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The influence of nitrogen on the mechanical behaviour of multilayered coatings

Vieira, M. T.; Pereira, C. M.; Castanho, J. M.
Fonte: Universidade de Coimbra Publicador: Universidade de Coimbra
Tipo: Artigo de Revista Científica Formato: aplication/PDF
ENG
Relevância na Pesquisa
46.07%
Multilayered films are a new kind of coating that belong to a more plentiful family of materials labelled as nanostructured materials. These kinds of coatings stand in the frontier of investigation in thin films for structural applications. In the present work, multilayered coatings with alternated layers of W---Ti---(N) and Ag were deposited to be used as wear resistant surfaces. The association of the high hardness, wear resistance of W---Ti---(N) layers [Proceedings of the Eleventh LAWPSP Symposium, SL1.1-SL1.7, Bombay, India (1998); Surf. Coat. Technol., 102 (1998), 50] and the good ductility of the silver ones is the guarantee of obtaining a better mechanical performant coating. However, to reach a satisfactory comprehension of the behaviour of the coatings in service a true understanding of some important properties is needed. For this reason, hardness, Young modulus, internal stresses and adhesion were evaluated, as well as function of the number and thickness of the layers.; http://www.sciencedirect.com/science/article/B6TVV-4281174-2W/1/a8df6cf48f479116b77754805370dd3b

Internal stresses and textures of nanostructured alumina scales growing on polycrystalline Fe(3)Al alloy

BRITO, Pedro; PINTO, Haroldo; KLAUS, Manuela; GENZEL, Christoph; KAYSSER-PYZALLA, Anke
Fonte: J C P D S-INT CENTRE DIFFRACTION DATA Publicador: J C P D S-INT CENTRE DIFFRACTION DATA
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.28%
The evolution of internal stresses in oxide scales growing on polycrystalline Fe(3)Al alloy in atmospheric air at 700 degrees C was determined using in situ energy-dispersive synchrotron X-ray diffraction. Ex situ texture analyses were performed after 5 h of oxidation at 700 degrees C. Under these conditions, the oxide-scale thickness, as determined by X-ray photoelectron spectroscopy, lies between 80 and 100 nm. The main phase present in the oxide scales is alpha-Al(2)O(3), with minor quantities of metastable theta-Al(2)O(3) detected in the first minutes of oxidation, as well as alpha-Fe(2)O(3). alpha-Al(2)O(3) grows with a weak (0001) fiber texture in the normal direction. During the initial stages of oxidation the scale develops, increasing levels of compressive stresses which later evolve to a steady state condition situated around -300 MPa. (C) 2010 International Centre for Diffraction Data. [DOI: 10.1154/1.3402764]

Impact of transition oxides on growth stresses and texture of alumina scales formed during oxidation of iron aluminides

BRITO, P.; PINTO, H.; GENZEL, Ch.; KLAUS, M.; KAYSSER-PYZALLA, A.
Fonte: PERGAMON-ELSEVIER SCIENCE LTD Publicador: PERGAMON-ELSEVIER SCIENCE LTD
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
56.22%
The internal stresses and crystallographic texture in alpha-Al(2)O(3) scales grown on iron aluminides at 1100 degrees C were determined in situ using synchrotron X-ray diffraction. In the first hour of oxidation, alpha-Al(2)O(3) was formed by direct nucleation and by conversion from transition oxides (either theta-Al(2)O(3) or a mixed Fe-Al oxide). A sharp texture develops connected with the direct nucleation of alpha-Al(2)O(3), in contrast to the weaker texture observed in alpha-Al(2)O(3) originated by previous transformations, which also yielded tensile stresses in early oxidation stages. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Validation of reference genes for RT-qPCR normalization in common bean during biotic and abiotic stresses

Borges, Aline; Mui, Tsai Siu; Gomes Caldas, Danielle Gregorio
Fonte: SPRINGER; NEW YORK Publicador: SPRINGER; NEW YORK
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
36.04%
Selection of reference genes is an essential consideration to increase the precision and quality of relative expression analysis by the quantitative RT-PCR method. The stability of eight expressed sequence tags was evaluated to define potential reference genes to study the differential expression of common bean target genes under biotic (incompatible interaction between common bean and fungus Colletotrichum lindemuthianum) and abiotic (drought; salinity; cold temperature) stresses. The efficiency of amplification curves and quantification cycle (C (q)) were determined using LinRegPCR software. The stability of the candidate reference genes was obtained using geNorm and NormFinder software, whereas the normalization of differential expression of target genes [beta-1,3-glucanase 1 (BG1) gene for biotic stress and dehydration responsive element binding (DREB) gene for abiotic stress] was defined by REST software. High stability was obtained for insulin degrading enzyme (IDE), actin-11 (Act11), unknown 1 (Ukn1) and unknown 2 (Ukn2) genes during biotic stress, and for SKP1/ASK-interacting protein 16 (Skip16), Act11, Tubulin beta-8 (beta-Tub8) and Unk1 genes under abiotic stresses. However, IDE and Act11 were indicated as the best combination of reference genes for biotic stress analysis...

Analise de tensões residuais em valvulas estampadas por meio da difração de raios-X e do metodo de elementos finitos; Analysis of the residual stresses in stamped valves by X-ray diffraction and finite element method

Jairo Aparecido Martins
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 23/04/2004 PT
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46.18%
A evolução dos materiais, de seus processos de transformação e de diversos componentes mecânicos vêm requerendo cada vez mais o desenvolvimento de técnicas e métodos para sua análise. A transformação de materiais por deformação plástica origina tensões internas chamadas tensões residuais que podem vir a alterar a resposta do componente e/ou sistema quando em uso. Este trabalho tem como objetivo a análise dessas tensões residuais em válvulas dinâmicas estampadas por difração de raios- X e pelo método de elementos finitos. Dentro deste contexto, foi desenvolvido um método alternativo ao usual sen2", para a determinação de tensões residuais por difração de raios- X em pequenas áreas, esse utiliza o método de análise da difração de raios-X usualmente empregada na determinação de tensões residuais em filme finos . Os resultados obtidos na difração de raios-X mostraram-se compatíveis com o processo de deformação estudado e também com os resultados da simulação numérica pelo método de elementos finitos. A comprovação prática desses resultados deu-se pela realização de ensaios de durabilidade em bancada por flexão alternada reversa de uma válvula dinâmica nas seguintes condições de fabricação: a) estampada...

Measurement of internal moisture distribution in concrete with relative humidity sensors

Padilla Quincot, Gonzalo
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Trabalho de Conclusão de Curso
Publicado em //2012 ENG
Relevância na Pesquisa
36.07%
Dissertação de mestrado integrado em Civil Engineering; The moisture content in concrete is closely related with its structural behaviour. The cement hydration process is the main responsible for the strength growth development and for heat generation, which in turn induces volumetric changes. Furthermore, the drying process of concrete creates tensile stresses that could lead to an initial stress state build-up and limit the concrete ability to carry further tensile stresses, or generate cracks during service life operating conditions. This is an issue that has been subject of attention of recent design codes but still a lot of research has to be developed to fully understand this behaviour. This is due to the enormous variations that may occur on the concrete compositions and on the in-situ environmental conditions, which makes difficult to predict the actual shrinkage deformations and the role of humidity on it. On this regard, the study of shrinkage, cracking, moisture loss, thermal deformations and the evolution of the mechanical properties in concrete since casting and throughout the service life are a crucial issue in order to predict the structural behaviour of concrete. The scope of the present research work is to approach the understanding of the concrete moisture loss process and to contribute with the lack of information in this domain. Different methods of moisture loss measurements inside concrete have been explored but the focus is through relative humidity measurements. On this regard...

Characterization of plant antioxidative system in response to abiotic stresses: a focus on heavy metal toxicity

Mourato, Miguel; Reis, Rafaela; Martins, Maria Luísa Louro
Fonte: InTech Publicador: InTech
Tipo: Parte de Livro
Publicado em /04/2012 ENG
Relevância na Pesquisa
36.13%
During their life span, plants can be subjected to a number of abiotic stresses, like drought, temperature (both high and low), radiation, salinity, soil pH, heavy metals, lack of essential nutrients, air pollutants, etc. When affected by one, or a combination of abiotic stresses, a response is induced by changes in the plant metabolism, growth and general development. Reactive Oxygen Species (ROS) are a natural consequence of the aerobic metabolism, and plants have mechanisms to deal with them in normal conditions, controlling the formation and removal rates. Under stress conditions, cell homeostasis is disrupted and ROS production can increase a lot putting a heavy burden on the those antioxidative mechanisms, some of which are activated in order to eliminate the excess ROS (Mittler et al., 2004). Trace element contamination cause abiotic stress in plants and it can affect crop production and quality. Certain metals, like copper, are essential for plants, but at high concentrations (depending on plant species) can be considered toxic. Other elements like cadmium and arsenic (a metalloid), while not essential elements for plants, are widespread pollutants that are present in nature due to both natural and manmade activities. Plants have developed different strategies to cope with these stresses. Some use an avoidance strategy to reduce trace element assimilation while others use internal defence mechanisms to cope with the increasing levels of the toxic species. Phytotoxic amounts of trace elements are known to affect several physiological processes and can cause oxidative stress. Plants have developed several trace element defence mechanisms...

Microcracking of High Performance Concrete Subjected to Biaxial Tension - Compression Stresses

Calixto,José Marcio F.
Fonte: ABM, ABC, ABPol Publicador: ABM, ABC, ABPol
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/09/2002 EN
Relevância na Pesquisa
36.04%
The results of an experimental investigation on the microcracking of high-performance concrete subjected to biaxial tension-compression stresses are presented. Short-term static tests and microcracking mapping were performed on 12.5 cm square by 1.25 cm thick plates. Strain controlled tests were executed in a biaxial testing machine constructed at the University of Texas. The primary variables studied were the deformations and the ultimate stress level at each stress ratio as well as the microcracking patterns and total crack lengths. For the microcracking study, the plates, after straining, were impregnated by an epoxy and then examined under a microscope. Microcracks were classified into simple and combined cracks, since this distinction allows for a much better representation of the microcracking process. A simple crack is either a bond or mortar crack where a combined crack contains both of these. For all stress ratios tested, the stress-strain behavior was directly related to the internal microcracking pattern. In all cases, the failure was directly related to the formation and propagation of the combined cracks.

Evaluation of subsurface contact stresses in railroad wheels using an elastic half-space model

Santos,F. de C.; Santos Jr,A. A. dos; Bruni,F.; Santos,L. T.
Fonte: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM Publicador: Associação Brasileira de Engenharia e Ciências Mecânicas - ABCM
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2004 EN
Relevância na Pesquisa
36.1%
Railroad wheels fail in two main modes: rolling surface defects like spalling, shelling and wear, and internal defects including cracks propagating after a change takes place in the original stress pattern. Although the effects of the latter are almost always catastrophic, the former is more usual. The onset of rolling surface defects depends on the strength of the surface and the applied loads. The strength is related to surface hardness and can be determined through experimental evaluation under controlled conditions. Evaluating the loads is one of the challenges for contact researchers. This paper presents the evaluation of the stress field inside elastic rolling bodies with an elliptic area of contact. This kind of model can be applied to wheel-rail contact phenomena. Typical high freight transportation loads are used in conjunction with regular recommended wheel and rail sizes. The results have shown that shear stress reaches the maximum magnitude below the surface of contact, and this explains the presence of shelling defects in service. They have also shown that a new model including plasticity is required, because the range of the stresses reached surpasses, by far, the elastic limit

Algorithms for the Calculation of Exact Displacements, Strains, and Stresses for Triangular Dislocation Elements in a Uniform Elastic Half Space

Meade, Brendan J.
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
EN_US
Relevância na Pesquisa
36.04%
We present algorithms for analytically calculating the displacements, strains, and stresses associated with slip on a triangular dislocation element (TDE) in a homogeneous elastic half space. Following previous efforts, the solution is constructed as a dislocation loop where the deformation fields for each of the three triangle legs are calculated by the superposition of two angular dislocations. In addition to the displacements at the surface we derive the displacements and strains at arbitrary depth. We give explicit formulas for the strains due to slip on an angular dislocation, the calculation of angular dislocation slip components, a method for identifying observation coordinates affected by a solid body translation, and rules for internally consistent vertex ordering allowing for the superposition of multiple TDEs. Examples of surface displacements and internal stresses are given and compared with rectangular representations of geometrically complex fault surfaces.; Earth and Planetary Sciences

Effects of internal stress on remanence intensity jumps across the Verwey transition for multi-domain magnetite

Liu, Quingsong; Yu, Yongjae; Muxworthy, Adrian R; Roberts, Andrew
Fonte: Elsevier Publicador: Elsevier
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
46.05%
The magnetic properties of magnetite (Fe3O4) are strongly dependent on the internal stress related to stress-controlled regions and to closure domains associated with defects. The contribution of internal stress to the low-temperature magnetic properties

Dynamics of Internal Stresses and Scaling of Strain Recovery in an Aging Colloidal Gel

Negi, Ajay Singh; Osuji, Chinedum O.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/06/2009
Relevância na Pesquisa
46.07%
We monitor the relaxation of internal stresses in a fractal colloidal gel on cessation of flow and find a weak power law decay, $\sigma_i \sim t^{-\alpha}$ over 5 decades of time where $\alpha \approx 0.07$. The system exhibits physical aging of the elastic modulus, $G' \sim t^{\beta}$, with $\beta \approx \alpha$. Imposition of zero stress after waiting time $t_w$ results in strain recovery as the system relaxes without constraint. Remarkably, recoveries at different $t_w$ can be shifted to construct a master curve where data are scaled vertically by $1/\sigma_i(t_w)$ and plotted horizontally as $(t-t_w)/t_w^{\mu}$ where $\mu\approx 1.25$, indicative of a super-aging response.; Comment: 4 pages, 5 figures

Interplay of internal stresses, electric stresses and surface diffusion in polymer films

Closa, Fabien; Ziebert, Falko; Raphael, Elie
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.04%
We investigate two destabilization mechanisms for elastic polymer films and put them into a general framework: first, instabilities due to in-plane stress and second due to an externally applied electric field normal to the film's free surface. As shown recently, polymer films are often stressed due to out-of-equilibrium fabrication processes as e.g. spin coating. Via an Asaro-Tiller-Grinfeld mechanism as known from solids, the system can decrease its energy by undulating its surface by surface diffusion of polymers and thereby relaxing stresses. On the other hand, application of an electric field is widely used experimentally to structure thin films: when the electric Maxwell surface stress overcomes surface tension and elastic restoring forces, the system undulates with a wavelength determined by the film thickness. We develop a theory taking into account both mechanisms simultaneously and discuss their interplay and the effects of the boundary conditions both at the substrate and the free surface.; Comment: 14 pages, 7 figures, 1 table

First order rigidity transition and multiple stability regimes for random networks with internal stresses

Head, D. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 18/03/2005
Relevância na Pesquisa
46.16%
By applying effective medium-style calculations to random spring networks, we demonstrate that internal stresses fundamentally alter the nature of the rigidity transition in disordered materials, changing it from continuous to first-order and increasing the mean coordination number z at which rigidity first occurs. Furthermore, we predict the existence of a novel stability regime at low z when the distribution of stresses is asymmetric. Means of verifying these predictions are suggested.; Comment: 9 pages in JPhysA-spec, 2 figs

Internal Stresses and Formation of Switchable Nanowires at Thin Silica Film Edge

Phillips, J. C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/10/2010
Relevância na Pesquisa
46.16%
At vertical edges, thin films of silicon oxide (SiO_{2-x}) contain semiconductive c-Si layered nanocrystals (Si NC) embedded in and supported by an insulating g-SiO2 matrix. Tour et al. have shown that a trenched thin film geometry enables the NC to form switchable nanowires (SNW) when trained by an applied field. The field required to form SNW decreases rapidly within a few cycles, or by annealing at 600 C in even fewer cycles, and is stable to 700C. Here we describe the intrinsic evolution of Si NC and SNW in terms of the competition between internal stresses and electro-osmosis. The analysis relies heavily on experimental data from a wide range of thin film studies, and it explains why a vertical edge across the planar Si-SiOx interface is necessary to form SNW. The discussion also shows that the formation mechanisms of Si NC and Si/SiO_{2-x} SNW are intrinsic and result from optimization of nanowire conductivity in the presence of residual host misfit stresses.

The probability distribution of internal stresses in externally loaded 2D dislocation systems

Ispánovity, Péter Dusán; Groma, István
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
36.14%
The distribution of internal shear stresses in a 2D dislocation system is investigated when external shear stress is applied. This problem serves as a natural continuation of the previous work of Csikor and Groma (Csikor F F and Groma I 2004 Phys. Rev. B 58 2969), where analytical result was given for the stress distribution function at zero applied stress. First, the internal stress distribution generated by a set of randomly positioned ideal dislocation dipoles is studied. Analytical calculations are carried out for this case. The theoretical predictions are checked by numerical simulations showing perfect agreement. It is found that for real relaxed dislocation configurations the role of dislocation multipoles cannot be neglected, but the theory presented can still be applied.; Comment: 27 pages, 20 figures

Internal stresses and breakup of rigid isostatic aggregates in homogeneous and isotropic turbulence

De Bona, Jeremias; Lanotte, Alessandra S.; Vanni, Marco
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/05/2014
Relevância na Pesquisa
46.28%
By characterising the hydrodynamic stresses generated by statistically homogeneous and isotropic turbulence in rigid aggregates, we estimate theoretically the rate of turbulent breakup of colloidal aggregates and the size distribution of the formed fragments. The adopted method combines Direct Numerical Simulation of the turbulent field with a Discrete Element Method based on Stokesian dynamics. In this way, not only the mechanics of the aggregate is modelled in detail, but the internal stresses are evaluated while the aggregate is moving in the turbulent flow. We examine doublets and cluster-cluster isostatic aggregates, where the failure of a single contact leads to the rupture of the aggregate and breakup occurs when the tensile force at a contact exceeds the cohesive strength of the bond. Due to the different role of the internal stresses, the functional relationship between breakup frequency and turbulence dissipation rate is very different in the two cases. In the limit of very small and very large values, the frequency of breakup scales exponentially with the turbulence dissipation rate for doublets, while it follows a power law for cluster-cluster aggregates. For the case of large isostatic aggregates it is confirmed that the proper scaling length for maximum stress and breakup is the radius of gyration. The cumulative fragment distribution function is nearly independent of the mean turbulence dissipation rate and can be approximated by the sum of a small erosive component and a term that is quadratic with respect to fragment size.; Comment: 31 pages...

Stresses in Ytterbium Silicate Multilayer Environmental Barrier Coatings

Stolzenburg, F.; Almer, J.; Lee, K. N.; Harder, B. J.; Faber, K. T.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Conference or Workshop Item; PeerReviewed Formato: application/pdf
Publicado em //2011
Relevância na Pesquisa
36.2%
The internal stresses of plasma-sprayed multilayer ytterbium disilicate environmental barrier coatings were measured using microfocused high-energy X-rays in a transmission geometry. Stresses were measured for as-sprayed and ex-situ heat-treated ytterbium disilicate topcoats at room temperature and during in-situ heating and cooling experiments. In-situ loading experiments were also performed on the topcoat in order to establish its elastic constants. The ytterbium disilicate was found to have a relatively low coefficient of thermal expansion resulting in compressive stresses of approximately 100 MPa throughout the topcoat. In-situ heating experiments revealed a statistically significant stress relaxation in the ytterbium disilicate topcoat upon thermal cycling to temperatures above 1300°C, indicating the onset of stress relaxation but no cracks were observed in SEM micrographs. The stress states were also modeled using a numerical solution; measured stresses were found to be very close to the predicted stresses in ytterbium dilisicate topcoats, while the experimentally determined stresses in the intermediate layers were of much smaller magnitude than the calculated stresses.

Analysis of stresses in ADI internal gears mounted with interference: distortion and residual stresses effects

Sosa,A. D.; Echeverría,M. D.; Moncada,O. J.
Fonte: Latin American applied research Publicador: Latin American applied research
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/07/2005 EN
Relevância na Pesquisa
36.35%
The stress state in ADI internal gears mounted with interference in aluminum casings is numerically simulated, considering working load as well as circularity distortion (ovalization) and residual stresses resulting from heat treatment. Ovalization exerts the greatest influence on interference and residual stresses, leading to a significantly high compressive stress which does not affect the gear structural integrity due to the high compression strength of ADI. This grants this alloy a competitive edge over steels of similar tensile strength. Still, ovalization has to be minimized considering its unfavorable effect on performance and working load capacity.

Effect of the molding temperature and cooling time on the residual stresses of crystal polystyrene

Acevedo-Morantes,María Teresa; Brieva-Sarmiento,María; Realpe-Jiménez,Alvaro
Fonte: DYNA Publicador: DYNA
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2014 EN
Relevância na Pesquisa
46.18%
The use of crystal polystyrene for high performance components requires knowledge of the distribution of residual stresses. The aim of this research was to analyze the influence of the molding temperature and cooling time on the residual stresses present in parts of two types of crystal polystyrene PS1 and PS2, processed by injection molding. The results obtained using photoelasticity showed that at low temperatures the residual stresses increase due to the processes of formation and destruction of intermolecular forces. Internal stresses were reduced in the polymer specimens with greater thickness because the molecular relaxation of chains of polystyrene is facilitated by the space increase between the walls of the mold. It was concluded that the photoelasticity technique can be applied effectively in the measurement of residual stresses in injection molded crystal polystyrene parts.