Showing papers by "Lehigh University published in 1982"

A theory of fatigue crack initiation at inclusions

Abstract: The dislocation dipole accumulation model for fatigue crack initiation previously proposed by the authors is extended to an analysis of the fatigue strength reduction due to inclusions in high strength alloys. The initiation of a fatigue crack is determined by an energy criterion under the assumption that the crack initiation takes place when the self strain energy of dislocation dipoles accumulated at the damaged part in the material reaches a critical value. Explicit formulae for the crack initiation criterion in several cases are derived as functions of the applied stress, the inclusion size, the slip band shape, and the shear moduli of the inclusion and matrix. The following three types of fatigue crack initiation at inclusions are considered: the slip-band crack emanating from a debonded inclusion, the inclusion cracking due to impinging of slip bands, and the slip-band crack emanating from an uncracked inclusion. The first mechanism was reported to be operative in high strength steels, while the last two mechanisms were reported in high strength aluminum alloys. The present theoretical results are in good agreement with the experimental data published for each case of fatigue crack initiation at inclusions.

Nonstoichiometry in Acceptor‐Doped BaTiO3

Abstract: The effect of added Al, as an acceptor impurity, on the equilibrium electrical conductivity of large-grained, polycrystalline BaTiO3, is consistent with a previously proposed defect model which involves only doubly ionized oxygen vacancies, electrons, holes, and acceptor impurities. The behavior is an extension of that of undoped BaTiO3, in which an accidental net acceptor excess already plays an important role. Comparison of the derived active acceptor content with the amount of added Al indicates that Al is <50% effective in creating acceptor levels. The magnitude of a small Po2-independent conductivity component, necessary to fit the observed conductivity minima, increases with added Al content. This is consistent with a contribution from extrinsic oxygen vacancy conduction.

Theory of the peroxy-radical defect in a -Si O 2

Abstract: We have investigated the peroxy-radical defect in glassy Si${\mathrm{O}}_{2}$ by means of MOPN, a semiempirical molecular-orbital program, applied to a cluster of atoms chosen to simulate the defect. Our calculations are consistent with important features of Griscom's model of the defect as a perturbed ${\mathrm{O}}_{2}^{\ensuremath{-}}$ ion substituted for a single-bridging ${\mathrm{O}}^{2\ensuremath{-}}$ ion in Si${\mathrm{O}}_{2}$ and attached to a single silicon, and they place geometrical constraints on the defect structure for this model to be valid. We predict the existence of a related defect (the small peroxy radical, or SPR) wherein the peroxy radical is strongly bonded to two silicons. We have also investigated the formation of the peroxy radical. Griscom and co-workers envision peroxy linkages substituting for single-bridging oxygens during the growth process. They suggest that upon annealing these linkages readily give up an electron to form the observed radical. Our calculations lead us to argue against this process; rather, capture of a free hole seems more likely. We suggest that the SPR could form via a process in which neutral oxygen molecules diffuse through the solid and combine with ${E}_{1}^{\ensuremath{'}}$ centers to form peroxy radicals.

Self-sustained low-frequency components in an impinging shear layer

Abstract: Oscillations of a cavity shear layer, involving a downstream-travelling wave and associated vortex formation, its impingement upon the cavity corner, and upstream influence of this vortex-corner interaction are the subject of this experimental investigation.Spectral analysis of the downstream-travelling wave reveals low-frequency components having substantial amplitudes relative to that of the fundamental (instability) frequency component; using bicoherence analysis it is shown that the lowest-frequency component can interact with the fundamental either to reinforce itself or to produce an additional (weaker) low-frequency component. In both cases, all frequency components exhibit an overall phase difference of almost 2kπ(k = 1, 2,…) between separation and impingement. Furthermore, the low-frequency and fundamental components have approximately the same amplitude growth rates and phase speeds; this suggests that the instability wave is amplitude-modulated at the low frequency, as confirmed by the form of instantaneous velocity traces.At the downstream corner of the cavity, successive vortices, arising from the amplified instability wave, undergo organized variations in (transverse) impingement location, producing a low-frequency component(s) of corner pressure. The spectral content and instantaneous trace of this impingement pressure are consistent with those of velocity fluctuations near the (upstream) shear-layer separation edge, giving evidence of the strong upstream influence of the corner region.

Corrosion of Painted Metals—A Review

Abstract: Seven types of corrosion and precorrosion of painted metals are reviewed: blistering, early rusting, flash rusting, anodic undermining, filiform corrosion, cathodic delamination, and wet a...

Origin and age of the Border Ranges Fault of southern Alaska and its bearing on the Late Mesozoic tectonic evolution of Alaska

Abstract: Local geologic relationships in the western Chugach Mountains, together with regional considerations, suggest that in the Early Cretaceous a subduction zone was formed along the southern edge of the Wrangellia-Peninsular-Alexander composite terrane (Talkeetna superterrane of Csejtey et al., 1982) of southern Alaska. The effects of this event include (1) a shattering of older (pre-Cretaceous) crystalline rocks along a complex fault system, (2) emplacement of a tectonic melange beneath the shattered crystalline rocks, and (3) a subgreenschist facies prograde metamorphism of the melange and retrograde metamorphism of the older crystalline rocks. This event created a regionally mappable structural contact between broken crystalline rocks and the melange; the Border Ranges fault of MacKevett and Plafker (1974). Regional stratigraphy as well as radiometric ages of rocks predating and postdating the Border Ranges fault appear to bracket the age of the Border Ranges fault and its associated deformational effects to the interval between about 135 and 120 Ma. Further regional tectonostratigraphic associations suggest that the deformation along the Border Ranges fault represents the nucleation of a north and (or) east dipping subduction zone beneath the Talkeetna superterrane and that the magmatic arc associated with this juvenile subduction zone is the Gravina-Nutzotin belt of southeast Alaska. Mismatches in the distribution of different elements of this Early Cretaceous arc-trench system are probably a result of Late Cretaceous or early Tertiary strike slip motion, but Early Cretaceous ridge-trench interaction (suggested by the occurrence of Early Cretaceous near-trench plutons) may have played a role as well. The Talkeetna superterrane is generally thought to be an exotic block that collided with the Cordillera in the middle Cretaceous (Coney et al., 1980). The age data commonly cited as evidence for a middle Cretaceous age for the collision are, however, misleading. A model is proposed here in which the initiation of convergence along the trailing edge of the Talkeetna superterrane records the time of initial impingement of two irregular margins whereas intense middle Cretaceous deformation recognized along the leading edge of the Talkeetna superterrane (Csejtey et al., 1982) records destruction of a syncollisional flysch basin during the final phase of the collision.

Vortex–leading-edge interaction

Abstract: Visualization of successive vortices impinging upon the leading edge of a wedge reveals patterns of deformation of each incident vortex; for certain offsets of the edge with respect to the incident vortex there is pronounced vortex shedding from the leading edge, whereby the shed vortex has a vorticity orientation opposite to that of the incident vortex. Simultaneous consideration of this visualization interaction and the force induced on the wedge gives the relation between the nature of the interaction mechanism and the relative magnitude and phase of the force exerted on the wedge. The amplitude of the induced force is found to be a strong function of the transverse offset of the leading edge with respect to the incident vortex and the degree of vorticity shedding from the leading edge. Application of Stuart's vortex model to the incident vortices provides a means for approximating the phase and relative amplitude of the induced force as a function of the transverse offset of the leading edge.

Oscillations of an unstable mixing layer impinging upon an edge

Abstract: The central features of lihear and nonlinear disturbance growth in the unstable shear layer, mechanisms of impingement of the resultant vortices on the edge, induced force on the wedge, and upstream influence in the form of induced velocity fluctuations at separation are examined by simultaneous visualization, velocity, and force-measurement techniques.The nature of the vortex–wedge interaction, and the associated force on the wedge, are directly related to the induced velocity at the upstream separation edge, thereby providing the essential ‘feedback’ for the self-sustained oscillation. Velocity fluctuations at the upper and lower sides of the separation edge tend to be π out of phase, a condition that is maintained along the outer boundaries of the downstream shear layer. Moreover, the phase between velocity fluctuations at separation and impingement satisfies the relation 2nπ, where n is an integer.The shear layer downstream of the separation edge initially forms an asymmetric wake, which evolves into large-scale vortices, all of which have a circulation appropriate to the high-speed side. The disturbance amplification associated with the high-speed side dominates from the separation edge onwards, precluding development of instabilities associated with the low-speed side.Regardless of the initial amplitude of the disturbance induced at the separation edge, the same saturation amplitude is attained in the downstream (nonlinear) region of the shear layer, underscoring the fact that variations in force amplitude at the wedge are dominated by the type of vortex–edge interaction mechanism. The sensitivity of this interaction to small offsets between the vortex centre and the leading edge entails that jumps in frequency of oscillation are also associated with jumps in the force amplitude.

The effects of C, P, and S on trace element partitioning during solidification in Fe‐Ni alloys

Abstract: Trace and minor element distributions in the iron meteorites are generally ascribed to partitioning during solidification of the parent body core or to partial melting within the parent body. A model involving fractional crystallization is considered. The model cannot account for differences between the measured values for the slopes on the log Ir-log Ni plots and the slopes predicted using experimentally determined distribution coefficients obtained in an investigation conducted by Goldstein and Friel (1978). The model has also other weaknesses. Part of the answer concerning the existing problems was provided by Narayan and Goldstein (1981, 1982). The present investigation is concerned with a further clarification of the effect of the minor elements P, S, and C on the distribution behavior of trace elements. Attention is given to measurements of the distribution coefficients for various elements (Ir, Ge, Ga, Au, Cu, Cr) in the presence of these minor elements.

Application of the line-spring model to a cylindrical shell containing a circumferential or axial part-through crack

Abstract: An approximate solution was obtained for a cylindrical shell containing a part-through surface crack. It was assumed that the shell contains a circumferential or axial semi-elliptic internal or external surface crack and was subjected to a uniform membrane loading or a uniform bending moment away from the crack region. A Reissner type theory was used to account for the effects of the transverse shear deformations. The stress intensity factor at the deepest penetration point of the crack was tabulated for bending and membrane loading by varying three dimensionless length parameters of the problem formed from the shell radius, the shell thickness, the crack length, and the crack depth. The upper bounds of the stress intensity factors are provided by the results of the elasticity solution obtained from the axisymmetric crack problem for the circumferential crack, and that found from the plane strain problem for a circular ring having a radial crack for the axial crack. The line-spring model gives the expected results in comparison with the elasticity solutions. Results also compare well with the existing finite element solution of the pressurized cylinder containing an internal semi-elliptic surface crack.

Removal of Sulfur Compounds from Coal by the Thermophilic Organism Sulfolobus acidocaldarius.

Abstract: The thermophilic, reduced-sulfur, iron-oxidizing bacterium Sulfolobus acidocaldarius was used for the removal of sulfur compounds from coal. The inclusion of complex nutrients such as yeast extract and peptone, and chemical oxidizing agents, 0.01 M FeCl3 into leaching medium, reduced the rate and the extent of sulfur removal from coal. The rate of sulfur removal by S. acidocaldarius was strongly dependent on the sulfur content of the coal and on the total external surface area of coal particles. Approximately 96% of inorganic sulfur was removed from a 5% slurry of coal which had an initial total sulfur content of 4% and an inorganic (pyritic S and sulfate) sulfur content of 2.1%. This resulted in removal of 50% of initial total sulfur present in coal.

Negative-U Properties for Interstitial Boron in Silicon

Abstract: Electrical detection of a single donor level of interstitial boron at ${E}_{c}\ensuremath{-}0.13$ eV using novel photo---deep-level transient spectroscopy techniques is reported. Complementary behavior between this level and the acceptor level at ${E}_{c}\ensuremath{-}0.45$ eV establishes that the defect levels have negative-$U$ ordering. The donor level exhibits a large Poole-Frenkel effect which, when properly accounted for, provides a direct and unambiguous connection to the EPR-identified interstitial boron atom. This represents the first definitive indentification of negative-$U$ properties for a defect in any solid.

Crack problems for a rectangular plate and an infinite strip

Abstract: The general plane problem for an infinite strip containing multiple cracks perpendicular to its boundaries is considered. The problem is reduced to a system of singular integral equations. Two specific problems of practical interest are then studied in detail. The first problem explores the interaction effect of multiple edge cracks in a plate or beam under tension or bending. The second problem is that of a rectangular plate containing an arbitrarily oriented crack in the plane of symmetry. Particular emphasis is placed on the problem of a plate containing an edge crack and subjected to concentrated forces.

A revision of metallographic cooling rate curves for chondrites

Abstract: New metallographic cooling rate curves for the chondritic meteorites are calculated. On the basis of these curves, estimated cooling rates for the chondrites are twice as fast as those determined using the Wood (1967) curves. This change in estimated rates derives from the use of the most recent Fe-Ni phase diagram and the use of more accurate computational techniques. The new cooling rate curves can be applied to meteorites with P contents in the metal phase less than 0.01 wt%. They should be applied with some caution to meteorites, such as the unequilibrated ordinary chondrites, where the metal grains may not have equilibrated above approximately 850K, or to metallic phases which contain P in quantities greater than 0.01 wt% and/or phosphides.

Correlation between grain boundary corrosion and grain boundary energy in niobium bicrystals

Abstract: Grain-boundary hardening of oriented niobium bicrystals with symmetric tilt boundaries has been determined using microhardness measurements. The boundary hardening was found to be misorientation-dependent and related to the boundary energy. For bicrystals with low-angle boundaries, the hardening varies with misorientation with a linear relationship of the Read-Shockley type. For bicrystals with high-angle boundaries, hardening cusps (minima) were observed near the coincidence-site-lattice boundaries.

Stress intensity factors in a hollow cylinder containing a radial crack

Abstract: An exact formulation of the plane elasticity problem for a hollow cylinder or a disk containing a radial crack is given The crack may be an external edge crack, an internal edge crack, or an embedded crack It is assumed that on the crack surfaces the shear traction is zero and the normal traction is an arbitrary function of r For various crack geometries and radius ratios, the numerical results are obtained for a uniform crack surface pressure, for a uniform pressure acting on the inside wall of the cylinder, and for a rotating disk

Citing statements: Computer recognition and use to improve retrieval

Abstract: Documents in computer-readable form can be used to provide information about other documents, i.e. those they cite. To do this efficiently requires procedures for computer recognition of citing statements. This is not easy, especially for multi-sentence citing statements. Computer recognition procedures have been developed which are accurate to the following extent: 73% of the words in statements selected by computer procedures as being citing statements are words which are correctly attributable to the corresponding documents. The retrieval effectiveness of computer-recognized citing statements was tested in the following way. First, for eight retrieval requests in inorganiic chemistry, average recall by search of Chemical Abstracts Service indexing and Chemical Abstracts abstract text words was found to be 50%. Words from citing statements referring to the papers to be retrieved were then added to the index terms and abstract words as additional access points, and searching was repeated. Average recall increased to 70%. Only words from citing statements published within a year of the cited papers were used. The retrieval effect of citing statement words alone (published within a year) without index or abstract terms was the following: average recall was 40%. When just the words of the titles of the cited papers were added to those citing statement words, average recall increased to 50%.

Self-generation of organized waves in an impinging turbulent jet at low Mach number

Abstract: Self-generation of highly organized waves in a nominally turbulent jet at very low Mach number can arise from its impingement upon the downstream orifice of an axisymmetric cavity, having an impingement length much shorter than the corresponding acoustic wavelength. The oscillation frequencies are compatible with the resonant modes of a long pipe located upstream of the cavity and with jet-instability frequencies based on the column mode (0·3 [siml ] SD [siml ] 0·6), as well as the near-field shear layer mode (0·016 [siml ] Sθ0 [siml ] 0·03). Moreover, the frequency of the organized wave is constant from separation to impingement; consequently vortex pairing does not occur.Within the cavity, the pressure amplitude associated with the organized wave is directly related to the phase difference between the organized velocity fluctuations at separation and impingement. Maximum pressure amplitude occurs when this phase difference, measured along the cavity (i.e. jet) centre-line, is 2nπ. Streamwise amplitude and phase distributions of the organized wave cannot be explained from purely hydrodynamic considerations; however, they can be effectively modelled by superposing contributions from hydrodynamic and acoustic waves. This aspect has important consequences for externally excited jets as well.

Optical Detection of Magnetic Resonance for a Deep-Level Defect in Silicon

Abstract: Optical detection of magnetic resonance is reported for the 0.97-eV luminescence in neutron-irradiated silicon. The resonance is of an excited triplet ($S=1$) state of the defect, which is not the radiative state, known to be a singlet ($S=0$). The spectrum is unusual in that it is characteristic of a statically distorted defect (from ${C}_{3v}$ to ${C}_{1h}$), but with residual dynamic tunneling effects where random strain stabilizes mixtures of the static ${C}_{1h}$ distortions. Vacancy-related models previously suggested for the defect are tentatively ruled out.

Poly(n-butyl acrylate)/polystyrene interpenetrating polymer networks and related materials I. Dynamic mechanical spectroscopy and morphology

Abstract: A series of interpenetrating polymer networks, IPN's, and semi-1 IPN's of poly(n-butyl acrylate) and polystyrene were prepared. The glass transition behavior via dynamic mechanical spectroscopy (DMS) and the morphology via transmission electron microscopy (TEM) were studied as a function of composition ratio and crosslink density. Transition-broadening was observed at low crosslink concentrations, while a single broad glass transition peak at an intermediate position was attained at high crosslink density levels. A cellular domain structure was the morphological characteristic of those IPN's and semi-1 IPN's possessing a low cross-link density and mid-range composition ratio. At higher levels of crosslink density, irregular shapes of the domain morphology prevailed. Phase connectivity was also observed at high polymer II compositions. Theoretical phase domain sizes of polymer II were calculated using both the theories developed by the present authors and that published earlier by Donatelli, et al., and were found to agree with the experimental domain sizes. While the theory was developed for uniform spheres, some of the domain structures observed experimentally for high polymer II contents had connectivity and/or a cylindrical shape.

Thermoplastic interpenetrating polymer network composition and process

Abstract: Chemically blended thermoplastic interpenetrating polymer network compositions, of improved physical and mechanical properties as compared to their mechanically blended counterparts, are produced by forming a solution or mixture of polymeric components and polymerizing in situ, with materials capable of forming physical crosslinks, through mechanisms including block copolymers, ionomeric crosslinking and the incorporation of crystalline regions in semicrystalline homopolymers. The resultant products are in the nature of thermoset materials at room temperature but become thermoplastic at elevated temperatures.

Determination of Calcium Carbonate Content in Soils

Abstract: A survey of laboratory methods is presented for the determination of the calcium carbonate content of soils. The survey looks at (1) the accuracy obtained, (2) operator skill required, and (3) relative equipment costs, inaddition to other variables. In addition, a summary of marine carbonate materials is also presented which illustrates their various sizes, shapes, locations, porosities, and chemical constituents. The conclusion from this survey is that the pressure calcimeter method ("Karbonat-Bombe") is the best method suited for geotechnical engineering applications.