Showing papers by "Michigan Technological University published in 1978"

Brittle fracture in iridium

Abstract: Brittle fracture in fcc metals is uncommon. It is not common knowledge that single crystals of iridium, a high melting point fcc metal, fail by brittle cleavage at room temperature. Furthermore, polycrystalline iridium fails predominantly by brittle inter granular fracture at temperatures below 1000°C. With the aid of several models of brittle fracture we have demonstrated that cleavage in iridium is intrinsic, resulting from apparently very strong and directed atomic binding forces. Intergranular fracture in iridium has been generally assumed to arise from the segregation of harmful impurities to the grain boundaries. We were able to demonstrate using Auger electron spectroscopy that impurity segregation to grain boundaries in iridium was not necessary for grain boundary fracture to occur, thereby demonstrating that intergranular brittle fracture in polycrystalline iridium is also intrinsic and not impurity related.

Precipitation at interphase boundaries

Abstract: Three problems in precipitation at interphase boundaries are examined. 1) The classu argument as to the particular phase in which such a precipitate nucleates is shown to be irrelevant; except in a special situation, the critical nucleus must normally penetrate both phases forming the interphase boundary. 2) The relative penetrations into the two phases achieved during growth can be very different than those expected during nucleation; hence, deductions about the nucleation process based upon observations on growth morphologies can be quite misleading. 3) The observations of Honeycombe and others that the nucleation of carbides at austenite: ferrite boundaries occurs predominantly at the low energy, immobile broad faces of ledges rather than at the higher energy, mobile risers of ledges are accounted for theoretically on the basis of the high velocities of the risers preventing nucleation. Example calculations on a Ti-Ni alloy indicate that precipitation at the risers of ledges may become possible in substitutional systems, but only at lower homologous temperatures, and if the migration of these boundaries is still controlled by volume diffusion while nucleation is controlled by interfacial diffusion.

Sulfur segregation to grain boundaries in Ni 3 Al and Ni 3 (AI,Ti) alloys

Abstract: The segregation of S to grain boundaries in Ni3Al and Ni3(Al, Ti) has been studied using Auger electron spectroscopy. The S concentration at the grain boundaries decreases more slowly with increasing temperature than would be predicted by segregation models based on a single solute binding energy to the grain boundaries. This behavior, which can be interpreted as an increase in the effective solute binding energy for a grain boundary as a function of temperature, is consistent with predictions of a model based on the existence of a spectrum of solute binding energies for grain boundaries.

A re-examination of the thermodynamics of the proeutectoid ferrite transformation in Fe-C alloys

Abstract: Three models of the statistical thermodynamics of interstitial solid solutions have been used to reevaluate the thermodynamics of the proeutectoid ferrite reaction. The models of Kaufman, Radcliffe and Cohen and of Lacher, Fowler and Guggenheim, which were em-ployed in a previous study of this type, together with the model recently developed by McLellan and Dunn are used in conjunction with the extensive experimental data of Ban-ya, Elliott and Chipman, of Lobo and Geiger and of Dunn and McLellan on the activities of carbon in austenite and ferrite. Application of the McLellan and Dunn model and that of Lacher, Fowler and Guggenheim to carbon in austenite yields activities of carbon which are numerically indistinguishable and activities of iron which are mathematically identi-cal. However, the new activity data have revealed important differences between the pres-ent calculations and those of Aaronson, Domian and Pound. An average carbon-carbon repulsion energy in austenite of 1925 cal/mole (8054 J/mole) was determined from the CO/CO2 data of Ban-yaet al. However, the C-C interaction energy in ferrite was found to be opposite in sign but exhibited erratic variations with temperature despite the large amount of activity data available. The γ/(α + γ) phase boundary calculated from the new data differs significantly, at lower temperatures, from the best curves reported by Aaron-sonet al. The calculateda/(α +γ) phase boundary also differs appreciably from the pre-vious results and exhibits only limited agreement with the experimentally determined phase boundary. Calculation of the free energy change associated with the proeutectoid ferrite reaction andT 0- composition curves differs little from previous results; internal agreement among the new sets of curves, however, is much improved.

Physical and chemical character of diesel particulate emissions -- measurement techniques and fundamental considerations

Abstract: The techniques used to characterize the chemical and physical nature of particulates in diesel exhaust emissions are reviewed. The emphasis is on understanding the broader aspects of the fundamental nature of not only diesel particulates, but particulate systems in general. Consideration is given to the special nature of particulates which make them significant pollutants and to the relative place of the diesel in the formation of man-made particles. The underlying combustion processes leading to carbon and sulfur based particulates are reviewed. The important variables in steps of the combustion processes which lead to particulate formation are considered, as well as major fuel and engine factors. Collection methods are examined with examples given from current diesel dilution techniques. Probes, sampling lines, and instrumentation are considered. Methods of physical and chemical characterization are presented and examples from the current and prior diesel work at Michigan Technological University and elsewhere are given.

Method for molding apertures in molded wood products

Abstract: A method is provided for forming a wood product comprised of wood flakes and binder intermixed therein, and including a hole or aperture molded into the product, the aperture including a densified, high strength periphery. The method includes the steps of providing a female die plate having a forming surface and a bore extending through the die plate, the bore converging in the direction away from the forming surface. A male die plate is also provided in opposed relation to the female die plate, the male die plate having a forming surface and a tapered forming member aligned with the bore in the female die plate. A mat comprised of wood flakes and intermixed binder is placed between the die plates, and the die plates are forced together to compress the mat between the forming surfaces, thereby forming a rigid composite body. The die plates also form a tapered aperture in the composite body, the tapered forming member and the complementary converging bore in the female die plate causing localized increased density of the periphery of the formed aperture.

Pallet having densified edge and method of making same

Abstract: A molded unitarily formed pallet is provided, the pallet including wood particles bonded together by a cured binder in compressed relation. Also provided is a method for making such pallets. The pallet includes a deck having an upper supporting surface, a lower surface, a plurality of integral leg sections extending downwardly from the deck, and a densified integral peripheral portion surrounding the deck to provide increased strength at the periphery of the pallet. The pallet may also include narrow elongated wooden strips bonded to the densified peripheral edge to further increase the strength of the pallet.

A survey of eutectoid decomposition in ten Ti-X systems

Abstract: The mechanism of eutectoid decomposition in ten Ti-X binary systems, wherein X was successively Bi, Co, Cr, Cu, Fe, Mn, Ni, Pb, Pd and Pt, has been investigated. In hypo-eutectoid alloys, the bainite reaction (defined in the present context as a nonlamellar dispersion of intermetallic compound particles amongst proeutectoid a) predominated in all alloys studied but Ti-Cu, where both bainite and pear lite were formed. In alloys of near eutectoid composition pearlite was the dominant product in some systems and bainite was in others. These results are essentially independent of reaction temperature. They are quite different from analogous ones in Fe-C alloys, where pearlite is the principal eutectoid structure formed at high temperatures and bainite plays this role at low tem-peratures. The difference between the Ti-X and Fe-C behaviors was explained in terms of the much more pronounced tendency for proeutectoid α plate formation in Ti-X than in Fe-C alloys and, on a theory due to Hillert, of the need for disordered interphase boundaries in order to develop the cooperative growth mode that leads to the evolution of pearlite.

The Characterization of the Hydrocarbon and Sulfate Fractions of Diesel Particulate Matter

Abstract: One of the most objectionable aspects of the use of diesel engines has been the emission of particulate matter. A literature review of combustion flames, theoretical calculations and dilution tunnel experiments has been performed to elucidate the chemical and physical processes involved in the formation of diesel particulate matter. A comparative dilution tunnel study of diluted and undiluted total particulate data provided evidence supporting calculations that indicate hydrocarbon condensation should occur in the tunnel at low exhaust temperatures. The sample collection system for the measurement of total particulate matter and soluble sulfate in particulate matter on the EPA 13 mode cycle is presented. A method to correct for hydrocarbon interferences in the EPA barium chloranilate method for the determination of sulfate in particulate matter is discussed.

Calculation of the elastic strain field of a cuboidal precipitate in an anisotropic matrix

Abstract: Using the anisotropic elastic Green's functions and their derivatives, the elastic strain field associated with a cuboidal precipitate in an anisotropic matrix is calculated. Uniform elastic constants for the precipitate and matrix are assumed, and the elastic constants of copper are used. Assuming a pure volumetric transformation strain, it is found that the dilatation is constant neither in the precipitate nor in the matrix. The dilatation inside the precipitate increases smoothly from the precipitate center to the interface, resulting in a maximum along the [110] direction. In the matrix, the dilatation exhibits a negative value near the interface in the directions [100], [110], and [111]. The elastic strain energy associated with a cuboidal precipitate is found to be ca. 93% of that of a spherical precipitate. Mit Hilfe von anisotropen elastischen Green-Funktionen und ihren Ableitungen wird das elastische Spannungsfeld fur wurfelformige Ausscheidungen in einer anisotropen Matrix berechnet. Es wird angenommen, das die elastischen Konstanten fur die Ausscheidungen und die Matrix gleichformig sind, und es werden die elastischen Konstanten fur Kupfer benutzt. Mit der Annahme einer reinen Volumentransformationsspannung ergibt sich, das die Dilatation weder in den Ausscheidungen noch in der Matrix konstant ist. Die Dilatation innerhalb der Teilchen nimmt gleichformig vom Mittelpunkt zur Grenzflache der Ausscheidungen zu und hat ein Maximum entlang der [110]-Richtung. In der Matrix ist die Dilatation an der Grenzflache negativ in den [100]-, [110]- und [111]-Richtungen. Es ergibt sich, das die elastische Spannungsenergie fur wurfelformige Ausscheidungen etwa 93% der fur kugelformige Ausscheidungen betragt.

Low-Cycle fatigue crack nucleation and early growth in Ti-17

Abstract: The mechanisms of low-cycle, fatigue crack nucleation and early growth were investigated at room temperature for Ti-17 (an α+ β titanium alloy). The investigation includedβ processed, high temperature α+ β processed, and low temperaturea + β processed material. The mechanisms of crack nucleation and the path of early crack growth were found to vary with microstructure. Low temperature α+ β processed material demonstrated later crack nucleation but more rapid early crack growth than the other two thermomechanically processed forms. High temperature α+ β processed material containing microstructural flaws, commonly referred to as β-flecks, showed a degradation of fatigue life at high cyclic strain ranges. Results are discussed in terms of microstructural sites of plastic strain concentration.

Dinitrogen Fixation Associated with Sporophores of Fomitopsis Pinicola, Fomes Fomentarius, and Echinodontium Tinctorium

Abstract: SUMMARYFixation of atmospheric dinitrogen by bacteria associated with contextual tissues of sporophores of Fomitopsis pinicola, Fomes fomentarius, and Echinodontium tinctorium is reported. Since ni...

The Development and Application of Ferrography to the Study of Diesel Engine Wear

Abstract: Ferrographic oil analysis of wear measurement is compared with both the radioactive tracer method and spectroscopic oil analysis, and is described in depth. Metallic wear debris is magnetically separated from a lubricant sample, systematically arranged according to size on a glass substrate, and examined by either a scanning electron microscope or transmission electron microscope. Ferrography is easily adaptable to either laboratory or field analysis. Its disadvantage is that it cannot detect the soluble portion of wear which is often due to corrosion. The technique is described in detail. Test data of the ferrographic oil analysis technique made with a direct injection, four-cycle, turbocharged diesel engine show that ferrography is sensitive enough to indicate changes in engine operating conditions. Data indicate operating time on engine oil for steady state engine operation to approach finite concentrations with time. Engine oil filtration is beneficial. Ferrography is shown to be the most versatile method of analyzing severe wear and detecting failure.

Physical size distribution characterization of diesel particulate matter and the study of the coagulation process

Abstract: Diesel particulate matter in both the diluted and undiluted state is subject to the processes of coagulation, condensation or evaporation, and nucleation which causes continuous changes in its physical characteristics. The Electrical Aerosol Analyzer (EAA) is used to measure the diesel particle size distribution in the Michigan Technological University dilution tunnel for a naturally aspirated direct-injection diesel engine operated on the EPA 13 mode cycle. The design and development of accurate and repeatable sampling methods using the EAA are presented. These methods involve both steady-state tunnel and bag measurements. The data indicate a bimodal nature within the 0.001 to 1 millimicron range. The first mode termed the "embryonic mode" has a saddle point between 0.005 to 0.015 millimicron and the second mode termed the "aggregation mode" lies between .08 to .15 millimicron for the number distribution. The particle concentration decreases with time and the resulting size distribution function approaches an asymptotic steady-state solution indicating the self-preserving nature of particulate size distributions. Coagulation constants have been calculated for the diesel particles and are compared to theoretical values in the literature.

Structure/property/continuum synthesis of ductile fracture in inconel alloy 718

Abstract: Two microscopic ductile fracture processes have been established in a fracture tough superalloy, Inconel 718, aged to five strength levels. At yield strengths less than 800 MPa, the mechanism is a slow tearing process within large pockets of inhomogeneous carbides and nitrides, giving rise to plane strain fracture toughness (KIC)values greater than 120 MPa-m1/2. At yield strengths greater than 900 MPa, the mechanism involves fracture initiation at carbides and nitrides followed by off crack plane void sheet growth nucleated at the Laves (σ) phases. Here, the fracture toughness drops to about 80 MPa-m1/2. A Mode I normal strain growth model for low yield strength conditions and a shear strain void sheet model for high yield strength ones are shown to model KIC data obtained from a J-integral evaluation of compact tension results.

Principal stress directions from a natural occurrence of stress-induced clinoenstatite

Abstract: Lamellae of clinoenstatite are common in enstatite grains in the high-grade ultramafic hornfelses around the Mount Stuart Batholith in the Central Cascades of Washington. Laboratory deformation experiments on enstatite have shown that shear stress on (100) planes parallel to [001] drastically promotes the formation of clinoenstatite. Petrofabric studies of a sample of the hornfels reveal a strong preferred orientation of clinoenstatite-bearing enstatite grains that is unrelated to the fabric of the complete set of enstatite grains. This preferred orientation is well explained by supposing that the clinoenstatite was produced by shearing due to N-S compression. Local and regional geological features are also consistent with N-S compression. These results suggest that there is considerable potential for the application of stress-induced clinoenstatite as a geopiezometer in rocks.

Dual-adjustment balance circuit for operational amplifiers

Abstract: A method and circuit for balancing the offset voltage of an operational amplifier having an input resistor connected to an inverting input, and a feedback resistor connected to and between the inverting input and the amplifier output. The circuit is made up of an adjustable voltage divider network connected to the positive and negative power supplies of the amplifier and includes coarse and fine potentiometers for applying a first adjustable voltage to the inverting input to set the inverting voltage to zero, and a third potentiometer for applying a second adjustable voltage to the non-inverting input to set the amplifier output voltage to zero. The resulting offset voltage balance is generally insensitive to changes in values of the input resistor and the feedback resistor.