emphasis was placed on the phenomenon of tempered martensite embrittlement, which occurs in the 500 to 700 F range of tempering temperatures, in order to see whether it can be detected by fatigue testing. The fatigue-crack-growth test results could be represented by an empirical equation of the form d2a/dN = C(ΔK)m. The exponent m was found to vary with tempering temperature and test temperature. The fatigue-crack-growth rate at -50 F was higher than at room temperature. No evidence of tempered martensite embrittlement was observed, since the crack-growth rate was actually a minimum in the embrittlement range, the crack-growth rates decreasing as the tempering temperature increases to 600 F, and then increasing again with higher tempering temperatures. The effect of ethyl alcohol on fatigue-crack growth and the relationship between KIc and the fracture-mode transition are discussed.
A New Apparatus for Investigating Friction and Metal-to-Metal Contact in Fretting Joints
Authors: Milestone WD
Published: March 2009

A new apparatus for investigating friction and metal-to-metal contact in fretting joints is described. This apparatus is used with a standard, flat-plate, reciprocating-bending fatigue machine to induce fretting at the surface of the critical section of a fatigue specimen. A practical range is possible for both the normal contact force and the cyclic amplitude of the relative sliding motion between the fatigue specimen and the second fretting surface, a cylindrically shaped fretting shoe. The most important part of the apparatus is a special force transducer which permits the friction between the two surfaces to be continuously observed. This force transducer and an electronic circuit for estimating contact between the surfaces are described. Data showing friction-force and metal-contact characteristics in the range from zero to 106 fretting cycles are presented for tests conducted with 7075-T6 aluminum alloy and Ti-6Al-4V titanium alloy. The friction data indicate an increase in friction during the first 104 to 105cycles followed by a relatively high, but stable, friction force for the remaining fretting cycles. Metal-contact data indicate good contact early in each test and poor contact later in each test.
Effect of Strength and Thickness on Notch Ductility
Authors: Gross JH
Published: March 2009

For a number of years, standards and code-writing bodies have been attempting to specify fracture toughness in terms of the Charpy V-notch rather than the Charpy keyhole test because various investigators have shown that V-notch test results correlate much better with service experience. However, the change to V-notch specifications has been deterred by uncertainty concerning the best criterion for establishing transition temperatures and the effect of strength and thickness on transition temperatures. Therefore, five steels covering a wide range of yield and tensile strengths (ABS-C: 39/63, A302-B: 56/88, HY-80: 81/99, A517-F: 121/134, and HY-130: 140/148) were tested as quarter-, half-, single-, and double-width (QW, HW, SW, and DW) Charpy V-notch specimens in the longitudinal and transverse directions and with through-thickness and surface notches. Transition temperatures were determined for various energy-absorption, lateral-expansion, and fracture-appearance criteria.

The results showed that energy-absorption criteria for determining transition temperature should increase with strength to ensure a constant notch ductility. Thus the best method for determining transition temperature was the direct measurement of lateral expansion. Of the lateral-expansion criteria evaluated, the 15 mil value agreed best with fracture-mechanics considerations.

The average increase in transition temperature was 60 F from QW to HW specimens, 26 F from HW to SW specimens, and 2 F from SW to DW specimens. This indication of maximum constraint for the SW specimen was not consistent with the effects produced when the standard V-notch was replaced with a fatigue crack. Consequently, the size of the Charpy test specimen that should be used for evaluating thick plates has not been established and requires additional study.

The effects of strength and thickness on transition temperature were much larger than the effects of testing direction, notch location, or notch acuity.

The results indicate that, of the various criteria for evaluating the Charpy V-notch impact-test performance of structural steels, lateral expansion is the best criterion for compensating for the important effects of steel strength and plate thickness. Moreover, its validity is supported by fracture-mechanics concepts.
Measurement of Fracture Toughness by Instrumented Impact Test
Authors: Turner CE
Published: March 2009

Previous studies of the Charpy impact test using instrumented pendulum or anvil with V-noteh steel specimens are reviewed. It is concluded that such results add little to the usefulness of the test since even cleavage fractures are normally well beyond yield. No fracture toughness index emerges other than the simple measure of energy from the pendulum. In a second generation of work, fatigue cracked and side grooved (fcsg) specimens promoted below yield fractures up to about the 50 percent fracture appearance transition temperature (fatt). These results have been analysed by linear fracture mechanics to give the dynamic fracture toughness KID. In this interpretation understanding of the oscillations in load records due to specimen vibration is important. Results are discussed in the light of recent studies including an analog model with which near quantitative agreement is found. An improved simple correction factor for inertia loading effects is presented. It is concluded from both this work and supporting measurements of KID by other techniques that dynamic fracture toughness KID can be measured for low-strength steels using the instrumented fcsg impact test subject to the precautions and corrections discussed. Typical values of KID for mild steel are 60 ksi √in. at 0 C falling to 30 ksi √in. at -60 C. The significance of these low values in relation to the much higher static toughness is discussed briefly.
Materials Sensitive to Slow Rates of Straining
Authors: Hartbower CE
Published: March 2009

In precrack Charpy slow-bend and impact tests of D6aC high-strength steel at 300 to 500 F, there was a reduction in slow-bend fracture energy as the test temperature was increased; whereas, there was an increase in impact fracture energy over the same temperature range. Thus, in high-strength steels, it is sometimes found that the precrack Charpy slow-bend and impact test results are approximately the same at room temperature, but attain a significant spread at moderately elevated temperature. In 6Al-4V titanium, the difference between slow-bend and impact was most pronounced at room temperature, again with the lowest fracture energy in slow bend; whereas, at 300 F, the slow-bend test indicated the material to be as tough or tougher than impact. In all-beta 3Al-13V-11Cr titanium in the solution-treated condition tested at room temperature, the slow-bend test result showed markedly higher toughness than impact, but, after aging, the slow-bend test result was appreciably lower than the impact value.

Differences in fracture appearance attending slow versus impact rates of loading confirm the above observations. The lower toughness in slow bending is believed to be the result of a combination of factors, including an adiabatic temperature rise in the plastic zone on impact, and a time-dependent-embrittlement mechanism occurring in slow bending. In a material with a sharply defined transition curve at or around room temperature, it is easy to see how an adiabatic temperature rise in the plastic zone ahead of the crack could markedly increase the resistance to crack propagation. At the same time, it is well known that embrittlement involving a diffusion mechanism is not detected by impact testing; for example, hydrogen embrittlement and strain aging. In 6Al-4V titanium, the difference between slow-bend and impact at room temperature is consistent with a hydrogen-embrittlement mechanism; namely, maximum embrittlement around room temperature and a decreasing embrittlement at higher (and lower) temperatures. In D6aC steel, on the other hand, the loss of toughness in slow-bend occurs at moderately elevated temperature, which is consistent with spontaneous strain aging as a time-dependent embrittling mechanism.

From these findings, it appears that the concept of strain-rate sensitivity should not be limited to the traditional interpretation that impact is the most severe test of a material. In a number of common structural metals, the situation is reversed; that is, the materials are in fact more “sensitive” to slow rates of straining.
Significance of the Drop-Weight Tear Test and Charpy V-Notch Impact Test Results
Authors: Eiber RJ , Duffy AR , McClure GM
Published: March 2009

The results of extensive research on piping and pressure vessels of plain carbon and low-alloy materials is providing an understanding of the significance of impact test results in terms of the full-scale fracture initiation and propagation characteristics.

The impact tests employed in the research work were the Charpy V-notch impact test and the drop-weight tear test (DWTT). The impact tests have been correlated with full-size cylindrical vessel tests in which the initiation and propagation characteristics have been determined under controlled conditions.

The results of the research indicate that, for the materials studied, the impact test fracture appearances relate to the structural fracture appearance with certain limitations. Specifically, the DWTT when conducted on material of the same thickness as the structure will predict directly the fracture propagation transition temperature. The Charpy V-notch test fracture appearance can be correlated to the structural fracture propagation transition temperature but is offset generally on the temperature scale because of the difference in thickness between the Charpy specimen and the structure.

Correlations have been attempted between Charpy or DWTT energies and the fracture initiation characteristics determined from full-scale cylindrical vessel experiments. These correlations to date between the plane stress-stress intensity factor Kc and the plateau impact energies have exhibited considerable scatter, and no consistent trends are indicated. Also, correlations were attempted between the impact energies and the fracture propagation behavior, but no consistent relationship was found.
Drop-Weight Tear Test—Effect of Variables on Test Results
Authors: Heberling TG , Selby GE
Published: March 2009

Variables studied in this evaluation of the Battelle type drop-weight tear test (DWTT) include operator, test machine, specimen thickness, notch type, and strength level of the material tested. Operator and machine variations were found to be small. For a given material, increasing the specimen thickness raises the plateau energy and the transition temperature. Energy at a given percent shear is proportional to thickness. Notches examined include pressed notch, machined notch, fatigue crack, and crack starter weld. Continued use of the pressed notch is recommended. A side grooved DWTT specimen is used to compare the toughness of heat affected zones of welded specimens to that of the base metal. Work in this area is continuing.
Dynamic Tear Energy—A Practical Performance Criterion for Fracture Resistance
Authors: Lange EA , Loss FJ
Published: March 2009

The dynamic tear (DT) method of testing for fracture toughness is described. Design of specimens, impact test machines, and methods for energy measurement are presented. The relationship between DT energy and KIc values is presented for steel, and procedures for translating the energy values to design parameters such as critical flaw size and stress level are outlined.

The current need for the use of the DT test in the development and selection of high-strength structural metals is illustrated by examples of conditions where the Cv test can be shown to be inadequate. Fracture toughness criteria defined by Cv and DT tests are compared for a high-strength titanium alloy, a 180-ksi yield strength steel, a 140-ksi yield strength steel weld metal, and a quenched and tempered 2¼ Cr-1 Mo steel of 90 ksi yield strength. In all of these examples the Cv test is shown to provide information in variance to that from the DT, DWT-NDT, and Robertson tests. It is concluded that the DT test method has desirable features for general industrial use, and it can provide broad-scope characterization of the fracture resistance of steels, titanium alloys, and aluminum alloys.
Dynamic Fracture Toughness Tests on A302-B Steel
Authors: Bush AJ
Published: March 2009

Using dynamic loading at K rates of 104 ksi in ½/s, fracture toughness tests were made on annealed, and normalized and tempered A302-B steel at temperatures from -320 to 125 F. Fatigue precracked compact tension specimens were used. The specimens were separated into two groups with one group fatigue precracked under a higher load level than the other. Higher fracture toughness values were obtained for the specimens precracked at the higher load. Dynamic KIc values determined in this investigation were lower than static KIc values for the same material as reported earlier by another investigator.
Metallography of Radioactive Materials at Oak Ridge National Laboratory
Authors: Gray RJ , Long EL , Richt AE
Published: March 2009

The preparation and examination of radioactive and toxic materials has required metallographers to discard the close “touch” which at one time was considered so important. Basically, the same preparation and examination steps are carried out with the specimen, but when working with radioactive and toxic materials the simplest operation may be highly involved and require the metallographer to use sensitive manipulators and remotely operated equipment while he is protected by biological shielding. Shielding demands are determined by the materials under study and can vary from a cell with 3-ft-thick, high-density concrete to ¼-in.-thick glass. Metallographs, microhardness testers, X-ray diffraction equipment, and microprobe analyzers have been fabricated with biological shielding as an integral part of the instruments. The in-cell equipment, in particular, may have to approach a “Rube Goldberg” design to be operable, repairable, or replaceable, all by remote methods, and still not downgrade its function by these basic requirements. An important variable—radiation—must be considered along with mechanical and physical effects in the interpretation of the often complex microstructures of metals, alloys, cermets, and ceramics. Some of the materials, as well as information concerning them, are extremely rare and some elements are a product of the nuclear reactor. Examples of equipment requirements and the microstructures of some nuclear fuels and structural materials after exposure in a nuclear reactor are presented.
A Review of Some Techniques and Metallurgical Applications for Transmission Electron Microscopy
Authors: Brimhall JL , Mastel B , Brager HR
Published: March 2009

The application of transmission electron microscopy in metallurgical studies is discussed. It is hoped that the reader will obtain an idea of what is involved in electron microscopy and some of the pitfalls to avoid. Specimen preparation techniques, analysis of the microstructure with specific examples, factors affecting quantitative analysis, and recent innovations are all discussed. Throughout, the recent advances and techniques will be emphasized. For a more complete description and background of the techniques, appropriate references are given at the end of the paper.
Transformation Kinetics of Thermomechanically Worked Austenite by Deformation Dilatometry
Authors: Smith YE , Siebert CA
Published: March 2009

A method was developed for monitoring the continuous cooling transformation of thermomechanically worked austenite by dilatometry. A commercially available, induction-heated, gas-quenching dilatometer was modified by the addition of a compression device that permitted the deformation of dilatometer specimens at high temperature. Continuous cooling transformation data were obtained on undeformed and thermomechanically worked specimens of a 0.1C-0.4Mo-B structural steel. The results clearly indicate the need for data on transformation kinetics in the selection of steel compositions for processing by thermomechanical working schedules.
The Electron Microprobe Analyzer as a Research Instrument
Authors: Eichen E , Kunz F , Tabock J
Published: March 2009

The use of an electron microprobe as a research tool will be considered. The theory of operation of this instrument will be briefly discussed. The different possible modes of data presentation will be given. These will include graphical representation on a recorder, video representation of scanned area using backscattered electrons, absorbed electrons, and X-rays, and the accumulation of quantitative data on scalers. Qualitative, semiquantitative, and quantitative analysis will be included in the discussion. Also included will be the importance of specimen preparation in microprobe analysis, and a number of different examples for various types of specimens will be given. These will include such materials as metals, glasses, ceramics, and semiconductors. Consideration will be given to the analysis of thin films as well as bulk materials. Some of the problems encountered in the analysis of thin films will be discussed as well as ways of circumventing these problems. Examples will be given to illustrate the type of problems and the means of approach in cases where qualitative analysis, semiquantitative analysis, and quantitative analysis are desired. In the latter case, the different types of corrective procedures which can be used will be discussed. These include correction for absorption, fluorescence, and atomic number.
Use of the Scanning Electron Microscope in the Materials Sciences
Authors: Russ JC
Published: March 2009

The scanning electron microscope is a relatively new instrument now finding rapidly growing use in the materials sciences. It scans a fine beam of electrons across the specimen surface and displays an image of that surface on a cathode-ray tube using any of the radiations that are generated by incident electrons. The characteristics of each of the images that can be formed using the different signals available are described, as well as its particular use for different types of specimens.

Many types of materials specimens can be examined in the scanning electron microscope with no preparation, but to obtain optimum results it is often necessary or desirable to coat the surface with a thin conductive layer. This and other steps of specimen preparation and handling techniques for solid and powder samples are outlined. Finally the interpretation of the various types of images and the dynamic observation of changes produced in the specimen by heating, straining, etc., are considered.
Progress in Fracture Testing of Metallic Materials
Authors: Kaufman JG
Published: March 2009

Progress in the development of fracture-toughness testing techniques by ASTM Committee E-24 is reviewed briefly. The evolution of the test method for plane strain stress-intensity factor, KIc, is described, including treatment of some of the problems dealing with fatigue cracking, thickness limitations and crack growth detection, and measurement. Attention is given also to the preparation of the screening test method for thin sections. Some cautions are presented concerning the necessity for meticulous standardization, despite the time required to do an acceptable job, and the timing problems in incorporating methods into specification requirements.
Evaluation of a Method of Test for Plane Strain Fracture Toughness Using a Bend Specimen
Authors: Heyer RH , McCabe DE
Published: March 2009

A task group of ASTM Committee E-24 conducted an interlaboratory test program on determination of KIc using the proposed “Recommended Practice for Plane Strain Fracture Toughness Testing of High-Strength Metallic Materials Using a Fatigue-Cracked Bend Specimen.”

Analysis of KIc data for an aluminum alloy and two high-strength alloy steels showed that laboratory mean values were within ±10 percent of grand mean values. Replication was generally satisfactory, although not as good as for smooth specimen tension tests.

Information obtained on fatigue cracking and other details of the procedure will be useful in planned revisions, leading to a standard method of test.
British Experience with Plane Strain Fracture Toughness (KIc) Testing
Authors: May MJ
Published: March 2009

This paper reviews the background to the formation of a Working Group in the United Kingdom concerned with fracture testing of high-strength metallic materials. The results are given of two collaborative test programs designed to familiarize participants with testing techniques based on linear elastic fracture mechanics and interpretation of load-displacement curves.

Results also are presented of specific studies on the influence of fatigue precracking stress intensity and the specimen dimensions such as thickness and crack length on KIc measurement.

The current objectives of the BISRA Fracture Toughness (High Strength steels) Committee are to produce a British standard for plane strain fracture toughness (KIc) testing and prove its workability by a further collaborative test program.
The Influence of Crack Length and Thickness in Plane Strain Fracture Toughness Tests
Authors: Jones MH , Brown WF
Published: March 2009

Results are presented from a systematic investigation of the influence of crack length and specimen thickness on the fracture properties of 4340 steel bend specimens heat treated to yield strength levels between 180 and 213 ksi. It is shown that KIc values determined in accordance with the present ASTM Tenative Method of Test for Plane Strain Fracture Toughness of Metallic Materials (E 399-70T) can vary moderately within the specimen size and geometric limitations imposed by the Test Method. The magnitude of these variations will depend on the material properties and would be increased by relaxation of the size requirements.

The possibility of employing subsized specimens for screening materials regarding their plane strain fracture toughness was explored as well as several methods for relating KIc values to uniaxial tensile data. The results indicated that use of subsized specimens with the ASTM Committee E-24 Test Method does not constitute a useful screening procedure. For steels subject to single aging or tempering reactions, it appears that the relation KIc ∼ σYS-m may be useful for estimating KIc values. However, on the basis of present knowledge, it is not possible to calculate KIc with useful accuracy from uniaxial tensile data alone.
Crack Toughness Measurements of High-Strength Steels
Authors: Steigerwald EA
Published: March 2009

The influence on fracture toughness of relative specimen thickness in the center-precracked tension specimen and crack length in the precracked bend specimen was evaluated. The results indicated that the nature of the crack growth curve in the precracked sheet tension test could be related directly to the fracture mode transition temperature. Tests conducted below the fracture mode transition region provided only catastrophic crack extension, while testing within the transition region resulted in measurable slow growth which was initiated by a sharp discontinuity (pop-in). Above the brittle-to-ductile transition slow crack growth was observed, but no meaningful fracture toughness could be measured.

The study of the influence of crack length on the fracture toughness obtained in the notch bend test indicated that valid values of KIc were obtained when the crack size (a) was 2.5 times the (K/σy)2 ratio in accordance with ASTM recommendations. However, it appears that the crack size requirements could be reduced by a factor of 2.5 without producing variations of greater than 5 percent in the measured fracture toughness value provided that the thickness requirement was satisfied.

The available KIc values for a variety of high-strength steel types were also presented graphically as a function of both strength level and test temperature.
Fractographic Analysis of the Low Energy Fracture of an Aluminum Alloy
Authors: Tanaka JP , Pampillo CA , Low JR
Published: March 2009

The brittle fracture of many high-strength alloys occurs by dimpled rupture. It is recognized that, as in ductile materials, voids which nucleate at non-metallic particles, grow and coalesce during deformation leading to final rupture. The density and distribution of impurity particles, therefore, may affect strongly the toughness of high-strength alloys without contributing significantly to their strength. To understand better this problem the fracture process of a high-strength aluminum alloy (2014-T6) was studied. Two types of large impurity particles (3 to 10 μm in diameter), where voids were nucleated, have been identified by microprobe analysis. Voids were nucleated at these inclusions by fracture of the inclusions, and this happened at rather low strains. From the examination of the fracture surface of plane strain fracture specimens, by replicas and directly with the scanning electron microscope, it was concluded that the joining of the large voids initiated at the large inclusions occurred through the matrix by a mechanism of void sheet formation. The void sheet formation seems to be developed through the formation of voids at small particles (0.1 to 0.2 μm in diameter) distributed uniformly in the matrix. These particles should be regarded as a dispersion which strengthens the matrix.
Review of Developments in Plane Strain Fracture Toughness Testing
Authors: Brown WF
Published: March 2009

Description

The object of this book is to bring together a series of papers which describe recent experience obtained in the United States and in England with the application of the ASTM E24 Proposed Method of Test for Plane Strain Fracture Toughness of Metallic Materials. This information supplements that which has appeared in ASTM STP 381 on Fracture Toughness Testing and its Application and in STP 410 on Plane Strain Crack Toughness Testing of High Strength Metallic Materials. This publication is a cooperative effort of ASTM and NASA. NASA research personnel have participated in ASTM Fracture Committee activities since their inception in 1959. This participation reflects the strong interest that NASA has maintained in the development of test methods for evaluation of the fracture resistance of engineering materials. This interest arises from the necessity for the use of high-strength alloys in critical parts of aerospace structures. By cooperation with ASTM in publication of this book NASA is helping to fulfill its obligation to provide the widest practicable and appropriate dissemination of results from its activities.
The Neurobiology of Reference-Dependent Value Computation
Authors: De Martino Benedetto , Kumaran Dharshan , Holt Beatrice , Dolan Raymond J.
Published: March 2009

A key focus of current research in neuroeconomics concerns how the human brain computes value. Although, value has generally been viewed as an absolute measure (e.g., expected value, reward magnitude), much evidence suggests that value is more often computed with respect to a changing reference point, rather than in isolation. Here, we present the results of a study aimed to dissociate brain regions involved in reference-independent (i.e., “absolute”) value computations, from those involved in value computations relative to a reference point. During functional magnetic resonance imaging, subjects acted as buyers and sellers during a market exchange of lottery tickets. At a behavioral level, we demonstrate that subjects systematically accorded a higher value to objects they owned relative to those they did not, an effect that results from a shift in reference point (i.e., status quo bias or endowment effect). Our results show that activity in orbitofrontal cortex and dorsal striatum track parameters such as the expected value of lottery tickets indicating the computation of reference-independent value. In contrast, activity in ventral striatum indexed the degree to which stated prices, at a within-subjects and between-subjects level, were distorted with respect to a reference point. The findings speak to the neurobiological underpinnings of reference dependency during real market value computations.
How Choice Reveals and Shapes Expected Hedonic Outcome
Authors: Sharot Tali , De Martino Benedetto , Dolan Raymond J.
Published: March 2009

Humans tend to modify their attitudes to align with past action. For example, after choosing between similarly valued alternatives, people rate the selected option as better than they originally did, and the rejected option as worse. However, it is unknown whether these modifications in evaluation reflect an underlying change in the physiological representation of a stimulus' expected hedonic value and our emotional response to it. Here, we addressed this question by combining participants' estimations of the pleasure they will derive from future events, with brain imaging data recorded while they imagined those events, both before, and after, choosing between them. Participants rated the selected alternatives as better after the decision stage relative to before, whereas discarded alternatives were valued less. Our functional magnetic resonance imaging findings reveal that postchoice changes in preference are tracked in caudate nucleus activity. Specifically, the difference in blood oxygenation level-dependent (BOLD) signal associated with the selected and rejected stimuli was enhanced after a decision was taken, reflecting the choice that had just been made. This finding suggests that the physiological representation of a stimulus' expected hedonic value is altered by a commitment to it. Furthermore, before any revaluation induced by the decision process, our data show that BOLD signal in this same region reflects the choices we are likely to make at a later time.
A Domain-Independent Source of Cognitive Control for Task Sets: Shifting Spatial Attention and Switching Categorization Rules
Authors: Chiu Yu-Chin , Yantis Steven
Published: March 2009

To optimize task performance as circumstances unfold, cognitive control mechanisms configure the brain to prepare for upcoming events through voluntary shifts in task set. A foundational unanswered question concerns whether different domains of cognitive control (e.g., spatial attention shifts, shifts between categorization rules, or shifts between stimulus–response mapping rules) are associated with separate, domain-specific control mechanisms, or whether a common, domain-independent source of control initiates shifts in all domains. Previous studies have tested different domains of cognitive control in separate groups of subjects using different paradigms, yielding equivocal conclusions. Here, using rapid event-related MRI, we report evidence from a single paradigm in which subjects were cued to perform both shifts of spatial attention and switches between categorization rules. A conjunction analysis revealed a common transient signal evoked by switch cues in medial superior parietal lobule for both domains of control, revealing a single domain-independent control mechanism.