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Microstructure dependent fatigue crack growth in aged hardened aluminium alloys

Borrego, L. P.; Costa, J. M.; Silva, S.; Ferreira, J. M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
36.09%
Fatigue crack propagation tests in constant amplitude loading, as well as with single peak overloads, have been performed in AlMgSi1-T6 aluminium alloys with different Mn and Cr contents. Crack closure was monitored in all tests by the compliance technique using a pin microgauge. A moderate stress ratio and a strong material dependence effects on the fatigue crack growth were observed. These effects are discussed in terms of the different dominant closure mechanism (plasticity-induced closure or roughness-induced closure). Roughness-induced closure dominates crack closure in the alloys with higher contents of Mn and Cr elements. In the alloy with a lower content of these elements, plasticity-induced closure is dominant. When roughness-induced closure is the prime pre-overload closure mechanism, the retardation effect is decreased in comparison to when plasticity-induced closure is dominant.; http://www.sciencedirect.com/science/article/B6V35-4CPD73M-3/1/e77472d32013689741e1021b5b6ffcce

Influence of the microstructure in the collapse of a residual clayey tropical soil

GUTIERREZ, Nelci Helena Maia; NOBREGA, Maria Teresa de; VILAR, Orencio Monje
Fonte: SPRINGER HEIDELBERG Publicador: SPRINGER HEIDELBERG
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.9%
A typical residual clayey soil originating from basalt in southern Brazil has been analyzed in order to assess the influence of wetting-induced deformation and microstructural features on the collapse behavior. Single and double oedometer tests were undertaken on a soil profile to 9 m depth. The results indicated collapsible behaviour at all profile depths. The influence of pre-consolidation stress and pedogenetic factors in the variability of the physical characteristics of the soil and in the magnitude of the collapse was noted. The collapse coefficient has been shown to be related to the both the microaggregate plasma and the varying nature of the pores and their interconnectivity.

Effect of processing induced particle alignment on the fracture toughness and fracture behavior of multiphase dental ceramics

GONZAGA, Carla C.; OKADA, Cristina Yuri; CESAR, Paulo F.; MIRANDA JR., Walter G.; YOSHIMURA, Humberto N.
Fonte: ELSEVIER SCI LTD Publicador: ELSEVIER SCI LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.14%
Objective. To investigate the processing induced particle alignment on fracture behavior of four multiphase dental ceramics (one porcelain, two glass-ceramics and a glass-infiltrated-alumina composite). Methods. Disks (empty set12mm x 1.1 mm-thick) and bars (3 mm x 4 mm x 20 mm) of each material were processed according to manufacturer instructions, machined and polished. Fracture toughness (K(IC)) was determined by the indentation strength method using 3-point bending and biaxial flexure fixtures for the fracture of bars and disks, respectively. Microstructural and fractographic analyses were performed with scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. Results. The isotropic microstructure of the porcelain and the leucite-based glass-ceramic resulted in similar fracture toughness values regardless of the specimen geometry. On the other hand, materials containing second-phase particles with high aspect ratio (lithium disilicate glass-ceramic and glass-infiltrated-alumina composite) showed lower fracture toughness for disk specimens compared to bars. For the lithium disilicate glass-ceramic disks, it was demonstrated that the occurrence of particle alignment during the heat-pressing procedure resulted in an unfavorable pattern that created weak microstructural paths during the biaxial test. For the glass-infiltrated-alumina composite...

Influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite

CVEJIC, Z.; ANTIC, B.; KREMENOVIC, A.; RAKIC, S.; Goya, Gerardo Fabian; Rechenberg, Hercilio Rodolfo; JOVALEKIC, C.; SPASOJEVIC, V.
Fonte: ELSEVIER SCIENCE SA Publicador: ELSEVIER SCIENCE SA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.1%
In this work we report results on the influence of heavy rare earth ions substitution on microstructure and magnetism of nanocrystalline magnetite. A series of Fe(2.85)RE(0.15)O(4) (RE = Gd, Dy, Ho, Tm and Yb) samples have been prepared by high energy ball milling. Structure/microstructure investigations of two selected samples Fe(2.85)Gd(0.15)O(4) and Fe(2.85)Tm(0.15)O(4), represent an extension of the previously published results on Fe(3)O(4)/gamma-Fe(2)O(3), Fe(2.85)Y(0.15)O(4) and Fe(2.55)In(0.45)O(4) [Z. Cvejic, S. Rakic, A. Kremenovic, B. Antic, C. Jovalekic. Ph. Colomban, Sol. State Sciences 8 (2006) 908], while magnetic characterization has been done for all the samples. Crystallite/particle size and strain determined by X-ray diffractometry and Transmission electron microscopy (TEM) confirmed the nanostructured nature of the mechanosynthesized materials. X-ray powder diffraction was used to analyze anisotropic line broadening effects through the Rietveld method. The size anisotropy was found to be small while strain anisotropy was large, indicating nonuniform distribution of deffects in the presence of Gd and Tm in the crystal structure. Superparamagnetic(SPM) behavior at room temperature was observed for all samples studied. The Y-substituted Fe(3)O(4) had the largest He and the lowest M(S). We discuss the changes in magnetic properties in relation to their magnetic anisotropy and microstructure. High field irreversibility (H>20kOe) in ZFC/FC magnetization versus temperature indicates the existence of high magnetocrystalline and/or strain induced anisotropy. (C) 2008 Elsevier B.V. All rights reserved.; Serbian Ministry of Science; Serbian Ministry of Science and Environmental Protection

Resistência à corrosão e ao trincamento induzido por hidrogênio de aços para tubos API 5L X65.; Corrosion and hydrogen induced cracking resistance of pipeline steels API 5L X65.

Hincapie Ladino, Duberney
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 26/10/2012 PT
Relevância na Pesquisa
36.17%
Com a descoberta de novas fontes de petróleo e gás, em regiões remotas e de difícil acesso, tem-se a necessidade do desenvolvimento de novas tecnologias para garantir a eficácia da exploração destes recursos. Essa exploração e extração muitas vezes se dão em ambientes altamente corrosivos e os equipamentos devem apresentar propriedades que garantam um fator de segurança em serviço. Os aços de alta resistência e baixa liga (ARBL) são utilizados em tubulações para o transporte de gás natural e petróleo. Estes estão constantemente expostos a ambientes ácidos os quais são compostos de umidade e sulfeto de hidrogênio (H2S), podendo causar falha induzida pela presença de hidrogênio (Hydrogen Induced Cracking HIC). Este tipo de falha é normalmente abordado na literatura através de ensaios em solução contendo ácido acético e/ou sais (cloreto de sódio, entre outros), sempre com a injeção de H2S. Há vários mecanismos propostos, no entanto, o assunto não está totalmente resolvido. As alterações de composição química dos aços, processos de refino do aço e processos de conformação mecânica são responsáveis pela microestrutura final e determinantes da resistência à fragilização por hidrogênio. O objetivo deste trabalho é analisar e comparar o comportamento quanto à resistência à corrosão e resistência à HIC de quatro materiais: tubo X65 sour...

Influência da microestrutura nas propriedades mecânicas e na fragilização por hidrogênio em um aço microligado.; Influence of microstructure on the mechanical properties and hydrogen embrittlement in microalloyed steel.

González Ramírez, Mario Fernando
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 28/09/2012 PT
Relevância na Pesquisa
36.26%
A tecnologia dos aços microligados para transporte de gás natural e petróleo tem sido pressionada pelo descobrimento das novas jazidas e o aumento da demanda no mundo. As solicitações ambientais e de resistência mecânica são os parâmetros para o desenvolvimento de aços de alta resistência baixa liga para o transporte de gás e petróleo a menor custo e de forma segura. Neste contexto esta pesquisa investiga, em um aço microligado para tubos API 5L X80, o efeito das transformações de fase obtidas por resfriamentos controlados na fratura induzida por hidrogênio Hydrogen Induced Cracking-(HIC) e nas propriedades mecânicas. Os testes de HIC foram realizados no material como recebido, na espessura da chapa submetida a resfriamentos contínuos e em amostras do material tratadas de forma a simular as regiões de grão grosso da zona afetada pelo calor (GGZAC). Segundo o ciclo de resfriamento, os aços microligados têm microestruturas complexas, como é caso do aço microligado em estudo, onde sua microestrutura, estudada em trabalhos anteriores, é formada principalmente por ferrita, bainita, perlita e microconstituinte austenita/martensita (AM). A morfologia, tamanho, quantidade e distribuição dos produtos de transformação na chapa mudam as propriedades do aço. Esses fenômenos são de grande interesse tecnológico em aços microligados para a fabricação de tubos soldados para o transporte de gás e petróleo...

Effect of deposition current on microstructure and properties of CoCrWC alloy PTA coatings

Paes,R. M. G.; Scheid,A.
Fonte: Associação Brasileira de Soldagem Publicador: Associação Brasileira de Soldagem
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2014 EN
Relevância na Pesquisa
36.13%
Cobalt-Based alloys are largely applied to the surface of components as welded coatings. Carbides reinforced CoCrWC system is used to extend the service life under harsh environments involving wear and corrosion in different media. This work aims to evaluate the effect of deposition current on the microstructure and properties of PTA coatings. So, CoCrWC alloy (Stellite #6) was processed on AISI316L stainless steel plates with the following main arc current: 100, 120, 150, 180 and 200A. So, different interaction with the substrate must be expected and its effect on coatings features was evaluated. The geometry of single track coatings, dilution, formed phases and phase volume fraction was assessed by laser Confocal, scanning electron microscopy and X-ray diffraction analysis. Vickers hardness and wear tests were carried out to correlate microstructure to properties of coatings. Coatings showed microstructure composed by hypoeutectic dendrites of Cobalt solid solution and interdendrictic carbides. Dilution increased with deposition current from 11,8 e 56,5% which reduced the carbides fraction and increased the Cobalt solid solution areas, resulting in hardness decrease from 500 to 310HV0,5. Higher deposition current induced mass loss rate increase on pin-on-disc sliding wear tests...

Microstructure and Properties of Nickel-based C276 Alloy Coatings by PTA on AISI 316L and API 5L X70 Steel Substrates

Ferreira,Luciano da Silva; Graf,Karin; Scheid,Adriano
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2015 EN
Relevância na Pesquisa
36.06%
This work assessed Ni-based C276 alloy coatings by PTA with different degree of interaction with AISI 316L and API 5L X70 steel substrates. Track geometry, dilution and microstructure of coatings were evaluated by optical, scanning electron microscopy and X-ray diffraction. Properties were evaluated by hardness and wear tests. Microstructure exhibited austenite Ni-FCC dendrites and interdendrictic regions containing carbides. Dilution from 4,9 to 25,4% for coatings on API 5L X70 leaded to hardness ranging from 283 to 243 HV0,5. Otherwise, dilution between 22,3 and 41,5% for coatings on AISI 316L induced hardness from 267 to 225 HV0,5. Higher interaction with the substrate leaded to 19,8% increase of mass loss rate on API 5L X70 coatings. The slight difference for coatings properties deposited on different substrates indicated that the degree of interaction was the most significant factor.

Role of isostaticity and load-bearing microstructure in the elasticity of yielded colloidal gels

Hsiao, Lilian C.; Newman, Richmond S.; Glotzer, Sharon C.; Solomon, Michael J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
EN
Relevância na Pesquisa
36.06%
We report a simple correlation between microstructure and strain-dependent elasticity in colloidal gels by visualizing the evolution of cluster structure in high strain-rate flows. We control the initial gel microstructure by inducing different levels of isotropic depletion attraction between particles suspended in refractive index matched solvents. Contrary to previous ideas from mode coupling and micromechanical treatments, our studies show that bond breakage occurs mainly due to the erosion of rigid clusters that persist far beyond the yield strain. This rigidity contributes to gel elasticity even when the sample is fully fluidized; the origin of the elasticity is the slow Brownian relaxation of rigid, hydrodynamically interacting clusters. We find a power-law scaling of the elastic modulus with the stress-bearing volume fraction that is valid over a range of volume fractions and gelation conditions. These results provide a conceptual framework to quantitatively connect the flow-induced microstructure of soft materials to their nonlinear rheology.

Microstructural evolution induced by micro-cracking during fast lithiation of single-crystalline silicon

Choi, Yong Seok; Pharr, Matt; Kang, Chan Soon; Son, Seoung-Bum; Kim, Seul Cham; Kim, Kee-Bum; Roh, Hyunchul; Lee, Se-Hee; Oh, Kyu Hwan; Vlassak, Joost J.
Fonte: Elsevier BV Publicador: Elsevier BV
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
46.14%
We report observations of microstructural changes in {100} and {110} oriented silicon wafers during initial lithiation under relatively high current densities. Evolution of the microstructure during lithiation was found to depend on the crystallographic orientation of the silicon wafers. In {110} silicon wafers, the phase boundary between silicon and LixSi remained flat and parallel to the surface. In contrast, lithiation of the {100} oriented substrate resulted in a complex vein-like microstructure of LixSi in a crystalline silicon matrix. A simple calculation demonstrates that the formation of such structures is energetically unfavorable in the absence of defects due to the large hydrostatic stresses that develop. However, TEM observations revealed micro-cracks in the {100} silicon wafer, which can create fast diffusion paths for lithium and contribute to the formation of a complex vein-like LixSi network. This defect-induced microstructure can significantly affect the subsequent delithiation and following cycles, resulting in degradation of the electrode.; Engineering and Applied Sciences

Effect of Microstructure on Retained Austenite Stability and Tensile Behaviour in an Aluminum-Alloyed TRIP Steel

CHIANG, JASMINE SHEREE
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado
EN; EN
Relevância na Pesquisa
36.3%
Transformation-induced plasticity (TRIP) steels have excellent strength, ductility and work hardening behaviour, which can be attributed to a phenomenon known as the TRIP effect. The TRIP effect involves a metastable phase, retained austenite (RA), transforming into martensite as a result of applied stress or strain. This transformation absorbs energy and improves the work hardening rate of the steel, delaying the onset of necking. This work describes two distinct TRIP steel microstructures and focuses on how microstructure affects the RA-to-martensite transformation and the uniaxial tensile behaviour. A two-step heat treatment was applied to an aluminum-alloyed TRIP steel to obtain a microstructure consisting of equiaxed grains of ferrite surrounded by bainite, martensite and RA -- the equiaxed microstructure. The second microstructure was produced by first austenitizing and quenching the steel to produce martensite, followed by the two-step heat treatment. The resulting microstructure (labelled the lamellar microstructure) consisted of elongated grains of ferrite with bainite, martensite and RA grains. Both microstructural variants had similar initial volume fractions of RA. A series of interrupted tensile tests and ex-situ magnetic measurements were conducted to examine the RA transformation during uniform elongation. Similar tests were also conducted on an equiaxed microstructure and a lamellar microstructure with similar ultimate tensile strengths. Results show that the work hardening rate is directly related to the RA transformation rate. The slower transformation rate...

Microstructural effects on the stability of retained austenite in transformation induced plasticity steels

Mark, Alison Fiona Lockie
Fonte: Quens University Publicador: Quens University
Tipo: Tese de Doutorado Formato: 127686542 bytes; application/pdf
EN; EN
Relevância na Pesquisa
36.31%
Transformation Induced Plasticity (TRIP) steels have both high strength and high ductility. Retained austenite in the microstructure, upon straining, transforms to martensite and this absorbs energy and improves the work hardening of the steel, giving improved elongation. The transformation can be either stress-assisted or strain-induced and the initiation and the mechanism depend on the composition of, the size and shape of, and the phases surrounding, the austenite grains. It is important to understand the relationship between these variables and the properties of the TRIP steel. The aim of this work was to determine how the microstructure of the TRIP steel affects the transformation. Four experimental microstructures were developed, containing austenite grains with different sizes, shapes, and surrounding phases. The Fine microstructure had thin elongated austenite laths between fine bainitic ferrite laths, the Coarse microstructure had elongated austenite grains between coarser bainitic ferrite laths, the Equiaxed microstructure had equiaxed austenite grains in a matrix of equiaxed ferrite and the Acicular microstructure had elongated austenite grains surrounded by recovered ferrite laths. Tensile tests were performed and detailed characterization...

Simulation of the stretch blow moulding process: from the modelling of the microstructure evolution to the end-use elastic properties of polyethylene terephthalate bottles

COSSON, Benoit; CHEVALIER, Luc; REGNIER, Gilles
Fonte: Springer Publicador: Springer
Relevância na Pesquisa
46%
The original publication is available at www.springerlink.com; The whole stretch blow-moulding process of PET bottles is simulated at the usual process temperature in order to predict the elastic end-use properties of the bottles. An anisotropic viscoplastic constitutive law, coupled with microscopic variables, is dentified from uniaxial tensile tests performed at different strain rates and temperatures. The microstructure evolution is characterised by crystallinity measurements from interrupted tests and frozen samples. For each specimen tested, the Young modulus is measured at room temperature. Numerical simulations of the blow moulding process are run using the C-NEM method. A micromechanical modelling is post-processed after the simulation to predict the elastic properties. Predictions of Young modulus distributions in bottles are in agreement with the ones measured on blow-moulded bottles.

Correlating phase and microstructure development versus dielectric properties in La3+ and Er3+ co-doped Bi4Ti3O12 ferroelectric ceramics

Santos, Valdeci Bosco dos; M'Peko, Jean Claude; Mastelaro, Valmor Roberto
Fonte: ELSEVIER SCIENCE SA; LAUSANNE Publicador: ELSEVIER SCIENCE SA; LAUSANNE
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36%
Bi3.25La0.75-xErxTi3O12 and Bi3.25La0.75Ti3-xErxO12-delta ceramics were prepared and studied in this work in terms of dopant-induced phase and microstructure development as well as dielectric response. The results show that introduction of Er3+ tends to reduce the materials' sintering temperature and average grain size. Moreover, it was noted that in these systems the substitution site of this dopant is controlled by valence state and ionic radii mismatch effects. In particular, even when a nominal substitution of Ti4+ is conceived, here it is found that Er3+ also incorporates at the (Bi,La)(3+) sites. These and other interesting concluding remarks from this work, including Er3+ tolerance, were possible only after comparing, especially, the X-ray diffraction results and the intrinsic ferroelectric characteristics extracted from the dielectric measurements. (C) 2011 Elsevier B.V. All rights reserved.; FAPESP; FAPESP; CNPq; CNPq

Implantation-induced Disorder in Amorphous Ge: Production and Relaxation

Ridgway, Mark C; Glover, Christopher; Desnica-Frankovic, I D; Furic, K; Yu, Kin Man; Foran, Garry J; Clerc, C; Hansen, Jeffrey; Nylandsted-Larsen, A
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.8%
Extended X-ray absorption fine structure and Raman spectroscopy have been utilised to measure implantation-induced micro-structural modifications in amorphous Ge including increases in bond length, broadening of the bond-angle distribution, and non-Gaussi

Substrate-induced microstructure effects on the dynamics of the photo-induced Metal-insulator transition in VO$_2$ thin films

Radue, E.; Wang, L.; Kittiwatanakul, S.; Lu, J.; Wolf, S. A.; Rossi, E.; Lukaszew, R. A.; Novikova, I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.84%
We investigate the differences in the dynamics of the ultrafast photo-induced metal-insulator transition (MIT) of two VO$_2$ thin films deposited on different substrates, TiO$_2$ and Al$_2$O$_3$, and in particular the temperature dependence of the threshold laser fluence values required to induce various MIT stages in a wide range of sample temperatures (150 K - 320 K). We identified that, although the general pattern of MIT evolution was similar for the two samples, there were several differences. Most notably, the threshold values of laser fluence required to reach the transition to a fully metallic phase in the VO$_2$ film on the TiO$_2$ substrate were nearly constant in the range of temperatures considered, whereas the VO$_2$/Al$_2$O$_3$ sample showed clear temperature dependence. Our analysis qualitatively connects such behavior to the structural differences in the two VO$_2$ films.; Comment: Changed formatting of figures, fixed some citations: Consistent with published version

Induced Minority Dynamics in a Stock Market Model

Li, Yi; Savit, Robert
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.84%
In this paper, we present a simple stock market model (the market game) which incorporates, as ab initio dynamics delayed majority dynamics, according to which agents (with heterogeneous strategies and price expectations) are rewarded if their actions at time t are the actions of the majority of agents at time t+1. We observe that for a range of parameter settings, minority dynamics are dynamically induced in this game, despite the fact that they are not introduced ab initio. Central to the emergence of minority dynamics is the introduction of the notion of price expectations for the agents. This leads to the possibility of an agent not participating in the market for some time steps. One consequence of the induced minority dynamics is an effective reduction in market volatility. We also discuss the phase structure and qualitative behavior of the market game for the entire parameter space.; Comment: 19 pages, 9 figures

Microstructure and rheology of finite inertia neutrally buoyant suspensions

Haddadi, Hamed; Morris, Jeffrey F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/03/2014
Relevância na Pesquisa
36%
The microstructure and rheological properties of suspensions of neutrally buoyant hard spherical particles in Newtonian fluid under conditions of finite inertia are studied using the lattice-Boltzmann method (LBM), which is based on a discrete Boltzmann model for the fluid and Newtonian dynamics for the particles. The suspensions are subjected to simple-shear flow and the properties are studied as a function of Reynolds number and volume fraction, $\phi$. The inertia is characterized by the particle-scale shear flow Reynolds number $Re = \frac{\rho \dot{\gamma}a^{2}}{\mu}$, where $a$ is the particle radius, $\dot{\gamma}$ is the shear rate and $\rho$ and $\mu$ are the density and viscosity of the fluid, respectively. The influences of inertia and of the volume fraction are studied for $0.005\leqslant Re \leqslant 5$ and $0.1\leqslant \phi \leqslant 0.35$. The flow-induced microstructure is studied using the pair distribution function $g(\boldsymbol{r})$. Different stress mechanisms, including those due to surface tractions (stresslet), acceleration, and the Reynolds stress due to velocity fluctuations are computed and their influence on the first and second normal stress differences, the particle pressure and the viscosity of the suspensions are detailed. The probability density functions of particle force and torque are also presented.

Verwey transition in Fe$_{3}$O$_{4}$ thin films: Influence of oxygen stoichiometry and substrate-induced microstructure

Liu, X. H.; Rata, A. D.; Chang, C. F.; Komarek, A. C.; Tjeng, L. H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/09/2014
Relevância na Pesquisa
45.99%
We have carried out a systematic experimental investigation to address the question why thin films of Fe$_3$O$_4$ (magnetite) generally have a very broad Verwey transition with lower transition temperatures as compared to the bulk. We observed using x-ray photoelectron spectroscopy, x-ray diffraction and resistivity measurements that the Verwey transition in thin films is drastically influenced not only by the oxygen stoichiometry but especially also by the substrate-induced microstructure. In particular, we found (1) that the transition temperature, the resistivity jump, and the conductivity gap of fully stoichiometric films greatly depends on the domain size, which increases gradually with increasing film thickness, (2) that the broadness of the transition scales with the width of the domain size distribution, and (3) that the hysteresis width is affected strongly by the presence of antiphase boundaries. Films grown on MgO (001) substrates showed the highest and sharpest transitions, with a 200 nm film having a T$_V$ of 122K, which is close to the bulk value. Films grown on substrates with large lattice constant mismatch revealed very broad transitions, and yet, all films show a transition with a hysteresis behavior, indicating that the transition is still first order rather than higher order.; Comment: 9 pages...

A study on the triaxial shear behavior and microstructure of biologically treated sand specimens

Ozdogan, Ayse
Fonte: University of Delaware Publicador: University of Delaware
Tipo: Tese de Doutorado
Relevância na Pesquisa
36%
Meehan, Christopher L.; The use of microbial calcite cementation for ground improvement presents a relatively new ground improvement option for geotechnical engineers, one that particularly has the potential to revolutionize the way that we improve soils to prevent liquefaction-induced damage. This technique uses non-pathogenic organisms which are found naturally in a soil environment to cement sand particles together at their particle-to-particle contacts. There is significant potential for a reduction in environmental concerns on various types of projects; in the long-term, this technique may also prove to be an extremely sustainable form of ground improvement. Consequently, the goal of the research described herein is to enhance the state-of-theart with respect to our understanding of controlling biological cementation processes in soil. This thesis describes the results from an experimental study that was conducted to examine the factors that influence microbial calcite cementation in sands. Bio-treatment of the sand was performed using a commonly encountered ureaproducing soil microorganism called Sporosarcina Pasteurii (ATCC-6453). Ottowa sand was selected as the soil for this initial study, as widespread information about this soil is available in the technical literature...