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Interferometric techniques in structural damage identification

Lopes, H.; Ribeiro, J.E.; Santos, J.V.A. Araújo dos
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
55.6%
This paper describes several interferometric techniques and their applications in structural damage identification. With that objective in mind, damaged aluminium beams with clamped-free and free-free boundary conditions are analyzed. Different damages cases are inflicted by creating small cuts perpendicular to the beams longitudinal axis, being the damage, therefore, characterized by the dimensions of these cuts. The out–of–plane displacement field of modal response is measured with an electronic speckle pattern interferometric system. The measurement of the static and dynamic rotation fields, defined as the spatial derivative of the displacement field, are measured with two different speckle shearography systems. Second and third order spatial derivatives of the displacement field, which are related to the bending moment and shear force, are computed by differentiation techniques. The cracks locations are determined by looking for maximum values and/or perturbations of damage indicators based on bending moments and shear forces. This method is validated by comparing its results with numerical ones, from which the most suitable interferometric technique is chosen.

Interferometric techniques in structural damage identification

Lopes, H.; Ribeiro, J.E.; Santos, J.
Fonte: IOS Press Publicador: IOS Press
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
55.6%
This paper describes several interferometric techniques and their applications in structural damage identification. With that objective in mind, damaged aluminum beams with clamped-free and free-free boundary conditions are analyzed. Different damages cases are inflicted by creating small cuts perpendicular to the beams longitudinal axis, being the damage, therefore, characterized by the dimensions of these cuts. The out-of-plane displacement field of modal response is measured with an electronic speckle pattern interferometric system. The static and dynamic rotation fields, defined as the spatial derivative of the displacement field, are measured with two different speckle shearography systems. Second and third order spatial derivatives of the displacement field, which are related to the bending moment and shear force, are computed by differentiation techniques. The cuts locations are determined by looking for maximum values and/or perturbations of damage indicators based on bending moments and shear forces. This method is validated by comparing its results with numerical ones, from which the most suitable interferometric technique is chosen.

Localization of damage in beams using interferometric techniques

Lopes, H.; Ribeiro, J.E.; Santos, J.; Maia, N.
Fonte: Instituto Politécnico de Bragança Publicador: Instituto Politécnico de Bragança
Tipo: Conferência ou Objeto de Conferência
ENG
Relevância na Pesquisa
45.61%
Two interferometric techniques and their applications in structural damage identification are presented in this paper. Out-of-plane displacement fields of modal response are measured with a pulsed electronic speckle pattern interferometric system(ESPI). The modal rotation fields, defined as the spatial derivative of the displacement field, are measured with a pulsed speckle shearography system. The measurements using these two interferometric systems are compared with measurements from experimental modal analysis and results from finite element analysis. This comparison shows that these two interferometric techniques, which allow non-contact, full-field measurements, are well suited to the measurement of modal response. A damaged beam with free-free boundary conditions is analyzed. The damages studied are small cuts perpendicular to the beams longitudinal axis. The bending moments and shear forces, which are related to the second and third order spatial derivatives of the modal displacement field, in the undamaged and damaged states are computed using numerical differentiation techniques. The damage is localized by looking for maximum values and/or perturbations of damage indicators based on bending moments and shear forces along the beam. The pulsed speckle shearography system leads to a significant improvement in the computation of bending moments and shear forces and...

Estudo do ensaio de determinação da tenacidade à fratura em deformação plana (KIc) em PMMA e análise das tensões desenvolvidas por fotoelasticidade.; Study of test for determining fracture toughness in plane strain (KIc) in PMMA and stress analysis developed by photoelasticity.

Souza, Joelmir Mariano de
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 20/12/2010 PT
Relevância na Pesquisa
55.61%
No presente trabalho produziu-se amostras de flexão em três pontos, SENB, a partir de placas moldadas por compressão feitas de uma resina de Poli(metacrilato de metila) comercial. Dois conjuntos contendo 6 amostras cada foram então pré-trincados por meio de uma lamina afiada de aço adotando-se dois métodos diferentes propostos pela literatura técnica: através de batidinhas (gentle tapping) e através da inserção controlada a velocidade constante da lâmina, ambas usando um dispositivo especialmente desenhado para este fim. Estas amostras foram então submetidas ao ensaio de tenacidade à fratura em deformação plana, KIc, com o intuito de se testar a hipótese de que os diferentes métodos introduzem diferentes padrões de dano na matriz próxima à região da ponta da pré-trinca, o que, por sua vez, influência os resultados obtidos. Adotou-se a norma ASTM D 5045 como padrão do ensaio. Todas as amostras produziram resultados válidos para KIc, considerando-se os critérios da norma. Os resultados confirmam a hipótese inicial mostrando que os diferentes métodos de introdução da pré-trinca influenciam o valor medido de KIc a um nível de significância de 5% para a diferença das médias obtidas nos dois grupos, sendo que o valor mais conservador é obtido quando as pré-trincas são introduzidas pelo método das batidinhas (KIc = 1...

Behavior of masonry infill panels in RC frames subjected to in plane and out of plane loads

Pereira, Manuel Fernando Paulo; Pereira, M. F. Neto; Ferreira, J. E. Dias; Lourenço, Paulo B.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Conferência ou Objeto de Conferência
Publicado em //2011 ENG
Relevância na Pesquisa
85.74%
The building envelope in Europe is usually made of masonry walls, with enclosure and infill functions. Masonry walls have a major economical importance and contribute significantly to the building performance. Even if infill walls have no load-bearing function, they contribute significantly to the seismic behavior of buildings. Therefore, their adequate structural performance is needed, avoiding the occurrence of severe in-plane damage, with very large economical losses, and the out-of-plane expulsion, which additionally represents a large risk for human life. Recent earthquake codes in Europe require the safety assessment of non-structural elements (parapets, veneer masonry walls, infill walls, etc.), when their collapse entails risks for people or for the main structure. The Eurocode standards, entering the mandatory stage now, incorporate new requirements to be fulfilled by buildings or their parts. Such is the case of masonry infilled RC frames whose panels, according to Eurocode 8, are explicitly required to withstand the out-of-plane movement induced by earthquakes. Appropriate measures should be taken to avoid brittle failure and premature disintegration of the infill walls, as well as the partial or total out-of-plane collapse of slender masonry panels. This paper presents the experimental work and results achieved by applying cyclic out-ofplane loads to damaged masonry infilled RC frames. The masonry panels were previously damaged by applying an in-plane cyclic load after which the cyclic out-of- plane loads were applied. The frames and panels tested follow the traditional Portuguese RC structure construction system to which different types of reinforcement have been introduced in the panels.

The old municipal chambers building : damaged but nor destroyed : will it be there in another 125 years?

Parker, Will; Uno, Masako; Lourenço, Paulo B.; Marques, Rui Filipe Pedreira; Pereira, João M.; Meyer, John; Mayes, Ron; Weaver, Ben
Fonte: Structural Engineering Society (SESOC) Publicador: Structural Engineering Society (SESOC)
Tipo: Conferência ou Objeto de Conferência
Publicado em //2012 ENG
Relevância na Pesquisa
45.67%
The Old Municipal Chambers is a Category I heritage building situated in Worcester Street, Christchurch. It was designed by architect Samuel Hurst Seager in the Queen Anne Arts and Crafts Style and was opened in 1887. The two storey building is constructed in solid brick and incorporates several decorative features, and it is an important part of the cultural heritage fabric of Christchurch. Some securing works were undertaken in 1989 to improve its performance under seismic loads. This paper will outline damage during the earthquake on 4 September 2010, subsequent aftershocks and the 22 February 2011 earthquake which resulted in some localised zones of collapse. The structure of the building has been stabilised externally, to secure or allow retrieval of very significant heritage features. The high cost to repair the building makes the future of the building uncertain despite its very significant heritage value.In response to the building’s seismic vulnerability and possible retrofitting, finite element and simplified equivalent frame models were used for pushover analysis, enabling a complementary seismic evaluation from both approaches. The predictions identify the weak parts of the building and its expected failure modes...

Avaliação do desempenho das envolventes dos edifícios face à acção dos sismos

Pereira, Manuel Fernando Paulo
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Tese de Doutorado
Publicado em 16/07/2013 POR
Relevância na Pesquisa
35.83%
Tese de doutoramento em Engenharia Civil; A envolvente dos edifícios em Portugal é constituída quase exclusivamente por paredes de alvenaria, que têm principalmente a função de vedação. Apesar de não terem função estrutural, as paredes ao interagirem com a estrutura, condicionam o comportamento sísmico dos edifícios, exigindo-se-lhe sob esta óptica, um desempenho adequado, evitando a ocorrência de danos severos nas paredes no seu plano, que conduzam a perdas económicas graves, e o colapso das paredes para fora do plano, que poderão colocar em perigo vidas humanas. Os actuais regulamentos estruturais europeus, no que concerne à segurança sísmica das estruturas exigem a verificação da segurança de elementos não estruturais quando o seu colapso acarreta riscos para pessoas ou para a estrutura principal. Os Eurocódigos estruturais quando entrarem na fase de implementação obrigatória irão impor novas exigências que deverão ser cumpridas pelos edifícios ou pelas suas partes. Tal é o caso das alvenarias de preenchimento, que deverão resistir ao movimento para fora do plano imposto pela acção dos sismos, devendo ser tomadas medidas adequadas para evitar a rotura prematura e desintegração das paredes de preenchimento...

Mechanical characterization of traditional timber connections : experimental results; Caracterização mecânica de ligações tradicionais em madeira : resultados experimentais

Poletti, Elisa; Vasconcelos, Graça; Branco, Jorge M.; Koukouviki, A. M.
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Conferência ou Objeto de Conferência
Publicado em 15/10/2014 ENG
Relevância na Pesquisa
45.56%
Timber connections are an important part of a timber structure and a great variability exists in terms of types of connections and mechanisms. Taking as case study the traditional timber frame structures, the half-lap joint was selected. Connections play a major role in the overall behaviour of a structure, particularly when assessing their seismic response, since damage is concentrated at the connections. Therefore, an experimental campaign was carried out on traditional half-lap joints to assess their in-plane response, carrying out pull-out and in-plane cyclic tests. Subsequently, the connections were retrofitted using self-tapping screws, steel plates and GFRP sheets. In this paper, the experimental results are presented taking into account factors such as dissipated energy, damping and influence on the wall behaviour.; As ligações em madeira constituem uma parte importante das estruturas em madeira e existe uma grande variabilidade em termos de tipologia de ligações e mecânismos. Considerando como caso de estudo os edifícios com paredes de madeira tradicionais (paredes de frontal), foi adotada a ligação madeira-madeira. As ligações tem uma função fundamental no comportamento global da estrutura, em particular na analise sismica...

Infill masonry : simple analytical methods for seismic design

Pereira, Manuel Fernando Paulo; Pereira, M. F. Neto; Ferreira, J. E. Dias; Lourenço, Paulo B.
Fonte: International Masonry Society Publicador: International Masonry Society
Tipo: Conferência ou Objeto de Conferência
Publicado em //2014 ENG
Relevância na Pesquisa
65.72%
The latest earthquake codes in Europe require the safety assessment of no-structural elements (parapets, masonry wall’s veneer, infill walls, etc.), as their collapse entails risks for people or for the main structure stability. This work made possible th e development of a design method, supported by previous experimental researches by applying cyclic out-of-plane loads to damaged masonry infill in RC frames. Panels tested reproduce Portuguese traditional RC structure construction system and two reinforced solutions were created as innovative solutions. The experimental campaign was carried out in order to determine: masonry properties; out-of-plane panel behaviour with previous in-plane damage; building behaviour subjected to dynamic tests performed in shaking table. Using finite element method to reproduce experimental tests and to broaden the range of samples it was possible to figure out equations according to parametric analysis which was able to reproduce in-plane and out-plane behaviour leading to an estimated load bearing capacity of each model and to determine frame strength and its stiffness. Those equations permit to design or verify the masonry infill panels in RC frames subjected to seismic loads.

A damage model for ductile crack initiation and propagation

Areias, Pedro; Van Goethem, Nicolas; Borges Pires, Eduardo
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
POR
Relevância na Pesquisa
45.74%
Damage-induced ductile crack initiation and propagation is modeled using a constitutive law with asymmetrical contraction of the yield surface and tip remeshing combined with a nonlocal strain technique. In practice, this means that the void fraction depends on a nonlocal strain. Finite strain plasticity is used with smoothing of the complementarity condition. The prototype constitutive laws take into account pressure sensitivity and the Lode angle effect in the fracture strain. Two plane idealizations are tested: plane stress and plane strain. Thickness variation in the former is included by imposing a null out-of-plane normal stress component. In plane strain, pressure unknowns and bubble enrichment are adopted to avoid locking and ensure stability of the equilibrium equations. This approach allows the representation of some 3D effects, such as necking. The nonlocal approach is applied to the strains so that the void fraction value evolves up to one and this is verified numerically. Three verification examples are proposed and one validation example is shown, illustrating the excellent results of the proposed method. One of the verification examples includes both crack propagation in the continuum and rigid particle decohesion based on the same model.

Design optimization of cruciform specimens for biaxial fatigue loading

Baptista, Ricardo; Cláudio, Ricardo; Reis, L.; Guelho, I.; Freitas, M.; Madeira, J. F. A.
Fonte: Repositório Comum de Portugal Publicador: Repositório Comum de Portugal
Tipo: Conferência ou Objeto de Conferência
Publicado em /09/2014 ENG
Relevância na Pesquisa
45.56%
Com o apoio RAADRI.; In order to correctly assess the biaxial fatigue material properties one must experimentally test different load conditions and stress levels. With the rise of new in-plane biaxial fatigue testing machines, using smaller and more efficient electrical motors, instead of the conventional hydraulic machines, it is necessary to reduce the specimen size and to ensure that the specimen geometry is appropriated for the load capacity installed. At the present time there are no standard specimen’s geometries and the indications on literature how to design an efficient test specimen are insufficient. The main goal of this paper is to present the methodology on how to obtain an optimal cruciform specimen geometry, with thickness reduction in the gauge area, appropriated for fatigue crack initiation, as a function of the base material sheet thickness used to build the specimen. The geometry is optimized for maximum stress using several parameters, ensuring that in the gauge area the stress is uniform and maximum with two limit phase shift loading conditions. Therefore the fatigue damage will always initiate on the center of the specimen, avoiding failure outside this region. Using the Renard Series of preferred numbers for the base material sheet thickness as a reference...

Damage to unreinforced masonry structures by seismic activity

Ingham, J.; Griffith, M.
Fonte: Structural Engineers Trading Organisation Ltd Publicador: Structural Engineers Trading Organisation Ltd
Tipo: Artigo de Revista Científica
Publicado em //2011 EN
Relevância na Pesquisa
55.69%
The extent of the damage caused to unreinforced masonry (URM) buildings during the 4 September, 2010 Darfield, NZ earthquake was recorded. General features of the 595 assessed URM buildings indicated that the majority were either one- or two-storey. The general observation from the debris of collapsed URM walls was that the kiln fired clay bricks were generally of sound condition, but that the mortar was in poor condition. In most cases the fallen debris had collapsed into individual bricks, rather than as larger chunks of masonry debris. Numerous parapet failures were observed along both the building frontage and along their side walls, and for several URM buildings located on the corners of intersections, the parapets collapsed on both perpendicular walls. Where walls exhibited some damage to in-plane deformation the cracks were mostly seen to pass vertically through the lintels over door or window openings. Perhaps the most striking aspect of this earthquake overall was the extensive amount of liquefaction and ground deformation that occurred.; http://www.scopus.com/record/display.url?eid=2-s2.0-79952330386&origin=resultslist&sort=plf-f&src=s&st1=Damage+to+unreinforced+masonry+structures+by+seismic+activity&sid=-xahsNbVhyAsqVkL930E9AA%3a20&sot=b&sdt=b&sl=76&s=TITLE-ABS-KEY%28Damage+to+unreinforced+masonry+structures+by+seismic+activity%29&relpos=0&relpos=0&searchTerm=TITLE-ABS-KEY(Damage to unreinforced masonry structures by seismic activity); J. Ingham and M. Griffith

Delamination prediction in orthogonal machining of carbon long fiber-reinforced polymer composites

Santiuste, Carlos; Olmedo, Álvaro; Xoldani, Xavier; Miguélez, Henar
Fonte: SAGE Publicador: SAGE
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em 17/07/2012 ENG
Relevância na Pesquisa
35.76%
Machining processes of composites are common operations in industry involving elevated risk of damage generation in the workpiece. Long fiber reinforced polymer composites used in high-responsibility applications require safety machining operations guaranteeing workpiece integrity. Modeling techniques would help in the improvement of machining processes definition; however, they are still poorly developed for composites. The aim of this paper is advancing in the prediction of damage mechanisms involved during cutting, including out-of-plane failure causing delamination. Only few works have focused on three-dimensional simulation of cutting; however, this approach is required for accurate reproduction of the complex geometries of tool and workpiece during cutting processes. On the other hand, cohesive interactions have proved its ability to simulate out-of-plane failure of composites under dynamic loads, as impact events. However, this interlaminar interaction has not been used up to date to model out-of-plane failure induced during chip removal. In this paper, both a classical damage model and cohesive interactions are implemented in a three-dimensional model based on finite elements, in order to analyze intralaminar and interlaminar damage generation in the simplified case of orthogonal cutting of carbon LFRP composite. More realistic damage predictions using cohesive interactions were observed. The strong influence of the stacking sequence on interlaminar damage has been demonstrated.; Financial support for this work has been provided by the Ministry of Science and Innovation of Spain under the projects DPI2011-25999 and TRA2010-19573.

Delamination prediction in orthogonal machining of carbon long fiber-reinforced polymer composites

Santuiste, Carlos; Olmedo, Álvaro; Soldani, Xavier; Miguélez, Henar
Fonte: SAGE Publications Publicador: SAGE Publications
Tipo: info:eu-repo/semantics/acceptedVersion; info:eu-repo/semantics/article Formato: application/pdf
Publicado em /07/2012 ENG
Relevância na Pesquisa
35.76%
Machining processes of composites are common operations in industry involving elevated risk of damage generation in the workpiece. Long fiber reinforced polymer composites used in high-responsibility applications require safety machining operations guaranteeing workpiece integrity. Modeling techniques would help in the improvement of machining processes definition; however, they are still poorly developed for composites. The aim of this paper is advancing in the prediction of damage mechanisms involved during cutting, including out-of-plane failure causing delamination. Only few works have focused on three-dimensional simulation of cutting; however, this approach is required for accurate reproduction of the complex geometries of tool and workpiece during cutting processes. On the other hand, cohesive interactions have proved its ability to simulate out-of-plane failure of composites under dynamic loads, as impact events. However, this interlaminar interaction has not been used up to date to model out-of-plane failure induced during chip removal. In this paper, both a classical damage model and cohesive interactions are implemented in a three-dimensional model based on finite elements, in order to analyze intralaminar and interlaminar damage generation in the simplified case of orthogonal cutting of carbon LFRP composite. More realistic damage predictions using cohesive interactions were observed. The strong influence of the stacking sequence on interlaminar damage has been demonstrated.; Financial support for this work has been provided by the Ministry of Science and Innovation of Spain under the projects DPI2011 25999 and TRA2010 19573.

Assessment of overlay masonry strengthening system under in-plane monotonic and cyclic loading using the diagonal tensile test

Almeida, João Alberto Pinheiro Pereira; Pereira, E. N. B.; Barros, Joaquim A. O.
Fonte: Universidade do Minho Publicador: Universidade do Minho
Tipo: Artigo de Revista Científica
Publicado em //2015 ENG
Relevância na Pesquisa
65.56%
The development of novel strengthening techniques to address the seismic vulnerability of masonry elements is gradually leading to simpler, faster and more effective strengthening strategies. In particular, the use of fabric reinforced cementitious matrix systems is considered of great potential, given the increase of ductility achieved with simple and economic strengthening procedures. To assess the effectiveness of these strengthening systems, and considering that the seismic action is involved, one important component of the structural behaviour is the in-plane cyclic response. In this work is discussed the applicability of the diagonal tensile test for the assessment of the cyclic response of strengthened masonry. The results obtained allowed to assess the contribution of the strengthening system to the increase of the load carrying capacity of masonry elements, as well as to evaluate the damage evolution and the stiffness degradation mechanisms developing under cyclic loading.; This research was carried in the framework of InoTec, Innovative material of ultra-high 16 ductility for the rehabilitation of the built patrimony, funded by COMPETE/QREN/FEDER 17 (NORTE-07-0202-FEDER-023024). InoTec project is promoted by CiviTest company 18 and University of Minho. S&P Clever Reinforcement Ibérica is gratefully acknowledged 19 for providing the materials used in the strengthening of the masonry specimens.

Postbuckling Investigations of Piezoelectric Microdevices Considering Damage Effects

Sun, Zhigang; Wang, Xianqiao
Fonte: MDPI Publicador: MDPI
Tipo: Artigo de Revista Científica
Publicado em 11/03/2014 EN
Relevância na Pesquisa
35.74%
Piezoelectric material has been emerging as a popular building block in MEMS devices owing to its unique mechanical and electrical material properties. However, the reliability of MEMS devices under buckling deformation environments remains elusive and needs to be further explored. Based on the Talreja's tensor valued internal state damage variables as well as the Helmhotlz free energy of piezoelectric material, a constitutive model of piezoelectric materials with damage is presented. The Kachanvo damage evolution law under in-plane compressive loads is employed. The model is applied to the specific case of the postbuckling analysis of the piezoelectric plate with damage. Then, adopting von Karman's plate theory, the nonlinear governing equations of the piezoelectric plates with initial geometric deflection including damage effects under in-plane compressive loads are established. By using the finite difference method and the Newmark scheme, the damage evolution for damage accumulation is developed and the finite difference procedure for postbuckling equilibrium path is simultaneously employed. Numerical results show the postbuckling behaviors of initial flat and deflected piezoelectric plates with damage or no damage under different sets of electrical loading conditions. The effects of applied voltage...

Reversible switching of in-plane polarized ferroelectric domains in BaTiO3(001) with very low energy electrons

Rault, J. E.; Menteş, T. O.; Locatelli, A.; Barrett, N.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 30/10/2014 EN
Relevância na Pesquisa
45.52%
The switchable bipolar ground state is at the heart of research into ferroelectrics for future, low-energy electronics. Polarization switching by an applied field is a complex phenomenon which depends on the initial domain ordering, defect concentration, electrical boundary conditions and charge screening. Injected free charge may also to be used to reversibly switch in-plane polarized domains. We show that the interaction between the initial domain order and the bulk screening provided by very low energy electrons switches the polarization without the collateral radiation damage which occurs when employing a beam of high energy electrons. Polarization switching during charge injection adds a new dimension to the multifunctionality of ferroelectric oxides.

Electrochemical synthesis of highly ordered nanowires with a rectangular cross-section using an in-plane nanochannel array

Sergelius, Philip; Moreno, Josep M. Montero; Rahimi, Wehid; Waleczek, Martin; Zierold, Robert; Görlitz, Detlef; Nielsch, Kornelius
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 30/03/2015
Relevância na Pesquisa
45.52%
Rapid and reproducible assembly of aligned nanostructures on a wafer-scale is a crucial, yet one of the most challenging tasks in the incorporation of nanowires into integrated circuits. We present the synthesis of a periodic nanochannel template designed for electrochemical growth of perfectly aligned, rectangular nanowires over large areas. The nanowires can be electrically contacted and characterized in situ using a pre-patterned multi-point measurement platform. During the measurement the wires remain within a thick oxide matrix providing protection against breaking and oxidation. We use laser interference lithography, reactive ion etching and atomic layer deposition to create cm-long parallel nanochannels with characteristic dimensions as small as 40 nm. In a showcase study pulsed electrodeposition of iron is carried out creating rectangular shaped iron nanowires within the nanochannels. By design of the device, the grown wires are in contact with an integrated electrode system on both ends directly after the deposition. No further processing steps are required for electrical characterization, minimizing the risk of damage and oxidation. The developed nanowire measurement device allows for multi-probe resistance measurements and can easily be adopted for transistor applications. The guided...

Roughness of Interfacial Crack Front: Correlated Percolation in the Damage Zone

Schmittbuhl, Jean; Hansen, Alex; Batrouni, G. George
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 22/07/2002
Relevância na Pesquisa
45.43%
We show that the roughness exponent zeta of an in-plane crack front slowly propagating along a heterogeneous interface embeded in a elastic body, is in full agreement with a correlated percolation problem in a linear gradient. We obtain zeta=nu/(1+nu) where nu is the correlation length critical exponent. We develop an elastic brittle model based on both the 3D Green function in an elastic half-space and a discrete interface of brittle fibers and find numerically that nu=1.5, We conjecture it to be 3/2. This yields zeta=3/5. We also obtain by direct numerical simulations zeta=0.6 in excellent agreement with our prediction. This modelling is for the first time in close agreement with experimental observations.; Comment: 4 pages RevTeX4

Properties of inelastic yielding zones generated by in-plane dynamic ruptures—II. Detailed parameter-space study

Xu, Shiqing; Ben-Zion, Yehuda; Ampuero, Jean-Paul
Fonte: Royal Astronomical Society Publicador: Royal Astronomical Society
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /12/2012
Relevância na Pesquisa
45.52%
We perform a detailed parameter-space study on properties of yielding zones generated by 2-D in-plane dynamic ruptures on a planar fault with different friction laws and parameters, different initial stress conditions, different rock cohesion values, and different contrasts of elasticity and mass density across the fault. The focus is on cases corresponding to large strike-slip faults having high angle (ψ = 45◦) to the maximum compressive background stress. The simulations and analytical scaling results show that for crack-like ruptures (1) the maximum yielding zone thickness T_(max) linearly increases with rupture distance L and the ratio Tmax/L is inversely proportional to (1 + S)^2 with S being the relative strength parameter; (2) the potency density ε^p_0 decays logarithmically with fault normal distance at a rate depending on the stress state and S; (3) increasing rock cohesion reduces T_(max)/L, resulting in faster rupture speed and higher inclination angle Ф of expected microfractures on the extensional side of the fault. For slip pulses in quasi-steady state, T is approximately constant along strike with local values correlating with the maximum slip velocity (or final slip) at a location. For a bimaterial interface with ψ = 45◦...