bluuebunny/crossref_metadata_2025_split huggingface dataset:
Electron Fractography of High Temperature, High Strain Rate Fracture
Authors: Wilber GA , Bucher JH 
Published: March 2009

It is shown that electron microfractography can be applied successfully to the study of high temperature, high strain rate fracture. Although the fracture surfaces exhibited some oxidation and thermal etching, the quality of the fractographs was adequate to identify the operative fracture modes for a variety of alloys and test conditions. Three alloys were studied: (1) a nickel base superalloy (Inconel 718), (2) an austenitic stainless steel (AISI 304), and (3) a low carbon steel (AISI 1008). High strain rate, hot tension tests were carried out in vacuum or in argon after direct heating to the test temperature and after cooling from a reheating temperature typical of actual hot rolling operations.
The hot ductility, as indicated by the reduction in area at fracture, is described in terms of various temperature-ductility ranges which cover incipient melting as well as normal hot working temperatures. Electron fractography was combined with metallographic observations to obtain a more detailed description of this hot ductility behavior. A variety of fracture modes were observed depending on the alloy and test conditions with examples of transgranular shear rupture, intergranular shear rupture, and brittle intergranular decohesion. Despite the high deformation temperatures, some of the fracture surfaces exhibited areas of cleavage and brittle interphase separation resulting from crack initiation at second phase particles. A description of the specific fracture modes in each temperature-ductility range is given for each alloy, and the reasons for the observed variations in hot ductility are discussed.
Toughness of Filamentary Boron/Aluminum Composites
Authors: Hancock JR , Swanson GD 
Published: March 2009

An exploratory study was carried out to determine whether, in terms of the definitions and test procedures developed for alloys, valid fracture toughness values could be measured for highly anisotropic and heterogeneous boron/aluminum composites. The mechanical test results were correlated with acoustic emissions from filament breakage, with fractography, and with high-speed movies of surface deformation and crack growth.
The plane strain fracture toughness, KIc, parallel to the filament axis of center notched specimens of 6061 aluminum-30 volume percent boron was determined to be ∼30,000±4000 psi √in. Filament pullout contributed negligibly to the fracture toughness of the composite. The minimum plate thickness, in terms of the plastic enclave size factor (KIc/σy) necessary to achieve plane strain conditions is about the same as that recommended for metals. The results indicate that conventional concepts of fracture toughness can be applied to filament reinforced metals to provide engineering design data.
Neutron Irradiation Effects on a Metal Matrix Composite
Authors: Kvam KC , Jones RC 
Published: March 2009

The study examined the effects of nuclear irradiation on the mechanical properties of a metal matrix composite to update composite theory to include nuclear effects and to determine the feasibility of nuclear applications of metal matrix composites. An NS 355 stainless steel fiber/2024-T6 aluminum matrix composite was cut into specimens which were then divided into four sample groups. Three of these groups were irradiated to fast neutron dosages of 1.56, 2.84, and 4.68 × 1018 n/cm2. Microhardness and flexure tests were performed on each of the four sample groups. Fracture surfaces of all sample groups were viewed by scanning electron microscopy.
Strength increases and ductility decreases with increasing dosages are generally observed in the aluminum matrix and the stainless steel fibers. The high degree of matrix hardening and subsequent saturation with increasing dosage, leading to changes in the relative failure strain of matrix and fiber, is identified as the controlling mechanism of the composite strength changes in flexure. Existing composite theory is concluded to be applicable to nuclear irradiated composites without modification. Nuclear applications are most feasible in fast reactors, where the tailorability of a metal matrix composite might provide the technical breakthrough needed to combat the severe materials problems inherent to fast reactors.
Cleavage Phenomena and Topographic Features
Authors: Burghard HC , Stoloff NS 
Published: March 2009

Cleavage fractures have been widely studied in body-centered-cubic and certain hexagonal-close-packed metals and alloys as well as ionic crystals. It is shown that the theoretical treatments due to Stroh, Cottrell, and Petch have successfully accounted for the effects of yield strength, grain size, and mode of deformation on crack nucleation and propagation. The results of these studies are summarized, and their application to the prediction of the ductile-to-brittle transition temperature is described. In addition, theoretical studies which have led to the prediction of cleavage planes and to an explanation of the influence of dispersed particles are reviewed.
Fractographic studies have established topographic features characteristic of cleavage fracture; namely, steps and river patterns, cleavage tongues, and herringbone patterns. Examples of these features are presented, and factors associated with their formation are described. It is shown that steps and river patterns are formed by secondary cleavage, slip, or plastic fracture and are influenced by crystallographic imperfections and microstructural discontinuities. Tongues and herringbone patterns are shown to be associated with deformation twins formed ahead of the advancing crack. In addition, a discussion of “cleavage-like” features observed in quenched and tempered steels, face-centered-cubic materials, and in certain environmentally induced fractures is presented.
Fracture by Microscopic Plastic Deformation Processes
Authors: Beachem CD , Meyn DA 
Published: March 2009

The various fracture surface features formed by fine-scale plastic flow processes are discussed, and the mechanisms by which they are formed are discussed where they are known.
Glide plane decohesion, as it has been used in the literature, is shown to be misleading, and a more descriptive term, “stretching,” is used in its place. The use of “ductile cleavage” to describe the same process is also misleading.
Since brief, descriptive, nonmisleading terminology is necessary for immediate communication, several terms have evolved to describe the surfaces created by unknown processes. Glide plane decohesion, serpentine glide, ripples, stretching, and three kinds of microvoid coalescence are shown to be parts of a spectrum of plastic rupture.
Engineering Applications of Fractography
Authors: Brothers AJ , Yukawa S 
Published: March 2009

To date the primary use of microfractography has been qualitative. For this purpose the characteristic features of a specific fracture mechanism are compared with those of the service failure to be identified. However, the optimum use of fractography is that of both a quantitative and qualitative tool. This paper illustrates its usefulness in interpreting quantitatively the microfractographic features of various failure mechanisms, and suggests some currently speculative but promising areas for future work.
The incidence of fatigue striations and their association with cyclic alternating loads provide the basis for quantitative interpretation of fatigue failures. It is shown that fractographic determination of microscopic crack growth rates, coupled with currently available analyses for macroscopic crack growth rates, permits one to estimate relative failure stress or strain level, approximate number of failure cycles, and, in some cases, the relative stress gradient and mode of loading. The general stress dependence of fatigue striations, if determined from component tests, can be used directly for estimating relative operating stress levels of service failed parts. However, the influence on crack growth rate of geometrical factors suggests caution in comparing service failures with fractographic features of laboratory specimens. For this general case the correlations of crack growth rate with Griffith-Irwin fracture mechanics concepts are recommended. Since these analyses consider both component and crack geometry and mode of stressing, they are more generally applicable to a service consideration.
The high magnification used in electron microfractography and its use of replica techniques are shown to be useful in interpreting quantitatively the metallurgical features associated with creep microvoid formation. It is shown that fractography, in combination with standard electron diffraction techniques, permits one to isolate and identify the distribution, size, and content of specific metallurgical phases.
Deterioration of Wood by Marine Fungi in the Deep Sea
Authors: Kohlmeyer J 
Published: March 2009

Wood panels exposed for 13 to 35 months at three Pacific and Atlantic Ocean locations at depths between 1616 and 2073 m were attacked by cellulose digesting fungi. Degradation was limited to the outer layers of the wood and was identical with the “soft rot” decay caused by terrestrial, fresh-water, and marine shallow water fungi.
Two new organisms were discovered belonging to the Ascomycetes and Deuteromycetes. Growth of fruiting bodies was slow, requiring more than 1½ years for development. One additional abyssal Ascomycete was collected with deep-water driftwood from 3710 m in the Gulf of Panama. No fungi were found on panels of seven wood species exposed at a Pacific site (722 m depth) with a low dissolved oxygen content. Cellulolytic bacteria developed in this “minimum oxygen zone” and also in two other test sites. Wood deterioration by bacteria differs distinctly from that caused by fungi. Influence of microorganisms on the settlement of wood boring molluscs is discussed.
The Information Background in the Field of Biological Deterioration of Nonmetallic Materials
Authors: Wessel CJ 
Published: March 2009

Important in the consideration of biological agents is the role of chemical and physical factors such as moisture, heat, light, oxygen, and salts. Crucial in determining the existence of the biological agents at the site of the deteriorative action, they also influence the rates of reaction of biological agents on their substrates. For the subsequent discussions of rubber, plastics, paint, textiles, and other nonmetallics, this paper will sketch the development of science in this field. A secondary goal will comprise outlining methods for obtaining published information on the subject.
There are many antecedent instances of biological deterioration of nonmetallic materials, but World War II assembled circumstances where the subject rose to the attention of the government. Environments of battle theaters and the need to concentrate immense amounts of materiel under primitive storage conditions caused the deterioration by biological agents to become critical. This paper will provide some history and describe events during and after World War II associated with the development of the field.
To perform biodeterioration research and development, it is essential to know the work done in the past. It is important to have under control that little bit of the information reservoir pertinent to the biodeterioration field. The paper, therefore, will identify the information resources which developed concomitant with the needs of research, development, test, and evaluation in the biodeterioration field. The intent is to leave the audience with a picture, not only of the subject matter highlights of this fascinating field, but also the sources where he can gain additional information.
Uptake and Assimilation of Nitrogen in Microecological Systems
Authors: Ehrlich GG , Slack KV 
Published: March 2009

A study of biological effects on water quality utilized recirculating laboratory streams. The sole nitrogen source in one stream was Ca(NO3)2 and in the other was yeast extract. Soluble organic nitrogen from the yeast extract decreased rapidly accompanied by large increases in bacteria and in ammonia. Nitrite and nitrate increased slightly. Bacteria and combined nitrogen decreased rapidly after the initial rise. In the stream with the inorganic nitrogen medium, about half of the nitrate disappeared in two weeks, and nitrate was undetectable after the third week. Bacterial counts were relatively low and constant. Periphyton increased in both streams as nutrients decreased, reaching quasi steady states after about four weeks. The rate of biomass increase was greater in the inorganic medium. Chlorophyll increased rapidly in both streams, reached a maximum the third week, then decreased.
Nitrogen assimilation followed characteristic patterns. Nitrate was directly assimilated by algae. A slight denitrification occurred at high-nitrate concentrations. Organic nitrogen was converted to ammonia by proteolytic bacteria, during which process some nitrogen might have escaped as gaseous ammonia. Ammonia from organic compounds was partly assimilated by algae and partly nitrified by bacteria. Nitrate of bacterial origin was assimilated by algae. Nitrification apparently was not of major importance in converting organic nitrogen to algal biomass.
Laboratory streams simulate natural streams in diurnal cycles of pH and dissolved oxygen, in periphyton growth rate and biomass, and in assimilation of nutrients. Use of model systems to study natural processes under controlled conditions appears justified.
Determination of Trace Amounts of Molybdenum
Authors: Armstrong R , Goldman CR 
Published: March 2009

Molybdenum is determined directly in solutions containing above 100 ppb. A spectrophotometric method using the extractable complex with diacetyldithiol was found to be the most convenient and the least subject to interference of a number of methods.
Preconcentration of dissolved molybdenum by coprecipitation with hydrated MnO2 followed by spectrophotometry of the dithiol complex allows the determination of a 1 μg of molybdenum in a 5 liter sample (0.2 ppb) with a relative error of 3 percent.
Particulate matter may be removed from water samples by HA Millipore filtration or by continuous flow (150 ml/min) centrifugation at 28,000 g. The latter method is more convenient for processing the large (10L to 50L) water samples needed for estimating the trace metal content of suspended particles in unpolluted waters.
Molybdenum is most conveniently released from organic materials by wet oxidation with perchloric acid, the residue being taken up in 3-N hydrochloric acid. Hydrofluoric acid digests of silicate samples were found to give higher recoveries than perchloric acid digests and were found to be more reproducible than fusion methods.
Thermal Fatigue Evaluation
Authors: Carden AE 
Published: March 2009

A test method for performing uniaxial low cycle thermal fatigue tests on ductile metals is described. The test method is built around the Instron testing machine. Both temperature and crosshead extension are programmed and the test cycle can be designed for either tensile or compressive loading at the maximum temperature.
The test method is described for hollow, tubular, threaded-end specimens, resistance heating and compressed air cooling, linear heating and cooling rates, and air environment. The stress dependence of the thermal coefficient of expansion causes no special problem in the determination of the strain values.
A strain measuring system is described that eliminates the thermal component of strain from strain record. Employment of such a system allows a direct recording of load versus mechanical deformation. From these hysteresis loops the pertinent information of the cycle can be determined.
The Influence of Composition and Heat Treatment on the Aqueous-Stress Corrosion of Titanium
Authors: Seagle SR , Seeley RR , Hall GS 
Published: March 2009

Chemical composition and heat treatment were found to have an effect on the aqueous-stress corrosion of titanium. Aluminum contents greater than 5 per cent and oxygen contents greater than about 0.3 per cent caused appreciable sensitivity to stress corrosion. The additions of beta-isomorphous type alloying elements, such as molybdenum, were beneficial for titanium-aluminum alloys but showed no improvement for titanium-oxygen alloys. The amount of oxygen that could-be tolerated was reduced substantially by the addition of aluminum.
Heat-treatment effects were very pronounced and not similar for the alloy systems investigated. The heat-treatment temperature for maximum sensitivity to stress corrosion increased from 1000 F for Ti-6Al alloys to 1200 F for Ti-8Al alloys. This corresponds to about 150 F below the estimated Ti3Al transus. The stress-corrosion resistance of Ti-6Al-4V alloy was reduced as a result of long annealing times prior to exposure in the Ti3Al region. Long annealing times also promoted stress corrosion in titanium-oxygen alloys. Microscopic examination did not reveal significant changes with annealing time. This finding indicates the metallurgical factors affecting the stress corrosion resistance are related to submicroscopic changes.
Strength and Stress-Strain Characteristics of Clays Subjected to Seismic Loading Conditions
Authors: Thiers GR , Seed HB 
Published: March 2009

An attempt is made to relate the results of unconfined compression tests on saturated clays to the strength and bilinear stress-strain parameters which will govern the behavior of the clay during and after earthquakes.
Simple-shear pulsating-load tests on three soils indicate that while the decrease in dynamic strength with number of cycles increases with the failure strain observed in static strength tests, a plot of the product of failure strain x dynamic strength (in percent of static strength) against number of cycles is about the same regardless of the failure strain.
Cyclic-loading triaxial compression tests in which the peak strain was controlled were also performed on the three soils. After 200 cycles of loading the compressive strength was measured under static conditions. It was found that when the peak cyclic strain is less than one half the static failure strain, the strength after cyclic loading is at least 80 percent of the original strength. For larger strains higher strength losses were observed.
The nonlinear stress-strain curves obtained from various cycles in the cyclic loading tests were approximated by a bilinear model defined by three parameters (two moduli and a yield strain). The decrease in the ratio of dynamic modulus/ original static modulus with the ratio of cyclic strain-failure strain is about the same for all three soils for a given number of cycles. A similar relationship for yield strain was found, although this parameter increases with cyclic strain and is virtually unaffected by number of cycles.
The static modulus of each soil tested was greatly reduced by the cyclic loading, decreasing to about one half its original value in tests where the cyclic strain was one half the failure strain.
Low-Cycle Fatigue Study of Columbium Alloy D-43
Authors: Swindeman RW 
Published: March 2009

A machine was developed to study the low-cycle fatigue characteristics of refractory metals in vacuum at high temperatures. Operating capability included temperatures up to 1400 C, loads to 4.45 × 104 N (10 ksi), and frequencies from static to 10 Hz. The machine operated in a push-pull mode and was stroke controlled.
To minimize material required for testing, grips were designed to operate at nearly the same temperature as the specimen. A typical specimen geometry was a rod, 76 mm long with a test section 12.7 mm long and 5.18 mm in diameter.
A series of tests was performed on a columbium alloy, D-43, at temperatures ranging from 20 to 1204 C and cyclic plastic strains from 0.3 to 4 percent. Data at 20, 871, and 1093 C revealed that D-43 conformed to the Coffin-Manson equation, wherein cycles to failure was related to plastic strain range by a power function.
The plastic strain resistance was found to increase with increasing temperature and to exhibit a maximum around 871 C. Up to 1024 C cyclic strain resistance remained better than or equivalent to that at room temperature.
Posttest examination of specimen revealed ductile, transgranular failures at all temperatures.
Influence of Temperature on Reversed Creep
Authors: Kitagawa M , Jaske CE , Morrow J 
Published: March 2009

Torsional reversed creep data are presented for tubular specimens of commercially pure aluminum to illustrate the influence of test temperature on creep deformation resistance under repeated stress reversals. Test temperatures range between 300 and 510 K. These data plus results on other metals show that multiple stress reversals cause a deceleration of creep deformation at test temperatures below about 0.4 of the absolute melting temperature. A significant acceleration of creep may occur at higher temperatures. An optimum temperature for maximum acceleration of creep occurs at a temperature of approximately half of the melting temperature.
The engineering significance of the decrease in creep deformation resistance at high temperatures due to multiple stress reversals is discussed. Creep rupture time and the failure life in high-temperature fatigue or thermal fatigue with large hold times may be reduced significantly by an acceleration of creep at high temperatures.
Effect of Microstructure on the Fatigue Properties of Ti-6Al-4V Bar
Authors: Bartlo LJ 
Published: March 2009

Microstructure can have a significant effect on the mechanical properties of titanium alloys. The extent of this effect on the fatigue properties of the Ti-6Al-4V alloy in small diameter bar (0.625 in., 15.875 mm) was studied. Microstructural variations were produced by heat treating from 1550 to 1950 F at 100 F intervals. Three different cooling rates (furnace cooling, air cooling, and water quenching) were employed for each temperature. The room-temperature tensile, smooth, and notch-fatigue properties were evaluated for each thermal condition.
Thermal treatments that resulted in grain coarsening were found to lower the fatigue strength of the alloy. Beta quenching resulted in good tensile and fatigue strengths but low tensile ductility. Optimum tensile and fatigue properties occur in material consisting of fine grained alpha-beta structures or in material containing mixtures of fine primary alpha and martinisitic alpha.
Atmospheric Exposure of Light Metals
Authors: Brandt SM , Adam LH 
Published: March 2009

This paper summarizes a ten-year atmospheric corrosion test program for aluminum and magnesium base alloys sponsored by the American Society for Testing and Materials under the direction of committee B-7 on Light Metals and Alloys Subcommittee VIII on Atmospheric Exposure Tests.
The program included fourteen cast, nine wrought, and three clad aluminum alloys and five cast and four wrought magnesium alloys. The specimens, exposed at five outdoor exposure sites in the United States, were tested after exposure periods of six months, one, three, five, and ten years.
The tensile strength of the exposed specimen was compared to that of the control specimen which was stored in a sealed container. The per cent changes in tensile strength for the exposed specimens compared to the control specimens are included in the data presented.